Thermal gasification has been proposed as one technical option for the conversion of coal to gaseous fuels and/or chemicals to supplement supplies presently derived from petroleum and natural gas. In the present study, a bench-scale fluidized bed reactor was used for the gasification of coal with steam as the fluidizing medium. A mixture of sand and limestone used as the bed material made it possible to gasify a caking coal without the problem of agglomeration. The gas composition and yield of the hydrogen-rich product gas were studied as a function of temperature.
To study the heterogeneous reactions taking place in the reactor and also the transient behavior of the system, a mathematical model was developed. The model assumed a reaction mechanism that accounted for the devolatilization of coal, cracking of volatiles, char gasification, and the water-gas shift reaction. Both the dynamic behavior and steady state performance of the gasifier were simulated based on the model. The steady state results of the simulation were compared with the experimental data. This comparison enabled us to ascertain that the proposed reaction mechanism and dynamic model predicted the correct trends.