Cold Experimental Study On Diffusion And Mixing Of Feed Materials In The Dense Zone Of Circulating Fluidized Beds

It is a big issue that feed materials can be diffused timely throughout the cross-sectional bed and mixed uniformly in the dense zone, which is directly related to the safety, economy and high efficiency operation of large scale circulating fluidized bed (CFB) boilers. The boilers’operation parameters and structure figures, and the physical features of feed materials directly affect the diffusion and mixing of feed materials in the dense zone of CFB boilers.Cold experiments were conducted in cold-test models of large scale CFB boilers with three different types of multi cyclones in parallel. The methods of hot particle tracer and sampling are used to investigate the effects of different factors, such as fluidizing velocity and static bed height, on the diffusion and mixing characteristics of feed materials in the dense zone of the cold-test models.Aimed at600MW supercritical CFB boilers, effects of static bed heights, fluidizing velocity and size of bed materials on diffusion characteristics were investigated on both H-shape and M-shape cold-test models. Experiment results demonstrate that diffusion intensity increases with the increase in fluidizing velocity and decreases with the increase in static bed height, returned materials are bad for the tracer’s diffusion toward the returning inlets, for H-shape cold-test model the diffusion along the entry direction of materials is intenser than that along the perpendicular direction within the cross section, and for M-shape cold-test model the diffusion intensity away from returning inlets is stronger than that toward returning inlet.On a cold-test model of CFB with annular furnace, the effects of fluidizing velocity, secondary air ratio, physical parameters of feed materials and structure parameters were investigated aimed at1000MW ultra-supercritical CFB boilers. The experimental results show that the increase in the fluidizing velocity can promote diffusion intensity, air supplying mode and material feeding location has little impact on diffusion and mixing characteristics, mixing characteristics can be improved by reducing secondary air ratio.