Filter Failure During High Humidity Conditions

The operation of a gas turbine, by its basic design, requires it to ingest enormous quantities of air. Even in relatively clean environments, a gas turbine may ingest hundreds of pounds of foreign matter each year of various sizes. Also, the more advanced the turbine design, the more sensitive it is to the quality of the air ingested. Filtration is applied to the inlet air to provide protection against the effects of contaminated air. Filters used with gas turbines are designed to remove a specified amount of particular contaminants. One type of filter is the high efficiency filter. These are often installed in order to capture particles less than ten microns. These filters are sometimes susceptible to water penetration. If the filter is not designed to remove water, then water can absorb soluble contaminants and carry them through the filter into the inlet of the gas turbine. In the case where harmful contaminants travel through the filter with the water, this can be potentially damaging to the gas turbine. For example, salt is soluble and can lead to hot corrosion in the turbine section. If water is allowed to reach the high efficiency filters then the water may carry contaminants through the gas turbine. In order to mitigate this phenomenon, many filter systems have mist removal systems. Even with a good mist removal system, humidity can reach the high efficiency filters. As humid air flows past the high efficiency filters, the decrease in air pressure can lead to water condensing on the filters. A procedure is presented in this paper which shows that filters that have been fully or near fully loaded with contaminants may experience condensation in an environment with high humidity. This paper reviews a thermodynamic analysis that is used to determine the conditions that must be met in order to experience this phenomenon. The possible occurrence of condensation further demonstrates the criticality of replacing inlet filters as soon as the filter pressure loss shows an upward trend.© 2010 ASME