Experimental and numerical study of coarse particle conveying in the small absorber sphere system: overview and some recent CFD-DEM simulations

Pneumatic conveying of absorber spheres in the pebble-bed high-temperature gas-cooled reactor is a special application of pneumatic conveying technique in the nuclear engineering. It may be regarded as an intermittent circulation of absorber spheres between the side reflector boring and the storage bin in the reactor. The whole process consists of several sub-processes, e.g., the granular discharge from the sphere storage bin into the boring, granular discharge from the side reflector boring into the feeder, particle entrainment in the feeder, sphere conveying in the transport pipe, and gas-solid separation in the storage bin. We give a brief summary of the experimental and discrete element simulation work done recently at the Institute of Nuclear and New Energy Technology of Tsinghua University, mainly from the viewpoint of gas-solid flow and granular flow. CFD-DEM coupling simulation is recently conducted to investigate the coarse particle conveying in the small absorber sphere system. We present some CFD-DEM simulation results of coarse particle conveying in ambient air and high-pressure helium gas. Based on the needs of engineering practice and scientific research, some research requirements are suggested. Further work is still needed, to make a comprehensive understanding of the conveying process, and to optimize the design and operation of the conveying system.