Numerical Analysis of Gas-Solid Behavior in a Cyclone Separator for Circulating Fluidized Bed System

Abstract

Cyclones are one of the most widely used gas-solid separators in circulating fluidized bed (CFB) systems. This paper focuses on numerical study of the gas-solid flow in a cyclone attached to the CFB system. The objective was to understand the flow pattern in the cyclone in order to run the CFB setup problem free. The previous works on cyclone separators do not include critical parameter such as coefficient of restitution which is responsible for swirling effect and increase in efficiency. Reynolds stress model (RSM) is used to obtain the gas flow characteristics. The resulting flow and pressure fields are verified by comparing with the measured experimental results and then used in the determination of solids flow that is simulated by the use of a discrete phase model. The simulation results show how the particle trajectories and cyclone efficiency change with varying coefficient of restitution and particle size keeping inlet velocity of gas and mean particle diameter constant. The separation efficiency, pressure drop and particle trapping time from the numerical analysis are shown to be comparable to those observed experimentally. The velocity distribution pattern obtained from the analysis exhibits strong flow recirculation with large turbulent eddies in the cyclone separator. The particle trajectories depend upon relative velocity of fluid/particles and concentration of particles. Efficiency of the cyclone is found to be dependent on particle size and coefficient of restitution. The results obtained are further utilized to optimize the velocity range of gas flow in the loop seal and riser for stable operation of CFB setup.

Keywords

• Cyclone; Reynolds stress model; Coefficient of restitution; Circulating fluidized bed.