Effects of pressure and type of gas on particle-particle interaction and the consequences for gas—solid fluidization behaviour

Abstract

The fluidization behaviour of cracking catalyst has been studied up to pressures of 15 bar with different fluidization gases (Ar, N 2, H 2). A number of parameters of both the homogeneous and heterogeneous fluidized bed has been examined experimentally. The experimental results reveal that the minimum fluidization velocity (U mf) is independent of the pressure. The bubble point velocity (U bp) and the maximum bed expansion (H bp) at this velocity increase with increasing pressure. This also holds for the dense phase voidage (ε d) and the dense phase gas velocity (U d) in the bubbling bed. The bubble size decreases drastically with increasing pressure. However, the above-mentioned parameters are also strongly dependent on the type of fluidization gas used. The cohesion constant of the powder was measured, using a tilting bed technique. The results reveal that the cohesion constant increases with increasing pressure. Analysis of the results of adsorption measurements of the different gases to the solid reveals for the adsorption as well as for the cohesion and for the beu expansion the same pressure dependence. It is believed that the gas adsorption influences the cohesion between the particles and hence the elasticity modulus introduced by Rietema and Mutsers [1,2]. The increasing elasticity modulus with increasing pressure also explains the increasing bed expansion with pressure.