Power output and compressor efficiency of the gas turbine decrease over time due to compressor fouling. A major part of this power and compressor efficiency loss can be recovered by compressor online and offline washing. Nevertheless, with an enhanced filtration in the EPA class, it is possible to reduce the deployment of degradation and the necessity of washings to a minimum. After providing an overview of published research work from the past, this paper presents a thorough investigation and quantification of the effect of different air filter classes on degradation based on fleet wide analysis.

The operating data of a total of 12 gas turbines (Alstom’s GT13E2, GT24 and GT26) from 6 power stations in 5 different countries are analyzed, giving a sum of 34 filter cycles for evaluation (1 cycle represents the time period between two filter exchanges or compressor offline washings). The filter houses of the assessed plants are equipped with 2- or 3-stage filtration systems with filter classes ranging from G4 to E11 and various combinations thereof. The relevant data for power output and compressor efficiency together with the exchange history of the air filters is used to determine the degradation as a function of the last filter stage class, which allows for a quantification of the degradation and reveals a clear correlation.

As it is shown that not only the last stage filter with the highest filter class determines the degradation, but the filter system with all stages as a combination, this paper additionally evaluates the effect of the second-last filter class on the degradation.

Due to more and more challenging market environments for the plant owners, the decision to opt for highly efficient EPA filters must be well-considered: more efficient filters generally have a higher pressure loss with a negative influence on power output and are generally more expensive. Nevertheless, EPA filtration can be a strong business case when all factors such as prices for electricity and gas, operating regime of the plant, pressure loss and exchange scenarios of the filters, necessity for compressor washing etc. are considered. An exemplary profitability analysis considering all the above mentioned factors is presented in this paper. The insights of this paper shall be used as a basis for decision making when it comes to the question of how to lay out the project specific GT air inlet filtration system, as well as of how to modify the existing GT air inlet filtration for improved performance and economics.

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