Evaluation of Calcite Scale Inhibitors: Impact of Metal Cations

Abstract

Over the past decade, electrolyte modeling software has been combined with proprietary scale inhibitor dosing guidelines to generate product dosages based on site-specific brine chemistries and operating conditions. While these programs signify a great advancement to geothermal plant operators, there is often a significant discrepancy in the recommended dosage and the necessary inhibitor concentration needed for effective scale control. In some cases, underdosing of a calcite antiscalant has led to severe scale formation and unanticipated plant shutdowns. Failures like these have emphasized the need for additional research to develop improved scale inhibitor dosing guidelines and more robust antiscalant chemistries. This paper summarizes laboratory performance testing of polymeric inhibitors after thermal treatment using a NACE calcium carbonate test protocol. The presence of metal cations commonly found in geothermal brines, such as aluminum and iron, was determined to have varying deleterious effects on antiscalant performance. The impact of the metal cations was dependent on concentration and scale inhibitor chemistry. Quantification of these negative effects on calcite inhibition performance will lead to the development of increasingly accurate and robust product dosage models for geothermal applications.