Simulation of biomass gasification in a BFBG using chemical equilibrium model and restricted chemical equilibrium method

Highlights: • The accuracy of CEM and RCEM for steam gasification of almond shell is investigated. • Better predictions for syngas composition and yield are obtained by using RCEM. • Effect of temperature, S/B ratio and moisture content are analyzed. • Hydrogen production increases while gasifier performance decreases with S/B. • Optimum gasifier temperature is found to be between 850 and 900 °C. -- Abstract: Biomass gasification in fluidized beds is a promising thermo-chemical conversion technology. Bubbling fluidized bed gasifier (BFBG) is considered in the present study, to specify an appropriate model for almond shell gasification. Therefore, the chemical equilibrium model (CEM) and restricted chemical equilibrium method (RCEM) are developed using Aspen Plus. Then, the accuracy of the results obtained from these two modelling approaches is evaluated by comparing with the experimental data. More consistent results are obtained by using RCEM. A sensitivity analysis study is also performed with the specified modelling approach (RCEM) to investigate the effect of operating parameters on the gasification performance. For this purpose, the range of the gasification temperature and steam to biomass ratio are extended and a new parameter (biomass moisture content) is incorporated into the parametric study. Increasing temperature is shown to have a positive effect on cold gas efficiency (CGE) while it has a negative effect on lower heating value (LHV). There is no considerable change in gas heating value and CGE above 850 °C. Both steam to biomass (S/B) ratio and biomass moisture content have a favorable effect on H₂ production. However, these parameters have adverse effect on gas heating value and CGE. LHV and CGE reach maximum values for S/B ratio of 0.5 and moisture content of 0.