Processing of Geothermal Brine Effluents for Injection

Abstract

The handling of brine effluents for injection is a critical part of any geothermal conversion process. Brine effluents from the San Diego Gas & Electric/Department of Energy - Geothermal Loop Experimental Facility were characterized for particulate concentration and chemical composition. Bench scale tests were conducted with inorganic and organic coagulants as a means of enhancing the sedimentation process for separation an removal of suspended solids, principally amorphous silica. The effects of temperature, retention time, and pH on the precipitation of supersaturated silica , subsequent flock settling properties, and supernatant clarity were determined. A pilot sized clarifier with mixed media sand and precoat pressure filtration have been successfully tested as a means of producing injectable brine effluents. Preliminary cost estimates range in the vicinity of 20 cents per 1000 gallons.