Biomedical Engineering Reference
In-Depth Information
Similarly, q
C
is defined. Thus, we have
T
H
;
out
Þ¼
1000
q
H
¼
_
m
H
C
PH
ð
T
H
;
in
3600
4:06 ð121 30Þ
kJ
=
s
¼ 102:628
kW
q
C
102:628
4:21 ð85 20Þ
m
C
¼
C
PC
T
C
;
out
T
C
;
in
¼
=
¼ 0:375
=
¼ 1350:1
=
_
kg
s
kg
s
kg
h
Example 3-7: Heat and material balances in combustion
The waste gas from a process of 1000 mol/h of CO at 473 K is burned at 1 atm pressure in
a furnace using air at 373 K. The combustion is complete and 90% excess air is used. The flue
gas leaves the furnace at 1273 K. Calculate the heat removed in the furnace.
Solution: A schematic diagram is shown in
Fig. E3-7
.Combustion stoichiometry
þ
1
=
2
O
CO
2
/
CO
2
Heats of formation can be found as
DH
f
;298
¼
10
3
kJ/kmol for CO and
10
3
kJ/kmol for CO
2
.
110.523
393.513
H
CO
;298
1
DH
R
;298
¼
H
O
2
;298
¼ DH
fCO
2
;298
DH
fCO
;298
DH
fO
2
;298
DH
R
;298
¼282:990 10
3
kJ
H
CO
2
;298
2
=
kmol
From stoichiometry, 1 mol of CO requires half a mole of O
2
to produce 1 mol of CO
2
at
complete combustion. Therefore, the minimum O
2
in feed is half of that of CO.
F
O
2
;
min
¼
1
F
CO
;0
2
and
F
O
2
;
min
¼
1:9
F
O
2
;0
¼ 1:9
F
CO
;0
¼ 950
mol
=
h
:
2
The O
2
is supplied by air. In air, there are about 21%mole percent of O
2
and 79%mole percent
of N
2
. Thus, the requirement of O
2
brings N
2
along from the air. That is,
F
N
2
;0
¼
0:79
F
O
2
;0
¼
1:9
2
0:79
F
CO
;0
¼ 3573:8
mol
=
h
0:21
0:21
Q
CO
F
CO,0
,
T
CO,0
Flue gas,
T
e
F
A,0
,
T
A,0
Air
W
s
= 0
FIGURE E3-7
A schematic flow diagram of a flue gas combustion furnace.
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