Lateral solids dispersion coefficient in large-scale fluidized beds

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. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.