Particle-wall interactions in entrained-flow slagging gasifiers

This paper aimed at the development of a phenomenological model of the fate of coal/ash particles in entrained-flow slagging coal gasifiers, which considers the establishment of a particle segregated phase in the near-wall region of the gasifier. In particular, near-wall phenomena were investigated and mechanistic understanding of particle–wall interaction patterns in entrained-flow gasifiers was pursued using the tool of physical modeling. Montan wax was used to mimic, at atmospheric conditions, particle-wall interactions relevant in entrained-flow gasifiers. As a matter of fact, this wax had rheological/mechanical properties resembling under molten state, those of a typical coal slag and, under solid state, those of char particles. Experiments have been carried out in a lab-scale cold entrained-flow reactor, equipped with a nozzle whence molten wax atomized into a mainstream of air to simulate the near-wall fate of char/ash particles in a real hot environment. The four particle-wall interaction regimes were investigated. The partitioning of the wax droplets/particles into the different phases was characterized by their selective collection at the reactor exhaust. Results showed that the particlewall interaction mechanisms and segregation patterns are deeply affected by the stickiness of both the wall layer and the impinging particle. In particular, the micromechanical interaction of a particle with a sticky wall enhances particle transport to the wall and the tendency to reach a segregationcoverage regime with the formation of a dense-dispersed phase in the near-wall region of the reactor. Furthermore, increasing the mainstream air flow rate induces particle segregation and accumulation phenomena.