Possible Circular Use of CO2 Waste Streams from Geothermal Power Plants

Geothermal fluid is usually characterized by the presence of water and minor percentages of non-condensable gases (NCG), including CO2. Relevant CO2 streams are currently released from the cooling towers of geothermal power plants operating in Tuscany. These emissions are largely of natural origin. The output streams of NCG are treated for removal of contaminants (Hg and H2S) and consist in nearly-pure CO2: that is the reason why it is worth to investigate about its potential circular use. Specifically, the possibility of transport and use as a long-distance heating or cooling fluid stream for local communities is investigated; integration with hydrogen production is also considered, with production of methanol to be used as synfuel or energy storage. Hydrogen can be harvested from several sources: a) from the captured H2S stream b) from industrial facilities already existing along the transport path c) from integrating an electrolyser in the power plant premises thereby providing load flexibility (currently not present in geothermal power plants). The study is tailored on the local geographical, productive structure and population situation. The remaining part of the CO2 stream is delivered to the sea where it can be finally destinated to transportation (pipeline or ship) and sequestration. The results are encouraging in inspiring a potentially new sustainable economy structure.