NEW APPROACH OF SIMULATING RDF COMBUSTION VIA DISCRETE ELEMENT METHOD USING EXPERIMENTAL PYROLYSIS AND COMBUSTION DATA FROM A PILOT SCALE PLANT

摘要

The continuing increase of CO2 in the atmosphere and the vanishing reserve of fossil energy sources demand efforts from everyone. That is why many industrial process operators try to substitute fossil fuels by alternative fuels such as biomass, municipal solid waste (MSW) or refuse derived fuels (RDF). This leads to an overall smaller CO2-addition to the atmosphere and a better carbon footprint of the products. Often an intensive preparation of these fuels is economically not feasible, therefore they are burnt "as delivered" or after minor processing. Thus the "fuel particles" have a size in the cm range, can be physically and thermo-chemically extremely inhomogeneous and the mixing with combustion air must be accomplished by mechanical interaction rather than by fluid flow forces. Packed beds or mechanically moved beds are typical devices to burn these fuels, resulting in a combustion behaviour which is different from their fossil counterparts. Not only particle size, but also calorific value, ignition temperature, duration of combustion, oxygen requirement and other properties exhibit a broad range of variation from particle to particle. Thus detailed physical and thermochemical characterisation is decisive in order to be able to design the combustion plants for these fuels efficient and economical. In addition to conventional chemically oriented methods like proximate and ultimate analysis of homogenised fuel, samples, new procedures which reveal the actual rate of devolatilisation for individual large fuel particles and the associated heat of reaction are required for a sufficiently large, statistically firm number of distinguishable particle fractions.