Study On Flow Characteristics In Horizontal Multi-tube Liquid-solid Circulating Fluidized Bed

The horizontal circulating fluidized bed heat exchanger combines the heat exchanger with the fluidized bed technology,and has good effects on heat transfer enhancement,scale prevention and descaling.This paper designed and constructed a set of horizontal single-pass liquid-solid circulating fluidized bed with a distributor and a set of horizontal two-pass liquid-solid circulating fluidized bed device.The hydrodynamic performance of the two horizontal multi-tube liquid-solid circulating fluidized bed exchangers was investigated by using CCD image measurement and acquisition system and pressure difference sensing device.In the first part,the effects of distributor inclination angle,circulation flow rate,the amount of added particles and particle diameter on particle distribution and pressure drop of the liquid-solid two-phase flow were investigated.The results show that:(1)The distributor can remarkably improve particle distribution in the front tube chamber and the tube bundle,and the effect when inclined upward is better than downward.With the increase in the absolute value of the distributor inclination angle,the particle distribution uniformity and the improvement of the particle distribution both increase first and then decrease.The optimal distributor inclination angle is 27°.The pressure drop and the pressure drop ratio first decrease and then increase with the increase in distributor inclination angle and is larger with distributor inclined upward.(2)With the optimal distributor inclination angle,the particle distribution nonuniformity in the bundle and the improvement of particle distribution both fluctuate with the increase in circulation flow rate and the amount of added particles.The pressure drop increases with the increase in circulation flow rate and fluctuates with the increase in the amount of added particles.The pressure drop ratio first decreases and then increases with the increase in circulation flow rate at low amount of added particles and is always positive.With the increase in circulation flow rate at higher amount of added particles,the pressure drop ratio increases and is negative at low circulation flow rate and positive at high circulation flow rate.(3)POM 1 with smaller diameter has a relatively small distribution non-uniformity and a wider application range under higher circulation flow rate,and the improvement effect of distributor is relatively good.POM 2 and POM 3 particles are not suitable for low circulation flow rate.In the second part,the effects of circulation flow rate and amount of added particles on the particle distribution and pressure drop in the horizontal two-pass liquid-solid circulating fluidized bed were investigated.The results show that:(1)The particle distribution in the upper tube pass is relatively uniform,while that in the lower tube pass is nonuniform.The solid holdup in the upper and lower tube passes both increase along the gravitational direction.A “dead zone” with low solid holdup exists in the lower tube pass.(2)With the increase in circulation flow rate,the non-uniformity of particle distribution in the upper tube pass fluctuates,but that in the lower tube pass initially rapidly increases and then gradually decreases.The non-uniformity of particle distribution in the upper and lower tube passes both fluctuate with the increase in the amount of added particles.(3)The pressure drop ratio fluctuates with the increase in circulation flow rate and the amount of added particles,and the maximum pressure drop ratio is 18.3% within the experimental range.