What is a Dust Collector

8/12/2019 What is a Dust Collector

1/31

What is a Dust Collector?After the contaminated air is captured by a DryDust Collection system,either by means of a Central Collection

System, or in a unit Collector. The dust filled air then needs to be treated and the contaminates removed, before the

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

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 airemission standards.

Types of Dust CollectorsThe 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 separatorswork by making use of one or more of the following forces centrifugal, gravitational, and inertial 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 only a rough air

filtration is desired, the main usage for this type of collector is as a precleaner, to remove larger 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 the

chamber. This type of collector is rarely used as the primary dust collector due to its large space requirements, and

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.
http://www.baghouse.com/products/dust-collection-systems/http://www.baghouse.com/products/dust-collection-systems/http://www.baghouse.com/products/dust-collection-systems/http://www.baghouse.com/category/dust-collection-blog/environmental-industry-news/pollution-emission-regulation/http://www.baghouse.com/category/dust-collection-blog/environmental-industry-news/pollution-emission-regulation/http://www.baghouse.com/category/dust-collection-blog/environmental-industry-news/pollution-emission-regulation/http://www.baghouse.com/products/dust-collectors/cyclone-collectors/http://www.baghouse.com/products/dust-collectors/cyclone-collectors/http://www.baghouse.com/category/dust-collection-blog/environmental-industry-news/pollution-emission-regulation/http://www.baghouse.com/products/dust-collection-systems/


2/31


3/31

reduction in airflow rate

Cannot process sticky dust

Multiple

CyclonesHave no moving parts

Have 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 precleanerImproper gas distribution may result in dirty

gas bypassing several tubes

Cannot process sticky dust

For a given gas volume, occupy more

space than single-cyclone separators

Common Operating Problems & SolutionsCyclone CollectorsSymptom Cause Solution

ErosionHigh concentrations of heavy, hard,

sharp-edged particles

Install large-diameter roughing cyclone upstream 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 stainless

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 seal

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

MulticlonesSymptom Cause Solution

ErosionHigh concentrations of heavy, hard,

sharp-edged particlesInstall cast iron tubes.

Install a wear shield to protect

tubes


4/31

Overloaded tubesUneven gas flow and dust

distribution

Install turning vanes in elbow, if

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 inlet

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 ductworkSeal all sections of ductwork and

multiclone to prevent leaks

Leakage in multiclone

Startup/Shutdown Procedures

Centrifugal CollectorsType Startup Shutdown

Cyclones 1. Check fan rotation.1. Allow exhaust fan to operate for a few minutes

after process shutdown until cyclone is empty.

2. Close inspection doors, connections, and

cyclone discharge.

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

Multiclones1. Conduct same startup procedures as cyclones. 1. Conduct same shutdown procedures as cyclones.

2. At least once a month, measure airflow by

conducting a pitot traverse across inlet to

determine 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 CollectorsType FrequencyProcedure

Cyclones Daily Record cyclone pressure drops.

Check stack (if cyclone is only collector).

Record fan motor amperage.


5/31

Inspect dust discharge hopper to assure dust is removed.

Weekly Check fan bearings.

Check gaskets, valves, and other openings for leakage.

Monthly Check cyclone interior for erosion, wear, corrosion, and other visible signs of deterioration.

MulticlonesDaily 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 normal

wear.

Fabric Dust CollectorsFabric Collectors(commonly known as a Baghouse) are among the most widely used dust collection systems. They

benefit from having the potential to be one of the most efficient (up to 99% of very fine particles) and cost effective

dust collection systems you can choose.

The way they workThe Gas stream enters into the Baghouse via the locations duct system. Once inside the dust filled gases come into

contact with the filter bags within. As the gases pass through the filters the dust particles are trapped on the 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

mediums high efficiency potential. Once the cake dust has formed, it further impedes the passage of dust through

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 fiber size.

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

dust particles due to their molecular motion.

Electrostatic Forces: An increased attraction can occur between the dust particles and the filter media when an

electrostatic charge is found on the dust particles.

Air to Cloth RatioAn understanding of the termAir to Cloth Ratiois vital to understand the mechanics of any Baghouse system

regardless of the exact type used. This ratio is defined as the amount of air or process gas entering the Baghouse

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

http://www.usairfiltration.com

(Bag diameter in inches x pi x bag length in inches)

Total Cloth area = 144 x total number of bags
http://www.baghouse.com/products/dust-collectors/baghouses/http://www.baghouse.com/products/dust-collectors/baghouses/


6/31

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

= (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 bags

Total 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 designsThere are three main types of Baghouse systems currently in use today. The same basic mechanics are present in all

of them, the main difference being how filter bags are cleaned.

Mechanical Shaker

Reverse Air

Reverse Jet (Or Pulse Jet)

A Mechanical Shakeris a design where the filter bags are suspended from the top of the Baghouse by horizontal

beams and fastened to a cell plate on the bottom. When the Gas stream enters at the bottom of the Baghouse it is

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 are attached 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 relatively low Air to Cloth Ratio

requiring large amounts of space. Despite this draw back, the simple design remains a noted 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 the interior of

the filter bags, thereafter leaving through the outlet port at the top. Again the main difference in this 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 the compartment to

become pressurized. The pressure causes the bags to collapse slightly releasing the cake dust to crack and fall off to

be collected by the hopper below. Since it is necessary to shut down normal airflow to the Baghouse during the


7/31

cleaning cycle, this type of Baghouse is normally compartmentalized so as to allow for only a partial shutdown of the

system.

With a Reverse Jet or Pulse JetBaghouse, 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, thebaghouse filterbags are individually

overlaid on a metal cage, which is then attached to a cell plate at the top of the compartment. The Gas stream enters

the Baghouse at the bottom and is forced through the outside to the inside of the filter bags after which the Gas

stream exits the compartment from the outlet port at the top. The main advantage of this Baghouse is that it does not

require a shutdown of any kind to run a cleaning cycle. A digital sequential timer is attached to the one of the filter

bags inside the Baghouse. This timer signals a solenoid valve to start the cleaning cycle when it detects 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 and reconditioning of the filter bags than

in the Shaker, and Reverse Air designs. Also the short nature of the cleaning cycle also leads to a reduction in therecirculation 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 CollectorsUnlike Baghouse collectors which feature the use of woven or felt filter bags, Cartridge Collectorsuse perforated

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

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 locations dust collection system.

Advantages and DisadvantagesBaghousesTypes 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 cycle to reduce residual

dust buildup

Cannot be used in high

temperatures

Simple to operate Require large amounts of space

Have low pressure drop for

equivalent collection efficienciesNeed large numbers of filter bags

Consist of many moving parts and

require frequent maintenance

Personnel must enter Baghouse
http://www.baghouse.com/products/dust-collector-filters/baghouse-filter/http://www.baghouse.com/products/dust-collector-filters/baghouse-filter/http://www.baghouse.com/products/dust-collector-filters/baghouse-filter/http://www.baghouse.com/products/dust-collector-filters/baghouse-filter/


8/31

to replace bags, creating potential

for exposure to toxic dust

Can result in reduced cleaning

efficiency if even a slight positive

pressure exists inside bags

Reverse Air

Baghouses

Have high collection efficiency for

respirable dust

Have low air-to-cloth ratio (1 to

2ft/min)

Are preferred for high

temperatures due to gentle

cleaning action

Require frequent cleaning

because of gentle cleaning action


equivalent collection efficiencies

Have no effective way to remove

residual dust buildup

Cleaning air must be filtered

Require personnel to enterbaghouse to replace bags, which

creates potential for toxic dust

exposure

Pulse Jet

(Reverse Jet)

Baghouses

Have a high collection efficiency

for respirable dustRequire 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 efficiency and

minimal residual dust buildup due

to aggressive cleaning action

Cannot be used if high moisture

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


equivalent collection efficiencies

Common Operating Problems and SolutionsBaghouses*Symptom Cause Solution


9/31

High Baghouse

pressure dropBaghouse undersized consult vendor

Install double bags

Add more compartments or

modules

Bag cleaning mechanism not

properly adjustedIncrease cleaning frequency

Clean for longer duration

Clean more vigorously

Shaking not strong enough (S) Increase shaker speed

Compartment isolation damper

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 necessary

Check 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 valves

Bag 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 all terminals

Not capable of removing dust

from bags

Check for condensation on

bags


10/31

Send dust sample and bags to

manufacturer for analysis

Dryclean or replace bags

Reduce airflow

Excessive reentrainment of

dustEmpty 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

stackBags 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 clamps

Failure of seals in joints at

clean/dirty air connectionCaulk or weld seams

Insufficient filter cake

Allow more dust buildup on

bags by cleaning less

frequently.

Use precoating on bags (S,

RA).

Bags too porous

Send bag in for permeability

test and review 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


11/31

Diaphragm valve failure Check diaphragm and springs

Check pilot valve

Reduced

compressed-air

pressure (PJ)

Compressed-air consumption

too highSee previous solutions

Restrictions in compressed-air

pipingCheck 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 workingCheck 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 is shut down

Wall temperature below

dewpointRaise gas temperature

Insulate unit

Lower dewpoint by keeping

moisture out of system

Cold spots through insulationEliminate direct metal line

through insulation

Water/moisture in compressed

air (PJ)Check automatic drains

Install aftercooler

Install dryer

Repressurizing air causing Preheat repressurizing air


12/31

condensation (PJ)

Use process gas as source of

repressurizing air

Material bridging in

hopper

Moisture in Baghouse See previous solutions

Dust stored in hoppers Remove dust continuously

Hopper slope insufficient Rework 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 frequent Slow down cleaning

Inlet air not properly baffled

from bagsConsult vendor

Shaking too violent (S)Slow down shaking

mechanism

Repressurizing pressure too

high (RA)Reduce pressure

Pulsing pressure too high (PJ) Reduce pressure

* S = Shaker

RA = Reverse Air

PJ = Pulse Jet

Startup/Shutdown ProceduresBaghousesStartup Shutdown

1. For processes generating hot, moist gases,

preheat Baghouse to prevent moisture

condensation, even if Baghouse is 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 20 minutes 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 prevent moisture condensation.

Preventive Maintenance ProceduresBaghouses

Frequency Procedure


13/31

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


14/31

Check fan belts.

Check welds.

Inspect hopper for wear

Wet ScrubbersAnother effective method of dust collection is the use of Wet Scrubbers(Air Washers). These systems use ascrubbing liquid (usually water) to filter out finer dust particles. After being filtered the Gas Stream is then sent

through a mist eliminator (demister pads) to remove the excess moisture from the Gas stream. Afterward the Gas

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 dust 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 have three

basic operations they perform:

Gas-humidification: The gas-humidification process conditions fine particles to increase their size so they can 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 impactiontakes 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.

Diffusionoccurs when a fine mist is created from the liquid being used. As the particles pass through the mist they

make contact with the surfaces of the droplets by means of the Brownian ef fect, or diffusion.

Condensation nucleationis the effect of a gas being cooled below its dew point while within a moisture rich

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 be removed

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 chain system to be


15/31

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 in this

article. However a brief overview of the most common types will enable you to understand the basic operational

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 enters at the

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

dirty water collects at the bottom of the tank and the clean air (mist) exits from the top of the collector. This collector

has a relatively low efficiency compared to other kinds of Wet Scrubbers. However its main advantage is it can

handle very heavy dust loads without getting backed up.

Dynamic wet precipitators also called Wet Fan Scrubbersare a popular design used for medium energy scrubbing

applications. In this system the Gas stream passes through a larger fan that is constantly kept wet with the cleaning

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

blades unto the sides of the collector where they eventually settle at the bottom enabling them to be collected.

Orifice Scrubberswork in a very similar way to inertial separators but with one important difference, Orifice

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

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

stream. A greater efficiency can be obtained by the addition of liquid spray nozzles to further separate the

contaminates from the Gas stream. While these are an effective filtration system one should note that they tend to 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 Scrubbersare nearly identical to their normal cyclone collector counterparts. In a Wet Cyclone

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 5um and above.

Medium to High Energy Scrubbers: Packed Bed Scrubbersconsist of a bed of packing media, which is then sprayed with water. The packing media

allows for a very wide distribution of the water, which in turn allows the Gas stream to have the maximum contact with

the water during its passage though the collector. Air enters at the bottom of the collector where it first makes contact


16/31

with the water in the recirculation tank. Then it is forced up through the various layers of the filtering media, and after

being sent through a Mist Eliminator is sent back into the system via the exit port at the top.

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

filtering mechanism they are:

Cross-flow scrubbersare designed to minimize height for low-profile applications. In this design the packed media

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 Scrubbersmake use of the Venturi effect to accelerate the Gas stream to speeds of 12,000 to 36,000

ft/min. The Gas stream enters into the Scrubber through a Venturi shaped inlet where it is sprayed with water. The

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

dust particles and form a slurry, which then falls to the bottom of the collector. After passing through a Mist eliminator

the Gas stream is sent back into the system.

Advantages and DisadvantagesWet ScrubbersAdvantages 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 acidic gases

Are able to collect gases as well as

particulates (especially sticky particulates)

Require a precleaner for heavy dust

loadings

Have no secondary dust sourcesCause water pollution; require further

water treatment

Are susceptible to erosion at high

velocities

Collect wet products

Require freeze protection

Common Operating Problems and SolutionsWetScrubbersProblem 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.


17/31

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 from operation.

2. Disconnect pump suction piping and flush it

with water from an external source.

2. Allow liquid system to operate as

long as possible to cool and reduce

liquid slurry concentrations.

3. Install temporary strainers in pump suction line

and begin liquid recycle.

3. Shut off makeup water and allow

to bleed normally.

4. With recycle flow on, set valves to determine

operating conditions for desired flow rates.

Record the valve positions as a future baseline.

4. When pump cavitation noise is

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.

7. Shut down fan, drain the system, and remove

temporary strainers.


18/31

Startup

1. Allow vessels to fill with liquid through normal

level controls. Fill large-volume basins from

external sources.

2. Start liquid flow to all pump glands and fan

sprays.

3. Start recycle pumps with liquid bleed closed.

4. Check insulation dampers and place scrubber

in series with primary operation.

5. Start fan and fan inlet spray. Leave inlet control

damper closed for 2 min to allow fan to reach

speed.

6. Check gas saturation, liquid flows, liquid levels,

fan pressure drop, duct pressure drops, and

scrubber pressure drop.

7. Open bleed to pond, thickener, or other drain

systems so slurry concentration can build slowly.

Check final concentration as cross-check on

bleed rate.

Preventative Maintenance ProceduresWet ScrubbersFrequencyProcedure

Daily

Check recycle flow.

Check bleed flow.

Measure temperature rise across motor.

Check fan and pump bearings every 8 hours for oil level, oil color, oil temperature, and vibration.

Check scrubber pressure drop.

Check pump discharge pressure.

Check fan inlet and outlet pressure.

Check slurry bleed concentration.

Check vibration of fan for buildup or bleeds.

Record inlet and saturation temperature of gas stream.

Use motor current readings to detect flow decreases. Use fan current to indicate gas flow.

Check pressure drop across mesh and baffle mist eliminators. Clean by high-pressure spraying, if necessary.

Weekly

Check wet/dry line areas for material buildup. Clean, if necessary.

Check liquid spray quantity and manifold pressure on mist eliminator automatic washdown.


19/31

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

Check bearings, drive mechanisms, temperature rise, sprocket alignment, sprocket wear, chain tension, oil level,

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 leakage.

Electrostatic PrecipitatorsElectrostatic Precipitatorsuse electrostatic forces to collect dust from the Gas stream. Several high power Direct

Current 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 ionized particles travel

pass the next set of electrodes (the collection section) that carry a positive charge. The positively charged 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 to 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 an

automated self-cleaning feature, this type of collector can very easily reach its maximum particle retention limit, which

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

Filtration (Baghouse) or Pleated Filtering Media (Cartridge Collectors) provide a much great surface area for dust

storage than Electrostatic Precipitator systems do. However the advantages of this system are great for their

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

within vary large temperature ranges (between 700 F and -1300F), and can have large flow rates with minimal

pressure and temperature changes. They are also very well suited for the collection of fine dust particles 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:


20/31

High Voltage Single State Precipitators (Cottrell type)

Low Voltage Dual State Precipitators (Penny type)

High Voltage Single State Precipitatorsare further divided between two main designs:

Plate Precipitatorsare made up of several flat parallel plate collectors that are usually between 8 and 12in apart.

Placed directly in the middle of each set of directly adjacent plates are a series of high voltage (40,000-70,000 volts)

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 the plates causing the

debris to fall into a hopper or collection bin below. The majority of Single State Precipitators in use today are of the

plate variety.

Tubular Precipitatorsoperate in the same manner as Plate Precipitators however in a different configuration. This

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

Gas stream flows through the tube it is first ionized by the Discharge Electrode in the center, and then the charged

particles are attracted to the inside of the positively charged tube. The cleaning mechanism can be one nearlyidentical to that of Plate Precipitators or it can be used as part of a Wet Static Precipitator system, wherein 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 high

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 Precipitatorscontain 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 70,000). This 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 StagePrecipitators 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. However 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 be used when

performing maintenance.

Advantages and Disadvantages

Electrostatic PrecipitatorsAdvantages Disadvantages

Have collection efficiencies in

excess of 99% for all

particulates, including sub-

micron-sized particles

Have high initial investment costs

Usually collect dust by dry Do not respond well to process changes such as


21/31

methods changes in gas temperature, gas pressure, gas flow

rate, gaseous or chemical composition, dust loading,

particulate size distribution, or electrical conductivity of

the dust

Have lower pressure drop andtherefore lower operating

costs

Have a risk of explosion when gas stream contains

combustibles

Can operate at high

temperatures (up to 1200 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 in collection

efficiency by increasing

precipitator size

Require special precautions to protect personnel from

exposure to high-voltage

Require little power Require highly skilled maintenance personnel

Unit CollectorsFor certain applications, Unit Collectorsare 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 are best

used when the dust source is isolated, portable or changes position often. Some examples of instances where thistype 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 Collectorsare very similar to their bigger relatives used in a Central Collection System. They usually

employ either a Mechanical Shaker, or a Pulse Jet system for cleaning. This type is well suited for the collection of

fine particles such as in the mineral processing industry.

Unit Cyclone Collectorsalso operate on the same principles are the kind used in Central Collection Systems. Dust is

collected and deposited into a hopper, which then can be removed later for cleaning. This type of collector is best

used in the collection of coarse of larger particles.

Central Collection System


22/31

Every Dust Collection System must have a Central Collection Systemin place in order to send the contaminated air

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

Fan and MotorChoosing the right Fan and Motor Systemrequires 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 fibrous

material 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 250 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 interlocked 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 Drivefan is run directly off of a

drive shaft from the motor, this provides for lower space needs, but places the fan at a constant unchangeable speed.

While Belt Drivenfan, which uses a belt to flywheel configuration needs more space, it can 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 with

blades (or ribs) surrounding a central hub. The air enters into the side of the fan and then turns 90 and is

accelerated 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


23/31

Forward CurvedBladed Fans have blades that are curved in the direction of the rotation of the fan. These fans are

highly sensitive to particulate buildup and are used for high airflow, low pressure applications.

Backward CurvedBladed 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 the particle load gets to be too

heavy. This fan type is most often employed in medium speed, high pressure, and medium airflow applications.

Straight RadialBladed 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 low volume

applications.

Fan dampenersFan dampenersare metal plates that can be adjusted to reduce the energy usage of the fan. Placed on the Outlet

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

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

Axial Flow FansAxial Flow Fanshave blades that are mounted unto a center drive shaft. They induce the air to move parallel to the

shaft the blades are mounted on by the screw-like action of the propellers. The air is blown across the axis of 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

PropellerFans 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 axial fan.

The Tube Axialdesign 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 Gas streams

filled with condensable fumes or pigments.

Vane AxialFans 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 relative

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

Fan Rating TableOnce 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 produced by a certain

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


24/31

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

normal operation range.

A fan that operates at a single or fixed speed and has a fixed blade setting will only have one possible rating. 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 installationOnce a system has been installed in the field, inevitably certain differences between design and field installation will

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 fans discharge will increase the systems resistance thereby lowering your fans

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 airflow which

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 proper belt

tension is present

Electric MotorsAn Electric Motoris 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 are 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 Dust Collection

Systems are:

Squirrel Cage Motorsare generally used where a constant speed is desired

Slip Ring Motorsby 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 ProofMotor 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 is not

suitable for application where particles that can damage the interior of a motor are found in the ambient atmosphere

around the motor.

Totally Enclosed Motorshave 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 totally enclosed this


25/31

design provides the best protection against dust and other contaminates that might damage the motor 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 company

restrictions on cold starts.

Sufficient power supply for cold starts

Overload protection needed for the particular motorFan & Motor Troubleshooting ChartSymtom Probable Cause Solution

Insufficient

airflow, low

ft3/min

Fan

Forward curved impeller

installed backwardsReinstall impeller

Fan running backwardsChange fan rotation by reversing two

of the three leads on the motor

Impeller not centered with inlet

collar(s)

Make impeller and inlet collar(s)

concentric

Fan speed too lowIncrease fan speed by installing

smaller diameter pulley

Elbows or other obstructions

restricting airflowRedesign ductwork

Install turning vanes in elbow

Remove obstruction in ductwork

No straight duct at fan inlet

Install straight length of ductwork, at

least 4 to 6 duct diameters long,

where possible

Increase fan speed to overcome this

pressure loss

Obstruction near fan outletRemove obstruction or redesign

ductwork near fan outlet


26/31

Sharp elbows near fan outlet

Install a long radius elbow, if

possible

Install turning vanes in elbow

Improperly designed turning

vanes

Redesign turning vanes

Projections, dampers, or other

obstructions near fan outletRemove all obstructions

Duct System

Actual system more restrictive

(more resistant to flow) than

expected

Decrease systems 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 much

airflow, high

ft3/min

Fan

Backward inclined impeller

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


installed backwards (highhorsepower)


manufacturer

Fan speed too high Reduce fan speed


Duct System

System has less resistance to

flow than expected

Reduce fan speed to obtain desired

flow rate


27/31

Gas Density

Gas Density lower than

anticipated (due to high

temperature gases or high

altitudes)

Calculate gas flow rate at desired

operating conditions by applying

appropriate correction factors for

high temperature or altitudeconditions

Low static

pressure, low

ft3/min

Duct System

Fan inlet and/or outlet conditions

not same as testedIncrease fan speed

Install smaller diameter pulley on fan

Redesign ductwork

High staticpressure, low

ft3/min

Duct System

Obstructions in system Remove obstructions

Duct system too restricted Redesign ductwork

Install larger diameter ducts

High

horsepowerFan


installed backwards


manufacturer

Fan speed too high Reduce fan speed


Duct System

Oversized ductwork Redesign ductwork

Access door open Close all access/inspection doors

Gas Density

Calculated horsepower

requirements based on light gas

(e.g., high temperature or high

altitude) but actual gas is heavy

(eg.,cold startup)

Replace motor

Install outlet damper, which will open

gradually until fan comes to its

operating speed

Fan Selection


28/31

Fan not operating at efficient

point of ratingRedesign system

Change fan

Change motor

Fan does not

operateElectrical

Blown Fuses Replace Fuses

Electricity turned off Turn on Electricity

Wrong voltage Check for proper voltage on fan

Motor too small and overload

protector has broken circuitChange motor to a larger size

Mechanical

Broken belts Replace belts

Loose pulleys Tighten or reinstall pulleys

Impeller touching scroll Reinstall impeller properly

Dust DisposalAfter the Airstream has been cleaned, the dust that has been collected must be disposed of in a proper way to ensure

that recontamination is avoided. In many cases where the collected material is of value, it can be returned 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 unloading of the collected

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

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

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 is done

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

maintain a positive air seal and thus avoid massive pressure loss that would be detrimental to the normal operation of

the system. Some materials display what is called a bridging tendency, which is a tendency to stick together and form

long strands that can over time build up into bridge like formations that can impede the normal operations within a

hopper. If material of this kind is present in the system, special equipment such as bin vibrators, rappers, or air jets


29/31

should be used to ensure that the material that has a bridging tendency does not interfere with normal operation of

the hopper.

Dust TransportationOnce the dust has been removed from the collector, it must be transported to a storage area where is can be given

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

collected material to holding there are:

Screw conveyers

Air conveyers

Air Slides

Pressurized piping system for wet material (Slurry)

Screw conveyersuse rotating shaft to move material to the desired location. These systems are very effective

methods of dust transportation. However several areas of concern in this type of system are that they tend to have 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 Conveyersare used mainly for dry dust applications. Making use of a high velocity low air volume principle, these

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

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

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

Air Slidesare widely used for light dust loads with nonabrasive materials. Air fluidization of the dust is the main

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 pipingsystems are needed when transporting the slurry made from using a Wet Scrubber design. This

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

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

pollution.

Dust StorageStorage 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 pondis 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 in 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 the water holding area can

only be decanted in the warmer, dryer part of the year, and in most instances two settling ponds are needed to


30/31

operate efficiently.

Final Disposal

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

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 for 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 CollectorThe differences in design, operation, efficiency, space requirement, construction, and maintenance needs, as well as

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 sizeWithin any kind application the specific sizes and dust concentrations can vary

enormously. Therefore, knowing the exact range of particle size and concentration levels that will be present will be

vital in your choosing the proper Collection System.

Degree of collection requiredHow 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 nuisance, site

location, the allowable emission rate by the regulatory body for the given substance, characteristics of the dust, and

any recyclable value.

Characteristics of the Gas streamDifferences in Gas stream temperatures and humidity levels can great affect

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

(Filter Bags) used in Fabric Collectors (Baghouses). Water vapor or steam can blind certain types of Filter Media.

Corrosive and other chemicals can erode certain metals and other materials used in the construction of many

Collectors.

Types of DustCertain 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 cause erosion

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 highly combustible. Under

these circumstances Electrostatic Precipitators are instantly ruled out, along with most Inertial Separators.

Disposal MethodsDifferences in disposal methods betweens different locations. Collectors can be arranged to

unload their collected matter either in a continuous mode or at a predetermined time interval. Removal of collected
http://www.baghouse.com/products/dust-collectors/what-kind-of-dust-collector-is-right-for-me/http://www.baghouse.com/products/dust-collectors/what-kind-of-dust-collector-is-right-for-me/


31/31

matter from dry systems can also result in secondary causes of dust pollution and contamination. While 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 proper care and maintenance of

the retention ponds.

Documents

What is a Dust Collector