Effect of Torrefaction on Steam Gasification of Biomass in Dual Fluidized Bed Reactor—a Process Simulation Study

In this study, a steam gasification with a dual fluidized bed reactor is constructed using a commercial process simulator and validated by experimental data to investigate the behaviors of raw and torrefied spruce wood during the conversion process. Effects of torrefaction, gasification temperature, and steam-to-biomass ratio on the performance of spruce gasification are examined. Main gasification indicators including product gas composition and heating value as well as cold gas efficiency are investigated. Simulation results show that both the H2 and CO2 contents in the product gas are reduced with increasing the gasification temperature or decreasing the steam-to-biomass ratio. On the other hand, the CO content shows an opposite trend. In addition, increasing the gasification temperature or decreasing the steam-to-biomass ratio enhances the heating value of the product gas but reduces the cold gas efficiency. Compared with the raw feedstock, the torrefied spruce offers lower H2 but higher CO content in the product gas at the same gasification condition. Nevertheless, gasification of the torrefied spruce always results in higher cold gas heating value and efficiency than that of the raw spruce. The increased values are up to 0.46 MJ/Nm3 for the heating value and 5.96% for the efficiency.