Imagine a misty Sunday evening, when the operators in the control room of a gas turbine room are just performing a shift change, changing the information on the daily events, no-one really paying attention to the monitors when it happens: compressor efficiency suddenly drops several percentage points and the control system is unexpectedly requesting an online-washing.
“Great start to the night, hopefully this is all the excitement we get tonight” thinks the night shift leader and without further consideration of the event gives the command to the GT operator to perform the on-line washing to recover the lost efficiency.
On Monday morning the operation engineer is going through the event log of the weekend and notices the on-line washing. A quick check of plant parameters shows that compressor efficiency is lagging a bit after the washing, but there´s still plenty of margin before an off-line washing is needed and the pressure drop of the filter house looks to be within the range. “Odd incident, but probably nothing to be alarmed about,” muses the operation engineer. “The peak in the dp could just be due to heavy fog last evening?” The operations manager tells himself that it looks fine now, and that on-line washing must have taken care of whatever the problem was. He continues his daily chores not noticing the peak in the filter house dp just before the drop of the compressor efficiency.
Off-line washing during operational regime is a serious production loss
During the next few weeks the compressor’s efficiency continues to decrease quicker than normally expected and eventually the plant needs to shut down to perform an off-line washing of the compressor to recover the lost efficiency. As the dp of the filter house is still not showing any alarming values no-one bothers to check the conditions of the filters as the plant has to be back on-line as soon as possible.
But the irreversible damage to the filters has already been done.
The problem here is Leaching, and it is a problem that doesn’t need to exist at all, if you have the right air filters already installed.
Leaching damages cannot be repaired or visually detected.
Leaching will wash dirt captured in filters to gas turbine compressors causing the sudden loss of compressor efficiency. This efficiency loss is only partially recovered by on-Line washing. Leaching also stretches filter material, causing damage inside the filtration material, and reducing the filtration effect. The reduced filtration effect can result in increased dust pass through filters, which can cause increased fouling of compressors.
Leaching can also cause lower than expected dp over the filters, which makes the damages even more difficult to detect. Leaching damages cannot be repaired so the only solution is to replace all of the filters if Leaching has happened.
When GT plant managers select a filter with higher tensile strength, leaching can be avoided. Any additional off-line washing needed during operational regime is a serious production loss worth several times the added cost of more robust filters.
If you suspect your plant may have suffered leaching damage or you want to protect yourself the next time you are changing your filters, I am more than happy to tell you more about Eagle Filters GT air filter solutions.
Author: Pertti Sundberg