I’ve been communicating a lot about degradation and fouling these past few months, but a recent discussion with a company representative offering Gas Turbine (GT) upgrades at one of the fairs I visited lately really gave me a new aspect to degradation particularly.
“We don’t care about degradation when selling an upgrade, it’s just more business for us in the future” was essentially his message. We talked a little more and it became clearer than ever that OEM´s don’t really regard the inlet filtration upgrades as an improvement to GT’s.
OEM´s don’t regard the inlet filtration upgrades as an improvement to GT’s.
But if you, as a GT plant owner, are paying up to a million euro to get a couple of your first rows coated with some space-age anti-fouling material to gain a few percentage points, you are definitely tackling the problem from the wrong angle. You may gain a higher output, but your machine is definitely NOT protected, even with the latest state of the art compressor blade coating against fouling.
Let´s look at other fouling mechanisms than the obvious pitting damages and loss of aerodynamic performance to the first compressor blade rows. It is true that after the particles have gone past the state-of-the-art coated blades they are typically not causing as much deposits or pitting on the blades to come.
Does this mean your performance is protected?
NO! – after the first blade row,s the tiny dust particles will enter the cooling air channels designed to lead the cooling air to the GT hot gas path blades. Once the accumulated particles block the cooling air, it doesn’t matter what thermo-barrier coating you have on your blades of the hot gas path, those blades will be seriously damaged and you will be looking at a long overhaul, changing more than just a few blades.
That is if you were lucky...
In the worst case, the overheating damages will require a partial or total rebuild of your machine. While compressor blade fouling is slowly eating up your GT performance, the hot gas path cooling air blockage will increase your blade temperature, limiting your GT loading and potentially leading to total GT destruction when the cooling air flow reduces so coating of the blades is not really protecting your machine.
While compressor blade fouling is slowly eating up your GT performance, the hot gas path cooling air blockage will lead to total GT destruction.
Even if the coating of the compressor blades managed to improve your performance by 2% and you are running now at 102% of your original performance, you could still be experiencing an off-line washing gain of 3% instead of the 5% you used to have before having your first compressor blades coated. Naturally, 102% x 0,97 is still more than your original 100% x 0,95 so you may think you did well on your upgrade.
But, is your average output higher than before the upgrade after a few months of operation? Or are you losing the upgrade benefits to fouling?
But, is your average output higher than before the upgrade after a few months of operation or are you losing the upgrade benefits to fouling?
Even if the GT upgrade company delivered on their promise and your output was increased with the space-age supercoating, you forgot to protect your performance. Coating the compressor and turbine blades is treating the symptoms but not curing the root cause - it´s the tiny, microscopic particles that will eventually take down your multi-million-euro, money-making machine, unless you upgrade your GT inlet air filtration system too.
Coating the compressor and turbine blades is treating the symptoms but not curing the root cause.
And not to mention that the power gain during off-line washing shouldn´t happen – off-line washing power gain is a clear indication that your plant is NOT optimized and you are in fact losing money.
Author: Pertti Sundberg