Cluster Properties Of Geldart B Particles In A High-flux Circulating-fluidized-bed Riser

Coal is the most important primary energy in China. It accounts for about 70% of total energy consumption, and the situation will not change significantly for a long period time in the future. Direct combustion is the mainly utility way of coal in China, exhibiting low utilization and serious pollution. With increasingly serious energy pressure and environmental protection, clean and efficient coal conversion technologies are needed. High-flux circulating-fluidized-bed gasification technology can overcome the deficiency of the current technology. This gasification process is suitable for the low rank coal and inferior coal of huge reserves, and has the advantages of high efficiency, low cost and simple maintenance. While most researches focus on the macroscopic flow characteristics in the high-flux circulating-fluidized-bed riser, the microscopic/mesoscopic particles behavior needs further exploration.Fiber probe was used to measure the flow characteristics of Geldart B particles (resin and quartz sand) in a circulating-fluidized-bed riser with 60mm ID and 5.5m height. Through comparing various identification method of particle clusters, wavelet decomposition method is determined to identify particle clusters in this thesis and the approximation signals of All is employed as the threshold for recognizing particle clusters. Then, the time and space distribution characteristics of clusters behavior are obtained and the influence of operating conditions are explored.Research results indicate that for Geldart B particles used in this thesis, the concentration and duration of clusters show high in center while low in near-wall zone. In the axial direction of the riser, the cluster concentration and duration decrease with the increase of riser height. These parameters increase with increasing solid circulation rate and/or reducing superficial gas velocity.Cluster frequency also shows non-uniform distribution in the axial and radial directions of the riser. With increasing the solid circulation rate, the clusters frequency of resin particles rises; but for quartz sand, its cluster frequency increases in the upper riser. In the bottom of the riser, clusters frequency first increases and then decreases with increasing the solid circulation rate. Besides, cluster frequency increases with increasing superficial gas velocity.It is found that in the riser center, the cluster concentration of resin particles is lower than that of the quartz sand particles. At the edge, the cluster concentration of the resin particles is higher. The cluster frequency of the resin is higher than that of quartz sand. The cluster duration of resin particle is much lower than that of quartz sand particles, especially at the wall. The differences in particle properties and the flow characteristics in the riser cause significantly different particle agglomeration characteristics.