Removal of Inorganic Constituents of Fresh Herbaceous Fuels: Processes and Costs

Inorganic constituents of ash in biomass fuels cause equipment failure and operating difficulties in thermochemical energy conversion facilities. Alkali metals, in the presence of chlorine and sulfur, are the leading contributors to this problem. Banagrass, an herbaceous species being considered for use in a dedicated energy crop, contains high levels of potassium and chlorine. Laboratory-scaleequipment, representing processes employed in the commercial extraction of sugar from cane, were used to prepare banagrass fuel treatments that included two degrees of comminution (coarse and fine) and two dewatering schemes (mechanical dewatering only, and a multi-step process consisting of initial mechanical dewatering followed by a water rinse and second dewatering). The treatment thatincluded fine comminution and multi-step dewatering substantially reduced in ash (45%), K (90%), Cl ((*%), S (55%), Na (68%), P (72%) and Mg (68%). The coarse comminution and multi-step dewatering scheme also resulted in reductions, but generally with 10 to 20% more of the initial constituent mass retained in the fuel. These two treatments produced fuels containing 0.11 and 0.23 kg (Na2O+K2O)Gj-1. By comparison, bagasse, the fibrous byproduct of sugarcane, contained 0.06 to 0.17 kg (Na2O+K2O) GJ-1.