Particle clustering (mesoscale structure) of high-flux gas-solid circulating fluidized bed

Particle clustering is an important dynamic phenomenon in circulating-fluidized-bed (CFBs) systems, and has been suggested as a key contributing factor to the non-uniform hydrodynamics of CFBs. Studies show that particle clusters can be affected by solids flux, in terms of frequency, duration, and solids holdup. To understand the characteristics of particle clusters under high-solids-flux conditions, experimental and modeling studies in high-solids-flux gas-solids CFBs were reviewed and summarized. Optical and electrical measurements and imaging methods were used to monitor the particle-clustering phenomenon in CFB5. Particles were found to cluster in high-flux CFBs, and were characterized by a denser cluster-solids holdup and a shorter time fraction, which was different from the behavior in low-flux CFBs. Particle properties affected particle clustering in high-flux CFB5 significantly. In modeling work, Eulerian-Eulerian and Eulerian-Lagrangian methods were used to study the particle-cluster characteristics. Good results can be obtained by using the Eulerian-Eulerian method to simulate the CFB system, especially the high-flux CFB5, and by considering the effects of particle clusters. The Eulerian-Lagrangian method is used to obtain detailed cluster characteristics. Because of limits in computing power, no obvious results exist to model particle clusters under high-solids-flux conditions. Because high-solids-flux conditions are used extensively in industrial applications, further experimental and numerical investigations on the clustering behavior in HF/DCFB5 are required. (C) 2019 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.