indrumator de proiectare cazan

UNIVERSITATEA TEHNICA DE CONSTRUCTII BUCURESTI

FACULTATEA DE INSTALATII

Conf.dr.ing. STANESCU PAUL-DAN Conf.dr.ing. ANTONESCU N. N.

Asist.ing. POPESCU (OLEA) LELIA LETITIA

INDRUMATOR DE PROIECTARE

CAZANE

CONSPRESS %8&85(ù7, 2006

UNIVERSITATEA TEHNICA DE CONSTRUCTII BUCURESTI

FACULTATEA DE INSTALATII

Conf.dr.ing. STANESCU PAUL-DAN Conf.dr.ing. ANTONESCU N. N.

Asist.ing. POPESCU (OLEA) LELIA LETITIA

INDRUMATOR DE PROIECTARE

CAZANE

In memoria domnului profesor doctor inginer Vasile CALUIANU

CONSPRESS %8&85(ù7, 2006

3

CUPRINS

1. CALCULUL ARDERII COMBUSTIBILULUI ......................................... 5

1.1. Calculul arderii combustibilului gazos ..................................................... 5

1.2. Calculul arderii combustibilului lichid sau solid ....................................... 8

1.3. Diagrama I – t ............................................................................................ 10

1.4. Diagrama cp – t .......................................................................................... 12

2. %,/$1�8/�7(50,&�$/�&AZANELOR ................................................. 17

2.1. Randamentul termic al cazanului .............................................................. 18

2.2. Consumul de combustibil .......................................................................... 24

2.3. %LODQ XO�GH�DQVDPEOX�DO�FD]DQXOXL�............................................................. 25

2.4. %LODQ XO�JUDILF�DO�FD]DQXOXL ....................................................................... 28

2.5. %LODQ XO�SDU LDO�SH�elemente al cazanului - stabilirea temperaturilor

úL�HQWDOSLLORU�JD]HORU�GH�DUGHUH�SH�WUDVHX� ................................................. 28

3. CALCULUL TERMIC AL CAZANELOR

'(�$3��&$/'��6$8�),(RBINTE ............................................................ 35

3.1. Calculul termic al cazanelor ignitubulare cu întoarcerea gazelor de

ardere în focar ............................................................................................ 35

3.2. Calculul termic al cazanelor ignitubulare cX�SLHV��GH�vQWRDUFHUH�D� gazelor de ardere în focar ........................................................................... 46

3.3. Calculul termic al cazanelor acvatubulare din elemente cu

vQWRDUFHUHD�JD]HORU�GH�DUGHUH�vQ�IRFDU�úL�XQ�GUXP�Fonvectiv ................... 62


GRX��GUXPXUL�FRQYHFWLYH�........................................................................... 75

3.5. Calculul termic al cazanelor acvatubulare cu baterie�GH� HYL�QHUYXUDWH

�úL�DU]�WRU�DWPRVIHULF�SHQWUX�FRPEXVWLELO�JD]RV�– „cazan mural”............... 89

3.6. Calculul termic al cazanelor acvatubulare verticale cu fascicol

GH� HYL�úL�DU]�WRU�DWPRVIHULF�SHQWUX�FRPEXVWLELO�JD]RV�............................. 110

3.7. Calculul termic al cazanelor ignitubulare verticale

�FX�XQ�GUXP�úL�DU]�WRU�DWPRVIHULF�SHQWUX�FRPEXVWLELO�JD]RV�...................... 123

3.8. &D]DQH�DFYDWXEXODUH�GH�DS��ILHUELQWH�GH�WLS�&$) ...................................... 138

4. CALCULUL TERMIC AL CAZANELOR DE ABUR ............................... 151

4.1. Calculul termic al cazanului ABA (Agregat Bloc Abur) ........................... 151

4.2. &DOFXOXO�WHUPLF�DO�FD]DQXOXL�FX� HYL�FX�LQFOLQDUH�PDUH��WLS�&5� ................ 170

5. CALCULUL TERMIC AL CAZANELOR CU CONDENSATIE .............. 193

5.1. 'HVFULHUHD�FD]DQXOXL��HOHPHQWH�FRPSRQHQWH��PRG�GH�IXQF LRQDUH�............ 193

5.2. Tema de proiectare .................................................................................... 198

5.3. &DOFXOXO�UDQGDPHQWXOXL�WHUPLF�DO�FD]DQXOXL�úL�D�GHELWXOXL�GH�FRPEXVWLELO. 199

5.4. Calculul termic al cazanului ..................................................................... 200

4

6. CALCULUL TERMIC AL CAZANELOR

)81&�,21Æ1'�&8�$5'(5($�/(018/8,�35,1 GAZEIFICARE

�$5'(5(�,19(56�� ................................................................................ 219

6.1. Analiza constructiv-IXQF LRQDO��D�FD]DQHOor cu

combistibil solid – lemne .......................................................................... 219

6.2. 6ROX LD�FRQVWUXFWLYý��HOHPHQWH�FRPSRQHQWH��PRG�GH�IXQF LRQDUH��.... 225

6.3. Tema de calcul de verificare ................................................................... 226

6.4. &DOFXOXO�UDQGDPHQWXOXL�WHUPLF�DO�FD]DQXOXL�úL�D�Gebitului

de combustibil ......................................................................................... 226

7. &$/&8/8/�+,'5$8/,&��*$=2',1$0,&��ù,�$/�,167$/$�,(,� DE EVACUARE A GAZELOR DE ARDERE ........................................ 239

7.1. &DOFXOXO�SLHUGHULORU�KLGUDXOLFH�GH�VDUFLQ� ................................................ 239

7.2. &DOFXOXO�SDUDPHWULORU�GH�ED]��DL�LQVWDOD LHL�GH�DOLPHQWDUH�FX�DHU� de ardere ................................................................................................. 247

7.3. &DOFXOXO�SDUDPHWULORU�GH�ED]��DL�LQVWDOD LHL�GH�WLUDM ................................. 249

7.4. &DOFXOXO�SDUDPHWULORU�GH�ED]��DL�LQVWDOD LHL�GH�LQVXIODUH� la cazanele cu ardere sub presiune .......................................................... 253

��&$/&8/8/�'(�5(=,67(1��$/�&$=$1(/25 .................................. 254

8.1. Date generale ........................................................................................... 254

8.2. 0DWHULDOH�IRORVLWH�SHQWUX�H[HFX ia elementelor metalice ale cazanelor ... 254

8.3. &DOFXOXO�JURVLPLL�SHUH LORU�FRUSXULORU�FLOLQGULFH ..................................... 257

8.4. &DOFXOXO�JURVLPLL�SHUH LORU�WXEXULORU�GH�IODF�U� ....................................... 260

8.5. &DOFXOXO�IXQGXULORU�úL�al capacelor .......................................................... 262

8.6. &DOFXOXO�SO�FLORU�WXEXODUH ........................................................................ 263

1. CALCULUL ARDERII COMBUSTIBILULUI

5

CAPITOLUL 1

CALCULUL ARDERII COMBUSTIBILULUI

Prin tema de proiect VH� G�� FRPSR]L LD� FRPEXVWLELOXOXL� SULQ� FRmponentele constitutive, masice sau volumice��IXQF LH�GH�WLSXO�FRPEXVWLELOXOXL�XWLOL]DW. In cazul combustibilului gazos componentele se exprLP�� vQ� SDUWLFLSD LL�volumice iar în cazul combustibilului lichid sau solid componentele se H[SULP� în SDUWLFLSD LL�PDVLFH. In cazul calculelor de proiectare, dimensionare, utilizându-se Sistemul ,QWHUQD LRQDO�GH�XQLW� L�GH�P�VXU��VH�FRQVLGHU��F��Drderea are loc în�FRQGL LL�QRUPDOH�fizice: 013,1p0 = �EDU��úL� 15,273T0 = K. În FD]XO� HYDOX�ULL� SDUDPHWULORU� GH� IXF LRQDUH� Di cazanelor încercate, pentru XúXUDUHD� FDOFXOHORU�� 6Wandardele Europene DGPLW� úL� FRQGL LLOH� WHKQLFH� GH� DUGHUH��

013,1p0 = bar �úL� 15,288T0 = K (150C) .

1.1. Calculul arderii combustibilului gazos Calculul arderii combustibilului gazos sH� UHIHU�� OD� DUGHUHD� XQLW� LL� GH� YROXP

(1 3Nm )�GH�JD]�vQ�FRQGL LL�QRUPDOe fizice.

Se GHWHUPLQ�: a) Volumul teoretic de aer necesar arderii stoichiometrice ( 0V ) (teoretice, I�U��

exces de aer) a unui metru cub normal de combustibil :

−

++++= ∑ 2220 4

5,15,05,00476,0 OHCn

mSHHCOV nm [ 3Nm / 3

Nm ] (1.1)

Elementele componente ale combustibilului se introduc în UHOD LH cu valorile

procentuale, iar ” nmHC ”�UHSUH]LQW��exSUHVLD�JHQHUDO��D�KLGURFDUEXULORU�FRPSRQHQWH.

b) Componentele gazelor de ardere pentru arderea stoichiometULF� �WHRUHWLF��I�U��H[FHV�GH�DHU)

Volumul de bioxid de carbon:

[ ]∑++= nmCOHmCCOCOV 201,0

2 [ 3

Nm / 3Nm ] (1.2)

INDRUMATOR DE PROIECTARE APARATE TERMICE

CAZANE

6

Volumul de bioxid de sulf din gazele de ardere:

[ ]SHVSO 201,02

= [ 3Nm / 3

Nm ] (1.3)

Volumul gazelor triatomice CO2� úL� 622 din gazele de ardere VH� QRWHD]�� FX�

2ROV :

2ROV =

2COV + 2SOV [ 3

Nm / 3Nm ] (1.4)

Volumul de azot din gazele de ardere:

100

79,0 202

NVVN += [ 3

Nm / 3Nm ] (1.5)

9ROXPXO�GH�YDSRUL�GH�DS� din gazele de ardere:

[ ]∑ +++= 022 016,02

01,02

VHCn

SHHV nmOH [ 3Nm / 3

Nm ] (1.6)

Volumul teoretic de gaze de ardere f�U��H[FHV�GH�DHU��( 1=α )

Vg0 = 2ROV + 2NV + OHV2

[ 3Nm / 3

Nm ] (1.7)

In cazul proceselor tehnice de ardere, specifice cazanelor, SHQWUX�D�VH�RE LQH�Fât PDL�SX LQH�SURGXVH�GH�DUGHUH�LQFRPSOHW��vQ�JD]HOH�GH�DUGHUH��VH�XWLOL]HD]��DPHVWHFXUL�combustibile cu aer în exces��$VWIHO��GDF��VH�QRWHD]��FX�´α” coeficientul de exces de aer ca fiind raportul dintre aerul efectiv de ardere (Va ) úL cel teoretic necesar arderii XQLW� LL�GH�FRPEXVWLELO� �90), sH�SRDWH�VSXQH�F��YDORULOH�X]XDOH�DOH�FRHILQFLHQWXOXL�GH�exces de aer în focar sunt: 1,105,1 ÷=α pentru focare cu ardere intensificaW�� 15,11,1 ÷=α pentru focare��FX�DUGHUH�QRUPDO�� /D� FD]DQHOH� � IXQF LRQkQG� FX� GUXPXULOH� GH� JD]H�de ardere în depresiune, prin S�WUXQGHULOH�GH�DHU�IDOV�VH�RE LQ valori ale coeficientului de exces de aer OD�FRú�de 1,3 ÷ 1,4. La cazanele fuQF LRQkQG�FX�GUXPXULOH�GH�JD]H� vQ� VXSUDSUHVLXQH��QX mai apar S�WUXQGHUL� GH� DHU� IDOV� úL� GHFL� H[FHVXO� GH� DHU� GLQ� IRFDU� VH�PHQ LQH� la aceeaúL�valoare SkQ��OD�FRú�

- Calculul arderii cu exces de aer. Volumul real de aer necesar arderii: Va = αV0 [ 3

Nm / 3Nm ] (1.8)


7

Volumul real al gazelor de ardere: 00

)1( VVV gg −+= α [ 3Nm / 3

Nm ] (1.9)

c) 'HQVLWDWHD�JD]HORU�GH�DUGHUH�OD�VWDUH�QRUPDO��

g

comb

V

V293,10

+=

ρρ [kg/ 3

Nm ] (1.10)

unde combρ este masa�VSHFLILF��D�FRPEXVWLELOXOXL�� 3UHVLXQHD�SDU LDO��D�JD]HORU triatomice ( 2RO ) din gazele de ardere:

g

g

RO

RO pV

VP 2

2= [bar] (1.11)

3UHVLXQHD�SDU LDO��D�YDSRULORU�GH�DS�:

g

g

OH

OH pV

VP 2

2= [bar] (1.12)

unde gp �HVWH�SUHVLXQHD�DEVROXW��D�JD]HORU�GH�DUGHUH� 1pp og ≅= bar .

d) 3XWHUHD�FDORULF��LQIHULRDU� a combustibilului gazos se deteUPLQ��FX�UHOD LD:

+⋅+⋅+⋅+⋅+⋅= 6242 3,6373582299,1074,126 HCCHSHHCOH i

10483 11844,912 HCHC ⋅+⋅+ [kJ/ 3Nm ] (1.13)

Componentele volumice ale combustibilului se introduc în procente. Pentru cazul combustibilului gazos natural�XWLOL]DW�vQ�UH HOHOH�GH�GLVWULEX LH, cu FRPSR]L LD�PHGLH�

CH4 C2H6 O2 N2 98,5 0,8 0,2 0,5 %

SXWHUHD�FDORULF��LQIHULRDU��este 36000H i = kJ/ 3

Nm 3HQWUX� FRPEXVWLELO� JD]RV� QDWXUDO� vQ� DPHVWHF� �� FX� JD]� GH� VRQG��GHJD]ROLQDW��FX�FRPSR]L LD�PHGLH:

CH4 C2H6 C3H8 C4H10 O2 N2 95,6 2,8 0,6 0,6 0,1 0,3 %

SXWHUHD�FDORULF��HVWH� 37000H i = kJ/ 3

Nm .


CAZANE

8

1.2. Calculul arderii combustibilului lichid sau solid . Calculul arderii combustibilului lichid sau solid sH�UHIHU��OD�DUGerea�XQLW� LL�GH�PDV� (1kg)� GH� FRPEXVWLELO� vQ� FRQGL LL� QRUPDOH� IL]LFH�� (OHPHQWHOH� FRPSRQHQWH� ale combustibilului se H[SULP��vQ�WHP�� prin�SDUWLFLSD LL�Pasice. DHRDUHFH�VXOIXO�VH�DIO��vQ�FDQWLWDWH�PLF�� vQ�FRPEXVWLELO� �VXE��VH�GHWHUPLQ�� DúD�]LVXO�ÄFDUERQ redus” (K) DGPL kQG� F�� SURGXVHOH� DUGHULL� FDUERQului sunt identice cu cele pentru „carbonul redus”. SCK ⋅+= 375,0 (%) (1.14) Se GHWHUPLQ�:

a) Volumul teoretic de aer necesar arderii stoichiometrice ( 0V ) (teoretice, I�U��exces de aer) a unui kg de combustibil:

OHKV ⋅−⋅+⋅= 0333,0265,00889,00 [ 3

Nm /kg ] (1.15) b) Componentele gazelor de ardere pentru arderea VWRLFKLRPHWULF� �WHRUHWLF��

I�U��H[FHV�GH�DHU)

- 9ROXPXO�GH�ELR[LG�GH�FDUERQ�úL�bioxid de sulf din gazele de ardere:

100866,1

2

KVRO = [ 3

Nm /kg] (1.16)

- Volumul de azot din gazele de ardere:

1008,079,0 02

NVVN += [ 3

Nm /kg] (1.17)

- 9ROXPXO�GH�YDSRUL�GH�DS� din gazele de ardere:

0OH V016,04,80

WH9V

2+

+= [ 3

Nm /kg] (1.18)

Volumul teoretic de gaze de ardere f�U��H[FHV�GH�DHU��( 1=α )

Vg0 = 2ROV + 2NV + OHV2

[ 3Nm /kg] (1.19)

- Volumul real de aer necesar arderii cu exces de aer:

Va = α · V0 [ 3Nm /kg] (1.20)

In cazul proceselor tehnice de ardere, specifice cazanelor,�SHQWUX�D�VH�RE LQH�FvW�PDL�SX LQH�SURGXVH�GH�DUGHUH�LQFRPSOHW��vQ�JD]HOH�GH�DUGHUH��VH�XWLOL]HD]��DPHVWHFXUL�combustibile cu aer în exces��$VWIHO��GDF��VH�QRWHD]��FX�´α” coeficientul de exces de aer ca fiind raportul dintre aerul efectiv de ardere (Va ) úL cel teoretic necesar arderii


9

XQLW� LL�GH�FRPEXVWLELO� �90�� VH�SRDWH�VSXQH�F��YDORULOH�uzuale ale coefincientului de exces de aer în focar sunt: 1,105,1 ÷=α pentru IRFDUH�FX�DUGHUH�LQWHQVLILFDW�� 15,11,1 ÷=α pentru focare��FX�DUGHUH�QRUPDO�� /D� FD]DQHOH� � IXQF LRQkQG� FX� GUXPXULOH� GH� JD]H�de ardere în depresiune, prin S�WUXQGHULOH�GH�DHU�IDOV�VH�DMXQJH�ca OD�FRú�valorile coeficientului de exces de aer V��ILH�de 1,3 ÷ 1,4 . /D�FD]DQHOH� � IXQF LRQkQG�FX�GUXPXULOH�GH�JD]H� vQ� VXSUDSUHVLXQH��QX mai apar S�WUXQGHUL� GH� DHU� IDOV� úL� GHFL� H[FHVXO� GH� DHU� GLQ� IRFDU� VH�PHQ LQH� la aceeaúL�valoare SkQ��OD�FRú�

- Calculul arderii cu exces de aer. Volumul real al gazelor de ardere:

00)1( VVV gg −+= α [ 3

Nm /kg] (1.21)

'HQVLWDWHD�JD]HORU�GH�DUGHUH�OD�VWDUH�QRUPDO�:

g

a

V

V⋅+=

293,110ρ [kg/ 3

Nm ] (1.22)

3UHVLXQHD�SDU LDO��D�JD]HORU�522 în gazele de ardere:

g

g

RO

RO pV

VP 2

2= [bar] (1.23)

3UHVLXQHD�SDU LDO��D�YDSRULORU�GH�DS�:

g

g

OH

OH pV

VP 2

2= [bar] (1.24)

unde pg�HVWH�SUHVLXQHD�DEVROXW��D�JD]elor de ardere: 1pp og ≅= bar .

c) 3XWHUHD�FDORULF��LQIHULRDU� a combustibililor lichizi sau solizi este:

OWSO

HCH i

−−⋅+

−+⋅=

8

91,257,104

812000,339 [kJ/kg] (1.25)


CAZANE

10

vQ� FDUH� FRPSRQHQWHOH� FRPEXVWLELOXOXL� VH� UHIHU�� OD� PDVD� GH� OXFUX� úL� VH� H[SULP�� vQ�procente. Pentru combustibilii lichizi uzuali� SXWHUHD� FDORULF�� LQIHULRDU�� DUH� XUP�WRarele valori:

&RPEXVWLELO�OLFKLG�XúRU (CLU) 42000 kJ/kg 3�FXU�� 38000 ÷ 39000 kJ/kg

Pentru lignit puterHD�FDORULF��LQIHULRDU��YDULD]��IRDUWH�PXOW, astfel:

Lignit inferior 6700 ÷ 7500 kJ/kg Lignit superior 10000 ÷ 14000 kJ/kg

1.3. Diagrama I - t Valoarea entalpiei (I) a JD]HORU� GH� DUGHUH� RE LQXWe� GLQ� DUGHUHD� XQLW� Li de combustibil ( 3

Nm �VDX�NJ��HVWH�GDW��GH�UHOD LD:

aerOHOHNNRORO iViViViVI 0)1(222222

−+++= α (1.26)

unde OHNRO iii222

,, �úL� aeri �UHSUH]LQW�� HQWDOSLLOH� specifice ale JD]HORU� FRPSRQHQWH� úL�VXQW�IXQF LH�GH�WHPSHUDWXUD�JD]HORU�GH�DUGHUH��W�� La diverse temperaturi ale gazelor de ardere (0÷2000 0C) se GHWHUPLQ� entalpia amestecului utilizându-se tabelul de calcul 1.1.

Conform tabelului 1.1., se GHWHUPLQ� valorile din coloanele 3, 5� úL� �� FDUH� vQVXPDWH� GDX�entalpia gazelor de ardere în FRQGL LL�WHRUHWLFH�(Igo).

Pentru diverse valori ale coeficientului de exces de aer (α1=αfocar, α2>α1; α3>α2 etc.) se RE LQ� YDORULOH� GLQ� FRORDQHOH� ��14, 16 etc.

Se traVHD]�� GLDJUDPHOH��IXQF LHL�

I = f(t, α) (1.27) asemenea familiei de curbe de parametru α, reprezentate în figura 1.1., XWLOL]kQG� VF�Ui convenabile (1:10; 1:20; 1:50 sau multipli). Diagrama I-t este VSHFLILF�� FRPEXVWLELOXOXL� SHQWUX�care a fost determinDW�.

kJ . m3

N kJ . kg

Fig. 1.1. Diagrama I – t

I

α 1

α 2

α 3

α 4

Ig=f(α , t)

t [oC] ti te

Ii

Ie

COMBUSTIBIL

C = ......... % H = ......... % N= ......... % etc. Vo = .......... Vgo = .......... Hi = .........

1.

CA

LC

UL

UL

AR

DE

RII C

OM

BU

ST

IB

IL

UL

UI

11

T

abel

ul 1

.1.(Q

WDOSLD

�JD]HO

RU�GH�DU

GHUH�

UH]XOW

DWH�GL

Q�DUGH

UHD�XQ

LW� LL�

GH c

ombu

stib

il (

kJ/

3 Nm

) sa

u (k

J/kg

)

2R

OV

=

2N

V=

O

H2

V=

∑

=V

V0g

0

V=

α

=

( α-1

)=

t g

0 C

2R

Oi

2

RO

i×

2R

OV

2

Ni

2Ni

×2

NV

O

H2

i

OH

2V

×O

H2

i

∑⋅

=)

Vi(

I0

g

aer

i

aer

i×

0V

=0

VI

( α-1

) ×

(ae

ri

×0

V)

I=0

gI+

( α-1

) ×

(ae

ri

×0

V)

în

cont

inua

re

ptr.

α�P

�ULW�

din

0,1

în

0,1

1 2

3 4

5 6

7 8

9 10

11

12

…

0 10

0 20

0

170,

0 35

7,5

12

9,5

259,

8

15

0,5

304,

4

130,

0 26

1,3

400

600

800

771,

8 12

24

1704

52

6,5

804,

0 10

93

62

6,2

968,

5 13

34

531,

6 81

3,7

1107

1000

12

00

1400

2203

27

16

3238

13

91

1697

20

08

17

22

2132

25

58

1409

17

19

2033

1600

18

00

2000

3772

43

03

4843

23

11

2643

29

34

30

01

3458

39

24

2353

26

75

3001


CAZANE

12

ModDOLW� LOH de utilizare a diagramei I–t sunt uUP�WRDUHle: a). DDF�� VH� GDX,� SHQWUX� R� VXSUDID �� GH� VFKLPE� GH� F�OGXU�� WHPSHUDWXULOH� GH�LQWUDUH� úL� LHúLUHa a gazelor de ardere�� SUHFXP� úL� FRHILFLHQ LL� GH� H[FHV� GH� DHU�FRUHVSXQ]�WRUL, se poate determina fluxul�GH�F�lGXU��FHGDW�GH�JD]HOH�GH�DUGHUH:

- se citesc în diagrama I-t:

),( iii tfI α= �úL� ),( eee tfI α= , apoi VH� GHWHUPLQ�� IOX[XO� GH� F�OGXU��cedat de gazele de ardere.

)( ei IIBQ −= (1.28)

unde B este consumul de combustibil [kg/s sau 3Nm /s].

b). DDF�� VH� GDX�� SHQWUX� R� VXSUDID �� GH� VFKLPE� GH� F�OGXU�� fluxul� GH� F�OGXU��cedat de gazele de ardere Q úL�SDUDPHWULL� LQL LDOL ai gazelor de ardere�� WHPSHUDWXUD�úL�excesul de aer, se poate determina� WHPSHUDWXUD� GH� LHúLUH� D� JD]HORU� GH� DUGHUH�� OD� XQ�coeficient de exces de aer cunoscut:

- se FLWHúWH�vQ�GLDJUDPD�,-t: ),( iii tfI α=

apoi se GHWHUPLQ� entalpia : B

QII ie

−= (1.29)

úL�vQ�ILQDO�VH�FLWHúWH�vQ�GLDJUDPD�,-t valoarea: ),( eee Ift α= . 1.4. Diagrama cp – t In ca]XO�FDOFXOHORU�UDSLGH�GH�YHULILFDUH�VDX�FKLDU�úL�D�FHORU�GH�GLPHQVLRQDUH�IDU��SUHWHQ LL� GH� H[DFWLWDWH�� HVWH� PDL� FRPRG� V�� VH� OXFUH]H� FX� F�OGXUL� VSHFLILFH�PHGLL� ale gazelor de ardere OD�SUHVLXQH�FRQVWDQW�, în loc de HQWDOSLL��5HOD LD�GH�OHJ�WXU��,–cp este: [ ] tcVVtcVI pgpg ⋅⋅−+=⋅⋅= 0)1(

0α (1.30)

úL� aerN

g

N

OH

g

OH

RO

g

RO

p cVg

Vc

V

Vc

V

Vc

V

Vc ⋅

−+⋅+⋅+⋅= 0)1(

2

2

2

2

2

2α

(1.31)

'HRDUHFH�YDULD LD�F�OGXULL�VSHFLILFH�FX�FRPSR]L LD�JD]HORU�GH�DUGHUH�HVWH�UHODWLY�PLF��WDEHOHOH�VDX�GLDJUDPHOH�GH�F�OGXUL�VSHFLILFH�IXQF LH�GH�WHPSHUDWXU��VXQW�SUDFWLF�utilizabile�SHQWUX�WR L�FRPEXVWLELOLL�GLQ�DFHHDúL�FODV� (gaz, lichid, solid). În continuare se SUH]LQW�� WDEHOHOH�� úL��SHQWUX�JD]HOH�GH�DUGHUH�SURYHQLWH�GLQ� DUGHUHD� FRPEXVWLELOLORU� JD]RúL�� UHVSHFWLY� OLFKL]L� FX� DMXWRUXO� F�URUD� SRW� IL� WUDVDWH�diagramele cp=f(t,α).


13

Tabelul 1.2. &�OGXUL�VSHFLILFH�PHGLL�vQ�kJ/ 3

Nm K, pentru gaze de ardere provenite din arderea FRPEXVWLELOLORU�JD]RúL

t (0C) α=1 α=1,1 α=1,2 α=1,5 α=2,0 0 100

1,3670 1,3762

1,3582 1,3699

1,3532 1,3645

1,3435 1,3532

1,3327 1,3410

200 300

1,3904 1,4067

1,3837 1,3992

1,3779 1,3929

1,3653 1,3804

1,3523 1,3657

400 500

1,4243 1,4432

1,4164 1,4344

1,4097 1,4277

1,3946 1,4130

1,3809 1,3967

600 700

1,4620 1,4808

1,4532 1,4716

1,4457 1,4641

1,4306 1,4478

1,4134 1,4306

800 900

1,4992 1,5177

1,4905 1,5076

1,4821 1,4997

1,4653 1,4821

1,4469 1,4628

1000 1100

1,5348 1,5516

1,5248 1,5411

1,5160 1,5319

1,4976 1,5126

1,4783 1,4925

1200 1300

1,5675 1,5825

1,5566 1,5717

1,5474 1,5616

1,5273 1,5411

1,5064 1,5198

1400 1500

1,5968 1,6102

1,5855 1,5984

1,5754 1,5884

1,5545 1,5662

1,5319 1,5436

1600 1700

1,6231 1,6361

1,6110 1,6231

1,6005 1,6123

1,5779 1,5892

1,5541 1,5645

1800 1900 2000

1,6470 1,6575 1,6675

1,6340 1,6445 1,6545

1,6231 1,6336 1,6428

1,5993 1,6093 1,6181

1,5746 1,5838 1,5922

Tabelul 1.3.

&�OGXUL�VSHFLILFH�PHGLL�vQ�kJ/ 3Nm K, pentru gaze de ardere provenite din arderea

combustibililor lichizi t (0C) α=1 α=1,1 α=1,2 α=1,5 α=2

0 100

1,3674 1,3825

1,3595 1,3741

1,3565 1,3703

1,3444 1,3569

1,3335 1,3440

200 300

1,3988 1,4164

1,3892 1,4055

1, 3854 1,4013

1,3720 1,3860

1,3590 1,3720

400 500

1,4356 1,4557

1,4252 1,4453

1,4201 1,4398

1,4030 1,4214

1,3850 1,4042

600 700

1,4766 1,4951

1,4649 1,4850

1,4586 1,4779

1,4386 1,4561

1,4206 1,4386

800 900

1,5135 1,5340

1,5030 1,5206

1,4955 1,5131

1,4737 1,4905

1,4545 1,4704

1000 1100

1,5516 1,5696

1,5378 1,5549

1,5306 1, 5476

1,5072 1,5223

1,4867 1,5018

1200 1300

1,5830 1,5995

1,5708 1,5846

1,5645 1,5763

1,5373 1,5507

1,5152 1, 5286


CAZANE

14

1400 1500

1,6143 1,6265

1,6005 1,6123

1,5909 1,6022

1,5641 1,5754

1,5411 1,5520

1600 1700

1,6411 1,6520

1,6265 1,6378

1,6169 1,6261

1,5880 1,5976

1,5637 1,5729

1800 1900 2000

1,6646 1,6734 1,6822

1,6482 1,6545 1,6637

1,6386 1,6478 1,6570

1,6085 1,6181 1,6277

1,5834 1,5917 1,6018

Modurile de utili]DUH� D� F�OGXULORU� specifice ale gazelor de ardere în calculele

termice: a)�� 'DF�� VH� GDX�� SHQWUX� R� VXSUDID �� GH� VFKLPE� GH� F�OGXU�� WHPSHUDWXULOH� GH�

LQWUDUH� úL� LHúLUH ale gazelor de DUGHUH�� SUHFXP�úL� H[FHVHOH�GH� DHU� FRUHVSXQ]�WRDUH�� VH�poate determina fluxul�GH�F�OGXU��FHGDW�GH�JD]HOH�GH�DUGHUH�

),( iip tfci

α= �úL� ),( eep tfce

α=

UH]XOW�� )( epgipg tcVtcVBQ

eeii⋅⋅−⋅⋅= (1.32)

unde: B – debitul de combustibil (kg/s, 3

Nm /s).

Vg – volumul de gaze de ardere pentru unitatea de combustibil ( 3Nm /kg, 3

Nm / 3Nm )

0)1(0

VVV gg −+= α

b). DDF�� VH� GDX�� SHQWUX� R� VXSUDID �� GH� VFKLPE� GH� F�OGXU�� fluxul� GH� F�OGXU��FHGDW� GH� JD]HOH� GH� DUGHUH� úL� SDUDPHWULL� LQL LDOL� ai gazelor de ardere �WHPSHUDWXU�� úL�exces de aer), se poate determina temperatura dH� LHúLUH� D� JD]HORU� GH� DUGHUH�� OD� XQ�DQXPLW�H[FHV�GH�DHU�FXQRVFXW��ILLQG�QHFHVDUH�vQV��÷��LWHUD LL de clacul.

Cu valorile (ti, αi),� GLQ� WDEHOH� UH]XOW�� F�OGXUa� VSHFLILF�� a gazelor la intrare ipc . Se

presupune o valoare 'et �úL�FX�DFHDVW��YDORDUH�úL�pentru excesul de aer αe�VH�RE LQH� '

epc .

Se GHWHUPLQ� ''et �FX�UHOD LD:

'"

e

i

pg

iipg

ecV

B

QtcV

t

−= (1.33)

GDF�� ''et GLIHU�� ID �� '

et cu mai mult de un gard, se reia calculul o cu noX� valoare

='et

''et . ,Q�ILQDO�VH�GHWHUPLQ��WHPSHUDWXUD�GH�LHúLUH�D�JD]HORU�GH�DUGHUH� et pentru

''

epc :

''

ee

i

pg

iipg

ecV

B

QtcV

t

−= (1.34)

$YkQG�vQ�YHGHUH��F��YDULD LD�F�OGXULL�VSHFLILFH�FX�WHPSHUDWXUD�HVWH�IRDUWH�PLF��QX�VXQW�QHFHVDUH�QLFLRGDW��PDL�PXOW�GH��LWHUD LL�


15

Pentru determinarHD� F�OGXULORU� VSHFLILFH� DOH� componentelor gazelor de ardere SRW�IL�XWLOL]DWH�XUP�WRDUHOH�UHOD LL: 701,03 )100(101759,47003,1

2−⋅+= −

tcRO [kJ/ 3Nm K] (1.35)

154,15 )100(104142,85051,12

−⋅+= − tc OH [kJ/ 3Nm K] (1.36)

35,16 )100(103464,92958,12

−⋅+= − tcN [kJ/ 3Nm K] (1.37)

169,13 )100(106974,33004,1 −⋅+= −tcaer [kJ/ 3

Nm K] (1.38) sau pentru valori medii ale caldurii specifice a amestecului de gaze de ardere pentru combustibili clasici (UHOD LL�YDODELOH�SHQWUX�LQWHUYDOXO�GH�WHPSHUDWXU��W=100÷900 0C):

- JD]RúL: )107393,331882,0(186,4 5tc pg

−⋅+= [kJ/ 3Nm K] (1.39)

- lichizi: )108107,332118,0(186,4 5 tc pg

−⋅+= [kJ/ 3Nm K] (1.40)

- solizi: )1045,432265,0(186,4 5tc pg

−⋅+= [kJ/ 3Nm K] (1.41)

ÌQ� ILJXULOH� �� úL� �� VXQW� SUH]HQWDWH� GLDJUDPHOH� GH� YDULD LH� D� F�OGXULL�VSHFLILFH� PHGLL� SHQWUX� JD]H� QDWXUDOH�� FRPEXVWLELOL� OLFKL]L� úL� XQ� DQXPLW� FRPEXVWLELO�solid. $FHVWH� WDEHOH� úL� JUDILFH� VXQW� RULHQWDWLYH� �VXILFLHQW� GH� FRUHFWH� SHQWUX� FDOFXOH�SUDFWLFH� LQJLQHUHúWL�� 3HQWUX� ILHFDUH� FRPEXVWLELO� vQ� SDUWH� F�OGXULOH� VSHFLILFH� YRU� IL�determinate folosind valorile din anexa 7 care reprezintû�F�OGXULOH�VSHFLILFH�PHGLL�DOH�gazelor componente.

Fig. 1.2. Diagrama cp – t pentru gaze naturale

0 1000 500 1500 2000 1,3

1,4

1,5

1,6

cp

kJ m

3NK

t (oC)

α =1 α =1,1 α =1,2

α =1,5

α =2 α =3 α =4


CAZANE

16

Fig. 1.3. Diagrama cp – t pentru combustibili lichizi

Fig. 1.4. Diagrama cp – t pentru combustibil solid

1,3

1,4

1,5

1,6

cp

kJ kg.K

0 1000 500 1500 2000 t (oC)

α =1 α =1,1 α =1,2 α =1,5

α =2

α =3 α =4

1,3

1,4

1,5

1,6

cp

kJ kg.K

0 1000 500 1500 2000 t (oC)

α =1 α =1,1 α =1,2 α =1,5

α =2

1,7

C =21,4 % H = 2,7 % S = 2,5 % O = 14,8 %

N = 1,4 % A = 26,3 % W = 30,9 %

2. BILANTUL TERMIC AL CAZANULUI

17

CAPITOLUL 2

%,/$1�8/�7(50,&�$/�&$=$18/8,� %LODQ XO� WHUPLF� OD� FD]DQXOXL�� H[SUHVLH�D�SULQFLSLXOXL�FRQVHUY�ULL�HQHUJLHL��SXQH�vQ� HYLGHQ �� fluxurile� GH� F�OGXU�� LQWURGXVH�� IOX[XULOH� XWLOH� úL� SLHUGHULOH� GH� F�OGXU��ale FD]DQXOXL� ID �� GH� FRQWXUXO� GH� ELODQ � úL� SHUPLWH� FDOFXOXO� UDQGDPHQWXOXL� WHUPLF� úL� DO�consumului de combustibil.

1. Cazan 2. Alimentare cu combustibil ��*U�WDU ��6XSUDIH H�GH�schimb de ��F�OGXU� ��(YDFXDUH�FHQXú��úL�]JXU� ��&RQWXU�GH�ELODQ

Fig. 2.1.�&RQWXUXO�GH�ELODQ �OD�XQ�FD]an cu arderea

combustibilului solid în strat�SH�JU�WDU &RQWXUXO� GH� ELODQ � vQFDGUHD]�� VXSUDID D� H[WHULRDU�� D� SHUH LORU� FD]DQXOXL��7HPSHUDWXUD�GH�UHIHULQ ��HVWH�WHPSHUDWXUD�PHGLXOXL�DPELDQW�VDX�FHD�QRUPDO�� (FXD LD�ELODQ XOXL�WHUPLF�DO�FD]DQXOXL�VH�VFULe sub forma :

evextchmecutac QQQQQQQQ +++++=+ cos (kW) (2.1) unde :

cQ - HVWH�GHELWXO�GH�F�OGXU��GLVSRQLELO��D�FRPEXVWLELOXOXL; aQ -�GHELWXO�GH�F�OGXU��DGXV�GH�DHUul utilizat la arderea combustibilului;

utQ - debitul dH�F�OGXU��XWLO��SURGXV�GH�FD]DQ;

mecQ -�GHELWXO�GH�F�OGXU��SLHUGXW�SULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��PHFDQLF� (este specific numai combustibilului solid);

Qext

Qmec

Qch

Qev

Qcos Qut Qc

Qa

1 2

3

4

5 6


CAZANE

18

chQ -�GHELWXO�GH�F�OGXU��SLHUGXW�SULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��FKLPLF�� cosQ -�GHELWXO�GH�F�OGXU��SLHUGXW�SULQ�HYDFXDUHD�JD]HORU��GH�DrGHUH�SH�FRú�� extQ - GHELWXO�GH�F�OGXU��SLHUGXW�SULQ�SHUH LL�H[WHULRUL�DL�FD]DQXOXL�� cenQ - debitul�GH�F�OGXU��SLHUGXW�SULQ�HYDFXDUHD�SURGXVHORU�VROLGH�de ardere din

cazan (este specific numai combustibilului solid) .

2.1. Randamentul termic al cazanului

Randamentul termic al cazanului poate fi determinat :

a) OD�XQ�FD]DQ�vQ�IXQF LXQH� când,�SULQ�P�VXU�UL,�VH�GHWHUPLQ�� utQ �úL� cQ :

100c

ut

AQ

Q=η (%) (2.2)

b) în faza de proiectare, când se impune��FD�GDW��GH�SURLHFWDUH� sarcina WHUPLF��XWLO��WHPSHUDWXUD�JD]HORU�GH�DUGHUH�OD�FRú�HWF��úL�VH�FDOFXOHD]� :

)(11 cos cenextmecchj

c

pjc

B qqqqqqQ

QQ++++−=−=

−= ∑∑η (%) (2.3)

unde jq �UHSUH]LQW��SLHUGHULOH�VSHFLILFH��UHODWLYH�ID ��GH� cQ ��GH�F�OGXU�� În cazul general al unui cazan în ID]�� GH� SURWRWLS, GXS�� FH� V-a determinat randamentul termic de proiectare DFHVWD�YD� WUHEXL�YDOLGDW�GH� vQFHUF�ULOH� WHUPRWHKQLFH�realizate conform standardului specific tipului constructiv de cazan. Randamentul GHFODUDW�GH�IXQF LRQDUH�DO�FD]DQXOXL�UHVSHFWLY�QX�YD�SXWHD�V��GLIHUH�FX�PDL�PXOW�GH��ID ��GH�FHO�RE LQXW�vQ�FDGUXO�vQFHUF�ULORU�WHPRWHKQLFH�GH�WLS��vQFHUF�UL�FH�VH�HIHFWXHD]��în laboratoare independente acreditate în acest scop.

��3LHUGHUL�VSHFLILFH�GH�F�OGXU��SULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��PHFDQLF��( mecq )

Acest tip de pierdere�GH�F�OGXU��UHSUH]LQW��SLHUGHUHD�SULQ�QHDUGHUHD�FDUERQXOXL�GLQ�FRPEXVWLELO�FD]XW�VXE�JU�WDU�� vQJOREDW�vQ�]JXU��VDX�DQWUHQDW�FX�FHQXúD�]EXU�WRDUH�FD]XUL� vQ�FDUH��GLQ� OLSVD�FRQGL LLORU�GH�DUGHUH��DFHVWD�QX�PDL�SRDWH�HOLEHUD�FDOGXUD�GH�UHDF LH��'H�DFHHD�DFHDVW��SLHUGHUH�GH�F�OGXU��HVWH�specific� numai pentru cazul arderii combustibililor solizi SH� JU�WDU� IL[� VDX� PRELO� �SHQWUX� FRPEXVWLELOL� OLFKL]L� úL� JD]RúL�

mecq =0)


19

i

mec

mecHB

Qq

*= sau exprimat în procente 100

* i

mec

mecHB

Qq = (%)

unde : *B este consumul de combustibil (kg/s) ;

iH -�SXWHUHD�FDORULF��LQIHULRDU��D�FRPEXVWLELOXOXL��NJ�NJ�� PierderHD�VSHFLILF��GH�F�OGXU� mecq se determin��FX�UHOD LD��

isb

sb

sb

zg

zg

zg

caz

caz

cazmecH

A

c

ca

c

ca

c

caq

100

32657

100100100

−+

−+

−= (2.4)

unde aj�HVWH�SURFHQWXO�GH�SDUWLFLSDUH�vQ�FHQXúH�D�GLIHULWHORU�IUDF LXQL�� 100=∑ ja ��úL�cj�HVWH�FRQ LQXWXO�SURFHQWXaO�GH�FDUERQ�IL[�GLQ�IUDF LXQHD�aj. Valorile medii orientative se SUH]LQW� în tabelul 2.1. pentru combustibil ligniW�SH�GLYHUVH�WLSXUL�GH�JU�WDUH�

Cu A VH�QRWHD]��SURFHQWXO�WRWDO�GH�FHQXúH�GLQ�FRPEXVWLELO.

Tabelul 2.1.

&�]XW�VXE�JU�WDU

Inglobat în zJXU�

Antrenat cu FHQXúD�

zEXU�WRDUH &RPEXVWLELO�úL�VLVWHP�GH�DUGHUH

caza cazc zga zgc sba sbc

/LJQLW�SH�JU�WDU�IL[�SODQ 4 10 76 15 20 9 /LJQLW�SH�JU�WDU�vQFOLQDW�IL[ 2 10 78 15 20 8 /LJQLW�SH�JU�WDU�FX�vPSLQJHUH�GLUHFW�

15 4 55 10 30 4

/LJQLW�SH�JU�WDU�cu împingere U�VWXUQDW�

20 10 50 10 30 4

Lignit P�FLQDW�ars în stare pulverizat�

0 - 10 10 90 3

În mod normal mecq poate avea valoarea FXSULQV�� vQ� LQWHUYDOXO� �÷12% pentru F�UEXQL�úL�0,5 ÷��SHQWUX�OHPQ�úL�YHJHWDOH uscate. Consumul efectiv de combustibil (B) va fi :

)1(* mecqBB −= [kg/s] (2.5)


CAZANE

20

2.1.2.�3LHUGHUL�VSHFLILFH�GH�F�OGXU��SUin evacuarea gazelor de ardere la�FRú�� cosq

sau q2 )

Se determin��FX�UHOD LD�:

i

a

HB

QQq

*cos

cos

−= în valori absolute sau,

100i

acoscos

H*B

QQq

−= în %

H[SOLFLWkQG�WHUPHQLL�UH]XOW�� )IIg(

H

qq coscoscos

i

meccos α−

−=

1 (2.6)

unde :

cosgI �VH�RE LQH�GLQ�diagrama I-t pentru cosα �úL�WHPSHUDWXUD� cost ;

cost - este un parametru FDUH� VH� VWDELOHúWH� SULQ� FDOFXOH� HFRQRPLFH�� GDU� SHQWUX�vQFHSHUHD�FDOFXOXOXL�VH�DSUR[LPHD]��OD�YDORUL�X]XDOH�IXQF LH�GH�WLSXO�FD]DQXOXL��$VWIHO, OD� FD]DQHOH� GH� DEXU�� IXQF LH� GH� WHPSHUDWXUD� GH� VDWXUD LH� D� DSHL� GLQ� FD]DQ (ts�� úL� GH�debitul de abur Dh [t/h] : PHQWUX�FD]DQH�I�U��VXSUDIH H�DX[LOLDUH��HFRQRPL]RU� SUHvQF�O]LWRU� :

h

sD

tt50

50cos ++≅ [0C] (2.7)

PentrX�FD]DQH�FX�VXSUDIH H�DX[LOLDUH:

hDt

100160cos +≅ [0C] (2.8)

Pentru cazane de ap��FDOG��VDX�ILHUELQWH��

)12080(cos ÷+= amtt [0C] unde 2

ei

am

ttt

+= (2.9)

aerI �UHSUH]LQW��HQWDOSLD�DHUXOXL�GH�DUGHUH��OD�WHPSHUDWXUD�DPELDQW� (ta≅200&��úL�se determin��FX�UHOD LD��

apaaer tcVI 0= [kJ/ 3Nm ] sau [kJ/kg] (2.10)


21

cu cpa=1,2971 [kJ/ KmN

3 ] VH�RE LQH:

cpa ta = iaer = 25,942 [kJ/ 3Nm ] (2.11)

ÌQ�FDOFXOXO� FX�F�OGXUi specifice�� SLHUGHULOH�GH�F�OGXU�� SULQ�HYDFXDUHD� la coú� VH�GHWHUPLQ��FX�UHOD LD� [ ]apapgg

i

tcVtcVH

q 0coscoscos

1 α−= (2.12)

(GDF��VH�DGPLWH qmec =0) cu 0cos )1( VVV gog −+= α (2.13)

( )[ ])()1(1

cos0coscoscos apaapggo

i

ttcVttcVH

q −−+−= α (2.14)

5HOD LH�SULQ care se pune�vQ�HYLGHQ ��

1. pLHUGHUHD�GH�F�OGXU�� prin cantitatea miniP��Ge gaze rezultate din ardere; 2. pierderea GH�F�OGXU��sXSOLPHQWDU��SULQ�DHUXO�vQ�H[FHV�

Aceste pierderi VSHFLILFH� GH� F�OGXU�� DX� YDORUL� X]XDOH� GH� �÷�� vQ� IXQF LH� GH�

WLSXO�LQVWDOD LHL�GH�DUGHUH��GH�natura combustibilului�úL�GH�WLSXO�FD]DQXOXL.

2.1.3. PierdHUL� VSHFLILFH� GH� F�OGXU�� SULQ� DUGHUH� LQFRPSOHW�� GH� QDWXU�� FKLPLF��( chq sau q3 )

Aceste pierderi GH�F�OGXU�� DSDU�GDWRULW�� IDSWXOXL�F��RPRJHQL]DUHD�DPHVWHFXOXL�combustibil-DHU�GH�DUGHUH�QX�SRDWH�IL�SHUIHFW��RULFkW�GH�SHUIRUPDQW��DU�IL�LQVWDOD LD�GH�DUGHUH��$VWIHO� F�� UHDOL]kQG� FKLDU� úL� DPHVWHFXUL� FX� H[FHV� GH� DHU�� în gazele de ardere rezultate VH�J�VHVF�FRPSRQHQWH�JD]RDVH�GH�DUGHUH� LQFRPSOHW��combustibile, ca: CO, H2, CH4 etc.

uscg

i

mec

i

chch V)H,CO,(

H

q

H*B

Qq 29810736126

1⋅+⋅

−== (2.15)

La proiectarea cazaneloU�VH�SRW�DGPLWH�XUP�WRDUHOH��YDORUL�RULHQWDWLYH�SHQWUX�qch:

- vQ�FD]XO�XWLOL]�ULL�XQHL�LQVWOD LL�GH�DUGHUH�SHUIRUPDQWH� chq ≅0 ;

- la focare cu ecranare�PLF� (calde): chq ≅0,005 ;

- la focare cu ecranare medie: chq ≅0,01 ;


CAZANE

22

- la focare cu ecranare SXWHUQLF� (reci): chq ≅0,015 ;

- OD�IRFDUH�FX�JU�WDUH� chq ≅0,02 . ��3LHUGHUL�VSHFLILFH�GH�F�OGXU��SULQ�SHUH L�H[WHULRUL�(qext sau q5)

Se determin��FX�UHOD LD��

i

apiii

i

ext

extHB

ttS

HB

Qq

*

)(

*∑ −

==α

(2.16)

unde: tpi – tHPSHUDWXUD�PHGLH�D�XQHL�VXSUDIH H�H[WHULRDUH�„i” a cazanului;

Si –�P�ULPHD�VXSUDIH HL�H[WHULRDUH�„i” a cazanului;

αi –�FRHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��OD�VXUDID D�H[WHULRDU��„i” a acazanului. 5HOD LD��SRDWH�IL�XWLOL]DW��QXPDL�SHQWUX�XQ�FD]DQ�H[LVWHQW pentru care s-au determinat��vQ�IXQF LRQDUH�OD VDUFLQD�QRPLQDO��WHPSHUDWXULOH�SH�VXSUDIH HOH�H[WHULRDUH�ale acestuia. În faza de proiectare se XWLOL]HD]��UHOD LL�experimentale:

• qext= 5,4643 · 10·-2

· Dh-0,6557

- pHQWUX�FD]DQH�GH�DEXU�I�U� (2.17) VXSUDIH H�DQH[H��Dh – debit de abur [t/h]);

• qext= 5,8797 · 10·

-2· Dh

-0,5185 - pentru cazane de abur cu (2.18)

VXSUDIH H�DQH[H��Dh – debit de abur [t/h]);

• qext= 4,6167 · 10·-2

· QMW - pentru cazane mari�GH�DS��FDOG��VDX�(2.19) fiebinte (QMW = 0,1 ÷ 6 MW). QMW – sarcina �WHUPLFD�D�FD]DQXOXL�H[SULPDW��vQ�0:�

• SHQWUX� FD]DQH� GH� DS�� FDOG�� VDX fiebinte,� PLFL� úL� PLMORFLL� �Q

<1000kW), se poate aprecia pentru qext o valoare în intervalul (0,5÷1,5 %) vQ�IXQF LH�GH�JUDGXO�GH�L]RODUH�WHUPLF� dorit.


23

��3LHUGHUL�VSHFLILFH�GH�F�OGXU��SULQ�HYDFXDUHD�SURGXVHORU�VROLGH�GLQ�FD]Dn (qcen

sau q6 ) $FHVW�WLS�GH�SLHUGHUH�GH�F�OGXU��UHSUH]LQW��F�OGXUD�HYDFXDW��RGDW��FX�FHQXúD�úL�zgura (produsele solide ale arGHULL�FRPEXVWLELOLORU�VROL]L��OD�R�WHPSHUDWXU��PDL�ULGLFDW��decât cea de refeULQ �� GH� ELODQ ��'H� DFHHD� DFHDVW�� SLHUGHUH� GH� F�OGXU�� HVWH� specific� numai pentru cazul arderii�FRPEXVWLELOLORU�VROL]L��SHQWUX�FRPEXVWLELOL�OLFKL]L�úL�JD]RúL�qcen=0)

)(1

1

100 aevpev

zgcaz

sb

i

cen ttccc

a

H

Aq −⋅

−−−

= (2.20)

unde : cpev –� HVWH�F�OGXUD� VSHFLILF��PHGLe� D�SURGXVHORU�HYDFXDWH� �FHQXúH�úL�]JXU��FRQIRUP�

tabelului 2.2. tev – temperatura de evacuare a produselor solide

Tabelul 2.2. &�OGXUD specific� medie a zgurii��FHQXúLL�

t (oC) 100 200 400 600 800 1000 1200 1400 1600 1800 cpev(kJ/kgK) 0,801 0,842 0,899 0,930 0,956 0,980 1,001 1,130 1,172 1,212 În mod uzual pierderile�VSHFLILFH�GH�F�OGXU� qcen nu dep�úHVF��

Pentru XQ� FD]DQ� FH� XWLOL]HD]�� FRPEXVWLELO solid, randamentul termic de proiectare al cazanului va fi:

)qqqqq( evextchcosmec ++++−= 1η (2.21) cu valori uzuale în intervalul 0,7–0,85.

Pentru XQ�FD]DQ�FH�XWLOL]HD]��FRPEXVWLELO lichid sau gazos, randamentul termic de proiectare al cazanului va fi:

)(1 cos extch qqq ++−=η (2.22) cu valori uzuale în intervalul 0,88÷0,93 (cazane clasice�I�U��FRQGHQVDUH�D�YDSRULORU�GH�DS��GLQ�JD]HOH�GH�DUGHUH�.


CAZANE

24

2.2. Consumul de combustibil

2.2.1. Consumul de combustibil, pentru cazanele ce produc abur este :

i

p

H

iiDiiDB

η)'()(

* 00 −+−= [Kg/s, m3

N/s] (2.23)

unde cu D s-a notat debitul de abur al cazanului [kg/s] �GDW�SULQ�WHP��.

Un mod de exprimare tehnic curent al debitului de abur al cazanului este ”Dh” , mãsurat vQ�>W�K@�úL�DVWIHO: D = Dh ⋅⋅ 0,278 [kg/s] i –�HQWDOSLD�ILQDO� a aburului la evacuare din cazan [kJ/kg]; i0 –�HQWDOSLD�LQL LDO��D�DSHL�de alimentare a cazanului [kJ/kg];

io= cpa· tal = 4,186· tai [kJ/kg]

cpa –�F�OGXUD�VSHFLILF��D�DSHL�� tal - temperatura apei de alimentare a cazanului

i’, i” –�HQWDOSLD�DSHL�úL�a aburului, OD�VDWXUD LH [kJ/kg] ;

Dp – debitul de purje (kg/s) pentru care se admite Dp =(0,03÷0,05)· D 3XUMDUHD�FD]DQXOXL�VH�IDFH�SHQWUX�D�VF�GHD�SHULRGLF�duritatea apei din cazan sub OLPLWD�DGPLVLELO��SHVWH�FDUH�V�UXULOH�GH�&D�úL�0J�vQFHS�V��VH�GHSXQ��SH�VXSUDIH HOH�GH�VFKLPE�GH�F�OGXU��

)�U��SXUMDUHD��SHUPDQHQW��VDX�SHULRGLF��D�DFHVWXL�GHELW�'p�GH�DS��OD�VDWXUD LH��FD]DQXO� QX� DU� SXWHD� IXQF LRQD� vQ� PRG� FRQWLQXX� úL�� GH� DFHHD�� VH� FRQVLGHU�� F�OGXUD�HYDFXDW��FX�SXUMD�FD�ILLQG�WHKQRORJLF�XWLO�� Pentru aburul umed, cu titlul $ entalpia ´L´�VH�FDOFXOHD]��FX�UHOD LD�� L� �L¶��$��L´- i’) (2.24) Pentru cazanele mari la care DU]�WRDUHOH�XWLOL]HD]��DEXU�VDWXUDW�ca agent motor SHQWUX�LQMHF LD�FRPEXVWLELOXOXL�OLFKLG��

)''(

)'()(*

0

00

iiWH

iiDiiDB

inji

p

−−⋅−+−

=η (2.25)


25

Winj – debitul relativ de abur XWLOL]DW� GH� F�WUH injectorul de combustibil lichid [kg.abur/kg.comb]. 2.2.2. Consumul de combustibil, pentru cazanele�GH�DS��FDOG��VDX�ILHUELQWH�

Pentru cazanele�GH�DS��FDOG��VDX�ILHUELQWH�VH G�,�SULQ�WHP�, debiWXO�GH�F�OGXU��XWLO�� SURGXV de cazan� �VDUFLQD� WHUPLF�� D� FD]DQXOXL�, Q [kW] úL� asfel se poate determina consumul de combustibil al cazanului:

iH

Q*B

η= (kg/s, m3

N /s) (2.26)

Pentru cazanele mari GH�DS�� FDOG�� VDX�DS�� ILHUELQWH�de peste 500 kW, debitul util GH�F�OGXU��Qh�VH�H[SULP��în [Gcal/h] – sistem tehnic.

În acest caz, consumul de combustibil VH�GHWHUPLQ��XWLOL]kQG�UHOD LD�RPRJHQ�:

i

h

H

Q,*B

η

3101631 ⋅⋅= (kg/s, m3

N /s)

Debitul de combustibil consumat efectiv în cadrul procesului de ardere, în cazan, este :

)q(*BB mec−= 1 (kg/s, m3N /s) (2.27)

B este debitul de combustibil ce se va utiliza în continuare în cadrul calculelor de dimensionare necesare întregului�FD]DQ��vQ�FHHD�FH�SULYHúWH�GHWHUPLQDUHD�GHELWHORU�de gaze de ardere. ��%LODQ XO�GH�DQVDPEOX�DO�FD]DQXOXL� %LODQ XO�GH�DQVDPEOX�DO�FD]DQXOXL�sH�HIHFWXHD]��SHQWUX�a se determina fluxurile GH�F�OGXU��DIHUHQWH�ILHF�UHL�VXSUDIH H�GH�VFKLPE�GH�F�OGXU�, în parte, a cazanului.

In cazul cel mai general de cazan, FX�VXSUDIH H�DQH[H�úL�cu producere de abur supraîQF�O]LW�� UHSUH]HQWDUHD� VFKHPDWLF�� D� ELODQ XOXL� GH� DQVDPEOX� HVWH conform figurii_2.2. 3HQWUX� FD]DQHOH� PDL� VLPSOH� VH� HOLPLQ�� GLQ� VFKHP�� HFRQRPL]RUXO� úL�preîQF�O]LWRUXO�GH�DHU��VDX�QXPDL�XQD�GLQ�DFHVWH�VXSUDIH H�DX[LOLDUH��GXS��FD]��

'H� DVHPHQHD�� SHQWUX� FD]DQHOH� GH� DEXU� VDWXUDW�� VH� HOLPLQ�� GLQ� VFKHP��VXSUDvQF�O]LWRUXO�


CAZANE

26

)OX[XO�GH�F�OGXU��WUDQVPLV�în cadrul economizorului : ))(( oecpec iiDDQ −+= (kW) (2.28)

unde iec se FRQVLGHU� pentru o tempeUDWXU�� D� DSHL� FX� FFD�� o&� PDL� VF�]XW�� GHFkW WHPSHUDWXUD�GH�VDWXUD LH��tec ≅ ts -100C) a aburului produs de cazan. )OX[XO�GH�F�OGXU��WUDQVPLV�în cadrul VLVWHPXOXL�ILHUE�WRU�� )]i'i(D)ii(D[Q ecpecsfsf −+−= (kW) (2.29)

Fig. 2.2.�6FKHPD�ELODQ XOXL�GH�DQVDPEOX�DO�FD]DQXOXL�GH�DEXU�VXSUDvQF�O]LW GH�PHQ LRQDW� F�� GDF�� VH� HIHFWXHD]�� R�EXQ�� VHSDUDUH�D�SLF�WXULORU�GH�DS�� OD� VDWXUD LH din aburul ce iese din tambur, se poate accepta isf = i’’ ($�=1). )OX[XO�GH�F�OGXU��WUDQVPLV�în cadrul supraîQF�O]LWRUXOXL�HVWH�� )ii(DQ sfsi −= (kW) (2.30)

)OX[XO�GH�F�OGXU��SUHOXDW�vQ cadrul preîQF�O]LWRUXOui de aer : )(0 aapfpa iiVBQ −⋅⋅⋅⋅= αϕ (kW) (2.31)

unde:

$S��alimentare

Abur VXSUDvQ�O]LW

BHi

QPA Focar

QSFR

Sistem ILHUE�WRU�convectiv

QSFC

6XSUDvQF�O- zitor

QSI

Econo- mizor

QEC

QPA

3UHkQF�O]LWRU de aer

Aer preîQF�O]LW

tPA

tEC

tt

It

tf

If

tsfc

Isfc

tsi

Isi

tec

Iec

tpaA�tcos

IpaAIcos

Aer ambiant

ta


27

ϕ – SURSRU LD de aer din aerul de ardere ce se preînF�O]HúWH, (50 ÷ 100%);

iap, ia – entalpiile specifice ale aerului preîQF�O]LW��UHVSHFWLY�DPELDQW��iap=cp ap tap;

ia=cpa ta). &X� DFHVWH� GDWH� VH� vQWRFPHúWH� WDEHOXO� GH� ELODQ � ��. pentru un caz de exemplificare pentru care qmec=0 úL qev=0.

Tabelul 2.3. Q cedat de arderea

combustibilului – pierderi [kW]

Q preluat de sXSUDIH Hle de VFKLPE�GH�F�OGXU�

[kW] QC=B*Hi

Qpa=B· αf · ϕ · V0(iap-ia)

-qFRú B* Hi

-qch B* Hi

-qext B* Hi

Qec

Qsf=Qsfc+Qsfr

Qsi

Qpa

∑= QQ' eroare max. 1% ∑= QQ''

(URDUHD�UHODWLY��GH�vQFKLGHUH�D�ELODQ XOXL�GH�DQVDPEOX�se determin��FX�UHOD LD�� %1100

'

'''≤

−=

Q

QQε (2.31”)

ÌQ� FD]XO� FD]DQHORU� � GH� DS�� FDOG�� VDX ILHUELQWH� ELODQ XO� HVWH� PXOW� VLPSOLILFDW�deoarece cazanul este compus numai din sistem radiant (focar)�úL�VLVWHP�FRQYHFWLY�GH�vQF�O]LUH�D�DSHL��6FKHPD�HVWH�GDW��vQ�ILJXUD��

5HOD LLOH� GH� ELODQ � VXQW� FRQIRUP� WDEHOXOui� �� SHQWUX� FD]DQH� IXQF LRQkQG� FX�combustibil lichid sau gazos).

Fig. 2.3. 6FKHPD�ELODQ XOXL�GH�DQVDPEOX�DO�FD]DQXOXL�GH�DS��FDOG��VDX�DS��ILHUELQWH.

Tabelul 2.4. Q cedat de arderea

combustibilului – pirderi [kW]

Q preluat de sXSUDIH Hle de VFKLPE�GH�F�OGXU�

[kW] + B Hi

-qFRú B Hi CRut QQQ +=

Focar

QR

Convectiv

QC

It If Ic A Icos


CAZANE

28

-qch B Hi

-qext B Hi

∑= QQ' eroare max. 1% ∑= QQ''

2.4. %LODQ XO�JUDILF�DO�FD]DQXOXL�

%LODQ XO� JUDILF� DO� Fazanului transpune grafic, la VFDU�� GHELWHOH� GH� F�OGXU��

conform celor din tabelele 2.3 sau 2.4.�IXQF LH�GH�WLSXO�FD]DQXOXL�OD�FDUH�VH�UHIHU��

Fig. 2.4.�%LODQ XO�JUDILF�DO�FD]DQXOXL

ÌQ� ILJXUD� �� VH� SUH]LQW�� VFKHPDWLF� ELODQ XO� JUDILF� DO� XQXL� FD]DQ� GH� DEXU�VXSUDvQF�O]LW�DOLPHQWDW�FX�FRPEXVWLELO�VROLG�

2.5. %LODQ XO�SDU LDO pe elemente al cazanului - stabilirea temperaturilor

úL�HQWDOSLLlor gazelor de ardere pe traseu.

A. Cazane de abur. 6H�FRQVLGHU�, ipotetic,�F��WHPSHUDWXUD�GH�vQFHSXW�D�SURFHVXOXL�GH�FHGDUH�GH�F�OGXU�

a gazelor de ardere,�HVWH�WHPSHUDWXUD�WHRUHWLF��GH�DUGHre (tt), corespunz�WRDUH entalpiei teoretice de ardere (It):

afapfmecch

mec

it

iViVqqq

HI 00 )1()1(

1αϕαϕ −++−−

−= (2.32)

DEBITE UTILE DE CALDURA

DEBITE DE CALDURA PIERDUTA

B*Hi

B*αcos Ia0

QPA

QR

QSFC

QSI

QEC

DEBITE DE CALDURA

INTRODUSE

B*Icos

B*qchHi

B*qmecHi

B*qextHi

B*qevHi


29

OD�FD]DQH�I�U��SUHvQF�O]LWRU�GH�DHU��ϕ =0)

afmecch

mec

it iVqq

q

HI 0)1(

1α+−−

−= (2.33)

7HPSHUDWXUD� WHRUHWLF��GH�DUGHUH�VH�GHWHUPLQ��Gin diagrama I-t, pentru entalpia teRUHWLF� de ardere It�úL�FRHILFLHQWXO�GH�H[FHV�GH�DHU�SHQWUX�IRFDU αf. )OX[XO�GH�F�OGXU��SUHOXDW�SULQ�UDGLD LH�vQ�IRFDU�� )()1( ftextR IIBqQ −−= [kW] (2.34)

7HPSHUDWXUD� OD� FDS�WXO� IRFDUXOXL� tf VH� DOHJH� LQL LDO� vQWUH 600÷11000C în

IXQF LH� GH� Qatura combustibilului� úL� GH� GH� tipul focarului, apoi se va verifica (modifica) pe baza criteriilor economice� VDX� IXQF LH� GH� QHFHVLW� LOH� GH� HFKLOLEUDUH�GLPHQVLRQDO��D�VXSUDIH HORU�GH�VFKLPE�GH�F�OGXU�� Din diagrama I-t UH]XOW� entalpia gazelor de ardere la iHúLUHD� GLQ� IRFDU If,

pentru temperatura tf� LQL LDOL]DW�� úL�excesul de aer de ardere FRUHVSXQ]�WRU� IRFDUXOXL�αf.

)OX[XO�GH�F�OGXU��SUHOXDW�vQ�VLVWHPXO�ILHUE�WRU�FRQYHFWLY�� ))(1( sfcfextRsfsfc IIqBQQQ −−=−= (KW) (2.35)

Entalpia JD]HORU�GH�DUGHUH�GXS��VLVWHPXO�ILHUE�WRU�FRQYHFWLY��YD�IL��

B

Q

qII

sfc

ext

fsfc −−=

1

1 (2.36)

Din diagrama I-t, pentru Isfc�úL�αsfc��VH�RE LQH�tsfc . $QDORJ��HQWDOSLD�JD]HORU�GH�DUGHUH�GXS��VXSUDvQF�O]LWRU�HVWH��

B

Q

qII si

ext

sfcsi −−=

1

1 (2.37)

Din diagrama I-t, pentru Isi�úL�αsi��VH�RE LQH�tsi.


CAZANE

30

(QWDOSLD�JD]HORU�GH�DUGHUH�GXS��HFRQRPL]RU��

B

Q

qII ec

ext

siec −−=

1

1 (2.38)

Din diagrama I-t, pentru Iec�úL�αec��VH�RE LQH�tec. (QWDOSLD�JD]HORU�GH�DUGHUH�GXS��SUHvQF�O]LWRUXO�GH�DHU��

B

Q

qII

pa

ext

ecpag −−=

1

1 (2.39)

Din diagrama I-t, pentru Igpa�úL�αpa��VH�RE LQH�tgpa.

9HULILFDUHD�WHPSHUDWXULL�JD]HORU�GH�FRú��GDF��FDOFXOHOH�DX�IRVW�FRUHFW�HIHFWXDWH�� - SHQWUX�FD]DQH�I�U��VXSUDIH H�DX[LOLDUH� cossf tt ≅

- pentru cazane cu economizor cosec tt ≅

- SHQWUX�FD]DQH�FX�HFRQRPL]RU�úL�SUHvQF�O]LWRU�GH�DHU cospag tt ≅

Eroarea DGPLVLELO��GH�vQFKLGHUH�D�ELODQ XOXL�paU LDO�SH�HOHPHQWH este de maxim

0,5 %�úL�VH�GHWHUPLQ��DVWIHO� %,

II

II

cost

cosc

I 50100 <−−

=ε

%,tt

tt

cost

cosc

t 50100 <−−

=ε

B. &D]DQH�GH�DS��FDOG�

(QWDOSLD�WHRUHWLF��GH�DUGHUH�HVWH�� aomecch

mec

it iVqq

q

HI 00)1(

1α+−−

−= (2.40)

6H�DOHJH�OD�FDS�WXO�IRFDUXOXL�R�WHPSHUDWXU��OD�OLPLWD�LQIHULRDU��D�WHPSHUDWXULORU�uzuale :


31

tf =600 ÷ 900 o&� � vQ� IXQF LH� GH� FRPEXVWLELlul utilizaW� úL� tipul focarului. Din GLDJUDPD� HQWDOSLH� IXQF LH� GH� WHPSHUDWXUm� VH� GHWHUPLQm� HQWDOSLD� JD]HORU� OD� LHúLUH� GLQ�focar If=f(tf,af) 5H]XOW�� ))(1( ftextR IIqBQ −−= (2.41)

)OX[XO�GH�F�OGXU��SUHOXDW�în sistemul conectiv este :

Rc QQQ −= (2.42) UH]XOW��HQWDOSLD gazelor de ardere�GXS��VLVWHPXO�FRQYHFWLY��

B

Q

qII c

ext

fc )1(

1

−−= (2.43)

Din diagrama I-t, pentru Ic�úL�αc��VH�RE LQH�tc. /D� XQHOH� FD]DQH� H[LVW�� GRX�� sau mai multe sisteme convective. Pentru cazul

cazanelor cu�GRX��GUXPXUL�FRQYHFWLYH�VH�DSUHFLD]� XUP�WRDUHOH�SRQGHUL: QCI = (0,7 ÷ 0,8) QC QCII = QC - QCI

úL�VH�FDOFXOHD]��HQWDOSLL�úL�WHPSHUDWXUL�LQWHUPHGLDUH��

(URDUHD�DGPLVLELO�� GH� vQFKLGHUH�D�ELODQ XOXL�SU LDO�SH�HOHPHQWH�HVWH�GH�PD[LP�0,5 ��úL�VH�GHWHUPLQ��DVWIHO�

%,II

II

cost

cosc

I 50100 <−−

=ε

%,tt

tt

cost

cosc

t 50100 <−−

=ε

C. 0HWRGH�GH�FDOFXO�FX�F�OGXUL�VSHFLILFH�

7HPSHUDWXUD� WHRUHWLF�� GH� DUGHUH� VH� poate determina, prin calcul iterativ, XWLOL]kQG�UHOD LD:


CAZANE

32

pgg

t

pgg

aoaerpfapaerpfmecch

mec

i

tcV

Q

cV

tcVtcVqqq

H

t =−++−−

−=

00'

)1()1(1

αϕαϕ

(2.44)

pentru cazul arderii FX�DHU�SUHvQF�O]LW�sau:

pggpgg

aopaerfmecchi

tcV

Q

cV

tcVqqHt 00' )1(

=+−−

=α

(2.45)

SHQWUX�FD]XO�DUGHULL�I�U��DHU�SUHvQF�O]LW��ϕ =0). Volumul de gaze de ardere cu exces de aer:

01 V)(VV fgg o−+= α

Deoarece YDORDUHD� F�OGXULL� VSHFLILFH� D� JD]HORUGH� DUGHUH� cpg esWH� IXQF LH� GH�

WHPSHUDWXU��UH]XOW��F��valoarea temperaturii teoretice de ardere tt trebuie LQL LDOL]DW�.

Astfel, se�DSUHFLD]��YDORDUHD� '

tt în intervalul 1800÷2000 oC.

6H� GHWHUPLQ�� GLQ� '

pgc conform Cap. �� IXQF LH� GH� WHPSHUDWXUD� WHRUHWLF�� GH�DUGHUH�LQL LDOL]DW��GXS��FDUH�VH�FDOFXOHD]�� ''

tt :

'

pgg

c''

tcV

Qt = (2.46)

'DF�� ''

tt FDOFXODW�GLIHU� de '

tt LQL LDO cu mai mult de 50 K se UHLWHUHD]��FDOFulul

FX� R� QRX�� YDORDUH� D� F�OGXULL� VSHFLILFH� cpg GHWHUPLQDW� la temperatura ''

tt � úL� VH�GHWHUPLQ��tt :

pgg

ct

cV

Qt = (2.47)

'HRDUHFH�YDULD LD�F�OGXULL�VSHFLILFH�FX�WHPSHUDWXUD�HVWH�IRDUWH�PLF��VXE��OD�100 grd.), nu�VXQW�QHFHVDUH�PDL�PXOW�GH�GRX��LWHUD LL pentru.

Pentru alegerea valorii de temperatur��D�JD]HORU�GH�DUGHUH� OD�FDS�WXO�IRFDUXOXL VH�IRORVHVF�LQGLFD LLOH�GH��OD� Cap. 2.5.A. sau 2.5.B.

)OX[XO�GH�F�OGXU��SUHOXDW�SULQ�UDGLD LH�vQ�IRFDU�YD�IL��


33

)()1( ftpggextR ttcBVqQ −−= (2.48)

unde pentru determinarea valorii� F�OGXULL� VSHFLILFH� a gazelor de ardere s-a luat

valoarea medie a�LQWHUYDOXOXL�GH�WHPSHUDWXU��2

ft

mf

ttt

+= úL�coeficientul de exces de

aer αf .

FOX[XO�GH�F�OGXU��SUHOXDW�vQ�VLVWHPXO�ILHUE�WRU�FRQYHFWLY�HVWH�� Rsfsfc QQQ −= (2.49)

úL�WHPSHUDWXUD�ILQDO��a gazelor de ardere:

pggext

sfc

fsfccBVq

Qtt

)1( −−= (2.50)

unde pgc se GHWHUPLQ� pentru αsfc�úL�WHPSHUDWXUD�PHGLH�2

sfct

msfc

ttt

+= :

01 V)(VV sfcgg o−+= α

ùL�vQ�DFHVW�FD]�VH�SUHVXSXQH�LQL LDO�R�YDORDUH�SHQWUX� '

sfct �úL�VH�UHFDOFXOHD]�� pgc

GDF��YDORDUHD�UH]XOWDW��SHQWUX� sfct �GLIHU��GH� '

sfct cu mai mult de 50 K.

Temperatura gazelor de ardere OD�HúLUH�GLQ supraîQF�O]LWRU��

pggext

sisfcsi

cBVq

Qtt

)1( −−= (2.51)

cu

+== si

sisfc

sipg ,tt

tfc α2

�úL� 01 V)(VV sigg o−+= α

GXS��HFRQRPL]RU��

pggext

ecsiec

cBVq

Qtt

)1( −−= (2.52)

cu

+

== ececsi

ecpg ,tt

tfc α2

�úL� 01 V)(VV ecgg o−+= α


CAZANE

34

úL�GXS��SUHvQF�O]LWRUXO�GH�DHU��

pggext

pa

ecpacBVq

Qtt

)1( −−= (2.52)

cu

+== pa

paec

papg ,tt

tfc α2

�úL� 01 V)(VV pagg o−+= α

&D� úL� în cadrul cap. 2.5.A se face verificarea corectitudinii calculului prin compararea temperaturii de iHúLUH�D�JD]HORU�GH�DUGHUH�GH�SH�XOWLPD�VXSUDID ��GH�VFKLPE�GH�F�OGXU��cu temperatura GH�HYDFXDUH�OD�FRú�

(URDUHD�DGPLVLELO�� GH� vQFKLGHUH�D�ELODQ XOXL�SU LDO�SH�HOHPHQWH�HVWH�GH�PD[LP�0,5 ��úL�VH�GHWHUPLQ��DVWIHO�

%,tt

tt

cost

cosc

t 50100 <−−

=ε

În cazul cazanelor de� DS�� FDOG� sau fierbinte�� GXS�� FDOFXOXO� WHPSHUDWXULL�

teoretice de ardere tt DúD� FXP� V-D� DU�WDW� PDL� VXV� úL� alegeUHD� WHPSHUDWXULL� OD� FDS�WXO�focarului tf�VH�FDOFXOHD]��4R . )OX[XO�GH�F�OGXU��SUHOXDW�vQ�VLVWHPXO�FRQYHFWLY�este :

Rc QQQ −= (2.53) úL�WHPSHUDWXUD�ILQDO��D�JD]HORU�GH�DUGHUH:

pggext

cfc

cBVq

Qtt

)1( −−= (2.54)

unde pgc se GHWHUPLQ��SHQWUX�FRQGL LLOH��

2cf

cm

ttt

+= �úL�αc (2.55)

iar volumul real al gazelor de ardere este:

01 V)(VV cgg o−+= α (2.56)

(URDUHD�DGPLVLELO�� GH� vQFKLGHUH�D�ELODQ XOXL�SU LDO�SH�HOHPHQWH�HVWH�GH�PD[LP�

0,5 ��úL�VH�GHWHUPLQ��DVWIHO� %,

tt

tt

cost

cosc

t 50100 <−−

=ε

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

35

CAPITOLUL 3

CALCULUL TERMIC AL C$=$1(/25� '(� $3��&$/'��6$8�),(5%,17(�

3.1. Calculul termic al cazanelor ignitubulare cu întoarcerea gazelor de

ardere în focar

3.1.1. Descriere constructiv��HOHPHQWH�FRPSRQHQWH��PRG�GH�IXQF LRQDUH� Acest tip de cazane au focarul sub forma unui� WXE� GH� IODF�U�� ODUJ�� I�U��

VWU�SXQJHUH� în LQWHULRUXO�F�UXLD�gazele de ardere�VXQW�QHYRLWH�V��VH�vQWRDUF��vQ�GLUHF LH�LQYHUV�� MHWXOXL� GH� IODF�U�� realizând astfel XQ� GUXP� FRQYHFWLY�� )XQF LRQHD]�� FX�combustibil gazos sau OLFKLG� úL� SURGXF� DS�� FDOG�� 70 o&� úL� PDL� UDU� DS�� ILHUELQWH�130/110 oC. Sunt de tip igQLWXEXODU��FX�YROXP�PDUH�GH�DS�� LDU�Srincipalele elemente componente ale cazanului sunt prezentate în figura 3.1.

Fig. 3.1. Cazan ignitubular cu întoarcerea gazelor de ardere în focar 1. corp cazan; 2. focar tubular�� HYL�GH�“fum”�FX�WXUEXOL]DWRUL��DU]�WRU��Xú��L]RODW��WHUPLF��LQWUDUH�DS��

��LHúLUH�DS��FXWLH�FROHFWDUH�JD]H��OHJ�WXU��OD�FRú��L]ROD LH�WHUPLF��SODF��WXEXODU��ID �� SODF��WXEXODU��VSDte; 13.vizor; 14. teacã termostate; 15. panou comandã úi reglaj.

$FHVWH�FD]DQH�VXQW�DOF�WXLWH�GLQWU-un cilindru cu diametru mare (1), în interiorul F�UXLD�VH�DIO�� VXSUDIH HOH�GH�VFKLPE�GH�F�OGXU�� WXEXO�GH� IODF�U�� FX�SHUHte neted, încastra L� în� SODFD� WXEXODU�� ID �� úL� HYLOH� GH� ”fum” cu turbulizatori, cu rol de

15

13

1 2 3 4

5

6

8

7

9

10

11

12 14 15

3

2 1

10 6


CAZANE

36

fascicul convectiv (3�� HYLOH� GH� “fum”� VXQW� IL[DWH� SULQ� VXGXU�� VDX� PDQGULQDUH� vQ�SO�FLOH�WXEXODUH�ID ��úL�VSDWH��. IntUDUHD�DSHL�vQ�FD]DQ��VH�IDFH�SH�OD�SDUWHD�GH�VXV�VDX�SH�OD�SDUWHD�LQIHULRDU��iar evacuarea apei calde (7) VH�IDFH�vQWRWGHDXQD�SH�OD�SDUWHD�VXSHULRDU�. 8úD� GH� vQFKLGHUH� a cazanului (5),� L]RODW�� WHUPLF�� permite trecerea gazelor de ardere din focar în siVWHPXO�FRQYHFWLY�úL�SR]L LRQDUHD�DU]�WRUXOXL. /D� DU]�WRU� HVWH� DGXV� FRPEXVWLELOXO� iar ventilatorul DVSLU� úL� LQWURGXFH� aerul necesar arderii în tubul de ardere din focar. ,Q� LQWHULRUXO� IRFDUXOXL� VH� DSULQGH� úL� VH� VWDELOL]H]�� IODF�UD�GH]YROWându-se debitul de gaze de ardere. Acestea ajung în partea din spate a focarului�úL�VXQW�REOLJDWH�V��VH�vQWRDUF��spre�SDUWHD�GLQ�ID �. 'DWRULW�� XúLL� FD]DQXOXL� JD]HOH� GH� DUGHUH� VH� vQWRUF� FX� ��0� úL� LQWU�� vQ� HYLOH�FRQYHFWLYH��6XQW�FROHFWDWH�vQ�FXWLD��úL�HYDFXDWH��SH�FRú�SULQ�úWX XO��. 3.1.2. Tema de proiectare

Prin tema de proiectare se dau: - Q -�VDUFLQD�WHUPLF��D�FD]DQXOXL��vQ�N:�� - te / ti - temperatura apei la�LHúLUH�úL�LQWUDUH�vQ�FD]DQ��70 oC) sau (80/60 oC); - natura�FRPSR]L Lei combustibilului.

Aceste cazaQH� IXQF LRQHD]�� FX� VXSUDSUHVLXQH� vQ� IRFDU�� GHFL� FRHILFLHQWXO� GH�excHV�GH�DHU�HVWH�FRQVWDQW�SkQ��OD HYFXDUHD�OD�FRú:

α = αf = αc = αFRú�= 1,05 ÷ 1,15 = ct.

&RQIRUP� LQGLFD LLORU� GLQ� FDSLWROXO� �� VH� HIHFWXHD]�� FDOFXOXO� DUGHULL�FRPEXVWLELOXOXL�úL�VH�GHWHUPLQ�: VO, Vgo, Vg, Hi, OH2

p , 2ROp ��VH�WUDVHD]��GLDJUDPD�,�– t

sau cp – t. ��&DOFXOXO�UDQGDPHQWXOXL�WHUPLF�DO�FD]DQXOXL�úL�D�GHELWXOXL�GH�FRPEXVWLELO� $FHVWH� FD]DQH� IXQF LRQHD]�� QXPDL� FX� FRPEXVWLELO� JD]RV� VDX� lichid, deci pierderea specific� GH�F�OGXU��SULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��mecanic� (qmec��úL�FHa prin evacuarea produselor solide ale arderii din cazan (qcen) sunt nule. De asemenea B* = B. 6H�FDOFXOHD]��SLHUGHULOH�VSHFLILFH�GH�F�OGXU�: a. Pierderea�VSHFLILF��GH�F�OGXU��SULQ�HQWDOSLD�JD]HORU�GH�DUGHUH�OD�FRú� )LLQG� XQ� FD]DQ� GH� DS�� FDOG�� VH� DGPLWH� R� WHPSHUDWXU�� OD� FRú� FH� VH� SRDWH�GHWHUPLQD�FX�UHOD LD de aproximare:

Ctt

t ei 0cos )8060(

2÷+

+≅ (3.1)

Din diagrama I – t se determin��YDORDUHD�HQWDOSLHL�JD]HORU�GH�DUGHUH�OD�FRú: IFRú = f (tFRú, α)

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

37

Entalpia aerului teoretic de ardere se determin�� OD� WHPSHUDWXUD� DPELDQW�� ta=20oC

apaoao tcVI ⋅⋅= (3.2)

cu cpa = 1,2971 kJ/ Km3N

5H]XOW��SLHUGHUHD�VSHFLILF��OD�FRú: )(

1coscos ao

i

IIH

q α−= (3.3)

b. 3LHUGHUL�VSHFLILFH�GH�F�OGXU��SULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��FKLPLF��

În cadrul calculelor de proiectare�� GDWRULW�� SHUIRUPDQ HORU� IXQF LRQDOH� DOH�DU]�WRDUHORU�PRGHUQH�VH�DGPLWH�R�SLHUGHUH�SULQ�DUGHUH�LQFRPSOHW� de natur��FKLPLF� de ordinul:

qch = 0,001 ÷ 0,005

c. 3LHUGHUL�VSHFLILFH�GH�F�OGXU��SULQ�SHUH LL�H[WHULRUL�DL�FD]DQXOXL�� În cadrul calculelor de proiectare�� SHQWUX� FD]DQH� UHODWLY� PLFL�� vQ� IXQF LH� GH�gradul dorit de izolare�WHUPLF��D�FD]DQXOXL��se poate alege o valoare:

qext = 0,005 ÷ 0,015 d. Randamentul cazanului 6H�FDOFXOHD]��FX�UHOD LD: )(1 cos extch qqq ++−=η (3.4)

úL�H[SULPDW�vQ�YDORDUH�SURFHQWXDO�� ηη ⋅= 100%

e. Debitul de combustibil consumat

iH

QB

⋅=

η (kg/s) sau ( s/m3

N ) (3.5)

��%LODQ XO�GH�DQVDPEOX�DO�FD]DQXOXL� Fluxul util GH�F�OGXU��DO�FD]DQXOXL�HVWH� Q �GDW�SULQ�WHP��. )OX[XO�GH�F�OGXU��produs

de arderea combustibilului: ic BHQ = (3.6)

)OX[XO�GH�F�OGXU��DGXV�FX�DHUXO�GH�DUGHUH�� apaoa tcVBQ α= (3.7)

)OX[XO�GH�F�OGXU��SLHUGXW�OD�FRú: coscos IBQ ⋅= (3.8)

)OX[XO�GH�F�OGXU��SLHUGXW�SULQ�DUGHUH�LQFRPSOHW�: ichinc BHqQ = (3.9)

)OX[XO�GH�F�OGXU��SLHUGXW�spre exterior: iextext BHqQ = (3.10) 5H]XOW��tabelul de�ELODQ termic al cazanului:


CAZANE

38

Tabelul 3.1. Fluxuri introduse -

pierdere Util

Qc

Qa

– QFRú – Qinc

– Qext

Q

∑ = 'QQ ''∑ = QQ

1RW�: În acest bilDQ �WHUPHQHXO�“– qcosBHi” s-a scris sub forma�H[SOLFLW�:

(–BIFRú�+ Bαcoscpata= –QFRú+Qa).

(URDUHD�UHODWLY�: %1100'

"'≤

−=

Q

QQε (3.11)

'DF��HURDUHD�UHODWLY��GH�vQFKLGHUH�D�ELODQ XOXL�este mai mare de 1% (cea maxim DGPLVLELO��SHQWUX�DFHVW�JHQ�GH calcule) vQVHDPQ��F��V-D�I�FXW�R�JUHúHDO��GH�FDOFXO sau de citire în diagrama I-t.

3.1.5. %LODQ XO� SDU LDO� SH� VXSUDIH H� �FDOFXOXO� WHPSHUDWXULORU� úL� HQWDOSLLORU�gazelor de ardere pe traseu).

(QWDOSLD�WHRUHWLF��D�JD]HORU�GH�DUGHUH�VH�determin��FX�UHOD ia: apafchit tcVqHI 0)1( α+−= (3.12)

DSRL�VH�GHWHUPLQ��WHPSHUDWXUD�WHRUHWLF��GH�DUGHUH�GLQ�GLDJUDPD�,-t: ),I(ft tt α= . 2�LPSRUWDQW�� FDUDFWHULVWLF�� IXQF LRQDO�� D� FD]DQHORU�FX� vQWRDUFHUH a gazelor de

ardere în focar,�R�UHSUH]LQW��LQF�UFDUHD�WHUPLF��VSHFLILF��PDUH�D�VXSUDIH HL�GH�VFKLPE�GH� F�OGXU� a focarului. De aceea intervalul de alegere a temperaturii� OD� FDS�WXO�focarului este:

tf =500÷700 oC.

6H� GHWHUPLQ�� DSRL� GLQ� GLDJUDPD� ,-t entalpia gazelor de ardere OD� FDS�WXO�focarului If=f(tf,α). )OX[XO�GH�F�OGXU��SUHOXDW�SULQ�UDGLD LH�vQ�IRFDU�YD�IL: )()1( ftextR IIBqQ −−= (kW) (3.13)

)OX[XO�GH�F�OGXU��SUHOXDW�în sistemul convectiv va fi: Rc QQQ −= (3.14) (QWDOSLD�JD]HORU�GH�DUGHUH�OD�VIkUúLWXO�GUXPXOXL�FRQYHFWLv este:

Bq

QII

ext

cfc )1( −

−= (3.15)

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

39

úL�GLQ�GLDJUDPD�,-W�UH]XOW�: ),( αcc Ift = .

ÌQFKLGHUHD�ELODQ XOXL�LPSXQH: Ic≅IFRú��úL�tc≅tFRú. úL�VH�DGPLW�HURULOH�UHODWLYH: 100

cos

cos

II

II

t

c

I −−

=ε � 0,5%

úL� 100

cos

cos

tt

tt

t

c

t −−

=ε � 0,5%

(URUL�PDL�PDUL�LQGLF��R�JUHúHDO��GH�FDOFXO��ÌQ�ILQDO�VH�vQWRFPHúWH�WDEHOXO��2. Tabelul 3.2.

Temperatura gazelor 6XSUDID D )OX[�GH�F�OGXU�

[kW] Intrare [oC]

IHúLUH [oC]

Focar Convectiv

QR

Qc

tt

tf

tf

tc

��%LODQ XO�JUDILF�DO�FD]DQului

'HELWHOH� GH� F�OGXU�� GLQ� WDEHOHOH� �� úL� �� VH� WUDQVSXQ� JUDILF�� OD� VFDU�� FD� vQ�figura 2.3 (cu particularizarea: B*=B; Qpa=0; Qsfc=Qc, Qsi=0; Qec=0; qmec=0; qev=0). 3.1.7. Calculul termic al focarului

Acest calcul are ca scop determinarea supraIH HL�GH�UDGLD LH�6R�FDSDELO��V��SUHLD�GHELWXO� GH� F�OGXU�� UDGLDQW�4R� GH� OD� IODF�U�� úL� JD]HOH� GH� DUGHUH. Deoarece în calcule

intervin gradul de ecranare

=Ψ

per

R

S

S úL� OXQJLPHD� GH� UDGLD LH� �s = 3,6 per

f

S

V) este

necesar un calcul iterativ. Se admite o valoare SUHOLPLQDU� 'RS care în final se va

FRPSDUD�FX�FHD�UH]XOWDW��GLQ�FDOFXO�6R. Valoarea SUHOLPLQDU� '

RS �SRDWH�IL�VWDELOLW��SULQ��GRX��PHWRGH: a) Se admite un IOX[�XQLWDU� UDGLDQW� �vQF�UFDUH� WHUPLF�� specific acestui tip de

focar: qR = 30÷50kW/m2

astfel, S

RR

q

QS =' (m2) (3.16)

E��6H�FDOFXOHD]��VXSUDID D�GH�UDGLD LH�vQ�IRFDU�FX�UHOD LD�de aproximare:


CAZANE

40

−

⋅⋅

=44

'

100100765,5 pf

RR

TT

QS

ε

(m2) (3.17)

cu: ε =0,65 pentru combustibil gazos ε =0,75 pentru combustibil lichid Tf=tf +273 (K)

Tp=tm +25+273 (K) unde 2

eim

ttt

+=

Din punct de vedere geometric:

4

2'' D

DLS RR

ππ += (m2) (3.18)

unde: D – diametrul focarului [m]. '

RL – lungimea SUHOLPLQDU� a focarului [m]. Se impune un raport�GH�VXSOH H�D�IRFDUXOXL�� '

RL / D=1,5÷2 �úL�VH�GHWHUPLQ�� 'RL úL�'.

6H�FDOFXOHD]�:

- volumul focarului: Vf = '

2

4 RLDπ

(m3) (3.19

- VXSUDID D�SHUH LOor camerei de ardere: Sper=π⋅D⋅ 'RL +

4

2 2Dπ

(m2) (3.20)

- grosimea stratului radiant de gaze: s = 3,6 per

f

S

V (m) (3.21)

- gradul de ecranare: per

R

S

S=Ψ (3.22)

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�JD]HORU�GH�DUGHUH�vQ�FDPHUD�GH�DUGHUH: )(

100038,01

)(

6,18,022

22

2

ROOH

f

ROOH

OH

g ppT

spp

pk +

−

⋅+

+= (3.23)

6H�FDOFXOHD]��FRHILFLHQWXO�GH�DEVRUE LH�DO�JD]HORU�GH�DUGHUH�GLQ�IRFDU:

LR

D

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

41

sk

g

gea⋅−−= 1 (3.24)

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IO�F�ULL�FX�UHOD LD�de aproximare:

5,01000

6,1 −= f

fl

Tk (3.25)

úL�FRHILFLHQWXO�GH�DEVRUE LH�DO�IO�F�ULL�FX�UHOD LD:

sk

fl

flea⋅−−= 1 (3.26)

3RQGHUHD�DEVRUE LHL�IO�F�ULL�ID ��GH cea a mediului radiant de gaze de ardere din focar VH�IDFH�GXS��Friterii experimentale, considerându-se�R�SURSRU LH�β, din volumul IRFDUXOXL��RFXSDW��GH�SDUWHD�OXPLQRDV��D�IO�F�ULL.

CoeficiHQWXO�GH�DEVRUE LH�DO�IO�F�ULL�úL�JD]HORU�GH�DUGHUH�HVWH�GDW�GH�UHOD LD: gfl aaa ⋅−+⋅= )1( ββ (3.27)

Valorile coeficientului de luminozitate β sunt prezentate în tabelul 3.3. Tabelul 3.3.

)ODF�U��QHOXPLQRDV��GH�FRPEXVWLELO�JD]RV� β = 0,2 )ODF�U��GH�FRPEXVWLELO�OLFKLG� β = 0,6

CRHILFLHQWXO�GH�PXUG�ULUH�D�VXSUDIH HORU�HVWH:

ξ =0,7 ÷ 0,9 combustibil gazos ξ =0,6 ÷ 0,7 combustibil lichid &X�DFHVWH�YDORUL�VH�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IRFDUXOXL:

ξΨ−+=

)1(

82,0

aa

aa f (3.28)

2�DOW��FDUDFWHULVWLF��D�IRFDUXOXL�HVWH�IDFWRUXO�GH�SR]L LH�D�IO�F�ULL�vQ�IRFDU ”M”. )DFWRUXO�GH�SR]L LH�D�IO�F�ULL��vQ�FDPHUD�GH�DUGHUH�HVWH�GDW�GH�UHOD LD�

fMM H

hbaM −=

Pentru combustibil lichid sau gazos constantele au valorile urmãtoare: aM=0,54 úL� EM �� úL� SHQWUX� UDSRUWXO� vQWUH� vQ�O LPHD� GH� DPSODVDUH� D� DU]�WRUXOXL� úL� vQ�O LPHD�camerei de ardere (Hf=Df):

fH

h =��VH�RE LQH�0� ��,44.

&X�DFHVWH�GDWH�VH�GHWHUPLQ��VXSUDID D�GH�UDGLD LH�D�IRFDUXOXL:

Hf

h


CAZANE

42

32

2

38

11

10765,5 MT

T

TTaM

QS

f

t

tff

RR

−

⋅= − ξ (m2) (3.29)

$FHDVW��VXSUDID ��YD�IL�GLIHULW��GH� '

RS dHWHUPLQDW�� vQ�FDOFXOXO�preliminar��'DF��GLIHUHQ D� HVWH�PDL�PDUH� GH�±10% se reia calculul cu valori recalculate de Vf� úL� 6per SHQWUX� QRXD� YDORDUH� D� VXSUDIH HL� GH� UDGLD LH� 6R (pentru calcule mai precise aceDVW� GLIHUHQ � se poate impune la max. ±2%). Rezult��OXQJLPHD�ILQDO��a focarului:

D

DS

LR

R π

π4

2

−= (m) (3.30)

3.1.8. Calculul termic al convectivului Convectivul cazanului este determinat, din punctul de vedere al transferului de cãOGXU�� din calculele anterioare,�SULQ�XUP�WRULL�SDUDPHtrii:

QC –� GHELWXO� GH� F�OGXU�� primit de agentul termic secundar de la sistemul convectiv (kW) ;

tf –�WHPSHUDWXUD�JD]HORU�GH�DUGHUH�OD�LQWUDUH�vQ� HYL��0C) ; tFRú –�WHPSHUDWXUD�JD]HORU�GH�DUGHUH�OD�LHúLUHD�GLQ� HYL��OD�FRú��0C) ; te/ti – temperatura apei (0C).

3HQWUX�VWDELOLUHD�VHF LXQLL�GH�WUHFHUH�D�JD]HORU�GH�DUGHUH�VH�DOHJH�un diametru de HDYã�GLQ�JDPD�GH� HYL�X]XDOH��GH�×δ). Pentru cazane caracterizate de o sarcinã termicã mai micã de 1MW se pot alege:

φ42 × 3; φ45× 3; φ51 × 3; φ 57 ×3; φ 60 × 3; φ 70 × 3,5.

'XS� alegerea diametrului� HYLORU� VH� alege viteza SUHOLPLQDU�� GH� FLUFXOD LH� D�gazelor de ardere w’ în intervalul economic pentru acest tip de cazan:

w’ = (2 ÷ 4) m/s. 6HF LXQHD�GH�FLUFXOD LH�D�JD]HORU�GH�DUGHUH�YD�IL:

273

273,

+⋅= gmg

circ

t

w

VBS (m2) (3.31)

)(2

0cosC

ttt

f

gm

+= este temperatura media a gazelor de ardere.

1XP�UXO�GH� HYL�DO�GUXPXOXL�FRQYHFWLY�YD�IL: 2

4'

i

circ

d

Sn

π= , acesta VH�URWXQMHúWH�superior sau inferior, la QXP�U�întreg par

úL�VH�UHFDOFXOHD]��YLWH]D de�FLUFXOD LH�D�JD]HORU�GH�DUGHUH:

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

43

273

273

4

2

+⋅= gm

i

g t

dn

VBw

π (3.33)

Pentru temperatura medie a gazelor de ardere tgm se GHWHUPLQ� din anexa 9, XUP�WRDUHOH�YDORUL:

- YkVFR]LWDWHD�FLQHPDWLF�� ν [m2/s] - FRQGXFWLELOLWDWHD�WHUPLF�� λ [W/mK] - QXP�UXO Prandtl Pr De asemenea se GHWHUPLQ� QXP�UXO Prandtl perete Prp la temperatura peretelui

tp cu

tp = tm +(10÷20) oC ; 2

eim

ttt

+= .

&RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�FRQYHF LH se determin��XWLOL]kQG�UHOD LL�criteriaOH�SHQWUX�FLUFXOD LD�JD]HORU�GH�DUGHUH�OD�LQWHULRUXO� HYLORU��conform anexei 10.

De exemplu, pentru 4i 103wd

Re ⋅>=ν

CL

dNu i

+

−+

−=

3/2

3/2

1

)1(Pr8

2,121

Pr)1000(Re8

ξ

ξ

(3.34)

cu )(0,2...0,4LL,Pr

PrC;1,64)(1,82logRe� R

0,11

p

2 +=

=−= −

.

Pentru 2300 < Re < 3 ⋅104:

[ ] CBPr

,A,,Nu

/ 31

30 221

27061513749

++−+= ε (3.35)

cu A=

11,0

p

32/1

i3 i

Pr

PrC;

L

dPrReB;

L

dPrRe

=

=

εo =1,2 ÷� �� UHSUH]LQW�� HIHFWXO� WXUEXOizatorilor ce se vor monta la interorul HYLORU� FRQYHFWLYH�� IXQF LH� GH� JUDGXO� GH� WXUbulizare realizat ce depinde de IRUP�� úL�pasul�GH�úLFDQDUH. Pentru regimul laminar: Re < 2300:


CAZANE

44

110313

30 7061513749

,

p

/

i*

Pr

Pr,

L

dPrRe,,Nu

−⋅+= ε (3.36)

cu *

0ε = 1,6÷2,2.

Pentru turbulizatorii în zig-zag,� FRHILFLHQ LL� GH� FRUHF LH�� 0ε �úL� *0ε pot fi

determinD L�FX�UHOD LLOH experimentale:

200

1422,

r

*

p

,=ε úL�

5

33 20

200

,

,

r

Re

p

, −=ε

unde i

rd

lp = este pasul relativ, cu l – pas zig-zaguri.

&RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�FRQYHF LH�

c

cl

Nuλα = (3.37)

&RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH�HVWH�GHWHUPLQDW�GH�P�ULPLOH:

- WHPSHUDWXU��PHGLH�D�JD]HORU�GH�DUGHUH: Tgm=tgm+273 (K); - grosimea stratului radiant: s = 0,9 di (m);

- SUHVLXQLOH�SDU LDOH�DOH�JD]HORU�GH�DUGHUH�WULDWRPLFH: 2ROp ; OHp

2

g

g

RO

RO pV

Vp 2

2= [bar.]��úL�� g

g

OH

OH pV

Vp 2

2= [bar.]

&RQVWDQWD�GH�UDGLD LH�D�JD]HORU�VH�GHWHUPLQ��FX�UHOD LD:

l

di

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

45

)(1000

38,01)(

6,18,022

22

2

ROOH

gm

ROOH

OHpp

T

spp

pkg +

−

⋅+

+= (3.38)

iar coeficientul de emisivitate al gazelor de ardere:

sk

ggea⋅−−=1 (3.39)

&RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH�VH�determin��FX�UHOD LD:

−

−

+⋅= −

gm

p

gm

p

gmg

p

r

T

T

T

T

Taa

1

1

2

110765,5

6,3

38α (W/m2K) (3.40)

XQGH�SHQWUX�FRHILFLHQWXO�GH�DEVRUE LH�DO�SHUHWHOXL�VH�FRQVLGHU� valoarea ap=0,82 � HDY��WUDV��GH�R HO��LDU�SHQWUX�WHPSHUDWXUD�DEVROXW��D�SHUHWHOXL� HYLL: 27320tT mp ++= (K)

Coeficientul de transfer GH�F�OGXUL��SH�SDUWHD�JD]HORU�GH�DUGHUH va fi: α1 = αc + αr

Coeficientul GH� WUDQVIHU�GH� F�OGXU��α2 pe partea apei, este mult mai mare (de ordinul miilor de W/m2K) în compara Le cu α1 (de ordinul zecilor de W/m2K). ÌQ� DFHVWH� FRQGL LL� FRHILFLHQWXO� JOREDO� GH� WUDQVIHU� GH� F�OGXU�� ”k” este dat de UHOD LD�

1

1

1 εαα

+=Ik (W/m2K) (3.41)

în care s-a QHJOLMDW�UH]LVWHQ D�WHUPLF��1/α2). Valorile coeficientului� GH� PXUG�ULUH� ε pentru gaze de ardere, provenite din

arderea de combustibil gazos, sunt prezentate în tabelul 3.4. Tabelul 3.4.

&RHILFLHQWXO�GH�PXUG�ULUH�– combustibil gazos Viteza w (m/s) 3 6 9 12 15 18 ε ⋅103 (m2K/W) 5,233 3,837 2,791 2,093 1,628 1,395

Se poate�XWLOL]D�úL�UHOD LD�DQDOLWLF�:

6474,031021,11 −− ⋅⋅= wε (m2K/W) (3.42) Pentru gaze de ardere provenind din arderea unui combustibil lichid se poate considera: 0163,0≅ε (m2K/W)


CAZANE

46

S SC

t

tma

tf

tc

∆tmax

∆tmin

'LIHUHQ D�PHGLH�GH�WHPSHUDWXU��VH�GHWHUPLQ��FRQIRUP�Iigurii 3.2.�úL�UHOD LHL��43):

min

max

minmax

lnt

t

tttm

∆∆

∆−∆=∆ (3.43)

6XSUDID D� GH� VFKLPE� GH� F�OGXU�� D�convectivului cazanului va fi:

ci

m

cc Ldn

tk

QS π=

∆= (m2) (3.44)

UH]XOW� lungimea convectivului:

i

cc

dn

SL

π= (m) (3.45)

Fig. 3.2.

a) 'DF�� /c > LR, în limitele Lc = LR + (0,2÷0,4) m, înseamn��F��GLVWDQ D�GLQWUH�SO�FLOH�WXEXODUH�DOH�FD]DQXOXL�HVWe suficient de mare, pentru a permite dilatarea libera a focarului,�GDU�QX�SUHD�PDUH�vQFkW�V��VH�FUHH]H�un volum inutilizabil la interiorul corpului cazanului;

b) 'DF��/c < LR��VH�UHGXFH�QXP�UXO�GH� HYL sau diametrul��DVWIHO�vQFkW�V��VH�DMXQJ��în cazul a);

c) 'DF��/c >> LR��VH�P�UHúWH�QXP�UXO�GH� HYL�DVWIHO�vQFkW�V��VH�DMXQJ��vQ�FD]XO�D�.

3.2. Calculul termic al cazanelor ignitubulare cu pies�� GH� vQWRDUFHUH� D�gazelor de ardere în focar

3.2��'HVFULHUHD�FD]DQHORU��HOHPHQWH�FRPSRQHQWH��PRG�GH�IXQF LRQDUH� 6XQW�FD]DQH�FX�IRFDU�WXEXODU�úL�XQ�GUXP�FRQYHFWLY�LGHQWLFH�FX�FHOH�SUH]HQWDWH�vQ�FDSLWROXO� �� $X� vQ� SOXV� XQ� FLOLQGUX� GLQ� R HO� UHIUDFWDU� PRQWDW� vQ� IRFDU� �SLHV�� GH�vQWRDUFHUH�� FDUH� HWDQúHD]�� SH� XúD� GH� vQFKLGHUH� úL� DVLJXU�� XQ� IRFDU� FDOG� SHQWUX�amestecul aer –� FRPEXVWLELO��&D]DQHOH� IXQF LRQHD]�� vQ� VXSUDSUHVLXQH�FX�FRPEXVWLELO�OLFKLG�VDX�JD]RV�úL�SURGXF�DS��FDOG��We / ti = 90 / 70 0C.

Aceste cD]DQH�VXQW�DOF�WXLWH�GLQWU-un cilindru cu diametru mare (1), în interiorul F�UXLD�VH�DIO�� VXSUDIH HOH�GH�VFKLPE�GH�F�OGXU�� WXEXO�GH� IODF�U�� FX�SHUHWH�QHWHG��vQFDVWUDW�vQ�SODFD�WXEXODU��ID ��SLHVD�GH�vQWRDUFHUH�D�JD]HORU�GH�DUGHUH�úL� HYLOH�GH�“fXP´� �� FX� WXUEXOL]DWRUL�� FX� URO� GH� IDVFLFXO� FRQYHFWLY� ��HYLOH� GH� ³IXP´� VXQW�IL[DWH�SULQ�VXGXU��VDX�PDQGULQDUH�vQ�SO�FLOH�WXEXODUH�ID ��úL�VSDWH�� ,QWUDUHD� DSHL� vQ� FD]DQ� �� VH� IDFH�SH� OD� SDUWHD�GH� VXV� VDX�SH� OD� SDUWHD� LQIHULRDU�� LDU�evacuarHD�DSHL�FDOGH�VH�IDFH��vQWRWGHDXQD�SH�OD�SDUWHD�VXSHULRDU��

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

47

8úD�GH�vQFKLGHUH��D�FD]DQXOXL��L]RODW��WHUPLF��HWDQú��SH�SLHVD��IL[DW��SULQ�DUFXO��úL�DVLJXUm�WUHFHUHD�LQWUDUHD�JD]HORU�GH�DUGHUH�GLQ�IRFDU�vQ�VLVWHPXO�FRQYHFWLY�

Fig. 3.3. Cazan igniWXEXODU�FX�SLHV��GH�vQWRDUFHUH�D�JD]HORU�GH�DUGHUH�vQ�IRFDU

1. corp cazan; 2. focar tubular�� HYL�GH�“fum”�FX�WXUEXOL]DWRUL��DU]�WRU��Xú��L]RODW��WHUPLF��LQWUDUH�DS�� LHúLUH�DS��FXWLH�FROHFWDUH�JD]H��OHJ�WXU��OD�FRú��L]ROD LH�WHUPLF��SODF��WXEXODU��ID ��

��SODF��WXEXODU��VSDte; 13.vizor; 14. teaca termostate; 15. panou comanda si reglaj; 16.SLHV��GH�vQWRDUFHUH�JD]H�de ardere în focar.

/D� DU]�WRU� HVWH� DGXV� FRPEXVWLELOXO� LDU� YHQWLODWRUXO� DVSLU�� úL� LQWURGXFH� DHUXO�

QHFHVDU� DUGHULL� vQ� WXEXO� GH� DUGHUH� GLQ� IRFDU�� ,Q� LQWHULRUXO� IRFDUXOXL� VH� DSULQGH� úL� VH��VWDELOL]H]�� IODF�UD�GH]YROWkQGX-se debitul de gaze de ardere. Acestea ajung în partea GLQ�VSDWH�D�FDPHUHL�GH�DUGHUH��SLHVD�GH�vQWRDUFHUH��úL�VXQW�REOLJDWH�V��VH�vQWRDUF��spre SDUWHD�GLQ�ID ��între�IRFDUXO�SURSULX�]LV�úL�SLHVD�GH�vQWRDUFHUH. 'DWRULW�� XúLL� FD]DQXOXL� JD]HOH� GH� DUGHUH� VH� vQWRUF� FX� ��0� úL� LQWU�� vQ� HYLOH�FRQYHFWLYH��6XQW�FROHFWDWH�vQ�FXWLD��úL�HYDFXDWH��SH�FRú�SULQ�úWX XO��. 3.2.2. Tema de proiectare

Prin tema de proiectare se dau: - Q -�VDUFLQD�WHUPLF��D�FD]DQXOXL��vQ�N:�� - te / ti -�WHPSHUDWXUD�DSHL�OD�LHúLUH�úL�LQWUDUH�vQ�FD]DQ��0C) ; - IHOXO�úL�FRPSR]L LD�FRPEXVWLELOXOXL.

$FHVWH� FD]DQH� IXQF LRQHD]�� GH� RELFHL� FX� Vuprapresiune în focar, deci FRHILFLHQWXO�GH�H[FHV�GH�DHU�HVWH�FRQVWDQW�vQ�IRFDU��vQ�FRQYHFWLY�úL�OD�FRú:

α = αg = αc = αFRú = 1,05 ÷ 1,15.

3

2

8

12

1

10

1 2 3 4

5

6 7

9

10

11

14 15 15


CAZANE

48

&RQIRUP� LQGLFD LLORU� GLQ� FDSLWROXO� �� VH� HIHFWXHD]�� FDOFXOXO� DUGHULL�

FRPEXVWLELOXOXL�úL�VH�GHWHUPLQ�: VO, Vgo, Vg, Hi, OHp2

, 2ROp ;�VH�WUDVHD]��GLDJUDPD�,�– t

sau cp – t. ��&DOFXOXO�UDQGDPHQWXOXL�WHUPLF�DO�FD]DQXOXL�úL�D�GHELWXOXL�GH�FRPEXVWLELO� $FHVWH� FD]DQH� IXQF LRQHD]�� QXPDL� FX� FRPEXVWLELO� JD]RV� VDX� OLFKLG�� GHFL�pierderile specifice mecanice (qmec��úL�FHOH�SULQ�HYDFXDUHD�SURGXVHORU�VROLGH�GLQ�FD]DQ�(qcen) sunt nule. De asemenea B* = B. 6H�FDOFXOHD]��SLHUGHULOH�VSHFLILFH�GH�F�OGXU��FDUDFWHULVWLFH�FD]DQXOXL: a. 3LHUGHUHD�VSHFLILF��GH�F�OGXU��SULQ�HQWDOSLD�JD]HORU�GH�DUGHUH�OD�FRú� )LLQG� XQ� FD]DQ� GH� DS�� FDOG�� VH� DGPLWH� R� WHPSHUDWXU�� OD� FRú� FH� VH� SRDWH�GHWHUPLQD�FX�UHOD LD de aproximare:

Ctt

t ei 0cos )8060(

2÷++≅ (3.46)

Din diagrama I –�W�VH�DIO��YDORDUHD�HQWDOSLHL�JD]HORU�GH�DUGHUH�OD�FRú: IFRú = f (tFRú, α)

��(QWDOSLD�DHUXOXL�WHRUHWLF�GH�DUGHUH�VH�FDOFXOHD]��OD�WHPSHUDWXUD�DPELDQW��Wa=20 0C apaoa tcVI ⋅⋅=0 (3.47)

cu cpa = 1,2971 kJ/ Km3

N

5H]XOW��SLHUGHUHD�VSHFLILF��OD�FRú: )(1

0coscos a

i

IIH

q α−= (3.48)

b. Pierderi spHFLILFH�GH�F�OGXU��SULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��FKLPLF�� ÌQ� FDGUXO� FDOFXOHORU� GH� SURLHFWDUH�� GDWRULW�� SHUIRUPDQ HORU� IXQF LRQDOH� DOH�DU]�WRDUHORU�PRGHUQH,�VH�DGPLWH�R�SLHUGHUH�SULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��FKLPLF� de ordinul:

qch = 0,001 ÷ 0,005

c. 3LHUGHUL�VSHFLILFH�GH�F�OGXU��SULQ�SHUH LL�H[WHULRUL�DL�FD]DQXOXL�� ÌQ� FDGUXO� FDOFXOHORU� GH� SURLHFWDUH�� SHQWUX� FD]DQH� UHODWLY� PLFL�� vQ� IXQF LH� GH�gradul dorit de izolarH�WHUPLF��D�FD]DQXOXL��VH�SRDWH�DOHJH�R�YDORDUH��

qext = 0,005 ÷ 0,015 d. Randamentul cazanului 6H�FDOFXOHD]��FX�UHOD LD� )(1 cos extch qqq ++−=η (3.4)

úL�H[SULPDW�vQ�YDORDUH�SURFHQWXDO�� η=η 100%

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

49


iH

QB

η= (kg/s) sau ( s/m3

N ) (3.5)

��%LODQ XO�GH�DQVDPEOX�DO�FD]DQXOXL�

• )OX[XO�XWLO�GH�F�OGXU��DO�FD]DQXOXL�HVWH� 4��GDW�SULQ�WHP��. • )OX[XO�GH�F�OGXU��SURGXV�

de arderea combustibilului: ic BHQ = (3.51)

• )OX[XO�GH�F�OGXU��DGXV�FX�DHUXO�GH�DUGHUH�� apaoa tcVBQ α= (3.52)

• )OX[XO�GH�F�OGXU��SLHUGXW�OD�FRú� coscos BIQ = (3.53)

• )OX[XO�GH�F�OGXU��SLHUGXW�SULQ�DUGHUH�LQFRPSOHW�� ichinc BHqQ = (3.54)

• )OX[XO�GH�F�OGXU��SLHUGXW�VSUH�H[WHULRU� iextext BHqQ = (3.55) 5H]XOW��WDEHOXO��GH�ELODQ �WHUPLF�DO�FD]DQXOXL.

Tabelul 3.5. Combustibil – pierderi Util

Qc

Qa

- QFRú - Qinc

- Qext

Q

∑ = 'QQ ''∑ = QQ

1RW��ÌQ�DFHVW�ELODQ �WHUPHQHXO�“– qcosBHi” s-D�VFULV�VXE�IRUPD�H[SOLFLW�� (–BIFRú�+ Bαcoscpata= –QFRú+Qa).

(URDUHD�UHODWLY��YD�IL: 100'

"'

Q

QQ −=ε (3.56)

úL�VH�YHULILF��HURDUHD�PD[LP��DGPLVLELO��GH��. 'DF��HURDUHD�UHODWLY��GH�vQFKLGHUH�D�ELODQ XOXL�HVWH�PDL�PDUH�GHFkW�YDORDUHD�GH�� FHD� PD[LP� DGPLVLELO�� SHQWUX� DFHVW� JHQ� GH� FDOFXOH�� vQVHDPQ�� F�� V-D� I�FXW� R�JUHúHDO��GH�FDOFXO�VDX�GH�FLWLUH�vQ�GLDJUDPD�,-t. ��&DOFXOXO�WHPSHUDWXULORU�úL�HQWDOSLLORU�JD]HORU�GH�DUGHUH�SH�WUDVHX� (QWDOSLD�WHRUHWLF��GH�DUGHUH�VH�FDOFXOHD]��FX�UHOD LD: apafchit tcVqHI 0)1( α+−= (3.57)


CAZANE

50

apoi se deWHUPLQ��WHPSHUDWXUD�WHRUHWLF��GH�DUGHUH�GLQ�GLDJUDPD�,-t: ),( αtt Ift = .

2�LPSRUWDQW�� FDUDFWHULVWLF�� IXQF LRQDO�� D� FD]DQHORU�FX� vQWRDUFHUH�D� JD]HORU�GH�DUGHUH�vQ�IRFDU�úL�SLHV��GH�vQWRDUFHUH��R�UHSUH]LQW�� LQF�UFDUHD�WHUPLF��VSHFLILF��IRDUWH�mare D�VXSUDIH HL�GH�VFKLPE�GH�F�OGXU��D� IRFDUXOXL��'H�DFHHD� LQWHUYDOXO�GH�DOHJHUH�D�WHPSHUDWXULL�OD�FDS�WXO�IRFDUXOXL�HVWH�

tf =450÷550 oC. 6H� GHWHUPLQ�� DSRL� GLQ� GLDJUDPD� ,-W� HQWDOSLD� JD]HORU� OD� FDS�WXO� IRFDUXOXL�If=f(tf,α). )OX[XO�GH�F�OGXU��SUHOXDW�SULQ�UDGLD LH�vQ�IRFDU�YD�IL: )()1( ftextR IIBqQ −−= (kW) (3.58)

)OX[XO�GH�F�OGXU��SUHOXDW�GH�VLVWHPXO�FRQYHFWLY�YD�IL:

Rc QQQ −= (3.59) (QWDOSLD�JD]HORU�GH�DUGHUH�OD�VIkUúLWXO�GUXPXOXL�FRQYHFWLY�HVWH: cos)1(

IBq

QII

ext

c

fc ≅−

−= (3.59a)

úL�GLQ�GLDJUDPD�,-W�UH]XOW�: coscc t),I(ft ≅α= . ÌQFKLGHUHD�ELODQ XOXL�LPSXQH: Ic ≅ IFRú��úL�tc ≅ tFRú. úL�VH�DGPLW�HURULOH�UHODWLYH: 100

cos

cos

II

II

t

c

I −−

=ε � 0,5% (3.60)

úL� 100

cos

cos

tt

tt

t

c

t −−

=ε � 0,5% (3.61)

Erori�PDL�PDUL�LQGLF��R�JUHúHDO��GH�FDOFXO��ÌQ�ILQDO�VH�vQWRFPHúWH�WDEHOXO��

Tabelul 3.6. Temperatura gazelor 6XSUDID D )OX[�GH�F�OGXU�

intrare LHúLUH Focar Convectiv

QR

Qc

tc

tf

tf

tc

∑ = QQi

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

51

��%LODQ XO�JUDILF�DO�Fazanului

'HELWHOH� GH� F�OGXU�� GLQ� WDEHOHOH� �� úL� �� VH� WUDQVSXQ� JUDILF�� OD� VFDU�� FD� vQ�figura 2.3 (cu B*=B; Qpa=0; Qspc=QcI+QcII, Qsi=0; Qec=0; qmec=0; qev=0). 3.2.7. Calculul termic al focarului

Calculul termic al focarului este foarte complex GHRDUHFH�WUDQVIHUXO�GH�F�OGXU��GH�OD�IODF�U��úL�JD]H�F�WUH�DS��VH�IDFH�SULQ�LQWHUPHGLXO�SLHVHL�GH�vQWRDUFHUH�GLQ�IRFDU. Un calcul exact se poate face utilizând un program de calcul, lucrând cu VXSUDIH H�úL�volume elementare. ÌQ�FHOH�FH�XUPHD]��VH�SUH]LQW� un calcul simplificat bazat pe valori medii ale SDUDPHWULORU�WHUPLFL�úL�JD]odinamici ce intervin în calcul. 'HELWHOH�GH�F�OGXU��FHGDWH�vQ�FDPHUD�GH�DUGHUH��interiorul piesei de întoarcere) úL�vQWUH�SLHV��úL�IRFDUXO�SURSULX�]LV�VXQW�FHOH�GLQ�ILJXUD��

Fig. 3.4. Schema de calcul termic a focarului

1. IRFDU��FDPHUD�GH�DUGHUH��PDQWD�� HYLOH�VLVWHPXOXL�FRQYHFWLY��DU]�WRU

'HELWHOH�GH�F�OGXU��FRQIRUP�ILJXULL��VXQW� • QRC –�)OX[XO�GH�F�OGXU��FHGDW�de mediul din focar SULQ�UDGLD LH�vQ�FDPHUD�GH�

ardere cãtre corpul de întoarcere; • QRCF –� )OX[XO� GH� F�OGXU�� WUDQVPLV� SULQ� UDGLD LHL�� de la corpul de întoarcere

cãtre pere LL�focarului ;

QRC

QRCF QGC QGF

DC DF

QFND

tt

tf’

tf tcos

Lf

Lc

1 2 3 4


CAZANE

52

• QGF –� )OX[XO� GH� F�OGXU�� FHGDW� GH� JD]HOH� GH� DUGHUH� IRFDUXOXL, convectiv, pe drumul de întoarcere;

• QGC –�)OX[XO�GH�F�OGXU��FHGDW�GH�JD]HOH�GH�DUGHUH�corpului de întoarcere prin FRQYHF LH;

• QFND –�)OX[XO�GH�F�OGXU��FHGDW�SULQ�VXSUDID D�GH�IXQG�D�IRFDUXOXL� • QR –�)OX[XO�GH�F�OGXU��SUHOXDW�GH�IRFDU� �4RCF + QGF + QFND.

Transferul de cãldurã realizat în focar este caracterizat de trei temperaturi care

odata cunoscute definesc complet toate fluxurile de cãldurã enumerate anterior. Aceste temperaturi sunt: - tf

’ – temperatura gazelor de ardere la intrarea în drumul de întoarcere; - tf – temperatura gazeloU�GH�DUGHUH�OD�LHúLUHD�GLQ�IRFDU� - tp – temperatura peretelui corpului de întoarcere (valoare medie);

Pentru determinarea acestui complex de necunoscute este necesar un sistem de WUHL�HFXD LL�FH�HVWH�SUH]HQWDW�vQ�FRQWLQXDUH� - HFXD LD� GH� ELODQ � D� JD]HORU� GH� Drdere vQWUH� VHF LXQHD� DU]mWRUXOXL� úL� VHF LXQHD� GH�

întoarcere: ))(1( '

ftextFNDRC IIqBQQ −−=+ (3.62.1)

- HFXD LD�GH�ELODQ �D�JD]HORU�GH�DUGHUH�SH�vQWUHJ�IRFDUXO�

(3.62.2)

- HFXD LD�GH�ELODQ �D�corpului de întoarcere:

(3.62.3)

unde fluxurile au urmãtoarele explicitãri:

)(2

110765,5 42

'28

pftRC

p

gRC TTTSa

aQ −+

×= − ξ (3.63)

unde Tp este temperatura medie a peretelui camerei de ardere.

(3.64)

)(10765,5 44

.8

pfpRCfcRCF TTSCQ −×= − (3.65)

QGF = SRF ⋅ kCF ⋅ ∆tmCF (3.66) cu kCF –�FRHILFLHQWXO�JOREDO�GH�WUDQVIHU�GH�F�OGXU��vQ�VSD LXO�LQHODU�

∆tmCF –�GLIHUHQ D�PHGLH�ORJDULWPLF��GH�WHPSHUDWXUL�vQ�VSD LXO�LQHODU�

))(1( ftextFNDGFRCF IIqBQQQ −−=++

RCFGCRCF QQQ +=

)(2

110765,5 42

'28

pfftFND

p

gFND TTTSa

aQ −+

×= − ξ

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

53

QGC = SRC ⋅ k*

CF ⋅ ∆tmCF (3.67) Mãrimile geometrice ce caracterizeazã focaUXO�VXQW��FX�QRWD LLOH�GLQ�ILJXUD��

- suprafa a corpului de întoarcere: SRC=π⋅dc⋅Lf

- VXSUDID D�IXQGXOXL�GH�IRFDU(utilã de transfer de cãldurã): SFND=4

2fdπ

- VXSUDID D�ODWHUDOã a focarului (utilã de transfer de cãldurã): ffRF LdS π=

Intr-o variantã simplificatã a calculului se admite o predimensionare a focarului

urmând a se face o verificare a parametrilor de transfer de cãldurã caracteriza L�VLQWHWLF�SULQ� WHPSHUDWXUD� GH� LHúLUH� GLQ� IRFDU��7LQkQG� FRQW� GH� FDUDFWHULRVWLFLOH� IXQF LRQDOH� DOH�focarului predimensionarea se va face împãr LQG�IOX[XO�WRWDO�FHGDW�GH�JD]HOH�GH�DUGHUH�OD�VWUmEDWHUHD� IRFDUXOXL� vQ�FRPSRQHQWm� UDGLDWLYm�úL�FRPSRQHQWm�FRQYHFWLYm��$VWIHO� VH�considerã componenta radiativã ca fiind caracteristicã pentru volumul interior al FRUSXOXL� GH� vQWRDUFHUH� �FRQVLGHUDW� FRQYHQ LRQDO� OD� WHPSHUDWXUD� SHUHWHOXL� GH� IRFDU�� úL�componenta convectivã ce ac LRQHD]ã pe suprafa D�ODWHUDOã a peretelui focarului. Uzual se admite o pondere a componentei radiative cuprinsã între 85-90% din fluxul de cãldurã total cedat pe focar (restul fiind afectat componentei convective).

3HQWUX�VWDELOLUHD�P�ULPLORU�preliminare dC�úL�/f se admite un flux radiant în camera

de ardere qR = 40 ÷ 60 kW/m2.

6H�GHWHUPLQ��FX�R�UHOD LH�GH�DSUR[LPDUe: SRC = ( )R

R

q

Q9,085,0 − .

Se admite Lf/dc = 1,5 ÷��úL�VH�GHWHUPLQ��P�ULPLOH�Lf úL dc.

3HQWUX�FDPHUD�GH�DUGHUH�VH�FDOFXOHD]�:

- volumul focarului: Vf = fc L

d

4

2π ;

- VXSUDID D�SHUH LORU�FDPHUHL�GH�DUGHUH: Sper=π⋅dc⋅Lf + 4

2 2cdπ

;

- grosimea stratului radiant de gaze: s = 4 per

f

S

V ;


RC

S

S=Ψ .

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�JD]HORU�GH�DUGHUH�vQ�FDPHUD�GH�DUGHUH:


CAZANE

54

)(1000

38,01)(

6,11,022

22

2

ROOH

mg

ROOH

OHpp

T

spp

pkg +

−

⋅+

+= (3.68)

6H�FDOFXOHD]��FRHILFLHQWXO�GH�DEVRUE LH�DO�JD]HORU�GH�DUGHUH�GLQ�IRFDU:

sk

g

gea−−= 1 (3.69)

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IO�F�ULL�FX�UHOD LD�de aproximare:

5,01000

6,1 −= f

fl

Tk (3.70)

úL�FRHILFLHQWXO�GH�DEVRUE LH�DO�IO�F�ULL�FX�UHOD LD:

sk

fl

flea−−=1 (3.71)

3RQGHUHD�DEVRUE LHL�IO�F�ULL�ID ��GH�FHD�D�PHGLXOXL�UDGLDQW�GH�JD]H�GH�DUGHUH�GLQ�

IRFDU�VH�IDFH�GXS��FULWHULL�H[SHULPHQWDOH��FRQVLGHUkQGX-VH�R�SURSRU LH�β, din volumul IRFDUXOXL��RFXSDW��GH�SDUWHD�OXPLQRDV��D�IO�F�ULL.

CoHILFLHQWXO�GH�DEVRUE LH�DO�IO�F�ULL�úL�JD]HORU�GH�DUGHUH�HVWH�GDW�GH�UHOD LD� gfl

aaa ⋅−+⋅= )1( ββ (3.72)

Valorile coeficientului de luminozitate β sunt prezentate în tabelul 3.3.

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�FDPHUHL�GH�DUGHUH:

ξΨ−+⋅

=)1(

82,0

aa

aa fc (3.73)

XQGH�FRHILFLHQWXO�GH�PXUG�ULUH: ξ =0,7 ÷ 0,9 combustibil gazos ξ =0,6 ÷ 0,7 combustibil lichid )DFWRUXO�GH�SR]L LH�D�IO�F�ULL��vQ�FDPHUD�GH�DUGHUH�HVWH�GDW�GH�UHOD LD:

fMM H

hbaM −= (3.74)

cu constantele: aM ��úL�EM=0,2 �SHQWUX�IODF�U��GH�FRPEXVWLELO�JD]RV�VDX�OLFKLG��úL SHQWUX�UDSRUWXO�vQWUH�vQ�O LPHD�GH�DPSODVDUH�D�DU]�WRUXOXL�úL�vQ�O LPHD�FDPHUHL:

fH

h= 0,3 (Hf = dc)

Hf

h

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

55

Diametrul corpului de întoarcere�VH�GHWHUPLQ�� LPSXQkQG�R�YLWH]��D�JD]HORU�GH�DUGHUH�vQ�VSD LXO�LQHODU, wg = 4 ÷ 6 m/s (cu valori mici pentru cazane mici):

273

273

)(4

22

' +⋅

−= gm

cf

g

g

t

dd

BVw

π ,

unde 2

'ff

gm

ttt

+=

5H]XOW�: 273

2734'

2 ++= gm

g

g

cf

t

w

BVdd

π (3.75)

Diametrul focarului astfel determinat sH�URWXQMHúWH�OD�YDORUL�vQWUHJL�(de preferat modul de 10 mm) úL�VH�UHFDOFXOHD]��YLWH]D�viteza gazelor de ardere (wg).

&X�DFHVWH�GDWH�VH�GHWHUPLQ��WHPSHUDXUD�GH�OD�FDS�WXO�IRFDUXOXL��

( ) 11

6,03

*

+

⋅⋅−⋅⋅⋅⋅

=

pginc

Rtfo

tf

cVBq

STaCM

TT

ξ [oK] (3.76)

unde T*f reprezintã temperatura pe care ar avea-R�JD]HOH�GH�DUGHUH�OD�LHúLUHD�GLQ�IRFDU�

dacã acesta ar fi în solu LH�FRQVWUXFWLYã cu strãpungere. Pentru a verifica temperatura UHDOm�D�JD]HORU�GH�DUGHUH�OD�LHúLUHD�GLQ�IRFDU�vQ�VROX LD�FX�vQWRDUFHUH�YD�WUHbui calculatã FRPSRQHQWD� FRQYHFWLYm� úL� GHWHUPLQDWm� VFmGHUHD� GH� WHPSHUDWXUm� FH� FRUHVSXQGH�DFHVWHLD�� 7HPSHUDWXUD� DVWIHO� RE LQXWm� YD� IL� FRPSDUDWm� FX� WHPSHUDWXUD� GH� LHúLUH� GLQ�focar impusã în bilan XO�SDU LDO�SH�VXSUDIH H�� Coeficientul global de transfHU�GH�F�OGXU��kGF�VH�FDOFXOHD]��FX�UHOD LD��:

1

1

1 εαα

+=GFk , cu ε�GDW�GH�WDEHOXO��VDX�UHOD LLOH��úL��.

rc ααα +=1 &RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�FRQYHF LH�VH�GHWHUPLQ��XWLOL]kQG�UHOD LL�criteriale pentru FLUFXOD LD� JD]HORU� GH� DUGHUH� OD� LQWHULRUXO� FDQDOHORU� FX� VHF LXQH�FLUFXODU��FRQIRUP�DQH[HL��SXQFWXO�� pentru:

g

cg lW

ν=Re

unde�OXQJLPHD�FDUDFWHULVWLF�:


CAZANE

56

cf

cf

cfcirc

c dddd

dd

P

Sl −=

+

−==

)(

)(4

4422

π

π

De exemplu, pentru Re>3· 104

CL

dNu i

+

−+

−=

3/2

3/2

0 1

)1(Pr8

2,121

Pr)1000(Re8

ξ

ξ

ε (3.34*)

cu )4,02,0(,Pr

Pr;)64,1Relog82,1(

11,0

2 ÷+=

=−= −

R

p

LLCξ , ε0=1

Pentru 2300 < Re < 3 ⋅104:

CBANu

3/1

30 Pr221

2]7,0615,1[37,49

++−+= ε (3.35*)

cu A=

11,032/1

3

Pr

Pr;PrRe;PrRe

=

=

p

ii CL

dB

L

d, εo=1.

Pentru regimul laminar: Re < 2300:

11,03/13

3*0 Pr

Pr7,0PrRe615,137,49

−⋅+=

p

i

L

dNu ε (3.36*)

cu *0ε = 1.

Practic se XWLOL]HD]��UHOD LLOH��úL��VDX��,notate acum suplimentar cu (*)

pentru care ε úL� *0ε sunt egale cu unitatea.


c

cl

Nuλα =

&RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH�VH�FDOFXOHD]��utilizând�UHOD LLOH��úL��pentru care care grosimea stratului radiant este:

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

57

)(9,0)(

)(46,36,3

22

cf

gcf

gcf

p

gdd

Ldd

Ldd

S

Vs −=

+

−==

ππ

π

úL 2732

*

++

= ff

gm

ttT

2732080 ++=pT (K)

'LIHUHQ D�PHGLH�D�WHPSHUDWXULORU�VH�FDOFXOHD]��FX�UHOD LD:

80

80ln

)80()80(*

*

−

−−−−

=∆

f

f

ff

GF

t

t

tttm

6H�FDOFXOHD]��QGF = ( ) GFffGF tmLdk ∆⋅⋅⋅⋅ π

Se calculeazã entalpia gazelor la LHúLUH� GLQ� IRFDU� � Bq

QII

ext

GCff )1(*

−−= ; din

diagrama I-W� �� IXQF LH� HQWDOSLH� úL�FRHILFLHQWXO�GH�H[FHV�GH�DHU�din focar se determinã WHPSHUDWXUD�JD]HORU�OD�LHúLUH�GLQ�IRFDU, tf. Deoarece calculul este aproximativ eroarea admisibilã este de ±10%. In cazul vQ�FDUH�VH�GHSmúHúWH�DFHDVWm�HURDUH�VH�YD�UHGLPHQVLRQD�VXSUDID D�GH�WUDQVIHU�GH�Fãldurã SULQ� UDGLD LH� �� GLDPHWUXO� úL� OXQJLPHD corpului de întoarcere ) cu o cotã procentualã HJDOm�FX�UDGLFDO�GH�RUGLQXO��GLQ�HURDUHD�SH�WHPSHUDWXUL��7RWXúL��GDFm�WHPSHUDWXUD�GH�LHúLUH�GLQ�IRFDU�FRUHVSXQGH�GRPHQLXOXL�HFRQRPLF�VH�SRDWH�DFFHSWD�FD�DWDUH�XUPkQG�D�se modifica sarcina pe convectiv în conVHFLQ ã conform rela LLORU�� 3.2.8. Calculul termic al convectivului Convectivul cazanului este determinat, din punctul de vedere al transferului de cãOGXU��GLQ�FDOFXOHOH�DQWHULRDUH�SULQ�XUP�WRULL�SDUDPHWULL��

QC –�GHELWXO�GH�F�OGXU��util preluat în sistemul convectiv (kW) ; tf –�WHPSHUDWXUD�JD]HORU�GH�DUGHUH�OD�LQWUDUH�vQ� HYL��0C) ; tFRú –�WHPSHUDWXUD�JD]HORU�GH�DUGHUH�OD�LHúLUHD�GLQ� HYL��OD�FRú��0C) ; te/ti – temperatura apei (0C).

0HWRGRORJLD�GH�FDOFXO�HVWH�LGHQWLF��FX�FHD�SUH]HQWDW��vQ�FDSLWROXO��. 3HQWUX� VWDELOLUHD� VHF LXQLL� GH� WUHFHUH� D� JD]HORU� GH� DUGHUH� VH� DOHJH� GLDPHWUXO� HYLORU�GLQ�JDPD�GH� HYL�X]XDOH��GH�×δ):

φ42 × 3; φ45× 3; φ51 × 3; φ 57 ×3; φ 60 × 3; φ 70 × 3,5. 'XS�� DOHJHUHD� GLDPHWUXOXL� HYLORU� VH� DOHJH� YLWH]D� SUHOLPLQDU�� GH� FLUFXOD LH� D�gazelor de ardere w’ în intervalul economic pentru acest tip de cazan:


CAZANE

58

w’ = (2 ÷ 4) m/s. 6HF LXQHD�GH�FLUFXOD LH�D�JD]HORU�GH�DUGHUH�YD�IL�

273

273

'

+⋅= gmg

circ

t

w

VBS (m2) (3.31)

)(2

0cosC

ttt

f

gm


1XP�UXO�GH� HYL�DO�GUXPXOXL�FRQYHFWLY�YD�IL� 2

4'

i

circ

d

Sn

⋅=

π

Acesta VH�URWXQMHúWH�VXSHULRU�VDX�LQIHULRU��OD�QXP�U�vQWUHJ�SDU�úL�VH�UHFDOFXOHD]��YLWH]D�GH�FLUFXOD LH�D�JD]HORU�GH�DUGHUH��

273

273

4

2

+⋅= gm

i

g t

dn

VBw

π (3.33)

Pentru temperatura medie a gazelor de ardere tgm� VH� GHWHUPLQ�� GLQ� DQH[D� ��XUP�WRDUHOH�YDORUL�

- YkVFR]LWDWHD�FLQHPDWLF�� ν [m2/s] - FRQGXFWLELOLWDWHD�WHUPLF�� λ [W/mK] - QXP�UXO�3UDQGWO� Pr 'H�DVHPHQHD�VH�GHWHUPLQ��QXP�UXO�3UDQGWO�SHUHWH�Prp la temperatura peretelui

tp cu

tp = tm +(10÷20) oC ; 2

eim

ttt

+= .

&RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�FRQYHF LH�VH�GHWHUPLQ��XWLOL]kQG�UHOD LL�FULWHULDOH� SHQWUX� FLUFXOD LD� JD]HORU� GH� DUGHUH� OD� LQWHULRUXO� HYLORU��conform anexei 10 punctul 5.

De exemplu, pentru 4103Re ⋅>=

νiwd

CL

d

x

Nu i

+

−+

−=

3/2

3/2

1

)1(Pr2,121

Pr)1000(Re8

ξ

ξ

(3.77)

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

59

cu )4,02,0(,Pr

Pr;)64,1Relog82,1(

11,0

2 ÷+=

=−= −

R

p

LLCξ .

Pentru 2300< Re < 3 ⋅104�úL��Gi/L < 1:

CBANu

3/1

30 Pr221

2]7,0615,1[37,49

++−+= ε (3.78)

cu A=

11,032/1

3

Pr

Pr;PrRe;PrRe

=

=

p

ii CL

dB

L

d

εo �� ·� �� UHSUH]LQW�� HIHFWXO turbulizatorilor ce se vor monta la interorul HYLORU�FRQYHFWLYH��IXQF LH�GH�JUDGXO�GH�WXOEXUL]DUH�UHDOL]DW��IRUP��úL�SDV�GH�úLFDQDUH�� Pentru regim laminar Re < 2300

11,03/13

3*0 Pr

Pr7,0PrRe615,137,49

−⋅+=

p

i

L

dNu ε (3.79)

cu *0ε = 1,6÷2,2.

Pentru turbulizatorii în zig-zag�� FRHILFLHQ LL� GH� FRUHF LH�� 0ε �úL� *0ε pot fi

GHWHUPLQD L�FX�UHOD LLOH�H[SHULPHQWDOH� 2,0

*0

142,2

br=ε ��úL��

5

Re3,3 2,0

2,00 −=br

ε (3.37)

unde id

lbr = este pasul relativ, cu l – pas zig-zaguri.

În toate cazurile:

c

cl

Nuλα =

l

di


CAZANE

60

&RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH�HVWH�GHWHUPLQDW�GH�P�ULPLOH:

- WHPSHUDWXU��PHGLH�D�JD]HORU�GH�DUGHUH: Tgm=tgm+273 (K) ; - grosimea stratului radiant: s=0,9 di (m) ;

- SUHVLXQLOH�SDU LDOH�DOH�JD]HORU�GH�DUGHUH�WULDWRPLFH: 2ROp ; OHp

2 (bar).

&RQVWDQWD�GH�UDGLD LH�D�JD]HORU�HVWH: )(

100038,01

)(

6,18,022

22

2

ROOH

gm

ROOH

OHpp

T

spp

pkg +

−

+

+= (3.81)

cu Tm = tm + 273 (K); iar coeficientul de emisivitate al gazelor de ardere:

kgs

g ea−−= 1 (3.82)

&RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH�VH�FDOFXOHD]��FX�UHOD LD:

−

−

+⋅= −

gm

p

gm

p

gmg

p

r

T

T

T

T

Taa

1

1

2

110765,5

6,3

38α (W/m2K) (3.83)

XQGH� SHQWUX� FRHILFLHQWXO� GH� DEVRUE LH� DO� SHUHWHOXL� VH� LD� YDORarea ap = �� úL� SHQWUX�WHPSHUDWXUD�DEVROXW��D�SHUHWHOXL� HYLL: 27320 ++= mp tT (0K)

Coeficientul de WUDQVIHU� GH� F�OGXU� pe partea gazelor de ardere (la interiorul HYLORU��YD�IL: α1 = αc + αr

Coeficientul α2 (pe partea apei) este mult mai mare (de ordinul miilor de W/m2K) în comparate cu α1 (de ordinul zecilor de W/m2K). ÌQ�DFHVWH�FRQGL LL�FRHILFLHQWXO�JOREDO�GH�WUDQVIHU�GH�F�OGXU��N�HVWH�GDW�GH�UHOD LD:

1

1

1 εαα

+=Ik (W/m2K) pentru care s-a neglijat 1/α2 (3.84)

CoeficieQWXO� GH� PXUG�ULUH� ε pentru gaze de ardere provenite din combustibil gazos este dat în tabelul 3.7.

Tabelul 3.7 &RHILFLHQWXO�GH�PXUG�ULUH�– combustibil gazos

Viteza wI (m/s) 3 6 9 12 15 18 ε ⋅103 (m2K/W) 5,233 3,837 2,791 2,093 1,628 1,395

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

61

Se poaWH�XWLOL]D�úL�UHOD LD�DQDOLWLF�:

6474,031021,11 −− ⋅⋅= wε (m2K/W) (3.85)

Pentru gaze de ardere provenind din combustibil lichid: 0163,0≅ε (m2K/W) 'LIHUHQ D� PHGLH� GH� WHPSHUDWXU�� VH� GHWHUPLQ�� FRQIRUP� ILJXULL� �� úL� UHOD LHL�(3.43):

min

max

minmax

lnt

t

tttm

∆∆

∆−∆=∆

Fig. 3.5. 6XSUDID D�GH�VFKLPE�GH�F�OGXU��D�GUXPXOXL�FRQYHFWLY�YD�IL: ci

m

cc Ldn

tk

QS π=

∆= (m2)

UH]XOW�:

i

cc

dn

SL

π= (m)

a) 'DF�� /c > LR, în limitele Lc = LR + (0,2÷0,4) m,� vQVHDPQ��F��GLVWDQ D�GLQWUH�

SO�FLOH�WXEXODUH�DOH�FD]DQXOXL�HVWH�VXILFLHQW�GH�PDUH�SHQWUX�D�SHUPLWH�GLODWDUHD�OLEHUD� D� IRFDUXOXL�� GDU� QX� SUHD� PDUH� DVWIHO� vQFkW� V�� VH� FUHH]H� XQ� YROXP�inutilizabil la interiorul corpului cazanului;

b) 'DF��/c < LR, se reduce num�UXO�GH� HYL�VDX�GLDPHWUXO��DVWIHO�vQFkW�V��VH�DMXQJ��în cazul a);

c) 'DF��/c >> LR��VH�P�UHúWH�QXP�UXO�GH� HYL�DVWIHO�vQFkW�V��VH�DMXQJ��vQ�FD]XO�D��

S SC

t

tma

tf

tc

∆tmax

∆tmin


CAZANE

62


vQWRDUFHUHD�JD]HORU�GH�DUGHUH�vQ�IRFDU�úL�XQ�GUXP�FRQYHFWLY� 3.3��'HVFULHUHD�FD]DQHORU��HOHPHQWH�FRPSRQHQWH��PRG�GH�IXQF LRQDUH�

6XQW� FD]DQH� FX� IRFDU� FDPHU�� ODUJ�� vQ� FDUH� VH� vQWorc gazele de ardere, au un GUXP� FRQYHFWLY� úL� SRW� IXQF LRQD� atât în suprapresiune� FkW� úL� vQ� GHSUHVLXQH, cu FRPEXVWLELO�JD]RV�VDX�OLFKLG��3URGXF�DS��FDOG��We / ti = 90 / 70 0C.

Principalele elemente componente ale cazanului sunt prezentate în figurile 3.6 úL��

Fig. 3.6. Schema unui cazan din elemente cu un drum convectiv.

��(OHPHQW�FXUHQW��(OHPHQW�vQFKLGHUH�ID ��(OHPHQW�vQFKLGHUH�VSDWH��$U]�WRU��9L]RU�� 3ODWEDQGH�GH�HWDQúDUH�vQWUH�HOHPHQWH��'LVWULEXLWRU��&ROHFWRU��7HDF��SHQWUX�WHUPRVWDWH�

��3URPRWRUL�GH�WXUEXOHQ ��5DFRUGXUL�LQWUDUH�LHúLUH�DSã�FDOG��vQF�O]LUH��5DFRUG�GH�HYDFXDUH�JD]H�GH�DUGHUH�OD�FRú��,]ROD LH�WHUPLF��úL�FDUFDV��H[WHULRDU��(úDIRGDM�GH�VXV LQHUH�

3

11

11

12

6

7

8 9 10 13

14

13

3

10

1

2

4

5

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

63

Elementele WLS� DOH� FD]DQXOXL� VXQW� H[HFXWDWH� GLQ� HYL� WUDVH� úL� QHWHGH� GLQ� R HO��vPELQDWH� vQWUH� HOH� SULQ� VXGXU�� VXE� IRUPD� D� GRX�� FDGUH� GUHSWXQJKLXODUH�� XQXO�FRUHVSXQ]�WRU� IRFDUXOXL�� FHO�ODOW� FRUHVSXQ]�WRU� VLVWHPXOXL� FRQYHFWLY�� (OHPHQWHOH� WLS�sunt asamblate între ele pULQ� VXGXU�� SULQ� LQWHUPHGLXO� XQRU� SODWEDQGH� PHWDOLFH��DOF�WXLQGX-VH� DVWIHO� XQ� FD]DQ� EORF�� FX� IRFDU� FDPHU�� I�U�� VWU�SXQJHUH� úL� XQ� GUXP�FRQYHFWLY�� 7RDWH� VXGXULOH� VH� H[HFXW�� GLQVSUH� H[WHULRUXO� FRUSXOXL� FD]DQXOXL� LDU�FRUGRDQHOH� GH� VXGXU�� VXQW� FRQWLQXH�� )LHFDUH� HOHPHQW� HVWH� OHJDW� SULQ� úWX XUL� OD�GLVWULEXLWRUXO�úL�FROHFWRUXO�GH�DS��DO�FD]DQXOXL�

)LJ��(OHPHQW�WLS��D��HOHPHQW�vQFKLGHUH�ID ��E��úL�HOHPHQW�vQFKLGHUH�VSDWH��F� �� HYL�QHWHGH�GLQ�R HO�� HDY��RUL]RQWDO��GH�OHJ�WXU��IRFDU� ��VLVWHPXO�FRQYHFWLY��SODWEDQGH�GH�OHJ�WXU� între elemente.

,Q�GUXPXO� FRQYHFWLY� DO� FD]DQXOXL� VH� UHDOL]HD]�� LQWHQVLILFDUHD� WUDQVIHUXOXL�GH�F�OGXU��DFROR� XQGH� JD]HOH� GH� DUGHUH� vQWkOQHVF� XQ� SDFKHW� GH� WXUEXOL]DWRUL�� VSHFLILFL�� H[HFXWD i GLQ�WDEO��GH�R HO�vQ�]LJ-zag.

Trecerea gazelor de ardere din focar în drumul convectiv se face prin partea din ID ��D�FD]DQXOXL��$LFL�HVWH�SUHY�]XW��R�Xú��GH�vQFKLGHUH�UDFLWm�úL�R�]RQm�GH�SULQGHUH�D�arzãtorului�F�SWXúLW�� FX�L]ROD LH�WHUPLF��GLQ�ILEU��FHUDPLF��UH]LVWHQW��OD�WHPSHUDWXUL�ridicate.

)XQF LRQDUHD� FD]DQXOXL� SRDWH� IL� vQ HOHDV�� XUP�ULQG� FHOH� GRX�� FLUFXLWH� DOH�DJHQ LORU�WHUPLFL��FLUFXLWXO�JD]HORU�GH�DUGHUH�úL�FLUFXLWXO�DSHi. Gazele de ardere formate vQ�IRFDU�SDUFXUJ�OXQJLPHD�FD]DQXOXL�úL�DMXQJ�vQ�SDUWHD�GLQ�VSDWH��'DWRULW��WLUDMXOXL�VXQW�REOLJDWH� V�� VH� vQWRDUF�� vQ� GLUHF LH� LQYHUV�� V�� SDUFXUJ�� GLQ� QRX� OXQJLPHD� FD]DQXOXL��DMXQJkQG�DVWIHO�vQ�SDUWHD�GLQ�ID ��XQGH�HOHPHQWXO�GH�vQFKLGHUH�ID ��OH�REOLJ��V��LQWUH�vQ�drumul convectiv. Gazele de ardere parcurg din nou lungimea cazanului, apoi sunt FROHFWDWH�vQ�FXWLD�GH�FROHFWDUH�úL�HYDFXDWH�SULQ�UDFRUGXO�OD�FRú�

(a) (c) (b)

1

2

3

4

5


CAZANE

64

$SD�UHFH�GLQ�UHWXUXO�LQVWDOD LHL�GH�vQF�O]LUH��LQWU��prin distribuitorul cazanului în WRDWH�HOHPHQWHOH�úL�SH�P�VXU��FH�SDUFXUJH� HYLOH�VH�vQF�O]HúWH��$SD�FDOG��HVWH�FROHFWDW��OD�SDUWHD�VXSHULRDU��D�FD]DQXOXL�úL�WULPLV��OD�FRQVXPDWRUL� &D]DQXO� HVWH� L]RODW� WHUPLF� FX� YDW�� PLQHUDO�� úL� SURWHMDW� OD� H[WHULRU� FX� WDEO��VXE LUH��6H�RE LQH�DVWIHO�XQ�FD]DQ�PRQREORF�SHQWUX�FDUH��PRGLILFkQG�GLPHQVLXQLOH�GH�gDEDULW�DOH�HOHPHQWHORU��GLDPHWUXO� HYLORU�úL�QXP�UXO�GH�HOHPHQWH�VH�SRW�RE LQH�GLYHUVH�YDULDQWH�GH�VDUFLQL�WHUPLFH��GXS��QHFHVLW� L� 'HúL� FRQVXPXO� GH� PDWHULDO� úL� GH� PDQRSHU�� SHQWUX� H[HFX LD� DFHVWRU� WLSXUL� GH�cazane este mare, se impune avantajul de a se SXWHD�LQWURGXFH�SH�HOHPHQWH��SULQ�VSD LL�vQJXVWH�úL�GH�D�VH�PRQWD�la�ORFXO�GH�IXQF LRQDUH� 3.3.2. Tema de proiectare

Prin tema de proiectare se dau:

- Q –�VDUFLQD�WHUPLF��D�FD]DQXOXL��vQ�N:�� - te / ti –�WHPSHUDWXUD�DSHL�OD�LHúLUH��LQWUDUH�vQ�Fazan, (90/70 0C sau 80/60 0C); - QDWXUD�úL�FRPSR]L LD�FRPEXVWLELOXOXL��OLFKLG�VDX�JD]RV��

$FHVWH� FD]DQH� IXQF LRQHD]�� GH� RELFHL� FX� VXSUDSUHVLXQH� vQ� IRFDU�� GHFL�

FRHILFLHQWXO�GH�H[FHV�GH�DHU�HVWH�DFHODúL�SHQWUX�IRFDU��SHQWUX�FRQYHFWLY�úL�OD�FRú� α = αf = αcv = αFRú = 1,05 ÷ 1,15 = ct. &RQIRUP� LQGLFD LLORU� GLQ� FDSLWROXO� �� VH� HIHFWXHD]�� FDOFXOXO� DUGHULL�

FRPEXVWLELOXOXL�úL�VH�GHWHUPLQ��Vo, Vgo, Hi, OH2p ,

2ROp úL�VH�WUDVHD]��GLDJUDPD�,�– t sau

cp – t. 3.3.3. Calculul randaPHQWXOXL�WHUPLF�DO�FD]DQXOXL�úL�D�GHELWXOXL�GH�FRPEXVWLELO� $FHVWH� FD]DQH� IXQF LRQHD]�� GH� RELFHL� FX� FRPEXVWLELO� JD]RV� VDX� OLFKLG� �SRW� IL�DGDSWDWH�úL�SHQWUX� IXQF LRQDUH�FX�FRPEXVWLELO� VROLG��GHFL�� vQ�FD]XO�GH�ID ��SLHUGHULOH�VSHFLILFH� GH� F�OGXU�� SULQ� DUGHUH� LQFRPSOHW�� GH� QDWXU�� PHFDQLF�� Tmec�� úL� FHOH� SULQ�evacuarea produselor solide ale arderii din cazan (qcen) sunt nule. De asemenea B* = B. 6H�FDOFXOHD]��SLHUGHULOH�VSHFLILFH�GH�F�OGXU�� a). 3ULQ�HYDFXDUHD�JD]HORU�GH�DUGHUH�SH�FRú�(qFRú):

)(1

0coscos a

i

IIH

q α−= (3.86)

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

65

6H�DOHJH�R�WHPSHUDWXU��D�JD]HORU�GH�DUGHUH�OD�FRú�

Ctt

t ei 0cos )8060(

2÷+

+≅ (3.87)

úL�GLQ�GLDJUDPD�,�–�W�VH�GHWHUPLQ��,FRú. Pentru temperatura aerului (ta ≅ 20 0&�� VH� FDOFXOHD]�� HQWDOSLD� DHUXOXL� WHRUHWLF�necesar arderii:


cu cpa = 1,2971 kJ/ Km3

N �F�OGXUD�VSHFLILF��D�DHUXOXL�OD��0C. b. PULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��FKLPLF�� ÌQ� FDGUXO� FDOFXOHORU� GH� SURLHFWDUH�� GDWRULW�� SHUIRUPDQ HORU� GH� IXQF LRQDUH� Dle DU]�WRDUHORU�PRGerne�� VH�DGPLWH�R�SLHUGHUH�SULQ�DUGHUH� LQFRPSOHW��GH�QDWXU��FKLPLF� de ordinul:

qch = 0,001 ÷ 0,005 c). 3ULQ�SHUH Li exteriori ai cazanului (qext): ÌQ� FDGUXO� FDOFXOHORU� GH� SURLHFWDUH�� SHQWUX� FD]DQH� UHODWLY� PLFL�� vQ� IXQF LH� GH�gradul�GRULW�GH�L]ROD LH�WHUPLF��D�FD]DQXOXL��VH�SRDWH�DOHJH�R�YDORDUH��

qext = 0,005 ÷ 0,015 Randamentul cazanului�VH�FDOFXOHD]��FX�UHOD LD� )(1 cos extch qqq ++−=η �úL� ηη ⋅=100% (%) (3.89)

Debitul de combustibil consumat va fi:

iH

QB

⋅=

η (kg/s) sau ( s/m3N )

��%LODQ XO�GH�DQVDPEOX�DO�FD]DQXOXL )OX[XO�GH�F�OGXU��XWLO�DO�FD]DQXOXL�HVWH�� Q ; )OX[XO�GH�F�OGXU��DGXV�GH�FRPEXVWLELO�� Qc = B ⋅ Hi ; )X[XO�GH�F�OGXU��DGXV�GH�DHUXO�GH�DUGHUH� Qa = B ⋅ α ⋅cpa ⋅ ta ;

)X[XO�GH�F�OGXU��SLHUGXW�OD�FRú�� QFRú = B ⋅ IFRú ; )X[XO�GH�F�OGXU��SLHUGXW�SULQ�DUGHUH�LQFRPSOHW�� Qinc = qch ⋅ B ⋅ Hi.


CAZANE

66

5H]XOW��WDEHOXO�GH�ELODQ � Tabelul 3.8.

Fluxuri introduse – pierderi

Fluxuri utile

Qc

Qa

- QFRú - Qinc

- Qext

Q

∑ = 'QQ ''∑ = QQ

1RW��ÌQ�DFHVW�ELODQ �WHUPHQHXO�“– qcosBHi” s-D�VFULV�VXE�IRUPD�H[SOLFLW��


(URDUHD�UHODWLY�� %1100

'

"'<⋅

−=

Q

QQε

3.3.5. Calculul temperDWXULORU�úL�HQWDOSLLORU�JD]HORU�GH�DUGHUH�SH�WUDVHX� (QWDOSLD�WHRUHWLF��D�JD]HORU�GH�DUGHUH�VH�FDOFXOHD]��FX�UHOD LD� apachit tcVqHI 0)1( α+−= (3.90)

Din digrama I –�W�VH�GHWHUPLQ��WHPSHUDWXUD�WHRUHWLF��GH�DUGHUH�� ),I(ft tt α= .

O imporWDQW�� FDUDFWHULVWLF�� IXQF LRQDO�� D� FD]DQHORU� FX� vQWRDUFHUH� D� JD]HORU� GH�DUGHUH� vQ�IRFDU�R�UHSUH]LQW�� LQF�UFDUHD� WHUPLF��VSHFLILF��PDUH�D�VXSUDIH HL�GH�VFKLPE�GH� F�OGXU�� D� IRFDUXOXL�� 'H� DFHHD� LQWHUYDOXO� GH� DOHJHUH� D� WHPSHUDWXULL� OD� FDS�WXO�focarului este:

tf =500÷700 oC.

Din diagrama I–W��VH�GHWHUPLQ��HQWDOSLD�JD]HORU�GH�DUGHUH�OD�LHúLUHD�GLQ�IRFDU� ),( αff tfI = .


)()1( ftextR IIBqQ −−= (kW) (3.91)

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

67

)OX[XO�GH�F�OGXU��SUHOXDW�GH�sistemul convectiv va fi:

,Rc QQQ −= (3.92)

(QWDOSLD�JD]HORU�GH�DUGHUH�OD�VIkUúLWXO�GUXPXOXL�FRQYHFWLY�va fi:

Bq

QII

ext

c

fc )1( −−=

úL�GLQ�GLDJUDPD�,–W�UH]XOW��WHPSHUDWXUD�� ),I(ft cc α= . ÌQFKLGHUHD�ELODQ XOXL�LPSXQe: Ic ≅ IFRú��úL��Wc ≅ tFRú��úL�VH�DGPLW�HURULOH�UHODWLYH� 100

cos

cos

II

II

t

c

I −−

=ε ��

úL� 100

cos

cos

tt

tt

t

c

t −−

=ε ��

��%LODQ XO�JUDILF�DO�FD]DQXOXL�

'HELWHOH�GH�F�OGXU��QR, Qc, Qa�úL�IOX[XULOH�SLHUGXWH�QFRú, Qinc, Qext se transpun JUDILF�DO�VFDU��FD�vQ�ILJXUD��FX�B* = B; Qpa = 0; Qsfc = 0; Qsi = 0; Qec = 0; qmec = 0 úL�qev = 0). 3.3.7. Calculul termic la focarului

$FHVW�FDOFXO�DUH�FD�VFRS�GHWHUPLQDUHD�VXSUDIH HL�GH�UDGLD LH�6R�FDSDELO��V��SUHLD�GHELWXO� GH� F�OGXU�� Uadiant QR� GH� OD� IODF�U�� úL� JD]HOH� GH� DUGHUe. Deoarece în calcule

intervin gradul de ecranare

=Ψ

per

R

S

S úL�OXQJLPHD�GH�UDGLD LH�este necesar un calcul

LWHUDWLY�� 6H� DGPLWH� R� YDORDUH� SUHOLPLQDU�� 'RS care în final se va compara cu cea

UH]XOWDW��GLQ�FDOFXO�6R.

9DORDUHD�SUHOLPLQDU�� 'RS �SRDWH�IL�VWDELOLW��SULQ��GRX��PHWRGH�

D��6H�DGPLWH�XQ�IOX[�XQLWDU�UDGLDQW��vQF�UFDUH�WHUPLF��VSHFLILF�� qR = 30 ÷ 50 kW/m2

��úL� ! S

RR

q

QS =' (m2) (3.93)


CAZANE

68

sau E��6H�GHWHUPLQ��VXSUDID D�GH�UDGLD LH�vQ�IRFDU�FX�UHOD LD��GH�DSUR[LPDUH�

−

⋅

=44

'

100100765,5 pf

RR

TT

QS

ε (m2) (3.94)

cu ε =0,65 pentru combustibil gazos ε = 0,75 pentru combustibil lichid Tf = tf + 273 (0K)

Tp = tm + 20 + 273 (0K) unde 2

ttt ei

m

+=

)RFDUXO��FX�SHUH L�PHPEUDQ��DUH�IRUPD�JHRPHWULF��SUH]HQWDW��vQ�ILJXUD�� Din punct de vedere geometric:

ahhaLSR ++= )(2' (m2) (3.95)

LhaVg ⋅⋅≅ (m3)

ahhaLS per 2)(2 ++= (m2)

6H�DOHJ� HYL�X]XDOH��din anexa 12: φ 57 × 3; φ 60 × 3,5; φ 70 × 3,5; φ 76 × 3,5 etc.

)LJ��)RFDU�FDPHU��FX�SHUHWH�PHPEUDQ� ��FDGUX�GLQ� HDY��SODWEDQG��GH�OHJ�WXU��QHUYXU��DU]�WRU��Xú�

1

4

2

3

1

a h

d s1

L

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

69

Se impun valori uzuale pentru: a = 300 ÷ 800 mm h = 600 ÷ 900 mm 'LQ�UHOD LD��VH�GHWHUPLQ��OXQJLPHD�IRFDUXOXL� &X�GDWHOH�SUHFL]DWH�DQWHULRU��VH�FDOFXOHD]�� - grosimea stratului radiant:

per

f

S

Vs 6,3= (m)


R

S

S'

=Ψ

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�JD]HORU�GH�DUGHUH��GLQ�IRFDU�

)(1000

38,01)(

6,18,022

22

2

ROOH

f

ROOH

OH

g ppT

spp

pk +

−

+

+= (3.96)

6H�FDOFXOHD]��FRHILFLHQWXO�GH�DEVRUE LH�DO�JD]HORU�GH�DUGHUH�GLQ�IRFDU�

sk

g

gea⋅−−= 1 (3.97)

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IO�F�ULL�FX�UHOD LD�GH�DSUR[LPDUH� 5,0

10006,1 −= f

fl

Tk (3.98)

úL�FRHILFLHQWXO�GH�DEVRUE LH�DO�IO�F�ULL�FX�UHOD LD�

sk

fl

flea⋅−−= 1 (3.99)

3RQGHUHD�DEVRUE LHL�IO�F�ULL�FX�FHD�D�PHGLXOXL�UDGLDQW�GH�JD]H�GH�DUGHUe se face GXS��FULWHULL�H[SHULPHQWDOH��FRQVLGHUkQG�R�SURSRU LH�β��GLQ�YROXPXO�IRFDUXOXL��RFXSDW��GH�SDUWHD�OXPLQRDV��D�IO�F�ULL� &RHILFLHQWXO�GH�DEVRUE LH�DO�IO�F�ULORU�úL�JD]HORU�GH�DUGHUH�HVWH�GDW�GH�UHOD LD� gfl aaa ⋅−+⋅= )1( ββ (3.100)

Valorile coeficientului de luminozitate β, sunt prezentate în tabelul 3.3. &RHILFLHQWXO�GH�PXUG�ULUH�D�VXSUDIH HORU�HVWH� ξ =0,7 ÷ 0,9 combustibil gazos ξ =0,6 ÷ 0,7 combustibil lichid


CAZANE

70

&X�DFHVWH�YDORUL�VH�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IRFDUului:

ξΨ−+⋅

=)1(

82,0

aa

aa f (3.101)

2� DOW�� FDUDFWHULVWLF�� D� IRFDUXOXL� HVWH� IDFWRUXO� GH� SR]L LH� D� IO�F�ULL� vQ� IRFDU� )DFWRUXO�GH�SR]L LH�D�IO�F�ULL��vQ�FDPHUD�GH�DUGHUH�HVWH�GDW�GH�UHOD LD�

f

MMH

hbaM −=

Pentru combustibil lichid sau gazos constantele: aM �� úL� bM =0,2 iar

vQ�O LPHD�GH�DPSODVDUH�D�DU]�WRUXOXL�raportatã la�vQ�O LPHD�FDPHUHL�: fH

h = 0,3 .

&X�DFHVWH�GDWH�VH�GHWHUPLQ��VXSUDID D�GH�UDGLD LH�D�IRFDUXOXL�

32

2

38

11

10765,5 MT

T

TTaM

QS

f

t

tff

RR

−

⋅= − ξ (m2) (3.102)

$FHDVW�� VXSUDID �� YD� IL� GLIHULW�� GH� '

RS � GHWHUPLQDW�� vQ� FDOFXOXO� DSUR[LPDWLY��'DF��GLIHUHQ D�HVWH�PDL�PDUH�GH��VH�UHLD�FDOFXOXO�FX�YDORUL�PRGLILFDWH�SHQWUX�Vf úL�Sper �SHQWUX�FDOFXOH�PDL�SUHFLVH�DFHDVW��GLIHUHQ ��VH�SRDWH�LPSXQH�OD�PD[��

5H]XOW��OXQJLPHD�ILQDO��D�IRFDUXOXL�

)(2 ha

ahSL R

+−

= (3.103)

FDUH�QX�WUHEXLH�V��GLIHUH�GH�FHD�SUHOLPLQDU��FX�PDL�PXOW�GH�5%.

Hf

h

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

71

3.3.8. Calculul termic al convectivului

Convectivul cazanului este deteUPLQDW� GLQ� FDOFXOHOH� DQWHULRDUH� SULQ� XUP�WRULL�parametrii: Qc –�GHELWXO�GH�F�OGXU��util al convectivului (kW) ; tf – temperatura gazelor de ardere la intrarea�vQ� HYL��0C) ; tFRú –�WHPSHUDWXUD�JD]HORU�GH�DUGHUH�OD�LHúLUHD�GLQ� HYL��OD�FRú��

te/ti – temperatura apei LHúLUH�LQWUDUH (0C). 6H�LPSXQH�YLWH]D�GH�FLUFXOD LH�D�JD]HORU�GH�DUGHUH�vQ�OLPLWHOH��w’ = 2 ÷ 4 m/s. 6HF LXQHD�GH�FLUFXOD LH�D�JD]HORU�GH�DUGHUH�YD�IL�

273

273

'

+⋅= gmg

circ

t

w

VBS (m2) (3.104)

)(2

0cosC

ttt

f

gm


ÌQ�O LPHD�SUHOLPLQDU��D�GUXPXOXL�FRQYHFWLY�YD�IL�

a

Sb circ='

6H�URWXQMHúWH�OD�vQWUHJ�úL�VH�UHFDOFXOHD]��YLWH]D��

273

273+

⋅

⋅= gmg t

ab

VBw (3.105)

Pentru temperatura medie a gazelor de ardere tgm se GHWHUPLQ�� GLQ� anexa 9, XUP�WRDUHOH�YDORUL�

- YkVFR]LWDWHD�FLQHPDWLF�� ν [m2/s] - FRQGXFWLELOLWDWHD�WHUPLF�� λ [W/mK] - QXP�UXO�3UDQGWO� Pr 'H�DVHPHQHD�VH�GHWHUPLQ��QXP�UXO�3UDQGWO�OD�WHPSHUDWXUD�SHUHWHOXL�3rp cu:

tp = tm +20 0C ; 2

eim

ttt

+= .

&RHILFLHQWXO� GH� VFKLPE� GH� F�OGXU�� SULQ� FRQYHF LH� VH� GHWHUPLQ�� XWLOL]kQd UHOD LLOH�SUH]HQWDWH�vQ�DQH[D�� pentru curgerea fluidelor transversal pe un fascicul de HYL�DúH]DW�vQ�OLQLH��´FRUidor”). În toate cazurile:

c

ocl

Nuλεα = . (3.111)

a h

d

b


CAZANE

72

&RHILFLHQWXO� GH� FRUHF LH� εo� LQH� FRQW� GH� H[LVWHQ D� WXUEXOL]DWRULORU� úL, pentru turbulizatori în zig – zag�DPSODVD L� vQ�FDQDO�UHFWDQJXODU, se poate determina utilizând UHOD LLOH:

2,0r

0 b

142,2=ε pentru Re < 2300 (3.112)

5

Re

b

3,3 2,0

26,0r

0 −=ε pentru Re > 2300 (3.113)

unde b

lbr = este pasul relativ, cu l – pas zig-zaguri.

Curgerea fluidelor transver-sal pe un rând de

HYL

2e

c

dl

⋅=

π

12,0

r

r2t

2l

pP

PNuNu3,0Nu

++= (3.106)

3l PrRe644,0Nu ⋅+= (3.107)

−⋅+

⋅⋅=

− 1PrRe443,21

PrRe037,0Nu

3

21,0

8,0

t (3.108)

νΨ= clw

Re

a41

π−=Ψ

610Re10 << 310Pr6,0 <<

*de – diametrul exterior al conductei *s1 – pasul dintre HYL� *a=s1/de *la gaze se înlocuieúWH��(Pr/Prp)^0,25 cu (Tmg/Tp)^0,12

Curgerea fluidelor transver-sal pe un fascicul GH� HYL�DúH]DUH�

„coridor”

2e

c

dl

⋅=

π

m

r

r1

pP

PNu

n

)1n(1Nu

ω−+= (3.109)

25,1

7,0a

b

3,0a

b

7,01

+

−

Ψ−=ω (3.110)

Nu1=Nu pentru un singur rând de HYL��FRQIRrm rel. (3.106)

νΨ= clw

Re

a41

π−=Ψ

pentru b≥1 m=0,25 pt. incãlzire fluid m=0,11 pt. U�FLUH�IOXLG�

610Re10 <<

*de – diametrul exterior al conductei *s1 – pasul transversal *s2 – pasul longitudinal * a = s1/de * b=s2/de * n –� QXP�UXO� GH�rânduri *la gaze se vQORFXLHúWH�(Pr/Prp)^0,25 cu (Tmg/Tp)^0,12

l

b

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

73

&RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH�HVWH�GHWHUPLQDW�GH�P�ULPLOH� - temperatura media a gazelor de ardere Tgm = tgm + 273 (0C) ; - SUHVLXQLOH�SDU LDOH�DOH�Jazelor triatomice OHRO pp

22, ;

- grosimea stratului radiant s = 0,9 leh; convper

conveh

S

Vl

4=

&RQVWDQWD�GH�UDGLD LH�D�JD]HORU�HVWH�

)(1000

38,01)(

6,18,022

22

2

ROOH

gm

ROOH

OH

g ppT

spp

pk +

−

+

+= (3.114)


sk

g

gea⋅−−= 1 (3.115)

&RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH�VH�FDOFXOHD]��FX�UHOD LD��

−

−

+⋅= −

gm

p

gm

p

gmg

p

r

T

T

T

T

Taa

1

1

2

110765,5

6,3

38α (W/m2K) (3.116)

XQGH� SHQWUX� FRHILFLHQWXO� GH� DEVRUE LH� DO� SHUHWHOXL� GH� R HO� DO� HYLL� se poate considera valoarea ap� ��úL�SHQWUX�WHPSHUDWXUD�DEVROXW��D�SHUHWHOXL� HYLL� 27320 ++= amp tT (K)

&RHILFLHQWXO�GH�WUDQVIHU�GH�F�OGXU��SH�SDUWHD�JD]HORU�GH�DUGHUH�YD�IL�

α1 = αc + αr

Coeficientul α2 (pe partea apei) este mult mai mare (de ordinul miilor de W/m2K) în coPSDUD LH�FX�α1 (de ordinul zecilor de W/m2K). ÌQ�DFHVWH�FRQGL LL�FRHILFLHQWXO�JOREDO�GH�WUDQVIHU�GH�F�OGXU��N�HVWH�GDW�GH�UHOD LD�(s-a neglijat α2 ):

1

1

1 αεα

⋅+=Ik (W/m2K) (3.117)

&RHILFLHQWXO� GH� PXUG�ULUH� ε pentru gaze de ardere provenite din combustibil gazos este dat în tabelul 3.9.


CAZANE

74

Tabelul 3.9. Viteza w (m/s) 3 6 9 12 15 18 ε⋅109 (m2K/W) 5,233 3,837 2,791 2,093 1,628 1,395

6H�SRDWH�XWLOL]D�úL�UHOD LD�DQDOLWLF��

6474,031021,11 −− ⋅⋅= wε (m2K/W) Pentru gaze de ardere provenind din combustibil lichid:

0163,0=ε (m2K/W) 'LIHUHQ D� PHGLD� GH� WHPSHUDWXU�� VH� GHWHUPLQ�� FRQIRUP� ILJXULL� �� úL� UHOD LHL�(3.118):

min

max

minmax

ln

)

t

t

tttm

∆∆

∆−∆=∆ (3.118)

Fig. 3.8.

6XSUDID D�GH�VFKLPE�GH�F�OGXU��D�Grumului convectiv va fi:

m

cc

tk

QS

∆= (3.119)

( )'

1'' ;

275,0 cc

e

c

c nsLdab

Sn ⋅=

⋅+⋅=

π

S SC

t

tma

tf

tc

∆tmax

∆tmin

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

75

Din calculul lungimii de focar se determinã numãrul de elemente ale focarului:

1

'

s

Ln

f

f = . Numãrul final de elemente al cazanului se ob LQH� vQ� XUPD� FDlculului de

echilibrare ce se realizeazã conform rela LHL�� 3.4. Calculul termic al cazanelor acvatubulare din elemente cu GRX� drumuri

convective

��'HVFULHUHD�FD]DQHORU��HOHPHQWH�FRPSRQHQWH��PRG�GH�IXQF LRQDUH� Sunt executate VXE�IRUP��GH�FDGUH�GUHSWXQJKLXODUH�GLQ� HYL�QHWHGH, sudate între ele pULQ� LQWHUPHGLXO� XQRU� SODWEDQGH� RE LQându-se cazane monobloc, cu focare tip FDPHU��FX�GRX��GUXPXUL�FRQYHFWLYH��ILJ��)LHFDUH�HOHPHQW�HVWH�OHJDW�GH�FROHFWRUXO�úL�GLVWULEXLWRUXO�FD]DQXOXL�SULQ�úWX XUL�

)LJ��&D]DQ�DFYDWXEXODU�GLQ�HOHPHQWH�WLS��FX�GRX��GUXPXUL�FRQYHFWLYH ��(OHPHQW�FXUHQW��(OHPHQW�vQFKLGHUH�ID ��(OHPHQW�vQFKLGHUH�VSDWH��$U]�WRU��9L]RU��

��3ODWEDQGH�GH�HWDQúDUH�vQWUH�HOHPHQWH��'LVWULEXLWRU��&ROHFWRU��7HDF��SHQWUX�WHUPRVWDWH� ��3URPRWRUL�GH�WXUEXOHQ ��5DFRUGXUL�LQWUDUH�LHúLUH�DSD�FDOG��vQF�O]LUH��5DFRUG�GH�HYDFXDUH�JD]H�GH�

DUGHUH�OD�FRú��,]ROD LH�WHUPLF��úL�FDUFDV��H[WHULRDU��(úDIRGDM�GH�VXV LQere.

7 14

6 8 9 10 11

13

3

11

12

1

2

4

5 F

C1

C2


CAZANE

76

6ROX LD�FRQVWUXFWLY��D�DFHVWXL�WLS�GH�FD]DQ�HVWH�DVHP�Q�WRDUH�FX�FHD�SUH]HQWDW��în capitolul 3.3. ”Calculul termic al cazanelor acvatubulare din elemente tip cu vQWRDUFHUHD�JD]HORU�GH�DUGHUH�vQ�IRFDU�úL�XQ�GUXP�FRQYHFWLY” cu deosebirea�F��IRFDUXO�estH�FX�VWU�SXQJHUH�vQ�SDUWHD�VXSHULRDU��VSDWH�XQGH�VH�UHDOL]HD]��úL�WUHFHUHD�vQ�SULPXO�GUXP�FRQYHFWLY��'XS�� FXP�VH�SRDWH�REVHUYD� vQ� ILJXUD��JD]HOH�GH�DUGHUH��GXS�� FH�parcurg primul drum convectiv (CI�� DX� SRVLELOLWDWHD� V�� vQWRDUF�� úL� V�� WUHDF�� vQ� DO�doilea drum convectiv (CII��SULQ�VSD LXO�O�VDW�OLEHU�vQWUH�HOHPHQtele�ID �. In continuare SDUFXUJ��GLQ�QRX�OXQJLPHD�FD]DQXOXL�úL�VXQW�HYDFXDWH�OD�FRú�

$FHVWH�FD]DQH�IXQF LRQHD]��FX�JD]H�QDWXUDOH�VDX�FX�FRPEXVWLELO�OLFKLG��GDU�SRW�

IXQF LRQD�úL�FX�OHPQH��EULFKHWH�VDX�F�UEXQH�VXSHULRU��ÌQ�DFHVW�FD]��vQ�ORFXO��DU]�WRUXOXL��VH�PRQWHD]��R�Xú��SHQWUX� vQF�UFDUHD�IRFDUXOXL�FX�FRPEXVWLELO�VROLG��'HDVXSUD� HYLORU�LQIHULRDUH�DOH�HOHPHQWHORU�VH�PRQWHD]��XQ�JU�WDU� IL[�VDX�� vQ�XQHOH�FD]XUL��FKLDU� HYLOH�innferioare ale cadreORU� UHSUH]LQW�� JU�WDUXO� SODQ� DO� FD]DQXOXL��/D�SDUWHD� LQIHULRDU�� VH�LQWURGXF�FXWLLOH�GH�FROHFWDUH�D�FHQXúLL��FHQXúDUXO�FD]DQXOXL��

&D]DQXO� HVWH� L]RODW� WHUPLF� FX� YDW�� PLQHUDO�� úL� SURWHMDW� OD� H[WHULRU� FX� WDEO��VXE LUH��6H�RE LQH�DVWIHO�XQ�FD]DQ�PRQREORF�SHQtru care, modificând dimensiunile de JDEDULW�DOH�HOHPHQWHORU��GLDPHWUXO� HYLORU�úL�QXP�UXO�GH�HOHPHQWH,�VH�SRW�RE LQH�GLYHUVH�YDULDQWH�GH�VDUFLQL�WHUPLFH��GXS��QHFHVLW� L�

'HúL� FRQVXPXO� GH� PDWHULDO� úL� GH� PDQRSHU�� SHQWUX� H[HFX LD� DFHVWRU� WLSXUL� GH�cazane este mare, se impune avantajul de a se putea introduce pe elemente, prin VSD LLOH�vQJXVWH�úL�GH�D�VH�PRQWD�GLUHFW�OD�ORFXO�GH�IXQF LRQDUH�

3.4.2. Tema de proiectare

Prin tema de proiectare se dau:

- Q –�VDUFLQD�WHUPLF��D�FD]DQXOXL��vQ�N:�� - te / ti –�WHPSHUDWXUD�DSHL�OD�LHúLUH��LQWUDUH�vQ�FD]DQ��0C sau 80/60 0C); - QDWXUD�úL�FRPSR]L LD�FRPEXVWLELOXOXL��OLFKLG�VDX�JD]RV��

$FHVWH� FD]DQH� IXQF LRQHD]�� GH� RELFHL� FX� VXSUDSUHVLXQH� vQ� IRFDU�� GHFL�

FRHILFLHQWXO�GH�H[FHV�GH�DHU�HVWH�DFHODúL�SHQWUX�IRFDU��SHQWUX�GUXPXULOH�FRQYHFWLYH�úL�OD�FRú�

15,105,1cos −===== αααααIII CCf .

&RQIRUP� LQGLFD LLORU� GLQ� FDSLWROXO� �� VH� HIHFWXHD]�� FDOFXOXO� DUGHULL�

FRPEXVWLELOXOXL�úL�VH�GHWHUPLQ��Vo, Vgo, Hi, OHp2

, 2ROp úL�VH�WUDVHD]��GLDJrama I – t

sau cp – t.

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

77

��&DOFXOXO�UDQGDPHQWXOXL�WHUPLF�úL�D�GHELWXOXL�GH�FRPEXVWLELO� PentUX� FD]XO� GH� IXQF LRQDUH� D� FD]DQXOXL� FX� FRPEXVWLELO� JD]RV� VDX� OLFKLG��SLHUGHUHD� VSHFLILF�� GH�F�OGXU�� SULQ�DUGHUH� LQFRPSOHW��GH�QDWXU��PHFDQLF�� úL�FHD�SULQ�evacuarea produselor solide ale arderii din cazan sunt nule (qmec=0; qcen=0). Pentru calculul randamentului pe cale indirectã�VH�FDOFXOHD]�� a. 3LHUGHUHD�VSHFLILF��GH�F�OGXU��SULQ�HQWDOSLD�JD]HORU�GH�DUGHUH�OD�FRú�(qFRú) 3HQWUX�FD]XO�GH�ID ��cazan de DS��FDOG�,�VH�DGPLWH�R�WHPSHUDWXU�� OD�FRú�FH�VH�SRDWH�GHWHUPLQD�FX�UHOD LD�GH�DSUR[LPDUH� C

ttt ei 0

cos )8060(2

÷++

≅ (3.120)

Din diagrama I –�W�VH�GHWHUPLQ��YDORDUHD�HQWDOSLHL�JD]HORU�GH�DUGHUH�OD�FRú�

IFRú = f (tFRú, α)

Entalpia aerului teoretic nHFHVDU�DUGHULL� VH�GHWHUPLQ�� OD� WHPSHUDWXUD�DPELDQW��ta=200C


cu cpa = 1,2971 kJ/ Km3

N 5H]XOW��YDORDUHD�SLHUGHULL�VSHFLILFH�GH�F�OGXU��SULQ�HQWDOSLD�JD]HORU�GH�DUGHUH�OD�FRú� )(

1coscos ao

i

IIH

q ⋅−= α (3.122)

b. 3LHUGHUHD�VSHFLILF��SULQ�DUGHUHD�LQFRPSOHW��GH�QDWXU��FKLPLF��(q inc) ÌQ� FDGUXO� FDOFXOHORU� GH� SURLHFWDUH�� GDWRULW�� SHUIRUPDQ HORU� GH� IXQF Lonare ale DU]�WRDUHORU�PRGHUQH�� VH�DGPLWH�R�SLHUGHUH�SULQ�DUGHUH� LQFRPSOHW��GH�QDWXU��FKLPLF� de ordinul:

qch = 0,001 ÷ 0,005 (3.123) c). 3LHUGHUHD�VSHFLILF��SULQ�SHUH Li exteriori ai cazanului (qext): ÌQ� FDGUXO� FDOFXOHORU� GH� SURLHFWDUH�� SHQWUX� FD]DQH� UHODWLY� PLFL�� vQ� IXQF LH� GH�JUDGXO�GRULW�GH�L]ROD LH�WHUPLF��D�FD]DQXOXL��VH�SRDWH�DOHJe o valoare: qext = 0,005 ÷ 0,015 (3.124) d. Randamentul cazanului 6H�FDOFXOHD]��FX�UHOD LD� ηηη 100;)(1 %cos =++−= extch qqq (3.125)


CAZANE

78

e. Consumul de combustibil Deoarece qmec = 0; B*= B;

iH

QB

⋅=

η (3.126)

3.4.4. BilDQ XO�GH�DQVDPEOX�DO�FD]DQXOXL� )OX[XO�GH�F�OGXU��XWLO�DO�FD]DQXOXL� Q. )OX[XO�GH�F�OGXU��DGXV�GH�FRPEXVWLELO� ic BHQ =

)OX[XO�GH�F�OGXU��DGXV�FX�DHUXO�GH�DUGHUH�úL�GH�LQILOWUDUH�� apaoa tcVBQ α=

)OX[XO�GH�F�OGXU��SLHUGXW�OD�FRú� coscos BIQ = )OX[XO�GH�F�OGXU��SLHUGXW�SULQ�

DUGHUH�LQFRPSOHW��GH�QDW��FKLPLF�� ichinc BHqQ =

)OX[XO�GH�F�OGXU��SLHUGXW�VSUH�H[WHULRU� iextext BHqQ = 5H]XOW��WDEHOXO�GH�ELODQ ��

Tabelul 3.10 Combustibil – pierderi Util

Qc

Qa

- QFRú - Qinc

- Qext

Q

∑ = 'QQ ∑ = "QQ

1RW��ÌQ�DFHVW�ELODQ ��–q2BHi) s-a scris sub forma: (-BIFRú�+ BαFRúVocpata); deci

IRUPD�H[SOLFLW�� (URDUHD�UHODWLY��YD�IL� %1100

'

"'<

−=

Q

QQε (3.127)

'DF��HURDUHD�HVWH�PDL�PDUH�HVWH�R�JUHúHDO��GH�FDOFXO� ��&DOFXOXO�WHPSHUDWXULORU�úL�HQWDOSLLORU�JD]HORU�GH�DUGHUH�SH�WUDVHX

(QWDOSLD�WHRUHWLF��GH�DUGHUH�VH�FDOFXOHD]��FX�UHOD LD�

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

79

apafchit tcVqHI 0)1( α+−= (3.128)

apoi se determin��WHPSHUDWXUD�WHRUHWLF��GH�DUGHUH�GLQ�GLDJUDPD�,-t: ),( ftt Ift α= .

6H�DOHJH�WHPSHUDWXUD�OD�FDS�WXO�IRFDUXOXL� tf = 700 ÷ 900 oC,

YDORULOH�DFHVWHD�ILLQG�QRUPDOH�SHQWUX�FD]DQH�FX�GRX��GUXPXUL�FRQYHFWLYH� Din diagrama I-W�VH�GHWHUPLQ��HQWDOSLD�JD]HORU�OD�FDS�WXO�IRFDUXOXL�If=f(tf,α). )OX[XO�GH�F�OGXU��SUHOXDW�SULQ�UDGLD LH�vQ�IRFDU�YD�IL� )()1( ftextR IIBqQ −−= (kW) (3.129)

)OX[XO�GH�F�OGXU��FDUH��VH�SUHLD�vQ�VLVWHPXO�FRQYHFWLY�vQ�DQVDPEOX�YD�IL� Rc QQQ −= (3.130) 6LVWHPXO�FRQYHFWLY�HVWH�vPS�U LW�vQ�GRX��GUXPXUL�GH�JD]H�GH�DUGHUH��DVWIHO�

III CCc QQQ += . (3.131)

Se admite:

cC QQI

)85,075,0( ÷=

DSRL�VH�GHWHUPLQ��HQWDOSLD�JD]HORU�GH�DUGHUH�OD�LHúLUHa din primul drum convectiv:

)1( ext

C

fCqB

QII I

I −−= (3.132)

Din diagrama I – t. VH� GHWHUPLQ�� WHPSHUWXUD� JD]HORU� GH� DUGHUH� OD� LHúLUH� GLQ�

drumul convectiv I (ICt )

(QWDOSLD�JD]HORU�GH�DUGHUH�OD�VIkUúLWXO�GUXPXOXL�FRQYHFWLY�,,� cos)1(

IqB

QII

ext

C

CCII

III≅

−−= (3.133)

úi din diagrama I-W�UH]XOW��WHPSHUDWXUD�OD�VIkUúLWXO�GUXPXOXL�FRQYHFWLY�,,� cos),( tIft

IIII CC ≅= α (3.134)

ÌQFKLGHUHD�ELODQ XOXL�LPSXQH� ICII ≅ IFRú��úL� tCII ≅ tFRú


CAZANE

80

úL�VH�DGPLW�HURULOH�UHODWLYH� 100

cos

cos

II

II

t

c

I −−

=ε �� (3.135)

úL�

100cos

cos

tt

tt

t

c

t −−

=ε �� (3.136)

(URUL�PDL�PDUL�LQGLF��R�JUHúHDO��GH�FDOFXO��ÌQ�ILQDO�VH�vQWRFPHúWH�WDEHOXO�� Tabelul 3.11.

Temperatura gazelor 6XSUDID D )OX[�GH�F�OGXU� intrare LHúLUH

Focar Convectiv I

ICQ

Convectiv IIIICQ

QR

QcI

QcII

tt

tf

tCI

tf

tCI

tFRú ��%LODQ XO�JUDILF�DO�FD]DQXOXL� 'HELWHOH�GH�F�OGXU��GLQ�WDEHOHOH��úL��VH�WUDQVSXQ�JUDILF��OD�VFDU��GXS��modelul general prezentat în capitolul 2 fig. 2.3. (cu B*=B; QSI=QPA=0; Qec=0; qmec ��úL��qcen=0). 3.4.7. Calculul termic al focarului

)RFDUXO�GH�WLS�FDPHU��DUH�XUP�WRDUHOH�GLPHQVLXQL�FRQIRUP�ILJ�� $FHVW�FDOFXO�DUH�FD�VFRS�GHWHUPLQDUHD�VXSUDIH HL�GH�UDGLD LH�6R�FDSDELO��V��SUHLD�

debitul de c�OGXU�� UDGLDQW� 4R. Deoarece în calcul intervine gradul de ecranare

=Ψ

per

R

S

S úL�OXQJLPHD�GH�UDGLD LH�HVWH�QHFHVDU�XQ�FDOFXO�LQWHUDWLY��,QL LDO�VH�DGPLWH�R�YDORDUH�RULHQWDWLY��6′R�FDUH�YD�IL�FRPSDUDW��FX�FHD�ILQDO��SR.

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

81

Fig. 3.10. Dimensiunile focarului 1. FDGUX�GLQ� HDY��SODWEDQG��GH�OHJ�WXU��QHUYXU��DU]�WRU��Xú�

S′R�SRDWH�IL�DSUHFLDW��SULQ�GRX��PHWRGH� a) 6H�DGPLWH�XQ�IOX[�XQLWDU�UDGLDQW��vQF�UFDUH�WHUPLF��VSHFLILF��

qR=30÷50 kW/m2 astfHO�F��UH]ult��R�YORDUH�SUHOLPLQDU��D�VXSUDIH HL�GH�VFKLPE�GH�F�OGXU��D�IRFarului:

R

RR

q

QS =' (m2) (3.137)

E��6H�GHWHUPLQ��VXSUDID D�SUHOLPLQDU��GH�UDGLD LH�vQ�IRFDU�FX�UHOD LD��

−

=

44

'

100100765,5 pf

RR

TT

QS

ε (m2) (3.138)

cu ε =0,65 pentru combustibil gazos ε =0,75 pentru combustibil lichid Tf = tf + 273 (oK)

Tp=tma+20+273 (oK) 2

eima

ttt

+=

XQGH� SHQWUX� WHPSHUDWXUD� SHUHWHOXL� HYLL� V-D� DGPLV� R� WHPSHUDWXU�� FX� �� 0C mai mare decât temperatura fluidului interior. Pentru alegerea dimensiunilor focarului se admit�XUP�WRDUHOH�YDORUL: a = 400÷800 mm úL

a

h = 1,2 ÷ 1,5.

1

4

2

3

1

a h

d s1

L


CAZANE

82

Dimensiunile laturilor se rotunjesc la valori întregi de zecimi de metru. 6XSUDID D�SHUH LORU�IRFDUXOXL�HVWH� ahhaLS per 2)(2 ++= (m2) (3.140)

ahhaLSR ++= )(2' (m2)

Grosimea stratului radiant de gaze este:

per

f

S

Vs 6,3= (m) (3.141)

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�JD]HORU�GH�DUGHUH�GLQ�IRFDU� )(

100038,01

)(

6,18,022

22

2

ROOH

f

ROOH

OH

g ppT

spp

pk +

−

+

+= (3.142)


sk

g

gea−−= 1 (3.143)

&DUDFWHULVWLFD�UDGLDQW��D�IO�F�ULL�VH�FDOFXOHD]��FX�UHOD LD�GH�DSUR[LPDUH� 5,0

10006,1 −= f

fl

Tk (3.144)


sk

flflea

⋅−−= 1 (3.145)

3RQGHUHD�DEVRUE LHL�IO�F�ULL�FX�FHD�D�PHGLXOXL�UDGLDQW�GH�JD]H�GH�DUGHUH�VH�IDFH,

GXS��FULWHULL�H[SHULPHQWDOH��FRQVLGHUkQG�R�SURSRU LH�β��GLQ�YROXPXO�IRFDUXOXL��RFXSDW��GH�SDUWHD�OXPLQRDV��D�IO�F�ULL��β - coeficient de luminozitate).

&RHILFLHQWXO�GH�DEVRUE LH�DO�IO�F�ULL�úL�JD]HORU�GH�DUGHUH�YD�IL� gfl aaa ⋅−+⋅= )1( ββ (3.146)

cu β = 0,2÷0,4 SHQWUX�IODF�U��GH�FRPEXVWLELO�JD]RV� β = 0,6 SHQWUX�IODF�U��SURGXV��GH�FRPEXVWLELO�OLFKLG� Gradul de ecranare al focarului este:

per

R

S

S '

=Ψ (3.147)

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

83

úL�coeficientul de PXUG�ULUH D�VXSUDIH HORU� ξ =0,7 – 0,9 combustibil gazos ξ =0,6 – 0,7 combustibil lichid

&X�DFHVWH�YDORUL�VH�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IRFDUXOXL� ξΨ−+

⋅=

)1(

82,0

aa

aa f (3.148)

2�DOW��FDUDFWHULVWLF��D�IRFDUXOXL��IDFWRUXO�GH�SR]L LH�D�IO�F�ULL�vQ�IRFDU�

f

MMH

hbaM

*−= (3.149)

cu: aM = 0,52 bM = 0,3 pentru combustibil lichid sau gazos.

h –�vQ�O LPHD�GH�SODVDUH�D�DU]�WRDrelor 2

* fHh =

Hf –�vQ�O LPHD�WRWDO��D�IRFDUXOXL�

&X�DFHVWH�GDWH�VH�GHWHUPLQ��VXSUDID D�GH�UDGLD LH�D�IRFDUXOXL� 3

238

11

10765,5 MT

T

TTaM

QS

f

t

tff

RR

−

⋅= − ξ (m2) (3.150)

$FHDVW��VXSUDID ��YD�IL�GLIHULW��GH� '

RS �GHWHUPLQDW��vQ�FDOFXOXO�DSUR[LPDWLY��'DF��GLIHUHQ D� HVWH�PDL�PDUH�GH��VH� UHLD� FDOFXOXO�prin atribuirea valorii calculate SR VXSUDIH HL�GH�SUHGLPHQVLRQDUH�6¶R.

6H�DOHJH�XQ�GLDPHWUX�GLQ� HYLOH�RELúQXLWH��GH�×d): φ 51×3; φ 57×3; φ 60×3,5;

φ 76×��úL�XQ�SDV�relativ s1 / de = 1,25 ÷ 1,5. 5H]XOW��QXP�UXO�GH�HOHPHQWH�vQ�IRFDU:

+= 1

1s

LINTN f (3.151)

Hf

h


CAZANE

84

3.4.8. Calculul termic al drumului convectiv I

Din calculele anterioare se cunosc: QCI, tf, tCI.

6H� S�VWUHD]�� DFHODúL� GLDPHWUX� DO� HYLORU� GH� OD� IRFDU� úL� DFHODúL� SDV� s1. Este de DVHPHQHD�GHWHUPLQDW��úL�O� LPHD�VHF LXQLL�GH�WUHFHUH�D�JD]HORU�SULQ�VLVWHPXO�FRQYHFWLY�,��6H�VWDELOHúWH�vQ�O LPHD�VLVWHPXOXL�FRQYHFWLY�,��bI��LPSXQkQG�R�YLWH]��GH�FLUFXOD LH�vQ�intervalul [ ]smwI 42' ÷= .

aw

tBV

bI

mg

I ⋅

+

='

273

273

, cu 2

CIf

m

ttt

+= (3.152)

6H�URWXQMHúWH�OD�YDORUL�vQWUHJL�úL�VH�UHFDOFXOHD]��YLWH]D wI. Pentru temperatura medie a gazelor de ardere tm� VH� GHWHUPLQ�� GLQ� anexa 9 XUP�WRDUHOH�YDORUL�

- vâscozitatea cinematiF�� ν (m2/s) - FRQGXFWLELOLWDWHD�WHUPLF�� λ (W/mK) - criteriul Prandtl Pr

&XUJHUHD�JD]HORU�GH�DUGHUH�VH�IDFH�WUDQVYHUVDO�SH�XQ�úLU�GH� HYL�DúH]DWH�vQ�linie. ÌQ�DFHVW�FD]�OXQJLPHD�FDUDFWHULVWLF��HVWH:

2

ec

dl

⋅=

π. (3.153)

Se calcuOHD]�� PDL� vQWkL� FULWHULXO� 1XVVHOW� SHQWUX� FXUJHUHD� JD]HORU� GH� DUGHUH�WUDQVYHUVDO�SH�XQ�UkQG�GH� HYL�

12,0

221 3,0

++=

p

mtl

T

TNuNuNu (3.154)

cu νΨ

= cI lWRe �úL�

141

s

deπ−=Ψ ;

3 PrRe644,0 ⋅+=lNu pentru 610Re10 << (3.155)

−⋅+

⋅⋅=

− 1PrRe443,21

PrRe037,0

3

21,0

8,0

tNu 310Pr6,0 << (3.156)

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

85

Cu 273202

+++

= iep

ttT (K) (3.157)

Curgerea gazelor de ardere transversal pe un fascicul de n� UkQGXUL�GH� HYL� �VH�admite N=Nf).

12,0

1

)1(1

−+=

p

m

f

f

T

TNu

N

NNu

ω (3.158)

cu 2

1

15,1

7,0

3,07,0

1

−

−

Ψ−=

s

b

s

b

I

I

ω (3.159)

În toate cazurile: c

cl

Nu λα ⋅= (3.160)

&RHILFLHQWXO� GH� VFKLPE�GH�F�OGXU�� SULQ� UDGLD LH este determinat de parametrii:

22, ROOH pp , gmT �úL�JURVLPHD�VWUDWXOXL�UDGLDQW�s:

e

e

I

e

dd

b

d

ss

−

+= 1,487,1 1

(m) (3.161)

&RQVWDQWD�GH�UDGLD LH�D�JD]HORU�HVWH� ( ) ( )

22

22

2

100038,01

6,18,0ROOH

gm

ROOH

OH

gpp

T

spp

pk +

−

⋅+

+= (3.162)


sk

g

gea⋅−−= 1


−

−

+⋅= −

gm

p

gm

p

gmg

p

r

T

T

T

T

Taa

1

1

2

110765,5

6,3

38α (W/m2K) (3.163)

XQGH�SHQWUX� FRHILFLHQWXO� GH� DEVRUE LH� DO� SHUHWHOXL�GH�R HO�se ia valoarea ap �� úL�SHQWUX�WHPSHUDWXUD�DEVROXW��D�SHUHWHOXL� HYLL� 27320 ++= map tT (0K) (3.164)


CAZANE

86

t

∆tmax

S SC

tma

tf

tcI ∆tmin

Coeficientul de schimb de�F�OGXU��SH�SDUWHD�JD]HORU�GH�DUGHUH�YD�IL��

αg = αc+αr.

Coeficientul global de VFKLPE�GH�F�OGXU�:

g

g

Ikαε

α

⋅+=

1 (3.165)

cu valorile pentru coeficientul de PXUG�ULUH ε din tabelul 3. 'LIHUHQ D� PHGLH� D�WHPSHUDWXULORU� VH� FDOFXOHD]� cu UHOD LD�

maCI

maf

maCImaf

mI

tt

tt

ttttt

−

−−−−

=∆ln

)()(

ÌQ�ILQDO�VXSUDID D�GH�VFKLPE�GH�F�OGXU��D�GUXPXOXL�FRQYHFWLY�,�VH�GHWHUPLQ��FX�

UHOD LD��

mII

cIcI

tk

QS

∆⋅= (3.166)

Pentru un singur element,�VXSUDID D�GH�VFKLPE�GH�F�OGXU��YD�IL� )](2)(2[1 eIeele dbdadS −+−⋅= π (m2) (3.167) 6H�GHWHUPLQ��QXP�UXO�GH�HOHPHQWH�vQ�FRQYHFWLY�

el

CI

CIS

SN

1

= (3.168)

'DF��QX�VH�YHULILF��NCI ≅ Nf�VH�PRGLILF��GLPHQVLXQLOH�VLVWHPXOXL�FRQYHFWLY�úL�se reia calculul. 3.4.9. Calculul termic al drumului convectiv II

Se cunosc: QCII, tCI, tcos. &DOFXOXO�HVWH�LGHQWLF�FX�FHO�SUH]HQWDW�SHQWUX�GUXPXO�FRQYHFWLY�,�FX�vQ�O LPHD bII, 2

costtt CI

m

+= ��úL�UHOD LLOH�FULWHULDOH�VSHFLILFH�SHQWUX�FDOFXOXO�OXL�αc.

��&$/&8/8/�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

87

De obicei tgm < 400 0&� úL� vQ� DFHVW� FD]�αr → 0 ceea ce înVHDPQ�� F�� VH� SRDWH�neglija.

Deci: c

cIIk

αεα

⋅+=

1�úL�

ma

maCI

mamaCImII

tt

tt

ttttt

−−

−−−=∆

cos

cos

ln

)()( (3.169)

6H�GHWHUPLQ��

mIIII

CIICII

tk

QS

∆= . (3.170)

Pentru un singur element:

)2(2*1 eIIeel dbadS −+= π . (3.171)

1XP�UXO�de elemente în convectiv II va fi:

*1el

CII

CIIS

SN = (3.172)

De obicei NCI ≠ NCII ≠ Nf úL� VH� SURFHGHD]�� OD� R� UHGLVWULEXLUH� D� VXSUDIH HORU�convective:

*11

*11

elel

elCIIelCI

CSS

SNSNN

++

= (3.173)

D��'DF��Nc ≅ Nf ± 1�FD]DQXO�YD�DYHD�QXP�UXO�GH�HOemente cel mai mare, dintre NC�úL�1f. E�� 'DF�� Nc ≠ Nf� VH� FDOFXOHD]�� VXSUDID D� GH� UDGLD LH� SHQWUX� XQ� HOHPHQW� DO�focarului.

t

S SC

tma

tcI

tcII ∆tmin


CAZANE

88

2))(( 11 ⋅++= hasdS f

el (3.174) 6H�FDOFXOHD]��XQ�QXP�U�GH�HOHPHQWH�FRPXQ�SHQWUX�R�PHGLH�SRQGHUDW�:

f

elelel

f

elfelCIIelCI

SSS

SNSNSNN

1*11

1*11

++

++= (3.175)

Se poate relua calculul de verificare al cazanului cu N elemente, fiind cunoscute suprafe HOH�GH�VFKLPE�GH�F�OGXU�� 6H�GHWHUPLQ��tf, Q’R, tCI, Q’CI�úL�Q’CII. 6H�YHULILF��GDF��Q’R + Q’CI + Q’CII = Q sau tCII=tcos initial.

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

89

3.5. Calculul termic al cazanelor acvatubulare�FX�EDWHULH�GH� HYL�QHUYXUDWH�úL�DU]�WRU�DWPRVIHULF�SHQWUX�FRPEXVWLELO�JD]RV�– „cazan mural” 3.5.��'HVFULHUHD�FD]DQHORU��HOHPHQWH�FRPSRQHQWH��PRG�GH�IXQF LRQDUH�

Fig. 3.11. Schema unui cazan DFYDWXEXODU�FX�EDWHULH�GH� HYL�QHUYXUDWH�úL�DU]�WRU� atmosferic pentru combustibil gazos – „cazan mural”

&D]DQHOH� VXQW� GHVWLQDWH� SURGXFHULL� GH� DS�� FDOG�� We / ti = 90 / 70 0C pentru

vQF�O]LUHD� XQRU� VSD LL�PLFL� ��–� �� N:�� úL� VH�mai numesc „cazane de apartament”. &D]DQXO� VH� LQVWDOHD]�� vQ� LQWHULRUXO� DSDUWDPHQWXOXL�� GH� RELFHL� vQ� EXF�W�ULH�� IL[DW� SH�SHUHWH�SULQ�LQWHUPHGLXO�XQHL�UDPH��8QHRUL��vQ�DFHLDúL�FDUFDV��FX�FD]DQXO�VH�DPSODVHD]��SRPSD�GH�FLUFXOD LH�D�DJHQWXOXL�WHUPLF��YDVXO�GH�H[SDQVLXQH�vQFKLV�úL�XQ�VFKLPE�WRU�GH�F�OGXU�� FX�SO�FL� SHQWUX�SURGXFHUHD� DSHL� FDOGH�GH� FRQVXP�� ,Q� DFHVW� FD]� DQVDPEOXO� VH�FXQRDúWH�VXE�GHQXPLUHD�GH�FHQWUDO��GH�DSDUWDPHQW�

A

d D

'HWDOLX�� HDY��QHUYXUDW�

a

1

2

3

4

PRINCIPALELE ELEMENTE COMPONENTE

1. HYL�QHUYXUDWH� 2. focar; 3. DU]�WRDUH�DXWRDVSLUDQWH� 4. LQWUDUH�LHúLUH�S��FDOG��vQF�O]LUH� 5. SLHV��GH�HYDFXUH�D�JD]HORU�GH�DUGHUH��

cu rupere de presiune.

5

b


CAZANE

90

3HQWUX� RE LQHUHD� XQHL� VROX LL� LHIWLQH� VH� DGRSW�� VLVWHPXO� GH� DUGHUH� FX� ´DU]�WRU�atmosIHULF´� �� 6XE� DFHDVW�� GHQXPLUH� VH� vQ HOHJH� DU]�WRUXO� GH� JD]� QDWXUDO� FX� DHU�DXWRDVSLUDW� SULQ� HMHF LH��'HRDUFHFH� SULQ� HMHF LH� QX� VH� SRDWH� DVSLUD�PDL�PXOW� GH��RUL�volumul de gaz combustibil, restul aerului de ardere se introduce ca aer secundar aspirat prin depresiune în camera de ardere din mediul ambiant. Pentru un exces de DHU�X]XDO�GH��.� ��UH]XO��F��WUHEXLH�DVSLUDW�FD�DHU�VHFXQGDU�XQ�YROXP�GH�FFD��RUL�volumul de gaz combustibil. $FHVW� VLVWHP� GH� IXQF LRQDUH� LPSXQH� H[LVWHQ D� XQHL� GHSUHVLXQL� VXILFLHQte în IRFDU�SHQWUX�R�DEVRE LH�GH�DHU��'HSUHVLXQHD�VH�FUHLD]��SULQ�autotirajul drumului de

gaze�DO�FD]DQXOXL��ÌQ�ILJXUD��VH�SUH]LQW��VFKHPD�IXQF LRQDO��

fig. 3.12 Componentele autotirajului drumului de gaze al cazanului DepUHVLXQHD�HIHFWLY��OD�ED]D�FD]DQXOXL�UH]XOW��GLQ�UHOD LD�

( ) ( ) ( )eigeoegcocgfofnet ppphghghgH ξξλ ∆∆∆ρρρρρρ −−−−⋅⋅+−⋅⋅+−⋅⋅=

XQGH�SLHUGHULOH�GH�VDUFLQ��ûS sunt: ûp� –�SLHUGHUH�GH�VDUFLQ��vQ�IDVFLFROXO�GH� HYL�QHUYXUDWH�DOH�FRQYHFWLYXOXL� ûp�L – SLHUGHUH�GH�VDUFLQ��ORFDOH�OD�LQWUDUHD�DHUXOXi;

ûp�H –�SLHUGHUH�GH�VDUFLQ��ORFDOH�OD�HYDFXDUHD�JD]HORU� 'HSUHVLXQHD�HIHFWLY�� OD�ED]D�FD]DQXOXL� WUHEXLH�V�� ILH�GH�FFD��÷��3D�úL�V��VH�PHQ LQ�� SH� FkW� SRVLELO� FRQVWDQW�� SHQWUX� D� QX� IL� IOXFWXD LL� PDUL� GH� H[FHV� GH� DHU� vQ�WLPSXO�IXQF LRQ�ULL��$FHVWD�HVWH�úL�PRWLYXO�SHQWUX�FDUH�OD�LHúLUHD�gazelor de ardere din

hf��vQ�O LPH�IRFDU temperatura tf��GHQVLWDWH�JD]H�!gf

hc în�O LPH�convectiv temperatura tc��GHQVLWDWH�JD]H�!gc

he în�O LPH�tronson de evacuare temperatura te �GHQVLWDWH�JD]H�!ge

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

91

FD]DQ� VH� IDFH�R� UXSHUH�GH�SUHVLXQH�SHQWUX� FD� WLUDMXO� FRúXOXL� �YDULDELO� FX� WHPSHUDWXUD�H[WHULRDU��V��QX�LQIOXHQ H]H�GHSUHVLXQHD�GLQ�FD]DQ� $U]�WRUXO�HVWH�IRUPDW�GLQWU-XQ�JUXS�GH�HOHPHQWH�GH�DU]�WRU�DWPRVIHULF��DVIHO�F��Y�]XW��GH�VXV��IODF�UD�DSDUH�FD�XQ�FRYRU�GH�PLFL�IO�F�UL�LQGLYLGXDOH�FDUH�VH�XQHVF�vQWU-o ]RQ��GH�DUGHUH�FRPXQ��FX�VXSUDID D�HJDO��SUDFWLF�FX�VHF LXQHD�FDPHUHL�GH�DUGHUH� Pentru a rezista temperaturilor înalte din camera de ardere, aceasta este F�SWXúLW��LQWHULRU�FX�SO�FL�GH�ILEU��FHUDPLF��UH]LVWHQW��OD�WHPSHUDWXUL�vQDOWH��0C). ÌQ� FRQWLQXDUHD� FDPHUHL� GH� DUGHUH� SH� YHUWLFDO�� VH� J�VHúWH� IDVFLFROXO� GH� HYL�nervurate care are rolul de sistem convectiv al cazanului. În acest convectiv, gazele de DUGHUH� FHGHD]�� DSHL� F�OGXUD� vQ� LQWHUYDOXO� GH� WHPSHUDWXUL� GH� OD� WHPSHUDWXUD� FDS�WXOXL�camerei de ardere tf la temperatura de la evacuare te� �� HYLOH� QHUYXUDWH� FDUH�DOF�WXLHVF� VLVWHPXO� FRQYHFWLY� VXQW� FRQIHF LRQDWH� GH� RELFHL� GLQ� FXSUX� FX� nervuri de WDEO��GH�DOXPLQLX��ÌQ�XQHOH�VROX LL�ILHFDUH� HDY��DUH�QHUYXUL�FLUFXODUH��vQ�DOWH�VROX LL�FkWH�GRX�� HYL� DX� QHUYXUL� GUHSWXQJKLXODUH� FRPXQH�� 6ROX LD� WHKQLF�� GH� QHUYXUDUH� QX�LQIOXHQ HD]��PXOW�FDUDFWHULVWLFLOH�GH�IXQF LRQDUH��GH�DFHLD�vQ�FDOFXOH�VH�LD�ILHFDUH� DY��FX�QHUYXUD�FLUFXODU��FDUH-L�UHYLQH�GLQ�SXQFWXO�GH�YHGHUH�DO�WUDQVIHUXOXL�GH�F�OGXU��

ILJ��'LPHQVLXQL� HDY��DULSDW��

3ULQFLSDOHOH�GLPHQVLXQL�JHRPHWULFH�DSDU�SH�ILJXU�� • GLDPHWUXO�H[WHULRU�DO� HYLL��G • diametrul exterior al nervurii D • vQ�O LPHD�QHUYXULL��K� ��'-d)/2 • grosimea nervurii g • pasul de nervurare s

d

D

h

s g


CAZANE

92

*D]HOH� VXQW� HYDFXDWH� OD� FRú� SULQWU-un dispozitiv de rupere de presiune. Acest GLVSR]LWLY�FRQVLVW��vQWU-R�KRW��vQ�FDUH�JD]HOH�GH�DUGHUH�LHV�OLEHU�GLQ�úWX XO�GH�HYDFXDUH�DO� FD]DQXOXL�� 'DWRULW�� FRPXQLF�ULL� FX� DWPRVIHUD� D� FDS�WXOXL� OLEHU� GLQ� úWX XO� GH�HYDFXDUH�� DLFL� VH� LQVWDOHD]�� SUHVLXQHD� VWDWLF�� DPELDQW�� úL� WLUDMXO� FRúXOXL� QX� PDL� DUH�nici-R�LQIOXHQ ��DVXSUD�UHJLPXOXL�GH�SUHVLXQL�GLQ�FD]DQ� Apa cald�� SURGXV�� GH� FD]DQ� LQWU�� GH� OD� UHWXUXO� LQVWDOD LHL� GH� vQF�O]LUH�� OD�FDS�WXO�LQIHULRU�DO�EDWHULHL�QHUYXUDWH�úL�SH�P�VXU��FH�SDUFXUJH� HYLOH�VH�vQF�O]HúWH��$SD�FDOG��HVWH�FROHFWDW��OD�SDUWHD�VXSHULRDU��D�FD]DQXOXL�úL�WULPLV��OD�FRQVXPDWRUL�� Cazanul este i]RODW� WHUPLF� FX� YDW�� PLQHUDO�� úL� SURWHMDW� OD� H[WHULRU� FX� WDEO��VXE LUH��6H�RE LQH�DVWIHO�XQ�FD]DQ�PRQREORF��FX�GLPHQVLXQL�UHGXVH�vQ�UDSRUW�FX�VDUFLQD�WHUPLF��SURGXV�� 3.5.2. Tema de proiectare

Prin tema de proiectare se dau : - Q – sarcina termiF��D�FD]DQXOXL��vQ�N:�� - te / ti –�WHPSHUDWXUD�DSHL�OD�LHúLUH�úL�LQWUDUH�vQ�FD]DQ��0C sau 80/60 0C); - QDWXUD�úL�FRPSR]L LD�FRPEXVWLELOXOXL��JD]�QDWXUDO�VDX�G.P.L.) .

Aceste cazane, cu depresiune în focar, au coeficientul de exces de aer relativ marH� GDWRULW�� VLVWHPXOXL� DXWRDVSLUDQW� FDUH� QX� DVLJXU�� R� EXQ�� RPRJHQHL]DUH� D�combustibilului cu aerul:

α = 1,6 ÷ 1,8.

&RQIRUP� LQGLFD LLORU� GLQ� FDSLWROXO� �� VH� HIHFWXHD]�� FDOFXOXO� DUGHULL�FRPEXVWLELOXOXL�úL�VH�GHWHUPLQ��VO, Vgo, Hi, OHp

2,

2ROp ��VH�WUDVHD]��GLDJUDPD�,�– t

sau cp – t . 3.5.��&DOFXOXO�UDQGDPHQWXOXL�WHUPLF�DO�FD]DQXOXL�úL�D�GHELWXOXL�GH�FRPEXVWLELO� $FHVWH�FD]DQH�IXQF LRQHD]�� întotdeauna cu combustibil gazos (gaz natural sau G.P.L.) deci pierderile specifice mecanice (qmec�� úL� FHOH� SULQ� HYDFXDUHD� SURGXVHORU�solide din cazan (qcen) sunt nule. De asemenea B* = B . 6H�FDOFXOHD]��SLHUGHULOH�VSHFLILFH�GH�F�OGXU�� a). 3ULQ�HYDFXDUHD�JD]HORU�GH�DUGHUH�SH�FRú��TFRú) :

)(1

0coscos a

i

IIH

q α−= (3.176)

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

93

6H�DGPLWH��LPSXQH��R�WHPSHUDWXU��DSUR[LPDWLY��D�JD]HORU�GH�DUGHUH�OD�FRú�� C

ttt ei 0

cos )8060(2

÷++

= (3.177)

úL�GLQ�GLDJUDPD�,�–�W�VH�GHWHUPLQ��IFRú . Pentru temperatura aerului (ta ≅ 20 0&�� VH� FDOFXOHD]�� HQWDOSLD� DHUXOXL� WHRUHWLF�necesar arderii :


cu cpa = 1,297 kJ/ Km3

N �F�OGXUD�VSHFLILF��D�DHUXOXL�OD��0C . b). PULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��FKLPLF��(qch) : 3HQWUX�DU]�WRDUH�DXWRDVSLUDQWH�FX�RPRJHQHL]DUH�GH�FDOLWDWH�medie:

qch = 0,005. c). 3ULQ�SHUH Li exteriori ai cazanului (qext) : Pentru cazane mici, foarte compacte, cu putere sub 80 kW, bine izolate, în faza de proiectare se poate adopta :

qext = 0,005 ÷ 0,008. 'LQ�SXQFW�GH�YHGHUH�HQHUJHWLF��F�OGXUD�SLHUGXW��OD�H[WHriorul cazanului este tot R� F�OGXU�� XWLO�� GHRDUHFH� FD]DQXO� IXQF LQHD]�� vQ� LQWHULRUXO� DSDUWDPHQWXOXL� SH� FDUH-l vQF�O]HúWH�� 'LQ� DFHVWH� FRQVLGHUHQWH� Text = 0� �� 7RWXúL�� SHQWUX� LSRWH]D� IXQF LRQ�UL�cazanului într-R� FDPHU�� FDUH� QX� QHFHVLW�� vQF�O]LUH�� VH� SRDWH� DFFHSWD� úL� LSRWH]D��qext = 0,5 – 0,8 %. Randamentul cazanului�VH�FDOFXOHD]��FX�UHOD LD�� )(1 cos extch qqq ++−=η �úL� ηη ⋅=100% (%) (3.179)

Debitul de combustibil va fi :

iH

QB

⋅=

η ( s/m3N ) (3.180)

3.5.��%LODQ XO�GH�DQVDPEOX�DO�FD]DQXOXL )OX[XO�GH�F�OGXU��XWLO�DO�FD]DQXOXL�HVWH�� Q ; )OX[XO�GH�F�OGXU��DGXV�GH�FRPEXVWLELO�� Qcomb = B ⋅ Hi ; )X[XO�GH�F�OGXU��DGXV�GH�DHUXO�GH�DUGHUH�� Qa = B ⋅ α ⋅Vo⋅ cpa ⋅ ta ;

)X[XO�GH�F�OGXU��SLHUGXW�OD�FRú�� QFRú = B ⋅ IFRú ;


CAZANE

94

)X[XO�GH�F�OGXU��SLHUGXW�SULQ�DUGHUH�LQFRPSOHW�� Qinc = qch ⋅ B ⋅ Hi .

5H]XOW��WDEHOXO�GH�ELODQ ��


Fluxuri utile

Qcomb

Qa

- QFRú - Qinc

- Qext

Q

∑ = 'QQ ''∑ = QQ

(URDUHD�UHODWLY�� %1100

'

"'<⋅

−=

Q

QQε (3.181)

'LQ� WDEHOXO� �� VH� SRDWH� VFULH� VXE� IRUP�� H[SOLFLW�� SLHUGHUHD� GH� F�OGXU�� OD�evacuare a gazelor:

- Qev = - qFRúBHi = - BIFRú�+ BαVocpata = - QFRú + Qa . (3.182)

3.5.5. Calculul tHPSHUDWXULORU�úL�HQWDOSLLORU�JD]HORU�GH�DUGHUH�SH�WUDVHX� (QWDOSLD�WHRUHWLF��D�JD]HORU�GH�DUGHUH�VH�FDOFXOHD]��FX�UHOD LD�� apachit tcVqHI 0)1( α+−= (3.183)

Din digrama I –�W�VH�GHWHUPLQ��WHPSHUDWXUD�WHRUHWLF��GH�DUGHUH��

),( αtt Ift = . 6H�LPSXQH��DOHJH��WHPSHUDWXUD�OD�LHúLUHD�JD]HORU�GH�DUGHUH�GLQ�IRFDU��

tf = 900 ÷ 1100 0C . Aceste valorile ULGLFDWH� GH� WHPSHUDWXUD� OD� VIkUúLWXO� IRFDUXOXL� sunt specifice

FD]DQHORU�FX�IRFDUH�IRDUWH�SX LQ�U�FLWH��/D�DFHVWH�FD]DQH�VXSUDID D�GH�UDGLD LH în focar HVWH� VXSUDID D� VHF LXQLL� VXSHULRDUH� D� FDPHUHL� GH� DUGHUH� XQGH�� SDUWHD� LQIHULRDU�� D�IDVFLFROXOXL�FRQYHFWLY�SULPHúWH�F�OGXU��úL�SULQ�UDGLD LH��

Din diagrama I –�W��VH�GHWHUPLQ��HQWDOSLD�JD]HORU�GH�DUGHUH�OD�LHúLUHD�GLQ�IRFDU��

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

95

),( αff tfI = (3.184)


)()1( ftextR IIBqQ −−= (kW) (3.185)

)OX[XO�GH�F�OGXU��SUHOXDW�GH�VLVWHPXO��FRQYHFWLY�YD�IL��

,Rc QQQ −= (3.186)

Entalpia gazelor de ardere la sfâUúLWXO�GUXPXOXL�FRQYHFWLY�HVWH��

Bq

QII

ext

c

fc )1( −−= (3.187)

úL�GLQ�GLDJUDPD�,�–�W�UH]XOW��WHPSHUDWXUD��

),( αcc Ift = (3.188)

ÌQFKLGHUHD�ELODQ XOXL�LPSXQH��Ic ≅ IFRú úL tc ≅ tFRú��úL�VH�DGPLW�HURULOH�UHODWLYH��

100cos

cos

II

II

t

c

I −−

=ε maxim 0,5%

úL

100cos

cos

tt

tt

t

c

t −−

=ε maxim 0,5% (3.189)

3.5.��%LODQ XO�JUDILF�DO�FD]DQXOXL�

'HELWHOH�GH�F�OGXU��Qcomb, QR, Qc, Qa� úL� IOX[XULOH�SLHUGXWH�QFRú, Qinc, Qext se WUDQVSXQ�JUDILF�DO�VFDU��FD�vQ�ILJXUD��FX�B* = B; Qpa = 0; Qsfc = 0; Qsi = 0; Qec = 0; qmec ��úL�qcen = 0) . 3.5.7. Predimensionarea cazanului

6HF LXQHD�LQWHULRDU��D�[�E��D�FD]DQXOXL�HVWH�GHWHUPLQDQW��SHQWUX�WRDW��IRUPD�FRQVWUXFWLY��Y��ILJ�3.11). 3HQWUX� DOHJHUHD� DFHVWHL� VHF LXQL� VH� � DOHJ� vQ� SUHDODELO� FDUDFWHULVWLFLOH� HYLL�nervurate . Dimensiunile (v. fig.3.13) X]XDOH�DOH� HYLL�QHUYXUDWH�VXQW� d = 16 ÷ 25 mm uzual d = 20 mm D = (2 ÷ 2,5) * d uzual D = 50 mm


CAZANE

96

g = 0,8 ÷ 1,2 mm uzual g = 1 mm s = g + (1,5 ÷ 2,5) mm uzual s = 3 mm 1XP�UXO�GH� HYL�SHUSHQGLFXODU�SH�GLUHF LD�GH�FXUJHUH�D�JD]HORU�GH�DUGHUH�11 se DOHJH�IXQF LH�GH�SXWHUHD�FD]DQXOXL�DVWIHO� Q = 20 ÷ 30 kW --> N1=2 Q = 30 ÷ 50 kW --> N1=3 Q = 50 ÷ 80 kW --> N1=4 6HF LXQHD� FDQDOXOXL� GH gaze se FRQVLGHU�� GUHSWXQJKLXODU�� FX raport dimensional:

a / b = (3 ÷ 5) 9LWH]D� PHGLH� D� JD]HORU� GH� DUGHUH� � vQ� GUXPXO� FRQYHFWLY� VH� LD� UHODWLY� PLF��wg� ��P�V��GHRDUHFH�GLVSRQLELOXO�GH�WLUDM�HVWH�PLF�úL�SLHUGHULOH�GH�VDUFLQ��SULQ IDVFLFROXO� GH� HYL� WUHEXLH� V�� ILH� PLFL�� 3HQWUX� FDOFXOHOH� SUHOLPLQDUH� VH� FRQVLGHU�� F��temperatura medie a gazelor în drumul convectiv este tmg = 600 C. Pentru a realiza viteza wg�D�JD]HORU�GH�DUGHUH�HVWH�QHFHVDU��R�VHF LXQH�OLEHU��GH�curgere Slc :

( )( )

273

27311

+⋅−+= gm

g

ogo

c

t

w

VVBS

α [m2] (3.190)

$FHDVW��VXSUDID ��OLEHU��HVWH�GDW��GH�VXSUDID D�FDQDOXOXL��a· b din care se scade VXSUDID D� GH� VHF LXQH� RFXSDW�� GH� HYL� úL� QHUYXUL�� 3HQWUX� VLPSOLILFDUHD� FDOFXOXOXL� VH�GHWHUPLQ��XQ��ÄJUDG�GH�VHF LXQH�OLEHU�´��0 dHILQLW�FD�ILLQG�VXSUDID D�OLEHU��GH�FXUJHUH�UDSRUWDW��OD�VXUDID D�WRWDO��D�FDQDOXOXL��

*UDGXO�GH�VHF LXQH� OLEHU��0�SHQWUX� vQWUHDJD�VXSUDID ��HVWH�DFHODúL�FD�SHQWUX�XQ�SDV�GH� HDY��GHRDUHFH�DFHVW�SDV�VH�UHSHW��SH�WRDW��VHF LXQHD��

Fig. 3.14.

Scanal = D*s Socupat = d*s + (D-d)*g Sliber = Scanal – Socupat 0� �6liber / Scanal Scanal = Sliber ��0

d

D

h

s g

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

97

/� LPHD�FDQDOXOXL�GH�FLUFXOD LH�D�gazelor de ardere�HVWH�GDW��GH�QXP�UXO�GH� HYL��N1�PXOWLSOLFDW� FX�GLDPHWUXO� QHUYXULL� �'� � �VH�FRQVLGHU�� F�� vQWUH�FDSHWHOH�QHUYXULORU� úL�SHUHWHOH�FDQDOXOXL��UHVSHFWLY�vQWUH�GRX��FDSHWH�GH�QHUYXU��QX�H[LVW��MRF�VHPQLILFDWLY��

b = N1 Ü D [m] (3.191) /XQJLPHD�FDQDOXL�HVWH�VXSUDID D�FDQDOXOXL�UDSRUWDW��OD�O� LPHD�FDQDOXOXL�

b

Sa

⋅=

ε1 (3.192)

Determinarea acestei cote GHILQHúWH VROX LD�GLPHQVLRQDO��ILQDO��D�FD]DQXOXL� - lungimea canalului a -�O� LPHD�FDQDOXOXL�� b -�QXP�UXO�GH� HYL�� N1 -�GLDPHWUXO� HYLL�� d - diametrul nerurii D - pasul nervurii s

3.5.8. Calculul termic la focarului

Acest calcul are ca scop determinarea tePSHUDWXULL� ILQDOH� D� IRFDUXOXL�� LQkQG�VHDPD�GH�IDSWXO�F��VXSUDID D�HIHFWLY��GH�UDGLD LH�6R�HVWH�VXSUDID D�FDQDOXOXL�FRQYHFWLY��$FHVW� OXFUX� HVWH� HYLGHQW� GHRDUHFH� UDGLD LD� HPLV�� GH� IRFDU� VSUH� SDUWHD� VXSHULRDU�� D�FDPHUHL�GH�DUGHUH�HVWH�LQWHJUDO�DEVRUELW��GH�SDUWHD�YL]LELO��D�VLVWHPXOXL�FRQYHFWLY��GHFL�GH�vQWUHDJD�VHF LXQH�D�FDQDOXOXL�GH�JD]H:

SR = b· a . (3.193)

Gradul de ecranare

=Ψ

per

R

S

S �DO�IRFDUXOXL�UH]XOW��GLQ�UDSRUWXO�GLQWUH�VXSUDID D�SHUH LORU�FDPHUHL�GH�DUGHUH�úL�VXSUDID D�HIHFWLY��GH�UDGLD LH��6R . )RFDUXO��DUH�IRUPD�JHRPHWULF��SDUDOHOLSLSHGLF��FX�VHF LXQHD�aÜb�úL�vQ�O LPHD�hf din figura 3.11. pHQWUX�GHVYROWDUHD�FRPSOHW��D�IO�F�ULL��DVWIHO�FD�VIkUúLWXO�SURFHVXOXL�GH�DUGHUH�V��QX�GHS�úHDVF��vQ�O LPHD�IRFDUXOXL�

Se FRQVLGHU��vQ�O LPHD�IRFDUXOXL� hf = 0,25÷0,35 m.

5H]XOW��XUP�WRDUHOH�GLPHQVLXQL�DOH�IRFDUXOXL�


CAZANE

98

- volumul focarului Vf = a· b· hf

-�VXSUDID D�SHUH LORU� ( ) bahbaS fper⋅⋅+⋅+⋅= 22

-�VXSUDID D�HIHFWLY��GH�UDGLD LH� baSR ⋅=

- gradul de ecranare per

R

S

S=Ψ

- grosimea stratului radiant : per

f

S

Vs 6,3= (m)

6H� FDOFXOHD]�� vQ� FRQWLQXDUH� FDUDFWHULVWLFD� UDGLDQW�� D� JD]HORU� GH� DUGHUH� � GLQ�focar:

)(1000

38,01)(

6,18,022

22

2

ROOH

f

ROOH

OHpp

T

spp

pkg +

−

⋅+

+= (3.194)

6H�FDOFXOHD]��FRHILFLHQWXO�GH�DEVRUE LH�DO�JD]HORU�GH ardere din focar :

sk

ggea⋅−−= 1 (3.195)

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IO�F�ULL�FX�UHOD LD�DSUR[LPDWLY�� 5,0

10006,1 −= f

fl

Tk (3.196)

úL�FRHILFLHQWXO�GH�DEVRUE LH�DO�IO�F�ULL�FX�UHOD LD��

sk

fl

flea⋅−−= 1 (3.197)

3RQGHUHD�DEVRUE LHL�IO�F�ULL�FX�FHD�D�PHGLXOXL�UDGLDQW�GH�JD]H�GH�DUGHUH�VH�IDFH�GXS��FULWHULL�experimentale, considerând o pondere β�D�S�U LL�OXPLQRDVH�D�IO�F�ULL� 3HQWUX�IO�F�UL��SX LQ�OXPLQRDVH�GH�FRPEXVWLELO�JD]RV�� CoeficieQWXO�GH�DEVRUE LH�DO�IO�F�ULORU�úL�JD]HORU�GH�DUGHUH�HVWH�GDW�GH�UHOD LD�� gfl aaa ⋅−+⋅= )1( ββ (3.198)

&RHILFLHQWXO�GH�PXUG�ULUH�D�VXSUDIH HORU�HVWH�� ξ=0,7 ÷ 0,9 combustibil gazos &X�DFHVWH�YDORUL�VH�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D focarului :

ξΨ−+⋅

=)1(

82,0

aa

aa f (3.199)

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

99

2� DOW�� FDUDFWHULVWLF�� D� IRFDUXOXL� HVWH� IDFWRUXO� GH� SR]L LH� D� IO�F�ULL� vQ� IRFDU��pentru combustibil lichid sau gazos :

f

MMH

hbaM −= (3.200)

XQGH�SHQWUX�IRFDUH�YHUWLFDOH�FX�IODF�U��SH�VXSUDID D�LQIHULRDU�� aM=0,54; bM=0,2; h/Hf = 0,2 &X�DFHVWH�GDWH�VH�GHWHUPLQ��WHPSHUDXUD�GH�OD�FDS�WXO�IRFDUXOXL��

( ) 11

6,03

+

⋅⋅−

⋅⋅⋅⋅=

pginc

Rtfo

tf

cVBq

STaCM

TT

ξ [oK] (3.201)

Temperatura GH�LHúLUH�D�JD]HORU�GH�DUGHUH�GLQ�IRFDU��în oC, este : tf = Tf -273 [oC] $FHDVW��WHPSHUDXWU��YD�IL�GLIHULW��GH�Wf �DOHDV��vQ�FDOFXOXO�GH�DSUR[LPDUH��'DF��GLIHUHQ D�HVWH�PDL�PDUH�GH��FFD��.��VH�UHLD�FDOFXOXO�FX�YDORDUHD�Wf��UH]XOWDDW��GLQ� FDOFXOXO� ILQDO�� 'DF�� HURDUHD� HVWH�PDL�PLF�� VH� FRQWLQX�� FDOFXOXO� FX� WHmperatura focarului tf� � UH]XOWDW��GLQ�FDOFXO�GDU�QX�VH�PDL�UHLD�FDOFXOXO�WUDQVIHUXOXL�GH�F�OGXU�� OD�VXSUDID D�GH�UDGLD LH� 3.5.9. Calculul termic al drumului convectiv

'UXPXO� FRQYHFWLY� HVWH� GHWHUPLQDW� GLQ� FDOFXOHOH� DQWHULRDUH� SULQ� XUP�WRULL�parametrii : Qc –�GHELWXO�GH�F�OGXU��FHGDW�GH�JD]HOH�GH�DUGHUH��N:�� tf –�WHPSHUDWXUD�JD]HORU�GH�DUGHUH�OD�LQWUDUH�vQ� HYL��0C) ; tFRú –�WHPSHUDWXUD�JD]HORU�GH�DUGHUH�OD�LHúLUHD�GLQ� HYL��OD�FRú��

te/ti – temperatura apei (0C) . Deoarece temperatura la� FDS�WXO� IRFDUXOXL� V-D� PRGLILFDW� ID �� GH� FHD� DOHDV��

LQL LDO� vQ� FDOFXOHOH� GH� ELODQ �� VH� UHFDOFXOHD]�� IOX[XO� GH� F�OGXU�� SUHOXDW� GH� VLVWHPXO�convectiv.

Din diagrama I –�W��VH�GHWHUPLQ��HQWDOSLD�JD]HORU�GH�DUGHUH�OD�LHúLUHD�GLQ�IRFDU��

),( αff tfI = . (3.202)


CAZANE

100


)()1( ftextR IIBqQ −−= (kW) (3.203)


,Rc QQQ −= (kW) (3.204) 6FKLPEXO�GH�FDOGXU��FRQYHFWLY�vQWUH�JD]HOH�GH�DUGHUH�úL�DS��VH�IDFH�FX�R�EDWHULH�

FX� HYL�QHUYXUDWH��DúD�FXP�V-D�SUH]HQWDW�vQ�GHVFULHUHD�VROX LHL�FRQVWUXFWLYH�D�FD]DQXOXL��&XP�VH�FXQRDúWH�GLQ� WHRULD�JHQHUDO��D�VFKLPE�WRDUHORU�GH�F�OGXU��VROX LD�FRQVWUXFWLY��GH� H[WLQGHUH� D� VXSUDIH HL� GH� WUDQVIHU� GH� F�OGXU�� SH� SDUWHD� JD]HORU� GH� DUGHUH�� SULQ�QHUYXUDUH��VH�DSOLF��SHQWUX�D�FRPSHQVD�vQWU-R�RDUHFDUH�P�VXU��UDSRUWXO�GHIDYRUDELO�FDUH�H[LVW��vQWUH�FRHILFLHQWXO�GH�WUDQVIHU�GH�F�OGXU� de la gaze fa � de cel de la ap�. Nervurile, circularH�� S�WUDWH� VDX� GUHSWXQJKLXODUH�� VXQW� GLVSXVH� HFKLGLVWDQW� SH�H[WHULRUXO� HYLL��VXE�IRUP��GH�GLVFXUL��'LPHQVLXQLOH�X]XDOH�DOH� HYLORU�úL�QHUYXULORU�V-au ales în calculul de predimensionare. Cotirea evilor se face prin coturi nenervurate, în exteriorul sec iunii de trecere a gazelor de ardere. Num�rul de rânduri de evi� vQ� GLUHF LD� GH� FXUJHUH� D� JD]HORU� GH� DUGHUH� �12 se stabileúte prin calculul termic al suprafe ei de transfer de c�ldur� necesar�.

Ecua ia de WUDQVIHU�GH�F�OGXU� este:

mapaapamggc tSKtSKQ ∆⋅⋅=∆⋅⋅= [W] (3.205)

unde : Kg si Kapa reprezint� coeficientul global de transfer de c�ldur�, raportat fie la suprafa a extins�, pe parte gazelor de ardere, “Sg” , fie la suprafa a lis�, pe partea apei, “Sapa”; ûtm� UHSUH]LQW�� GLIHUHQ D� PHGLH� ORJDULWPLF�� GH� WHPSHUDWXU�� vQWUH� FHL� GRL� DJHQ L�termici, corectat� cu un coeficient depinzând de geometria curgerii úi parametri agen ilor.

Temperatura medie a gazelor de ardere este tgm = (tf + tFRú�)/ 2. Temperatura medie a apei este tapam = (ti + te )/ 2.

3HQWUX�WHPSHUDWXULOH�PHGLL�DOH�DJHQ LORU�WHUPLFL�VH�GHWHUPLQ��F�OGXULOH�VSHFLILFH��

cpaer si capa��GLQ�DQH[H�VDX�GLQ�UHOD LLOH�GH�UHJUHVLH�SUH]HQWDWH�vQ�DQH[HOH�UHVSHFWLYH�

Debitul de ap� FDUH�SDUFXUJH� HYLOH�este:

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

101

( )ieapa ttc

QG

−⋅= [kg/s] (3.206)

Deoarece apa trece prin N1� � HYL� vQ�SDUDOHO�� HDYD�DYkQG�GLDPHWUXO�LQWHULRU� �Gi , YLWH]D�DSHL�VH�FDOFXOHD]��FX�UHOD LD�

( )21

4

iapa

apadN

Gw

⋅⋅⋅

=πρ [m/s] (3.207)

Deoarece s-au facut rotunjiri care afecteaz� viteza de curgere a gazelor de ardere, aceasta se recalculeaz�:

( )( )273

2731

1

+⋅

−+= gm

c

ogo

g

t

S

VVBw

α [m/s] (3.208)

TRANSFERUL DE CüDURü DE LA GAZELE DE ARDERE LA PERETELE METALIC

Transferul de c�ldur� este de tip convectiv. Gazele circul� prin canalele realizate între nervuri, care au la imea (s-g). Considerând canalul format din doua evi al�turate, cealalt� latur� a sec iunii de curgere este�GXEOXO�vQ�O LPLL�QHUYXULL� 2Üh .

Relatiile de calcul, de tip experimental, sunt date func ie de o lungime caracteristic� fix� pentru baterie care este pasul nervur�rii : s .

Pentru calcule este necesar� cunoaúterea unor parametri fizici caracteristici gazelor de ardere care se determin� din tabela anexa 9, pentru temperatura medie a gazelor de ardere tgm:

- viscozitatea cinematic�, #g ; - conductibilitatea termic�, �g ; - criteriul Prandtl, Prg .

Coeficientul de convec ie “αg” se calculeaz� dup� metodologia convec iei în curgere for at� prin canale úi este acelaúi pentru partea de suprafa � lis� a evii úi partea de suprafa � extins� a nervurii.


CAZANE

102

Pertele evii are la suprafa a de contact cu aerul o anumit� temperatur� “tp” , care se reg�seúte úi la baza nervurii. Din cauza rezisten ei termice conductive, temperatura peretelui nervurii “tpn” este din ce in ce mai ULGLFDW� spre vârful nervurii. Pentru a nu complica sistemul de calcul, se consider� temperatura suprafe ei nervurii constant�, aceeaúi cu a peretelui evii, dar se afecteaz� suprafa a nervurii cu un "randament" subunitar “�nerv” care face compensarea fluxului mai sc�zut de c�ldur� a suprafe ei cu temperatura mai ULGLFDW� decât cea a evii. Rela ia criterial� pentru transferul de c�ldur� este func ie de turbulen a curgerii, deci de criteriul Re. Se calculeaza criteriul Reg , inând seama c� lungimea caracteristic� este pasul de nervurare, din relatia:

Reg

g

g

sw

ν⋅

= (3.209)

Coeficientul de transfer de c�ldur� prin convec ie de la gazele de ardere la peretele exterior se calculeaz� cu rela iile peQWUX�IDVFLFRO�GH� HYL�vQ�OLQLH��FX�QRWD LLOH :

��Pnerv = s; Hnerv = h; de = d; Dnerv = D; Bnerv = g. * evi cu nervuri rotunde

0,140,54

72,0Re104,0

⋅

⋅⋅=

nerv

nerv

e

nerv

ggH

P

d

PNu (3.210)

* evi cu nervuri p�trate

Re096,00,140,54

72,0

⋅

⋅⋅=

nerv

nerv

e

nervgg

H

P

d

PNu (3.211)

in continuare, pentru ambele cazuri :

⋅⋅

=Km

W

P

Nu

nerv

gg

g 2*

λα (3.212)

Aúa cum s-a ar�tat, în metodica uzual� de calcul se ine seama de un randament subunitar al suprafe ei nervurilor. Acesta depinde de dou� constante adimensionale ale nervurii:

e

nervD

d

DX = (3.213)

si

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

103

2

0,5*

⋅

⋅=

nervnerv

nervIB

HXg

λ

α (3.214)

unde conductibilitatea termica a metalului nervurii este pentru o el �nerv = 50 W/(m.K), pentru cupru �nerv = 300 iar pentru aluminiu �nerv = 175 . Curbele de randament se calculeaza, pentru XD > 2, cu relatiile :

• pentru XI > 0.8 : (3.215)

• pentru XI < 0.8 : (3.216)

Cu acest randament, care îns� afecteaz� numai suprafa a extins�, se determin� coeficientul corectat de transfer de c�ldur� pe partea gazelor de ardere, dup� cum urmeaz�:

- se determin� suprafa a de schimb de c�ldur� a unei nervuri :

( ) [ ] 4

2 222

mdD

Se

nerv

nerv−⋅

⋅=π

(3.217)

- suprafa a lis� a evii pe partea gazelor de ardere între dou� nervuri este:

( ) [ ] m dBPS enervnervl

2 ⋅⋅−= π (3.218)

( )( )( )

( ) 8,0

20,071-0,525

20,140,363

20,05-0,8

2,359

0,631-

0,797

ηηη

η

η

η

η C

Inerv

D

D

D

XBA

XC

XB

XA

−⋅−=

−⋅=

−⋅+=

−⋅=

( )( )

( )

20,093-,7371

20,0660,295

1

1,13

0,71

ηηη

η

η

η

η C

Inerv

D

D

XBA

XC

XB

A

⋅−=

−⋅=

−⋅+=

=


CAZANE

104

- suprafa a total� pe un pas este suma celor dou� suprafe e anterior calculate:

[ ] m SSS lnervtot

2 += (3.219)

- iar coeficientul de transfer de caldura corectat se determin� din rela ia:

Km

W

S

SS

tot

lnervnervgg

⋅+⋅

⋅= 2*

ηαα (3.220)

REZISTENTA TERMICü A PERETELUI �EVII ùI A DEPUNERILOR DE

PE PERE�I Rezisten a termic� a peretelui evii este (/per / �per), în care /per este grosimea peretelui evii úi �per conductibilitatea termic� a metalului evii (pentru o el �per=50(W/m.K), pentru cupru �per=300(W/m.K) iar pentru aluminiu �per= 175(W/m.K)). $FHDVW�� UH]LVWHQ �� WHUPLF��DUH�vQV��R�YDORDUH�IRDUWH�PLF��úL�GH�RELFHL�VH�neglijeaz� în calculele curente. 5H]LVWHQ D� WHUPLF� a depunerilor de piatr� (/p/�p) pe pere ii evilor este foarte mare, ea constituind principala rezisten � în schimbul de c�ldur��9DORULOH�UH]LVWHQ HORU�WHUPLFH�� IXQF LH� GH� FDOLWDWHD� DSHL�� GH� YLWH]D� GH� FXUJHUH� úL� GH� WHPSHUDWXUD� PHGLH� D�agentului termic sunt prezentate în capitolul 1� DO� ,QGUXP�WRUXOXL� Ge Proiectare pentru 6FKLPE�WRDUH� GH� &�OGXU�� 3HQWUX� DSD� GLQ� LQVWDOD LL� GH� vQF�O]LUH� VH� SRDWH� considera , SHQWUX�GHSXQHULOH�GH�SLDWU�� /p� ��P��úL��p = 1 W/(m K)

Rezistentele termice conductive se însumeaz�:

2

W

Km

p

p

per

per

⋅+=∑ λ

δλδ

λδ

(3.221)

TRANSFERUL DE CüLDURü LA PERETELE INTERIOR AL �EVILOR

Transferul de c�ldur� GH� OD�SHUHWHOH� HYLL� OD� DS��este de tip convectiv, în regim permanent, f�r� schimbare de stare, curgere prin interiorul evilor. Pentru calcule este necesar� cunoaúterea unor parametrii fizici caracteristici apei. Aceútia se determin� din tabela anex� pentru temperatura medie a apei tapam:

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

105

- viscozitatea cinematic�, #apa ;

- conductibilitatea termic�, �apa ; - criteriul Prandtl, Prapa .

Rela ia criterial� pentru transferul de c�ldur� este func ie de turbulen a curgerii, deci de criteriul Re. Se calculeaza criteriul Reapa, inând seama c� lungimea caracteristic� este diametrul interior al evii, din rela ia:

dw

Reapa

iapa

apa ν⋅

= (3.222)

În func ie de valoarea ob inut� pentru Reapa se aplic� una din XUP�WRUHOH� rela ii

criteriale:

pentru Rea > 10000 40800240 ,,

apa PrRe.Nu ⋅⋅= (3.223)

pentru 2300 < Rea < 10000

PrRe.Nu Re

,,

apa ε⋅⋅⋅= 40800240 (3.224)

unde 0Re = 1- 6.105· Re-1,8

pentru Re < 2300

PrReLt

d,

PrReLt

d,

,Nu,

aai

aai

apa 660

04501

06880653

⋅⋅⋅+

⋅⋅

⋅

+= (3.225)

Lungimea Lt a tevilor se FRQVLGHU��D�IL�lungimea unei evi nervurate.

Coeficientul de transfer de c�ldur� de la ap� la peretele interior al evii se calculeaz� cu rela ia:

Km

W

d

Nu

i

apaapa

apa

⋅⋅

=2

λα (3.226)


CAZANE

106

COEFICIENTUL GLOBAL DE TRANSFER DE CüLDURü

Se alege o suprafa � de control deoarece suprafe ele de transfer de c�ldur� nu sunt egale pentru cele doua fluide. Pentru un pas de nervur� suprafa a pe partea sc�ldat� de gazele de ardere este:

( ) ( )gsddDS g −⋅⋅+−⋅⋅

= ππ 22*

4

2 (3.227)

Tot pentru un pas de nervurare suprafa a pe partea interioar� a tevii este: iapa dSS ⋅⋅= π* [m2] (3.228)

• Daca se alege ca suprafa � de control interiorul evilor (suprafa a pe partea

apei), coeficientul global de transfer de c�ldur� va fi:

Km

W

S

S

K

apa

aeraer

apa

apa

⋅

⋅++

=∑

2111

αλδ

α (3.229)

• Dac� se alege ca suprafa � de control exteriorul evilor (suprafa a pe partea

gazelor de ardere), coeficientul global de transfer de c�ldur� va fi:

11

12

⋅+⋅

+

=

∑Km

W

S

SK

gapa

g

apa

g

αλδ

α

(3. 230)

DIFEREN�A MEDIE DE TEMPERATURI ùI DIMENSIONü5, FINALE Se consider� un curent incruciúat între ap� úi gazele de ardere úi se utilizeaz� metoda “0 - NTC” pentru determinarea diferen ei medii de temperatur�. Se consider� diferen a medie de temperaturi în contracurent, urmând ca aceasta s� fie corectat� ulterior prin coeficientul de eficien � “0” .

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

107

Din diagrama de evolu ie a temperaturilor, se determin� diferen ele de temperaturi maxim� úi minim�, ûtmax = tf – ti si ûtmin = tFRú – te .

Se calculeaz� diferen a medie de temperaturi în contracurent:

[ ] C

t

tln

ttt

o

min

max

minmaxccm

∆∆

∆∆∆

−=− (3.231)

6XSUDID D�VLVWHPXOXL�FRQYHFWLY�UH]XOW��

[ ] 2m

tK

QS

ccmg

cbat

−∆⋅= (3.232)

Se determin� echivalen ii termici ai celor doi agen i��IXQF LH�GH�'g) :

cDW ggg ⋅=

unde Dg [m3N/s] este debitul volumic de gaze de ardere ; Dg=B· Vg

apaapaapa cDW ⋅=

unde Dapa�>NJ�V@�HVWH�GHELWXO�PDVLF�GH�DS�. (3.233) Se identific� dintre cei doi echivalen i�vQ�DS� Wmin úi Wmax úi se determin�:

Wrap=Wmin/Wmax. (3.234)

S SC

t

ti

tf

tcos

∆tmax

∆tmin

te


CAZANE

108

Se determin� m�rimile NTC (QXP�UXO�GH�unit� i termice) pentru cele doi agen i termici din rela iile:

g

batg

gW

SKNTC

⋅= úL�

apa

batg

apaW

SKN

⋅=TC . (3.235)

Se identific� NTCmin si NTCmax úi în continuare, pe baza diagramelor de tipul 0�� = f (NTCmax , Wmin/Wmax , schema de curgere - curent încruciúat) se poate determina

coeficientul de reducere 0�. Într-un calcul numeric, în func ie de valorile relative ale W úi NTC se aplic� urm�toarele rela ii:

• Dac� Wmax = Wapa ; Wmin = Wg :

eB max

minmax

W

WNTC

⋅−

−=1 �úL�

⋅−

−= min

max

W

WB

e 1ε (3.236) • Daca Wmax = Wg; Wmin = Wapa :

( ) eB maxNTC−−=1 ��úL��

−⋅=

⋅−

max

min

W

WB

min

max eW

W1ε (3.237)

Cu valoarea 0 calculat�� se determin�� VXSUDID D� GH� WUDQVIHU� GH� F�OGXU�� D�convecWLYXOXL�OXkQG�FD�VXSUDID ��GH�FRQWURO�VXSUDID D�de pe partea apei:

mccapa

capa

tK

QS

∆ε ⋅⋅= (3.238)

Deorace s-a ales suprafa a de control interiorul evilor (suprafa a pe partea apei),

coeficientul global de transfer de c�ldur� va fi:

Km

W

S

S

K

apa

g

gapa

apa

⋅

⋅++

=∑

2111

αλδ

α (3.239)

6XSUDID D�GH�VFKLPE�GH�F�OGU��QHFHVDU��SH�SDUWHD�DSHL�VH�SRDWH�determina�úL�FX�UHOD LD�

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

109

( ) [ ]2 mNTC

tt

K

QS

apa

ie

apa

capa

−⋅= (3.240)

Lungimea necesar� de eav��nervurat� va fi:

[ ]m d

SL

i

apa

teava ⋅=

π (3.241)

úL�QXP�UXO�GH�UkQGXUL�GH� HYL�vQ�GLUHF LD�FXUJHULL�gazelor de ardere:

1Na

LN teava

rand ⋅= (3.242)

FDUH�VH�URWXQMHúWH�OD�YDORDUHD�vQWUHDJ��VXSHULRDU��

Dac� se alege ca suprafa � de control exteriorul evilor (suprafa a extins�, pe partea gazelor de ardere), pentru care s-a calculat coeficientul global de transfer de c�ldur� Kg :

( ) [ ]2cos mNTC

tt

K

QS

g

f

g

cg

−⋅= (3.243)

iar lungimea necesara de eav� nervurat� va fi:

[ ]mPS

SL nerv

g

g

teava * ⋅= (3.244)

úi num�rul de rânduri de evi în direc ia curgerii gazelor de ardere:

1Na

LN teava

rand ⋅= (3.245)

care se rotunjeúte la valoarea întreag� superioar�.

'HVLJXU��DPEHOH�VLVWHPH�GH�FDOFXO�VXQW�HFKLYDOHQWH��GHFL��FX�RULFH�VXSUDID ��GH�FRQWURO�VH�OXFUHD]��QXP�UXO�GH�UkQGXUL�GH� HYL�UH]XOWDWH�GLQ�FDOFXOXO�ILQDO�HVWH�DFHODúL�


CAZANE

110

3.6. Calculul termic al cazanelor acvatubulare�YHUWLFDOH�FX�IDVFLFRO�GH� HYL�úL� ��DU]�WRU�DWPRVIHULF�SHQWUX�FRPEXVWLELO�JD]RV� 3.6.��'HVFULHUHD�FD]DQHORU��HOHPHQWH�FRPSRQHQWH��PRG�GH�IXQF LRQDUH� Cazanele sunt dH�WLS�YHUWLFDO��FX�IRFDUXO�DPSODVDW�vQ�SDUWHD�GH�MRV�úL�GHVYROWDUHD�IO�F�ULL� SH� YHUWLFDO�� $YDQWDMXO� DFHVWRU� FD]DQH� HVWH� F�� RFXS�� R� VXSUDID �� PLF�� vQ�FHQWUDOD� WHUPLF��(OH�SRW�IL� IRORVLWH�GUHSW�FD]DQH�GH� vQF�O]LUH�SHQWUX�R�FDV��FX�SX LQH�apartamente (sarciQD� WHUPLF�� XWLO�� – 80 kW) sau drept cazane separate pentru SURGXFHUH�GH�DS��FDOG��GH�FRQVXP�vQWU-R�FHQWUDO��PDL�PDUH��SkQ��OD��N:��$VWIHO�GH�FD]DQH�VH�DPSODVHD]��vQ�FHQWUDOD�WHUPLF�� Din punct de vedere constructiv, deasupra focarului, în cotinuarH� SH� DFHODúL�FDQDO�� VH� J�VHúWH� GUXPXO� FRQYHFWLY� UHDOL]DW� VXE� IRUPD� XQXL� IDVFLFRO� GH� HYL� QHWHGH��'HDVXSUD�FRQYHFWLYXOXL�JD]HOH�GH�DUGHUH�VXQW�FROHFWDWH�úL�HYDFXDWH�OD�FRú� Principalele elemente componente ale cazanului sunt prezentate în figura 1

Fig. 3.15. Schema unui cazan acvatubular vertical cu fascicol�GH� HYL�úL�DU]�WRU� autoaspirant pentru combustibil gazos

�� HYL�orizontale convective��IRFDU��DU]�WRDUH�DXWRDVSLUDQWH��LQWUDUH�LHúLUH�aS��FDOG��vQF�O]LUH; 5. pieV��GH�HYDFXUH�D�JD]HORU�GH�DUGHUH��FX�UXSHUH�GH�SUHVLXQH�

&D]DQHOH� VXQW� GHVWLQDWH� SURGXFHULL� GH� DS�� FDOG� te/ti = 90/70 oC pentru vQF�O]LUH� Uneori, pentru puteri relativ mici�� vQ� DFHLDúL� FDUFDV�� FX� FD]DQXO� VH�DPSODVHD]�� SRPSD�GH�FLUFXOD LH� D� DJHQWXOXL� WHUPLF��YDVXO�GH�H[SDQVLXQH� vQFKLV�úL�XQ�VFKLPE�WRU� GH� F�OGXU�� FX� SO�FL� SHQWUX� Sroducerea apei calde de consum. Pentru RE LQHUHD� XQHL� VROX LL� LHIWLQH� VH� DGRSW�� VLVWHPXO� GH� DUGHUH� FX� DU]�WRU autoaspirant (”atmosferic”)� ��6XE�DFHDVW��GHQXPLUH�VH� vQ HOHJH�DU]�WRUXO�pentru combustibil gazos cu aer primar de ardere DXWRDVSLUDW� SULQ� HMHF LH��'HRDUFHFH�SULQ� HMHF LH� QX� VH�SRDWH�

'HWDOLX�GH�DúH]DUH�D� HYLORU�vQ�HúLFKLHU

s1

s2

1

2

3

4

5

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

111

aspira mai mult de 4 ori volumul de gaz combustibil, restul aerului de ardere se introduce ca aer secundar aspirat din mediul ambiant prin depresiuneD� UHDOL]DW� în camera de ardere. Pentru un exces de aer uzual, pentru acest tip de cazane, .�= 1,4 UH]XOW�� F�� WUHEXLH� DVSLUDW� FD� DHU� VHFXQGDU� XQ� YROXP� GH� FFD�� RUL� YROXPXO� GH� JD]�combustibil. $FHVW� VLVWHP� GH� IXQF LRQDUH� LPSXQH� H[LVWHQ D� unei depresiuni suficiente în focar pentru absorE La de aer de ardere�� 'HSUHVLXQHD� VH� FUHLD]�� SULQ� autotirajul drumului de gaze� DO� FD]DQXOXL� úL� SULQ� FRúXO� OD� FDUH� HVWH� UDFRUGDW��8QHRUL� WLUDMXO� HVWH�DFWLYDW�GH�XQ�H[KDXVWRU�GDF��vQ�O LPHD�FRúXOXL�QX�HVWH�VXIicient de mare. Este de aceia QHFHVDU� V�� VH� IDF�� XQ�FDOFXO�JD]RGLQDPLF� ULJXURV�DO� FD]DQXOXL�SHQWUX� WRDWH�FRQGL LLOH�posibile de fuQF LRQDUH� $U]�WRUXO�HVWH�IRUPDW�GLQWU-XQ�JUXS�GH�HOHPHQWH�GH�DU]�WRU�DWPRVIHULF��DVIHO�F��Y�]XW��GH�VXV��IODF�UD�DSDUH�FD�XQ�FRYRU�GH�PLFL�IO�F�UL�LQGLYLGXDOH�FDUH�VH�XQHVF�vQWU-o ]RQ��GH�DUGHUH�FRPXQ��FX�VXSUDID D�HJDO��SUDFWLF�FX�VHF LXQHD�FDPHUHL�GH�DUGHUH� 3HQWUX� D� UH]LVWD� WHPSHUDWXULORU� vQDOWH� GLQ� FDPHUD� GH� DUGHUH� úL� SHQWUX� D� SUHOXD�F�OGXU��XWLO��SULQ�UDGLD LH�SHUH LL�IRFDUXOXL�VXQW�VXE�IRUP��GH�FKHVRQ��U�FLW�FX�DSD�GLQ�FLUFXLWXO�GH�vQF�O]LUH� ÌQ� FRQWLQXDUHD� FDPHUHL� GH� DUGHUH� SH� YHUWLFDO�� VH� J�VHúWH� IDVFLFROXO� GH� HYL�netede care are rolul de sistem convectiv al cazanului. În acest convectiv, gazele de DUGHUH� FHGHD]�� DSHL� F�OGXUD� vQ� LQWHUYDOXO� GH� WHPSHUDWXUL� GH� OD� WHPSHUDWXUD� FDS�WXOXL�camerei de ardere tf la temperatura de la evacuare tFRú� �� HYLOH� FDUH� DOF�WXLHVF�VLVWHPXO�FRQYHFWLY�VXQW� HYL�RELúQXLWH�GH�R HO�FX�GLDPHWUXO�H[WHULRU��÷ 42 mm. 3DVXO�GH�DúH]DUH�D� HYilor în fascicol este:

• pasul perpendicular pe curgerea gazelor de ardere s1 = ( 1,4 ÷ 2 ) · d

• SDVXO�SH�GLUHF LD�GH�FXUJHUH�D�JD]HORU�GH�DUGHUH��s2 = ( 1,2 ÷ 1,6 ) · d SDúLL�VH�DOHJ�DVWIHO�FD�JURVLPHD�PLQLP��GH�PHWDO�vQWUH�GRX�� HYL�V��ILH��÷ 10 mm Apa� FDOG�� GH� vQF�O]LUH�� GH� OD� UHWXUXO� LQVWDOD LHL�� LQWU�� SH� lD� FDS�WXO� LQIHULRU� DO�FD]DQXOXL�úL�GXS��FH�DFHDVWD�SUHLD�F�OGXUD�XWLO��GH�OD�IODF�U��úL�GH�OD�JD]HOH�GH�DUGHUH HVWH�FROHFWDW��OD�SDUWHD�VXSHULRDU��D�FD]DQXOXL�úL�WULPLV��OD�FRQVXPDWRUL�� Cazanul esWH� L]RODW� WHUPLF� FX� YDW�� PLQHUDO�� úL� SURWHMDW� OD� H[WHULRU� FX� WDEO��VXE LUH��6H�RE LQH�DVWIHO�XQ�FD]DQ�PRQREORF��FX�GLPHQVLXQL�UHGXVH�vQ�UDSRUW�FX�VDUFLQD�WHUPLF��SURGXV�� 3.6.2. Tema de proiectare

Prin tema de proiectare se dau : - Q – sarcina termic��D�FD]DQXOXL��vQ�N:�� - te / ti –�WHPSHUDWXUD�DSHL�OD�LHúLUH�úL�LQWUDUH�vQ�FD]DQ��0C sau 80/60 0C); - QDWXUD�úL�FRPSR]L LD�FRPEXVWLELOXOXL��JD]�QDWXUDO�VDX�G.P.L.) .


CAZANE

112

Aceste cazane, cu depresiune în focar, au coeficientul de exces de aer relativ mare GDWRULW�� VLVWHPXOXL� DXWRDVSLUDQW� FDUH� QX� DVLJXU�� R� EXQ�� RPRJHQHL]DUH� D�combustibilului cu aerul:

α = 1,6 ÷ 1,8.

&RQIRUP� LQGLFD LLORU� GLQ� FDSLWROXO� �� VH� HIHFWXHD]�� FDOFXOXO� DUGHULL�FRPEXVWLELOXOXL� úL�VH�GHWHUPLQ�� VO, Vgo, Hi, OH2

p , 2ROp ��VH� WUDVHD]��GLDJUDPD�I – t

sau cp – t .

3.6.��&DOFXOXO�UDQGDPHQWXOXL�WHUPLF�DO�FD]DQXOXL�úL�D�GHELWXOXL�GH�FRPEXVWLELO� $FHVWH� FD]DQH� IXQF LRQHD]�� GH� UHJXO�� FX� FRPEXVWLELO� JD]RV� �JD]� QDWXUDO� VDX�G.P.L.) deci pierderile specifice mecanice (qmec�� úL� FHOH� SULQ� HYDFXDUHD� SURGXVHORU�solide din cazan (qcen) sunt nule. De asemenea consumul de combustibil B* = B . Se determin��SLHUGHULOH�VSHFLILFH�GH�F�OGXU�� a). 3ULQ�HYDFXDUHD�JD]HORU�GH�DUGHUH�SH�FRú��TFRú) :

)II(H

q aocos

i

cos ⋅−= α1 (3.246)

6H�DGPLWH��LPSXQH��R�WHPSHUDWXU��DSUR[LPDWLY��D�JD]HORU�GH�DUGHUH�OD�FRú�� C)(

ttt oei

cos 80602

÷++

= (3.247)

úL�GLQ�GLDJUDPD�,�–�W�VH�GHWHUPLQ��IFRú . Pentru temperatura aerului (ta ≅ 20 0&�� VH� FDOFXOHD]�� HQWDOSLD� DHUXOXL� WHRretic necesar arderii :

apaoa tcVI ⋅⋅=0 (3.248)

cu cpa = 1,297 kJ/ Km3N �F�OGXUD�VSHFLILF��D�DHUXOXL�OD��oC .

b). PULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��FKLPLF��(qch) : 3HQWUX�DU]�WRDUH�autoaspirante cu omogeneizare de calitate medie:

qch = 0,005 c). 3ULQ�SHUH Li exteriori ai cazanului (qext) : Pentru cazane mici, foarte compacte, cu putere sub 80 kW, bine izolate, în faza de proiectare se poate adopta o valoare:

qext = 0,005÷0,008.

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

113

Randamentul cazanului se calculHD]��FX�UHOD LD�� )qqq( extchcos ++−= 1η �úL� ηη ⋅= 100% (%) (3.249)

Debitul de combustibil va fi:

iH

QB

⋅=

η ( s/m3N ) (3.250)

3.6.��%LODQ XO�GH�DQVDPEOX�DO�FD]DQXOXL )OX[XO�GH�F�OGXU��XWLO�DO�FD]anului este : Q ;

)OX[XO�GH�F�OGXU��DGXV�GH�FRPEXVWLELO�� Qcomb = B ⋅ Hi ;

)X[XO�GH�F�OGXU��DGXV�GH�DHUXO�GH�DUGHUH�� Qa = B ⋅ α ⋅cpa ⋅ ta ;

)X[XO�GH�F�OGXU��SLHUGXW�OD�FRú�� QFRú = B ⋅ IFRú ; )X[XO�GH�F�OGXU��SLHUGXW�SULQ�DUGHUH�LQFRPSOHW�: Qinc = qch ⋅ B ⋅ Hi .



Fluxuri utile

Qcomb

Qa

- QFRú - Qinc

- Qext

Q

∑ = 'QQ ''QQ∑ =

(URDUHD�UHODWLY��GH�vQFLGHUH�D�ELODQ XOXL: %

'Q

"Q'Q1100 <⋅

−=ε (3.251)

'LQ� WDEHOXO� �� VH� SRDWH� VFULH� VXE� IRUP�� H[SOLFLW�� SLHUGHUHD� GH� F�OGXU�� OD�evacuare a gazelor:

–Qev = –qFRú· B· Hi = –B· IFRú�+ B· α· Vo· cpa· ta = – QFRú + Qa .


CAZANE

114

3.6.��&DOFXOXO�WHPSHUDWXULORU�úL�HQWDOSLLORU�JD]HORU�GH�DUGHUH�SH�WUDVHX� Entalpia WHRUHWLF��D�JD]HORU�GH�DUGHUH�VH�FDOFXOHD]��FX�UHOD LD�� apachit tcV)q(HI 01 α+−= (3.252)

Din digrama I –�W�VH�GHWHUPLQ��WHPSHUDWXUD�WHRUHWLF��GH�DUGHUH�� ),I(ft t α= . 6H�LPSXQH��DOHJH��WHPSHUDWXUD�OD�LHúLrea gazelor de ardere din focar:

tf = 600 ÷ 800 oC.

9DORULOH� DFHVWHD� VXQW� VSHFLILFH� FD]DQHORU� FX� IRFDUH� IRDUWH� U�FLWH�� /D� DFHVWH�FD]DQH� VXSUDID D� GH� UDGLD LH� vQ� IRFDU� HVWH� VXSUDID D� SHUH LORU� ODWHUDOL� DL� IRFDUXOXL� úL�VHF LXQHD� VXSHULRDU�� D� FDPHUHL� GH� DUGHUH� XQGH� SDUWHD� LQIHULRDU�� D� IDVcicolului FRQYHFWLY�SULPHúWH�F�OGXU��úL�SULQ�UDGLD LH��

Din diagrama I –�W��VH�GHWHUPLQ��HQWDOSLD�JD]HORU�GH�DUGHUH�OD�LHúLUHD�GLQ�IRFDU:

),I(ft ttα= .


)II(B)q(Q ftextR −−= 1 (kW) (3.253)


,QQQ Rc −= (3.254)

Entalpia gazelor de ardere la sfkUúLWXO�GUXPXOXL�FRQYHFWLY�HVWH:

B)q(

QII

ext

cfc −

−=1

(3.255)

úL�GLQ�GLDJUDPD�,�–�W�UH]XOW��WHPSHUDWXUa : ),I(ft cc α= .

ÌQFKLGHUHD�ELODQ XOXL�LPSXQH��Ic ≅ IFRú�úL�tc ≅ tFRú��úL�VH�DGPLW�HURULOH�UHODWLYH��

100cost

ccos

III

II

−−

=ε � 0,5%

100cost

ccos

ttt

tt

−−

=ε � 0,5%

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

115


'HELWHOH�GH�F�OGXU��QR, Qc,Qcomb,Qa�úL� IOX[XULOH�SLHUGXWH�QFRú, Qinc, Qext

VH�WUDQVSXQ�JUDILF�DO�VFDU��FD�vQ�ILJXUD��FX�B* = B; Qpa = 0; Qsfc = 0; Qsi =

0; Qec = 0; qmec = 0 úL� qcen = 0) .

3.6.7. Calculul termic al focarului

)RFDUXO�GH�WLS�FDPHU��DUH�XUP�WRDUHOH�GLmensiuni conform fig. 3.16.

Fig. 3.16. Dimensiunile focarului $FHVW�FDOFXO�DUH�FD�VFRS�GHWHUPLQDUHD�VXSUDIH HL�GH�UDGLD LH�6R�FDSDELO��V��SUHLD�GHELWXO� GH� F�OGXU�� UDGLDQW� 4R. Deoarece în calcul intervine gradul de ecranare

=

per

R

S

SΨ úL�OXQJLPHD�GH�UDGLD LH�este necesar un calcul interativ.

,QL LDO�VH�DGPLWH�R�YDORDUH�RULHQWDWLY�� S′R FDUH�YD�IL�FRPSDUDW�� FX�FHD�ILQDO��SR.

S′R poatH�IL�DSUHFLDW��SULQ�GRX��PHWRGH: a) Se admite un flux unitar radiant qR =30 ÷ 50 kW/m2

R

RR

q

Q'S = (m2) (3.256)

sau b) 6H�FDOFXOHD]��VXSUDID D�SUHOLPLQDU��GH�UDGLD LH�vQ�IRFDU�FX�UHOD LD��

−

=

44

1001007655 pf

R'

R

TT,

QS

ε (m2) (3.257)

A

h

a

6HF LXQH��A - A

a a

A


CAZANE

116

cu ε = 0,65 pentru combustibil gazos

Tf = tf + 273 (0K)

Tp = tma + 20 + 273 (0K) 2

eima

ttt

+=

XQGH� SHQWUX� WHPSHUDWXUD� SHUHWHOXL� HYLL� V-D� DGPLV� R� WHPSHUDWXU�� FX� �� 0C mai mare decât temperatura fluidului interior . 6H�DOHJH�R�VHF LXQH�S�WUDW��GH�IRFDU�FX�ODWXUD��a.

ÌQ�O LPHD�IRFDUXOXL se alege în domeniul:

251 ÷== ,a

h χ (3.258)

&RPSRQHQWHOH�VXSUDIH HL�GH�UDGLD LH�YRU�IL�

- VXSUDID D�SHUH LORU�ODWHUDOL: χ⋅⋅=⋅⋅= 244 ahaS latR (3.259)

- VXSUDID D�WDYDQXOXL�XQGH�IDVFLFROXO�GH� HYL�SUHLD�F�OGXUD�úL�SULQ�UDGLD LH: aaS tavR ⋅= (3.260)

- sXSUDID D�WRWDO��GH�UDGLD LH:

S’R = SRlat + SRtav. (3.261)

5H]XOW��ODWXUD�úL�vQ�O LPHD�IRFDUXOXL�

14 +=

χ

'

RSa [m]��úL�� ah ⋅= χ [m] (3.262)

úL�VH�URWXQMHVF�YDORULOH�OD�XQ�QXP�U�vQWUHJ�GH�FP� CALCULUL EXACT AL FOCARULUI

6XSUDID D�SHUH LORU�IRFDUXOXL�HVWH��

224 aahS per += (m2) (3.263)

6XSUDID D�GH�UDGLD LH�HVWH��

24' aahS R += (m2) (3.264)

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

117

Volumul focarului este:

2ahV f ⋅= (m3) (3.265)

Grosimea stratului radiant de gaze este :

per

f

S

Vs ⋅= 4 (m) (3.266)

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�JD]HORU�GH�DUGHUH�GLQ�IRFDU�� )pp(

T,

s)pp(

p,,kg ROOH

f

ROOH

OH

22

22

2

10003801

6180+

−

+

+= (3.267)

6H�FDOFXOHD]��FRHILFLHQWXO�GH�DEVRUE LH�DO�JD]HORU�GH�DUGHUH�GLQ�IRFDU��

sk

ggea

⋅−−= 1 (3.268)

&DUDFWHULVWLFD�UDGLDQW��D�IO�F�ULL�VH�FDOFXOHD]��FX�UHOD LD�DSUR[LPDWLY�� 5,0

10006,1 −= f

fl

Tk (3.269)


sk

flglea

−−= 1 (3.270)

3RQGHUHD�DEVRUE LHL�IO�F�ULL�FX�FHD�D�PHGLXOXL�UDGLDQW�GH�JD]H�GH�DUGHUH�VH�IDFH�GXS��FULWHULL�experimentale, considerând o pondere β�D�S�U LL�OXPLQRDVH�D�IO�F�ULL�

&RHILFLHQWXO�GH�DEVRUE LH�DO�IO�F�ULL�úL�JD]HORU�GH�DUGHUH�YD�IL�� gfl aaa )1( ββ −+⋅= (3.271)

cu β� ��SHQWUX�IODF�U��QHOXPLQRDV��GH�FRPEXVWLELO�JD]RV� Gradul de ecranare al focarului este :

per

'

R

S

S=Ψ (3.272)

iar�JUDGXO�GH�PXUG�ULUH�D�VXSUDIH HORU�� ξ = 0,7 ÷ 0,9 (pentru combustibil gazos)

Cu acHVWH�YDORUL�VH�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IRFDUXOXL��


CAZANE

118

ξΨ)a(a

a,a f −+

⋅=

1

820 (3.273)

2�DOW��FDUDFWHULVWLF��D�IRFDUXOXL�HVWH�IDFWRUXO�GH�SR]L LH�D�IO�F�ULL�vQ�IRFDU��

f

*

MMH

bbaM −= (3.274)

unde pentru combustibil lichid� VDX� JD]RV� úL� SHQWUX� IRFDUH� YHUWLFDOH� FX� IODF�U�� SH�VXSUDID D�LQIHULRDU�� cu : aM=0,52; bM=0,3; b*/H = 0,2 –�vQ�O LPHD�UHODWLY��D�IO�F�ULL� &X�DFHVWH�GDWH�VH�GHWHUPLQ��VXSUDID D�GH�UDGLD LH�D�IRFDUXOXL��

32

2

38

11

10765,5 MT

T

TTaM

QS

f

t

tff

RR

−

⋅= − ξ (m2) (3.275)

AceDVW�� VXSUDID �� YD� IL� GLIHULW�� GH� '

RS � GHWHUPLQDW�� vQ� FDOFXOXO� DSUR[LPDWLY��'DF�� GLIHUHQ D� HVWH� PDL� PDUH� GH� ±10% se reia calculul cu valori modificate ale geometriei. 3.6.8. Calculul termic al drumului convectiv

�HYLOH� VXQW� GLVSXVH� vQ� HúLFKLHU� FRQIRUP� VFKL HL� JHQHUDOH� D� FD]DQXOXL� GLQ�fig.3.15.

)LJ��'HWDOLX�GH�DúH]DUH�D� HYLORU�vQ�HúLFKHU 'UXPXO� FRQYHFWLY� HVWH� GHWHUPLQDW� GLQ� FDOFXOHOH� DQWHULRDUH� SULQ� XUP�WRULL�parametrii :

s1

s2

N1 HYL�SH�XQ�UkQG

'LUHF LH�GH�GHSODVDUH�D�gazelor de ardere

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

119

Qc –�GHELWXO�GH�F�OGXU��FHGDW�GH�JD]HOH�GH�DUGHUH��N:�� tf – temperatura gazelor de ardere la intrare în sistemul convectiv (0C) ;

tFRú –�WHPSHUDWXUD�JD]HORU�GH�DUGHUH�OD�LHúLUHD�GLQ�sistemul convectiv�OD�FRú�� te/ti – temperatura apei (0C) .

3HQWUX� VWDELOLUHD� VHF Lunii de trecere a gazelor de ardere se alege diametrul HYLORU�GUXPXULORU�FRQYHFWLYH�GLQ�JDPD�GH� HYL�X]XDOH�SHQWUX�FD]DQHOH�GH�DS��FDOG��

φ 24 × 3 φ 28 × 3 φ 32 × 3 φ 42 x 3 6H�DOHJH�SDVXO�UHODWLY�GH�DúH]DUH�WUDQVYHUVDO��D� HYLORU��

• pasul perpendicular pe curgerea gazelor de ardere s1 = ( 1,4 ÷ 2 ) · d

• SDVXO�SH�GLUHF LD�GH�FXUJHUH�D�JD]HORU�GH�DUGHUH��s2 = ( 1,2 ÷ 1,6 ) · d SDúLL�VH�DOHJ�DVWIHO�FD�JURVLPHD�PLQLP��GH�PHWDO�GH�SODF��WXEXODU��vQWUH�GRX�� HYL,�V��fie 8 ÷ 10 mm 6H�FDOFXOHD]��QXP�UXO�GH� HYL�SH�XQ�UkQG� N1:

sss

sNa ++⋅=21

11 �úL��1

1

12s

ss

a

Ns−−

= (3.276)

DSRL�VH�URWXQMHúWH�SDVXO�s1 al HYLORU�DVIHO�vQFkW�QXP�UXO��N1�V��ILH�vQWUHJ� 5H]XOW��R�DúH]DUH�SH�SULPD�OLQLH�D� HYLORU�FRQIRUP�ILJXULL��3.18.

Fig. 3.18��$úH]DUHD� HYLORU�vQ�IDVFLFRO

s1/ 2

s1 ss

a

N1 HYL


CAZANE

120

6H�FDOFXOHD]��DSRL�VHF LXQHD�OLEHU��GH�WUHFHUH�D�JD]HORU�GH�DUGHUH�vQ�LSRWH]a�F��VHF LXQHD�EUXW��D�IRFDUXOXL�U�PkQH�QHVFKLPEDW��úL�vQ�GUXPXO�FRQYHFWLY��a × a) :

−=

−=

1

2

1

12 1s

da

s

dsaScirc (m2) (3.277)

unde termenul

−

1

1

s

ds � UHSUH]LQW�� UHGXFHUHD� VHF LXQLL de trecere� GDWRULW�� HYLORU�convective. Debitul de gaze ce trece prin convectiv este :

273

273+⋅= gm

gg

tVBD (Nm3/s) (3.278)

unde tgm este temperatura medie a gazelor de ardere :

2

cosf

gm

ttt

+= (0C) (3.279)

5H]XOW��YLWH]D�JD]HORU�GH�DUGHUH��

circ

g

S

DW = (m/s) (3.280)

Pentru temperatura media a gazelor de ardere tgm se GHWHUPLQ�� GLQ� DQH[D� ��XUP�WRDUHOH�YDORUL�

- YkVFR]LWDWHD�FLQHPDWLF� ν (m2/s)

- FRQGXFWLELOLWDWHD�WHUPLF�� λ (W/mK)

- criteriul Prandtl Pr

6H� DOHJH�SDVXO� vQ�GLUHF LD� FXUJHULL�JD]HORU�GH�DUGHUH�s2 = ( 1,2 ÷ 1,6 )· d. Se

FDOFXOHD]�� FRHILFLHQWXO� GH� VFKLPE�GH� F�OGXU�� αc) pentru curgerea gazelor de ardere transversal pe un fasciFXO�GH� HYL�DúH]DWH�vQ�HúLFKLHU��

ÌQ�DFHVW�FD]�OXQJLPHD�FDUDFWHULVWLF��YD�IL�GLDPHWUXO�H[WHULRU�DO� HYLL��d . Criteriul hidrodinamic este:

νdw

Re⋅

= (3.281)

Pentru 10 < Re < 106� úL� ��Pr < 10, curgerea fluidelor transversal pe un IDVFLFRO�GH� HYL�vQ�HúLFKLHU��

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

121

s

,,cPrRe,Nu

40601570 ⋅= (3.282) unde cs�HVWH�R�FRUHF LH�SHQWUX�SDVXO� HYLORU� cs = 1 + 0,1· (s1/d) pentru (s1/d) < 3

cs = 1,3 pentru (s1/d) > 3

5H]XO��c

cl

Nuλα = . (3.283)

&RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH�HVWH�GHWHUPLQDW�GH�SDUDPHWULL��

OHp2

, 2ROp úL� s - grosimea stratului radiant :

ed,d

s

d

s,s

−

+= 14871 21

(m) (3.284)

&RQVWDQWD�GH�UDGLD LH�D�JD]HORU�HVWH��

( ) ( )22

22

2

10003801

6180ROOH

m

ROOH

OHpp

T,

spp

p,,kg +

−

+

+= (3.285)

Coeficientul de emisie al gazelor de ardere :

sk

ggea

⋅−−=1 (3.286)


−

−

+⋅= −

m

p

,

m

p

mg

p

r

T

T

T

T

Taa

,

1

1

2

1107655

63

38α (W/m2K) (3.287)

unde pentru coeficientul GH� DEVRUE LH� DO� SHUHWHOXL� VH� LD� YDORDUHD�ap� �� úL� SHQWUX�WHPSHUDWXUD�DEVROXW��D�SHUHWHOXL� HYLL�� 27320 ++= amp tT [K]

Coeficientul de transfer de�F�OGXU��HVWH�:

αi = αc + αr. (3.288)


CAZANE

122

&RHILFLHQWXO�JOREDO�GH�VFKLPE�GH�F�OGXU��HVWH��

i

ikεα

α+

=1

(3.289)

FX�YDORULOH�SHQWUX�FRHILFLHQWXO�GH�PXUG�ULUH�conform tabelului 3.9. 'LIHUHQ D� PHGLH� D�WHPSHUDWXULORU� VH� GHWHUPLQ�� FRQIRUP�UHOD LHL��

min

max

minmax

lnt

t

tttm

∆∆

∆−∆=∆ (3.290)

Fig. 3.19.�'LIHUHQ D�PHGLH�a temperaturilor ÌQ� ILQDO� VXSUDID D�GH�VFKLPE�GH�F�OGXU�� D�GUXPXOXL�FRQYHFWLY�VH�GHWHUPLQ�� FX�UHOD LD:

m

cc

tk

QS

∆= (m2) (3.291)

Determinarea geometriei drumului convectiv se face astfel :

- QXP�UXO�GH� HYL�SH�XQ�UkQG�11 (perpendiculDU�SH�GLUHF LD�JD]HORU�GH�DUGHUH��s-D�GHWHUPLQDW�LQL LDO�

- QXP�UXO�GH�UkQGXUL�GH� HYL�12��vQ�GLUHF LD�FXUJHULL�JD]HORU�GH�DUGHUH��UH]XOW��GLQ�UHOD LD��

adNNSc ⋅⋅⋅⋅= π21 => adN

SN c

⋅⋅⋅=

π12 (3.292)

�VH�URWXQMHúWH�OD�YDORDUHD�vQWUHDJ��VXSHULRDU�� 6H� UHPDUF�� IDSWXO� F�� V-D� QHJOLMDW� SUHOXDUHD� F�OGXULL� GH� F�WUH� SHUH LL� GH� WDEO��OLPLWDWRUL�DL�GUXPXOXL�FRQYHFWLY��'H�RELFHL�VH�FRQVLGHU��FD�UH]HUY��GH�VXSUDID ��VH�SRW�OXD�vQ�FDOFXO��FD]�vQ�FDUH�LQWU��vQ�FRPSRQHQ D�VXSUDIH HL�Sc .

S SC

t

tma

tf

tcos

∆tmax

∆tmin

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

123

&X� QXP�UXO� GH� UkQGXUL� GH� HYL� SH� YHUWLFDO�� VH� FDOFXOHD]�� OXQJLPHD� GUXPXOXL�convectiv:

22 sNLc ⋅= (3.293)

úL�VH�GHWHUPLQ��vQ�O LPHD�WRWDO��D�FD]DQXOXL�

3.7. Calculul termic al cazanelor ignitubulare verticale

��FX�XQ�GUXP�úL�DU]�WRU�DWPRVferic pentru combustibil gazos 3.7.��'HVFULHUHD�FD]DQHORU��HOHPHQWH�FRPSRQHQWH��PRG�GH�IXQF LRQDUH� &D]DQHOH�VXQW�GH�WLS�YHUWLFDO��FX�IRFDUXO�DPSODVDW�vQ�SDUWHD�GH�MRV�úL�GHVYROWDUHD�IO�F�ULL� SH� YHUWLFDO�� $YDQWDMXO� DFHVWRU� FD]DQH� HVWH� F�� RFXS�� R� VXSUDID �� PLF�� vQ�FHQWUDOD� WHUPLF��(OH�SRW�IL� IRORVLWH�GUHSW�FD]DQH�GH� vQF�O]LUH�SHQWUX�R�FDV��FX�SX LQH�DSDUWDPHQWH��VDUFLQD�WHUPLF��XWLO��– 30 kW) sau drept cazane pentru producere de DS��FDOG��GH�FRQVXP��'DF��VXQW�FD]DQH�SHQWUX�SURGXFHUH�GH�DS��FDOG��Ge consum se DPSODVHD]��vQ�EDLH�úL�XQHRUL�FDS�W��GHQXPLUHD�GH�ÄFD]DQ�GH�EDLH´� 'LQ� SXQFW� GH� YHGHUH� FRQVWUXFWLY�� GHDVXSUD� IRFDUXOXL�� vQ� FRWLQXDUH� SH� DFHODúL�FDQDO��VH�J�VHúWH�GUXPXO�FRQYHFWLY�UHDOL]DW�VXE�IRUPD�XQXL�IDVFLFRO�GH� HYL�QHWHGH�FDUH�VWU�EDW� XQ� FLOLQGUX� FX� YROXP�PDUH� GH� DS�� 'HDVXSUD� FRQYHFWLYXOXL� JD]HOH� GH� DUGHUH�VXQW�FROHFWDWH�úL�HYDFXDWH�OD�FRú� Principalele elemente componente ale cazanului sunt prezentate în figura 3.19.

Fig. 3.19. Schema unui cazan acvatubular vertical ignitubular FX�XQ�GUXP�úL�DU]�WRU�DWPRVIHULF�SHQWUX�FRPEXVWLELO�JD]RV

�� HYL�YHUWLFDOH��LJQLWXEXODUH��FRQYHFWLYH��IRFDU��DU]�WRDUH�DXWRDVSLUDQWH��LQWUDUH�LHúLUH�aS��FDOG��vQF�O]LUH��SLeV��GH�HYDFXUH�D�JD]HORU�GH�DUGHUH��FX�

rupere de presiune.

6(&�,81(��A - A

A A

1 2

3

4 1

4


CAZANE

124

3HQWUX� RE LQHUHD� XQHL� VROX LL� LHIWLQH� VH� DGRSW�� VLVWHPXO� GH� DUGHUH� FX� ´DU]�WRU�atmosferic”�� 6XE� DFHDVW�� GHQXPLUH� VH� vQ HOHJH� DU]�WRUXO� GH� JD]� QDWXUDO� FX� DHU�DXWRDVSLUDW� SULQ� HMHF LH��'HRDUFHFH� SULQ� HMHF LH� QX� VH� SRDWH� DVSLUD�PDL�PXOW� GH��RUL�volumul de gaz combustibil, restul aerului de ardere se introduce ca aer secundar aspirat prin depresiune în camera de ardere din mediul ambiant. Pentru un exces de DHU�X]XDO�GH��.� ��UH]XOW��F��WUHEXLH�DVSLUDW�FD�DHU�VHFXQGDU�XQ�YROXP�GH�FFD��RUL�volumul de gaz combustibil. $FHVW� VLVWHP� GH� IXQF LRQDUH� LPSXQH� H[LVWHQ D� XQHL� GHSUHVLXQL� VXILFLHQWH� vQ�IRFDU� SHQWUX� R� DEVRE LH� GH� DHU�� 'HSUHVLXQHD� VH� FUHLD]�� SULQ� autotirajul drumului de gaze� DO� FD]DQXOXL� úL� SULQ� FRúXO� OD� FDUH� HVWH� UDFRUGDW�� 5H]LVWHQ HOH� KLdraulice ale WUDVHXOXL�GH�JD]H�GH�DUGHUH�VXQW�PLFL��IDVFLFRO�VFXUW�GH� HYL�úL�YLWH]H�PLFL�GH�FXUJHUH�D�JD]HORU��GH�DFHLD�QX�HVWH�QHFHVDU��DFWLYDUHD�WLUDMXOXL�FX�XQ�H[KDXVWRU��3HQWUX�UHGXFHUHD�WHPSHUDWXULL�JD]HORU�OD�FRú��GHRDUHFH�YLWH]HOH�GH�FXUJHUH�vQ� HYile convective sunt mici VH�SRW�LQWURGXFH�vQ�LQWHULRUXO� HYLORU�WXUEXOL]DWRUL�FDUH�LQWHQVLILF��WUDQVIHUXO�GH�F�OGXU��GH� SkQ�� OD� �� RUL�� (VWH� QHFHVDU� V�� VH� IDF�� XQ� FDOFXO� JD]RGLQDPLF� DO� FD]DQXOXL� SHQWUX�WRDWH�FRQGL LLOH�SRVLELOH�GH�IXQF LRQDUH� $U]�WRUXO�HVte format dintr-XQ�JUXS�GH�HOHPHQWH�GH�DU]�WRU�DWPRVIHULF��DVIHO�F��Y�]XW��GH�VXV��IODF�UD�DSDUH�FD�XQ�FRYRU�GH�PLFL�IO�F�UL�LQGLYLGXDOH�FDUH�VH�XQHVF�vQWU-o ]RQ��GH�DUGHUH�FRPXQ��FX�VXSUDID D�HJDO��SUDFWLF�FX�VHF LXQHD�FDPHUHL�GH�DUGHUH� Pentru a rezisWD�WHPSHUDWXULORU�vQDOWH�GLQ�FDPHUD�GH�DUGHUH�SHUH LL�IRFDUXOXL�VXQW�U�FL L�FX�DSD�GH�DOLPHQWDUH�D�FD]DQXOXL�� ÌQ� FRQWLQXDUHD� FDPHUHL� GH� DUGHUH� SH� YHUWLFDO�� VH� J�VHúWH� IDVFLFROXO� GH� HYL�QHWHGH��VWU�E�WXW� OD� LQWHULRU�GH�JD]HOH�GH�DUGHUH��FDUH�DUH�UROXO�GH sistem convectiv al FD]DQXOXL�� ÌQ� DFHVW� FRQYHFWLY�� JD]HOH�GH� DUGHUH� FHGHD]�� DSHL� F�OGXUD� vQ� LQWHUYDOXO�GH�WHPSHUDWXUL� GH� OD� WHPSHUDWXUD� FDS�WXOXL� FDPHUHL� GH� DUGHUH� � Wf la temperatura de evacuare tFRú��HYLOH�FDUH�DOF�WXLHVF�VLVWHPXO�FRQYHFWLY�VXQW� HYL�RELúQXLWH�GH�R HO�FX�diametrul interior 35 ÷��PP��HYLOH�VWDQGDUG�X]XDOH�VXQW:

φ 42 x 3 ; φ 48 x 3,5 ; φ 54 x 4. 3DVXO� GH� DúH]DUH� D� HYLORU� vQ� VHF LXQH� HVWH� DOHV� DVWIHO� FD� JURVLPHD�PLQLP�� GH�PHWDO�vQWUH�GRX�� HYL�V��ILH��÷ 15 mm. 1XP�UXO�GH� HYL�VH�DOHJH�DVWIHO�FD�V��VH�RE LQ��R�DúH]DUH�XQLIRUP��D� HYLORU�SH�VHF LXQH��1XP�UXO�X]XDO�GH� HYL�HVWH�GDW�vQ�WDEHO�

N -�QXP�U�GH� HYL PRG�GH�DúH]DUH 3 triunghi echilateral 7 R� HDY��FHQWUDO��úL�� HYL�SH�XQ�KH[DJRQ 12 WUHL� HYL�SH�XQ�WULXQJKL�HFKLODWHUDO�FHQWUDO�úL�� HYL�SH�XQ�FHUF 19 ��KH[DJRDQH�FX�R� HDY��FHQWUDO�� HYL�SH�SULPXO�KH[DJRQ�úL�

�� HYL�SH�DO�GRLOHD�KH[DJRQ $SD� UHFH� LQWU�� OD� FDS�WXO� LQIHULRU� DO� FD]DQXOXL�� $SD� FDOG�� LHVH� SH� XQ� úWX � OD�SDUWHD�VXSHULRDU��D�FD]DQXOXL�úL�HVWH�WULPLV��OD�Fonsumatori .

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

125

&D]DQXO� HVWH� L]RODW� WHUPLF� FX� YDW�� PLQHUDO�� úL� SURWHMDW� OD� H[WHULRU� FX� WDEO��VXE LUH��6H�RE LQH�DVWIHO�XQ�FD]DQ�PRQREORF��FX�GLPHQVLXQL�UHGXVH�vQ�UDSRUW�FX�VDUFLQD�WHUPLF��SURGXV��úL�FX�R�UH]HUY��UHODWLY�PDUH�GH�DS��FDOG�� 3.7.2. Tema de proiectare

Prin tema de proiectare se dau : - Q –�VDUFLQD�WHUPLF��D�FD]DQXOXL��vQ�N:�� - te / ti –�WHPSHUDWXUD�DSHL�OD�LHúLUH�úL�LQWUDUH�vQ�FD]DQ�� - QDWXUD�úL�FRPSR]L LD�FRPEXVWLELOXOXL��JD]�QDWXUDO�VDX�G.P.L.) .

Aceste cazane, cu depresiune în focar, au coeficientul de exces de aer relativ PDUH� GDWRULW�� VLVWHPXOXL� DXWRDVSLUDQW� FDUH� QX� DVLJXU�� R� EXQ�� RPRJHQHL]DUH� D�combustibilului cu aerul:

α = 1,4 ÷ 1,8.

&RQIRUP� LQGLFD LLORU� GLQ� FDSLWROXO� �� VH� HIHFWXHD]�� FDOFXOXO� DUGHULL�FRPEXVWLELOXOXL�úL�VH�GHWHUPLQ��Vo, Vgo, Hi, OH2

p , 2ROp ��VH�WUDVHD]��GLDJUDPD�,�– t sau

cp – t . 3.7.��&DOFXOXO�UDQGDPHQWXOXL�WHUPLF�DO�FD]DQXOXL�úL�D�GHELWXOXL�GH�FRPEXVWLELO� $FHVWH� FD]DQH� IXQF LRQHD]�� GH� UHJXO�� FX� FRPEXVWLELO� JD]RV� �JD] natural sau G.P.L.) deci pierderile specifice mecanice (qmec�� úL� FHOH� SULQ� HYDFXDUHD� SURGXVHORU�solide din cazan (qcen) sunt nule. De asemenea B* = B . 6H�FDOFXOHD]��SLHUGHULOH�VSHFLILFH�GH�F�OGXU�� a). 3ULQ�HYDFXDUHD�JD]HORU�GH�DUGHUH�SH�FRú��TFRú) :

)II(H

qacos

i

cos 0

1 α−= (3.294)

6H�DGPLWH��LPSXQH��R�WHPSHUDWXU��DSUR[LPDWLY��D�JD]HORU�GH�DUGHUH�OD�FRú�� C)(

ttt ei

cos

080602

÷++

= (3.295)

úL�GLQ�GLDJUDPD�,�–�W�VH�GHWHUPLQ��IFRú . Pentru temperatura aerului (ta ≅ 20 0&�� VH� FDOFXOHD]� entalpia aerului teoretic necesar arderii :

apaoa tcVI ⋅⋅=0 (3.296)

cu cpa = 1,297 kJ/ Km3N �F�OGXUD�VSHFLILF��D�DHUXOXL�OD��0C .


CAZANE

126

b). PULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��FKLPLF��(qch) : 3HQWUX�DU]�WRDUH�DWPRVIHULFH�FX�RPRJHQHL]DUH�GH�FDOLWDWH�VODE��

qch = 0,005 c). 3ULQ�SHUH L�H[WHULRUL�DL�FD]DQXOXL (qext) :

Pentru cazane mici, în faza de proiectare se poate adopta : qext = 0,005÷0,008.

Randamentul cazanului�VH�FDOFXOHD]��FX�UHOD LD�� )qqq( extchcos ++−= 1η �úL� ηη ⋅= 100% (%) (3.297)

Debitul de combustibil va fi :

iH

QB

η= ( s/m3

N ) (3.298)

3.7.��%LODQ XO�GH�DQVDPEOX�DO�FD]DQXOXL )OX[XO�GH�F�OGXU��XWLO�DO�FD]DQXOXL�HVWH�� Q ;

)OX[XO�GH�F�OGXU��DGXs de combustibil : Qcomb = B ⋅ Hi ;

)X[XO�GH�F�OGXU��DGXV�GH�DHUXO�GH�DUGHUH�� Qa = B ⋅ α ⋅cpa ⋅ ta ;

)X[XO�GH�F�OGXU��SLHUGXW�OD�FRú�� QFRú = B ⋅ IFRú ; )X[XO�GH�F�OGXU��SLHUGXW�SULQ�DUGHUH�LQFRPSOHW�� Qinc = qch ⋅ B ⋅ Hi .



Fluxuri utile

Qcomb

Qa

- QFRú - Qinc

- Qext

Q

∑ = 'QQ ''QQ∑ =

(URDUHD�UHODWLY��

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

127

%'Q

"Q'Q1100 <⋅

−=ε (3.299)

'LQ� WDEHOXO� �� VH� SRDWH� VFULH� VXE� IRUP�� H[SOLFLW�� SLHUGHUHD� GH� F�OGXU�� OD�evacuarea gazelor�GH�DUGHUH�OD�FRú�:

-Qev = –qFRú· B· Hi = -B· IFRú�+ B· α· Vo · cpa · ta = - QFRú + Qa . 3.7.��&DOFXOXO�WHPSHUDWXULORU�úL�HQWDOSLLORU�JD]HORU�GH�DUGHUH�SH�WUDVHX� (QWDOSLD�WHRUHWLF��D�JD]HORU�GH�DUGHUH�VH�FDOFXOHD]��FX�UHOD LD�� apachit tcV)q(HI 01 α+−= (3.300)

Din digrama I –�W�VH�GHWHUPLQ��WHPSHUDWXUD�WHRUHWLF��GH�DUGHUH�� ),I(ft t α= .

6H�LPSXQH��DOHJH��WHPSHUDWXUD�OD�LHúLUHD�JD]HORU�GH�DUGHUH�GLQ�IRFDU��Wf = 900 ÷ 1100 0C . Valorile acestea sunt specifice cazanelor cu focare mici� U�FLWH�� /D� DFHVWH�FD]DQH�VXSUDID D�GH�UDGLD LH�vQ�IRFDU�HVWH�VXSUDID D�ODWHUDO��úL�FHD�D�VHF LXQLL�VXSHULRDUH�D�FDPHUHL�GH�DUGHUH�XQGH�SDUWHD�LQIHULRDU��D�FRUSXOXL�FD]DQXOXL�FX�IDVFLFROXO�FRQYHFWLY�SULPHúWH�F�OGXU��úL�SULQ�UDGLD LH��

Din diagrama I –�W��VH�GHWHUPLQ��HQWDOSLD�JD]HORU�GH�DUGHUH�OD�LHúLUHD�GLQ�IRFDU��tt = f (It, α). )OX[XO�GH�F�OGXU��SUHOXDW�SULQ�UDGLD LH�vQ�IRFDU�YD�IL��

)II(B)q(Q ftextR −−= 1 (kW) (3.301)

)OX[XO�GH�F�OGXU��SUHOXDW�GH�VLVWHPXO��convectiv va fi :

,QQQ Rc −= (3.302)

(QWDOSLD�JD]HORU�GH�DUGHUH�OD�VIkUúLtul drumului convectiv este:

B)q(

QII

ext

cfc −

−=1

(3.303)

úL�GLQ�GLDJUDPD�,�–�W�UH]XOW��WHPSHUDWXUD��tc = f (Ic, α).

ÌQFKLGHUHD�ELODQ XOXL�LPSXQe : Ic ≅ IFRú�úL�tc ≅ tFRú��úL�VH�DGPLW�HURULOH�UHODWLYH�� 100

t

ccos

II

II −=ε � 0,5%


CAZANE

128

D h

100t

ccos

tt

tt −=ε � 0,5% (3.304)


'HELWHOH�GH�F�OGXU��QR, Qc, Qa, Qcomb úL�IOX[XULOH�SLHUGXWH�QFRú, Qinc, Qext

se transpun JUDILF�DO�VFDU��FD�vQ�ILJXUD��FX�B* = B; Qpa = 0; Qsfc = 0; Qsi = 0;

Qec= 0; qmec� ��úL�qcen = 0) .

3.7.7. Calculul termic al focarului

)RFDUXO�GH�WLS�FDPHU��DUH�XUP�WRDUHOH�GLPHQVLXQL�FRQIRUP�ILJ��3.20.

f

Fig. 3.20. Dimensiunile focarului.

$FHVW� FDOFXO� DUH� FD� VFRS� GHWHUPLQDUHD� WHPSHUDWXULL� ILQDOH� D� IRFDUXOXL�� LQkQG�VHDPD�GH� IDSWXO� F�� VXSUDID D�HIHFWLY�� GH� UDGLD LH�SR� HVWH�VXSUDID D�VHF LXQLL�FRUSXOXL�cazanului�SOXV�VXSUDID D�ODWHUDO��D�IRFDUXOXL. Acest lucru este evLGHQW�GHRDUHFH�UDGLD LD�HPLV�� GH� IRFDU� VSUH� SDUWHD� VXSHULRDU�� D� FDPHUHL� GH� DUGHUH� HVWH� LQWHJUDO� DEVRUELW�� GH�SDUWHD�YL]LELO��D�FRUSXOXL�FD]DQXOXL�úL�VLVWHPXOXL�FRQYHFWLY��GHFL�GH�vQWUHDJD�VHF LXQH�D�canalului de gaze:

4

2D

hDS fR

⋅+⋅⋅=

ππ (m2) (3.305)

Gradul de ecranare

=

per

R

S

SΨ � DO� IRFDUXOXL� UH]XOW�� GLQ� UDSRUWXO� GLQWUH�

VXSUDID D�SHUH LORU�FDPHUHL�GH�DUGHUH�úL�VXSUDID D�HIHFWLY��GH�UDGLD LH��SR .

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

129

)RFDUXO� � DUH� IRUPD� JHRPHWULF�� FLOLQGULF�� FX� GLDPHWUXO�D� úL� vQ�O LPHD�hf din figura 3.20�� 3HQWUX� GHVYROWDUHD� FRPSOHW�� D� IO�F�ULL�� DVWIHO� FD� VIkUúLWXO� SURFHVXOXL� GH�DUGHUH�V��QX�GHS�úHDVF��vQ�O LPHD�IRFDUXOXL��VH�LD�vQ�O LPHD�IRFDUXOXL:

hf = 0,25÷0,35 m. 5H]XOW��XUP�WRDUHOH�GLPHQVLXQL�DOH�IRFDUXOXL�

- volumul focarului 4

2D

hV ff

π= (m

3)

-�VXSUDID D�SHUH LORU�� 4

22

DDhS fper

ππ += (m2)

-�VXSUDID D�HIHFWLY��GH�UDGLD LH�� 4

2D

DhS fR

ππ += (m2)

- gradul de ecranare per

R

S

S=Ψ

- grosimea stratului radiant : per

f

S

V,s 63= (m)

Se caOFXOHD]�� vQ� FRQWLQXDUH� FDUDFWHULVWLFD� UDGLDQW�� D� JD]HORU� GH� DUGHUH� � GLQ�focar:

)pp(T

,s)pp(

p,,k ROOH

f

ROOH

OH

g 22

22

2

10003801

6180+

−

+

+= (3.306)


sk

ggea

⋅−−=1 (3.307)

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IO�F�ULL�FX�UHOD LD�DSUR[LPDWLY�� 50

100061 ,

T,k

f

fl −= (3.308)


sk

flflea

⋅−−= 1 (3.309)

3RQGHUHD�DEVRUE LHL�IO�F�ULL�FX�FHD�D�PHGLXOXL�UDGLDQW�GH�JD]H�GH�DUGHre se face

GXS��FULWHULL�experimentale, considerând o pondere β�D�S�U LL�OXPLQRDVH�D�IO�F�ULL� 3HQWUX�IO�F�UL��SX LQ�OXPLQRDVH�GH�FRPEXVWLELO�JD]RV se poate considera:


CAZANE

130

� = 0,2 &RHILFLHQWXO�GH�DEVRUE LH�DO�IO�F�ULORU�úL�JD]HORU�GH�DUGHUH�HVWH�GDW�GH�UHOD ia :

gfl aaa )1( ββ −+⋅= (3.310)

&RHILFLHQWXO�GH�PXUG�ULUH�D�VXSUDIH HORU�HVWH�� ξ=0,7 ÷ 0,9 , pentru combustibil gazos. &X�DFHVWH�YDORUL�VH�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IRFDUXOXL�� ξΨ)a(a

a,a f −+

⋅=

1

820 (3.311)

2�DOW��FDUDFWHULVWLF��D�IRFDUXOXL�HVWH�IDFWRUXO�GH�SR]L LH�D�IO�F�ULL�vQ�IRFDU��

f

MMh

bbaM

*

−= (3.312)

XQGH� SHQWUX� FRPEXVWLELO� OLFKLG� VDX� JD]RV� úL� SHQWUX� IRFDUH� YHUWLFDOH� FX� IODF�U�� SH�VXSUDID D�LQIHULRDU�� cu : aM=0,54; bM=0,2; b*/hf = 0,2 –�vQ�O LPHD�UHODWLY��D�IO�F�ULL� &X�DFHVWH�GDWH�VH�GHWHUPLQ��WHPSHUDXUD�GH�OD�FDS�WXO�IRFDUXOXL:

( ) 11

6,03

+

⋅⋅−

⋅⋅⋅⋅=

pginc

Rtfo

t

f

cVBq

STaCM

TT

ξ [oK] (3.313)

7HPSHUDWXUD�GH�LHúLUH�D�JD]HORU�GH�DUGHUH�GLQ�IRFDU��vQ�oC, este : tf = Tf -273 [oC] $FHDVW��WHPSHUDXWU��YD�IL�GLIHULW��GH�Wf �DOHDV��vQ�FDOFXOXO�GH�DSUR[LPDUH��'DF��GLIHUHQ D�HVWH�PDL�PDUH�GH��FFD��.��VH�UHLD�FDOFXOXO�FX�YDORDUHD�Wf��UH]XOWDDW��GLQ� FDOFXOXO� ILQDO�� 'DF�� HURDUHD� HVWH�PDL�PLF�� VH� FRQWLQX�� FDOFXOXO� FX� WHPSHUDWXUD�focarului tf rezuOWDW�� GLQ� FDOFXO� úL� QX� VH�PDL� UHLD� FDOFXOXO� WUDQVIHUXOXL� GH� F�OGXU�� OD�VXSUDID D�GH�UDGLD LH� 3.7.9. Calculul termic al drumului convectiv

�HYLOH�VXQW�GLVSXVH� vQ� LQWHULRUXO�FRUSXOXL�FD]DQXOXL��DúD�FXP�se poate observa în fig.3.19.

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

131

Drumul convectiv esWH� GHWHUPLQDW� GLQ� FDOFXOHOH� DQWHULRDUH� SULQ� XUP�WRULL�parametrii : Qc –�GHELWXO�GH�F�OGXU��FHGDW�GH�JD]HOH�GH�DUGHUH��N:�� tf –�WHPSHUDWXUD�JD]HORU�GH�DUGHUH�OD�LQWUDUH�vQ� HYL��0C) ;

tFRú –�WHPSHUDWXUD�JD]HORU�GH�DUGHUH�OD�LHúLUHD�GLQ� HYL��OD�FRú) ; te /ti – temperatura apei (0C) .

3HQWUX� VWDELOLUHD� VHF LXQLL� GH� WUHFHUH� D� JD]HORU� GH� DUGHUH� VH� DOHJH� GLDPHWUXO� HYLORU�GUXPXULORU�FRQYHFWLYH�GLQ�JDPD�GH� HYL�X]XDOH�SHQWUX�FD]DQHOH�GH�DS��FDOG��

φ 42 x 3 di = 36

φ 48 x 3,5 di = 41

φ 54 x 4 di = 46

φ 60 x 4 di = 52

6H� FDOFXOHD]�� QXP�UXO� GH� HYL� 1t� GLQ� FRQGL LD� FD� YLWH]D�PHGLH� D� JD]HORU� GH�DUGHUH�V��ILH��wg = 1,5 ÷ 3 m/s

Debitul de gaze de ardere, la temperatura medie din convectiv 2

costtt

f

gm

+= , este:

273

273+⋅= gm

gg

tVBD (Nm3/s) (3.314)

6HF LXQHD�QHFHVDU��GH�FXUJHUH�

g

g

cw

DS = (m2) (3.315)

1XP�UXO�preliminar GH� HYL�

2

4

i

c'

td

SN

⋅=

π (3.316)

DSRL� VH� URWXQMHúWH� SDVXO� s1 al HYLORU� DVIHO� vQFkW� QXP�UXO� �11� V�� ILH� XQ� QXP�U� vQWUHJ�acceSWDELO�SHQWUX�DúH]DUHD�DOHDV��1t = 3, 7, 12, 19 etc.) 6H� FDOFXOHD]�� DSRL� YLWH]D� JD]HORU� vQ� VHF LXQHD� OLEHU�� GH� WUHFHUH� D� JD]HORU� GH�DUGHUH�SHQWUX�QXP�UXO�ILQDO�GH� HYL�DOHV��Nt .

2

4

it

g

gdN

Dw

⋅⋅=

π (m/s) (3.317)


CAZANE

132

Pentru temperatura media a gazelor de ardere tgm� VH� GHWHUPLQ�� GLQ� anexa 9, XUP�WRDUHOH�YDORUL��

- YkVFR]LWDWHD�FLQHPDWLF� ν (m2/s)



6H� FDOFXOHD]�� FRHILFLHQWXO� GH� VFKLPE�GH� F�OGXU��(αc) pentru curgerea gazelor GH�DUGHUH�vQ�LQWHULRUXO� HYLORU�

ÌQ�DFHVW�FD]�OXQJLPHD�FDUDFWHULVWLF��YD�IL�GLDPHWUXO�LQWHULRU�DO� HYLL� di Criteriul hidrodinamic este:

νidw

Re⋅

= (3.318)

3HQWUX�FXUJHUHD�IOXLGHORU�SULQ�LQWHULRUXO� HYLORU�UHOD LLOH�FULWHULDOe de transfer de F�OGXU��VXQW��

* pentru Re > 10000

PrRe.Nu,, 40800240 ⋅⋅= (3.319)

* pentru 2300 < Re < 10000

PrRe.Nu Re

,, ε⋅⋅⋅= 40800240 (3.320)

unde 0Re = 1- 6.105.Re-1,8

* pentru Re < 2300

PrReLt

d,

PrReLt

d,

,Nu,

i

i

660

04501

06880653

⋅⋅⋅+

⋅⋅

⋅

+= (3.321)

Lungimea Lt a tevilor se ia Lt §��· di � úL� OD� DFHVW� RUGLQ�GH�P�ULPH�GH�YDORUL�LQIOXH D�OXQJLPLL� HYLL�DVXSUD�OXL��Nu��HVWH�QHJOLMDELO��

5H]XO��i

cd

Nu λα ⋅= (3.322)

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

133

Coeficientul de schimb GH�F�OGXU��SULQ�UDGLD LH�HVWH�GHWHUPLQDW�GH�P�ULPLOH�

- WHPSHUDWXU��PHGLH�D�JD]HORU�GH�DUGHUH�� Tgm=tgm+273 (K); - grosimea stratului radiant: s = 0,9 di (m);

- SUHVLXQLOH�SDU LDOH�DOH�JD]HORU�GH�DUGHUH�WULDWRPLFH��2ROp ; OHp

2

g

g

RO

RO pV

Vp 2

2= [bar�@��úL�� g

g

OH

OH pV

Vp 2

2= [bar.] (3.323)

&RQVWDQWD�GH�UDGLD LH�D�JD]HORU�VH�GHWHUPLQ��FX�UHOD LD�

)(1000

38,01)(

6,18,022

22

2

ROOH

gm

ROOH

OHpp

T

spp

pkg +

−

+

+= (3.324)


sk

ggea⋅−−= 1 (3.325)

&RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH�VH�GHWHUPLQ��FX�UHOD LD�

−

−

+⋅= −

gm

p

gm

p

gmg

p

r

T

T

T

T

Taa

1

1

2

110765,5

6,3

38α (W/m2K) (3.326)

XQGH�SHQWUX� FRHILFLHQWXO� GH� DEVRUE LH� DO�SHUHWHOXL�GH� VFKLPE�GH�F�OGXU�� VH� FRQVLGHU��valoarea ap �� HDY��WUDV��GH�R HO��LDU�SHQWUX�WHPSHUDWXUD�DEVROXW��D�SHUHWHOXL� HYLL� 27320tT mp ++= (K)

&RHILFLHQWXO�GH�WUDQVIHU�GH�F�OGXU��SH�SDUWHD�JD]HORU�GH�DUGHUH�YD�IL� α1 = αc + αr (3.327) CoeILFLHQWXO� GH� WUDQVIHU� GH� F�OGXU��α2 pe partea apei, este mult mai mare (de ordinul miilor de W/m2.��vQ�FRPSDUD LH�FX�α1 (de ordinul zecilor de W/m2K). ÌQ� DFHVWH� FRQGL LL� FRHILFLHQWXO� JOREDO� GH� WUDQVIHU� GH� F�OGXU�� ´k” este dat de UHOD LD�

1

1

1 εαα

+=Ik (W/m2K) (3.328)


CAZANE

134

S SC

t

tma

tf

tc

∆tmax

∆tmin

în care s-a neglijat UH]LVWHQ D�WHUPLF��1/α2).

9DORULOH� FRHILFLHQWXOXL� GH� PXUG�ULUH� ε pentru gaze de ardere, provenite din arderea de combustibil gazos, sunt prezentate în tabelul XUP�WRU�

&RHILFLHQWXO�GH�PXUG�ULUH�– combustibil gazos

Viteza w (m/s) 3 6 9 12 15 18 ε ⋅103 (m2K/W) 5,233 3,837 2,791 2,093 1,628 1,395

6H�SRDWH�XWLOL]D�úL�UHOD LD�DQDOLWLF�� 647403102111 ,w, −− ⋅⋅=ε (m2K/W) (3.329) Pentru gaze de ardere provenind din arderea unui combustibil lichid se poate considera: 0163,0≅ε (m2K/W) (3.330) 'LIHUHQ D�PHGLH�GH�WHPSHUDWXU��VH�GHWHUPLQ��FRQIRUP�ILJXULL��21��úL�UHOD LHL��331):

min

max

minmaxm

t

tln

ttt

∆∆

∆∆∆ −= (3.331)

6XSUDID D� GH� VFKLPE� GH� F�OGXU�� D�convectivului cazanului va fi:

cit

m

cc LdN

tk

QS ⋅⋅⋅== π

∆ (m2).

(3.332)

RezuOW��OXQJLPHD�FRQYHFWLYXOXL�

it

cc

dN

SL

⋅⋅=

π(m) (3.333)

Fig. 3.21.

Lungimea Lc�VH�URWXQMHúWH�OD�o valoare�vQWUHDJ��GH�FP��

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

135

INTENSIFICAREA TRANSFERULUI DE Cü/'85ü�&8�785%8/,=$725,

'DF�� OXQJLPHD� HYLORU� UH]XOW�� SUHD�PDUH� �FRQVWUXFWLv L/D = 3 ÷ 4 ) se poate P�UL�FRHILFLQWXO�GH�VFKLPE�GH�F�OGXU��FRQYHFWLY��.c �SULQ�LQWURGXFHUHD�vQ� HYL�D�XQRU�turbulizatori.

&HL�PDL�XWLOL]D L�VXQW�WXUEXOL]DWRULL�EDQG��vQGRLW��VDX�WXUEXOL]DWRULL�HOLFRLGDOL� 7XUEXOL]DWRULL� GH� WLS� EDQG�� vQGRLW�� SURGXF� R intensificare mai mare a

WUDQVIHUXOXL�GH�F�OGXU��OD�DFHLDúL�FUHúWHUH�GH�SLHUGHUH�GH�VDUFLQ��FX�WXUEXOL]DWRULL�GH�WLS�EDQG��HOLFRLGDO��

6FKHPD�WXUEXOL]DWRUXOXL�FX�EDQG��RQGXODW��HVWH�GDW��vQ�ILJ��3.22.

fig. 3.22 Schema turbulizatorului din�EDQG��RQGXODW��

Intensificarea� WUDQVIHUXOXL� GH� F�OGXU�� SULQ� FRQYHF LH� VH� GHILQHúWH� FD� UDSRUWXO��,� � .int� �.� � vQWUH� WUDQVIHUXO� GH� F�OGXU�� FX� WXUEXOL]DWRU� úL� WUDQVIHUXO� GH� F�OGXU�� I�U��turbulizator. Pentru regim laminar de curgere (Re < 2300) coeficientul de intensificare a VFKLPEXOXL�FRQYHFWLY�GH�F�OGXU��HVWH�QXPDL�IXQF LH�GH�SDVXO�UHODWLY��prel :

p

di

p

di

pasul relativ: prel = p / di UH]XOW� prel = 1,41 · �WJ��

� di · cos45

0


CAZANE

136

30

1422,

rel

int

p

,I ==

αα

(3.334)

Pasul relativ este dat în fig. 3.22.

Pierderile relative de sarciQ��LQGXVH�GH�WXUEXOL]DWRU�VXQW�

ûSrel� �ûS��ûS0 = 6,53 (3.335) În tabelul XUP�WRU�VH�GDX�FkWHYD�YDORUL�SHQWUX�JUDGXO�GH�LQWHQVLILFDUH�úL�SHQWUX SLHUGHULOH�UHODWLYH�GH�VDUFLQ��IXQF LH�GH�θ.

----------------------------------------------------------------------------------------

� prel I ûprel � prel I ûprel

---------------------------------------------------------------------------------------- 90 1.41 1,93 6,53 125 2,72 1,59 6,53

95 1.54 1,88 6,53 130 3,03 1,54 6,53

100 1,69 1,83 6,53 135 3,41 1,48 6,53

105 1,84 1,78 6,53 140 3,89 1,43 6,53

110 2,02 1,73 6,53 145 4,49 1,37 6,53

115 2,22 1,69 6,53 150 5,28 1,30 6,53

120 2,45 1,63 6,53 155 6,38 1,23 6,53

160 8,02 1,14 6,53

------------------------------------------------ 6H� UHPDUF�� R� LQWHQVLILFDUH� D� WUDQVIHUXOXL� GH� F�OGXU�� DSURDSH� GH� Gublare

(la � = 90o��GDU�úL�R�SLHUGHUH�GH�VDUFLQ��PDL�PDUH�GH��RUL� 'H� UH LQXW� F�� R� PLFúRUDUH� D� XQJKLXOXL� GH� vQGRLUH� D� SODWEDQGHORU� GXFH� OD� R�

FUHúWHUH� D� � WUDQVIHUXOXL� GH� F�OGXU�� GDU� QX� úL� OD� R� FUHúWHUH� D� SULHUGHULORU� GH� VDUFLQ��DILUPD LH�YDODELO��vQ�GRPHQLXO�H[SHULPHQWDW�GH�XQJKL�GH�vQGRLUH�� ÷ 1600 ). Pentru regim tranzitoriu de curgere (2300 <Re < 10000) coeficientul de LQWHQVLILFDUH�D�VFKLPEXOXL�FRQYHFWLY�GH�F�OGXU��HVWH�IXQF LH�GH�SDVXO�UHODWLY��Srel�úL�GH�criteriul Re:

5

33 20

261

,

,

rel

int Re

p

,I −==

αα

(3.336)

3LHUGHULOH�UHODWLYH�GH�VDUFLQ��LQGXVH�GH�WXUEXOL]DWRU�VXQW�

ûSrel� �ûS��ûS0 = 10350

17,,

rel ReP (3.337)

În XUP�WRUXO�WDEHO�VH�GDX�FkWHYD�YDORUL�SHQWUX�JUDGXO�GH�LQWHQVLILFDUH�úL�SHQWUX�piHUGHULOH�UHODWLYH�GH�VDUFLQ��

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

137

� prel Re I ûSrel � prel Re I ûSrel

90 1.41 3000 2,02 7,25 95 1.54 3000 1,96 7,15 4000 1,97 7,04 4000 1,90 6,94 5000 1,92 6,89 5000 1,85 6,80 6000 1,88 6,76 6000 1,80 6,67

100 1.69 3000 1,89 7,05 105 1.84 3000 1,82 6,96 4000 1,83 6,86 4000 1,76 6,77 5000 1,78 6,71 5000 1,71 6,62 6000 1,74 6,58 6000 1,68 6,50

110 2,02 3000 1,76 6,87 115 2,22 3000 1,69 6,77 4000 1,70 6,67 4000 1,63 6,58 5000 1,65 6,53 5000 1,58 6,44 6000 1,61 6,41 6000 1,54 6,32

120 2,45 3000 1,62 6,67 125 2,72 3000 1,55 6,57 4000 1,56 6,48 4000 1,49 6,38 5000 1,52 6,34 5000 1,44 6,24 6000 1,47 6,23 6000 1,41 6,13

130 3,03 3000 1,48 6,46 135 3,41 3000 1,41 6,35 4000 1,42 6,28 4000 1,35 6,17 5000 1,37 6,14 5000 1,30 6,03 6000 1,33 6,03 6000 1,26 5,92

140 3,89 3000 1,33 6,23 145 4,49 3000 1,24 6,09 4000 1,27 6,05 4000 1,18 5,92 5000 1,22 5,92 5000 1,14 5,79 6000 1,18 5,81 6000 1,09 5,69

150 5,28 3000 1,15 5,95 155 6,38 3000 1,05 5,78 4000 1,09 5,78 4000 1,00 5,62 5000 1,04 5,65 5000 1,00 5,49 6000 1,00 5,55 6000 1,00 5,39

160 8,02 3000 1,00 5,59 4000 1,00 5,43 5000 1,00 5,31 6000 1,00 5,21

,QWHQVLILFDUHD� WUDQVIHUXOXL�GD�F�OGXU��FRQYHFWLY�HVWH�FHD�PDL�PDUH� vQ�UHJLm de FXUJHUH� ODPLQDU� úL� HILFDFLWDWHD� VFDGH� FX� FkW� WXUEXOHQ D� HVWH�PDL� ULGLFDW��$SDUH� DVIHO�UHJXOD�GH�FDUH�WUHEXLH�V��VH� LQ��VHDPD�WRWGHDXQD��SURPRWRULL�GH�WXUEXOHQ ��QX�VXQW�HILFDFH�vQ�UHJLPXUL�GH�WXUEXOHQ ��ULGLFDW�� ÌQ� UHJLPXUL�GH� WXUEXOHQ �� ULGLFDW��promotorii nu fac altceva decât V� P�UHasc� semnificativ�SLHUGHULOH�GH�VDUFLQ�� 2� DOW�� UHJXO�� HVWH� F�� XWOL]DUHD� SURPRWRULORU� GH� WXUEXOHQ �� GXFH� WRWGHDXQD� OD�FUHúWHUHD� SLHUGHULORU� GH� VDUFLQ�� vQ� FRQVHFLQ �� calculul gazodinamic al cazanului

WUHEXLH�V��YHULILFH�GDF��WLUDMXO�SHUPLWH�LQWURGXFHUHD�SURPRWRULORU�GH�WXUEXOHQ �.


CAZANE

138

3.8��&D]DQH�DFYDWXEXODUH�GH�DS��ILHUELQWH�GH�WLS�&$)� 3.8.1. 'HVFULHUHD�FD]DQHORU��HOHPHQWH�FRPSRQHQWH��PRG�GH�IXQF LRQDUH� 6XQW�FD]DQH�GH�UDGLD LH�FX�SXWHUL�WHUPLFH�PDUL�úL�XWLOL]HD]��FRPEXVWLELOL�OLFKL]L�úL�JD]RúL� &D]DQXO�HVWH�GHVWLQDW�SURGXFHULL�GH�DS��ILHUELQWH�vQ�UHJLP�GH�ED]��0C sau în regim de vârf 110 / 150 0&�� 6XQW� FD]DQH� PRGHUQH� FX� SHUH L� PHPEUDQ��DOLPHQWDWH�FX�DU]�WRDUH�SH�GRL�SHUH L�RSXúL�úL�VXSUDSUHVLXQH�vQ�IRFar. 'UXPXULOH�GH�JD]H�VXQW�GLVSXVH�SH�YHUWLFDO�� /D� FD]DQHOH� PDUL� �4� !� �� 0:�� VHF LXQHD� IRFDUXOXL� HVWH� PHQ LQXW�� úL� FD�VHF LXQH� D� GUXPXOXL� FRQYHFWLY��/D� FD]DQHOH�PDL�PLFL�GXS�� IRFDU�DSDUH�R� vQJXVWDUH�D�drumului de gaze. 6FKHPD�FRQVWUXFWLY��D�FD]DQXOXL�HVWH�GDW��vQ�ILJXUD�3.23.

Fig. 3.23. Cazan CAF ��DU]�WRU��IRFDU��FROHFWRU��IDVFLFXO�FRQYHFWLY��FROHFWRU�FRQYHFWLY��

��OHJ�WXU��OD�FRú��QHUYXUL��L]ROD LH�WHUPLF�

A A

B B

A - A

B - B

1

2

3

4 5

6

7

8

4

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

139

6LVWHPXO�FRQYHFWLY�FRQWLQX�� IRFDUXO�SH�YHUWLFDO�� úL�HVWH�IRUPDW�GLQ�SDQRXUL�GH�EXFOH�GH� HYL�FDUH�SRUQHVF�DOWHUQDWLY�GLQ�FROHFWRDUHOH�GH�SH�SHUHWHOH�GUHDSWD�úL�VWkQJD� 6ROX LD� FX� SHUHWH� PHPEUDQ�� HOLPLQ�� VROX LLOH� VFXPSH� úL� JUHOH� GH� vQ]LGLUH� úL�DVLJXU��un VFKLPE�GH�F�OGXU��SXWHUQLF�SULQ�UDGLD LH� &D]DQXO�QHFHVLW��R�VXSUDID ��PLF��GH�DúH]DUH�úL�VH�GH]YROW��PXOW�SH�YHUWLFDO�� 3.8.2. Tema de proiectare

3ULQ�WHPD�GH�SURLHFWDUH�VH�LPSXQ�XUP�WRDUHOH�GDWH�

- GHELWXO�GH�F�OGXU��DO�FD]DQXOXL� Q (kW) ; - WHPSHUDWXUD�DSHL�OD�LHúLUH�GLQ�FD]DQ�� te (

0C) ; - temperatura de intrare a apei în cazan: ti (

0C) ; - FRPEXVWLELO� FX� FRPSR]L LH� �ILH� XQ� FRPEXVWLELO� OLFKLG� ILH� XQ� FRPEXVWLELO�

gazos) - FD]DQ�FX�SHUH L�PHPEUDQ��vQ�FRQVWUXF LH�HWDQú��FX�VXSUDSUHVLXQH�vQ�IRFDU�

&D]DQXO�HVWH�GH� WLS�HWDQú�FX�SHUH L�PHPEUDQ�� vQ�FRQVHFLQ ��H[FHVXO�GH�DHU�QX�

VH�PRGLILF��SkQ��OD�FRú��'H�DOWIHO��dUXPXULOH�VXQW�vQ�VXSUDSUHVLXQH�úL�GHFL�QX�SRDWH�IL�vQ�QLFL�XQ�FD]�YRUED�GH�S�WUXQGHUL�GH�DHU�IDOV�GLQ�H[WHULRU�

Astfel în tot cazanul excesul de aer este α = 1,05 ÷ 1,15. &RQIRUP� LQGLFD LLORU� GLQ� FDSLWROXO� �� VH� HIHFWXHD]�� FDOFXOXO� DUGHULL�

FRPEXVWLELOXOXL��6H�GHWHUPLQ��VO, Vgo, Hi, OHp2

, 2ROp , Vg�úL�VH�WUDVHD]��GLDJUDPD�

I– t sau cp – t. 3.8��&DOFXOXO�UDQGDPHQWXOXL�WHUPLF�úL�D�GHELWXOXL�GH�FRPEXVWLELO 3HQWUX� FDOFXOXO� UDQGDPHQWXOXL� SH� FDOH� LQGLUHFW�� VH� FDOFXOHD]�� SLHUGHULOH�

VSHFLILFH�GH�F�OGXU�� a. 3LHUGHUHD��GH�F�OGXU��SULQ�HQWDOSLD�JD]HORU�OD�FRú� )LLQG� XQ� FD]DQ� GH� DS�� ILHUELQWH�� GHFL� FX� WHPSHUDWXU�� relativ MRDV�� D�agentului termic secundar, se DGPLWH�LQL LDO�R�WHPSHUDWXU��OD�FRú�GDW��GH�UHOD LD�GH�DSUR[LPDUH�: tFRú = tam + 80 ÷ 100 (0C); în care temperatura medie a apei este:

)(2

0 Ctt

t ie

am

+≅ (3.338)

Entalpia aerului de ardere stoichiometric� VH�FDOFXOHD]�� OD� WHPSHUDWXUD�DPELDQW�� ta = 20 0C úL� cpa = 1,2971 kJ/ Km3

N .

apaoa tcVI ⋅⋅=0 (3.339)


CAZANE

140

5H]XOW��SLHUGHUHD�VSHFLILF��OD�FRú� )(

101coscos a

i

IIH

q α−= (3.340)

b. 3LHUGHUHD�GH�F�OGXU��SULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��FKLPLF�� În� SURLHFWDUH� VH� DGPLWH� R� SLHUGHUH� SULQ� DUGHUHD� LQFRPSOHW�� FD]DQXO� ILLQG� FX�HFUDQDUH�SXWHUQLF�� 005,0=chq (3.341) c. 3LHUGHULOH� GH� F�OGXU�� SULQ� DUGHUH� LQFRPSOHW�� GH� QDWXU�� PHFDQLF�� úL� SULQ�HQWDOSLD�FHQXúLL Combustibilul nefiind de tip solid:

qmec = 0 úL� qcen = 0; (3.342) d. 3LHUGHULOH�GH�F�OGXU��SULQ�VXSUDID D�H[WHULRDU��D�FD]DQXOXL� )XQF LH�de debitul cazanului Q �0:��VH�FDOFXOHD]��

6569021061674 ,

MWext Q,q−−×= (3.343)

e. Randamentul cazanului

6H�FDOFXOHD]��FX�UHOD LD� )qqq( extchcos ++−= 1η (3.344) DSRL�VH�FDOFXOHD]��úL�YDORDUHD�SURFHQWXDO�� ηη ⋅= 100% (%) (3.345) f. Consumul de combustibil 6H�FDOFXOHD]��FX�UHOD LD�

iH

QB

η

310⋅= (3.346)

B*B = deoarece qmec = 0.

3.8��%LODQ XO�GH�DQVDPEOX�DO�FD]DQXOXL� )OX[XO�GH�F�OGXU��util al cazanului este: Q (MW)

Fluxul�GH�F�OGXU��DGXV�GH�FRPEXVWLELO: ic HBQ ⋅=

)OX[XO�GH�F�OGXU��DGXV�FX�DHUXO�GH�DUGHUH�� apao tcVBQ ⋅⋅⋅⋅= α

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

141

FlX[XO�GH�F�OGXU��SLHUGXW�OD�FRú� coscos IBQ ⋅=

)OX[XO�GH�F�OGXU��SLHUGXW�SULQ�DUGHUH�LQFRPSOHW�� ichinc HBqQ ⋅⋅=

)OX[XO�GH�F�OGXU��SLHUGXW�VSUH�H[WHULRU� iextext HBqQ ⋅⋅= 5H]XOW��WDEHOXO�GH�ELODQ �

Combustibil – pierderi Util

Qcomb

Qa

- QFRú - Qinc

- Qext

Q

∑ = 'QQ ''QQ∑ =

1RW�� ÌQ� DFHVW� ELODQ � �–q2BHi) s-a scris sub forma: (-BIFRú� + BαVocpata), deci

IRUPD�H[SOLFLW�� (URDUHD�UHODWLY��GH�vQFKLGHUH�D�ELODQ XOXL��va fi:

(%)100

'

"' ⋅−

=Q

QQε (3.347)

ùL�VH�YHULILF��HURDUHD�PD[LP��DGPLVLELO��GH�� 3.8��&DOFXOXO�WHPSHUDWXULORU�úL�HQWDOSLLORU�JD]HORU�GH�DUGHUH�SH�WUDVHX� (QWDOSLD�WHRUHWLF��GH�DUGHUH�VH�FDOFXOHD]��FX�UHOD LD� apachit tcV)q(HI 01 α+−= (3.348)

apoi sH�GHWHUPLQ��WHPSHUDWXUD�WHRUHWLF��GH�DUGHUH�GLQ�GLDJUDPD�I-t: ),I(ft tt α= . 6H�DOHJH�WHPSHUDWXUD�OD�FDS�WXO�IRFDUXOXL:

tf = 900 ÷ 1100 0C úL� VH� GHWHUPLQ� apoi, din diagrama I – t,� HQWDOSLD� JD]HORU� OD� FDS�WXO� IRFDUXOXL�� If = f(tf,α). Fluxul�GH�F�OGXU��SUHOXDW�SULQ�UDGLD LH�vQ�IRFDU�YD�IL� )II(B)q(Q ftextR −−= 1 (kW) (3.349)

)OX[XO�GH�F�OGXU��FDUH�VH�SUHLD�vQ�VLVWHPXO�FRQYHFWLY�HVWH�


CAZANE

142

,QQQ Rc −= cu Q exprimat în (kW) (3.350) (QWDOSLD�JD]HORU�GH�DUGHUH�OD�VIkUúLWXO drumului convectiv este:

B)q(

QII

ext

cfc −

−=1

(3.351)

úL�GLQ�GLDJUDPD�,�–�W�UH]XOW��WHPSHUDWXUD�OD�VIkUúLWXO�GUXPXOXL�FRQYHFWLY:

),I(ft cc α= (3.352) ÌQFKLGHUHD�ELODQ XOXL�LPSXQH� Ic = IFRú�úL�tc = tFRú úL�VH�DGPLW�HURULle relative:

(%)I

II

t

ccos 100−

=ε � 0,5%

(%)t

tt

t

ccos 100−

=ε � 0,5% (3.353)

(URUL�PDL�PDUL� LQGLF�� R� JUHúHDO�� GH� FDOFXO�� ÌQ� ILQDO� VH� vQWRFPHúWH� XUP�WRUXO�tabel:


Focar

Convectiv

QR

Qc

tc

tf

tf

tFRú 3.8��%LODQ XO�JUDILF�DO�FD]DQXOXL� 'HELWHOH�GH�F�OGXU��VH�WUDQVSXQ�JUDILF��OD�VFDU��GXS��PRGHOXO�JHQHUDO�SUH]HQWDW�în capitolul 2 fig. 2.3. (cu B*=B; QSI=QPA ��úL�Tmec=qcen=0). 3.8.7. Calculul termic al focarului

)RFDUXO�GH�WLS�FDPHU��GLQ�SHUHWH�PHWDOLF�FRQWLQXX�DUH�XUP�WRDUHOH�GLPHQVLXQL�

a

a

a

h

a

h

ϕ ϕ h

’ h

’

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

143

Fig. 3.24. Focarul unui cazan CAF

6H�FDOFXOHD]��VXSUDID D�SUHOLPLQDU��GH�UDGLD LH�vQ�IRFDU�FX�UHOD LD��

−

⋅

=−

44

3

100100107655 pf

R'

R

TT,

QS

ε (m2) (3.354)

cu ε = 0,65 pentru combustibil gazos

ε = 0,75 pentru combustibil lichid

Tf = tf +273 (0K)

Tp = tma +20+273 (0K) 2

eima

ttt

+=

XQGH� SHQWUX� WHPSHUDWXUD� SHUHWHOXL� HYLL� V-D� DGPLV� R� WHPSHUDWXU�� FX� �� 0C mai mare decât temperatura medie a fluidului interior.

Se poate calcula '

RS ��DGPL kQG�XQ�IOX[�UHODWLY�XQLWDU�q’R=30 ÷ 50 kW/m2

'

R

R'

Rq

QS = (m2) (3.355)

6XSUDID D�SHUH LORU�IRFDUXOXL�HVWH�

2

'2

cos42 aha

aahaS per +++=ϕ (3.356)

cu 010≅ϕ .

Grosimea stratului radiant de gaze de ardere este:

per

f

S

Vs ⋅= 4 (m) (3.357)

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�JD]HORU�GH�DUGHUH�GLQ�IRFDU� )(

100038,01

)(

6,18,022

22

2

ROOH

f

ROOH

OH

g ppT

spp

pk +

−

+

+=

6H�FDOFXOHD]��FRHILFLHQWXO�GH�DEVRUE LH�DO�JD]HORU�Ge ardere din focar :

sk

ggea

⋅−−=1 (3.358)

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IO�F�ULL�FX�UHOD LD�DSUR[LPDWLY��


CAZANE

144

501000

61 ,T

,kf

fl −=


sk

flflea

⋅−−= 1 (3.359)

3RQGHUHD�DEVRUE LHL�IO�F�ULL�FX�FHD�D�PHGLXOXL�UDGLDQW�GH�JD]H�GH�DUGHUH�VH�IDFH�GXS��FULWHULL�H[SHULPHQWDOH��FRQVLGHUkQG�R�SRQGHUH�β�D�S�U LL�OXPLQRDVH�D�IO�F�ULL�

&RHILFLHQWXO�GH�OXPLQR]LWDWH�DO�IO�F�ULL�HVWH�� β = 0,7 combustibil gazos

β = 0,9 combustibil lichid

SH�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IO�F�ULL�úL�JD]HORU�GLQ�IRFDU�

gfl aaa )1( ββ −+⋅= (3.360)

Gradul de ecranare al focarului este per

'

R

S

S=Ψ §��

Se impune coeficientul de murd�ULUH al�VXSUDIH HORU� ξ=1 combustibil gazos ξ=0,9 combustibil lichid &X�DFHVWH�YDORUL�VH�FDOFXOHD]��FRHILFLHQWXO�GH�DEVRUE LH�al focarului:

ξΨ)a(a

a,a f −+

⋅=

1

820 (3.361)

2� DOW�� FDUDFWHULVWLF�� D� IRFDUXOXL�� IDFWRUXO� GH� SR]L LH� D� IO�F�Uii în focar, pentru combustibil lichid sau gazos:

f

MMH

abaM −= (3.362)

cu: aM = 0,52, bM = 0,3 , 3020 ,,H

a

f

÷≅ (3.363)

&X�DFHVWH�GDWH�VH�GHWHUPLQ��VXSUDID D�GH�UDGLD LH�D�IRFDUXOXL�

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

145

32

2

38

11

107655 MT

T

TTaM,

QS

f

t

tff

RR

−

⋅= − ξ (m2) (3.364)


RS � GHWHUPLQDW�� vQ� FDOFXOXO� DSUR[LPDWLY��'DF�� GLIHUHQ D� HVWH� PDL� PDUH� GH� �� VH� UHLD� FDOFXOXO� FX� YDORUL� SHQWUX�Vf� úL�Sper

FRUHVSXQ]�WRDUH�OXL�SR. 6H�UHFDOFXOHD]��dimensiunile reale ale focarului: 6XSUDID D� HFUDQDW�� D� IRFDUXOXL� ILLQG� VXSUDID �� PHWDOLF�� FRQWLQX�� JUDGXO� GH�ecranare este 1x = � úL�GHFL�SR� UHSUH]LQW�� úL� VXSUDID D�HIHFWLY��GH�UDGLD LH�úL�VXSUDID D�JHRPHWULF�� 3.8.8. Calculul termic al drumului convectiv

'UXPXO� FRQYHFWLY� HVWH� GHWHUPLQDW� GLQ� FDOFXOHOH� DQWHULRDUH� SULQ� XUP�WRULL�parametrii : Qc –�IOX[�GH�F�OGXU�� (kW)

tf – temperatura gazelor la intrare (0C)

tFRú –�WHPSHUDWXUD�JD]HORU�OD�LHúLUH (0C)

tam – temperatura media a apei în cazan (0C)

PenWUX� VWDELOLUHD� VHF LXQLL� GH� WUHFHUH� D� JD]HORU� GH� DUGHUH� VH� DOHJH� GLDPHWUXO� HYLORU�GUXPXULORU�FRQYHFWLY�GLQ�JDPD�GH� HYL�X]XDOH�SHQWUX�FD]DQHOH�GH�DS��ILHUELQWH� Φ 24 × 3, Φ 28 × 3, Φ 32 × 3. Pentru�FD]DQHOH�GH�FRQVWUXF LH�URPkQHDVF��V-D�XWLOL]DW� HDY��φ 28 × 3. 'DWRULW��IDSWXOXL�F��VHUSHQWLQHOH�SOHDF��DOWHUQDWLY�GLQ�FROHFWRDUH�GLVSXVH�ID ��vQ�ID ��SDVXO�WUDQVYHUVDO�DO� HYLORU�SRDWH�IL�PDL�PLF��ILJ��


CAZANE

146

Fig. 3.25. Sistemul convectiv

6H�DOHJH�SDVXO�UHODWLY�GH�DúH]DUH�WUDQVYHUVDO��D� HYLORU� 51211 ,,

d

s÷=

6H�FDOFXOHD]��DSRL�VHF LXQHD�OLEHU��GH�WUHFHUe a gazelor de ardere în ipoteza�F��VHF LXQHD�EUXW��D�IRFDUXOXL�U�PkQH�QHVFKLPEDW��úL�vQ�GUXPXO�FRQYHFWLY��D�× a):

−=

−=

1

2

1

12 1s

da

s

dsaScirc (m2) (3.365)

unde termenul

−

1

1

s

ds �UHSUH]LQW��UHGXFHUHD�VHF LXQLL�GDWRULW�� HYLORU� Debitul de gaze ce trece prin convectiv este:

273

273+⋅= m

gg

tVBD (m3/s) (3.366)

unde tm este temperatura medie a gazelor de ardere:

2

cosf

m

ttt

+= (0C)

5H]XOW��YLWH]D�JD]HORU�GH�DUGHUH�

circ

g

S

DW = (m/s) (3.367)

'DF��YLWH]D�JD]HORU�GH�DUGHUH�HVWH�vQ�LQWHUYDOXO��÷ 20 (m/s) se poate accepta DFHLDúL�VHF LXQH�EUXW��D�× a) UH]XOW��pentru sistemul convectiv�FD�úL�SHQWUX�IRcar.

s2

a

s1

a Gaze de ardere

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

147

'DF��W� !� �� P�V�� FDQDOXO� � WUHEXLH� P�ULW� úL� VH� UHLD� FDOFXOXO� IRFDUXOXL� FX� R�VHF LXQH�P�ULW�� 'DF��W < 12 (m/s) canalul convectiv trebuie îngustat. PHQWUX�FDOFXOXO�vQJXVW�ULL�VH�DOHJH�YLWH]D�GH�FLUFXOD LH� W = (12 ÷ 20) (m/s) (3.368) úL�VH�GHWHUPLQ��VHF LXQHD�OLEHU��QHFHVDU��GH�FXUJHUH�

W

DS

g

circ = (m2) (3.369)

8QD�GLQ�ODWXULOH�IRFDUXOXL�U�PkQH�QHVFKLPEDW��a��LDU�FHDODOW��VH�PLFúRUHD]��OD�valoarea (a’��5H]XOW��ODWXUD�

−⋅=

1

1's

daaScirc (m2) (3.370)

úL�

−

=

1

1s

da

S'a circ

(m) (3.371)

Pentru temperatura media a gazelor de ardere tm� VH� GHWHUPLQ�� GLQ� anexa 9, XUP�WRDUHOH�YDORUL�

- YkVFR]LWDWHD�FLQHPDWLF�� ν (m2/s)



Se alege pasul longitudinal s2 = (1,5 ÷ 2,5)· de��6H�FDOFXOHD]��FRHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��αc) pentru curgerea gazelor de ardere transversal pe un fascicul de HYL�DúH]DWH�vQ�FRUGRQ��OLQLH��

ÌQ�DFHVW�FD]�OXQJLPHD�FDUDFWHULVWLF��YD�IL�

2ed

l⋅

=π

(3.372)

Criteriul hidrodinamic:

ψνcWl

Re = (3.373)

cu 14

1s

deπΨ −= .


CAZANE

148

Pentru 10 < Re < 106�úL��3U��3�úL curgere a gazelor de ardere transversal SH�XQ�UkQG�GH� HYL�

120

221 30

,

p

mtl

T

TNuNu,Nu

++= (3.374)

unde:

36440 PrRe,Nul ⋅+= ��úL

−⋅+

⋅⋅=

− 144321

0370

3

210

80

PrRe,

PrRe,Nu

,

,

t

Pentru n UkQGXUL�GH� HYL (n = 40 ÷ 60):

120

1

11,

p

m

T

TNu

n

)n(Nu

−+=

ω (3.375)

cu 2

1

2

1

2

51

70

3070

1

+

−

−=

,s

s

,s

s

,,Ψ

ω

Se determin�:

c

cl

Nuλα = (3.378)

&RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH HVWH�GHWHUPLQDW�GH�P�ULPLOH�

- WHPSHUDWXU��PHGLH�D�JD]HORU�GH�DUGHUH�� Tgm=tgm+273 (K);


2

g

g

RO

RO pV

Vp 2

2= [bar�@��úL�� g

g

OH

OH pV

Vp 2

2= [bar.] (3.379)

- grosimea stratului radiant:

ed,d

s

d

s,s

−

+= 14871 21

(m) (3.380)

3. CALCULUL�7(50,&�$/�&$=$1(/25�'(�$3��&$/'��6$8�),(5%,17(

149

&RQVWDQWD�GH�UDGLD LH�D�JD]HORU�HVWH� ( ) ( )

22

22

2

10003801

6180ROOH

m

ROOH

OHpp

T,

spp

p,,kg +

−

⋅+

+= (3.381)

Coeficientul de emisivitate al gazelor de ardere:

sk

g

gea⋅−−= 1 (3.382)

&RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH�VH�determin��FX�UHOD LD��

−

−

+⋅= −

m

p

,

m

p

mg

p

r

T

T

T

T

Taa

,

1

1

2

1107655

63

38α (W/m2K) (3.383)

XQGH� SHQWUX� FRHILFLHQWXO� GH� DEVRUE LH� DO� SHUHWHOXL� VH� LD� YDORDUHD�ap� �� úL� SHQWUX�WHPSHUDWXUD�DEVROXW��D�SHUHWHOXL� HYLL� 27320 ++= amp tT

CoeficienWXO�GH�WUDQVIHU�GH�F�OGXU��HVWH: αi = αc + αr (3.384)

&RHILFLHQWXO�JOREDO�GH�VFKLPE�GH�F�OGXU��HVWH�

i

ikεα

α+

=1

(3.385)

în care s-D�QHJOLMDW�UH]LVWHQ D�WHUPLF��1/α2).

Valorile coeficientului de PXUG�ULUH� ε pentru gaze de ardere, provenite din DUGHUHD�GH�FRPEXVWLELO�JD]RV��VXQW�SUH]HQWDWH�vQ�WDEHOXO�XUP�WRU�

&RHILFLHQWXO�GH�PXUG�ULUH�– combustibil gazos

Viteza w (m/s) 3 6 9 12 15 18 ε ⋅103 (m2K/W) 5,233 3,837 2,791 2,093 1,628 1,395

Se pRDWH�XWLOL]D�úL�UHOD LD�DQDOLWLF�� 647403102111 ,w,

−− ⋅⋅=ε (m2K/W) (3.386) Pentru gaze de ardere provenind din arderea unui combustibil lichid se poate considera:


CAZANE

150

0163,0≅ε (m2K/W) (3.387) 'LIHUHQ D�PHGLH�D�WHPSHUDWXULORU�VH�GHWHUPLQ��FRQIRUP�UHOD LHL��

min

max

minmax

lnt

t

tttm

∆∆

∆−∆=∆ (3.388)

ÌQ� ILQDO� VXSUDID D�GH�VFKLPE�GH�F�OGXU�� D�GUXPXOXL�FRQYHFWLY�VH�GHWHUPLQ�� FX�UHOD LD��

m

cc

tk

QS

∆⋅= (m2) (3.389)

Determinarea geometriei drumului convectiv se face astfel:

- QXP�UXO�GH� HYL�SH�XQ�UkQG�ntr��SHUSHQGLFXODU�SH�GLUHF LD�JD]HORU�GH�DUGHUH��este:

1s

antr = sau

1s

'antr = (3.390)

GXS��FXP�FDQDOXO�D�IRVW�QHvQJXVWDW�VDX�vQJXVWDW� ntr�VH�URWXQMHúWH�OD�YDORDUHD�vQWUHDJ��SDU��LQIHULRDU��

- QXP�UXO�GH�UkQGXUL�GH� HYL�n��vQ�GLUHF LD�FXUJHULL�JD]HORU�GH�DUGHUH��

adn

Sn

etr

c

⋅⋅⋅=

π (3.391)

VH�URWXQMHúWH�OD�YDORDUHD�SDU��VXSHULRDU�� 6H� UHPDUF�� IDSWXO� F�� V-D�QHJOLMDW�SUHOXDUHD�F�OGXULL�GH�F�WUH�SHUH LL�PHPEUDQ��limitaWRUL�DL�GUXPXOXL�FRQYHFWLY��'H�RELFHL�VH�FRQVLGHU��FD�UH]HUY��GH�VXSUDID ��VH�SRW�OXD� vQ� FDOFXO�� FD]� vQ� FDUH� LQWU�� vQ� FRPSRQHQ D� VXSUDIH HL� GH� VFKLPE� GH� F�OGXU�� D�convectivului cazanului Sc. $úH]DUHD�QXP�UXOui de rânduri „n”�SH�YHUWLFDO��VH�IDFH�vQ�SDFKHte cuprinzând 8, ��VDX�� HYL��DGLF��VDX��EXFOH� 3DFKHWHOH�QX� WUHEXLH�V�� DLE�� DFHODúL�QXP�U�GH� HYL��SDFKHWXO�FX�XQ�QXP�U�PDL�PLF�GH� HYL�VH�DúHD]��SULPXO��GXS�� IRFDU��GHRDUHFH� �DUH�R�FLUFXOD LH� LQWHULRDU��D�DSHL�PDL�LQWHQV�� 'LVWDQ D� vQWUH�SDFKHte este de (4 ÷ 8)· s2 iar pasul la bucla din mijlocul unui

pachet este de 2· s2��SHQWUX�D�SHUPLWH�vQGRLUHD� HYLL�OD��0). &X�DFHVWH�GDWH�VH�FDOFXOHD]��OXQJLPHD�GUXPXOXL�FRQYHFWLY�


CAZANE

151

CAPITOLUL 4

CALCULUL TERMIC AL CAZANELOR DE ABUR 4.1. Calculul termic al cazanului ABA (Agregat Bloc Abur)

��'HVFULHUHD�FD]DQXOXL��HOHPHQWH�FRPSRQHQWH��PRG�GH�IXQF LRQDUH� (VWH� XQ� FD]DQ� LJQLWXEXODU�� FX� WXE� GH� IODF�U�� úL� GRX�� GUXPXUL� FRQYHFtive. )XQF LRQHD]��FX�FRPEXVWLELO��JD]RV�VDX�OLFKLG�úL�SURGXFH�DEXU�VDWXUDW� )DFH�SDUWH�GLQ�FDWHJRULD�FD]DQHORU�FX�YROXP�PDUH�GH�DS��3ULQFLSDOHOH�HOHPHQWH�component ale cazanului sunt prezentate în figura 4.1.

��$U]�WRU��7XE�GH�IODF�U��ùDPRWDUH��&XWLH�vQWRDUFHUH�VSDWH��)LHUE�WRU�FRQYHFWLY�,��&XWLH�întoarcere�ID ��FierE�WRU�FRQYHFWLY�,,��&Rú��7DPEXU��6XSDS��GH�VLJXUDQ ��,QGLFDWRU�GH�QLYHO��&RQGXFW��GH�DEXU��

��$OLPHQWDUH�FX�DS�

Fig. 4.1. Schema conven LRQDO��D�FD]DQXOXL�ABA

5 5

F

C1 C2

7

1

2 3 4

6

8 10 12 13 11

13

13

9

4. CALCULUL TERMIC AL CAZANELOR DE ABUR

152

Cazanul ABA� HVWH� DOF�WXLW� GLQWU-un tambur (9) cu diametru mare în interiorul F�UXLD�VH�DIO��VXSUDIH HOH�GH�VFKLPE�GH�F�OGXU��WXEXO�GH�IODF�U��FX�SHUH LL�RQGXOD L��FX�URO�GH�IRFDU�úL� HYLOH�GH�IXP�FX�URO�GH�IDVFicoO�ILHUE�WRU�–�FRQYHFWLY��úL�� Întoarcerea gazelor de pe un drum pe altul se face prin cutii de întoarcere. Cutia GH� vQWRDUFHUH� VSDWH� �� HVWH� U�FLW�� FX� HYL� GH� DS�� LDU� FHD� GH� vQWRDUFHUH� ID �� HVWH�UHDOL]DW��GLQ�WDEO��F�SWXúLW��FX�PDWHULDO�UHIUDctar. 9ROXPXO� PDUH� GH� DS�� OD� VDWXUD LH� GLQ� FD]DQ� DVLJXU�� R� PDUH� LQHU LH� WHUPLF��DGLF��R�PDUH�FDSDFLWDWH�GH�DFXPXODUH�GH�F�OGXU��FHHD�FH�RIHU��DYDQWDMXO�SRVLELOLW� LL�pUHOX�ULL�IOXFWXD LLORU�GH�VDUFLQ��SULQ�YDULD LL�PLFL�GH�SUHVLXQH�vQ�WDPEXU� Volumul mDUH� GH� DS�� QHFHVLW�� vQV�� WLPS� vQGHOXQJDW� GH� SRUQLUH� úL� LQWUDUH� vQ��regim. &D� XUPDUH� D� IDSWXOXL� F�� WRDWH� HOHPHQWHOH� FD]DQXOXL� VH� DIO�� LQ� LQWHULRUXO�tamburului, acesta are dimensiuni foarte mari (diametre de 1600 –� �� PP� úL�lungimi de ordinul 1600 – 4600 PP��FHHD�FH�DQWUHQHD]��FRQVXPXUL�PDUL��GH�PHWDO�úL�iPSXQH�OLPLWDUHD�GHELWHORU�OD�FFD��W�K�úL�D�SUHVLXQLORU�GH�OXFUX�OD�FFD��EDU� $VDPEODUHD�ULJLG��vQWUH�WDPEXU��WXE�GH�IODF�U��úL� HYL�GH�IXP��HOHPHQWH�care se GLODW��GLIHULW�GDWRULW��WHPSHUDWXULORU�GLIHULWH�GH�OXFUX��DQWUHQHD]��DSDUL LD�vQ�IXQF LRQDUH�úL� vQ� VSHFLDO� OD� YDULD iL� GH� VDUFLQ�� LQFOXVLY� SRUQLUH�� D� XQRU� VROLFLW�UL�PHFDQLFH�PDUL��FDUH�GXF�XQHRUL�OD�GLVWUXJHUHD�HWDQú�ULORU��(OLPLQDUHD�vQ�SDUWH�D�DFHVWXL�LQFRQYHQLHQW�VH�UHDOL]HD]��SULQ�XWLOL]DUHD�WXEXULORU�GH�IODF�U��GH�WLS�HODVWLF�– tuburi ondulate –�úL�SULQ�ULJLGL]DUHD�VXSOLPHQWDU��D� HYLORU�GH�IXP�vQ�SO�FLOH�WXEXODUH�SULQ� HYL�DQFRU�� 4.1.2. Tema de proiectare

Prin tema de proiectare se dau: Dh – debitul de abur saturat produs, în t/h sau D=0,278 Dh, în kg/s ; p – presiunea aburului, în bar ; ti – temperatura apei la intrare în cazan; $ – titlul de vapori;

– compozi LD combustibilului utilzat. &RQIRUP� LQGLFD LLORU� GLQ� FDSLWROXO� �� VH� HIHFWXHD]�� FDOFXOXO� DUGHULL�combustibiluOXL�úL�VH�GHWHUPLQ�� ig0 H,V,V

o .

'DF�� IXQF LRQDrea cazanului este cu suprapresiune în focar, coeficientul de H[FHV� GH� DHU� HVWH� FRQVWDQW� úL� HJDO� FX� FHO� GLQ� IRFDU� � �FFD�� ·��SH� WRW� WUDVHXO�gazelor de ardere. 'DF�� IXQF LRQDUHD� FD]DQXOXi este în depresiune (cu exhautor la evacuarea JD]HORU�GH�DUGHUH�SH�FRú��VH�DGPLWH��GH�H[HPSOX�� αf în focar = 1,1 (α1) În fiecare FXWLH�GH�vQWRDUFHUH�VH�DGDXJ��∆α=0,1.


CAZANE

153

5H]XOW�� - )( 2CI αα �GXS��SULPD�FXWLH�GH�vQWRDUFHUH��vQ� HYLOe fascicolului convectiv I: α2=1,2 .

- )( 3ααCII �GXS��D�GRXD�FXWLH�GH�vQWRDUFHUH�vQ� HYLOH�IDVFLFROXOXL�FRQYHFWLY�,,��α3 ��úL�

HVWH�SUDFWLF�HJDO�FX�FRHILFLHQWXO�GH�H[FHV�GH�DHU�OD�FRú��αFRú). Fiind VF�ldare interioar�, coeficientul de exces de aer mediu pe un drum este cel de la intrare. 6H�WUDVHD]��GLDJUDPHOH�,-t sau cp-t. ��&DOFXOXO�UDQGDPHQWXOXL�WHUPLF�DO�FD]DQXOXL�úL�D�GHELWXOXL�GH�FRPEXVWLELO� $FHVWH� FD]DQH� IXQF LRQHD]�� QXPDL� FX� FRPEXVWLELO� JD]RV� VDX� OLFKLG� �SLHUGHULOH�specifice GH�F�OGXU��SULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��mecanic� qmec�úL�SULQ�HYDFXDUHD�produselor solide din cazan qcen sunt nule). a) 3LHUGHUHD�VSHFLILF��GH�F�OGXU��SULQ�HQWDOSLD�JD]HORU�de ardere OD�FRú� )LLQG�XQ�FD]DQ�GH�DEXU��I�U��VXSUDIH H�DX[LOLDUH��VH�DGPLWH�LQL LDO�R�WHPSHUDWXU��OD�FRú�GHWHUPLQDW��GLQ�UHOD LD :

h

scosD

tt50

50 ++≅ [0C] (4.1)

Din diagrama I-W�VH�DIO��YDORDUHD�HQWDOSLHL�JD]HORU�GH�DUGHUH�OD�FRú��

),t(fI coscoscos α=

(QWDOSLD� DHUXOXL� WHRUHWLF� GH�DUGHUH� VH�FDOFXOHD]�� SHQWUX� WHPSHUDWXUD�DPELDQW��(de exemplu ta=20 0C).

apaao tcVI 0= (4.2)

5H]XOW��SLHUGHUHD�VSHFLILF��OD�FRú�� )II(

Hq aocoscos

i

cos α−=1

(4.3)

b) 3LHUGHUHD�VSHFLILF��GH�F�OGXU��SULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��FKLPLF� În proiecWDUH� VH� DGPLWH� R� SLHUGHUH� SULQ� DUGHUH� LQFRPSOHW�� FD]DQXO� ILLQG� FX�ecranare medie) qch= 0,001÷0,008 c) 3LHUGHUL�VSHFLILFH�GH�F�OGXU��SULQ�VXSUDID ��H[WHULRDU��D�FD]DQXOXL�


154

6H�SRDWH�XWLOL]D�UHOD LD�H[SHULPHQWDO� (2.17) ;

6577021046435 ,

hext D,q−−×= (4.4)

SHQWUX�FD]DQH�GH�DEXU�I�U��VXSUDIH H�DQH[H� d) Randamentul cazanului 6H�FDOFXOHD]��FX�UHOD LD�:

)qqq( extchcos ++−= 1η (4.5)

úL� %% ηη 100= (4.6) e) Consumul de combustibil Se admite debitul de purje al cazaQXOXL�� vQ� FRQGL LLOH� DSHL� ELQH� WUDWDWH�� GH��din debitul cazanului :

Dp=0,03D (4.7) Din tabelele de SURSULHW� L�WHUPRGLQDPLFH�DOH�aburului (Anexa 4��VH�GHWHUPLQ��SHQWUX�SUHVLXQHD�DEXUXOXL�S��XUP�WRDUHOH�P�ULPLL��

- WHPSHUDWXUD�GH�VDWXUD LH�Wsat - entalpia aburului saturat uscat i” - HQWDOSLD�DSHL�OD�VDWXUD LH�L¶ - HQWDOSLD�DSHL�OD�LQWUDUH��FRUHVSXQ]�WRDUH�WHPSHUDWXULL�ti : io=4,186⋅ ti (kJ/kg)

Deoarece aburul are un titlu $��HQWDOSLD�ILQDO��D�DEXUXOXL�HVWH��

'i)(''ii ⋅−+⋅= χχ 1 (4.8) DHRDUHFH�SHQWUX�FD]DQH�GH�DFHVW� WLS�QX�VH�XWLOL]HD]�� LQMHFWRDUH�GH�FRPEXVWLELO�lichid cu agent de pulverizare abur��UH]XOW� Winj ��(YLGHQW�úL�vQ�FD]XO�FRPEXVWLELOXOXL�gazos Winj=0. 'H� DVHPHQHD� VH� LD� vQ� FRQVLGHUDUH� F�� SHQWUX� FRPEXVWLELO� OLFKLG� VDX� JD]RV�qmec ��úL�GHFL�B*=B . 5H]XOW��GHELWXO�GH�FRPEXVWLELO consumat de cazan:

i

opo

H

)i'i(D)ii(DB

η−+−

= (4.9)


CAZANE

155

��%LODQ XO�GH�DQVDPEOX�DO�FD]DQXOXL� )OX[XO�GH�F�OGXU��XWLO�DO�FD]DQXOXL�HVWH�� )i'i(D)ii(DQ opout −+−= [kW] (4.10)

Fluxul de�F�OGXU��DGXV�GH�FRPEXVWLELO�� ic HBQ ⋅= (4.11)

)OX[XO�GH�F�OGXU��DGXV�FX�DHUXO�GH�DUGHUH�úL�GH�QHHWDQúHLW� L : apacosa tcVBQ 0α= (4.12)

)OX[XO�GH�F�OGXU��SLHUGXW�OD�FRú�� coscos BIQ = (4.13) Fluxul�GH�F�OGXU��SLHUGXW�SULQ��DUGHUH�LQFRPSOHW�� ichinc BHqQ = (4.14) )OX[XO�GH�F�OGXU��SLHUGXW�VSUH�H[WHULRU�� iextext BHqQ = (4.15)

5H]XOW��WDEHOXO�GLQ�ELODQ � Tabelul 4.1.

Combustibil – pierderi Util Qc Qa

- QFRú - Qinc - Qext

Qut

∑ = 'QQ ''QQ∑ =

1RW��vQ�DFHVW�ELODQ �(qFRúBHi) s-a scris sub forma: (BIFRú-BVoαFRúcpata ).

6H�GHILQHúWH�HURDUHD�UHODWLY��:

%100'Q

''Q'Q −=ε (4.16)

,DU�GDF� eroarea este mai PLF� de 1% calculul este corect .


156

4.1.5. CDOFXOXO�WHPSHUDWXULORU�úL�HQWDOSLLORU�JD]HORU�GH�DUGHUH�SH�WUDVHX� (QWDOSLD�WHRUHWLF��GH�DUGHUH�VH�FDOFXOHD]��FX�IRUPXOD�� apafchit tcV)q(HI 01 α+−= (4.17)

DSRL�VH�GHWHUPLQ��WHPSHUDWXUD�WHRUHWLF��GH�DUGHUH�GLQ�GLDJUDPD�,-t : ),I(ft ftt α=

6H�DOHJH�WHPSHUDWXUD�OD�FDS�WXO�IRFDUXOXL:

tf = 900 ÷ 1100 0C , cu valori mici pentru debite mici. Aceste valori înalte sunt specifice cazanelor cu tub GH�IODF�U�� 6H� GHWHUPLQ�� DSRL� GLQ� GLDJUDPD� ,-W� HQWDOSLD� JD]HORU� OD� FDS�WXO� IRFDUXOXi

If=f(tf,αf) . )OX[XO�GH�F�OGXU��SUHOXDW�SULQ�UDGLD LH�vQ�IRFDU�YD�IL�� )II(B)q(Q ftextR −−= 1 [kW] (4.18)

)OX[XO�GH�F�OGXU��FDUH��VH�SUHLD�vQ�VLVWHPXO�FRQYHFWLY��&,�úL�&,,��HVWH��

Rutc QQQ −= (4.19)

Acest flux convectiv VH�vPSDUWH�SH�FHOH�GRX��IDVFLFROH�DVWIHO�� ccI Q),,(Q ⋅−= 85070 úL� cIccII QQQ −= (4.20)

$FHDVW�� UHSDUWL LH� DSDUH� deoarece pe primul drum convectiv temperaturile

gazelor de ardere sunt mai ridicate FHHDFH� GHWHUPLQ�� XQ� IOX[� XQLWDU� GH� F�OGXU��PDL�mare. Entalpia gazelor de ardere lD�VIkUúLWXO�SULPXOXL�GUXP�FRQYHFWLY�HVWH��

B)q(

QII

ext

cIfcI −

−=1

(4.21)

úL�GLQ�GLDJUDPD�,-W�UH]XOW��WHPSHUDWXUD�� ),I(ft cIcIcI α= (4.22) (QWDOSLD�JD]HORU�GH�DUGHUH�OD�VIkUúLWXO�FHOXi de-al doilea drum convectiv este :

B)q(

QII

ext

cIIcIcII −

−=1

(4.23)


CAZANE

157

úL�GLQ�GLDJUDPD�,-W�UH]XOW��WHPSHUDWXUD�� ),I(ft coscIIcII α= (4.24) ÌQFKLGHUHD�ELODQ XOXL�LPSXQH�� IcII=IFRú úL� tcII=tFRú Se admit erorile relative :

100⋅−−

=cost

cIIcos

ttt

ttε ��0,5% (4.25)

úL� 100⋅

−−

=cost

cIIcos

III

IIε � 0,5% (4.26)

(URUL�PDL�PDUL�LQGLF��R�JUHúHDO��GH�FDOFXO��ÌQ�ILQDO�VH�vQWRFPHúWH�WDEHOXO�� Tabelul 4.2.


Focar Convectiv I Convectiv II

QR

QcI

QcII

tc

tf

tcI

tf

tcI

tFRú ∑ =

uti QQ

��%LODQ XO�JUDILF�DO�FD]DQXOXL 'HELWHOH� GH� F�OGXU�� GLQ� WDEHOHOH� �� úL� ��2� VH� WUDQVSXQ� JUDILF�� OD� VFDU�� FD� vQ�figura 2.3 (cu B*=B; Qpa=0; Qsfc=QcI+QcII, Qsi=0; Qec=0; qmec=0; qcen=0) . 4.1.7. Calculul termic al focarului

$FHVW�FDOFXO�DUH�FD�VFRS�GHWHUPLQDUHD�VXSUDIH HL�GH�UDGLD LH�6R�FDSDELO��V��SUHLD�GHELWXO� GH� F�OGXU�� UDGLDQW� 4R. Deoarece în calcule intervine gradul de ecranare

=

per

R

S

SΨ úL�OXQJLPHD�GH�UDGLD LH�

⋅=

per

f

S

Vs 4 , este necesar un calcul interativ. Se

SRUQHúWH�FX�R�YDORDUH�DSUR[LPDWLY��6’R�FDUH�� vQ�ILQDO��VH�YD�FRPSDUD�FX�FHD�UH]XOWDW��din calcul SR.


158

9DORDUHD�LQL LDO�� '

RS poate fi stDELOLW��SULQ�GRX��PHWRGH��

a) Se admite un flux unitar radiant qR =30 ÷ 50 kW/m2

R

R'

Rq

QS = [m2] (4.27)

E��6H�FDOFXOHD]��VXSUDID D�GH�UDGLD LH�vQ�IRFDU�FX�UHOD LD�DSUR[LPDWLY��

−

⋅⋅

=44

1001007655 pf

R'

R

TT,

QS

ε [m2] (4.28)

cu ε = 0,65 pentru combustibil gazos ε = 0,75 pentru combustibil lichid Tf = tf+273 [K] Tp= tsat+273 + (20 ÷40) [K] )RFDUXO�GH�WLS�WXE�GH�IODF�U��DUH�XUP�WRDUHOH�GLPHQVLXQL��ILJXUD��

Fig. 4.2. FocaruO�WLS�WXE�GH�IODF�U��FX�SHUH L�RQGXOD L

6H� DOHJH� GLDPHWUXO� WXEXOXL� GH� IODF�U�� GXS�� P�ULPHD� FD]DQXOXL� FRQIRUP�LQGLFD LLORU�RULHQWDWLYH�GLQ�WDEHOXO��

Tabelul 4.3. Debit Dh [t/h] Diametru D [m]

0,4 ÷ 1 1 ÷ 4 4 ÷ 10

0,400 ÷ 0,600 0,600 ÷ 0,900 0,700 ÷ 1,500

LR LS

L

D

60


CAZANE

159

6H�GHWHUPLQ��OXQJLPHD�DFWLY��GH�WUDQVIHU�GH�F�OGXU��D�IRFDUXOXL�GLQ�UHOD LD��

D

DS

L

'

R'

R π

π4

2

−= [m] (4.29)

S-D� FRQVLGHUDW� F�� VXSUDID D� FRUHVSXQ]�WRDUH� fundului focarului

4

2Dπ

preia

F�OGXU�� SULQ� UDGLD LH deoarece la cazanele bloc-abur cutia de întoarcere spate este U�FLW��FX� HYL�GH�DS��

9ROXPXO�IRFDUXOXL�� LQkQG�VHDPD�GH�R�OXQJLPH�GH�úDPRWDUH�Lú = 0,6÷1,2 m úL�R�JURVLPH�GH�úDPRWDUH� δ=0,060 m , este :

4

2

4

22)D(

LD

LV s

'

Rf

δππ −+= [m3] (4.30)

6XSUDID D�SHUH LORU�IRFDUXOXL�HVWH��

422

2D]L)D(LD[S s

'

Rper

⋅⋅+⋅⋅−+⋅⋅=πδπ [m2] (4.31)

Grosimea stratului radiant de gaze este :

per

f

S

Vs ⋅= 6,3 [m] (4.32)

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�JD]HORU�GH�DUGHUH�GLQ�IRFDU��

)pp(1000

T38,01

s)pp(

p6,11,0k

22

22

2

ROOHf

ROOH

OHg +⋅

−⋅

⋅+

⋅+= (4.33)

3UHVLXQLOH�SDU LDOH�DOH gazelor triatomice�VH�GHWHUPLQ��FX�UHOD LLOH

g0fg

OH

OH pV)1(V

Vp

o

2

2⋅

−α+= [bar] ; g

0fg

RO

RO pV)1(V

Vp

o

2

2⋅

−α+= [bar] (4.34)

unde : pg=1 bar.


160


sk

g

gea⋅−−= 1 (4.35)

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IO�F�ULL�FX�UHOD LD�DSUR[LPDWLY�� 50

100061 ,

T,k

f

fl−⋅= (4.36)


sk

fl

flea⋅−−=1 (4.37)

PonderarHD� DEVRUE LHL� IO�F�ULL� FX� FHD� D�PHGLXOXL� UDGLDQW� GH� Jaze de ardere se

IDFH� GXS�� FULWHULL� experimentale,� FRQVLGHUkQG� R� SURSRU LH� β din volumul focarului RFXSDW��GH�SDUWHD�OXPLQRDV��D�IO�F�ULL��

&RHILFLHQWXO�GH�DEVRUE LH�DO�IO�F�ULL�úL�JD]HORU�GH�DUGHUH�HVWH�GDW�GH�UHOD LD�� gfl a)(aa ⋅−+⋅= ββ 1 (4.38)

Coeficientul de luminozitate β este dat în tabelul 4.4.

Tabelul 4.4. )ODF�U��QHOXPLQRDV��GH�FRPEXVWLELO�JD]RV� β = 0,2 )ODF�U��GH�FRPEXVWLELO�OLFKLG β = 0,6

Gradul de ecranare al focarului este :

per

'

R

S

S=Ψ (4.39)

úL�PXUG�ULUHD�VXSUDIH HORU�� ξ= 0,7 ÷ 0,9 combustibil gazos ξ= 0,6 ÷ 0,7 combustibil lichid &X�DFHVWH�YDORUL�VH�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IRFDUXOXL��

ξΨ ⋅⋅−+⋅

=)a(a

a,a f 1

820 (4.40)

FDFWRUXO�GH�SR]L LH�D�IO�F�ULL�vQ�IRFDU��SHQWUX�FRPEustibil lichid sau gazos, este GDW�GH�UHOD LD:


CAZANE

161

430,H

hbaM

f

MM =−= (4.41)

cu : aM=0,52; bM=0,3�úL fH

h = 0,3 pentru focare orizontale

&X�DFHVWH�GDWH�VH�GHWHUPLQ��VXSUDID D�GH�UDGLD LH�D�IRFDUXOXL��

32

2

38

11

107655 MT

T

TTaM,

QS

f

t

tff

RR ⋅

−⋅

⋅⋅⋅⋅⋅⋅= − ξ [m2] (4.42)

unde Tt�HVWH�WHPSHUDWXUD�WHRUHWLF��GH�DUGHUH��Wt+273) [K]. $FHDVW��VXSUDID ��YD�IL�GLIHULW��GH� '

RS �GHWHUPLQDW��vQ�FDOFXOXO�DSUR[LPDWLY��'DF��GLIHUHQ D�HVWH�PDL�PDUH�GH��VH�UHLD�FDOFXOXO�FX�YDORUL�PRGLILFDWH�SHQWUX�9f�úL�6per

(pentru calcule mai precise efectuate pe calculator aceast�� GLIHUHQ � se impune la max.1%). 5H]XOW��OXQJLPHD�DFWLY��GH�WUDQVIHU�GH�F�OGXU��D�IRFDUXOXL:

D

DS

LR

R π

π4

2

−= [m] (4.43)

4.1.8. Calculul termic al drumului convectiv I

'UXPXO� FRQYHFWLY� ,� HVWH� GHWHUPLQDW� GLQ� FDOFXOHOH� DQWHULRDUH� SULQ� XUP�WRULL�parametrii : QcI –�GHELWXO�GH�F�OGXU��FHGDW�GH�JD]HOH�GH�DUGHUH�[kW] ; tf –�WHPSHUDWXUD�JD]HORU�GH�DUGHUH�OD�LQWUDUH�vQ� HYL�[0C] ;

tcI – temperatura gazelor de ardere la LHúLUH�GLQ�� HYL�[0C] ; tsat –�WHPSHUDWXUD�DSHL�OD�VDWXUD LH�[0C]; 3HQWUX� VWDELOLUHD� VHF LXQLL� GH� WUHFHUH� D� JD]HORU� GH� DUGHUH� VH� DOHJH� GLDPHWUXO� HYLORU�GLQ�JDPD�GH� HYL�X]XDOH��φ 51×3; φ 57×3; φ 60×3; φ 70×3,5; φ 76×3,5 mm . Se alege viteza de circXOD LH�D�JD]HORU�GH�DUGHUH�vQ�OLPLWH�HFRQRPLFH�� WI=10 ÷ 18 m/s 6HF LXQHD�GH�WUHFHUH�D�JD]HORU�GH�DUGHUH�YD�IL��

273

273+⋅

⋅= m

I

g

I

t

W

VBS [m2] (4.44)


162

unde: Vg VH�FDOFXOHD]��FX�UHOD LD:

01 V)(VV cIgg o−+= α

tm – este temperatura media a gazelor de ardere :

2cIf

m

ttt

+= [0C]

1XP�UXO�GH� HYL�DO�GUXPXOXL�FRQYHFWLY�,��

2

4

i

II

d

Sn

⋅⋅

=π -�VH�URWXQMHúWH�OD�QXP�U�întreg par (4.45)

ÌQ�ILQDO�VH�UHFDOFXOHD]��YLWH]D�JD]HORU�GH�DUGHUH��

273

273

4

2

+⋅

⋅⋅

⋅= m

iI

g

I

t

dn

VBW

π [m/s] (4.46)

Pentru temperatura medie a gazelor de ardere tm� VH� GHWHUPLQ�� GLQ� anexa 9,

XUP�WRDUHOH�YDORUL�� - YkVFR]LWDWHD�FLQHPDWLF�� ν [m2/s]

- FRQGXFWLELOLWDWHD�WHUPLF�� λ [W/mK]

- criteriul Prandtl Pr DSRL�VH�GHWHUPLQ��FULWHULXO�KLGURGinamic :

υiI

e

dWR

⋅= (4.47)

úL�VLPSOH[XO�GH�OXQJLPL�� 250

3,

i

l)d/L(

C = pentru L/di < 80 (4.48)

1=lC pentru L/di > 80 unde L este lungimea cazanului, care se ia HJDO��FX�cea a focarului. Se calculeD]��DSRL�FRHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�FRQYHF LH�� GDF� Re > 10000 :


CAZANE

163

80

350

02630 ,

i

,

rlc Re

d

PC, ⋅

⋅⋅⋅=λ

α [W/m2K] (4.49)

iar în cazul 2300 < RH��VH�IRORVHúWH�UHOD LD�

80

350

02630 ,

i

,

rlc Re

d

PC, ⋅

⋅⋅⋅⋅=λ

εα [W/m2K] (4.50)

cu

81

51061

,Re

⋅−=ε (4.51)

&RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH�HVWH�GHWHUPLQDW�GH�P�ULPLOH��

- WHPSHUDWXU��PHGLH�D�JD]HORU�GH�DUGHUH��7gm=tgm+273 [K] - grosimea stratului radiant : s = 0,9 . di [m] - SUHVLXQLOH�SDU LDOH�DOH�JD]HORU�triatomice în gazele de ardere:

g

cIg

RO

RO pV)(V

Vp

o 012

2 −+=

α [bar]; g

cIg

OH

OH pV)(V

Vp

o 012

2 −+=

α [bar] (4.52)

cu pg ≅ 1 bar. &RQVWDQWD�GH�UDGLD LH�D�JD]HORU�este :

)pp(T

,s)pp(

p,,K

ROOH

gm

ROOH

OH

g 22

22

2

10003801

6180+⋅

⋅−⋅

⋅+

⋅+= (4.53)

iar coeficientul de emisie al gazelor de ardere :

sk

ggea

⋅−−=1

CRHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH�VH�FDOFXOHD]��FX�UHOD LD��

−

−

⋅⋅⋅+

⋅⋅= −63

38

1

1

2

1107655

,

gm

p

gm

p

gmg

p

r

T

T

T

T

Taa

,α [W/m2K] (4.54)

XQGH� SHQWUX� FRHILFLHQWXO� GH� DEVRUE LH� DO� SHUHWHOXL� VH� LD� YDORDUHD� Dp �� úL� SHQWUX�WHPSHUDWXUD�DEVROXW��D�SHUHWHOXL� HYLL�� 27320 ++= satp tT [K]


164

Coeficientul de WUDQVIHU�GH�F�OGXU� pe partea gazelor de ardere va fi :

rci α+α=α Coeficientul αe (pe partea apei) este mult mai mare (de ordinul miilor de W/m2K) în comparate cu αi (de ordinul zecilor de W/m2K). În aceVWH�FRQGL LL�FRHILFLHQWXO�JOREDO�GH�WUDQVIHU�GH�F�OGXU��N�HVWH�GDW�GH�UHOD LD�(s-a neglijat 1/αe în raport cu 1/αi) :

i

iIk

αεα

⋅+=

1 [W/m2K] (4.55)

&RHILFLHQWXO� GH� PXUG�ULUH� ε pentru gaze de ardere provenite din combustibil gazos este dat în tabelul 4.4.

Tabelul 4.4. &RHILFLHQWXO�GH�PXUG�ULUH�– combustibil gazos

Viteza [m/s] 3 6 9 12 15 18 ε ⋅103 [m2K/W] 5,233 3,837 2,791 2,093 1,628 1,395

6H�SRDWH�XWLOL]D�úL�UHOD LD�DQDOLWLF��: 647403102111 ,

Wg,−− ⋅⋅=ε [m2K/W]

iar pentru gaze de ardere provenind din combustibil lichid : 01630,=ε [m2K/W] 'LIHUHQ D�PHGLH�GH�WHPSHUDWXU��VH�GHWHUPLQ��FRQIRUP�ILJXULL��úL�UHOD LHL�

min

max

minmaxmI

t

tln

ttt

∆∆

∆∆∆ −

= (4.56)


CAZANE

165

)LJ��'LIHUHQ D medie de temperatur�� mIt∆ ÌQ�ILQDO�VXSUDID D�GH�VFKLPE�GH�F�OGXU��D�GUXPXOXL�FRQYHFWLY�,�VH�GHWHUPLQ��FX�formula :

mII

cIcI

tk

QS

∆⋅= [m2] (4.57)

úL�UH]XOW��OXQJLPHD� HYLORU��

Ii

cIcI

nd

SL

⋅⋅=

π [m] (4.58)

4.1.9. Calculul termic al drumului convectiv II

Drumul convectiv II� HVWH� GHWHUPLQDW� GLQ� FDOFXOHOH� DQWHULRDUH� SULQ� XUP�WRULL�parametrii : QcII –�IOX[�GH�F�OGXU��[kW] ; tcI – temperatura gazelor la intrare;

tFRú –�WHPSHUDWXUD�JD]HORU��OD�LHúLUH�� tsat – temperaturD�IOXLGXOXL�OD��VDWXUD LH� Diametrul HYLORU�VH�DOHJH�DFHODúL�FD�SH�GUXPXO�,�GLQ�PRWLYH�WHKQRORJLFH� 9LWH]D�GH�FLUFXOD LH�D�JD]HORU�GH�DUGHUH�VH�LD�vQ�OLPLWHOH�� WII=8 ÷ 12 m/s

S SC1

t

tsat

tf

tc1

∆tmax

∆tmin


166

6HF LXQHD�GH�WUHFHUH�D�JD]HORU�GH�DUGHUH�YD�IL��

273

273+⋅

⋅= m

II

g

II

t

W

VBS [m2] (4.59)

unde: – Vg�VH�FDOFXOHD]��FX�UHOD LD� 01 V)(VV cIIgg o−+= α

– tm – este temperatura media a gazelor de ardere : 2

ttt coscI

m

+= [0C]

1XP�UXO�GH� HYL�DO�GUXPXOXL�FRQYHFWLY�,,��

2

4

i

IIII

d

Sn

⋅⋅

=π -�VH�URWXQMHúWH�OD�vQWUHJ�QXP�U�SDU (4.60)

9D� UH]XOWD� XQ� QXP�U� GH� HYL� PDL� PLF� GHFkW� OD� GUXPXO� ,� GLQ� FDX]D� GHELWXOXL�volumic mai mic de gaze de ardere. 'XS��VWDELOLUHD�QXP�UXOXL�GH� HYL�VH�UHFDOFXOHD]��YLWH]D�JD]HORU�GH�DUGHUH :

273

273

4

2

+⋅

⋅⋅

⋅= m

iII

g

II

t

dn

VBW

π [m/s] (4.61)

Pentru temperatura medie a gazelor de ardere tm�� VH� GHWHUPLQ�� GLQ� anexa 9 valoriOH�XUP�WRULORU�SDUDPHWULL:

- YkVFR]LWDWHD�FLQHPDWLF�� ν [m2/s]



DSRL�VH�GHWHUPLQ��FULWHUiul hidrodinamic :

υiII dW

Re = (4.62)

9DORDUHD�VLPSOH[XOXL�GH�OXQJLPL�HVWH�DFHODúL�FD�SH�GUXPXO�FRQYHFWLY�,��

( ) 250

3,

i

Id/L

C = pentru L/di < 80 (4.63)

1=IC pentru L/di > 80


CAZANE

167

6H�FDOFXOHD]��DSRL�FReficientul de sFKLPE�GH�F�OGXU��SULQ�FRQYHF LH� în ipoteza Re > 10000 :

80

350

02630 ,

i

,

rIc

Red

PC, ⋅

⋅⋅=

λα [W/m2K] (4.64)

LDU�vQ�FD]XO��5H��VH�IRORVHúWH�UHOD LD�

80350

02630 ,

i

,

rIc Re

d

PC, ⋅

⋅⋅⋅=

λεα [W/m2K] (4.65)

cu

81

51061

,Re

⋅−=ε (4.66)

&RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH�VH�FDOFXOHD]��QXPDL�GDF��

4002

>+

= coscIm

ttt 0C (4.67)

FD]�vQ�FDUH�PHWRGLFD�HVWH�DFHLDúL�FD�FHD�IRORVLW��OD�GUXPXO�FRQYHFWLY�,��VFKLPEkQGX-se

22 ROOH P,P úL gT .

'DF��tm < 400 0&�HIHFWXO�UDGLD LHL�VH�QHJOLMHD]��úL�αr=0. Coeficientul de WUDQVIHU�GH�F�OGXU� este :

rci ααα += (4.68) &RHILFLHQWXO�JOREDO�GH�VFKLPE�GH�F�OGXU��HVWH��

i

iIIk

αεα

⋅+=

1 [W/m2K] (4.69)

cX�YDORULOH�SHQWUX�FRHILFLHQWXO�GH�PXUG�ULUH�GLQ�WDEHOXO�� 'LIHUHQ D� PHGLH� GH� WHPSHUDWXUL� VH� GHWHUPLQ�� FRQIRUP� VFKHPHL� ILJXULL� �� úL�UHOD LHL��

min

max

minmaxmII

t

tln

ttt

∆∆

∆∆∆

−= (4.70)


168

)LJ��'LIHUHQ D�PHGLH�D�WHPSHUDWXULORU mIIt∆ ÌQ�ILQDO�VXSUDID D�GH�VFKLPE�GH�F�OGXU��D�GUXPXOXL�FRQYHFWLY�,,�VH�GHWHUPLQ��FX�formula :

mIIII

cIIcII

tk

QS

∆⋅= [m2] (4.71)

úL�UH]XOW��OXQJLPHD�GUXPXOXL�convectiv:

IIi

cIIcII

nd

SL

⋅⋅=

π [m] (4.72)

��&DOFXOXO�GH�HFKLOLEUDUH�D�VXSUDIH HORU� 'LQ� ILJXUD� �� UH]XOW�� FRQGL LD� FRQVWUXFWLY�� Fa lungimea focarului L=LR+LúDP V�� ILH� HJDO��cu lungimea drumurilor convective (úL� DFHVWHD� HJDOH� vQWUH�ele) : L = LI = LII (4.73) Dintr-XQ� SULP� FDOFXO� � DFHDVW�� FRQGL LH� QX� HVWH� vQGHSOLQLW�� úL� DWXQFL� VH�SURFHGHD]��OD�R�echilibrare�D�VXSUDIH HORU��

S SC2

t

tsat

tc1

tcos

∆tmax

∆tmin


CAZANE

169

6H� LD� vQ� SULPXO� UkQG� FD� OXQJLPH� D� GUXPXULORU� FRQYHFWLYH�PHGLD� �UDSRUWDW�� OD�VXSUDID ��D�FHORU�GRX��GUXPXUL��

convIIIIIIIIIL)nn(LnLn +=+ (4.74)

deci :

III

IIIIIIconv

nn

LnLnL

++

= (4.75)

În acest fel s-D�PHQ LQXW�VXSUDID D�GH�VFKLPE�GDU�V-a repartizat altfel între cele GRX��GUXPXUL� 2� D� GRXD� HFKLOLEUDUH� WUHEXLH� I�FXW�� vQWUH� OXQJLPHD� IRFDUXOXL� /� úL� OXQJLPHa drumurilor convective Lconv . D�� 'DF�� /conv este mai mic decât L, dar mai mare decât LR, atunci partea IRFDUXOXL� FDUH�GHS�úHúWH� OXQJLPHD�FRQYHFWLY�� VH� VFRDWH� vQ�DIDUD�FD]DQXOXL� VXE� IRUP��de antefocar. E��'DF��/conv�HVWH�PDL�PLF�GHFkW�/�úL�PDL�PLF�FKLar ca LR��DWXQFL�VH�SURFHGHD]��OD� VF�GHUHD� WHPSHUDWXULL� OD�FRú� �WFRú��DVWIHO� vQFkW�QHFHVDUXO�GH�VXSUDID �� FRQYHFWLY��V��FUHDVF��úL�V��DMXQJ��vQ�OLPLWHOH�/�≥ Lconv ≥ LR . Se poate, GH�DVHPHQHD��P�UL�GLDPHWUXO� HYLORU�FRQYHFWLYH�Gi�VDX�úL�P�UL�YLWH]D�de ciUFXOD LH�D�JD]HORU��I�U��D�VH�GHS�úL�OLPLWHOH�HFRQRPLFH� c��'DF��/conv�HVWH�PDL�PDUH�GHFkW�/�VH�SURFHGHD]��OD�R�ULGLFDUH�a temperaturii la FRú�DVWIHO�vQFkW�QHFHVDUXO�GH�VXSUDID ��FRQYHFWLY��V��VFDG��úL�V��DMXQJ��OD�/�≥ Lconv ≥ LR . Se poate de asemenea� PLFúRUD� GLDPHWUXO� HYLORU� FRQYHFWLYH� VDX�úL� YLWH]H� GH�FLUFXOD LH�D�JD]HORU��I�U��D�GHS�úL�OLPLWHOH�HFRQRPLFH�

2� DOW�� PHWRG�� GH� HFKLOLEUDUH� vQ� DFHVW� FD]� �GDF�� /conv ≥ L) este repartizarea drumurilor convective pe 3 fascicole. $FHDVW��GLQ�XUP��VROX LH neFHVLW��R� LQYHVWL LH�VXSOLPHQWDU��SULQ�SODFD�WuEXODU��FH� WUHEXLH� SXV�� OD� FDS�WXO� IRFDUXOXL�� FD]DQXO� GHYHQLQG� FX� WXE� GH� IODF�U�� úL� HYL� vQ�prelungire. 6ROX LLOH�GH�PDL�VXV�VXQW�VROX LL�GH�HFKLOLEUDUH�vQ�FDGUXO�XQXL�SURLHFW�WHKQLF� /D� SURLHFWXO� GH� H[HFX LH� VH� PDL� LDX� vQ� GLVFX LH� úL� HOHPHQWHOH� HFRQRPLFH� DOH�ILHF�UHL�VROX LL� 2� DOW�� SRVLELOLWDWH� GH� HFKLOLEUare este aceea în care se iau în considerare VXSUDIH HOH�GH�VFKLPE�GH�F�OGXU�� FX� IOX[XULOH�GH�F�OGXU�� UHVSHFWLYH��'DF��VH�QRWHD]��IOX[XULOH�GH�F�OGXU��


170

cII

cIIcII

cI

cIcI

R

Rf

S

Qq;

S

Qq;

S

Qq === [kW/m2] (4.76)

UH]XOW��

)(

4

2

cIIIIcIIff

cIIcIsfffR

qnqndqD

QQLqDqD

Q

L⋅+⋅⋅⋅+−⋅⋅

++

⋅⋅⋅+⋅

⋅−

=ππ

ππ

[m] (4.77)

'DF�� VH� UHLD� FDOFXOXO� GH� YHULILFDUH� FX� DFHVWH� GLPHQVLXQL�� VH� UHFDOFXOHD]��

'cII

'cI

'R Q,Q,Q úL�VH�GHWHUPLQ�� '

ft �úL� 'cIt .

��&DOFXOXO�WHUPLF�DO�FD]DQXOXL�FX� HYL�FX�LQFOLQDUH�PDUH��WLS�&5�� 'HVFULHUHD�FD]DQXOXL��HOHPHQWH�FRPSRQHQWH��PRG�GH�IXQF LRQDUH� &D]DQHOH� FX� HYL� FX� vQFOLQDUH� PDUH�� WLS� &5� �FD]DQH� GH� UDGLD LH�� sunt cazane DFYDWXEXODUH�� FX� GRX�� WDPEXUXUL�� XQ� GUXP� FRQYHFWLY� úL� SUHvQF�O]LWRU� GH� DHU�� 3URGXF�DEXU� VDWXUDW� úL� IXQF LRQHD]�� FX� JD]H� QDWXUDOH� VDX� FX� FRPEXVWLELO� OLFKLG�� 3ULQFLSDOHOH�elemente componente sunt prezentate în schema din figura 4.5. $FHVWH�FD]DQH�DX� HYLOH�ILHUE�WRDUH�DOH�HFUDQHORU�úL�VLVWHPXOXL�FRQYHFWLY�OHJDWH�GLUHFW�OD�WDPEXUXUL�úL�R�vQFOLQDUH�PHUJkQG�SkQ��OD�YHUWLFDOLWate. Acest mod de prindere DVLJXU��R�EXQ��FLUFXOD LH�LQWHULRDU��D�DSHL�úL�HPXOVLHL�vQ�FD]DQ� ÌQ�WHKQLFD�PRGHUQ��DX�OXDW�H[WLQGHUH�WRW�PDL�PDUH�FD]DQHOH�FX� HYi cu înclinare PDUH�FX�ÄSHUHWH�PHPEUDQ�´�DYkQG� HYLOH�DO�WXUDWH�VXGDWH cu platbande. Se înlRFXLHúWH DVWIHO� ]LG�ULD� JUHRDLH� D� FD]DQXOXL� FX� XQ� VWUDW� WHUPRL]RODQW� SURWHMDW� FX� WDEO�� úL� VH�P�UHúWH�VXEVWDQ LDO�WUDQVIHUXO�UDGLDQW�vQ�IRFDU��GH�DLFL�úL�GHQXPLUHD�GH cazare tip CR). 7HKQLFD� VXGXULL� DXWRPDWH� FX� VWUDW� SURWHFWRU� GH� IOX[� VDX� vQ� FXUHQW� GH� vQDOW��IUHFYHQ �� HVWH�ELQH�SXV�� OD�SXQFW�úL�DVWIHO�ÄSHUH LL�PHPEUDQ�´�VXQW�HFRQRPLFL�úL� I�U��defecte. (WDQúHLWDWHD�SHUIHFW�� vQ�IRFDU�SHUPLWH�DUGHUHD�FRPEXVWLELOXOXL�OLFhid sau gazos VXE�SUHVLXQH�vQ�YHGHUHD�LQWHQVLILF�ULL�SURFHVHORU�GLQ�IRFDU�úL�UHDOL]�ULL�XQRU�YLWH]H�PDUL�GH�FLUFXOD LH�D�JD]HORU�GH�DUGHUH�vQ�drumurile convective. *D]HOH� GH� DUGHUH� VFKLPE�� F�OGXU�� SULQ� UDGLD LH� vQ� IRFDU, parcurg lungimea IRFDUXOXL�úL�GDWRULW��WLUDMXOXL�VXQW�REOLJDWH�V��WUHDF��vQ�VLVWHPXO�ILHUE�WRU�FRQYHFWLY��De aici parcurg� GLQ� QRX� OXQJLPHD� FD]DQXOXL� úL� VXQW� SUHOXDWH� GH� canalul de colectare� úL�LQWURGXVH�vQ� HYLOH�SUHvQF�O]LWRUXOXL�GH�DHU��/D�LHúLUH�sunt aspirDWH�GH�F�WUH un exhautor úL�HOLminate la�FRú� Astfel de cazane pot produce 5 – 50 t/h abur cu presiuni de 8 – 30 bar.


CAZANE

171

��HFUDQ�ODWHUDO��HFUDQ�VSDWH��ILHUE�WRU�FRQYHFWLY��FDQDO�JD]H�VSUH�3$��SUHvQF�O]LWRU�GH�DHU��WDPEXU�VXSHULRU��tambur iQIHULRU��FRQGXFW��GH�DEXU��FDQDO�GH�DHU��FROHFWRU�HFUDQ�VSDWH��DU]�WRU��DOLPHQWDUH�FX�DS��13. purje.

)LJ��&D]DQ�FX� HYL�FX�vQFOLQDUH�PDUH

4.2.2. Tema de proiectare

7HPD�GH�SURLHFWDUH�LPSXQH�XUP�WRDUHOH�GDWH��

- debitul cazanului : Dh [t/h] sau D [kg/s] ; - presiunea aburului saturat : ps [bar] ; - titlul aburului: $; - temperatura apei la intrarea în cazan: ti [

0C]; - FRPSR]L LD�FRPEXVWLELOXOXL�XWLOL]DW��OLFKLG�VDX�JD]RV��; - IRFDUXO�IXQF LRQHD]��vQ�VXSUDSUHVLXQH�VDX�vQ�GHSUHVLXQH; - cazaQ�FX�SUHvQF�O]LWRU�GH�DHU�; - temperatura de prHvQF�O]LUH�D aerului: tpa [

0C]; - WHPSHUDWXUD�DHUXOXL�LQWURGXV�vQ�SUHvQF�O]LWRU��Wa [0C]; &D]DQXO� IXQF LRQHD]�� vQ� VXSUDSUHVLXQH� úL� FRHILFLHQWXO� GH� H[FHV� GH� DHU� HVWH�

constant pe traseul gazelor de ardere αf = αsfc = α1 =1,05 – 1,15. Coeficientul de exces GH� DHU� � vQ� SUHvQF�O]LWRUXO� GH� DHU� SRDWH� V�� FUHDVF�� αPA = α2 = α1� �� GDF��VXSUDSUHVLXQHD� GLQ� IRFDU� DVLJXU�� R� SUHVLXQH� ]HUR� VDX� QHJDWLY�� OD� LHúLUHD� JD]HORU� GLQ�focar.

a hF bhC lF

1

2

2

3

3

4

5 6

7

8 9

10

11

12

13

14


172

ConforP� LQGLFD LLORU� GLQ� FDSLWROXO� �� se HIHFWXHD]�� FDOFXOXO� DUGHULL�FRPEXVWLELOXOXL��6H�GHWHUPLQ�� ig0 H,V,V

o�úL�VH�WUDVHD]��GLDJUDPHOH�,-t sau cp – t.

��&DOFXOXO�UDQGDPHQWXOXL�WHUPLF�DO�FD]DQXOXL�úL�D�GHELWXOXL�GH�FRPEXVWLELO� $FHVWH�FD]DQH�IXQF LRQHD]��QXPDL�FX�FRPEXVWLELO�JD]RV�VDX�OLFKLG��GHFL�Tmec=0 úL�Tcen=0) . a). 3LHUGHUHD�VSHFLILF��GH�F�OGXU��SULQ�HQWDOSLD�JD]HORU de ardere�OD�FRú )LLQG�XQ�FD]DQ�GH�DEXU�FX�VXSUDIH H�DX[LOLDUH��VH�DGPLWH�LQL LDO�R�WHPSHUDWXU��OD�FRú FDOFXODW� cu formula H[SHULPHQWDO� de optimizare :

h

cosD

t100

160 +≅ [0C] (4.78)

Din diagrama I-W�VH�DIO��YDORDUHD�HQWDOSLHL�JD]HORU�GH�DUGHUH�OD�FRú��

),t(fI coscoscos α= (QWDOSLD� DHUXOXL� WHRUHWLF� GH�DUGHUH� VH�FDOFXOHD]�� SHQWUX� WHPSHUDWXUD�DPELDQW�� ta=20 0C; apaao tcVI 0=

5H]XOW��SLHUGHUHD�VSHFLILF��OD�FRú�� )II(

Hq aocoscos

i

cos α−=1

(4.79)

b) 3LHUGHUHD�VSHFLILF��GH�F�OGXU��SULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��FKLPLF� În proiectare se admite o pierdere prin arGHUH� LQFRPSOHW�� FD]DQXO� Iiind cu HFUDQDUH�PDUH�úL�DU]�WRUXO�GH�vQDOW��SHUIRUPDQ �:

0010,qch = c) 3LHUGHUL�VSHFLILFH�GH�F�OGXU��SULQ�VXSUDIe ele exterioare ale cazanului 6H�SRDWH�XWLOL]D�UHOD LD�DSUR[LPDWLY�� 5185021087975 ,

hext D,q −−×= pentru cazane de abur cu�VXSUDIH H�DQH[H� d) Randamentul cazanului 6H�FDOFXOHD]��FX�UHOD LD�: )qqq( extchcos ++−= 1η úL�

%% ηη ⋅= 100


CAZANE

173

e) Consumul de combustibil $GPL kQG�F��GHELWXO�GH�SXUM��vQ�FRQGL LLOH�XQHL�DSH�ELQH�WUDWDWH��este de 3% din debitul de abur al cazanului:

Dp=0,03•D .

'LQ�WDEHOHOH�GH�SURSULHW� L�WHUPRGLQDPLFH�DOH�DEXUXOXL�(Anexa 4��VH�GHWHUPLQ��pentru presiunea aburului ps �XUP�WRDUHOH�P�ULPL��

- WHPSHUDWXUD�GH�VDWXUD LH� - ts

- entalpia aburului saturat uscat - i”

- HQWDOSLD�DSHL�OD�VDWXUD LH� - i’

- HQWDOSLD�DSHL�OD�LQWUDUH��FRUHVSXQ]�WRDUH�WHPSHUDWXULL ti :

io=4,186•ti (kJ/kg)

Deoarece aburul are un titlul c��HQWDOSLD�ILQDO��D�DEXUXOXL�HVWH�� 'i)(''ii ⋅−+⋅= χχ 1 (4.80) Deoarece pentru cazanele de acHVW�WLS�QX�VH�XWLOL]HD]��LQMHFWRDUH�GH�FRPEXVWLELO�OLFKLG�FX� LQMHF Le de abur�� UH]XOW� Winj ��(YLGHQW�úL� vQ�FD]XO�FRPEXVWLELOXOXL�JD]RV�Winj =0. 'H� DVHPHQHD� VH� LD� vQ� FRQVLGHUDUH� F�� SHQWUX� FRPEXVWLELO� OLFKLG� VDX� JD]RV�qmec ��úL�GHFL�B* =B . 5H]XOW��F��:

i

opo

H

)i'i(D)ii(DB

⋅

−⋅+−⋅=

η [u.c.*/s] (4.81)

*(unitati de combustibil) ��%LODQ XO�GH�DQVDPEOX�DO�FD]DQXOXL� )OX[XO�GH�F�OGXU��XWLO�DO�FD]DQXOXL�HVWH�� )i'i(D)ii(DQ opout

−⋅+−⋅= (4.82)

Fluxul�GH�F�OGXU��DGXV�GH�FRPEXVWLELO: ic HBQ ⋅= (4.83) Fluxul de c�OGXU��DGXV�FX�DHUXO�DWPRVIHULF:

apacosa tcVBQ ⋅⋅⋅⋅= 0α (4.84)


174

)OX[XO�GH�F�OGXU��DGXV�SULQ�SUHvQF�O]Lrea aerului:

)tt(cVBQ apapafPA −⋅⋅⋅⋅= 0α (4.85)

)OX[XO�GH�F�OGXU��SLHUGXW�OD�FRú�� coscos IBQ ⋅= (4.86) )OX[XO�GH�F�OGXU��pierdut�SULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��FKLPLF� :

ichch HBqQ ⋅⋅= (4.87) )OX[XO�GH�F�OGXU��SLHUGXW�VSUH�H[WHULRU�� iextext HBqQ ⋅⋅= (4.88)

5H]XOW��WDEHOXO�Ge�ELODQ ��

Tabelul 4.5. Combustibil – pierderi Util

Qc

Qa + QPA

- QFRú - Qinc

- Qext

Qut

QPA

∑ = 'QQ ''QQ∑ =

1RW�� vQ� DFHVW� ELODQ � �-q2BHi) s-a scris sub forma: (-BIFRú+BαFRúV0cpata); deci

IRUPD�H[SOLFLW��

6H�GHILQHúWH�HURDUHD�UHODWLY�� %100'Q

''Q'Q −=ε úL� VH� YHULILF�� HURDUHD�

PD[LP��DGPLVLELO��GH�� 'DF��HURDUHD�HVWH�PDL�PDUH�H[LVW��R�JUHúHDO��GH�FDOFXO�� &DOFXOXO�WHPSHUDWXULL�úL�HQWDOSLLORU�JD]HORU�GH�DUGHUH�SH�WUDVHX

(QWDOSLD�WHRUHWLF��GH�DUGHUH�VH�FDOFXOHD]��FX�IRUPXOD�� apafchit tcV)q(HI 01 α+−⋅= [kJ/u.c.] (4.89a)

DSRL�VH�GHWHUPLQ��WHPSHUDWXUD�WHRUHWLF��GH�DUGHUH�GLQ�GLDJUDPD�,-t :

),I(ft fttα= [oC].


CAZANE

175

6H�DOHJH�WHPSHUDWXUD�OD�FDS�WXO�IRFDUXOXL�tf = 900 ÷ 1100 0C aceste valori fiind normale pentru focare de cazane mari de abur. Se GHWHUPLQ� apoi din diagrama I-t

entalpia gazelor de ardere OD�FDS�WXO�IRFDUXOXL�� If =f(tf,αf) . )OX[XO�GH�F�OGXU��SUHOXDW�SULQ�UDGLD LH�vQ�IRFDU�YD�IL: )II(B)q(Q ftextR −⋅⋅−= 1 [kW] (4.89b)

)OX[XO�GH�F�OGXU��FDUH�VH�SUHLD�vQ�VLVWHPXO�ILHUE�WRU�vQ�DQVDPEOX�HVWH��

)i'i(D)ii(DQ oposf −⋅+−⋅= [kW] (4.90)

iar�IOX[XO�GH�F�OGXU��FDUH�VH�SUHLD�vQ�VLVWHPXO�ILHUE�WRU�FRQYHFWLY�HVWH: Rsfsfc QQQ −= [kW] (4.91)

Entalpia gazelor de ardere lD�VIkUúLWXO�VLVWHPXO�ILHUE�WRU�convectiv este:

B)q(

QII

ext

sfc

fsfc ⋅−−=

1 [kJ/u.c.] (4.92)

úL�GLQ�GLDJUDPD�,-W�UH]XOW��WHPSHUDWXUD�� ),I(ft sfcsfcsfc α= [0C].

)OX[XO�GH�F�OGXU��SUHOXDW�GH�SUHvQF�O]LWRUXO�GH�DHU�HVWH�� )tt(cVBQ aPApafPA −⋅⋅⋅⋅= 0α [kW] (4.93)

Entalpia gazeORU�GH�DUGHUH�OD�VIkUúLWXO�SUHvQF�O]LWRUXOXL�GH�DHU�HVWH��

B)q(

III

ext

PAsfcPA −

−=1

[kJ/u.c.] (4.94)

úL�GLQ�GLDJUDPD�,-W�UH]XOW��WHPSHUDWXUD�� ),I(ft PAPAPA α= [0C]. ÌQFKLGHUHD�ELODQ XOXL�LPSXQH�� IPA=IFRú��úL�tPA=tFRú úL�VH�DGPLW�HURULOH�relative :

(%)I

II

t

PAcos

I 100⋅−

=ε � 0,5 %

úL� (%)t

tt

t

PAcos

t 100−

=ε � 0,5 % (4.95)

(URUL� PDL� PDUL� LQGLF�� R� JUHúHDO�� GH� FDOFXO�� ÌQ� ILQDO� VH� vQWRFPHúWH� WDEHOXO�centralizator 4.6. Tabelul 4.6.


176


Focar Convectiv I Convectiv II

QR Qsfc QPA

tt tf

tsfc

tf tsfc tFRú

��%LODQ XO�JUDILF�DO�FD]DQXOXL 'HELWHOH� GH� F�OGXU�� GLQ� WDEHOHOH� �� úL� �� VH� WUDQVSXQ� JUDILF�� OD� VFDU�� GXS��modelul general prezentat în capitolul 2 figura 2.3 (cu B*=B, QSI=0; Qec=0; qmec ��úL�qcen=0). 4.2.7. Calculul termic la focarului

)RFDUXO�GH�WLS�FDPHU��DUH�XUP�WRDUHOH�GLPHQVLXQL��

Fig. 4.6. Dimensiuni focar

Acest calcul are ca scop determinarea suprafH HL�GH�UDGLD LH�SR�FDSDELO��V��SUHLD�GHELWXO� GH� F�OGXU�� UDGLDQW� QR. Deoarece în calcule intervine gradul de ecranare

=

per

R

S

SΨ �úL�OXQJLPHD�GH�UDGLD LH�

⋅=

per

f

S

Vs 4 , este necesar un calcul interativ. Se

SRUQHúWH�FX�R�YDORDUH�DSUR[LPDWLY��S’R�FDUH��vQ�ILQDO��VH�YD�FRPSDUD�FX�FHD�UH]XOWDW��din calcul SR.

'

RS �SRDWH�IL�DSUHFLDW��SULQ�GRX��PHWRGH�� a) Se admite un flux unitar radiant qR=30 ÷ 50 kW/m2

~500

60

60

h

h’

h”

A

A

A

Sectiunea A-A

A

l

L


CAZANE

177

úL�UH]XOW�� '

RS =QR /qR [m2] b) Se calFXOHD]��VXSUDID D�SUHOLPLQDU��GH�UDGLD LH�vQ�IRFDU�FX�UHOD LD��

−

⋅⋅

=44

1001007655 pf

R'

R

TT,

QS

ε [m2] (4.96)

cu : ε = 0,65 pentru combustibil gazos

ε = 0,75 pentru combustibil lichid

Tf = tf + 273 [K]

Tp = ts + 273 [K] Pentru alegerea dimensiunilor focaUXOXL��VH�FDOFXOHD]��YROXPXO�IRFDUXOXL�GLQWU-R�FRQGL LH�GH�vQF�UFDUH�WHUPLF��YROXPHWULF��DGPLVLELO�� 250150 ÷=vq [kW/m3] (4.97) úL�UH]XOW��

v

i

v

cf

q

HB

q

QV

⋅== [m3] (4.98)

Se alege apoi un raport de laturi Ah ⋅÷≅ )43(

úL�VH�GHWHUPLQ��ODWXULOH�GLQ�UHOD LD�� LhAV f ⋅⋅=

/DWXULOH� VH� URWXQMHVF� OD� YDORULOH� vQWUHJL� GH� ]HFLPL� GH� PHWUX�� 'DF�� ODWXULOH� DX�GLPHQVLXQL�SUHD�GLIHULWH�GH�VROX LLOH�X]XDOH�VH�DOHJH�DOW��vQF�UFDUH�WHUPLF��D�IRFDUXOXL� &XQRVFkQG�F��VXSUDID D�SHUH LORU�IRFDUXOXL�HVWH�� hAL

cos

ALhLhS

o

'"

per ⋅⋅+⋅⋅+⋅+⋅= 26

2 [m2]

úL�F��Jrosimea stratului radiant de gaze este :

per

f

S

Vs ⋅= 4 [m] (4.99)

sH�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�JD]HORU�GH�DUGHUH�GLQ�IRFDU��

)pp(T

,s)pp(

p,,k ROOH

f

ROOH

OH

g 22

22

2

10003801

6180+⋅

⋅−⋅

⋅+

⋅+= (4.100)

Valorile lui OHp2��úL�

2ROp s-au calculat pentru α1 = αf�FX�UHOD LLOH��


178

g

fg

OH

OH pV)(V

Vp

o 012

2 −+=

α ; g

fg

RO

RO pV)(V

Vp

o 012

2 −+=

α (4.101)

cu : pg =1 bar. 6H�FDOFXOHD]��FRHILFLHQWXO�GH�DEVRUE LH�DO�JD]HORU�Ge ardere din focar :

sk

g

gea⋅−−= 1 (4.102)

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IO�F�ULL�FX�UHOD LD�DSUR[LPDWLY�� 5,0

1000

T6,1k f

fl −⋅= (4.103)


sk

fl

flea⋅−−=1 (4.104)

PondHUHD�DEVRUE LHL�IO�F�ULL�FX�FHD�D�PHGLXOXL�UDGLDQW�GH�JD]H�GH�DUGHUH�VH�IDFH�

GXS��FULWHULL�experimentale�FRQVLGHUkQG�R�SURSRU LH��GLQ�YROXPXO�IRFDUXOXL��RFXSDW��GH�SDUWHD�OXPLQRDV��D�IO�F�ULL��β - coeficient de luminozitate) .

&RHILFLHQWXO�GH�DEVRUE LH�DO�IO�F�ULL�úL�JD]HORU�GH�DUGHUH�VH�FDOFXOHD]��FX�UHOD LD� gfl a)(aa ⋅−+⋅= ββ 1 (4.105)

cu β = 0,2 –��SHQWUX�IODF�U��OXPLQRDV��GH�FRPEXVWLELO�JD]RV��úL β� ��SHQWUX�IODF�U��SURGXV��GH�FRPEXVWLELO�OLFKLG�

Gradul de ecranare al focarului este :

per

'

R

S

S=Ψ §�� (4.106)

úL�PXUG�ULUHD�VXSUDIH HORU�� ξ = 0,7 ÷ 0,9 combustibil gazos

ξ = 0,6 ÷ 0,7 combustibil lichid &X�DFHVWH�YDORUL�VH�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IRFDUXOXL�� ξΨ ⋅⋅−+

⋅=

)a(a

a,a f 1

820 (4.107)

2� DOW�� FDUDFWHULVWLF�� D� IRFDUXOXL�� IDFWRUXO� GH� SR]L LH� D� IO�F�ULL� vQ� IRFDU�� SHQWUX�combustibil lichid sau gazos�VH�GHWHUPLQ��FX�UHOD LD:


CAZANE

179

foc

arzMM

H

hbaM ⋅−= (4.108)

cu : aM = 0,52; bM = 0,3; foc

arz

H

h =�FRQIRUP�VFKL ��IRFar §�

3

1.

&X�DFHVWH�GDWH�VH�GHWHUPLQ��VXSUDID D�GH�UDGLD LH�D�IRFDUXOXL��

32

2

38

11

107655 MT

T

TTaM,

QS

f

t

tff

RR ⋅

−⋅

⋅⋅⋅⋅⋅⋅= − ξ

[m2] (4.109)

unde Tt�HVWH�WHPSHUDWXUD�WHRUHWLF��GH�DUGHUH��tt+273) [K].


RS � GHWHUPLQDW�� vQ� FDOFXOXO� DSUR[LPDWLY��'DF��GLIHUHQ D�HVWH�PDL�PDUH�GH�� % se reia calculul cu valori modificate pentru ψ (pentru calcule automate�GLIHUHQ D�HVWH�GH��PD[� 1 % ). 6XSUDID D� SHUH LORU� HFUDQD L� �VROX LD� FX� ]LG�ULH�� YD� IL� GLIHULW�� GH� SR datRULW��FRHILFLHQWXOXL�VXEXQLWDU�GH�HILFLHQW��D�HFUDQHORU�GH�SHUHWH�( χ ). Amplasarea ecranelor se face astfel : a) Ecranul de tavan (VWH� FRQVWLWXLW� GLQ� HYLOH� VHPLvQJURSDWH� DOH� WDYDQXOXL�� HYLOH� GH� HFUDQH� OD�FD]DQXO�FX� HYL�FX�vQFOLQDUH�PDUH�DX�GLPHQsiunea : φ 51×3; φ 51×5; φ 57×3; φ 57×5; φ 60×3; φ 60×5 Se alege pasul ecranelor :

8121 ,,d

s÷= cu d –�GLDPHWUXO�H[WHULRU�DO� HYLL�

Pasul este� IRDUWH� PLF� SHQWUX� FD� U�FLUHD� ]LG�ULHL� V�� VH� IDF�� IRDUWH� LQWHQV� úL�JURVLPHD�QHFHVDU��a ]LG�ULHL�V��ILH�PLF�� $VWIHO� OD� FD]DQHOH�&5�� JURVLPHD� ]LG�ULHL� IRFDUXOXL� HVWH� ��PP�� ID �� GH� DOWH�cazane la care grosimea ajunge la 300 – 500 mm. Din diagrama din figura� �� UH]XOW�� YDORDUHD� FRHILFLHQWXOXL� GH� HILFLHQ �� χ al ecranului.


180

)LJ��'LDJUDPH�GH�FDOFXO�SHQWUX�FRHILFLHQ LL�GH�HILFLHQW��DL�HFUDQHORU

6XSUDID D�HFUDQDW��HVWH: 06

1

cosLASa ⋅= (4.110)

b) Ecranul lateral stânga eVWH� vQ� FRQWLQXDUHD� HFUDQXOXL� GH� WDYDQ� GDU� HYLOH� Qu mai sunt semiîngropate ci sunt GLVWDQ DWH�ID ��GH�SHUHWH�OD�GLVWDQ D�s =(1,2 ÷ 1,8)d. 'LQ�GLDJUDPD�ILJXULL��UH]XOW��FRHILFLHQWXO�GH�HILFLHQ ��χ al ecranului.

(ILFLHQ ��HFUDQ�GH�UDGLD LH�VHPLvQJURSDW

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

s/d

X

(ILFLHQ ��HFUDQ�GH�UDGLD LH�GLVWDQ DW

0.4

0.5

0.6

0.7

0.8

0.9

1

1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

s/d

X

s d

s d


CAZANE

181

6XSUDID D�HFUDQDW��HVWH�� L"hSb ⋅= (4.111)

Cu: h”=h+206

2tg

A

c). Ecranul lateral dreapta Este un ecran independent, legat la tamburi. 'LQ� PRWLYH� FRQVWUXFWLYH� GLDPHWUXO� úL� SDVXO� HYLORU� VH� S�VWUHD]�� DFHODúL� FD� OD�HFUDQXO�VWkQJD��7RWXúL��GDF��HVWH�QHFHVDU��VH�SRDWH�P�UL�SDVXO��QHILLQG�LPSXVH�FRQGL LL�GH�U�FLUH�D�]LG�ULHL� 'LQ�GLDJUDPD�ILJXULL��UH]XOW��FRHILFLHQWXO�GH�HILFLHQ ��χ al ecranului.

6XSUDID D�HFUDQDW��HVWH�� L'hSb ⋅= (4.112)

Cu: h’=h-206

2tg

A

d) Ecranul spate (VWH�XQ� HFUDQ� OHJDW� SULQ�GRX� colectoare exterioare de tamburi. Montarea lui DUH�vQ�VSHFLDO�UROXO�GH�U�FLUH�D�SHUHWHOXL�GLQ�VSDWH��GDU�SRDWH�V��úL�OLSHDVF�� Tot�GLQ�PRWLYH�FRQVWUXFWLYH�VH�UHFRPDQG��PHQ LQHUHD diametrului�úL�SDVului de DúH]DUH�GH�OD celelalte ecrane de perete. Din�GLDJUDPD�ILJXULL��UH]XOW��FRHILFLHQWXO�GH�HILFLHQ ��χ al ecranului.

6XSUDID D�HFUDQDW��HVWH�� LhSb ⋅= e) Ecranul ID �

(VWH�XQ� HFUDQ� OHJDW� SULQ�GRX�� FROHFWRDUH� H[WHULRDUH�GH� WDPEXUL�� 0RQWDUHD� OXL�DUH�vQ�VSHFLDO�UROXO�GH�U�FLUH�D�SHUHWHOXL�ID ��DYkQGX-VH�JULM��V��VH�SUHYDG��VSD LL�vQWUH� HYL� SHQWUX� DPSODVDUHD� DU]�WRDUHORU�� 6SD LLOH� GLQWUH� HYL� VH� UHDOL]HD]�� SULQ� VF�GHUHD�SDVXOXL� GH� DúH]DUH� GH� R� SDUWH� úL� GH� DOWD� D� ]RQHL� GH� DPSODVDUH� D� DU]�WRUXOXL�� )RUPD� HYLORU�QX�YD�PDL�IL�GUHDSW��ci va avea bucle cu îndoiri specifice rezultate constructiv. 6XSUDID D�HFUDQDW��HVWH�DFHHDvL�FX�FHD�D�SHUHWHOXL�VSDWH��


182

În final se vQWRFPHúWH un tabel centralizator (4.7) al ecranelor . Tabelul 4.7.

Amplasare ecran Dimensiuni

[m] 6XSUDID D

Si [m2]

Coeficient de

HILFLHQW��χ i

6XSUDID D�GH�UDGLD LH�Si χ i

[m2] Tavan Perete lateral stânga Perete lateral dreapta Perete spate 3HUHWH�ID �

∑ ii xS

7UHEXLH�V��VH�UHDOL]H]H�� ∑ ii xS

RS≥ (4.113)

'DF�� VH� UHQXQ �� OD� VROX LD� GH�]LG�ULH� vQ� IDYRDUHD� VROX LHL�GH�SHUHWH�PHPEUDQ��

FDOFXOHOH� U�PkQ� YDODELOH� FX� SUHFL]DUHD� F�� SHQWUX� WRDWH� VXSUDIH HOH� FRHILFLHQ LL� GH�HILFLHQ ��Di ecranelor devin egali cu 1.

'DF��∑ ii xSRS> se va reduce lungimea de ecranare L��VDX�VH�SRDWH�UHQXQ D�

la ecranul de fund.

'DF�� ∑ ii xSRS< � VXSUDID D� SHUH LORU� QX� HVWH� VXILFLHQW�� SHQWUX� DPSODVDUHD�

HFUDQHORU� � úL� WUHEXLH� DOHV� XQ� IRFDU� PDL� PDUH�� &DOFXOul se reia de la început cu o vQF�UFDUH�WHUPLF��YROXPHWULF��qv�PDL�PLF��

'XS�� VWDELOLUHD� P�ULPLORU� JHRPHWULFH� DOH� HFUDQHORU� VH� FDOFXOHD]�� QXP�UXO� GH�

HYL� SHQWUX� ILHFDUH� HFUDQ�� SULQ� vPS�U LUHD� O� LPLL� SHUHWHOXL� OD� SDVXO� GH� HFUDQDUH� s. Se face apoi R�VHF LXne OD�VFDU��D�IRFDUXOXL�HFUDQDW�

��&DOFXOXO�WHUPLF�OD�VLVWHPXOXL�ILHUE�WRU�FRQYHFWLY� 'UXPXO� FRQYHFWLY� HVWH� GHWHUPLQDW� GLQ� FDOFXOHOH� DQWHULRDUH� SULQ� XUP�WRULL�parametrii : Qsfc –�IOX[�GH�F�OGXU��[kW] ;

tf – temperatura gazelor la intrare;

tsfc –�WHPSHUDWXUD�JD]HORU��OD�LHúLUH�� tsat –�WHPSHUDWXUD�IOXLGXOXL�OD��VDWXUD LH�


CAZANE

183

3HQWUX� VWDELOLUHD� VHF LXQLL� GH� WUHFHUH� D� JD]HORU� GH� DUGHUH� VH� DOHJH� GLDPHWUXO� HYLORU� GUXPXlui convectiv din gama X]XDO�� GH� HYL� φ 60×3; φ 57×3 sau φ 51×�� úL�pasul relativ transversal 8131 ,,

d

s÷= .

6H� DOHJH� LQL LDO� GLDPHWUXO� HYLORU� úL� YLWH]D� GH� FLUFXOD LH� D� JD]HORU� GH� DUGHUH� vQ�limitele economice : w’=10 ÷ 15 m/s 6HF LXQHD�QHFHVDU��GH�WUHFHUH�D�JD]HORU�GH�DUGHUH�YD�IL��

273

273+⋅= mgg

sfc

t

'w

BVA [m2] (4.114)

unde: Vg s-D�FDOFXODW�FX�UHOD LD� 01 V)(VV sfcgg o⋅−+= α .

tmg – este temperatura medie a gazelor de ardere :2

sfcf

mg

ttt

+= [0C]

*HRPHWULF��VHF LXQHD�GH�WUHFHUH�OLEHU��HVWH��

−⋅⋅=

−=

11

1 1s

dh'bh

s

ds'bAsfc (4.115)

úL�UH]XOW��O� imea provizorie a canalului convectiv :

−

=

1

1s

dh

A'b

sfc

[m] (4.116)

úL�QXP�UXO�GH� HYL�SH��UkQG�� 21'

11 +

−=

s

bn r -�VH�URWXQMHúWH�OD�QXP�UXO�vQWUHJ�FHO�

mai apropiat. Uzual : rn1 = 4÷�� HYL�� 'DF�� r1n este în afara acestui domeniu se UHFRPDQG��UHFDOFXODUHD�FX�R�vQ�O LPH�K�GLIHULW��DVWIHO�încât�V��VH�UHVSHFWH�LQWHUYDOXO� 5H]XOW��O� LPHD�UHDO��D�FDQDOXOXL�FRQYHFWLY�� ( ) 11 1 snb r ⋅+= [m] ÌQ�ILQDO�VH�UHFDOFXOHD]��YLWH]D�JD]HORU�GH�DUGHUH :

)(

273

273

1 dnbh

tVB

wr

mg

g

⋅−⋅

+⋅⋅

= [m/s] (4.117)

Pentru temperatura medie a gazelor de ardere tmg� VH� GHWHUPLQ�� GLQ� DQH[a 9

XUP�WRDUHOH�YDORUL��


184



- criteriul Prandtl Pr apoL�VH�GHWHUPLQ��FULWHULXO�KLGURGLQDPLF�� υ

ee

dwR

⋅=

úL�VLPSOH[XULOH�GH�OXQJLPL�� .s

s;

d

s;

d

s

ee 2

121 Pentru

ed

s2 se aleg valori de 1,7 ÷ 2,2.

&RUHF LD�GH�DúH]DUH�D�IDVFLFROXOXL�HVWH��

150

2

,

ed

sc

−

=σ pentru coridor

61

2

1

/

s

sc

=σ SHQWUX�HúLFKHU�FX�

2

1

s

s < 2

121,c =σ SHQWUX�HúLFKHU�FX�2

1

s

s ≥ 2

6H�FDOFXOHD]��DSRL�FRHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�FRQYHF LH�OD�VF�OGDUH�WUDQVYHUVDO��D�IDVFLFROXOXL�vQ�HúLFKHU��vQ�LSRWH]D�� 103 < Re < 105

250

33060410

,

rp

r,,

tP

PPrRec

d,

⋅⋅⋅⋅⋅= σ

λα [W/m2K] (4.118)

tcN

,N αα ⋅−

=70

(4.119)

'HRDUHFH�QXP�UXO�GH�UkQGXUL�HVWH�GH�RELFHL�N >15; tc αα ≅ . &RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD ie este determinat de parametrii :

* OHp2� �úL�

2ROp �FDOFXOD L�vQ�FDSLWROXO��UHOD LD��úL�VH�FDOFXOHD]��pentru sfc

αα = .

* s – grosimea stratului radiant, care va fi :

d,d

s

d

s,s ⋅

−

+⋅= 14871 21

[m] (4.120)

&RQVWDQWD�GH�UDGLD LH��D�JD]HORU�HVWH��


CAZANE

185

)pp(T

,s)pp(

p,,k ROOH

mg

ROOH

OH

g 22

22

2

10003801

6180+⋅

⋅−⋅

⋅+

⋅+= (4.121)

cu Tmg = tmg + 273 [K] iar coeficientul de emisie al gazelor de ardere :

sk

g

gea⋅−−= 1 (4.122)

Coeficientul de schimb de F�OGXU��SULQ�UDGLD LH�VH�FDOFXOHD]��FX�UHOD LD��

−

−

⋅⋅⋅+

⋅⋅=α −6,3

mg

p

mg

p

3mgg

p8r

T

T1

T

T1

Ta2

1a10765,5 [W/m2K] (4.123)

XQGH� SHQWUX� FRHILFLHQWXO� GH� DEVRUE LH� DO� SHUHWHOXL� VH� LD� YDORDUHD� ap �� úL� SHQWUX�WHPSHUDWXUD�DEVROXW��D�SHUHWHOXL� HYLL��

27320 ++=satp tT [K] (4.124)

Coeficientul de WUDQVIHU�GH�F�OGXU��HVWH�: rci αωαα += (4.125)

cu ω=0,95 ÷��SHQWUX�VF�OGDUHD�LPSHUIHFW��D�IDVFLFROXOXL�� &RHILFLHQWXO�JOREDO�GH�VFKLPE�GH�F�OGXU��HVWH��

i

ikαε

α⋅+

=1

(4.126)

cu valorile SHQWUX�FRHILFLHQWXO�GH�PXUG�ULUH�ε din tabelul 4.4. 'LIHUHQ D� PHGLH� GH� WHPSHUDWXUL� VH� GHWHUPLQ�� FRQIRUP� VFKHPHL� ILJXULL� �� úL�UHOD LHL��

min

max

minmaxm

t

tln

ttt

∆∆

∆∆∆ −= (4.127)

ÌQ�ILQDO�VXSUDID D�GH�VFKLPE�GH�F�OGXU��D�GUXPXOXL�FRQYHFWLY��VH�GHWHUPLQ��FX�UHOD LD��


186

m

sfcsfc tk

QS

∆⋅= [m2] (4.128)

)LJ��'LIHUHQ D�PHGLH�D�WHPSHUDWXULORU úL�UH]XOW��QXP�UXO�GH�UkQGXUL�GH�� HYL��

hnd

SN

re

sfc

⋅⋅⋅=

1π ;

care VH�URWXQMHúWH�OD�YDORDUH�vQWUHDJ�� Lungimea drumului convectiv este:

2sNlc ⋅= [m]. ÌQ� FD]XO� FkQG�QXP�UXO� GH� UkQGXUL� HVWH�1!��HVWH�X]XDO� V�� VH� vPSDUW�� în� GRX��SDFKHWH�IDVFLFROXO�FRQYHFWLY��FX�XQ�VSD LX�GH�YL]LWDUH� vQWUH�HOH�GH�DSUR[LPDWLY��P��În acest caz:

502 ,sNlc +⋅= [m] . ��&DOFXOXO�WHUPLF�DO�SUHvQF�O]LWRUXOXL�GH�DHU� 3UHvQF�O]LWRUXO� GH� DHU� HVWH� GHWHUPLQDW� GLQ� FDOFXOHOH� DQWHULRDUH� SULQ� XUP�WRULL�parametrii : QPA –�IOX[�GH�F�OGXU��[kW] ;

tsfc – temperatura gazelor la intrare [oC] ;

tFRú – temperatura gazelor OD�LHúLUH��[oC] ;

t

S Ssfc

tsat

tf

tsfc

∆tmax

∆tmin


CAZANE

187

ta – temperatura aerului la intrare (ambiant) [oC] ;

tap –�WHPSHUDWXUD�DHUXOXL�SUHvQF�O]LW�OD�LHúLUH [oC] . 6ROX LD� FRQVWUXFWLY�� QX� HVWH� OHJDW�� GH� GLPHQVLXQLOH� UHVWXOXL� FD]DQXOXL�� FX�H[FHS LD�OXQJLPLL�FDUH�QX�WUHEXLH�V��GHS�úHDVF��OXQJLPHD�FD]DQXOXL� 3UHvQF�O]LWRUXO�VH�UHDOL]HD]��GLQ� HYL�VF�OGDWH�vQ�LQWHULRU�GH�JD]HOH�GH�DUGHUH�úL�vQ� H[WHULRU�� WUDQVYHUVDO�� GH� DHU�� 6H� DOHJH� XQ� GLDPHWUX� DO� HYLORU�� vQ� JDPD� YDORULORU�uzuale : N22×2; N25×2; N32×2; N38×2; N42×2; N45×2; N54×2; N57×2 6H�GHWHUPLQ��DSRL�GLDPHWUHOH�FDUDFWHULVWLFH��

- interior di [m]

- exterior de [m]

3HQWUX� FDOFXOXO� WUDQVIHUXOXL� GH� F�OGXU�� SH� SDUWHD� JD]HORU� GH� DUGHUH� VH� DOHJH� R�YLWH]��wg ��·��P�V��YLWH]��UHODWLY�PLF�,�GHRDUHFH�VXSUDID D�ILLQG�PDUH�SLHUGHULOH�GH�sarcin��ce vor rezulta sunt mari.

1XP�UXO�GH� HYL�SUHOLPLQDU�QHFHVDU�vQ�IDVFLFXO�HVWH�GDW�GH�VHF LXQHD�QHFHVDU��GH�curgere a gazelor de ardere :

273

273+⋅

⋅= m

g

g

PA

t

W

VBA [m2] (4.129)

úL�

4

2i

PA

d

A'n

π= (4.130)

unde temperatura medie a gazelor este : 2

cossfc

m

ttt

+= [0C]

úL�YROXPXO�GH�JD]H: 01 V)(VV cIgg o−+= α .

1XP�UXO�GH� HYL�VH�UHSDUWL]HD]��DSRL��ILJXUD��vQWU-R�DúH]DUH�vQ�HúLFKHU��SH�XQ��dreptunghi cu raportul laturilor hp=(1,5 – 2)•bp .

3DVXO� HYLORU� VH� DOHJH� 12712 21 ,,d

s;

d

s

ee

−== ceea ce duce la un pas pe

GLDJRQDO�� 5121 ,,d

s

e

−= .


188

)LJ��$úH]DUHD� HYLORU�vQ�3$

'LQ�DúH]DUH�UH]XOW��QXP�UXO�UHDO�GH� HYL�n. 6H�UHFDOFXOHD]��DSRL�YLWH]D�JD]HORU�GH�DUGHUH��

273

273

4

2

+⋅

⋅

⋅= m

i

g

g

t

dn

VBW

π [m/s] (4.131)

Pentru temperatura medie a gazelor de ardere tm� VH� GHWHUPLQ�� GLQ� DQH[a 9 XUP�WRDUHOH�YDORUL��




DSRL�VH�GHWHUPLQ��FULWHULXO�KLdrodinamic : υig

e

dWR =

Valoarea simplexului de lungimi este, luând ca lungime lungimea focarului :

250

3,

i

l)d/L(

C = pentru L/di < 80

1=lC pentru L/di > 80 6H�FDOFXOHD]��DSRL�FRHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�FRQYHF LH�vQ�LSRWH]D�VF�OG�ULL�LQWHULRDUH�úL�WXUEXOHQ HL�VWDELOL]DWH��5H�≥10000 :

8035002630 ,,

r

i

lc RePd

C, ⋅⋅⋅⋅=λα [W/m2K] (4.132)

LDU�vQ�FD]XO��5H��VH�DSOLF��úL�FRUHF LD�VXEXQLWDU� pentru αc :

Directia de

circulatie a aerului

s

hp

bp

s2

s1


CAZANE

189

81

51061

,Re

⋅−=ε (4.133)

CoHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH�VH�FDOFXOHD]��QXPDL�GDF��

2cossfc

m

ttt

+= ≥400 0C (4.134)

vQ� FDUH� FD]� PHWRGLFD� HVWH� DFHLDúL� FX� FHD� IRORVLW�� OD� VLVWHPXO� ILHUE�WRU� FRQYHFWLY��schimbându-se OHp

2,

2ROp , Tm úL 2732

++

= mam

p

ttT �� 'DF�� tm<400 0C efectul

UDGLD LHL�VH�QHJOLMHD]��úL�αr=0. Coeficientul de WUDQVIHU�GH�F�OGXU� este :

αg = αc + αr sau αg = αc (4.135) 3HQWUX� FDOFXOXO� WUDQVPLVLHL� GH� F�OGXU�� SH� SDUWHD� DHUXOXL� VH� DOHJH� VFhema de VF�OGDUH�FX�PDL�PXOWH�WUHFHUL��FRQIRUP�ILJXULL�� ÌQ�GLUHF LD�SHUSHQGLFXODU��SH�LQWUDUHD�DHUXOXL�VXQW�Q1� HYL��

11

s

hn

p= (4.136)

úL�vQ�GLUHF LD�GH�FXUJHUH�D�DHUXOXL�Q2� HYL��

22

s

hn

p= (4.137)

VLWH]D�GH�FXUJHUH�D�DHUXOXL��DFHLDúL�vQ�WRDWH�WUHFHULOH�VH�DOHJH�vQ�OLPLWHOH�� 105 ÷=aW m/s 5H]XOW��VHF LXQHD�OLEHU��QHFHVDU��WUHFHULL�DHUXOXL��

273

273+⋅

⋅⋅= am

a

fa

a

t

W

VBA

α [m2] (4.138)

cu

2

apa

am

ttt

+= [0C]

úL�GHRDUHFH�JHRPHWULF�VHF LXQHD�HVWH��

1

11

s

dslbA e

a

−⋅⋅= [m2] (4.139)


190

sau )dnb(lA ea ⋅−⋅= 11 UH]XOW��

1

11

s

dsb

Al

e

a

−⋅

= [m] (4.140)

Canalul de aer este astfel complet deterPLQDW�úL�DUH�GLPHQVLXQLOH�b x l1 . Pentru temperatura medie a aerului tam�VH�GHWHUPLQ��GLQ�anexa 9, din coloanele SHQWUX�DHU��XUP�WRDUHOH�YDORUL��




DSRL�VH�GHWHUPLQ��FULWHULXO�KLGURGLQDPLF�� υ

ia dWRe

⋅=

a –�VHF LXQH�WUDQVYHUVDO�� b –�VHF LXQH�ORQJLWXGLQDO�

�� HYL�PHWDOLFH��úWX �LQWUDUH�–LHúLUH�DJHQW�WHUPLF�VHFXQGDU��DHU��FDPHU��GH�vQWRDUFHUH��SHUH L�GHVS�U LWRUL��úLFDQH��SO�FL�WXEXODUH��L]ROD LH�WHUPLF��úWX �LQWUDUH�–LHúLUH�DJHQW�WHUPLF primar

(gaze de ardere).

)LJ��3UHvQF�O]LWRUXO�GH�DHU &RUHF LD�GH�DúH]DUH�D�IDVFLFROXOXL�HVWH��

150

2

,

ed

sC

−

=σ pentru coridor

s2

A

A

AER CALD

AER RECE

GAZE DE ARDERE

GAZE DE

ARDERE

s1

12 34

5

62

7

7


CAZANE

191

61

2

1

/

s

sC

=σ SHQWUX�HúLFKHU�FX�

2

1

s

s < 2

121,C =σ SHQWUX�HúLFKHU�FX�2

1

s

s ≥ 2

6H�FDOFXOHD]��DSRL�FRHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�FRQYHF LH�OD�VF�OGDUH�WUDQVYHUVDO��D�IDVFLFROXOXL�vQ�HúLFKHU��vQ�LSRWH]D� 103 < Re < 105 :

250

330603 410

,

rp

,,

e P

PrPrReC

d,

⋅⋅⋅⋅⋅= σ

λα [W/m2K] (4.141)

32

2 70 αα ⋅−

=n

,nc (4.142)

unde n2�HVWH�QXP�UXO�GH� HYL�vQ�GLUHF LD�GH�FXUJHUH�. &RHILFLHQW�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH�QX�H[LVW��vQ�FD]XO�DHUXOXL (format din gaze biatomice).

3HQWUX�IDFWRUXO�GH�VF�OGDUH�neunifiUP��VH�DGRSW��YDORDUHD�ω =0,95 – 0,98. Coeficientul de WUDQVIHU�GH�F�OGXU� este :

ca αωα ⋅= &RHILFLHQWXO�JOREDO�GH�VFKLPE�GH�F�OGXU��HVWH��

ga

gak

αααα

ξ+⋅

⋅= [W/m2K] (4.143)

FX�YDORULOH�SHQWUX�FRHILFLHQWXO�GH�PXUG�ULUH�� 800700 ,, ÷=ξ pentru combustibil gazos

750650 ,, ÷=ξ pentru combustibil lichid 'LIHUHQ D�PHGLH�GH�WHPSHUDWXUL�HVWH��FRQIRUP�VFKHPHL��

min

max

minmaxm

t

tln

ttt

∆∆

∆∆∆ −

= (4.144)

6XSUDID D�GH�VFKLPE�GH�F�OGXU��QHFHVDU��HVWH�

m

PA

PAtk

QS

∆⋅= [m2] (4.146)


192

)LJ��'LIHUHQ D�PHGLH�D�WHPSHUDWXULORU *HRPHWULF�VXSUDID D�GH�VFKLPE�GH�F�OGXU��HVWH�� ndlnS mtrPA ⋅⋅⋅⋅= π1 (4.146’)

unde ”dm´�HVWH�GLDPHWUXO�PHGLX�DO� HYLL�LDU�´ trn ´�HVWH�QXP�UXO�GH�WURQVRDQH�úL�UH]XOW��

nld

Sn

m

PAtr ⋅⋅⋅

=1π (4.147)

'DF��QXP�UXO�GH�WURQVRDQH�UH]XOW��IUDF LRQDU��VH�URWXQMHúWH�OD�YDORDUHD�vQWUHDJ��LPHGLDW� VXSHULRDU��&KLDU� GDF�� DFHVW� OXFUX� vQVHDPQ�� R�RDUHFDUH� VXSUDGLPHQVLRQDUH a SUHvQF�O]LWRUXOXL�GH�DHU��IDSWXO�QX�QHFHVLW��R�UHDMXVWDUH�GHRDUHFH�VXSUDID D�OXFUHD]��vQ�FRQGL LL� GH� PXUG�ULH� PDL� LQWHQV�� úL� QLFL� WHPSHUDWXUD� DHUXOXL� SUHvQF�O]LW� QX� HVWH� XQ�SDUDPHWUX�D�F�UXL�YDORDUHD�WUHEXLH�PHQ LQXW��VWULFW�OD�R�DQXPLW��P�ULPH� LungiPHD�WRWDO��D�SUHvQF�O]LWRUXOXL�GH�DHU�HVWH�� trnlL ⋅= 1 [m] (4.148) $FHDVW�� OXQJLPH� QX� WUHEXLH� V�� GHS�úHDVF�� OXQJLPHD� FD]DQXOXL�� 6H� SRDWH�LQWHUYHQL�SHQWUX�PLFúRUDUHD�OXQJLPLi astfel :

- GLDPHWUX�PDL�PLF�DO� HYLORU�; - vitez� mai mare a aerului ; - vitez� PDL�PLF� a gazelor de ardere . 6H� YHULILF�� GDF�� WHPSHUDWXUD� SHUHWHOXL� HYLL� OD� FDS�WXO� FDOG� �Wsfc, tap) este mai

PLF�� GH� �� o&�� 'DF�� DFHDVW�� FRQGL LH� QX� HVWH� vQGHSOLQLW�� VH� VFKLPE�� VROX LD�FRQVWUXFWLY��SULQ�WUHFHUH�OD�FLUFXOD LH�HFKLFXUHQW��6H�UHGLPHQVLRQHD]��VFKLPE�WRUXO�GH�F�OGXU��LDU�vQ�ILQDO�VH�YHULILF��vQGHSOLQLUHD�FRQGL LHL�OD�DPEHOH�FDSHWH��QX�VH�úWLH�FDUH�HVWH�FDS�WXO�PDL�FDOG��

t

S SPA

ta

tcos

tsfc

∆tmax

∆tmin

tap


CAZANE

193

CAPITOLUL 5

CALCULUL TERMIC AL CAZANELOR

CU CONDENSATIE

5.1. �'HVFULHUHD�FD]DQXOXL��HOHPHQWH�FRPSRQHQWH��PRG�GH�IXQF LRQDUH�

,Q� FDGUXO� SUHRFXS�ULORU� JHQHUDOH� GH� HILFLHQWL]DUH� HQHUJHWLF�� D� FRQVXPDWRULORU�PLFL� úL� PHGLL� GH� F�OGXU�� GH]YROWDUHD� GRPHQLXOXL� FD]DQHORU� FX� FRQGHQVD LH�� YLDELOH�WHKQLF�úL�DYDQWDMRDVH�HFRQRPLF��UHSUH]LQW��R�GLUHF LH�GH�PDUH�DFWXDOLWDWH� )HQRPHQXO�SDUWLFXODU�XUP�ULW� HVWH�FRQGHQVDUHD�YDSRULORU�GH�DS��GLQ�JD]HOH�GH�DUGHUH�SH�VXSUDIH HOH�GH�WUDQVIHU�GH�F�OGXU��DOH�FD]DQXOXL�vQ�YHGHUHD�H[WUDJHULL�F�OGXULL�ODWHQWH� GH� YDSRUL]DUH�� $VWIHO� VH� SRDWH� WUHFH� GH� OD� SRWHQ LDOXO� HQHUJHWLF� DO�FRPEXVWLELOXOXL�UHSUH]HQWDW�GH�SXWHUHD�FDORULF��LQIHULRDU��OD�SRWHQ LDOXO�UHSUH]HQWDW�GH�SXWHUHD�FDORULF��VXSHULRDU��

,Q�YHGHUHD�SUHFL]�ULL�FRQGL LLORU�GH�DSDUL LH�D� IHQRPHQXOXL�GH�FRQGHQVDUH�XWLO��vQ�FD]DQH�úL�FXDQWLILFDUHD�HQHUJHWLF��D�HIHFWHORU�VH�SRUQHúWH�GH�OD�DQDOL]D�FRQ LQXWXOXL�GH�YDSRUL�GH�DS��GLQ�JD]HOH�GH�DUGHUH��(VWH�LPSRUWDQW�GH�SUHFL]DW�GH�OD�vQFHSXW�F��GLQ�gama de combustibili se va studia numai gazul natural (metanul) deoarece în cazul FRPEXVWLELOLORU� OLFKL]L� VDX� VROL]L�� GDWRULW�� FRQ LQXWXOXL� GH� VXOI� LQHUHQW� DFHVWRUD��FRQGHQVXO� UH]XOWDW� DUH� XQ� FDUDFWHU� DFLG� FDUH� QHFHVLW�� WUDW�UL� XOWHULRDUH� I�FkQG�QHSUDFWLF��XWLOL]DUHD�vQ�JDPD�GH�SXWHUL�PLFL�úL�PHGLL��'H�DVHPHQHD��QX�YRU�IL��DQDOL]D L�QLFL� DO L� FRPEXVWLELOL� JD]RúL�� GH� H[HPSOX� FRPEXVWLELOLL� JD]RúL� OLFKHILD L� GHRDUHFH�FRQ LQXWXO� GH� YDSRUL� GH� DS�� vQ� JD]HOH� GH� DUGHUH� HVWH� LQIHULRU� FHOXL� GLQ� FD]XO� JD]XOXL�metan, fenomenul de condensare fiind dezavDQWDMDW�� LDU� SH� GH� DOW�� SDUWH� JUDGXO� GH�IRORVLUH� vQ� LQVWDOD LLOH� WHUPLFH� FDVQLFH� HVWH� UHODWLY� UHGXV�� 'HVLJXU�� SDUWLFXODUL]DUHD�PHWRGRORJLHL� GH� FDOFXO� OD� DFHúWL� FRPEXVWLELOL� vúL� YD� J�VL� RSRUWXQLWDWHD� SH�P�VXU�� FH�VLVWHPHOH�GH�FRQGHQVDUH�YRU�F�S�WD�vQ�YLLWRU o extindere mai mare.

)HQRPHQXO� GH� FRQGHQVDUH� DO� YDSRULORU� GH� DS�� GLQ� JD]HOH� GH� DUGHUH� DSDUH� vQ�FRQGL LLOH�H[LVWHQ HL�XQHL�VXSUDIH H�GH�WUDQVIHU�GH�F�OGXU��FX�R�WHPSHUDWXU��OD�LQWHUID D�FX�JD]HOH�GH� DUGHUH�PDL� VF�]XW�� GHFkW� WHPSHUDWXUD�SXQFWXOXL�GH� URX� al vaporilor de DS�� GLQ� DPHVWHFXO� GH� JD]H� UHSUH]HQWDW� GH� JD]HOH� GH� DUGHUH�� ,Q� FRQFOX]LH�� SHQWUX�RE LQHUHD� HIHFWXOXL� WHUPLF� XWLO� OD� FRQGHQVDUH� QX� VH� LPSXQH� FRQGL LD� GH� VF�GHUH� D�WHPSHUDWXULL� JD]HORU� GH� DUGHUH� VXE� WHPSHUDWXUD� SXQFWXOXL� GH� URX�� FL� GRDU� FRQGL LD�VF�GHULL� WHPSHUDWXULL� VXSUDIH HL� GH� FRQWDFW� VXE� WHPSHUDWXUD� SXQFWXOXL� GH� URX��&RQGHQVDUHD�DUH�HIHFW�XWLO�GLQ�SXQFW�GH�YHGHUH�HQHUJHWLF�GDF��VXSUDID D�vQ�FDX]��HVWH�XQD�GLQ�VXSUDIH HOH�GH�WUDQVIHU�GH�F�OGXU��DOH�FD]DQXOXL��

5. CALCULUL TERMIC AL CAZANELOR CU CONDENSATIE

194

Pentru exemplificarea grafLF�� D� FRQGL LLORU� FH�GHWHUPLQ�� DSDUL LD� IHQRPHQXOXL��în figura 5.��VXQW�SUH]HQWDWH�FHOH�GRX��VLWXD LL�FH�VH�SRW�vQWkOQL�vQ�VLVWHPHOH�FRQYHFWLYH�ale cazanului. �

�� Fig.5.��D��/LSV��FRQGHQVDUH Fig5.��E��$SDUL Le condensare

6WDELOLUHD� FX� DSUR[LPD LH� D� ]RQHL� XQGH� vQFHSH� FRQGHQVDUHD� VH� IDFH� LPSXQkQG�FRQGL LD� GH� DSDUL LH� D� FRQGHQV�ULL� OD� XQ� QLYHO� DO� WHPSHUDWXULL� SHUHWHOXL� HJDO� FX�WHPSHUDWXUD� GH� URX�� D� JD]HORU� GH� DUGHUH� FX� XPLGLWDWH� LQL LDO�� &RQGL LD� JHQHUDO�� GH�condensare este: tper ��WURX��.

&DQWLWDWHD�WRWDO��GH�FRQGHQV�GLQ�JD]HOH�GH�DUGHUH�VH�FDOFXOHD]��DVWIHO� Cantitatea de H2 în combustibil este:

H2 = 16

4 [kg(H2)/kg(CH4)]

&DQWLWDWHD�GH�DS��SURGXV��GH�DUGHUHD�KLGURJHQXOXL�HVWH� H2 O =

2

18 [kg(H2O)/kg(H2)]

&DQWLWDWHD�GH�DS��SURGXV��GH�DUGHUHD�D��NJ�GH�PHWDQ�HVWH� H2O/CH4 =

16

4•

2

18 = 2,25 [kg(H2O)/kg(CH4)]

Gaze de ardere Gaze de ardere

Apa Apa

t t

Punct de roua

Punct de roua t perete

t perete t apa

t apa

Canal curgere gaze de ardere

Profil temperatura


CAZANE

195

'HQVLWDWHD�PHWDQXOXL�VH�FDOFXOHD]��GLQ�UHOD LD��

1 kg(CH4) =16

4,22 Nm3(CH4) = 1,4 Nm3(CH4)

&DQWLWDWHD�GH�DS��SURGXV��GH�DUGHUHD�D��1P3 de metan este:

607,14,1

25,2

4

2 ==CH

OH [kg(H2O)/Nm3(CH4)]

(FKLYDOHQWXO� vQ� F�OGXU�� DO� DFHVWHL� FRQGHQV�UL� HVWH�� LQkQG� VHDPD� F�� OD�temperatura de 60 0&�F�OGXUD�GH�FRQGHQVDUH�HVWH��U� ��NFDO�NJ�� Qcond = 623· 1,607 = 1001 kcal/Nm3(CH4) La o FRQGHQVDUH� WRWDO�� D� YDSRULORU� GH� DS�� GLQ� JD]HOH� GH� DUGHUH�� F�OGXUD� GH�FRQGHQVDUH� UHSUH]LQW�� UDSRUWDW�� OD� SXWHUHD� FDORULF�� LQIHULRDU�� XQ� VXUSOXV�GH� F�OGXU��FHGDW��GH� û4� ��•100 = 11,78 %

&XQRVFkQG�FRQ LQXWXO�LQL LDO�GH�YDSRUL�GH�DS��GLQ�JD]HOH�GH�DUGHUH�VH�GHWHUPLQ��SUHVLXQHD�SDU LDO��D�YDSRULORU�GH�DS��GLQ�JD]HOH�GH�DUGHUH��SH2O� ��úL�DSRL�WHPSHUDWXUD�SXQFWXOXL�GH�URX��LQL LDO�WURX��, GXS��R�UHOD LH�GH�DSUR[LPDUH�FX�R�HURDUH��

TEMPERATURA DE ROUA A GAZELOR DE

ARDERE FUNCTIE DE PRESIUNEA PH2O

30

35

40

45

50

55

60

65

0,05 0,1 0,15 0,2 0,25

PRESIUNE PH2O [bar]

TE

MP

ER

AT

UR

A D

E R

OU

A [

C]

TEMPERATURA PUNCTULUI DE ROUA

FUNCTIE DE EXCESUL DE AER

52

53

54

55

56

57

58

59

60

61

1 1,1 1,2 1,3 1,4 1,5

EXCES DE AER - ALFA

TE

MP

ER

AT

UR

A P

UN

CT

UL

UI

DE

RO

UA

- T

RO

UA

[C

]


196

Fig.5.��9DULD LD�WURX��IXQF LH�GH�SUHViunea�SDU LDO��D�YDSRULORU�GH�DS� Pentru pH2O < 0,18 bar : tURX�� = 44,778 + 67,25219 • ( pH2O – 0,08 ) 0,6461199

(5.1) Pentru pH2O > 0,18 bar : tURX�� = 59,969 + 80,5883 • ( pH2O – 0,18 ) 0,9693625

(5.2) Alte surse bibliografice ( Remi Guillet –�'H� OD�SRPSH�D�YDSHXUV�G¶HDX��RIHU��UHOD LL�HPSLULFH�GH�OHJ�WXU��vQWUH�SUHVLXQHD�GH�VDWXUD LH�úL�WHPSHUDWXUD�GH�URX��

667,231

5,3928

4,140972

+−

= rouat

OH ep (5.3)

667,231

4,14097ln

5,3928

2

−−=OH

roua pt

(5.4)

$PEHOH�VHWXUL�GH�UHOD LL�RIHU��DFHOHDúL�YDORUL�ILLQG�GHFL�FRQFRUGDQWH�

In figura 5.�� HVWH� LOXVWUDW�� JUDILF� GHSHQGHQ D� GLQWUH� WHPSHUDWXUD� SXQFWXOXL� GH�URX��úL�SUHVLXQHD�SDU LDO��D�YDSRULORU�GH�DS��vQ�JD]HOH�GH�DUGHUH�H[SULPDW��H[SOLFLW�VDX�implicit prin valoarea excesului de aer.

6ROX LH�FRQVWUXFWLY��GH�FD]DQ�DFYDWXEXODU�FX�FRQGHQVDUH� UHDOL]DW�GLQ� HDY��JRIUDW�

�5HDOL]DUHD�FD]DQHORU�GLQ� HDY��JRIUDW��GHWDOLXO�GH� HDY��JRIUDW��HVWH�SUH]HQWDW�

în figura 5.3.) aduce avantajul FUHúWHULL�VXSUDIH HL�GH�WUDQVIHU�GH�F�OGXU��SH�XQLWDWHD�GH�OXQJLPH�GH� HDY�� vQ�FRQGL LLOH�PHQ LQHULL� OD�YDORDUH�PLQLP��D� WHPSHUDWXULL�GH�SHUHWH��VSUH� GHRVHELUH� GH� VLVWHPHOH� GH� H[WLQGHUH� D� VXSUDIH HL� GH� WLS� DULSLRDU�� OD� FDUH�WHPSHUDWXUD� VXSUDIH HL� SH� SDUWHD� JD]HORU� GH� DUGHUH� HVWH� GLIHULW�� GH� WHPSHUDWXUD�SHUHWHOXL� GLUHFW� VF�OGDW� GH� DJHQWXO� WHUPLF� VHFXQGDU�� 3H� OkQJ�� DFHVW� DYDQWDM� HVWH� GH�PHQ LRQDW� FDOLDWHD� LQWULQVHF�� GH� SUHOXDUH� D� GLODW�ULORU� úL� WUDQVIRUPDUHD� FXUJHULL� vQ�WUDQVIHUXO� GH� F�OGXU�� GLQ� FXUJHUH� WUDQVYHUVDO�� SHVWH� IDVFLFXO� GH� HYL� vQ� FXUJHUH� SULQ�canale înguste.

6ROX LD�FRQVWUXFWLY��HVWH�SUH]HQWDW��vQ�ILJXUD�� $OLPHQWDUHD� FX� DS�� D� FD]DQHORU� VH� IDFH� SH� OD� SDUWHD� LQIHULRDU�� DVLJXUkQGX-se

DVWIHO�FRQGL LD�GH�FRQWUDFXUHQW�FX�JD]HOH�GH�DUGHUH��$U]�WRUXO�FX�SUHDPHVWHF�úL�GR]DM�constant aer-FRPEXVWLELO�DUH�IURQWXO�GH�IODF�U��VWDELOL]DW�SH�R�VLW��GH�IRUP��FLOLQGULF��UHDOL]DW�� GLQ� ILEUH� PHWDOLFH� WHUPRUH]LVWHQWH�� 'DWRULW�� VXSUDIH HL� PDUL� GH� VWDELOL]DUH�


CAZANE

197

OXQJLPHD�IURQWXOXL�GH�IODF�U��HVWH�PLF��GH�RUGLQXO�]HFLORU�GH�PP��SHUPL kQG�PRQWDUHD�]RQHL�FRQYHFWLYH�DSURDSH�GH�FLOLQGUXO�DU]�WRUXOXL� 'DWRULW�� VWDELOL]�ULL� SH� vPSkVOLWXUD� UHIUDFWDU�� DFHDVWD� VH� vQF�O]HúWH� OD� R�WHPSHUDWXU��FXSULQV��vQWUH��úL��oC.

)LJXUD��'HWDOLX�GH� HDY��JRIUDW��úL�SULQFLSDOHOH�FDUDFWHULVWLFL�GLPHQVLRQDOH *D]HOH� GH� DUGHUH� FH� UH]XOW�� vQ� IRFDU� SULQ� DUGHUHD� FRPEXVWLELOXOXL� WUDYHUVHD]D�

UDGLDO� SULPD� VHUSHQWLQ�� DMXQJkQG� vQ� VSD LXO� GLQWUH� DFHDVWD� úL� SHUHWHOH� H[WHULRU� DO�FD]DQXOXL�� 6SD LXO� GH� FXUJHUH� HVWH� FRQVWLWXLW� GH� XQ� QXP�U� GH� FDQDOH� GHWHUPLQDW� GH�QXP�UXO�GH�VSLUH�DOH�IRFDUXOXL�

8UPHD]�� FLUFXOD LD�D[LDO��D�JD]HORU�GH�DUGHUH�SHVWH�R�VHUSHQWLQ��DúH]DW�� OkQJ��

SHUHWHOH� H[WHULRU�� FDUH� IRUPHD]�� FDQDOH� GH� FXUJHUH� D[LDO�� vQWUH� HDY�� úL� SHUHWH��GHWHUPLQDWH�GH�QXP�UXO�GH�VSD LL�JRIUDWH�FDUH�VH�DIO��SH�R�FLUFXPIHULQ ��GH�VHUSHQWLQ�� $FHVW�WLS�GH�FXUJHUH�D�JD]HORU�VH�vQWkOQHúWH�OD�H[WHULRUXO�VHUSHQWLQHL��úL�OD�VHUSHQWLQD��IRUPkQG�GUXPXULOH�FRQYHFWLYH��úL��DOe cazanului.

*D]HOH� GH� DUGHUH� VWU�EDW� HYLOH� VFKLPE�WRUXOXL� GH� F�OGXU�� DVWIHO� GLPHQVLRQDW�vQFkW� V�� DVLJXUH� R� U�FLUH� SXWHUQLF�� D� DFHVWRUD� úL� FRQGHQVDUHD� YDSRULORU� GH� DS�� $SD�FLUFXO��vQ�FRQWUDFXUHQW�FX�JD]HOH�de ardere, iar condensul format�VH�VFXUJH�F�WUH�SDUWHD�LQIHULRDU�� D� FD]DQXOXL� XQGH� HVWH� GLULMDW� F�WUH� R� FRQGXFW�� GH� FROHFWDUH� úL� HYDFXDW� OD�FDQDOL]DUH� SULQ� LQWHUPHGLXO� XQXL� VLIRQ� FX� JDUG�� KLGUDXOLF�� *DUGD� KLGUDXOLF�� HVWH�DEVROXW�QHFHVDU��GHRDUHFH�JD]HOH�GH�DUGHUH�vQ�]RQD�GH�FROHFWDUH�D�FRQGHQVXOXL�VXQW�vQ�VXSUDSUHVLXQH� ID �� GH� PHGLXO� DPELDQW� úL� vQ� UHJLPXULOH� I�U�� FRQGHQVDUH� DU� UHIXOD� SH�traseul de drenaj condens.

s

a

b


198

�Fig.5.4��6ROX LH�FRQVWUXFWLY��GH�FD]DQ�FX� HDY��JRIUDW�

3HUIRUPDQ HOH� FD]DQXOXL� JDUDQWHD]�� XQ� HFDUW� GH� WHPSHUDWXU�� între gazele de ardere úL apa de alimentare de maxim 15oC ceea ce face ca nici în regimurile maxime GH� WHPSHUDWXU�� DOH� FD]DQXOXL� �� oC) gazele de ardere evacuate V�� QX� GHS�úHVF� 80o&��'DWRULW��DFHVWHL�SDUWLFXODULW� L�VH�IRORVHVF�WXEXODWXUL�GLQ�SODVWLF�SHQWUX�HYDFXDUHD�gazelor de ardere. Pentru a preveni deteriorarea traseului dH� HYDFXDUH� OD� FUHúWHUHD�DFFLGHQWDO�� D� WHPSHUDWXULL� JD]HORU� GH� DUGHUH�� OD� LHúLUHD� GLQ� FD]DQ� SH� WUDVHXO� DFHVWRUD�HVWH�PRQWDW�XQ�WHUPRVWDW�GH�VLJXUDQ ��VHWDW�OD�FLUFD�� oC. �� 5.2. Tema de proiectare

Prin tema de proiectare se dau: Qut – sarcina termiF��XWLO��D�FD]QXOXL, în [kW] ; tal – temperatura apei de alimentare a cazanului [oC] ; te – temperatura apei la LHúLUHD�GLQ�FD]DQ�>oC]; Combustibilul utilzat – metan. &DUDFWHULVWLFLOH�GLPHQVLRQDOH�DOH�FD]DQXOXL�úL�DOH� HYLL�JRIUDWH�


CAZANE

199

Prin calcul se YD�XUP�UL�YHULILFDUHD�VDUFLQLL� WHUPLFH�D�FD]DQXOXL�SHQWUX�VROX LD�FRQVWUXFWLY��GDW��vQ�LSRWH]D�IXQF LRQ�ULL�vQ�UHJLP�GH�FRQGHQVDUH� &RQIRUP� LQGLFD LLORU� GLQ� FDSLWROXO� �� VH� HIHFWXHD]�� FDOFXOXO� DUGHULL�FRPEXVWLELOXOXL�úL�VH�GHWHUPLQ�� ig0 H,V,V

o .

FXQF LRQDUHD�FD]DQXOXL�HVWH�FX�VXSUDSUHVLXQH�vQ�IRFDU��FRHILFLHQWXO�GH�H[FHV�GH�aer fiind�FRQVWDQW�úL�HJDO�FX�FHO�GLQ�IRFDU��FFD��5 ÷ 1,15) pe tot traseul gazelor de ardere. 6H�WUDVHD]��GLDJUDPHOH�,-t sau cp-t. 5.3. Calculul randamentului terPLF�DO�FD]DQXOXL�úL�D�GHELWXOXL�GH�FRPEXVWLELO� �

,Q� ELODQ XO� JHQHUDO� DO� FD]DQXOXL� YD� DSDUH� UDQGDPHWXO� WHUPLF� I�U�� FRQGHVDUH��XUPkQG� FD� HIHFWXO� FRQGHQV�ULL� V�� VH� DGDXJH� HIHFWXOXL� GH� WUDQVIHU� GH� F�OGXU�� FD� XQ�IHQRPHQ� VXSUDSXV�� /D� WHPSHUDWXUD� OD� FRú� GH� FFD�� 0 0&� UDQGDPHQWXO� WHUPLF� I�U��condensare este GH� FFD�� LDU� HIHFWXO� FRQGHQV�ULL� VH� YD� DG�XJD� VXSOLPHQWDU� SULQ�WHUPHQXO��û�� 4FRQG�4FRPE�FDUH�DUH�R�YDORDUH�GH�RUGLQXO��– 8 %.

$VWIHO��vQ�DQVDPEOX��FD]DQXO�YD�DYHD�HILFLHQ D�WHUPLF� ( efη ) de 103 – 105 %, UDSRUWDW��OD�YDORDUHD�SXWHULL�FDORULFH�LQIHULRDUH�D�FRPEXVWLELOXOXL (Hi) úL un randament

( czη ) inferior valorii de 100 %� SHQWUX� UDSRUWDUHD� �FRUHFW�� GLQ� SXQFW� GH� YHGHUH� DO�ELODQ XOXL�WHUPLF��OD�SXWHUHD�FDORULF��VXSHULRDU��a combustibilului (Hs) :

100⋅⋅

=i

utef

HB

Qη [%] ; 100100 <⋅

⋅=

s

ut

czHB

Qη [%] (5.5)

'HRDUHFH�FRQFHQWUD LLOH�GH�R[LG�GH�FDUERQ�vQ�JD]HOH�GH�DUGHUH�OD�FRú�VXQW�IRDUWH�

PLFL� �GH� RUGLQXO� XQLW� LORU� GH� SSP�� QX� VH� SXQH� SUREOHPD� FRQVLGHU�ULL unei pierderi VSHFLILFH�SULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��FKLPLF��

'H� DVHPHQHD�� GDWRULW�� VROX LHL� FRQVWUXFWLYH� GH� FHQWUDO�� FH� vQJOREHD]�� FRUSXO�

FD]DQXOXL� vQ�VSD LXO�GLQ�FDUH�VH�SUHOHYHD]��DHUXO�GH�DUGHUH��VH�SRDWH�QHJOLMD�úL�HIHFWXO�pierderilor specifice�GH�F�OGXU��SULQ�VXSUDIH HOH�H[WHULRDUH�

'HELWXO� GH� FRPEXVWLELO� VH� FDOFXOHD]�� FX� PHWRGD� FODVLF�� SULQ� UDSRUWDUHD�GHELWXOXL�XWLO�GH�F�OGXU��OD�HILFLHQ ��úL�SXWHUH�FDORULF��LQIHULRDU��D�FRPEXVWLELOXOXL��

ief

ut

H

QB

⋅=

η [m3N/s] (5.6)


200

cu varianta de exprimare ca debit orar de combustibil :

Bh=B•3600 [m3N/h] (5.7)

5.4. Calculul termic al cazanului

'HILQLUHD�IOX[XULORU�GH�F�OGXU� �

8UP�ULQG� FLUFXOD LD� JD]HORU� GH� DUGHUH�� FRQIRUP� VROX LHL� FRQVWUXFWLYH�� VH� SRW�LGHQWLILFD�XUP�WRDUHOH�IOX[XUL�GH�F�OGXU��SHQWUX�VHUSHQWLQD�IRFDU�– convectiv1:

• ,Q�IRFDU��]RQD�GH�DUGHUH�úL�UDGLD LH��GRX��IOX[XUL�GH�F�OGXU��UDGLDQWH�úL�DQXPH�

IOX[XO�GH�F�OGXU��UDGLDW�GH�VXSUDID D�SHUHWHOXL�DU]�WRUXOXL��FDUH�VH�FDOFXOHD]��FD�XQ� IHQRPHQ� GH� UDGLD LH� vQWUH� XQ� FRUS� VROLG� FX� HPLVLYLWDWH� FLUFD� �� úL� LQFLQWD�PDWHULDOL]DW�� GH� VHUSHQWLQ�� FDUH� DUH� WHPSHUDWXUD� DSHL� GLQ� VHUSHQWLQ�� úL� IOX[XO�GH�F�OGXU�� UDGLDW�GH�JD]HOH�GH�DUGHUH�FDUH�DX�IRVW�SURGXVH�GH�DU]�WRU�úL�XPSOX�YROXPXO�GLQ�FDPHUD�FLOLQGULF��GLQWUH�DU]�WRU�úL�SULPD�VHUSHQWLQ��

• ,Q�]RQD�FRQYHFWLY��D�VHUSHQWLQHL�IRFDU�

¾�8Q� IOX[� GH� F�OGXU�� SH� FDUH� JD]HOH� GH� DUGHUH� vO� FHGHD]�� FRQYHFWLY�VHUSHQWLQHL� �� OD� WUDYHUVDUHD� SULQ� FDQDOHOH� HYLL� JRIUDWH� GLQ� ]RQD� GH�DUGHUH� F�WUH� SHUHWHOH� H[WHULRU� DO� FD]DQXOXL��&XUJHUHD� HVWH� UDGLDO�� ID ��de axa cazanului.

¾�8Q� IOX[� GH� F�OGXU�� FHGDW� FRQYHFWLY� GH� JD]HOH� GH� DUGHUH� OD� FXUJHUHD�SULQ� SRU LXQHD� OLEHU�� GLQWUH� H[WHULRUXO� VHUSHQWLQHL� IRFDU� úL� SHUHWHOH�exterior, în sens axaial al cazanului.

'XS�� FXP� UH]XOW�� GLQ� GHVFULHUHD� IXQF LRQDO�� D� FD]DQXOXL�� FLUFXOD D�JD]HORU� GH�

DUGHUH�ID ��GH�VHUSHQWLQ��SRDWH�IL�GH�GRX��IHOXUL�

• &LUFXOD LH� D� JD]HORU� GH� DUGHUH� UDGLDO�� SH� R� VHUSHQWLQ�� FD]� vQ� FDUH� JD]HOH� GH�DUGHUH�VWU�EDW�vQ�GLUHF LH�UDGLDO�� HYLOH��VSD LXO�GH�FXUJHUH�ILLQG��FRQVWLWXLW�GH�XQ�QXP�U� GH� FDQDOH�GHWHUPLQDW� GH�QXP�UXO�GH� VSLUH�FDUH�FRQVWLWXLH�FLOLQGUXO�SULQ�FDUH�WUHF�JD]HOH�UDGLDO��FD]XO�VH�vQWkOQHúWH�OD�IRFDUXO�FD]DQXOXL�

• &LUFXOD LD�JD]HORU�GH�DUGHUH�D[LDO��SH�R�VHUSHQWLQ��FD]�vQ�FDUH�VHUSHQWLQD�HVWH�

DúH]DW�� OkQJ��XQ�SHUHWH�� úL� VH� IRUPHD]�� FDQDOH�GH�FXUJHUH�D[LDO�� vQWUH� HDY�� úL�SHUHWH��GHWHUPLQDWH�GH�QXP�UXO�GH�VSD LL�JRIUDWH�FDUH�VH�DIO��SH�R�FLUFXPIHULQ ��GH� VHUSHQWLQ�� FD]XO� VH� vQWkOQHúWH� OD� VHUSHQWLQD� �� GLQ� GUXPXO� FRQYHFWLY� DO�FD]DQXOXL�úL�OD�H[WHULRUXO�VHUSHQWLQHL��FDUH�HVWH�P�UJLQLW��GH�F�PDúD�H[WHULRDU��a cazanului.


CAZANE

201

Pentru calcul s-D�DSOLFDW�PRGHOXO�GH� WUDQVIHU�GH�F�OGXU��VSHFLILF�SHQWUX�FDQDOH�de forme necirculare. Deoarece regimul termic al gazelor de ardere nu depinde de IHQRPHQXO�GH�FRQGHQVD LH�FDUH�DSDUH�SH�XQHOH�VHUSHQWLQH��FRQGHQVDUHD�QX�LQIOXHQ HD]��vQ� SULQFLSLX� WUDQVIHUXO� GH� F�OGXU�� VHQVLELO�� FL� QXPDL� WUDQVIHUXO� GH� F�OGXU�� ODWHQW�� úL�VFKLPEXO� GH� PDV�� 2� XúRDU�� DOWHUDUH� D� UH]XOWDWHORU� VH� SRDWH� vQV�� SURGXFH� GDWRULW��DFHVWHL� LSRWH]H�� SH� GH� R� SDUWH� GDWRULW�� PRGLILF�ULL� UHJLPXOXL� GH� WHmperaturi al apei FDUH��SUHOXkQG�úL�F�OGXUD�GH�FRQGHQVDUH�GLQ�JD]H��YD�DYHD�R�vQF�O]LUH�PDL�LQWHQV��LDU�SH�GH� DOW�� SDUWH� GDWRULW�� YDULD LHL� YROXPXOXL� GH� YDSRUL� GH� DS�� GLQ� JD]HOH� GH� DUGHUH��'LIHUHQ D�GH�WHPSHUDWXU��SH�FLUFXLWXO�DSHL�HVWH�vQV��UHODWLY�UHGXV�, maxim 8 % din 20 o&��DGLF��o&��úL�QX�DOWHUHD]��VHQVLELO�UH]XOWDWHOH��LDU�YDULD LD�GH�SUHVLXQH�SDU LDO��D�YDSRULORU� GH� DS�� GLQ� JD]HOH� GH� DUGHUH� QX� GXFH� OD� PRGLILF�UL� PDMRUH� DOH� YDORULORU�principalilor parametrii fizici ai acestora.

6H� FRQVLGHU�� GLQ� SXQFW� GH� YHGHUH� JD]RGLQDPLF� WUDYHUVDUHD� XQLIRUP�� D�

VHUSHQWLQHL� IRFDU� GH� F�WUH� JD]HOH� GH� DUGHUH�� 1XP�UXO� GH� FDQDOH� VLPSOH� FDUH� VH�IRUPHD]�� HVWH� GH� �� FRUHVSXQ]�WRU� FHORU� �� VSLUH� FH� GHOLPLWHD]�� IRFDUXO�� SULQ� ILHFDUH�canal circulând astfel 1/8 din debitul total de gaze de ardere.

*D]HOH� GH� DUGHUH�� GXS�� WUDYHUVDUHD� UDGLDO�� D� VHUSHQWLQHL�� LQWU�� SURJUHVLY� �GLQ�SXQFW� GH� YHGHUH� DO� GLUHF LHL� D[LDOH�� vQ� VSDWHOH� DFHVWHLD��$VWIHO�� GHELWHOH� GH� JD]H� FDUH�VFDOG�� ILHFDUH�VHUSHQWLQ�� vQ�VHQV�D[LDO�DO�FD]DQXOXL�� UH]XOW��GLQ�DGunarea debitului de SH� VHUSHQWLQD� DQWHULRDU�� FX� FHO� FH� FXUJH� SULQ� FDQDOHOH� UDGLDOH� GH� JD]H�� OD� QLYHOXO�VHUSHQWLQHL�vQ�GLVFX LH��

,Q� FXUJHUH� D[LDO�� GLQ� SXQFWXO� GH� YHGHUH� DO� DQVDPEOXOXL�� SHVWH� SULPD� VSLU�� D�serpentinei 1, vor fi numai 1/8 din debitul de gaze�DO�FD]DQXOXL��SHQWUX�D�GRXD�VSLU��D�VHUSHQWLQHL� VH�PDL�DGDXJ�� SULQ� LQWUDUH� UDGLDO�� GLQ�GHELWXO�GH�JD]H�DO�FD]DQXOXL� úL�GHFL�YD�SDUWLFLSD�OD�WUDQVIHUXO�GH�F�OGXU��GLQ�GHELWXO�GH�JD]H�DO�FD]DQXOXL��

3H� XOWLPD� VSLU�� D� VHUSHQWLQHL� �� GHELWXO� GH� JD]H� HVte de 7/8 din cel total al cazanului deoarece 1/8 din debitul de gaze de ardere trece direct din focar în serpentina 2 prin canalele de traversare.

3HQWUX� FRQYHFWLYXO� GRL�� FRQGL LLOH� JHRPHWULFH� GH� FXUJHUH� VXQW� VLPLODUH� FX�SULPXO� FRQYHFWLY�� DGLF�� DFHDVWD� VH� GHVI�úRDU�� ORQJLWXGLQDO� SULQ� FDQDOHOH� QHFLUFXODUH�IRUPDWH�GH�JRIUDUH�GDWRULW��SUH]HQ HL�úQXUXULORU�GH�XPSXWXU��DWkW�vQWUH�SHUHWHOH�H[WHULRU�úL� VHUSHQWLQ�� FkW� úL� vQWUH� VHUSHQWLQ�� úL� SHUHWHOH� LQWHULRU� DO� FRUSXOXL� GHIOHFWRU� �GRS�ceramic sau metalic).

EfectXO�DFHVWRU�úQXUXUL�HVWH�DVWIHO�GHRVHELW�GH�LPSRUWDQW��QX�DWkW�SULQ�UHDOL]DUHD�GH�YLWH]H�P�ULWH��FkW�SULQ�VFKLPEDUHD� OXQJLPLL�FDUDFWHULVWLFH�D� WUDQVIHUXOXL�GH�F�OGXU��SULQ� FRQYHF LH�� vQ� VHQVXO� VF�GHULL� GUDVWLFH�� GH� FLUFD� �-�� RUL� ID �� GH� FD]XO� FXUJHULL�tranVYHUVDOH� SHVWH� IDVFLFXO� GH� HYL� FDUH� DU� DYHD� FD� OXQJLPH� FDUDFWHULVWLF�� GLDPHWUXO�H[WHULRU�DO� HYLL�

&RQYHFWLYXO� �� VH� PDWHULDOL]HD]�� úL� vQ� VXSUDID �� GH� FRQGHQVDUH�� DWkW� GDWRULW��UHJLPXULORU�GH� WHPSHUDWXUL�DOH�DJHQ LORU�FkW� úL�GDWRULW�� FDUDFWHULVWLFLORU�IXQF LRQDOH�FH�DYDQWDMHD]��GUHQDUHD�SHOLFXOHL�GH�FRQGHQV��


202

3HQWUX� FDOFXO�� FRQIRUP�PRGHOXOXL� IL]LF� DO� FXUJHULL�� VH� YRU� GHILQL� XUP�WRDUHOH�zone de calcul conform figurii 5.5.:

Fig. 5.5. –�'LVFUHWL]DUHD�VXSUDIH HL�GH�WUDQVIHU�GH�F�OGXU��úL�PDV�

1. VXSUDID D� HYLL� JRIUDWH�� RULHQWDW�� F�WUH� D[XO� FD]DQXOXL�� GHWHUPLQDW�� GH�VHF LRQDUHD�FRQYHFWLYXOXL�FX�XQ�FLOLQGUX�FH�WUHFH�SULQ�D[D� HYLL��HVWH�R�VXSUDID ��VXSXV�� UDGLD LHL� JD]HORU� GH� DUGHUH� GLQ� IRFDU� úL� UDGLD LHL� VXSUDIH HL� VROLGH�cilindrice�FDUH�PDWHULDOL]HD]��DU]�WRUXO�

2. VXPD� VXSUDIH HORU� VFDOGDWH� GH� JD]HOH� GH� DUGHUH� OD� VWU�EDWHUHD� UDGLDO�� D�

serpentinei focar-convectiv 1;

5.3

5.2

5.1

4

1 3.1 - 3.4

2


CAZANE

203

3. ILHFDUH� MXP�WDWH� GH� VSLU�� vQ� SDUWH�� vQ� ]RQD� GLQWUH� FRQYHFWLYXO� �� úL� SHUHWHOH�GHVS�U LWRU�� DYDQVkQG� ORQJLWXGLQDO� vQ� GLUHF LD� WUHFHULL� GLQ� FRQYHFWLYXO� �� vQ�FRQYHFWLYXO��SHQWUX�ILHFDUH�VXSUDID �� vQ�SDUWH�VH�PRGLILF��GHELWXO�GH�JD]H�GH�DUGHUH�FH�R�VSDO��ILHFDUH�VXSUDID ��HVWH�GHSHQGHQW��GH�UH]XOWDWHOH�GH�FDOFXO�DOH�VXSUDIH HORU�DQWHULRDUH�

4. serpentina convectivului 2 în ansDPEOX��SHQWUX�FDOFXOXO�WUDQVIHUXOXL�GH�F�OGXU��

VHQVLELO��GH�OD�JD]HOH�GH�DUGHUH�OD�DS�� 5. ILHFDUH� VSLU�� D� FRQYHFWLYXOXL��SH� UkQG��GH� OD� LHúLUHD�JD]HORU�GH�DUGHUH� OD�FRú�

DPRQWH�vQ�VHQVXO�D[HL�FD]DQXOXL��SHQWUX�FDOFXOXO�FRQGHQV�ULL�

Calculul termic al zonei de focar

Calculul termic începe prin determinarea temperaturii teoretice de ardere. Pentru aceasta se�LQL LDOL]HD]��WHPSHUDWXUD��WHRUHWLF��OD�R�YDORDUH�FXSULQV��vQWUH��úL�2000 o&� úL� SHQWUX� YDORDUHD� LQL LDOL]DW�� VH� GHWHUPLQ�� F�OGXUD� VSHFLILF�� D� JD]elor de ardere cpg. 6H�IRORVHúWH�UHOD LD�GH�GHWHUPLQDUH�

pgogo

aopaoi

tcVV

tcVHt

⋅⋅−+

⋅⋅⋅+=

))1(( αα

[oC] (5.8)

6H�YHULILF�� GDF�� WHPSHUDWXUD�DVWIHO�FDOFXODW�� HVWH� vQWU-un interval de +/- 50 oC ID �� GH� WHPSHUDWXUD� WHRUHWLF�� LQL LDOL]DW�� 'DF�� QX� HVWH� vQGHSOLQLW�� FRQGL LD�� VH�UHLQL LDOL]HD]��WHPSHUDWXUD�WHRUHWLF��úL�VH�UHLD�FDOFXOXO�SkQ��OD�vQGHSOLQLUHD�FRQGL LHL� )OX[XULOH�GH�F�OGXU��GLQ�IRFDU�VH�GHWHUPLQ��LQGHSHQGHQW�DVWIHO�

¾�SHQWUX� IOX[XO� UDGLDW� GH� VXSUDID D� GH� VWDELOL]DUH� D� DU]�WRUXOXL� F�WUH�VHUSHQWLQD�IRFDU�VH�XWLOL]HD]��UHOD LD�

)( 44perazazazoaf TTSCQ −⋅⋅⋅= ε [kW] (5.9)

unde : Co = 5,76•10-5 , FRQVWDQWD�GH�UDGLD LH�6WHIDQ�– Boltzmann; azε = 0,7 , coefiFLHQW�GH�DEVRUE LH�DO�VXSUDIH HL�DU]�WRUXOXL� Saz – sXSUDID D�ODWHUDO��D�DU]�WRUXOXL:

azazaz LDS ⋅⋅π= [m2] (5.10)

Taz� ��.��YDORDUH�X]XDO��


204

Tper = tper + 273 = te + 273 [K]

¾�LDU� SHQWUX� IOX[XO� GH� F�OGXU�� UDGLDW� GH� PHGLXO gazos din focar se IRORVHVF� UHOD LLOH� VSHFLILFH� GHWHUPLQ�ULL� FRHILFLHQ LORU� GH� UDGLD LH� vQ�convective� �LQFLQWH� FX� OXQJLPH� GH� UDGLD LH� PLF�� I�U�� UDGLD LH�OXPLQRDV��:

3102

−⋅

−

+⋅⋅= per

ft

frfgf ttt

SQ α [kW] (5.11)

unde : rfα este coefiFLHQWXO�FRQYHFWLY�GH�UDGLD LH�D�JD]HORU�GH�DUGHUH�GLQ�IRFDU; Sf�HVWH�SURLHF LD�SH�GLDPHWUXO�LQWHULRU�DO�VHUSHQWLQHL�IRFDU:

fiff LDS ⋅⋅= π [m2] (5.12)

cu Dif – GLDPHWUXO�LQWHULRU�DO�VHUSHQWLQHL�IRFDU�úL Lf – lungimea foFDUXOXL�vQ�GLUHF LD�axei longitudinale a cazanului; ft � WHPSHUDWXU�� HVWLPDW�� D� JD]HORU� GH� DUGHUH� OD�LQWUDUHD� vQ�]RQD�GH�VFKLPE�GH�F�OGXU��FRQYHFWLY�D�VHUSHQWLQHL�IRFDU��WUHFHUHD�UDGLDO�� conform graficului din figura 5.6.

1350

1400

1450

1500

1550

1600

1650

1700

1750

6,5 7 ,5 8,5 9,5

B com b [N m c/h ]

tg [

C] a = 1 ,1

a = 1 ,2

a = 1 ,3

Figura 5.6. – VDORUL�GH�LQL LDOL]DUH�SHQWUX�WHPSHUDWXUD�GH�LHúLUH�D�

gazelor de ardere din focar


CAZANE

205

Pentru frα VH�YD�IRORVL�UHOD LD��

−

−

⋅⋅⋅+

⋅⋅= −

gm

per

gm

per

gmg

p

fr

T

T

T

T

Taa

1

1

2

110765,5

6,3

38α [W/m2K] (5.13)

XQGH� SHQWUX� FRHILFLHQWXO� GH� DEVRUE LH� DO� SHUHWHOXL� VH� LD� YDORDUHa ap=0,84� úL�temperatura medie a gazelor de ardere este:

Tgm = (Tt+Tf)•0,5 [K] (5.14)

&RHILFLHQWXO�GH�DEVRUE LH�DO�PHGLXOXL�JD]RV�– ag –�HVWH�GDW�GH�UHOD LD�

sk

g

gea⋅−−= 1 (5.15)

cu grosimea stratului radiant:

pf

f

S

Vs ⋅= 4 [m] (5.16)

unde volumul focarului este:

( )

f

2az

2if

f L4

DDV ⋅

−⋅π= [m3] (5.17)

iar�VXSUDID D�WRWDO��D�SHUH LORU�GHOLPLWDWRUL�DL�IRFDUXOXL este:

( ) ( )4

222azif

fazifpf

DDLDDS

−⋅⋅+⋅+⋅=π

π [m2] (5.18)

úL�FRQVWDQWD�GH�UDGLD LH�D�JD]HORU�

)(1000

38,01)(

6,18,022

22

2

ROOH

gm

ROOH

OH

g ppT

spp

pK +⋅

⋅−⋅

⋅+

⋅+= (5.19)


206

g

cIg

RO

RO pVV

Vp

o 0)1(2

2 −+=

α [bar];

g

cIg

OH

OH pVV

Vp

o 0)1(2

2 −+=

α [bar] (5.20)

cu : pg ≅ 1 bar.

'XS��GHWHUPLQDUHD�IOX[XULORU�4af�úL�4gf�VH�GHWHUPLQ��IOX[XO�WRWDO�GH�F�OGXU��transmis în focar: Qf = Qaf + Qgf [kW] (5.21)

7HPSHUDWXUD�UHDO��D�JD]HORU�GH�DUGHUH�OD�LHúLUHD�GLQ�IRFDU�VH�GHWHUPLQ��FX�UHOD LD�

pggN

f

tfcD

Qtt

⋅−= [oC] (cu cpg determinat pentru tgm) (5.22)

úL

DgN = B•Vg – debitul normal de gaze de ardere [m3N/s].

$FHDVW�� WHPSHUDWXU�� HVWH�FHD�FX�FDUH�JD]HOH�GH�DUGHUH� LQWU�� vQ�]RQD�GH� WUHFHUH�UDGLDO�� GLQ� IRFDU� vQ� VSDWHOH� VHUSHQWLQHL� IRFDU�–� FRQYHFWLY��GHQXPLW�� FRQYHQ LRQDO� úL�serpentina 1).

Calculul termic al serpentinHL�IRFDU�OD�VF�OGDUHD�UDGLDO�

��ID ��GH�D[XO�FD]DQXOXL� 3HQWUX� D� FDOFXOD� IOX[XO� GH� F�OGXU�� WUDQVPLV�GH�JD]HOH�GH� DUGHUH� vQ� WUDYHUVDUHD�UDGLDO�� D� VHUSHQWLQHL� �� HVWH� QHFHVDU�� LQL LDOL]DUHD� WHPSHUDWXULL� GH� LHúLUH� D� JD]HORU� GH�DUGHUH�GLQ� WUDYHUVDUHD� UDGLDO�� (tr) la valoarea de 500 o&�úL�GHWHUPLQDUHD�SDUDPHWULORU�fizici ai gazelor de ardere la

2

ttt rf

mr

+= :

- YkVFR]LWDWHD�FLQHPDWLF�� ν = [m2/s] - FRQGXFWLELOLWDWHD�WHUPLF�� λ = [W/mK] - criteriul Prandtl Pr = [-] - F�OGXU��VSHFLILF�� cpg = [J/m3

NK]


CAZANE

207

&RQYHF LD� OD� WUDYHUVDUHD� WUDQVYHUVDO�� D� VHUSHQWLQHL� DUH� XUP�WRDUHOH�caracteristici: - FRQYHF LH�IRU DW�� - I�U��VFKLPEDUH�GH�ID]�� - FXUJHUH�WUDQVYHUVDO��SHVWH� HYL�JRIUDWH�DO�WXUDWH� - OD�U�FLUHD�IOXLGXOXL� 0�ULPLOH�JHRPHWULFH�LPSOLFDWH�vQ�DFHDVW��FRQYHF LH�VXQt: - lungimea�FDUDFWHULVWLF��= GLDPHWUXO�KLGUDXOXLF�DO�FDQDOHORU�FH�VH�IRUPHD]��

SULQ� DO�WXUDUHD� HYLORU� JRIUDWH�� FRQIRUP� ILJXULL� 5.3.; DFHDVW�� OXQJLPH� VH�SRDWH�DSUR[LPD�FX��O� LPH�FDQDO��

- VHF LXQHD� GH� FXUJHUH� UDGLDO�, conform figurii 5.4. este (Scr) = suma

VHF LXQLL��SH�GLUH LD�SHUSHQGLFXODU��FXUJHULL��D�WXWXURU�FDQDOHORU�GH�FXUJHUH�IRUPDWH�SULQ�DO�WXUDUHD�VSLUHORU�GLQ�VHUSHQWLQD��

1/ tmfmlcctr nDSS ⋅⋅⋅= π [m2] (5.23)

unde Sc/ml�HVWH�VHF LXQHD�GH�FXUJHUH�WUDQVYHUVDO��SH�XQ�PHWUX�GH�OXQJLPH�

GH� HDY��JRIUDW��LDU�Qt1�HVWH�QXP�UXO�GH�VSLUH�DO�VHUSHQWLQHL��

- VXSUDID D� GH� VFKLPE� GH� F�OGXU�� vQ� FXUJHUHD� UDGLDO�� 6scr�� MXP�WDWH� GLQ�VXSUDID D�WRWDO��GH�WUDQVIHU�GH�F�OGXU��D�VHUSHQWLQHL��GHRDUHFH�VH�FRQVLGHU��FRQYHF LD�OD�WUHFHUHD�UDGLDO��FD�DF LRQkQG�GH�OD�ID D�LQWHULRDU��a serpentinei �F�WUH� IRFDU�� SkQ�� OD� LQWHUVHF LD� FX� MHWXO� GLQ� VSDWHOH� VHUSHQWLQHL�� DGLF�� vQ�VHF LXQHD�GH�GLDPHWUX�PHGLX�al serpentinei:

1/2

1tmfmltscr nDSS ⋅⋅⋅⋅= π [m2] (5.24)

unde St/ml� HVWH�VXSUDID D�GH� WUDQVIHU�GH�F�OGXU��SH�XQ�PHWUX�GH� lungime GH� HDY��JRIUDW� 6H�GHWHUPLQ��YLWH]D�FDUDFWHULVWLF��WUDQVIHUXOXL�GH�F�OGXU��

ctr

mr

gN

grS

tD

w 273

273+⋅

= [m/s] (5.25)

unde DgN este debitul normal de gaze de ardere

úL�FULWHULXO�5H�SHQWUX�FXUJHUH��


208

υcgr lw ⋅

=Re .

Pentru determLQDUHD�FRHILFLHQWXOXL�GH� WUDQVIHU�GH�F�OGXU��FRQYHFWLY� la trecerea

UDGLDO�� crα ) VH�IRORVHVF�UHOD LLOH� Pentru Re > 2300 :

Re33,08,0

3

2

PrRe1024,0 ελ

α ⋅⋅⋅

+⋅⋅=

e

c

c

crd

l

l [W/m2K] (5.26)

cu: 8,1

5

Re Re

1061

⋅−=ε �SHQWUX�5H��úL� 1Re =ε pentru Re >10000,

unde de HVWH�GLDPHWUXO�H[WHULRU�DO� HYLL�JRIUDWH� Pentru Re < 2300 :

⋅⋅⋅+

⋅⋅⋅+⋅=

3

2

PrRe04,01

PrRe0668,0

65,3

e

c

e

c

c

cr

d

l

d

l

l

λα

[W/m2K] (5.27)

&RHILFLHQWXO�GH�WUDQVIHU�GH�F�OGXU��SULQ�UDGLD LH�VH�QHJOLMHD]��GDWRULW��OXQJLPLL�

GH�UDGLD LH�IRDUWH�PLFL��GH�RUGLQXO�GHschiderii dintre gofre). $VWIHO��FRHILFLHQWXO�JOREDO�GH�WUDVIHU�GH�F�OGXU��vQ�WUHFHUHD�UDGLDO��GHYLQH�

crcrK α⋅= 9,0 [W/m2K] (5.28) XQGH��HVWH�XQ�FRHILFLHQW�GH�UHGXFHUH�FH� LQH�VHDPD�GH�UH]LVWHQ D�WHUPLF��GH�

tip conductiv a peretelui mHWDOLF� úL� GH� UH]LVWHQ D� WHUPLF�� GH� WLS� FRQYHFWLY� SH� SDUWHD�apei.

6H� GHWHUPLQ�� WHPSHUDWXUD� UHDO�� GH� LHúLUH� D� JD]HORU� GH� DUGHUH� GXS�� WUHFHUHD�

UDGLDO��SHVWH�VHUSHQWLQ��FX�UHOD LD�GH�YHULILFDUH�


CAZANE

209

( ) pggN

scrcr

cD

SK

amfamr etttt⋅

⋅−

⋅−+= [oC] (5.29)

unde tam este temperatura medie a agentului secundar (apa). 5H]XOW��IOX[XO�GH�F�OGXU��WUDQVPLV�vQ�WUHFHUHD�UDGLDO��D�JD]HORU�GH�DUGHUH��

( ) 310−⋅−⋅⋅= rfpggNr ttcDQ [kW] (5.30)

&DOFXOXO�WHUPLF�DO�VHUSHQWLQHL�IRFDU�OD�VF �OGDUHD�ORQJLWXGLQDO�

��ID ��GH�D[XO�FD]DQXOXL� Cunoscând� WHPSHUDWXUD� JD]HORU� GH� DUGHUH� OD� LHúLUHD� GLQ� WUHFHUHD� UDGLDO�� úL�

GHELWXO�GH�JD]H�GH�DUGHUH�vQ�FXUJHUHD�ORQJLWXGLQDO��ID ��GH�D[D�FD]DQXOXL��GLQ�VSDWHOH�SULPHL�VSLUH�D�VHUSHQWLQHL��VH�SRDWH�FDOFXOD�WUDQVIHUXO�GH�F�OGXU��FRQYHFWLY�FH�UH]XOW��

Pentru a cDOFXOD� DFHVW� IOX[� GH� F�OGXU�� VH� LQL LDOL]HD]�� WHPSHUDWXUD� GH� LHúLUH� D�

gazelor de ardere OD�VIkUúLWXO�WUDQVIHUXOXL�GH�F�OGXU� SHVWH�SULPD�VSLU��Ws1) la valoarea

de 200 o&�úL�se determiQ� parametrii fizici ai gazelor de ardere la 2

ttt 1sr

ml

+= :

- vkVFR]LWDWHD�FLQHPDWLF�� ν = [m2/s] - FRQGXFWLELOLWDWHD�WHUPLF�� λ = [W/mK] - criteriul Prandtl Pr = [-] - F�OGXU��VSHFLILF�� cpg = [J/m3

NK]

&RQYHF LD�DUH�XUP�WRDUHOH�FDUDFWHULVWLFL� - FRQYHF LH�IRU DW�� - I�U��VFKLPEDUH�GH�ID]�� - FXUJHUH�WUDQVYHUVDO��SHVWH� eDY� gofrat� P�UJLQLW��GH�SHUHWH; - OD�U�FLUHD�IOXLGXOXL�

0�ULPLOH�JHRPHWULFH�LPSOLFDWH�vQ�DFHDVW��FRQYHF LH�VXQW� - OXQJLPHD�FDUDFWHULVWLF�� GLDPHWUXO�KLGUDXOXLF�DO�FDQDOHORU�FH�VH�IRUPHD]��

între� Hava gofrat��úL�SHUHWH, conform figurii 5.5.; DFHDVW��OXQJLme se poate DSUR[LPD�FX�O� LPHa canalului (lcanal §�Kcanal).


210

Figura 5.7. – Formarea canalelor de trecere la serpentina 1

- VHF LXQHD� GH� FXUJHUH� �6c�� VXPD� VHF LXQLL�� SH� GLUH LD� SHUSHQGLFXODU��curgerii, a tuturor canalelor de curgere formate:

mfmlcc DSS ⋅⋅⋅= π/5,0 [m2] (5.31)

- VXSUDID D� GH� VFKLPE� GH� F�OGXU�� vQ� FXUJHUHD� UDGLDO�� 6scr�� MXP�WDWH� GLQ�

VXSUDID D� WRWDO�� GH� WUDQVIHU� GH� F�OGXU�� D� spirei�� GHRDUHFH� VH� FRQVLGHU��FRQYHF LD� de OD� WUHFHUHD� UDGLDO�� SkQ�� OD� LQWHUVHF LD� FX� XUP�WRUXO� jet din FXUJHUH� UDGLDO� (DGLF�� SkQ�� în XUP�WRDUHD� VHF LXQH� GH� GLDPHWUX�PHGLX� D�serpentinei):

mfmltsc DSS ⋅⋅⋅= π/5,0 [m2] (5.32)

6H�GHWHUPLQ��YLWH]D�FDUDFWHULVWLF��WUDQVIHUXOXL�GH�F�OGXU��

c

ml

g

gS

tD

w 273

273+⋅

= [m/s] (5.33)

unde Dg este debitul normal de gaze de ardere prin spatele spirei 1

úL�FULWHULXO�5H�SHQWUX�FXUJHUH�� υcg lw ⋅

=Re .

Dint

b

h = a / 2


CAZANE

211

3HQWUX�GHWHUPLQDUHD�FRHILFLHQWXOXL�GH�WUDQVIHU�GH�F�OGXU��FRQYHFWLY�VH�IRORVHVF�UHOD LLOH (5.26) sau (5.27).

Coeficientul de� WUDQVIHU�GH�F�OGXU��SULQ�UDGLD LH�VH�QHJOLMHD]��GDWRULW��OXQJLPLL�

GH�UDGLD LH�IRDUWH�PLFL��GH�RUGLQXO�GHVFKLGHULL�GLQWUH�JRIUH�� $VWIHO��FRHILFLHQWXO�JOREDO�GH�WUDVIHU�GH�F�OGXU��GHYLQH�

ccK α⋅= 9,0 [W/m2K] (5.34) unde 0,9 este un coefiFLHQW�GH�UHGXFHUH�FH� LQH�VHDPD�GH�UH]LVWHQ D�WHUPLF��GH�

WLS� FRQGXFWLY� D� SHUHWHOXL�PHWDOLF� úL� GH� UH]LVWHQ D� WHUPLF�� GH� WLS� FRQYHFWLY� SH� SDUWHD�apei.

6H� GHWHUPLQ�� WHPSHUDWXUD� UHDO�� GH� LHúLUH� D� JD]HORU� GH� DUGHUH� FX� UHOD LD� GH�

verificare:

( ) pgg

scc

cD

SK

amrams etttt⋅⋅

−

⋅−+=1 [oC] (5.35)

unde tam este temperatura medie a agentului secundar (apa). 5H]XOW�� IOX[XO� GH� F�OGXU�� WUDQVPLV� vQ� WUHFHUHD� UDGLDO�� D� JD]HORU� GH� DUGHUH la

exteriorul spirei 1:

( ) 311 10−⋅−⋅⋅= srpggs ttcDQ [kW] (5.36)

Modelul de calcul aplicat pentru prLPD� VSLU�� VH� UHLD� SHQWUX� XUP�WRDUHOH� VSLUH�

�� úL� �� FX� GLIHUHQ D� F�� LQWUDUHD� vQ� ]RQD� GH� WUDQVIHU� GH� F�OGXU�� QX�PDL� HVWH� D� XQXL�GHELW� FX� VXUV�� XQLF�� GH� SURYHQLHQ �� FL� D� XQXL� DPHVWHF� GH� JD]H� GH� DUGHUH�� FRQIRUP�schemei de curgere.

Astfel:

- la exteriorul spirei 2 va curge un amestec de : • 1/8 DgN cu temperatura ts1 rezultat din trecerea la exteriorul spirei 1 • 2/8 DgN cu temperatura tr UH]XOWDW�GLQ�WUHFHUHD�UDGLDO��vQWUH�VSLUD��úL�

spira 2. úL�YD�JHQHUD�IOX[XO�GH�F�OGXU��XWLO�4s2.

- la exteriorul spirei 3 va curge un amestec de :

• 3/8 DgN cu temperatura ts2 rezultat din trecerea la exteriorul spirei 2


212

• 2/8 DgN cu temperatura tr UH]XOWDW�GLQ�WUHFHUHD�UDGLDO��vQWUH�VSLUD��úL�spira 3.

úL�YD�JHQHUD�IOX[XO�GH�F�OGXU��XWLO�4s3.

- la exteriorul spirei 4 va curge un amestec de :

• 5/8 DgN cu temperatura ts3 rezultat din trecerea la exteriorul spirei 3 • 2/8 DgN cu temperatura tr UH]XOWDW�GLQ�WUHFHUHD�UDGLDO��vQWUH�VSLUD��úL�

spira 4. úL�YD�JHQHUD�IOX[XO�GH�F�OGXU��XWLO�4s4.

Calculul global al serpentinei focar Fluxul dH�F�OGXU��WRWDO�VFKLPEDW�GH�VHUSHQWLQD��GHYLQH��

∑=

++=4

11

i

sirfserp QQQQ [kW] (5.37)

Intr-XQ� FDOFXO� DXWRPDW�� VH� IDF� YHULILF�UL� GH� FRQFRUGDQ �� vQWUH� WHPSHUDWXULOH�

LQL LDOL]DWH�SH�SDUFXUVXO�FDOFXOXOXL�úL�FHOH�UH]XOWDWH�GLQ�FDOFXO��I�FkQGX-VH�QXP�UXO�Ge LWHUD LL�QHFHVDU�SHQWUX�vQFKLGHUHD�DFHVWRUD�VXE�R�HURDUH�DGPLVLELO��GH�H[HPSOX��oC). In cazul calculului manual acest lucru nu este posibil, acceptându-se erorile rezultate GLQ� SUHGLF LLOH� DSUR[LPDWLYH�� 'DWRULW�� DFHVWHL� SDUWLFXODULW� L�� WHPSHUDWXUD� ILQDO�� D�JD]HORU�GH�DUGHUH�OD�LHúLUHD�GLQ�VHUSHQWLQD��úL�LQWUDUHD�vQ�VHUSHQWLQD��VH�YD�FDOFXOD�FX�UHOD LD�JOREDO��

1

1

1 tserp

pg

gN

serp

t

tt

pg

serpc

D

Qtc

t

−⋅

= [oC] (5.38)

(unde tt

pgc úL 1tserp

pgc VXQW� F�OGXULOH� VSHFLILFH� ale gazelor de ardere la

WHPSHUDWXUD� WHRUHWLF�� úL� UHVSHFWLY� OD� WHPSHUDWXUD� GH� LHúLUH� GLQ� VHUSHQWLQD� �� FDOFXO�iterativ) )

úL�QX�FX�UHOD LD�GH�FDOFXO�D�WHPSHUDWXULL�DPHVWHFXOXL�GH�JD]H�

• 7/8 DgN cu temperatura ts4 rezultat din trecerea la exteriorul spirei 4 • 1/8 DgN cu temperatura tr UH]XOWDW�GLQ�WUHFHUHD�UDGLDO��vQWUH�VSLUD��úL�

corpul central deflector.


CAZANE

213

Calculul termic al serpentinei 2 (serpentina convectiv)

3HQWUX�D�FDOFXOD�IOX[XO�GH�F�OGXU��VHQVLELO��VFKLPEDW�GH�VHUSHQWLQD��SDUWHD�GLQ�

serpentina cazanului cupULQV�� vQWUH� FRUSXO� FHQWUDO� GH� GLULMDUH� D� JD]HORU� GH� DUGHUH� úL�peretele exterior al cazanului) se GHWHUPLQ�� SDUDPHWULL� IL]LFL� DL� JD]HORU� GH� DUGHUH� OD�

221

2serpserp

m

ttt

+= , unde cos2 tt serp = :

- YkVFR]LWDWHD�FLQHPDWLF�� ν = [m2/s] - conductibiliWDWHD�WHUPLF�� λ = [W/mK] - criteriul Prandtl Pr = [-] - F�OGXU��VSHFLILF�� cpg = [J/m3

NK]

&RQYHF LD�DUH�XUP�WRDUHOH�FDUDFWHULVWLFL� - FRQYHF LH�IRU DW�� - I�U��VFKLPEDUH�GH�ID]�� - FXUJHUH�WUDQVYHUVDO��SHVWH� HDY��JRIUDW��P�UJLQLW��GH�SHUH L� - OD�U�FLUHD�IOXidului. 0�ULPLOH�JHRPHWULFH�LPSOLFDWH�vQ�DFHDVW��FRQYHF LH�VXQW� - OXQJLPHD�FDUDFWHULVWLF�� GLDPHWUXO�KLGUDXOXLF�DO�FDQDOHORU�FH�VH�IRUPHD]��

vQWUH� HDYD�JRIUDW��úL�SHUHWH��FRQIRUP�ILJXULL�5.8.; DFHDVW��OXQJLPH�VH�SRDWH�DSUR[LPD�FX�O� LPHD�FDQDOXOXL��Ocanal §�Kcanal).

- VHF LXQHD� GH� FXUJHUH� �6c2�� VXPD� VHF LXQLL�� SH� GLUH LD� SHUSHQGLFXODU��curgerii, a tuturor canalelor de curgere formate:

mfmlcc DSS ⋅⋅= π/2 [m2] (5.39)

- VXSUDID D� GH� VFKLPE� GH� F�OGXU�� 6sc2�� VXSUDID D� WRWDO�� GH� WUDQVIHU� GH�

F�OGXU� a serpentinei:

2/2 tmfmltsc nDSS ⋅⋅⋅= π [m2] (5.40)

unde nt2 este nuP�UXO�GH�VSLUH�DO�VHUSHQWLQHL��

6H�GHWHUPLQ��YLWH]D�FDUDFWHULVWLF��WUDQVIHUXOXL�GH�F�OGXU��

2

2

2273

273

c

m

gN

gS

tD

w

+⋅

= [m/s] (5.41)


214

Figura 5.8. – formarea canalelor de trecere la serpentina 2

úL�FULWHULXO�5H�SHQWUX�FXUJHUH�� υcg lw ⋅

= 2Re .

3HQWUX�GHWHUPLQDUHD�FRHILFLHQWXOXL�GH�WUDQVIHU�GH�F�OGXU��FRQYHFWLY�VH�IRORVHVF�

UHOD LLOH��5.26) sau (5.27). &RHILFLHQWXO�GH�WUDQVIHU�GH�F�OGXU��SULQ�UDGLD LH�VH�QHJOLMHD]��GDWRULW��OXQJLPLL�

GH� UDGLD LH� IRDUWH� PLFL� �GH� RUGLQXO� GHVFKLGHULL� GLQWUH� JRIUH�� úL� D� WHPSHUDWXULL� PHGLL�VF�]XWH.

$VWIHO��FRHILFLHQWXO�JOREDO�GH�WUDVIHU�GH�F�OGXU��GHYLQH�

22 9,0 ccK α⋅= [W/m2K] (5.42) unde 0,9 este�XQ�FRHILFLHQW�GH�UHGXFHUH�FH� LQH�VHDPD�GH�UH]LVWHQ D�WHUPLF��GH�

WLS� FRQGXFWLY� D� SHUHWHOXL�PHWDOLF� úL� GH� UH]LVWHQ D� WHUPLF�� GH� WLS� FRQYHFWLY� SH� SDUWHD�apei.

6H� GHWHUPLQ�� WHPSHUDWXUD� UHDO�� GH� LHúLUH� D� JD]HORU� GH� DUGHUH� FX� UHOD LD� GH�

verificare:

( ) pggN

scc

cD

SK

amsams etttt⋅⋅

−

⋅−+=22

12 [oC] (5.43)


CAZANE

215

5H]XOW��IOX[XO�GH�F�OGXU��WUDQVPLV�vQ�serpentina 2:

( ) 3212 10−⋅−⋅⋅= sspggNs ttcDQ [kW] (5.44)

)OX[XO�WRWDO�GH�F�OGXU��VHQVLELO��WUDQVPLV�vQ�FD]DQ�GHYLQH�

21 ss

sensibil

tot QQQ += [kW] (5.45)

&DOFXOXO�WHUPLF�OD�IXQF LRQDUHD�vQ�UHJLP�GH�FRQGHQVD LH��VHUSHQWLQD�� 6H�YHULILF��vQ�SULPXO�UkQG�H[LVWHQ D�FRQGL LHL�GH�FRQGHQVDUH�

rouaper tt ≤ , unde amper tt = (5.46)

GXS�� FDUH� VH� FDOFXOHD]�� WHPSHUDWXUD� VWUDWXOXL� OLPLW�� GH� FRQGHQVDUH� FD� R�PHGLH� vntre WHPSHUDWXUD�JD]HORU�GH�DUGHUH�úL�WHPSHUDWXUD�SHUHWHOXL�

2limpergm tt

t+

= (5.47)

6H�FDOFXOHD]��DSRL�FRQVWDQWHOH�IL]LFH�DOH�JD]HORU�GH�DUGHUH�GLQ�VWUDWXO�OLPLW��

��FRHILFLHQWXO�GH�GLIX]LH�PROHFXODU��'if ��coeficientul de viscozitate cinematLF��ng

úL�UH]XOW��FULWHULXO�6&+0,'7�

if

g

DSc

ν= (5.48)

Pentru calculul criteriului SHERWOOD, caracteristic difuziei turbulente, se

FDOFXOHD]��FLIUD�5(<12/'6�SHQWUX�JD]HOH�GH�DUGHUH�GLQ�VWUDWXO�OLPLW��

g

echg

g

dw

ν⋅

=limRe úL apoi

33,08,0limRe023,0 ScSh g ⋅⋅= (5.49)

&RHILFLHQWXO� GH� WUDQVIHU� GH� PDV�� DQDORJ� FX� FRHILFLHQWXO� GH� WUDQVIHU� GH�F�OGXU��.��VH�FDOFXOHD]��FX�UHOD LD�


216

ech

if

d

DSh ⋅=β (5.50)

&DOFXOXO� GHELWXOXL� GH�FRQGHQV�SH� VXSUDID �� VH� IDFH�GXS�� UHOD LD�GH� WUDQVIHU�GH�

PDV��vQ�FDUH�JUDGLHQWXO�PRWRU�HVWH�GLIHUHQ D�GH�FRQFHQWUD LL��UHVSHFWLY�SUHVLXQL�SDU LDOH�D�YDSRULORU�GH�DS��vQWUH�JD]HOH�GH�DUGHUH�úL�SHUHWH�

( )273

02157,022 +

⋅−⋅=gm

per

OH

gaz

OHmast

ppJ β [kg/s•m2] (5.51)

În care termenul ( )

+⋅−

273

02157,022

gm

per

OH

gaz

OHt

pp reprH]LQW�� GLIHUHQ D� GLQWUH�FRQFHQWUD LLOH� GH�H2O� vQ� JD]H� úL� OD�SHUHWH��GHRDUHFH�FRQFHQWUD LD�YDSRULORU�GH�DS�� vQ�amestec este:

27322 +

⋅=gm

OHOHt

R

M

pC ; 98066dim22 ⋅= a

OHOH pp [Pa] (5.52)

cu dim2

a

OHp exprimat adimensional (conform calculului de ardere). 'DF��VXSUDID D�GH�FRQGHQVDUH�OXDW��vQ�FRQVLGHUDUH�SHQWUX�HOHPHQWXO�GH�FDOFXO�HVWH�Scond��UH]XOW��F��GHELWXO�GH�FRQGHQVDW�RE LQXW�SH�VXSUDID D�HOHPHQWXOXL�YD�IL�

condmascond SJG ⋅= [kg/s] (5.53)

)OX[XO� GH� PDV�� GHWHUPLQ�� XQ� IOX[� HFKLYDOHQW� GH� F�OGXU�� GH� FRQGHQVDUH� SULQ PXOWLSOLFDUH� FX� F�OGXUD� ODWHQW�� GH� FRQGHQVDUH� r�� 6H� UHYLQH� OD� R� UH]LVWHQ �� WHUPLF��GLIX]LY��5dif�SULQ�UDSRUWDUHD�OD�VXSUDID ��úL�OD�GLIHUHQ D�GH�WHPSHUDWXU��JD]H�GH�DUGHUH�– DS��,QYHUVXO�UH]LVWHQ HL�GLIX]LYH�HVWH�FRHILFLHQWXO�HFKLYDOHQW�GH�FRQYHF LH�GLIX]LY��.dif.

,Q�JD]HOH�GH�DUGHUH�LQL LDOH�FDQWLWDWHD�GH H2O a fost: in

OHgN

in

OH CDG 22 ⋅= [kg/s] (5.54)

In gazele de ardere finale cantitatea de H2O va fi:

GH2Ofin = GH2Oin – Gcond [kg/s] (5.55)

5H]XOW��FRQFHQWUD LD�ILQDO��GH�+2O :


CAZANE

217

gN

fin

OHfin

OHD

GC 2

2 = (5.56)

127$��SHQWUX�VLPSOLILFDUHD�FDOFXOXOXL��GDWRULW�� WHPSHUDWXULL�VF�]XWH�D�JD]HORU�de ardere nu s-DX�PDL�FRQVLGHUDW�FRUHF LLOH�GH�WHPSHUDWXU��SHQWUX�WUHFHUHD�GH�OD�GHELWXO�normal la cel real�úL�LQYHUV.

3UHVLXQHD�SDU LDO��DEVROXW��>3D@�ILQDO� va fi:

pH2O

fin = CH2O

fin • 461,9 • (tgm + 273) (5.57)

úL�SUHVLXQHD�SDU LDO��>EDU@��

( )5,98066

2

2

fin

fin OH

OH

padmp = (5.58)

&RHILFLHQWXO�FRQYHFWLY�DO�FRQGHQV�ULL�SH�SHUHWH�HVWH��.cd=1/Rcd �úL�VH�FDOFXOHD]��

FX�UHOD LD�FODVLF��GH�FRQGHQVDUH� ( )( )4

1

652,0 per

roua

gaz

rouaeccd ttdA −⋅⋅⋅=α (5.59)

unde Ac�HVWH�R�FRQVWDQW��IXQF LH�de parametri fizici ai apei din pelicula de condens la WHPSHUDWXUD�GH�FRQGHQVDUH��SUH]HQWDW��vQ�WDEHOXO�XUP�WRU:

&DUDFWHULVWLFL�IL]LFH�DOH�DSHL�OD�VDWXUDWLH�úL�FRQVWDQWD�$c tr

[oC] λ

W/m•K r

J/kg ρapa

kg/mc ρab

kg/mc

ν m/s2

Ac [ - ]

40 0,6338 2406000 992,16 0,05115 6,59E-7 9752,67 50 0,6478 2383000 988,04 0,08306 5,56E-7 10308,5 60 0,6594 2358000 983,19 0,1302 4,79E-7 10801,3 70 0,6676 2333000 977,71 0,1982 4,15E-7 11253,8 80 0,6745 2308000 971,82 0,2934 3,66E-7 11653,5 90 0,6804 2282000 965,34 0,4235 3,26E-7 12019,5 100 0,6827 2257000 958,31 0,5977 2,95E-7 12297,7 PHQWUX�FDOFXO�DXWRPDW�VH�SRDWH�XWLOL]D�UHOD LD�GH�UHJUHVLH�H[SRQHQWLDO��

Ac = 9130 + 141,37 • ( tURX�� - tpe ) 0,774553 (5.60)

&RHILFLHQWXO�FRPSXV�GH�WUDQVIHU�GH�F�OGXU��SULQ�FRQGHQVDUH�YD�IL� .cond = 1 / Rcond (5.61)


218

unde

Rcond = Rdif + Rcd (5.62)

&X�DFHVWH�GDWH�VH�SRDWH�FDOFXOD�FRPSOHW�WUDQVIHUXO�GH�F�OGXU� úL PDV��vQ�SURFHVXO�GH�FRQGHQVDUH�úL�VH�RE LQ�SDUDPHWULL�ILQDOL��

,Q� FRQWLQXDUH� VH� SXQH� FRQGL LD� FD� YDORDUHD� LQL LDO� DWULEXLW�� VDUFLQLL� WHUPLFH��randamentului (eficieQ HL��úL�UHVSHFWLY�WHPSHUDWXULL�JD]HORU�GH�DUGHUH�OD�FRú��V��QX�GLIHUH�FX�PDL�PXOW�GH��ID ��GH�YDORDUHD�FDOFXODW��'DF��QX�VH�vQGHSOLQHúWH�FRQGL LD��VH�UHLD�calculul cu noua valoare a parametrilor de intrare.

6. CALCULUL TERMIC AL C$=$1(/25�)81&�,21Æ1' CU ARDEREA

LEMNULUI PRIN GAZEIFICARE (ARDERE INVERS��

219

CAPITOLUL 6.

CALCULUL TERMIC AL C$=$1(/25� )81&�,21Æ1'

CU ARDEREA LEMNULUI PRIN GAZEIFICARE

�$5'(5(�,19(56��

6.1. Analiza constructiv-IXQF LRQDO��D�FD]DQHOor cu combistibil solid - lemne

&D]DQHOH�PLFL� GH� vQF�O]LUH� FX� OHPQH� DSOLF�� GLQ�FH� vQ�FH�PDL�PXlt sistemul de DUGHUH� LQYHUVDW�� 6LVWHPXO� UHSUH]LQW�� DUGHUHD� úDUMHL� GH� OHPQH� vQWU-R� ]RQ�� ELQH�GHOLPLWDW��OD�ED]D�VWUDWXOXL��)D]HOH�VSHFLILFH�DUGHULL�FRPEXVWLELOLORU�VROL]L�VH�VXFFHG�FX�rapiditate într-R� ]RQ�� vQJXVW�� ID �� GH� JURVLPHD� VWUDWXOXL� GH� úDUM�� D� Oemnelor împiedicându-VH�IXQF LRQDO�DSDUL LD�IHQRPHQXOXL�GH�³DPEDODUH´�D�DUGHULL�vQ�WRDW��PDVD�de combustibil.

In figura 6.�� HVWH� VFKHPDWL]DW�� DUGHUHD� VWUDWXOXL� vQ� VLVWHP� FODVLF�� GLUHFW�� &D�SULQFLSLX�JHQHUDO��OD�DUGHUHD�GLUHFW��vQ�VWUDW��DHUXO�SULPDU�GH�DUdere produce un debit de JD]H�GH�DUGHUH�FH�VWU�EDWH�VWUDWXO� úL�GXFH� OD�DSDUL LD�GLYHUVHORU�ID]H�GH�DUGHUH��DUGHUH�UH]LGXX�FDUERQRV��GHYRODWLOL]DUH�úL�vQF�O]LUH�FX�XVFDUH��vQ�WRDW��PDVD�GH�FRPEXVWLELO�FH�IRUPHD]�� R� úDUM�� GH� DOLPHQWDUH�� 5H]XOW�� OD� SDUWHD� VXSHULRDU�� D� VWUDWXOXL� XQ� GHELW� GH�JD]H�GH�DUGHUH�LQFRPSOHW�� vQ�DPHVWHF�FX�VXEVWDQ H�YRODWLOH�FRPEXVWLELOH�úL�XPLGLWDWH��Acest debit de gaze combustibile, rezultat practic din întreaga grosime a stratului, SULPHúWH�DHUXO�VHFXQGDU�GH�DUGHUH�úL�JHQHUHD]��JD]H�GH�DUGHUH�FRPSOHW��

Fig. 6.1 Focar cu gr�tar cu ardere direct� a stratului de lemne 1. corp cazan cu pereti raciti cu apa; 2. gratar; 3. strat de lemne; 4. insuflare de aer primar de ardere;

5. zona de ardere a cocsului; 6. camera de ardere a produselor de gazeificare; 7. insuflare de aer secundar; 8. tevi convective; 9. evacuarea gazelor de ardere.

1

2

3

4

5

6 7

8

9


CAZANE

220

&RQFOX]LD�HVWH�F�� vQ�UHJLPXO�QRUPDO�GH�OXFUX�DO�JU�WDUXOXL�DSDUH�IHQRPHQXO�GH�

³DPEDODUH´� D� VWUDWXOXL�� DGLF�� DSDUL LD� XQHL� VDUFLQL� WHUPLFH� FDUH� GHS�úHúWe sarcina WHUPLF�� SURLHFWDW�� D� FD]DQXOXL��5H]XOWDWXO� HVWH� GHS�úLUHD� WHPSHUDWXULL�PD[LPH� D� DSHL�GLQ� FD]DQ� FKLDU� úL� vQ� FRQGL LLOH� XQRU� VLVWHPH� PHFDQLFH� GH� LQWURGXFHUH� D� DHUXOXL� GH�DUGHUH�úL�DSDUL LD�VLWXD LHL�GH�DYDULH�GH�VXSUDWHPSHUDWXU��3HQWUX�D�HYLWD�DFHst fenomen WUHEXLH�UHGXV��JURVLPHD�VWUDWXOXL�GH�FRPEXVWLELO��FHHDFH�GXFH�OD�úDUMH�FX�WLPS�VFXUW�GH�acoperire a necesarului termic.

In cazul arderii inverse, conform schemei din figura 6.2.�� GDWRULW�� SURSDJ�ULL�IURQWXOXL� GH� IODF�U�� vQ� FRQWUDFXUHQW� FX� DHUXO� de ardere (primar), fenomenul de DSULQGHUH�QHFRQWURODW��D�VWUDWXOXL�QX�PDL�DSDUH��FHHDFH�SHUPLWH�UHDOL]DUHD�XQRU�UH]HUYH�semnificative de combustibil printr-R�JURVLPH�IRDUWH�PDUH�GH�VWUDW��$VWIHO�VH�UHDOL]HD]��DXWRQRPLL� GH� IXQF LRQDUH� FX� R� vQF�UF�WXU�� úDUM�� GH� SkQ�� OD� �� RUH� GH� IXQF LRQDUH�QRUPDO��GLQ�VDUFLQD�QRPLQDO��

Fig. 6.2. Focar cu gr�tar cu ardere invers� a stratului de lemne. 1. corp cazan cu pereti raciti cu apa; 2. gratar; 3. buncar de lemne;

4. insuflare de aer de ardere; 5. zona de aprindere a lemnelor; 6. camera de ardere a produselor de gazeificare; 7. intoarcere a gazelor de ardere; 8. tevi

convective; 9. evacuarea gazelor de ardere. ÌQ�FRQWDFW�FX�R�]RQ��VWDELO��GH�DUGHUH��OHPQHOH�GH�GHDVXSUD�JU�WDUXOXL�VH�DSULQG�

úL�VXIHU��XQ proces de gazeificare��ÌQ�SUH]HQ D�XQHL�FDQWLW� L�VXILFLHQWH�GH�DHU�SHQWUX�DUGHUH�FRPSOHW��FDUH�DQWUHQHD]��VXE�JU�WDU�SURGXVHOH�GH�JD]HLILFDUH��DFHVWHD�DUG�vQWU-o FDPHU��GH�DUGHUH��$LFL�HVWH�GH�PHQ LRQDW�GLIHUHQ D�GH�SURFHV�ID ��GH�DUGHUHD�GLUHFW��D�straWXOXL��/D� DUGHUHD�GLUHFW�� VWUDWXO�GH�FRPEXVWLELO� vQ�DUGHUH� VH�GH]YROW�� SH�YHUWLFDO��

1

2

3

5

6

4

8

7

9



221

RULFkW�GH�PXOW�� vQ�OLPLWD�DHUXOXL�GLVSRQLELO��úL� vQWRWGHDXQD��GDWRULW��UHDFWLYLW� LL�PDUL�D�FDUERQXOXL� OD� WHPSHUDWXUL� ULGLFDWH�� DUGHUHD� HVWH� LQFRPSOHW�� 'H� DFHHD� HVWH� WRWGeauna QHFHVDU�FD�OD�DUGHUHD�GLUHFW��V��VH�LQVXIOH�GHDVXSUD�VWUDWXOXL�DHU�VHFXQGDU��DSUR[LPDWLY�FX�DFHODúL�GHELW�FD�úL�DHUXO�SULPDU��SHQWUX�D�GD�R[LJHQXO�QHFHVDU�DUGHULL�YRODWLOHORU�úL�gazelor de gazeificare a cocsului. /D� DUGHUHD� LQYHUV�� VWUDWXO� GH� cocs este numai pe periferia buF� LORU� GH� OHPQ�� OD� SRU LXQHD� LQIHULRDU�� D� VWUDWXOXL�� úL� QX� VH� GH]YROW�� vQ�VXVXO� VWUDWXOXL� GHRDUHFH� FXUHQWXO� GH� DHU� GH� DUGHUH� YLQH� GH� VXV� vQ� MRV�PHQ LQkQG� UHFH�FRPEXVWLELOXO�� $FHVW� IHQRPHQ� GH� DSULQGHUH�� QXPDL� SULQ� FRQGXF LH� úL� UDGLD LH� ORFDO��GLIHUHQ LD]�� IXQGDPHQWDO� DUGHUHD� LQYHUV�� GH� DUGHUHD� GLUHFW�� XQGH� DSULQGHUHD� VH� IDFH�PDL�DOHV�FRQYHFWLY��SULQ�JD]HOH�ILHUELQ L�SURGXVH�GH�VWUDWXULOH�LQIHULRDUH��

'DWRULW�� DFHVWRU� SDUWLFXODULW� L� IXQF LRQDOH�� FD]DQHOH� FX� FRPEXVWLELO� VROLG� FX�

aUGHUH�LQYHUV��DX�GLVWULEX LD�DHU�SULPDU��DHU�VHFXQGDU�vQ�GRPHQLXO��- 60% / �� VSUH� GHRVHELUH� GH� VLVWHPHOH� FX� DUGHUH� GLUHFW�� FDUH� DX� DFHODúL� UDSRUW� YDULLQG� vQ�domeniul 50% / 50% - 40% / 60%.

6LVWHPXO�GH� DUGHUH� LQYHUV�� D� FRPEXVWLELOXOXL� VROLG� vQ� VWUDW� DGXFH� úL� R� VHULH�GH�

alte avantaje importante. 'LQ�SXQFW�GH�YHGHUH�DO�FDOLW� LL�DUGHULL��GHRDUHFH� LQVXIODUHD�GH�DHU�VHFXQGDU�VH�

UHDOL]HD]��GH�RELFHL�FRQFHQWUDW��DúD�FXP�UHLHVH�GLQ�VFKHPD�IXQF LRQDO��GLQ�ILJXUD�6.3., SH�R�]RQD�GH�VHF LXQH�UHGXV��VHF LXQHD�GH�WUHFHUH�GLQWUH�EXQF�UXO�FH�DUH�OD�ED]� zona GH� DUGHUH� úL� FDPHUD� IRFDU� U�FLW� GH� DUGHUH� D� SURGXVHORU� JD]RDVH�� VH� UHDOL]HD]�� R�DPHVWHFDUH� IRDUWH� EXQ�� FX� SURGXVHOH� GLQ� FDPHUD� GH� JD]HLILFDUH�� DVLJXUkQGX-se QHFHVDUXO�GH�DHU�GH�DUGHUH�vQ�FRQGL LLOH�XQRr excese de aer�VF�]XWH��&KLDU�GDF��DUGHUHD�VH�UHDOL]HD]��QXPDL�FX�DHU�SULPDU��SULQ�DFFHOHUDUHD�GHELWXOXL�FRPELQDW�GH�DHU�vQ�H[FHV cu produsele� GH� DUGHUH� LQFRPSOHW�� úL� cu volatilele la trecerea prin reducerea de VHF LXQH�� VH� UHDOL]HD]�� GH� DVHPHQHD� FRQGL LL� IDYRUDELOH� GH� DPHVWHFDUH�� FH� FUHHD]��SUHPL]HOH� XQHL� DUGHUL� FRPSOHWH� OD� H[FHVH� GH� DHU� PLFL�� $G�XJkQG� HOHPHQWXO� GH�VWDELOL]DUH� D� DUGHULL� FRQVWLWXLW� GH� WHPSHUDWXUD� ULGLFDW�� D� FDQDOXOXL� GH� WUHFHUH� úL�SRVLELOLWDWHD�vQ�FDPHUD�GH�DUGHUH�U�FLW�, de dirijare a gazHORU�GH�DUGHUH�SHVWH�VXSUDIH H�UHIUDFWDUH�ILHUELQ L��UH]XOW��R�UHGXFHUHD�VXEVWDQ LDO��D�&29�QHDUVH�HOLPLQDWH�FX�JD]HOH�GH� DUGHUH� úL� XQ� QLYHO� GH� FRQFHQWUD LL� GH� R[LG� GH� FDUERQ� FRPSDUDELOH� FX� FHOH�FDUDFWHULVWLFH�DUGHULL�FRPEXVWLELOLORU�JD]RúL�vQ�VLVWHPH�DXWRaspirante.

'LQ� SXQFW� GH� YHGHUH� IXQF LRQDO�� GHRDUHFH� SULQ� FDUDFWHULVWLFLOH� SDUWLFXODUH�VLVWHPXOXL��RSULUHD�SURFHVXOXL�GH�DUGHUH�HVWH�DSURDSH�FRPSHW��SULQ�RSULUHa�LQVXIO�ULL�GH�DHU��VSUH�GHRVHELUH�GH��DUGHUHD�GLUHFW��vQ�VWUDW�XQGH�RSULUHD�LQVXIO�ULL�GH�DHU�QX�GXFH�úL�OD� RSULUHD�GHJDM�ULORU� GH�YRODWLOH� GLQ� VWUDW�� UH]XOW�� SRVLELOLWDWHD�XQXL� FRQWURO� úL� D�XQHL�DVLJXU�UL�D�FD]DQHORU�PXOW�PDL�VWULFWH�úL�HILFLHQWH��

0DL� PXOW�� GDWRULW�� VLVWHPXOXL� VSHFLILF� GH� DSULQGHUH� úL� VWDELOL]DUH� D� DUGHULL� vQ�strat, ce permite înc�UFDUHD� FX� úDUMH� PDUL�� VH� FRQVWLWXLH� vQ� DYDQWDM� IXQF LRQDO� úL�FRQWLQXLWDWHD�SURFHVXOXL�GH�DUGHUH��GH�WLS�SURFHV�VWD LRQDU�


CAZANE

222

Fig. 6.��6FKHPD�IXQF LRQDO��GH�DUGHUH�OD�VROX LLOH�FX�³GX]�´

de trecere a produselor de gazeificare /D� QLYHOXO� H[SORDW�ULL� FXUHQWH� HVWH� GH� UHPDUFDW� vQ� SULPXO� UkQG� IDSWXO� F��

GHVFKLGHUHD�XúLL�GH�DOLPHQWDUH�QX�GXFH�OD�FRQWDFWXO�FX�VWrDWXO�GH�DUGHUH��FHHDFH�HOLPLQ��SRVLELOLWDWHD�GH�DFFLGHQWDUH�GLUHFW��VDX�SULQ�F�GHUL�GH�FRPEXVWLELO�DSULQV�GLQ�FD]DQ� În cDPHUD�GH�DUGHUH�LQIHULRDU��DHUXO�ILLQG�vQ�GHELW�VXILFLHQW��VH�SURGXFH�DUGHUHD�FRPSOHW��*D]HOH�GH�DUGHUH�XUPHD]��DSRL�WUDVHXO�SULQ� HYLOH�GUXPXOXL�FRQYHFWLY�úL�VXQW�DSRL� HYDFXDWH� OD� FRú�� FLUFXOD LD� ORU� ILLQG� DVLJXUDW�� GH� XQ� H[KDXVWRU��(VWH� DYDQWDMRDV��funF LRQDUHD�FD]DQXOXL�vQ�GHSUHVLXQH�GHRDUHFH�VH�HYLW��VF�S�ULOH�GH�JD]H�GH�DUGHUH�SULQ�QHHWDQúHLW� L� Procesul din camera de deasupra stratului fiind preponderent de gazeificare, WHPSHUDWXUD�QX�HVWH�vQDOW��6SHFLILFH�SHQWUX��SURFHVXO�GH�JD]HLILFDUH�VXQW�WHmperaturile de 600 – 900 0&��&RQWDFWXO��JU�WDUXOXL�FX�XQ�FRPEXVWLELO�FX�WHPSHUDWXU��UHODWLY�MRDV��úL�FX�DHUXO�GH�DUGHUH�FDUH�DUH�XQ�SXWHUQLF�HIHFW�GH�U�FLUH��IDFH�FD�WHPSHUDWXUD�EDUHORU�GH�JU�WDU� VDX� a DPEUD]XULL� GH� LHúLUH� D� JD]HORU� V�� ILH� PXOW� PDL� MRDV�� Gecât în arderea GLUHFW�� GHFL� QX� YRU� IL� QHFHVDUH� PDWHULDOH� UHIUDFWDUH� GH� FDOLWDWH� VXSHULRDU�� SHQWUX� D�DVLJXUD�GXUDELOLWDWHD�JU�WDUXOXL�� 3DUWLFXODULWDWHD� GH� SRUQLUH� OD� FD]DQHOH� FX� DUGHUH� LQYHUV�� HVWH� GDW�� GH� WUHFHUHD�curgerii gazelor din sistem invers, cX�VWU�EDWHUHD�FRQYHFWLYXOXL, în sistem direct,� I�U��VWU�EDWHUHD� FDPHUHL� GH� DUGHUH� U�FLWH� úL� D� FRQYHFWLYXOXL�� SULQWU-R� VHF LXQH� GH� VFXUW-FLUFXLW�� FX� HYDFXDUH� GLUHFW�� OD� FRú�� 6LVWHPXO� GH� WUHFHUH� HVWH� vQ� JHQHUDO�PDQXDO� úL� QX�ULGLF�� SUREOHPH� GH� UHDOL]DUH� WHKQRORJLF�� VDX� GH� PDQLSXODUH� vQ� H[SORDWDUH� FXUHQW��

=RQ��úDPRWDW� ��³JU�WDU´ activ )

Post-ardere SULPDU�

Post-ardere VHFXQGDU�

(cu stabilizare)

Produse de DUGHUH�FRPSOHW�

Corp refractar

Aer primar 100 % - 60 %

Aer secundar 0 % - 40 %

6HF LXQH�GH�trecere a produselor de gazeificare

Strat de combustibil

&DPHU��GH�DS�



223

3UH]HQ D�DFHVWXL�VLVWHP�DUH�vQV��DYDQWDMXO�DVLJXU�ULL��OD�SRUQLUHD�VLVWHPXOXL�GH�OD�UHFH��D�XQXL�GHELW�GH�JD]H�GH�DUGHUH�GH�WHPSHUDWXU��ULGLFDW��FHHDFH�GXFH�OD�DWLQJHUHD�UDSLG��D�regimului de autotiraj pentrX�FRúXO�GH� IXP��HOHPHQW� IXQF LRQDO�GHRVHELW�GH�DYDQWDMRV�DWkW�SHQWUX�IXQF LRQDUHD�FD]DQXOXL�FkW�úL�SHQWUX�FRQGL LLOH�GH�VLJXUDQ ��D�IXQF LRQ�ULL�vQ�FHQWUDO��VH�HYLW��DSDUL LD�UHIXO�ULORU�GH�JD]H�WR[LFH�VDX�IRUPDUHD�GH�DFXPXO�UL�GH�JD]H�FX�SRWHQ LDO�GH�H[Slozie).

3HULRDGD�GH�DUGHUH�GLUHFW��OD�SRUQLUHD�GH�OD�UHFH�D�VLVWHPHORU�FX�DUGHUH�LQYHUV��WUHEXLH�V��ILH�VXILFLHQW�GH�OXQJ��SHQWUX�D�DVLJXUD�vQF�O]LUHD�]RQHL�UHIUDFWDUH�GH�OD�ED]D�EXQF�UXOXL�GH�FRPEXVWLELO�FH�FRQ LQH�JU�WDUXO� úL� IRUPDUHD�VWUDWXOXL�VXSHUIicial de cox UHDFWLY�OD�VXSUDID D�LQIHULRDU��D�FRPEXVWLELOXOXL�GH�OD�ED]D�VWUDWXOXL��$FHDVW��SHULRDG��HVWH�vQV��PXOW�PDL�VFXUW��GHFkW�FHD�QHFHVDU��VLVWHPHORU�FODVLFH�GH�DUGHUH�FDUH�QHFHVLW��WLPS�DWkW�SHQWUX�vQF�O]LUHD�]RQHORU�úDPRWDWH�FkW�PDL�DOHV�SHQWUX�Iormarea unui strat de MDU� JURV� úL� XQLIRUP� QHFHVDU� LQL LHULL� DUGHULL� OD� vQF�UFDUHD� FX� úDUMD� GH� FRPEXVWLELO�SURDVS�W��6FXUWDUHD�WLPSXOXL�GH�SRUQLUH�OD�UHFH��FRQMXJDW��FX�P�ULUHD�WLPSXOXL�GH�úDUM��GXFH� OD� VLPSOLWDWH� VSRULW�� vQ� H[SORDWDUH� D� VLVWHPHORU� FX� DUGHUH� LQYHUV�� SDUDOHO� FX�UHGXFHUHD�HPLVLLORU�JOREDOH�OD�QLYHOXO�VLVWHPXOXL��HVWH�FXQRVFXW�IDSWXO�F��XQ�VLVWHP�GH�ardere cu combustibil solid are emisii maxime de noxe în perioadele de pornire).

Din punct de vedere al combustibilului utilizat, la cazanele cu�DUGHUH�LQYHUV��VH�

UHFRPDQG��IRORVLUHD�XQRU�OHPQH�GH�VHF LXQH�PHGLH��GH�FLUFD��[��PP��VH�YD�HYLWD�VHF LXQHD� URWXQG�� SUHIHUkQGX-VH� FHOH� FX� ]RQH� GH� FRO � XQGH� VH� LQL LD]�� DUGHUHD� FX�XúXULQ ��FX�OXQJLPH�FDUH�V��SHUPLW��UHOL]DUHD�XQHL�DFRSHULUL�FRUHFWH�D�JU�WDUXOXL�úL�D�]RQHL�GH�ED]��úDPRWDWH�úL�FX�XPLGLWDWH�PD[LP��GH��-��&RQGL LD�GH�XPLGLWDWH�HVWH�PDL� UHVWULFWLY��GHFkW� vQ�FD]XO�VLVWHPHORU�GH�DUGHUH�GLUHFW�� FDUH�SHUPLW�X]XDO�IRORVLUHD�XQRU� OHPQH� FX� XPLGLWDWH�PD[LP�� GH� ��–� ��GDU�QX� UHSUH]LQW�� XQ� LPpediment în IRORVLUHD� VLVWHPHORU� FX� DUGHUH� LQYHUV�� GHRDUHFH� XPLGLWDWHD� FHUXW�� HVWH� DWLQV�� GH�FRPEXVWLELO�SULQ�XVFDUH�QDWXUDO��SH�SHULRDG��GH�FLUFD��DQL�vQ�GHSR]LW�vQFKLV�

7UHEXLH�GH�DVHPHQHD�UHPDUFDW��GLIHUHQ D�FRQVWUXFWLY��FH�DSDUH�OD�QLYHOXO�]RQHL�

de gU�WDU��$VWIHO��OD�VLVWHPXO�GH�DUGHUH�GLUHFW��D�FRPEXVWLELOXOXL��VH�FRQVWLWXLH�vQ�]RQ��GH�JU�WDU�VWULFW�VXSUDID D�SH�FDUH�VH� LQVXIO��DHU�SULPDU�GH�DUGHUH�� IRUPDW��GLQ�EDUH�GH�JU�WDU� VSULMLQLWH� vQ� GLYHUVH� VLVWHPH�� 5H]XOW�� QHFHVLWDWHD� DVLJXU�ULL� XQRU� VLVWHPH�FRPSOH[H�GH�GLVWULEX LH�XQLIRUP��D�DHUXOXL�SH�VHF LXQL�GH�FXUJHUH�PDUL��SHQWUX�D�QX�VH�UHDOL]D�GH]HFKLOLEUH�GH�DUGHUH�úL�D�VH�DVLJXUD�GHELWHOH�VSHFLILFH�GH�FRPEXVWLELO�DUV��/D�FD]DQHOH� FX� DUGHUH� LQYHUV�� GDWRULW�� SUH]HQ HL� DHUXOXL� QHFHVDU� GH� UHDF LH� SULPDU�� úL� D�VF�OG�ULL�]RQHL�GH�ED]��FX�JD]H�GH�DUGHUH��UH]XOW��R�IXQF LRQDUH�FD�VXSUDID ��GH�JU�WDU��JHQHUDWRDUH�GH�DSULQGHUH��D�vQWUHJLL�]RQH�úDPRWDWH�GH�OD�ED]D�VWUDWXOXL��)XUQL]DUHD�GH�DHU�VHFXQGDU��VDX�DPHVWHFDUHD�JD]HORU�GH�DUGHUH�LQFRPSOHW��FX�DHUXO�GLVSRnibil de tip SULPDU�� QX� VH� UHDOL]HD]�� vQV�� GHFkW� vQ� ]RQD� GH� WUHFHUH� GLQWUH� EXQF�U� úL� IRFDUXO� U�FLW��]RQ��FDUDFWHUL]DW��GH�YLWH]H�úL�WXUEXOHQ H�PDUL�úL�GH�VHF LXQH�UHGXV��6H�FUHHD]��DVWIHO�SUHPL]HOH� XQHL� LQVXIO�UL� HILFLHQWH� GH� DHU� GH� DUGHUH� I�U�� QHFHVLWDWHD� DVLJXU�ULL�XQLIRUPLW� LL�GH�FXUJHUH�SH� VHF LXQL�PDUL��0DL�PXOW��DHUXO�SULPDU�FH�VFXUW-FLUFXLWHD]��DQXPLWH�]RQH�GLQ�EXQF�U�YD�IL�IRORVLW�FD�DHU�GH�DUGHUH�VHFXQGDU�OD�WUHFHUHD�SULQ�]RQD�GH�


CAZANE

224

OHJ�WXU�� PDL� VXV� DPLQWLW�� 5H]XOW�� GHFL� F�� VLVWHPXO� GH� DUGHUH� LQYHUV�� QX� QXPDL� F��HOLPLQ�� FRPSOLFD LLOH� OHJDWH� GH� GLVWULEX LD� GH� DHU� GH� DUGHUH� GDU� úL� FRPSHQVHD]��constructiv scurt-circuitele de aer inerente curgerii prin stratul de combustibil aleatoriu úL�vQ�FRQWLQX��PRGLILFDUH�

Referitor la sarcinile termice ale cazanelRU� vQ� GLVFX LH� HVWH� LPSRUWDQW� GH�PHQ LRQDW� F�� VH� XWLOL]HD]�� XQ� GRPHQLX� X]XDO� PDL� UHGXV� GH� SXWHUL� WHUPLFH� QRPLQDOH�SHQWUX�FD]DQHOH�FX�DUGHUH�LQYHUV��–��N:��ID ��GH�FD]DQHOH�FX�DUGHUH�GLUHFW��–� �� N:�� ([SOLFD LD� SHQWUX� GRPHQLXO� UHODWLY� UHGXV� VSHFLILF� VROX LLORU� FX� DUGHUH�LQYHUV�� UH]LG�� SH�GH�R�SDUWH� vQ�QRXWDWHD� VROX LHL� FDUH�QX�D�SHUPLV� vQF�� ODQVDUHD�XQRU�cazane de puteri mari,�GDWRULW��OLSVHL�XQRU�PRGHOH�FODUH�GH�FDOFXO�úL�IXQF LRQDUH, iar pe GH�DOW��SDUWH�GDWRULW��FDUDFWHUXOXL�QHSUDFWLF�DO�XQXL�EXQF�U�FX�DOLPHQWDUH�VXSHULRDU��vQ�cazul unor cazane mari.

Un parametru important,�DWkW�SHQWUX�SHUIRUPDQ HOH�WHUPLFH�FkW�úL�SHQWUX�FHOH�GH�ardere,�HVWH�H[FHVXO�GH�DHU��'DF��OD�FD]DQHOH�FX�DUGHUH�GLUHFW��HVWH�QHFHVDU��PHQ LQHUHD�unui nivel de oxigen în gazele de ardere de circa 10 –��vQ�YHGHUHD�PHQ LQHULL�XQHL�FRQFHQWUD LL�GH�&2�OD�XQ�QLYHO�FRUHFW�GH�FLUFD��SSP�OD��22 , pentru cazanele FX�DUGHUH�LQYHUV��HVWH�VXILFLHQW��R�FRQFHQWUD LH�GH�R[LJHQ�vQ�JD]HOH�GH�DUGHUH�GH�QXPDL�4 – 8 %. Aceste concenWUD LL�GH�R[LJHQ�VH�H[SULP��SULQ�H[FHVH�GH�DHU�FXSULQVH�vQWUH��úL� �� OD� FD]DQHOH� FX� DUGHUH� GLUHFW�� VSUH� GHRVHELUH� GH� FD]DQHOH� FX� DUGHUH� LQYHUV�� FH�QHFHVLW��H[FHVH�GH�DHU�GH�GRDU��– 1,65.

5H]XOW��SLHUGHUL�GH�F�OGXU��SULQ�HQWDOSLD�JD]HORU�GH�DUGHUH� OD�FRú�FX��SkQ�� OD�� SURFHQWH�PDL�PDUL� OD� FD]DQHOH� FX� DUGHUH� GLUHFW�� ID �� GH� FHOH� FX� DUGHUH� LQYHUV�� vQ�FRQGL LLOH�FRPSDU�ULL�XQRU�FD]DQH�FX�PDVH�úL�FRVWXUL�GH�SURGXF LH��UDSRUWDWH�OD�VDUFLQD�WHUPLF��XWLO��DSURSLDWH� ,Q� FRQFOX]LH�� GLQ� DQDOL]D� HIHFWXDW�� UH]XOW�� R� VHULH� GH� DYDQWDMH� FODUH� SH� SODQ�HQHUJHWLF� úL� OHJDWH� GH� FDOLWDWHD� DUGHULL� �HFRORJLFH�� JHQHUDWH� GH� IRORVLUHD� WHKQLFLL� GH�DUGHUH� LQYHUVDW�� GDU� úL� LPSRVLELOLWDWHD� DSOLF�ULL� DFHVWHL� WHKQLFL�� I�U�� FRPSOLFDUHD�sistemului de alimentare, la puteri termice PDUL�� ,Q� SOXV�� GDF�� V-DU� GRUL� PHQ LQHUHD�caracteristicii de autonomie la 10 – 12 ore, s-ar ajunge la volume neeconomice de VWRFDUH�SHQWUX�FRPEXVWLELO��5H]XOW��F��VROX LD�FX�DUGHUH�LQYHUV��VH�SUHWHD]�� OD�VDUFLQL�WHUPLFH� SkQ�� OD� �� N:�� ILLQG� UHFRPDQGDELO�� GDWRULW�� DYDQWDMHORU� GH� H[SORDWDUH�VHPQLILFDWLYH��GDU�HVWH�GLVFXWDELO��DSOLFDUHD�DFHVWHLD�OD�VDUFLQL�WHUPLFH�PDL�PDUL�

6.2. 6ROX LD constructiv��HOHPHQWH�FRPSRQHQWH��PRG�GH�IXQF LRQDUH�



225

Din varietatea mare de tipuri constructive de cazane cu ardere cu gazeificare a lemnelor se alege pentru exemplificarea calculului modelul prezentat în fig. 6.4.

Fig. 6.4. Cazan de ap� cald� cu gazeificare. 6ROX LD�SDUWLFXODU��D�ILHF�Uui�WLS�GH�FD]DQ��GLQ�DFHDVW��FDWHJRULH�GH�FD]DQH��IDFH�ca un calcul de dimensiRQDUH�V��vQWkPSLQH�PDUL�GLILFXOW� L�vQ�DúH]DUHD�VXSUDIH HORU�GH�WUDQVIHU� GH� F�OGXU�� DVWIHO� FD� V�� ILH� vQGHSOLQLWH� úL� FRQGL LLOH� WHKQRORJLFH� úL cele de IXQF LRQDUH�QHFHVDUH��'H�DFHLD�VH�SUHIHU��WRWGHDXQD�VROX LD�GH�verificarea prin calcul

termic a cazanului ��DGLF�,�GXS��DOHJHUHD�FRQVWUXFWLY��D�PRGHOXOXL�úL�D�GLPHQVLXQLORU�HVWLPDWH� FD� ILLQG� FHOH� DGHFYDWH�� V�� VH� IDF�� R� YHULILFDUH� SULQ� FDOFXO� D� IXQF LRQDOLW� LL�VROX LHL� &D]QXO�HVWH�DOF�WXLW�GLQ�GRX��GUXPXUL�

• drumul descendent: EXQF�UXO� GH� FRPEXVWLELO� FDUH� DUH� OD� SDUWH� LQIHULRDU��LQVWDOD LD�GH�DUGHUH�úL�IRFDUXO;

• drumul ascendent: în continuarea focarului, drumul convectiv ignitubular. 'HRDUHFH��vQ�ID]D�GH�SRUQLUH�D�FD]DQXOXL��vQ�UHJLP�GH�DUGHUH�GLUHFW��D�VWUDWXOXL��GH� MRV� vQ� VXV�� WHPSHUDWXUD� vQ� EXQF�U� SRDWH� IL� UHODWLY� ULGLFDW�� VH� DOHJH� VROX LD� GH�EXQF�U� FX� SHUH L� U�FL L� FX� DS��1XPDL� vQ� UHJLXQHD� GLQ� GUHSWXO� XúLL� GH� vQF�UFDUH� úL� OD�SDUWHD�VXSHULRDU��WDYDQ��QX�VH�IDFH�FDPHU��GXEO��U�FLW�� 3vOQLD� LQIHULRDU�� D�EXQF�UXOXL�HVWH�úL�HD� U�FLW��GDWRULW�� WHPSHUDWXrii ridicate de IXQF LRQDUH�

1

2

3

5

6

4

8

7

9


CAZANE

226

&DPHUD� IRFDUXOXL� HVWH� DOF�WXLW�� GLQ� SHUH L� U�FL L�� SDUWHD� GH� GX]�� úL� GH� FRUS�UHIUDFWDU� D� DOELHL� GH� vQWRDUFHUH� GH� IODF�U�� ILLQG� DG�XJDte� SH� SHUH LL� U�FL L� DL� FDPHUHL�focarului��5H]XOW��F� partea�HILFLHQW��GH�SUHOXDUH�D�IOX[XOXL�GH�F�OGXU��UDGLDW�GH�IRFDU�este în principal LQFLQWD�LQIHULRDU��D�FD]DQXOXL�GLQ�FDUH�VH�VFDG�VXSUDID HOH�úDPRWDWH� 6LVWHPXO�FRQYHFWLY�HVWH�FRQVWLWXLW�GLQ� HYL�FX�GLDPHWUXO��F45x3 ... F76x3,5 mm distribuite uniform pe supUDID D�GH�WUHFHUH�D�GUXPXOXL�� In cazul constructiv ales sunt �� HYL�-��[�� /XQJLPHD� FRQYHFWLYXOXL�� HJDO�� FX� OXQJLPHD� EXQF�UXOXL�� HVWH� GH� ��mm. 6.3. Tema de calcul de verificare

Prin tema de proiectare se dau: - Q -�VDUFLQD�WHUPLF��D�FD]DQXOXL��vQ�N:�� - te / ti -�WHPSHUDWXUD�DSHL�OD�LHúLUH�úL�LQWUDUH�vQ�FD]DQ��oC) sau (80/60 oC); - FRPSR]L La combustibilului��GHILQLW�� vQ�VSHFLDO�SULQ�XPLGLWDWHD�OHPQXOXL��GHRDUHFH�

QX� H[LVW�� GLIHUHQ H� VHPQLILFDWLYH� GH� FRPSR]L LH� D� OHPQXOXL� IXQF LH� GH� HVHQ D� GH�SURYHQLHQ ��.

In tabelul 6.1 se dau caracteristicile de ardere ale� OHPQXOXL� IXQF LH�GH�XPLGLWDWHD�

W. &DOFXOXO� SURFHVXOXL� GH� DUGHUH� D� OHPQXOXL� VH� IDFH� GXS��PHWRGLFD� FODVLF�� D� DUGHULL�

FRPEXVWLELOXOXL� OLFKLG� VDX� VROLG�� FRQIRUP� LQGLFD LLORU� GLQ� FDSLWROXO� �� 6H� HIHFWXHD]��calFXOXO�DUGHULL�FRPEXVWLELOXOXL�úL�VH�GHWHUPLQ��VO, Vgo, Vg, Hi, OH2

p , 2ROp ��VH�WUDVHD]��

diagrama I – t sau cp – t.

$FHVWH� FD]DQH� IXQF LRQHD]�� FX� VXSUDSUHVLXQH� vQ� IRFDU�� GHFL� FRHILFLHQWXO� GH�exces de aer este constant SkQ��OD�HYFXDUHD�OD�FRú�

α = αf = αc = αFRú�= 1,4 ÷ 1,6 = ct.

��&DOFXOXO�UDQGDPHQWXOXL�WHUPLF�DO�FD]DQXOXL�úL�D�GHELWXOXL�GH�FRPEXVWLELO� $FHVWH� FD]DQH� IXQF LRQHD]�� FX� FRPEXVWLELO� VROLG�� GHFL� SLHUGHUHD� VSHFLILF�� GH�F�OGXU�� SULQ� DUGHUH� LQFRPSOHW�� GH� QDWXU�� PHFDQLF�� Tmec�� úL� FHD� SULQ� HYDFXDUHD�produselor solide ale arderii din cazan (qcen��VH�SRW�OXD�vQ�FRQVLGHUDUH��7RWXúL��GDWRULW��SURFHVXOXL� GH� DUGHUH� SULQ� JD]HLILFDUH�� SLHUGHUHD� SULQ� DUGHUH� LQFRPSOHW�� GH� QDWXU��PHFDQLF��Tmec��úL�FHD�SULQ�HYDFuarea produselor solide ale arderii din cazan (qcen) pot fi considerate nule deoarece produsele de gazeifiare ard complet în regim de ardere VSHFLILF�FRPEXVWLELOXOXL�JD]RV��ÌQ�DFHVWH�FRQGL LL��% � �%�



227

COMPOZITIE uscat

C uscat 49.6 49.6 49.6 49.6 49.6 49.6 49.6 49.6 49.6 49.6 49.6 49.6 49.6

H uscat 6 6 6 6 6 6 6 6 6 6 6 6 6

O uscat 43 43 43 43 43 43 43 43 43 43 43 43 43

N uscat 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

A uscat 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2

COMPZITIE umed

W 8 9 10 11 12 13 14 15 16 17 18 19 20

x 92 91 90 89 88 87 86 85 84 83 82 81 80

C 45.63 45.14 44.64 44.14 43.65 43.15 42.66 42.16 41.664 41.17 40.67 40.176 39.68

H 5.52 5.46 5.4 5.34 5.28 5.22 5.16 5.1 5.04 4.98 4.92 4.86 4.8

O 39.56 39.13 38.7 38.27 37.84 37.41 36.98 36.55 36.12 35.69 35.26 34.83 34.4

N 0.184 0.182 0.18 0.178 0.176 0.174 0.172 0.17 0.168 0.166 0.164 0.162 0.16

A 1.104 1.092 1.08 1.068 1.056 1.044 1.032 1.02 1.008 0.996 0.984 0.972 0.96

SUMA 100 100 100 100 100 100 100 100 100 100 100 100 100

ARDERE

Vo 4.202 4.156 4.111 4.065 4.019 3.974 3.928 3.882 3.837 3.791 3.745 3.700 3.654

VCO2 0.851 0.842 0.833 0.824 0.814 0.805 0.796 0.787 0.777 0.768 0.759 0.750 0.740

VN2 3.321 3.285 3.249 3.213 3.177 3.141 3.105 3.068 3.032 2.996 2.960 2.924 2.888

VH2O 0.785 0.790 0.795 0.800 0.805 0.810 0.815 0.820 0.825 0.830 0.835 0.840 0.845

Vgo 4.957 4.917 4.877 4.836 4.796 4.755 4.715 4.675 4.634 4.594 4.554 4.513 4.473

PUTERE CALORICA

Hi -kJ/kg 17076 16863 16650 16437 16224 16011 15798 15585 15372 15160 14947 14734 14521

Hi -kcal/kg 4079 4028 3977 3927 3876 3825 3774 3723 3672 3621 3571 3520 3469

Dupa SR>EN

Hi -kJ/kg 17285 17070 16856 16642 16427 16213 15998 15784 15570 15355 15141 14926 14712

Hi -kcal/kg 4129 4078 4027 3976 3924 3873 3822 3771 3719 3668 3617 3566 3515

CARACTERISTICI DE ARDERE LEMN

Tabelul 6.1 - Caracteristicile de ardere ale lemnXOXL�IXQF LH�GH�XPLGLWDWHD�:

6H�FDOFXOHD]��SLHUGHULOH�VSHFLILFH�GH�F�OGXU�� a. 3LHUGHUHD�VSHFLILF��GH�F�OGXU��SULQ�HQWDOSLD�JD]HORU�GH�DUGHUH�OD�FRú� )LLQG� XQ� FD]DQ� GH� DS�� FDOG�� VH� DGPLWH� R� WHPSHUDWXU�� OD� FRú� FH� VH� SRDWH�GHWHUPLQD�FX�UHOD LD�GH�DSUR[imare, pentru cazane cu lemne:

Ctt

t ei 0cos )140100(

2÷+

+≅ (6.1)

Din diagrama I –�W�VH�GHWHUPLQ��YDORDUHD�HQWDOSLHL�JD]HORU�GH�DUGHUH�OD�FRú�

IFRú = f (tFRú, α)


CAZANE

228

(QWDOSLD� DHUXOXL� WHRUHWLF� GH� DUGHUH� VH� GHWHUPLQ�� OD� WHPSHUDWXUD� DPELDQW��ta=20oC


cu cpa = 1,297 kJ/ Km3N

5H]XOW��SLHUGHUHD�VSHFLILF��OD�FRú�� )(

1coscos ao

i

IIH

q α−= (6.3)

b. 3LHUGHUL�VSHFLILFH�GH�F�OGXU��SULQ�DUGHUH�LQFRPSOHW��GH�QDWXU��FKLPLF��

În cadrul calculelor de proiectarH�� GDWRULW�� SURFHVXOXL� GH� DUGHUH� GLIX]LY�� D�OHPQXOXL� vQ� UHJLP� GH� JD]HLILFDUH�� FX� SUHSRQGHUHQ D� GHJDM�ULL� GH�&2� vQ� FRQGL LLOH� GH�DUGHUH� UHGXF�WRDUH��se admite, conform standardelor europene, uQ�FRQ LQXW�GH�QHDUVH�CO=2000 ppm (0,2% CO) în gazele de ardere, ceeace corespunde unei pierderi prin DUGHUH�LQFRPSOHW��GH�QDWXU��FKLPLF�:

uscg

i

mec

i

chch VCO

H

q

HB

Qq )36,126(

1

*⋅

−== (6.4)

unde CO este exprimat în %. c. 3LHUGHUL�VSHFLILFH�GH�F�OGXU��SULQ�SHUH LL�H[WHULRUL�DL�FD]DQXOXL�� În cadrul calculelor pentru cazane relativ micL�� vQ� IXQF LH� GH� JUDGXO� GRULW� GH�L]ROD LH�WHUPLF��D�FD]DQXOXL��VH�SRDWH�DOHJH�R�YDORDUH��

qext = 0,005 ÷ 0,015 d. Randamentul cazanului 6H�FDOFXOHD]��FX�UHOD LD� )(1 cos extch qqq ++−=η (6.4)

úL�H[SULPDW�vQ�YDORDUH�SURFHQWXDO�� ηη ⋅= 100%


iH

QB

⋅=

η (kg/s) (6.5)

SHQWUX� R� H[SULPDUH� IL]LF� LQWHOLJLELO�� VH� XWLOL]HD]�� FRQVXPXO� RUDU� GH� FRPEXVWLELO� � %h GHILQLW��GH�UHOD LD� Bh = 3600 * B [kg/h]

6.5��%LODQ XO�GH�DQVamblu al cazanului



229

)OX[XO�XWLO�GH�F�OGXU��DO�FD]DQXOXL�HVWH� 4��GDW�SULQ�WHP��. )OX[XO�GH�F�OGXU��din arderea combustibilului: iombc BHQ = (6.6)

)OX[XO�GH�F�OGXU��DGXV�FX�DHUXO�GH�DUGHUH�� apaoa tcVBQ α= (6.7)

Fluxul dH�F�OGXU��SLHUGXW�OD�FRú� coscos IBQ ⋅= (6.8)

)OX[XO�GH�F�OGXU��SLHUGXW�SULQ�DUGHUH�LQFRPSOHW�� ichinc BHqQ = (6.9)

)OX[XO�GH�F�OGXU��SLHUGXW�VSUH�H[WHULRU� iextext BHqQ = (6.10) 5H]XOW��WDEHOXO�GH�ELODQ �WHUPLc al cazanului:.

Tabelul 6.1. Fluxuri introduse -

pierdere Util

Qcomb

Qa

– QFRú – Qinc

– Qext

Q

∑ = 'QQ ''∑ = QQ

1RW��ÌQ�DFHVW�ELODQ �WHUPHQHXO�“– qcosBHi” s-D�VFULV�VXE�IRUPD�H[SOLFLW��


(URDUHD�UHODWLY�� %1100'

"'≤

−=

Q

QQε (6.11)

'DF�� HURDUHD� UHODWLY�� GH� vQFKLGHUH� D� ELODQ XOXL� HVWH� PDL� PDUH� GH� �� FHD�PD[LP� DGPLVLELO�� SHQWUX� DFHVW� JHQ� GH� FDOFXOH�� vQVHDPQ�� F�� V-D� I�FXW� R� JUHúHDO�� GH�calcul sau de citire în diagrama I-t.

6.5��%LODQ XO�JUDILF�DO�FD]DQXOXL 'HELWHOH� GH� F�OGXU�� GLQ� WDEHOHOH� 6.�� úL� 6.�� VH� WUDQVSXQ� JUDILF�� OD� VFDU�� FD� vQ�figura 2.3 (cu particularizarea: B*=B; Qpa=0; Qsfc=Qc, Qsi=0; Qec=0; qmec=0; qcen=0). 6.6. Calculul focarului

Pentru metodologia de�FDOFXO�VSHFLILF��DFHVWXL�FD]DQ�WUHEXLH�I�FXW�XQ�FDOFXO�GH�YHULILFDUH� D� IRFDUXOXL� GHRDUHFH� VXSUDID D� GH� UDGLD LH� HVWH� FXQRVFXW�� SULQ� SUHFL]DUHD�


CAZANE

230

LQL LDO��D�VROX LHL�FRQVWUXFWLYH��1HFXQRVFXWD�FDOFXOXOXL�HVWH�WHPSHUDWXUD�GH�OD�VIkUúLWXO�focarului tf . 3URFHGXUD�GH�FDOFXO�HVWH�XUP�WRDUHD� - calculul temperaturii teoretice de ardere, -�FDOFXOXO�VXSUDIH HORU�GH�UDGLD LH� -�FDOFXOXO�FDUDFWHULVLWLFLL�GH�UDGLD LH�D�IRFDUXOXL� - calculul temperaturii la finele focarului.

Calculul temperaturii teoretice de ardere

(QWDOSLD�WHRUHWLF��D�JD]HORU�GH�DUGHUH�VH�GHWHUPLQ��FX�UHOD LD� apafchit tcVqHI 0)1( α+−= (6.12)

DSRL�VH�GHWHUPLQ��WHPSHUDWXUD�WHRUHWLF��GH�DUGHUH�GLQ�GLDJUDPD�,-t: ),I(ft tt α= .

&DOFXOXO�VXSUDIH HORU�GH�UDGLD LH

Calculul este un cDOFXO� JHRPHWULF� GH� VXSUDIH H�� 7RDWH� VXSUDIH HOH� GH� UDGLD LH�ILLQG� VXSUDIH H� PHWDOLFH� FRQWLQXH�� FRHILFLHQWXO� GH� HILFLHQ �� HVWH� � 0� �� 6FKHPD�IRFDUXOXL�HVWH�GDW��vQ�ILJ��6.5

6H�vQVXPHD]��XUP�WRDUHOH�VXSUDIH H�

• VXSUDID D�VXSHULRDU��D�FDPHUHL�GH�DUGHUH�úL�D�LQWU�ULL�vQ�FRQYHFWLY�� S1 = l · b – a · b • VXSUDID D�IURQWDO��D�FDPHUHL�GH�DUGHUH�

Sfr = hf · b

• baza camerei de ardere: Sb = l · b – ls · bs

• VXSUDID D�VSDWH�D�FDPHUHL�GH�DUGHUH�

Ssp = hc · b • 6XSUDID D�SHUHWHOXL�GHVS�U LWRU��SH�DPEHOH�IH H��

Sp = ((hf – hp) + (hc – hp)) · b

• 6XSUDID D�ODWHUDO��

Slat = 2· (ca· hf +(l-ca) · h)



231

fig. 6.��6FKHPD�GLPHQVLRQDO��D�IRFDUXOXL

6XSUDID D� WRWDO�� HIHFWLY�� GH� UDGLD LH� HVWH� �FRHILFLHQW� GH� HILFLHQ �� XQLWDU� SHQWUX�supraIH H�PHWDOLFH�FRQWLQXH��

• SR = S1 + Sfr + Sb +Ssp + Sp + Slat [m

2]

Calculul volumului focarului

6H�vQVXPHD]��XUP�WRDUHOH�YROXPH�

• volumul camerei de ardere Vca = hf · b · ca • volumul camerei de întoarcere spre convectiv: Vc = hc · b · ( l – ca )

Volumul total al focarului:

Vf = Vca + Vc [m3]

&DOFXOXO�VXSUDIH HL�SHUH LORU�úDPRWD L�

6H�vQVXPHD]��XUP�WRDUHOH�VXSUDIH H�

• VXSUDID D�VXSHULRDU��D�]RQHL�úDPRWDWH�GH�LQWDUDUH�� Si = a · b • VXSUDID D�FRUSXOXL�UHIUDFWDU�GH�DUGHUH�

Sref = ls · bs

hf hc

l

a

b ca

hp

ls bs


CAZANE

232

6XSUDID D�WRWDO��D�SHUH LORU�úDPRWD L� Ss = Si + Sref &DOFXOXO��VXSUDIH HL�SHUH LORU�IRFDUXOXL�

6XSUDID D� SHUH LORU� IRFDUXOXL� HVWH� VXPD� VXSUDIH HL� GH� UDGLD LH� úL� D� VXSUDIH HL�úDPRWDWH�

Sper = SR + Ss [m

2]

,QL LDOL]DUHD�WHPSHUDWXULL�GH�OD�VIkUúLWXO�IRFDUXOXL

2�LPSRUWDQW��FDUDFWHULVWLF��IXQF LRQDO��D�FD]DQHORU�FX�DUGHUH�SULQ�JH]HLILFDUH�D�OHPQHORU�R�SUH]LQW�� tHPSHUDWXUD�UHODWLY�FRERUkW��a focarului�GDWRULW��H[FHVXOXL�ULGLFDW�GH�DHU�úL� VXSUDIH HL�PDUL�GH� UDGLD LH. De aceea intervalul de alegere a temperaturii la FDS�WXO�IRFDUXOXL�HVWH�

tf =600÷800 oC.

Calculul caracteristicii GH�UDGLD LH�D�IRFDUXOXL�

S-au determinat anterior: - volumul focarului: Vf (m

3) - VXSUDID D�SHUH LORU�IRFDUXOXL�� Sper (m

2) - VXSUDID D�GH�UDGLD LH�� SR (m

2) 6H�GHWHUPLQ��vQ�FRQWLQXDUH�� - grosimea stratului radiant de gaze: s = 3,6

per

f

S

V (m) (6.21)


R

S

S=Ψ (6.22)

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�JD]HORU�GH�DUGHUH�vQ�FDPHUD�GH�DUGHUH� )(

100038,01

)(

6,18,022

22

2

ROOH

f

ROOH

OH

g ppT

spp

pk +

−

⋅+

+= (6.27)


sk

g

gea⋅−−= 1 (6.24)

6H�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IO�F�ULL�FX�UHOD LD�GH�DSUR[LPDUH�



233

5,01000

6,1 −= f

fl

Tk (6.25)


sk

flflea⋅−−= 1 (6.26)

3RQGHUHD�DEVRUE LHL�IO�F�ULL�ID ��GH�FHD�D�PHGLXOXL�UDGLDQW�GH�JD]H�GH�DUGHUH�GLQ�

IRFDU�VH�IDFH�GXS��FULWHULL�H[SHULPHQWDOH��FRQVLGHUkQGX-VH�R�SURSRU LH�β, din volumul IRFDUXOXL��RFXSDW��GH�SDUWHD�OXPLQRDV��D�IO�F�ULL�

&RHILFLHQWXO�GH�DEVRUE LH�DO�IO�F�ULL�úL�JD]HORU�GH�DUGHUH�HVWH�GDW�GH�UHOD LD� gfl aaa ⋅−+⋅= )1( ββ (6.27)

Valoarea coeficientului de luminozitate β pentru volatilele de combustibil solid

este β = 0,6 .

&RHILFLHQWXO�GH�PXUG�ULUH�D�VXSUDIH HORU�HVWH ξ =0,7 pentru combustibil solid. &X�DFHVWH�YDORUL�VH�FDOFXOHD]��FDUDFWHULVWLFD�UDGLDQW��D�IRFDUXOXL�

ξΨ−+=

)1(

82,0

aa

aa f (6.28)

&DUDFWHULVWLFD�GH�XPSOHUH�FX�IODF�U��D�IRFDrului.

2�DOW��FDUDFWHULVWLF��D�IRFDUXOXL�HVWH�IDFWRUXO�GH�umplere a focarului cu IO�F�U��”M”. Pentru combustibil solid cu IODF�U� de volatile din ambrazura focarului M=0,44.

7HPSHUDWXUD�OD�FDS�WXO�IRFDUXOXL�

6H�GHWHUPLQ��FULWHULXO��%2/7=0$11�

380 10 tR

pgg

TSC

cVBBo

⋅⋅⋅

⋅⋅⋅= − ξ

ϕ (6.29)

unde extq−= 1ϕ ; cpg �VH�GHWHUPLQ��GLQ�WDEHOH�SHQWUX�WHPSHUDWXUD�WHRUHWLF�� ,Q�FRQWLQXDUH�VH�GHWHUPLQ��LQYDULDQWXO�GH�WHPSHUDWXU��D�IRFDUXOXL��VLPOSOH[XO�

t

f

T

T=θ


CAZANE

234

( ) 6,06,0

6,0

BoaM

Bo

f +⋅=θ (6.30)

GH�XQGH�UH]XOW��WHPSHUDWXUD�OD�FDS�WXO�IRFDUXOXL�

15,273−⋅= θtf Tt [oC]

'DF��VH�FDOFXOHD]��FX�YDORULOH�GH�ED]��VH�DSOLF��UHOD LD�GH�FDOFXO�

( )

15,273

11

6,03

−

+

−

=

pggext

Rto

tf

cVBq

STCM

Tt

ξ [0C] (6.31)

Cunoscându-se tf VH�GHWHUPLQ��IOX[XO�GH�F�OGXU��VFKLPEat radiativ în focar.

'DF�� DFHDVW�� WHPSHUDWXU�� YD� IL� GLIHULW�� GH� WHPSHUDWXUD� DOHDV�� LQL LDO� �SULQ�estimare) cu mai mult de ±10% se reia calculul cu valori recalculate SHQWUX�F�OGXUL�VSHFLILFH�úL�FRHILFLHQW�GH�UDGLD LH�D�IRFDUXOXL�FX�WHPSHUDWXUD��ILQDO��Wf . ,Q�ILQDO�VH�RE LQH�YDORDUH�WHPSHUDWXULL�OD�FDS�WXO�IRFDUXOXL��Wf [ 0C]. 6.8. Calculul termic al drumului convectiv Convectivul cazanului este determinat, din punctul de vedere al transferului de FOGXU��GLQ�FDOFXOHOH�DQWHULRDUH�SULQ�XUP�WRULi parametrii:

tf –�WHPSHUDWXUD�JD]HORU�GH�DUGHUH�OD�LQWUDUH�vQ� HYL��0C) ; tFRú – temperatura HVWLPDW�� D� JD]HORU� GH� DUGHUH� OD� LHúLUHD� GLQ� HYL� �OD� FRú��

te/ti – temperatura apei (0C). 'HRDUHFH� vQ� ELODQ XO� JHQHUDO� DO� FD]DQXOXL� WHPSHUDWXUD� OD� FRú� D� Iost estiPDW��

calculul termic al drumului convectiv are rolul de a confirma (sau infirma) WHPSHUDWXUD�HVWLPDW��'DF��GLQ�FDOFXOXO�WHUPLF�GH�YHULILFDUH�YD�UH]XOWD�F��WHPSHUDWXUD�HVWLPDW�� QX� HVWH� FHD� FRUHFW�� VH� YD� UHOXD� FDOFXOXO� FX� R� QRX�� WHPSHUDXWU�� OD� FRú �vQFHSkQG�GH�OD�ELODQ XO�WHUPLF�DO�FD]DQXOXL��

ÌQ�FRQVHFLQ ��FDOFXOXO�WHUPLF�DO�GUXPXOXL�FRQYHFWLY�HVWH�XQ�FDOFXO�GH�YHULILFDUH�

a temperaturii finale a unui drum convectiv.

SHF LXQea de trecere a gazelor de ardere UH]XOW��GLQ alegeUHD�QXP�UXOXL�GH� HYi

n úL�DO diametrului� HYLORU,�GLQ�JDPD�GH� HYL�X]XDOH��GH�×δ):

φ51 × 3; φ 57 ×3; φ 60 × 3; φ 70 × 3,5; φ 76 × 3,5 mm.



235

'XS�� DOHJHUHD� QXP�UXOXL� úL� GLDPHWUXOXL� HYLORU� VH� FDOFXOHD]�� YLWH]D� GH�FLUFXOD LH�D�JD]HORU�GH�DUGHUH��

273

273

4

2

+⋅= gm

i

g t

dn

VBw

π (6.32)

)(2

0cosC

ttt

f

gm


Viteza de�FLUFXOD LH�D�JD]HORU�GH�DUGHUH�Z�WUHEXLH�V��ILH� în intervalul economic pentru acest tip de cazan: w = (2 ÷ 4) m/s.�'DF��QX�HVWH�vQ�DFHVW�GRPHQLX�VH�PRGLILF��VROX LD�constructiv prin QXP�UXO�GH� HYL sau diametrul acestora. Pentru temperatura medie a gazelor de ardere tgm� VH� GHWHUPLQ�� GLQ� anexa 9, XUP�WRDUHOH�YDORUL�

- YkVFR]LWDWHD�FLQHPDWLF�� ν [m2/s] - FRQGXFWLELOLWDWHD�WHUPLF�� λ [W/mK] - QXP�UXO�3UDQGWO� Pr De�DVHPHQHD�VH�GHWHUPLQ��QXP�UXO�3UDQGWO�SHUHWH�3rp la temperatura peretelui

tp cu

tp = tm +(10÷20) oC ; 2

eim

ttt

+= . (6.33)

Coeficientul de transfer�GH�F�OGXU��SULQ�FRQYHF LH�VH�GHWHUPLQ��XWLOL]kQG�UHOD LL�criteriale�SHQWUX�FLUFXOD LD�JD]HORU�GH�DUGHUH�OD�LQWHULRUXO� HYLORU��FRQIRUP�anexei 10 .

De exemplu, pentru 4i 103wd

Re ⋅>=ν

CL

dNu i

+

−+

−=

3/2

3/2

1

)1(Pr8

2,121

Pr)1000(Re8

ξ

ξ

(6.34)

cu B

0,11

p

2 LL,Pr

PrC;1,64)(1,82logRe� =

=−= −

unde LB� HVWH� vQ�O LPHD�EXQF�UXOXL�de combustibil. Pentru 2300 < Re < 3 ⋅104:


CAZANE

236

[ ] CBPr

,A,,Nu

/ 31

30 221

27061513749

++−+= ε (6.35)

cu A=

11,0

p

32/1

i3 i

Pr

PrC;

L

dPrReB;

L

dPrRe

=

=

εo �� ·� �� UHSUH]LQW�� HIHFWXO� WXUEXOL]DWRULORU� FH� VH� YRU� PRQWD� OD� LQWHURUXO� HYLORU�FRQYHFWLYH��IXQF LH�GH�JUDGXO�GH�WXOEXUL]DUH�UHDOL]DW��IRUP��úL�SDV�GH�úLFDQDUH�� Pentru regimul laminar: Re < 2300:

110313

30 7061513749

,

p

/

i*

Pr

Pr,

L

dPrRe,,Nu

−⋅+= ε (6.36)

cu *

0ε = 1,6÷2,2.

Pentru turbulizatorii în zig-zag coeficien LL� GH� FRUHF LH 0ε � úL� *0ε pot fi

GHWHUPLQD L�FX�UHOD LLOH�H[SHULPHQWDOH� 200

1422,

r

*

p

,=ε ��úL��

5

33 20

200

,

,

r

Re

p

,−=ε

unde i

rd

lp = este pasul relativ, cu l – pas zig-zaguri.


c

cl

Nuλα = (6.37)

CoeficiHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH�HVWH�GHWHUPLQDW�GH�P�ULPLOH�

l

di



237

- WHPSHUDWXU��PHGLH�D�JD]HORU�GH�DUGHUH�� Tgm=tgm+273 (K); - grosimea stratului radiant: s = 0,9 di (m);


2

g

g

RO

RO pV

Vp 2

2= [bar�@��úL�� g

g

OH

OH pV

Vp 2

2= [bar.]

&RQVWDQWD�GH�UDGLD LH�D�JD]HORU�VH�GHWHUPLQ��FX�UHOD LD�

)(1000

38,01)(

6,18,022

22

2

ROOH

gm

ROOH

OHpp

T

spp

pkg +

−

⋅+

+= (6.38)


sk

ggea⋅−−=1 (6.39)

&RHILFLHQWXO�GH�VFKLPE�GH�F�OGXU��SULQ�UDGLD LH�VH�GHWHUPLQ��FX�UHOD LD�

−

−

+⋅= −

gm

p

gm

p

gmg

p

r

T

T

T

T

Taa

1

1

2

110765,5

6,3

38α (W/m2K) (6.40)

XQGH�SHQWUX� FRHILFLHQWXO� GH� DEVRUE LH� DO�SHUHWHOXL�GH� VFKLPE�GH�F�OGXU�� VH� FRQVLGHU��valoarea ap=0,8�� HDY��WUDV��GH�R HO��LDU�SHQWUX�WHPSHUDWXUD�DEVROXW��D�SHUHWHOXL� HYLL� 27320tT mp ++= (K)

Coeficientul de transfer GH�F�OGXU��SH�SDUWHD�JD]HORU�GH�DUGHUH�YD�IL� α1 = αc + αr

&RHILFLHQWXO� GH� WUDQVIHU� GH� F�OGXU��α2 pe partea apei este mult mai mare (de ordinul miilor de W/m2.��vQ�FRPSDUD LH�FX�α1 (de ordinul zecilor de W/m2K). ÌQ� DFHVWH� FRQGL LL� FRHILFLHQWXO� JOREDO� GH� WUDQVIHU� GH� F�OGXU�� ´k” este dat de UHOD LD�

1

1

1 εαα

+=Ik (W/m2K) (6.41)


CAZANE

238

în care s-D�QHJOLMDW�UH]LVWHQ D�WHUPLF��1/α2).

9DORULOH� FRHILFLHQWXOXL� GH� PXUG�ULUH� ε pentru gaze de ardere, provenite din arderea de combustibil VROLG�FX�UH]LVWHQ ��WHUPLF��SURYHQLQG�GLQ�GHSXQHULOH�GH�FHQXú��YRODQW�, sunt :

Tabelul 6.4.

&RHILFLHQWXO�GH�PXUG�ULUH� Viteza w (m/s) 3 6 9 12 15 18 ε ⋅103 (m2K/W) 5,233 3,837 2,791 2,093 1,628 1,395

6H�SRDWH�XWLOL]D�úL�UHOD LD�DQDOLWLF��

6474,031021,11 −− ⋅⋅= wε (m2K/W) (6.42) 6H� FDOFXOHD]�� vQ� ILQDO� WHPSHUDXWUD� GH� LHúLUH� D� JD]HORU� GH� DGHUH� GLQ� � GUXPXO�convectiv de gaze, conform�UHOD LHL�GH�YHULILFDUH�D�VXSUDIH HORU�FRQYHFWLYH�

( ) ϕ⋅⋅⋅⋅

−

⋅−+= pgg cVB

Sk

mafmae etttt [0C] (6.43)

Temperatura te� � HVWH� WHPSHUDWXUD� GH� FRú� D� Fazanului, care s-D� LQL LDOL]DW� la vQFHSXWXO�FDOFXOXOXL�GH�DOHJHUH�D�VROX LHL�FRQVWUXFWLYH�

6.��9HULILF�UL�ILQDOH

DaF�� WHPSHUDWXUD�ILQDO�� We� �HVWH�GLIHULW��FX�PDL�PXOW�GH��.�GH�WHPSHUDWXUD�presupXV��LQL LDO�SHQWUX�FRú��Wcos��VH�SURFHGHD]��vQ�GRX� moduri:

• GDF��QX�HVWH�R�GLIHUHQ ��SUHD�PDUH��GH�RUGLQXO��.��VH�UHIDFH�FDOFXOXO�pentru g�sirea temperaturii corecte la cRú��UHOXkQG�FDOFXOXO��GH�OD�ELODQ XO�WHUPLF��FX�QRXD�WHPSHUDWXU��GH�FRú�RE LQXW��

• GDF�� HVWH� R� GLIHUHQ �� SUHD� PDUH� �peste 20 K)� VROX LD� FRQVWUXFWLY�� QX�UHDOL]HD]�� SDUDPHWULL� GRUL L� úL� WUHEXLH� V�� VH� UHSURLHFWH]H� FD]DQXO� FX�VXSUDIH H�GH�WUDQVIHU�GH�F�OGXU��Podificate.


CAZANE

239

CAPITOLUL 7

CALCULUL HIDRAULIC (*$=2',1$0,&��ù,�$/

,167$/$�,(,� '(� (9$&8ARE A GAZELOR DE

ARDERE Calculul gazodimanic al cazanelor are ca scop determinarea pierderilor de VDUFLQ��SH�FHOH�GXS��FLUFXLWH��

- circuitul aerului de ardere úL� - circuitul gazelor de ardere

Circuitul aerului de ardere vQFHSH�GH�OD�DVSLUD LD�DHUXOXL�din mediul ambint SkQ��

la focar, iar ciUFXLWXO�JD]HORU�GH�DUGHUH�GH�OD�IRFDU�SkQ��OD�LHúLUHD�ORU�SH�FRú�� Aerul de ardere se introduce în cazan, cel mai frecvent, cu ventilatoare de aer. /D� FD]DQHOH� FX� GHELW� PLF� DFHVWHD� SRW� OLSVL�� DHUXO� S�WUXQ]kQG� vQ� IRFDU� SULQ� HIHFWXO�LQVWDOD LHL�GH�WLUDM�� *D]HOH� GH� DUGHUH� VH� SRW� HYDFXD� SULQ� WLUDM� IRU DW� �DUWLILFLDO�� FX� YHQWLODWRDUH� GH�gaze de ardere (exhaustoare), sau prin tirajul natural al coúXOXL�� /D�FD]DQHOH�FX�DUGHUH�VXE�SUHVLXQH��SUHVXUL]DWH��YHQWLODWRDUHOH�GH�DHU�UHDOL]HD]��VXSUDSUHVLXQHD�GLQ�IRFDU�FDUH�DVLJXU��úL�DFRSHULUHD�WRWDO��VDX�SDU LDO��D�UH]LVWHQ HORU�GH�FLUFXOD LH� SH� FLUFXLWXO� JD]HORU� � GH� DUGHUH�� SkQ�� OD� ED]D� FRúXOXL� úL� HYDFXDrea lor în exterior . 7.1. Calculul pierderilor hidraulice GH�VDUFLQ�� &DOFXOHOH�VH�IDF�DWkW�SHQWUX�WUDVHXO�JD]HORU�GH�DUGHUH�FkW�úL�SHQWUX�WUDVHXO�DHUXOXL�GH�DUGHUH��5HOD LLOH�GH�FDOFXO�XWLOL]DWH�QX�GLIHU��vQWUH�HOH�SHQWUX�DHU�VDX�SHQWUX�JD]H�GH�ardere�� vQV�� SDUDPHWULL� DHURGLQDPLFL� úL� GH� IOXLG� �Z��ρ�� VXQW� VSHFLILFL� ILHF�UXL� ORF� GH�calcul.

3LHUGHULOH�GH�VDUFLQ��SH�WUDVHXO�DHUXOXL�GH�DUGHUH�úL�SH�WUDVHXO�JD]HORU�GH�DUGHUH�DSDU�GDWRULW��QHFHVLW� LL�vQYLQJHULL�XQRU�UH]LVWHQ H�KLGUDXOLFH�FH�VH�PDLQLIHVW��în cadrul LQVWDOD Lei� GH� FD]DQ�� OD� FXUJHUHD� IOXLGHORU� UHVSHFWLYH�� $FHVWH� UH]LVWHQ H� VXQW� GH� PDL�multe feluri;

- UH]LVWHQ H�GH�IUHFDUH��ce se produc în canalele de aer sau de gaze de ardere

FX�VHF LXQH�FRQVWDQW��(OH�GXF�OD�DSDUL LD�SLHUGHULORU�liniare de sarFLQ��∆pλ); - UH]LVWHQ H� ORFDOH�� FDUH� DSDU� OD� VFKLPE�UL� GH� IRUP�� VDX� GH� GLUHF LH� DOH�

FDQDOHORU�úL�GXF�OD�DSDUL LD�SLHUGHULORU�ORFDOH�GH�VDUFLQ��∆pξ) concentrate în VHF LXQLOH�FDUH�PDUFKHD]��VFKLPEDUHD�GH�IRUP��VDX�GH�VHF LXQH��

- efecte gazodinamice produse dH� IRU HOH� DVFHQVLRQDOH� DS�UXWH� GDWRULW��GLIHUHQ HORU� GH� WHPSHUDWXU�� DOH� IOXLGXOXL� SH� WUDVHHOH� YHUWLFDOH�� SR]LWLYH� VDX�negative (∆ph) :

∑ ∑ ±±+= fhg ppppp ∆∆∆∆ ξλ (N/m2) (7.1)

7. &$/&8/8/�+,'5$8/,&��*$=2',1$0,&��ù,�$/�,167$/$�,(,�'(�EVACUARE A GAZELOR DE ARDERE

240

unde pf este presiunea (sau depresiunea) din focar . La determinarea rezisteQ HORU��SLHUGHULORU�GH�VDUFLQ��VH�IRORVHVF�GDWHOH�VWDELOLWH�OD� FDOFXOXO� WHUPLF�� FX� H[FHS LD� GLDPHWUXOXL� HFKLYDOHQW� WHUPLF� FH� VH� vQORFXLHúWH� FX�diametrul echivalent hidraulic . ��&DOFXOXO�SLHUGHULORU�GH�VDUFLQ��OLQLDUH� Pierderile liniare de sarcin��VH�FDOFXOHD]��FX�XUP�WRDUHOH�UHOD LL��

- în cazul curgerii unui curent izoterm :

2

2w

d

lp

ρλ∆ λ = (N/m2) (7.2.)

- vQ�FD]XO�FXUJHULL�FX�VFKLPE�GH�F�OGXU��

22

1

2

2

+=

T/T

w

d

lp

p

h

ρλ∆ (N/m2) (7.3.)

l – lungimea liniare prin care curge fluidul, (m) d – diametrul echivalent hidraulic, diametrul exterior sau interior, (m) w –�YLWH]D�PHGLH�D�IOXLGXOXL�SH�SRU LXQHD�FRQVLGHUDW��P�V�� ρ –�GHQVLWDWHD�IOXLGXOXL�OD�WHPSHUDWXUD�úL�OD�SUHVLXQHD�FRQVLGHUDW��NJ�P3) 7�úL�7p – temperaturD�PHGLH�D�IOXLGXOXL��UHVSHFWLY�D�SHUH LORU�VS�OD L�GH�IOXLG��SH�

SRU LXQHD�FRQVLGHUDW��.�� λ –�FRHILFLHQWXO�GH�IUHFDUH��GHSHQGHQW�GH�QXP�UXO�5H\QROGV�úL�uneori de

UXJR]LWDWHD�SHUH LORU�(coeficientul lui Darcy). Valorile lui λ pentru conducte sau canale netede se pot determina utilizând UHOD LLOH�

Re

64=λ pentru Re < 2000 (7.4.)

290

3030

),Re(lg

,

−=λ pentru 2000 < Re < 4000 (7.5)

4

31640

Re

,=λ pentru 4000 < Re < 105 (7.6)

3HQWUX� HYL�UXJRDVH��OD�YDORUL 35 10512108 −− ⋅÷⋅= ,d

k �úL� 4000>Re :


CAZANE

241

23068

110,

Red

k,

+=λ (7.7)

unde : k�HVWH�UXJR]LWDWHD�DEVROXW��SHQWUX�FRQGXFWH�VDX�FDQDOH��GDW� pentru câteva cazuri practice în tabelul 7.1.

Tabelul 7.1. 1DWXUD�SHUH LORU�FRQGXFWHL�VDX�FDQalului 103 × k(m)

�HYL�GLQ�R HO�I�U��VXGXU�� - noi, neintrate în exploatare - FXUDWH��GXS��H[SORDWDUH� - FX�GHSXQHUL�PLFL�GH�SLDWU��OD�XWLOL]DUHD�DSHL�WUDWDWH�

úL�GHJD]DWH� - FX� GHSXQHUL� PHGLL� GH� SLDWU�� OD� XWLOL]DUHD� DSHL�

WUDWDWH�PHGLL�úL�I�U��GHJD]DUH - cu depunerL� PDUL� GH� SLDWU�� úL� FRUR]LXQL� OD�

XWLOL]DUHD�DSHL�QHWUDWDWH�úL�I�U��GHJD]DUH� &DQDOH�GLQ�WDEO�� &DQHOH�GLQ�F�U�PLG��VDX�EHWRQ�� - tencuite - QHWHQFXLWH��FX�VXSUDID ��UHODWLY�QHWHG�� - QHWHQFXLWH��FX�VXSUDID ��UXJRDV��

�HYL�GLQ�IRQW�� &DQDO�GH�]LG�ULH�EHWRQDW�� Canale din beton �HYL�GH�VWLFO��

0,02 0,04

0,1

0,04

1,0

(0,1 ÷ 0,15)

(2 ÷ 3) (3 ÷ 9)

0,8 0,8 ÷ 6 (medie 2,5) 0,8 ÷ 6 (medie 2,5)

0,0015 ÷ 0,01 (medie 0,005) Valoarea lui λ, pentru conducte sau canale rugoase, SHQWUX�FDUH�HVWH�vQGHSOLQLW��FRQGL LD�

>

k

dRe 560 (7.8)

VH�FDOFXOHD]��FX�UHOD LD�� 2

570

250

−

=

d

klog,

,λ (7.9)

ÌQ� FD]XO� FDQDOHORU� GH� JD]H� UHDOL]DWH� GLQ� PDWHULDO� WHUPRL]RODQW�� PLFúRUDUHD�WHPSHUDWXULL� GLQ� FDX]D� SLHUGHULORU� GH� F�OGXU�� SULQ� SHUH L� F�WUH�PHGLXO� vQFRQMXU�WRU� VH�SRDWH�QHJOLMD�LDU�FXUJHUH�VH�SRDWH�FRQVLGHUD�L]RWHUP��


242

��&DOFXOXO�SLHUGHULORU�GH�VDUFLQ��ORFDOH� Pierderile GH�VDUFLQ��ORFDOH�DWkW�vQ�FD]XO�FXUJHULL�L]RWHUPH�FkW�úL�vQ�FD]XO�FXUJHULL�FX�VFKLPE�GH�F�OGXU��VH�FDOFXOHD]��FX�UHOD LD�:

2

2wp

⋅=

ρξ∆ ξ (N/m2) (7.10)

în care:

ξ –� FRHILFLHQW� GH� UH]LVWHQ �� ORFDO�� FDUH� GHSLQGH� GH� IRUPD� JHRPHWULF��QHUHJXODULW� LL�GH�FXUJHUH�úL�XQHRUL�GH�QXP�UXO�5H\QROGV�

w�úL�ρ – viteza, respectiv densitatea fluidului în locul considerat. 'DF�� DSDUH� R� YDULD LH� GH� YLWH]�� vQ� ORFXO� VWXGLDW� �vQJXVWDUH� GH� VHF LXQH�� O�UJLUH� GH�VHF LXQH�� VH� FRQVLGHU�� vQ� FDOFXO�� YLWH]D� FHD�PDL�PDUH�� FRUHVSXQ]�WRDUH� VHF LXQLL�PDL�mici . a. 0RGLILF�UL�GH�VHF LXQH

3HQWUX�UH]LVWHQ H�ORFDOH�FUHDWH�GH�PRGLILF�UL�GH�VHF LXQH�FRHILFLHQWXO�ξ este dat de tabelul 7.2.

Tabelul 7.2. &RHILFLHQWXO�GH�UH]LVWHQ ��ORFDO��SHQWUX�PRGLILF�ULOH�GH�VHF LXQH

Denumirea 6FKL D� Coeficientul ξ raportat la YLWH]D�LQGLFDW��vQ�VFKL �

Intrare în canal cu PXFKLLOH�vQ�DFHODúL�

plan cu peretele

ξ = 0,5

Intrare în canal cu PXFKLLOH�LHúLWH

La s/d ≅ 0,2 - ξ = 0,5 s/d ≥ 0,2 - ξ = 1 0,05 < a/d < 0,2 - ξ = 0,85 la s/d ≥ 0,04 - ξ = 0,5

Intrare în canal cu muchiile rotunjite

La r/d = 0,25 PXFKLLOH� vQ� DFHODúL� SODQ� FX�peretele ξ = 0,5 FX�PXFKLLOH�LHúLWH�ξ = 0,4 la r/d = 0,1 - ξ = 0,12 la r/d = 0,2 - ξ = 0,05

w

r

w

s

a

w


CAZANE

243

,HúLUH�GLQ�FDQDO

ξ = 1

,HúLUH�GLQ�FDQDO�SULQ�JU�WDU�VDu prin GLDIUDJP�

ξ = (1,707 m

M

f

f-1)2

fm –� VHF LXQHD� OLEHU�� GH�FXUJHUH� D� JU�WDUXOXL� VDX� D�diafragmei fM –� VHF LXQHD� OLEHU�� D�canalului

Intrare în canal prin JU�WDU�VDX�SULQ�GLDIUDJP�

ξ =

m

M

f

f+0,707

2

m

M

m

M

f

f1

f

f

−

*U�WDUXO�VDX�diafragma în

interiorul canalului

ξ =

m

M

f

f-1+0,707

2

m

M

m

M

f

f1

f

f

−

&ODSHW��FRPSOHW�GHVFKLV�

ξ = 0,1

b. &RWXUL��FLUFXODUH��VDX�S�WUDWH Cot de 900�FX�UD]D�5�GH�FXUEXU��úL�GLDPHWUXO�G�DO�FRQGXFWHL��

Tabelul 7.3. &RHILFLHQWXO�GH�UH]LVWHQ ��SHQWUX�FRWXUL�GH��0�FLUFXODUH�VDX�S�WUDWH

d

R 05 06 07 08 09 1 15 2 3 4 5 10 15 20

ξ 1,2 0,9 0,65 0,45 0,35 0,28 0,19 0,17 0,14 0,13 0,11 0,08 0,06 0,05 Când unghiul de cotire ϕ este diferit de 900�VH�DSOLF��FRHILFLHQWXO�GH�FRUHF LH�%�� BC ⋅= ξξ (7.11)

Tabelul 7.4. &RUHF LH�SHQWUX�XQJKLXO�GH�FRWLUH

ϕ 0 300 600 900 1200 1500 1800

B 0 0,48 0,80 1 1,18 1,32 1,41 &kQG�VHF LXQHD�HVWH�GUHSWXQJKLXODU��D�E��FX�FRWD�E�vQ�SODQXO�FXUEXULL�VH�DSOLF��FRHILFLHQWXO�GH�FRUHF LH�&��

w

w w

w w

w w

w


244

CBC ⋅⋅= ξξ (7.12)

Tabelul 7.5 &RUHF LH�SHQWUX�VHF LXQH�GLIHULW��GH�S�WUDW

b

a 0,2 0,4 0,6 0,8 1 1,5 2 3 4 6 8

C 1,22 1,13 1,08 1,04 1 0,90 0,86 0,86 0,90 0,97 1 &RHILFLHQWXO� GH� UH]LVWHQ �� SHQWUX� FRWXUL� EUXúWH� �I�U�� UDFRUG�UL�� vQ� FD]XO� XQXL�unghi de cotire de 900�úL��D�XQHL�VHF LXQL�S�WUDWH�VDX�FLUFXODU��GH�FRQGXFW��HVWH�� 21,C =ξ (7.13) În cazul unui unghi diferit de cotire :

B,C ⋅= 21ξ (7.14) ÌQ�FD]XO�XQHL�VHF LXQL�GUHSWXQJKLXODUH�GH�FDQDO�� CB,C ⋅⋅= 21ξ (7.15) Când în cotire�VH�IDFH�úL�R�PRGLILFDUH�D�VHF LXQLL�FDQDOXOXL��F�GHULOH�GH�SUHVLXQH�VH�FDOFXOHD]��FX�YLWH]D�FHD�PDL�PDUH�úL�FX�XUP�WRDUHOH�FRUHF LL��

- SHQWUX�FRWXUL�EUXúWH�QX�VH�DSOLF��FRUHF LD� - pentru coturi line cu 10,

b

R> :

2

⋅⋅⋅=

i

eC

f

fCBξξ (7.16)

unde fe�HVWH�VHF LXQHD�GH�LHúLUH�úL�fi�VHF LXQHD�GH�LQWUDUH�� c. 9DULD LL�GH�VHF LXQH 1RWkQG�VHF LXQHD�PLF��FX�fm�úL�FX�fM�VHF LXQHD�PDUH��FRHILFLHQWXO�GH�UH]LVWHQ ��OD�O�UJLUHD�VHF LXQLL�YD�IL�ξ’�úL�OD�vQJXVWDUHD�VHF LXQLL�ξ’’ .

Tabelul 7.6. &RHILFLHQWXO�GH�UH]LVWHQ ��OD�YDULD LD�VHF LXQLL

fm/ fM 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 ξ’ 0,81 0,64 0,49 0,36 0,25 0,16 0,09 0,04 0,01 ξ’’ 0,47 0,43 0,38 0,33 0,28 0,23 0,17 0,12 0,06


CAZANE

245

3HQWUX�O�UJLUH�úL�vQJXVWDUH�EUXVF��GH�VHF LXQH�SRW�IL�XWLOL]DWH�UHOD LLOH��

2

1

−=

m

M

f

f'ξ respectiv

2

150

−=

M

m

f

f,''ξ (7.17)

d. )DVFLFXO�GH� HYL�DúH]DWH�vQ�OLQLH��FRULGRU� rn⋅= 0ξξ în care : nr –�QXP�UXO�GH�UkQGXUL�GH� HYL�SH�GLUHF LD�GH�FXUJHUH�D�IOXLGXOXL�� ξ0 – coefLFLHQWXO�GH�UH]LVWHQ ��DO�XQXL�UkQG�GH� HYL��

Coeficientul ξ0 depinde de pasurile relative s1/d�úL s2/d GLQWUH� HYL�SUHFXP�úL�GH� QXP�UXO� 5H\QROGV�� s2� úL� s1� UHSUH]LQW�� SDVXULOH� GLQWUH� HYL� vQ� VHQVXO� FXUJHULL�IOXLGXOXL��UHVSHFWLY�SHUSHQGLFXODU�SH�GLUHF LD�de curgere iar d este diametrul exterior al HYLORU�IDVFLFROXOXL�� 'DF��VH�QRWHD]�� 1

1

2

1

2

1

−−

=−−

=)d/s(

)d/s(

ds

dsΨ (7.18)

atunci pentru : 21 ss ≤ �úL��≤ ϕ < 1 :

201

0

521,

Re)()d/s(

,

ϕξ

⋅= (7.19)

iar pentru : s1 > s2 úL��ϕ ≤ 8 :

2

20680

1

0

90

320

Ψϕξ

,

,(Re)),()d/s(

,

−⋅

= (7.20)

'DF�� XQJKLXO�GLQWUH�GLUHF LD�GH�FXUJHUH�D� IOXLGXOXL� úL� D[HOH� HYLORU� IDVFLFROXOXL�este β ≤ 750, coeficientul ξ�WUHEXLH�P�ULW�FX�� e. )DVFLFROXO�GH� HYL�DúH]DWH�GHFDODW� )n( r 10 += ξξ (7.21)

în care: 270

0,

s ReC−=ξ (7.22)


246

Coeficientul CS� LQH� VHDPD� GH� SDVXULOH� GLQWUH� HYL�� SDVXO� UHODWLY� SH� GLDJRQDO��fiind :

2

2

2

12

4

1

+

=

d

s

d

s

d

s'

(7.23)

VH�QRWHD]��

1

1

2

1

−−

=)d/s(

)d/s('

ϕ (7.24)

GDF��≤ ϕ < 1,7 :

CS = 3,2 +(4,6 – 2,7ϕ)(2 - s1/d) în cazul în care s1/d < 2 (7.25) sau : CS = 3,2 în cazul în care s1/d ≥ 2 (7.26)

'DF��≤ ϕ ≤ 5,2 ; CS = 0,44 (ϕ +1)2

'DF��XQJKLXO�GLQWUH�GLUHF LD�GH�FXUJHUH�D�IOXLGXOXL�úL�D[HOH� HYLORU�HVWH�β ≤ 750,

coeficientul ξ�WUHEXLH�P�ULW�FX�� f. 3HQWUX�FDOFXOXO�FRHILFLHQWXOXL�GH�UH]LVWHQ ��ORFDO��DO�WHXULORU�VLPHWULFH se poate IRORVL� XUP�WRDUHD�PHWRG�� DSUR[LPDWLY�� WHXO� VH� vQORFXLHúWH� vQ�PRG� FRQYHQ LRQDO� SULQ�GRX�� FRWXUL� LQGHSHQGHQWH�� DGPL kQGX-VH� F�� VHF LXQea canalului comun se împarte ORQJLWXGLQDO�vQ�GRX��S�U L�SURSRU LRQDOH�FX�GHELWHOH�UDPXULORU��FRHILFLHQWXO�GH�UH]LVWHQ ��ORFDO��SHQWUX�ILHFDUH�FXUHQW�VH�FDOFXOHD]��FD�SHQWUX�XQ�FRW�FX�PXFKLLOH�QHURWXQMLWH��FX�VHF LXQL�LQHJDOH�OD�LQWUDUH�úL�OD�LHúLUH�� &DOFXOXO�SLHUGHULORU�GH�VDUFLQ�� OD�FXUJHUHD�DHUXOXL� VDX�D�JD]HORU�GH�DUGHUH�SULQ�VXSUDIH HOH� GH� vQF�O]LUH� DOH� DSDUDWXOXL� FX� UHOD LLOH� LQGLFDWH�� HVWH� YDODELO� vQ� FD]XO��VXSUDIH HORU��GH�vQF�O]LUH�FXUDWH�� $YkQG�vQ�YHGHUH�IDSWXO�F��vQ�FDOFXOH�QX�VH�SRDWH� LQe seama de o serie de aspecte VSHFLILFH�� FDUDFWHULVWLFH� FXUJHULL� vQ� FRQGL LL� UHDOH�� SLHUGHULOH� GH� VDUFLQ�� GHWHUPLQDWH�WHRUHWLF� VH� FRUHFWHD]�� SULQ� vQPXO LUHD� FX�XQ�FRHILFLHQW�GH�FRUHF LH�ε0� DOH� F�UXL�YDORUL��SHQWUX�FD]XO�PXUG�ULULL�PHGLL�D�VXSUDIH HORU�GH�vQF�O]LUH�VXQW��

- IDVFLFROH�GH� HYL�ILHUE�WRDUH�YHUWLFDOH�«««««««««««««��1 - VXSUDIH H�GH�vQF�O]LUH�UHDOL]DWH�GLQ�VHUSHQWLQH� �VXSUDvQF�O]LWRDUH�HFRQRPL]RDUH��««««««««««««««�� - preîQF�O]LWRDUH�GH�DHU�GLQ� HYL�QHWHGH��

o pe partea aerului de ardere 1,05 o pe partea gazelor de ardere …………………………………….. 1,1


CAZANE

247

��&DOFXOXO�SLHUGHULORU�GH�VDUFLQ��vQ�FDQDOH�YHUWLFDOH��HIHFWH�GH�WLUDM�� 9DORDUHD� DXWRWLUDMXOXL� �WLUDMXO� QDWXUDO�� RULF�UeL� SRU LXQL� YHUWLFDOH� GLQ� FLUFXLW��LQFOXVLY�FRúXO��VH�FDOFXOHD]��FX�UHOD LD�� g)(hp gah ρρ∆ −±= (N/m2) (7.27)

unde : h -��HVWH�vQ�O LPHD��SH�YHUWLFDO��D�WUDVHXOXL��P�� ρa – densitatea aerului exterior (kg/m3)

ρg – densitatea medie a gazului afODW�vQ�FRQGXFW��(kg/m3) 'DF�� IOXLGXO� HVWH� GLULMDX� vQ� VXV�� DXWRWLUDMXO�PLFúRUHD]�� SLHUGHUHD� GH� VDUFLQ�� vQ�circuit (-∆ph�� LDU� GDF�� IOXLGXO� HVWH� GLULMDW� vQ� MRV�� DXWRWLUDMXO� YD� P�UL� SLHUGHUHD� GH�VDUFLQ��vQ�FLUFXLW��+∆ph) . În cazul tirajului natural, autoWLUDMXO� FRúXOXL�� FD� GH� DOWIHO� úL� UH]LVWHQ HOH� OD�FXUJHUHD�JD]HORU�GH�DUGHUH�SULQ�FRú��VH�GHWHUPLQ��VHSDUDW��

7.2. CDOFXOXO�SDUDPHWULORU�GH�ED]��Di�LQVWDOD LHL�GH�DOLPHQWDUH�FX�DHU�GH� ardere

7.2.1. Debitul de aer

Introducerea aerului de ardere în focar se face cu ajutorul ventilatoarelor de aer. /D�XQHOH�FD]DQH�PLFL�DGPLVLD�OXL�VH�IDFH�SULQ�HIHFWXO�LQVWDOD LHL�GH�WLUDM�� 'HELWXO�GH�FDOFXO�DO�YHQWLODWRDUHORU�GH�DHU�VH�GHWHUPLQ��FX�UHOD LD��

273

27301611 01

arfa

tBV,D

+⋅= αβ (m3/s) (7.28)

B – debitul de combustibil care arde efectiv în focar, în kg/s sau Nm3/s .

1,0161 V0 – volumul teoretic de aer umed necesar arderii, în Nm3/kg sau Nm3/Nm3

αf – coeficientul de exces de aer în focar

tar – temperatura aerului aspirat de ventilator, în 0C

β1 – coeILFLHQW�GH�UH]HUY��HJDO�FX�� ÌQ�FD]XO�vQ�FDUH�FRQ LQXWXO�GH�XPLGLWDWH�DO�DHUXOXL��[��HVWH�GLIHULW�GH��NJ�NJ�aer uscat, termenul 1,0161 V0��VH�vQORFXLHúWH�FX��[��90 .


248

7.2.2. Calculul presiunii ventilatoarelor de aer de ardere PierGHUHD� GH� VDUFLQD� WRWDO�� D� WUDVHXOXL� GH� DHU� YD� IL�� LQkQG� VHDPD� GH� H[LVWHQ D�depresiunii din focar (pf = 30 ÷ 50 N/m2) :

∑ ∑ ∑ −+±++= fAha pppppp ∆∆∆∆∆ ξλ (7.29)

Termenul ∆pa�UHSUH]LQW��SLHUGHUHD�GH�VDUFLQ��vQ�DU]�WRU��7HUPHQXO�∑∆ph poate IL�QHJOLMDW�GDF��DHUXO�QX�HVWH�SUHvQF�O]LW�VDX�GDF��GLIHUHQ HOH�GH�FRWH�GLQWUH�SUHvQF�O]LWRU�GH�DHU�úL�DU]�WRDUH�QX�vQWUHF��P� 3H�WUDVHXO�DHUXOXL�GH�DUGHUH��SLHUGHULOH�GH�VDUFLQ��KLGUDXOLF��vQVXPHD]�:

- UH]LVWHQ HOH�FRQGXFWHL�GH�DVSLUD LH�SkQ��OD�YHQWLODWRU�� - UH]LVWHQ HOH�FRQGXFWHL�GH�UHIXODUH�GH�OD�YHQWLODWRU�OD�SUHvQF�O]LWRUXO�GH�DHU�� - UH]LVWHQ HOH�WUDVHXOXL�GH�OD�SUHvQF�O]LWRUXO�GH�DHU�OD�IRFDU�� - UH]LVWHQ HOH� LQVWDOD LLORU� IRFDUXOXL�� vQ� FD]XO� DUGHULL� FRPEXVWLELOXOXL� VROLG� SH�

JU�WDU,� VH� FRPSXQ� GLQ� UH]LVWHQ HOH� FXWLLORU� GH�GLVWULEX LH� SHQWUX� DOLPHQWDUHD�FX� DHU� SH� ]RQH� D� JU�WDUXOXL� úL� GLQ� UH]LVWHQ D� JU�WDUXOXL� úL� D� VWUDWXOXL� GH�FRPEXVWLELO��LDU�OD�IRFDUHOH�I�U��JU�WDU�VH�FRPSXQ�GLQ�UH]LVWHQ HOH�FDUH�SDU�OD�FXUJHUHD� DHUXOXL� SULQ� DU]�WRU� �DHUXO� VHFXQGDU�� LQFOXVLY� SLHUGHUHD� GH� VDUFLQ��GLQDPLF��OD�LHúLUHD�DHUXOXL�GLQ�DU]�WRU�vQ�FDPHUD�GH�DUGHUH) .

5H]LVWHQ D� JU�WDUXOXL� úL� DOH� VWUDWXOXL� GH� FRPEXVWLELO� VH� LDX� vQ� FRQVLGHUDUH� SULQ�SUHVLXQHD�SH�FDUH�DHUXO�GH�DUGHUH�WUHEXLH�V��o DLE��VXE�JU�WDU��FRQIRUP�LQGLFD LLORU�GLQ�tabelul 7.7.

Tabelul 7.7 3UHVLXQHD�QHFHVDU��VXE�JU�WDU

Tipul focarului Combustibil Presiunea aerului VXE�JU�WDU��1�P2)

(valori orientative) )RFDU�FX�JU�WDU�UXODW� &�UEXQL� EUXQL� VXSHULRUL�� KXLOH�

necocsificabile 600 - 800

)RFDUH� FX� JU�WDUH�înclinate, mecanizate

&�UEXQL�bruni cu w≤40% 600- 800

)RFDUH�FX�JU�WDU�IL[ &�UEXQL�EUXQL &�UEXQL�EUXQL�LQIHULRUL��OLJQL L

800 – 1000 1000 - 1200

3UHVLXQHD�GH�FDOFXO�D�YHQWLODWRDUHORU�GH�DHU�VH�GHWHUPLQ��FX�UHOD LD�� av pH ∆β2= (N/m2) (7.30)

unde : β2 este un coeILFLHQW�GH�UH]HUY��SHQWUX�SUHVLXQH��HJDO�FX��


CAZANE

249

3XWHUHD�PRWRUXOXL�HOHFWULF�FH�DQWUHQHD]��YHQWLODWRUXO�YD�IL��

v

vvv

HDN

η⋅⋅

=1000

(kw) (7.31)

unde : ηv este randamentul ventilatorului (0,6 ÷ 0,8) . 7.3. CDOFXOXO�SDUDPHWULORU�GH�ED]��DL�LQVWDOD LHL�GH�WLUDM�

��'HELWXO�LQVWDOD LHL�GH�WLUDM� 'HELWXO�GH�FDOFXO�DO� LQVWDOD LHL�GH�HYDFXDUH�D�JD]HORU�GH�DUGHUH�VH�GHWHUPLQ��FX�UHOD LD��

273

2731

g

gg

tBVD

+= β (m3/s) (7.32)

Vg – volumul gazelor de ardere din cazan la excesul de aer αFRú, [ Nm3/kg sau

Nm3/ Nm3]

β1 –�FRHILFLHQW�GH�UH]HUY��β1 = 1,05 pentru cazan cu debitul nominal > 20 t/h ��úL�β1 = 1,1 pentru cazane cu debitul nominal ≤ 20 t/h) .

tg –�WHPSHUDWXUD�JD]HORU�GH�DUGHUH�OD�H[KDXWRU��UHVSHFWLY�OD�ED]D�FRúXOXL��>�0C ]. 7.3.2. Calculul presiunii ventilatoarelor de gaze de ardere

([KDXWRUXO�WUHEXLH�V��vQYLQJ��WRDWH�UH]LVWHQ HOH��GH�SH�WUDVHXO�JD]HORU�GH�DUGHUH��GH�OD�SDUWHD�GH�vQFHSXW�D�IRFDUXOXL�SkQ��OD�HYDFXDUHD�JD]HORU�GH�DUGHUH��OD�ED]D�FRúXOXL��unde de regul��VH�LPSXQH��p = 0 . 'HFL�� vQ� FD]XO� WLUDMXOXL� DUWLILFLDO� FRúXO� QX� VHUYHúWH� DWkW� SHQWUX� FUHDUHD� WLUDMXOXL��FkW� SHQWUX� HYDFXDUHD� JD]HORU� GH� DUGHUH� vQ� DWPRVIHU�� 'H� DFHHD�� vQ�O LPHD� FRúXOXL� VH�DOHJH� vQ� IXQF LH� GH� FRQGL LLOH� VDQLWDUH�� GH� SURWHMDUH� D� YHJHWD LHL� HWF�� VH� FDOFXOHD]��QXPDL�GLDPHWUXO�FRúXOXL��FDUH�VH�GHWHUPLQ��vQ�IXQF LH�GH�GHELWXO�WRWDO�GH�JD]H�GH�DUGHUH�SHQWUX�R�YLWH]��OD�LHúLUHD�GLQ�FRú�GH��-��P�V��'LDPHWUXO�PHGLX�DO�XQXL�FRú��vQ�IXQF LH�GH�FHOH�GRX��YDORUL�G1�úL�G2�GH�OD�H[WUHPLW� L��YD�Ii :

21

212

dd

dddm +

= (7.33)

'XS�� FDOFXOXO� UH]LVWHQ HORU� VHSDUDWH� GH� SH� vQWUHJ� WUDVHXO� JD]HORU� GH� DUGHUH� VH�LQWURGXFH� R� FRUHF LH� FDUH� LQH� VHDPD� GH� FRQFHQWUD La� GH� FHQXú�� vQ� JD]HOH� GH� DUGHUH�provenite din arderea combustibilului solid . PHQWUX� WUDVHXO�JD]HORU�GH�DUGHUH��DWXQFL�FkQG�IRFDUXO� OXFUHD]�� vQ�GHSUHVLXQH�� OD�SLHUGHUHD�GH�VDUFLQ��WRWDO��D�WUDVHXOXL�VH�DGDXJ��úL�GHSUHVLXQHD�SURGXV��vQ�IRFDU�Sf . 6H� DGRSW�� vQ� JHQHUDO� R� GHSUHVLXQH� GH� �� ·� �� 1�P2� OD� QLYHOXO� DU]�WRDUHORU��Pierderea totDO��GH�VDUFLQ��SHQWUX�WUDVHXO�JD]HORU�GH�DUGHUH�YD�IL�


250

∑ ∑ ∑ +±+++= fhg p)]p(pp)[(p ∆∆∆µ∆ ξλ1 (N/m2) (7.34)

µ -� HVWH� FRQFHQWUD LH� GH� FHQXú�� vQ� JD]HOH� GH� DUGHUH� úL� VH� FDOFXOHD]�� SHQWUX� R�WHPSHUDWXU��PHGLH�VL�XQ�FRHILFLHQW�GH�H[FHV�PHGLX��

gg

an

V

aA

⋅⋅⋅

=−

ρµ

210 �NJ�FHQXú��NJ�JD]H�GH�DUGHUH�� (7.35)

unde : A�HVWH�SURFHQWXO�WRWDO�GH�FHQXú�� aan –�IUDF LXQHD�DQWUHQDW��GH�JD]HOH�GH�DUGHUH�GLQ�FDQWLWDWHD�WRWDO��GH�FHQXú��UH]XOWDW��prin arderea a ��NJ�GH�FRPEXVWLELO��'DF��FHQXúD�úL�]JXUD�VXQW�HYDFXDWH�vQ�VWDUH�VROLG��aan este :

- ��SHQWUX�IRFDUHOH�FX�F�UEXQH�SXOYHUL]DW�úL� - ��·��SHQWUX�IRFDUHOH�FX�JU�WDU��

Pentru combustibil lichid sau gazos µ = 0 . 3UHVLXQHD�GH�FDOFXO�D�H[KDXVWRUXOXL�VH�GHWHUPLQ��FX�UHOD LD�� gex pH ∆β ⋅= 2 (N/m2) (7.36)

unde : β2�HVWH�XQ�FRHILFLHQW�GH�UH]HUY��SHQWUX�SUHVLXQHD�HJDO��FX�� 3XWHUHD�PRWRUXOXL��HOHFWULF�FH�DQWUHQHD]��H[KDXVWRUXO�YD�IL��

ex

exg HDN

η1000

⋅= (kw) (7.37)

unde : ηex – este randamentul exhaustorului (0,6 ÷ 0,8) .

7.3.3. Calculul coúXOXL�OD�LQVWDOD LLOH�FX�WLUDM�QDWXUDO� 'LDPHWUXO�FRúXOXL� VH�GHWHUPLQ�� vQ� IXQF LH�GH�GHELWXO� WRWDO�GH�JD]H�GH�DUGHUH�DO�FD]DQHORU�OHJDWH�OD�FRú��9LWH]D�JD]HORU�GH�DUGHUH�OD�LHúLUHD�GLQ�FRú�VH�DOHJH�vQWUH��úL��m/s, cu valorile mici ale vitezei la cazane de debit mic. ÌQ� FD]XO� FkQG� FRúXO� FD]DQXOXL� HVWH� GHVWLQDW� SHQWUX� SUHOXDUHD� vQWUHJXOXL� WLUDM�necesar cazanului :

gp,H ∆210 = (7.38)

unde H0�HVWH�WLUDMXO�QHW�DO�FRúXOXL�� ÌQ� FD]XO� FkQG� FRúXO� HVWH� GHVWLQDW� exclusiv dispersiei emisiilor poluante în PHGLXO�vQFRQMXU�WRU�� gp,H ∆210 < (7.39)

restul tirajului fiind asigurat de exhaustor.


CAZANE

251

7LUDMXO�EUXW�DO�FRúXOXL��+��FDUH�VH�GHWHUPLQ��I�Uk�SLHUGHULOH�SURSULL�GH�VDUFLQ��SH�traseul acestuia, este :

g)(hH gmac ρρ −= (7.40)

hc –�vQ�O LPHD�FRúXOXL��P�� ρa – densitatea aerului exterior, (kg/m3); ρa = 1,293

at273

273

+ (7.41)

ρgm –�GHQVLWDWHD�JD]HORU�GH�DUGHUH�OD�WHPSHUDWXUD�PHGLH�GLQ�FRú��NJ�P3) Densitatea gazelor de ardere la stare normal��VH�FDOFXOHD]��FX�UHOD LLOH�

00

0

1

29317170

V)(V

V,,

g

gN −++

=α

αρ pentru combustibil gaz natural (7.42)

00

0

1

29311

V)(V

V,

g

gN −++

=α

αρ pentru combustibil lichid sau gazos (7.43)

Densitatea medie a gazelor de ardere, la temperatura tgm va fi :

gm

ggmtN +

=273

273ρρ (7.44)

7HPSHUDWXUD�PHGLH�D�JD]HORU�vQ�FRú�HVWH��

2c

igm

ttt

∆−= (0C) (7.45)

3HQWUX� GHWHUPLQDUHD� F�GHULL� GH� WHPSHUDWXU�� vQ� FRú� ûtc� VH� XWLOL]HD]�� UHOD LL�H[SHULPHQWDOH�VWDELOLWH�vQ�IXQF LH�GH�F�GHUHD�GH�WHPSHUDWXU��SH�XQLWatea de lungime ∆t:

tht cc ∆∆ ⋅= (0C) (7.46)

cu valorile pentru ∆t:

- FRú�GH�WDEO��QHL]RODW��

hQ

,t

761=∆ sau

hDt

2=∆ (0C) (7.47)

- FRú�GH�WDEO��L]RODW��


252

hQ

,t

70=∆ sau

hD

,t

80=∆ (0C) (7.48)

- FRú�GH�F�U�PLG��FX�SHUH LL�FX�JURVLPH�GH�FFD��PP��

hQ

,t

60=∆ sau

hD

,t

220=∆ (0C) (7.49)

- FRú�GH�F�U�PLG��FX�SHUH LL�F�JURVLPH�GH�FFD��PP��

hQ

,t

130=∆ sau

hD

,t

130=∆ (0C) (7.50)

unde Dh este debitul de abur al cazanului în t/h iar Qh�GHELWXO�GH�F�OGXU��vQ�MW . 'H� PHQ LRQDW� F�� hc�� vQ�O LPHD� FRúXOXL�� WUHEXLH� DSUR[LPDW�� LQL LDO� SHQWUX� D� VH�putea calcula ∆tc FX�UHOD LD��úL H�FX�UHOD LD�� &D�R�SULP��LQGLFD LH�WLUDMXO�EUXW�DO�FRúXOXL� *

oh în N/m2��P�vQ�O LPH�GH�FRú�HVWH�dat în tabelul 7.8 .

Tabelul 7.8. 7LUDMXO�XQLWDU�DO�FRúXOXL

tgm 0C 120 130 140 150 160 170 180

*oh N/m2/1 m 2,66 2,88 3,1 3,3 3,5 3,7 3,86

tgm 0C 190 200 210 220 230 240 250

*oh N/m2/1 m 4,04 4,2 4,36 4,51 4,65 4,8 4,9

7DEHOXO� �� HVWH� FDOFXODW� SHQWUX� R� WHPSHUDWXU�� D� DHUXOXL� DPELDQW� GH� ��0C,

GHQVLWDWHD�QRUPDO��ρa0 = 1,293 kg/Nm3�úL�ρg0 = 1,34 kg/Nm3 . 7LUDMXO�QHW�DO�FRúXOXL�VH�GHWHUPLQ��FX�UHOD LD�

HphHH c 9,0cos0 ≅∆⋅−= (N/m2) (7.51)

unde : ∆pFRú�HVWH�SLHUGHUHD�GH�VDUFLQ��OLQLDU��SH��P�GH�OXQJLPH�GH�FRú��FDS�� 5HOD LLOH� SUHFHGHQWH� SRW� IL� IRORVLWH� úL� SHQWUX� YHULILFDUHD� YDORULL� PD[LPH� D�SLHUGHULL�GH�VDUFLQ��ce SRDWH�IL�DFRSHULW��SULQ�WLUDM�QDWXUDO��GH�XQ�FRú�FX�GLPHQVLXQL�GDWH�.


CAZANE

253

7.��&DOFXOXO� SDUDPHWULORU� GH� ED]�� DL� LQVWDOD LHL� GH� LQVXIODUH� OD� FD]DQHOH� FX�ardere sub presiune

7.��'HELWXO�LQVWDOD LHL�GH�LQVXIODUH� &X�QRWD LLOH�IRORVLWH�DQWHULRU��GHELWXO de aer al ventilatorului este :

273

27301611 01

a

fa

tBV,D

+= αβ (m3/s) (7.52)

în care : αf este coeficientul de exces de aer din focar . 7.4.2. Calculul presiunii de refulare a ventilatorului de insuflare La cazanele lucrând cu focarele sub presiune delimitarea drumului de gaze pe WUDVHXO�DHUXOXL�QX�HVWH�QHFHVDU��GHRDUHFH�HIHFWXO�GH�FLUFXOD LH�HVWH�SURGXV�GH�R�VLQJXU��VXIODQW��ÌQ�DFHVW�FD]� gag,a ppp ∆∆∆ −= (7.53)

Presiunea de calcul a ventilatorului de aer insuflat va fi :

g,ai,v pH ∆β2= (N/m2) (7.54)

3XWHUHD�PRWRUXOXL�HOHFWULF�QHFHVDU�DQWUHQ�ULL�YHQWLODWRUXOXL��YD�IL��

v

i,va

i,v

HDN

η1000= (kw) (7.55)

unde: ηv este randamentul ventilatorului .

INDRUMATOR DE PROIECTARE APARATE TERMICE CAZANE

254

CAPITOLUL 8 CALCULUL DE REZISTENŢĂ AL CAZANELOR

8.1. Date generale Calculul de rezistenţă se efectuează pentru dimensionarea sau verificarea tamburilor (mantalei) ţevilor, colectoarelor, plăcilor tubulare, fundurilor şi tubului de flacără. Elementele metalice se dimensionează sau se verifică considerându-le supuse la presiune interioară sau exterioară ca solicitare principală. În calcule se ţine seama şi de alte solicitări ce pot avea loc, datorate:

a) greutăţii proprii şi a fluidului în timpul exploatării; b) diferenţelor de temperatură şi a dilatării termice diferite a materialelor; c) sarcinii hidrostatice a fluidului; d) efectul concentrărilor de eforturi produse de suporturi, racorduri de conducte

şi alte similare.

8.2. Materiale folosite pentru execuţia elementelor metalice ale cazanelor Principalul material utilizat în execuţia cazanelor este oţelul, a cărui compoziţie

chimică, conform SR EN 297 + A2 / 2001 este cea din tabelul 8.1. Tabelul 8.1.

Caracteristici mecanice şi compoziţia chimică a oţelurilor carbon şi inoxidabile

Material Tip oţel

Rezistenţă la

tracţiune σr

N/mm2

C

masa %

P

masa %

S

masa %

Si

masa %

Mn

masa %

Cr

masa %

Mo

masa %

Ni

masa %

Ti

masa %

Nb/Ta

masa %

Carbon ≤ 520 ≤

0,25 ≤

0,05 ≤

0,05 - - - - - - -

Feritic ≤ 600 ≤

0,08 ≤

0,045 ≤

0,030 ≤ 1,0 ≤ 1,0 15,5-18 ≤ 1,5 - ≤ 7×

% C ≤ 12× % C

Table, ţevi

Austenitic ≤ 800 ≤

0,08 ≤

0,045 ≤

0,030 ≤ 1,0 ≤ 2,0 16,5-20

2,0-3,0 9-15 ≤ 5×

% C ≤ 8× % C

Pentru armături din fontă şi la realizarea ţevilor cu aripioare sau nervurate, caracteristicile minime pentru fontă sunt cele centralizate în tabelul 8.2.

Tabelul 8.2. Caracteristici minime pentru fontă

Fontă cu grafit lamelar (ISO 185) : Rezistenţă la tracţiune σr

Duritate Brinell

≥ 150 N/mm2 160 – 220 HB 2,5/187,5

Fontă cu grafit nodular (recopt feritic) : Rezistenţă la tracţiune σr

Rezilienţă

≥ 400 N/mm2 ≥ 23 J/c m2

8. CALCULUL DE REZISTENŢĂ AL CAZANELOR

255

Reperele turnate executate din aluminiu sau din cupru sunt centralizate în tabelele 8.3 şi 8.4.

Grosimile minime ale pereţilor sunt prezentate în tabelele 8.5 şi 8.8.

Tabelul 8.3. Repere turnate executate din aluminiu sau din aliaje de aluminiu

Rezistenţă la tracţiune

σr N/mm2

Domeniu de temperatură 0C

Al 99,5 ≥ 75 până la 300 Al Mg2 Mn 0,8 ≥ 275 până la 250

Tabelul 8.4.

Repere turnate executate din cupru sau din aliaje de cupru

Rezistenţă la tracţiune

σr

N/mm2

Domeniu de temperatură 0C

SF - Cu ≥ 200 până la 250 Cu Ni 30 Fe ≥ 310 până la 350

Grosimile minime ale pereţilor sunt prezentate în tabelele 8.5 şi 8.8.

Tabelul 8.5. Grosimi minime pentru reperele laminate

Oţeluri carbon, aluminiu Oţeluri protejate, oţeluri inoxidabile, cupru a

mm b

mm c

mm a

mm b

mm c

mm 4 3 2,9 2 2 1

Coloana a) pentru pereţii camerelor de ardere expuşi la apă şi la foc şi pentru pereţii orizontali ai suprafeţelor de schimb prin convecţie . Coloana b) pentru pereţii care nu sunt expuşi decât la apă şi pentru formele de consolidare, ca ambutisările suprafeţelor de încălzire prin convecţie de deasupra camerei de ardere . Coloana c) ţevi ale schimbătorului convectiv .

Tabelul 8.8. Grosimile nominale minime ale elementelor cazanelor executate din materiale turnate

supuse la presiune

Debit caloric nominal Qn Debit caloric nominal Qn Fontă cu grafit nodular (recopt feritic), cupru

kW mm mm ≤ 35 > 35

3,5 4,0

3,0 3,5


256

Oţelurile pentru tamburi şi colectoare de diametru mare, executate în general din tablă sudată, sunt oţeluri OLK (tabelul 8.7) . Valoarea rezistenţei admisibile (σa), calculată după necesităţi în raport cu temperatura de calcul a peretelui elementului de cazan, se determină din relaţia de calcul corespunzătoare :

tfa

tra

tcara σσσσσσσσ ≤≤≤≤ ;5,1/;5,1/;6,2/20

(8.1) unde :

tr

20G ,σσ - este rezistenţa la limita de rupere la 200C, respectiv la temperatura

peretelui; tcσ - rezistenţa la limita de curgere, la temperatura tp;

fσ - rezistenţa la limita de fluaj, la temperatura tp. Temperatura de calcul a peretelui tp este temperatura pentru care se stabileşte valoarea rezistenţei admisibile a metalului :

C)(tt fp05025 ±+= şi în general

+=

δλα ,,qftt fp

unde: tf este temperatura fluidului de lucru.

Tabelul 8.7. Oţel carbon laminat în table groase pentru cazane de abur şi recipiente sub presiune

Limita de curgere la 200C

σc (daN/cm2) Marca Rezistenţa la tracţiune σr (daN/cm2) I II III

Alungirea relativă la rupere (%)

OLK 1 3400…4200 3400-3800 3900-4000 4100-4200

2200 2000 1900 31 30 28

OLK 2 3800…4700 3800-4000 4100-4300 4400-4700

2400 2200 2100 27 26 25

OLK 3 3500…4400 2300 2200 2100 24 OLK 4 4100…5000 2600 2500 2400 22 OLK 5 4400…5300 2800 2700 2600 20

În tabelul 8.8 sunt date rezistenţele admisibile în funcţie de temperatură pentru unele oţeluri utilizate la cazane .


257

Tabelul 8.8. Rezistenţele admisibile σa în daN/cm2 pentru diferite oţeluri, în funcţie de temperatură

OL 34

OLC 10

OL 37

OLC 15

OL 42

OLK 2

OLC 25 OLK 3

Temperatura de calcul a pereţilor

(0C) σa în daN/cm2 20

200 240 260 280

11700 1050 970 930 890

1200 1090 1000 960 920

1300 1170 1070 1030 980

1330 1210 1110 1060 1010

1430 1280

… 1110

-

1470 1330 1220 1160 1110

1600 1400 1340 1270 1210

300 360 400 440 500

050 - - - -

885 750 670 525 250

940 - - - -

970 820 730 580 300

- - - - -

1050 900 800 630 300

11500 980 875 670 300

8.3. Calculul grosimii pereţilor corpurilor cilindrice 8.3.1. Calculul tamburilor (mantalelor cilindrice) Grosimea necesară a tablei este :

cp

pDs

a

i +−⋅

=ϕσ2 (cm) (8.2)

unde : Di – diametrul interior al tamburului (cm) ; p – presiunea de lucru (bar) ; σa – efortul unitar admisibil (daN/cm2) ; ϕ – coeficientul de slăbire conform tabelului 8.9 ; c – adaos de coroziune cu valori :

c=0,1 pentru s ≤ 30 mm c=0 pentru s > 30 mm

Presiunea de calcul este presiunea înscrisă pe placa de timbru corectată cu un coeficient de siguranţă (1,1 ÷ 1,3). Relaţia (8.2) este aplicabilă pentru cazurile când sunt îndeplinite condiţiile corespunzătoare mantalelor cu pereţi subţiri :

- raportul s/Di < 0,1 - raportul De/Di < 1,5 - în cazul mantalelor sudate liniile medii trebuie să fie în prelungire una cu

alta pentru fiecare îmbinare longitudinală


258

- nu au loc solicitări suplimentare locale datorită racordurilor sau unor sarcini ciclice etc.

- solicitările de natură termică sunt păstrate în limite reduse, ca urmare a respectării grosimilor limită ale pereţilor admişi în drumul gazelor de ardere.

Tabelul 8.9

Coeficienţi de slăbire pentru tamburi Tamburi cu găuri pe generatoare (la pasul s1) ϕ = s1-d/s1 Tamburi cu găuri transversale (la pasul s’) ϕ =2(s’-d)/s’ Gaură cu diametru mare : do ≤ 0,6 Di ϕ =1-do/531Di6

Manuală, cap la cap cu completare la rădăcină

ϕ =0,85

Idem, fără completare la rădăcină

ϕ =0,7

Suduri transversale ϕ =0,8 Sudură T pe ambele părţi prelucrate

ϕ =0,85

Sudură

Suduri T neprelucrate ϕ =0,7

Grosimea minimă a peretelui tamburului, indiferent de rezultatul calcului, nu poate fi mai mică de 6 mm. Temperatura de lucru a pereţilor în acest caz se ia conform indicaţiilor din tabelul 8.10.

Tabelul 8.10 Temperatura tp a pereţilor tamburilor

Felul tamburilor tp Tambur neîncălzit tp=tf Tambur neizolat, cu s ≤ 50 mm, încălzit cu gaze de ardere având tg < 600 0C

tp=tf+1,2 s* +100C

Tambur neizolat, cu s ≤ 30 mm, încălzit cu gaze de ardere având tg = 600-900 0C

tp=tf+2,5 s* +200C

Tambur neizolat, cu s ≤ 22 mm, încălzit cu gaze de ardere având tg > 900 0C

tp=tf+4 s* +300C *) s în mm

Verificări suplimentare. Grosimea tamburului calculată cu relaţia (8.2) se verifică ţinând seama de solicitarea a încovoiere datorită greutăţii proprii, apei, izolaţiei şi a ţevilor suspendate de tambur . Determinarea momentului de încovoiere, se face considerând tamburul ca o grindă simplu rezemată, încărcată cu o sarcină uniform distribuită :

8

2lqM max⋅

= (daN.cm) cu q în daN/cm (8.3)

unde : l este diferenţa între reazime (m) .


259

Modulul de rezistenţă W se calculează pentru secţiunea circulară cea mai slăbită, din cauza orificiilor, luând în considerare deplasarea centrului de greutate faţă de centrul geometric. Pentru o secţiune inelară fără orificii :

)DD(D

W iee

44

32−=

π (cm3) (8.4)

În cazul când Mmax şi Wmin sunt în secţiuni diferite se stabileşte secţiunea cu solicitare maximă după relaţia :

ari

i WM

σσ ≤= (daN/cm2) (8.5)

aar ),,( σσ 9080 −= pentru ţevi tambure încălzite . Pentru a evita solicitări termice defavorabile se ţine seama de racordul de alimentare cu apă al tamburului să fie prevăzut cu o manta interioară de protecţie; de asemenea, prin modul de distribuţie în tambur a apei de alimentare, trebuie să se ferească orificiile şi pereţii de contactul cu acesta. Calculul camerelor de apă şi emulsie este identic cu al tamburelor . Coeficientul de adaos este : c ≥ 1 mm . Grosimea camerei nu poate fi mai mică de 5 mm. Camerele în care se mandrinează ţevi vor avea grosimea minimă a pereţilor de 16 mm . 8.3.2. Calculul ţevilor Ţevile folosite în construcţii suprafeţelor de încălzire a cazanelor şi a conductelor aferente în porţiunile drepte, se calculează cu relaţia :

cp

Dps

a

e ++⋅⋅

⋅=

ϕσ2 (cm) (8.6)

Relaţia este valabilă în cazurile : - s/De ≤ 0,2 pentru ţevi are conţin apă, amestec apă – abur sau abur saturat - s/De ≤ 0,28 pentru ţevi are conţin abur supraîncălzit .

Temperatura de calcul a peretelui se ia : tp=tr + 25 ÷ 500C . Adaosul la grosimea de calcul va fi: c ≥ 0,5 mm . Verificările suplimentare: ţevile supuse la sarcini constante exterioare mari,

provenite din greutatea proprie, a izolaţiei termice, trebuie să fie verificare cu privire la solicitările suplimentare introduse de acestea. Solicitarea dezvoltată de sarcinile exterioare trebuie să satisfacă condiţia :


260

a

ararext ,,

σσσσ −≤ 21870 (8.7)

în care : arσ este (0,8 ÷ 0,9) eσ pentru elemente încălzite .

isext , σσσ 80+= (8.8)

unde : o

s SN

=σ şi WM i

i =σ .

În aceste relaţii N şi Mi sunt solicitările în ţeavă, So secţiunea şi W modulul de rezistenţă al ţevii . Conductele cu temperatura mediului interior de cel puţin 3500C trebuie să fie verificare, după necesitate, în raport cu felul construcţiei, la solicitarea de încovoiere datorită efortului termic dat de dilatarea termică. Efortul datorită încovoierii trebuie să satisfacă condiţia :

exta

ararac ,, σ

σσ

σσ 2512112

−

−≤ (8.9)

iar

WM i

ac =σ

Verificarea la efort termic, trebuie făcută în condiţiile extreme ale stării la cald şi la rece ale conductei . Pentru ţevi supuse la presiune exterioară, grosimea minimă a peretelui ţevii (cu diametrul exterior peste 200 mm) se determină cu relaţia (8.6) cu menţiunea că rezistenţa admisibilă este egală cu 0,7 din mărimea adoptată pentru calculul sub presiune interioară . 8.4. Calculul grosimii pereţilor tuburilor de flacără Tuburile de flacără se execută netede sau ondulate şi cu grosimi cuprinse între 7 şi 20 mm . Grosimea peretelui tubului de flacără se calculează cu relaţiile:

- pentru tuburi netede :

20110150 ,)Dl(p

alpD,s

ir

i +

+++=

σ (cm) (8.10)

- pentru tuburi ondulate :


261

20030 ,pD

,sr

i +=σ (cm) (8.11)

în care: Di – diametrul interior al tubului de flacără sau diametrul interior minim la tuburile

ondulate, în cm ; σr – rezistenţa la rupere la 200C, în daN/cm2 ; l – lungimea tubului cuprinsă între două consolidări (fig. 8.1) sau între consolidări şi funduri sau plăci tubulare, în cm ; a – un coeficient egal cu :

- 75 pentru tuburi uzuale fără îmbinare sau cu îmbinare longitudinală, aşezate orizontal ;

- 45 pentru tuburi aşezate vertical .

Înălţimea ondulaţiei la tuburile de flacără trebuie să fie de cel puţin 35 mm iar pasul ondulaţiei nu mai mare de 200 mm . Înălţimea consolidărilor trebuie să fie de cel puţin 35 mm şi să ofere elasticitate suficientă tubului care se dilată mai mult decât mantaua cazanului . În figura 8.1 sunt arătate câteva consolidări folosite la tuburile de flacără netede sau ondulate . Lungimea l între două consolidări nu trebuie să fie mai mare decât 6Di şi cel mult de 5 m .

Fig. 8.1. Consolidări ale tubului de flacără

s

>s

l l

>5s

Di

l l

Di

s

s

Di

r1 r2 r2 90

80

s

l l

b>2s

h>5s

Di


262

8.5. Calculul fundurilor şi al capacelor Dimensiunile principale ale fundurilor bombate sunt indicate în figura 8.2 . Normele pentru construcţia acestor funduri prevăd ca : R ≤ Di şi r ≥ 0,1 Di . Grosimea de tablă necesară este dată de relaţia :

cypD

s e +⋅

=σ2 (cm) (8.12)

Adaosul c se ia 0,10 cm la d < 30 mm şi 0 la d > 30 mm . unde d este diametrul găurii (gaură de vizitare sau de inspectare).

Fig. 8.2. Fund bombat. Valoarea coeficientului de forma y este dată în tabelul 8.11, în funcţie de bombajul relativ al fundului şi de prezenţa găurilor neîntărite sau a gurilor de vizitare

cu caracteristica geometrică : sD/d e ⋅ .

Tabelul 8.11

R

s

Di

De

r

h

e

d


263

Coeficienţii de forma y

sD/d e ⋅ 0 0,5 1 2 3 4 5 h/De

y la fund fără găuri y la funduri cu găuri neîntărite sau guri de vizitare 0,18 0,2

3,14 2,9

3,4 2,9

3,4 2,9

3,92 3,7

4,85 4,6

5,75 5,5

6,75 6,5

0,225 0,25

2,4 2,0

2,4 2,0

2,58 2,3

3,42 3,2

4,35 4,1

5,25 5,0

6,2 5,9

0,30 0,40 0,50

1,55 1,15 1,1

1,61 1,27 1,2

2,0 1,7 1,6

2,9 2,5 2,2

3,75 3,32 3,0

4,6 4,05 3,7

5,4 4,75 4,35

Relaţia (8.12) este valabilă în următoarele condiţii: - raportul s/De are valorile: 0,003 ≤ s/De ≤ 0,16 ; - funduri semisferice, în orice condiţii; - funduri eliptice dacă h/De ≥ 0,18; d/De ≤ 0,5 ; - funduri mâner de coş dacă R ≤ De, r ≥ 0,1 De :

r1 ≥ 3 mm ; h ≥ 0,18 De 8.6. Calculul plăcilor tubulare Plăcile tubulare se consolidează în porţiunea rămasă în afara fascicolului de ţevi, cu mijloace adecvate, ori de câte ori valoarea presiunii de lucru a cazanului impune aceasta . În porţiunea în care se fixează fascicolului de ţevi în placa tubulară pot avea loc două cazuri :

a. Placa tubulară se consolidează prin ancore speciale sau mai multe, prin ţevi – ancore, filetate, grosimea peretelui calculându-se cu relaţia :

arc

Pdksσ

⋅= (cm) (8.13)

în care: dc – diametrul cercului cel mai mare care se poate înscrie în spaţiul liber dintre locurile ancorate ; k – este un coeficient egal cu 0,34 ÷ 0,5 . Ţevile se madrinează, iar pentru placa tubulară grosimea minimă va fi

s = 0,5 + 0,125 dc (cm), unde dc este diametrul orificiului. Distanţa dintre ancore se alege de cel mult 200 mm .


264

b. Placa tubulară nu se consolidează în mod special, în acest caz se verifică rezistenţa îmbinării prin mandrinare a ţevilor în ceea ce priveşte smulgerea din orificiu, determinându-se valoarea încărcării specifice q (daN/cm) pe unitatea de lungime a circumferinţei ţevii cu relaţia :

cdApq

⋅⋅

=π (daN/cm) (8.14)

în care: A este suprafaţa plăcii tubulare dintre patru ţevi (figura 8.2 suprafaţa haşurată).

Fig. 8.3. Aşezarea ţevilor în placa tubulară

4

2cdhtA π

−⋅= (cm2)

de – diametrul exterior al ţevii (cm) ; do – diametrul orificiului (do = de + 0,1), (cm) p – presiunea în daN/cm2 . Încărcarea q trebuie să corespundă valorilor : q ≤ 4 pentru ţevi mandrinate în orificii netede sau în canale inelare ; q ≤ 5 pentru ţevi mandrinate şi cu unul din capete răsfrânt ;

q ≤ 7 pentru ţevi mandrinate şi cu ambele capete răsfrânte . Pentru ţevile sudate în placa tubulară, îmbinarea trebuie să corespundă condiţiilor :

)dd(,hd ie22

4251 −≥⋅⋅

ππ din care se deduce valoarea lui h .

Plăcile tubulare, supuse la încovoiere în interiorul porţiunii haşurate, se verifică cu relaţia :

h

t

de/di

M

N P

R

Q


265

54701360

2 ,es

ed

,

P r

ei

σσ ≤

−

= (daN/cm2) (8.15)

în care : 2ECAEe +

= (mm)

În calculul suprafeţelor marginale ale plăcilor tubulare se poate considera că sarcina este preluată până la 1/2 din valoarea sa direct de către peretele cazanului aflat în vecinătate .


CAZANE

266

ANEXA 1

ECHIVALENTA INTRE UNITATILE DE MASURA DIN

SISTEMELE SI si MkgS

Sistemul de unitati Nr.

crt. Denumirea

SI MkgS Relatii de conversie

1 Masa kg kgf ⋅ s2/m -

2 Densitate kg/m3 kgf ⋅ s

2/m

4 -

3 Forta N kgf 1N ≅ 0,102 kgf; 1 kgf ≅ 9,81 N

4 Presiune N/m

2 (Pa);

bar

kgf/cm2; at;

kgf/m2

1 N/m2 = 10

-5 bar = 0,102 kgf/m

2 = 7,5⋅10

-3 torr;

1 bar = 105 N/m

2 = 750 torr;

1 kgf/m2 = 1 mm H2O;

at = 1 kgf/cm2 = 735,6 torr.

5 Energie J; kWh kgf ⋅ m; kcal;

BTU

1 J = 0,102 kgf⋅m = 1/4185,5 kcal;

1 kWh = 3,6⋅106 J;

1 BTU = 0,252 kcal = 1,055 kJ;

1 kcal = 4,185 kJ = 3,968 BTU.

6 Putere W = J/s;

kW

kgf⋅m/s;

kcal/h; CP;

BTU/h

1 W ≅ 0,102 kgf⋅m/s = 1,36⋅10-3

CP;

1 kW = 103 W = 860 kcal/h;

1 kcal/h = 1,163 W = 3,968 BTU/h;

1CP = 0,735 kW.

7 Calduri specifice J/kg⋅K kcal/kgf⋅oC 1 kcal/kgf⋅

oC = 4,1855 kJ/kg⋅K

8 Conductivitate

termica W/m⋅K kcal/m⋅h⋅

oC 1 kcal/m⋅h⋅

oC = 1,163 W/mK

9

Coeficient de

schimb superficial

prin convectie W/m

2⋅K kcal/m

2⋅h⋅

oC 1 kcal/m⋅h⋅

oC = 1,163 W/mK

10 Vascozitate

cinematica m

2/s m

2/s -

11 Vascozitate

dinamica N⋅s/m

2 kgf⋅s/m

2 1 kgf⋅s/m

2 = 9,81 N⋅s/m

2


CAZANE

267

ANEXA 2

35235,(7��,/(�),=,&( ALE AERULUI, LA p = 0,981 bar

t

[oC]

ρ

[kg/m3]

cp

[kJ/Nm3

K]

λ· 102

[W/m

K]

a· 106

[m2/s]

η· 106

[Ns/m2]

ν· 106

[m2/s]

Pr

1 2 3 4 5 6 7 8

-50

-20

1,532

1,350

1,2963

1,2969

2,00

2,28

13,1

16,8

14,538

16,157

9,490

11,97

0,71

0,71

0

10

20

30

40

50

1,251

1,207

1,166

1,127

1,091

1,057

1,2971

1,2971

1,2971

1,2971

1,2971

1,2971

2,438

2,51

2,58

2,65

2,72

2,79

19,2

20,7

22,0

23,4

24,8

26,2

17,197

17,697

18,198

18,688

19,169

19,640

13,75

14,66

15,61

16,58

17,57

18,58

0,71

0,71

0,71

0,71

0,71

0,71

60

70

80

90

100

1,026

0,996

0,967

0,941

0,916

1,3044

1,3044

1,3044

1,3044

1,3059

2,86

2,92

2,99

3,06

3,12

27,6

29,2

30,6

32,2

33,6

20,111

20,572

21,023

21,474

21,906

19,60

20,65

21,74

22,82

23,91

0,71

0,71

0,71

0,71

0,71

120

140

160

180

200

0,869

0,827

0,789

0,754

0,7220

1,3096

1,3147

1,3147

1,3199

1,3239

3,25

3,37

3,49

3,62

3,74

37,0

40,0

43,3

47,0

49,7

22,779

23,622

24,446

25,251

26,016

26,21

28,66

31,01

33,49

35,03

0,71

0,71

0,71

0,71

0,71

250

300

350

400

500

0,6530

0,5960

0,5482

0,5075

0,4418

1,3367

1,3502

1,3639

1,3808

1,4118

4,06

4,37

4,64

4,91

5,45

60,0

68,9

80,0

89,4

113,2

27,919

29,724

31,431

33,099

36,160

42,75

49,87

57,33

65,22

81,85

0,71

0,71

0,72

0,72

0,72

600

700

800

900

1000

0,3912

0,3510

0,3183

0,2916

0,2683

1,4411

1,4679

1,4918

1,5127

1,5311

5,98

6,47

7,00

7,40

7,84

133,6

162,0

182

216

240

39,063

41,751

44,301

46,696

49,011

99,83

118,95

139,18

160,14

182,67

0,73

0,73

0,73

0,74

0,74

1100

1200

0,2487

0,2319

1,5470

1,5617

8,26

8,66

277

301

51,218

53,376

205,94

230,17

0,74

0,74


CAZANE

268

ANEXA 3

PROPRIE7��,/(�7(502',1$0,&(�$/(�$3(,�ù,�$/(�$%858/8,�Ì1�67$5(�'(�6$785$�,(��Ì1�)81&�,(�'(�7(03(5$785�

t

[oC]

T

[K]

p

[bar]

v’

[m3/kg]

v”

[m3/kg]

ρ”

[kg/m3]

i’

[kJ/kg]

i”

[kJ/kg]

r

[kJ/kg]

1 2 3 4 5 6 7 8 9

99 372,15 0,9775 0,0010427 1,730 0,5780 414,9 2674 2259

100

101

102

103

104

373,15

374,15

375,15

376,15

377,15

1,0132

1,0499

1,0876

1,1265

1,1666

0,0010435

0,0010443

0,0010450

0,0010458

0,0010466

1,673

1,618

1,566

1,515

1,466

0,5977

0,6181

06386

0,6601

0,6821

419,1

423,3

427,5

431,7

436,0

2676

2677

2679

2680

2681

2257

2254

2251

2248

2245

105

106

107

108

109

378,15

379,15

380,15

381,15

382,15

1,2079

1,2504

1,2941

1,3390

1,3852

0,0010474

0,0010482

0,0010490

0,0010498

0,0010507

1,419

1,374

1,331

1,289

1,249

0,7047

0,7278

0,7513

0,7758

0,8006

440,2

444,4

448,6

452,9

457,1

2683

2685

2687

2688

2689

2243

2241

2238

2235

2232

110

112

114

116

118

383,15

385,15

387,15

389,15

391,15

1,4326

1,5316

1,6361

1,7464

1,8628

0,0010515

0,0010532

0,0010549

0,0010567

0,0010585

1,210

1,137

1,069

1,005

0,9465

0,8264

0,8795

0,9354

0,9950

1,056

461,3

469,8

478,2

486,7

495,2

2691

2694

2697

2700

2703

2230

2224

2219

2213

2208

120

122

124

126

128

393,15

395,15

397,15

399,15

401,15

1,9854

2,1144

2,2502

2,3932

2,5434

0,0010603

0,0010621

0,0010640

0,0010638

0,0010677

0,8917

0,8407

0,7930

0,7486

0,7074

1,121

1,189

1,261

1,336

1,414

503,7

512,2

520,8

529,2

537,7

2706

2709

2712

2715

2718

2202

2197

2191

2186

2180

130

132

134

136

138

403,15

405,15

407,15

409,15

411,15

2,7011

2,8668

3,041

3,222

3,414

0,0010697

0,0010717

0,0010737

0,0010757

0,0010777

0,6683

0,6321

0,5981

0,5664

0,5366

1,496

1,582

1,672

1,765

1,864

546,3

554,8

563,2

571,8

580,4

2721

2723

2725

2728

2731

2174

2168

2162

2156

2151

140

142

144

146

148

413,15

415,15

417,15

419,15

421,15

3,614

3,823

4,042

4,271

4,510

0,0010798

0,0010819

0,0010840

0,0010862

0,0010884

0,5087

0,4824

0,4379

0,4347

0,4130

1,966

2,073

2,184

2,300

2,421

589,0

597,6

606,2

614,8

623,4

2734

2737

2739

2742

2744

2145

2139

2133

2127

2121

150

152

154

156

158

423,15

425,15

427,15

429,15

431,15

4,760

5,020

5,293

5,576

5,872

0,0010906

0,0010928

0,0010950

0,0010974

0,0010998

0,3926

0,3733

0,3552

0,3381

0,3220

2,547

2,679

2,815

2,958

3,106

632,2

641,0

649,6

658,2

666,9

2746

2749

2752

2754

2756

2114

2108

2102

2096

2089


CAZANE

269

t

[oC]

T

[K]

p

[bar]

v’

[m3/kg]

v”

[m3/kg]

ρ”

[kg/m3]

i’

[kJ/kg]

i”

[kJ/kg]

r

[kJ/kg]

1 2 3 4 5 6 7 8 9

160

162

164

166

168

433,15

435,15

437,15

439,15

441,15

6,180

6,502

6,836

7,183

7,545

0,0011021

0,0011044

0,0011069

0,0011094

0,0011119

0,3068

0,2925

0,2790

0,2662

0,2541

3,238

3,419

3,584

3,757

3,935

675,5

684,2

692,9

701,7

710,5

2758

2760

2762

2764

2767

2082

2076

2069

2062

2056

170

172

174

176

178

443,15

445,15

447,15

449,15

451,15

7,920

8,311

8,716

9,137

9,574

0,0011144

0,0011169

0,0011195

0,0011221

0,0011218

0,2426

0,2318

0,2215

0,2118

0,2026

4,122

4,314

4,515

4,721

4,936

719,2

727,9

736,7

745,5

754,3

2769

2771

2773

2774

2776

2050

2043

2036

2029

2022

180

185

190

195

200

453,15

458,15

463,15

468,15

473,15

10,027

11,234

12,553

13,989

15,551

0,0011275

0,0011344

0,0011415

0,0011489

0,0011566

0,1939

0,1739

0,1564

0,1409

0,1272

5,157

5,750

6,394

7,097

7,662

763,1

785,2

807,5

829,9

852,4

2778

2782

2786

2790

2793

2015

1997

1979

1960

1941


CAZANE

270

ANEXA 4

PROPR,(7��,/(�7(502',1$0,&(�$/(�$3(,�ù,�$/(�$%858/8,�Ì1�67$5(�'(�6$785$�,(�Ì1�)81&�,(�'(�35(6,81(

p

[bar]

t

[oC]

v’

[m3/kg]

v”

[m3/kg]

ρ”

[kg/m3]

i’

[kJ/kg]

i”

[kJ/kg]

r

[kJ/kg]

1 2 3 4 5 6 7 8

1,00

1,1

1,2

1,3

1,4

99,01

102,32

104,81

107,14

109,23

0,0010432

0,0010452

0,0019472

0,0010492

0,0010510

1,694

1,550

1,429

1,325

1,230

0,5903

0,6453

0,0999

0,7545

0,8098

417,4

428,9

432,4

449,2

458,5

2675

2679

2683

2687

2690

2258

2499

2244

2238

2232

1,5

1,6

1,7

1,8

1,9

111,38

113,32

115,47

116,94

118,62

0,0010527

0,0010543

0,0010559

0,0010575

0,0010590

1,159

1,091

1,031

0,9772

0,9290

0,8627

0,9164

0,9699

1,223

1,076

467,2

475,4

483,2

490,7

497,9

2693

2696

2699

2702

2704

2226

2221

2216

2211

2206

2,0

2,2

2,4

2,6

2,8

120,23

123,27

128,09

128,73

131,20

0,0010605

0,0010633

0,0010659

0,0010685

0,0010709

0,8834

0,8098

0,7465

0,6925

0,6461

1,129

1,235

1,340

1,444

1,548

504,8

517,8

529,8

540,9

551,4

2707

2711

2715

2719

2722

2202

2193

2185

2178

2171

3,0

3,2

3,4

3,6

3,8

133,34

135,35

137,86

139,87

141,79

0,0010723

0,0010784

0,0010776

0,0010797

0,0010817

0,6057

0,5701

0,5386

0,5404

0,4852

1,651

1,754

1,867

1,959

2,001

561,4

571,1

580,2

588,7

596,8

2720

2728

2731

2734

2736

2164

2157

2151

2145

2139

4,0

4,2

4,4

143,62

143,39

147,09

0,0010836

0,0010855

0,0010874

0,4624

0,4416

0,4227

2,163

2,264

2,366

601,7

612,3

619,8

2738

2741

2743

2133

2129

2123

4,6

4,8

5,0

5,4

5,8

6,2

6,6

148,73

150,31

151,84

154,76

157,52

166,12

162,59

0,0010892

0,0010910

0,0010927

0,0010960

0,0010992

0,0011022

0,0011052

0,4054

0,3895

0,3747

0,3485

0,3258

0,3060

0,2885

2,467

2,568

2,669

2,869

3,069

3,268

3,467

626,9

633,7

640,1

652,7

664,7

670,0

686,9

2745

2747

2749

2752

2755

2758

2761

2118

2113

2109

2009

2090

2082

2074

7,0

7,4

7,8

8,2

8,6

164,96

167,21

169,37

171,44

173,43

0,0011081

0,0011109

0,0011136

0,0011162

0,0011187

0,2728

0,2588

0,2462

0,2347

0,2243

3,666

3,864

4,062

4,250

4,458

697,2

707,1

715,4

725,4

734,2

2764

2766

2768

2770

2772

2067

2059

2052

2045

2038

9,0

9,4

9,8

10,0

175,35

177,21

179,01

179,88

0,0011213

0,0011237

0,0011261

0,0011273

0,2149

0,2061

0,1982

0,1940

4,654

4,852

5,045

5,139

742,8

750,9

758,8

762,7

2774

2776

2778

2778

2031

2025

2019

1015


CAZANE

271

ANEXA 5

35235,(7��,/(�),=,&(�$/(�$3(,��3(�&85%$�'(�6$785$�,(

t

[oC]

ρ

[kg/m3]

β · 10 4

[grd]-1

i’

[kJ/kg] λ

[W/m· K

]

a · 10 4

[m2/h]

η · 10 4

[Ns/m2]

ν · 10 6

[m2/s]

Pr

1 2 3 4 5 6 7 8 9

0

10

20

30

40

50

999,8

999,6

998,2

995,6

992,2

988,0

-0,7

0,95

2,1

3,0

3,9

4,6

0

12,03749

83,90788

25,69374

67,52187

209,30813

0,5513

0,5745

0,5989

0,6176

0,6338

0,6478

4,71

4,94

5,16

5,35

5,51

5,66

1788,363

1305,711

1004,544

801,477

653,346

549,360

1,790

1,300

1,000

0,805

0,659

0,556

13,7

9,5

7,0

5,4

4,3

3,55

60

70

80

90

100

983,2

977,7

971,8

965,3

958,3

5,3

5,8

6,3

7,0

7,5

251,13626

293,00626

334,96000

376,99748

419,11870

0,6594

0,6676

0,6745

0,6804

0,6827

5,79

5,89

5,97

6,03

6,08

469,899

406,134

355,122

314,901

282,528

0,479

0,415

0,366

0,326

0,295

3,00

2,55

2,25

1,95

1,75

110

120

130

140

150

951,0

943,1

934,8

926,1

916,9

8,0

8,5

9,1

9,7

10,3

461,36553

503,6961

546,4035

589,1109

832,2370

0,6850

0,6862

0,6862

0,6850

0,6838

6,12

6,15

6,18

6,20

6,21

258,984

277,592

217,782

201,105

186,390

0,268

0,244

0,226

0,212

0,202

1,57

1,43

1,32

1,23

1,17

160

170

180

190

200

907,4

397,3

886,9

876,0

864,7

10,8

11,5

12,1

12,8

13,5

657,3631

719,3266

763,2901

807,6723

852,4732

0,6827

0,6792

0,6745

0,6699

0,6629

6,21

6,20

6,19

6,16

6,11

173,637

162,846

153,036

144,207

136,359

0,191

0,181

0,173

0,166

0,160

1,10

1,05

1,01

0,97

0,95

210

220

230

240

250

852,8

840,3

827,3

813,6

799,2

14,3

15,2

16,2

17,2

18,6

897,6928

943,7498

989,8068

1037,5386

1085,6891

0,6548

0,6455

0,6373

0,6280

0,6176

6,06

6,00

5,92

5,84

5,74

130,473

124,587

119,582

114,777

109,872

0,154

0,149

0,145

0,141

0,137

0,92

0,90

0,88

0,86

0,86

260

270

280

290

300

784,0

767,9

750,7

732,3

712,5

20,0

21,7

23,8

26,5

29,5

1135,7957

1185,8897

1236,8398

1290,8147

1344,8644

0,6048

0,5896

0,5745

0,5582

0,5396

5,62

6,18

6,30

5,05

4,75

105,943

102,024

98,100

94,176

91,233

0,135

0,133

0,131

0,129

0,128

0,86

0,87

0,89

092

098


CAZANE

272

ANEXA 6

35235,(7��,/(�),=,&(�$/(�*$=(/25�'(�$5'(5(�/$�35(6,81($�'(��EDU

�&RPSR]L LD�JD]HORU�� 76,0r;11,0r;13,0r222 NOHCO

=== )

t

[oC]

ρ

[kg/m3]

cp

[kJ/Nm3

K]

λ· 10 2

[W/m]

a · 10 2

[m2 /h]

η· 10 2

[N s/m2]

ν· 10 6

[m2/s]

Pr

1 2 3 4 5 6 7 8

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

0,295

0,950

0,748

0,617

0,525

0,457

0,405

0,363

0,329

0,301

0,275

0,257

0,240

1,0425

1,0676

1,0969

1,1221

1,5114

1,1849

1,2142

1,2393

1,2644

1,2895

1,3063

1,3230

1,3398

2,2794

3,1284

4,0123

4,8380

5,6987

6,5593

7,4199

8,2689

9,1528

10,0134

10,8973

11,7463

12,6185

6,08

11,10

17,60

25,16

35,04

43,61

54,32

66,17

79,09

92,87

109,21

124,37

141,27

15,7842

20,3943

24,1955

28,2331

31,6863

43,8549

37,8666

40,6918

43,3798

45,9108

48,3633

50,7078

52,9936

12,20

21,54

32,80

45,81

60,38

76,30

93,61

112,1

131,8

152,8

174,3

197,1

221,0

0,72

0,69

0,67

0,65

0,64

0,63

0,62

0,61

0,60

0,59

0,58

0,57

0,56


CAZANE

273

ANEXA 7

&�/'85,/(�63(&,),&(�$/(�8125�*$=(�>N-�1P3· K]

pc [kJ/Nm3

· K] t

[oC]

CO2 N2 O2 H2O Aer usc.

Aer um.

1 2 3 4 5 6 7

0

100

200

300

400

1,5998

1,7003

1,7873

1,8627

1,9297

1,2946

1,2958

1,2996

1,3067

1,3163

1,3059

1,3176

1,3352

1,3561

1,3775

1,4943

1,5051

1,5223

1,5424

1,5654

1,2971

1,3004

1,3071

1,3172

1,3235

1,3188

1,3243

1,3318

1,3423

1,3544

500

600

700

800

900

1,9887

2,0411

2,0884

2,1311

2,1692

1,3276

1,3435

1,3536

1,3670

1,3720

1,3980

1,4168

1,4344

1,4499

1,4637

1,5897

1,6148

1,6412

1,6680

1,6954

1,3427

1,3565

1,3708

1,3842

1,3975

1,3652

1,3829

1,3975

1,4114

1,4248

1000

1100

1200

1300

1400

2,2035

2,2349

2,2638

2,2898

2,3136

1,3917

1,4034

1,4143

1,4252

1,4348

1,4775

1,4892

1,5005

1,5106

1,5203

1,7229

1,7501

1,7769

1,8028

1,8280

1,4097

1,4214

1,4327

1,4432

1,4528

1,4373

1,4499

1,4612

1,4725

1,4830

1500

1600

1700

1800

1900

2,3354

2,3555

2,3743

2,3915

2,4074

1,4440

1,4528

1,4612

1,4687

1,4788

1,5294

1,5378

1,5462

1,5541

15617

1,8527

1,8761

1,8895

1,9213

1,9423

1,4620

1,4708

1,4788

1,4867

1,4938

1,4926

1,5018

1,5102

1,5177

1,5257

2000

2100

2200

2300

2400

2500

2,4221

2,4359

2,4484

2,4602

2,4700

2,4811

1,4825

1,4892

1,4951

15010

1,5064

1,8114

1,5892

1,5759

1,5830

1,5897

1,5964

1,6027

1,9628

1,9824

2,0009

2,0189

2,0365

2,0628

1,5010

1,5072

1,5135

1,5194

1,6252

1,5303

1,5128

1,5399

1,5462

1,5526

1,5583

1,5638


CAZANE

274

ANEXA 8

ENTALPIA GAZELOR PRODUSE ALE ARDERII [kJ/ Nm3]

t

[oC]

CO2 N2 O2 H2O Aer usc.

Aer um.

1 2 3 4 5 6 7

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

2200

2300

2400

2500

0

171,27

395,12

561,15

774,80

798,05

1229,28

1467,27

1711,04

1959,21

2212,50

2469,17

2728,80

2989,87

3253,88

3519,60

3787,04

4056,54

4327,56

4598,95

4872,00

5146,26

5420,80

5698,02

5969,76

6251,00

0

129,59

260,02

391,80

526,24

663,65

804,00

947,31

1092,96

1240,92

1391,80

1544,29

1697,76

1852,24

2009,98

2166,75

2324,64

2484,04

2643,84

2804,97

2966,00

3127,53

3291,20

3452,30

3614,40

3778,75

0

131,73

267,06

406,86

551,00

698,80

850,14

1003,80

1159,92

1317,78

1477,10

1637,79

1800,24

1963,26

2127,72

2293,50

2459,84

2627,86

2796,66

2966,47

3136,80

3308,55

3461,72

3654,47

3830,40

4005,75

0

150,52

304,30

462,60

626,00

794,45

968,40

1148,56

1334,40

1525,68

1722,40

1924,56

2131,68

2343,12

2559,06

2778,30

3001,60

3228,30

3458,16

9690,18

3924,40

4162,83

4401,54

4842,09

4886,16

5130,50

0

130,00

261,42

395,18

531,58

671,15

813,90

959,56

1107,28

1257,39

1408,30

1563,50

1718,76

1876,16

2034,48

2193,60

2353,92

2514,64

2678,08

2838,98

3001,80

3165,96

3329,70

3495,54

3660,48

3826,50

0

132,39

268,28

402,57

541,60

683,90

829,50

977,97

1128,72

1281,87

1436,90

1594,34

1752,84

1913,60

2075,50

2238,15

2402,08

2566,49

2730,95

2897,88

3064,60

3232,74

3400,54

3569,60

3738,72

3908,25


CAZANE

275

ANEXA 9

VALORILE CONSTANTELOR FIZICE

$/(�*$=(/25�'(�$5'(5(�ù,�$/(�$(58/8,

Gaze de ardere Aer

ν· 106 λ· 10

2 Pr ν· 106 λ· 10

2 Pr

t

[oC]

[m2/s] [W/m· K] - [m

2/s] [W/m· K] -

1 2 3 4 5 6 7

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1500

1600

12,2

21,5

32,8

45,8

60,4

76,3

93,6

112

132

152

174

197

221

245

272

297

323

2,28

3,13

4,01

4,85

5,70

6,55

7,42

8,27

9,16

10,02

10,9

11,75

12,55

13,5

14,42

15,33

16,3

0,72

0,69

0,67

0,66

0,64

0,63

0,62

0,61

0,60

0,59

0,58

0,57

0,56

0,55

0,54

0,53

0,52

13,3

23,0

34,8

48,2

63,0

79,3

96,8

116

135

155

178

199

223

248

273

300

328

2,43

3,12

3,74

4,37

4,91

5,45

5,98

6,47

7,00

7,40

7,84

8,26

8,66

9,45

9,98

10,39

10,8

0,71

0,71

0,71

0,71

1U��F

UW�&R

QGLWLL�

IL]LFH

�GH�SU

RFHV

/XQJ

LPHD

�FD

UDFWH�

��

ULVWLFD

(FXD

WLD�FU

LWHULD

OD'R

PHQLX

�GH�YD

ODELOLWD

WH2E

VHUYD

WLL

�6X

SUDIDW

D�RUL]RQ

WDOD�F

LOLQGUL

FDG

G��GL

DPHWU

XO�H[

WHULRU

�DO�

FLOLQG

UXOXL

�&R

QGXF

WH�FX

�DULSLR

DUH�GH

�JUR

VLPH�F

RQVWD

QWDG��

�KK��

�LQDOW

LPHD

�DUL

SLDRD

UHL��

��

E��GL

VWDQWD

�OLEHUD

�GLQ

WUH�DU

LSLRDUH

�3OD

FL�SODQ

H�SDUD

OHOHV

V��GL

VWDQWD

�GLQWU

H�SOD

FL

II.

Co

nv

ec

tia

lib

era

in

sp

ati

i li

mit

ate

AN

EX

A 1

0

EC

UA

TII C

RIT

ER

IAL

E P

EN

TR

U D

ET

ER

MIN

AR

EA

CO

EF

ICIE

NT

UL

UI D

E C

ON

VE

CT

IE

Ec

ua

tii

cri

teri

ale

la

co

nv

ec

tia

fa

ra s

ch

imb

are

a s

tari

i d

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gre

ga

re

I. C

on

ve

cti

a l

ibe

ra i

n s

pa

tii

ne

lim

ita

te

[]

()41

916

169

2

61

Pr

40

,0

Pr

559

,0

1(P

r)

(Pr)

.P

r387

,0

60

,0

⋅⋅

=

+

=

⋅⋅

+=

−

Gr

Nu

sau

f

fG

rN

u

95

10

G

r.P

r

1

0<

<

51

0

Gr.

Pr

<

aer

pen

tru

-

Pr

24

,0

31

⋅⋅

⋅=

dbG

rN

u7

31

0

Gr.

Pr

10

<<

()

()

35

,041

Pr

09

2,

0

Pr

20

8,

0

⋅⋅

=

⋅⋅

=

Gr

Nu

Gr

Nu

4

4

10

2,2

G

r.P

r

10

2,2

G

r.P

r

1708

708

1 G

r.P

r

⋅>

⋅<

<<1

=N

u

1U��F

UW�&R

QGLWLL�

IL]LFH

�GH�SU

RFHV

/XQJ

LPHD

�FD

UDFWH�

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��ULV

WLFD(F

XDWLD

�FULWH

ULDOD

'RPH

QLX�GH

�YDODE

LOLWDWH

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UYDWLL

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UJHUHD

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ORU�LQ

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XO�VX

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LPHD

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dia

me

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al

conducte

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circula

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ch��G

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III.

Co

nv

ec

tia

fo

rta

ta

25

,0

22

32

1,0

8,031

21

PrPr

1P

rR

e443

,2

1

Pr

Re

037

,0

Pr

Re

664

,0

⋅

+=

−⋅

⋅+

⋅⋅

=

⋅⋅

=

−

p

turb

lam

turb

lam

Nu

Nu

Nu

Nu

Nu

7

75

5 10

Re

10

10

Re

10

5

10

5

Re

<<

<<

⋅

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()

()

11

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2

32

32

11

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2

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ra

cire

pt.

0,1

1

m

fluid

in

c.

pt.

0,2

5m

1b

pt.

4

1

1b

pt.

4

1

Re ==

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⋅−

=

≥⋅

−=

⋅⋅=

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lw

πψ

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υψ

61

0

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01

<<

()

rel.7

co

nform

tev

i,de

rand

sing

ur

un

pen

tru

3

21

PrPr

11

1

1

Nu

Nu

b

Nu

n

nN

u

m

p

=

⋅+

=

⋅

⋅⋅

−+

=

ω

ω

()

fort

ata

co

nvec

tia

la de

re

l.

conf

orm

liber

a

conv

ectia

la

de

re

l.

conf

orm

:fo

rtat

a

curg

erea

de

fa

ta

opus

se

nsin

leas

cens

iona

F

ort

ele

:fo

rtat

a

curg

erea

cu

se

ns

acel

asi

in

le

asce

nsio

na

Fort

ele

33

313

3

−−

−=

+= fo

rta

t

lib

er

lib

erfo

rta

t

fort

at

lib

er

Nu

Nu

Nu

Nu

Nu

Nu

Nu

Nu

5

cr

10

7P

rRe

R

e

⋅>

⋅<

Gr


CAZANE

281

ANEXA 11

180�58/�'(��(9,�3(�3/�&,/(�78%8/$5(

$úH]DUHD�vQ�KH[DJRQ

1XP�UXO�GH� HYL�VXSOLPHQWDUH�SH�rândurile sectoarelor, m

1XP�

UXO�G

H� HYL�

SH�

latu

ra h

exagon

ulu

i

a

1XP�

UXO�G

H� HYL�

SH�

GLDJRQD

O��

b

1XP�

UXO�G

H� HYL�

SH�

VXSUDID

D�FHD�P

DL�m

are

din

tre

hex

agoan

e

Pe

pri

mu

l râ

nd

m1

Pe

al

doil

ea

rân

d

m2

Pe

al

trei

lea

rân

d

m3

1XP�

UXO�G

H� HYL�

sup

lim

enta

re î

n t

oate

sect

oare

le

1XP�

UXO�WR

WDO�GH

� HYL�

n

1 2 3 4 5 6 7 8

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

31

33

35

37

39

41

43

45

47

49

1

7

19

37

61

91

127

169

217

271

331

397

469

517

631

721

817

919

1027

1141

1261

1387

1519

1657

1851

-

-

-

-

-

-

-

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

-

-

-

-

-

-

-

-

-

-

-

-

-

2

5

6

7

8

9

12

13

14

15

16

17

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

4

7

8

9

10

-

-

-

-

-

-

-

18

24

30

36

42

48

66

90

102

114

126

138

162

198

228

246

267

282

1

7

19

37

61

91

127

187

241

301

367

439

517

613

721

823

931

1045

1165

1303

1459

1615

1765

1981

2083


CAZANE

282

ANEXA 12

Tevi din otel fara sudura laminate la cald (SR 404/1-98)

Grosimea peretelui (mm)

3,0 3,5 4,0 5,0 6,0 8,0 10 12 14 16 18 20 22 Dia

met

rul

exte

rio

r (m

m)

Masa (kg/ml)

25 1,63 - - - - - - - - - - - -

29 1,85 2,11 - - - - - - - - - - -

32 2,14 2,46 2,76 - - - - - - - - - -

34 2,29 2,63 2,96 - - - - - - - - -

38 2,59 2,98 3,35 4,07 - - - - - - - - -

42 2,88 3,32 3,75 4,56 - - - - - - - - -

45 3,11 3,58 4,04 4,93 5,77 - - - - - - - -

48 3,33 3,84 4,34 5,30 6,21 7,89 9,37 - - - - - -

51 3,55 4,10 4,64 5,67 6,66 8,48 10,11 - - - - - -

54 3,77 4,36 4,93 6,04 7,10 9,07 10,85 12,43 - - - - -

57 3,99 4,62 5,23 6,41 7,55 9,67 11,60 13,22 - - - - -

60 - 4,88 5,52 6,78 7,99 10,26 12,33 14,20 - - - - -

63,5 - 5,18 5,87 7,21 8,51 10,95 13,19 15,24 - - - - -

70 - 5,74 6,51 8,01 9,47 12,23 14,80 17,16 19,33 21,30 - - -

73 - 6,00 6,81 8,38 9,91 12,82 15,54 18,05 20,37 22,49 - - -

76 - 6,26 7,10 8,75 10,36 13,42 16,28 18,94 21,41 23,67 - - -

83 - 6,86 7,79 9,62 11,39 14,80 18,00 21,01 23,82 26,44 28,85 - -

89 - 7,38 8,38 10,36 12,28 15,98 19,48 22,79 25,89 28,80 31,52 - -

95 - 7,90 8,98 11,10 13,77 17,16 20,96 24,56 27,97 31,17 34,18 - -

102 - - 9,67 11,96 14,20 18,54 22,69 26,63 30,38 33,93 37,29 - -

108 - - 10,30 12,70 15,09 19,73 24,20 28,41 32,45 36,30 39,95 - -

114 - - 10,85 13,44 15,98 20,91 25,65 30,19 34,53 38,67 42,61 46,36 49,91

121 - - 11,54 14,30 17,02 22,29 27,37 32,26 36,94 41,43 45,72 49,82 53,71

127 - - 12,10 15,04 17,90 23,47 28,85 34,03 39,01 43,80 48,39 52,77 56,97

133 - - 12,70 15,78 18,79 24,66 30,33 35,81 41,08 46,16 51,05 55,73 60,22

140 - - - 16,65 20,12 26,04 32,06 37,88 43,50 48,93 54,16 59,19 64,02

146 - - - 17,39 20,72 27,23 33,54 39,66 45,57 51,30 56,82 62,15 67,27

152 - - - - 21,60 28,41 35,02 41,43 47,65 53,66 59,48 65,11 70,53

159 - - - - 22,64 29,79 36,75 43,50 50,66 56,42 62,59 68,56 74,33

168 - - - - 23,97 31,57 38,96 46,17 53,17 59,98 66,59 73,00 79,21

178 - - - - 25,45 33,51 41,43 49,13 56,62 63,92 71,02 77,93 84,64

194 - - - - 27,82 36,70 45,38 53,86 62,15 70,24 78,12 85,82 93,32

219 - - - - 31,52 41,63 51,54 61,26 70,78 80,10 89,22 98,15 106,89

245 - - - - - 46,76 57,95 68,95 79,75 90,36 100,77 110,98 120,99

273 - - - - - 52,28 64,86 77,24 89,42 101,41 133,20 124,79 136,18

324 - - - - - 62,34 77,44 92,33 107,72 121,53 135,83 149,94 163,85

356 - - - - - 68,66 85,33 101,80 118,07 134,16 150,04 165,72 181,21

377 - - - - - 72,80 90,51 108,02 125,33 142,44 159,36 176,08 192,61


CAZANE

283

ANEXA 13

Tevi din otel fara sudura pentu cazane

si schimbatoare de caldura (SR 9377-90)

Grosimea peretelui (mm)

1,5 2,0 2,5 3,0 3,5 4,0 5,0 6,0 8,0 Dia

met

rul

exte

rior

(mm

)

Masa (kg/ml)

12 0,388 0,493 0,586 0,666 - - - - -

14 0,462 0,592 0,709 0,814 - - - - -

16 0,536 0,690 0,832 0,962 - - - - -

18 0,610 0,789 0,956 1,11 1,25 - - - -

20 0,684 0,888 1,08 1,26 1,42 1,58 1,85 - -

25 0,869 1,13 1,39 1,63 1,85 2,07 2,47 2,81 -

30 1,05 1,38 1,69 2,00 2,29 2,56 3,08 3,55 4,34

38 1,35 1,77 2,19 2,59 2,98 3,35 4,07 4,73 5,92

45 1,61 2,12 2,62 3,11 3,58 4,04 4,93 5,77 7,30

48 - 2,27 2,80 3,33 3,84 4,34 5,30 6,21 8,29

57 - - 3,36 3,99 - - - - -

60 - - 3,54 4,22 4,88 5,52 6,78 7,99 10,26

70 - - - 4,96 5,74 6,51 8,01 9,47 12,23

76 - - - 5,40 6,26 7,10 8,75 10,36 13,42

80 - - - 5,70 6,60 7,50 9,25 10,95 14,20

89 - - - - 7,38 8,38 10,36 12,28 15,98


CAZANE

ANEXA 14

FLANSE ROTUNDE PENTRU SUDARE

Teava FLANSE ROTUNDE PENTRU SUDARE

CONFORM STAS :

8011-84 (Pn 2,5) si 8012-84 (Pn 6) Dn

d a d1 d2 d3 b Masa

mm kg/buc

10 14 75 50 0,25

15 20 80 55 0,28

20 25 90 65

10

0,44

30 0,55 25

34 100 75

11

12 0,53

38 0,93 32

42 120 90

0,90

45 1,03 40

48 130 100

1,00

57 1,14 50

60 140 110

1,11

65 76 160 130

14 14

1,39

80 89 190 150 2,29

108 2,66 100

114 210 170

16

2,53

133 3,68 125

140 240 200 18

3,46

159 4,68 150

168 265 225 20

4,32

200 219 320 280 22 6,35

250 273

1

375 335

18

8,39

300 324 440 395 24

10,80

356 15,60 350

377 490 445 26

13,10

400 406,4 540 495 28 18,70

500 508 645 600

22

25,10

600 609,6

2

755 705 26 30

25,70

45

d2

d1

d3

b

a

d

285

AN

EX

A 1

4 (

con

tin

uare)

Tea

va

FL

AN

SE

RO

TU

ND

E P

EN

TR

U S

UD

AR

E C

ON

FO

RM

ST

AS

:

8013

-84 (

Pn 1

0)

80

14

-84

(P

n 1

6)

Dn

d

a d

1

d2

d3

b

d1

d2

d3

b

mm

Mas

a

kg/b

uc

mm

Mas

a

kg/b

uc

10

14

90

60

0,4

5

90

60

0

,45

15

20

95

65

12

0,5

0

95

65

1

2

0,5

0

20

25

105

75

0,7

4

105

7

5

0,7

4

30

0,8

8

0,8

8

25

34

115

85

14

14

0,8

6

115

8

5

14

14

0,8

6

38

1,5

0

1,5

0

32

42

140

100

1,4

7

140

1

00

1,4

7

45

1,6

4

1,6

4

40

48

150

110

16

1,6

1

150

1

10

16

1,6

1

57

2,2

2

2,2

2

50

60

165

125

2,1

8

165

1

25

2,1

8

65

76

185

145

18

2,6

6

185

1

45

18

2,6

6

80

89

200

160

20

3,2

7

200

1

60

20

3,2

7

10

8

4,1

6

4,1

6

10

0

11

4

220

180

22

3,9

7

220

1

80

22

3,9

7

13

3

5,7

5

5,7

5

12

5

14

0

250

210

18

5,4

7

250

2

10

18

5,4

7

15

9

7,0

5

7,0

5

15

0

16

8

285

240

24

6,6

6

285

2

40

24

6,6

6

20

0

21

9

340

295

26

9,4

2

340

2

95

22

26

9,1

3

25

0

27

3

1

395

350

12,1

0

405

3

55

14

,90

30

0

32

4

445

400

28

13,6

0

460

4

10

32

17

,80

35

6

20,6

0

28

,20

3

50

3

77

505

460

22

30

17,9

0

520

4

70

26

36

24

,80

40

0

40

6,4

565

515

32

16,1

0

580

5

25

30

38

34

,60

50

0

50

8

670

620

26

34

34,7

0

715

6

50

33

44

59

,30

60

0

60

9,6

2

780

725

30

36

38,6

0

840

7

70

36

48

79

,00


CAZANE

286

ANEXA 15

Dn d s H h

mm

25 31 20

28 3; 4

32

25 34 3 33

32 42 4; 6 35

40 48 4; 8 37

4; 6 40

25

50 60 10 55 40

4; 6 43 25 73

10 58 40

4; 6 44 25 65

76 10 59 40

4; 8 47 25 80 89

12 62 40

5; 8 53 25 100 114

14 68 40

6 67 25 125 140

10; 16 82 40

6 67 25 150 158

10; 16 82 40

6 80 25 200 219

12; 13 95 40

6 93 25 250 273

12; 20 108 40

6 106 25 300 324

12; 20 121

8 114

14 129

40

350 356

25 139 50

8 126 25

16 141 40 400 406

25 151 50

10; 18 154 40 450 457

25 164 50

10; 18 167 40 500 508

25 177 50

d

s

h

H

287

ANEXA 16

CRITERII DE SIMILITUDINE

Denumirea

criteriului Simbol 5HOD LH�GH�FDOFXO 6HPQLILFD LH�IL]LF��XWLOL]DUH�

1 2 3 4

Arhimede Ar Ï©Ï*DÏ

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−

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Euler Eu �ZÏS⋅

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conducte)

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Froude

(Boussinesq)

(Vedernikov)

Fr

(B)

(V) OJZ�

⋅

)RU H�GH�LQHU LH�)RU H�JUDYLWD LRQDOH

(curgerea fluidelor compresibile)

Galileu Ga ��

ÑOJ ⋅

)RU H�JUHYLWD LRQDOH�)RU H�GH�YkVFR]LWDWH

(curgerea fluidelor vâscoase)

Grashoff Gr ��

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Kutateladze Ku �W�W SOS −F

U

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tl – temperatura lichidului

tp – temperatura peretelui

Nusselt Nu ÊO.⋅

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Peclet Pe PrRe⋅=

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Prandtl Pr D

F ÌÊ

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Reynolds Re ÌOZ ⋅

)RU H�GH�LQHU LH�)RU H�GH�YkVFR]LWDWH

(curgerea fluidelor)

indrumator de proiectare cazan

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