Apparent kinetics of the water-gas-shift reaction in biomass gasification using ash-layered olivine as catalyst

Abstract

Substitution of fossil fuels for production of electricity, heat, fuels for transportation and chemicals can be realized using biomass steam gasification in a dual fluidized bed (DFB).Interaction between biomass ash and bed material in a fluidized bed leads to transformation of the bed particle due to enrichment of components from the biomass ash resulting in the development of ash layers on the bed particle surface. These ash-rich particle layers enhance the catalytic activity of the bed material regarding the water-gas-shift reaction and the reduction of tars.The water-gas-shift reaction at conditions typical for dual fluidized bed biomass gasification at a temperature of 870 °C was investigated. Diffusion and heat transfer limitations were minimized using a lab-scale experimental set-up consisting of a gas mixing section and a quartz glass reactor in which the catalyst is investigated.The following new rate expression for the water-gas-shift reaction in dual fluidized bed gasification of biomass was empirically developed, which takes ash layer formation into account: rOlivine_ash-layer=8,9·10-6exp-95000RTpCO1,96pH2O1,81pCO2-0,75pH2-1,69