KWG 4 Unit 1 Optimization Through Steam Path Refurbishment

摘要

For maintenance to be effective, it must be planned. When symptoms of de-rating, frequent and often severe forced outages or depletion of efficiency are detected, the necessity for remedial intervention is compelling. Performing in-depth maintenance inspection of steam turbine parts is critical. The cardinal philosophy being to detect and arrest potential defects before manifestation. KenGen Wellhead Generator 4 is a geothermal power plant in Kenya installed in 2014 at Olkaria geothermal field by Green Energy Geothermal AS on behalf of Kenya Electricity Generating Company Ltd with a rated capacity of 3,200kW. During the 2016 scheduled annual inspection for KenGen Wellhead Generator No. 4-1 turbine, diaphragm ring welds were discovered to have suffered erosion, consequently fixed vanes had drifted downstream and were scrubbing on three rotor shrouds. This disrepair was untenable and infringing on rotor operating clearances. If the plant returned to service without remedying this anomaly, it risked suffering grave damage. KenGen Wellhead Generator No. 4-1 turbine diaphragms are precision parts designed to operate under exact conditions. Anchored on turbine casing, diaphragms house a rotor revolving at 6,804rpm with allowable axial float of 0.25mm. The repair of diaphragms is a delicate process, the finished product has to be free from blemishes to guarantee that recommended operating clearances are maintained at all operating conditions. At the moment there are no known firms in Kenya dealing in such high precision welding repairs. However, considering the long lead times associated with procurement of such repair services and the loss the plant was already making in down time, it was considered judicious to attempt an in-house refurbishment of the defective diaphragms together with steam path components and resume revenue generation thereby break the lossmaking cycle. This paper discusses the experiences drawn from on-site repair of KenGen Wellhead Generator No. 4-1 steam path components culminating into availing the plant on schedule at rated load of 3200kW from an average de-rated output of 2501kW.