Air Filtration in Gas Turbine Applications NAFA Technical

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 Exhaust Combustor Compressor

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 Road Dust Smog Fog Bacteria Viruses Mist Human Hair Pollens Lung Damaging Dust Oil Smoke Tobacco Smoke Plant Spores Coal Dust

Most Penetrating Particle Size Erosion Fouling Sand Road Dust Smog Fog Bacteria Viruses Mist Human Hair Pollens Lung Damaging Dust Oil Smoke Tobacco Smoke Plant Spores Coal Dust

Particle Concentrations of Different Regions Region Rural area Particle Concentration (mg/m 3) Particle Size Range (mm) 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 0. 3 -100 Tropical 0. 02 -10 0. 01 -30 0. 01 -0. 25 1 -15 Arctic

Inlet Air House Schematic 1 2 3 4 5 6 Weather Hood Bird Screen Evaporative Cooling Unit Filtration – Stage #1 7 5 6 7 8 8 Filtration – Stage #2 Trash Screen Bypass Doors Silencer

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 Fouling Erosion Sand Road Dust Smog Fog Bacteria Viruses Mist Human Hair Pollens Lung Damaging Dust Oil Smoke Tobacco Smoke Plant Spores Coal Dust 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 Fouling Erosion Sand Road Dust Smog Fog Bacteria Viruses Mist Human Hair Pollens Lung Damaging Dust Oil Smoke Tobacco Smoke Plant Spores Coal Dust 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 costs for 30 MW unit 5 hour off-line wash = 150, 000 k. W*hr of lost power production If electricity is sold for $0. 05/k. W*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?