Evaluation of the Efficiency of an Organic Corrosion Inhibitor in the Upper Rhine Graben Under Geothermal Conditions

Abstract

The Upper Rhine Graben in Central Europe has a significant thermal anomaly, which makes it a promising candidate for the geothermal exploitation. However, the high saline, CO2-enriched geothermal brines can potentially cause corrosion leading to material failure and expensive downtimes of geothermal power plants. One possibility to prevent corrosion is the addition of chemical inhibitors into the circulating geothermal fluids. In this contribution, the inhibitor efficiency of an imidazoline based corrosion inhibitor is evaluated. Apart from testing of an original geothermal brine sampled at a geothermal power plant at the western part of the Upper Rhine Graben artificial brines with different Na-Ca-Cl contents are examined. To assess the inhibition effect of the tested inhibitor, selected electrochemical (potentiodynamic polarization, impedance spectroscopy) and weight loss tests are applied. Thereby, the corrosion behavior of a common mild steel is examined which is a typical example for the materials used in geothermal power plants. Experiments are performed at 80°C under CO2 conditions. As one major outcome of the study, the inhibition effect of the examined inhibitor turned out to be largely dependent on the interplay of the chemically active species in the brine and the inhibitor itself. Based on the experimental results, a conceptual model of the adsorption/desorption behavior of the inhibitor and its mutual interaction with the studied brines is developed.