| Abstract |
Deep geothermal systems were identified in the Upper Rhine Graben, and geothermal plants have been commissioned these last years on either side of the Rhine River (Soultz-sous-Forêts, Rittershoffen, Landau, Insheim and Bruchsal), exploiting geothermal fluid at 150°C and more for industrial heat or electricity generation. The fluid exploited in the geothermal site of Rittershoffen reaches 170°C and contains around 100 g/L of dissolved salts (mostly Cl-, Na+, K+ and Ca2+), as well as dissolved gases (mostly CO2 (90 mol.%) with a gas-to-liquid ratio close to 1). Thus, this geothermal fluid represents an aggressive medium, requiring the use of corrosion inhibitors to ensure a suitable lifetime of the steel installations. In France, many geothermal sites are exploiting the Parisian Dogger, where relatively low temperatures are met (55-85°C), with the use of inhibitors for several decades already. However, there is currently a lack of knowledge on high temperature (HT) inhibitors for geothermal systems: suitable products need therefore to be identified and this is the purpose of the project presented here. First, a preselection of inhibitor products is made based on their hazard statements, their thermal stability, and their compatibility with the brine present in Rittershoffen. The corrosion rate of steel tube sample and the performance and mechanism of the selected products on the corrosion inhibition are then evaluated through electrochemical measurements in the mentioned brine at 80°C. Further weight-loss and electrochemical measurements are performed at utilization temperature (170°C) using an autoclave to evaluate the inhibiting performance at HT. Such HT electrochemical experiments were rarely performed in the literature for geothermal applications. The inhibitors will be ranked based on their performance (resulting steel corrosion rate), their suitability with needs of geothermal plant’s operator (annual cost, compatibility with the scale inhibitor used on site, lifetime during storage and utilization…) and their environmental impact, to se1ect at least one candidate to be used in Rittershoffen. The final step will be to validate the suitability of the selected inhibitor in real operating conditions through on-site measurements. The authors thank GEOTHERMICA and ADEME for financial support. |