Filtration FAQ

We cannot define our knowledge as “exact” because it would not be a precise answer to your question. However, we have a general knowledge on contaminants in various gas turbine environments including marine, desert, rural, off-shore, residential, etc. As you know, gas turbine environments are extremely varied. Particle concentration, particle size distribution, and chemical composition depend on geographic locations, weather conditions, season of the year, location of the air intake, and industrial activities. Therefore, detailed evaluation of gas turbine specific environmental parameters is usually needed. In the past we detected, for instance, the following components in both a rural, forested Massachusetts and a rural Nevada environment: aluminum, silicon, potassium, calcium, barium, copper and zinc. Particle analysis detected aluminum, silicon, potassium, calcium, barium, iron, copper, and zinc. Particle analysis also detected a combination of aluminum, silicon, chlorine, potassium, calcium, barium, copper and zinc. Combinations of Al, Si, K, Ca, Ba, Fe, Cu and Zn or Al, Si, K, Ca, Ba, Cu and Zn were also detected with particle analysis. In general, contaminants are formed by a mixture of minerals, organics, and water. In some industrial areas air contaminants may contain 10-85% soot. Soot particles are composed of impure black carbon with oily compounds. They tend to form aggregates on filter media surfaces clogging some types of filters.

As stated above, the accurate data on gas turbine environment can be obtained by isokinetic air sampling at the gas turbine location. In general, the size of atmospheric particles can be described by a bi-modal distribution. The fine mode contains particles in the range of .1 – 2.5 µm, while the coarse mode is in the range of 2.5 – 30 µm. However, the size distribution of dusts entering the air intake may be different. In some areas, particle size distribution is tri-modal with some particles in the nanometer range. However, the nanoparticle mode is unstable. Because the settling velocity of large particles is high (the settling velocity of a 100 µm particle of AC coarse test dust is 80 cm/s), particles larger than 20 µm are rarely suspended in the air (Morton, 1970). In other words, large, dense particles suspended in the air by moving vehicles, the wind, or emitted by industrial chimneys will settle rapidly. In general, particle sizes range from approximately .002 – 100 µm. However, only particles with sizes smaller than approximately 10 µm remain suspended in air for a long time. Large, dense particles generated by mechanical action or re-suspended by wind will settle rapidly. However, these heavy particles may enter the filter intake when it is located close to the dust source or the dust is carried by a strong wind. Some contaminants, like insects, seeds, fragments of grass, leaves, pollens, and other vegetative debris are very large. Although they can be removed by inefficient filters, they may clog filter inlets. Mineral and organic particles and their aggregates found at filter inlets may be larger than 100 µm.

Example: Dust Concentration in Various Environments (mg/m3)

The efficiency of fine filters is greater than 99.99% when using the gravimetric method. Therefore, no more than .01% of particles penetrate the filter and get through to the turbine. However, the penetration depends on the inlet and filter design. For the standard T-60 and T-70 filter lines, we have both barrier and pulse type filters, which use different types of filter elements. The standard barrier (non-pulse) filter element has an average ASHRAE atmospheric dust spot efficiency of 80-85% (EU7 rating). This corresponds to approximately 99+% removal of particles 3 microns in diameter and larger. The standard pulse type filter element has an average ASHRAE atmospheric dust spot efficiency of 90-95% (EU8 rating), which corresponds to approximately 99+% removal of particles 2 microns and larger.

Since the dust distribution and its physical and chemical properties depend upon geographical location, environmental conditions, and because the segregation of particles can occur prior to the air inlet, there is no universal data that can describe real field conditions in all areas under all environmental conditions. Claims to the contrary should be met with skepticism. However, knowing the that the density of air under standard conditions is approximately 1.2 kg/m3 (1,200,000 mg/m3), and knowing real (measured) particle mass concentration of every chemical component at the gas turbine site in mg/m3, a simple algebraic calculation can provide the required data in ppm.

Universal is capable of measuring particle gravimetric and number concentration at any location in the world. Our isokinetic sampling probes can be connected to an absolute filter sampler or to a particle counter. The probes can be placed in the filter influent and effluent.

The following data is needed: particle concentration, particle size distribution, and chemical composition of air contaminants. Based on this data, we will recommend a filter to minimize not only the corrosive wear but also other types of wear cause by particles including erosion, friction, etc.

We have extensive experience in that area. These photos show one of our available field samplers: