Gas Turbine filter remaining lifetime is a question we encounter quite often and as much as we would like to take a few of the filters to our test bench to measure the increased weight and dp as well as do a few microscope pictures to see the material status, we really don’t recommend doing Once a year analysis of the GT inlet air filters, but we always recommend doing Continuous monitoring of the Filter condition.

For a Continuous GT inlet air filter monitoring you only need to monitor the dp across filter stages and compressor efficiency.

dp

• dp is the most important indicator of the remaining expected lifetime of the filtration stage
• dp will increase during the lifetime of the filters as the filter media gets blocked by the particles it eliminates from the GT inlet air stream. With each filter material there is different characteristics how the filter will behave when closing on its end of lifetime and you may have different End of life dp value.
• Unfortunately the type of contaminants as well as other Site specific factors - such as proximity of industrial plants or coastal environment with high humidity and salt - will affect the lifetime of the Filters and that is why it is NOT sufficient to look at the dp alone. E.g a single sandstrom may block your prefilters or salt induced leaching will perforate your fine filters with pinholes showing a low dp increase value (if any) while letting through most of the contaminants.
  
  This is why you also need to monitor your Compressor efficiency as that is also a health indicator of your Filtration system.

Compressor efficiency

• You can monitor the Compressor efficiency continuously looking for any sudden changes. if you see a  sudden spike of dp followed by sudden drop of dp followed by sudden drop of Compressor efficiency (and typically an on-line washing) you know you are in trouble as your filtration system is seriously compromised and you should inspect the filters looking for ruptures, leaching is caused by pin holes which you would not see with naked eyes.
  
  Main rule of thumb: any sudden change to the compressor efficiency is a clear indicator that something has changed in your Filtration system and needs to be investigated.

Typically you have the means to do the Continuous Filtration condition monitoring on your DCS - but if you only have the local dp gauges, the investment is not that big to add a few remote dp measurements to start Continuous monitoring of your Filtration condition - or let us do your Filter condition monitoring for you!