A single flash integrated gas turbine-geothermalpower plant with non condensable gas combustion

In this work the possibility of improving the performance of the 20 MW standardgeothermal power plant of ENEL (Italian Electric Power Company) has been studied Theconventional 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 steamsuperheater and by the ORC The results of a thermodynamic analysis have been applied to a testcase based on the Mt Amiata geothermal field where geothermal fluid has a water mass fractionranging from 30 to 50% by wt and about 8% by wt of the steam fraction is non condensablegases (NCG) The non condensable gases are a mixture of CO2 (about 95% byweight)H2S, H2Hg,NH3 and CH4 Legislation onthe emission of some of these substances into the atmosphere means that geothermal powerplants are now equipped with gas clean-up devices but these increase the plant capital costs andreduce performance Some of the components contained in the NCG however such as H2S H2 and CH4 have an acceptable lower heating value (LHV) andcan be considered a source of energy Hence they could be burned to reduce their environmentalimpact while recovering energy that would otherwise be lost In the power plant presented in thispaper NCG are mixed with inlet air in the gas turbine and burnt in the combustion chamber thushelping to increase hybrid cycle performance © 1999 CNR Published by Elsevier Science LtdAll rights reserved