Parametric analysis of a steady state equilibrium-based biomass gasification model for syngas and biochar production and heat generation

Abstract

In this study, a comprehensive steady-state model of downdraft biomass gasification process was developed using Aspen Plus simulation software. All four major gasification zones: drying, pyrolysis, oxidation, and reduction were modeled separately. Oxidation and Reduction zones were modeled using the Gibbs free energy minimization method with restricting chemical equilibrium approach. The simulated model was compared with the results of a wood-fed downdraft and sawdust fed gasifier reported in the literature. A parametric analysis was performed to analyze the effect of the gasifying agent, gasification temperature (500–1000 °C), equivalence ratio (0.1–0.5), and moisture content (0–25%) on the performance of gasifier. Performance evaluation of gasifier for syngas production and heat generation was performed by determining the low heating value of syngas, cold gas efficiency and thermal efficiency. The results indicated that the Equivalence ratio (ER) is the most important factor in gasification. Changes in the ER shows a very significant variation in syngas composition. Moreover, the increase in cold gas and thermal efficiencies was also very prominent until 700 °C after which it becomes constant. Biochar production increases with a decrease in moisture content and equivalence ratio.