ASH CHARACTERISTICS OF PERENNIAL ENERGY CROPS AND THEIR INFLUENCE ON THERMAL PROCESSING

Perennial grasses offer potential for providing a year round supply of low cost biomass when grown in southern European conditions. Four crops, Giant reed, Cardoon thistle, Miscanthus and Switchgrass have been assessed for ash content, composition and melting behaviour. Ash content for all four crops is high compared to wood and initial data suggests soil contamination is a major contributor. All crops have naturally high levels of potassium and chlorine but it is notable that Cardoon also has high levels of calcium and sodium. Ash melting temperatures are between 1000°C and 1160°C in oxidizing conditions except for Cardoon where some samples have sintered at ca 750°C. Pilot scale combustion tests on Giant reed, Miscanthus and Switchgrass at Graz showed slag accumulation on the grate, high rates of fouling and high emissions. Corrosion problems would also be expected. Preliminary fluidized bed gasification of Switchgrass was successful, however testing on Cardoon was abandoned due to rapid bed agglomeration. Preliminary fast pyrolysis tests on Giant reed and Cardoon gave poor liquid yields and quality, although ash reduction by cold water washing has shown promising results.