The Upper Rhine Graben is an area of interest for geothermal energy since 1990’s where the European EGS pilot plant has been developed at Soultz-sous-Forêts, North East of France. The thermal gradient anomaly coupled with a dense naturally fractured network represents a good potential for geothermal brine production from sediment-basement interface and even fractured basement. In the French part of the Upper Rhine Graben, two industrial geothermal plants in Soultz-sous-Forêts and Rittershoffen were commissioned in 2016 and have been successfully in continuous exploitation since then. The Soultz-sous-Forêts power plant is producing electricity using an Organic Ranking Cycle, with an installed gross capacity of 1.7 MWe. The Rittershoffen geothermal plant is providing superheated water for industrial needs, with an installed capacity of 24 MWth. The commissioning and further exploitation of both plants have been followed notably by a physico-chemical monitoring of the produced geothermal brine. Indeed, geothermal brine is a Na-Ca-Cl fluid with a Total Dissolved Solids content of about 100 g/L and a Gas Liquid Ratio of about 1. Electrical conductivity, pH, and elementary chemistry, are monitored periodically. Results of this monitoring campaign show the stability of the brine chemistry and identified common trends for both sites, suggesting that geothermal reservoir exploited at Soultz and at Rittershoffen are connected. Based on the Soultz-sous-Forêts plant experience, the geothermal brine production generates sulfate and sulfide precipitations. These deposits can trap radioactive elements, like 226Ra and 210Pb. Within the aim to reduce radioactivity levels and also OPEX costs (maintenance stop for cleaning and waste disposal management), both geothermal plants are continuously using scaling inhibitors during exploitation. Surface facilities have been opened once at maintenance stops for both plants one year after commissioning. Grey-black deposits, in small quantity, were observed and have been chemically analyzed, highlighting lead, arsenic and antimony sulfide deposits into heat exchangers. Some barium sulfate deposit has been highlighted at Soultz geothermal site and is present as traces in Rittershoffen surface facilities. These analyses highlight the efficiency of scaling inhibitors used at geothermal plants, reducing the barium sulfate precipitation, but promoting metallic sulfides growth, however without impacting mainly the production. Research and monitoring are ongoing as well as quantification of radioactive elements within these scaling in order to select best chemical treatment ensuring the durability of geothermal loop and energy production, and preserving from environmental and safety at work issues.

Press the Back button in your browser, or search again.

Copyright 2018, Stanford Geothermal Program: Readers who download papers from this site should honor the copyright of the original authors and may not copy or distribute the work further without the permission of the original publisher.