If it Ain’t Broke, Don’t Ignore It

If your turbine seems to be running smoothly, it’s tempting not to think about your filtration system and whether it is optimal. Who wants to go looking for trouble?

Indeed, filter maintenance is too often an afterthought, something people usually reserve for 24,000-hour turndowns, if they consider it at all. But hidden filter inefficiencies and dangers can threaten turbine performance and even life, and you don’t need a full outage to spot them.

Figure 1 shows evaporative cooler media that had snapped. A random inspection of the filter house discovered this. Fortunately, we found it as a courtesy inspection to the customer. Here are some of the things that could have happened if they had waited months or even years for their next outage or had not done anything at all.

A failure of the cooler media and the release of the accumulated scale deposits within of this magnitude it is almost certain the turbine would have ingested some of it, in the turbine world this is called foreign object damage (FOD). This type of FOD would damage the profile of the compressor blades and to the extreme, could cause a blade to liberate. ?A turbine compressor may have 14 stages of blades so if you damage one, it is likely you will take out other stages of the compressor, leading to complete turbine failure. With turbines costing upwards to 100,000 USD, this would not be a very happy situation.

Or, if an object hits the leading edge of a blade, it will cause erosion, making flow through the compressor much less efficient. Reducing its effect and making the compressor less efficient, ultimately reducing power output known as non-recoverable degradation.?This degradation in performance is considered permanent unless the blade or rotor is replaced which is likely only to take place at a major outage, it doesn’t happen overnight!

Most hidden problems, however, are more subtle. Filters accumulate dust and particles over time, which increases differential pressure. Every inch increase in differential pressure reduces megawatt output by 0.4%. and performance slowly degrades. The solution is often just to replace or clean it, but, of course, that requires knowing that it needs service.

Frequent inspections could be integrated with any of the maintenance strategies illustrated in Figure 2 and your approach may vary with the age of your turbine. If it is more than two years old and running at full cycle, you might want to think about a visit to the filter house for condition monitoring or performance checks.?Checking the cleanliness of the water going to the evaporation cooler, for example, might have thwarted the contamination build-up that caused the damage shown in Figure 1. Readings from a differential pressure gauge might give early warnings that differential pressure over the fouling media is creeping up. Monitoring such filtration-related indicators can help you keep your systems operating at peak performance.

If you have an older turbine that is running less frequently, you might not want to invest as much in fine performance tuning; a time-based approach might be more appropriate. Filter testing and analysis could help set that time interval. Testing during the spring outage, for example, could help determine whether the filters would be adequate until the fall outage, or could help revise whatever time intervals you are using. This type of testing can also help plan for budgeting and even give the return on investment (ROI) needed when requesting fund approval.?Turbine vendors will provide guidance in maintenance intervals for filtration doesn’t always make the list.

Figure 3 shows the impact of having a maintenance program on your filtration system.?For example, keeping on top of filter replacements and evaporative cooler media changes means the performance gains and reliability achieved easily pay for themselves when translated into dollars.

As a general rule, the more care you take of your filtration system, the more consistent your megawatt output and heat rate will be, the lower the risk of failure and the lower the potential for more serious damage. And when it comes to determining just when to replace them remember what baseball legend Yogi Berra said: “You can observe a lot by just watching.”

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