A mathematical model for predicting the flow behavior through a CFB reactor U type loop - seal

Abstract

A mathematical model for predicting the flow behavior through a conventional U type loop-seal was developed by considering the loop-seal as a lumped system. The change rate of the gross forward particle flow rate (GG) with respect to the fluidization number at its bottom (Fn), GG', is assumed to be a function of the products of the gross forward particle flow rate coefficient (k) and the differential head across it. In addition, the flow resistance is considered as the virtual backward particle flow rate (Gr). Its change rate (Gr') is assumed to be a function of the products of the virtual backward flow coefficient (f) and the solid circulation rate provided by the loop-seal (Gs). The effects of the side aeration at the recycle side walls and heat exchanger in the chamber on the performance of the loop-seal was investigated. It was found that the relation between Gs and Fn is an asymptotic or a saturated function. From the regression analysis of the experimental data from a cold model circulating fluidized bed system according to the function, the function constants are obtained with the coefficient of determination of not less than 0.97. GG' is constant, while Gr' increases with Fn. The loop-seal with heat exchanger (LSHE) has a lower Gs. The LSHE with side aeration has a change rate of the forward particle flow rate with respect to Fn, and the virtual backward flow coefficient higher than the conventional loop-seal for the side aeration flow rate less than a certain value. After that, the opposite trend was found. The loop-seal having a higher fwill have a lower Fnor side aeration flow rate corresponding to saturated Gs. The developed model may be applied to any types and sizes of loop-seal and suggests that in order to have a high Gs, loop-seals should have their configuration provide a high gross forward particle flow rate coefficient (k) and a low virtual backward flow coefficient (f).