Experimental and Numerical Investigation on Agglomerates in Fully-Developed Riser Flows

The behavior of cohesive particles is studied in the riser section of a circulating fluidized bed, where gas-solid flows are fully-developed. The effects of cohesion are quantified by the distribution of agglomerates experimentally measured by shadowgraphy. In additional to relative humidity, which induces cohesion via small capillary bridges that condense between particles, agglomerate properties are affected by superficial gas velocity and solid concentration. To predict agglomerates in risers, DEM-CFD simulations were conducted with a smaller domain than the experiments and used cyclic boundary conditions for both gas and solid phases, in an attempt to mimic the fully-developed flow in experiments. By incorporating a capillary force model that considers particle surface roughness and applying the same agglomeration detection method in simulations, direct comparison between numerical and experimental results are performed. Based on the validated simulation conditions, the response of agglomerate properties to relative humidity, superficial gas velocity and solid concentration was systematically studied, which helps aid the understanding of particle entrainment in riser flows.