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Air Filtration in Gas Turbine Applications
NAFA Technical Seminar Kent Mertz Filtration Group April 20, 2005
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Overview Basic components of gas turbine engine
Different types of gas turbines Importance of air filtration for gas turbines Static air filtration systems Pulse air filtration systems Factors affecting filter selection
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Components of Gas Turbine Engine
Three basic components Compressor Combustor Turbines
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Gas Turbine Schematic Output Shaft Turbines Combustor Compressor
Exhaust
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Turbofan
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Different Categories of Industrial Gas Turbines
Large Industrial Units > 75 MW output GE, ABB, Siemens-Westinghouse, several others Aeroderivatives < 50 MW output Shaft output version of aircraft engines GE, Rolls-Royce, Pratt & Whitney Microturbines
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Different Categories of Industrial Gas Turbines
Differ by hours of operation Base Load – near continuous operation Intermediate Load – operation for approximately ½ of the year Peak Load – operation dictated by demand
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Importance of Air Filtration
Protect rotor and stator blades of compressor from damage Keep compressor efficiency high Keep cooling air passages open Maintain gas turbine output performance
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Types of Engine Damage Caused by Improper Filtration
Foreign Object Damage (FOD) Erosion Fouling Corrosion
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Foreign Object Damage (FOD)
Most catastrophic of all types of damage Caused by large objects Easily filterable Usually a result of poor maintenance
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Erosion Caused by particles ~ 5 mm and greater in size
Particles blunt leading edges of compressor blades, decreasing efficiency Thinning of blades, which increases thermal fatigue Requires a good level of filtration for protection
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Fouling Most common reason for gas turbine performance loss
~70% off all gas turbine performance losses attributed to compressor fouling* Caused by smoke, oil vapors, and various other contaminants Particles adhere to rotor and stator blades, decreasing compressor efficiency Particles are in the sub-micron to 5 mm size range Requires a high level of filtration for protection * According to International Gas Turbine Institute
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Corrosion Caused by solvated salts suspended in an air stream
Salts can oxidize compressor blades Occurs mainly in offshore and coastal applications Also occurs in turbine section with the presence of sulfur in fuel source
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Particle Sizes of Common Contaminants
Fouling Erosion Sand and Road Dust Smog Fog Mist Viruses Lung Damaging Dust Pollens Oil Smoke Plant Spores Tobacco Smoke Coal Dust Bacteria Human Hair Notes: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
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Most Penetrating Particle Size
Sand and Road Dust Smog Fog Mist Viruses Lung Damaging Dust Pollens Oil Smoke Plant Spores Tobacco Smoke Coal Dust Bacteria Human Hair Fouling Erosion
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Particle Concentrations of Different Regions
Particle Concentration (mg/m3) Particle Size Range (mm) Rural area Urban Coastal 0.01-7 Offshore 0.1-10 Desert Tropical Arctic 1-15
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Inlet Air House Schematic
1 3 4 5 6 7 8 2 Weather Hood Bird Screen Filtration – Stage #1 Bypass Doors Evaporative Cooling Unit Filtration – Stage #2 Silencer 1 2 3 4 5 6 7 8 Trash Screen
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Types of Inlet Air Filtration Systems
Static Uses a barrier style or pocket style filter Elements are usually subjected to air flows between 2000 and 3000 CFM per element Air filter house usually will have multiple sides Pulse Typically uses a canister or cartridge style filter Have many different configurations of each canister Air flow rates between 600 CFM and 900 CFM per element are common
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Static Air Filtration Systems
Advantages Compact design Least number of filter elements Low resistance Ideal for areas with large amounts of hydrocarbon contaminants Disadvantages Filters can become quickly plugged in very high dust concentration environments
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Static Air Filtration Systems
Use barrier style filters Box V-style Pockets Generally have multiple stages of filtration Some units use HEPA final filtration, because of extreme fouling environment Large static inlet manufacturers Braden Pneumafil AAF
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Particle Collection Efficiency Static Filters
Erosion Fouling Sand and Road Dust Smog Fog Mist Viruses Lung Damaging Dust Pollens Oil Smoke Plant Spores Tobacco Smoke Coal Dust Bacteria Human Hair MERV 14 MERV 8
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Pulse Filtration System
Advantages Designed for very high dust concentration environments Longer filter life with heavy dust loads Very effective in desert and arctic areas Disadvantages Higher resistance than barrier filters Lower efficiency than static filters for a given resistance Filter dust cake disrupted with reverse pulsing High number of filter elements
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Pulse Air Filtration System
Most commonly use the cartridge/canister style filter Quite often use a conical/cylinder combination of filters Donaldson is largest producer of this style of filter house Large pulse house manufacturers Donaldson AAF Camfil-Farr
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Particle Collection Efficiency of Canister Filters
Erosion Fouling Sand and Road Dust Smog Fog Mist Viruses Lung Damaging Dust Pollens Oil Smoke Plant Spores Tobacco Smoke Coal Dust Bacteria Human Hair Canister #1 Canister #2 Canister #3
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Some Factors Affecting Filter Selection
Particle collection efficiency Resistance to air flow Performance under turbulent conditions Resistance to high moisture environments Filter life Burst strength Filter rigidity
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Issues to Consider for Filter Selection
Ambient dust concentration Type of dust present in ambient air Seasonal changes in dust concentration Configuration of inlet air house
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Factors Affecting Filter Selection - Efficiency
Balance between efficiency and pressure drop is different for different environments Higher particulate removal results in better heat rate across turbine Higher efficiency products require fewer washing cycles of compressor blades In-line Off-line
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Factors Affecting Filter Selection - Efficiency
Material Costs Cost to produce de-mineralized water - $0.05/gallon Amount of water needed per wash – 500 gallons Material cost per wash - $25 Number of annual washes – 104 Total material cost - $2600
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Factors Affecting Filter Selection - Efficiency
Off-line washing has two separate costs Material cost Lack of production cost Lack of production costs for 30 MW unit 5 hour off-line wash = 150,000 kW*hr of lost power production If electricity is sold for $0.05/kW*hr $7500 in lost production
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Factors Affecting Filter Selection – Pressure Drop
For a given filter efficiency, lower pressure drop leads to increased output Less work for compressor leads to increased efficiency Actual output increase will depend on the specific engine Overall output increase can be between 0.07% and 0.1% for every 0.2”WG reduction in inlet pressure drop
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Summary Gas turbines are very expensive machines that need to be properly maintained Many different factors go into selection of air filters for gas turbines Most times filter selection is restricted by type of housing Proper filter selection can pay dividends to the end user Questions?
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