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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.
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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
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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.
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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
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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
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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
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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
Have low pressure drop for
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
Have low pressure drop for
equivalent collection efficiencies
Common Operating Problems and SolutionsBaghouses*Symptom Cause Solution
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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
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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
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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
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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
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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
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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
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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
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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.
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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.
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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.
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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:
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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
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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
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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
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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:
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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
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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
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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
Backward inclined impeller
installed backwards (highhorsepower)
Install impeller as recommended by
manufacturer
Fan speed too high Reduce fan speed
Install larger diameter pulley on fan
Duct System
System has less resistance to
flow than expected
Reduce fan speed to obtain desired
flow rate
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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
Backward inclined impeller
installed backwards
Install impeller as recommended by
manufacturer
Fan speed too high Reduce fan speed
Install larger diameter pulley on fan
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
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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
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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
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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
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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.