Searching for a universal scale inhibitor: A multi-scale approach towards inhibitor efficiency

Abstract Scale inhibition is of crucial importance in harvesting geothermal energy, an attractive, renewable and sustainable energy source. The majority of the geothermal reservoir waters around the world contain a variety of anions and cations, which are prone to precipitation when subjected to vast transformations of both temperature and pressure, causing failures to many parts of the plants. Our goal is to prevent the formation, precipitation and deposition of such scales by stabilizing their respective components. Our working brines are designed based on the saturated conditions of geothermal well waters. Common inorganic scales tested include amorphous silica, magnesium silicate, aluminum silicate, iron (III) silicate, zinc sulfide, lead sulfide, iron (II) sulfide, and calcium carbonate. Against these scales, four interrelated methacrylate-structured polymers were tested as inhibitors, grafted either with polyethylene glycol (PEG), or phosphonic acid (PHOS) side-chains, or both. Based on several results obtained the inhibitor PEGPHOS-LOW (containing 34 PEG grafts and 14 phosphonate grafts) was selected as the most efficient, and was subsequently tested in artificial geothermal brines of variable stress, containing all the scales together.