Particle-wall interaction phenomena occurring in entrained-flow slagging gasifiers by granular flow simulations and experiments in a cold flow model reactor

The slagging conditions occurring during combustion/gasification of solid fuels play a key role in the design of modern entrained-flow reactors. In these systems, solid particles migrate toward the reactor walls, due to swirled/tangential flow and to turbophoresis. Different char-slag micromechanical interaction patterns may establish, depending on the stickiness of both the wall layer and the impinging char particle. This study aims to improve the mechanistic understanding of particle-wall interactions, by 1) granular flow simulation and 2) experimental physical modelling. In the line 1), the results of a simplified configuration highlight the role of the four different interaction regimes that can be envisaged when considering particles and confining walls as either sticky or non sticky. 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. In the line 2), a montan wax is used to mimic, at atmospheric conditions, the near-wall fate of char/ash particles in entrained-flow gasifiers. The experiments are carried out in a 0.10 m-ID lab-scale cold entrained-flow reactor (length 0.1-0.6 m), optically accessible, equipped with a nozzle whence molten wax atomized into a mainstream of air. The assessment of the flow and segregation patterns is based on direct observation by means of a progressive scan CCD camera, while the partitioning of the wax droplets/particles into the different phases is characterized by their selective collection at the reactor exhaust.