Air Filtration in Gas Turbine Applications NAFA Technical Seminar Kent Mertz Filtration Group April 20, 2005

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

Components of Gas Turbine Engine Three basic components Compressor Combustor Turbines

Gas Turbine Schematic Output Shaft Turbines Combustor Compressor Exhaust

Turbofan

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

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

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

Types of Engine Damage Caused by Improper Filtration Foreign Object Damage (FOD) Erosion Fouling Corrosion

Foreign Object Damage (FOD) Most catastrophic of all types of damage Caused by large objects Easily filterable Usually a result of poor maintenance

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

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

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

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: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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

Particle Concentrations of Different Regions Particle Concentration (mg/m3) Particle Size Range (mm) Rural area 0.02-10 0.01-30 Urban 0.05-0.50 0.01-10 Coastal 0.01-0.1 0.01-7 Offshore 0.1-10 0.3-100 Desert 0.1-700 Tropical Arctic 0.01-0.25 1-15

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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?