Operational Results of a Dry-Steam Resource Chloride Corrosion Mitigation System

Abstract

The Aiden geothermal power plant, located in the West Geysers steam field, began commercial operation in June of 1989. Unique to this plant is a comprehensive corrosion mitigation/steam scrubbing system that has been in service since inception. This system was designed by Mission Power Engineering Company for Geothermal Energy Partners, Ltd. to prevent acidic chloride induced corrosion of the gathering system and to protect the turbine from pitting corrosion, stress corrosion cracking and erosion related to the presence of chloride in the steam. To date, no failures of steam piping have occurred and ultrasonic testing (UT) has shown no significant pipe wall losses downstream of the injection points, in spite of the relatively high initial chloride concentrations in the steam. A range of chemical process conditions have been defined to effectively remove chloride from the steam, while maintaining the liquid pH and salinity at levels necessary to minimize corrosion rates and to prevent the deposition of scales. In addition, a two stage steam scrubbing system at the plant inlet was optimized to maintain the steam purity at least 5 to 20 times higher than specified by the turbine manufacturer. In March of 1990, both units were brought off line for inspection and non destructive testing of the turbines and ancillary equipment. This inspection revealed only minor scale deposits and no apparent corrosion damage in the turbines. This system, effectively operated, is projected to extend turbine and piping life to expectancies equal to or greater than those encountered in geothermal areas producing little or no valuable chloride.