Process simulation of staging pyrolysis and gasification of biomass in a dual fluidized bed system

The present study developed an ASPEN plus model for the study of the gasification behaviors of biomass in a dual fluidized bed (DFB) using steam as gasification agent. Model validation was performed by comparing the predicted results with the experimental data obtained from a steam-blown DFB gasification system and, a good agreement was attained. Sensitivity analysis was done to obtain producer gas composition using wood pellets and different gasification parameters like H-2 yield, gas yield, H-2/CO, tar yield, cold gas efficiency (CG-E) and char conversion efficiency (CC-E) using gasification temperature (750-900 degrees C), steam/biomass ratio, S/B (0.28-1.72) and steam temperature, ST (300-700 degrees C). Increasing the temperature and S/B contributed to the yield of H-2 and the tar conversion rate. The results showed that both variables (temperature and S/B) have a strong positive influence on the quality and quantity of the produced syngas. Results showed that H-2 content increased while CO and CH4 decreased with increasing S/B from 0.28 to 1.72 at 850 degrees C. The gas yield and H-2/CO increased from 0.83 to 1.21 Nm(3)/kg and 0.9 to 1.87 with increasing S/B from 0.28 to 1.72, respectively, while tar yield decreased from 9.1 to 8.02 g/Nm(3). The content of H-2, H-2 yield and CG-E increased with the rise of ST from 300 to 700 degrees C, while an opposite trend was achieved for tar yield.