New chemistry development to address stibnite scale inhibition in geothermal plants

Abstract

Among all the inorganic scale species that affect geothermal applications, stibnite is one of the most difficult to treat due to its extremely low solubility constant. Stibnite typically occurs in binary systems and is more commonly found in geothermal fields in countries such as Italy, Turkey, and the USA. Its precipitation in the heat exchangers of geothermal plants often reduces heat exchange efficiency, leading to a decrease in power output and increased operational costs. Various methods, such as offline mechanical cleaning, offline chemical cleaning with acid or caustic, and the continuous application of scale inhibitors and dispersants, have been applied to prevent or eliminate stibnite precipitation. However, these approaches can be expensive when plant downtime is considered and may pose safety risks due to the formation of H2S. While chemical treatment can offer a more cost-effective and safer solution, only a few technologies are currently available on the market, and many of them fail to provide complete inhibition, particularly under severe conditions. This paper introduces a new stibnite inhibitor, providing a detailed description of its development, with a focus on the challenges and testing conditions designed to mimic real- world scenarios. An analysis of the mechanism of action of this innovative technology is also discussed. Preliminary results indicate that the new inhibitor outperforms standard solutions, functioning effectively under more severe conditions and achieving a reduction in the Minimum Inhibitor Concentration (MIC) by 2x to 3x. It has demonstrated the ability to control stibnite in brine containing approximately 10 ppm of antimony—around twice the maximum antimony level found in geothermal brines. Ongoing field trials in Europe and North America are validating the lab results, showing a significant improvement in mitigating stibnite scaling compared to previously adopted solutions. The technology’s ability to reduce environmental risks, such as H2S formation, and its potential to save up to 30-50% in operational costs, make it a promising solution for broader industrial applications beyond stibnite control.