Hydrodynamics and operation of a multistage fluidized bed with particles of super-high density

•Higher fluidization quality in the multistage fluidized bed than that in the conical fluidized bed.•Feasibility of super-high-density particles in a multistage fluidized bed proved.•Hydrodynamics and operation characteristics of heavy particles in a multistage fluidized bed.•Stable operating range of wolfram carbide particles in the multistage fluidized bed determined. High-density particles are commonly used in fluidized bed reactors in uranium recycling processes of nuclear industry, where high fluidization quality (i.e. low gas-solids contacting efficiency) is difficult to achieve, resulting in various problems such as reduced conversion, low product selectivity, stronger equipment vibration and bad operating stability, etc. The objective of this study was to validate the feasibility and advantages of a multistage fluidized bed in processing a super-high-density powder. Wolfram carbide powder of true density of 15630 kg/m3 was used in a cold-model counter-current three-stage fluidized bed with downcomers. Stability of operation, operating range and hydrodynamics were systematically studied. The fluidization quality and operating stability were also compared with a single-stage conical fluidized bed of similar diameter and same solids inventories. The experimental results demonstrated that this high-density wolfram carbide powder could be fluidized and circulated continuously at this multistage fluidized bed, but lower fluidization quality was observed and the stable operating range is narrow. Narrower stable operating range was observed at higher solids circulation rates. At corresponding operating conditions, the fluidization quality of multistage fluidized bed is significantly better than that of the conical fluidized bed with a similar solids inventory.