POWER PLANT PRIMER

-.-:?-/

POWER PLANT PRIMERby

Ntdrcw W. l(nner

hPyrigtn 1954

Rcvisecl October 1972

Rcviscd January 1979

Rcprintcd 1983

Rcprinted t987

Rcprinted t988

Rcprinted 19w

Frprintcd 1993

POWER ENG|NEER|NG Magazineo Copyright 1988 by PennWefl Publishing Company

To order, contact the Reprint Department.

Reprint DepartmentPOWER ENGINEER|NG MagazineP.O. Box 1260Tufsa, OK 741A1(918) 882-9363

Power Plant Pri mer

STEAM

\G E I V E R A T O R

M A G N E T

T U R E I N E

FIR E

A s team powe : ' p l an t i s a means f o r conven ing t he po ten t i a l

chemica l ene! ' cy o f fue f in ro e lec t r i ca l energy . In i t s s im-p les t f o r rn i t c cns i s t s o f a bo i l e r and a t u rb ine d r i v i ng anelectr ic aene! 'a ic i ' .

The bo i le r i s a c jev ice fo r tu rn ing water in to s team. The

s team je t i ssu ing f rom the spout sp ins the fan ( tu rb ine) and

a lso the genera io r . In the ske tch the very s imp les t k ind o f

bo i l e r and t u r c i ne a re shown . The bo i l e r i s a t ea ken le , andthe tu : 'b ine is no th ing more than a l in le w indmi l l . Ac tua ltu rb ines are rnore compl ica ted bu t the pr inc ip le i s the same.

energy by rn eans of the type of p lants we hac about 60years ago, we wou ld have needed th ree t i rnes :he coa l , o rover 1 .34 b i l l i on tons . Coaf - f i red p lan ts supp l ied 46 .4o /o o fto ta l e lec i r i c i t y p roduc t ion by e lec t r i c u t i f i t y ccmpan iesin 1977. Oi l - f i red p lants suppl ied 16.8o/o, gas- f i red 14.4o/o,nuc fear 11-8%, hydro 10 .4o /o , and a l l o ther 0 .2%.

The reason for the great decrease in the consurnpt ion ofcoa l l ies in the graduaf improvement o f our power sys tems,both wi th respect to the indiv idual p ieces of equ ioment andin the system as a whole. Just how do we go about improv-ing the sysrem shown in the sketch?

Boiler componentsLooking at i t again, i t is obvious that i t can be brokendown into several d iv is ions. F i rs t , there is the f i re underthe bo i ler . This invof ves not only the fuei i tse l f but a lsothe method o f p lac ing the fue l under the bo i le r and thearrangement for burning i t proper ly .

So le t us ex iend the d iagram to look l i ke th is :

Here, w€ see a bef t conveyor t ransponing ccaf to thefurnace where i t is burned on a ravel ing grate stoker. Ai rfor combust ion is suppi ied by a bel lows.

Remernber, when you burn coal you are reaf ly promot ing

a chemical reactioo-E chain reaction. When coal is heatedto a high enough temperature in the presence of air, thecarbon in the coal combines with the oxygen of the air toform ei ther carbon diox ide (COz ) or carbon monoxide(CO). These, of course, are both gases. Which gas is formeddepends upon the guanti ty of oxygen present. The COmeans that the coal is onf y part ia f f y bu rned, indeed, theCO can be combined with more oxygen to forrn CC2.

In burning coal we do not want CO because that means thecoal is onf y par t ia l ly burned: there is s t i f l energy lef t in thegas, energy that we can recover i f we can burn i t to CO2.I t is desi rable, in the operat ion of our boi ler furnaces,always to get as much COZ as we can because in that waywe get a l l the heat out of the fuel .

We can obta in the COz by supply ing more a i r to the fuefas i t i s burn ing . But we do no t want to supp ly too much a i r ,because i ' f we do we wi l l be supply ing more oxygen thanis actual ly needed to combine wi th the carbon, and th isexcess oxygen wi l l p lay no part in the combust ion process.Not on ly wi l l i t p lay no part but i t wi l l actual ly detractfrom the eff iciency by absorbing heat that otherwise couldbe used to heat the water in the boi ler . In acrrra l pract ice i ti s no t poss ib le to supp ly exac t ly the requ i red amount o f a i r ,so somewhat more than enough is suppl ied. This is com-

A word about :he generator shown in the sketch. To mostpeople the prccess of generat ing e lectr ic i ty is very rnyste-r ious, yet the aciual process is easy to understand. As

shown, the gene! 'ator consists of a l i t t f e bar magnet soinningins ide a s ta t ionary co i l o f w i re . Th is may seem an absurd lys i rnple af fa i r , yet that is exact ly what a real generator

consists of -a nnagnet rotat ing ins ide of a coi l o f wire. Asthe magnet ic ; ie id i ssu ing f rom the ends o f the magnetmoves across :he tu rns of wire in the stat ionary coi l anelectr ic curreni is set up in the wire. By winding a largenum ber of tu rns of wire into a r ing or dough nut , thecurrent set up in each turn is added to the current set upin the other iurns of wire, and so a much more powerfu l

current is prociuced.

This is a l l you need to know about an e lectr ic generatornow- just th ink of i t as a rapid ly rotar ing magnet ins ide ofa co i l o f w i re l th is p roduces an e lec t r i c cur ren t in the w i re .La ter we w i l l e labora te on th is s imp le descr ip t ion .

You may wonder, i f a power p lant is basicaf fy as s imple asth is , why we bu i ld the complex p lan ts we see descr ibed inP O W E R E N G I N E E R I N G M a g a z i n e ? T h e a n s w e r i s q u i t es imple: the p lant shown in the sketch is not very ef f ic ient-indeed i ts eff iciency is close to zero-and since we want toget as much power as possib le out of a g iven quant i ty of fuefi t is necessary io rnake our p lants as ef f ic ient as possib le.

Unt i l the ear ly 1920s , the e lec t r i c pows: ' p lan ts o f thenat ion used over 3 pounds o f good coa l to p roduce aki f owat thour o f e lectr ic i ty . Today, the nat ional averageis f ess than I pcund o f coa l per k i lowanhour . ln o therwords , p lan ts cu i l t d t tha t t ime used th ree t imes as muchcoaf to p roduce a k i lowaf thour as we use today . ln 1977 ,the e lec t r i c u t i l i r ies o f th i s count ry p roduced over 985b i l l i on k i lowanhours by means o f coa l - f i red p lan ts . Th isrequ i red the curn ing o f 447.2 mi l l ion tons o f coa l . l f ,however, we haC had to produce th is amount of e lectr ica l

P O W E R E N G I N E = R I N G 3

rnonf y referrec io es excass a/r.

So , i n t he p rocess o f combus t i on , we a re dea l i ng w i : h chem-

i s t r y . l t i nvc i ves a know ledge o f t he comPos i t i on o f t he

coa l , i t s phys i ca l con i i t i on , i t s behav io r unde r va r i ous con -

d i t i ons o f I enpe ra tu re , mo i s tu re , e t c . Ac rua i l y , i he com '

bus t ion o f cca l i s a very corno lex process reou i r ing a good

know ledge c ; l c t h phys i cs and chemis t r y . I n a l a rge p lan t

i t i nvo l ves a nna j o r p rob lem i n ma te r i a l s hand l i ng - fue l ,

ashes , a i r and f l ue gas . R emember , t o bu rn cOa l , you have

to supp ly about 11 pounds o f d ry a i r fo r eac i r pound o f

dry coa l used. 3ecause o f w ic je ly vary ing coa l cornpos i t ions ,

and a l low ing fo r excess a i r and mois tu re , the ac iua l amount

requ i red is usua l lv somewhat more than th is .

So fa r , we heve mere ly ment ioned ashes and f lue gas . These

have to be re rnoved cont inuous ly . ln the c iays o f hand

f i r ing the remova l o f ash was s imp le , though labor ious . The

f i reman mereiy raked the ash out of the ashpi t anci carr ied

i t away in w,heelbarrows. Tocjay, in large p lants, the re-

moval of ash is a compl icared process regu i r ing rather

e labora te equ ipment . So, we must add ash remova l egu ip '

ment to our c i iag: 'am , a lso a chim ney for the rennoval of

f l ue gas .

Funhermore , the process o f combust ion is s i imu la ted by

heat ; indee i , the process w i l f no t s ta r t un t i l the fue l i s

b rough t t o :ne k i nd l i ng t empera tu re . Eve ry th i ng mus t be

dOne, there fore , to ma in ta in a h igh tempera ture in the

furnace. Th is makes i t c jes i rab le to heat the a i r io r com'

bus t ion be fc : 'e i r i s de l i vered to the fu rnace. Th is a ids

combust ion and increases the e f f i c iency .

With these facts in m ind, le t us redraw our d iagram to in '

cc rpora te thesa improvemen$. Th is way:

t h e b e l l o w s w i l l b e b l o w i n g w a r r n a i r

i n t h e s k e t c h .

i n t o t he f i r e as shown

C O L D a t n r n r I//

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A l f t h i s p robab l y seems absu rd l y s imp le , anc i t i s . The

reason fo r exp la in ing i t in th i s way , howsver , i s io show,

by means o f t he s imp les t k i nd o f equ iomen t , how eng inee rsgo about improv ing the e f f i c iency o f any sys tenn. S tep by

s tep , add ing someth ing here , sav ing somelh ing there ,

es tab l i sh ing c l ose r supe rv i s i on ove r eve ry th i ng g radua l l y

improves the e f fec t i veness and the e f f i c iency o f a lmost any

k ind o f svs iem. These are the k inds o f th ings eng ineers a re

concerned w i th . Near ly a l l o f them are rnore or less com-p lex and reou i re a g rea t dea l o f spec i f i c as we l i as genera l

knowlec jge . In the example jus t c jescr ibed, fo r example ,just how much sur face should ihe heater in the stack have

to heat the a i r to a cena in te rnpera ture? How not shou ld

the a i r be io r bes t combust ion , how much a i r shou ld be

supp l i ed , how much power w i l l i t t ake t o run :he be l l ows ,what haooens to the f lue gases i f too much heat i s ex '

t racted f rom the gases, what happens to the s lack? None

of these is a ioo l i sh ques t ion .

Cons ider the las t ques t ion , fo r example , tha t o f coo l ing the

f lue gases too much. What happens? Wel l , there is a lways a

cena in amount a f water vapor in the f lue gases ; f rom the

a i r and f rom the hydrogen in the ' fue l . As the tempera ture

of the gases is lowered, there comes a t ime when the

satu rat ion point is reached and the moisture condenses . l f ,a t the same t ime, there happens to be any su f fu r in the gas(and there usua l ly i s ) , su l fu r ic ac id w i l l be fo rmed, resu l t ing

in the spread o f a th in bu t ex t re rne ly cor ros ive layer o fl iqu iC on the ins ide sur faces o f the f lues .

Th is s ing le example , then, shows what the eng ineer runs

into when he begins to ref ine the s impfe system we beganwi th . He may add someth ing to improve i t bu t hp may f ind

tha t the imgrovement i s no t an unmixed b less ing ; i t may

a lso have de le te r ious e f fec ts . These he must guarc i aga ins t .

But le t 's get on wi th our power system. The tea ket t fe

represent ing the bo i le r i s no t a very e f f i c ien t genera tor o f

s team. Le t ' s see i f we cannot des ign a be t te r one. Look a t

the ske tch on the nex t page. Here we have a bo i le r cons is t -

ing of two steel drums connected by a number of s teel

tubes, and arranged in a furnace so that the hot gases have

to pass th rough the bank o f tubes on the i r way to the s tack .

The tota l sur face of the tubes is large, f f iEking i t possib le to

absorb a great deal of heat . The steam bubbles formed in

the tubes r i se to the upper d rurn (ca l led the s ieam drum)

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As you see, i t i s becoming more compl ica ted . Now, we have

a ch imney or s tack to remove the gas o f combust ion and

a heater to heat the a i r f rom the bel lows before i t is b lown

in to the fu rnace. A lso , w€ have pu t in an ash conveyor .

Now, i f you e re o f an ana l y t i ca l r n i nd , you w i l l see t ha t i t

takes addi t ional heat to heat the a i r . We have shown a

cand le . S ince cand fes cos t money , i t i s obv ious t ha t we a re

nOt go ing tO save muCh money tha t way . Why can ' t we use

sorne o f the ne a t f rom the f i re under the bo i le r i t se l f to heat

the a i r? Maybe tha t wou ld be cheaper than buy ing cand les?

Wel f , i t i s , and moreover , there is heat go ing to waste up thestack. You know f rom exger ience that i f you hold yourhand above a tea ker t le on a s tove tha t there is a f o t o f heatbe ing wastec - So, le t us pu i a heat ing co i l in the s tack so

4 P O W E R E N G I N E E R I N G

^ a r r t r- ; i - l L j t y l - STAC K

+WATE R

A ^ F F

U A U C

S T E A M : C ; U R B I N E

\ - n t R H : A ; = R

V A L V E\

3 C t L = RF = = D P U M P

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IW A T E E S C U R C E

ASH PIT

(KK

\WATE R IN

where the s i :3 rx cc l lec ts be fore i t f lows in to the c ioe lead.i ng t o t he t u : -3 i ne .

Th i s i s t he : as i c t r i nc i p l e o f t he mode rn wa re r i uce co i l e r .No te t ha t a l c i l e r f eed pump has been i nc luoec i n t he

EX H AUST STE NruIF R C M B . F P U M P A N DOTH E R STEAMD R I V E N A U X I L I A R I = S

F : = 3 W A T E Rf ' l 3 .n r 3 i1

d iagram. S inc : s iearn f lows ou t o f the bo i le r i t obv ious lybecomes nec3ssary to replenish the water that is evaporated.For th is reason a bo i le r feed pump is necessary .Th is pumpmust operate at e cressure h igh enough so that i t can over-corne the pressure in the bo i le r .

In the ooera i ion o f any bo i le r , even a tea ke i t le , i t i sessen t i a l a lwavs i o keep enough wa te r i n t he bo i l e r . l f i tshou ld run c :v ine meta f woufd become red ho t , so f ten ,and rup tu re . A . i : he same t ime i t shou ld no t be f i l l ed t o apo in t where : : ' r3 re i s no room fo r the s team to cc l lec t . Tocheck th e v,/e--er ievel a water gage is f i t ted to the stearndrum. Th is sno ' r , ' s ihe water leve f in the bo i le r a t a l l t i rnes .

Now, i t i s obv ious t ha t i f t he amoun t o f s team leav ing t hebo i le r was e l , r ;evs ine same as the amount o f water en ter ing ,the wate r leve : v rou ld remain the same. Th is s ta te o f a f fa i rsse ldom occu rs . ' Ja r i a t i ons i n l oad causes va r i a t i ons i n s teamf low : va r i a t i c : s i n t he f ue l supp l y and a i r supp i y causeva r i a t i ons i n : r e i ' a t e o f combus t i on , wh i ch i n t u rn resu l t sin var ia t ions in t ; re ra te o f evapora t io f , , and a l t o f thesecause chanoes in the water leve l . Th is makes i t necessaryfo r the opera t?r io ma in ta in a cont inua l watch on the waterf eve f . l t i t c ro3s , he i nc reases t he wa te r supp l y ; i f i t r i ses ,he dec reases ; : .

P o w E R E N G r r . l = = p l r . l G

This cons ian t v ig i lance on the par i o f ooera to ' ' s v /as a p rob-lem, so feec iwater regu la to rs were deve loped wn icn cont ro lthe f low au iomat ica f fy as the water in the bo i le r c ru rn r i sesand fa l l s . These a re ve ry he lp fu l even w i t h sma i l bo i l e r s ,

F E = D W A T : RC C N ; R C L V A L V E

but in the case of modern h ighfressure boi lers they area lmost impera t ive . A la rge h igh-pressure bo i ie r , evapora t ingin the ne ignborhood o f a mi l l ion pounds o f water le r hour ,wou ld run c i ry in about 90 secon is i f the ware i ' suppfy wassudd en ly cu t o f f .

Now, ge t t ing back to our water supp ly io the bo i ie r , so fa rnoth ing h as been said about the temperature of the waterbe ing de f i vered to the bo i le r . l t shou id be obv ious , however ,that i t would not be wise to pump coid warer in to a boi lersince that would cjecrease the temperature of the wateral ready in the bo i ler and so reduce the rate at wn ich stearnwas being macie. Also, the int roc iuct ion of cold warer mightse t up s t ra ins in the bo i le r by v inue o f the orea t temper -ature d i f ference. Therefore, i t becomes expedient to heatthe water be fore pumping i t in to the bo i le r . So i t i s runthrough a feecjwater heater.

The feeciwater heater cou ld be heated by a seearate fuel-f i red furnace but , as in the case of the a i r heater , i t wouldbe much more economicaf i f i t could be heated by heat thatwould otherwise be wasted. Suppose , for example, that theboi ler feed pump was a steam dr iven pump, and we coulduse the exhaust s tearn f rom th is pump. This would costv inuaf f y noih ing. So, we add a heater , BS shown at le f t .

Af ter the steam has done i ts work dr iv ing the purnp, i t isdel ivered to the feedwater heater , which, as shown here, isnoth ing more ihan a large tank in wh ich the sream mixesdirect fy wi th the water to be heated. l t is cal led an op€nheater . As w i l l be shown la te r , there are o ther k inds o ffeedwater heaters cal lC c losed heaters in wh ich the steamand water c io not m ix .

So fa r , so good; we have saved a l in te by us ing ihe heat inexhaust s team which otherwise would have been wasted.Le t ' s look a b i t funher , however ; maybe we can save somemore heat somewhere e lse . In the bo i le r , f o r exarnp le ,remem ber that we picked up some heat in the f lue gasesby means o f the a i r heater . Have we go t a l l o f i t?

An ai r heater may or may not remove al l the heat we wantto remove f rom the f lue gases. But i f we want to. we canmodi fy the bo i le r and ins ta f l one secr ion o f tu bes to heat

t he f eedware r be fo re i t i s de l i ve red t o t he bo i l e r d rum.Look a t t h i s ske t ch :

f a n b l a d e s a n C c a u s e s t h e e n t i r e r o t o r a s s e r r b l v : 3 t u r n . I ntu rn ing the : lades in the f i rs t s rage the s te a rn g i . l?s up someo f i t s ene rcy , r esu l t i ng i n a d rop i n p ressu i ' e . l nus , a t as l i gh t l y l o r ve r p ressu re , i t en te rs t he seeonc s :aqe nozz lea n d a g a i n i l o i v e s u p s o m e o f i t s e n e r c y i n : : : n i n g t h esecond s rage o f t h i s r o to r . A f t e r Dass rng rh roug r , t he t h i r ds tage i n rn i s r va ! , p rac r i ca l i y a l f o f i he ene rg y o : : ne s tea rnh a s b e e n c i v e n u p I o t h e r o t o r a n d i t l e a v e s : , : e t u r b i n eas exhaus i s :eam.

Th is a r rancernent , obv ious ly , p rov ic ies a rnuch.nore e f f i -c i e n t m e a n s f o r s p i n n i n g t h e r o t o r s h a f t : h a n : n e s i m p f el i n l e f an snown i n t he f i r s t d i ag ram. o f ccu rse , i t i s s t i l lme re l y a o i ag ; ' am-no t u rb ine wou ld eve r be cu i i : t h i s way .The on l y s i ep rema in ing t o make th i s e l e rnen :a l t u rb ineinto a cornmercia l rnach ine is to int roduce nui t io /e nozzleso f P ro9e r ces ign and cnange the shape o f t he i ne f f i c i en tpadd les io an e f f i c ien t b lade hav ing curvec en i iances andex i ts . Here is a c ie ta i led c i rawing o f rhe nozz tes a ; rd b lades( they are a isc ca l led buckets ) o f a modern tu rc ins , and nex tto i t is a c ' 'css 'sect ion through a tu rb ine showir ic how theefements are ar ianged on the shaf t .

Here we have acc ied a separa te bank o f tubes ih rough wh ichthe feeowaier Jasses be fore i t goes in to the bo i le r d rum.Th is bank o f ruces is p laced in the pa th o f the gases t rave l -ing towards the a i r heater and the stack. Most of the heatin these gases has been absorbed in the bo i le r tupes , bu tno t a l l o f i t . The gases probab ly s t i l l have a remperarureo f about 600 oegrees Fahrenhe i t . By mak ing thenn t rave lt h rough th i s acced i ube bank , s i i l l mo re o f t he hea r w i l l beabsorbed. Conseauent ly ihe economy o f the bo i ie r as awho le w i l l be inc reased. Hence, th is bank o f tubes is knownas an economizer. With this arrangement, the water is f i rstheated to a temperature of about 212 F in the feeciwaterheater by tne exnaust s team t rom the feed pump, and then,in the economizer , the tempera ture is funher ra ised to apo int not very :ar below the tem perature of the wateri n t h e b o i l e r .

S team tu rb ine and condenserOur bo i fe r -o r s ieam genera tor , as i t i s ca l led-has nowbecome qu i te co .no lex , so be fore we do any th ing more to i tle t ' s hook i t uD ro the res t o f the sys tem, As a l reac jy men-t i oned , a t u rb ine i s essen t i a l l y a w indm i l l ; no t a s imp le f anl i ke the one shown but a more complex one w i th manyhundreds of b lac ies, some stat ionary and some rotat ing.These blades are arranged in groups or stages, so that thesteam is compel led to pass successively through the var iousstages. Here is a very s imple d iagrann.

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l n t h i s d i ag ram, t h ree f ans a re shown moun ted on a com-mon shaf t , each one in a separa te compaf tment . S teamissuing f rom the nozzle in the f i rs t s tage pushes against the

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So, now we have e bo i le r and a tu rb ine coup led to an e lec-

t r ic generator as shcwn above.

Here you see s ieam f rom ine bo i le r be ing fed in to the

turb ine by meens o f the connect ing p io ing and ar te r pass ing

through the vai ' ious stages of the turbine the stea m exhaus?.s

th rough an ocen ing in the bo t tom o f the tu rb ine . The

steam has g iven up i ts energy to the turb ine rotor and th is

in tu rn sp ins the genera tor ro to r . The genera tor ro to r

remember , i s s i rnp iy a magne: .

But what shal l we c jo wi th the exhaust s team? ls i t o f anyuse? Wel l , i f you measure the temperature of the exhaust

steam r ight a i the point of the exhaust opening, you wi l l

f ind that i t nas a temDerature of 212 F. This is the temper-

ature of s tearn e i armospher ic pressure.

Obviously, we cen use i t to heat the water in the feedwater

heater in the same way thai we used the exhaust s teamfrom the bo i le r ieed pump. However , you wou ld f ind tha tthere is far more exhaust Eteam coming f rom the turb inethan you ccuici use in the feedwater heater.. R emember,practical ly the entire bo i ier output passes through theturbine and ou: in to the exhaust .

l f you want, you can pipe this exhaust steam to radiators

and use i t to heat houses and bui ld ings in winter .

This way

Note that ean of the exhaust s team goes tc the feed-

water heater . Most of i t , however, goes to the bu i ld ing

heat ing sysienn.

Now, th is i s f ine i f you have a bu i ld ing you wan i to heat o r

i f you neec s ieam heat for other purposes sucn as cooking,

heat ing st i t ls in food or chemical p lants or any of sccres of

d i f ferent cur?oses in industry, and in pract ice :nat is how

a grea t Cea l o f exhaust s team is used. lnc ieeC, :h is i s one

of the reascns i t pays the owners of an industr ia l p lant , a

paper rn i l l fo r example , o t a tex t i le mi l l o r a food produc ts

plant , to have thei r own power p lant i they can use prac '

t ica l ly a l l or the exhausi s team from the turb ine for heat ing

and other" purpcses.

l f they c j id no t have the tu rb ine , they s t i l l wcu ld need a

boi ler to generate steam. By f i rs t ru nning the $eam through

a turbine they can gei the elestr ic power so prcduced for

a very low ccs:.

Suppose, however, there is no bui ld ing to be heated or no

factory process to use Up the exhaust steam; what then?

Take a pub i ic u t i l i t y p lan t fo r example . A oub l ic u t i l i t y

p lant is designed sole ly to generate e lectr ic i ry to sel l . Such

plants usual ly are tar away f rom bui ld ings where the

exhaust sream might be used for heating. Shall the exhaust

steam be permitted to be wasted to the atmosphere?

No. There is a much bet ter way of d isposing of th is exhaust

F O \ ^ / E R E N G I N € = R I r u G

s team. That i s by us ing i t to c rea te a vacuum a t the exhaust

end o f the tu rc ine

A vacuum? Why a vacuum? Wha t good wou ld t ha t do? We l l ,r emember :ha : i ne t u rb ine i s su r rounded on a l l s i oes by t heatmosphere rvn ich , a t sea leve f , €Xer ts a p ressure o f about1 5 l b pe r scua re i nch (ps i ) . I n o rde r i o ge t ou t o i t he ex '

haus t open ing , i ne s team has t o push aga ins t t n i s 15 ps i

p ressure , and : ; r i s requ i res work , jus t as i t does to push the

turb ine b lades around. But suppose, by some means, wB

could remove the atmosphere f rom around the exhaust

opening so that tne steam issuing f rorn the exhaust openingwou ld encoun ier no res is tance whatever ; you wou ld f ind

tha t you cou lC deve lop more power in the tUrb ine , indeed,

i t would be ecuivalent to an increase in stearn pressure.

To understand how we can accompl ish th is ( removal of theatmospheric pressure) i t is necessary to know a iew facts

about steam. Steam, remember, is evaporated water . Whenwater is heateci to a temperature of 212 F at atmosphericpressure i t turns into steam. l f the water is enclosed in at ight ly c losed vessel such as a boi ler , the temperature atwh ich the wa ie : ' tu rns in to s team wi l l be h igher ' . In any

case, the volu i 'ne of the steam produced wi l l be very muchlarger than the volume of the water f rom which i t wasproduced. At atmospher ic pressure, for example, a pound

of stearn occupies a volume of 26 cubic feet .

Suppose, now, ihat you had a pou nd Of steam at at rno-

spher ic pressure in a c losed vessel wi th a volurne of exact ly

26 cu f r . This vessel would be a t r i f ie less than 3 ieet on a

s ide-assuming i t to be a cube. l t wou ld be fu l l o f s team.

There wou ld D€ no a i r . l f you sudden ly p laced th i s vesse l

on a la rge b iock o f i ce , a r cco led i t by spray ing co ld water

on i t , what wcu i i happen? The s team wou ld condense- i t

wou ld tu rn back in to water - in to one pound o f water . Th is

pound o f wate : ' , however , wou ld occupy on ly 1 /6Qth o f a

cub i c f co t . l t wou iC l ook abou t l i ke t h i s

\\\

ST:AM

WATER

This i s very i i ; le water . Most o f the in te r io r i s now occu-pied by noth ing-gg .93Vo of the tota l volume. This meansa vacuum .

The to ta l suna=e a f th is cube has an area o f 7776 sq in .S ince each scuare inch has 1 5 tb o f a tmosphere press ing

8

down on i t {and w i th no th ing ins ide to ccunterec t i t ) theto ta l a tmospher ic p ressure on the cube is nov / 7776 x 15o r abou t 1 16 ,640 l b .

l f you wan t t o see whe the r t h i s i s r ea l l y t r ue , i r y i t some-t ime . Take an o rd ina ry rec rangu la r ga l l on can w i : n a sc rewcap c l osu re , pou r i n abou i a ha l f - i nch o f wa ie r , and b r i ngthe wa te r t o a bo i l by p l ac ing i t on a gas bu rne r l c r a f ewminu tes . Do t h i s w i t h t he sc rew cap o f f . Then , when thewa te r i s bo i l i ng v i go rous l y , sc rew the cap on and qu i ck l yp lace the can under a s t ream o f cc ld water . The can w i l lc rumple up { i ke so much paper .

G A L I - C N C A N

1 5 L 8 P € R S O . f N .

orJTsr oE .p R A C T 1 C A g L y N O' R E S S U R E I N S I O ER g S U L T : C A NC C L L A P S E S

15 L8 P€R SO. lN .ATMOSPHERICPR€SSUREBALANCED 8YSTEAM ANOAIR PRESSUREINSIOE CAN

-

This spec tacu ia r exoer iment i s one wh ich anvbo iy can do

at home but i t i s ex t remely conv inc ing in cernons t ra t ing

the proc ju* ion o f a vacuum by the condensat icn o f s team.

Remember, we wanted to create a vacuum at the exhaust

end of the turb ine. Now that we know how io create a

vacuum, ju f i how can we appfy the pr inc ip le to our tu rb ine?Wel l , suppose we a t tach a ia rge ho l low vesse l to :ne exhaust

open ing o f the tu rb ine anc i ins ta l l a bank o f snna l l tubes in

the vessel through which we can pump cold water ' .

In th is fash ion -

. -TU F 3IN 5

Sil1A L I- TU B E5

With such an arrangement, the steam issu ing f rom theturb ine w i l l come in contac t w i th the co ld tubes andthereby turn back into water . Th is wi l l create a vacuumin the vesse l jus t as i t d id in the case o f the ga l lon can. Thevessel now, however, is made of heavy. s teef , capable ofw i ths tand ing the pressure o f the a tmosphere , and w i l lno t co l lapse.

P O W E R E N G T N E E R I N G

- s ;Ac KH P . S T E A M

L_tI

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r . 1 E A l = | 1

ECCNCtv t tZ=A

3 . F . P U M P +frd,t\

l -

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STO K: N

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U J A P M W A T E Ri C P I V E R

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xOTWE I- L

A S H P I T-corvDENsA; : euMp

C C L D W A T : RF R O M R I V E RO N L A K E

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T U N B I N E

Since co id warer cont inues to f low th rough the tubes , theprocess is a ccn t inuous one. There w i l l be a s teady con-vers ion of s :earn into water , and a steady s ia ie of vacuumwi l l ex i s t ins ide ine vesse l .

Techn ica l l y , such a vesse l i s ca l led a ccndenser . l t s purpose

is twofo ld : ; i r s : , to c rea te a vacuum a t the tu rc ine exhaust ,and second, ic recover the condensare ( the ccndensedsteam) so ina i i t can be useC over aga in in the bo i le r . S inceth i s condensa :e i s r ea l l y d i s t i l l ed wa re r , i t i s ve ry ou re , and ,there f o re , h ig r lv des i rab le fo r use as bo i le r feec iwater ' .

So , we bu i i c another smal le r chamber a t the bonom o f theconcjenser io provide a p lace where the condensate cancol lect anci ; rom which i t can be pumped back to theboi ler , or ra; rer , f i rs t to the boi ler feedwater heater . Thisreservoi r is cal led the hotwel l s ince the water wh icn col lectsin i t i s fa i r l y warm.

Now, our sysiern looks l ike the drawing above.

Steam produced in the boi ler f lows through the main steamheader to the turb ine. ln the turb ine i t passes, successively,through the var ious stages, los ing pressure at each $age andgiv ing up i ts energy to the b lades on the rotor . Th is tu rnsthe e lectr ic generator and produces e lectr ic i ty . Emergingfrom the exhaust opening at the bonom of the iurb ine, theSteam enters i i te condenser where i t condenses on the tubesthrough which the cool circulating water flows.

Condensat ion of the steam creates a vacuum wh ich reducesthe back pressure which otherwise would impede the f lowof steam to a considerable extent . The condensed steamcol lects in the hotwel l of the condenser and is drawn of fby the conciensate pump wh ich pumps the water in to thefeedwater heater . Here the water i s funher heated by the6xhaust s tea in f rom the bo i fe r feed pump (or o ther s team-d r i ven aux i i i a r i es ) and t hen i s pumped back i n to t he bo i l e rby the bo i le r feed pump. The la f te r , i r w i l l be no ted , i s runby steam from the main h igh pressure header. We now havea com p le te ly c losed sy$em. ,A l l the water tha t i s tu rnedin to s team in the bo i le r i s condensed back in to warer in thecondenser anc f pumped back in to the bo i le r aga in . Ofcourse , there are s l igh t losses a t var ious po in ts in the

P O W E R E N G I r . { 5 E R I N G

sys tem, leakage th rough pum p bear ings , s ieam leakagethrough va lve pack ing , e tc . To make up fo r th is loss a smal lquant i ty of raw water has to be pumped into lhe system.Th is i s known as rnakeup water c r s imp ly makeup.The idea

is to keep the amount o f .

The re i s on l y one add i t i ona l r equ i remen t t o make a wo rk -ing system, Wherever there is a vacuuf f i , there wi l l be someair leakage into the system, and tn is a i r rnusi ce removed

or i t w i l l g radua l ly bu i ld up anc j c jes i roy the vacuum. l f thevacuum recu i red is no t too h igh , a combina t ion condensate-a i r remova i pump can be used. F o r h igher vacuuf t i s , separa tea i r remova i equ ipment i s neec ied . Conc ienser a i r pumps

separate the a i r f rom the water vapor and return the waterto the conciensate system. They general ly are of the steamejector tyoe. Even these are f i t ted with heat exchangers torecover ihe heat that might otherwise be lost in extract ingthe a i r f rorn the condenser.

l f you are interested only in the basic pr inc ip le of a powerp fan t , th is i s a f l you need to know. True , many moreref inements can be added wh ich wi l l funher improvethe eff icienqy but the system shown in the last diagramwould work .

f f th i s exp lanat ion , so f a r , has made sense to you and i f i thas been of in terest , maybe you would l ike ro go a l i t t lefur ther and learn someth ing about actual p lanr as theyare bu i f t today .

The bo i le r p lan t shown in the d iagrarns is f i rec by a cha in -gra te s toker . Most peop le a re reasonab ly fami l ia r w i th as toker . Power p lan t bo i le rs a re a iso f i red by o i l o r pu lver -ized coal . Where pulver ized ccaf is used, the ccal is f i rs tpassed th rough a pu lve r izer wh ich gr inds the coa I to thecons is tenry o f f lour and then, by means o f a fan , thepowdered coal is b lown into the furnace where i t burnsvery much as a gas f lame,

Most of the large coal- f i red p lanrs roday are f i red by pul .ver ized coal . One reason for th is is that the contro l ofpu lver ized coa l f i r ing is much more f lex ib le ihan s tokerf i r ing . Wi th s toker f i r ing there is a lways a bed o f coa l onthe gra te wh ich conta ins a cons iderab le amount o f heat .

I

S imp le d iag ra rn o f p r l ve r i zed coa l f i r i ng .

\N N A G N E TR S i \ I O V : SS T R A Y I R O N

P U L V E R I Z E R

. - A I F S U P P L Y

,WVlr- ; L A M E

' - - B U R N E R

Even i f the cca l sucp ly were cu t o f f comOle te ly , the coa l

on t he g ra te wou lC con t i nue t o bu rn f o r an app rec iab le

length of t ime. Vr / i th pulver ized coal there is no sucn reser '

voi r of heat anc i f the coal supply is cut of f ccrnbust ion

ceases ins ian t ly . The same is t rue o f o i l o r gas . A lso , the

rnax imum ra r i ng o f s toke rs i s l im i t ed . W i th pu l ve r i zeC coa l

f i r i ng , ve ry mucn !a rge r bo i l e r s can be bu i l t .

The use o f pu lver ized coa l ins tead o f s tokers eoes no t

change the bas ic c r inc ip le o f opera t ion as fa r as ine power

p lan t as a who ie i s concerned; i t mere ly invo lves a c i f fe ren t

type o f equ ip rnen i .

Ef f ic iencyNow, what aocut s team pressure? In one o f the io regOing

paragraphs we sa id someth ing about e f f i c iencY be ing re '

la ted to s tearn pressure . l s th is t rue?

Yes, but largefy because steam pressure is re late i to tem-

pera ture . The h igner the pressure o f s tearn , the h igher i tS

tempera ture . A t a tmospher ic p ressure , tha t i s , 15 cs i abso '

lute pressure, f ieam has a temoerature of 212 F. At 500 psi

abso lu te , the te rnpera ture o f s team is 449 F .

The ef f ic iency of a turb ine, or any other k ind of heat

engine suCh as a steam engine or a gas engine, ioes not

depend upon the na tu re o f the work ing med ium-s team,

compressed a i r , ammonia , e tc . -bu t upon the quan l i tY and

the abso lu te ie rncera ture o f the heat rece ived and the heat

re jec ted . Th is means mere fy tha t a tu rb ine supp l ied w i th

s team ar 400 7 and exhaust ing i t a t 212 F is more e f f i c ien t

than o ne rece iv ing the s team a t 300 F and exhaust ing a t

212 F . A l so , a t u rb ine rece i v i ng s team a t 400 F and ex '

haus t ing a t 2 i2 ? i s /ess e f f i c ien t than one rece iv ing the

s team a t the same tempera tu re (400) bu t exhaus i ing i t a t

1OO F . Th i s no i on l y exp la i ns t he va lue o f t he condense r

but a lso tha t o i h igh s team pressure . Wi thout the condenser ,the lowest tencera ture a t wh ich s team can be exhaustedis 212 F , s ince tha t i s the tempera ture o f s team a t a tmo-

sphe r i c p ressu re . 3y meanS O f t he condense r , hOweve r , a

vacuum can be c rea ted so tha t the s team wi l l exhaus t a t apressure o f , sey , 10 pounds be low a tmospher ic p ressure ,

t ha t i s , a t 5 ps i (mode rn t u rb ines exhaus t a t abou t 2 ps ia ,

o r even l ower i . A t 5 ps i abso lu te , t he s team tempera tu rewou ld be 162 7 .

The t h i ng t ha t i s i r npo r tan t i n t he ope ra t i on o f a t u rb ine o r

10

any o ther k ind o f heat eng ine , then, i s the te rnpera ture

range th rough wh ich the heat energy fa l l s in i t s passage

th rough the eng ine . The t he rma l e f f i c i ency o f t ne eng ine

depends uDon th i s t empera tu re range . Th i s Qn be ex '

p l a i ned ve ry s imp l y by imag in ing a pe r fec t eng ine -one i n

wh i ch t he re a re no hea t o r f r i c t i on l osses o f any k i nd .

O f cou rse , sucn a mach ine cou ld neve r be bu i l t . Assum ing

tha t we had such an eng ine , however , le t us ccnneCt i t to a

source o f s team hav ing a tempera ture o f 400 7 . A lso ,

assume tha t the eng ine exhausts aga ins t a t rnospher ic

pressure . Thd exhaust s team then wou ld have a temper '

a tu re o f 212 F .

Now the thermai e f f i c iency o f such a per f ec : eng ine is

eas i l y f i gu red bv means o f a ve ry s imp le equa t i on . He re i t i s :

T ' - T "E = { - x 1 0 0

1 . 1

In th is express ion , E s tands fo r e f f i c iency in pereent , T1 is

the abso lu te tempera ture o f the s team enter ing the eng ine ,

and T2 is the abso lu te tempera tu re o f the s team leav ing the

eng ine . So , w i t h 400 F (860 abso lu te ) ' f o r t he en te r i ng

s team and 2 i2 F fo r the exhaust , the e f f i c iency o f th i s

theoretical engine is:

860 - 672 188i00 x - = - = 21 . 8 Pe rcen t

860 860

I ns tead o f len ing the s team f rom th i s eng ine exhaus i aga ins t

atmospher ic cressure, suppose we acach a concjenser to the

exhaust ooen ing to p roduce a back pressure o f 5 ps ia . As

exp la ined prev ious ly , a t th is p ressure the tempera ture o f

steam is 162 7 (162 + 460 = 622 abs) . Now the eguat ion

wi l l g ive us an e f f i c iency o f

860 - 622 238 .,_ ?A'1 n n v - = 1 t - = J : ' -

860 860

So, by the add i t ion o f the condenser , we have ra i sed the

ef f i c iency o f the eng ine f ro m 21 .8 to 27 .SYo.

Th is s imp le example , then, shows why power eng ineers

have been str iv ing, not on ly for h igher and h igher steam

temperatures, but a lsO fOr lower exhaust temperatures. The

greater the range between the temperature of the steam

enter ing and leav ing the tu rb ine , the h igher w i f l be the e f f i -

c iency of the turb ine.

Of course, there is no such th ing as a per fect heat engine,

and in pracr ice the ef f ic iencies obta ined are much lower

than those cons idered in th is example fo r s im i la r temper '

a tu re ranges . By us ing much h igher tempera tures , h igher

actual ef f ic iencies can be obta ined. The most ef f ic ient con'

vent iona l s team power p lan t in opera t ion has an overa l l

eff iciency of about 40o/o.

I t shouf d be per fec t l y c lear a lso , tha t when a condenser i s

added to a syf iem, large guant i t ies of cool ing water must be

pumped th rough i t . A lso , the condensate has to be pumped

out o f the condenser . Th is requ i res power and th is added

power has to be subtracted f rom that developed by the

turb ine when the e f f i c iency o f the sys tem as a who le i s con '

s i de red " We do no t ge t some th ing f o r no th ing i n t h i s wo r l d .

And th is is as i t shou ld be; i t makes the power engineer 'sjob in te res t ing regard less o f wh ich branch o f the f ie ld he

*Temp. Absolutedegrees below zero

Temp. F + 460. Absolute zero is 460

F.

P O W E R E N G I r u E E R I N G

may spec ia i i te in . Take th is ques t fo r the a t ' ia innent o fhigher steam :gmperatures and lower exhaust ternperatures.fo r example . Th is has led the power eng ineer in io a l l sor tso f complex th ings invo lv ing chemis t ry , phys ics , rne :a l lu rgy ,techn iques o f manufac ture and cons t ruc t ion , an i , c f course ,economics . H ic l s team tempera tures and pressures :ogetherw i th sys terns c f h igner and h i -oher capac i ry necess i ta re a l loys tee ls capab ie o f w i ths tand ing the h igh temperarures andpressures; hign rates of evaporation in boi lers io,oeiher withhigh pressures and remperatures make elaborate feeCwatertreating systens necessary, involving constant, ciose chem.ical control; hi_oh pressures and temoeratures also affectthe character oi the piping arrangements, valves, f i t t ings,and methods o i insu ia t ion as we l l as many o ther th ings .

With the use oi high pressures and temperatures the simplemethod of hea:in_o ihe feedwater by exhaust stearn fromthe bo i le r feeC pump or o ther s team dr iven aux i l ia r iesshown in the les: version of our system ion page 9) wi l l nolonger suff ice, because the feedwater must be heated to afar higher remgerature before i t enters the boi lers. Modernboilers operaring ai sieam pressures of 2500 or 3500 psirequire higher ieedwater temperatures to avoic severestrains. The usa of higher temperatures and more heatersa lso improves g ian t e f f i c iency , as exp la ined be low.

So we have the oroblem of increasing the feedwa:er tem-perature. Whar is the besr way of doing i t? Of ccurse, oneway of cioing i : would be to use high-pressure, hign-tem-perature l ive steam irom the main header anc ieei i t intoa special feecjwater heater capable of withstancin-o thehigh pressure. This, however' , would be wastefui. The steamin the main header is the most valuable commodity we havein the systern, and every pound of i t should ce cjei iveredto the main turoing where i t can do the most good.

Another me iho i rvou ld be to supp ly the heat regu i reC fo rfeedwater heai ing from a separately f ired water hea:er butthis would be even less eff icient rhan taking i ive stear,:r fromthe bo i le r i t se l f .

Suppose, however, that feecjwater is heated by siaam ex-tracted from an inrermediate stage of the main tur.bine;then power wil l be developed bv the steam used for feed-water heating. Moreover, this addit ional power _oeneratedby the extraced sream wil l be produced at a very higheff iciency and - ir is, in turn, wi l l increase the avera_oe eff i-ciency at whim the total power output of tne svstemis generared.

Now, why is this so? Why cioes this extracted steam oro-duce power at a much lower fuel cost than that of powerproduced by steam f lowing ro the condenser? The answerto th is ques t ion l ies deep in thermodynamic theory bu t fo rprac t ica l purposes i t can be exp la ined as fo l lows. ln eventhe best modern condensing turbine power planrs, approx.imately two-thirds of the heat present in the steam at theturb ine in le t i s s t i l l i n the s team a t the exhausr . Even i f i twere possible tc have a 10Qo/o eff icient turbine, the arnounto f heat th rown ?way a t the exhaust wou ld no t be-orea t lyreduced. Ac tua l l v , th is heat i s car r ied away by the cco l ingwater f low ing th rcugh the condenser .

Th is means, rhen, tha t even a t bes t , less than one- th i rd o fthe heat in the fuel can be turned into power in a straightcondensing cycle. l f however, we extract a port ion of thesteam from the turbine before i t reaches the condenser, anduse i t to hear the feedwater , none o f the heat in th is s team

P O W E R E N G I T { E : 2 I N G

wi l l be w 'as tec j because i t w i f l a l l be abso rbed i n rhe bo i l e rf eedwa te r . Thus i t dec reases , hea t un i t f o r hea t un i t , t hehea t wh i ch n rus t be supp l i ed t o rhe bo i l e r .

Pu t t i ng i t ano the r way ; o f t he s team f l o r ru i ng : r om theth ro t t l e t o t ne condense r , ove r iwo - th i rCs o f i he hea t w i l lbe t h rown away , wh i l e o f t he s team f l ow in_c f r om theth ro t t l e t o an ex t rac t i on open ing , no hea t w i l l De was ted .I t f o l f ows c j i r ec t l y , t hen , t ha t t he more power t ha t can begenera ted DV ex t rac ted s team, the h igher w i l l be the averagep lan t e f f i c iencv . Of course , the amount o f s team vrh ich canbe used f o r feedwater heat ing is oererm ined by the amounto f heat neeoeC to ra ise the tempera tu re a f the bo i ie r feed-water to the requ i red leve l . Th is p laces an uoDer l im i t onthe ga in in e t f i c iency wh ich can be mac je in rh is way.

As i n t he p rev ious d iag rams , s team f rom the bo i i e r en te rsthe tu rb ine and f lows th rough the tu rb ine s rages , genera t ingpower . Mos i o f the s team passes th rough the en i i re tu rb ineand exhausrs in to the condenser . A pan o f the s team,however, is extracted f rom an intermediate s iage of theturbine at a pressu re and tem peratu re h igher than thata t the exnaus i .

Here is ihe way in wh ich we can take advan iage o f th isschem e .

In order that the temperature of the feedwater be h ighenough, i t is necessary in th is case to extract the s ieam ata point in the turb ine where the temperatu! 'e is some-where in the neighborhood of the temperature of the waterin the bo i le r . Th is , o f course , l im i ts the amount o f powerthat can be obta ined f rom th is extracted steam. l t wouldbe bener i f an extract ion po int cou f d be locared c loserto the exhaust end o f the tu rb ine in the manner shownbe low.

M A I N S T E A M

CONDENSED STEAMDRAINS TO CONDENSER

H 2

>

t-T O B O I L E R B . F . P U M P P U M P . r '

1 1

\TWE LLr = n

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I n hea t i ng wa ie r o r anv o the r subs tance t o a h i ghe r t em-gera ture , hon,ever , cn ly a gOr t ion o f the tq ta l heat neces '

sa ry need be e t l he h i ghes t t e rnpe ra tu re ; much o f t he t o ta l

hea t i s used i n hea t i ng t he l va te r t h rough a l owe r range o f

I empera tu res . \ ^u i i h t h i s f ac : i n m ind , i t beco rnes Doss ib l e

to heat ine :eedr ,va ts r succgss ive ly in two or rncre s tages .

He re we have iwo f eedwa te r hea te rs , a l ow-p ressu re , l ow '

t empera tu re ccen hea te r r ece i v i ng ex t rac ted s team f rom a

s tage c l ose i o i he con iense r , and ano the r One rece i v i ng

s team f rom an ex i i ' ac t ion po in t c loser to the th ro f l le . Water

f rom the ho iwe l l i s f i r s i purnped to heater H 1 where i t i s

ra ised to a re ia t i ve iy low lem pera ture . Then i t ! s pumped

through the seccnd hearer where i t i s ra ised to a temper '

a tu re c l ose : o i ne t empera tu re o f t he wa te r i n i ne bo i l e r .

Th is i s a c losed heater . The leedwater passes th rough tubes

and the s tearn ccnoenses on rhe ou ts ide o f the tubes . Wi th

th i s a r rangemen t , i t w i l l be Obv ious , more power Can be

obta ined f rom tne to ta l amount o f ex t rac ted s team. In

Other w9rd5, by ihe use o f two heaters ins tead o f one, w€

have increased tne e f f i c iency o f the sys tem.

So the ques i i cn a r ises , i f iwo heaters a re be t te r than one

why wOulc j no t th ree be be t te r than two , Of four be t te r

than th ree? The answer , o i course , i s tha t each ac id i t iona i

s tage o f ex t rec i ion improves the thermal e f f i c iency . F low '

eve r , i n t h i s i ns tancg , as i n a l l eng inee r i ng p ro jec i s , t he re i s

a p o i n t o f o i r n i n i s n i n g r e l u r n s b e y o n d w h i c h : h e f u r t h e r

add i t io n o f hearers becorn es unecono m ica l . Theore t ica l l y

max imum e i ; i c i ency wou ld De ob ta ined bV meens o f an

in f in i te numcer o ; ex t rac t ion co in ts and feec iwa ier heaters .

Ac tua l l y , f ou r o r f i ve s tages a re common ly usec j and some

of the most r i roc jern star ions use seven or e ight .

The methoc j c f heat ing the co i le r feedwater in th is fash ion

is known as regenera t ive fee iwater heat ing ; i t i s used in a l l

modern s iear i " t cower generai ing sysiems. With sucn systems

a to ta l o f 20 io 30Yo o f the th ro t t le s team may De w i th '

d rawn f rom ine tu rb ine ar var ious po in ts and usec j to heat

th e f eeciwater.

In the d iagram be iow we have incorpora ted four s tages Of

feedwater heat ing in our sys tem wi th th ree open heaters

ind ica ted and one c iosed h ea ter . A t each heater the water

i s r a i s e d t o a h i g h e r t e m p e r a t u r e . S i n c e t h e 3 r a s s u r e i n

eaCh Open hea te r i s h i ghe r t han i n t he one C reced ing , a

pump i s necessa rY De lween success i ve hea :e rs . F ina l l y ,

a f t e r t h e w a t e ! ' p a s s e s t h r o u g h t h e l a s t o O e n h e a t s r , t h e

bo i l e r f eed cu ,T c cu n cs i t t h r cugn t he c l osac nea te r and

de f i ve rs i t t c l ne eccno i ' n i ze r sec i i on o f t he bo i i e : .

f t i s ve ry ev i cen t f r o rn t h i s c i ag ram tha t e i ea rn powerp lan t can beccn re cu i i e connc lex when we : r v r o t akeadvantage o f a l l the n ' ' re lhoc js ava i iab le Io inc :ease i t s e f f i -c i ency . I nQeec , t he c i ag ram, as shoWf , , i s s : i l l ; a r f r om

co rnp f e te . Wh i i e an a i r hea te r i s snown , t he ; ans and con -nec t ion to the a i r heater have beer i le i t ou i sc as io keep

the d iag ram s i r nc le . Ac iua l l y , o f ccu r se , t he a i r i s f o r ced

through the a i ; ' hea ter oy means o f a f an , anc a f r .e r be inghea ted i t i s f o r ced i n t c t ne ru rnace ; i n t h i s manne r :

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This shows horv ihe forced draft fan forces cold air ihroughthe a i r heater anC how the warm a i r i s fo rced th rougn duc ts(wh ich mus i b€ insu la red) in to a p lenum chamber under -neath the s ioKer . Here i t passes th rough the coa l ceC andthus supoor ts ccmbust ion . A por t ion o f the warm a i r i s a lsoadmi t ted abovs ine f ue l bed.

The a i r hearer , i i w i l l be no ted , i s p laced d i recr ly acove theout le t o f the i . . l fnace. S ince i t i s bu i l t o f a g rea t many tubes ,i t introduces a cer:ain amount of resistance to tne f low ofthe ho t gases o f combust ion . In o lder p lan ts where a i rheaters were nor used, a ta l l s tack or ch imney usua l ly p ro-duced suff icien: draft to pul l rhe gases out of the furnace;but where air neaters are used i t has become gener.al prac-t ice to place an exnaust fan in the passage to ihe siack.Such fans are known as inciuced draft fans. In some cases,the forced o; 'a- ian is macie powerful enough tc ,-naintainf low through :;re boi ler without the need for an induceddraft fan. Sincg inciuced draft fans have to operare at com.paratively hign ternDeratures and handle al l the gases ofcombustion, ihey ofren are very large. Motors as large as5000 hp, or even larger, may be used, and stearn turbinedrives may be used for the largest plants,

The plant as we have now designed i t is a fair ly -oood cowerplant but i t lacks several imoortant elements. One oi theseis a superhear:: ' . The purpose of a superheater is ro heatsteam above i1e temperature at which i t is procjuced in theboiler. ln prac:icg, the superheater is merely an arrange-ment of al loy s:eel tubes placed in the gas path through thebo i le r . A f te r :ne $eam co l lec ts in the bo i le r d runn i i cassesthrough the suoerheater tubes and is thus heatec io a tem-perature higher :han that associated with the pressure atwhich i t is crocjuced. For example. saturated sieem at1000 psi absoiure oressure has a temperature c; 556 F(remember sieain ai atmospheric pressure has a iemper-ature of 212 ?i. Now, by passing the 1OOO psi sieamthrough the suo€rheater, i t can easi ly be heated to a tem-perature of 2OO de-orees higher, or 756 F. The pressure wil lremain the sarne.

Such superheared steam has two advantages over steam thatis not superheatec; f i rst, i t increases the thermal ;-ange ofthe steam cycie, and hence the eff iciency; and seccnd,being drier, i r is less l ikely to condense in the lower stagesof the turbine. In large turbines, the formation of cjrops ofwater on the blacies near the exhaust end of the turbinecan be quite cjamaging. By the use of superheared f ieam,however, this conoensation can be minimized to a pointwhere i t is harmless. Hence, al l modern fossi l . f i red powerplants use superheated steam; indeed in the most modernplants, in acicj i t ion to the superheater, the steam is re-heated in a seccnd superheater after i t has passed througha ponion of ne turbine. With such an arrangement, , teamcollected in the f leam drum of the boi ler passes f irstthrough the grimary superheater, then through the f irstfew stages of :he turbine, then back to the boi ler whereit is reheated in the reheat superheater, and f inal ly is sentback to the lower pressure stages of the turbine anc so tothe condenser.

As a ru le , the reheated s team has a tempera ture on lv al inle below the of the primary steam but the pressure iscons iderab ly lower . As an example , the pr imary s ream mayhave a pressure of '1400 psi and a temperarure of 1050 F.After this has passed through a number of stages in theturbine i t is extracred at, say. 200 psi where i ts iemper-

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ature w i i l De around 400 F . I n tne reheat sec : ion o f thebo i ld r th is s ieam wi l l then be heated to a re ! :ncerarure o f1000 F . l r s s ressure , however , w i l l s t i l l be near ly 200 ps i ,w i th jus t a s rna l l p ressure drop in the p ip ing .

So now we nave superheat , reheat , and regenera t ive feed-water hear ing in our sysrem (d iagram above) and i t i s be-coming very e f ; i c ien t , ds s team cyc les go . w i th sys iems o fth is k ind, thernnaf ef f ic iencies of about 3?o,6 can be ob-ta ined-tha: is , 32oio of the heat energy in rhe fuel wi l l beconvertec inro e lectr ic i ty .

You may wcncer why th is f igure is so low. The reason, asimp l ied ear i ie : ' in rh i s r rea t ise , r ies in the f ac : tha t mosro f the hear i s car r ied away by the condenser coc i ing water .Unfor tuna ie iy , :h is low e f f i c iency is a conseeuence o f thesecond law o i thermodynam ics and there is Drac t ica l l yno th ing tha : eng ineers can do about i t . t f the iempera tureo f the s teann a : :he exhaust o f the tu rb ine cou lc j 5e broughtdown to acso iu te zero , we coufd reccver a lmos i a l l o f theheat energy in :he fue l , bu t we l i ve in a wor tc where theambient temoera ture is sorne 490 F above abso lu te zero ,and there is nc economica l way by wh ich we can reduce thetempera ture o f the ex i t s team be low ambien t tempera ture .Of course , we ccu ld do i t by re f r igera t ion , bu t the re f r igera-t ion system wou id regu i re power and so we wou ld ga innoth ing . Inc iee i , we wou ld lose e f f i c iency .

We have now incorporated into ou r system about a l l theknown methods fa r improv ing the e f f i c iency . Funher im-provement can be made in any sysrem by going to st i l lh igher pressures and temperatures, by ref inemen$ in thecondensing systern, and by the funher reduct ion of heatlosses wherever they occur by improved equ ipment , insu la -t ion , and recovery o f m inor wastes , bu t the ga ins to beexpected by these means are re la t i ve ly smal l . In la rge powersSat ions, however, each increment, each f ract ion of a per-cent in the overal l e f f ic iency is wonhwhi le because suchs ta t ions use mi l l ions o f tons o f coa l a year , and even smal lgains in therrnal ef f ic iency ref lect large savings in fuel costs.As ind ica tec ar the beg inn ing o f th is d iscuss ion , moderns team-e lec t r i c genera t ing s ta t ions use less than one- th i rdthe amount o f coa f fo r the same k i lowat t ou tDut tha t theyd id in ear ly years . Th is sav ing has been brought about bycont inua l re f inements such as descr ibed in these pages.

I t i s obv ious , then, tha t in the opera t ion o f a power s ta t ion ,every ef fon has to be made to keep the temperaturei , pres-sures , and the vacuum in the condenser a t the i r op t imumva lues a t a l l i i rnes . A change in any one o f these va luesaffects the eff iciency of the systern as a whof e, In the con-

13

d e n s e r , f o r e x a n n D l e , t h e v a c u u m m u s t b e m a i n t a i n e d a t i t s

h i g h e s t v a i u e 3 y t h e u s e o f t h e c o l d e s t a v a i l a b i e c i r c u l a t i n g

w a t e r . S i n c s : n e c i r c u l a t i n g w a t e r u s u a l l y i s C i ' a w n f r O m

r i ve rs o r l axes , t he t empera tu re va r i es t h roughou i t he yea r ,

wa rm ing uc i n su i im e r and becoming coo le r i n v / i n te r . Th i s

means , gene ra l l y , i ha t a bene r vacuum can be rna in ta i ned

in t he w in :e : ' : han i n t he summer , and a SOmewna t g rea te r

power p ro iuc : i on i s poss ib l e .

One e lemenr i n power s ta t i on ope ra t i on t ha t has rece i ved

an eve r i nc reas ing amoun t o f a t t en t i on i n r ecen t yea rs i s

t ha t hav inc : c do w i t h t he de l i ve ry o f pu re f eecwa te r t o

the bo i ie r . i ' ' i c ie rn h igh-pressure bo i le rs evaoora ie severa f

m i t l i on pouncs o f wa te r pe r hou r , and t hey do t h i s 24 hou rs

a day , 365 Cays a yea r . W i th such t r emendous ra tes o f

evapora t ion , i r i s obv ious tha t i f the water de l i vered to such

bo i l e r s con ia i ned even sma l l amoun ts o f sca le - f o rm ing

mater ia ls , ine in te rna l heat ing sur faces o f the bo i ie rs wou ld

soon becorne so coated w i th sca le tha t overheat ing and

subsequen i ; a i i u re wou ld resu l t .

Because o f :n is , e labora te sys tems o f chemica i feedwater

t rearment have been deve ioped wh ich no t on ly rec juce the

sca le - fo r rn ing mater ia ls to p rac t ica l l y zero bu t a iso reduce

the oxygen :cn ten t to reduce cor ros ion . Oxygen in ho t

water i s an ex t remely cc r ros ive agent . Somet imes these

feedwater r ; 'ea tment sy$ems invo lve evapora tors in wh ich

raw waier is evaporated by steam extraCted f rOm the

turb ine anc inen condensed. Other sys tems use ion ex '

change iyce oeminera l i zers , o r chern ica l t rea t i :nent wh ichprec ip i ta tes :ne sca le - fo rm ing mater ia ls in the fo rm o f

s l udge be fo re :he wa te r en te rs t he bo i l e r .

I t shou lC be obv ious tha t the amount o f water tha t need be

added ro i ne sys rem wh i l e i t i s i n ope ra t i on i s sma l l , s i nce

a l l the s iea i i f low ing th rough the tu rb ine is conc iensed and

re turnec i to ine bo i le r . There are s rna l l losses , however ,

wh ich have to be replaced by what is known as makeup

water . Th is makeup is the water tha t has to be t rea ted .

Another iaccr that has beccme important in the operat ion

of la rge power s ta t ions is the emiss ion o f dus t and f l yash

from the nacks. In p lants where many thousancjs of tons

of ' coa l a re burned a day , the emiss ion o f f ine ash f rom the

stacks can beccme a ser ious nu isance and in most com-muni t ies o rd inances have been enac ted requ i r ing power

s ta t ions to re iuce the emiss ion o f f l yash and dus t to a min-

imum. Th is nas no t been an easy prob lem to so lve and many

rn i l l i ons o i co l l a r s have been spen t i n deve lop ing equ ipmen tfo r co l lec t ing such dus t be fore i t en ters the s tacks .

A number o f d i f fe ren t methods are in use . In one type o f

system, the f lue gases are passed between electr ica l ly

charged pla ies. The intense electrostat ic f ie ld charges the

dus t pan ic ies , eus ing them to be a t t rac ted to the p la tes .

Af te r the cu f i has accumula ted to a cena in tn i ckness onthe p la tes i : i s sc raped or knocked o f f . In o ther sys tems,the f lue gas is u rh i r led th rough cyc lone separa tors o r passed

through sprcvs o f water . In any case, whatever sys tem is

used , t hey e i? expens i ve and i nvo l ve h igh o rc i e r s o f eng i -n e e r i n g s k i l l i n t h e i r d e s i g n .

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A l l new cca l - f i r ed bo i l e r s w i l l p robab l y a l so have t o beequ ipped w i :h f lue gas desu l fu r iza t ion sys tems to remove

su l f u r ox ides f r om the f l ue gases . Th i s i s ano the r h i gh l ycomplex sys ie rn tha t inc reases opera t ing prob lems.

1 4

The comp le te p l an t

So fa r we nave been conce rned on l y w i t h t he s t?a rn end o f

t h e p o w e r s y s t e m , a n d h a v e o n l y m e n t i c n e C : n e e l e C t r i cgene ra ro r i n pass ing .Th i s i s due t o t he f ac t i ha : r nos t o f t he

economies t ha t can be ach ieved i n t he ope ra t i on o f a s team-

e lec t r i c gene ra l i ng s ta t i on l i e on t he s team s ioe . The mode rn

e lec t r i c - oene ra lo r i s an ex t reme ly re l i ao le anC e f f i c i en t

mach ine . ' Modern genera tors have e f f i c ienc ies as h igh as

99Yo so ine adc j i t iona l ga ins tha t can be maie in the im 'provement o f genera tors i s smal l .

As po in tec ou t a t t he beg inn ing o f t h i s bcok ie : , an e lec t r i c

gene ra to ! ' cons i s t s bas i ca l l y o f a magne t sc i nn i ng i ns i de a.g roup o ; cc i l s o f w i re . As t he ro ta t i ng r "nagne l i c f i e l d cu t s

the convo iu t i ons o f t he s ta t i ona rV co i l s , e l e f i r i c cu r ren t s

are se t uO in the co i i s , and by proper ly ccnnect ing them

Curren ts o f a lmost any requ i red vo l tage can 3s produced.

Mocjern generators produce current anvwhere between

1 3,000 ancj 26,000 vol ts . Where the e lec l r ic i ly has to be

t ransm ined over long c j i s tances , the genera is r vo l tage is

Stepped uc by means Of t rans fOrmers . A t t 'ans ;c rmer i s a

sor t o f e lec t r i ca l lever by means o f wh icn vc l ta -oes can be

stepped up or rec juced to any c ies i red value. Transformers

are the most ef f ic ient large mach ines m an has yet devised ;

some o f tne la rger un i ts have e f f i c ienc ies h igher ' :nan 99o, to .

Now, i n i ne l i gh t o f a l l t h i s , l e t us f i na l l v r e i r aw the d ia -g ram o f cu r power p l an t ( page 15 ) t o i ncc r3c ra te eve ry -

th ing we have ment ioned. As you see, i t ; " ias become ah igh ly cc rnp fex a f ia i r invo lv ing many brancnes o f sc ience-phys ics , chemis t ry , meta l lu rgy , thermocynarn ics , hydrau-

l i cs , s t ruc iu ra l eng ineer ing , e lec t r i c i t y , e tc .

Comp lex as i t may seem, t h i s d i ag ram i s s i i l l cn l y t he s im 'p les t o f schemat ic d iagrams; an ac tua l power c lan t layout

has in i t count less o ther smal l and la rge dev ices and sub-

sys tems no t shown o r on l y i nd i ca ted on t h i s 3 ! ' aw ing .Fo r

example , so fa r in th is t rea t ise we have sa iC no th ing about

the comoust ion cont ro l sys tem. l t i s ind ica tec on th is d ia '

g ram mere ly in bare de ta i l , showing on ly the bas ic dev ices .

Ac tua l l y the combust ion cont ro l sys tem in a la rge p lan t

would require a large separate drawing, s ince i t is very im'

portant and the operat ion of the stat ion woulc i be v inual ly

imposs ib le w i thout i t . In i t s s imp les t fo rm , i t cons is ts o f a

dev ice wh ich is sens i t i ve to s l igh t var ia t ions in s team pres '

sure . Th is dev ice , in tu rn , con t ro ls a var ie tY o f re lays and

?ctua t ing mechan isms wh ich au tomat ica l l y con t ro l the f low

of fue l , a i r , and water to the bo i le r in acccrdance w i th the

vary ing ioad cond i t ions .

The diagram also incorporates reheat and both h igh - and

low-pressure turb ines. Af ter the steam has passed through

the h igh-pressure tu rb ine , i t i s re tu rned to the bo i le r and,

a f te r be ing heated aga in , i t i s de l i vered to the low-pressure

turb ine . A lso , there are two se ts o f water neaters , th ree

low-pressure heaters tak ing ex t rsc t ion s team f rcm the low-pressure tu rb ine , and two h igh-pressure heaters us ing ex-

t r ac t i on f i eam f rom the h igh -p ressu re t u rb ine .3e tween the

two sets of heaters is a deaerating heater in wh ich the

oxygen in the f eedwater i s bo i led o f f . Oxygen in bo i le r

water a t h igh pressures is ex t remely cor ros ive and must be

removed be fore the water i s de l i vered to the bo i le r . Th is

is done by the deaerat ing heater which, in e i fect , is merely

a l a rge i ank o f wa te r bo i l i ng unde r a tmosohe r i c p ressu re .

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EVAPORATOR

The necessity for proper feedwater treatm ent has a t readybeen ment ioned. On the d iagram, the feedwarer t reat ing sys.tem is merely indicated. l t consists of a chem ical r reat ingsystem feeding into the plant system through an evaporator.Af l the makeup into the p lant sysrem passes through theevaporator. Thus the makeup water (the water which has tobe added to the system cont inual ly to replenish warer lostby feakage and blowdownl enters the system in the form ofvapor, which is del ivered, ?s shown, to the deaerat ing feed-water heater . ln the evaporator the incoming water is heatedby exhaust s team from the boi ler feed pump turb ine oro ther s team dr iven aux i l ia r ies . As a l ready ment ioned, a de-mineral izer may be used instead of an evaporator .

Note that the boi ler feed pump turb ine receives sream fromthe main s team header th rough a reduc ing va lve and a de-superheater . l t is not usual to use su perheated steam forsmal l aux i l ia ry tu rb ines fo r severa f reasons . F i rs t , the meta lsthat must be used wi th superheated steam are very ex-pens ive ; and second, h igh thermaf e f f i c iency is nor so im-ponant in an auxi l iary turb ine s ince the heat in the exhaustis returned to the system. l t becomes expedient , thereforeto f i rs t reduce t f re h igh-pressure steam from the main steamsystem to a lower pressure by means of a reducing valveand then to dauperhear th e stea m by sp ray ing ware r into

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i t . In th is way, low-pressure, saturated steam is c je l iveredto the auxi l iary turb ines.

The diagram shows a symbof labeled ' -

*f in." Because of the continual recycl ing of the waterthrough the boi ler and because of s t ight leakages in thesystem, the boi ler water tends to increase i ts concentrat ionof impur i t ies {ca le - fo rming sa f ts . To keep th is concent ra -t ion to a min imum, i t i s necessary to b low down the bo i le rper iod ica l l y o r con t inuous ly . In smal l power p lanrs , th is i sdone per iod ica l l y by the operaror by mere ly open ing ablowoff valve for a few seconds and blowing out the waterin the lowest paf t of the boi fer where the concentrat ion ish ighes t . ln la rge p lan ts , the amount o f heat los t by suchb lowdown prac t ice tends to be ra ther h i lh , so ccnr inuousblowdown syf lems are used. With such systems a smal lamount o f water i s w i thdrawn cont inuous ly and runthrough a heat exchanger in wh ich the heat f rom tne b low-down is t ransferred to the incoming feedwater .

These are some o f the thousand and one de ta i l s o f a modernpower p lan t tha t make i t the compf ex th ing i t i s . l t i s no tthe intent here to consider af l these deta i ls but m erely topoint out that they exist . L i t t le has been said about contro lexcept b r ie f ment ion o f the combust ion cont ro f . The ta t te r ,

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however. cons: i tu tes only one e lement of the sta i ion con'

t ro l as a whoie. Today, most power s iat ions are contro l led

from a s in-o ie ccntro l room where quant i t ies f rorn a l l par ts of

the p lant are r reasured, ind icated, recorded and' in tegrated.

The mociern generat ing s iat ion is one of the most com'plete ly automated systems man has c jev ised; i t has to be

because it w,ould be virtually impossible for operators to

watch and ac3urately conirol all the varying quantit ies in'

vo lved in the ccerat ion of the p lant . Indeed, i t has become

impossib le to keep t rack of a l l the pressures. temperatures.l iqu id levels and speeds of a l l the var ious machines wi th '

out some tvpe of automat ic moni tor ing or suoerv isory

system for recording and announcing all the huncireds ofi tems involvei .

The oroteciive features of the station are complex and in-

volved. ln case of t rouble due to fa i lure of a p iece of

apparatus or an electrical fault on the external electrical

system, events happen rapidly. lf the load on a large gen'

erator suddenlv dropped and the turbine governors failed

to act, the macnine, normally rotating at 3600 rpm, would

suddenly increase its speecj and would explocje from cen'

trifugal force within just a few seconds. The 40-ton rotor

of a modern eiectric generator spinning at 3600 rpm has a

rotational energy of 650 mill ion foot'pounds. This is

approximateiy the same kinetic energy that a 40'ton jet

a i r l iner woul i have at a speed of 500 mi les per hour . On

the boiler side, if the feecjwater supplv faiied, the boiler,producing, say, a mi l l ion pounds of s team per hour , would

run drv in 90 seconos.

Since these various types of equipment are valued in terms

of mill ions or dollars, it is obvious that every possible

measure musi be taken to insure their protection. There

are complex insiruments which measure not only the speed

of a turbo-oenerator to a iraction of a revolution' but also

the degree of shan eccentricity and the vibration charac'

teristics of the machine. An expansion indicator shows the

axia l expansion of the turb ine casing.

The large ciia-oram shows the generaior somewhat differ'

ently than the early diagrams; here it is shown symbolically'Also. it is associated with an exciter, a device which, so far,

has not been mentioned. lu purpose is to supgly the mag-

netizing current for the rotating magnet.

ln an actual electric generator the rotating magnet is not

simply a permanent magnet such as is indicated in the

earlier diagrams. A permanent magnet would not provide

a strong enough magnetic f ield, so an electromagnet is used.An elec:rornagnet is magnetized by electricity f lowing

through coils wound around the magnet structure. In thecase of a lar-oe generator a verY powerful direct current issent through the coils on the rotor. These windings areknown as the field coils, since they produce the magneticfield in the generator.

To supply the field coils with current makes it necessary toprovide an arrangement of sliding contacts to conciuct thecurrent from the stationarv to the rotating pan of themachine. Also, it becomes necessary to provide a separatesource of current to exc i te the f ie ld coi ls .

Basical ly , here is how i t is done, though in an actual gen'

erator the shape of the rotor is quite different from thesimple bar magnet shown in th is d iagram.

Two collector rings are mounted on the main generator

shaft as shovrn. These rings are connected to the ends of

I t )

t he f i e l d w inc j i ng .S ta t i ona ry b rushes moun ted on t he co l '

lector r ings conduct the exci t ing current f rom the source to

the w inc j ings on the ro ta t ing member o f the genera tor .

The d i rec t cur ren t needed to exc i te the f ie id w ind ing is

usua l ly supp i ied by a separa te smal l d i rec t -cur ren t genera tor

mounteC on the same shaf t as the main ro to r - Such a smal l

d -c aenera tor i s ca l led the exc i te r because i t fu rn ishes the

exc i ta t ion cur ren t fo r the main genera tor .

The exc i te r c i rcu i t a lso prov ides a means o f co n t ro l l ing the

vo l tage o f the main genera tor . t sy vary ing the exc i ta t ion

current bV means of the f ie ld rheostat , the vol tage of the

genera tor can be cont ro l led be tween normal opera t ing

l im i ts . The speed o f the genera io r , however , i s con t ro l led

by the s team- turb ine governor and th is cont ro l i s ex '

ceed ing l y c l ose .

tn fac t , the genera tor speed is so c lose ly cont ro l led tha t i t

serves as our t ime standard. Most of us these days measure

our t ime DV means o f synchronous e lec t r i c c locks . These

clocks c iecend upon the constani speed of the generator .

Means are prov ided to check th is speed in re la t ion to

accurate inc jependent c locks at the Nat ional Bureau of

Standarc is. Temperature recorders measure the temperature

deep in the in te r io rs o f the w ind ings o f the genera tor ;

d i f ferent iaf re lays guard against in ternal e lectr ica l fa i lure

o f the mach ine . E labora te hydrogen coo l ing sYstems are

provided to remove heat f rom the generator and, by means

of hydrogen coolers in the concjensate system, th is heat is

returned to the feedwater. No heat is lost that possibly can

be saved. Even the heat produced in the bear ings is returned

to the feedwater by means of the o i l coolers in the con'

densate system.

From a f l th is , i t shou ld be c lear tha t a modern power p lan t

engineer has to be a specia l is t of a very h igh order. Al though

the system operates automat ical ly , i t s t i l l needs the gu id '

ance of engineers who are thoroughly conversant not only

w i th de ta i l s o f the egu ipment bu t w i th the bas ic p r inc ip les

upon wh icn i t opera tes . Power eng ineer ing is a f ie id ca l f ing

for the h ighes t eng ineer ing ta len t in bo th des ign and opera-

t ion . l t p rov ides an occupat ion tha t i s a t once s t imu la t ing

and cha l leng ing , and a t the same t ime a f fo rds s teady em-

p loyment in a rap id ly g rowing f ie ld w i th p rac t ica l l y un-

l im i ted oppor tun i ty .

A lso , desp i te th is ra ther long t rea t ise on power p lan t des ign

and ope ra t i on , i t shou ld be obv ious t ha t i t i s , bas i ca l l y , s t i l l

o n f y a p r i m e r . -

B R U S H : S

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