Application of CPFD method in the simulation of a circulating fluidized bed with a loop seal Part II—Investigation of solids circulation

Abstract

The Computational Particle Fluid Dynamics (CPFD) numerical method was used to study the gas solid flow characteristics in a circulating fluidized bed (CFB) with a loop seal in this work. The influences of operating parameters, including loop seal aeration rate (Ql), fluidized air velocity in the riser (Ur) and total bed inventory (Mp) on the solid circulation characteristics were mainly investigated in this part. The solid circulating rate (Gs), total pressure drop in the riser (ΔPr), particle packed height (Hs), pressure gradient (ΔPs/Hs) and gas flow rate (Gg) in the standpipe, as well as the particle concentration and pressure distributions in the loop were carefully analyzed under different operating conditions. The simulation results were compared with the experimental results also reported in this work and good agreements were obtained. The results showed that the increase of Ql resulted in a decrease of Hs and increases of Gs, ΔPr and ΔPs/Hs. By increasing Ur, the increase of Gs was limited and the maximum value was approaching. An increase of Mp also had a positive effect on Gs while an elevated Hs was obtained as a result of mass and pressure balance. No gas bypass flow phenomenon occurred in the operating cases of this work from the simulation results. The pressure drop in the riser could be properly predicted while the gas–solid interactions in the standpipe and loop seal were slightly underestimated by the CPFD method, where a relatively lower ΔPs/Hs was obtained for CFB modeling.