Multiphase models of slag layer built-up in solid fuel gasification and combustion

Abstract

A steady-state model has been developed to describe the flow and heat transfer characteristics of slag. The model incorporates two submodels for particle capture and wall burning; takes into consideration the temperature and composition dependent properties of slag, the contribution of momentum of captured particles and the possibility of slag resolidification. The model predicts the local thickness of molten and solid slag layers as well as the average slag velocity. Moreover, it is capable of predicting heat losses and the inner as well as outer wall temperatures, taking into account the influence of molten and resolidified slag layers coating the combustor or reactor wall. An equally important issue is the interaction of the particles colliding with the slag layer. High inertia particles tend to rebound whereas slower particles are trapped in the slag layer. Since only trapped particles are relevant to the slag layer built-up, a particle capture criterion for colliding particles is introduced. Particles with combustibles may be captured by the slag layer while they continue to bum at a different rate. To take this into account, a wall burning submodel is proposed to predict a correction factor for both solid and porous char combustion models.