Gasification performances of raw and torrefied biomass in a downdraft fixed bed gasifier using thermodynamic analysis

The gasification performances of three biomass materials, including raw bamboo, torrefied bamboo at 250°C (TB250), and torrefied bamboo at 300°C (TB300), in a downdraft fixed bed gasifier are evaluated through thermodynamic analysis. Two parameters of modified equivalence ratio (ER_m) and steam supply ratio (SSR) are considered to account for their impacts on biomass gasification. The cold gas efficiency (CGE) and carbon conversion (CC) are adopted as the indicators to examine the gasification performances. The analyses suggest that bamboo undergoing torrefaction is conducive to increasing syngas yield. The higher the torrefaction temperature, the higher the syngas yield, except for TB300 at lower values of ER_m. Because the higher heating value of TB300 is much higher than those of raw bamboo and TB250, the former has the lowest CGE among the three fuels. The values of CC of raw bamboo and TB250 are always larger than 90% within the investigated ranges of ER_m and SSR, but more CO₂ is produced when ER_m increases, thereby reducing CGE. The maximum values of syngas yield and CGE of raw bamboo, TB250, and TB300 are located at (ER_m, SSR) = (0.2, 0.9), (0.22, 0.9), and (0.28, 0.9), respectively. The predictions suggest that TB250 is a more feasible fuel for gasification after simultaneously considering syngas yield, CGE, and CC.