Biomedical Engineering Reference
In-Depth Information
overall gasification reaction (
Eq. (8.17)
) may be found from the heat of for-
mation of the products and reactants:
Heat of reaction
heat of formation of product
heat of formation of reactant
5
A
0
U
B
0
CO
2
1
C
0
U
5
heat of formation of
½
C
1
CO
D
0
U
E
0
U
F
0
U
1
CH
4
1
H
2
O
1
H
2
heat of formation of
½αU
1
βU
H
2
O
O
2
1
biomass
(8.18)
The heat of formation at 25
C, or 298K, is available in Table C.6
(Appendix C). The heat of formation at any other temperature, T, in Kelvin,
can be found from the relation:
X
ð
T
product
2
X
ð
T
298
α
H
T
5
Δ
H
298
1
A
0
C
p
;
j
dT
Δ
C
p
;
j
dT
reactants
(8.19)
where C
p,i
is the specific heat of a substance i at temperature T Kelvin, and
A
0
,B
0
,C
0
,D
0
,E
0
,D
0
,
298
are the stoichiometric coefficients of the pro-
ducts and reactants, respectively. The specific heat of gases as a function of
temperature is given in Table C.4 (Appendix C).
The net heat, Q
gasification
, to be supplied to the reactor is the algebraic
sum of heat of reactions.
α
, and
β
Q
gasification
5
Δ
H
T
kJ
=
mol
(8.20)
This expression takes into account both exothermic combustion and endother-
mic gasification reactions. If the value of Q
gasification
works out to be negative, the
overall process is exothermic, and so no net heat for the reactions is required.
Example 8.2
Find the heat of reaction for the following reaction at 1100K:
1
2
CH
4
1
2
CO
2
C
H
2
O
ð
gas
Þ
5
1
1
Solution
Taking values at the reference temperature, 298K from Table C.6, we have
Heat of formation at 298 K for C for CH
4
0
H
2
O
ð
g
Þ
52
241
:
8kJ
=
mol
5
;
;
74
:
8kJ
=
mol
CO
2
393
:
5kJ
=
mol
52
;
52
H
298
5
Total
Δ
product
reactant
2
1
2
ð
2
74
:
8
393
:
5
Þ
2
ð
2
241
:
8
Þ
7
:
65 kJ
=
mol
5
2
5
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