Process and Reactor Level Simulations of Coal-Direct Chemical-looping Combustion - Novel Combustion Concepts for Sustainable Energy Development - page 344

t = 40 ms 80 ms 120 ms 160 ms 200 ms 240 ms 280 ms 320 ms 360 ms 400 ms

440 ms 480 ms 520 ms 560 ms 600 ms 640 ms 680 ms 720 ms 760 ms 800 ms

Fig. 13 Particle tracks colored by velocity magnitude in the complete CD-CLC con guration

presence. This is because the critical pressure buildup required to form a gas bubble
arises when the injected air experiences the isotropic resistance in a static bed. Due
to the unsteady pathway, the energy transferred to the particles becomes minimal
since most of the air bypasses the

fluidized bed through the pathway and it becomes
impossible for the particles to reach the top and participate in the recirculation.
Additionally, the recirculation of the solid particles appears to stagnate once the
bubble in the fuel reactor is formed. Because the formation of the gas bubble and
solids

fl

recirculation is primarily driven by the pressure at various locations in the
system, the static pressure readings at various pressure tap locations are investigated
to better understand the behavior observed from the particle tracks in Fig. 13 ; the
pressure tap data at t = 400 and 800 ms are shown in Fig. 14 .
In Fig. 14 , a large drop in pressure can be noted as the particles move from the

'

fl fluidized bed (P1) to the top of the fuel reactor (P2) and then to the cyclone (P3). As

the particles deposit in the downcomer, the pressure builds up (P4) and exceeds that
in the loop seal (P5) and flow for

particle recirculation. At both times t = 400 and 800 ms, there is a small positive
pressure difference between the downcomer and the

fl fluidized bed (P1), providing the necessary gas fl

fl fluidized bed of about 100 Pa.

With such a small pressure difference, the gas flow is not likely to provide enough

momentum to the particles to trigger the solids recirculation, which implies poor
recirculation of solid particles from the loop seal to the fuel reactor; this result
quantitatively con

fl

rms the qualitative observations made from Fig. 13 .