PowerPlantTheoryDesign_2

8/3/2019 PowerPlantTheoryDesign_2

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POWER PLANTrrHEORY AND DESI(~N

Copyright, , 19,59,byTHE RONALD PRESS COM~ANY

PHILIP J. POTTERCopyright , 1949, by

THE RONALD PRERS COMPANY

HEAD PROl"ESSOItDJ


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ToN. U. P.

PR.EFACE

Thi~ ])l)()k P)'(':-'('III" till' fIlIHi:IIIII'III:i1" of l'II!'IIH'I'rlli", :1'< :II'I,lil'd IIIjlO\\TI' pl :t III I k" i,gl l, " ,ll il 'll :1n' 1 ':-'''1'1I i :11I II :1 III1Jl"(1I1".11'oil, '..,I' 11':1111II!; IIIlll('('liallil'al 1'llgiIH'('rillg. ,\" ill 1111' l ir,d I'


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CHAPTEH 1INTRODUCTION

1-1. Magnitude of the Power Industry. During the year uf 19m,prime moyers in "kilowatt-hour factories" in the Unitod States generated(i33 JOn kwhr (about 4OC~. of the world' s total), with an installedcapacity of slightly more than 128 > < l O" kw. The energy delivered torust ()]1l(']'S, after deducting for the amount consumed hy producers andfor transmission and distribution losses, was 561 X IO n kwhr. These fig-me" do not include power generation for mining, manufacturing, and rail-way classifications. Note that these figures show an average generationof approximately GOOOkwhr pCI' kw o r installed capacity.

Prime movers are 1 '0011Tl ' ' ; of Po\H1' such as steam turbines, hydraulicturbines, intcrnal-comhu-l ion cngin(' .s , ga" t.nrhinos, and stoum engines.l\Tore prune-mover capur- i ty is in tll(' Iorm of intcrnal-corubust.ionengines, primarily in automobiles and airplanes, than in any of the otherform". The output of such units if ' not included in the above f igu res ;nevertheless, intornal-combustion engine-driven generators accounted for2.0'/ of t he ' instullcd generating capacity in 19:)7. hydro units accountedfor 21.2~'{!,and "team unit" accounted for 7(j.8j!~.Itis intcre"ting to note that the energy gl'l1l'rat('(i in 1957 is more than11:36'/;, of that ge1lerated in 192;) ami :384'{ of that generated in 1941.During t .h past five yenrs, the annual increase in electrical energy produc-t ion lias beeIl OY('l' 10'/ pl'!' year (compounded nunun.llyl .Another interr-st ing point it' that gOYl'l'lllllent-owl1ed plant" accounted

for about 3j:;, of Ihe ( 'llcrgy g('lJ(Ttdcd in Hl2:3; t h remainder was gl'!l-prated by privately owned plants, The figures for 1957 are radicallydifferent. In that year, cooperative" (primarily cOl l lpan ies whose f inan-cial support is obtained from the Rural Elcct.nflcation Administration.abbreviated REAl generated O.5S{; municipal, stute. aud public powerdistrict systems generated 6.1 ; federal agency plant" generated 17.3'/;;and privately owned utilities generated 7(i.1 ';. of the electrical output.This ilustratce the tremendous growth of various form" of govcrmnentalinroads into the electric power field.Tho national average co-t of electrical energy to l 'l 'C'i(kntial customers

has (jpcreaspd from 3.841 ' IXT kwhr ill Hl40 In 2 ..')(i(.' 1)('1 'kwur in 19;)7.while the aVl'rag(' use has illc] '('a:'Td frullI \)[)2 t o :~](i '1 kwhr durillg theI:Hlll!C' period.


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Of each dollar of revenue received by private utility companies in 1957for the sale of electrical encrgy, 17.0~!.was spent for fuel, 17.11 was spentfor "alaries and wage", and 22.30 was paid to various governments fortaxes . In contrast, RE A systems paid only 2.86f/. of each dollar of revenuefor tax('s.Probably, generation by federal, state, municipal, and publicpower dil-itrirts was simi larly devoid of taxation. The 101'8 in tax rev-enues due to governmental plant!" rnust he eompelH.;ated for by other taxrevenues.These advaJ1e('s in t.h lllagnitl1clc of the power industry have been

accompanied by adY:llH'CS in 1 he s izr- , rdiahiJity, and eff ic iency of sta-tions. In 1920, :~ I II of coul \\'(1"( required to gencrate 1 kwh!'. Now, thesame amount of energy CIlI1 be producer] in large modern plants by lessthan D .G I I> of coal with thermal dficiencies of 42%. The national averagefor ('oal-fueIPd plants in 19;)7 was 0.93 II> per kwhr for the 34 9 X I O ! ) kwhrgpnprated hy this Iuol. In 1940, this figure was 1.34 I II per kwhr of coal.1-2. An Industrial Plant Cycle. A study of some of these modern

plants will show their equipment and facilities. Fig. 1-1 represents anindustrial plant that generateR steam primarily for prOcrKS purposes.However, by g


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.----, ~ ~U""vn.r lU~.u lJ.ESIGN [Ch.lAn important differencc exists between the p oc .'

The Iormer cquipmcnt docs not have a pipe lea~in~sfr:~~I~t~ent 5 antdJ .9,part of the svstem for tl t 1 a any a ierThis indieat 'e 's ' that ei thc:etl: :I~tr~~ of the condensed ~team, called drains,. . . . s edm was consumed m the ' , Idrams were so conhmin'lted "'I'tll'l I.nie I . .' process or t ie, , . vv 01 or c l('Hnca s that it Ids.afe to return them to the boiler Procn, 91 ' . . I'. I. wo.u not bef ,S8 ias a sma Idram I I rrom the .equipment, to return the drains back to the svstc I )Ipe e.aemgbelow ,9 IS a trap or drainer 10 in tIl. lrai I' A -V c em. mmedIately. . eel am me. trap pe' its itmittent flow of drains out of tl . .IIllI S rn er-, .'. . ie eqUI)lInent hut do' t, 1 1pal's into the drain line A I ' . ' " es no. a ow steam toc . , .. (rame]' IS Sllghtlv dIfferent . ,from a trap and permit" continuous flow of c1!-';i I. t . III constructIon~ d.raiI~er ha~ more capacity than a trap bu~ ~s JU,' n~ steam. Usuallym(iJ:-;(T1minately. ' ie "ore s are often usedSince water was lost from the ~ stern wh Jwas wasted, additional water kno~:" . /n t 1~ s~eam used by process 5wafer Jnlmp 11 I 1 1 It. ' n as rna .e-up ISmtrodueed by the raw-, . .n a HI , exceptional eases ,t 1(, .Ither before or after entering the boiler (or ' raw" ater s iould be treated

t10n8 inside the boiler that eventuall will bot:l) t~ prevent seals forma-t .heplnnt of Fi g 1-1 . 't.. Y cause faIlure. of the tubes. In" a 11 0 -process softener 12 h tl ifiraises its temperature with steaJ~ f ' ,0 I !1Ufl es the water andheader. The softener (W('II ' " 1 . . . rolm a lead winch eomcs off the LP. . -,. anges cs~ iarrn fu ] c l . I fllllpuritips that are in the raw water EjJl ~enllca s or the harmfulwhere an v "llld"'e f"()lll tIl!' hot ' ..". " uent IS pumped to a filter 13 h -proee~s soft ' .sand. A filter such '18 t 1 1 1 C ' 11111.'t. .'. ' , ,en(.,1'Il' removed by layers of

ctc ." ~,)( aJT'u)O'ed s tl t tl('leaned periodi("lllv I, ",I' .' 'h ,.0, iar ie sand Iwd can be, .. l} \\ as llng III the reverse r ' ti fwater tuav 1 ) ( ' IIS('(j for thi C rurc ('JOn 0 flow. Raw- r . . , , s purposp.Next, til(' make-np got's to tht' deaerato- !.., .1'ai"ed still [u1'(h(,1' 'lTld (lb'1('('t' J I . .1 " where Its temperature is. '. .trona 1 (' aascs 'He re "d TJhonable gal


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8 POWER PLANT THr';ORY AND DESIGN [Ch.l Ch.1] INTRODUCTION 9

air unci('J'Iwnth t Iw st okt-r ],V wuv o r the (IiI" lJr('III'(ltD/ '('I' l: tt .f ' " . . ' ~,c. us a, (',r piece.. (qlll]lIlJ('ld I" a 1\1],111:11'1(': (1exchanger wi th air ou one side of the tubes' : IJ(,I.I,H~t, ~hl(' ga~\'~ on til(' other. By using the air prchenrcr , sorue of the(~H 1L,), _t 1(:lll. the Ilur ~:I"('" I," ~an'd for tile system, and better combustion1 ' 1 ( , )h t. 111lu l Ill, til\' l . o i l r- r . ~Olll(, of t Il( ' com bus tion air is supplied in j etst 11(lugll t .he t ront of the 1"("11' 'LJ"(iI TI,', 1 . . . '. . ' , . \J:-; 11 ' ~n()\\n as ouerfire alT andassl~.t" III. t lu- ('Olll],\lst ion pro('\'se: bv ('J'("ltin


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10 POWER PLANT THEORY AND DESIGN [Ch.linto the st I It I,' ~eam leaf cr. A stop valve if' shown in the steam line to th eur line. ,~team, to be used f fItt J or pel wa er heating, is extracted from theur line at four points.Exhaust steam flows to the 8/lrface-h} t, " .water is tnken from the inl t t' ,I J.11e ',"IIl c~ndenser . CIrculatingc ,unne )y circula tmg II,Ja,sRinghrough the cond"n~('l' is ( 1 1 ' ' ' ' ' 1 ',! I' ik " pumps anr after

'" '" '0 ov. Iargc( lac t tl . I(h.wliarge tunnel. ' ,. 0 1(' river t trough theCondensate leaving the condenser is firs J , , , 'type of f eedwafer heate I" ", " k '1', st !Ca,ted by a closed or surface

, ".1 ' ) } passmc t ie water till' '1 t 1rounded hv steam from tho I . t h ',' " ',oug 1 u,res th[,tt are sur-, . .' .nc 0\\ Ci) ]l]'('Sf'Ul'C' extracti int fl'1us steam is eond " ' '. , ,Ill" Iom 1e !eater are returned ttl, .tspace ol the condenser throu .) I' ' 0 .nc seam. ' ,. ,g 1 a ( ! 'amer., Next II1 the water cycle is the deaerator B " ,Icedwater from the d("wrator' 1 . ' J " Oller feed pumps take the1 t ' , "


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12 POWER PLANT THEORY AND DESIGN [Ch.1BY, learning the function and operation of the eq" t' Icentral ,t , ti t I uiprnen marge., ;.: .\'1,ons, a srur cnt will be able to under ts d tl ,II .


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14 POWER PLANT THEORY AND DESIGN rci..i1-7. Plant Performance. The term thermal efficiency is of prac-

tically no importance to either the designer or the operator as a means ofexprcRsing stenm-planr pcrformancc. The energy input to the plant foreach kilowatt-h01ll' of output is the accepted criterion of plant efficiency.It is interesting to note that the addition of Home equipment to the plantmay be justified economieally with an improvement in thermal efficiencyof less than 0.02';{,.Plant pcrfol'luancc is usua lly expl 'csRcd as ei ther gross station. h ea t r ateor net sta tion hm i ra t e o In order to illustrate these terms, refer to the

plant portrayed in Fig. 1-2. The performance of this plant could bedetermined by lll('a~llring the kilowatt-hours generated at the generatorterminal:- during a suitable period, and by measuring the coal input to theboiler during the same period. Laboratory tests of the coal burned wouldindieate the Btu of energy released by the combustion of each pound ofthe coal, called the heating value of the coal (sec Chap. 5). The perform-ance could then he expressed as

Gross station heat rate = WIRVkwh I' generatedwhere Wi= weight of fuel burned during the test, lb

HV = JlPating value of the fuel, Btu per lbBtukwhr ( 1 - 1 )

However, some of the eJectl'ieal energy generated must be used withinthe plant 1 0 drive the auxiliary equipment. This includes power requiredby circulating water pumps, eonden:mte purnps, boiler feed pumps, fans,jlllivC'J'izlT;-;01' stoker, de. At rated load on the generator, these aux-iiitlries require Irorn 4.5 to 6 'X , of the generator output for a large modernplant and c :011l( 'what more for 11 small plant. At lower loads, the per-eentage IS greater.Net station heat rate is based on the output of the station after deduct.ing for the power consumed by the auxiliaries.

NT t t . J W,HVet station ieat rate =I Icw II' generated lesskwhr used in plantObserve that the net f:ltation heat rate is always numerically higher thanthe grot's station heat rate and that

Btunet kwhr (1-2)

'I'l I ffi . 3413ierrna e iciency = hcat rate (1-3)Most plants maintain a continual record of their heat rate as a meas-ure of their eff iciency of operation.

INTIWDUCTIONh.1] 15Net station heat rates have decreased steadily during the past years.

In the early 1920's, a net station heat rate of about. 4.1,000 Btu per kwhrwas considered satisfactory; modern units ha vc heat rates of about9000 Btu per kwhr.

EXAMPLE 1-1. During a test a unit was opcrut od at. its rn.tcd load of100000 kw for 12 hr. The coal consumption was 4:29 tons, WIth a h~~atmg valueof 12,670 Btu per lb. Auxiliary power amounted to (j:2,700 kwhr. l'md (a) thegross station heat rate and (b) the net stat ion heat rate.

SOLUTION. (a) From Eq. (1-1),0" 2000 X 19 f~O. - 4 "", X ~,2'__ = nOri\) Btu per kwhrGross stat ion heat rate - 12 x 100,000 '

(b) From Eq. (1-2),. . ' - __i~2_0 .__20 (JQ_~l~~il0 _ =Of).5SBtn per net kwhrNet station heat rate - 12 X 100,000 - (i :2,700

Conventional expressions for costs of fuels, such as ~lollars p~r ton ofcoal, cents per gallon of oil, and cents per thousand cubic feet 0 : , gas, arcmore comparative when converted to cents per million Btu. I'hen theunit fuel cost of electrical energy is:

net station heat rateUnit fuel cost = co s t of IO n Btu of fue lIo n 0-4)EXAMPLE 1-2. The cost of coal for the plant of the preceding example is

$6.30 per ton delivered to the plant. Whnt is the unit fuel cost?SOLUTION.

_$() . :30_xlOn = 24.9 )er IOn Btu2000 X 12,670 IFrom Eq. (1-4),Unit fuel cost =n~,58i~}1.2= 0.238 per kwhr, or 2.:38m ill" per kwhrE 'S 1 tion of Equipment Building a steam-po,ver.-8. conormc e ec . .. C. ' plant is a business enterprise, as is nearly all en~I~een~lg 'York. It 1::;

anticipated that the power plant will return the o.ngmal lIlye~t:ll~nt ~~l~in addition will show a profit. A plant tha~ conforms to these requirements will not necessarily be the most efficient plan.t tb~\t can be ('011-structed. Ithas been previously mentioned tha~ turl:111e~ 1Il , tl:e ~m;~e ,~:2000 to 3000 kw normally have two stages of Ieedw ater heating. I hc~cunits could be constructed with more stages; the plant wo~ld ~)e mot effici t d f I costs mould be lower However, in the typical lllstalla.-CIen an ue .,"" ' ., . 1tion, the increased cost of the additional stages of Ieedwater heating am

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