Char-slag interaction during entrained-flow gasification: from experimental evidence to numerical simulations

Entrained-flow gasifiers are characterized by operating conditions that promote ash migration/deposition onto the reactor walls, whence the ash is drained as a molten phase. Previous investigations have shed light on the fate of char particles as they impinge on the wall slag layer: both char entrapment inside the melt and carbon-coverage of the slag can occur, as suggested by experimental investigation of ashes generated by full-scale plants. Because of the wide range of spatial and temporal scales involved in these phenomena, numerical simulation of the fate of the flying fine char particles is a very difficult task. Simulation is most frequently based on the RANS (Reynolds Averaged Navier Stokes Simulation) approach, in which the particle-boundary interaction needs to be modelled by means of empirical models that already postulate the leading interaction mechanism. On the other hand, application of more detailed models to full-scale configurations is computationally prohibitive. Therefore, detailed simulations based on a Eulerian LES (Large Eddy Simulation) approach for the turbulent gas phase and a Lagrangian particle tracking approach for the solid phase have been performed to explore, in a simplified flow configuration, near-wall particle segregation and the role of relevant parameters. In this work, the role of the properties of the slag layer, specifically its inelastic behaviour, has been investigated. Results of numerical simulations have been critically discussed with reference to the experimental observations.