Physical and mathematical modelling of multiphase flow in the near-wall region of entrained flow reactors

During slagging combustion/gasification of solid fuels, particles move toward the film of slag covering the reactor walls, establishing a very complex multiphase particle-wall interaction. This study aims to improve the understanding of the different char-slag micromechanical interaction patterns which occur in the near-wall region, on the basis of the stickiness of both the wall layer and the impinging char particle. A 0.10 m-ID lab-scale cold entrained-flow reactor (length 0.1-0.6 m), optically accessible, and equipped with a nozzle whence molten wax is atomized into a mainstream of air, is used to mimic, at atmospheric conditions, the near-wall fate of char/ash particles in entrained-flow gasifiers. The flow and segregation patterns are observed by means of a high speed CMOS camera. The partitioning of the wax droplets/particles into solid and liquid phases is characterized by their selective collection at the reactor exhaust. The same configuration is simulated, adopting simplifying assumptions, with a granular flow model. Particle-particle collisions are modelled with an Hertzian approach, including torque and cohesion effects. Results illustrate the different structures of near-wall particle layer that establish in the four interaction regimes between particles and confining walls under sticky (molten) or non sticky (solid) conditions.