Post on 04-Jun-2018
transcript
8/14/2019 DK1998_ch6.doc
1/77
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 $as5uantities in t'e absence of fuel data
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
2/77
6.116.12
6.13
6.146.1
6.16a6.16b6.1!6.1"
6.1#
6.20
6.216.226.23
6.246.2a6.2b6.2c6.2d6.26a
6.26b6.26c
6.26d6.26e
6.26f
6.2!a6.2!b6.2!c6.2"
Estimatin$ 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$
8/14/2019 DK1998_ch6.doc
3/77
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$.
f a burner 'as a ca-acity of D Btu:' &million Btu:') on HH% basis,its ca-acity on *H% basis +ould be
D*H%? DHH%@*H%
HH%I3aJ
9imilarly, if KHH%and K*H%are t'e efficiencies of a boiler on HH% and *H%
basis, res-ecti(ely, t'ey are related as follo+s
KHH%@ HH% ? K*H%@ *H% I3bJ
6.02a
D
Ho+ can +e estimate t'e HH% and *H% of a fuel oil in t'e absence of itsultimate analysis
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
4/77
////
=enerally, t'e / of a fuel oil +ill be no+n, and t'e follo+in$ 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,!#
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
5/77
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.
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
6/77
LB*E6.1Ly-ical Heat Contents of %arious 7ils
9-. $r. 9-. Lem-. irLy-ical 60F =ross =ross t> ;et ;et 9-. 'eat 'eat at corr. 60F C72
0
24
6"
10
12
1.0!6
1.0601.044
1.02#1.0141.000
0.#"6
".#6#
"."34".!04
".!!".44".33".21#
1,0!
1,0#1,043
1,002"1,0131,000
#".0
160,426
1#,03"1!,6#2
16,3"41,1113,""1
12,6"1
10,6"1
10,"#10,4##
10,41210,32"10,24610,166
".3#
".601"."36
#.064#.2"
10.00
10.21
13,664
12,1"310,!2
14#,36"14",02"146,31
14,100
10,231
10,13310,03!
#,#4#,"6#,!44#,661
0.3#1
0.3#40.3#!
0.4000.4030.406
0.40#
0.04
0.0"0.12
0.160.1#0.23
0.2!
0.04
OO
0.04"0.000.01
0.02
1"1
OO
12#11310#
14#4
O
O1".0
1!.61!.116.!
16.4;o. 6 oil
;o. oil
;o. 4 oil
;o. 2 oil
;o. 1 oil
14161"20
2224262"303234363"
404244
0.#!30.##0.#460.#34
0.#220.#100."#"0.""!0."!60."60."0."40."3
0."20."160."06
".106!.##6!.""#!.!"
!.6"3!."!.4""!.3#4!.303!.213!.126!.0416.#"
6."!!6.!#"6.!20
#!1.#".3#4.#33.0#20.##0#.#"#!.""6.2"!.2"64."4.1"43.#"33.#"24.2"14.!"0.4
11,110,3"014#,2!14",200
14!,13146,13214,13"144,16"143,223142,300141,400140,2113#,664
13","2613",00!13!,20!
10,0""10,013
#,#3##,"6!#,!#"#,!30#,664#,###,36#,4!#,41#,36#,2###,243#,1"##,136
10.4110.6110."010.##
11.3!11.11.!211."#12.0612.4!12.6312.!"12.#3
13.0!OO
143,"""142,!12141,!2140,466
13#,2113",21013!,1#"136,21413,2"134,163133,2#132,3"0131,24
130,6"#OO
#,"0#,02#,426#,33#,2!2#,202#,13#,06##,006",#33","!3","14",!!",!02
OO
0.4120.410.41!0.420
0.4230.4260.42"0.4310.4340.4360.43#0.4420.444
0.44!0.400.42
0.300.340.3"0.41
0.40.4"0.20.0.#0.620.660.6#0.!2
0.!60.!#0."2
0.040.060.0"0.060
0.0610.0630.060.06!0.0"#0.0!20.0!40.0!60.0!#
0.0"20.0"0.0""
14!"1463144"1433
1423140#13#13"1136"1360134!13341321
130#OO
16.11."1.1.2
14.#14.!14.14.314.013."13.613.413.3
13.113.012."
opyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
7/77
6.04
D
Estimate t'e annual fuel cost for a 300 coalPfired -o+er -lant if t'e o(erall
efficiency is 40> and t'e fuel cost is N1.1: Btu. L'e -lant o-erates for6000 ':yr.
/o+er -lants 'a(e efficiencies in t'e ran$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
8/14/2019 DK1998_ch6.doc
8/77
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
9/77
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$y costs N4: Btu
L'e fuel consum-tion at standard conditions is found as follo+s.
%s? %a/aLs
/sLaI"J
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
10/77
+'ere
%s %a? fuel consum-tion, standard and actual, cu ftM'
Ls? reference tem-erature of 208
La? actual tem-erature, 8
/s /a? standard and actual -ressures, -sia
%s? 100 @ I30 A 1422J@
? 2#00 scf'
20
146 @ 40
Hence
Ener$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
8/14/2019 DK1998_ch6.doc
11/77
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
12/77
8/14/2019 DK1998_ch6.doc
13/77
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
14/77
%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 $ra(ity, 60F:60F
40 4
Lem-.&F)
32
60
1.0000
0
0#
0.#6#
0
0#3
0.#340
0
0#2
0.#042
0
0#0
0."!62
0
0"#
0."4#"
0
0"!
0."21
0
0"6
0."01!
0
0"
#6100 23! 233 22# 226 222 21# 21
106 1062120 310 30 300 2# 2#0 2"6 2"1
1116 1112140 3"4 3!" 3!1 366 360 3 34#
116# 1164160 460 43 44 43" 431 42 41"
1236 1223 121!1"0 3" 2# 20 11 03 4#6 4""
12#3 12!" 12!2200 61! 60! #6 "! !! 6# 60
13!1 132 133 132!220 6#! 6"6 6!4 663 62 643 633
1434 1412 13#3 13"4240 !!# !66 !3 !41 !2# !1" !0!
14#" 14!4 142 1442260 "62 "4" "33 "20 "0! !# !"3
163 13! 113 102300 1034 101! ### #"4 #6" #4 #3#
16## 166" 163# 1626400
00
600
!00
"00
14"#
1#"1
211
30!"34!"36"3400"
146320""1#4!
24#!246!2#42302342361#3#44
143#20641#14
246424262#012#!433!43#3""4
141620411""4
243423"!2"622#2!332!3023"2!
13#3201"1"4
24042302"22""132"1344!3!!2
13!21##!1"26
23!623142!"#2"3!323!33#3!20
1321#!!1!##
234#22"12!62!#631#633436!0
13331#"1!!4
2324224"2!232!631632#!3622
a
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
15/77
14,0#3
0.0#10# 10.#!# 1.1$#"
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.
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
16/77
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.
8/14/2019 DK1998_ch6.doc
17/77
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
8/14/2019 DK1998_ch6.doc
18/77
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
19/77
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
8/14/2019 DK1998_ch6.doc
20/77
+da? 121! @ ? 1#2# lb dry air:lb fuel
? 1#2 lb +et air:lb fuel++a? 1#2# A
+d$?
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
21/77
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
8/14/2019 DK1998_ch6.doc
22/77
+da? 113 @ C A 3434 @ H22A 42# @ 9
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
23/77
8/14/2019 DK1998_ch6.doc
24/77
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:'
8/14/2019 DK1998_ch6.doc
25/77
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
26/77
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.pdf8/14/2019 DK1998_ch6.doc
27/77
? #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
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
28/77
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.
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
29/77
+'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
8/14/2019 DK1998_ch6.doc
30/77
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
8/14/2019 DK1998_ch6.doc
31/77
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
32/77
? 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.
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
33/77
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
8/14/2019 DK1998_ch6.doc
34/77
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
35/77
+'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.
8/14/2019 DK1998_ch6.doc
36/77
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
37/77
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 $as -roduced.
8/14/2019 DK1998_ch6.doc
38/77
*et t'e molecular +ei$'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.
8/14/2019 DK1998_ch6.doc
39/77
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
40/77
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$.
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
41/77
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 $as loss.)
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
42/77
6.1#c
D
etermine t'e efficiency of a boiler firin$ 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%.
8/14/2019 DK1998_ch6.doc
43/77
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
44/77
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.
8/14/2019 DK1998_ch6.doc
45/77
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
46/77
&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%
8/14/2019 DK1998_ch6.doc
47/77
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
48/77
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%).
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
49/77
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 $as tem-erature 2"0F
and ambient tem-erature "0F. etermine t'e boiler efficiency. E ? 11 andL ? 2"0 "0 ? 200 F.
9olution.
KHH%? "#4 I0001123 A 001# @ 11J
@ I2"0 "0J ? "464>
K*H%? ##0 I0001244 A 00216 @ 11J
@ I2"0 "0J ? #3!">
L'e abo(e e5uations are based on 1> radiation -lus unaccounted losses.
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
50/77
440 A 6#@A 02#6 @ I1"0 "J
6.23
D
L'e a(era$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+
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
51/77
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 $ases G#,11.
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
52/77
F=) H27 ? 12,972? 0.02, HCl ? 0.001 and t'e rest oy$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$.
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
53/77
F=
8/14/2019 DK1998_ch6.doc
54/77
Ld-is de+ -oint tem-erature &R), and / is -artial -ressure &mmH$).
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
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
55/77
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$er to -re'eat t'e +ater.
6.2d
D
8/14/2019 DK1998_ch6.doc
56/77
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
57/77
L'e -artial -ressures are in atmos-'eres and de+ -oint is in de$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 $ases
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
58/77
L'e (alue of % obtained +it' E5. &1#) must be con(erted to 1> oy$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
8/14/2019 DK1998_ch6.doc
59/77
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
60/77
;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.
8/14/2019 DK1998_ch6.doc
61/77
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 &
8/14/2019 DK1998_ch6.doc
62/77
8/14/2019 DK1998_ch6.doc
63/77
8efer toLable 6.10, +'ic' s'o+s t'e results of combustion calculations for oiland $aseous fuels at (arious ecess air le(els. e can obtain
8/14/2019 DK1998_ch6.doc
64/77
2!6" @ 1"
%u? < @ 106@
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
65/77
Eac' -ound of sulfur in fuel con(erts to 2 lb of 972. ecess air, 9 lb: Btu of 972is e5ui(alent to
%s? 9 @ 106@100
"2C#2 @2!6" @ 1"
64 @ #14 @ I21 31" @ 100:"2#2J
? #"9 --m(d
0.1 lb: Btu of 97 is e5ui(alent to 60 --m(. Ge are sim-ly usin$ 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 $ases after combusP
tion is
# A #0 @
23,!#0
21,43# @ 00 ? 14 lb:'
8/14/2019 DK1998_ch6.doc
66/77
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
67/77
14 100 2"C2
? 14421 1
Because t'e burner 'eat in-ut is on *H% basis and emissions are on HH% basis,+e correct t'e (alues usin$ 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
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
68/77
=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 @ $@ 7 @ 106
@
*H%
@ HH%I24J
8/14/2019 DK1998_ch6.doc
69/77
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
70/77
8/14/2019 DK1998_ch6.doc
71/77
lso, it +ill increase C72by
1626 @ I44:16J ? 44!1 lb:'
H27 +ill increase by
1626 @ I36:16J ? 36# lb:'
Con(ert t'e (olume -ercent in incomin$ 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"!
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
72/77
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>.
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
73/77
8/14/2019 DK1998_ch6.doc
74/77
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)
8/14/2019 DK1998_ch6.doc
75/77
Copyright 2003 Marcel Dekker, Inc.
8/14/2019 DK1998_ch6.doc
76/77
*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
8/14/2019 DK1998_ch6.doc
77/77
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#"!.