Performance study of a single-flash geothermal power plant cold end : a case study of Olkaria II power plant

Abstract

The Olkaria II power plant operating conditions of different systems have diverged from the ideal design values over time. The main focus of this study were two systems in the cold end of the geothermal power production process, i.e., the circulating water and the non-condensable gases (NCG) removal systems. The main components studied included the condenser, the cooling tower, NCG removal steam ejectors, inter-condensers and Liquid Ring Vacuum pumps. A comparison study between the original design parameters and the current operating parameters was carried out. The conservation of heat and mass balance throughout the circulation process has been the basis of the analysis. The main operating parameters under investigation are the condenser pressure and circulating water temperatures. The heat load exerted upon the condensers of the three units seems to have risen with an increase in steam consumption. This might have led to an increase of the NCG content in the steam. In addition, the effectiveness of the cooling tower was calculated and found to have deteriorated by almost 20% from the design conditions. The study has taken the maintenance strategies employed on these systems into account with the aim to enhance them.

Previous condenser shell punctures and main steam pipe punctures indicated that the corrosive property of the cooling water results from oxidation reactions and a necessity for deaerating. The abundance of oxygen in the cooling water is thought to be a result of the open cooling tower basin and air leakages into the condenser. Eventually most of the focus was on the cooling tower cooling capabilities and the possible factors leading to deterioration in its effectiveness. Fouling has been identified as one of the main causes of deterioration in the performance of the condenser, pipes, cooling tower fills and basin. The chemical dosing process at the power plant has been considered and the sulphur depositions in the cooling water seem to increase with a rise of the pH values. The study compared the design and current parameters but further analysis will be necessary to map out the deterioration trend over time and to improve mitigation strategies.