Upgrading and Life Extension Technologies for Geothermal Steam Turbines

In some aging geothermal steam turbines, the increased steam consumption is found out due to time deterioration of the turbine parts, mainly caused by erosion, corrosion damages or deposits of impurities on the steam paths. Furthermore the heavy damage due to stress corrosion cracking or corrosion fatigue damage, etc. are observed on rotors, blades and other parts and components. On the other hand in other units, the turbine output capacity decreases according to aging decrease of geothermal well pressure, that is, inlet steam pressure of turbine. Under these circumstances, upgrading and life extension are required for reliability and performance on geothermal steam turbines, particularly the existing ones. And as the effective utilization of geothermal energy is important from the viewpoint of decreasing carbon dioxide on environment problem, these technologies can, needless to say be applied to new geothermal projects as well as the existing ones. This paper describes development and application of advanced steam path design such as nozzle and blade for improving reliability and performance, and of advanced rotor design and material including overlay coating technology for improving reliability and extending life. And also it describes uprating of the existing units in opposition to aged decreasing in the inlet steam pressure.