Process and Reactor Level Simulations of Coal-Direct Chemical-looping Combustion - Novel Combustion Concepts for Sustainable Energy Development - page 323

potential for use in CLC. The utilization of coal in a CLC process can be achieved
by two pathways. The coal can be er to subse-

quently introduce the freshly converted syngas to the fuel reactor. From the per-
spective of CLC process, such a scenario is essentially identical to the one that uses
gaseous fuel. The CLC process utilizing gaseous fuel has been widely studied
both numerically and experimentally (Dennis et al. 2006 ; Lyngfelt et al. 2001 ;
Mahalatkar et al. 2011 ). On the other hand, if solid coal (pulverized) is directly fed
into the CLC system, such a process is known as the coal-direct chemical-looping
combustion (CD-CLC). The CD-CLC concept eliminates the necessity of a gasi-

first gasi ed in a standalone gasi

fication chamber and therefore reduces the complexity of the entire power gener-
ation system. In case of CD-CLC, there have been two proposed options as to how
the metal oxide will participate in the coal combustion. One of these options is to
make the coal gasi

cation occur in an identical reactor by the oxygen carrier
wherein the coal is gasi fluidization

agent (Cao et al. 2006 ). Such a process is known as the in situ gasi

ed in situ by H 2 O and/or CO 2 supplied as a fl

cation
chemical-looping combustion (iG-CLC). The other option is to utilize special
oxygen carrier which releases gaseous oxygen under reactor conditions to sustain
the combustion of solid coal in the fuel reactor. Mattison et al. ( 2009a ) have
proposed the so-called chemical-looping combustion with oxygen uncoupling
(CLOU) as a variant of CD-CLC process.
There are two major concerns about the CD-CLC process due to the solid/gas
mixing in the fuel reactor and the agglomeration between oxygen carrier and the
coal ash. It has been identi cation is the bottleneck of the fuel

conversion rate in the iG-CLC process (Leion et al. 2009a ) and agglomeration-
induced loss of reactivity can occur when the ash concentration is high (Rubel et al.
2011 ). To address both these concerns, the spouted

ed that char gasi

guration for
the fuel reactor has been proposed for CD-CLC where instead of evenly distributing
the gas feeding at the inlet, a high-speed center jet is assigned. The presence of the
center jet can lead to high circulation rates of solid particles, which enhance the
solid

fl fluidized bed con

cation process. The enhanced particle circulation
can also help to rub off the deposit of ash on oxygen carrier to reduce agglomeration
(Shen et al. 2009 ).
In this article, two CD-CLC systems

gas mixing for a faster gasi

-

—
have been considered for process-level modeling. Process-level simulations are
performed for the CLOU process using ASPEN Plus and the results are compared
with the experimental data. The validated model is then used to investigate the
scale-up for industrial-scale plants. In addition, detailed numerical simulations of
multiphase cold

— an iG-CLC system and a CLOU system

flow are performed using the Eulerian/
Lagrangian approach by combining the computational

fl flow and reacting fl

fl fluid dynamics (CFD)

modeling for gas flow with Descrete element method (DEM) for particle move-

ment. The commercial software ANSYS Fluent is used in these simulations. The
simulations show excellent agreement with the experimental results for cold

fl

fl ow