Design considerations for reliable electrical, control and instrumentation systems in geothermal power plants with emphasis on hydrogen sulphide related problems

Abstract

Hydrogen sulphide is a corrosive gas widely present in the air at most geothermal power plants. This report describes the mechanism and some of the effects of corrosion in electrical equipment in the presence of hydrogen sulphide at geothermal power stations. Electrical and control equipment are often not designed to operate in corrosive environments; hydrogen sulphide is a corrosive gas, particularly to copper and silver. Therefore, special measures and systems must be considered in order to keep this corrosive gas from contacting sensitive equipment containing those metals. Other equipment in the plant can also suffer from the attack of hydrogen sulphide, but it is possible to minimize the adverse effects by making a careful selection of the materials used and maintaining appropriate environmental conditions. Instrumentation is also exposed to the particularities of the geothermal fluids; the performance and expected problems of some of the main instruments used in the power plant are presented. By appropriate design of geothermal power stations, and taking into consideration and addressing the possible ways in which hydrogen sulphide and geothermal fluids can attack equipment, it is possible to avoid premature failures and attain high plant reliability.