Filter Replacement Strategies

Substantial savings can be realised by replacing filters at the right time. The quality of air inlet filters is essential for optimal gas turbine performance. Harmful particulates that bypass filters can lead to power and engine degradation, requiring costly maintenance to recover output. Protecting the turbine with a site-specific filtration solution assures that profits are kept high.

Nevertheless, maximising profitability requires more than a good filter. As a filter loads with contaminants, the rise in pressure drop (dP) impacts overall profitability. Typically, 1” w.g. of dP (250 Pa) reduces turbine power output by 0.375% and increases heat rate by 0.125%. Although you may have planned a scheduled maintenance, an alarm caused by a peak in pressure drop might force an unplanned shutdown for filter replacement to normalise output.

What if there was a better method of replacing your filters? The following points are three strategies to optimise filter change-out:

  • When a certain pressure drop value is reached
  • Through previously scheduled maintenance
  • Through lab testing of filters

Pressure Drop Trigger

Since replacement of filters typically means downtime, planners tend to leave filters installed as long as possible, or until a planned maintenance cycle. As noted above, running at a higher pressure drop will reduce the performance of the turbine.

When considering overall profitability, every filter solution has an optimal change-out point that results in the highest operational profits. Graph 1 shows an example of a static filter analysed over time and it clearly demonstrates that by leaving filters in beyond the optimal point (in this case at 8000hrs), additional costs are generated and thus profits are reduced.

  • Replacing filters at an estimated dP of 1.6” w.g. (in this case, 8000 hours) was shown to be the optimal point. This point coincides with the plant’s scheduled maintenance, allowing for more efficient operations and no profit loss.
  • Replacing filters at the filter manufacturer recommended dP of 2.4” w.g. (in this case, 13000 hours) would incur 4.6% higher operating costs* due to higher dP.
  • Replacing filters at the OEMs recommended dP of 5” w.g. (in this case, 24000 hours) would result in 39% higher operating costs* than the optimal point due to higher dP.

Generally, it is more profitable to change filters before the manufacturer’s recommended dP is reached. 

Graph Filter Replacement Strategies

*Operating costs:
Value of lost MWh due to decrease in turbine performance
Value of filter replacement costs
Value of fuel

Calculations assumed for base load plant operations

75 MW, 8000 hrs per year, $35 per MWh, 2250 CFM per filter

 

A CamGT 4V-300 F9 static air filter

with recommended 2.4” w.g. was tested

to determine the most profitable

change-out time. The graph shows that

the optimal time is at approximately

8000 hours (during a scheduled maintenance)

at 1.6” w.g., when total cost

would be the lowest.

Scheduled Maintenance Trigger

The challenge of this trigger is to determine which shutdown date is optimum for the operator. Many plants change filters between 18 - 24 months when pressure drop is higher, however, as demonstrated in Graph 1, letting a filter operate beyond its recommendation could cause pressure drop to increase exponentially, requiring the plant to operate at a reduced load. Consider the following advantages of aligning your optimal change-out point with a scheduled maintenance:

  • Since a scheduled shutdown includes general maintenance, there is no lost revenue due to filter change-out.
  • An earlier planned shutdown reduces the risk of a forced outage and assures availability and reliability.
  • Planning a general maintenance that considers the optimal pressure drop change out point is most profitable.

Filter Testing Trigger

Plants typically send filters to a lab for testing every one to two years when they do not have a good monitoring pressure drop system, or if the filter has aged. It is essential to send in filters early since heavy storms or high humidity peaks may cause pressure drop spikes on filters loaded with contaminants. Consider the following:

  • Sending filters to the lab ensures a thorough quality and performance check. In addition to testing pressure drop, lab experts will use multiple testing methods to verify the filter’s integrity, strength, efficiency, as well as other characteristics such as rusting, gasket cracks, and more.
  • Filters that are being tested need to be replaced.

Which change out trigger is right for your plant?

  • Maximize Profitability:
    • Scheduled maintenance is more important for base load plants because they need to operate continuously since the cost of lost production is too important. Choosing the right annual scheduled maintenance based on the optimal pressure drop point will maximise profits. Contact Camfil and request an analysis to determine the best option for your site.
  • Ensure Turbine Protection:
    • For plants that do not track pressure or see little increases in pressure, filter lab testing allows plants to ensure filter integrity and performance as they age. As outlined previously, lab tests will consider other parameters that pressure drop does not measure, such as efficiency, media strength, corrosion on metal parts, etc.
  • Maximize Filter Life:
    • Filter replacement at the manufacturer recommended pressure drop should be considered the upper limit. If an operator is not able to change at the optimal point or unable to send its filter for testing, they should, at the latest, change at the manufacturer recommendation.