In recent years, users and OEMs of gas turbines are focusing more and more on the quality of the combustion air, since turbo machines have become more sensitive to fouling of the compressor blades. High-quality air filters are able to reduce the fouling on the blades and enable stable power output P and efficiency η. Continuous development of filter media and filter construction have improved the filter performance in the past. Will there be further steps towards even better air filtration for gas turbines or has the development reached a plateau? The answer to this question can be found in an economic analysis taking into account a reduction of fouling due to better combustion air quality on the one hand and higher investment costs and higher pressure drop in the air intake on the other hand. The evaluations and calculations are accomplished at so-called static filter systems where air filters with depth loading characteristics are used. With static filter systems several steps of filtration are arranged in a sequence and therefore the examined upgrades of the filtration efficiencies can be implemented relatively easy so that the effect could be studied. A comparison of two- and three-stage filter systems for intake air filtration at gas turbines produces important findings regarding the most operationally cost-efficient filter sequence overall. The upgrade of the air intake system on the one hand resulted in an increased static pressure loss in the air intake causing reduced turbine efficiency and less power output. On the other hand at the same time the soiling of the blades mainly in the compressor section (compressor fouling) is lowered and as a consequence efficiency and power output are enhanced. The effects of a higher pressure drop entailed by three-stage filtration are compared with those arising from reduced soiling on the blades. In the cases examined, including case studies from actual operation, definite advantages are found for three-stage filtration with the filter sequence F6-F9-H11 in conformity with EN 779 and EN 1822. Even the modification costs for installing another filter stage can be amortized in what will sometimes be significantly less than two years.

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