The document discusses various methods for controlling air pollution, including particulate contaminants. It describes factors that affect the selection of control equipment such as gas-particle interaction and efficiency required. Several types of control equipment are examined, including gravity separators, centrifugal separators, fabric filters, particulate scrubbers and electrostatic precipitators. The document also discusses methods to reduce air pollution through process changes, treatment of emitted gases, and reducing polluted streams. Key considerations for air pollution control technology include the pollution source, effluents, regulations, waste generated and disposal.

1. Air Pollution and Control
Control of Particulate Contaminants
Factors affecting Selection of Control Equipment
– Gas Particle Interaction – Working principle,
Design and performance equations of Gravity
Separators, Centrifugal separators Fabric filters,
Particulate Scrubbers, Electrostatic Precipitators
– Operational Considerations.

2. Methods of Reduction of Air Pollution
• Reducing the volume of polluted streams
• Changing the process of causing the pollution
• Treatment to the emitted gas

3. Factors to be Considered for Control of Air
Pollution Technology
• Nature of Source
• Effluents from the source
• Air Pollution Regulations
• Waste Generated from Surroundings
• Disposal of Waste

4. Objectives of Air Pollution Control
• To save the public from air pollution
• To protect animals and plants
• To protect the properties
• To ensure comfortable environment to
Human, living organisms and aquatics

5. Factors Affecting Selection of Control Equipment
• Type of industry
• Concentration and characteristics of pollutant
• Career Gas Characteristics
• Process Factors
• Efficiency Required
• Operational Factors
• Constructional Measures

6. Type of Industry
• Equipment can be selected based on type of
pollutant (gaseous or particulate matters).
• Pollutants from cement industries are fugitive
dust and sulphur oxides.
• Pollutants from automotives are carbon
monoxide and hydrocarbons
• To control the pollution it is essential to know
the type of pollutant.

7. Concentration and Characteristics of Pollutant
• Particulate characteristics include
- Particle size spectrum
- Effective particle shape
- Particle density
- Physical and chemical properties such as
stickiness, fluidity, corrosiveness, electrical
conductivity etc.

8. Career Gas Characteristics
• Pressure
• Temperature
• Density
• Viscosity etc.

9. Process Factors
• Flow Variability
• Volumetric Gas Rate
• Particulate Concentration
• Allowable Pressure Drop

10. Efficiency Required (Control Efficiency)
• Measure of emission reduction efficiency and
its percentage value
• Selection of particular air pollution control
equipment is based on control efficiency.
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11. Operational Factors
• Maintenance
• Continuity of Operation
• Safety
• Health Protection
• Ultimate Use of Collected Materials

12. Natural Cleansing Properties of Environment
• Quantity of air pollution created by human beings or
industry is within the limit of natural self-cleansing
capacity of the atmosphere.
• When the discharge or emission from industries in
human activities exceeds the limits it pollutes the
environment.
• Pollutants from industries are controlled by
mechanical devices such as high-rise chimneys to
improve the dispersion and dilution of polllutants.

13. Natural Self Cleansing Properties of Atmosphere
• Dispersion
• Gravity settling with flocculation
• Gravity settling without flocculation
• Absorption
• Adsorption
• Rainout

14. Natural Self Cleansing Properties of Atmosphere
• Dispersion – Chemical or physical process of
distributing the air pollutants over the wide area of
atmosphere by wind speed..
• Gravitational Settling – Larger particles of air
pollutants in air, settles down on building, trees and
other tall objects.
• Absorption - Gaseous and particulate matters are
collected either in mist or rain and settle down with
mist or rain.
- It is carried out below the cloud level in
atmosphere.

15. Natural Self Cleansing Properties of Atmosphere
• Washout or Scavenging – Process of absorbing the
pollutants and falling with rain drops is called
washout or scavenging.
• Rainout – Process of dropping out the pollutants.
- Involving the precipitation process above cloud
level where sub-micron particles present in
atmosphere.

16. Air Pollution and Control
• Prevention at Source
- For manufacturing and other engineering sources it
is better to change raw material
- It reduces the installing costly equipment for
pollution control
• Air Pollution Control Equipments
- Costlier method to prevent mixing of pollutants in
air .
- Selection of equipment is based on pollutant
emitted in industry.

17. Types of Emissions
• Uncontrolled (fugitive) emission
• Controlled (steady-state) emission
• Transient emission
• Accidental (emergency) emission

18. Fugitive Emission
• Emission from faulty and damaged joints, flanges,
valves and opening.
• It happens during energy transferring, recycling,
packaging and storage.
• Fugitive emission is also called diffusive emission.
Control of Fugitive Emission
• Regular maintenance of valves, fittings, etc.
• Installing the gas detectors to identify leaks
• Using good quality accessories and fittings.

19. Types of Emissions
Controlled Emission
• Emission during normal emission is allowed.
• It is guided through the chimneys of the plant.
Transient Emission
• Heavy emissions occur during start-up and shutting down
operation of plant.
Accidental or Emergency Emission
• Heavy emissions occur during major fault in one or more
major equipment.
• Total emission period change with capacity of service person
to rectify it.
• Very dangerous to atmosphere.
• It affects employees and public outside the plant.

20. Pollution Control Techniques without
Control Devices
• Process Change
• Change in Fuel
• Good Operating Practice
• Plant shutdown or Relocation

21. Process Change
• Modification of existing process or introduction of
new process.
• Process modification is a popular technique.
• Changes in raw materials, fuels etc.
• Promotions to use fluorescent lights to conduct
electric audits.
• Use of wind energy, geothermal energy, hydroelectric
power and solar energy.

22. Change in Fuel
• Use of less polluting fuel to reduce air pollution.
• Use of low sulphur fuel instead of high sulphur fuel
• Adopting electric utilities
• Using natural gas as fuel
• Nuclear power plants are pollution free when
compared to coal fired power plants.

23. Good Operating Practices
• Releasing of pollutants can be controlled by
good house keeping in industry.
• For e.g. chemical spread over the floor
evaporates rapidly and cause emission
• Poorly maintained automotives cause more
emission.

24. Controlling Air Pollution by Installing Equipments
• Replacement of burning fuel by electricity or solar
energy.
• Use of high quality cereals and efficient engines
• Replacement of old machines with new machines
• Using mechanical air pollution controlling devices

25. Control of Particulate Pollutants in Industries
• Gravitational Settling
• Centrifugal Impaction
• Inertial Impaction
• Direct Interception
• Diffusion
• Electrostatic Attraction

26. Inertial Impaction
• Large particles in gas stream have high inertia
to follow the gas streamlines around the
impactor.
• Small particles in the gas tend to diverge and
pass around the interseptor.

27. Direct Interception
• The particles have less inertia and rarely
follow the gas streamlines around the fiber.
• Distance between centre of fiber and outside
the fiber is less than particle radius.
• The particle will hit the fiber is less than
particle radius.
• The particle will graze or hit the fiber and be
intercepted.

28. Equipments to Control Particulate Matter
• Gravitational Settling Chambers
• Centrifugal Collectors
• Wet Scrubbers
• Electro-Static Precipitators
• Fabric Filters

29. Gravity Settling Chamber

30. Horizontal Flow Settling Chamber

31. Gravity Separators
• Also known as gravitational settling chamber
• Consists of enclosed chamber, through which dirty
air will pass through.
• The smokes (with dirty air) will be passed through
settling chamber.
• As per Stoke’s law, the larger particles settle down at
the bottom of the chamber.
• Velocity should be kept as low as possible.
• Velocity ranges from 0.3 m/s to 2.5 m/s.
• Coarse particle size of 40 μm will be removed.

32. Merits and Demerits of Gravity Chamber
Merits
• Simple design and maintenance
• Less pressure losses
• Low initial cost
• Dry and continuous disposal of solid particles.
Demerits
• Larger size particles are only settled
• Low collection efficiency
• Requires large space

33. Centrifugal Collector
• Used to separate particulate matter of size
5 μm to 25 μm by centrifugal force.
Types of centrifugal collector
• Dynamic Precipitator
• Cyclone Collector
• Impellers

34. Centrifugal Collectors

35. Merits and Demerits of Centrifugal Collector
Merits
• Low cost arrangement
• Simple design, easy installation and maintenance
• Requires less area
• Continuous disposal of dusts
• Less pressure losses
• Suitable for separating large particulate matters.
Demerits
• Requires high head rooms
• Less efficiency for smaller particles
• Collection rate vary with flow rate

36. Cyclone Collectors

37. Cyclone Collector
• Air flows in a helical or spiral pattern beginning at the
top of the cyclone beginning at the top (Wide end).
• Cyclonic action ends at bottom end (narrow end).
• At the bottom larger particles are collected and
removed.
• In conical system, rotational radius of air stream gets
reduced and thus smaller particles are settled.
• Cut-point of the cyclone is the size of particle that
will be removed from the stream with 50% efficiency.
• Particulate matters larger than cut point are removed
by greater efficiency.

38. Factors affecting Cyclone Efficiency
• Inlet velocity of dust laden gas
• Diameter of dust profile
• Density of dust profile
• Dust concentration of career gas
• Smoothness of inner cyclone wall
• Cyclone length or cone length
• Ratio of body diameter to gas outlet diameter

39. Advantages of Cyclones
• Low initial cost
• Simple in construction
• Less pressure losses
• Low maintenance requirement
• Continuous disposal of solid particulate
matter
• Use of any material in their construction that
can withstand the temperature and pressure.

40. Disadvantages of Cyclones
• Low collection efficiency for particles below 5-
10μ in diameter.
• Low collection efficiency at low particulate
concentration.
• Severe abrasion problem during striking of
particles on wall of cyclone.

41. Operating Problems of Cyclones
• Erosion – Heavy and hard particles moving with high
velocity continuously scrap against the wall and
erode the metallic surface.
• Corrosion – When the cyclone is operated below the
condensation point and if reactive gases present in
the gases, then corrosion occurs.
• Build-up – Dust cake builds up on the cyclone walls
especially around vortex finder, at the end of any
internal vanes, if the dust is hygroscopic.

42. Applications of Cyclones
• Large scale cyclones used in saw mills, to
remove saw dust from extracted air.
• Used in oil industries to separate oil and gas.
• Used in cement industry to separate large
particulate matters.
• Used in ventilation to separate the grease
from exhaust air.

43. Fabric Filters
• Used to collect dust
particles of size 1 μm
• When dust gases pass
through the fabric
filters and the
streamline of gas
diverges, collection of
particulate matters
occurs.
• Fabric filters are based
on the principle of
filtration (separation
of solid from liquid
(gases).

44. Bag Filter

45. Fabric Filter (Bag Filter) – Working
• Flue gas coming out of the Boiler, traveling through the duct,
enters the casing of the bag filter
• Because of suction created by the ID Fan, the flue gases come
in contact with the bags and enters the hollow portion
because of pressure gradients
• Heavy particles get collected on the bag’s external surface
because of its impermeability to them.
• Filtered flue gases then enter a separate chamber from the
bag’s outlet and get supplied to id fan inlet and then
to chimney to be released into the atmosphere.

46. Cyclonic Scrubbers
• The inlet gas enters the chamber
tangentially, swirls through the
chamber in a corkscrew motion,
and exits.
• At the same time, liquid is sprayed
inside the chamber
• As the gas swirls around the
chamber, pollutants are removed
when they impact on liquid
droplets, are thrown to the walls,
and washed back down and out.

47. Venturi Scrubber
• Clean about 400 litres of gas
per minute.
• The mist can be removed by
venturi scrubbers followed
by cyclonic scrubbers.
• It consists of a venturi throat,
through which gas is pushed
at a velocity of 3400 – 12600
m/min.
• Scrubbing liquid is added in
the direction of flow of gas at
a rate of 0.3 – 1.5 lpm.

48. Thank you
Dr A R Pradeep Kumar, B.E., M.E, Ph.D.
Professor and Head/Mech.
Dhanalakshmi College of Engineering
Chennai 601 301
Email : dearpradeepkumar@gmail.com
99 41 42 43 37