A CFD two-dimensional model has been developed for simulating the gasification process within an air-blown updraft coal gasifier. Fixed-bed gasification processes are characterized by a complex behaviour since they involve different space- and time-dependent sub-processes where coal preheating and drying, devolatilization and char reactions take place. Simplified models, such as non-dimensional ones, useful for preliminary gross mass and energy balance, are unable to correctly simulate in detail the overall gasification phenomena and more sophisticated CFD models are required for their understanding. The complexity of the physical processes in the updraft gasifier is compounded by the multiphase nature of the flow and by the interphase processes. Considering the high volume fraction of the solid phase, close to the packing condition, the Euler-Euler approach is required to model the interpenetrating phases. The solid phase is considered as a continuum according to the kinetic theory of granular flows. The aim of this work is to characterize the spatial and time-dependent behaviour of updraft gasifiers in terms of gas velocity, temperature and species concentration. In particular, the dynamic behaviour of the process is fundamental to understanding the time required for complete coal conversion.
Two-dimensional CFD model of air-blown coal-fired updraft gasifier
CAU, GIORGIO
2009-01-01
Abstract
A CFD two-dimensional model has been developed for simulating the gasification process within an air-blown updraft coal gasifier. Fixed-bed gasification processes are characterized by a complex behaviour since they involve different space- and time-dependent sub-processes where coal preheating and drying, devolatilization and char reactions take place. Simplified models, such as non-dimensional ones, useful for preliminary gross mass and energy balance, are unable to correctly simulate in detail the overall gasification phenomena and more sophisticated CFD models are required for their understanding. The complexity of the physical processes in the updraft gasifier is compounded by the multiphase nature of the flow and by the interphase processes. Considering the high volume fraction of the solid phase, close to the packing condition, the Euler-Euler approach is required to model the interpenetrating phases. The solid phase is considered as a continuum according to the kinetic theory of granular flows. The aim of this work is to characterize the spatial and time-dependent behaviour of updraft gasifiers in terms of gas velocity, temperature and species concentration. In particular, the dynamic behaviour of the process is fundamental to understanding the time required for complete coal conversion.
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