Lateral solids dispersion coefficient in large-scale fluidized beds

摘要

The design of fuel feed ports in a large-scale fluidized bed combustor depends on the fuel characteristics and lateral solids mixing. However, the reported values of the effective lateral solids dispersion coefficient (D_(sr)) are scattered in the broad range of 0.0001-0.1 m~2/s. With the aim of predicting D_(sr) in wider fluidized beds which is difficult to measure directly or deduce from experimental results in lab-scale facilities, a computational method is proposed. It combines the Eulerian-Granular simulation and fictitious particle tracing technique. The value of D_(sr) is calculated based on the movement of the tracers. The effect on D_(sr) of bed width (W) ranging from 0.4 m up to 12.8 m at different levels of superficial gas velocity (U_0) is investigated. It is found that increasing W whilst maintaining U_0, D_(sr) initially increases markedly, then its increase rate declines, and finally it stays around a constant value. The computed values of D_(sr) are examined quantitatively and compared with a thorough list of the measured D_(sr) in the literature since 1980s. Agreed with the measurements performed in the pilot-scale fluidized beds, the value of D_(sr) in wider facilities at higher fluidizing velocities is predicted to be around the order of magnitude of 0.1 m~2/s, much higher than that in lab-scale beds. Finally, the effect of D_(sr) on the distribution of fuel particles over the cross section in fluidized beds with the specified layout of feed ports is discussed.