Transient modeling of biomass steam gasification with Co3O4

Abstract

Co3O4 was subjected alternatively to argon/steam as reducing and air/steam as oxidizing agents in a bubbling fluidized bed reactor. Ten grams of biomass was injected to the reactor at the beginning of the reduction interval. Oxygen was released from Co3O4 in the reduction period and together with the steam gasified the biomass. The reduced cobalt oxide (CoO) was regenerated to Co3O4 during the oxidation. The produced gas is free of nitrogen and has a higher calorific value compared to gasification with air. From 825°C to 875°C, H2 yield increased up to 60%. From 0% to 18% of steam, H2 yield increased 4 times. Substituting 50% of the sand as bed material with Co3O4, increased the CO yield up to 45%, lowering the H2:CO ratio. For reactor modeling, a two phase model for the dense bed and a plug flow model for the freeboard region were used. The presented hydrodynamic model together with the kinetic expression from the literature characterized the transient gas compositions at the reactor outlet very well.