Particle Fluidization And Distribution In A Liquid–solid Circulating Fluidized Bed Boiler

The problem of fouling is common in boiler operations.With the advantage of online heat-transfer enhancing and self-cleaning,the circulating fluidized bed(CFB)heat transfer(CFBHT)technology is considered to be a good choice to solve the problem of boiler fouling.In this research,the CFBHT technology is combined with boiler.A cold model liquid-solid circulating fluidized bed boiler was built and its hydrodynamics characteristics and particle distribution were investigated by visualization with a charge coupled device(CCD).Polyformaldehyde(POM)particles and water were selected as working media.The effects of feedwater flow rate,amount of added particles and particle size on particle distribution were systematically discussed.Results showed each kind of particle cannot be fluidized and accumulates in the boiler under the condition of low feedwater flow rate and amount of added particles.With the increase of feedwater flow rate and amount of added particles,particles are fluidized by the water cycle in the boiler.In the riser bundle,the increase of feedwater flow rate leads to the increase of solid holdup and the decrease of nonuniform degree.The increase of amount of added particles is beneficial to the increase of solid holdup,but has no effect on the distribution of particles.The distribution of particles with small size is more uniform than particles with large size.In the vertical part of water wall tube,the particle distribution is relatively uniform,the nonuniform degree is lower when feedwater flow rate is high and particle size is small.The variation of nonuniform degree with the increase of amount of added particles has no rule.In the title part of flush tube,nonuniform degree of particle distribution is high due to the effect of gravity.High feedwater flow rate and small particle size are beneficial to uniform particle distribution.Three-dimensional phase diagrams are established to present the effects of feedwater flow rate,amount of added particles and particle size on nonuniform degree.The optimal range of the operating parameters can be seen from three-dimensional diagrams.The findings are beneficial to the industrial application of the CFBHT technology to boilers.