Prediction of bed fluctuation ratio for gas solid fluidization in cylindrical and non-cylindrical beds

Abstract

Gas flow in a gas-solid fluidized bed is characterized by the predominance of bubbles. This bubbly flow exhibits considerable bed fluctuation at fluid mass velocity higher than the minimum fluidization velocity leading to instability in operation, which affects the fluidization quality adversely. In the present paper, equations have been developed for the prediction of bed fluctuation ratio for gas-solid fluidization in cylindrical and non-cylindrical (viz. semi-cylindrical, hexagonal and square) beds. A fairly good agreement has been obtained between calculated and experimental values. Based on the experiments it is concluded that, under similar operating conditions bed fluctuation ratio is maximum in case of square bed and it is least in case of semi-cylindrical bed. The fluctuation ratio becomes maximum at a particular velocity ratio Gf /Gmf, for a particular bed and then it either decreases (due to slug formation) or remains constant at higher velocity ratio thereafter. It has also been observed that transformation from bubbling to slugging mode was latest in case of semi-cylindrical bed and earliest in case of a square one, thus providing a larger span of effective gas – solid fluidization in the bubbling regime in a semi-cylindrical bed as compared to other non-cylindrical and cylindrical beds