Effect of Modified Equilibrium Constants of Comprehensive Thermodynamic Equilibrium Model on Prediction of Constituents of Producer Gas for Rubber-Wood Biomass

Thermodynamic equilibrium models (TEM) are widely used for predicting producer gas composition in biomass downdraft gasifiers due to their simplicity and computational efficiency. However, conventional TEM often overpredicts hydrogen and carbon monoxide because of the assumption of complete chemical equilibrium. In this work, a Comprehensive Thermodynamic Equilibrium Model (CTEM) incorporating modified equilibrium constants (Kwgs = 1.01 and Km = 0.65) is validated for rubber-wood biomass under varying equivalence ratio (0.274–0.420) and moisture content (0.076–0.185). Mass balance, equilibrium constant formulation, and energy balance equations are solved simultaneously using an iterative approach. Model predictions are evaluated using Mean Percentage Error (MPE) and Root Mean Square Error (RMSE). Results indicate significant reduction in hydrogen prediction error and improved nitrogen estimation compared to conventional TEM. The modified model demonstrates improved robustness across operating ranges and can be used for preparing generalized gasification performance tables.