Process and Reactor Level Simulations of Coal-Direct Chemical-looping Combustion - Novel Combustion Concepts for Sustainable Energy Development - page 337

Fig. 8 a CO 2 concentration in fl flue stream at fuel reactor outlet and b overall energy output

concentration in the flue stream and the power output for different types of coal

have similar increasing trend with higher coal feeding rate. However, the perfor-
mance of the CLOU process depends greatly on the coal reactivity, which is mainly
related to the coal rank. The high-rank coal can produce CO 2 of almost twice the
purity compared to the low-rank one, which suggests that a more active oxygen
carrier is needed when low-rank coal is utilized as fuel in a CLOU process.

fl

4 CFD/DEM Simulations Using ANSYS Fluent

The APSEN Plus simulations discussed above are rich in information on the overall
validity and performance of a conceptual system-level design. However, they lack
the capability of capturing the equally critical detailed physics expected in a CLC
process, such as solid/gas mixing, separation, and erosion. The successful design
and optimization of a CD-CLC system also requires the development of credible
simulation models for multiphase fl uid fl flow which include solid particle dynamics

and chemical kinetics.
The introduction of spouted fluidized bed in the context of CD-CLC has gen-

erated a great deal of interest in recent years because of its several technical ben-
e

fl

ts. First, the introduction of high-velocity jet is likely to create strong mixing of
solids and gas avoiding loss of reactivity due to the ash agglomeration with the
oxygen carrier (Rubel et al. 2011 ). Second, the oxygen carrier particles need to be
of a relatively large diameter to be spoutable (Geldart 1973 ) and the relatively larger
particles are likely to lead to easier separation of ash from the recirculating oxygen
carrier. A signi cant differentiation of a spouted fl fluidized bed from others (e.g., a

bubbling wall collision.

The research of Gryczka et al. ( 2009 ) on spouted beds with 2-mm-diameter par-
ticles has suggested that accurate numerical representation of particle dynamics is
not likely to be achieved using the multiphase granular solid-phase approximation
due to

fl fluidized bed) is the intense particle - particle and particle -

“ the inadequacies of the continuum model. ” Such inaccuracy has been