Numerical simulation of coal gasification in a counterflow fluidized bed reactor

摘要

This study focuses on modeling and simulation of coal gasification in a bench-scale counterflow fluidized bed. The mathematical model is based on Eulerian-Eulerian description of multi-phase flows. The flow governing equations are solved by a finite volume method in which a time-splitting scheme is used to integrate the chemical reaction source term in a separate step using a stiff ordinary differential equation solver. The solid phase consists of Kansas bituminous coal, which contains four pseudo-species: ash, moisture, volatile matter and fixed carbon. The gas phase includes six species: CO, CO2, CH4, H2, H2O and N2. The bed is a counterflow gasifier in which coal is fed to the reactor from the top by gravity. Steam serves as the fluidizing media which enters form the bottom. Gasification occurs following devolatilization and cracking processes as incoming coal particles heated rapidly to the gasification temperature. The char gasification and water-gas shift reactions are described by a four-step global mechanism. Simulations are conducted in a three-dimensional domain and capture the transient behavior of the reactor. Results show good agreement with experimental data.