Modeling gasification and percolation of ash-bearing porous carbon particles

A Monte Carlo simulation model of the gasification of a porous carbon particle is presented. The model considered the occurrence of percolation phenomena and of the associated loss of particle connectivity; as a gasifying species diffuses and reacts within the pore network extending throughout the particle. The influence of ash on percolative phenomena was considered by assuming that they are initially uniformly dispersed in the carbon matrix. During gasification, ash undergoes a displacement/coalescence process driven by surface tension of die ash material ill a fluid or ill a glassy state. A constitutive expression for the ash mobility parameter was derived based on the mechanical energy balance on coalescing droplets accounting for the work done by surface tension and by viscous forces. The simulation procedure was able to reproduce the process by which a coherent ash layer is built up as gasification proceeds. The effect of such a layer on die apparent gasification reactivity was evaluated by assuming that the gasifying species can diffuse through the ash laver with a specified value of the effective diffusivity. The effect of model parameters, namely ash mobility and ash effective diffusivity, oil the apparent gasification reactivity and on the ultimate number and size of percolated fragments was assessed and is discussed here.