Superheated steam injection as primary measure to improve producer gas quality from biomass air gasification in an autothermal pilot-scale gasifier

Abstract

This work evaluated the influence of superheated water steam injection in an autothermal 80 kWth pilot-scale bubbling fluidized bed during biomass direct (air) gasification, focusing on the effect of steam to biomass ratio in the producer gas composition and gasification efficiency parameters. The process was also evaluated in an externally heated 3 kWth bench-scale bubbling fluidized bed and simulated in a thermodynamic equilibrium model.For low-density biomass, the steam injection resulted in a producer gas with higher H2 concentration and H2/CO molar ratio, although with lower energy content, and in a decrease of the process efficiency. Thus, steam injection promoted a trade-off between parameters, that can be associated with a higher occurrence of the water-gas shift reaction. For high-density biomass, along with an increase of H2 concentration and H2/CO molar ratio, steam injection promoted an increase of the producer gas energy content and process efficiency, which can be justified by a higher char accumulation in the reactor bed and consequent higher occurrence of char-steam reforming reactions.Therefore, steam injection shows high potential to improve the producer gas quality from high-density biomass air gasification, however, for low-density biomass, it shows limited potential and should only be used to adjust H2/CO molar ratio.