This paper presents a 2D soft sphere discrete element method (DEM) simulation study of fluidization behaviour of Geldart Group A powders and Geldart Group B powders in the presence of externally imposed cohesive interparticle force. In the presence of externally imposed cohesive interparticle force, beds of Group B powders exhibit some of the characteristics of Group A powders (homogeneous bed expansion and pressure drop hysteresis), but show other characteristics (e.g. bed collapse) which are quite different. The homogeneous bed expansion for Group B particles with imposed cohesive interparticle force is found to follow the Richardson-Zaki relationship, with the exponent n being independent of the magnitude of interparticle force and with the degree of expansion increasing with the magnitude of interparticle force. Group A particles show homogeneous bed expansion even in the absence of cohesive interparticle force. (c) 2006 Elsevier B.V. All rights reserved.