Equilibrium modeling and analysis of the formation of inorganic contaminants during biomass gasification

Gasification generates producer gas for synthesizing renewable fuel and chemicals. Producer gas contains primary products (carbon monoxide [CO], carbon dioxide [CO2], hydrogen [H2], methane [CH₄], water vapor [H2O]) and deleterious impurities (ammonia [NH₃], hydrogen cyanide [HCN], hydrogen sulfide [H2S], and carbonyl sulfide [COS]). This study predicts the composition of lignocellulosic biomass-derived primary products and four major inorganic contaminants (H₂S, COS, NH₃, and HCN) using a non-stoichiometric equilibrium modeling approach implemented with the Lagrange multipliers method for efficient computation. Based on our findings, H₂S, NH₃, and HCN are not thermodynamically controlled during lignocellulosic biomass gasification, as our simulations considerably over- or underpredicted them. At equilibrium, a large fraction of biomass-nitrogen is converted to nitrogen (N2). Biomass-sulfur was mostly transformed into H₂S and smaller quantities of COS. Moreover, the formation of H₂S, COS, and HCN was predominantly influenced by moisture content, while temperature and equivalence ratio had limited effects on these species. Besides the contaminants, CO, H₂, and CO₂ were well predicted by our model, while CH₄ was underpredicted.