filter bag performance & maintenance best practices · • best maintenance practices • key...

Filter Bag Performance & Maintenance

Best PracticesMay 2020Presented by Lonnie Glen & Jeremy Rupp

• Bag cleaning system problem symptoms

• Best maintenance practices

• Key operational tips to increase operational life

Key points today

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.

What is the purpose of the Dust Collection System and Filter Bags specifically?

Dust collection points

Dust discharge

Fan

Baghouse Filter

Dust collection ductwork

Basic system equipment list: hoods, dampers, ductwork, baghouse & suction fan

Example of a Dust Collection System

Common Terminology

• 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

Common Terms

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 CFMStatic: 26” WC

Speed 3,500 RPMPower: 41 BHP

ACTUAL Performance:(CLEAN bags)



Result: OVERAMP

ACTUAL Performance:(DIRTY bags)



Result: Need to make change to balance

Dust collection points

Dust discharge

Fan

Baghouse Filter

Dust collection ductwork

Basic system equipment list: hoods, dampers, ductwork, baghouse & suction fan

Brings us back to a complete system

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

Confirm settings of controls for bag cleaningThe air pressure and timer board regulate frequency, duration, and amplitude of reverse air cleaning of bags.

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 life.

• Waste of Energy!

Baghouse Cleaning Systems Problems & Symptoms

“On” settingadjustment

“Off” settingadjustment

Firing sequence wiring

“On Demand”jumper

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 ProblemsKice Venturi-Jet Valve

Baghouse Cleaning System Valve & Solenoid ProblemsKice 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 ProblemsKice Pneu-Jet Valve or any “PD Blower air system

Baghouse Cleaning System Valve & Solenoid ProblemsKice 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

• 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

Filter Bag Media

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

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

Standard Filter Bags versus Pleated Filter Bags

Standard Filter Bags versus Pleated Filter Bags

“TL” Top Load

“BL463” Bottom Load

Area comparison (sq. ft of filter media):• 10’ standard Kice filter bag: 11.78 sq. ft.• 2m (6.5’) 45 pleat Kice pleated filter bag: 35 sq. ft.

Poor Baghouse Performance – Bag Media Issues• Premature increase in pressure drop, short bag life, lower air volumes

thru filter due to incorrect bags for application.– A/C ratio may be acceptable but demanding conditions such as high

temperature, sticky product, fine product, etc. present in airstream.• Switch to higher quality Polyester that is coated, glazed, or treated• Switch to media utilizing “surface” filtration such as Gore Tex, P-84, Teflon.

– Higher A/C ratio and using polyester bags with depth filtration.• Switch to “surface” filtration media, or pleated filter bags.

• Dusting out or Stack emissions to atmosphere.– Worn bag(s) with holes or tears– Bag(s) missing that were not installed or have fallen from tube sheet

connection.– Bags may be ok, but tube sheet is worn or damaged and has crack(s),

hole(s), etc.

Poor Baghouse Performance – Bag Media Issues

• Temperature differentials lead to condensation on interior baghouse surfaces and bags.

– High airstream temperature coming in contact with cool air or equipment.– Airstream moisture content higher than outside ambient air moisture content

(dewpoint reached).– Problems more common in cold climates or high process temperature

applications

Poor Baghouse Performance– High Temperature and/or Moisture Issues

• Baghouse and any exterior ducting, cyclone, fan, etc. should be insulated or protected.

– Spray on foam thermal insulation.– Thermal insulation in sheets– Baghouse surrounded by exterior steel skin building (“doghouse”, “penthouse”,

etc.)• Especially practical for outdoor installation(s).

• Using temperature probes and other controls to change logic to allow internal temperatures to get as close to process temperature as possible

– This reduces the mass of moisture the interior of the filter will see– This take additional engineering and design time

• Be careful about “recycling the air” in these applications to save BTU’s• Use filter bags designed for moisture and heat

– Polypropylene, Oleophobic, Hydrophobic, etc.

Poor Baghouse Performance– High Temperature and/or Moisture Issues

Moisture?Discharge Size?

Dust Load?Interstitial Velocity?

Missing bags

Moisture?Discharge Size?

Dust Load?Interstitial Velocity?

Fine product?Interstitial Velocity?

Moisture?Low cleaning

pressure?

Heavy dust load;Not ran cleaning system

in over a year Clogged hopper; Not running airlock after system

is shut downGood product (Fiber) and

dust building up on internal bars

Maintenance Best Practices

• When changing filter bags change all bags at same time• Periodic cleaning of bags “off-line” when system is down

– Improves bag life and filter performance over time– Keep airlock running to discharge dust

– If bags were blinded over (due to any number of reasons), they can be cleaned to functionality again, or at least recover sufficient performance until they can be changed

Best Practices

Why and When to change filter bags?

• Rule of Thumb on when to change filter bags:– Use 6” w.c. as the indication to change bags.– The Magnehelic gauge reads 0 – 10” w.c. pressure differential

• Pressure drop across the filter bags will be very low and gradually rise from the time of the initial startup until a permanent dust cake builds up on the surface of the bags.

• At that point, the pressure drop should remain constant for the life of the bags.• When enough dust particles have become embedded into the filter media such that they

are unable to be dislodged by the cleaning cycle, the bags become blinded over and the pressure drop begins to rise again.

• The pressure drop will continue to rise until the bags are replaced.• Most filters operate with a pressure drop of between 3”-4” w.c., so designing the system

for a maximum pressure drop of 6” w.c. allows the plant time to schedule a shut down in order to change the filter bags before the design pressure is reached.

• Once the filter bags are changed, the pressure drop will go back down and the cycle begins again.

Filter Bags Installation

Filter Bag Installation – A right way and…..Bags are 2” longer than cages and tuck the extra

2” INSIDE for sealing inside and outside

Filter Bag Installation – every other way• Not tucked in so there is no seal on inside• Not over the bead; will slip off

Top Bag Filter Bag Installation

What is the problem?

Which piece of equipment?

What is the issue?

Baghouse Filter Operation & Maintenance

What equipment could it be?

• Filter?• Fan?• Airlock?• Screw Conveyor?• Hoods and/or dampers?• Ducting?• Product?• Air system under discharge?• Dust Bin?

What to look for if your Dust Collection System has issues?• What changed?• Is the fan on and going the correct

rotation?• Is the cleaning air system operating?• Is the filter discharging product?• Is there a lack of suction at the pickup

points?• Is dust coming out through the suction

fan discharge?• Is the dust dry, wet, or different in any

way?• Is it bridged above or below the

airlock?• Does it happen at certain times?

• Are the filter bags dirty and need to be changed?

• Are there “noises” that are new or “noises” you don’t hear anymore?

• Did someone “adjust” the dampers?• Pulling good product over?• Filter bags need changing too often?• Is the bag cleaning pump getting too

hot?• Potential for fire or explosion?• Are the cleaning valve “popping” too

often or not often enough?• Is the explosion vent prematurely

failing?• Did it work and now it doesn’t?

What changed?• Someone or something has changed the damper setting?

– Opening or Closing a damper can change every setting• Should be a SLIGHT NEGATIVE• A motor was changed out• Filter bags changed out (or never changed)• A new dust port was “stubbed in”• A dust port was “closed off”

Is the fan on and going the correct direction?• Often associated with a motor change out• Motor leads reversed; fan runs backward• Fan will still pull air, just not as much and not as much static

Is the cleaning systems operating?• Is the compressed air on?• Should hear noise from air discharge – “puff test”• Should hear motor noise• Short filter bag life• The controls not working properly• Gauge connections “clogged” with dust• Timer board “fried” (water in enclosure)

Is the filter discharging product?• Airlock is leaking by (worn out airlock) – “sheet of paper test”• Hopper is full• Light chaff, hulls, bees wings, etc. not dropping out• Connection under the discharge is full, plugged, etc.…• High Can/Interstitial velocity

Is there lack of suction at the pickup points?• Someone made changes to dampers• Fan running backward• Filter bagged blinded over• Line plugged with dust• Leaks in ducting (robbing air system)• Hood design

Is dust coming out through the suction fan discharge?• Broken, ripped, torn filter bag• Filter bags installed correctly• Cracked or broken tube sheet• Material is now in the clean air section as well

Is the dust dry, wet, or different in any way?• Wet indicated leaks in ducting, housing, etc.… during rain, snow weather

conditions• Dust gets heavier and lays in the line• Builds up into “chunks”• Wet, damp dust has blinded the filter bags over

Is it bridged above or below the airlock?• Airlock is leaking by (worn out airlock) – “sheet of paper test”• Hopper is full• Hopper angle too shallow angle• Hopper outlet too small• Stopping airlock too soon• Light chaff, hulls, bees wings, etc.• Connection under the discharge is full, plugged, etc.…

Does it happen at certain times?• Light product collection• Works “sometimes”• Spring/Fall?

Are the filter bags dirty and need to be changed?• Magnehelic gauge “pegged out” to the right• Magnehelic gauge working• Gauge connection ports clogged• Hoses in good shape and connected• Dust on bags is okay (to a degree)• Build up between the filter bags

Are there “noises” that are new or “noises” you don’t hear anymore?• Screech?• Squall?• Quiet?• Bearings, belts, sheaves, air leaks, plugged filters, metal-on-metal?

Did someone “adjust” the dampers• Once balanced, changes cause issues

– Changing one changes the others• Mark dampers for future reference• Lockout if possible

Pulling good product over?• Changes to dampers so one pulls more air and/or product at higher velocity• Closing off of a dust collection point• Hood too close to product

Filter bags need changing too often?• Too many additions over time – Air-to-Cloth ratio too high• Dampers not adjusted properly, pulling in more CFM than designed for• Fan speed too fast – over designed at the beginning (or for future)• Over cleaning the filter bags

Is the bag cleaning pump getting too hot?

Are the cleaning valves “popping” too often or not often enough?

• PD blower has too little CFM and too high of pressure• PD blower speed too high• Decrease “OFF time to no allow tank to get to the higher set pressure. Easy,

“no cost” solution• Respeed blower, increase blower size, etc….

• Each application can be different• Adjust “On” and “Off” times for your application

Potential for fire or explosion?• Are filter bags grounded?

Is the explosion vent prematurely failing?

Did it work and now it doesn’t?• Might be as simple as opening the fan damper slightly• As bags become dirty, they increase the static pressure of the system, “robbing”

the dust collection system of static pressure needed for CFM and velocity

• Explosion vents are considered “consumables” and will fatigue over time• Shut down timer board with fan so housing is not pressurized by the bag

cleaning system• Change to a “domed” or “foam filled” vent or different backup grid

Explosion Venting

Explosion Protection ConsiderationsOSHA and NFPA are making changes and they will affect your operations through the Dust Emphasis Program and DHA• Are the filter bags grounded?• Is the filter located inside or outside? If

inside how close to outside wall?• Is the fan on the dirty side of the filter?

Spark detection, prevention?• Calculation of the filter specifications,

Kst, and Pmax determine the explosion vent size. Length of duct to outside wall also affects vent size.

• Is suppression the best alternative? Cost, maintenance?

• Is isolation needed?

Dust Control System Summary

Dust System Maintenance

• Change filter bags when differential pressure is too high.• Routine checking/changing of solenoids, diaphragms, springs.• Duct cleaning if buildup due to condensation or out of balance.• Airlock leaking by - Check bearings, seals, and clearances.• Fan bearing lubrication, check sheaves, belts, vibration monitoring.• Bag Cleaning Air Power Unit inlet filter check, lubrication, check sheaves,

belts, and relief valve.• Explosion venting – check for wear

Maintaining the SolutionTo Review:

• Locate the source of dust• Close up sources of dust where you can• Chose proper hood design for the application• Apply the correct air and velocity• Taper the ducting size back to the cyclone or filter as the air volume increases• Decide on a cyclone or a baghouse filter system (or both)

After Installation:• Balance the system (set the dampers) and then leave alone

- Opening a damper “here” only hurts you over “there”….• Maintain the equipment – bag changes, fan bearings, ducts, etc.…• Learn to “measure the air” to make adjustments

Allow for the future:• If possible, add a free air inlet today to handle additional CFM for equipment that may be installed down the road.• Re-speed the fan• Move capped off line to another pick up point

Typical Air Measuring Kit

Blower will run hot and the line might plug due

to lack of air

If gauge never leaves “0”, gauge is typically not working correctly

Dust will dischargethe fan to atmosphere

Won’t have much suction, and relief valve always going

off

Look for and resolve common issues

Fan Rotation


Leakage

DuctworkOrientation


Hopper is goingto have trouble

discharging

Installation issues

Air tank would not fill and PD blower relief valve will

keeps going offAirlock inlet piping and layout issues

In Closing…….

• Understand the equipment and processes that you have in operation• Understand system behavior in both optimal and upset conditions

• If in doubt or confused, rely on the manufacturer or system designer for advice

• Learn to identify and resolve issues before failures occur• Regular and effective maintenance pays off • BE SMART / BE SAFE

Always work smartly and practice safety!!

Questions?

Thank you for the opportunity to speak today

filter bag performance & maintenance best practices · • best maintenance practices • key...

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