A predictive mathematical model is proposed based on the bed hydrodynamics, reaction kinetics and the empirical correlation of pyrolysis yields to predict gasification characteristics in an internally circulating fluidized bed gasifier with a draught tube. With the justifiable assumptions, steady state mathematical equations are derived and solved numerically. The simulated results of product gas composition, gas yield, carbon conversion, cold gas efficiency and calorific value of the product gas in each reaction region are compared with the obtained experimental data. The proposed model can explain the reaction behavior in the present reactor system within the range of variables studied. (C) 1999 Elsevier Science Ltd. All rights reserved.