Cluster particle number and granular temperature for cork particles at the wall in the riser of a CFB

Abstract

Operating conditions within a circulating fluidized bed (CFB) many times results in the grouping of circulating particles into clusters. Because of their different relative motion with respect to the balance of the flow, these clusters are believed to demonstrate different transport properties when compared to the balance of the particles. To investigate these differences, it is first necessary to have an objective means of identifying those particles that are within a cluster and those that are not. The concept of granular temperature is used to make this distinction. Using laser Doppler velocimetry (LDV) data for 800-μm cork particles, it has been found that groupings of six or more particles demonstrate a different distribution of granular temperatures than groupings with fewer particles. Based on this fact, it is concluded that groups of six particles as measured in the axial flow direction are the fewest number which can be still considered to be in a cluster for this bed material. Additionally, particles considered to be in the dispersed phase have granular temperatures which are low at low solids concentrations, again low at very high solids concentrations and pass through a maximum at intermediate values of solids flow and gas flow.