Scale and corrosion inhibition is critical in operating effectively geothermal plants for power generation and heat production. 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 geothermal brine, but also with corrosion inhibitors.
Geothermal fluid produced has a Total Dissolved Solid content of ~100 g/L and main dissolved gases in these fluids are CO2 (90%), N2 (8%) and CH4 (2%). 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 this geothermal plant requires an effective control of scaling and corrosion.
The work described in this paper is related to the development of a new solution for a geothermal plant located in Europe. 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.