Investigation of Char-Slag Interaction Regimes in Entrained-Flow Gasifiers: Linking Experiments with 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. Experimental investigation on ashes generated by full-scale plants suggested that both char entrapment inside the melt and carbon-coverage of the slag can occur. 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. Simulations based on a Eulerian large eddy simulation (LES) approach for the turbulent gas phase and a Lagrangian particle tracking (LPT) 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 particular, particles' inertia and slag layer restitution coefficient). Results of numerical simulations have been critically discussed with reference to the experimental observations. Numerical results confirm that near-wall accumulation of particles may be extensive, and promoted by large Stokes numbers and by small restitution coefficients.