Gas-solid flow characteristics in turbulent fluidized bed with variable gas velocity

Abstract

In turbulent fluidized bed (TFB), the superficial gas velocity usually varies since chemical reactions can change the number of gas moles. However, information from the study without considering the variation of gas velocity is usually used to guide the design and operation of industrial TFB reactors. In order to reveal the difference of constant and variable gas velocity and to address the possible effect of without considering variation of gas velocity, experiment and three-dimensional Computational Fluid Dynamics (3D CFD) simulation were performed on the gas-solid flow characteristics in TFB. Results show that the nonuniformity of axial flow field can be overestimated while the nonuniformity of radial flow field can be underestimated without considering the variation of gas velocity for the system in which the number of gas mole increases due to chemical reactions. Such different flow hydrodynamics with and without considering the variation of gas velocity can be more clearly observed at higher solids handle capacity. CFD simulation results indicate that the presence of particle clusters can provide reliable explanations on the different flow behavior at constant and variable gas velocity. The particle tracer information and the residence time distribution (RTD) of gas phase indicate that the back-mixing of gas and solids can be overestimated without considering the variation of gas velocity. Results indicated that the guiding information from the constant gas velocity study can largely misguide the estimation of the conversion process if this guiding information is applied in the actual industrial process with the number change of gas moles in chemical reactions.