Flow maldistribution was investigated in an 8.5 m high circulating fluidized bed with a rectangular cross section of 1m ×0.3m employed a 14-bubble cap distributor and a 33-bubble cap distributor. Experimental results indicate that the bubble caps in the centre region have large flow rate and the bubble caps at the wall region have small flow rate. The extent of the flow maldistribution is quantitatively characterized by the ratio of the maximum flow rate through a bubble cap to the average flow rate through all bubble caps, maldistribution number, Vmax/Vav. A correlation is proposed forpredicting flow rate distribution, maldistribution number, in the bubble cap distributor by the ratio of distributor pressure drop to riser pressure drop, pressure drop ratio, △Pd/△Pr.
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