Filter Bag Performance & Maintenance Best Practices May 2020 Presented by Lonnie Glen & Jeremy Rupp
Key points today • Bag cleaning system problem symptoms • Best maintenance practices • Key operational tips to increase operational life
What is the purpose of the Dust Collection System and Filter Bags specifically? To collect fugitive dust in a central location and safely vent clean air back into the atmosphere, protecting personnel, equipment, the process, and the environment.
Example of a Dust Collection System Dust collection points Baghouse Filter Dust collection ductwork Fan Dust discharge Basic system equipment list: hoods, dampers, ductwork, baghouse & suction fan
Common Terminology
Common Terms • FPM • Measured as Feet per minute • Speed or velocity of air • CFM • Volume or Amount of air typically being moved through the system • Measured as Cubic Feet per Minute • Duct Velocity • How fast the air, dust or product “flies’” through the duct. • Measured in FPM • Grain dust typically has minimum of 3400 FPM. Wheat typically conveys at 4200 FPM
Common Terms • Static Pressure • Pressure used to overcome the resistance to flow or…. • The amount of resistance of friction (including the hood, ducting, product and all other components) • Usually the longest run, but not always • Velocity Pressure • Pressure required to accelerate the flowing mass from rest to its’ existing velocity or….. • Air traveling at a given velocity or…. • Way to measure velocity • Area • Measurement of the inside of a duct • Measured in square feet
Common Terms • Air-to-Cloth Ratio • Establishes design capacity of a baghouse filter • Ratio between the total amount of CFM and total area of the filter bags • 15,000 CFM / 1,555 sq ft of filter area = 9.65:1 Air-to-Cloth Ratio • Rule of Thumb • 7-10:1 for Elevator, Cleaning House, and General Suction • 7:1 for Secondary Collectors and High Humidity Air Systems • 5:1 for Filter/Receiver, Centro-Vacs, and Bin Vents • 3-5:1 for filters using pleated cartridges • Can Velocity • Velocity measured inside the filter (in open space below the bags) CAN VELOCITY • Interstitial Velocity • Velocity measured inside the filter (between the filter bags) INTERSTITIAL VELOCITY
Fans and Fan Curves
Fans Centrifugal Fan Material handling (radial blade) - product or dust in air • stream High air volume low static pressure (normally <20” w.c.) • General suction/Dust control • Air volume reduces as static pressure increases (lazy) •
DESIGN Performance: Volume: 5,400 CFM Static: 26” WC Speed 3,500 RPM Power: 41 BHP
ACTUAL Performance: (CLEAN bags) Volume: 6,200 CFM Static: 21” WC Speed 3,500 RPM Power: 46 BHP Result: OVERAMP ACTUAL Performance: (DIRTY bags) Volume: 4,800 CFM Static: 29” WC Speed 3,500 RPM Power: 37 BHP Result: Need to make change to balance
Brings us back to a complete system Dust collection points Baghouse Filter Dust collection ductwork Fan Dust discharge Basic system equipment list: hoods, dampers, ductwork, baghouse & suction fan
Typical Baghouse Filter Controls
Baghouse Cleaning Systems • Pressure gauge • Reads air tank pressure • Push Palm button to read tank pressure • Magnehelic Gauge • Measures Pressure Differential (aka “Delta P”) across baghouse filter bags/media • The difference in static pressure upstream (dirty air side) and downstream (clean air side) of the bags = pressure drop. • Magnehelic gauge mounted to filter, visible to operator. • A “Photohelic” or “Digihelic” gauge can send the signal as a 4-20ma signal to your control system. • Timer Board in Enclosure • Holds the electronic timer board and allows for adjustment for the application
Baghouse Cleaning Systems Problems & Symptoms Confirm settings of controls for bag cleaning “On Demand” The air pressure and timer board regulate frequency, jumper duration, and amplitude of reverse air cleaning of bags. “On” setting “Off” setting adjustment adjustment If pressure, frequency, amplitude settings are too low: • “Dust cake” layer can build up too thick and bags don’t get cleaned, resulting in: • Higher pressure drop • Shortened bag life • Lower than anticipated air volumes in system If pressure, frequency, amplitude settings are too high: • May result in over cleaning of bags: • Causing premature bag failure in the form of rips in seams or holes allowing stack emissions. • May prevent “dust cake” build up on bags utilizing “depth” filtration, resulting in: • Particles allowed to “bleed-through” bags, producing emissions to atmosphere. • Bags blinded over by small particulate imbedding in bags without “dust cake” – resulting in increased pressure drop, reduced air volume, and shortened bag Firing sequence life. wiring • Waste of Energy!
Baghouse Cleaning Systems Basic Settings • Typical default setting • “On” time is 150 milliseconds (ms) • “Off” time is 50 seconds • Adjustments • ADJUST FOR YOUR APPLICATION • Adjust “Off’” time so that pressure can build back up in the blower or compressed air system • Adjust “On” time to provide a better “blast of air to clean the bags better • Adjust regulator pressure to provide a higher “blast” of air • There are Positive & Negatives to all adjustments…..
Baghouse Cleaning System Valve & Solenoid Problems Kice Venturi-Jet Valve
Baghouse Cleaning System Valve & Solenoid Problems Kice Venturi-Jet Valve or any Compressed air system • Bent or broken nipple between solenoid and blast valve • Cracked diaphragm • Missing/broken spring • Solenoid epoxy coil loose or open – (Red Hat missing) • Hose connection to lateral leaking/dried out • No regulator or filter installed ahead of air tank • Moisture in the line • Low bag cleaning pressure When valve operating correctly, will feel slight “puff/blast” of air here when operated
Baghouse Cleaning System Valve & Solenoid Problems Kice Pneu-Jet Valve or any “PD Blower air system
Baghouse Cleaning System Valve & Solenoid Problems Kice Pneu-Jet Valve or any “PD Blower air system • Cracked large or small diaphragm • Worn seat • Broken spring • Solenoid epoxy coil loose or open – (Red Hat missing) • 3” gasket to lateral leaking/dried out • Timer board damaged • PD blower issues When valve operating correctly, will feel slight “puff/blast” of air here when operated
Filter Bags
Filter Bag Media • Selection of proper media plays a major role in filter performance. • Must consider several factors of application: – Operating temperatures – Humidity and moisture levels – Type and size of particulate being handled – Resistance to abrasion, chemicals, moisture, etc. – Filter Air-to-Cloth Ratio – NFPA compliant
Filter Bag Media • Most common media in our industry is singed felted or woven polyester 12- 16 oz./sq. yd. • Kice standard is a 16 oz, singed polyester felt material or 12 oz singed felt Durates material – Function using “Depth Filtration” where a “dust cake” build-up on surface of media filters particulate from airstream. – Limited by A/C ratio of baghouse • High A/C ratio causes decreased bag life and increased pressure drop across filter bags. • High moisture and temperatures may also limit the use of polyester bags.
Filter Bag Media • Media for challenging applications such as where warm and moist air from pneumatic conveying systems is handled: – Polyester bags can be glazed or coated with finishes known as Eggshell or Defender coats – Polypropylene and/or Oleophobic Polyester can be used in high moisture/temperature application – Consider media utilizing “surface filtration” • Demanding applications with conditions such as high moisture, sticky product, vapors from solvents, acids etc. require quality media that uses “Surface Filtration” – Surface filtration occurs totally on media surface so that little or no particulate penetrating media structure. – P-84, Gore-tex, Teflon are a few examples – Very costly, up to 5+ times price of Polyester
Types of Filter Bag Media Reprinted from BWF 04/2002
Reprinted from Donaldson Torit: Ensuring Effective Dust Collection in Challenging Environments by Tom Godbey, Donaldson Torit Senior Application Specialist
Standard Filter Bags versus Pleated Filter Bags PROS: • Pleated filter bags increase filter media area (2-3X) • Common for 25-45 pleats • Require less compressed air pressure for cleaning (60-90 PSIG) • Can reduce overall heights for new applications • Decreases “can” velocity (not interstitial velocity) in replacement applications (due to shorter height) • Typically FDA “Food Safe” compliant materials • Sewn in grounding wire CONS: • Requires lower air-to-cloth ratio (typically 3-5:1) • Can clog in between the pleats (Free flow design helps prevent this) • Air Pressure is usually not changed and can cause pleat damage • Dust/product entrapment • More expensive to replace
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