Liquid dominated geothermal sources, which are broadly distributed and characterized by rather low temperature, can be profitably integrated with a heat source characterized by a higher temperature in order to generate power by means of a thermodynamic cycle working between both hot sources and the ambient temperature of the surroundings. A number of options are available for the higher temperature heat source: biomass plant combustion gas, landfill gas and urban waste incineration combustion gas are just a few examples. In all cases a high performance is obtained by properly joining a topping regenerative ORC cycle, fed by the higher temperature source, with a bottoming saturated ORC cycle, in such a way that the heat required for the evaporation of the bottoming cycle working fluid comes from the condensation of the topping cycle, and the heat required for the liquid preheat comes from the geothermal source. If both cycles are properly optimized and matched, excellent conversion efficiency can be obtained.

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