With the industry’s rapid development and upgrading, the energy market demand continues to grow. At the same time, due to the extensive use of renewable energy, gas turbines have shown huge market potential in distributed energy supply, pressurization stations, industrial power generation, and other fields.
At the same time, I have found that the demand for gas turbine inlet filters has been increasing in recent years, which means that inlet filtration is essential for gas turbine components.
After being involved in dozens of gas turbine filtration projects worldwide, I have compiled some key points about gas turbine inlet filtration and written this article.
Point 1: How important is clean air to gas turbines?
A gas turbine’s performance and operational reliability are closely related to the quality and cleanliness of the air entering the gas turbine.
Therefore, to ensure the unit’s high efficiency and reliable operation, good air inlet filters must be configured to filter the air entering the unit and filter out impurities in the air.
The regular operation of the gas turbine is based on qualified air. In the real natural environment, the impurities in the air are also diverse in different regions.
After these impurities enter the gas turbine, they will cause scaling (less than 2 μm) of the flow part of the compressor. Fine particles or viscous particles such as water and oil in the air enter the interior of the gas turbine and adhere to the surface of the compressor and turbine blades, reducing the rotational smoothness of the blade surfaces and causing the compressor flow area to decrease.
Particles of 5~10 μm or larger enter the interior of the gas turbine, causing impact and wear on the metal surface inside the flow channel, reducing the smoothness and fatigue strength of the metal surface, and even causing damage to the blades and reduction in the output power of the gas turbine.
Point 2: How does a poor air filter impact a gas turbine?
Gas turbine fouling, corrosion, and erosion problems are related to unclean air quality caused by poor air filters.
Scale buildup can be caused by natural plant matter or solid particles in the air. It can also be caused by artificial air pollutant hazards, such as soot or hydrocarbon fumes, which can deposit on turbine blades, creating a sticky substance.
Erosion
When particulate matter’s equivalent diameter is greater than 10 µm, its mass is enough to cause irreversible wear to internal rotating parts. Their hardness, speed, and concentration in the air will gradually erode the leaves over time.
These particles can be easily removed with an inertial air filter or pre-filter. Particles with an equivalent diameter of 10 µm are considered massive particles, but as a comparison, the human eye can typically only see particles > 40 µm in diameter. Erosion can cause irreversible damage to a gas turbine but can be easily avoided with a qualified air filter.
Scaling
Contaminants with an equivalent diameter of less than 5 µm do not have enough mass kinetic energy to cause impact wear on the blades, but they can impact the surfaces of rotating and static components and deposit within a short period, causing the blade profile to deviate from its ideal shape. This is commonly referred to as gas turbine fouling and is a common problem.
However, the effects of dirt can be significant, and although cleaning with detergent and water can restore efficiency, combustion efficiency, and power output continue to slowly but steadily deteriorate.
However, the effects of dirt can be significant, and although cleaning with detergent and water can restore efficiency, combustion efficiency, and power output continue to slowly but steadily deteriorate.
On the other hand, small particles that cause gas turbine fouling can also clog the cooling holes in the blades, reducing cooling efficiency, increasing the operating temperature of components, and shortening the life of the gas turbine.
Corrosion
If salts in the air pass through the filtration system, corrosion can occur in the low-pressure and hot-pressure components of the gas turbine. This is a chemical process that is generally independent of particle size. Chemical corrosion reactions will occur between salt and different types of metals in the presence of moisture.
Gas hot corrosion
Gas hot corrosion is of particular concern, especially in coastal and offshore areas, where sodium chloride is ubiquitous in the form of dry particles and aqueous solutions. When mixed with sour (sulfur-containing) fuels, it can cause accelerated degradation of critical hot section components of the gas turbine.
A good quality air filter can filter out many pollutants and particles during the air intake stage, ensuring the regular operation and life of the gas turbine.
Ponit3:What is the process of gas turbine intake air filtration?
During the operation of the air intake system, the compressor inhales air from the atmosphere through the filter chamber. The filter chamber includes a weather cover and anti-bird net, folding plate defogging, frame-type primary filtration, and pulse filtration.
The clean air passes through the clean air chamber, through the muffler piece, and then through the transition duct and the air inlet end to reach the compressor air inlet.
pre-filter
The anti-bird net made of stainless steel wire mesh is placed at the front of the air intake system to prevent flying birds from entering. It can also block larger floating objects in the air, such as leaves or other foreign objects.
A folding plate demister is installed behind the anti-bird net. When the air is diverted during the operation of the folding plate demister, larger dust particles and mist particles hit the folding plate due to inertia, effectively removing particle impurities above 15 μm. The pocket filter at the back performs primary air filtration, reaching the M5 level, and has some dehumidification effect.
Pulse backflush cartridge filter
The air then enters the pulse filter cartridge.
Pressure difference measuring devices are on both sides of the pulse filter cartridge. When the pulse filter cartridge accumulates a certain amount of dust and the pressure difference reaches the set value, the PLC control automatically opens the relevant electromagnetic pulse valve. The compressed air flow is ejected through a special nozzle; backflushing from the inside of the filter cartridge to the outside will blow off the dust accumulated on the outer surface of the filter cartridge, thereby completing the self-cleaning process.
The pulse backflush module consists of 4 vertical backflush filter modules; each module is equipped with 68 sets of backflush filter cartridges. The APU compressed air system provides the air source for backflushing.
At this point, the air filtration stage is completed, and the clean air flows into the clean air chamber.
After the clean air chamber, the clean air flows through the muffler elbow, transition duct, expansion joint, and air inlet end.
Finally, it enters the compressor inlet of the gas turbine.
Point 4 What are the air filter standards for gas turbine air intake systems?
Determine the filter element’s key performance parameters based on the gas turbine’s operating characteristics and regional climate conditions. The core of the filtration system is the air filter (filter cartridge). The general industrial ventilation filter testing standards include the European standard EN779 and the American standard ASHRAES2.2.
According to the “Gas Turbine Intake Filtration System Guidelines” jointly issued by the U.S. Gas Machinery Council (GMRC) and the Southwest Design Institute (SWRI), the gas turbine air inlet filter refers to the EN779 standard.
According to the “Gas Turbine Air Inlet System Selection Guide” jointly issued by the American Natural Gas Machinery Equipment Council and the Southwest Design Institute, air filters for gas turbines should be F7 or above.
Using the F7 filter, the output of the gas turbine will be reduced by about 7-9%; using the F9 will be reduced by about 2-3%; and using the E12 filter, the output of the gas turbine will only be reduced by 1% at most.
Point5: Air intake cartridge filter
The filter cartridge is the core component of the entire intake filtration and is responsible for filtering fine particles.
The filter cartridge is installed in the air intake system as the primary filter element. It adopts a combined structure of cylindrical filter cartridges and conical filter cartridges. It is fixed to the bracket seat through the end fixed point. The joint surface is designed with an elastic sealing gasket to eliminate short circuits in the air path.
When the cartridge filter is over-pressured, or the relative humidity is ≥80% due to a large number of particles gathering during the operation of the filter (ice blockage or wet blockage may occur when the ambient temperature is low), the control system automatically performs a pulse backflush.
3 backflush modes
When the unit is running normally, the pulse backflush system performs automatic backflush according to the following three conditions:
- In clock timing mode, the control system performs a backflush according to the timing time.
- In automatic mode, when the humidity is ≥80%, the control system automatically performs a backflush.
- In automatic mode, when 96TF-1≥55mmH2O, the control system automatically performs a backflush.
Point 6: How to choose a gas turbine air inlet filtration system?
Air pollution sources are mainly divided into natural sources and industrial pollution. The particles of natural sources have a wide range, generally between 0.1 and 0.5 μm, and the particle composition has obvious regional characteristics;
Industrial pollution mainly comes from waste gas emissions from industrial activities. In addition to dust, metals such as sodium, potassium, lead, and vanadium have high content. The particle diameter is generally 2 to 3 μm or less, which is difficult to filter.
When selecting a gas turbine site, if the concentration of metals in the working environment is less than 0.01mg/kg, its impact on the gas turbine is much smaller than particle damage, and it can be ignored;
Otherwise, the filtration precision standard of the air filter can be appropriately increased, and the vertical gas turbine air intake system using a square filter is recommended.
Secondly, in areas with regular wind direction, the air intake system should be installed in the gas turbine intake direction to achieve a good filtration effect; especially the vertical air intake system will reduce the air filter load to a great extent.
Extra: Some aspects to pay attention to when operating air intake filtration
1. Note the changes in gas turbine output, efficiency, and exhaust gas temperature after the gas turbine air inlet filter pressure difference increases.
2. In rainy weather, due to the high air humidity, pay attention to the humidity changes after starting pulse backflush when the humidity reaches.
3. To achieve a good backflush effect, the backflush air source pressure should be above 0.5MPa.
4. If the control system performs backflush due to high differential pressure during the gas turbine operation, the change in differential pressure after backflush should be observed. If the backflush effect is not apparent, the air inlet filter cartridge should be inspected after shutdown to see if dust accumulates on the filter element. Clumping makes it difficult to blow clean when the humidity is high.
Last Thought
The gas turbine air intake system is a large and essential device. Likewise, its costs are not cheap either.
As a professional and leading filter cartridge and air filter manufacturer, I have profound experience in design and production. I have also helped many owners finish their projects.
In addition, our delivery is speedy. Usually, it only takes 2-4 weeks to complete the production of 2,000 filter cartridges. Working with us, the only thing you get is fast and good.
