Factorial Tests on Process Operating Conditions and Bed Fines on the Circulating Fluid Bed Performance

Abstract

A cold-flow circulating fluid bed (CFB) was operated using coke breeze with a packed-bed standpipe over a range of riser and standpipe air flows. The bed materials were selected to simulate solids flow in a CFB gasifier (carbonizer) but are generally relevant to most CFB processes. CFB tests were conducted primarily in the transport mode with sufficient gas velocity to achieve a uniform axial riser pressure profiles over most of the riser height. The independent variables tested included the riser gas velocity, aeration at the base of the standpipe, and concentration of fines (average particle size). The solids inventory and riser outlet pressure were maintained constant. Factorial tests were conducted in randomized order and in duplicate to provide and an unbiased estimate of the error. Fines were tested as a blocked variable. The gas velocity, standpipe aeration, and relative amount of fine particles were all found to be significant factors affecting both the riser solids holdup and solids flux. The riser pressure drop and mass circulation increased at the higher level of fines contrary to some earlier reports in the literature. The riser pressure drop was fitted using the general linear model (GLM), which explained more than 98% of themore » variation within the data, while a GLM for the mass circulation rate explained over 90%. The uncertainty of process operating variables was characterized independently through a series of duplicated flow proving experiments.« less