| Title | Development of a novel NORMs inhibitor for Rittershoffen geothermal plant in the Upper Rhine Graben |
|---|---|
| Authors | Davide Parravicini, Alessandro Guidetti, Daniele Zambolin, Guillaume Ravier, David Fries |
| Year | 2023 |
| Conference | World Geothermal Congress |
| Keywords | #NORMS #Barite #UpperRhineGraben #scale #scaleinhibitors #corrosion #compatibility |
| Abstract | Scale and corrosion inhibition is critical in operating effectively geothermal plants for power generation and heat production in the Upper Rhine Graben (URG). Indeed, these phenomena are often responsible for loss of system efficiency and premature equipment failure or replacement. In this study, we focus on finding a new scales inhibitor compatible with the URG geothermal brine, but also with corrosion inhibitors. The URG is a rifting formation part of the European Cenozoic rift system, which extent for 300 km of length from Basel (Switzerland) to Mainz (Germany). Geothermal fluids produced in the URG have a Total Dissolved Solid content of ~100 g/L, and is considered as Na–Ca–Cl type with minor and traces elements like lithium, lead, arsenic or antimony and a pH comprised between 5.00 and 5.77. Additionally, main dissolved gases in these fluids are CO2 (90%), N2 (8%) and CH4 (2%) with a Gas Liquid Ratio in a range of 1.0 to 1.3. Consequently, the combination of low pH and high content of chlorine contributes to enhanced geothermal fluids natural corrosive effect on most steel grades. Moreover, during the heat transfer in geothermal plants, liquid-solid equilibrium is changing, leading to barium sulphate precipitation and metal-rich (Pb, Fe, As, Sb) sulfides. They can co-precipitate together with radioactive isotopes, creating Naturally occurring Radioactive Materials (or NORMs). These by-products enriched with radioactive elements leads to health hazards for operators, and environmental damages in case of discharge. All of these reasons, clearly highlight why geothermal plants in the URG require an effective control of scaling and corrosion. The work described in this paper is related to the development of a new solution for the Rittershoffen geothermal plant, located in the URG. Although, the facility is currently using two separate technics for controlling sulphate / sulfide deposition and corrosion issues, a manual hazardous (mostly due to the presence of NORMS) cleaning of the heat exchangers is required once a year. Scales have a significant impact on plant efficiency and power generation, therefore, it is necessary to develop a scale inhibitor with higher performance. Furthermore, this anti-scaling technology needs to be compatible with the current anti-corrosion agent. Therefore, both products would be injected close together before the heat exchanger where main scaling and corrosion issues are typically observed. To produce this new technical solution, an extensive work in the lab has been done. Due to high amount of calcium in the solution, insuring compatibility with the geothermal brine was a critical point. Several compatibility tests with geothermal brine and the current corrosion inhibitor, in addition to performance against barite and lead sulfide, have been assessed. All of these experiments were achieved by applying conditions close to geothermal brine operation. As a result of this work, a new technology having significantly better performance has been developed and industrialized to be used onsite during several months. This period of trial allows to check under real field conditions the efficiency of new NORMs inhibitor and to confirm all the results obtained in the lab. |