High-temperature entrained flow gasification of biomass

摘要

Biomass (wood and straw) gasification has been studied in a laboratory scale atmospheric pressure entrained flow reactor. Effects of reaction temperature, steam/carbon molar ratio, excess air ratio, and biomass type on the solid, liquid and gas products were investigated. The biomass was completely converted at all investigated operating conditions and the syngas contained nearly no tar but some soot at the highest applied reaction temperature of 1350 ℃. With a rise of reaction temperature from 1000 ℃ to 1350 ℃, the yield of producer gas (defined as the sum of H_2, CO, CO_2 and hydrocarbons up to C_3 species) increased dramatically by 72%. The H_2/CO molar ratio in syngas was close to 1 at reaction temperature above 1200 ℃ with steam addition. Higher temperature was beneficial to lower the amount of tar while the soot yield showed a peak of 56.7 g/kg fuel at 1200 ℃. With steam addition, the producer gas yield and in particular the H_2 yield increased gradually, while the CO yield decreased slowly. The molar ratio of H_2/CO was equal to 1 with the largest supplied amount of steam addition (H_2O/C = 1). Steam addition gave an obvious reduction in the soot yield, but it was not possible to completely avoid soot. Increasing excess air ratio from 0.25 to 0.50 gave no significant change in the producer gas yield, but the yields of H_2, CO, and soot decreased, the CO_2 yield increased, and the molar ratio of H_2/CO decreased. Moreover, wood and straw gasification provided similar product compositions. At 1350 ℃ and with steam addition, the syngas composition is close to equilibrium as verified by calculation.