Process and Reactor Level Simulations of Coal-Direct Chemical-looping Combustion - Novel Combustion Concepts for Sustainable Energy Development - page 345

1 1

P2

0.1

0.1

P2

P3

0.9 0.9

P3

P5

P5 0.05

0.05

0.8 0.8

P4

P4 P1

P1

0.7 0.7

0

0

2350 2450 2550

2250 2350 2450

0.6 0.6

0.5 0.5

0.4 0.4

0.3 0.3

0.2 0.2

P5 P5

0.1 0.1

P1 P4 P1 P4

0 0

1400 1600 1800 2000 2200 2400 2600

1400 1600 1800 2000 2200 2400

Static Pressure (Pa) Static Pressure (Pa)

Fig. 14 Static pressure at pressure taps P1 - P5att = 400 ms (left) and 800 ms (right) in the
complete CD-CLC configuration

4.3 Cold Flow Simulation of Modi ed Complete CD-CLC

System Using Spouted Fluidized Bed Fuel Reactor

The formation of new gas bubbles and continuous solid recirculation from the loop
seal to the fuel reactor are the two key factors for successful CD-CLC operation,
which were not satisfactorily achieved in the simulation results for the CD-CLC
con guration

are necessary to address these two factors for improved performance. We introduce
three modi

guration considered in the previous section; modi cations to the con

guration as shown in Fig. 15 . First, a chute
is added to the bottom of the fuel reactor. The dimensions of the central jet injection
nozzle remain unchanged, while the two side panels of the chute are at about 60 °
from the horizontal. Second, the loop seal and solid recirculation duct are elevated
by 20 mm. Finally, the height of the fuel reactor and downcomer is reduced by
250 mm. The rationale behind each of these modi

cations to the CD-CLC con

cations is discussed below.
The addition of the chute at the bottom is to induce gravity-driven particle
circulation into the central jet. Such a consideration originates from the critical
angle of repose (

) for particulate materials (Lee and Herrmann 1993 ; Miller and
Byrne 1966 ; Samadani and Kudrolli 2001 ; van Burkalow 1945 ; Zhou et al. 2001 ),
which is de

θ

ned as the steepest angle of descent of the slope relative to the hori-
zontal plane when the particulate material on the slope face is on the verge of
sliding. Due to the existence of , a dead zone in which particles are stagnant can be

θ

identi fluidized bed as discussed by Takeuchi et al. ( 2004 , 2005 )

and as evident from Fig. 13 . The poor recirculation of solid particles observed in
Fig. 13 is thus also partially explained by the fact that the recirculation duct was
connected to the bottom of the fuel reactor, i.e., to the dead zone. Since the particles
in the dead zone are stationary regardless of ambient gas

ed in a spouted fl

flow, high pressure is
always present at the bottom of the fuel reactor, impeding the transport of the
particles pneumatically from the loop seal. Introducing the bottom chute eliminates
the dead zone, relieving the pressure in the fuel reactor for better recirculation of
particles. Similarly, elevating the loop seal and recirculation duct serves to reduce
the pressure at the connecting point of the recirculation duct into fuel reactor for
further improved particle recirculation. Lastly, the reduction in height of the fuel

fl