Maintenance challenges in the operation of a geothermal power station : a case for Olkaria II plant - Kenya

Abstract

The performance status of a power plant and its generating equipment can be determined by monitoring their running parameters. This is carried out by recording the individual equipment operating parameters from various instruments e.g. turbine inlet pressure, steam flowrate, steam chest pressure, etc. in logs and computer back-ups of the same, and by analyzing the data obtained to determine power plant performance. Operation of Olkaria II power plant was started in the year 2002, with Unit I turbine taking steam at a flowrate of 69.4. After operating for 2 years, steam chest pressure increased from 3.5 bar-a to 4.1 bar-a and steam consumption increased to 72.2 kg/s, with the turbine power generation capacity at 34.3 MWe out of rated 35.0 MWe. After dismantling and inspecting the turbine and its major auxiliary equipment, it was found that significant sulphur deposition and scaling and related compounds had occurred on the turbine shroud, the gas cooler and the cooling tower, reducing their efficiency and leading to reduced power. The main non-condensable gases in steam at Olkaria II are CO2 and H2S (0.75% of steam by weight). Sulphur is formed by partial oxidation of H2S and scaling occurs from solutes in brine carried over to steam pipelines due to inefficient separation. Constant inspection/maintenance and good operating practices have proved to be useful in restoring the plant to its optimal operating condition. On the other hand, corrosion and erosion of the turbine blades have been a major challenge in the operation of the plant.