Prediction of Falling Solids Film Thickness near the Wallin Circulating Fluidized Bed Risers

Abstract

The solid particles distribution in circulating fluidized beds (CFB) has been extensively studied because of its importance in the design of CFB boilers and reactors. The previous studies report that in the circulating fluidized beds, the solids near the wall move down ward as a film with axial variable thickness. Therefore, it is very important to predict solids film thickness near the wall to estimate the heat transfer between a solid suspension in the bed and wall surface. In the present paper, an expression for the local solids film thickness has been suggested from the data of local solids flux measurements by using U-tube probe. The data measured in two laboratory scale CFB units which consist of 0.0508m diameter & 3 m height and 0.1016m diameter & 6m height. Sand (182 µm and 2560 kg//m3) and FCC particles (99 µm and 1600 kg/ m3) are used as bed material. The operating gas velocity and solid circulation rates are in the range of 1-6m/s and 5-125kg/m2-s respectively for the material considered. The R2 values for the correlation developed are 0.577 for literature data, 0.3904 for small column (0.0508m ID & 4m Height) and 0.886 for large column (0.1016m ID & 6m height).