Mechanisms of alkali metal release during biomass combustion

The conversion of biomass materials into electricity via combustion poses several technical and economic challenges. One of the more pressing technical challenges associated with biomass combustion is fouling and stagging in combustors. Accelerated fouling and stagging in current biomass combustion facilities has been linked to the alkali metal content of the fuel. Alkali metal release during biomass combustion causes significant problems in terms of severe fouling and stagging of heat transfer surfaces in boilers thus reducing efficiency, and in the worst case leads to unscheduled plant downtime. Future biomass to electricity facilities that will incorporate integrated combined cycle systems that use biomass combustion gases directly to drive an aeroderivative turbine will have even lower tolerances for alkali metal vapor release because accelerated erosion and corrosion of turbine blades results in shorter turbine lifetimes. The release of alkali metal vapors during biomass combustion was monitored using a direct sampling, molecular beam mass spectrometer.