pH Modification Scale Control Technology

Abstract

The kinetics of silicic acid polymerization is retarded when the pH of an aqueous solution is decreased. Therefore, a potential method for controlling siliceous scaling from geothermal brine is treatment with acid. Early attempts to control siliceous scaling in geothermal brine-handling equipment by retarding polymerization implied that the pH had to be reduced to less than 4, which was considered too corrosive for practical use. In 1980, the author and colleagues examined acidification of hyper-saline brine to mitigate ferric silicate scaling. Field studies showed that a compromise between scaling and corrosion could be achieved by reducing the brine pH to no lower than 4.5.

The pH modification process was operated commercially by 1982 at two fields in the Imperial Valley of California, USA. In 1994, this process was installed on a bottoming cycle power plant to control scaling in heat exchangers and injection wells. Today, additional pH modification processes have been deployed at geothermal fields around the world to control amorphous silica and silicate scale deposition. The history and development improvement of pH modification technology will be reviewed.