Combined-cycle gas & steam turbine power plants

198 Pages·1999·55.81 MB·English

by  Rolf Bachmann

TE,
TURBINE POWE R PLANTS

Ralf Kehlhofer
CONTENTS

Chapeer
Tatredection:

Chanter 2
"Thermodynamic Principles ot
‘The Onmbined-Cysle Pant,

‘Chapter s
Lo Byetem Layouts
* y'Shaaten 4

‘Goubine’Cyele Planes or
Goiganesatinn

Ghapter 6
Components,

Fe Chapler 8
Cau, and Automation

Ghiaper?
‘Oparaling and Part-Loull Beluavior

perme

Engeht W82 27
real ishing Cage

2: South Nataan Ga
Ta Cena

Cadgoye 8
» Comparison of The Coxchinwd-Cyele Psat
‘ith Other ‘Thermal Poser Seations,

lieben 9
2 Rovironmentat Considerations
ESBW 9-8 /HAU-73K-5 i
ESBM 9-8 /NEM- 7b. Saige 10
{_Davelopmental

Connect yb oy ane
[Einar home pansy a
SRIID eeu he aw es season of
tesa

‘his Typical Curtsined-Cycle
Plants Already Hoi

fet “hea See 2A

ur

wl

a
Chaylee 12
Cot

Conversions 8
Symbols aed. ss
{odious Used 8B
Appondix se
DeGu'tion efter and Smbnls si

‘infioneaphy ot

Chapter }

INTRODUCTION

“fli aberaLure haw often suggested combining two ox more ther-

eo El pee within singe power plot tn all caves he tter-
Seo GEV eG come sec oerintofsingoorae, Derma
£ suc wy tba hw ete

TES cycon with diferent working media is more ihr”
‘Agua tecause their advantages can cncoplensent one another.

sb me cyte canbe classed won “typing” a ot
“SE mea! eycte. The frst eyele, to whick most of the heat is sup-
es atid the “Honizy eyee,” The wt produows

"BiG ancgyerlt process that makes oplimata thermodynamic
‘hg hoot in the upper range of temperatures and returns
AAS bet ete a tw a eer
Normally the “topping” end “hottoming” cycles are
on IEE hea exchan.

te. ithe present time, only our: combined eye}e huss found
Rapes the combination gus turinestenm turbine
2 COMBINED CELE GAS & SIEAAL TURKINE POWER PLANTS

Fig. 4 is a simplified Mow diagram for an ioslallation of this
type, im which aa open eycle ses kurbine is Followed by a stent
process, ‘ihe heat give of] by tke gas Lusbine is med to Ket,
ernie steam

Dlker combinacions are also pussibie, e.g., 8 mencury ware
peveess oF replacing the waler with organie fbvids or auton.

‘Tho mercury vapor prucess isto longer uf iterost tertay since
even conventional steam power plants achieve higher efficient:
fos. Onganie fluids or amronia have cersain advantages Over Wit
erin the low temperature range, such as reduced volame flows,
no wetness. However, the disadvantages, Le., development cout,
seuvisonmencit iapoet, le. appear greut enough to prevent te
ver tepliciag the wleam process in a combined-eycle power
laut, The discussion Hat folows dents mainly with the combini,
on of an opeaccycle gas turbine with a wateristesrs cycle. Cat-
tain special applications using vlosed-cycle gas Lurbines Nl also
be dealt with brietty.

Why has lhe combination gus tuhine/steam turbine power
lant, vnlike other combined-cycle power plants, managed to
Td wide acceptance? Two main reasons ean be given

2 friv made up of components that have alzesdly proven’
Tremnelves ta power plants with a single cyele, Dev
Spenent cows ave therefore low

# Airis a relatively non-probiematic aud inexpensive,
moedium tae ean be ged Jo modern gad turbines at
ih levated temperature level (abave 1000 °C), That
provides tly optimum prerequisites Cur 2 good “top
ping eyele-”

‘The stenmn process uses water, Which is likewise inexpensive
and widely available, but heleer suited for the modium und low
Temperature ranges, The waste heat from a morse gas turhinwe
hha Lemperalare level advantageous for u good steam process,

INFRODUTTION 3

1: Miovefore iy qite ruasunable to use Line shears prewess fae
ibe “Inttoming eyele.” That such combiratrion gas turbines eat
Jarbine power pz wert uot mere widely used even warlier

Shiga deadly boos dive to Rue historical developinent of rhe gas
irbing, Only in recent yours have das turbines attained! islet

“<lggaperatnres that make i possible ter design a vere Six
feficiency eyele, Today, hwwover. the installed pawer rapicity
peenmbinerbcycle gas turbinessteam nirkise: power ploncs weed

ide, ori tota's moze: Lran 30,000 MAW
Chapter 2

{3.1 Bildie Considerations

ee! ait efficioney is the niaxinvum elficwney of sn ideal

POS hermak process

om

Carnot effieioney
‘Temperature uf the ecwrgy supplied
Tempeniture of the envieneuucat

“(@aigtion und couverion), ard are thus exeryy Wat is
‘efile process, Exergetc Hewson, on the other kaud, are in-
toss eased ly ieeevouisble prowesscsin accomance with

“Ene an two major ess why the elTiciencios of rex! pro
8 gesigf he lower than the Cacuot efteieney
JE SyremoDyNAsve Peiveanies OF ThE COMBINEDACYCKE ANE 7

2 pg theL ofa conned egule plant On the other hand, dhe x
irgebe icnees in Ucomboned cycle are higher becouse te te

Justa diterenial for exchanging heat barween the exhasis
‘Tage gaa tothe ard the walexuoun cpeleisroorively rt
“eden clear why tl differences bocweer the semal etic

“egos altained by &vombineatyelé power plant ad the other
ppjtaons ave not quire Sh ange

1» CORGINFD CYCLE GAS & STEAM TURBIE POWER PLANTS

BIOK (980°F), while Uw ecbusation lem perabure ia Ube luilee is
appros. 200K. Thon. loo, iw vemyeralure of Ube wasle heat
from the process is hiyhor thw tho ambien: temperature. Both
Ihoat exchange prowsses euust: ss.

‘Ths best way’ to improve the process efficienry is.rn reduce
vere Instes, which eau be accomp:isiod by raising the mani

mam temperature ia Lie eyele, ur by seicasing Ce waste heat
st as low a tes

shure as possible

idneeauera mre differential in the heat supped, even though
shgpe an adethnal exergetc fone batoeen the a ae
iu processes

The intorest int cotnhinad-eyctes arises partivutadly Crome hese
twerreonsidera-ionts. Uy Hts nature, ne singe eyes can make both

ienprovemems li at equal exbetl. Wh chess sequns easimale ts
rombine wo eyulus: one with high process Lemmperalures, aud,
lve other with @ good 2d end.

Sigable 2-4: Thermuniynanue Comparizon of Gas Tartine,
Sceam ‘Turbine, and Conbined Cyele Power Planes

nan eperreyele gis Carbine, the process temperatures attain
shle ave wary high bocause its energy is supplied directly to the
vole withoat heut exelougers. The exhaust lust leer la,
uwever, is alse quice sigh. In live stem eyele, De maxiean
Process temperature iy wol very big, but the exhaust heat is
retuned lo Uke envieurmene an rhe cold end ak a very tow

feign ado 700 552-099) WH
Tso} ebay BBE} au 140)

f

temperature,

Gan Sms SH) Gasca ect)

bine aut a sleaien Urbina afters ule

Combining a gas
vest nossible basis fur & high effivieney Userural process (Table
en,

he last ive in the table stiows the “Carol efficieaties* of
the various processes, Le. the offioveucies that woul be alusaa
ble f the procwsscs too. placo without internal cxerglie owas.
Altkougl a sraiueelly is ul the cust, Unis Tigre en be used
fs an inulivstor 0) Lie qualily of a thems. proves. "The ue
shown makes cleat just hew iaveresting the combined-eyele
power plantis wlten compared to che single cycle processes. Even.
Ssuphisticated installation such as a reheat stcasu trbine power
brane has a therorecieal Caznol afficiwncy 10 to JB points lower
8 COMBINE

Kiguee ©

tenpeRavare

ee

re

1a CHEE GAS & STEAK! TURBINE POWER PLANIS

seek ane

Ea)

eure,

angestoe knee Dian

THERMODYNAMIC PRINCIPLES OF VE COMBINED-CYCLE PLANT 9
2.2 Thermal Efficiency of the Combined-Cyele Fient

Hoa assuaned in Section 21 Ukal fel energy is being sup
plied only in the gas turbine. There are, howecy, also comitud-
vele installations with sdditional fixing in the steam enerutor,
fe., in which a portion of the Reat is supplied dizectiy to the
sieam process.

Accordingly, the general definition of Ine thermal etticieacy
of a combined-cyele plant is

Por fae
Qor + Ose

“Pe chor: is ue supplementary firiny io che waate hsal bovter
form spies iso:

aK

a

hte general cu, the efficiencies uf the single cycles eat.
defined ag follows:

Satie the gag turbine process

ro)
@
40 COMBIND CYCLE GAS & STEAM TURBINE POWES PLANTS

Combining there two equations yields:

Ps

Se ee a
Base + Gast (L~ iGs)

ase

2. The Fftect uf Additional Firing in the Waste
Heat Boiler on Overall Htficioncy

ensoblaine

‘Substituting Euuations (4) and {Dine Equation

nex Qos + ney ise |. son"
Opt + On

‘Adiitona) ieingin Ine waste heat Pallet
efficiency uf the combined-cyele installation whenever

cy
™

improves the overall

oa o
# Ose
Dirteventistion of Equation (8) produces the bvequabty
am. 2, nes 28° Qs + ns)
Ose” Gen + Da [ner or (7s,

Wor + O50) = nor Ose + [5 BE Qov th nan] 00) °

(ar + O59) — nav Qc V- nes} >a

“Unis yields

EASt [Bes 2 Orr (l- ev] + As

Ose

~, netrQert 1 sy Wee «Gort — Hi
‘Dor + Osr

{THERMODYNAMIC PRINCIPLES OF TIE COMBINED-CYCLE PLANT TF

Since the second term of the imequality is equal to &, the ine
tnquallty roeluces ta’

[Ose + Berl — nel > an v8 2}

Ose

The erm Qge 1 Ger (Mer is ute ober Unt Ube be
2 Fyn! to the steam cycle, The formula thus becom:

ns. as)

#Bquation (13) means that increasing the additional Firing in.
{ pboves the efficiency of the combined-cycle plane only if it ime
ER rowan the efficiency of the steam process. The greater the
J flerence isbotweon the efficiencies uf te oumbined eyele aul
fy ateain poocuss, aud Ue lower tue Ceayperature i of Le baal
SCoeingut to the steam process, the nore effective that jraprave-
‘iygat will be. For that reason, additional firing is becoming less

SYigea creases far more rapidly than tha ofthe steam proces,
‘koitinually inercasing Iko differance Ic = 57). In view of the
2g) Selsidoratious in Soction 2.1, ik is genorely belie we Dasu the

Feelin w wocdors ga Usbute, Decase the Heat Is sul to
SSyyIERMODYNAMIC PRIVCIPLES OF THEE COMBINED CYCLE PLANT 1

COMBINED EYEE GAS & STEAM TURBINE POWER PLANTS

ile 22s Allwwable Reduction ie Sloan Process biivhuney
fu: a auction of Gas Tarbisse Eaficiony (Shout
eMliccency = 0.25

22.2 Bfficleney of Combined-Cvele Plants without
‘Addisional Fising in Ge Wuste Heat Boller

Willnut additional ising, Reuation (8) car, be waitten us fol-
lows: (14)
rages urd ass: Ber ae)

Des

yer - Hea

76

941.07

DiiVerentiueions motes it possible to eslunare the offer. Hk

a change inelfictency of the gat turbine hus on overall tfieienty:

tle. Bur 2 gas turbine with a anass
jigepltieieney LIL dvs aol pouvide an wp
$30 unl. Dor ena wit & eons une neh

(= ag) ner it) van cement i

Increasing lhe gas turbine efTicioney inyeoves the overall cf

feiescy ely if: 2
: spo llowsves, te effcenty of tneennbireye plat
FEE eS resbsecoeonet nachane ssigatiasy better
an 3 28 gatas betLer because tw sor
> a8) “le the follows operates for more efiieutly wilh the ger

vst Salut gas Lomyaralure aud prutuces 4 xreatr ul

From Bawatinn (15) oc obtains :
Pram Baran) fg,2-2a shows dhe offlcieney of the gas tase aloe as a

Spliquoncof the wubine inlet and exhaust tersperatunvs, The maa:
"Afuiie efficiency is roach whon The cxlaust gas lemperalares

any, J asp an
any F787
Inproving the gas Lusbive etficloney is helpfa ouly WHE des
aut eanse tow grees adrupin Noe efficiemey of the sleampraces
omg

‘Table 2-5 shows tine maxima allowable restaelion—
asa function of the gas eurbiew efTicienty anor

Aenrallyoulimized with resp au! Lolicieacy hub ia ean
‘IBS iver dersity. Fortunately, this optimum enincides fairy
J Beestely with the opcinum elficiency of the combined cycle
Spek SA8 a reste most uf wday's gas Larbiues ave uptiweally

‘Thia tate iudicates that the higher che efficiency wf she Fas “2
turbinc, de greater miy be the mduction in elfic'eney ut the ae
steam process. The proparliva of the overall output rie pro
Trided by the gas lurbine inercases. reducing rhe elfect of lower