Multiphase flow patterns in entrained-flow slagging gasifiers: Physical modelling of particle-wall impact at near-ambient conditions

Particle-wall interaction phenomena relevant to multiphase flow in entrained-flow slagging coal gasifiers have been investigated. The micromechanical patterns of particle impingement on the reactor walls have been characterized in a model system by high speed imaging and tracking of wax particles impacted onto a flat surface at near-ambient conditions. The solid/plastic versus fluid state of the wax particles was controlled by proper selection of the particle, ambient and target temperatures. Particle-wall collision was described in terms of normal and lateral restitution coefficients and capture efficiency. The influence of the particle stickiness, impact velocity and angle, and surface properties and structure of the target on the rebound patterns was studied. Results indicate that the elastic-plastic adhesive model provides an adequate representation of the non sticky particle-wall collisions. Moreover, the presence of a powder layer on the target favours energy dissipation and accumulation of particles close to the surface. This pattern promotes the establishment of a dense-dispersed phase in the near-wall zone of entrained-flow slagging gasifiers. Increasing the temperature, particles shift from the solid/plastic to the fluid state and the coefficient of restitution drops to vanishingly small values, confirming that deposition is the prevailing phenomenon during the collision of sticky particles on a wall.