Keynote Talk: A Definition of Micro Fluidized Bed in Terms of in-Bed Gas Back-Mixing

Micro fluidized bed (MFB) has received good attention in recent years because of its many traits different from traditional large fluidized beds and potential specific applications. This work systematically studied the gas back-mixing characteristics in MFB through experiments, simulation and verification by application. It revealed the fact that the gas flow in MFBs can maximally approach the plug flow and in turn for the first time defined what is “micro fluidized bed” in terms of gas back-mixing. We found that the residence time distribution (RTD) of gas is subject to an unique quantitative correlation between E(t)_h and σ_t², the peak and variance of RTD for MFB, respectively. The critical values of E(t)_h and σ_t² ensuring the actual gas residence time to deviate within 10% from the ideal plug flow are identified to define "micro fluidized bed" as the bed with gas flow maximally approaching the gas plug flow. Computational Fluid Dynamics (CFD) simulation was further performed to verity the experimental observations and the gas flow patterns in the bed. Measurement of a gas-solid reaction was also finally carried out using MFB to show the influence of operating conditions and the necessary to ensure the conditions guaranteeing the maximal approach of the in-bed gas flow to gas plug flow.