Biomedical Engineering Reference
In-Depth Information
individual components are calculated using the relations from Table C.4
(Appendix C). For example, the specific heat of CO at 1173K is:
27
:
62
1
0
:
005
3
1173
5
33
:
48 kJ
=
kmol K
From Example 8.3, the amount of product gas is 0.145 kmol/kg fuel. The
enthalpy of CO in the product gas that contains 27.5% CO above the ambient
temperature, 25
C or 298K, is:
10
2
3
MJ
ð
0
:
145
0
:
275
Þ
kmol
=
kg feed
33
:
48 kJ
=
kmol K
3
ð
1173
298
Þ
K
=
kJ
3
3
2
3
kg feed
Similarly enthalpy of other products,
CO
2
: (0.145
1
:
168MJ
=
5
10
2
3
0.035)
56.06
(1173
298)
0.249 MJ/kg feed
3
3
3
2
3
5
10
2
3
H2: (0.145
0.15)
31.69
(1173
298)
0.603 MJ/kg feed
3
3
3
2
3
5
10
2
3
N
2
: (0.145
0.515)
32.13
(1173
298)
2.099 MJ/kg feed
3
3
3
2
3
5
10
2
3
0.249 MJ/kg feed
The amount of steam in the flue gas was calculated as 0.1908 kg/kg of feed.
To find the enthalpy of this steam above 298 K, we take values of the steam
enthalpy at 1 bar of pressure at 1173 and 298 K. The values are 4398.05 and
104.93 kJ/kg, respectively, so the enthalpy in water is:
CH
4
: (0.145
0.025)
78.65
(1173
298)
3
3
3
2
3
5
10
2
3
kg feed
Adding these, we get the total enthalpy of the product gas at 900
C.
1
H
2
O:0
:
1908
3
ð
4398
:
05
104
:
93
Þ
3
0
:
819 MJ
=
2
5
:
168
0
:
249
0
:
603
2
:
099
0
:
249
0
:
819
4
:
368 MJ
=
kg feed
1
1
1
1
1
5
The total thermal energy is:
Heating value
enthalpy
20
:
6
4
:
368
24
:
968 MJ
=
kg coal
1
5
1
5
The total gasifier efficiency is:
24
968
28
:
Total thermal energy
=
heat in feedstock
100%
5
3
:
4
5
87
:
92%
8.12.1.3 Net Gasification Efficiency
The enthalpy or energy content of the gasification medium can be substan-
tial, and so, for a rigorous analysis, these inputs should be taken into consid-
eration. At the same time, part of the input energy is returned (energy credit)
by the tar or oil produced as well as by any recovery of the heat of vaporiza-
tion in the product gas. A more rigorous energy balance may thus be written
as:
Total gross energy input
fuel energy content
heat
in gasifying
5
1
mediums
Net energy input
energy recovered through burning
tar, oil, and condensation of steam in the gas
total energy input
5
2
Search WWH ::
Custom Search