Modified equilibrium modelling of coal gasification with in situ CO2 capture using sorbent CaO: Assessment of approach temperature

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, H2, H2O, CH4, CO, CO2, and N2 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 1200 K, 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.

► Thermodynamic equilibrium model is modified by introducing approach temperature.
► Modified model is in agreement with experimental data.
► Temperature, pressure, air ratio, and sorbent/feed ratio are effective parameters.
► Pressure is a secondary parameter for the gasification process.
► Molar content of H2 and CH4 increases by increasing sorbent/feed ratio.