Techno-economic analysis of gas turbine compressor fouling and washing.

Abstract

Gas turbine engines ingest large quantities of air from the surrounding atmosphere that often contains contaminants of different concentrations depending on the type of environment, atmospheric condition, seasonal changes, and wind direction. Deposition of contaminants and build-up on the compressor blades lead to compressor fouling. On-line and off-line compressor washing have been shown to relatively improve engine performance by decelerating or eliminating (in the case of off-line) the rate of engine degradation due to fouling during operation. There are a number of influencing parameters that determine the economic benefits of washing, some of which include the frequency of washing, effectiveness of washing liquid, and the power output produced. This research explores the cost-benefit analysis for on-line washing from 72hrs to 480hrs frequency, focusing on the viability of compressor washing for various gas turbine engines or rated capacities, ranging from a 5MW single machine to a 300MW unit. Fouling degradation trends obtained from actual machine operation have been implemented in this study. The application of different washing frequencies and time-based recoveries of lost power shows a significantly higher return on investment for the larger engines in comparison to the smaller engines. This is partly because the washing equipment cost, though increases with engine size, does not increase proportionally. Some of the key aspects captured in this study are the capital and maintenance costs used for washing, relating to the different engine sizes, thus ensuring a more indicative basis for comparing the viability of the different engines. This also includes the estimation of washing liquids utilized based on their respective typical mass flows. The study also presents an economic benefit for off-line washing from 720hrs to 4320hrs, focusing on costs that are related with off-line washing, specific cost of energy produced and net profit after deducting washing cost for different engines, related to their rated capacity. The result shows that at higher losses, off-line or on-line washing should be directly proportional to deposition or rate of degradation, and as the degradation rate increases, off-line or on-line washing is more frequent. However, when the degradation rate decreases, off- line or on-line washing should be less frequent. When off-line and on-line washing at different combinations are incorporated, the study shows that adopting the least possible off-line washing case combined with a fair amount of on-line washing case of 36 times a year provides higher net profit after deducting washing cost compared to other washing combinations. The study also presents an optimization method for on-line and off-line washing capable of evaluating compressor washing performance and economics using non-dominated sorting genetic algorithms approach. The result shows an optimum on-line washing frequency ranging from 90hrs to 110hrs for all the engine sizes at 7.2% power drop except for light-duty engine that was found to be not viable.