Coalescher – Blast from the past
Combustion technology in Gas Turbines has had vast improvements over time with latest models reaching to new record efficiencies. At the same time the Filtration technology has improved to protect the high efficiency of the pants plants, but rarely do we see a new plant equipped with proper filtration, and therefore the peak efficiency is lost to Degradation fairly quick after the start up
One example of the ancient filtration technology are the Coaleshers and Droplet eliminators, which had a crucial role of reducing (reducing, not eliminating!) the moisture content of inlet air back in the days when filters were primarily made out of Cellulose based materials. Cellulose is an organic material easily available with affordable cost – but just like all paper based products Cellulose is absorbing moisture. As cellulose absorbs moisture it also swells causing the air flow to reduce and dp to shoot up. Cellulose is also a weak material and does not recover from swelling causing deformations of the pleats so the life time of Cellulose filters is often short.
Coaleschers are needed only to protect Cellulose filters, not hydrophobic filters
When Synthetic Hydrophobic materials were introduced to Filtration the need of Coaleshers was eliminated as the Hydrophobic material was taking care of the moisture elimination – but in most cases the Coaleshers survived in the filtration systems as a relic “that has always been there”.
Typical coalesher is a set of guide vanes or porous material that is basically designed to divert the heavy droplets from the air steam by colliding the droplets to a surfaces to be drained with gravity. Coaleshers are not effective against smaller droplets or particles but especially the porous Coaleshers may have dust accumulated to the pores causing problems during the rainy season.
In a recent case there was a porous Coalesher placed in front of the fine filters in a high dust (sand) and high humidity area. In a dry days the Coalesher pores had caught some of the larger sand particles while most of the airborne particles were going to the the surface of the cartridge. Dry season is followed by a rainy season and on one day the dp started to spike above GT alarm limits causing GT power to be dropped – but actions or even the pulse type filters didn’t save the GT from emergency shut down due to inlet dp.
Analysis of the event is putting all blame on the Coaleshers – the pores were filled with sand during dry season and rainy season added water to the sand transforming sand into mud. Mud blocked the pores until the pressure difference over the Coaleshers blasted the sticky mud onto the Fine filters. Even the best pulse filters cannot survive such mud blasting so GT emergency shut down was unavoidable.
But this event could have been easily avoided if the Plant would have upgraded the whole filtration and not looking just on the cartridges.
With modern Synthetic Hydrophobic Prefilters like PanelS-G4-SP available there is NO need to keep the costly, high maintenance unnecessary dp items like Coaleshers/Droplet eliminators in the filtration setup. By replacing the coaleshers with Synthtic Hydrophobic Prefilters we are able to combine the proper pre-filtration and coalesher into one filtration stage saving dp and in most cases also cost, but foremost we are once again able to protect the GT performance against unnecessary and harmfull emergency shut downs!
Just like you have a GT specialist come by and proposing the latest improvements to your GT - the single most expensive equipment in your plant - don′t you think it would be the time to have a Filtration expert over to have a closer look at what improvements there are available in Filtration that could benefit your plant and would provide up-to-date Protection for the performance of your Combustion Turbine!
If you haven′t had your filtration setup looked at since the start-up you can always reach out to Your Friendly Filter Guy!