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In this work the possibility of improving the performance of the 20 MW standard geothermal power plant of ENEL (Italian Electric Power Company) has been studied. The conventional geothermal cycle was modified by adding a gas turbine, an organic Rankine cycle (ORC), and a flash separator. Exhaust heat from the gas turbine is recovered in a geothermal steam superheater and by the ORC. The results of a thermodynamic analysis have been applied to a test case based on the Mt. Amiata geothermal field, where geothermal fluid has a water mass fraction ranging from 30 to 50% by wt, and about 8% by wt, of the steam fraction is non condensable,Oases (NCG). The non condensable gases are a mixture of CO2 (about 95% by weight), H2S, H-2, Hg, NH3 and CH4. Legislation on the emission of some of these substances into the atmosphere means that geothermal power plants are now equipped with gas clean-up devices but these increase the plant capital costs and reduce performance. Some of the components contained in the NCG, however, such as H2S, H-2 and CH4, have an acceptable lower heating value (LHV) and can be considered a source of energy. Hence, they could be burned to reduce their environmental impact while recovering energy that would otherwise be lost. In the power plant presented in this paper, NCG are mixed with inlet air in the gas turbine and burnt in the combustion chamber, thus helping to increase hybrid cycle performance. (C) 1999 CNR. Published by Elsevier Science Ltd. All rights reserved.