Impianti ibridi RSU/combustibile fossile. Configurazioni e prestazioni

The integration between grate combustors fired with municipal solid waste (Msw) and fossil fuel fired power stations gives substantial benefits in terms of efficiency, cost and environmental impact. This paper illustrates the plant configuration and assesses the performance of systems comprising medium- and large-scale combined cycles (gas turbine power output of 70 and 250 MW el ) and a 320 MW el Enel steam-Rankine plant. The rationale of the integrated schemes considered here consists in the realization of a single steam cycle serving both the section fired with Msw and the section fired with fossil fuel, while warranting a strict separation between the combustion products of Msw and those of the fossil fuel. Saturated steam generated in the grate combustor is exported to the boiler of the power station, where it is superheated and then fed to the steam turbine. Using a single steam turbine reduces costs and increases efficiency; in addition, superheating steam with the gases generated by the fossil fuel avoids all penalties (and extra-costs) caused by the corrosive gases generated by Msw. The integrated schemes considered here grant efficiencies of electricity generation from Msw in excess of 30%, in some case above 36% - a performance far beyond the possibilities of conventional waste-to-energy plants.