Study On Flow Characteristics Of Liquid–solid Circulating Fluidized Bed Heat Exchanger

Circulating fluidized bed heat exchanger can effectively solve the scaling problem of heat exchange equipment and play a role in enhancing heat transfer.In order to investigate the flow characteristics of liquid–solid circulating fluidized bed heat exchangers,two sets of circulating fluidized bed heat exchangers were designed and built.The effects of the amount of added particles,circulation velocity and particle types on pressure drop in down-flow bed,vertical tube bundle and up-flow bed were systematically investigated by pressure sensors.At the same time,the particle distribution in vertical tube bundle was visualized by using the image measurement and acquisition system of a charge-coupled device(CCD).Firstly,the pressure drop of liquid–solid two-phase flow in down-flow bed was investigated.The results show that the pressure drop of liquid–solid two-phase flow is always greater than that of single-liquid-phase flow in the down-flow bed.The pressure drop ratio fluctuates with the increase of the amount of added particles,circulation velocity and settling velocity of the particles.The difference in pressure drop ratio generally decreases with the increase in circulation velocity,but decreases or fluctuates with the increase in the amount of added particles,depending on circulation velocity.Then the flow characteristics of liquid–solid two-phase flow in the vertical tube bundle and up-flow bed were investigated.The results show that the non-uniform degree of the particle distribution decreases with the increase in circulation flow rate and the amount of added particles,increases with the increase in settling velocity of particles,and generally increases with the increase in particle diameter.Circulation flow rate has the greatest influence on particle distribution.The pressure drop of liquid–solid two-phase flow is not always greater than that of single-liquid-phase flow in vertical tube bundle and up-flow bed.Circulation flow rate has the greatest influence on pressure drop.The pressure drop in vertical tube bundle accounts for the largest proportion of the whole up-flow bed pressure drop.When the amount of added particles exceeds 2%,it is appropriate to choose Si C for the engineering application.In addition,the phase diagrams of pressure drop and pressure drop ratio in the down-flow bed,vertical tube bundle and up-flow bed are established,and the phase diagrams of non-uniformity of particle distribution in vertical tube bundle are also established,which are helpful to the selection of operation parameters in industrial application of circulating fluidized bed.