Biomedical Engineering Reference
In-Depth Information
8.12.1.1 Cold-Gas Efficiency
Cold-gas efficiency is the potential energy output over the energy input. If
M
f
kg of solid fuel is gasified to produce M
g
kg of product gas with an LHV
of Q
g
, the efficiency is expressed as:
Q
g
M
g
LHV
f
M
f
η
cg
5
(8.40)
where LHV
f
is the LHV of the solid fuel.
Example 8.3
Air
steam gasifier data includes the mass composition of the feedstock:
C: 66.5%
O: 7%
H: 5.5%
N: 1%
Moisture: 7.3%
Ash: 12.7%
LHV: 28.4 MJ/kg
and the volume composition of the product gas:
CO: 27.5%
CO
2
: 3.5%
CH
4
: 2.5%,
H
2
: 15%
N
2
: 51.5%
The dry air supply rate is 2.76 kg/kg of feed, the steam supply rate is
0.117 kg/kg of feed, the moisture content is 0.01 kg of H
2
O per kg of dry air,
and the ambient temperature is 20
C.
Find:
2
The amount of gas produced per kg of feed
The amount of moisture in the product gas
The carbon conversion efficiency
The cold-gas efficiency
Solution
Table C.3 (Appendix C) shows the mass fraction of N
2
and O
2
in air as 0.755
and 0.232, respectively. The nitrogen supply from air is:
0
kg feed
The total nitrogen supplied by the feed air and the fuel feed, which carry 1%
nitrogen, is:
2
:
755
2
:
76
2
:
08 kg N
2
=
3
5
:
08
0
:
01
2
:
09 kg N
2
=
kg feed
5
ð
2
:
09
=
28
Þ
5
0
:
0747 kmol N
2
=
kg feed
1
5
noting that volume percent equals molar percent in a gas mixture.
Since the product gas contains 51.5% by volume of nitrogen, the amount of
the product gas per kilogram of feed is:
0
:
0747
=
0
:
515
0
:
145 kmol gas
=
kg feed
5
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