Electricity generation from NCG (non- condensable gases) expansion in Latera geothermal plant, Latium, Italy

Aim of this paper is the presentation of an innovative project for increasing the electric power generation in Latera geothermal plant, by means of a turbine expander, recovering the pressure energy from the non-condensable gases (NCG) separated from the geothermal fluid. The new plant is designed for a peak power of 3.6 MW, in addition to the 26 MW generated by the geothermal plant, whose commissioning is at present under way. Latera plant is based on the NCG separation upstream from the turbine inlet, because this solution allows a higher efficiency, in comparison with other schemes, where the geothermal fluid is directly fed to the turbine. The energy recovery, by means of a turbine expander driven by the separated NCG, will therefore give a significant increase to the overall efficiency of the plant. The single-stage turbine expander will operate with a NCG stream at 10.5 bar abs. and 136°C at the inlet. The working fluid will be discharged to the atmosphere after the expansion in the turbine. While the technology of natural gas expansion is proven, this project is aimed to demonstrate the possibility of obtaining a consistent and reliable energy generation from geothermal off-gases. The expansion of the NCG requires a tailored approach, due to the chemical and physical characteristics of the NCG.