Biomedical Engineering Reference
In-Depth Information
CO
2
Cyclone
Product
gas
CFB/transport
regenerator
Bubbling fluidized-
bed gasifier
Heat
exchanger
Water
Fuel
Steam
Product gas
for application
External heating
of regenerator
CO
2
for
sequestration
CO
2
FIGURE 8.14
Chemical looping gasification with CaO as the carrier of CO
2
between the gas-
ifier and the regenerator.
produced is captured by the calcium oxide that makes up the bubbling fluid-
ized bed (Acharya et al., 2009) as follows:
Gasification reaction: C
n
H
h
O
o
1
ð
2n
p
Þ
H
2
O
nCaO
2
nCaCO
3
2
1
H
2
(8.1)
h
2
1
2n
o
1
2
CO
1
H
2
O
2
CO
2
1
H
2
(8.2)
CO
2
-
CaCO
3
(8.3)
The removal of the reaction product, CO
2
, from the system as it is
produced increases the rate of forward reaction (
Eq. (8.2)
), enhancing the
water
gas shift reaction, therefore yielding more hydrogen in the product
gas. The calcium carbonate formed in the gasifier (
Eq. (8.3)
) is transferred to
a circulating/transport regenerator, where it is calcined into calcium oxide
and carbon dioxide.
CO
2
removal reaction: CaO
1
Regeneration: CaCO
3
-
CaO
1
CO
2
1
178
:
3kJ
=
mol
(8.4)
The carbon dioxide and the product gas leave the regenerator and gas-
ifier, respectively, at a high temperature. The hot product can be used for
generation of steam needed for gasification. The extent of calcination of cal-
cium carbonate depends on several factors including the fluidizing medium
in the regenerator section, temperature, and residence time. If the medium is
carbon dioxide as shown in
Figure 8.14
, the conversion is relatively low
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