The chemical thermodynamic behaviour of gas tars under temperature changes in the system was evaluated. The initial composition and caloricity of the mixture were determined according to biomass and waste gasification. The chemical composition was simulated applying the Gibbs free energy thermodynamic equilibrium calculation with the help of a computational program. The obtained results were compared with the results found in the literature, identifying tar conditioning systems’ characteristics and the impact of initial mixture changes at a varying air equivalence and steam-to-carbon ratios. It was found efficient to use water vapour at temperatures of 900–1050 K, whereas at lower temperatures a more intensive oxidation should be used.

Keywords: gasification, tar, gibbs energy, thermodinamic equilibrium