A non-stoichiometric equilibrium model for the simulation of the biomass gasification process

This paper presents a non-stoichiometric equilibrium model for the simulation of the biomass gasification process in downdraft gasifiers to be used within simulation models of complex energy systems. The chemical equilibrium is determined by minimizing the Gibbs free energy. The feedstock is composed of five elements, while fifteen chemical species are considered for the syngas. The model calculates the relative quantities of gasification products and the lower heating value of the syngas. An advantage of the non-stoichiometric approach is that it can easily calculate not only the concentrations of the main gasification products, but also the concentrations of minor products, especially the pollutant chemical species containing nitrogen and sulfur. To analyse the behaviour of the model, a sensitivity analysis of its process parameters is presented. The model is then validated by comparing its results with the results of the simulation carried out with equilibrium models and with experimental data found in literature. Finally, the model is applied to the study of the gasification of forest waste.