Environmental Engineering Reference
In-Depth Information
In Fig. 11 b, it is seen that the initial pressure buildup is immediately felt at both
locations z = 2 and 12 cm, suggesting the rapid propagation of a pressure wave.
However, due to the momentum exchange from gas to solids, such pressure buildup
is not felt at z = 22 and 40 cm until about 80 and 300 ms, respectively. Figures 10
and 11 clearly demonstrate that the Fluent CFD/DEM solver is capable of accu-
rately capturing the dynamics of the solid
gas interaction in the fuel reactor of a
-
CD-CLC con
guration. There is excellent agreement between the computed
expansion of bed height with the experimental result including the expansion rate
and also for the prediction of bubble burst. These results show the technical
advantage of the Eulerian
Lagrangian modeling approach in modeling the spouted
-
fl
fluidized bed. It should, however, be noted that the computed transient pressure
response shown in Fig. 11 b is likely to be underestimated because of the relatively
coarse mesh employed in the
field; the volume fraction calculation in the
computational cells for the CFD/DEM approach is a technical
fl
ow
limitation that
requires a minimum cell volume and precludes further mesh re
nement.
4.2 Cold Flow Simulation of Complete CD-CLC System
Using Spouted Fluidized Bed Fuel Reactor
With the successful numerical simulation of the TU-Darmstadt experiment in the
previous section, we consider the simulation of bed expansion, particle separation,
and oxygen carrier recirculation in a complete three-dimensional CD-CLC model.
Necessary peripherals such as a cyclone separator and loop seal are added to the
Plexiglas test rig of the TU-Darmstadt experiment to form a complete recirculating
CD-CLC con
guration. The geometry and computational model of such a con-
figuration are shown in Fig. 12 .
In the 3D CD-CLC con
guration shown in Fig. 12 , the fuel reactor is where the
coal particles get combusted by the oxygen carrier. The reduced oxygen carrier is
then transported to the cyclone for separation from the
flue gas and then transferred
into the downcomer. Additional gas supply is introduced from the bottom of the
loop seal to aerate the particle deposition and enable their recirculation back into the
fuel reactor. To ensure the adequacy of particle deposition in the system for its
recirculation, an additional 11,000 particles are deposited into the downcomer and
the loop seal during the initialization stage of simulation. The velocity of the central
jet is increased to 40 m/s so that suf
fl
cient gas momentum can be transferred to the
particles for them to reach the top of the reactor. The aeration velocity in the loop
seal is set at 1 m/s. All other parameters in the simulation remain unchanged from
the quasi-3D study of the TU-Darmstadt experiment reported in the previous sec-
tion. With the same computer hardware platform, each run requires about 24 h of
CPU time per 200 ms of simulation time. The particles
'
velocities and their dis-
tributions in this CD-CLC con
guration for the
first 800 ms are examined and are
presented in Fig. 13 .
Search WWH ::




Custom Search