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6

Fuels, Combustion, and Efficiency of Boilersand Heaters

6.01

6.026.03

6.04

6.06.06

6.0!

6.0"

6.0#

6.10

Estimatin$ HH% &'i$'er 'eatin$ (alue) and *H% &lo+er 'eatin$ (alue) offuels from ultimate analysis relatin$ 'eat in-uts based on HH% and *H%

relatin$ boiler efficiencies based on HH% and *H%Estimatin$ HH% and *H% of fuel oils if / is no+nCalculatin$ cost of fuels on Btu &million Btu) basis com-arin$electricity cost +it' cost of fuelsEstimatin$ annual fuel cost for -o+er -lants relatin$ 'eat rates +it'efficiency of -o+er -lantseterminin$ $as re$ulator settin$s for different fuelsCorrectin$ fuel o+ meter readin$s for o-eratin$ fuel $as -ressures andtem-eratures

eterminin$ ener$y, steam 5uantity, and electric 'eater ca-acity re5uiredfor 'eatin$ aireterminin$ ener$y, steam 5uantity, and electric 'eater ca-acity re5uiredfor 'eatin$ fuel oilsCombustion calculations from ultimate analysis of fuels determinin$ +etand dry air and ue $as 5uantities (olumetric analysis of ue $as on +etand dry basis -artial -ressures of +ater (a-or and carbon dioide in ue$as molecular +ei$'t and density of ue $asCombustion calculations on Btu basis determinin$ air and ue $as5uantities in t'e absence of fuel data

Copyright 2003 Marcel Dekker, Inc.

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6.116.12

6.13

6.146.1

6.16a6.16b6.1!6.1"

6.1#

6.20

6.216.226.23

6.246.2a6.2b6.2c6.2d6.26a

6.26b6.26c

6.26d6.26e

6.26f

6.2!a6.2!b6.2!c6.2"

Estimatin$ ecess air from ue $as C72readin$sEstimatin$ ecess air from C72and 72readin$s estimatin$ ecess airfrom 72readin$s aloneEffect of reducin$ oy$en in ue $as calculatin$ ue $as -roduced

calculatin$ ener$y sa(ed and reduction in fuel costEffect of fuel 'eatin$ (alues on air and ue $as -roduced in boilerseterminin$ combustion tem-erature of different fuels in t'e absence offuel analysisCalculatin$ as' concentration in ue $ases8elatin$ as' concentration bet+een mass and (olumetric unitseterminin$ meltin$ -oint of as' no+in$ as' analysis

eterminin$ 972and 973in ue $ases in lb: Btu and in --m&(olume)

eterminin$ efficiency of boilers and 'eaters efficiency on HH% basisdry $as loss loss due to moisture and combustion of 'ydro$en loss dueto moisture in air radiation loss efficiency on *H% basis +et ue $asloss relatin$ efficiencies on HH% and *H% basiseterminin$ efficiency of boilers and 'eaters on HH% and *H% basisfrom ue $as analysis*oss due to C7 formation9im-le formula for efficiency determinationeterminin$ radiation losses in boilers and 'eaters if casin$ tem-eratureand +ind (elocity are no+n

%ariation of 'eat losses and efficiency +it' boiler load9ulfur de+ -oint of ue $asesCom-utin$ acid de+ -oints for (arious acid (a-orsEffect of $as tem-erature on corrosion -otentialnot'er correlation for sulfuric acid de+ -oint

Con(ertin$ ;7 and C7 from lb:' to --m for turbine e'aust$asesCon(ertin$ ;7 and C7 from lb:' to --m for fired boilersCon(ertin$

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HH% ? 14,00 @ C A 62,000 @ H22A 4000 @ 9

000

6.01

D

Ho+ are t'e HH% &'i$'er 'eatin$ (alue) and *H% &lo+er 'eatin$ (alue) of fuels

estimated +'en t'e ultimate analysis is no+n

e can use t'e e-ressions G1

7"

*H% ? HH% #!20 @ H2 1110

I1J

I2J

+'ere is t'e fraction by +ei$'t of moisture in fuel, and C H2 72, and 9 are

fractions by +ei$'t of carbon, 'ydro$en, oy$en, and sulfur in t'e fuel.f a coal 'as C ? 0"0 H2? 0003 72? 000 ? 00!3 9 ? 0006,and t'e rest as', find its HH% and *H%. 9ubstitutin$ into E5s. &1) and &2), +e'a(e

HH% ? 14,00 @ 0"0 A 62,000 @ 0003 "

A 4000 @ 0006 ? 11,!!1 Btu:lb

*H% ? 11,!!1 #!20 @ 0003 1110 @ 00!3

? 11,66" Btu:lb

Fuel in-uts to furnaces and boilers and efficiencies are often s-ecified +it'outreference to t'e 'eatin$ (alues, +'et'er HH% or *H%, +'ic' is misleadin$.

f a burner 'as a ca-acity of D Btu:' &million Btu:') on HH% basis,its ca-acity on *H% basis +ould be

D*H%? DHH%@*H%

HH%I3aJ

9imilarly, if KHH%and K*H%are t'e efficiencies of a boiler on HH% and *H%

basis, res-ecti(ely, t'ey are related as follo+s

KHH%@ HH% ? K*H%@ *H% I3bJ

6.02a

D

Ho+ can +e estimate t'e HH% and *H% of a fuel oil in t'e absence of itsultimate analysis


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////

=enerally, t'e / of a fuel oil +ill be no+n, and t'e follo+in$ e-ressions canbe used

HH% ? 1!,""! A ! @ / 1022 @ >9*H% ? HH% #123 @ >H2

+'ere >H2is t'e -ercent 'ydro$en by +ei$'t.

I4aJI4bJ

>H2? F

+'ere

2122

/ A 131IJ

FFFF

? 240 for? 200 for? 220 for? 24 for

0#2030

#203040

HH% and *H% are in Btu:lb.

6.02b

D

etermine t'e HH% and *H% of 30 / fuel oil in Btu:$al and in Btu:lb.ssume t'at >9 is 0..

From E5. &4a),

HH% ? 1!,""! A ! @ 30 1022 @ 0

? 1#,61 Btu:lb

Lo calculate t'e density or s-ecific $ra(ity of fuel oils +e can use t'e e-ression

s ?141

131 A / ?

141

131 A 30? 0"!6 I6J

Hence

ensity ? 0"!6 @ "33 ? !3 lb:$al

".33 is t'e density of li5uids in lb:$al +'en s ? 1.

HH% in BtuM$al ? 1#,61 @ !3 ? 142,!#


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From E5. &),

>H2? 22 2122

131 A 30? 120

*H% ? 1#,61 #123 @ 120 ? 1",460 Btu:lb? 1",460 @ !3 ? 134,!" Btu:$al

6.03a

D

$ood +ay to com-are fuel costs is to c'ec t'eir (alues -er Btu fired. f

coal 'a(in$ HH% ? #00 Btu:lb costs N2:lon$ ton, +'at is t'e cost in N:

Btu

1 lon$ ton ? 2240 lb. 1 Btu 'as 106:#00 ? 10 lb of coal. Hence 10 lb+ould cost

10 @2

2240? N11!: Btu

6.03b

Df ;o. 6 fuel oil costs 30 cents:$al, is it c'ea-er t'an t'e coal in D6.03a

Lable 6.1$i(es t'e HH% of fuel oils. t is 12,400 Btu:$al. Hence 1 Btu+ould cost

106

12,400@ 030 ? N1#6: Btu

6.03c

D

'ic' is less e-ensi(e, electricity at 1. cents:' or $as at N3: Btu

3413 Btu ? 1 '. t 1. cents:', 1 Btu of electricity costs&106:3413) @ 1.:100 ? N4.4. Hence in t'is case, electricity is costlier t'an$as. L'is eam-le ser(es to illustrate t'e con(ersion of units and does notim-ly t'at t'is situation +ill -re(ail in all re$ions.


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LB*E6.1Ly-ical Heat Contents of %arious 7ils

9-. $r. 9-. Lem-. irLy-ical 60F =ross =ross t> ;et ;et 9-. 'eat 'eat at corr. 60F C72

0

24

6"

10

12

1.0!6

1.0601.044

1.02#1.0141.000

0.#"6

".#6#

"."34".!04

".!!".44".33".21#

1,0!

1,0#1,043

1,002"1,0131,000

#".0

160,426

1#,03"1!,6#2

16,3"41,1113,""1

12,6"1

10,6"1

10,"#10,4##

10,41210,32"10,24610,166

".3#

".601"."36

#.064#.2"

10.00

10.21

13,664

12,1"310,!2

14#,36"14",02"146,31

14,100

10,231

10,13310,03!

#,#4#,"6#,!44#,661

0.3#1

0.3#40.3#!

0.4000.4030.406

0.40#

0.04

0.0"0.12

0.160.1#0.23

0.2!

0.04

OO

0.04"0.000.01

0.02

1"1

OO

12#11310#

14#4

O

O1".0

1!.61!.116.!

16.4;o. 6 oil

;o. oil

;o. 4 oil

;o. 2 oil

;o. 1 oil

14161"20

2224262"303234363"

404244

0.#!30.##0.#460.#34

0.#220.#100."#"0.""!0."!60."60."0."40."3

0."20."160."06

".106!.##6!.""#!.!"

!.6"3!."!.4""!.3#4!.303!.213!.126!.0416.#"

6."!!6.!#"6.!20

#!1.#".3#4.#33.0#20.##0#.#"#!.""6.2"!.2"64."4.1"43.#"33.#"24.2"14.!"0.4

11,110,3"014#,2!14",200

14!,13146,13214,13"144,16"143,223142,300141,400140,2113#,664

13","2613",00!13!,20!

10,0""10,013

#,#3##,"6!#,!#"#,!30#,664#,###,36#,4!#,41#,36#,2###,243#,1"##,136

10.4110.6110."010.##

11.3!11.11.!211."#12.0612.4!12.6312.!"12.#3

13.0!OO

143,"""142,!12141,!2140,466

13#,2113",21013!,1#"136,21413,2"134,163133,2#132,3"0131,24

130,6"#OO

#,"0#,02#,426#,33#,2!2#,202#,13#,06##,006",#33","!3","14",!!",!02

OO

0.4120.410.41!0.420

0.4230.4260.42"0.4310.4340.4360.43#0.4420.444

0.44!0.400.42

0.300.340.3"0.41

0.40.4"0.20.0.#0.620.660.6#0.!2

0.!60.!#0."2

0.040.060.0"0.060

0.0610.0630.060.06!0.0"#0.0!20.0!40.0!60.0!#

0.0"20.0"0.0""

14!"1463144"1433

1423140#13#13"1136"1360134!13341321

130#OO

16.11."1.1.2

14.#14.!14.14.314.013."13.613.413.3

13.113.012."

opyright 2003 Marcel Dekker, Inc.

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6.04

D

Estimate t'e annual fuel cost for a 300 coalPfired -o+er -lant if t'e o(erall

efficiency is 40> and t'e fuel cost is N1.1: Btu. L'e -lant o-erates for6000 ':yr.

/o+er -lants 'a(e efficiencies in t'e ran$e of 3Q42>. not'er +ay ofe-ressin$ t'is is to use t'e term 'eat rate, defined as

Heat rate ?3413

efficiencyBtu:'

n t'is case it is 3413:0.4 ? "30 Btu:'.

nnual fuel cost ? 1000 @ me$a+att @ 'eat rate @ I':yrJ @ cost of fuel

in N: Btu

? 1000 @ 300 @ "30 @ 6000

@

11106

? N16# @ 106

L'e fuel cost for any ot'er ty-e of -o+er -lant could be found in a similar

fas'ion. Heat rates are -ro(ided by -o+er -lant su--liers.

6.0

D

20 Btu:' burner +as firin$ natural $as of HH% ? 100 Btu:scf +it' as-ecific $ra(ity of 0.6. f it is no+ re5uired to burn -ro-ane 'a(in$HH% ? 2300 Btu:scf +it' a s-ecific $ra(ity of 1., and if t'e $as -ressure tot'e burner +as set at 4 -si$ earlier for t'e same duty, estimate t'e ne+ $as-ressure. ssume t'at t'e $as tem-erature in bot' cases is 60 F.

L'e 'eat in-ut to t'e burner is s-ecified on HH% basis. L'e fuel o+ rate +ould

be D:HH%, +'ere D is t'e duty in Btu:'. L'e $as -ressure differential bet+eent'e $as -ressure re$ulator and t'e furnace is used to o(ercome t'e o+ resistanceaccordin$ to t'e e5uation

/ ?Rf2

rI!J

+'ere

/ ? -ressure differential, -si

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R ? a constant

r ? $as density ? 0.0!s &s is t'e $as s-ecific $ra(ity s ? 1 for air)f? fuel o+ rate in lb:' ? o+ in scf' @ 0.0!s

*et t'e subscri-ts 1 and 2 denote natural $as and -ro-ane, res-ecti(ely.

f 1?

f 2?

20 @ 106

100

20 @ 106

2300

@ 00! @ 06

@ 00! @ 1

/1? 4 r1? 00! @ 06, and r2? 00! @ 1. Hence, from E5. &!),

/1

/2?

Ff21r2

Ff22r1?

4

/2?

06

I100J2@

I2300J2

1

or

/2? 20" -si$

Hence, if t'e $as -ressure is set at about 2 -si$, +e can obtain t'e same duty. L'ecalculation assumes t'at t'e bac-ressure 'as not c'an$ed.

6.06

D

=as o+ measurement usin$ dis-lacement meters indicates actual cubic feet of$as consumed. Ho+e(er, $as is billed, $enerally, at reference conditions of 60 Fand 14.6 -sia &4 oS). Hence $as o+ 'as to be corrected for actual -ressure and

tem-erature. /lant en$ineers s'ould be a+are of t'is con(ersion.n a $asPfired boiler -lant, 1000 cu ft of $as -er 'our +as measured, $as

conditions bein$ 60 -si$ and "0 F. f t'e $as 'as a 'i$'er calorific (alue of

100 Btu:scf, +'at is t'e cost of fuel consumed if ener$y costs N4: Btu

L'e fuel consum-tion at standard conditions is found as follo+s.

%s? %a/aLs

/sLaI"J


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+'ere

%s %a? fuel consum-tion, standard and actual, cu ftM'

Ls? reference tem-erature of 208

La? actual tem-erature, 8

/s /a? standard and actual -ressures, -sia

%s? 100 @ I30 A 1422J@

? 2#00 scf'

20

146 @ 40

Hence

Ener$y used ? 2#00 @ 100 ? 3.0 Btu:'

Cost of fuel ? 3.0 @ 4 ? N12.2:'.

f -ressure and tem-erature corrections are not used, t'e dis-lacement

meter readin$ can lead to incorrect fuel consum-tion data.

6.0!

DEstimate t'e ener$y in Btu:' and in ilo+atts &) for 'eatin$ !,000 lb:' of airfrom #0F to 22 F. 'at is t'e steam 5uantity re5uired if 200 -sia saturatedsteam is used to accom-lis' t'e duty noted abo(e 'at siSe of electric 'eater+ould be used

L'e ener$y re5uired to 'eat t'e air can be e-ressed as

D ? aC-L

+'ere

D ? duty, BtuM'

a? air flo+, lbM'

C-? s-ecific 'eat of air, BtuMlbF

L ? tem-erature rise, F

C-may be taen as 0.2 for t'e s-ecified tem-erature ran$e.

D ? !,000 @ 02 @ I22 #0J ? 23 @ 106Btu:'

I#J

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%alues in re$ular ty-e are for li5uid bold (alues are for (a-or.

LB*E6.2Heat Content &Btu:$al) of %arious 7ilsa

=ra(ity, / at 60F &1.6C)

10 1 20 2 30 3

9-ecific $ra(ity, 60F:60F

40 4

Lem-.&F)

32

60

1.0000

0

0#

0.#6#

0

0#3

0.#340

0

0#2

0.#042

0

0#0

0."!62

0

0"#

0."4#"

0

0"!

0."21

0

0"6

0."01!

0

0"

#6100 23! 233 22# 226 222 21# 21

106 1062120 310 30 300 2# 2#0 2"6 2"1

1116 1112140 3"4 3!" 3!1 366 360 3 34#

116# 1164160 460 43 44 43" 431 42 41"

1236 1223 121!1"0 3" 2# 20 11 03 4#6 4""

12#3 12!" 12!2200 61! 60! #6 "! !! 6# 60

13!1 132 133 132!220 6#! 6"6 6!4 663 62 643 633

1434 1412 13#3 13"4240 !!# !66 !3 !41 !2# !1" !0!

14#" 14!4 142 1442260 "62 "4" "33 "20 "0! !# !"3

163 13! 113 102300 1034 101! ### #"4 #6" #4 #3#

16## 166" 163# 1626400

00

600

!00

"00

14"#

1#"1

211

30!"34!"36"3400"

146320""1#4!

24#!246!2#42302342361#3#44

143#20641#14

246424262#012#!433!43#3""4

141620411""4

243423"!2"622#2!332!3023"2!

13#3201"1"4

24042302"22""132"1344!3!!2

13!21##!1"26

23!623142!"#2"3!323!33#3!20

1321#!!1!##

234#22"12!62!#631#633436!0

13331#"1!!4

2324224"2!232!631632#!3622

a


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14,0#3

0.0#10# 10.#!# 1.1$#"

Con(erted to mean Btu -er lb &1:1"0 of t'e 'eat -er lb of +ater from 32 to 212 F) from data by Frederic . 8ossini,

LB*E6.3Combustion Constants

Heat of combusionc

ol. *b -er Cu ft

9- $r

air ?

Btu:cu ft Btu:lb

;o. 9ubstance Formula +ta cu ftb -er lbb 1,000b =ross ;etd =ross ;etd

1

2346

Carbon

Hydro$en7y$en;itro$en &atm)Carbon monideCarbon dioide

C

H272;2C7

C72

12.01

2.01632.0002".0162".0144.01

O O

0.0032! 1"!.!230.0"461 11."1#0.0!43#c13.443c0.0!404 13.060.11!0 ".4"

O

0.06##1.1030.#!1"e0.#6!21.2"2

O

32.0OO

321."O

O

2!.0OO

321."O

61,100

OO4,34!O

$ 14,0#3

1,623OO

4,34!O

/araffin series CnH2nA2! et'ane" Et'ane# /ro-ane

10 nPButane11 sobutane12 nP/entane13 so-entane14 ;eo-entane1 nPHeane

CH4C2H6C3H"

C4H10C4H10CH12CH12CH12C6H14

16.04130.06!44.0#2

".11"".11"!2.144!2.144!2.144"6.16#

0.042430.0"02#c0.11#6c

0.1"2c0.1"2e0.1#04e0.1#04e0.1#04e0.22!4e

23.612.4c

".36c

6.321c6.321e.22e.22e.22e4.3#$e

0.431.04""2e1.61!c

2.0664e2.0664e2.4"!2c2.4$!2e2.4"!2e2.#!04c

1013.21!#22#0

33!033634016400"3##34!62

#13.1164123"

31133103!0#3!1636#34412

23,"!#22,32021,661

21,30"21,2!21,0#121,0220,#!020,#40

21,2020,4321#,#44

1#,6"01#,62#1#,1!1#,4!$1#,3#61#,403

7lefin series CnH2n16 Et'ylene1! /ro-ylene1" nPButene &butylene)1# sobutene20 nP/entene

C2H4C3H6C4H"C4H"CH10

2".0142.0!!6.1026.102!0.12"

0.0!460.1110e0.14"0e0.14"0e0.1"2e

13.412#.00!e6.!6e6.!6e.400e

0.#!401.404e1.#336e1.#336e2.41#0e

1613."233630"4306"3"36

113.221"62$$2$6#3"6

21,64421,04120,"4020,!3020,!12

20,2#1#,6#11#,4#61#,3"21#,363

romatic series CnH2n621 BenSene C6H622 Loluene C!H"23 Tylene C"H10

!6.10! 0.2060c#2.132 0.2431c

106.1" 0.2"03e

4."2c2.6#20e4.113e3.1!60e3.6!e3.661"e

3!144"4230

360142"44#"0

1$,2101",4401",60

1!,4"01!,6201!,!60

iscellaneous $ases24 cetylene2 ;a-'t'alene26 et'yl alco'ol2! Et'yl alco'ol2$ mmonia

C2H2 26.036 0.06#!1C10H" 12".162 0.33"4eCH37H 32.041 0.0"46eC2H7H 46.06! 0.1216e;H3 1!.031 0.046e

14.3442.#e

11."20e".221e

21.#14e

0.#10!4.420"e1.102e1."#0e0.#61e

14##"4f$6!.#1600.3441.1

144"64f!6".0140.36.1

21,00 20,!!61!,2#"f16,!0"f10,2# #,0!"13,161 11,#2##,66" ",001

2# 9ulfur 9 32.06 O O O O O 3,#"3 3,#"3

30

313233

Hydro$en sulfide

9ulfur dioideater (a-orir

H29

972H27O

34.0!6

64.061".01626.#

e

0.1!330.04!"e0.0!6

e

.!!021.01!e13.063

e

2.2640.621e1.0000

64!

OOO

#6

OOO

!,100 6,4

O OO OO O

ll $as (olumes corrected to 60 F and 30 in. H$ dry. For $ases saturated +it' +ater at 60 F, 1.!3> of t'e Btu (alue must be

deducted.a

b

Calculated from atomic +ei$'ts $i(en in Uournal of t'e merican C'emical 9ociety, February 1#3!.

ensities calculated from (alues $i(en in $* at 0 C and !60 mmH in t'e nternational Critical Lables allo+in$ for t'e no+n

de(iations from t'e $as la+s. 'ere t'e coefficient of e-ansion +as not a(ailable, t'e assumed (alue +as taen as 0.003!

-er C. Com-are t'is +it' 0.003662, +'ic' is t'e coefficient for a -erfect $as. 'ere no densities +ere a(ailable, t'e

(olume of t'e mole +as taen as 22.411 *.c

;ational Bureau of 9tandards, letter of -ril 10, 1#3!, ece-t as noted.


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From t'ird edition of Combustion.

Cu ft -er cu ft of combustible *b -er lb of combustibleE-erimental

8e5uired for 8e5uired for error incombustion Flue -roducts combustion Flue -roducts 'eat of

combustion72

O

0.OO0.

O

2.03..0

6.6.".0".0".0#.

3.04.6.06.0!.

;2

O

1.""2OO

1.""2O

!.2"13.1!1"."21

24.46!24.46!30.11430.11430.1143.!60

11.2#316.#3#22."22."2".232

ir

O

2.3"2OO

2.3"2O

#.2"16.6!23."21

30.#6!30.#6!3".1143".1143".1144.260

14.2#321.43#2"."2"."3.!32

C72

O

OOO1.0O

1.02.03.0

4.04.0.0.0.06.0

2.03.04.04.0.0

H27

O

1.0OOOO

2.03.04.0

.0.06.06.06.0!.0

2.03.04.04.0.0

;2

O

1.""2OO

1.""2O

!.2"13.1!1"."21

24.46!24.46!30.11430.11430.1143.!60

11.2#316.#3#22."22."2".232

72

2.664

!.#3!OO0.!1O

3.##03.!23.62#

3.!#3.!#3.4"3.4"3.4"3.2"

3.4223.4223.4223.4223.422

;2

"."63

26.40!OO

1.#00O

13.2!12.3#412.0!4

11.#0"11.#0"11."011."011."011.!3"

11.3"11.3"11.3"11.3"11.3"

ir

11.2!

34.344OO

2.4!1O

1!.2616.11#1.!03

1.4"!1.4"!1.331.331.331.266

14."0!14."0!14."0!14."0!14."0!

C72

3.664

OOO1.!1O

2.!442.#2!2.##4

3.02#3.02#3.003.003.003.064

3.13"3.13"3.13"3.13"3.13"

H27

O

".#3!OOOO

2.2461.!#"1.634

1.01.01.4#"1.4#"1.4#"1.464

1.2"1.2"1.2"1.2"1.2"

;2

"."63

26.40!OO1.#00

O

13.2!12.3#412.0!4

11.#0"11.#0"11."011."011."011.!3"

11.3"11.3"11.3"11.3"11.3"

& V >)

0.012

0.01OO

0.04O

0.0330.0300.023

0.0220.01#0.020.0!10.110.0

0.0210.0310.0310.0310.03!

!.#.0

10.

2".232 3.!32 6.033."!" 32.$!" !.03#.24 0.024 ".0

3.04.0.0

2".232 3.0!3 10.224 13.2#! 3.3"1 0.6#2 10.22433."!" 3.126 10.401 13.2! 3.344 0.!"2 10.4013#.24 3.16 10.30 13.6# 3.31! 0."4# 10.30

0.120.210.36

2. #.411 11.#11 2.012.0 4.1!0 !.1!0 10.01. .646 !.146 1.03.0 11.2#3 14.2#3 2.00.! 2."23 3.!3 O

1.04.02.03.01.

#.4114.1!0

.64611.2#3

3.323

3.0!3 10.224 13.2#! 3.3"1 0.6#22.##6 #.#6" 12.#64 3.434 0.621.4#" 4.#"4 6.4"2 1.3!4 1.122.0"4 6.#34 #.01" 1.#22 1.1!01.40# 4.6"" 6.0#! O 1."!

10.224#.#6"4.#"46.#34.11

0.16O

0.02!0.0300.0""

972O O O O O O 0.##" 3.2"! 4.2" 1.##" O 3.2"! 0.0!1

972 9721.

OOO

.646 !.146 1.0O O OO O OO O O

1.0OOO

.646 1.40# 4.6"" 6.0#! 1.""0 0.2#O O O O O OO O O O O OO O O O O O

4.6""OOO

0.30OOO

deduction from $ross to net 'eatin$ (alue determined by deductin$ 1",#1# Btu:lb mol +ater in t'e -roducts of combustion.

7sborne, 9timson and =innin$s, ec'anical En$ineerin$, -. 163, arc' 1#3, and 7sborne, 9timson, and Floc, ;ational

Bureau of 9tandards 8esearc' /a-er 20#.eenotes t'at eit'er t'e density or t'e coefficient of e-ansion 'as been assumed. 9ome of t'e materials cannot eist as

$ases at 60 F and 30 in.H$ -ressure, in +'ic' case t'e (alues are t'eoretical ones $i(en for ease of calculation of $as

-roblems.

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6.0#a

D

;atural $as 'a(in$ CH4? "34> C2H6? 1">, and ;2? 0"> by (olume

is fired in a boiler. ssumin$ 1> ecess air, !0F ambient tem-erature, and "0>relati(e 'umidity, -erform detailed combustion calculations and determine ue$as analysis.

FromC'a-ter +e no+ t'at air at !0F and "0> 8H 'as a moisture content of

0.012 lb:lb dry air.Lable 6.3can be used to fi$ure air re5uirements of (ariousfuels. For eam-le, +e see t'at CH4re5uires #.3 mol of air -er mole of CH4, andC2H6re5uires 16.6" mol.

*et us base our calculations on 100 mol of fuel. L'e t'eoretical dry air

re5uired +ill be"34 @ #3 A 166" @ 1" ? 10"3 mol

Considerin$ 1> ecess,

ctual dry air ? 1.1 @ 10".3 ? 121! mol

Ecess air ? 0.1 @ 10".3 ? 1".! mol

Ecess 72? 1".! @ 0.21 ? 33.3 molEcess ;2? 121! @ 0.!# ? #61 mol&ir contains 21> by (olume 72, and t'e rest is ;2.)

oisture in air ? 121! @ 2#

@

00121"

? 23 mol

&e multi-lied moles of air by 2# to $et its +ei$'t, and t'en t'e +ater 5uantity

+as di(ided by 1" to $et moles of +ater.)

Lable 6.3 can also be used to $et t'e moles of C72 H27, ;2and 72G3.

C72? 1 @ "34 A 2 @ 1" ? 11 mol

H27 ? 2 @ "34 A 3 @ 1" A 23 ? 23!! mol

72? 333 mol

;2? #61 A 0" ? #61" mol

L'e total moles of ue $as -roduced is 11 A 23!.! A 33.3 A #61." ? 134!.".

Hence

>C72?

9imilarly,

11

134!"@ 100 ? "

>H27 ? 1!! >72? 2 >;2? !13

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L'e analysis abo(e is on a +et basis. 7n a dry ue $as basis,

>C72? " @

9imilarly,

100

100 1!!? 103>

>72? 30> >;2? "6!>

Lo obtain +da,++a,+d$, and ++$, +e need t'e density of t'e fuel or t'e molecular+ei$'t, +'ic' is

1

100@ I"34 @ 16 A 1" @ 30 A 0" @ 2"J ? 1"30

2#

100 @ 1"3

23 @ 1"1"3 @ 100

11 @ 44 A 333 @ 32 A #61 @ 2"1"30

? 1" lb dry $as:lb fuel

++$?11 @ 44 A 333 @ 32 A 23!! @ 1" A #61" @ 2"

1"30

? 2040 lb +et $as:lb fuel

L'is -rocedure can be used +'en t'e fuel analysis is $i(en. ore often, -lanten$ineers +ill be re5uired to estimate t'e air needed for combustion +it'out afuel analysis. n suc' situations, t'e Btu basis of combustion and calculaPtions +ill come in 'andy. L'is is discussed in D6.10a.

6.0#b

D

For t'e case stated in D6.0#a, estimate t'e -artial -ressure of +ater (a-or, -+, and

of carbon dioide, -c

, in t'e ue $as. lso estimate t'e density of ue $as at300F.

L'e -artial -ressures of +ater (a-or and carbon dioide are im-ortant in t'edetermination of nonluminous 'eat transfer coefficients.

-+?(olume of +ater

(a-or

total flue $as

(olume

? 01!! atm ? 26 -sia

-c?(olume of carbon

dioide

total flue $as (olume

? 00" atm ? 12! -sia

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+da? 121! @ ? 1#2# lb dry air:lb fuel

? 1#2 lb +et air:lb fuel++a? 1#2# A

+d$?


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Lo estimate t'e $as density, its molecular +ei$'t must be obtained &see D.0).

F ? /

Ii@ yiJ

?2" @ !13 A 1" @ 1!! A 32 @ 2 A 44 @ "

100? 2!!

Hence, from E5. &6),

r$? 2!! @ 4#2

@

14!

3# @ !60 @

14!

? 00 lb:cu ft

L'e $as -ressure +as assumed to be 14.! -sia. n t'e absence of ue $asanalysis, +e can obtain t'e density as discussed in D.03.

r$? 40

!60? 002 lb:cu ft

6.10a

D

iscuss t'e basis for t'e million Btu met'od of combustion calculations.

Eac' fuel suc' as natural $as, coal, or oil re5uires a certain amount ofstoic'iometric air -er Btu fired &on HH% basis). L'is 5uantity does not(ary muc' +it' t'e fuel analysis and 'as t'erefore become a (aluable met'od ofe(aluatin$ combustion air and ue $as 5uantities -roduced +'en fuel $as analysisis not a(ailable.

For solid fuels suc' as coal and oil, t'e dry stoic'iometric air +dain lb:lbfuel can be obtained from

7"

+'ere C H2 72, and 9 are carbon, 'ydro$en, oy$en, and sulfur in t'e fuel infraction by +ei$'t.

For $aseous fuels, +dais $i(en by

+da? 24! @ C7 A 3434 @ H2A 1!2! @ CH4

A 133 @ C2H2A 14"1 @ C2H4

A 1612 @ C2H6 432 @ 72

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+da? 113 @ C A 3434 @ H22A 42# @ 9


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LB*E6.4Combustion Constant For Fuels

;o.

1

2346!"#

Fuel

Blast furnace $as

Ba$asseCarbon monoide $as8efinery and oil $as;atural $asFurnace oil and li$niteBituminous coalsnt'raciteCoe

!

606!0!20!30!4Q!0!60!"0"00

L'e amount of fuel e5ui(alent to 1 Btu +ould be &1 @ 106):23,1"1 ? 43.1 lb, +'ic' re5uires 43.1 @ 16.! ? !22 lb of air, or 1 Btufired +ould need !22 lb of dry air t'is is close to t'e (alue indicated in Lable 6.4.

*et us tae t'e case of 100> met'ane and see 'o+ muc' air it needs forcombustion. FromLable 6.3, air re5uired -er -ound of met'ane is 1!.26 lb, and

its 'eatin$ (alue is 23,"!# Btu:lb. n t'is case 1 Btu is e5ui(alent to&1 @ 106):23,"!# ? 41."" lb of fuel, +'ic' re5uires 41."" @ 1!.26 ? !23 lbofdry air.

Lain$ t'e case of -ro-ane, 1 lb re5uires 1.!03 lb of air.

1 Btu ?1 @ 106

21,661? 461! lb fuel

L'is +ould re5uire 46.1! @ 1.!03 ? !2 lb of air.

L'us for all fossil fuels +e can come u- +it' a $ood estimate of t'eoreticaldry air -er Btu fired on HH% basis, and $as analysis does not affect t'is(alue si$nificantly. L'e amount of air -er Btu is termed and is s'o+n in

Lable 6.4 for (arious fuels.

6.10b

D

fired 'eater is firin$ natural $as at an in-ut of ! Btu:' on HH% basis.etermine t'e dry combustion air re5uired at 10> ecess air and t'e amount ofue $as -roduced if t'e HH% of fuel is 20,000 Btu:lb.

From Lable 6.4, is !30 lb: Btu. Hence t'e total air re5uired is

a? ! @ 11 @ !30 ? 60,200 lb:'

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L'e ue $as -roduced is

$? aA f? 60,200

A

106

20,000? 60,20 lb:'

L'ese (alues can be con(erted to (olume rates at any tem-erature usin$ t'e-rocedure described inC'a-ter .

L'e Btu met'od is 5uite accurate for en$ineerin$ -ur-oses suc' as fanselection and siSin$ of ducts and air and $as systems. ts ad(anta$e is t'at fuelanalysis need not be no+n, +'ic' is $enerally t'e case in -o+er and -rocess-lants. L'e efficiency of 'eaters and boilers can also be estimated usin$ t'e Btu met'od of combustion calculations.

6.10cD

coalPfired boiler is firin$ coal of HH% ? #00 Btu:lb at 2> ecess air. fambient conditions are "0 F, relati(e 'umidity "0>, and ue $as tem-erature300F, estimate t'e combustion air in lb:lb fuel, t'e (olume of combustion air incu ft:lb fuel, t'e ue $as -roduced in lb:lb fuel, and t'e ue $as (olume in cuft:lb fuel.

Because t'e fuel analysis is not no+n, let us use t'e Btu met'od. From

Lable 6.4, ? !60 for coal. 1 Btu re5uires !60 @ 1.2 ? #0 lb of dry air.t "0> 'umidity and "0F, air contains 0.01" lb of moisture -er -ound of air&C'a-. ). Hence t'e +et air re5uired -er Btu fired is #0 @ 1.01" lb. lso,

1 Btu fired e5uals 106:#00 ? 10 lb of coal. Hence#0

10101"10

? #21

4#2

3# @ 40? 00!36 lb:cu ft Isee C'a- D03J

Hence

%olume of air ?

40

!60#0 A 10

10

%olume of flue $as, cu ft:lb fuel ? ? 1#1
http://var/www/apps/conversion/tmp/scratch_2/DK1998_ch5.pdfhttp://var/www/apps/conversion/tmp/scratch_2/DK1998_ch5.pdf

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? #0+da? dry air, lb:lb fuel ?

++a? +et air, lb:lb fuel ? #0 @

ra? density of air at "0 F ? 2# @

? 12 cu ft:lb fuel#21

00!36

? 0026 lb:cu ftr$? density of flue $as ?

? 100+d$? dry flue $as in lb:lb fuel ?

100

0026


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E ? 100 @ 1 I10aJ

1"6

6.11

D

s t'ere a +ay to fi$ure t'e ecess air from ue $as C72readin$s

Wes. $ood estimate of ecess air E in -ercent can be obtained from t'e e5uation

R1

>C72

>C72is t'e -ercent of carbon dioide in dry ue $as by (olume, and R1is aconstant de-endin$ on t'e ty-e of fuel, as seen in Lable 6.. For eam-le, if>C72? 1 in ue $as in a coalPfired boiler, t'en for bituminous coal&R1? 1".6),

E ? 100 @ 1 ? 24>1

6.12

D

iscuss t'e si$nificance of >C72and >72in ue $ases.

Ecess air le(els in ue $as can be estimated if t'e >C72and >72in dry ue$as by (olume are no+n. L'e 'i$'er t'e ecess air, t'e $reater t'e ue $as5uantity and t'e $reater t'e losses. /lant en$ineers s'ould control ecess airle(els to 'el- control -lant o-eratin$ costs. L'e cost of o-eration +it' 'i$' ecessair is discussed in D6.13.

formula t'at is +idely used to fi$ure t'e ecess air is G1

E ? 100 @ 72 C7:2

0264 @ ;2 I72 C7:2JI10bJ

LB*E6.R1Factors for FuelsFuel ty-e

Bituminous coals

Coe7il8efinery $as and $as oil;atural $asBlast furnace $as

9ource 8ef. 1.

R1

1".6

20.1.13.412.2.


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+'ere 72 C7, and ;2are t'e oy$en, carbon monoide, and nitro$en in dry ue$as, (ol>, and E is t'e ecess air, >.

not'er formula t'at is 5uite accurate is G1

E ? R2@ 72

21 72 I10cJ

+'ere R2is a constant t'at de-ends on t'e ty-e of fuel &see Lable 6.6).

6.13

D

n a natural $as boiler of ca-acity 0 Btu:' &HH% basis), t'e oy$en le(el int'e ue $as is reduced from 3.0> to 2.0>. 'at is t'e annual sa(in$s in

o-eratin$ costs if fuel costs N4: Btu L'e HH% of t'e fuel is 1#,000 Btu:lb.L'e eit $as tem-erature is 00 F, and t'e ambient tem-erature is "0 F.

L'e ori$inal ecess air is #0 @ 3:I21 3J ? 1> &see D6.12). L'e ecess air isno+

E ? #0 @20

21 B 2? #4!>

it' 1> ecess, t'e a--roimate air re5uired &see D6.10a) is 0 @ !46 @

1.1 ? 42,"# lb:'.

Flue $as ? 42,"# A 0@

106

1#,000? 4,26 lb:'

LB*E6.6Constant 2

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it' #.4!> ecess air,

ir re5uired ? 0 @ !46 @ 10#4! ? 40,"32 lb:'

Flue $as -roduced ? 40,"32 A

0 @

106

1#,000

? 43,463 lb:'

8eduction in 'eat loss ? I4,26 43,463J @ 02 @ I00 "0J

? 022 Btu:'

L'is is e5ui(alent to an annual sa(in$s of 0.22 @ 4 @ 300 @ 24 ? N6336. &eassumed 300 days of o-eration a year.) L'is could be a si$nificant sa(in$sconsiderin$ t'e life of t'e -lant. Hence -lant en$ineers s'ould o-erate t'e -lant

realiSin$ t'e im-lications of 'i$' ecess air and 'i$' eit $as tem-erature.7y$en le(els can be continuously monitored and recorded and 'ooed u- tocombustion air systems in order to o-erate t'e -lant more efficiently. &t may benoted t'at eit $as tem-erature +ill also be reduced if ecess air is reduced. L'ecalculation abo(e indicates t'e minimum sa(in$s t'at can be realiSed.)

6.14

D

Fuels are often interc'an$ed in boiler -lants because of relati(e a(ailability andeconomics. t is desirable, t'en, to analySe t'e effect on t'e -erformance of t'e

system. iscuss t'e im-lications of burnin$ coal of #"00 Btu:lb in a boilerori$inally intended for 11,400 Btu:lb coal.

*et us assume t'at t'e duty does not c'an$e and t'at t'e efficiency of t'e unit isnot altered. Ho+e(er, t'e fuel 5uantity +ill c'an$e. Combustion air re5uired,bein$ a function of Btu fired, +ill not c'an$e, but t'e ue $as -roduced +illincrease. *et us -re-are a table.

Coal 1 Coal 2

Fuel HH%, Btu:lb

Fuel fired -er Btu &106:HH%)ir re5uired -er Btu &2> ecess air)Flue $as, lb8atio of ue $as

11,400

"!!60 @ 1.2 ? #0103!1

#"00

102!60 @ 1.2 ? #01021.01

e can use t'e same fans, because t'e (ariation in ue $as -roduced is notsi$nificant enou$' to +arrant 'i$'er $as -ressure dro-s. e must loo into ot'er

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? 3400 F

as-ects, suc' as t'e necessity of 'i$'er combustion air tem-erature &due to 'i$'ermoisture in t'e fuel), as' concentration, and foulin$ c'aracteristics of t'e ne+fuel. f a different ty-e of fuel is $oin$ to be used, say oil, t'is +ill be a maXorc'an$e, and t'e fuelP'andlin$ systemYs burners and furnace desi$n +ill 'a(e to be

re(ie+ed. L'e $as tem-erature -rofiles +ill c'an$e o+in$ to radiation c'aracterPistics, and absor-tion of surfaces suc' as su-er'eaters and economiSers +ill beaffected. discussion +it' t'e boiler desi$n en$ineers +ill 'el-.

6.1

D

'at is meant by combustion tem-erature of fuels Ho+ is it estimated

L'e adiabatic combustion tem-erature is t'e maimum tem-erature t'at can beattained by t'e -roducts of combustion of fuel and air. Ho+e(er, because ofdissociation and radiation losses, t'is maimum is ne(er attained. Estimation oftem-erature after dissociation re5uires sol(in$ se(eral e5uations. For -ur-oses ofestimation, +e may decrease t'e adiabatic combustion tem-erature by 3Q> toobtain t'e actual combustion tem-erature.

From an ener$y balance it can be s'o+n t'at

tc? *H% A a @ HH% @ C-a @ Ita "0J:106I1 >as':100 A a @ HH%:106J @ C-$

I11J

+'ere

*H% HH% ? lo+er and 'i$'er calorific (alue of fuel, Btu:lb ? t'eoretical air re5uired -er million Btu fired, lba ? ecess air factor ? 1 A E:100

ta tc? tem-erature of air and combustion tem-erature, F

C-a C-$? s-ecific 'eats of air and -roducts of combustion, Btu:lb FFor eam-le, for fuel oil +it' combustion air at 300 F, *H% ? 1!,000 Btu:

lb, HH% ? 1",000 Btu:lb, a ? 1.1, and ? !4 &seeLable 6.4). e 'a(e

tc?1!,000 A !4 @ 11 @ 1",000 @ 02 @ I300 "0J:106

I1 A !4 @ 11 @ 1",000:106J @ 032

C-aand C-$+ere taen as 0.2 and 0.32, res-ecti(ely.


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6.16a

D

Ho+ is t'e as' concentration in ue $ases estimated

/articulate emission data are needed to siSe dust collectors for coalPfired boilers.n coalPfired boilers, about !> of t'e as' is carried a+ay by t'e ue $ases and2> dro-s into t'e as' -it. L'e follo+in$ e-ression may be deri(ed usin$ t'e Btu met'od of combustion calculation G

Ca?240,000 @ I> as':100J

L @ Z!6 @ 106@ HH% @ I100 A EJ A 1 I>

as':100J[

I12aJ

+'ereCa? as' concentration, $rains:cu ftE ? ecess air, >

L ? $as tem-erature, 8

HH% ? 'i$'er 'eatin$ (alue, Btu:lb

Eam-le

f coals of HH% ? 11,000 Btu:lb 'a(in$ 11> as' are fired in a boiler +it' 2>ecess air and t'e ue $as tem-erature is "08, determine t'e as' concentration.

9olution. 9ubstitutin$ into E5. &12a), +e 'a(e

Ca?240,000 @ 011

"0 @ I!6 @ 106@ 11,000 @ 12 A 1 011J

? 2! $rains:cu ft

6.16b

DHo+ do you con(ert t'e as' concentration in t'e ue $as in +t> to $rains:acf or$rains:scf

Flue $ases from incineration -lants or solid fuel boilers contain dust or as', and

often t'ese com-onents are e-ressed in mass units suc' as lb:' or +t>, +'ereasen$ineers in(ol(ed in selection of -ollution control e5ui-ment -refer to +or interms of $rains:acf or $rains:scf &actual and standard cubic feet). L'e relationPs'i- is

Ca? 001 @ @ !000 @ r ? !0 I12bJ

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+'ere

r ? $as density, lb:cu ft ? 3#.:&460 A t)t ? $as tem-erature, F

Ca? as' content, $rains:acf or $rains:scf de-endin$ on +'et'er density iscom-uted at actual tem-erature or at 60F ? as' content, +t>

L'e e-ression for density is based on atmos-'eric ue $ases 'a(in$ a molecular

+ei$'t of 2"." &see D.03).

Flue $ases contain 1. +t> as'. L'e concentration in $rains:acf at 400F is

Ca? !0 @ 1@

and at 60F,

Ca? !0 @ 1@

3#C

"60

3#C

20

? 4" $rains:acf

? !#" $rains:scf

6.1!

D

iscuss t'e im-ortance of t'e meltin$ -oint of as' in coalPfired boilers. Ho+ is itestimated

n t'e desi$n of steam $enerators and as' remo(al systems, t'e as' fusiontem-erature is considered an im-ortant (ariable. *o+ as' fusion tem-erature maycause sla$$in$ and result in de-osition of molten as' on surfaces suc' assu-er'eaters and furnaces. L'e furnace +ill t'en absorb less ener$y, leadin$ to

'i$'er furnace eit $as tem-eratures and o(er'eatin$ of su-er'eaters. 5uic estimate of as' meltin$ tem-erature in C can be made usin$ t'ee-ression G6

tm? 1# @ l273A 1 @ I9i72A Li72J

A 10 @ ICa7 A $7J

A 6 @ IFe273A ;a27 A R27J

+'ere tmis t'e fusion tem-erature in C, and t'e rest of t'e terms are -ercent as'content of oides of aluminum, silicon, titanium, calcium, ma$nesium, iron,sodium, and -otassium.

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Eam-le

nalysis of a $i(en as' indicates t'e follo+in$ com-osition

l273? 20> 9i72A Li72? 30>Fe273A ;a27 A R27 ? 20>

Find t'e fusion tem-erature.

Ca7 A $7 ? 1>

9olution. 9ubstitutin$ into E5. &13), +e find t'at tm? 1100C.

6.1"a

D

'at is t'e emission of 972in lb: Btu if coals of HH% ? 11,000 Btu:lb and'a(in$ 1.> sulfur are fired in a boiler

L'e follo+in$ e-ression $i(es e, t'e emission of 972in lb: Btu

e ? 2 @ 1049

HH%I14J

+'ere 9 is t'e -ercent sulfur in t'e fuel.

e ? 2 @ 104@1

11,000? 2!3 lb: Btu

f an 972scrubbin$ system of !> efficiency is installed, t'e eitin$ 972concentration +ill be 0.2 @ 2.!3 ? 0.6" lb: Btu.

6.1"bD

'at is t'e 972le(el in --m &-arts -er million) by (olume if t'e coals in D6.1"aare fired +it' 2> ecess air

e 'a(e to estimate t'e ue $as -roduced.

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*et t'e molecular +ei$'t be 30, +'ic' is a $ood estimate in t'e absence of ue$as analysis. L'en,

oles of flue $as?

1041

30? 34! -er Btu fired

oles of 972?2!364

? 0042 &from D6.1"a andLable .1)

&64 is t'e molecular +ei$'t of 972. i(idin$ +ei$'t by molecular +ei$'t $i(est'e moles.)

Hence --m of 972in ue $as +ill be 0.042 @ 106:34.! ? 1230 --m.

6.1"c

D

f > of t'e 972$ets con(erted to 973, estimate t'e --m of 973in t'e ue $as.

oles of 973? 00

@

Hence

2C!3

"0? 0001! -er Btu

--m by (olume of 973

?

0001!

34!@ 106? 4# --m

&"0 is t'e molecular +ei$'t of 973.)

6.1#a

D

Ho+ is t'e efficiency of a boiler or a fired 'eater determined

L'e estimation of t'e efficiency of a boiler or 'eater in(ol(es com-utation ofse(eral losses suc' as t'ose due to ue $ases lea(in$ t'e unit, unburned fuel,radiation losses, 'eat loss due to molten as', and so on. 8eaders may refer to t'e9E /o+er Lest Code G! for details. L+o met'ods are +idely used, one basedon t'e measurement of in-ut and out-ut and t'e ot'er based on 'eat losses. L'elatter is -referred, because it is easy to use.

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L'ere are t+o +ays of statin$ t'e efficiency, one based on HH% and t'eot'er on *H%. s discussed in D6.01,

KHH%@ HH% ? K*H%@ *H%

L'e (arious losses are G1, on an HH% basis,

1. ry $as loss, *1

*1? 24+d$t$ ta

HH%I1aJ

2. *oss due to combustion of 'ydro$en and moisture in fuel, *2

*2? I# @ H2A J @ I10"0 A 046t$ taJ

@100

HH%

3. *oss due to moisture in air, *3

*3? 46 +dat$ ta

HH%I1cJ

4. 8adiation loss, *4. L'e merican Boiler anufacturers ssociation&B) c'art G! may be referred to to obtain t'is (alue. 5uic

estimate of *4is

*4? 10062042 lo$ D

For E5s. &1a)Q&1d),

+d$? dry ue $as -roduced, lb:lb fuel

+da? dry air re5uired, lb:lb fuelH2 ? 'ydro$en and moisture in fuel, fraction ? moisture in air, lb:lb dry air &see D.0#b)t$ ta? tem-eratures of ue $as and air, FD ? duty in Btu:'

I1dJ

. Lo losses *1Q*4must be added a mar$in or unaccounted loss, *.Hence efficiency becomes

KHH%? 100 I*1A *2A *3A *4A *J I1eJ

;ote t'at combustion calculations are a -rere5uisite to efficiency determination.

f t'e fuel analysis is not a(ailable, -lant en$ineers can use t'e Btu met'od

to estimate +d$rat'er easily and t'en estimate t'e efficiency &see D6.20).L'e efficiency can also be estimated on *H% basis. L'e (arious losses

considered are t'e follo+in$.


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1. et ue $as loss

++$C-t$ ta

HH%I1f J

&C-, $as s-ecific 'eat, +ill be in t'e ran$e of 0.26Q0.2! for +et ue$ases.)

2.3.

8adiation loss &see D6.23) ecess air. f t'e eit $as tem-erature is 300F and ambient tem-eratureis "0 F, determine t'e efficiency on HH% basis and on *H% basis.

From t'e Btu met'od of combustion calculations, assumin$ t'at moisture in

air is 0.013 lb:lb dry air,

++$?1013 @ !60 @ 12 A 106:13,00

106:13,00

?1036

!4? 140

&!60 is t'e constant obtained fromLable 6.4.) Hence

+et flue $as loss ? 100 @ 140 @ 026

@300 "0

12,600? 63>

*et radiation and unaccounted losses be 1.3>. L'en

K*H%? 100 I63 A 13J ? #234>

KHH%? #234 @12,600

13,00? "61">

&8adiation losses (ary from 0.> to 1.0> in lar$e boilers and may $o u- to 2.0>

in smaller units. L'e maXor loss is t'e ue $as loss.)


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6.1#c

D

etermine t'e efficiency of a boiler firin$ t'e fuel $i(en in D6.0#a at 1> ecess

air. ssume radiation loss ? 1>, eit $as tem-erature ? 400F, and ambienttem-erature ? !0 F. Ecess air and relati(e 'umidity are t'e same as in D6.0#a&1> and "0>).

8esults of combustion calculations are already a(ailable.

ry flue $as ? 1" lb:lb fuel

oisture in air ? 1#2 1#2# ? 023 lb:lb fuel

ater (a-or formed due to combustion of fuel ?

204 1" 023 ? 21! lb:lb fuel

HH% ? "34 @ 10132 A 1" @

1!#2100

? 112" Btu:cu ft

Fuel density at 60F ? 1".3:3!# ? 0.4"3 lb:cu ft, so

HH% ?

L'e losses are

112"

004"3? 23,364 Btu:lb

1. ry $as loss,

*1? 100 @ 1" @ 024

@

400 B !0

23,364? 61>

2. *oss due to combustion of 'ydro$en and moisture in fuel,

*2? 100 @ 21!

@

? 111>

10"0 A 046 @ 400 !023,364

3. *oss due to moisture in air,

*3? 100 @ 023 @ 046

@

400 B !0

23,364? 01>

4. 8adiation loss ? 1.0>

.

Lotal losses ? 61 A 111 A 01 A 10 ? 1"3>Hence

Efficiency on HH% basis ? 100 1"3 ? "16>

7ne can con(ert t'is to *H% basis after com-utin$ t'e *H%.

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6.1#d

D

Ho+ do ecess air and boiler eit $as tem-erature affect t'e (arious losses and

boiler efficiency

Lable 6.! s'o+s t'e results of combustion calculations for (arious fuels atdifferent ecess air le(els and boiler eit $as tem-eratures. t also s'o+s t'e

amount of C72$enerated -er Btu fired.t can be seen t'at natural $as $enerates t'e lo+est amount of C72.

C72:Btu, natural, $as

?

10623,!"#

@ 1#1! @#06 @ 44

2!! @ 100? 116 lb

LB*E6.!Combustion Calculations for %arious Fuels

=as 7il Coal

L$oFE, >

30

40

301

401

30

40

301

401

402

02

C72

H27;272972$:f*1, >*2, >*3, >

#.06

1#.11!0.#30.#0

1#.1!4.!4 6.440.0# 0.12

10."# 11.32

".34

1!.!0!1.4"2.4"

20.#.23 !.0#0.10 0.13

10."# 11.32

12.""

12.3!!3."30.#2

16.31.13 6.#60.0# 0.126.63 6."#

11."2

11.4!!4.1#2.3

1!.!!.62 !.630.10 0.146.63 6."#

13.3"

!.10!.433.#40.1

13.42".#1 11.20.1 0.1#4.3 4.46

=as 7il Coal

L$o, FE, >

30

40

301

401

30

40

301

401

402

02

*4, > 1.0

E', >El, >

"3.2 "1.1#2.3 "#.#

2!.!

"2.# "0.#1.! "#.2

2!.66

"!.1 ".0#2." #0.0

2"."6

"6.! "4.3#2.3 "#.#

2".#!

".6 "3.0"#.0 "6.4

2#.64

Coal &+t>) C ? !2.", H2? 4.", ;2? 1., 72? 6.2, 9 ? 2.2, H27 ? 3., as' ? #.0

HH% ? 1313# Btu:lb *H% ? 12,634 Btu:lb.

7il &+t>) C ? "!., H2? 12., / ? 32 HH% ? 1#,!2! Btu:lb *H% ? 1",12 Btu:lb.

=as &(ol>) CH4? #! C2H6? 2, C3H"? 1 HH% ? 23,!"# Btu:lb *H% ? 21,462 Btu:lb.

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&L'e abo(e is obtained by con(ertin$ t'e (olumetric analysis to +ei$'t basisusin$ t'e molecular +ei$'ts of C72and t'e ue $as.) For oil, C72$eneraPted ? 162.4 lb, and for coal, 202.# lb.

6.20

D

fired 'eater of duty 100 Btu:' &HH% basis) firin$ ;o. 6 oil s'o+s t'efollo+in$ dry ue $as analysis

C72? 13> 72? 2> ;2? "4>

L'e eit $as tem-erature and ambient tem-erature are 300 F and "0 F, res-ecP

ti(ely. f moisture in air is 0.013 lb:lb dry air, estimate t'e efficiency of t'e unit

on *H% and HH% basis. *H% ? 1",400 Btu:lb and HH% ? 1#,00 Btu:lb.

Because t'e fuel analysis is not no+n, let us estimate t'e ue $as -roduced byt'e Btu met'od. First, com-ute t'e ecess air, +'ic' is

E ? #4 @2

21 B 2? 12">

L'e factor #4. is fromLable 6.6&see D6.12). L'e +et ue $as -roduced is

Hence

!4 @ 112" @1013

106

106:1#,00

? 1!6 lb:lb fuel

A 1061#,00

et $as loss ? 100 @ 1!6 @

026 @

300 B "0

1",400? 4!>

L'e radiation loss on HH% basis can be a--roimated by E5. &1d)

8adiation loss ? 10062042 lo$ D? 060>

D ? 100 Btu:'

*et us use 1.0> on *H% basis, alt'ou$' t'is may be a bit 'i$'. Hence t'e

efficiency on *H% basis is 100 ! 6.4! ? #3.3>. L'e efficiency on HH% basis+ould be GE5. &3b)

KHH%@ HH% ? K*H%@ *H%

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or

KHH%? #3 @1",4001#,00

? ""2

L'us, e(en in t'e absence of fuel ultimate analysis, t'e -lant -ersonnel can c'ect'e efficiency of boilers and 'eaters based on o-eratin$ data.

6.21

D

Ho+ is t'e loss due to incom-lete combustion suc' as t'e formation of C7determined

Efforts must be made by t'e boiler and burner desi$ners to ensure t'at com-letecombustion taes -lace in t'e furnace. Ho+e(er, because of (arious factors suc'as siSe of fuel -articles, turbulence, and a(ailability of air to fuel and t'e miin$-rocess, some carbon monoide +ill be formed, +'ic' means losses. f C7 is

formed from carbon instead of C72, 10,600 Btu:lb is lost. L'is is t'e differencebet+een t'e 'eat of reaction of t'e t+o -rocesses

C A 72\ C72 and C A 72\ C7

L'e loss in Btu:lb is $i(en by G1

* ?C7

C7 A C72@ 10,160 @ C

+'ere C is t'e carbon in t'e fuel, fraction by +ei$'t, and C7 and C72are (ol>of t'e $ases.

Eam-le

etermine t'e losses due to formation of C7 if coal +it' HH% of 12,000 Btu:lbis fired in a boiler, $i(en t'at C7 and C72in t'e ue $as are 1.> and 1!> andt'e fuel 'as a carbon content of 6>.

9olution. 9ubstitutin$ into t'e e5uation $i(en abo(e,

* ?1C

1"C@ 10,160 @

06

12,000? 003"

or * ? 3."> on HH% basis &di(idin$ loss in Btu:lb by HH%).


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6.22

D

s t'ere a sim-le formula to estimate t'e efficiency of boilers and 'eaters if t'e

ecess air and eit $as tem-erature are no+n and t'e fuel analysis is nota(ailable

Boiler efficiency de-ends mainly on ecess air and t'e difference bet+een t'e ue$as eit tem-erature and t'e ambient tem-erature. L'e follo+in$ e-ressions'a(e been deri(ed from combustion calculations for ty-ical natural $as and oilfuels. L'ese may be used for 5uic estimations.

For natural $as

KHH%, > ? "#4 I0001123 A 001# @ EJ @ LK*H%, > ? ##0 I0001244 A 00216 @ EJ @ L

I16aJI16bJ

For fuel oils

KHH%, > ? #2# I00012#" A 001#0 @ EJ @ L

K*H%, > ? ##0 I00013"3 A 00203 @ EJ @ L

+'ere

E ? ecess air factor &E ? 1.1 means 1> ecess air)

L ? difference bet+een eit $as and ambient tem-eratures

Eam-le

;atural $as at 1> ecess air is fired in a boiler, +it' eit $as tem-erature 2"0F

and ambient tem-erature "0F. etermine t'e boiler efficiency. E ? 11 andL ? 2"0 "0 ? 200 F.

9olution.

KHH%? "#4 I0001123 A 001# @ 11J

@ I2"0 "0J ? "464>

K*H%? ##0 I0001244 A 00216 @ 11J

@ I2"0 "0J ? #3!">

L'e abo(e e5uations are based on 1> radiation -lus unaccounted losses.


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440 A 6#@A 02#6 @ I1"0 "J

6.23

D

L'e a(era$e surface tem-erature of t'e aluminum casin$ of a $asPfired boiler +as

measured to be 1"0F +'en t'e ambient tem-erature +as " F and t'e +ind(elocity +as m-'. L'e boiler +as firin$ 0,000 scf' of natural $as +it'

*H% ? 10! Btu:scf. etermine t'e radiation loss on *H% basis if t'e totalsurface area of t'e boiler +as 200 ft2. ssume t'at t'e emissi(ity of t'ecasin$ ? 0.1.

L'is eam-le s'o+s 'o+ radiation loss can be obtained from t'e measurement ofcasin$ tem-eratures. L'e +ind (elocity is m-' ? 440 f-m. From D".1 +e see

t'at t'e 'eat loss 5 in Btu:ft2' +ill be

5 ? 01!3 @ 10"@ 01 @ ZI460 A 1"0J4 I460 A "J4[r]]]]]]]]]]]]]]]]]]

12

6#I1!J

? 22 Btu:ft2'

L'e total 'eat loss +ill be 200 @ 22 ? 0.63 @ 106Btu:'. L'e radiation loss on

*H% basis +ill be 0.63 @ 106@ 100:&0,000 @ 10!) ? 1.1!>. f t'e HH% oft'e fuel +ere 11"2 Btu:scf, t'e radiation loss on HH% basis +ould be

0.63 @ 11"2:10! ? 1.06>.

6.24

D

Ho+ does t'e radiation loss (ary +it' boiler duty or load Ho+ does t'is affectt'e boiler efficiency

L'e 'eat losses from t'e surface of a boiler +ill be nearly t'e same at all loads if

t'e ambient tem-erature and +ind (elocity are t'e same. %ariations in 'eat lossescan occur o+in$ to differences in t'e $as tem-erature -rofile in t'e boiler, +'ic'(aries +it' load. Ho+e(er, for -ractical -ur-oses t'is (ariation can be consideredminor. Hence t'e 'eat loss as a -ercent +ill increase as t'e boiler duty decreases.

L'e boiler eit $as tem-erature decreases +it' a decrease in load or dutyand contributes to some im-ro(ement in efficiency, +'ic' is offset by t'e increasein radiation losses. Hence t'ere +ill be a sli$'t increase in efficiency as t'e loadincreases, and after a certain load, efficiency decreases.

L'e abo(e discussion -ertains to fired +ater tube or fire tube boilers and not+aste 'eat boilers, +'ic' 'a(e to be analySed for eac' load because t'e $as o+


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and inlet $as tem-erature can (ary si$nificantly +it' load de-endin$ on t'e ty-eof -rocess or a--lication.

6.2aD

iscuss t'e im-ortance of de+ -oint corrosion in boilers and 'eaters fired +it'fuels containin$ sulfur.

urin$ t'e -rocess of combustion, sulfur in fuels suc' as coal, oil, and $as iscon(erted to sulfur dioide. 9ome -ortion of it &1Q>) is con(erted to sulfurtrioide, +'ic' can combine +it' +ater (a-or in t'e ue $as to form $aseoussulfuric acid. f t'e surface in contact +it' t'e $as is cooler t'an t'e acid de+-oint, sulfuric acid can condense on it, causin$ corrosion. / &acid de+ -oint)is de-endent on se(eral factors, suc' as ecess air, -ercent sulfur in fuel, -ercent

con(ersion of 972to 973, and -artial -ressure of +ater (a-or in t'e ue $as.anufacturers of economiSers and air 'eaters su$$est minimum coldPendtem-eratures t'at are re5uired to a(oid corrosion.Fi$ures 6.1and6.2are ty-ical.9ometimes t'e minimum uid tem-erature, +'ic' affects t'e tube metaltem-erature, is su$$ested. L'e follo+in$ e5uation $i(es a conser(ati(e estimateof t'e acid de+ -oint G"

Ld-? 1!"42 A 0026# lo$ -+ 012# lo$ -973

A 032# lo$ -+@ lo$ -973I1"aJ

+'ere

Ld-? acid de+ -oint, R

-+? -artial -ressure of +ater (a-or, atm

-973? -artial -ressure of sulfur trioide, atm

Lable 6."$i(es ty-ical -973(alues for (arious fuels and ecess air. D6.1"c

s'o+s 'o+ --m 973can be com-uted from +'ic' -973is obtained. -ractical +ay to determine Ld-is to use a de+ -oint meter. n estimation

of t'e coldPend metal tem-erature can $i(e an indication of -ossible corrosion.

6.2b

D

Ho+ is t'e de+ -oint of an acid $as com-uted

Lable 6.#s'o+s t'e de+ -oint correlations for (arious acid $ases G#,11.


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F=) H27 ? 12,972? 0.02, HCl ? 0.001 and t'e rest oy$en and nitro$en. =as -ressure? 10 in. +$. Com-ute t'e de+ -oints of sulfuric and 'ydroc'loric acids $i(en

t'at 2> of 972con(erts to 973. n order to use t'e correlations, t'e $as -ressuresmust be con(erted to mmH$. tmos-'eric -ressure ? 10 in. +$ ? 10:40! ?0.024! atm$ or 1.024! atm abs.

-H27? 012 @ 1024! @ !60 ? #344 mmH$

ln /H27? 43!

/HCl? 0001 @ 1024 @ !60 ? 0116" mmH$

ln -HCl? 214!3

/artial -ressures of sulfuric acid and 973are e5ual. Hence

/973? 002 @ 00002 @ !60 @ 1024 ? 00031 mmH$

ln /973? !!16

9ubstitutin$ into t'e e5uations, +e obtain t'e follo+in$.


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F=

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Ld-is de+ -oint tem-erature &R), and / is -artial -ressure &mmH$).

LB*E6.#e+ /oints of cid =asesa

Hydrobromic acid

1000:Ld-? 3.63# ! 0.130 ln /H27! 0.03#" ln /HBr

A 0.0023 ln /H27ln /HBr

Hydroc'loric acid

1000:Ld-? 3.!36" ! 0.1#1 ln /H27! 0.0326 ln /HCl

A 0.0026# ln /H27ln /HCl

;itric acid

1000:Ld-? 3.6614 ! 0.1446 ln /H27! 0.0"2! ln /H;73

A 0.00!6 ln /H27ln /H;73

9ulfurous acid

1000:Ld-? 3.#26 ! 0.1"63 ln /H37A 0.000"6! ln /972

! 0.000#13 ln /H27ln /972

9ulfuric acid

1000:Ld-? 2.2!6 ! 0.02#4 ln /H27! 0.0"" ln /H3974

A 0.0062 ln /H27ln /H2974

a

Com-ared +it' -ublis'ed data, t'e -redicted de+ -oints are +it'in

about 6 R of actual (alues ece-t for H2974, +'ic' is +it'in about # R.

9ource HCl, HBr, H;73and 972correlations +ere deri(ed from(a-orQli5uid e5uilibrium data. L'e H2974correlation is from 8ef. .

For sulfuric acid

1000

Ld-? 22!6 002#4 @ 43! A 00"" @ !!16

00062 @ 43! @ !!16 ? 24!

orLd-? 404 R ? 131C ? 26"F

L'e de+ -oints of ot'er $ases can be obtained in a similar manner.

6.2c

D

oes t'e -otential for acid de+ -oint corrosion decrease if t'e $as tem-erature att'e economiSer is increased


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cid de+ -oints +ere com-uted in D6.2a. f t'e tube +all tem-eratures can bemaintained abo(e t'e de+ -oint, t'en condensation of (a-ors is unliely.Ho+e(er, t'e tube +all tem-erature in a $asPtoPli5uid 'eat ec'an$er suc' as

t'e economiSer is $o(erned by t'e $as film 'eat transfer coefficient rat'er t'an t'etubePside +ater coefficient, +'ic' is (ery 'i$'.

t can be s'o+n by usin$ t'e electrical analo$y and ne$lectin$ t'e effects offoulin$ t'at G#

tm? to Ito tiJ'i

'iA 'o

+'ere

tm? tube +all tem-erature

to? $asP and tubePside uid tem-erature'i? tubePside 'eat transfer coefficient'o? $asPside 'eat transfer coefficient

n an economiSer, 'iis ty-ically about 1000 Btu:ft2' F and '0is about1 Btu:ft2' F.

*et us assume t'at +ater tem-erature ti? 20F and com-ute t'e +alltem-erature tmfor t+o $as tem-eratures, 30F and !0F.

tm1? 30 I30

20J

tm2? !0 I!0

20J

1000

101

1000

101

? 22F

? 2"F

Hence for a (ariation of 400 F in $as tem-erature, t'e tube +all tem-eraturec'an$es by only 6F because t'e $as film 'eat transfer coefficient is so lo+com-ared to t'e +aterPside coefficient. E(en +it' finned tubes t'e difference+ould be mar$inal.

e see t'at if +e s-ecify a 'i$'er stac $as tem-erature +'en selectin$ ordesi$nin$ an economiSer +e cannot a(oid corrosion concerns if t'e +atertem-erature is lo+ or close to t'e acid de+ -oint. better +ay is to increaset'e +ater tem-erature enterin$ t'e economiSer by raisin$ t'e deaerator -ressureor by usin$ a 'eat ec'an$er to -re'eat t'e +ater.

6.2d

D

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L'e -artial -ressures are in atmos-'eres and de+ -oint is in de$rees Celsius.

oy$en in t'e $as. L'e con(ersion can be done as follo+s.

f + lb:' is t'e o+ rate of ;7 &usually re-orted as ;72) in a turbinee'aust o+ of lb:', t'e follo+in$ e-ression $i(es ;7 in (olumetric unitson dry basis G#.

% ? 100 @I+:46J:I :J

100 >H27I1#J

+'ere

>H27 ? (olume of +ater (a-or ? molecular +ei$'t of t'e e'aust $ases


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L'e (alue of % obtained +it' E5. &1#) must be con(erted to 1> oy$en on drybasis to $i(e --m(d of ;7

%n?% @ I21 1J @ 106

21 100 @ >72:I100 >H27J

? % @ F I20J

+'ere >72is t'e oy$en -resent in t'e +et e'aust $ases and factor F con(erts% to 1> oy$en basis, +'ic' is t'e usual basis of re-ortin$ emissions. 9imilarly,C7 emission in --m(d can be obtained as

%c? 1642 @ %n &for t'e same + lb:' rateJ

because t'e ratio of t'e molecular +ei$'ts of ;72and C7 is 1.642.

Eam-le

etermine t'e ;7 and C7 concentrations in --m(d, 1> oy$en dry basis if

2 lb:' of ;7 and 1 lb:' of C7 are -resent in 0,000 lb:' of turbine e'aust$as t'at 'as t'e follo+in$ analysis by (olume -ercent &usually ar$on is added tot'e nitro$en content)

C72? 3

9olution.First,

H27 ? 10 ;2? ! 72? 11

? I3 @ 44 A 10 @ 1" A ! @ 2" A 11 @ 32J:100 ? 2"*et us com-ute ;7 on dry basis in t'e e'aust.

% ?100 @ I2:46J

I0,000:2"J:I100 B

10J

? 0000030!4

F ?106@ I21 1J

21 Z100:I100 10J @

11

? 0!3 @ 106

Hence

%n? 0000030!4 @ 0!3 @ 106? 224 --m(d

9imilarly, %c? &1:2) @ 1.642 @ 22.4 ? 22.0 --m(d.

6.26b

D

Ho+ can t'e emissions due to ;7 and C7 in fired boilers be con(erted from

--m to lb: Btu or (ice (ersa G10

/aca$ed steam $enerators firin$ $as or oil must limit emissions of -ollutants inorder to meet state and federal re$ulations. Criteria on emissions of common

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;atural $as analysis assumed C1? #!, C2? 2, C3? 1 (ol>. &HH% and **% ? 23,!# and

;o. 2 oil analysis assumed C ? "!.>, H2? 12.> / ? 32. &HH% and **% ? 1#,!2! and

-ollutants suc' as carbon monoide &C7) and oides of nitro$en &;7) are oftens-ecified in -arts -er million (olume dry &--m(d) at 3> oy$en. 7n t'e ot'er'and, burner and boiler su--liers often cite or $uarantee (alues in -ounds -ermillion Btu fired.

Lable 6.10 demonstrates a sim-le met'od for calculatin$ t'e con(ersion. ts'ould be noted t'at ecess air 'as little effect on t'e con(ersion factor.

Lable 6.10 s'o+s t'e results of combustion calculations for natural $as and;o. 2 oil at (arious ecess air le(els. L'e table s'o+s t'e ue $as analysis,molecular +ei$'t, and amount of ue $as -roduced -er million Btu fired on 'i$'er'eatin$ (alue &HH%) basis.

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FromLable 6.10 for Sero ecess air

$m? I106:23,!"#J @ 1"3 ? !6#

W ? 100:I100 1##1J ? 124"

? 2!3 72? 0

9ubstitutin$ t'ese into E5. &21) +e 'a(e

%n? 106 @ 124" @ ; @ 2!2

@

1"

46 @ !6# @ 21? "32 ;

9imilarly, to obtain --m(d C7 &-arts -er million (olume dry C7), one +ould use

2" instead of 46 in t'e denominator. L'us t'e molecular +ei$'t of ;7 +ould be46 and t'e calculated molecular +ei$'t of C7 +ould be 2".

%e? 136! C7

+'ere C7 is t'e -ounds of C7 -er Btu fired on 'i$'er 'eatin$ (alue &HH%)

basis.;o+ re-eat t'e calculations for 30> ecess air

$m? #"66

? 2!!!

100

100 1#6

72? 443

? 11"#

%n? 106@ 11"#

@

;46

@ 2!!!#"66

@1"

21 I443 @ 11"#J? "32;

L'us, inde-endent of ecess air, +e obtain "32 as t'e con(ersion factor for ;7

and 136! for C7.9imilarly, for ;o. 2 oil and usin$ (alues from Lable 6.10,

%n? !"3; and %c? 12"6 C7

Eam-le

f a natural $as burner $enerates 0.1 lb of ;7 -er Btu fired, t'en t'e

e5ui(alent +ould e5ual "32 @ 0.1 ? "3 --m(d.

6.26c

D

Ho+ can t'e emissions of unburned 'ydrocarbons &

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8efer toLable 6.10, +'ic' s'o+s t'e results of combustion calculations for oiland $aseous fuels at (arious ecess air le(els. e can obtain

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2!6" @ 1"

%u? < @ 106@


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Eac' -ound of sulfur in fuel con(erts to 2 lb of 972. ecess air, 9 lb: Btu of 972is e5ui(alent to

%s? 9 @ 106@100

"2C#2 @2!6" @ 1"

64 @ #14 @ I21 31" @ 100:"2#2J

? #"9 --m(d

0.1 lb: Btu of 97 is e5ui(alent to 60 --m(. Ge are sim-ly usin$ E5. &21)and substitutin$ for and W .

9imilarly, for ;o. 2 oil at 20> ecess air

%s? 9 @ 106@100

""C#3@

2""4 @ 1"

64 @ I21 324 @

100:"2#2J

? 349 --m(d

6.26e

D

$as turbine H89= 'as t'e follo+in$ data

E'aust $as o+ ? 00,000 lb:' at #00 F=as analysis (ol> C72? 3 H27 ? ! ;2? ! 72? 1. L'e e'aust

$as 'as # lb:' of ;7 and C7. L'e H89= is fired to 100F usin$ natural $asconsistin$ of (ol> met'ane ? #!, et'ane ? 2, -ro-ane ? 1. Fuel in-ut ? #0

*H%. HH% of fuel ? 23,!#0 Btu:lb, and *H% ? 21,43# Btu:lb. L'e burnercontributes 0.0 lb: Btu of ;7 and C7. lso see +'at 'a--ens +'en t'eburner contributes 0.1 lb: Btu of t'ese -ollutants. Flue $as analysis aftercombustion (ol> C72? 442, H27 ? #!", ;2? !3#1, 72? 11"6, and ue$as o+ ? 04,1#" lb:'. Com-ute t'e ;7 and C7 le(els in --m(d corrected to1> oy$en before and after t'e burner.

e 'a(e to con(ert t'e mass o+ of ;7 and C7 to (olumetric units and correctfor 1> oy$en dry basis.

t t'e burner inlet, usin$ E5s. &1#) and &20),

--m(d ;7 ?#

46@

100

#3@

2"3"

00,000@ 106@

21 1

21 1 @ 100:#3? 14!

n t'is eam-le, t'e molecular +ei$'ts of ;7 ? 46, ue $as ? 2".3". L'e mass

of C7 remains t'e same, so --m(d C7 ? &46:2") @ 14.! ? 24.2.t t'e burner eit t'e mass of ;7 in t'e e'aust $ases after combusP

tion is

# A #0 @

23,!#0

21,43# @ 00 ? 14 lb:'

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14 100 2"C2

? 14421 1

Because t'e burner 'eat in-ut is on *H% basis and emissions are on HH% basis,+e correct t'e (alues usin$ t'e abo(e e-ression.

--m(d ;7 ?

@

@ @ @ 106

46 #022 04,1#"

21 11"6 @ 100:#022

--m(d C7 ? I46:2"J @ 14 ? 23!

it' 0.1 lb: Btu emissions from t'e burner, ;7 --m(d ? 1#. and C7--m(d ? 32.1 L'us bot' t'e burner contribution and t'e initial -ollutant le(els int'e turbine e'aust $ases affect t'e --m( (alues after combustion. --m(d (aluesafter t'e burner can be lo+er or 'i$'er t'an t'e inlet --m(d (alues, t'ou$' in

terms of mass o+ t'ey +ill al+ays be 'i$'er.

6.26f

D

9team $enerator emissions are usually referred to 3> oy$en dry basis, and $asturbine or H89= emissions are referred to 1> oy$en dry basis. Ho+e(er, ino-eration, different ecess air rates are used t'at $enerate ue $ases +it' differentoy$en le(els. 'at is t'e -rocedure for con(ertin$ from actual to 3> oy$enbasis

--m &^ 3> dry) ? --m&actual) @

21 3

21 72IactualJ

f dry oy$en in ue $ases is 1.!> and 12 --m of a -ollutant is measured, t'en at3> oy$en,

Emission ? 12 @21 3

21 B 1! ? 112 --m

6.2!a

D

n $as turbine co$eneration and combined cycle -roXects, t'e 'eat reco(ery steam$enerator may be fired +it' auiliary fuel in order to $enerate additional steam.7ne of t'e fre5uently ased 5uestions concerns t'e consum-tion of oy$en in t'ee'aust $as (ersus fuel 5uantity fired. ould t'ere be sufficient oy$en in t'e

e'aust to raise t'e e'aust $as to t'e desired tem-erature


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=as turbine e'aust $ases ty-ically contain 14Q16> oy$en by (olume com-aredto 21> in air. Hence $enerally t'ere is no need for additional oy$en to fireauiliary fuel suc' as $as or oil or e(en coal +'ile raisin$ its tem-erature. &f t'e

$as turbine is inXected +it' lar$e amounts of steam, t'e oy$en content +ill belo+er, and +e s'ould refer t'e analysis to a burner su--lier.) lso, if t'e amountof fuel fired is (ery lar$e, t'en +e can run out of oy$en in t'e $as stream.9u--lementary firin$ or auiliary firin$ can double or e(en 5uadru-le t'e steam$eneration in t'e boiler com-ared to its unfired mode of o-eration G1. L'e ener$y

D in Btu:' re5uired to raise $lb:' of e'aust $ases from a tem-erature of t1tot2is $i(en by

D ? $@ I'2 '1J

+'ere'1 '2? ent'al-y of t'e $as at t1and t2, res-ecti(ely

L'e fuel 5uantity in lb:' is fin D:*H%, +'ere *H% is t'e lo+er 'eatin$

(alue of t'e fuel in Btu:lb.f 0> (olume of oy$en is a(ailable in t'e e'aust $ases, t'e e5ui(alent

amount of air ain t'e e'aust is G#

a?100 @ $ @ 7 @ 32

23 @ 100 @ 2#

n t'is e5uation +e are merely con(ertin$ t'e moles of oy$en from (olume to+ei$'t basis. molecular +ei$'t of 2#. is used for t'e e'aust $ases, and 32 for

oy$en. L'e factor 100:23 con(erts t'e oy$en to air.

a? 004!1 @ $@ 7 I22J

;o+ let us relate t'e air re5uired for combustion +it' fuel fired. From D.03Q

D..0 +e no+ t'at eac' Btu of fuel fired on HH% basis re5uires a constant

amount of air. is !4 for oil and !30 for natural $as t'us, 106:HH% lb of fuelre5uires lb of air. Hence D:*H% lb of fuel re5uires

D*H%

@ @ HH%106

lb air

and t'is e5uals afrom &22).

D

*H%@ @

HH%

106? a? 004!1$@ 7 I23J

or

D ? 004!1 @ $@ 7 @ 106

@

*H%

@ HH%I24J

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lso, it +ill increase C72by

1626 @ I44:16J ? 44!1 lb:'

H27 +ill increase by

1626 @ I36:16J ? 36# lb:'

Con(ert t'e (olume -ercent in incomin$ e'aust $ases to +ei$'t -ercent

basis as follo+s. L'e molecular +ei$'t of incomin$ $ases is 003 @ 44 A00! @ 1" A 0! @ 2" A 01 @ 32 ? 2"3"

Fraction by +ei$'t of C72? 003 @ 44:2"3" ? 0046

H27 ? 00! @ 1":2"3" ? 00444

;2? ! @ 2":2"3" ? 0!4

72? 01 @ 32:2"3" ? 016#1L'e amounts of t'ese $ases in incomin$ e'aust $as in lb:'

C72? 10,000 @ 0046 ? 6#! lb:'

H27 ? 10,000 @ 00444 ? 6660 lb:'

;2? 10,000 @ 0!4 ? 111,000 lb:'

72? 10,000 @ 016#1 ? 2,36 lb:'

L'e final -roducts of combustion +ill 'a(e

C72? 6#! A 44!1 ? 11,446 lb:'

H27 ? 6660 A 36# ? 10,31# lb:'

;2? 111,000

72? 2,36 604 ? 1","61 lb:'

Lotal e'aust $as flo+ ? 11,446 A 10,31# A 111,000 A 1","61

? 11,626 lb:'

+'ic' matc'es t'e sum of e'aust $as o+ and t'e fuel $as fired.

Lo con(ert t'e final e'aust $as to (ol> analysis, +e 'a(e to obtain t'enumber of moles of eac' constituent.

oles of C72? 11,446:44 ? 2601

H27 ? 10,31#:1" ? !32

;2? 111,000:2" ? 3#643

72? 1","61:32 ? "#4

Lotal moles ? 3"!


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Hence

C72? 2601:3"! ? 004"3, or 4"3> by (olume

9imilarly,H27 ? !32:3"! ? 01064, or 1064 (ol>

;2? 3#642:3"! ? 0!3# or !3# (ol>

72? "#4:3"! ? 010#4, or 10#4 (ol>

C72, (ol>72, (ol>

22.

11,03!#.334.1#12.3"

41."3

11,#4!11.2#.1"10.1"

62.#"

12,#313.3#6.26!."3

"6.4

14,031.6!!.42.2!

111.1

1,1!41".00".62.6!

10,000 lb:' of e'aust $ases at #00 F. E'aust $as analysis &(ol>) C72? 3, H27 ? !,

;2? !, 72? 1. ;atural $as C1? #! (ol>, C2? 3 (ol>.


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6.2"

D

Ho+ can t'e fuel consum-tion for -o+er -lant e5ui-ment suc' as $as turbines

and diesel en$ines be determined if t'e 'eat rates are no+n

L'e 'eat rate &H8) of $as turbines or en$ines in Btu:' refers indirectly to t'eefficiency.

Efficiency ?3413

H8

+'ere 3413 is t'e con(ersion factor from Btu:' to . 7ne 'as to be carefulabout t'e basis for t'e 'eat rate, +'et'er it is on HH% or *H% basis. L'e

efficiency +ill be on t'e same basis.Eam-le

f t'e 'eat rate for a $as turbine is #000 Btu:' on *H% basis and t'e 'i$'er

and lo+er 'eatin$ (alues of t'e fuel are 20,000 and 22,000 Btu:lb, res-ecti(ely,t'en

Efficiency on *H% basis?

3413

#000? 03!# or 3!#>

Lo con(ert t'is efficiency to HH% basis, sim-ly multi-ly it by t'e ratio of t'e'eatin$ (alues

Efficiency on HH% basis ? 3!#

@

;7E;C*L

C C7 C72CaC-eEEHH%H8

'i 'o

RR1 R2

L'eoretical amount of air for combustion -er Btu fired, lb

Carbon, carbon monoide, and carbon dioides' concentration in ue $as, $rains:cu ft9-ecific 'eat, Btu:lb FEmission rate of sulfur dioide, lb: BtuEcess air, >Ecess air factor

Hi$'er 'eatin$ (alue, Btu:lb or Btu:scfHeat rate, Btu:'nside and outside 'eat transfer coefficients, Btu:ft2' F

Constant used in E5. &!)Constants used in E5. &10a) and &10c)

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*1Q**H%

/c /+,/H27

/973/a /s/5Ds9

ta t$tm

Ld-Ls La%s %a%c %n+

a $ fKr

*osses in steam $enerator, >*o+er 'eatin$ (alue, Btu:lb or Btu:scfolecular +ei$'t/artial -ressures of carbon dioide and +ater (a-or, atm

/artial -ressure of sulfur trioide, atmctual and standard -ressures, -siaifferential -ressure, -si

Heat loss, Btu:ft2'Ener$y, Btu:' or 9-ecific $ra(ity9ulfur in fuel

Lem-eratures of air and $as, Feltin$ -oint of as', C tube +all tem-erature, C

cid de+ -oint tem-erature, R9tandard and actual tem-eratures, 89tandard and actual (olumes, cu ftC7 and ;7 --m(d

ei$'t of air, lb:lb fuel subscri-t da stands for dry air +a, +etair +$, +et $as d$, dry $asoisture, lb:'Flo+ rates of air, $as, and fuel, lb:'Efficiency subscri-ts HH% and *H% denote t'e basisensity, lb:cu ft subscri-t $ stands for $as, f for fuel

8EFE8E;CE9

1.

2.

3.

4.

.

6.

!.

".

#.

% =ana-at'y. --lied Heat Lransfer. Lulsa, 7R /ennell Boos, 1#"2, -- 14Q24.

;ort' merican Combustion Handboo. 2nd ed. Cle(eland, 7H ;ort' mericanf$. Co., 1#!", -- #Q40.Babcoc and ilco. 9team ts =eneration and

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10.

11.

12.

13.

14.

% =ana-at'y. Con(ertin$ --m to lb: Btu an easy met'od. /o+er En$ineerin$,-ril 1##2, - 32.RW Hsiun$. /redictin$ de+ -oints of acid $ases. C'emical En$ineerin$, Feb #, 1#"1,- 12!.

C Baual Ur. L'e Uo'n Kin Combustion Handboo. Boca 8aton, F* C8C /ress,2001.Babcoc and ilco, 9team, its $eneration and use, 40t' ed. L'e Babcoc andilco Com-any, Barberton, 7'io, 1##2.= 7es. =et acid de+ -oint of ue $as. Hydrocarbon /rocessin$, Uuly 1#"!.

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