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

This paper focuses on developing correlations for better prediction of soli ds holdups at the dense and dilute regions of circulating fluidized bed ris ers based on experimental data from the literature and our laboratory. Anal ysis of the experimental axial profile of solids holdup and the data on eps ilon(sd) and epsilon(s)* has identified a critical solid circulation rate: saturation carrying capacity of gas, G(s)*, which distinguishes two differe nt variations of epsilon(sd) and epsilon(s)* with solid circulation rate. I n the case of G(s) < G(s)*, epsilon(sd) and epsilon(s)* increase with incre asing solid circulation rate and may vary with other system properties, whe reas epsilon(sd) and epsilon(s)* are only the functions of gas velocity and gas-solid properties and change little with the solid circulation rate, th e 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, m ore generalized empirical correlations for estimation of epsilon(sd) and ep silon(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.