| Abstract |
The steam supply equipment (Nittetsu Kagoshima Geothermal Co., Ltd.) of the Ogiri power plant was designed assuming a 24-hour watch. On the other hand, the power generation equipment (Kyushu Electric Power Co., Ltd.) was designed assuming a centralized, remote watch of two or more power plants, and plant start up is done remotely. Therefore, the steam supply equipment was remodeled in the regular repair period in May, 1997 for the automated operation at nighttime. The components of the main steam supply control equipment are as follows. ï The LCV controls the water level in the hot water tank at a constant level. ï The BDV opens automatically when the water level in the tank rises abnormally. ï To prevent silica scaling in piping, the pressure downstream of the LCV is controlled at a constant value, higher than flash pressure, with the water balance control valve of the re-injection well. ï The PCV controls the steam pressure of the turbine inlet. ï The BDV opens automatically at turbine trip, and blows off the whole quantity of steam into atmosphere. This BDV has the function of a PCV. In manned operation, the operator sees changes in equipment immediately and the action of switching to an alternative control valve etc. can be taken. The problem in an unmanned operation is that the equilibrium of the hot water system is lost if these control valves fail and the hot water overflows from the hot water pit into the surroundings. Therefore, the following remodeling was executed. ï Automatic change into the alternative well in the case of a water balance control valve breakdown or the re-injection capacity decrease of the well being used for balance control. ï Prevention of complete shut down when the water balance control valve breaks down. ï Automatic change into the alternative LCV when the LCV for the hot water tank level breaks down. ï To prevent the hot water tank level rising, the injection capacity was increased to more than the quantity of produced water by automatically making the PCV of the re-injection well full open. ï Installation of radio link alarms. As a result, the number of operators could be reduced substantially, from 6 to 2. Moreover, there has been no major trouble and high equipment availability has been maintained in over a year since this remodeling. |