| Abstract |
A variety of processes has been deployed at geothermal fields to inhibit or control siliceous scale deposition. It has been known for decades that 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 led to the belief that the pH had to be reduced to < 4. Acidifying brine was discouraged due to corrosion concerns. 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 (Gallup, 1996b). Today, the pH modification process has been deployed at a number of geothermal fields around the world to control amorphous silica and metal silicate scale deposition. The history of and development of improvements to pH modification technology will be reviewed. The present paper is an update of a prior publication on the subject (Gallup, 1996a). |