Experiments on the combustion behavior of RDF- and biomass-lignite mixtures in a shaft furnace are conducted. The experimental results are interpreted by characteristic numbers in order to establish a fuel catalogue which allows a quantitative comparison of the combustion behavior of different solid fuel on the combustion grate. A mechanistic model is derived in order to transfer the batch operated shaft furnace results to the continuously operated grate furnace. Basic experimental results are: - co-combustion of RDF and biomass with lignite increases the reactivity of the fuel, expressed as reaction front velocity RFV, by up to a factor of 5 - this effect is much more pronounced for RDF as compared to biomass - with increasing RDF fraction in lignite the ignition rate IR increases, whereas the mass conversion rate MCR is about constant for RDF ratio above 20 wt percent. Consequences for the operation of a grate furnace as derived from the shaft furnace experiments are: - 20 percent wt of RDF in lignite reduces the required grate length for complete burn-out of fixed carbon by about 30 percent as compared to pure lignite - increased ignition rate IR with increasing RDF ratio indicates a stronger volatile release from the fuel bed, thus influencing mixing requirements and temperature regimes in the primary and secondary combustion chamber; an adjustment of primary and secondary air supply is required.
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