Abstract
This work studied a multistage gasification system that is designed for producing a syngas with a low tar content. The proposed system is an atmospheric bubbling fluidized-bed gasifier and comprises mainly pyrolysis, combustion, and gasification zones. The numerical investigation is performed using Aspen Plus to study Prosopis Juliflora gasification. Chemical reactions as well as tar treatment in the process are investigated. Two different pyrolysis temperatures were considered: 500 and 600 ?, along with three different particle size ranges: 0.2-0.5, 0.5-1, and 1-2 mm. The effect of the air-to-biomass ratio, with values from 0.2 to 1.2, and the gasification reactor temperature, from 800 to 1000 ?, on the composition of product gas and tar species formation during the process (phenol, naphthalene, benzene, and toluene), its lower heating value (LHV), and cold gasification efficiency (CGE) were studied. Results showed that a pyrolysis temperature of 600 ? and a particle size range of 0.2-0.5 mm displayed less tar produced from both combustion and gasification zones and were associated with greater CO, H-2, and CH4 yields, compared to the other pyrolysis parameters tested. Increasing the gasification temperature led to increasing the CO, H-2, and tar yields and decreasing the CH4 yield and CGE. The maximum CGE combined with the minimum tar amount produced could be obtained with values of 800 ?and 1.2 for the gasification temperature and the air-to-biomass ratio, respectively. The numerical simulation results will be used to improve the performance of the proposed system.