Environmental Engineering Reference
In-Depth Information
feeding in two separate blocks is de
ned to be identical to represent the circulation
of oxygen carrier within the system; such circulation cannot be de
ned explicitly in
the ASPEN Plus modeling. More detailed descriptions of the model setup can be
found in the authors
other work (Zhou et al.
2013
). As outputs of the process
simulations, gas concentrations at the fuel reactor outlet, oxygen carrier ef
'
ciency,
energy analysis, system scale-up, and effects of different compositions of the coal
are investigated.
Concentrations of CO
2
,H
2
O, O
2
,O
2
S, NO, NO
2
, and N
2
are monitored at the
fuel reactor
fl
fuel stream of CO
2,
and concentration of O
2
is measured at the air
reactor
flue stream of N
2
and O
2
. Dry CO
2
and H
2
O concentrations are evaluated by
Eq. (
1
) below.
fl
CO
2
;
Flue
O
2
;
Flue
CO
2
;
Dry
¼
O
2
;
Dry
¼
ð
1
Þ
ð
1
H
2
O
Flue
Þ
ð
1
H
2
O
Flue
Þ
In Eq. (
1
), CO
2,Flue
and H
2
O
Flue
are the fractional concentrations of the
respective gases at the outlet
flue stream of the reactors. The dry concentration is
used to obtain a purer CO
2
stream without water since impurities in the CO
2
streams could have an effect on their sequestration behavior. Power output is
monitored at Q-Burn, Q-A, Q-C-A, and Q-C
fl
F at locations marked by
“
Q
”
in the
-
ASPEN Plus
fl
flow sheet in Fig.
4
.
3.2.1 Oxygen Carrier Ef
ciency
One of the most important indicators of the performance of a CLOU system is the
oxygen carrier ef
ned as the fraction of oxygen carrier
conversion of CuO into Cu
2
O and O
2
. It is the ratio of transferable oxygen in the
current oxygen carrier to that in the fully oxidized oxygen carrier as given by
Eq. (
2
).
ciency,
OC, which is de
D
f
H
2
O
M
H
2
O
þ
f
O
M
O
F
CO
2
;
out
;
FR
þ
F
O
2
;
out
;
FR
þ
0
5 F
CO
;
out
;
FR
þ
F
H
2
O
;
out
;
FR
0
5m
coal
M
O
2
:
:
OC
¼
D
0
25F
CuO
:
ð
2
Þ
flue stream of the fuel
reactor, m
coal
is the coal feeding rate, fi
i
is the mass fraction of coal in the compound
i, and M
x
is the molecular weight of compound x.
As shown in Fig.
5
,
In Eq. (
2
), F
x
is the concentration of dry gas x in the
fl
OC varies linearly with the coal feeding rate. This implies
the abundance of oxygen carrier in the system. However, the air reactor ef
D
ciency,
de
ned as the fractional oxygen carrier conversion of Cu
2
O and O
2
into CuO, does
not have a linear relation with respect to coal feeding rate due to variation in air
fl
flow within the air reactor. It is also important to obtain the conversion charac-
teristics of the CLOU system. Hence, the CO
2
and O
2
concentrations in the fuel
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