(442a) CFD Modeling of gas-liquid-solid flow in a circulating fluidized bed

CFD
Modeling of gas-liquid-solid flow in a circulating fluidized bed

Circulating
fluidized bed is extensively used in many industrial applications such as
fluidized catalytic cracking (FCC) riser. The detailed investigation of the
flow circumstances in the fluidized bed is important to the process optimization.
As Geldart A paticles, FCC catalysts make the simulation of the flow conditions
difficult because of the agglomeration phenomena. Many models have been developed
to represent the gas and solid interactions among which EMMS model proposed by
Li et al.^[1] has been proved to
be applicable. With the increasing of resid-ratio in the FCC feedstock, the
heavy component which is hard to vaporize can no longer be ignored. However,
most studies until now has assumed that the atomized
feed oil vaporized instantaneously and totally in the riser. Li et al.^[2] model the interactions between
hot particles and cold droplets in an evaporative spray riser considering the momentum
exchange between the gas, solid and liquid pahse. However, the adopted Gidaspow
correlation is not applicable for characterizing the whole gas and solid flow
in the riser.

In this paper, using the gas-liquid
drag model proposed by Issa and Oliveira^[3] and the liquid-solid
model by Ge and Fan.^[4] which has also been employed by Li et al.,^[2]
coupling the EMMS method,^[1] a compositive flow model has been
developed to reveal the gas-liquid-solid flow in the FCC riser. It can be seen
from Fig.1 that the solid volume fraction exhibits turbulent flow characteristics
with the lower dense bed and the upper dilute bed. The liquid phase shows
double-peak distributions, as plotted in Fog.2. There are many droplets
accumulates at the bottom of the riser which will undoubtedly influence the FCC
reaction effect.

Fig.1 Solid
volume fraction distributions        
Fig.2 Liquid volume fraction distributions

[1] N. Yang, W.
Wang, W. Ge, et al. CFD simulation of concurrent-up gas-solid flow in
circulating fluidized beds with structure-dependent drag coefficient. Chem Eng
J. 2003, 96: 71-80.

[2] T.
Li, K. Pougatch, M. Salcudean, et al. Numerical modeling of an evaporative
spray in a riser. Powder Technology. 2010, 201:213-229.

[3]
R.L. Issa, P.J. Oliveira. Validation of two-fluid model in
shear-free mixing layers. ASME- PUBLICATIONS- FED. 1996,
236:112-120.

[4] Y.
Ge, L.S. Fan. Three-dimensional direct numerical simulation
for film-boiling contact of moving particle and liquid droplet. Physics of Fluids. 2006, 18:11.