Effect of operating pressure on the hydrodynamics of agglomerating gassolid fluidised bed was investigated using a combination of discrete element method (DEM) for describing the movement of particles and computational fluid dynamic (CFD) for describing the flow of the gas phase. The inter-particle cohesive force was calculated based on a time dependent model developed for solid bridging by the viscous flow. Motion of agglomerates was described by the multi-sphere method. Fluidisation behaviour of an agglomerating bed was successfully simulated in terms of increasing the size of agglomerates. The results showed that increasing the operating pressure postpones de-fluidisation of the bed. Since the DEM approach is a particle level simulation and study about particleparticle interactions is possible, a micro-scale investigation in terms of cohesive force and repulsive force during agglomeration at elevated pressures was done. The micro-scale results showed that although the number of contacts between particles was decreased by increasing operating pressure, stronger solid bridge formed between colliding particles at higher pressures. (c) 2012 Canadian Society for Chemical Engineering