The effect of the silica crust on the blades on the efficiency of the steam turbine in geothermal power plant

Abstract

Geothermal energy is one of renewable energy sources. The potential of geothermal resources owned by Indonesia is very large about 29 GW. Geothermal resources that have been utilized for power plants is still small about 1.4 GW. Geothermal resources utilized for power generation are hot steam. Furthermore, this steam heat is converted into mechanical energy of shaft rotation by using turbine. The mechanical energy of this turbine shaft is converted into electrical energy by using an electric generator. This state of geothermal steam state is expressed by the vapor pressure and temperature and its quality depends on the geothermal location being raised. Geothermal power plant production location under study is geothermal power plant of Indonesia Power Unit Kamojang, Garut, West Java, Indonesia. This study focuses on the study of turbine performance. One of the turbine performance parameters is the isentropic efficiency. The action taken by geothermal unit Unit 2 Kamojang to maintain isentropic efficiency with turbine overhaul maintenance. This overhaul is done after the turbine operates for two years. As the turbine operates, the surface of the blade forms a silica crust. As the turbine operation increases, the silica crust gets thicker. The silica crust on these blades creates friction and disturbance on the steam flow in the turbine. This friction and disturbance of steam flow increases the irreversibility of the steam turbine system. This irreversibility is losses and causes decreased isentropic efficiency. This study was conducted to determine the effect of silica scale on the blade against the isentropic efficiency of the turbine. This research activity begins by collecting turbine operation data for two years, starting from time after overhaul until overhaul time again. The turbine operation data consists of pressure, temperature, vapor mass rate, and electrical power. Based on the operation data collected then performed analysis and evaluation. Based on the results of operation data analysis, it is found that the isentropic efficiency decreases with the increase of turbine operation time. The turbine isentropic efficiency on the first day of operation after the overhaul is about 97.55% and the last operation day before the overhaul is about 78.18%. Thus the formation of the silica crust on the blade causes a decrease in turbine isentropic efficiency. When turbine overhaul maintenance is carried out, the blade is cleaned by water.