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almost an order of magnitude, which con
rms the improved solid particle recir-
culation in the modi
guration of Fig.
15
. In addition, it is believed that the
elimination of the dead zone and enhanced solid recirculation from the loop seal
makes the central jet experience a greater solid load in the fuel reactor in the
modi
ed con
guration, which in turn prevents the formation of the
unsteady pathway seen in the original con
ed
fl
fluidized bed con
guration and triggers the formation of
the gas bubble. However, more in-depth study of this aspect is needed in future
work to gain better understanding of this key mechanism. Nevertheless, the sim-
ulation results shown in Figs.
16
and
17
clearly demonstrate that the two major
concerns in the original CD-CLC con
guration of Fig.
12
, i.e., the failure to form
new gas bubbles and poor recirculation of solid particles have been eliminated in
the modi
ed con
guration of Fig.
15
.
4.4 Reacting Flow Simulation of Modi
ed CD-CLC System
Using Spouted Fluidized Bed Fuel Reactor
The next step in developing a complete CD-CLC model for design and optimization
is to incorporate chemical reactions into the CFD/DEM approach. This is achieved
by considering the simple reaction described in Eq. (
3
) and applying the surface
combustion model in ANSYS Fluent (ANSYS
2012a
,
b
).
12Fe
2
O
3
ð
s)
þ
CH
4
!
8Fe
3
O
4
ð
s)
þ
CO
2
þ
2H
2
O
ð
3
Þ
Iron (Fe) being one of the cheapest and most abundant metals available on Earth,
Fe-based metal oxides such as Fe
2
O
3
are well-suited for use as the oxygen carrier in
CD-CLC operation. However, given the density of Fe
2
O
3
being 5,240 kg/m
3
,
experience has shown that when using particles of relatively large diameter as
required for a spouted bed, the large mass compared to the glass beads prevents
successful
fluidization. There are also issues with particle agglomeration with
Fe
2
O
3
at high temperatures. To mitigate these drawbacks, it has been proposed to
consider iron dispersed on various support materials (Hossain and de Lasa
2008
).
Johansson et al. (
2004
) showed that 60 % Fe
2
O
3
supported on MgAl
2
O
4
spinel
sintered at 1,100
fl
cient hardness, and its
apparent density of 2,225 kg/m
3
makes it an ideal candidate for spouted
°
C provided excellent reactivity and suf
fluidized
bed operation. Therefore, this material is used as the oxygen carrier in the reacting
fl
fl
flow simulation.
The MgAl
2
O
4
is non-reacting, so the only reaction that takes place in the fuel
reactor in the modi
guration of Fig.
15
is that described in Eq. (
3
)
whereby the Fe
2
O
3
is reduced to Fe
3
O
4
. The components of the inlet
ed CD-CLC con
ow and the
reaction rates are taken from the experimental work of Son and Kim (
2006
). The
flow injection in the simulation comprises 10 % CH
4
and 10 % H
2
O by mass
fraction; the remaining 80 % is N
2
unlike the experiment where 75 % N
2
and 5 %
CO
2
were used by Son and Kim (
2006
). This change is necessary to isolate the CO
2
fl
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