A major North African pipeline is a typical case of a pulse installation facing seasonal high humidity and high concentrations of coarse dust. The pipeline has a total of twenty 30 MW engines, half of which are inland and equipped with pulse filtration systems.
These turbines were originally equipped with M6/MERV 16 pulse filters and they faced average relative humidity of over 50%. Dust is typical of the area and contains mainly sand, both in calcium and silicon form, combustion particles and some salts. After a major audit done by a third party inspection, the operator found dust in the gas turbines and decided to upgrade the inlet filtration efficiency.
Single stage systems have typically offered lower filtration efficiency, and combined with moisture, they are more likely to suffer from particle re-entrainment, with the particles dissolving in ambient humidity and passing through the media to the clean side.
Changing to a higher efficiency filter, minimally F9 per EN779:20121, and choosing media with hydrophobic properties can solve these issues. Most operators understand the added value of higher efficiency filtration but many fear that raising efficiency might negatively impact the filter life and increase maintenance needs for filter replacement.
The Solution
Camfil proposed the installation of the CamPulse HemiPleatTM GTC as an upgrade. The GTC, an F9/MERV 16 cartridge with depth loading properties has proven itself to be a product of choice when both large quantities of dust and humidity are present.
The filters were installed in the spring of 2012 and, two years later, they now have over 3500 hours of operation. The gas turbine suffered no apparent power degradation and filter pressure drop curve showed impressive stability. Averaging at 181 Pa
(0.73" w.g.), the filter is still performing like new, promising many more years of service (see Figure 1).
To confirm the engine performance data, one filter was sent for testing in an EN779:2012 test rig. The results confirmed the filters were performing above expectation concerning the efficiency; reaching 92.5% on 0.4 microns, a very strong F9 (minimal efficiency needs to be 70% to qualify as an F9), providing excellent engine protection.
Impact
Pressure drop (DP) and efficiency have an impact on the turbine power output. Pressure drop is directly linked to filter life, but high DP also negatively affects power output - generally, 1" of DP (250 Pa) reduces turbine power output by 0.375% and increases heat rate by 0.125% - but most of all, pressure drop spikes can have a negative impact by tripping the turbine and forcing an outage for filter replacement.
When filtration efficiency is inadequate, the turbine is subject to fouling and corrosion. There is also a risk of plugging the cooling holes which can cause an increase in temperature and shorten a turbine blade's life.
Low pressure drop should never be achieved at the expense of high efficiency filtration, but rather, with good filter construction and the right media. Combining both low DP and high efficiency will provide operators with:
- Less unplanned outages
- Lower maintenance cost
- More engine availability
- Higher power output
1 F9 EN779:2012 classification: Minimal efficiency rating at 70% and 95% average efficiency at 0.4 µm.
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