Computational fluid dynamics and discrete element simulation of the formation of inorganic syngas contaminants during lignocellulosic biomass gasification

Abstract

We report in this study the development of a computational fluid dynamics and discrete element method (CFD-DEM) model to predict the yield of deleterious nitrogen and sulfur contaminants (NH₃, HCN, H₂S, COS, and SO₂) during biomass gasification. Additionally, the yields of major producer gas species (CO, CO₂, CH₄, and H₂) were predicted. The formation of nitrogen contaminants was assumed to follow a heterogeneous reaction producing HCN, which was later hydrolyzed to form NH₃. Similarly, the formation of sulfur contaminants was assumed to follow a heterogeneous reaction producing H₂S, which was later oxidized to form COS and SO₂. The effects of two important gasification process variables (temperature and equivalence ratio) were evaluated. The results of the CFD-DEM simulation were validated against experimental data in the literature. The CFD-DEM model yield predictions for the main syngas species (CO, CO₂, H₂, and CH₄) compares well with the experimental results. Also, the predicted yields of NH₃ and H₂S generally fit within a 95% confidence interval of the experimental data. However, the predicted yields of HCN were about 20–50% lower than the experimental data. The main outcome of this work is a computational tool that can be used to gain in-depth knowledge to better understand how to optimize process variables for mitigating the formation of nitrogen and sulfur contaminants during gasification.