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7/25/2019 Lic Teorie

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Introducere

Obiectivele lucrrii de fa sunt determinarea modului de funcionare al unei centrale electricede condensaie pur cu grupuri de 400 de MW care funcioneaz in regim normal i

predimensionarea circuitului de rcire aferent grupului. O central termoelectric este o central care produce energie electric pe baza conversieienergiei termice obinut prin arderea combustibililor. Pe parcursul lucrrii sunt prezentate transformrile pe care le sufer ciclul ap!abur" i variaiaparametrilor acestuia la trecerea prin punctele importante ale centralei care sunt reprezentate pesc#ema termic. $%emple de astfel de puncte sunt cele situate &n cadrul circuitlui de pre&nclzire regenerativsau &n cadrul procesului de destindere a aburului &n turbin. 'urbina este compus din trei corpuridup cum urmeaz()orp de *nalt Presiune+).I.P,)orp de Medie Presiune+).M.P., si )orp de -oas Presiune +).-.P, &n dublu flu% i este prevazutcu un condensator .

Pre&nclzirea regenerativ este se face cu autorul a opt pri%e fi%e la turbin de abur.Prinintermediul acestora este asigurat alimentarea cu abur a circuitului regenerativ care este compusdin(trei Pre&nclzitoare de *nalt Presiune +P.I.P.,/egazorul+/eg, i trei Pre&nclzitoare de -oasPresiune+P.-.P,.


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umea se confrunta acum la nivel mondial cu incalzirea globala si protectia mediului . Pede alta parte cererea de energie electrica este in crestere rapida datorita cresterii populatiei sicresterii economice . )u luarea in considerare a problemelor de mediu si dezvoltarea durabila indomeniul energiei sursele regenerabile cum ar fi energia eoliana solara energia valurilor nupot acoperi necesarul de energie electrica momentan . 1enerarea de energie electrica utilizandcombustibili fosili este inevitabila iar folosirea carbunelui este foarte importanta datorita

proprietatilor si pretului accesibil pe care acesta il are. )entralele termoelectrice conventionale auin imens impact asupra mediului si o producere a energiei cu eficienta scazuta . Orice nouacentrala pe carbune trebuie sa fie mai curata in comparatie cu centralele electrice traditionale .)entralele electrice cu parametri supracritici sunt alegerea cea mai potrivita luand in considerareimpactul acestora asupra mediului imbunatatirea eficientei energetice si economice.

Primele unitati cu parametrii supracritici au fost dezvoltate &n anii 230 250 +&ndeosebi &n678 si fosta 7966,. $le au dovedit &nsa o fiabilitate relativ cobor:ta &n principal datoritamaterialelor din care erau confectionate partile sub presiune. *n ceea ce privesc puterile unitareacestea nu au depasit &n general limita de 500MWe.

/upa anul ; )iclul termodinamic pentru o unitate conventionala cu aburcu parametrii supracritici


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Prin comparaie cu stadiul pe plan mondial &n 9om:nia producia de energie electric pebaz de crbune se realizeaz &n mod e%clusiv &n grupuri cu ardere a crbunelui &n starepulverizat dotate cu cicluri cu abur cu parametrii subcritici. Pentru un orizont de timp de ;0

;? ani centralele convenionale cu abur cu parametrii supracritici vor reprezenta principalasoluie de utilizare a crbunilor &n scopul producerii energiei electrice cu o eficien netsuperioar celor cu parametrii subcritici respectiv peste 40 @ &n cazul lignitului i peste 4? @ &ncazul #uilei.

Particularitati ale centralelor cu parametrii supracritici

;.)azanul de abur/isparitia evaporarii impune modiicarea cazanului care nu mai poate contine tambur . 8ceastaconduce la necesitatea utilizarii pentru ciclurile supracritice doar a cazanelor cu circulatiefortata unica.

=luidul de lucru trece direct din starea lic#ida in cea gazoasa in sisteme de tevi careimbraca peretele cazanului . Au mai e%ista deci un punct unic de convergenta ci o zona deconvergenta . 8cest lucru are o inluenta directa asupra suprafetei de scimb care va fi in general mai mare decat cazul cazanelor cu parametrii subcritici . Pe ansamblu inertia termica a unuiastfel de cazan este relative scazuta permitand variatii de sarcina pana la ?@ pe minut . 8cestecentrale sunt adaptate deci pentru proniri rapide si sc#imbari frecvente de sarcina .

>.Materialele)entralele cu parametrii supracritici implica cresterea atat a temperaturii cat si presiunii

aburului avand ca restrictie limitele de rezistenta ale materialelor disponibile. 6unt necesare noimateriale cu o rezistenta mare la temperatura si coroziune indeosebit la (

!)omponentele cu pereti grosi ale cazanului cum ar fi colectoarelel supraincalzitorului colectroarele supraincalzitorului intermediar

! 'evile supraincalzitorului si supraincalzitorului intermediar!9otorul si mantaua turbine de inalta presiune

Parametrii aburului centralei supercritice genereaza temperaturi inalte in tevilesuprainczalitorului si maresc ratele potentiale de coroziune pe parte atat de gaze de ardere cat side abur . Otelurile cu crom ca B>0 pot fi utilizare in acest caz sau ca alternatica pentru

carbuni corozivi sau temperature ridicate se pot folosi oteluri austentice mai scumpe ca 'C;D si'C43 . In aceste conditii temperatura maima a aburului la iesirea din cazan poate atinge D;0 o) .In centralele proiectate la parametrii >?0 bar E ?D0 o) pentru colectoare si tevile de abur s!auutilizat otteluri feritice cu continut de crom de pana la ;>@ . Pentru centrale cu parametri de panala C00 bar E D00 o) sunt necesare materiale mult mai rezistente.9ezumand la ora actuala parametrii reprezentativi pentru un cazan pot aunge pana la C00barED00!D;0o)


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C.'urbina)onceptia unei turbine utilizata intr!o centrala cu parametrii supracritici nu difera

fundamental de aceea a turbinei destinata unei centrale cu parametrii subcritici . 'otusi datoritanivelului de presiune si temperatura ridicat trebuie reconsiderate grosimea si materialele pentrupartea de inalta presiune a turbinei

'urbinele moderne din cadrul centralelor cu parametrii supracritici se caracaterizeaza prinputeri unitare mari cuprinse in intervalul C00!;>00 MW . =ata de cazul unei centrale cuparametrii subcritici nivelul ridicat al presiunii initiale si aparitia celei de!a doua supraincalziriintermediare va conduce la complicarea turbinei cu abur si aparitia unui numar sporit de corpuri

4.'ratarea apei)azanele cu parametrii supracritici sunt foarte sensibile la calitatea apei de alimentare . In

consecinta este necesara prezenta unei instalatii de demineralizare totala pe de!o parte si buna degazare a apei de alimentare pe de alta parte.

)azanele de acest tip nu au nevoie de pura ceea ce are un efect pozitiv asupra balantei

de apa a centralei

?.8lte ec#ipamente ale centralei)omparatiile efectuate privin ec#ipamentele din ciclul apa abur ale celor doua tipuri de

centrale cu parametri supracritici respectiv subcritici au aratat ca diferentele sunt limitate laun numar relativ mic de componente si anume(

!pompele de apa de alimentare!ec#ipamentele din zona de inalta presiune a circuitului de apa de alimentare + in aval de

pompele de apa de alimentare,8ceste ec#ipamente reprezinta mai putin de D@ din cosutl unei centrale pe carbune

1rupurile energetice cu parametrii supracritici s!au dezvoltat &ndeosebi &n4 tari( 1ermania /anemarca -aponia si 678. *n 'abelele ;.C si ;.4 suntprezentate o serie de realizari.

;.C. )entrale cu parametrii supracritici din 1ermania


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;.4. )entrale cu parametrii supracritici din /anemarca

)osturile actuale de investitie ale centralelor cu parametrii supracritici cuputeri unitaremari sunt doar cu apro%imativ > @ mai mari dec:t ale centralelor cuparametri subcritici.)#eltuielile cu combustibilul sunt considerabil mai micidatorita randamentelor superioare aleciclurilor supracritice iar c#eltuielile dee%ploatare sunt de acelasi nivel cu cele din centralele cuparametrii subcritici.

Turbine Generator Set

There are several turbine designs available for use in supercritical power plants. These designs need not

fundamentally differ from designs used in subcritical power plants. However, due to the fact that the steam

pressure and temperature are more elevated in supercritical plants, the wall-thickness and the materials

selected for the high-pressure turbine section need reconsideration. Furthermore, the design of the turbine

generator set must allow flexibility in operation. While subcritical power plants using drum-type boilers are

limited in their load change rate due to the boiler drum a component re!uiring a very high wall thickness",

supercritical power plants using once-through boilers can achieve !uick load changes when the turbine is of

suitable design.

High-Pressure Turbine (HPT)

#n this section, the steam is expanded from the live steam pressure to the pressure of the reheat system, which

is usually in the order of $ to % &'a. #n order to cater for the higher steam parameters in supercritical cycles,

materials with elevated chromium content, which yield higher material strength, are selected. The wall thickness

of the H' turbine section should be as low as possible and should avoid massive material accumulation e.g. of

oxides" in order to increase the thermal flexibility and fast load changes.

Intermediate-Pressure Turbine (IPT)

The steam flow is further expanded in the #' turbine section. #n supercritical cycles, there is a trend to increase

the temperature of the reheat steam that enters the #' turbine section in order to raise the cycle efficiency. (s

long as the reheat temperature is kept at a moderate level approximately )%*+", there is no significant

difference between the #' turbine section of a supercritical plant and that of a subcritical plant.

Low-Pressure Turbine (LPT)


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#n the ' turbine section the steam is expanded down to the condenser pressure. The ' turbine sections in

supercritical plants are not different from those in subcritical plants.

Turbine technology trends

aising the rated steam temperatures demands a transition to new materials for steam turbines, too. #n

doing so, cast casings are replaced where possible with forged ones. /esign materials used by 0apanese

manufacturers for ma1or components of modern steam turbines with rated steam temperatures of )23-%**

4 are shown in Table 5 and compared with those used in steam turbines with rated steam temperatures

of )36-)%% 4.

7ew materials for supercritical-pressure power units with advanced steam temperatures have also beendeveloped and researched under the 8uropean 9:T o-9peration in the field of :cientific and

Technical research" programme.

The results of these developments and research programmes, as well as those in 0apan, should make it

possible to commission the first :' units with steam conditions of ;6 &'a, %3*


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That is why all the %* HA 0apanese :' units of 2** to 5*)* &W capacity incorporate cross-compound

" steam turbines, with the H' and #' cylinders located on the full-speed 3%** rpm" shaft-line and two

' cylinders on the low-speed 56** rpm" shaft-line.

With the emergence of longer full-speed :Ds with bigger annular exit areas see below", it became

possible to design 5***-&W-class T steam turbines with a five-cylinder configuration for %* HA as well.

(ll three leading 0apanese producers of large steam turbines G Hitachi, &H#, and Toshiba G have such

turbines at their disposal.;

For )* HA and relatively low vacuum in the turbine condenser, it became possible to have a 5*** &W T

steam turbine with four cylinders, that is, with two double-flow ' cylinders. 0ust this configuration was

realised by :iemens at uhuan four 5*** &W :' power units".

The same scheme is adopted for turbines produced by (lstom for ?erman :' units 7eurath F and ?,

Doxberg , &oorburg ( and D, /atteln $, and :taudinger %, as well as 'ort of (ntwerp in Delgium G all

with a gross capacity of about 55** &W, Figure 3. ( similar :' unit for &aasvlakte in the 7etherlands

will employ a f ive-cylinder version same (lstom steam turbine, with three double-flow ' cylinders, making

use of colder cooling water and, as a result, deeper vacuum in the condenser.

#f the turbine capacity does not exceed >** &W, the H' and #' sections can be united in an integrated

H'-#' cylinder, so the turbineIs total number of cylinders decreases to three with two ' cylinders". :uch

a configuration is employed, for example, at 0apanese :' unit Tomato-(tsuma $, with a turbine

manufactured by Hitachi G Figure $. #f the set capacity decreases to %** &W with a rotation speed of 3***

rpm, the turbine could be designed according to &H#" with 1ust two cylindersB one H'-#' cylinder and one

double-flow ' cylinder.

/espite the many indisputable advantages of an integrated H'-#' structure, turbine manufacturers such

as :iemens and (lstom still prefer to design their turbines with separate H' and #' cylinders, even if this

makes for longer machines. To decrease the overall turbine length, both :iemens and (lstom design their

large turbines with shared 1ournal bearings for ad1acent cylinders as well as for the turbine and generator"

G see Figure 3.

The most efficient steam turbines for :' units put into operation by the beginning of this century are

presented in Table ;. 9f significance is that the very similar efficiency values were achieved with very

different steam conditions. This suggests that, at least for some turbine types, there are considerable

reserves for raising efficiency by reducing energy losses in the steam path. &oreover, there exists a

reserve for raising the turbine efficiency to )*@ and beyond, even without transition to =: steam

parameters. Table 3 presents the guaranteed heat-rate data for steam turbines manufactured by hinese

turbine works based on foreign licences.

(long with the efficiency or heat-rate" data for turbines as a whole, also of interest are the internalefficiency values for individual turbine cylinders sections". :o, for the 2** &W :iemens turbine of the

Doxberg E :' unit, the acceptance field tests gave internal efficiencies for the H' and #' cylinders of

2$.;@ and 2%.5@, respectively. These figures, even though record-breaking, can be considered

consistent with the evolutionary stage that modern turbomachinery finds itself in.;,$

7oteworthy is that the internal efficiencies of individual turbine sections depend only to a small extent on

steam parameters, more important is the voluminous amount of steam flow through the sections. This

makes it possible to meaningfully compare the data for turbines with different steam conditions.


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:o, for example, after refurbishment by (lstom, the H'-#' cylinder of the ?8 steam turbine at the 0. .

:pruce power plant in the =:(, the acceptance tests gave internal efficiencies for the H' and #' sections

of 23@ and 2).>@ respectively, whereas for the best steam turbines of this type manufactured in the

526*s the corresponding values were 2*@ and 23@. (nother example is the >)* &W turbine of the

&ehrum unit in ?ermany, where, after refurbishment by :iemens, the internal efficiencies for the H' and

' cylinders were 23.%@ and 62.2@, respectively, compared with the pre-refurbishment figures of 6).)@

and 6>.;@.

:uch increases in internal efficiency are attained by reducing all the various kinds of energy losses in the

turbine steam path.; (part from using new blade profiles, traditional cylindrical blades are replaced with

Jthree-dimensional 3/"J blades, bowed and twisted throughout the entire steam path.

#n addition, in the late 522*s :iemens developed a new concept for shaping the turbine steam pathB

setting the degree of reaction for each stage individually, varying it from 5*@ to %*@, to minimise energy

losses.

This approach was first applied in full measure to the 5*** &W class :' turbine at 7iederaussem and

since then has been implemented on all :iemens new-build pro1ects.

While :iemens came to this concept from designing reaction-type turbines, ?8 traced a similar path for

impulse-type turbines. Their concept of J/ense 'ackingJ means increasing the number of stages and their

reaction degrees compared with a purely impulse-type steam path. #n particular, this idea is realised in

steam turbines designed and manufactured by the orean company /oosan Heavy #ndustries for the

newest orean )** &W and 6** &W :' power units, based on the ?8 licence.

Three-dimensional design is applied not only to the turbineIs steam path, but also to all the bladeless

channels and pathsB steam-admission and exhaust sockets and chambersC intercasing and bleeding

chambersC crossover pipesC and so on. /ecreases in steam pressure drop in these parts have a

considerable influence on turbine efficiency.

Karious types of parasitic steam leakages are reduced without increasing the danger of rubbing in the

steam path by using different types of advanced gland seals, including so called Jretractable packings.J

For such seals, at the initial start-up stages, when the probability of rubbing is maximum because of

vibration, thermal bowing of the turbine shaft and


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( further key factor in raising turbine efficiency is to decrease the energy loss by reducing the exit steam

velocity through use of longer :Ds, with bigger annular exit area. 7owadays, practically all the worldIs

leading turbine producers have at their disposal titanium :Ds that make it possible to increase

considerably the exit area. (n additional advantage of these blades is their higher resistance to erosion-

corrosion compared with steel blades.

#n the case of low-speed ' shaft-lines of cross-compound steam turbines, there still exists significant

margin for increasing the length of the steel :Ds, but the concept of cross-compound steam turbines as

such has essentially become obsolete. Tables $-% present data for the :Ds used by the leading turbine

producers for newly designed and refurbished steam turbines with rotation speeds of 3***, 3%**, and

56** rpm the latter as applied to large cross-compound turbines with grid fre!uency of %* HA".

:upercritical-pressure turbines are usually e!uipped with advanced regenerative systems that heat the

boiler feedwater up to the final temperature of ;6*-;2* 4 and for =: units for example, (vedLre ;" up

to as high as 3;* 4. The number of feedwater heaters FWHs" varies from eight four ' FWHs M

deaerator M three H' FWHs" to 55.

Doiler-feed pumps DF's" in modern :' units are typically driven by condensing turbines with a unit

capacity of up to ;* &W. &any :' power units have three turbine-driven DF's each providing )*@ ofthe maximum rated feed capacity or two )*@ turbine-driven DF's and one start-up motor-driven DF' with

3*@ of maximum capacity. :ome :' power units mainly those in the lower power range, )**-%** &W"

are e!uipped with three motor-driven DF's with )*@ capacity each.

Pentru turbinele cu abur de putere mare dilatarea termica impune folosirea a unei turbinecu cel mult ? corpuri ( un corp de inalta presiune un corp de medie presiune in dublu flu% si treicorpuri de oasa presiune in dublu flu% . 8ceasta este sc#ema adoptata de 8lstom si 6iemenspentru unitatile de ;000 MW si cu parametri supracritici din $uropa de Fest cu o frecventa de?0 Gz + C000 rpm,

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