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

摘要

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 CFBs.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 CFBs 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 CFBs,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/DCFBs are required.