Process and Reactor Level Simulations of Coal-Direct Chemical-looping Combustion - Novel Combustion Concepts for Sustainable Energy Development - page 351

Fig. 20 Particle tracks colored by mass fraction of Fe 3 O 4 relative to original mass of Fe 2 O 3

Fig. 21 Contours of CO 2 mass fraction produced by reaction of Fe 2 O 3 with CH 4

It should be noted that the mass fraction of Fe 3 O 4 in Fig. 20 is in relation to the
mass of Fe 2 O 3 ; the total mass of each particle also includes 40 % inert MgAl 2 O 4 by
mass; thus, the mass fraction of Fe 3 O 4 as a function of total particle mass would be
proportionately smaller. Figure 20 indicates that the mass fraction of Fe 3 O 4 pro-
gressively increases for the particles inside the fuel reactor as the simulation
advances as expected. From Fig. 21 , the mass fraction of CO 2 rises quickly for the

first 640 ms of simulation, after which it becomes steady, representing nearly a
constant rate of formation of CO 2 . The initial spike corresponds to the time frame of
the first gas bubble formation as seen in Fig. 18 . This is an encouraging result

because it validates the motivation for utilizing the spouted g-

uration for CD-CLC operation. The heavy mixing of gases and solids facilitated by
the bubble or spout creates vortical pathways, which increase the residual time and
the exposure of the solid particles with the fuel and improve the reactivity. Overall,
the observations from Figs. 20 and 21 indicate that the chemical reactions have
been successfully incorporated into the CFD/DEM model for the complete CD-
CLC reactor. The particles with a lower mass fraction of Fe 3 O 4 near the left wall of
the fuel reactor indicate that these particles originate in the loop seal where the

fl fluidized bed con

ow
is non-reacting; the constant stream of such particles provides further evidence of
continuous recirculation from the loop seal into the fuel reactor.

fl