External bed materials for the oxy-fuel combustion of biomass in a bubbling fluidized bed

Abstract

This paper presents an experimental study of various bed materials for oxy-fuel combustion of biomass in a bubbling fluidized bed (BFB). A silica sand with three particle size distributions (PSDs) and a lightweight ceramic aggregate (LWA) made of thermally expanded clay with two particle size distributions were chosen as potentially suitable materials. The experiments of biomass combustion in oxy-fuel mode with these materials were carried out to study their suitability as fluidized bed materials. The experiments were performed using a 30kWth lab-scale BFB facility with A1 wood pellets as a fuel.The fluidized bed temperature was controlled at approx. 800°C and the volumetric fraction of O2 in dry off-gas at 10%. The resulting volumetric fraction of CO2 in dry off-gas was approximately 85%. At these conditions, there were no problems with sintering and forming of agglomerates. In the case of ceramic materials, it was possible to control the combustion process in a significantly wider range of operating parameters. Compared to silica sand, the experimental facility could be operated at a lower excess of oxygen (below 6% in dry off-gas) without significant influence on the temperatures in the facility. In terms of the consumption of the combustion facility itself, ceramic materials seem to be more suitable, as they are lighter. The pressure drop of the fluidized bed made of LWA is lower than that of the bed of the same volume made of silica sand, which means that less power is required to drive the fluidization fan.