A general mathematical model for a moving bed gasifier

Abstract Cocurrent and countercurrent units are common configuration of biomass and coal gasifiers. Moving solid beds contact a flowing gas phase, usually air, steam or their mixtures. Batch and fluidized bed reactors, or drop tube gasifiers are also alternative units. The complexity of these systems relies in several aspects: the chemistry of the released species in the first devolatilization and gasification step, the large number of species and reactions in the gas phase, the definition of a well balanced description of the gasifier and finally the necessity to adopt a stable ODE solver to numerically handle the large system of balance equations. The different process units are schematized in terms of a series of elementary cells where the solid particles release volatile components with effective material and energy exchanges with the flowing gas phase. Gasification reactions in the coal or biomass particles are properly accounted including mass and thermal diffusion limitations. Reactions in the gas phase are finally accounted by using a detailed kinetic scheme of pyrolysis and combustion reactions. Preliminary comparisons with experimental measurements support the proposed approach.