electrostatic precipitation for dust collection

8/3/2019 Electrostatic Precipitation for Dust Collection

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machine will quickly fill up the collection plates. Heavy dust collection requires storage for alarge volume of dust. Surface area of pleated media filters, fabric bags or pleated cartridgemedia is much greater than surface area of electrostatic collection plates and work better forsource capture and direct machine ducted dust capture than ESP would.

The basic components of an electrostatic precipitator are (i) power supply unit (to impart highvoltage, uni- directional current) (ii) an ‘ionizing’ section where charge is imparted to dust filled air stream (iii) cleaning system to remove dust particles and (iv) housing for the precipitator.

ESP Advantages

Electrostatic precipitators have the following advantages:

They have high efficiencies (exceeds 99.9% in someapplications)

Fine dust particles are collected efficiently

Can function at high temperatures (as high as 700

degree F – 1300 degree F) Pressure and temperature changes are small

Difficult material like acid and tars can be collected

They withstand extremely corrosive material

Low power requirement for cleaning

Dry dust is collected making recovery of lost producteasy

Large flow rates are possible

ESP Disadvantages

High initial cost

Materials with very high or low resistivity are difficult to collect

Inefficiencies could arise in the system due to variable condition of airflow (thoughautomatic voltage control improves collector efficiency)

They can be larger than baghouses (fabric collectors) and cartridge units, and can occupygreater space

Material in gaseous phase cannot be removed by electrostatic method

Dust loads may be needed to be reduced before precipitation process (precleaner may beneeded)

The efficiency of electrostatic precipitators can be increased by:(i) larger collection surface areas and lower air flow rates give more time and area for dustparticles to collect

(ii) increased speed of dust particles towards collection electrodes

Variation in Electrostatic Dust Collection Technology

Electrostatic precipitators are either single stage precipitators (high voltage) or two stageprecipitators (low voltage).

Single Stage PrecipitatorSingle stage precipitators are of two types (i) Plate precipitators or(ii) Tubular precipitators.

Plate Precipitators

Single stage plate precipitators consist of a number of groundedplates (collecting plates), suspended parallel to one another with

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equal spacing between them (4-6 inch) and high voltage discharge (4000-6000 volts) electrodesthat are suspended vertically between the plates from an insulated mounting frame. Thedischarge voltage causes the air stream to ionize and dust particles are negatively charged. Asthe negatively charged dust particles pass along the positively charged collection plates, theyadhere to them. The collecting electrode is cleaned, and dust particles are collected in a hopper.

Design Considerations

Efficiency is affected by the speed of the air stream. It is important to maintain evenvelocity distribution through precipitator from side to side and from top to bottom

Care must be taken in design of distribution baffles

Discharge electrodes are either hanging wires with weights or fixed frames. Hanging wiresare economical.

The closer the electrodes are to grounding plates, the more effective the charging forcesare at lower voltage

Factors That Affect EfficiencySome factors that could affect the efficiency of the electrostatic precipitator are as follows:

Other gases in the air stream could affect efficiency

Some dusts have high charge and greater forces may be required to attract them to thecollection plates

Sulfur compounds in boiler gas increase collector efficiency

Pressure drop usually in the range of 0.2 to 0.5 inches

Dust Discharge ConsiderationsDust is removed by rapping or vibrating the collection plates with an air-powered anvil (afterturning the power supply off) so dust falls into the hopper. Sometime dust particles collect onhigh voltage insulator (since they can migrate to any grounded or uncharged surface) forming apath for the high voltage to ground. This could cause failure of power supply and can be

corrected by pressurizing insulators with a blower while maintaining a flow of outside air incollecting compartment. Charged particles do not have enough attraction by this to settle oninsulators.

Tubular PrecipitatorsTubular precipitators consist of collection electrodes that are tubular (similar to a pipe) withdischarge electrodes placed in the center of the tube. The dust laden air stream flows throughthe tubes, gets negatively charged and collects on the inside wall of the ‘collecting’ tube. Thedust is cleaned from the bottom of the tube.

This type of an electrostatic precipitator can be used with wet electrostatic precipitators bykeeping the walls continuously wet or by washing the collection electrodes. Pipe collectionelectrodes provide highly effective gas distribution within the precipitator.

Uses of Tubular PrecipitatorsThey are widely applied to high temperature gas streams such as boiler exhausts in powerplants since they are able to adjust to expansion and contraction of parts. They are also used formist or fog collection or for adhesive, sticky, radioactive, or extremely toxic materials. Tubularprecipitators find application in operations involving mineral processing.

Two Stage PrecipitatorIn the Two Stage Precipitator grounded plates are placed about an inch apart with anintermediate plate that is also charged. With the two-stage system, instead of 4000-6000 DCsupply, it has 13000-15000 volt supply with intermediate supply at 7500 volts. Dust load in thissystem is normally between 0.01 to 0.1 grains per 1000 cu.ft

Two Stage ESP Advantages



Highly efficient

Self cleaning washing systems

The washing system is a light duty unit designed for 250 cycles.

Has longer life since cleaning is required only monthly.

Air distribution is even since dust collecting filtering device operates at same velocities asheating and cooling coils

Uses of Two Stage PrecipitatorsTwo stage precipitators are generally used in plants where welding, grinding and burningoperations are performed. However since maintenance requires removal of precipitator framesand manual cleaning of delicate assemblies, the electrode wires had the problem of beingbroken. This caused collection efficiencies to suffer.Two stage precipitators are used in hooded and ducted automatic welding machines or weldingbooths when dust load has increased to 30-50 grains per cu.ft per minute

Design Considerations

Plates have to be maintained at precise distances. This calls for special tooling.

Installing insulators in compartments through which air is blown or drawn from outside,reduces dust particles collection on insulators. This increases life of insulator in heavy loadconditions as well.

Since even flow distribution is critical to achieve 99% precipitation, care must be takensuch that charged particles quickly lose static charge. In poor velocity distributioncircumstances under atmospheric conditions of low humidity, particles may not losecharge, sometime indefinitely. In such cases all surfaces become collecting surfaces andthis phenomenon is called plating.

Plating is a major disadvantage in Two Stage Precipitators and can be avoided by havingeven flow, lower speed air stream flow. Plating can also be countered by applying analternating current to the high voltage power supply that effectively removes charge fromparticles coming through the collector. This method can be used effectively even at fairlyhigh speeds velocities.



Media Filtration inDust Collectors

Filter media is used to filter out dustparticles from the polluted air stream,normally by using a screening material(such as fabric), placed in the path ofthe air stream. The dust particles

stopped in the dust collector by thefilter media form a ‘dust cake’ on the

incoming surface and as more dust particles collect on the filter media the thickness of the dustcake increases. This increases the efficiency of the dust collector filter media (capturing up to99.99 % of dust particles in some cases).

The two main functions of media filters in major types of industrial dust collectors are:

i. to stop dust particles on its surface while allowing clean air molecules to pass through andii. to provide easy release of the dust cake during cleaning.

Media filter cleaning is normally done by a burst of clean air in the reverse direction to the air

stream with a velocity greater than air stream. The greater force of the cleaning air burstdislodges the dust cake from the filter media and drops it into the hopper area. For greaterefficiency, a fan is used to push or pull air through filter media openings.

Media filtration in specific applications – important considerations:

Temperature: Upper limits of filter media handling dust filled air stream temperaturesare - 200° F for cellulose and 500° F for Fiber glass material

Combustion: Filter media is not fireproof. Combustion can be countered with fireretardant coatings

Static removal: Static electrical charges may build up on the filter media and coulddischarge, causing an explosion. Static charge can be defused by,

o carbon impregnation in wet laid media (cellulose) ando metalloid finish in polyester media, (spun bodied) for better dust cake release

http://en.wikipedia.org/wiki/Filtration





and superior static dispersion qualities.

Hydro and Oleophobic finish imparts moisture and oil mist resistance to polyestermedia. It also improves dust collection efficiency and strength

DUST COLLECTOR EXPERT HINT: A common term used in dust collectors is pressure drop.This is a term related to static air pressure. Any aerodynamic resistance that an air stream mustovercome causes a pressure change. For example, woven filter material standing in the path ofthe air stream slows down the air as it tries to pass through. Air pressure in front of the filter ishigh, while air pressure beyond the filter is low. The filter causes increased static pressure infront of it, and a pressure drop (drop in static air pressure) beyond it.

Mathematical Variables to be considered in design of filter media: Static pressure is an important variable in design of filter media. It is the positive or negativepressure that causes surface to expand or contract (expressed in water gage). In the case ofdust collectors, it is the resistance to be overcome by air in the dust collector duct. Velocitypressure (VP) is the pressure needed to effect a change in velocity of the air molecules and

Velocity V, the rate of speed of matter.

The value of air density is important in efficient design of filter media.

i) Air density (mass per unit volume of air) at standard conditionsUsing the perfect gas equation (relates to pressure, density, temperature and the gasconstant for air), air density is calculated as 0.075 lbm per cu.ft at a standard conditions

(STP) (temperature at 70 F, zero water content and standard atmospheric pressure of14.7 pounds per square inch absolute). This value is used in fan and air flow equations.

ρ (greek letter rho) or density of air (at STP conditions) = P/RT (where P = atmospheric pressure, T = temperature, R = gas constant for air)

ρ = 0.075 lbm per cu.ft

ii) Relationship between volumetric flow rate (Q), velocity (V) and cross sectionalarea (A):Q = volumetric flow rate expressed as cubic feet per minute (CFM)V= average velocity expressed in feet per minute (fpm)A = area (sq. ft)Q = (V) (A)

Eg. Determining flow rate of air (Q), through an 8 inch diameter (A) duct, at avelocity (V) rate of 4000 fpm

Q = 1396 ft³/min

This equation is used in flow pipe applications.

iii) Relationship between velocity and velocity pressure:This relationship helps to determining critical pressure requirement to move air streamthrough air ducts and the fan.

VP (velocity pressure) =ρ [ V² / 1096² ]

ρ = mass density (lbm/cu. ft)







VP = velocity pressure (inches of water gauge)V = velocity (feet/minute)

When ρ equals 0.075 lbm/cu. ft at standard conditions for air

VP = [ V ft/min / 4005² ]

When air is traveling at 4000 ft/min through any duct size at standard conditions

VP = [ 4000² ] / [ 4005² ]

VP = 1” WG

By using the equation Q = VA it is easy to determine actual flow rate Q (CFM) throughduct size.

iv) Frasier permeability rating for Filter Media:

It states that volumetric air flow rate number is determined at ½ inch of water gaugepressure through an area of one square foot of media. The Frasier permeability numberis 20-40 CFM for standard filter bag media and 4-30 CFM for Cartridge Filter Media.The working status of filter cartridge or bag can be gauged by the magnehelic differentialpressure gauge that measures pressure between a port in the dirty air chamber and aport in the clean air chamber. If the value of this velocity pressure differential is low (1 ½to 2 wg) it indicates good balance and if high (5 to 7 WG), it indicates that the system isout of balance.(The differential pressure reading is not the Frasier Permeability rating)

Main types of Filter media that are used in various types of dust collection filters.

i) Media used in Baghouse filters

Media Use/Characteristic

Polyester Commonly used material in the industry

Singed polyester Improves dust cake release

PTFE membrane polyester Captures fine particles where artificial dust cake is needed

Aramid Suitable for high temperature applications

Polypropelene Known for superior chemical resistance

ii) Media used in Cartridge filters


Cellulose Commonly used cartridge media material.

Cellulose/polyester Has high durability and good abrasion resistance

Spun bonded polyester Has good dust cake release and excellent moisture tolerance and abrasion resistance

iii) Media used in Pleated bag filters


Spun bonded polyester Commonly used pleated bad media

Properties of various fabric media for low-medium temperature, dry filtration:

Fiber Generic name Cotton Polyamid Polypropelene Polyester

Fiber Trade name Nylon 66 Herculon Dacron®

Recommended continuousoperation temperature (dryheat)

180 º F82 º F

200 º F94 º F

200 º F94 º F

270 º F132 ºF



Water vapor saturatedcondition (moist heat)

180 º F82 º F

200 º F94 º F

200 º F94 º F

200 º F94 º F

Maximum operationtemperature (dry heat)

200 º F94 º F

250 ºF121 º F

225 º F107 º F

300 º F150 º F

Specific density 1.50 1.14 0.9 1.38

Relative moisture regain in% (at 68 degree F and 65%relative moisture)

8.5 4.0-4.5 0.1 0.4

Supports combustion Yes Yes Yes Yes

Biological resistance(bacteria, mildew)

No (on treatment) No effect Excellent No effect

Resistance to alkalies* Good Good Excellent Fair

Resistance to mineralacids*

Poor Poor Excellent Fair (notrecommended)

Resistance to organicacids*

Poor Poor Excellent Fair

Resistance to oxidizingagents*

Fair Fair Good Good

Resistance to organicsolvents*

Very good Very good Excellent Good

* at operating temperatures. Based on fiber manufacturers published specifications.

Properties of various fabric media for high temperature, dry filtration:

Fiber Generic name Aramid Glass PTFE PolyethyleneSulfide

Fiber Trade name Nomex® Fiberglass® Teflon® Rylon®

Recommended continuous

operation temperature (dryheat)

400 º F

204 º F

500 º F

260 º F

500 º F**

260 º F

375 º F

190 ºF

Water vapor saturatedcondition (moist heat)

350 º F177 º F

500 º F260 º F

500 º F**260 º F

375 º F190 º F

Maximum operationtemperature (dry heat)

450 º F232 º F

550 ºF290 º F

550 º F**290 º F

450 º F232 º F

Specific density 1.38 2.54 2.3 1.38

Relative moisture regain in% (at 68 degree F and 65%relative moisture)

4.5 0 0 0.6

Supports combustion No No No No

Biological resistance(bacteria, mildew) No effect No effect No effect No effect

Resistance to alkalies* Good Fair Excellent Excellent

Resistance to mineralacids*

Fair Very Good Excellent Excellent

Resistance to organicacids*

Fair Very Good Excellent Excellent

Resistance to oxidizingagents*

Poor Excellent Excellent (PPS fiber isattacked bystrong oxidizingagents)

Resistance to organic

solvents*

Very good Very good Excellent Excellent

* at operating temperatures. Based on fiber manufacturers published specifications.



** 475 degrees for reverse air shakers

Methods to Improve Filtering Properties of Fabric

1. Weaving of fabric material in any of the following ways.a. Plain weave – Fabric can be made porous or tight by number of counts per inch.b. Twill weave – Has fewer weaves and is more porous and flexiblec. Sateen weave – has least number of weaves and is porous, flexible and smooth

2. Use of needled-felt material – With its short felt fibers pressed together and mechanicallyfixed by needle punch machine, this material has high dust collection efficiency and flowrate.

3. Use of singed material – It improves the surface of the bag.

Dust Cake Characteristics on Bag Filters

The high efficiency of fabric collectors depends on the formation of a good filter cake. For a

good filter cake to form, dust particles must have interlocking characteristics. Porous cakesincrease dust collection and retains more dust and can operate at a lower pressure drop. A goodmix of collectors, inlets and operational procedures can deal with any dust or powder.The thickness of dust cakes on baghouse collectors varies between 1/16th and 1/8th inchesand on cartridge collectors the cake is less than 1/64th inch thick.

Media Filtration Aids

A ‘precoat’ of inert material applied on the filter surface helps when the dust collector containsmoisture, oil and small dust particles sizes. Applying the precoat on the clean surface of the filtermedia forms a protective dust cake layer. The use of this type of a filtration aid helps in efficientrelease of the dust cake, captures small particles and increases overall efficiency. However

‘precoats’ have limited use. Frequent applications may be needed to maintain the protectivecoating and there could be difficulties in recycling product dust from hopper if precoat materialmixes with dust. Ideally, precoats must be applied on job specific basis after considering the costand benefits of the system.



What You Never KnewAbout Your CycloneDust Collector

Cyclone dust collectors,named after the cyclone

weather phenomenon, arelarge funnel shaped sheetmetal tubes connected toducts often used inwoodshops, machineshops, manufacturingplants, and powderprocessing plants. Dustand debris are sucked in atthe top. Air containing fine dust blows out ofthe other side of the top, while chips andlarge dust particles fall out of the bottom intoa drum or bin. Dusty exhaust air is either

blown outside or filtered again using mediafiltration.

Looking for a CycloneDust Collector?

If you haven't noticed, they come in allshapes and sizes from differentmanufacturers.

If you choose the wrong size, it will not work.Equipment choice depends on the type ofdust, types of machines, sizes of take-offcollars, source capture hood design andmore. Get the ball rolling and fill out thisonline application form.

Or call our central office.We'll find you the best deal.

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You may find a cyclone dust collector in a variety of sizes for applications ranging from small,home wood shops to CNC machines and even large industrial plants. Our main focus is on thelarger, CNC and industrial cyclone air cleaners. Cyclones are the most commonly known form ofinertial separators. Though simple construction, the concept is genius.

Inertial Separators

Inertial separators use inertia and gravity to separate dust particles from the dust filled air streami.e. by slowing the flow of dusty air stream. When the speed of the dust filled air stream is slowed

down, heavier dirt particles settle out from the air stream by gravity and fall into a hopper wherethey are collected.

http://en.wikipedia.org/wiki/Cyclone



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There are two types of inertial separators. They are (i) settling collectors (ii) baffle collectors.

Settling Dust Collectors:Settling collectors separate dust from the dusty air stream by using a settling chamber (a largebox) in ductwork carrying dusty air. When the dust filled air stream enters the large settling

chamber its speed come down considerably owing to the sudden increase in size of its passage.Heavier dust particles settle out due to gravity from the slow air stream and are collected.

Baffle Dust Collectors:Baffle collectors have a baffle plate (a flat plate) in the path of the dust filled air stream to slow itdown. The air stream strikes the baffle plate and undergoes a sudden change in direction. Theair stream flow and the baffle are designed in a way that the stream is first forced in a downwarddirection, followed by an upward 180 degree turn. With such abrupt changes in direction, the airflow slows down sharply. The heavier dust particles either strike the baffle plates due to theirinertia or settle out by gravity when the flow slows down and slide into the hopper where they arecollected. As they collect, the larger dust particles mop up the finer particles that escape theaction of gravity and inertia, and improve the overall efficiency.

Uses of Inertial Dust Collectors:Inertial separators are the simplest type of dust collector. They are normally used as a precleaner or a pre filter for collectors with greater efficiencies. As pre cleaners their main function isto separate large particles that could damage some dust collectors. In metal working operationsthey are also used as a spark trap and protect filters in collectors in a limited way.

Cyclones or Centrifugal Collectors

Cyclones (or centrifugal collectors) create a ‘cyclonic’ or centrifugal force, similar to water going down a drain, toseparate dust from the polluted air stream. The centrifugal force

is created when dust filled air enters the top of the cylindricalcollector at an angle and is spun rapidly downward in a vortex(similar to a whirlpool action). As the air flow moves in a circularfashion downward, heavier dust particles are thrown against thewalls of the collector, collect, and slide down into the hopper.

Cyclone Collector Design Considerations:Cyclone dust collector efficiencies depend on,

i. particle size (particles with larger mass being subjected togreater force),

ii. force exerted on the dust particles and,

iii. time that the force is exerted on the particles

Cyclone dust collectors can be designed with either large or narrow diameters depending onthe application. Small diameter cyclones have high dust collection efficiencies at low dust loads(0.1 to 6 grains per cubic foot) and high pressure drop of 6 to 10 inches w.c. (water column).Owing to the small diameter they have the tendency to plug at high dust loads. Large diametercyclones can handle high dust loads (50-100 grains per cu.ft) with low pressure drops (1.5 to 3inch w.c.) efficiently. They are not very efficient at low dust loads.

To improve efficiencies, design considerations are,

a. high narrow inlets reduce distances traveled by dust to the wall and thereby improvecollection efficiencies

b. small diameters have higher forces than larger diameter cyclonesc. smooth transition ensures maximum efficiency.







Use of expansion hoppers in dust discharge:In high pressure drop cyclones, dust collecting at the discharge point could be swept upward tothe outlet tube. This phenomenon occurs due to the powerful inner vortex that is formed insidethe main swirling stream at the discharge point. Use of expansion hoppers allows dust to bedischarged through an airtight feeder. Expansion hoppers effectively squeeze out moisture insome heavy moisture applications.

Multiple Cyclone Separators:Multiple cyclone separators consist of a number of small diameter cyclones (6 inch diameter)placed parallel to one another with vane spinners. The multiclones have a common inlet andoutlet for air. The smaller diameter of the barrels and longer length makes them more efficientthan regular cyclones. By being longer dust is retained inside for greater amount of time andsmaller diameter of barrel increases centrifugal force, causing efficient separation of dust. Theinclined dirty air plenum facilitates effective air and dust distribution in the dusty area and evendistribution of clean air in the clean area. This type of collectors are commonly used in boilers oras preliminary cyclones.

Rotary Dry Centrifugal Unit:

They are centrifugal collectors with centrally designed blades that effectively disperse dustparticles from the air stream against the walls of the collector. The dust particles slide down andare collected in a hopper while clean air is let out from the outlet. These units are commonlyused in grinding applications. Limited to small volume flows, the housing of these centrifugalcollectors is normally made of cast iron due to high abrasion.

Louver Type Collectors

In this type of a dust collector, louvers with narrow spacings are used in the collector to causeabrupt change in direction of incoming dust-filled air stream. Dust particles in the air streamcollide against the flat surfaces and collect in the lower part of the collector. Louver typecollectors are highly effective at light loads of fine dust (their use is limited to less than 0.5 grainsper cu.ft.) and are used to reduce the load entering replaceable panel filters. These collectorsplug at heavier loads. A part of the air stream is diverted into a small centrifugal collector. Theyare used for some specialized applications of collecting fine dust.

Being basic designs, the efficiency of these collectors is limited despite the advantage of havingfew internal parts. Inertial separators are normally used as a) preliminary filters b) to trap largeparticles from an air stream and c) to increase efficiency of a solid separation process with waterscrubbers or electrostatic precipitators.



Air Washers & Wet GasScrubbers OverviewA Safe Way to minimize dust fireand explosion hazards

Inertial separators had the drawback of dust

particles not accumulating properly on thecollecting surface, resulting in finer particlesbeing swept back into the air stream. Airwashers or wet scrubbers, use liquid

(usually water) to absorb the finer dustparticles (scrubbed). Water comes intocontact with the dust filled air stream andcaptures dust in water droplets. The dirtywater droplets accumulate, and are collectedand removed. The cleaned air in air washerscontains fine water droplets forming a mist.These water droplets can be removed fromthe cleaned air by a mist eliminator. Misteliminators are similar in design to inertialseparators where mist and air are separatedeither by change in air flow or by the spin inair stream which creates the centrifugal

forces. The dust-water mixture is eithercleaned or recycled into the scrubber. Theaccumulated dust is removed by using aclarification tank or a drag chain tank, wheredust particles can be cleaned after they settleto the bottom.

Do you need to collectpotentially explosive orvolatile dust? Are you worried about aluminumdust dangers and hazards?

Do you think a wet dust collector will safelyhandle your hazardous dust problems? Wantto find out for sure? Click the orange buttonand answer a few questions about your

application. A dust collector expert will knowexactly how to tackle your problem... Andfind you the best deal on equipment - directfrom the manufacturer!

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The diagram to the right shows a standard design of a packed bed wet scrubber or spray tower wetscrubber.

The three important operations of air washers or wet gasscrubbers:

a. Humidification (of air): This process increases size offine dust particles and makes collection easier

b. Contact of liquid and dust filled air: This is the keyoperation that governs collection efficiency of thescrubber. Water droplets in the path of the air streamcollect dust particles while the air stream flows around it

c. Separation of dirty liquid and clean air: During thisoperation, the dust-water mixture accumulates, and asthey grow larger, they collect into the hopper.

How do Wet Scrubbers Work? In the simplest form of air scrubbers, water is sprayed on theinterior walls of the cyclone to improve collection efficiency.Water thus mops up fine dust particles that otherwise do notstay on the collection surfaces and tend to be swept back intothe air stream. However air scrubbers suffered operationalproblems of(i) keeping the interior walls coated,(ii) maintaining water distribution on interior walls and(iii) cleaning mud and sludge from collection interior.

An improvement of this design sprayed water into the polluted air inlet. In these collectors, thedust-water slurry had to travel a long distance inside the collector. Another drawback was thatslurry droplets were swept upward to the outlet with the inner vortex that disturbed waterdropping on the expansion chamber. The collection efficiencies of these units was however,much higher than the dry units.

High collection efficiencies can be achieved in scrubbers by maintaining velocities of air that arehigh enough to drive dust through the surface tension of water droplets. A good design scrubberproduced a secondary generation of water droplets and induced a mist collection section.

Wet scrubbers are normally categorized on the basis of pressure drop (the difference in pressurebetween two points in a system, caused by resistance to flow, and measured in inches watergauge) as the following:i) Low energy scrubbers (between 0.5 to 2.5 inches wg)ii) Low medium energy scrubbers (between 2.5 to 6 inches wg)iii) Medium to high energy scrubbers (between 6 to 15 inches wg)iv) High energy scrubbers (greater than 15 inches wg).

Low Energy Wet Scrubbers

Dynamic wet precipitators are similar to centrifugal type dry collectors in design. Thedifference is that they are equipped with water sprays and accordingly the blade is designed tohandle dust and water. Centered in the inlet the water sprays spray the blades with water. Whendust filled air stream enters the inlet, water and dust come into contact, mix, and form a slurry.The slurry is thrown against the walls of the collector due to the centrifugal force and is collectedin the drain. Water and mist (clean air) have separate outlets, the water going into the centrifugalseparator and the mist into the drain. This type of collectors have limited use due to high wear onthe blades caused by high solid content in dust particles.

Orifice scrubbers are similar to inertial separators. The difference being that instead of baffles,

orifice scrubbers use a water surface. The air stream changes its direction abruptly after collidingagainst the water surface, causing a pressure drop of almost 3-6 inch w.c. Greater dispersion is

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Considering a DustCollection System?

A complete dustcollection system will improve indoorair quality byremoving dust from aseries of work

stations, machines and tools. Furthermore,one large centrally ducted dust collectionsystem addresses the need for using anindustrial air cleaner on each workstation.

One large central dust collector system canoften do the work of dozens of smaller,individual air cleaners, providing complete

industrial plant dust collection for the entirefacility.

Are you worried about OSHA orother environmental agenciesshutting you down?

Have you or your workers begunexperiencing lung or skin problems?

It may be too late to help some irreversibleeffects of occupational respiratory diseases .But you can still cut down explosion & fire risk, damage to equipment and problemswith community relations.

Our experts will set you up with the correctequipment to obtain threshold limit values(TLV's) that will keep the MSHA off yourback.

Toll Free 1-800-525-6018Serious Inquiries Only!

Central dust collection systems generallyconsists of large media dust collectors (suchas cartridges or baghouses) with an inertialseparator used as a pre-sorter (such as acyclone or drop out box). The pre-sorterremoves large chips, then the mediafiltration removes fine particles. Large chipsare collected in bins or drums.

Filtration media often uses some form of

cleaning such as mechanical shaking or asudden pulse of air that knocks built up dustcake from the filters. Electrostaticprecipitators are rarely used for large dustcollectors, since they do not have thecapacity to store a large volume of dust.Though, electrostatic air cleaners arefrequently used along side central systems toclean atmospheric background dust that isnot captured by the ducted system.

Are you feeling overwhelmedwith the thought of planning adust collection system?

Answer a few questions and we'll get youstarted in the right direction.

Advantages of a Central Dust Collection System

Equipment Cost: Often the deciding factor whenchoosing a dust collection solution. Depending on thecost of ductwork and installation, a central dustcollection system can initially cost less thanpurchasing 12 or more individual dust collectors.

Waste Removal: As dusty air is filtered, waste dust iscollected in bines, drawers or hoppers. Wasteremoval from one location verses many locations iseasier and thus more cost effective.

Filter Replacement: Replacing filters from 12 ormore separate machines will cost more than regularfilter replacement of one large dust collector designed

for heavy loads. Energy Consumption: Your energy bill will be lower











when powering one big dust collector than if you try to power a dozen or so dust collectormotors.

Noise: Imagine the noise from 12 or more dust collector motors and blowers running in awork area. Now take that noise, put it all in one big motor / blower and tuck it away in itsown area, away from workers.

Maintenance: You can go either way on maintenance. With multiple air cleaners, you

have that many more parts to replace. With one central dust collector, you only have oneset of components to maintain. On the other hand, if your central dust collection systemgoes down, all workstations go down.

Disadvantages of a Central Ducted Dust Collector

Flexibility: A central system is designed for a predeterminedsituation. It must keep a constant air flow and air to cloth ratio. Ifyou need to add machines or move stations, the system must bere-engineered.

Downtime: In using one dust collection system for an entire

network of machines, downtime for the air cleaner meansdowntime for all workstations.

Design & Installation: In order to function, a dust collection system must be designedcarefully taking in account airflow requirements for each workstation, media filtrationrequirements, size and amount of ductwork and pressure drop of filters.

Air Balancing: Ducts have adjustable dampers at each work station that are set by atechnician for optimum air pressure balance throughout the system. Often workers willtake it upon themselves to open or close the dampers to adjust airflow going to theirstation. Unfortunately, this affects the airflow at all other workstations, too. Using oneblower, the air must remain balanced and cannot fluctuate to accommodate individualworkstations.

Space Limitation: Floor space and overhead space are needed for a large dust collectorand network of ducts. Overhead cranes or tight floor space will not allow for a central

ducted dust collection system.



Ambient Dust Collectors Explained & Compared

Do you think you need an industrial air purifier? Ambient dust collectors are usually the first thingpeople picture when you say air cleaner or air purifier. Though many times, an ambient dustcollector should not be the first thing you buy. (If in doubt, give us a call - our expert panel

includes suppliers of equipment from various manufacturers.) As the name implies, ambientdust collectors filter airborne dust particles as they circulate through the air and into the machine.In most dust producing processes, it is more effective to capture dust from the source, as it iscreated, before it has a chance to go airborne.

Yet ambient dust collectors are crucial for avoiding respiratory health conditions. Larger, heavierparticles 10 microns and bigger will most likely fall before reaching the ambient dust collector.Smaller particles that escape source capture will be thrown into the air where they will remainsuspended. Ambient air cleaners should be used to remove this suspended atmospheric dust.Small dust particles have a tendency to become permanently lodged in lung tissue, causingirreversible health problems. While heavy loading dust collectors handle the big particles,ambient dust collectors address the smaller background dust that clouds the air.

Types of Ambient Dust Collectors

There are three configurations for ambient dust collectors: self contained (free hanging), HVACintegrated and independently ducted.

Self Contained Air CleanersSelf contained ambient dust collectors have onecabinet with everything in it to move the air, filter theair and collect the dust. Self contained units createan airflow pattern to obtain complete air exchanges.One air cleaner working alone can use the COANDA

airflow pattern in a contained area. In an open area,multiple units can interact to create a larger airflow pattern or air curtains.

HVAC Integrated Dust CollectorsUsing air exchanges generated by the HVAC system, an integrated dust collector installs inlinewith the your facility's HVAC. Integrated air cleaning systems can be self maintainingelectrostatic or disposable media. A dust collector that installs into your HVAC is limited to airflowand air exchanges of an HVAC, which are generally not as aggressive as a dedicated dustcollection system.

Centrally Ducted Ambient Dust Collection SystemsBy adding ducts to a self contained dust collector, one air cleaner can be expanded to create a

highly focused, customized airflow pattern. Because the system is independent from HVAC, ductplacement and airflow is not restricted. In an independently ducted dust collection system,ambient capture can be combined with source capture, downdraft benches and direct ducting tomachine enclosures.

Ambient Industrial Air Purifier Product ComparisonsDust Collector Filtration Specs Options Application Advantages

AirBoss M2500

Ambient Dust

Collector

• 28 sq ft Pre-filter 4" pleated

35%

• Primary filter

95% bag filter66 sq ft.

• 1240-2010CFM

• 0.75 HP motor

• 180 lbs

• 3 speed

• Filter gauge kit

• 2" Pre-filterpolyester pad 4

sq ft

• 2" Prefilter 3way wrap around

• Welding smoke

• Grinding dust

• Plastic dust

• Very fineatmospheric dust

• Quiet operation50-70 dB at 5 ft.

• Small size

47"x25"x25"




http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8977624&dopt=Abstract







• Other filter

options available selector switch

• Direct drive,forward curved

blower

10 sq ft

• 65% bag filter

66 sq ft.

AirBoss M3000

Ambient Dust

Collector

Similar to biggerversion M6000

• 35% pre-filterpleated 4"

• 95% primary

bag filter

• Optional pre-filters, primaryfilters and

secondary filters

• 3000 CFMpreset by factory

• 2 HP motor

• 260 lbs

• Direct drive,forward curved

blower

• 68"L x 25"W x

26.25"H

• Filter gauge kit

• Different 2 or 3HP motors

available

• Belt drive,backwardinclined, airfoil, 3HP high static

blower

• Motor starter

• 2" alum meshprefilter

• 2" impinger

prefilter

• 3-way wrap

around prefilter • 65-95%extended surface

primary filter

• HEPA primary

filter

• 2 adsorber 25lb carbon

modules

• 95% short bag

secondary filter

• Wet or dryparticulates

• Ambient or

ducted

• Smoke

• Dust

• Fumes

• Quiet 74dB at 5ft.

• 72.5dB with

optional silencer

• Modularupgradeable

design

• Air dischargechoices for better

control

• Odor and highefficiency filters

available

• High staticblower optionsfor more

contaminant pickup points

• Belt drivenblower withvariable pitchsheave providesadjustment forprecise CFM

operatring range

AQE M73 Ambient

Dust Collector• 2 prefilters 30-35% cottonsynthetic blend59 sq ft

12"x24"x4"

• 2 rigid V-bank24"x24"x12"primary filtersmini-pleatedmicro-glass fiber

400 sq ft.

• Primary filteroptions rangefrom 45-95%

ASHRAE

• 4500-6000CFM

• 3 HP motor • Adjustablesheave allowsfield adjustmentsto airflow up to

800 CFM

• 405 lbs

• 50"L x 47"W x

32H"

• Filter gauge

• 4 wayadjustable

exhaust louvers

• Motor starter

and circuitryincluded

• • Fine dusts

• Smoke

• Mist • Soot

• Excellent CFMand media



Do You Need aPortable Dust Collectoron Your Shop Floor?Scroll down to see a few of the portable dust

collectors available from our dust experts.

If you have workers making dust or fumes asthey move fabrication from station to station,a portable dust collector can provide theneeded flexible solution. Small, mobile,portable dust collectors work well withintermittent use in small spaces such aswood shops or tight production facilities. Youcan choose from a wide range of cartridgemedia, HEPA, washable media orelectrostatic filtration with blowers rangingfrom 200 to 3000 Cubic Feet per Minute. Allportable units use at least one sourcecapture arm. Many are modular with add-onsand options.

Are you shocked by the priceof dust collectors? Do you think a portable dustcollector will cost less?

Maybe you can get by with one small dustcollector that travels from station to station.Its possible. But are you aware of other costsinvolved besides your initial capital expense?

Find the most economical and efficientsolution. Click this button. Answer somequestions. An expert will contact you withanswers to your dust problems.

Questions?Call Toll Free 1-800-525-6018

Compare Portable Dust Collectors

The table below gives an unbiased comparison between portable dust collectors from a few ofthe top brands on the market. Note the "Advantages" column. Here you can see features thatmake that product unique or specialized.

Dust Collector Filtration Specs Options Application Advantages

AQE 2000

Portable Dust

Collector

• 2 mediacartridges

• 382 sq ft of

media

• 99.8% efficient

at 0.5 micron

• Reverse pulse

cleaning system

• 1100 CFM

• 1.5 HP motor

• Source capturearm 11'-1"

• 46"H x 28.5"W x

37"D

• HEPA post filter

• Lighted Hood

• DamperAssembly

• 14' arm

• HO treatedpolyester

cartridge

• Weldingsmoke

• Grinding

dust

• Plastic dust

• Fine

particles

• Quiet operation 73dB at 6 ft.

• Reverse pulse

cleaning

Trion Air Boss

One Man Portable

Dust Collector

• HEPA media

• 3.2 sq ft 35%

ASHRAE

• 53 sq ft 99.97%

HEPA

• 220 CFM

• 2 direct drive

fan motors

• Flexible capture

hose 10'

• 12"D x 27"W x

19"H

• Aluminummesh pre-filterinstead of 35%

ASHRAE pre-filter

• Smoke

• Dust

• Powders

• Dry process

particles

• Welding

• Grinding

• Sanding

• Soldering

• Magnetic base fornozzle - easy

mounting

• Extractor nozzlecan be 3" fromwelding w/out

effecting shielding

gasses

• Lightweight 45 lbs

AQE M66VPortable Dust

• 3 stages of

media • Up to 3000 CFM • Dual

mechanical or• Smoke • Modular design for

upgrades, options




http://www.diracdelta.co.uk/science/source/c/u/cubic%20foot%20per%20minute/source.html










Collector

Smaller AQEM32V is similar.

• Full range of media options

from 50% to 99%including HEPA

and Carbon

• 1 HP motor

• Externallysupported flexible

capture hose 10'

• 40"L x 31"W x

72"H

hose capture

arms

• 1.5 HP motor

• 2 HP motor

• 3 HP motor

• Silencer

• HEPA

• Impinger

• 45 lb carbon

filter module

• Lighted hood

• Minihelic gages

• Various multi-

pocket bags

• Various dry and

mist bag filters

• Dust

• Mist

• Soot

• Vapors

• VOCs

• Wet or dry

particles

• Wet

grinding

and changes

Trion Port-A-Cart

Portable Dust

Collector

• 1 media

cartridge

• 190 sq ft of

media

• Up to 99.999%efficient at 0.5

microns

• Up to 1000 CFM

• 1.5 HP motor • Externallysupported flexiblespurce capture

arm 6'-5"

• Parabolic hood

design

• Minihelic gauge

included

• Fire retardant

cardridge

• Impregnated

carbon post filter

• 48" x 30" x 34"

• Offline reversepulse cleaning

system • Bolt-on HEPA

post filter

• Smoke

• Dust • Powders

• Dry process

particulates

• Very quiet 70dB at

5 ft.

• Packaged withmost commonly

needed accessories



Dust Collection ViaCartridge Filtration

Both shaker collectors and fabric pulse jetcollectors had limited dust collection efficiencywhen it came to applications such as highdensity dust from powder coating booths.The high-density dust from these powder-coating booths caused the fabric pulse jetcollectors to operate at a high pressure dropand thereby increased compressed airrequirements for cleaning. Another problemwas that exhaust air could not be recycledinto work areas due to high amount of dustpenetration into adjacent bags. Cartridgedust collectors overcame the aboveproblems effectively.

Do You Think You Need aCartridge Dust Collector? Are you sure its what you need?

How do you really know? Find out for sure.

Ask an expert. Just click the orange buttonand answer a few questions. An expert willreview your responses and contact you.

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The Cartridge dust collector uses a perforated metal cartridge with acellulose filter pleated, non woven filter media, bound by steel caps at thetop and bottom. The end caps were joined with the cellulose media andouter and inner cores by an adhesive. Cellulose media was used because ithas pressure drop qualities similar to those of felted media in pulse jetcollectors. Pleated media filter elements with narrow pleat spacing (8 pleatsper inch) are efficient for filter cakes (formed with fine dusts) that are lessthan 0.02 inch thickness. Narrow pleat spacing loses its relevance whendust particle size is beyond 0.03 inch. The pleated design provides greateramount of filtering area while occupying lesser space. Consequently the air- filter media ratio, pressure drop and cartridge collector size reduceconsiderably.

Are you looking for a Cartridge Dust Collector?Contact Dust Collector Experts

Dust Collector Cartridges Use

Cartridge collectors are highly efficient in collection of dust with high bulk densities and finedust particles. Filter cake forms well at low pressure drop and has high filtration efficiency. In astudy conducted by the American Foundry Society it was found that the outlet dust flow incartridge collectors was the least in comparison with other dust collectors in foundry operationsas shown below:

Collector type Outlet dust flow

Pulse jet fabric collector 0.0660 grains/cu.ft

Shaker collector 0.00035 grains/cu.ft

Cartridge collector 0.00005 grains/cu.ft

At an inlet load of 1-2 grains/cubic foot

A version of the filter media elements of the cartridge collectors was used as intake air filtercartridges for trucks. The pleats were pushed deep into the media surface, 0.014 inch deep, andtightly spaced. These truck filters had a long life since inlet loads were only 0.0002 grains percubic feet. The fine dusts collected on the top of the filter media or on adjacent pleats and thefilter operated on the principle that more media contributes to longer filter life.

Main differences between truck engine filter and dust collector:




http://www.whatman.com/repository/documents/s3/Filter_Typical_Properties_pg12.pdf


http://www.dustcollectorexperts.com/contactus.html









i. Loads: Dust collector loads are 1-20 grains per cu. ft whereas dust loads for truck filters are0.0002 grins per cu.ft (5000 to 100000 times more than engine filters)

ii. Dust cake: Dust cake in dust collector forms on the filter media surface as well as withinthe media. The dust cake in truck filters forms only within the filter media.

iii. Pressure drop: Pressure drop in the dust collector is 2-3 times more than the pressure dropin the truck filter.

Cyclic Pulse Cleaning Increases Cartridge Efficiencies

Thicker dust cakes on filter elements that were cylindrical were found to be efficient and reducedthe requirement of compressed air. An efficient solution to clean coarse dusts was by introducinga cleaning ‘cycle’ (as opposed to continuous cleaning) that activated on pressure setting. Apressure switch such as a photohelic gage was used for this application and pressure switchsetting was at 3 ½ inches water gage. By operating the collector at a pressure of ¼ inch watercolumn above the initial pressure drop, the pressure actuated cleaning system is best utilized. Byshortening off time cleaning interval, the pressure drop can be stabilized. The frequency of thecycles can be reduced if greater amount of dust can be removed in each cycle. The lowerpulsing frequency in cylindrical cartridges implies that dust penetration to adjacent filter media is

reduced since dust penetration is directly related to pulsing frequency.

Though pleated filter elements can also operate with a pressure switch actuation system, wemust understand that the pressure drop setting in these elements is normally limited by pleatspacing. The dust loading could be minimal in applications such as fume dusts and weldingoperations that may require only one or two cleaning cycles per day. Further compressed airutilization increases with narrow pleat spacing.

Eg. Considering the initial pressure drop across a pleated filter media to be 0.1 inches watergage, we can see that if ‘bridging’ (filling up) of pleat groove with dust occurs, then cleaning airflow is obstructed in the portion below the dust bridge. In such a case cleaning air has no optionbut to take the path of least resistance that makes all the media below the bridge ineffective. Insuch cases pressure switches can be set for dusts that can filter effectively at a wide range of

pressure settings.

Assuming a dust load of 2 grains per cubic foot and pressure switch settings are provided at 1 ½,2 ½ or 3 ½ inches water column, we get the following results:

Pressure switch Cleaning cycle time Compressed air usage at 85 psig

1 ½ inch w.c. 5 minutes 0.7 scfm per 1000 acfm filtered air

2 inch w.c. 5 minutes 0.6 scfm per 1000 acfm filtered air



If pleats are spaced narrowly, compressed air usage would increase. From the table we can seethat the air usage is higher initially (due to shallow cake) and reduces despite bridging. Asbridging increases so does the cleaning cycle and compressed air usage.

Cleaning Action in Cartridge Collectors

Cleaning action is achieved by compressed air jet. The jet enters the top of the filter element andexpands at an angle of 14-16 degrees, drawing clean air from the clean air plenum. When thisexpanding air flow enters the filter element, it loses its capability to draw more clean air becausethe filter and the dust cake offer resistance to the flow. The air jet starts compressing the cleanair in the filter element causing a pressure wave that expels the fan air present in the filterelement. Once fan air is expelled, a positive pressure is created which sweeps out accumulated

dust that has collected on the outside surface of the filter media in the dirty air chamber.



In pleated design, dust is displaced at the speed of cleaning air jet in a perpendicular path fromthe filter media surface. This prevents dust from striking the adjacent media, which is alsoejecting dust at an angle. This advantage is lost in cylindrical and envelope bag pulse collectorswhere dust is thrown on to the adjacent rows during cleaning action. Pleated cartridge filterdesign has one of the better collection efficiencies due to this factor of not propelling dust to theadjacent bags.

DrawbacksOne drawback of pleated filter elements is that dust leaks through the filter media duringcleaning cycles. This happens before the dust cake is properly formed. This dust then leaks onto the clean air chamber. Over a period of time, it can cause problems such as creating highpressure drop, frequent need of cleanings and reduced filter element life.

Cartridge Filter PlacementThe old method of filter placement within the cartridge was in vertical rows. By virtue of thevertical placement of these elements in the polluted air section of the collector, they posed ahealth hazard to workers who had to enter the polluted section to change the filter elements. Tocounter this hazard filter placement was designed such that they could be removed from the

outside of the collector. An efficient variation of filter placement from the outside is the horizontalplacement of filter elements in vertical rows. Cleaning sequence was from the top to the bottomrow.

Dust Collection Considerations

Fine dust normally adheres to surface of filter element and accumulates other fine dustparticles as well

When accumulated dust cake formed properly and is large enough and unaffected byupward air streams, it falls into the hopper

Drawbacks of Cleaning Action in Horizontal RowsDuring cartridge cleaning in horizontal rows, dust falls from the filter elements in the top rows(that are cleaned first) on to the filter elements in rows below. Accumulation of dust in thisfashion on the rows below makes the cleaning action in the affected rows inefficient.

This problem can be countered by using a baffle arrangement at the inlet. The bafflearrangement splits the incoming polluted air into smaller channels and distributes dusty airevenly to the filter elements and helps the down flow of process air. This arrangement reducesdusty air flow speed and mitigates problems of dust particles settling on other rows.

Filter Ratio DesignCartridges with large amount of filter media require greater cleaning jet speed. Cartridges withless filter media however, stand to benefit by the advantage of a greater cleaning jet speed sinceit promotes effective cleaning – an advantage that cannot be enjoyed conversely.

Normally the cleaning air to process air ratio is between 4:1 or 6:1 (which means that thecleaning flow of 1600 and 2400 CFM is required for a cartridge filter that is rated for 400 CFM).However, in spite of the high cleaning air flow rate, cartridges collect dust and get plugged. Thiscauses active filter media to be plugged and thus the inactive filter media are activated.The operating pressure drop across the filter media remains constant as long as there areinactive filter media in reserve. But when all the filter media get plugged and there are no moreinactive filter media left, pressure drop rises and consequently cleaning frequency must beincreased. When pressure drop increases to a point where it is difficult to sustain required fan airflow in the system, the cartridges must be substituted. In circumstances when dust accumulatesin uncleaned pleats and bridges the system undergoes mechanical stresses on the structure andthe seals.

Cartridge Cleaning System ImprovementsThe cleaning action in cartridge collectors can be made more efficient by the use of anappropriately designed nozzle that increases speed of compressed air jet from 1000 fps to 1750



fps. This increased speed of the air jet now enables it to draw more clean air (when it expands inan angle) and gives cleaning air jet good cleaning characteristic.

Venturi is placed at inlet to filter media to improve cleaning efficiency of cartridge. It also helps in

blocking fan air from escaping the cartridge

pushing out fan air when cleaning air jet is off with less instability

By increasing space between cartridges, the problem of dust falling on adjacent cartridges isreduced.

It must be remembered that the system efficiencies of cartridge collectors depend upon goodcleaning of the cartridge and not by adding more filter media in the cartridge. Additional filtermedia neither improve function nor life of the cartridge. By merely adding filter media it is likelythat even the initial advantages in terms of airflow and pressure drop may be lost. The amount offilter media should be decided based on nature and size of dust particle.

Proper Seal Design

Seals are useful for separating dusty air from cleaned filter air. They are also used to maintaindifferential working pressures (separating atmospheric pressure from system pressure). If theseal design is flawed, cartridges could quickly get plugged and system loses efficiency.The use of a compression spring mitigates seal deflection problems. Seal design must take intoaccount an appropriate size of seal as well as material strength such that it is robust and doesnot get crushed. The cartridge opening is sealed by an inner door cover, an outer door plate thatseparates the dust chamber from the atmospheric pressure and washers that seal outside doorhandle from internal dirty air chamber. The door parts are attached to one another andinstallation or dismantling of the door assembly is easy.



Baghouse DustCollectors

Fabric dust

collectors arecommonly knownas baghouses andfor someapplications areone of the mostefficient and costeffective dustcollector models.In baghousecollectors, thedust filled airstream passes

through fabric bags that filter the dustparticles. Bags are made of different materialsuch as woven or felted cotton, synthetic, orglass-fiber.

Need a New BaghouseDust Collector? Are you concerned aboutchoosing the right company todesign and install your baghousedust collection system?

We can help. Our panel of dust collectorexperts provides a network of professionalsrepresenting many different manufacturers.Call or click the orange button to contact ourcentral office. We'll make your job a loteasier.


Selecting Baghouse Filter Bag Media

Important considerations while selecting fabric filter material for baghouse collectors:

Temperature of incoming dusty air stream

Moisture levels in the collector and hydroscopic nature of dusts

Electrostatic nature of dust particles

Abrasion levels caused by dust particles

Acid chemical resistance and Alkali chemical resistance of fabric

Fabric’s capability to release dust cake easily

Fabric’s permeability to allow air to pass

Size of dust particles

Fabric cost

Continue following the tutorial for more in depth information on dust collectors baghouses. Wewill cover different cleaning mechanisms, types of bags, operating parameters, applications, andvarious advantages / disadvantages of available technologies.

Do You Need a Baghouse Dust Collector Installed?

Contact us online or by phone. Some of our dust collector expert members specialize inengineering and installation of high performance baghouse dust collector systems. Thepictures below show the installation of one of our recent baghouse installations.





http://www.scapca.org/documents/baghouses(1).pdf













Shakers & Mechanical Cleaning Dust Collector

Mechanical cleaning dust collectors are used inprocesses where non-cleanable filters become anexpensive option due to large dust content. It consists

of bags with an inlet for dusty air stream at the bottom.The bags are suspended from a rope for improvedagitation and fixed at the bottom. Dust filled air entersthe bag, passes through the filter and collects on theinside walls of the bag. As dust collects inside the bag,the pressure drop rises (initial pressure drop could beat 0.1 to 0.2 inches w.c.). When pressure dropreaches between 2 to3.5 inches of w.c., filter media iscleaned by pulling up and down on the pipe (byshaking). After cleaning, pressure drop readjusts to0.5 – 1.0 inch w.c.

The fan is on the dusty side and its paddle wheel

moves the air and receives incoming dust. Used in manual paper trim operations, these shakersused sateen weave cloth as filter material because of the tight weave and flexibility.

The operating parameters of shaker collectors are normally as follows:

Air volume flow 500 – 1000 CFM

Bag size 24 inch diameter

Bag length 10-14 feet

Bag area 88sft @ 14 feet

Filtering velocity 5.7 fpm at 500 CFM11.4 fpm at 1000 CFM

Initial pressure drop 0.1 inches w.c.

Average dust holding capacity at 3” w.g. 8-16 oz

Dust holding capacity after cleaning at 1’ w.g. 2-4 oz

Inlet load 5 grains/cu.ft

Time between cleanings 10-20 hrs at 500 CFM5-10 hours at 1000 CFM

While selecting mechanical cleaning shaker collectors the basic criteria to be considered are:

filtering velocity

dust load residual pressure drop

Since time is consumed while cleaning, the inlet load into the dust collector must take intoaccount (a) the time required for cleaning and (b) intervals of time between cleanings. Forexample, inlet load capacity could be 1000 CFM where cleaning is done twice in an eight hourlyshift. But where cleaning is done only once in an eight hourly shift a capacity of 500 CFM wouldsuffice. It is important to remember that the residual pressure drop is related to dust holdingcapacity of filter media. Dust holding capacity of filter media is related to dust characteristics.

Envelope Filter Bags

The collector bags are sewn into envelopes in this type. The envelopes are provided withspacers made of wire inserts or open foam between them to keep the filter media fromcollapsing. Envelope filter bags save space. Cleaning can be done by manual shaking or

http://www.epa.gov/ttn/catc/dir1/ff-shaker.pdf









automatically by motor power. Springs are attached to the closed end of the envelope bags tokeep the bags taut. This arrangement prevents filter media from stretching after cleaning cycles.Spring tension must be checked and readjusted at appropriate intervals

Envelope filter bags are effective at transfer points on belt conveyors, screening, clampingstations, grinding and abrasive blast cabinets where dust is mechanically generated. However

their efficiency suffers in processes such as dryers and furnaces where dust particles get stuckin the filter media. This drawback is because the cleaning mechanism in these processes is notgood enough to sustain filter element life and low residual pressure drops.

Tubular Shakers

Tubular shakers are tube shaped dust collectors that effectively handle the problem of dustparticles that get stuck in the filter media. In these type of shaker collectors, an inlet opening isprovided at the bottom of the bag. Dust filled air enters through the inlet and dust particles collecton the inside of the bags. The cloth on the bags is kept taut by the use of a tension device.Cleaning process is a variation of the shaker mechanism.

The high cleaning efficiency of this type of shaker collectors is due to the high ratio between thebag opening diameter (3-12 inches) to length of the bag (20-35 inches). This provides tubularshakers with better cleaning than other shaker collector types.

These shakers however require continuous cleaning, which stops the industrial process. Tocounter this drawback, a continuous cleaning compartmental collector system was designed withseparate modules inside the collector with separate ‘dampers’. This facilitates cleaning of individual modules by closing a damper while directing the flow into other compartments, therebykeeping the process continuous. Individual compartments can be thus cleaned ‘off line’ bystopping fan flow into that compartment. Compartments can range from 2 to 20.

Continuous cleaning shakers hold an advantage in low volume applications and inenvironments where compressed air is not available for filter cleaning requirements. They

however suffer from the drawbacks of the ‘off line’ cleaning process and high maintenance sincethey have large number of internal moving parts. The low air to cloth ratio makes these collectorslarger in size and they are more expensive than other collectors.



Reverse Air CleaningBaghouse DustCollectors

Also known as the reverse blower dustcollector, the reverse air cleaning baghousecollects dust which forms regularly forms intoa hard 'dust cake' on the dirty side of the filterbag. This type of a dust collector uses high-pressure ‘cleaning’ air, blown in the ‘reverse’or opposite direction of the dust ladenstream, to clean the dust cake. Also calledhigh pressure reverse fan cleaning, thesemodels are continuous or ‘online’ cleaningdust collectors and mitigate the drawbacksof the ‘offline’ collectors. In these collector s,cleaning could be done continuously withoutinterrupting the process and the numerouscompartments that featured in the offline dustcollectors were done away with.

In a reverse fan cleaning dust collector,polluted air enters the filter bags from theinlet at the bottom and passes through theinside of the bag. Dust particles collect onthe walls of the bag. A chain driven motorpowered traveling manifold moves across themouth of the envelope filter bags to providethe cleaning air. The flexing of the collecting

bags causes the dust cake to crack and fallinto the hopper. The reverse air stream canbe used to clean one bag or one row of bagsat a time.

Does your application requirean online reverse air cleaningbaghouse? Is it unclear exactly what you may

need for your dust collection?

We are a network of dust collector experts.We represent just about all types and makesof dust collectors. By answering a fewquestions, we can help you determine theright equipment. And find you the best price.

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Improvements in Reverse Fan Cleaning Collector Design

bags need not be kept stretched by use of tension devices since filter bags are pressurizedfrom cleaning manifold

cleaning flow is directly related to filtering capacity of the bag.

they have higher air-to-cloth ratio (volume of air passed through the filtering bag per unit

area of the bag) than shaker collectors and thereby occupy lesser space they are versatile models that can be used effectively for a range of applications

Considerations for Cleaning ProcessIn a sixteen-bag dust collector with an inlet dust load of 100 cu.ft per minute per bag, the totalflow is calculated as:

16 (bags) X 100 cu.ft/min = 1600 cu.ft/min

Typically in these collectors, 3% of the collector is cleaned. So, cleaning (or reverse) airflow mustbe at three times the pressure drop. Reverse flow required to clean one bag would be:










100 cu.ft/min X 3 = 300 cu.ft/min

Flow required to be drawn by the exhaust fan to maintain 1600 cu.ft/min in the collector wouldbe:

1600 + 300 = 1900 ft/min

While considering fan selection, reverse air f low has to be considered as a different source in thesystem. The negative pressure in the system must be maintained for greater cleaning efficiency.When negative pressure drop falls below 10 inches w.c., an auxiliary reverse air blower helps tomaintain the efficiency of cleaning air stream, and when negative pressure drop exceeds 10inches w.c., the pressure can be adjusted by providing a slide gate in the reverse air cleaningcircuit.

Care must be taken to block the bags adjacent to bags that are being cleaned because thesedust particles could settle on the adjacent bags, thereby reducing the collection efficiency of the

system. By blocking the flow, collected dust falls from targeted bag directly into collection hopperinstead of collecting on adjacent bags.

Power requirement can be calculated as under:3% X 3 times power drop = 9% power consumption

Variations in Reverse Blower Dust CollectorsAnother version of the reverse fan cleaning or reverse blower dust collector is the cylindricaldust collectors with filtering bags arranged in a circular pattern. A rotating arm moves thetraveling manifold in a circular fashion atop the filter bags. The rotating arm is also designed tocover the adjacent bags to block airflow during the cleaning process.

ApplicationsThey are commonly used in wood dust filtering where dust loads are about 10-15 grains percu.ft. The vent stream is generally positive. Additional positive pressure blowers can also ventinto one collector. Though positive blowers are less efficient than backward inclined designs,they have their own advantages.

Use of multiple fans divides branches of vent system with low and high pressure drops.Power draw can thus be reduced between different branches. Further system fans getactivated only when specific branches are in operation. In these designs, dust cannot enterinactive branches due to the back draft dampers.

Changes can be carried out easily to branches. For example change in airflow can beachieved by merely changing fan drive for individual branch.

Single point collection of dust facilitates efficient disposal Hopper design (cone shaped) facilitates smooth flow of product to hopper outlet incomparison to other hopper designs

These collectors can be installed on the same structures that support low pressure cyclonecollectors

Upgrading to other fabric collectors is easy with few changes in ductwork

The reverse air fan provides great flexibility to positive pressure systems. Positive pressuresystems have the capability of increasing the flow capacity by increasing flow through thereverse fan. By adding heat to the reverse air fan, any requirement of additional temperaturespread between dry bulb and dew point temperature can be taken care of.

Since hopper openings are at atmospheric pressure in positive pressure systems dust collection

is easily achieved. Hopper openings collect wood dust easily being 16-24 inches in diameter and



thus prevent bridging of wood dust on opening. The reverse air fan cleaning collectors are usedin grain collection and such processes.

Fan Pulse Dust CollectorsThese collectors ‘pulse’ or provide short bursts of cleaning air flow for efficient cleaning. By thismethod a very high percentage of dust is expelled from the bags during the first tenth of the

second that the bag was being cleaned. Dampers can be opened and closed by the rotating armduring cleaning pulse flow or by solenoids, which are used in some rectangular designs. Damperopens typically for ½ second and the entire cleaning operation in the collector takes 3 to 6minutes.

Some Advantages of Reverse Air Cleaning Dust CollectorsIn these collectors the cleaning air is flowing continuously even when the dampers are closed.However, reverse fan pulse cleaning collectors use less cleaning air to clean the bags than othercollectors and thus have all the advantages of continuous cleaning collectors with the additionalbenefit of lower power usage.

Eg. Power required to clean the bags considering a collector with 30 circular rows:Reverse air flow requires cleaning flow of 9% (similar to the continuous fan cleaningsystem example given above).

Power requirement is then calculated as:

( 30 rows ) ( 9% ) X ( 0.5 seconds )( 3 min ) X ( 60 sec/min )

= .75%

Reverse fan pulse collectors are ideal for grain and other food applications due to the gradualincrease of cleaning flow in the system. Fine dust leaves at lower velocities itself and does notcome into play when higher cleaning velocities are reached.

DisadvantagesReverse fan pulse collectors have the following disadvantages:

Limited use. High manufacturing costs for fans with both high positive air pressure and athigh air flow rates

Expensive and slow damper cleaning operations

Reversing air fan motor operates continuously to provide pulsed air for cleaning

Variations in Air Pump Fan Pulse CollectorsA variation in air pump fan pulse was achieved by increasing pressure of the cleaning arm to 7 ½psig and using a positive displacement air pump. The design features of this variation were:

8-12 inch diaphragm valves that operated faster (opening and closing) than dampers

Adequate exhaust velocity from openings on the rotating arms that facilitated openings tobe placed inches from the clean air plenum. This flexibility in location of openings led toeasier adaptability in mounting various types of bags and aided easier top approach withclean air plenums

High pressure cleaning action allowed clean air pumps to be placed next to the collectorwith minimal pressure drop losses

http://www.eionet.europa.eu/gemet/concept?langcode=en&cp=3209






Reverse Pulse Jet DustCollectors Information

The term reverse pulse or

jet dust collector refers tothe air cleaner's cleaningcycle. To clean the filter, aquick burst of compressedair is shot through the filtermedia in the oppositedirection of the dusty airstream. During normal dust

collection, dusty air flowsthrough the filter, and asolid layer of dust forms onthe filter surface. This dustbuild-up is called a dust

cake or filter cake. A quickburst of air shot through the filter in theopposite direction knocks the dust cake offthe filter, breaking it apart. The dust cakecrumbles and falls into a collection bin orbarrel.

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Some dust collectors must stop in order to clean, while other can pulse clean while running.Reverse pulse cleaning was first used in fabric bag filters. Later the reverse jet dust collectorcleaning technology was adapted to cartridge filters.

Variations of Continuous Pulse Jet Cartridge Collectors

Portable Reverse Jet Dust Collectors:Portable cartridge jet dust collectors range in size of a vacuum cleaner to arefrigerator. A moveable source capture arm can be positioned to directlysuck up the dust before it can disperse into the air. The beauty of aportable reverse jet dust collector is serious dust collection power you cancarry or wheel around from workstation to workstation.

Stationary Intermittent Duty Cartridge Collectors:Using one or two cartridge filters in a stationary cabinet, can offer highlyefficient dust filtration. As the name implies, intermittent duty dust collectorsare appropriate for workstations or tools that do not run continuously, yet

produce a considerable amount of dust. A stationary cartridge dustcollector can be used for several workstations or dedicated to oneworkstation, depending on the application. These dust collectors can useeither flexible source capture arms or permanent ducting.

Modular Cartridge Dust Collectors:Multiple rows of cartridge filters can be joined side by side for limitlessfiltration. These systems are custom engineered for each installation,providing heavy duty dust collection for continuously running productionfacilities. For noise and space concerns, a large multiplex of cartridgereverse jet dust collector can be installed outside of a building. A carefullyengineered system of air ducts transport dusty air to the filtration area fromworkstations and tools throughout the plant.

Designs for Continuous Fabric Jet Dust Collectors





http://www.osti.gov/bridge/servlets/purl/835879-D7nRSk/native/835879.pdf















Blow Ring CollectorsBlow ring collectors are the first version of continuous cleaning pulse jet fabric collectors. Theyconsist of tubular bags (14-16 inch in diameter and 6 to 20 feet long) with an inlet for dusty airprovided at the top of the collector. This is a common inlet to all the bags in the system (normallyin multiples of four).

Each bag is fitted with a blow ring on the outside. The rings move vertically along the length ofthe bags in a continuous up-down motion (powered by a chain and sprocket arrangement) andprovide cleaning action. The rings have outlets facing the outside of the collector bags throughwhich clean air is ‘blown’ out. A blower fan is connected to the bags by hoses.

How They WorkDusty air travels from the inlet at the top and enters the bags in a downward flow at 425 feet perminute. The slow air speed aids efficient dust collection at the bottom of the bags and protectsthe surface of the bag from abrasion as well. Cleaning is continuous. Clean air flows out from theblow ring outlets to the outside of the bags while dust is collected in the hopper.

The filtering velocity (filter ratio) is about 18-22 feet/minute while exit velocity of blower air

(cleaning air) is normally at 14000 to 15000 feet/minute. With a cleaning blower flow of about 50ACFM (6% of the filter flow), 1% of the filter media was cleaned during continuous cleaningoperation. Cleaned width of the bag was about half an inch.

Standard specifications of blow ring collectors:

Length of bag 8 feet

Diameter 18 inches

Area of the bag 38 sq.ft.

Filter flow pressure 750 CFM

Number of filtering bags 4

Total flow per collector 3000 CFM Average pressure drop 2 inch water column

Average dust penetration at 10 grains per cubic feet load 0.0002 grains per cubic feet

Advantages of Blow Ring Dust Collectors

They can operate at low pressure drops (1-1 ½ to 3 inch w.c.)

They can handle high dust loads (upper limit of 150 grains per sft)

Air can be re-cycled (mostly)

Long bag life with an average of 5 years or greater

Forms stable dust cake

Versatile system. Can operate under different types of dust loading without adjusting speed

of blow rings. Flexible system that easily adapts for different dust loads. Shortening of bags for heavy

dust loading and lengthening bags lighter dust loading.

Disadvantages of Blow Ring Dust Collectors

They are not designed to withstand high temperature or corrosive action

Regular maintenance is required for the mechanical drives that operate blow tubes

Improvements of Fabric Jet Dust Collectors

The next generation fabric collectors were designed to handle process air streams with high

temperatures and corrosive conditions - a limitation in early continuous cleaning pulse jet fabriccollectors such as blow ring collectors. In these improved design, bags (diameter of 4-6 inch and



length of 6 feet) are arranged in rows of 6 to 10 bags each. Cleaning action is done by directinga continuous stream of compressed air jet into each bag through holes in a compressed air pipethat is placed atop the row of bags. The compressed air jet holes were located at the throat ofeach bag.

The cleaning action is based on the principle that ‘compressed air jet expands until stopped’

(Law of Conservation of momentum). The expansion of the air jet can be limited by

i. The bag opening (size)ii. By inserting a tube in the bag’s throat. The tube is designed with an appropriate diameter

to generate appropriate jet speed, given the size of the hole in the pipeiii. By a venturi, to reduce pressure drop when air flows from the bag into the clean air

chamberiv. By installing an orifice plate at the center of the throat of the bag.

This design of fabric pulse jet collector could handle high temperature and corrosive conditionseffectively.

The older designs were modified in 1971. The specifications of the early designs and ‘generic’collectors are compared in the following table:

Comparison between specifications of older design and modified designs of fabric pulse jetcollectors:

Older design, 1963 Modified design, 1971(Generic collector)

Average air flow speed at mouth of the tube 15000 feet per minute 25000 feet per minute

Diameter of venturi throat 17/8 inches 17/8 inches

Jet flow 290 CFM 500 CFM

Bag dimensions (diameter X length) 4 ½ inches X 72 inches 4 ½ inches X 120 inches Bag area 7 sq. ft 12 sq. ft

Filter flow ratio 100 CFM 90 CFM

Nominal filter ratio 14 FPM 8 FPM

Average air utilization ¾ SCFM per 1000 CFM of filtered air

1 ¼ SCFM per 1000 CFM of filtered air

Average pressure drop 3 ½ inches water column 6 inches water column

Average dust penetration at 10 grains percubic feet load

0.0005 grains per cubic feet 0.008 grains per cubic feet

The effects of the modifications are discussed below.

Effects of Lower Filter RatioThe new design had lower filter ratio (filtering velocity) which caused air utilization, pressure dropand dust penetration to increase while bag life reduced by 2-3 years. The problems of themodified version can be attributed to two main considerations (i) speed of dust moving upwardfrom hopper inlets to filter compartment (ii) change in cleaning jet attributes

Effects of Change in Jet Speed From 15000 to 25000 ft/minWith increased jet speed, the bags ballooned into a cylindrical shape in the new design duringthe cleaning operation. This ‘flexing’ movement of the bag helped in providing an effectivecleaning action. (When cleaning process was not on, the bags were normally in a concave shape

between the vertical wires on the cage).When the collective open area of dust cake is larger than the jet area, pressure does not build up



enough to dislodge the bag from the wires and the ‘flexing’ does not occur (when pressure dropis below 2 inch water column, w.c.). At 3 ½ inches w.c., flexing occurs on generic jet based fabriccollectors.After cleaning, total area of the opening in the bag/ cake is increased and facilitates moreefficient dust collection. Pressure equilibrium can be achieved by lowering the pressure drop.

Effect of Increase in Dust Flow Speed During CleaningA feature of the new design was the increase in jet flow speeds from 15000 fpm to 25000 fpmwhich when converted into velocity pressure translates to 14 inches w.c. and 38 inches w.c.respectively. From the above we can see that dust is now being expelled from the bag at 2.7times the original force during cleaning.With increase in speed, the dust that is expelled normally landed on adjacent bag and cake. Thecake grows denser and becomes an efficient filter until pressure balance is reached. This cakecan collect fine dusts that are less than 20 microns.In certain cases, depending on the density of dust, outlet of collecting bags expanded after acompressed air jet burst. This is known as ‘puffing’. Lower density dusts thrust themselves ontoadjacent bags more easily and can operate with low pressure drop, air utilization and lowpenetration.

Effect on Selection of Filter MediaThe prime consideration for filter media selection in this case is to restrict dust that is pushedthrough the bag and its cake. To counter this problem the following options could be considered:

Laminated construction: By laminating PTFE media to the fabric, filter media developsexcellent filtering characteristics. The fine openings of the laminate obstruct water whileletting air pass through them since the laminate has waterproofing qualities. This type of afilter is expensive.

Fabricate filter cloth: By providing finer threads at the filter surface and coarser threadsbelow the surface, the fabric becomes a mangled path, which is not easy to infiltrate bydust. This type of a fabric is a characteristic of dual dernier felts and woven felts.

Effects on Bag and Suggested Modifications Therein

Pleated filter elements: Dust penetration during cleaning can be eliminated by usingpleated filter elements. In pleated filter elements dust can be propelled at high speedsagainst adjacent bags but since that collecting surface is also blowing dust in the reversedirection, dust penetration does not occur or is reduced.

Bag diffusers: By inserting bag diffusers such as perforated cylinders that fit into the cageoutside the venturi, the cleaning jet speed can be slowed down.Baffles: By inserting baffles between rows of bags, dust is prevented from being propelledagainst adjacent bags.

Pulse Jet Collector Variations and ImprovementsThe next variation developed a pulse jet collector that can operate at low pressure drops andhigh filter ratios (18 to 22:1). The principle was that the better the cleaning capability of the filtermedia, greater was the air flow.

By slowing down compressed air jet speed, the following were achieved in these dust collectors:

pressure drop was reduced to levels used in the blow ring collector

dust penetration came down by 80%

bag life increased by 200%.

Specifications of a fabric pulse jet collector – the high ratio design: Average speed of air flow at bag opening 10000 fpm



Bag inlet size 4 ½ inch diameter

Jet flow 740 cfm

Diameter and length of bag 4 ½ inches X 96 inches

Area of the bag 10 sq. ft

Filter flow per bag 190 CFM Nominal filter ratio 20 FPM

Pressure drop (average) 2 ½ inch per water column

Air consumption (average) ½ SCFM/1000 CFM of flow

Dust penetration at 10 gr/cu.ft. load (average) 0.0005 gr/cu/ft

Adaptations made to achieve greater efficiencies in High Ratio collectors:

Changes to Inlet:Inlets were provided at the top of the collector to create a downward flow of air enabling thesystem to collect finer dusts that were not collected by hopper inlets in the earlier design (sincefine dusts do not accumulate properly, they have the tendency to be carried away by the upwardair streams prevailing near the hopper inlet and may not collect in the hopper). The efficiency ofthe new inlet design increased due to a change in direction of the airflow that facilitated easyremoval of heavier dust particles from the air stream.

Baffles and Bag Spacing:Perforated vertical baffles controlled direction of air stream and dust in the filter compartment.Wider bag spacing was provided.

Uses:Highly versatile, the high ratio dust collectors can be used in all the applications of fabric andcartridge filters. They are effective even in efficient collection of very fine sub micron dusts that

are normally associated with smelting, welding and combustion processes.

Advantages of High Ratio Fabric Collectors:

They require the least space among all other dust collectors.

They can operate at 14-18 % filter ratio (twice the filter ratio of ‘generic’ collectors)

200% increase in bag life

50% reduction in compressed air requirement

Pulse Jet Considerations With Regard to Compressed Air:Compressed air at the pipe outlet reaches the speed of sound (sonic speed) when the pressure

in front of the outlet is about 13 psig. At this speed, by increasing pressure, airflow increases butthe speed does not increase anymore. Pressure at the pipe outlet is constant at 0.528 timesabsolute pressure in the pipe, and the difference in pressure goes unused.

Comparison of efficiency of orifices (in pipe) and nozzles at various pressures is shown in thetable below:

Air pressure in

pipe (psig) Exit pressure in

orifice (psig) Efficiency % Exit pressure in

nozzle Efficiency %

13 0 100 N/A N/A

25 6.5 74 0 95

50 19.3 61 0 95

75 32.5 57 0 95



90 40.0 55 0 95

The results indicate higher efficiencies in nozzles.

NozzlesNozzles help in conversion of pressure energy to velocity energy. Airflow at the orif ice is

normally at sonic velocity or 1000 fps. but by using a converging diverging nozzle, air flow speedincreases to 1750 fps at nozzle with 90 psig in the pipe. Cleaning efficiency is thus increasedsharply by taking advantage of the higher jet speed and using it in the cleaning jet.

Expansion of air jet can be limited during cleaning process as done in the generic cleaningsystem. Instead of a tube or a venturi, the open area of the bag mouth can be used to preventexpansion of air jet. Since filtering fan speed is low, the compressed air jet can be reduced aswell.

Generic Pulse Jet CleaningIn this type, a 1 ¾ inch diameter venturi is used to prevent expansion of air jet. Jet speed beinghigh, it sweeps through the opposing filtering fan air by compressing it, until it reaches thebottom of the bag. The air jet bounces off the bottom, expands and fills the bag with cleaning air.

The jet air reverses the direction of filtered air flow and dislodges the dust cake from the outersurface of the bag by the jet air.

A comparison between Generic dust collectors and Pulse jet collectors characteristics:

Generic dust collector Pulse jet collector

Length of bag 8’ 8’

Diameter of bag 4 ½ “ 4 ½ “

Area of bag 9.46 sq. ft 9.46 sq. ft

Air-to-cloth ratio 5:1 10:1

Filtered air volume (per bag) (5) (9.46) = 47.3 CFM (10) 9.46) = 94.6 CFM

Bag/venturi diameter (at mouth) 1 ¾ “ at venturi 4 ½ “ at bag opening

Bag/venturi area (at mouth) π (1-3/4)²= 0.0167 sq. ft π (4-1/2)²= 0.1104 sq. ft

(4) (144) (4) (144)

Filtered air velocity at bag/venturi (atmouth)

47.3 = 2,832 fpm fan air 94.6 = 857 fpm fan air

0.0167 0.1104

Cleaning air jet velocity at bag/venturi throatopening

Higher Lower

Cleaning air jet in generic collectors is lower than the filtering fan air, which is the reason why thecleaning efficiencies are low when compared to pulse jet collectors.

electrostatic precipitation for dust collection

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