Modelling of bubbling fluidised bed coal gasifiers

A previous numerical model of fluidised-bed coal gasifiers has been further improved to incorporate an overall energy balance. The improved model has been used to simulate the performance of bubbling fluidised-bed coal gasifi ers of different stales. Simulations show that the predicted overall carbon conversion, operating bed temperature and concentrations of individual gas species compare well with the experimental data from three pilot-scale and a full-scale fluidised bed coal gasifier, The water-gas shift reaction, ei ther driven by kinetics or in equilibrium in the dilute phase has significa nt effects on the predictions for the pilot scale air-blown gasifiers but h as little effect on a commercial-scale oxygen-blown gasifier. This is attri buted to the much faster oxidation rate of H-2 and CO near the distributor in the oxygen-blown commercialized gasifier than in the air-blown pilot-sca le gasifiers. Results also illustrate that about 26-41% of feed oxygen is c onsumed in the homogeneous combustion reactions in the gasifiers simulated, the percentage of which increases with a decrease in coal rank and with an increase in operating pressure and temperature. Carbon conversions due to char gasification are significant when compared to those due to char combus tion in the gasifiers simulated. (C) 1999 Elsevier Science Ltd. All rights reserved.