Water condensation in carbon-dioxide-based engineered geothermal power generation

• Published in: Geothermics
• Main Authors: Atrens, Aleks D., Gurgenci, Hal, Rudolph, Victor
• Format: Article in Journal/Newspaper
• Language: English
• Published: Pergamon Press 2014
• Subjects: Carbon dioxide; EGS; Engineered geothermal systems; Geothermal; Phase diagram; Supercritical; Thermosiphon; Water; 1907 Geology; 1909 Geotechnical Engineering and Engineering Geology; 2105 Renewable Energy; Sustainability and the Environment; Carbonic acid
• Online Access: https://espace.library.uq.edu.au/view/UQ:328230

Engineered geothermal systems (EGS) may utilise carbon dioxide as a heat extraction fluid instead of water. Nevertheless, water present in the geothermal reservoir will be extracted into the working fluid, affecting fluid flow behaviour and the required surface plant design for such a system. Dissolved water in a carbon dioxide-rich phase changes thermodynamic properties, and causes corrosion, and erosion where water droplets condense. The conditions for condensation of water in such a system have not been examined. We present condensation curves that predict conditions for water condensation, and bubble curves that predict carbonic acid concentration in a condensed HO-rich phase. These diagrams predict concentration thresholds for condensation in the production wellbore and surface equipment. Predicted concentration thresholds for condensation do not change significantly in response to change in water content. The probable minimum CO concentration allowable for direct use of carbon dioxide as a working fluid is 95% for the turbine.