- Raw Material Handling Plant - Dust Generation & Necessity of Control - Types of Dust Control System - Dust Collection System - Air Cleaning Devices - Bag House Dust Collector

1. Dust Collection System
Presented By;
Bhavesh Solanki
Raw Material Handling Plant

2. Content
o Raw Material Handling plant
o Dust generation
o Necessity of dust control
o Dust Collection System
o Advantages of System
o Component of System
o Air Cleaning Devices
o Gravity Separator
o Centrifugal Separator
o Bag Filter
o Electro Static Precipitator
o Bag House Dust Collector
oPrinciple of Operation
oComponents of System
o Particle Collection Mechanism
o Types of Filtration
o Fabric Material
o General Theoretical Design Guideline
o Bag and Cage Installation
o Bag Cleaning System
o Valves on a pulse jet System
o Cleaning Sequence & Pulse Cycle
o Comparison of Different Bag Filter
o Maintenance and Troubleshooting

3. Raw Material Handling
• Raw material is basic need of any industry and its improper management and
handling can lead to serious production losses and delay in the delivery of output
products.
• Keeping this in mind and to avoid any type of production losses and down time every
plant has a separate department that looks after the management of raw material and
its handling.
• Functions of plant are Feeding of row material at Boiler and Kiln, Maintain Proper
size and Quality, Unloading of Row material, Maintain Stock of different row
materials.

4. Hammer Mill Impact Crusher Double Roller Crusher

5. Blade Type Impact Crusher Double Deck Vibrating screen

6. Double Boom Luffing Type Stacker
Wore rope Mechanism for Up – Down Boom
Scrapper Type Reclaimer

7. Coal Truck
Truck
Tippler
Grizzly
Hopper
Vibrating
Feeder
Belt
Conveyor
Raw Coal
Storage
Primary
Screen
Over Size
Size Coal
Coal
Crusher
Secondary
Screen
Over Size
Reverse
Belt
Size Coal
Day Storage Bin
Feeder
Belt
Conveyor
Boiler
Bunker
Reclaiming
Flow Chart of a Typical Coal Handling System

8. Dust generation
• Solid particles carried by air currents.
• In Material handling plant, during broking, dumping, crushing, grinding, screening, belt conveying,
transferring, stocking, loading and milling materials to a finer size and movement of workers and
machinery.
• The amount of dust emitted by these activities depends on the physical characteristics of the
material and the way in which the material is handled.
• Inhalable dust: which enters the body, but is trapped in the nose, throat, and upper respiratory tract.
The aerodynamic diameter of this dust is about 100 μm.
• Respirable dust: are small enough to penetrate the nose and upper respiratory system and deep into
the lungs where gas exchange take place. particle sizes of respirable dust are up to 10 microns.

9. Necessity of dust control
• Health: The small particulate matter affects humans as it is inhaled, forcing the heart and lungs to work
harder to provide oxygen to the body. This can lead to a decreased breathing ability and damage to the heart.
• Reduced Plant Safety: There is a higher risk of explosions when combustible material is allowed to build
up on and around conveyors. Poor visibility due to emission may lead to an accident.
• Increased Maintenance Costs: Excessive spillage leads to premature belt, idler and pulley failure leading
to increase in downtime and maintenance costs. The clean-up cost also increases.
• Reduced Efficiency: Productivity and moral of employs will decrease when they continuously work in
polluted and unsafe environment.

10. Necessity of dust control

11. Dust Control Systems
• Dust control systems are an important factor in meeting environmental and health and safety
requirements, while also helping and protecting employees and reducing site emissions.
• Prevention of dust in the bulk material handling operation is an impossible task. properly designed
bulk material handling components can play an important role in reducing dust generation, emission,
and dispersion.
• After all prevention the dust still remaining in the workplace can be controlled by one or more of the
following techniques.
1. Dust Suppression System
2. Dust Collection System

12. Dust Collection System
• This is also known as dust separation system or dust extraction system. This is a dry way to control
dust emission at dust generation source.
• These systems capture dust generated by various processes such as crushing, milling, screening,
drying, bagging, and loading, and then transport this dust via ductwork to a dust collection filtering
device.
• By capturing the dust at the source, it is prevented from becoming liberated into the processing plant.
• System use a negative pressure exhaust ventilation technique to capture the dust before it escapes from
the processing operation. Effective systems typically incorporate a capture device (enclosure, hood,
chute, etc.) designed to maximize the collection potential.

13. Advantages
• It has ability to capture and eliminate very fine particles that are difficult to control using wet
suppression techniques.
• The option of reintroducing the material captured back into the production process or discarding the
material so that it is not a detriment later in the process.
• Consistent performance in cold weather conditions because of not being greatly impacted by low
temperatures, as are wet suppression systems.
• For some operations whose product is hygroscopic or suffers serious consequences from even small
percentages of moisture (e.g., clay, fine limestone or shale operations).

14. Dust Collection System

15. Major Components
Typical active mechanical dust collection system consists of four major components:
1. Exhaust hoods : Exhaust hoods or Pickups are provided at Dust sources to capture mixture of air
and dust.
2. Ductwork: It is required to transport the captured air + dust mixture to a collector.
3. Collector or cleaning device: Collector removes dust from air by filtration or separation process.
4. Fan & Motor: Fan use to create negative pressure at pickups and provide necessary exhaust
volume.

16. Demonstration of how a complex exhaust system is a combination of branches
linking simple exhaust systems

17. Exhaust hoods
• Hoods are specifically designed to meet the characteristics of the type of ore or product being
processed.
• An effective hood is a critical part to any system because if the hood does not capture the dust, the rest
of the exhaust ventilation system becomes meaningless.
• A properly designed hood will create an effective flow rate and airflow pattern to capture the dust and
carry it into the ventilation system.
• Hoods have a vast range of different configurations, but usually fall into three different categories:
enclosing, capturing, and receiving.

18. Enclosing Hood
• Enclosing hoods are those in which the source is either partially or totally enclosed to provide the
required airflow to capture the dust and prevent it from contaminating the work environment.
• The most effective way to capture dust generated is a hood that encompasses the entire dust generation
process.
• This situation is normally used when worker access is not necessary and openings are only necessary for
the product to enter and exit a piece of machinery or a work process.
• These types of enclosing hoods can have numerous applications throughout the mining and minerals
processing sequence, and are most often used in crushing, grinding, milling, and screening applications.
• When access is necessary into the dust generation process or area, it is then common to use some type of
booth or tunnel - a type of partial enclosure application.

20. Capturing Hood
• When it is not applicable to either totally or partially enclose the dust generation source or area,
capturing hoods are normally used and are located as near as possible to the dust source.
• Because the dust generation source is exterior to the hood, the ability of the hood to capture the dust-
laden air is paramount to the success of the system.
• These types of hoods must be able to overcome any exterior air current around this area.

21. Receiving Hood
• Receiving hoods are normally located close to the point of
generation to capture the dust and not allow it to escape.
In most cases, these hoods are relatively small in size.
• The hood uses the directional inertia of the
contaminant to lower the necessary capture velocity.
• These types of hoods have only minor applications in
mining and mineral processing and are most common in
small machinery and tool applications in laboratory and
shop areas.

22. Air cleaning Devices
• The types of dust control equipment used for air cleaning range from very crude gravity separators to
more sophisticated electrostatic precipitators.
1. Gravity separators (drop-out boxes)
2. Centrifugal collectors or cyclones
3. Baghouse collectors
5. Electrostatic precipitators (ESPs)
• The choice of air cleaner for any particular application will depend on dust concentration and
characteristics, particle size, efficiency of particulate removal required, air stream temperature and
moisture content, method of disposal.
• Distinguishing dust characteristics that affect the collection process include abrasive, explosive, sticky
or tacky, and light or fluffy.

23. 1. Gravity separators

24. Woking Principle:
• Large particle separate due to gravity from main air stream as velocity Of airstream drastically reduced and
change of direction from horizontal to vertical.
• Finer particles not affected by this will continue to flow in the airstream and exit the separator.
Applications:
• Due to its relatively low efficiency and relatively high residual emissions, a gravity separator is most commonly
used as a pre-separator to remove the large particles before another system, such as a scrubber or fabric filter.
• Is primarily used as a pre-separator in various dust filtration systems:
❖ wood and furniture industry,
❖ the building sector, brick ovens,
❖ glass industry,
❖ ferrous and non-ferrous industry: removal of particles to protect connected systems.

25. Advantages:
Disadvantages:
❖ Low dust collection efficiency
❖ They take up significant plant space
❖ A gravity separator has a low separation efficiency. For example, only 10% for 30 µm
particles and up to 90% for 150 µm particles.
❖ Fairly suitable for separating large to medium-sized particles (> 15 µm)
❖ Simple construction ❖Low investment costs
❖ No moving parts ❖ Simple operation
❖ Little maintenance ❖ Low pressure drop
❖ No energy use ❖ Reduce load on primary separator

26. 2. Centrifugal collectors or Cyclones

27. Working Principle:
• Cyclones are a dust collection device that separates particulate from the air by centrifugal force.
• The cyclone works by forcing the incoming airstream to spin in a vortex. As the airstream is forced to change
direction, the inertia of the particulates causes them to continue in the original direction and to be separated from
the airstream.
• A simple way to explain the action taking place inside a cyclone is that there are two vortices that are created
during operation.
• The main vortex spirals downward and carries the coarser particles. An inner vortex, created near the bottom of
the cyclone, spirals upward and carries finer dust particles.
Applications:
• Coal fired boiler, Iron and steel industry/blast furnaces and non ferrous industries, Food industry, Chemical
plants (plastics, elastomers, polymers, etc), Wood chip, wood mill and building material plants, Sand plants,
Cement plants.

28. Advantages:
❖ Cyclones are cost-effective and low-maintenance devices, and they can handle high temperatures.
No moving parts.
❖ They also reduce loading on the primary collector and allow for the dry recovery of product.
❖ Separate liquid or solid particulates, sometime both in combination with proper design.
Disadvantages:
❖ Cyclones have low efficiencies in removing fine particulate.
❖ Usually higher pressure loss than other separating types, including bag filters, low pressure drop
scrubbers , ESPs.
❖ Subjected to erosive wear and fouling if solids being processed are abrasive or ‘sticky’.

29. • Bulk Material consist of relatively large and
heavy particles, with no fine dust, it may be
possible to collect using gravity settler and for
slightly smaller particles cyclone separators are
used.
• If particles are fine and especially if they are also
of low density, separation in cyclone may not
fully effective, and in this case fabric filters are
used.
• Bag filter applications: Metallurgy, Mining,
Cement, Foundry, Chemicals, food, bulk
material handling etc.
3. Baghouse collectors

30. Components 1. Dust laden air
2. Diffuser
3. Bag Cage
4. Clean gas outlet (Plenum)
5. Tube sheet
6. Filter bag
7. Venturi
8. Locking ring (or snap band fixation)
9. Blowpipe
10. Header (Compressed air tank)
11. Diaphragm pulse valve
12. Pulse control timer
13. Rotary valve
14. Differential pressure gauge
15. Closing valve
16. Compressed air bin
17. Regulation damper valve
18. Fan
19. Purge unit with hand reducer and filter set

31. Working Principle:
• Dust laden air collected from different sources by hoods and transmit it to hopper by duct work.
• Dust laden gas or air enters the baghouse through hoppers by suction (normally) or positive pressure
and is directed into the baghouse compartment.
• The heavier dust particles fall off at the entry itself, while the lighter dust particles along with gas get
carried upward to the bags. And clean air exits from plenum exhaust.
• Separation occurs by the particles colliding and attaching to the filter fabric and subsequently building
upon themselves, creating a dust cake.
• Dust accumulation increases the resistance to gas flow, periodic cleaning required. Bags are clean by
pulse of high pressure air.
• Dust collected at bottom hopper is then removed from collector by hopper valve.

32. Particle Collection Mechanisms in a Fabric Filter
• Fabric filters take advantage of the fact that particles are larger than gas molecules. Therefore, when
dirty gas is filtered through a filter, the particles are captured on the filter while the clean gas
escapes.
• Fabric filters operate through a combination of mechanical particle capture mechanisms.
1. Straining: Larger than Filter pore /opening
2. Impaction: Larger particles
3. Direct Interception: Medium size Particles
4. Diffusion: Very small particles
(Almost 99% Collection of particles grater than 1 μm)

33. Straining:
• Occurs when the opening between the media members (fibers) is smaller than the diameter of the
particle.
• This principle spans across most filter designs, and is entirely related to the size of the particle, media
spacing, and media density.
Impaction:
• In case of large particles, because of their too much inertia, they can’t make turn around the fiber and
keep going straight ahead until they impact on the fiber’s surface and stay there as shown in above
figure.
• Almost 99% Collection of particles grater than 1 μm occur by impaction and interception.
Straining

34. Direct Interception:
• Medium sized particles have less inertia. Actually they tend to start going around the fiber with the gas
stream, but they can’t quite make it.
• So, instead of hitting the fiber head on, as shown in figure (if the distance between the center of the particle
and the outside of the fiber is less than the particle radius), they end up grazing it on the side or being
“intercepted”.
Diffusion:
• Very small particles less than 1 μm in aerodynamic diameter. This particles deflect slightly when they are
stuck by gasmolecules.
• This individual or random motion causes them to be distributed throughout the gas. The particle may have a
different velocity than the gas stream and at some point could come in contact with the fiber and be
collected. This behavior is called diffusion.

35. Fabric: A fabric is a stable collection of fibers attached to each other so as to retain a permanent
structure.
Woven fabrics are the traditional textile fabric. Fibers are first formed into yarns (threads) and the yarns
are then woven together to make a woven fabric. Woven fabrics have a definite repeated weave pattern.
Nonwoven (felted) fabric is made from long fibers, bonded together by chemical, mechanical, heat or
solvent treatment. Most bags are either completely or partially made by weaving since nonwoven
fabrics are generally attached to a woven base called a scrim.
Fabric filtration can be subdivided into two mechanisms: 1. Cake filtration and 2. Depth filtration.
Fabric Filtration Mechanisms

36. 1. Cake Filtration
• Woven Fabric
• Particles are collected by Straining mechanism
• Particles are to large to pass through the mesh of fabric,
caught and retained on the surface of filter.
• The caught particles gradually build up the cake, the
effective path of gas flow continually increases while
mesh size decreases.
• Filtering takes place primarily due to presence of the dust cake, this type of filtering is called cake
filtration.
• The collection efficiency of the filter will therefore tend to improve with use. However, the pressure
drop across the filter increases. Optimization required.

37. 2. Depth / Non-cake Filtration
• Nonwoven fabric
• Particles caught by impingement on the fibres within fabric
• Gas passing through the complicated path in fabric, but
particles are unable to follow this path and sooner or later
make contact with fibre and remain attached with the fibres.
• Primary cleaning media is dust-loaded fabric itself. This type
of filtration is often referred to as ‘depth filtration’.
• Dust cake forms slower in non woven fabric but never becomes fully established because relatively high
cleaning frequency. Referred as Non-cake filtration.
• Felted bags should not be used in high humidity situations, especially if the particles are hygroscopic
(affinity to absorb moisture) because clogging or blinding could result in such situations.

38. Fabric Material
• Fabric filter bags are generally round tubes, made of woven fabric or nonwoven fabric. Filter fabric is
manufactured from various materials, which provide different beneficial characteristics.

39. Characteristics and use
Polypropylene • It is non-hygroscopic (does not chemically react with water).
• Polypropylene is widely used in the food, detergent, chemical processing, pharmaceutical,
and tobacco industries.
• oxidizing agents, copper, and related salts damage polypropylene.
Acrylic • Good hydrolytic resistance over a limited temperature range, 127°C for continuous and 135°C
for surge application.
• Used in the manufacture of ferrous and nonferrous metals, carbon black, cement, lime, and
fertilizers. They are also used extensively in wet filtration applications.
Polyester • widely used fabrics for general applications
• The primary damaging agents are water (hydrolysis) and concentrated sulfuric, nitric, and
carbolic acids.
[Ryton]
Polyphenylene-
Sulfid (PPS)
• It will hydrolyze, but only at temperatures above 190°C.
• Its early applications have been on industrial coal-fired boilers, waste-to-energy incineration
(with and without spray dryers), titanium dioxide, and installations where Nomex does not
perform well due to chemical or hydrolytic attack.

40. Aramid
[Nomex]
• It has excellent thermal stability, shrinking less than 1% at 177°C.
• The fiber is flame resistant, but when impregnated with combustible dusts, will support combustion that will melt and
destroy the fabric.
• Unacceptably short bag life will result where sulfur oxides (SOx) and moisture are present and frequent dew point
excursions occur, such as in coal-fired boilers.
P84 • P84 is an aromatic polymer fiber produced in felt form only. The unique shape of the fiber produces improved capture
efficiency characteristics.
• Any of the felted materials can be combined with P84 to produce a fabric composite that exhibits the characteristics
of both materials.
Fiberglass
(Glass Fibers)
• Most fiberglass fabrics are woven from minute 0.0038 mm (0.00015 inch) filaments.
• Fiberglass has the highest operating temperature range available in conventional fabrics.
• Fiberglass is noncombustible, has zero moisture absorption (cannot hydrolyze), has excellent dimensional
stability, and has reasonably good strength characteristics.
• They also have poor resistance to hot solutions of weak alkalis, acid anhydrides, and metallic oxides.
• Fiberglass fabrics are used extensively with coal-fired boilers and high temperature metals applications.
Teflon • Teflon is unique among synthetics in its ability to resist chemical attack across the entire pH range throughout its
operating temperature range of 232°C continuous.
• This fluorocarbon fiber is non-adhesive, has zero moisture absorption, and is unaffected by ultraviolet light.
• Applications of Teflon include coal-fired boilers, waste-to-energy incinerators, carbon black, titanium dioxide, primary
and secondary smelting operations, and chemical processing.

41. Surface Treatment of Filtration Media
• Various types of finishes are available to enhance the filter media performance. The principal aim being
to reduce the adhesion of caked solids to the fabrics, and thus make the cleaning process easier and
more effective.
• For applications that demand the highest filtration
efficiencies (near ZERO emissions), the filter media
may be laminated with expanded PTFE (Polytetra-
fluorethylene) membrane.
• However, since expanded PTFE membrane
is delicate and can get easily damaged, care
should be taken in handling the filter bags
laminated with expanded PTFE membrane.
Normal filter bag PTFE membrane + filter bag

42. General theoretical design guidelines
❖ Differential Pressure (P)
• The pressure drop, called differential pressure (ΔP) between the clean gas side and the dirty gas side of
the baghouse is one of the most important variables that must be considered in baghouse design.
• Pressure drop through a baghouse is caused due to the air flow's resistance when air passes through the
filtering bag and the filter cake.
• This parameter is important because higher pressure drop means higher energy cost. The energy
generally will be consumed by the fans that are used to push or pull the air stream through the baghouse.
• A sudden drop in the differential pressure denotes a leak in the system. Whereas a sudden or sharp
rise in the differential pressure denotes that the filter bags are becoming blinded or “caked” with
particulate.

43. ❖ Air to Cloth Ratio
Air-to Cloth Ratio =
Total volume of gas (or air) handled by the Bag filter [m3/min]
Total filtration area provided in the Bag Filter [m2]
• m3/min-m2 = m/min, ➔ velocity unit; hence also called filtration velocity, and is
actually the velocity at which the dust laden gases travel
across the filter element.
• The more critical the dust { fine, light, sticky, non-agglomerating, abrasive, etc} or higher the dust
loading, the larger is the filtration area provided, i.e. lower is the air-to-cloth ratio maintained.
• A/C ratio with pulse jet cleaning for different materials are,
1.2 Τ𝑚3
𝑚2
× 𝑚𝑖𝑛 - for slag, coal, clinker dust
1.5 Τ𝑚3 𝑚2 × 𝑚𝑖𝑛 - for limestone and cement dust

44. ❖ Can Velocity
• Can velocity is a velocity at which the gas travels upwards across the cross section of the Bag filter at bag
bottom area.
• Can velocity =
Total volume of gas (or air) handled by the Bag filter [m3/min]
(Cross sectional area of bag house − Total bag cross section area)[m2]
Filter handling Q CFM
Cross section of housing : H
Cross section area of Bags : B
Can velocity = Q / (H - B)
• This is an important aspect and has to be restricted especially for fine, light, and non-agglomerating dust
(lime, carbon black are typical examples) as otherwise the dust may remain in a fluidized state in the bag
filter and not get discharged from the unit at all.
• Vertical vector of the gas flow velocity should be between 1.0 to 1.3 m/sec.

45. Dust Collecting system design guidelines
❖ Venting air Volume
• It has to be determined how much vent air is required at each dust sources. The recommended
standard venting air volume for typical application is given below.
Machine unit Size Τ𝒎 𝟑 𝒉 Remarks
Vibrating Feeder
800 mm 1500
1000 mm 2400
1200 mm 3600
Vibrating screen 450 Per 𝑚2 (Closed)
Roller Crusher 15 - 20
Per tone (Depending on supplier and
rpm)
Hammer Crusher 30 - 50
Impact Crusher 35 – 75
Bin
< 50 𝑚3 1000
Mechanical feeding< 500 𝑚3 3000
> 500 𝑚3 5000

46. ❖Amount Dust sources to vent
• No more than 6 to 8 dust sources to vent should be connected to one collector.
❖ Venting Hood design
• The most important parameters in the design of an exhaust hood are as follows:
1. The rate of airflow through the hood.
2. The location of the hood.
3. The shape of the hood.
• Air flow is most important because without adequate air velocity at inlet of hood, sufficient dust capture not
possible. Air velocity required at dust source to pull all dust particles in to hood is capture velocity.
• The hooding design at pickup points should provide ventilation of the dust point without capturing product
from main material flow. If it will be done in this way only airborne particles will be introduced in to system

47. Improved belt conveyor hooding
Improved elevator vent placement

48. Illustration of a dry (exhaust) dust control system at the
discharge of a hammermill crusher onto a belt conveyor.
Hooding For Airslide

49. ❖Ductwork design
• Once the volume on each individual vent point is known, the ductwork has to be design correctly.
• General rule for good ductwork design is to size the duct cross-sectional area for a velocity of 15 to 18 m/s. For
explosive dust the pipes should be sized to an air velocity between 18 and 24 m/s. Guide values of gas velocity
are,
- 16 m/sec for abrasive dust (clinker, slag)
- 18 m/sec for non abrasive dust (limestone, cement, row meal)
• Duct with lower velocity (<3500 FPM or 1067 m/min) will encourage material to fall out. Duct that have
higher velocities (>4000 FPM or 1219 m/min) encourage abrasion
• System with excessive numbers of vent point connected cannot be calibrated/controlled in a way that pollution
control is effective.
• The minimum duct diameter shall be 133mm (5’’) outside, and the minimum duct and hood thickness 3mm
(1/8’’).

50. • Common ductwork design problems include poorly designed branch entries, poorly designed elbows, and
size variations that hamper airflow and/or cause accelerated wear.

54. Dust Collector construction design guidelines
❖ Gas Flow / Dust distribution
• Uneven dust distribution results in short cleaning cycles with high cleaning air consumption and
shorter bag life expectance. Ladder vane baffles distribute airflow more evenly, reducing uneven grain
loading and turbulence.

55. ❖ Dust hopper
• The valley angles of the hoppers should not be
lower than 55° in all applications.
• A very serious problem in most group plant is the
agglomeration of dust in pyramid hoppers due to
a much small discharge. In such cases rotary
feeder with screw conveyor are used.
❖ Fan
• All fan should be selected with 15% safety
margin, as a consequence, air quantity for fans is
at least 15% higher than required
• Damper provided at inlet duct of fan.

56. Bags and Cages

57. Bag and cage Installation
• Lower the bottom of the bag through the hole in
the tubesheet.
• Fold the snap band (bag top) to insert it into the
tubesheet hole.
• Fit the groove of the snap band to the edge of
the tubesheet and allow the band to snap into
place.
• Check the fit of the snap band. It should fit
securely all around with no wrinkles in the snap
band. The top of the bag should be above the
tubesheet approximately 3/8”.
• Slide the cage into the bag until it rests on the
tubesheet

58. Bag Cleaning System
• Base on cleaning technique use for cleaning of bags, classified in three types.
1. Mechanical Shaker Collectors
2. Reverse Air Collectors
3. Reverse Jet (Pulse Jet) Collectors
• Bag cleaning is initiated at a predetermined high pressure drop and stops when the pressure drop
reaches a predetermined low set point. This method ensures that the bags always have a sufficient
amount of dust cake.

59. ❖ Mechanical Shaker Collectors

60. • Shaker collectors employ tubular filter bags fastened on the bottom and suspended from a shaker
mechanism (horizontal bar/beam) at the top.
• Dust-laden air enters the collector and is deposited on the inside of the tubular bags. Fine particles are
then caught on the insides of the fabric bags as the gas flows upwards through the unit.
• Cleaning of the mechanical shaker baghouse is carried out by shaking the top horizontal bar from
which the bags are suspended. Motion may be imparted to the bags in several ways, but the general
effect is to create a rippling movement (simple harmonic or sinusoidal) along the fabric.
• Due to movement of the bags dust dislodge from the fabric and fall in to the collecting hopper.
• Parameters that affect cleaning include the amplitude and frequency of the shaking motion and the
tension in the mounted bag.

61. When using mechanical shakers, a number of recommendations should be followed:
• Pressure gauges should be installed on each compartment to monitor differential pressures during the
cleaning cycles.
• Differential pressures should be as close as possible to 0.0 inches wg to ensure that the dust cake breaks
and is released from the bags..
• Bags should only be shaken when differential pressures across a section of bags have increased by 1/2-
inch wg.
• The cleaning will not function properly when on load, and so the filter can only be shaken effectively at
the end of a conveying cycle in the absence of gas/air and material flow.
• Experiments to determine the optimum time interval between the shaking of bags should be performed so
that bags are not shaken excessively. This also lessens wear on the bags as well as the mechanical parts.

62. ❖ Reverse air Collector
• in a reverse air baghouse, the bags are fastened to
the tube sheet at the bottom of the baghouse and
suspended from adjustable hangers (for adjusting
bag tension) at the top.
• Dirty gas flow normally enters the baghouse and
passes through the bags from the inside, and the
dust collects on the inside of the bags.
• Reverse air collector low-pressure cleaning air
(30-40 mbar) to the filter bags for reconditioning.
• The collectors must be compartmentalized for
continuous service.

63. • Before a cleaning cycle begins, filtration is stopped in the compartment to be cleaned. Bags are cleaned by
injecting clean air into the dust collector in a reverse direction, which pressurizes the compartment.
• The pressure gently collapses the bags partially toward their centerlines, which causes the dust cake to crack
and detach from the fabric surface causing the dust cake to fall into the hopper below.
• Because felted fabrics retain dust more than woven fabrics and thus, are more difficult to clean, felts are
usually not used in reverse air baghouses.
• Improper tensioning is one of the main causes of bag failure in
reverse air baghouses.
Bag Diameter, inch Tensioning Level, lbs
5 30 – 40
8 50 – 65
11.5 - 12 75 – 95

64. ❖ Reverse Jet (Pulse Jet) Collectors
• Reverse jet collectors use bags supported from a
metal cage fastened onto a tube sheet at the top of the
collector.
• Dust-laden air enters the collector and flows from
outside to inside the bag.
• The dust cake deposits on the outside of the bag and
is cleaned by short bursts of compressed air injected
inside the bag.
• A major difference between reverse air baghouse
cleaning and pulse jet baghouse cleaning is primarily
one of time scale.

65. • The short burst of compressed air creates a rapidly moving air
bubble (shock wave) which results in flexing of the bags.
• This flexing of the bags breaks the dust cake, and the dislodged dust
falls into a storage hopper below.
• The compressed air must be clean and dry or moisture can build up on
the bags, hindering the bag cleaning efficiency.
• Pulse jet collectors are not compartmentalized, allowing bags to be
reconditioned without removing a section from service.
• The advantage of using reverse jet collectors is high product recovery and high collection efficiency. Due
to more frequent cleaning intervals, these collectors provide more complete bag cleaning.
• Pulse jet collectors are more cost-effective than earlier styles of collector such as mechanical shaker
collectors.

66. Valves on a Pulse Jet System

67. • The air pressure in the back cell pushes the diaphragm against the outlet of the valve and the valve
remains in the "closed" condition.
• On receiving electrical signal, the solenoid valve’s port opens to the atmosphere and the
compressed air escapes from the back cell quickly. Due to this, the diaphragm moves back and the
compressed air blows through the valve outlet.
• When the electrical signal disappears, port of the solenoid valve closes again and the compressed air
pressure in the back cell rises. This pushes the diaphragm closely against the valve outlet and the
diaphragm valve gets closed.
• For trouble free operation of diaphragm valves, solenoid valves and filter bags, the compressed air
should be clean and dry.
• A purge valve is installed to help eliminate water accumulation in the air header. Without the
purge, water from the compressed air can enter the baghouse and cause corrosion to filter bags and an
agglomerated, hard-to-clean dust cake.

69. Pulse Jet– Blowpipe Misalignment Problem
• The critical factor for providing thorough bag
cleaning and to prevent damage to venturis and
bags is to make sure that the hole in the blow pipe
are properly aligned above the filter bags.
• If holes of the blow pipe are not properly aligned
above the filter bags, it may damage venturis.
• Rotation of the blow pipe could cause the
compressed air pulse to strike the side of the bag
near the top, and create hole in the bag.

70. Cleaning Sequence
• The pulsing sequence can play an important part in minimizing material recirculation. Pulsing the rows in
order can cause the submicron material to migrate to the cleaned row.
• Staggering the pulsing order so the recently cleaned rows are separated from those yet to be cleaned can
improve the dust cake, resulting in better filtration.

71. Pulse cycle
• To ensure Proper cleaning frequency, an automatic
‘cleaning on demand’ system utilizing a
pressure switch gauge.
• Pulse time generally 0.10 to 0.150 second in order
to create effective shock wave. Pulse cycles
generally range from 5 to 30 seconds but may be
much higher.
• This type of system will automatically step through
a cleaning cycle that starts when the high
differential pressure set point is reached and stops
when it cleans down to the low differential
pressure set point.

72. Comparison of Bag Filter Parameter
Parameter Shaker cleaning Reverse air cleaning Pulse jet cleaning
Relative Size of bag
house
Medium Size Large due to low filtration velocity Small due to longer bags
Number of chambers No Separate chamber Separate chamber for offline cleaning No Separate chamber necessary
Filter Dust Collection
Surface
Inside Inside Outside
Filter Cleaning method Electric Motor Reverse flow from low pressure fan Compressed air
Mode Of cleaning Off Stream Off Stream On Stream or Off stream
Duration 10 to 100 cycles, 30 sec to few
minutes
1 to 2 min, including valve opening,
closing, dust settling period (reverse air
flow: 10 -30 sec
Compressed air(40-100 psi) Pulse
duration 0.1 sec
Relative Maintenance
required
Most Least Medium
Relative Filter Life Shortest Longest Medium
A/C Ratio 1 to 3:1 0.5 to 2:1 1 to 7.5:1

73. Advantages and Disadvantages
• Fabric filters provide high collection efficiencies on both coarse and fine particulates (99% efficiency).
• Operation is relatively simple. Unlike ESP, fabric filter systems do not require the use of high voltage,
therefore, maintenance is simplified and flammable dust may be collected with proper care.
• Designed to operate at low pressure drop thus reducing the power consumption. Low maintenance easy
to remove bags.
• However, there are gas temperature limits because of the limits of the fabric itself. At high temperatures,
the fabric can thermally degrade, or the protective finishes can volatilize.
• They cannot be operated in moist environments; hygroscopic materials, condensation of moisture, or tarry
adhesive components may cause crusty caking or plugging of the fabric.
• Fabric life may be shortened at elevated temperatures and in the presence of acid or alkaline particulate or
gas constituents.

74. Maintenance
❖ Cleaning and repair
• The external portion of this unit should be treated as any other metal surface that is subject to corrosion.
Periodic cleaning and painting when required.
• Dust may enter the clean air plenum through a leaking or broken filter element. Remove accumulated dust
from clean air plenum and replace filter element immediately. Dust in the clean air side of a filter element
will reduce the life and performance of the element.
❖ Solenoid and Diaphragm Valves
• The solenoid and diaphragm valves may require periodic maintenance depending on the quality of the
compressed air supplied to the unit.
• A ruptured diaphragm valve or a stuck solenoid valve will drain a compressor. A cracked or broken line
from the solenoid valve to the diaphragm valve will have the same effect. Result in low header pressure.

75. ❖ Filter Elements
• Filter elements do not require any periodic maintenance. However, at some point the elements will require
replacement. This will be indicated by persistent high differential pressure across the.
• When low pressure drop or dust in exhaust air found there is possibility that bags are damaged or holes in
bags. Need to replace.
❖ Screw Conveyor & Rotary Valve (Airlock)
• The roller chain drive should be kept tight enough so that the chain cannot "climb the sprocket" and should
be oiled lightly once per month.
• Bearing required periodic lubrication when service is abnormal with respect to speed, temperature,
exposure to moisture, dirt or chemical.
• Air leakage through a worn out valve rotor into the filter hopper will re-entrain dust onto the filter bags.
Replace the airlock.

76. ❖ Pressure Gauge
• Gauge lines leakage or clogging will give wrong indication in gauge. Small filter inside the bag house
below the tube sheet need cleaning or replacement. Replace the gauge if needle does not move.
❖ Timer adjustment
• The pulse interval can be extended until an increase in differential pressure is observed in the filter. Do not
change the pulse duration. It should be 40 to 50 milliseconds for best results.
❖ Outlet and inlet duct
• Inspection of outlet and inlet ducts needed to prevent from corrosion, leaks, particulate build up.
❖ Fan
• Inspection of fan for corrosion, wear in rotating part, bearing lubrication and vibration of fan and
drive assembly.

77. Troubleshooting
Problem Possible causes Solution
High differential
pressure across
tube-sheet
Bad Gauge Check the gauge by blowing into it. Replace the gauge if the needle does not move.
Leaking Gauge
Lines
Check the full length of both lines for cracks, splits or breaks. Replace both lines with
new tubing. Check the small filter, Clean or replace it as required.
Media Blinding
Excessive moisture is the most common cause of blinding. High humidity, condensation,
and leaks in the duct are typical sources. It may be necessary to preheat and insulate the
filter to avoid dew point issues. Duct leaks are found by inspection and routine
preventive maintenance.
Rotary Valve
(Airlock) Leakage
Air leakage through a worn out valve rotor into the filter hopper will re-entrain dust onto
the filter bags. Replace the airlock.
High Dust Load
When somethings are changed in process result in to higher material flow or smaller
particle size. It may be necessary to install a larger filter or reduce airflow to the original
design.
Bag fit on cages
Check the bag fit on cages with a pinch test. Replace the bags if they are too tight
because tight bags will not clean properly.

78. Low
differential
pressure
across the
tube-sheet
Holes in Bags Replace all bags. See section on poor bag life.
System Air Volume too
low
Check the main system fan for correct RPM or a closed damper.
Bag & Cage Installation
Look for dust in the clean air plenum or discharging from the system fan. Bags may be
missing or may not be properly installed in the tube-sheet.
Dust in
exhaust air
Start Up Period
Allow the filter to run for 48 to 96 hours to establish a dust cake. Some applications will
require “seeding” or pre-coating the bags with an appropriate material to establish a cake.
Holes in Bags Replace all bags. See section on poor bag life.
Bag & Cage Installation Refer to the instruction manual for correct installation.
Poor Bag
Life
Damaged Cages
Filter cages that are bent, have broken wires, or have corrosion will cause premature
failure of the filter bags. Inspect and replace as soon as possible. Corrosion problems may
require coated or stainless steel cages.
High Air Volumes
High air to cloth ratios can shorten filter bag life. Compare current operating conditions
to the original design.
Media blinding Excessive moisture is the most common cause of blinding.
Incorrect filter media
High temperatures, chemical content, and dust composition will affect filter media life.
Select suitable media.

79. Electrostatic Precipitator

80. ❖ Working Principle
• Electrostatic precipitation is a method of dust collection that uses electrostatic forces, and consists of
discharge wires and collecting plates.
• A high voltage is applied to the discharge wires to form an electrical field between the wires and the
collecting plates, and also ionizes the gas around the discharge wires to supply ions.
• When gas that contains an aerosol (dust, mist) flows
between the collecting plates and the discharge wires,
the aerosol particles in the gas are charged by the
ions.
• The Coulomb force caused by the electric
field causes the charged particles to be collected
on the collecting plates, and the gas is purified.

81. • The precipitation process involve 4 main Functions,
1. Corona Generation 2. Particle Charging
3. Particle Collection 4. Removal of Particles
Corona Generation:
• When high voltage is applied in the charging
electrodes ,a blue luminous glow called “Corona”
is generated around the electrode.
• And it causes ionization of gas molecules , due to
which +ve ions, -ve ions , and free electrons are
generated.

82. Particle Charging:
• The –ve charges of ions and free electrons move towards +ve electrodes and the +ve charges of ions move
towards –ve electrodes.
• When –ve ions travel towards +ve electrodes, the –ve charges get attached to the dust particles and thus the
dust particles are electrically charged.
Particle Collection:
• The –vely charged particles get attracted towards the +vely charged collecting electrodes and form a layer
on the surface of the electrode.
• Similarly the +vely charged particles are deposited on the discharging electrode.
Removal of Particles:
• The deposited particles forms a layer on the electrodes, and after certain time interval they are removed
from the electrodes by mechanisms depending upon the type of ESP.
• Ash particles are collected in the hopper , and from there they aretransported to somewhere else.

83. Thank You