GRANULAR FLOW SIMULATIONS OF LIMITING REGIMES OF PARTICLES–WALL INTERACTION RELEVANT TO SLAGGING COAL GASIFIERS

In pilot entrained-flow slagging coal gasifiers, high conversion efficiency and low pollutant emission levels have been observed, but the mechanism leading to this behaviour is not fully understood. Recent literature proposes several different mechanisms as playing an important role, ranging from the sticking properties of both particles and slag-covered walls to the thermal and chemical history along the trajectory of the particles in the entire gasifier. Nonetheless, very few attention has been devoted to the role of particle–particle interactions, even if it has been shown that this mechanism can lead to new regimes likely to occur in slagging gasifiers and to promote the rise in the coal conversion efficiency. This study presents the results of a simplified configuration that allows to highlight the role of the four different interactions that can be envisaged when considering particles and confining walls as either sticky or non sticky. Particles are subjected to a body force that mimics the action of the drag exerted by a swirling flow field in a cylindrical vessel. Particle–particle collisions are modelled with an Hertzian approach that includes torque and cohesion effects. Results clearly indicate the different structure of the layer of particles establishing on the wall surface in the different interaction regimes. They confirm the importance to adequately take into account particle–particle interactions for a correct prevision of the fate of coal particles in slagging gasifiers.