Encyclopedia of Dust Collector

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The Encyclopedia Of Filters – Dust Collection

Systems

Posted by dominickdalsanto on Feb 1, 2011 in Baghouse.com News, Dust Collection Blog, Dust Collector Maintenance, Operation & Optimization | 1 comment

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By Dominick DalSanto Environmental Expert & Author

This article has been designed to educate customers by giving a brief overview of all the Dust Collection Syste

available today. A detailed explanation of the benefits and drawbacks of each type of system can be found in

further articles on Baghouse.com

What is a Dust Collector?

After the contaminated air is captured by a Dry Dust Collection system, either by means of a Central CollectioSystem, or in a unit Collector. The dust filled air then needs to be treated and the contaminates removed, befor

the air can be recirculated back into the facility or dispersed into the atmosphere. The Dust Collector separates

particles from the airstream and sends it on to its final destination.

Why are Dust Collectors Needed?

There are many reasons why having a proper Dust Collection System installed in your facility is needed, a few

important reasons are:

• To protect employees and society from exposure to pollution,

• To recover valuable products from the dust filled air • To facilitate compliance with health and air emission standards.

Types of Dust Collectors

The five principal types of industrial dust collectors that will be discussed in this article are:

• Cyclone Collectors (Inertial separators)

• Baghouses (Fabric collectors)• Wet scrubbers

• Electrostatic precipitators

• Unit collectors

Cyclone Collectors (Inertial Separators)

Inertial separators work by making use of one or more of the following forces centrifugal, gravitational, andinertial in order to separate dust from the airstream. Once separated, the dust is removed to a hopper by gravity

for temporary storage. While this type of collect can be used in applications where particle sizes are large and

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only a “rough” air filtration is desired, the main usage for this type of collector is as a precleaner, to remove la particles and debris and avoid overloading and damaging more efficient dust collectors.

The three types of Inertial Separators are:

• Settling Chambers

• Baffle Chambers• Centrifugal Collectors

A Settling Camber is a large box installed into the ductwork. The sudden larger area for the airstream to pass

through causes the air stream to slow down, which in turns causes the larger particles to settle to the bottom of

chamber. This type of collector is rarely used as the primary dust collector due to it’s large space requirementsand low efficiency. However, the fact that it can be fashioned from almost any material and its simple design,

which requires little maintenance, leads it to being a wise choice as a precleaner for a more efficient Dust

Collector.

A Baffle Chamber has a fixed baffle plate that causes the airflow to rapidly change its direction, first turningdownward, and then making a 180 degree turn back up. In the process, the larger particles fall to the bottom of

chamber and can be collected from there. As with Settling Chambers this type of collector is best used as a

precleaner for another more efficient collector further in the collection system. Also like a Settling Chamber itrelatively simple design and low maintenance needs make it an excellent choice for the beginning of any large

scale collection system.

Centrifugal Collectors create a vortex in the airstream within an enclosure, similar to water going down a drai

Normally this is done by having the airstream enter the collect at an angle, which causes it to spin. As theairstream is spun around the collector, the particles strike the wall and fall into the hopper below.

Within this category there are two main types of systems in use:

• Single Cyclone systems

• Multiple Cyclone systems

A Single Cyclone Collector creates a dual vortex, a main downward vortex to disperse the coarser matter, and secondary upward vortex to remove the finer particles on the return to the outlet to the duct system.

A Multiple Cyclone Collector works in the same manner as the Single Cyclone variety albeit with several sma

dynamiter cyclones instead of just one. The multiple cyclones work in parallel and share the same air input and

output.

Between the two, the Multiple Cyclone Collector will operate more efficiently because of being longer in leng

and smaller in dynamiter. The smaller dynamiter cause the centrifugal force generated to be greater, and the

longer length allows for more contact with the surface of the collector by the particles thereby causing more

particles to be removed from the airstream. However, a greater loss of pressure is found in Multiple CycloneCollectors than in Single Cyclone Collectors.

Again as with the other kinds of Inertial Separators, this systems main advantage is the lack of moving parts th

requiring less maintenance and repair. While it can be designed to remove a specific size range of particles, it remains best used as a precleaner to eliminate coarse particles and ease the load on more efficient Dust Collect

further along in the system.

Advantages & Disadvantages – Centrifugal Collectors

Types Advantages Disadvantages



Cyclones Have no moving partsHave low collection efficiency for

respirable particulates

Can be used as precleaners to remove coarser

particulates and reduce load on more efficient dustcollectors

Suffer decreased efficiency if gas viscoor gas density increases

Can be designed to remove a specific size range of particles

Are susceptible to erosion

Have drastically reduced efficiency duereduction in airflow rate

Cannot process sticky dust

Multiclones Have no moving partsHave low collection efficiency for

respirable particulates

Are more efficient than single-cyclone separatorsAre prone to plugging due to smaller

diameter tubes

Have low pressure drop when used as a precleaner Improper gas distribution may result in

dirty gas bypassing several tubes

Cannot process sticky dust

For a given gas volume, occupy more s

than single-cyclone separators

Common Operating Problems & Solutions – Cyclone Collectors

Symptom Cause Solution

ErosionHigh concentrations of heavy,

hard, sharp-edged particles

Install large-diameter “roughing” cyclone upstr

of high-efficiency, small-diameter cyclone.

Line high-efficiency cyclone with refractor or

erosion-resistant material.

CorrosionMoisture and condensation in

cycloneKeep gas stream temperature above dewpoint.

Insulate cyclone.

Use corrosion-resistant material such as stainles

steel or nickel alloy.

Dust Buildup Gas stream below dewpoint Maintain gas temperature above dewpoint.

Very sticky material Install vibrator to dislodge material.

Reduced Efficiency or

Dirty Discharge Leakage in ductwork of cyclone Clean cyclone routinely.

Check for pluggage and leakage and unplug or s

the ductwork.

Close all inspection ports and openings.

Reduced gas velocity in cycloneCheck the direction of fan rotation; if rotation is

wrong, reverse two of the tree leads on motor.

Common Operating Problems and Solutions – Multiclones




ErosionHigh concentrations of heavy, hard,

sharp-edged particlesInstall cast iron tubes.

Install a wear shield to protect

tubes

Overloaded tubesUneven gas flow and dust

distribution

Install turning vanes in elbow, i

elbow precedes inlet vane.

Loss of volume in tubes

Uneven pressure drop across tubes

Plugging in inlet vanes, clean gas outlet

tubes, and discharge hopperLow gas velocity Install turning vanes in elbow in

Uneven flow distribution Insulate multiclone

Moisture condensationInstall bin-level indicator in

collection hopper.

Overfilling in discharge hopper Empty hopper more frequently.

Reduced efficiency or dirty gas stack Leakage in ductwork

Seal all sections of ductwork an

multiclone to prevent leaks

Leakage in multiclone

Startup/Shutdown Procedures – Centrifugal Collectors

Type Startup Shutdown

Cyclones 1. Check fan rotation.1. Allow exhaust fan to operate for a few minuteafter process shutdown until cyclone is empty.

2. Close inspection doors, connections, and

cyclone discharge.

2. If combustion process is used, allow hot, dry

to pass through cyclone for a few minutes after process shutdown to avoid condensation.

3. Turn on fan. 3. Turn off exhaust fan.

4. Check fan motor current. 4. Clean discharge hopper.

5. Check pressure drop across cyclone.

Multiclones 1. Conduct same startup procedures as cyclones. 1. Conduct same shutdown procedures as cyclo

2. At least once a month, measure airflow by

conducting a pitot traverse across inlet todetermine quantity and distribution of airflow.

3. Record pressure drop across multiclone.4. If flow is significantly less than desired, block off rows of cyclone to maintain the necessary

flow per cyclone.

Preventative Maintenance Procedures – Centrifugal Collectors

Type Frequency Procedure

Cyclones Daily Record cyclone pressure drops.

Check stack (if cyclone is only collector).



Record fan motor amperage.

Inspect dust discharge hopper to assure dust is removed.

Weekly Check fan bearings.

Check gaskets, valves, and other openings for leakage.

MonthlyCheck cyclone interior for erosion, wear, corrosion, and other visible signs of

deterioration.

Multiclones Daily Same as cyclones.

Weekly Same as cyclones.

MonthlyCheck multiclone interior for erosion, wear, corrosion, and improper gas and dust

distribution.

Inspect individual cyclones and ducts for cracks caused by thermal expansion or norm

wear.

Fabric Dust Collectors

Fabric Collectors (commonly known as a Baghouse) are among the most widely used dust collection systemsThey benefit from having the potential to be one of the most efficient (up to 99% of very fine particles) and co

effective dust collection systems you can choose.

The way they work

The Gas stream enters into the Baghouse via the location’s duct system. Once inside the dust filled gases comeinto contact with the filter bags within. As the gases pass through the filters the dust particles are trapped on th

filter media. Over time a layer of cake dust is built up on the surface of the filter bags. This is the secret to this

filter medium’s high efficiency potential. Once the cake dust has formed, it further impedes the passage of dusthrough the filters in four different ways:

• Inertial Collection: The incoming Gas stream strikes the filter media, which is located perpendicular to the

Gas flow before changing direction causing the dust particles to remain on the filter.

• Interception: Particles that do not cross the fluid streamlines come in contact with fibers because of the fibesize.

• Brownian movement : By means of diffusion, there is an increased chance of contact between the filter and

dust particles due to their molecular motion.• Electrostatic Forces: An increased attraction can occur between the dust particles and the filter media when

electrostatic charge is found on the dust particles.

Air to Cloth RatioAn understanding of the term Air to Cloth Ratio is vital to understand the mechanics of any Baghouse systemregardless of the exact type used. This ratio is defined as the amount of air or process gas entering the Baghou

divided by the sq. ft of cloth in the Baghouse. An example of an Air to Cloth Ratio is provided below courtesy

http://www.usairfiltration.com

(Bag diameter in inches x pi x bag length in inches)Total Cloth area = 144 x total number of bags

A standard 6” bag has a 5-7/8” diameter

This bag is 12’ long

There are a total of 132 bags in the Baghouse

http://www.baghouse.com/products/dust-collectors/baghouses/

http://www.baghouse.com/products/dust-collectors/baghouses/



= (5-7/8” x 3.1416 x 144”) ÷ 144 x 132= (5.875” x 3.1416 x 144”) ÷ 144 x 132

= (2657.79) ÷ 144 x 132

= 18.46 SF of cloth per bag x 132 bagsTotal cloth area = 2,436 sq. ft.

Assume the Baghouse is handling 13,000 ACFM of air

Air to cloth ratio = ACFM ÷ total cloth area= 13,000 ÷ 2,436

= 5.34 : 1

Different Baghouse designs

There are three main types of Baghouse systems currently in use today. The same basic mechanics are presentall of them, the main difference being how filter bags are cleaned.

• Mechanical Shaker

• Reverse Air

• Reverse Jet (Or Pulse Jet)

A Mechanical Shaker is a design where the filter bags are suspended from the top of the Baghouse by horizon beams and fastened to a cell plate on the bottom. When the Gas stream enters at the bottom of the Baghouse it

then forced up through the inside of the tubular filter bags, thereafter passing unto the airflow outlet at the top.

The cleaning of this type of Baghouse is done by a shaking of the top horizontal bar that the filter bags areattached to. This is caused by a motor driven shaft and cam system that sends waves down the surface of the

filter bags causing the dust to fall off the interior of them into the hopper below. This Baghouse has a relative

low Air to Cloth Ratio requiring large amounts of space. Despite this draw back, the simple design remains anoted advantage, leading to this system being widely used in the mineral processing industry.

In a Reverse Air Baghouse, Filter bags are connected to a cell plate on the bottom of the Baghouse and are

suspended from an adjustable hanger frame on top. The Gas stream, as in the Mechanical Shaker design enters

into the Baghouse and passes through the filter bags from the bottom leading to the dust collecting again on thinterior of the filter bags, thereafter leaving through the outlet port at the top. Again the main difference in thi

style of Baghouse system when compared to others is the cleaning mechanism. In this system, a cleaning cycle

starts with injecting clean air into the Collector in the reverse direction of the normal flow. This causes thecompartment to become pressurized. The pressure causes the bags to collapse slightly releasing the cake dust t

crack and fall off to be collected by the hopper below. Since it is necessary to shut down normal airflow to th

Baghouse during the cleaning cycle, this type of Baghouse is normally compartmentalized so as to allow for o

a partial shutdown of the system.

With a Reverse Jet or Pulse Jet Baghouse, the same basic design is found as in the other types of Baghouse

design, however, with a few very important differences. In a Pulse Jet Baghouse, the filter bags are individuall

overlaid on a metal cage, which is then attached to a cell plate at the top of the compartment. The Gas streamenters the Baghouse at the bottom and is forced through the outside to the inside of the filter bags after which t

Gas stream exits the compartment from the outlet port at the top. The main advantage of this Baghouse is that

does not require a shutdown of any kind to run a cleaning cycle. A digital sequential timer is attached to the on

of the filter bags inside the Baghouse. This timer signals a solenoid valve to start the cleaning cycle when itdetects a certain amount of build up on the bag. It consists of a small burst of compressed air being fired down

through the filter bags. Which cause the excess cake dust to fall off into hopper at the bottom of the Baghouse

where it can be collected. The cleaning cycle of the Pulse Jet collectors provides a more complete cleaning andreconditioning of the filter bags than in the Shaker, and Reverse Air designs. Also the short nature of the clean

cycle also leads to a reduction in the recirculation and redeposit of dust. Finally, enabled by the continuous

cleaning feature of the design, this kind of collection system has a higher Air to Cloth Ratio so the space

requirements are much lower than in other systems.



Cartridge Collectors

Unlike Baghouse collectors which feature the use of woven or felt filter bags, Cartridge Collectors use perfora

metal cartridges that are cylindrical shaped and open on one or both ends lined with a pleated nonwoven filteri

media. Once installed, one end of the cartridge is sealed off and the open end is used for the clean exhaust.Similar to a Baghouse, the Gas stream is forced through the outside of the cartridge to the inside where it then

exits back into the system. Cartridge Collectors are also compatible with Reverse or Pulse Jet cleaning. Large

numbers of these Collectors can be installed and used for continuous filtration for a location’s dust collection

system.

Advantages and Disadvantages – Baghouses

Types Advantages Disadvantages

Shaker

Baghouses

Have high collection

efficiency for respirable

dust

Have low air-to-cloth ratio

(1.5 to 2 ft/min)

Can use strong woven bags, which can withstand

intensified cleaning cycleto reduce residual dust

buildup

Cannot be used in high

temperatures

Simple to operateRequire large amounts of

space

Have low pressure drop for equivalent collection

efficiencies

Need large numbers of filter

bags

Consist of many moving

parts and require frequent

maintenancePersonnel must enter Baghouse to replace bags,

creating potential for

exposure to toxic dust

Can result in reduced

cleaning efficiency if even a

slight positive pressureexists inside bags

Reverse Air

Baghouses

Have high collection

efficiency for respirabledust

Have low air-to-cloth ratio

(1 to 2ft/min)

Are preferred for high

temperatures due to gentlecleaning action

Require frequent cleaning

because of gentle cleaningaction


efficiencies

Have no effective way toremove residual dust

buildup

Cleaning air must be filtered

Require personnel to enter



baghouse to replace bags,

which creates potential for toxic dust exposure

Pulse Jet

(Reverse Jet)

Baghouses

Have a high collectionefficiency for respirable

dust

Require use of dry

compresses air

Can have high air-to-cloth

ratio (6 to 10ft/min)

May not be used readily in

high temperatures unless

special fabrics are used

Have increased efficiencyand minimal residual dust

buildup due to aggressive

cleaning action

Cannot be used if highmoisture content or

humidity levels are present

in the exhaust gases

Can clean continuously

Can use strong woven bags

Have lower bag wear

Have small size and fewer

bags because of high air-to-cloth ratio

Some designs allow bag

changing without entering

Baghouse


efficiencies

Common Operating Problems and Solutions – Baghouses*


High Baghouse

pressure dropBaghouse undersized consult vendor

Install double bags

Add more compartmentsor modules

Bag cleaning mechanismnot properly adjusted

Increase cleaningfrequency

Clean for longer duration

Clean more vigorously

Shaking not strongenough (S)

Increase shaker speed

Compartment isolationdamper valves not

operating properly (S,

RA)

Check linkage

Check valve seals

Check air supply of



pneumatic operators

Compressed air pressure

too low (PJ)Increase pressure

Decrease duration and

frequency

Check compressed-air

dryer and clean it if

necessaryCheck for obstructions in piping

Repressurizing pressure

too low (RA)

Speed up repressurizing

fan.

Check for leaks

Check damper valve

seals

Pulsing valves failed (PJ) Check diaphragm

Check pilot valvesBag tension too tight

(RA)Loosen bag tension

Bag tension too loose (S) Tighten bags

Cleaning timer failureCheck to see if timer is

indexing to all contacts

Check output on allterminals

Not capable of removingdust from bags

Check for condensationon bags

Send dust sample and bags to manufacturer for

analysis

Dryclean or replace bags

Reduce airflow

Excessive reentrainmentof dust

Empty hopper continuously

Clean rows of bags

randomly instead of

sequentially (PJ)

Incorrect pressure-drop

readingClean out pressure taps

Check hoses for leaks

Check for proper fluid

level in manometer

Check diaphragm in

gauge

Dirty Discharge at

stack

Bags leaking Replace bags



Isolate leaking

compartment or module

Tie off leaking bags and

replace them later

Bag clamps not sealingSmooth out cloth under

clamp and re-clamp

Check and tighten

clampsFailure of seals in jointsat clean/dirty air

connection

Caulk or weld seams

Insufficient filter cake

Allow more dust buildup

on bags by cleaning lessfrequently.

Use precoating on bags

(S, RA).

Bags too porous

Send bag in for

permeability test andreview with

manufacturer

High compressed-

air consumption

(PJ)

Cleaning cycle too

frequent

Reduce cleaning cycle, if

possible

Pulse too long Reduce pulsing duration

Pressure too highReduce supply pressure,if possible

Diaphragm valve failureCheck diaphragm andsprings

Check pilot valve

Reduced

compressed-air

pressure (PJ)

Compressed-air

consumption too highSee previous solutions

Restrictions in

compressed-air piping

Check compressed-air

piping

Compressed-air dryer

plugged

Replace dessicant in the

dryer

Bypass dryer temporarily, if possible

Replace dryer

Compressed-air supply

line too smallConsult design

Compressor worn out Replace rings

Check for worn

components

Rebuild compressor or

consult manufacturer



Pulsing valves not

working

Check pilot valves,

springs, and diaphragms

Timer failed Check terminal outputs

Moisture in

BaghouseInsufficient preheating

Run the system with hot

air only before process

gas flow is introduced

System not purged after

shutdown

Keep fan running for 5 to

10 min after process isshut down

Wall temperature below

dewpointRaise gas temperature

Insulate unit

Lower dewpoint by

keeping moisture out of

system

Cold spots through

insulation

Eliminate direct metal

line through insulation

Water/moisture in

compressed air (PJ)Check automatic drains

Install aftercooler

Install dryer

Repressurizing air

causing condensation (PJ)

Preheat repressurizing

air

Use process gas as

source of repressurizingair

Material bridgingin hopper

Moisture in Baghouse See previous solutions

Dust stored in hoppersRemove dustcontinuously

Hopper slope insufficientRework or replace

hoppers

Screw conveyor opening

too smallUse a wide, flare trough

High rate of bag

failure, bags

wearing out

Baffle plate worn out Replace baffle plate

Too much dust Install primary collector

Cleaning cycle too

frequentSlow down cleaning

Inlet air not properly

baffled from bagsConsult vendor

Shaking too violent (S)Slow down shakingmechanism

Repressurizing pressure Reduce pressure



too high (RA)

Pulsing pressure too high

(PJ)Reduce pressure

* S = Shaker

RA = Reverse Air

PJ = Pulse Jet

Startup/Shutdown Procedures – Baghouses

Startup Shutdown

1. For processes generating hot, moist

gases, preheat Baghouse to prevent

moisture condensation, even if Baghouseis insulated. (Ensure that all compartments

of shaker or reverse-air Baghouses are

open.)

1. Continue operation of

dust-removal conveyor and

cleaning of bags for 10 to 20minutes to ensure good

removal of collected dust.

2. Activate Baghouse fan and dust-

removal conveyor.

3. Measure Baghouse temperature and

check that it is high enough to preventmoisture condensation.

Preventive Maintenance Procedures – Baghouses

Frequency Procedure

Daily

• Check pressure drop.

• Observe stack (visually or with opacity meter).

• Walk through system, listening for proper operation.• Check for unusual occurrences in process.

• Observe control panel indicators.

• Check compressed-air pressure.• Assure that dust is being removed from system.

Weekly

• Inspect screw-conveyor bearings for lubrication.• Check packing glands.

• Operate damper valves.• Check compressed-air lines, including line filters and dryers.

• Check that valves are opening and closing properly in bag-cleaning sequence.

• Spot-check bag tension.• Verify accuracy of temperature-indicating equipment.

• Check pressure-drop-indicating equipment for plugged lines.

Monthly



• Check all moving parts in shaker mechanism.• Inspect fans for corrosion and material buildup.

• Check drive belts for wear and tension.

• Inspect and lubricate appropriate items.• Spot check for bag leaks.

• Check hoses and clamps.

• Check accuracy of indicating equipment.• Inspect housing for corrosion.

Quarterly

• Inspect baffle plate for wear.

• Inspect bags thoroughly.

• Check duct for dust buildup.• Observe damper valves for proper seating.

• Check gaskets on doors.

• Inspect paint, insulation, etc.• Check screw conveyor for wear or abrasion.

Annually

• Check fan belts.

• Check welds.• Inspect hopper for wear

Wet Scrubbers

Another effective method of dust collection is the use of Wet Scrubbers (Air Washers). These systems use a

scrubbing liquid (usually water) to filter out finer dust particles. After being filtered the Gas Stream is then sethrough a mist eliminator (demister pads) to remove the excess moisture from the Gas stream. Afterward the G

stream exits the collector through the outlet port and returns back into the system. Wet Scrubbers are ideal:

• For the collection of explosive material

• Where “slurry” produced could be reused (either in other parts of process or sold)• Where chemical reactions could be generated with other collection methods

• To absorb excess air

Wet scrubbers have the advantage of low start up costs and low space requirements. They are well suited for

treating high temperature and high humidity Gas streams. They also are able to process both air and “sticky” particulates. The main disadvantages are that they are costly to operate, require a precleaner for any heavy du

loads, cause water pollution that then needs to be addressed, and can erode with high air velocities.

There are a vast variety of different designs and applications of this type of filtration system but all of them hathree basic operations they perform:

• Gas-humidification: The gas-humidification process conditions fine particles to increase their size so they c

be collected more easily.

• Gas-liquid contact: This is the entire basis for the operation of this type of system. The method of contact between the liquid is done in four main ways:

• Inertial impaction takes place when the Gas stream is forced to flow around the droplets in its path. The

stream separates and flows around the droplet. However the larger particles continue to be carried by inertial



force in a straight path coming in direct contact with the liquid.• Interception: Finer particles while not directly coming in contact with the droplets, do however brush up

against the side of them causing them to be absorbed into the liquid.

• Diffusion occurs when a fine mist is created from the liquid being used. As the particles pass through the mthey make contact with the surfaces of the droplets by means of the Brownian effect, or diffusion.

• Condensation nucleation is the effect of a gas being cooled below its dew point while within a moisture ric

environment, causing the vapor to condense of the surface of the particles thereby encapsulating them.

• Liquid separation: After going through the cleaning phase the remaining liquid and contaminates must beremoved before the Gas stream can be sent back into the system. This is accomplished by means of a Mist

Eliminator (Demister Pads). Which remove the liquid and dust mixture from the Gas stream and send it to a

collector. Once in the collector, the solid waste settles to the bottom where it is removed by means of a drag chsystem to be deposited in a dumpster or another collection area.

Wet Scrubbers are further categorized by pressure drop (in inches water gauge) as follows:

• Low-energy scrubbers (0.5 to 2.5)

• Low- to medium-energy scrubbers (2.5 to 6)• Medium- to high-energy scrubbers (6 to 15)

• High-energy scrubbers (greater than 15)

The large amount of different Wet Scrubbers in use makes it impossible to comment on every single design inarticle. However a brief overview of the most common types will enable you to understand the basic operation

procedures present in all of them.

Low Energy Scrubbers:

• The most basic design is that of a Gravity Spray Tower Scrubber . In this system the contaminated air enter

the bottom of the cylindrically shaped scrubber and rises through a mist of water sprayed from nozzles at the t

The dirty water collects at the bottom of the tank and the clean air (mist) exits from the top of the collector. Thcollector has a relatively low efficiency compared to other kinds of Wet Scrubbers. However it’s main advanta

is it can handle very heavy dust loads without getting backed up.

• Dynamic wet precipitators also called Wet Fan Scrubbers are a popular design used for medium energyscrubbing applications. In this system the Gas stream passes through a larger fan that is constantly kept wet wi

the cleaning liquid. The particles are trapped in the liquid and are then by means of centrifugal force thrown of

the spinning fan blades unto the sides of the collector where they eventually settle at the bottom enabling them

be collected.

• Orifice Scrubbers work in a very similar way to inertial separators but with one important difference, Orifi

Scrubbers use a water surface to capture the dust particles. When the Gas stream enters the collector it is rapid

redirected when it comes in contact with the water surface. Causing the dust particles to be removed from the G

stream. A greater efficiency can be obtained by the addition of liquid spray nozzles to further separate thecontaminates from the Gas stream. While these are an effective filtration system one should note that they tend

be ineffective against fine particles as these tend to be redirected off of the water surface by the high surface

tension.

Low to Medium Energy Scrubbers:

• Wet Cyclone Scrubbers are nearly identical to their normal cyclone collector counterparts. In a Wet Cyclon

Scrubber the Gas stream enters the collector and is then forced into a cyclone movement by the strategic placement of stationary scrubbing vanes. Liquid is introduced at the top of the collector allowing the dust

particles to stick to the wet walls of the collector when they are thrown off by the vortex. As with dry Cyclone

Collectors, this type of system has the benefit of few to no moving parts and it is efficient for particles up to 5uand above.



Medium to High Energy Scrubbers:

• Packed Bed Scrubbers consist of a bed of packing media, which is then sprayed with water. The packingmedia allows for a very wide distribution of the water, which in turn allows the Gas stream to have the maxim

contact with the water during its passage though the collector. Air enters at the bottom of the collector where i

first makes contact with the water in the recirculation tank. Then it is forced up through the various layers of thfiltering media, and after being sent through a Mist Eliminator is sent back into the system via the exit port at t

top.

Within the category of Packed Bed Scrubbers there are three different variations on the implementation of this

filtering mechanism they are:

• Cross-flow scrubbers are designed to minimize height for low-profile applications. In this design the packemedia is laid as sheets perpendicular to the Gas stream. The Gas stream enters in one side of the Scrubber and

flows horizontally through it passing though the packing media and then exiting out the opposite side

• Co-current flow scrubbers• Counter-current flow scrubbers

High energy Scrubbers:

• Venturi Scrubbers make use of the Venturi effect to accelerate the Gas stream to speeds of 12,000 to 36,00ft/min. The Gas stream enters into the Scrubber through a Venturi shaped inlet where it is sprayed with water.

water hitting the extremely high speed air causes it to instantly atomize. The very fine water droplets attach to

dust particles and form a slurry, which then falls to the bottom of the collector. After passing through a Misteliminator the Gas stream is sent back into the system.

Advantages and Disadvantages – Wet Scrubbers

Advantages Disadvantages

Have low capital costs and small

space requirements

Have high operating and

maintenance costs

Have low capital costs and small

space requirements

Require corrosion-resistant

materials if used with acidicgases

Are able to collect gases as well as particulates (especially “sticky”

particulates)

Require a precleaner for heavydust loadings

Have no secondary dust sourcesCause water pollution; require

further water treatment

Are susceptible to erosion athigh velocities

Collect wet products

Require freeze protection

Common Operating Problems and Solutions – Wet Scrubbers

Problem Solution

Wet/dry buildup Keep all areas dry or all areas flooded.



Use inclined ducts to a liquid drain vessel.

Ensure that scrubber is installed vertically.

Maintain liquid seal.

Dust buildup in

fanInstall clean water spray at fan inlet.

Excessive fan

vibrationClean fan housing and blades regularly.

Liquid pump

failure

Divert some of the recycle slurry to a thickener,

settling pond, or waste disposal area and supply

clean water as makeup.

Increase the water bleed rate.

Worn valvesUse wear-resistant orifice plates to reduce erosion on

valve components.

Jammed valvesProvide continuous purge between valves and

operating manifold to prevent material buildup.

Erosion of slurry

piping

Maintain pumping velocity of 4 to 6 ft/s to minimize

abrasion and prevent sedimentation and settling.Plugged nozzles Replace nozzles or rebuild heads.

Change source of scrubbing liquid.

Supply filtered scrubbing liquid.

Buildup on mist

eliminators

For vane-type demisters, spray the center and

periphery intermittently to clean components.

For chevron-type demisters, spray the water from

above to clean the buildup.

Startup/Shutdown Procedures – Wet Scrubbers

Prestart Checklist Shutdown

1. Start fans and pumps to check their rotation.

1. Shut down fan and fan

spray. Insulate scrubber fromoperation.

2. Disconnect pump suction piping and

flush it with water from an external

source.

2. Allow liquid system tooperate as long as possible to

cool and reduce liquid slurry

concentrations.

3. Install temporary strainers in pumpsuction line and begin liquid recycle.

3. Shut off makeup water andallow to bleed normally.

4. With recycle flow on, set valves todetermine operating conditions for

desired flow rates. Record the valve

positions as a future baseline.

4. When pump cavitation noiseis heard, turn off pump and

pump gland water.

5. Record all system pressure drops

under clean conditions.

5. Open system manholes,

bleeds, and other drains.

6. Perform all recommended

lubrications.





• Check wet/dry line areas for material buildup. Clean, if necessary.• Check liquid spray quantity and manifold pressure on mist eliminator automatic washdown.

• Inspect fans on dirty applications for corrosion, abrasion, and particulate buildup.

• Check bearings, drive mechanisms, temperature rise, sprocket alignment, sprocket wear, chain tension, oillevel, and clarifier rakes.

• Check ductwork for leakage and excessive flexing, Line or replace as necessary.

• Clean and dry pneumatic lines associated with monitoring instrumentation.

Semiannually

• Verify accuracy of instruments and calibrate.

• Inspect orifice plates.

• Clean electrical equipment, including contacts, transformer insulation, and cooling fans.• Check and repair wear zones in scrubbers, valves, piping, and ductwork.

• Lubricate damper drive mechanisms and bearings. Verify proper operation of dampers and inspect for leak

Electrostatic Precipitators

Electrostatic Precipitators use electrostatic forces to collect dust from the Gas stream. Several high power DirCurrent Discharge Electrodes are places inside the collector. The incoming Gases pass by the first set of

Discharging Electrodes (ionizing section) that give the particles a negative charge (ionization). The now ionize

particles travel pass the next set of electrodes (the collection section) that carry a positive charge. The positivecharged plates attract the negatively charged particles causing them to collect on the plates. Cleaning is

accomplished by vibrating the electrodes either continuously, or at a timed interval, causing the captured dust

fall off into a hopper below. All of this can be done while the system is operating normally.

Electrostatic Precipitators are best used in an ambient capture type system with low particle loads. Without anautomated self-cleaning feature, this type of collector can very easily reach its maximum particle retention lim

which will result in a system failure. Further, for a high dust load system a great amount of dust storage is need

Media Filtration (Baghouse) or Pleated Filtering Media (Cartridge Collectors) provide a much great surface arfor dust storage than Electrostatic Precipitator systems do. However the advantages of this system are great fo

their intended applications. They have the ability to be extremely efficient (in excess of 99.9% in some cases),

function within vary large temperature ranges (between 700 °F and -1300°F), and can have large flow rates wiminimal pressure and temperature changes. They are also very well suited for the collection of fine dust partic

as well as materials like acids and tars which other system may have difficulty with.

All electrostatic Precipitators have four main components:

• A Power supply to provide the system with electricity

• An Ionizing section to negatively charge the incoming particles• A cleaning system designed to remove collected particles from the Electrode collection plates

• A housing to enclose the Precipitator section

Within the category of Electrostatic Precipitator Collectors, there are two main types of systems:

• High Voltage Single State Precipitators (Cottrell type)• Low Voltage Dual State Precipitators (Penny type)

High Voltage Single State Precipitators are further divided between two main designs:

Plate Precipitators are made up of several flat parallel plate collectors that are usually between 8 and 12in apa

Placed directly in the middle of each set of directly adjacent plates are a series of high voltage (40,000-70,000volts) DC Discharge Electrodes. As the Gas stream passes through the plates it is ionized by the Discharge

Electrodes and then immediately deposited unto the collection plates. The plates are then cleaned by vibrating



plates causing the debris to fall into a hopper or collection bin below. The majority of Single State Precipitatoruse today are of the plate variety.

Tubular Precipitators operate in the same manner as Plate Precipitators however in a different configuration. T

design uses a tubular shaped collection device with the Discharge Electrodes placed in the middle of the tube.

the Gas stream flows through the tube it is first ionized by the Discharge Electrode in the center, and then thecharged particles are attracted to the inside of the positively charged tube. The cleaning mechanism can be one

nearly identical to that of Plate Precipitators or it can be used as part of a Wet Static Precipitator system, wher

the sides of the Precipitator are flushed with water thereby cleaning them.Tubular Precipitators are widely used in the mineral processing industry. They are highly valuable for use in h

temperature Gas streams (boiler exhaust gas on power plants) because of their ability to adjust to the expansion

and contraction of metal parts in the system. In addition this type of collector is also able to handle vapor collection, containing adhesive, “sticky”, radioactive, and extremely toxic compounds.

Low Voltage Dual Stage Precipitators contain several grounded plates about one inch from each other with

another intermediate plate that also contains a charge. This system uses a much lower voltage than the High

Voltage type (a 13,000-15,000 volt DC supply with intermediate supply of 7,500 compared to 40,000 to 70,00This type of system is widely used to collect fumes and particles generated by welding, grinding or burning

operations. They are also used in hooded and ducted welding machines and welding booths.

Low Voltage Dual Stage Precipitators have the advantages of being highly efficient, the possibility of a self contained washing system, and a longer service life since cleaning is only required on a monthly basis. Howev

because maintenance requires removing the Precipitator Frames and the manual cleaning of the cleaning

assemblies which are quite delicate, this type of Precipitator requires a great amount more care and caution to

used when performing maintenance.

Advantages and Disadvantages – Electrostatic Precipitators

Advantages Disadvantages

Have collection

efficiencies in excess of

99% for all particulates,including sub-micron-

sized particles

Have high initial investment costs

Usually collect dust bydry methods

Do not respond well to process changes such

as changes in gas temperature, gas pressure,

gas flow rate, gaseous or chemicalcomposition, dust loading, particulate size

distribution, or electrical conductivity of the

dust

Have lower pressure drop

and therefore lower operating costs

Have a risk of explosion when gas stream

contains combustibles

Can operate at high

temperatures (up to 1200º

F) and in colder climates

Product ozone during gas ionization

Can remove acids and tars

(sticky dust) as well as

corrosive materials

Require large space for high efficiency, and

even larger space for dust with low or high

resistivity characteristics

Allow increase incollection efficiency by

increasing precipitator

Require special precautions to protect personnel from exposure to high-voltage



size

Require little power Require highly skilled maintenance

personnel

Unit Collectors

For certain applications, Unit Collectors are a better choice for a facilities needs than a conventional Central

Collection System. These collectors control contamination at their source. They benefit from low initial cost,direct return of captured material to the main material flow, and very low space requirements. These collectors

best used when the dust source is isolated, portable or changes position often. Some examples of instances wh

this type of collector might be useful are dust-producing operations, such as bins and silos or remote belt-

conveyor transfer points.

Depending on the particular desired application is there are a number of different designs available to choose

from with a capacity of 200 to 2,000 ft3/min. The two main types are:

• Fabric Collectors• Cyclone Collectors

Unit Fabric Collectors are very similar to their bigger relatives used in a Central Collection System. They usuemploy either a Mechanical Shaker, or a Pulse Jet system for cleaning. This type is well suited for the collectio

of fine particles such as in the mineral processing industry.

Unit Cyclone Collectors also operate on the same principles are the kind used in Central Collection Systems. Dis collected and deposited into a hopper, which then can be removed later for cleaning. This type of collector i

best used in the collection of coarse of larger particles.

Central Collection SystemEvery Dust Collection System must have a Central Collection System in place in order to send the contaminate

air to the filtration system. A Central Collection System consists of a series of collection inlets, and the necess

duct work to transport the dust laden Gas stream to the collector and afterward on to be either recirculated back

into the facility or dispersed into the atmosphere. The pressure in this duct system is supplied by the Fan andMotor System.

Fan and Motor

Choosing the right Fan and Motor System requires a number of different factors to be taken into consideration

including but not limited to:

• Volume required

• Fan static pressure

• Type of material to be handled through the fan (For example, a Radial Blade Fan should be used with fibromaterial or heavy dust loads, and a nonsparking construction must be used with explosive or flammable

materials.)

• Limitations in space

• Acceptable levels of noise caused by the fan• Required operational temperature (For example, sleeve bearings are suitable to 250º F; ball bearings to 550

F.)

• Adequate size to handle pressure and volume requirements with minimum horsepower usage



• Whether any corrosive materials are going to be handled and what protective coatings may be needed• Ability of fan to accommodate small changes in total pressure while maintaining the necessary air volume

• Need for an outlet damper to control airflow during cold starts (If necessary, the damper may be interlocke

with the fan for a gradual start until steady-state conditions are reached.)

Also to be considered is what type of drive system for the fan you plan to use. A Direct Drive fan is run directoff of a drive shaft from the motor, this provides for lower space needs, but places the fan at a constant

unchangeable speed. While Belt Driven fan, which uses a belt to flywheel configuration needs more space, it c

allow for the fan speed to be easily changed which is vital for some applications.

There are two main types of fan designs that are used in industrial applications:

• Centrifugal fans

• Axial-flow fans

A Centrifugal Fan (also called a Squirrel-cage fan for its resemblance rodent exercise devices) is a fan build w

blades (or ribs) surrounding a central hub. The air enters into the side of the fan and then turns 90° and isaccelerated and thrown out of the fan by means of centrifugal force. The diverging shape of the scroll also

converts a portion of the velocity pressure into static pressure. The fan is driven by means of a drive shaft that

extends out from the center hub of the fan.

There are three main types of Centrifugal fan blades that can be used:

• Forward Curved Blades

• Backward Curved Blades

• Straight Radial Blades

Forward Curved Bladed Fans have blades that are curved in the direction of the rotation of the fan. These fanshighly sensitive to particulate buildup and are used for high airflow, low pressure applications.

Backward Curved Bladed Fans contain blades that are positioned away from the fans rotation direction. These

fans will provide an efficient operation, and can be used in Gas streams with light to medium particle

concentration. While they can be fitted with wear protection, this type of blade can still become backed up if th particle load gets to be too heavy. This fan type is most often employed in medium speed, high pressure, and

medium airflow applications.

Straight Radial Bladed Fans provide the best choice for heavy particle loads. This design features a series of

blades that extend straight out from the center hub. This design is used for high pressure, high speed and lowvolume applications.

Fan dampeners

Fan dampeners are metal plates that can be adjusted to reduce the energy usage of the fan. Placed on the Outle

port of a fan, they are used to impose a flow resistance to control the Gas stream. They also can be placed on t

Inlet port, which can perform the same function, as well as redirect how the Gas stream enters into the fan.

Axial Flow Fans

Axial Flow Fans have blades that are mounted unto a center drive shaft. They induce the air to move parallel t

the shaft the blades are mounted on by the screw-like action of the propellers. The air is blown across the axis the fan hence the name Axial Flow Fans. This type of fan is commonly used in systems with low resistance

levels.



The three main different designs of Axial Flow Fans are:

• Propeller

• Tube Axial

• Vane Axial

Propeller Fans is the most simple fan design. It is used to move large an amount of air against very low static pressure from the rest of the system. General and Dilution ventilation are two common uses for this type of ax

fan.

The Tube Axial design is very similar to a normal propeller type fan, except that the propeller is enclosed in an

open ended cylinder. This design is more efficient than simple propeller types and is often used in moving Gasstreams filled with condensable fumes or pigments.

Vane Axial Fans are nearly identical to Tube Axial Fans. But these contain specially attached vanes that are

designed to straighten the Gas stream as is passes through the fan. These can produce high static pressures rela

to this type of fan. However these fans are in most applications used only for clean air.

Fan Rating Table

Once all of the preceding material has been examined, the final step in the selection of the proper fan for your system is to consult a Fan Rating Table. This is used to list all of the specifications for the various fans produc

by a certain manufacturer. When reviewing a Fan Rating Table one must keep these few points in mind:

• The rating tables show all of the possible pressures and speeds that can be achieved within the limits of the

fan’s normal operation range.• A fan that operates at a single or fixed speed and has a fixed blade setting will only have one possible ratin

The only way to gain multiple ratings is by varying the speed and the blade setting.

• It may be possible to obtain the same fan in different construction classes• Increasing the exhaust volume will in turn increase the static and total pressure in the system

Fan installation

Once a system has been installed in the field, inevitably certain differences between design and field installatiowill require a field test to be done to find the exact measurements of static pressure and volume. This step is

crucial in order for a proper fan system to be selected. A few brief points are good to keep in mind during the

installation process that can cause your real world values to change from the original design specifications:

• Elbows and bends near the fan’s discharge will increase the systems resistance thereby lowering your fan’s performance

• Make sure to install the impeller in the proper direction desired.

• Certain types of fittings such as elbows, mitered elbows and square ducts, can cause a nonuniform airflowwhich in turn will again lower performance

• Build up of debris in the inlets, blades, passages as well as obstructions should be checked and remedied

• In a belt driven system one must check the motor sheave and fan sheave are properly aligned and that prop belt tension is present

Electric Motors

An Electric Motor is what supplies the power necessary to operate the fan (Blower) in the Dust Collection

System. Electric Motors are usually grouped as either Induction, or Synchronous designs. Induction designs a

the only ones that are used in Dust Collection Systems today.



Induction Motors normally operate on three phase AC current. The two most common types used in DustCollection Systems are:

• Squirrel Cage Motors are generally used where a constant speed is desired

• Slip Ring Motors by contrast are general purpose or continuous rated motors that are used in applications

where there is a need for an adjustable speed in the motor.

Another important design consideration is whether the Motor is one of these two enclosure designs:

• Drip Proof and Splash Proof Motor are types of Open Enclosed Motors, which use a kind of electric motor

enclosure that has vents to allow airflow but to prevent liquids and solids from entering the motor. This design

not suitable for application where particles that can damage the interior of a motor are found in the ambientatmosphere around the motor.

• Totally Enclosed Motors have an exterior fan mounted unto the backside of the motor drive end. The fan

blows air over the motor enclosure to provide additional cooling for the motor. Since the actual motor is totallyenclosed this design provides the best protection against dust and other contaminates that might damage the mo

if allowed inside.

Both Types can also be constructed in explosion and dust ignition proof models to protect against accidental

ignition of dust particles.The following factors need to be considered when choosing which motor meets your needs:

• Horsepower and RPMs

• Power supply needs such as voltage, single or three phase AC and frequency• The environment in which the motor will have to operate (humidity, temperature, open flames or corrosive

elements

• What kind of load is going to be placed on the motor (fan and other drive mechanisms) and power compan

restrictions on cold starts.• Sufficient power supply for cold starts

• Overload protection needed for the particular motor

Fan & Motor Troubleshooting Chart

Symtom Probable Cause Solution

Insufficient

airflow, low

ft3/min

Fan

Forward curved impeller

installed backwardsReinstall impeller

Fan running backwards

Change fan rotation by

reversing two of the three

leads on the motor Impeller not centeredwith inlet collar(s)

Make impeller and inletcollar(s) concentric

Fan speed too lowIncrease fan speed byinstalling smaller diameter

pulley

Elbows or other

obstructions restricting

airflow

Redesign ductwork

Install turning vanes in elbow



Remove obstruction in

ductwork

No straight duct at faninlet

Install straight length of

ductwork, at least 4 to 6 ductdiameters long, where

possible

Increase fan speed to

overcome this pressure loss

Obstruction near fan

outlet

Remove obstruction or

redesign ductwork near fanoutlet

Sharp elbows near fanoutlet

Install a long radius elbow, if possible

Install turning vanes in elbow

Improperly designed

turning vanesRedesign turning vanes

Projections, dampers, or

other obstructions near fan outlet

Remove all obstructions

Duct System

Actual system more

restrictive (more resistant

to flow) than expected

Decrease system’s resistance

by redesigning ductwork

Dampers closedOpen or adjust all dampers

according to the design

Leaks in supply ducts Repair all leaks in supply duct

Too muchairflow, high

ft3/min

Fan

Backward inclinedimpeller installed

backwards (high

horsepower)

Install impeller as

recommended by

manufacturer

Fan speed too fast Reduce fan speed

Install larger diameter pulley

on fan

Duct System

Oversized ductwork; less

resistance

Redesign ductwork or add

restrictions to increase

resistance

Access door openClose all access and

inspection doors

Low static

pressure, high

ft3/min

Fan

Backward inclined Install impeller as



impeller installed

backwards (highhorsepower)

recommended by

manufacturer

Fan speed too high Reduce fan speed


on fan

Duct System

System has lessresistance to flow thanexpected

Reduce fan speed to obtaindesired flow rate

Gas Density

Gas Density lower than

anticipated (due to high

temperature gases or high

altitudes)

Calculate gas flow rate atdesired operating conditions

by applying appropriate

correction factors for high

temperature or altitudeconditions

Low staticpressure, low

ft3/min

Duct System

Fan inlet and/or outlet

conditions not same astested

Increase fan speed

Install smaller diameter pulley

on fan

Redesign ductwork

High static

pressure, low

ft3/min

Duct System

Obstructions in system Remove obstructions

Duct system too

restrictedRedesign ductwork

Install larger diameter ducts

High

horsepowerFan

Backward inclined

impeller installed backwards

Install impeller as

recommended bymanufacturer

Fan speed too high Reduce fan speed


on fan

Duct System

Oversized ductwork Redesign ductwork

Access door openClose all access/inspection

doors



Gas Density

Calculated horsepower

requirements based on

light gas (e.g., hightemperature or high

altitude) but actual gas is

heavy (eg.,cold startup)

Replace motor

Install outlet damper, which

will open gradually until fancomes to its operating speed

Fan Selection

Fan not operating atefficient point of rating

Redesign system

Change fan

Change motor

Fan does not

operateElectrical

Blown Fuses Replace Fuses

Electricity turned off Turn on Electricity

Wrong voltageCheck for proper voltage on

fan

Motor too small and

overload protector has broken circuit

Change motor to a larger size

Mechanical

Broken belts Replace belts

Loose pulleys Tighten or reinstall pulleys

Impeller touching scroll Reinstall impeller properly

Dust Disposal

After the Airstream has been cleaned, the dust that has been collected must be disposed of in a proper way toensure that recontamination is avoided. In many cases where the collected material is of value, it can be return

to the product stream and reused. However this is not practical in all applications. Minimizing secondary dust problems is also a key component in an effective dust disposal system. Operations such as loading and unloadi

of the collected material, or the transportation of wet slurry can present further contamination problems that neto be addressed.

All Disposal Systems have to accomplish these four objectives without further contaminating the environment

order to be effective in their role in the Dust Collection System:

• Collected material from the hopper must be removed

• Transportation to storage

• Storage of the collected material

• Treatment necessary before final disposal



Removal Of Dust From The Hopper

The hopper must be emptied of the collected dust on a regular basis to prevent overfilling. Often this process i

done while the collector is still operating. If this is the case, rotary air locks, or tipping valves need to be used

order to maintain a positive air seal and thus avoid massive pressure loss that would be detrimental to the norm

operation of the system. Some materials display what is called a bridging tendency, which is a tendency to stictogether and form long strands that can over time build up into bridge like formations that can impede the norm

operations within a hopper. If material of this kind is present in the system, special equipment such as bin

vibrators, rappers, or air jets should be used to ensure that the material that has a bridging tendency does notinterfere with normal operation of the hopper.

Dust Transportation

Once the dust has been removed from the collector, it must be transported to a storage area where is can be giv

any final treatments needed before it is disposed of. There are four main systems that can be used to transport

collected material to holding there are:

• Screw conveyers• Air conveyers

• Air Slides

• Pressurized piping system for wet material (Slurry)

Screw conveyers use rotating shaft to move material to the desired location. These systems are very effectivemethods of dust transportation. However several areas of concern in this type of system are that they tend to h

a noted lack of easy access for maintenance purposes, the castings and bearings can wear out easily when used

with abrasive materials with air leaks being the end result.

Air Conveyers are used mainly for dry dust applications. Making use of a high velocity low air volume princip

these collectors are a great choice because of their few moving parts and their ability to move dust both vertica

and horizontally. The main concerns with this system are that the piping can over time suffer from excessive w

from abrasive compounds. They also require large initial investments of capital and have higher operating cost

Air Slides are widely used for light dust loads with nonabrasive materials. Air fluidization of the dust is the ma

operating principle behind this system. This system while able to transport great amounts of material has the

downside of only being able to do so in a horizontal direction. Areas of concern are the need to maintain a

constant down pitch in the ductwork, and greater maintenance costs.

Pressurized piping systems are needed when transporting the slurry made from using a Wet Scrubber design. T

system is used to send the slurry to a settling pond for further treatment. Great care must be taken by the opera

of this system to ensure that no leakage occurs which would result in an environmental hazard caused by wate pollution.

Dust Storage

Storage tanks and Silos are the most common storage locations for dry dust compounds after their collection.These sites are then fitted to allow loading of the material into enclosed trucks or rail cars below.

When using a wet collection system often times a settling pond is needed. In a settling pond the captured

particles are separated by means of the process of decantation. The slurry from the Wet Scrubbers is left to sit

a large pond or basin, allowing the captured particles to over time slowly settle to the bottom of the pond;afterwards the clean water is discharged. Again certain factors to consider in the use of a settling pond are that

water holding area can only be decanted in the warmer, dryer part of the year, and in most instances two settlin

ponds are needed to operate efficiently.



Final Disposal

When deciding on a final disposal method, one must remember that great care needs to exercised in order to av

recirculation of the dust by the wind. Sometimes in because of this concern, and for easier transportation, the

captured material is processed into pellets before final disposal. Generally four different options are available

the final disposal of the collected material:• Placement in a landfill

• Recycling

• Byproduct utilization• Collected material may be suitable for backfilling land fills and quarries

Selection of a Dust Collector

The differences in design, operation, efficiency, space requirement, construction, and maintenance needs, as was the initial start up, operating, and maintenance costs differ greatly between various products and systems.

However in choosing which system will meet your needs the best, the following point should be considered:

Dust concentration and Particle size – Within any kind application the specific sizes and dust concentrations c

vary enormously. Therefore, knowing the exact range of particle size and concentration levels that will be preswill be vital in your choosing the proper Collection System.

Degree of collection required – How intensive of a filtration action is needed is determined by several factors.

The exact dangers and hazards of the contaminates to be captured, its potential as a public health risk or nuisan

site location, the allowable emission rate by the regulatory body for the given substance, characteristics of thedust, and any recyclable value.

Characteristics of the Gas stream – Differences in Gas stream temperatures and humidity levels can great affe

certain types of collectors. For example Gas temperatures above 180° F (82°C) will destroy many types of filt

media (Filter Bags) used in Fabric Collectors (Baghouses). Water vapor or steam can blind certain types of FilMedia. Corrosive and other chemicals can erode certain metals and other materials used in the construction of

many Collectors.

Types of Dust – Certain types of Collectors have a great deal of physical contact between the particles and the

Collector itself. A number of different materials such as silica or metal ore are quite abrasive and can causeerosion through prolonged contact with the Collector. Other “sticky” compounds can attach themselves to the

interior surfaces of the collector and cause blockages. The size and distinct shape of some types of dust render

certain collection methods useless. When certain types of materials are fluidized into the air they become highcombustible. Under these circumstances Electrostatic Precipitators are instantly ruled out, along with most Ine

Separators.

Disposal Methods – Differences in disposal methods betweens different locations. Collectors can be arranged

unload their collected matter either in a continuous mode or at a predetermined time interval. Removal of collected matter from dry systems can also result in secondary causes of dust pollution and contamination. Wh

using a Wet Scrubber System will eliminate this concern, proper handling of slurry created during the cleaning

cycle will involve an entirely different set of problems, such as precautions against water pollution, and propercare and maintenance of the retention ponds.

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Documents

Encyclopedia of Dust Collector