Study On Fluidization And Drying Of The Group C Particles In A CFB System

As a new generation of reactor, circulating fluidized bed is becoming a new trend of the research of gas-solid two-phase flow drying technology for its simple structure, large capacity, high efficiency of gas-solid contact and available fluidization of cohesive particles.In order to apply the CFB reactor to the drying of group C particles, cold-state and drying experiment were conducted respectively in a CFB (0.104m ID×2.35m high) dryer. Corn starches (dp=8μm,ρp=800kg/m3) as group C particles were used. The results demonstrate that CFB system is feasible in fluidizing and drying group C particles; the CFB with higher riser has a larger operation elasticity and a more stable material circulation.The gas-solid flow characteristics under different superficial gas velocities and inventories were investigated by cold-state test. The results indicate: normal pressure curve of the whole loop takes the shape of 8 ; the average cross section particle concentration decreases with the increasing axial height of the riser; system pressure, average cross section particle concentration and circulating rate are all in close relation with the gas velocity and inventory, the empirical formula of the solids circulation rate in this lab as follows:Drying experiments were conducted in a batch system as well as in a continuous system. The effects of varying operation parameters including initial moisture content,gas velocity and inlet air temperature on the drying characteristics and separation efficiency were determined in the batch system. The results indicate: with the increasing gas velocity and inlet air temperature, the average drying rate,separation rate increases, the separation moisture content decreases, the critical moisture content decreases first and then increases; the discharge time lags first and then advances with the increasing gas velocity and advances gradually with the increasing inlet air temperature; the effect of gas velocity on the drying characteristics and separation efficiency is the most pronounced.The effects of varying value of the parameters including the feed rate, inlet air temperature and gas velocity on the average residence time of corn starches and its final moisture content were determined in the continuous system. And the results were compared with the fast fluidized bed dryer's. The results indicate: the average residence time of corn starches and the final moisture content decreases with the increasing inlet air temperature and gas velocity; the average residence time of corn starches is slightly affected by the feed rate, the final moisture content increases with the increasing feed rate; the drying effect of the corn starches in the CFB system is better than in the fast fluidized bed at the same conditions.On the basis of Luikov drying theory, a mathematical model on the instantaneous moisture content of corn starches associates with time in the process of CFB drying has been established, as follows:It was proved that the theoretical values compared well with the experimental measurements.