Numerical simulation of flow behavior of top-gas jet in a gas-particles bubbling fluidized bed

Abstract

Flow behavior of top-gas jet and particles is simulated by means of gas-solids two-fluid model incorporating the kinetic theory of granular flow (KTGF) in a top-gas jet bubbling fluidized bed. The RNG k-ε model is used to model gas turbulence of the top-gas jet. The effects of the top-jet gas velocity and fluidizing gas velocity on distributions of volume fractions and velocities of gas and particles are evaluated, and the results are quantified in terms of top-gas jet penetration length. Numerical simulations show that the fluidized gas-particle mixture along bed height is divided into three regions as (a) the top-gas jet region in the freeboard, (b) the concentrating region near the bed surface and (c) the diluting region near the bottom in terms of the axial distribution of solids volume fraction. By increasing the top-jet gas velocity, particles circulate through the down-flow at the center from the concentrating region to the diluting region and the up-flow near the walls from bottom to bed surface along bed height. The distributions of volume fraction and velocity of gas and particles considerably change with the variation of top-jet gas velocities. Moreover, the top-gas jet penetration length with the change of top-jet gas velocity and fluidizing gas velocity is identified and discussed.