Gasification process has become more attractive around the globe due to the energy crisis and environmental issues. An equilibrium model based on minimization of Gibbs energy is developed to predict the product gas composition of an air-blown coal gasifier. This paper further proposes a method for modifying the thermodynamic equilibrium model. The presented method includes the introduction of an approach temperature which corresponds to the deviation from equilibrium condition. The major components in produced gas, H-2, H2O, CH4, CO, CO2, and N-2 have been determined and compared with the pure equilibrium modelling as well as the experimental data. Comparison with experimental measurements revealed that the modification of the equilibrium model has significantly reduced the error in predicting the product gas composition. In situ CO2 capture using sorbent (CaO) is also investigated in order to enhance the hydrogen production and also to address the environmental regulations on Green House Gas (GHG) emissions. The effect of important process parameters on the product gas composition is studied and the temperature of 1200K, pressure of 1 bar, air ratio of 0.4, and sorbent to feed ratio of 2.2 have been predicted as the optimum operating conditions for the purpose of maximum hydrogen production. (C) 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.