Equilibrium Modeling and Analysis of the Formation of Inorganic Contaminants During Biomass Gasification

Abstract

Highlights Equilibrium process promotes destruction of nitrogen contaminants but depresses destruction of sulfur contaminants. The reactions H₂S + CO₂ ↔ COS + H₂O and HCN + H₂O ↔ NH₃ + CO play significant roles in sulfur and nitrogen partitioning. The formation of inorganic contaminants is most influenced by the moisture content of the feedstock. Abstract. 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.