Catalytic steam gasification of soy hull pellets in a fluidized bed gasifier

Abstract

The catalytic effects of inherent alkali-based metal catalysts present in biomass residues on biomass pellets were explored in this work. Gasification experiments were carried out in a pilot scale fluidized bed gasifier in the presence of alkali metal catalysts. By using a response surface methodology experimental design technique, soy hull biomass pellets were subjected to steam gasification within a temperature range of 750–950 °C. Additionally, the effects of steam-to-biomass (S/B) ratio and the catalyst loading on the gas and tar yields, and gaseous compositions were investigated. It was found that lower temperature resulted in the formation of more tar residue since the temperature was insufficient to crack the tar formed. Lower S/B ratio led to increased tar yield. Addition of catalyst significantly reduced the tar residue produced during the gasification experiments. An increase in the catalyst loading led to a steady decrease in the tar yield with up to 52% reduction at 950 °C. Further increasing catalyst loading beyond 5% had no significant effect on tar reduction. Gas yield increased slightly with catalytic gasification of the biomass pellets compared to the non-catalyzed reactions earlier studied. The reaction mechanism of the catalyzed reactions and effect on tar decomposition were discussed. Catalytic effects on tar composition were also investigated. The results from these experiments provide further insight into considering co-pelletization of catalysts during production of pellets for better gasification performance in terms of increased yields of the major gaseous components.