Research Of Flow Characteristics In The Vapor-Liquid-Solid Multi-Pipe Circulating Fluidized Bed Evaporator

The multiphase circulating fluidized bed evaporator has a promising applicationprospect and the relevant studies about its pressure drop, distribution of particles, heattransfer enhancement as well as antiscale and descaling have attracted lots ofresearchers. In order to study further about it, a transparent multi-tubevapor-liquid-solid circulating fluidized bed evaporator was designed and built. Theinfluence of circulating flow rate, heat flux of tube bundle, the amount and kind ofinert particles was investigated with water as the working fluid by using CCD imagegathering and processing system, pressure sensor and data acquisition and processingsystem.The study about the distribution of solid particles shows that thenonhomogeneity of particle distribution decreases as the circulating flow rateincreases, but the degree goes smaller and smaller. When the circulating flow rate islow, the growth of the heat flux can help to decrease the nonhomogeneity. However,accompanied with the growth of circulating flow rate, the influence of the heat fluxwill decay to none as the percent of cyclic power brought by the vapor goes down.Increasing the amount of the particles can also help to decrease the nonhomogeneityto some extent; however, it will increase the running resistance of the equipment andcause it to wear faster, so it should choose the most suitable conditions on the basis ofconsidering the various factors. While the settling velocity of the particles increases,the nonhomogeneity increases.The investigation about the pressure drop shows that the pressure drop of thetube bundles increases while the circulating flow rate increases. But the influence ofthe heat flux can be divided into two aspects. For one thing, the increasing of thecirculating flow rate and the amount of particles increase the pressure drop; foranother, the density of working fluid goes down while the percent of the vaporincreases. Both of them bring about the fluctuant state. And the pressure drop growswith the growth of the amount of particles, which indicates that the loop resistancebecomes greater. There’s no relevance between pressure drop and the settling velocityof the particles, so the circulating flow rate as well as the amount of the particles mustbe taken into consideration when investigate the change of pressure drop. At last, pressure drop in the upper horizontal tube, separator, falling circulation tube andbottom horizontal tube were analyzed based on the research of bundle pressure drop.