Gas Turbine Performance Deterioration
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IToday, gas turbines are generally used to produce electricity and drive natural gas compressors on offshore installations. The performance of gas turbines is reduced gradually, and this lead to reduced production capacity of the platform. Degradation of performance of a gas turbine also carry with them higher fuel consumption and higher emissions. Degradation rate of gas turbines have proven to be very site-specific, but compressor fouling is generally the largest contributor to reduced performance. Therefore, it is important to have good procedures for detecting performance deterioration, and regain lost performance. Today, all gas turbines equipped with standard instrumentation from the manufacturer. Through these sensors performance data is logged continuously, and can be used to make an assessment of the performance and condition of gas turbine. To regain performance offline water wash is typically used. This method has proven to be the most reliable, with a high degree of performance recovery. In the recent years, increasingly stringent demands require higher gas turbine availability and lower environmental emission rates. Online water washing can be a means to achieve this. Daily injection of water into the compressor section reduces the possibility of fouling formation in the compressor section. This allows offline water wash intervals to be extended, while the gas turbine operates with better performance and lower emissions rates. This report contains an evaluation of suitable parameters for detecting compressor fouling. Data was obtained from 9 different LM2500 gas turbines operating in the North Sea. The results from the evaluations are that it is difficult to say anything concrete on the basis of the collected data. It is possible to detect a degradation trend for several of the machines, but nothing that would indicate that the current water wash program should be reassessed. Pressure loss over the bellmouth of a gas turbine has been pointed out by several sources in the literature review as the simplest and most sensitive parameter to detect compressor fouling. This measurement was not been available for any of the investigated gas turbines.