LES-DEM investigation of gas-solid flow dynamics in an internally circulating fluidized bed

摘要

Gas-solid flow dynamics is numerically simulated in an internally circulating fluidized bed (ICFB) featuring a centrally located baffle plate and uneven aeration. Its detailed features are derived using the computational fluid dynamics-discrete element method (CFD-DEM). The gas motion is resolved by means of large eddy simulation (LES) while the dynamics of solid phase is handled by the soft-sphere model. The internal circulation of the solids (spherical particles, with diameter of 1.2mm and density 1000kg/m~3) is modeled to clarify the flow characteristics of the bed for different design or operating parameters, such as superficial gas velocity, gap height, inclination angle of the gas distributor, baffle plate or side wall of the bed. Both the gas-solid flow and the underlying mechanisms of solids circulation are addressed together with the simulation results. Meanwhile, the operational control behavior of different parameters is quantified by estimating both the solids circulation flux (SCF) and the gas bypassing flux (GBF). The computational results indicate that the performance of the bed can easily be regulated by adjusting the aeration to each chamber of the bed and that within the range tested, increasing gap height enhances solids circulation and suppresses gas bypassing. There is an optimal value for the inclination angle of both side wall and baffle plate. However, increasing the inclination angle of the gas distributor continuously suppresses solids circulation. Furthermore, the residence time of solids in each chamber is figured out and its variations with these design and operating parameters are examined.