Quantitative estimation of solids holdups at dense and dilute regions of circulating fluidized beds

This paper focuses on developing correlations for better prediction of solids holdups at the dense and dilute regions of circulating fluidized bed risers based on experimental data from the literature and our laboratory. Analysis of the experimental axial profile of solids holdup and the data on epsilon(sd) and epsilon(s)* has identified a critical solid circulation rate: saturation carrying capacity of gas, G(s)*, which distinguishes two different variations of epsilon(sd) and epsilon(s)* with solid circulation rate. In the case of G(s) < G(s)*, epsilon(sd) and epsilon(s)* increase with increasing solid circulation rate and may vary with other system properties, whereas epsilon(sd) and epsilon(s)* are only the functions of gas velocity and gas-solid properties and change little with the solid circulation rate, the riser diameter, the solids inventory as well as the solid feeding system in the case of G(s) greater than or equal to G(s)*. Based on these facts, more generalized empirical correlations for estimation of epsilon(sd) and epsilon(s)* are obtained. Comparisons with experimental data and the existing literature correlations confirmed the validity of the present correlations. (C) 1999 Elsevier Science S.A. All rights reserved.