equipment to control particulate matter air pollution and control control of air pollution control of particulate matter

1. Equipment to Control
Particulate Metter [part-2]
Ravi Kumar GARRE

2. Contents covered
• Introduction
• Settling chambers
• Inertial separators
• Cyclones
• Filters
• Electrostatic precipitators
• Scrubbers/ wet collectors
[Note: settling chambers, inertial separators,
cyclones are not covered in this presentation]

3. Introduction
• To remove particulate matter from gaseous
streams various types of equipments are in
practice.
 Settling chambers
 Inertial separators
 Cyclones
 Filters
 Electrostatic precipitators
 Scrubbers/ wet collectors

4. Introduction
• The data to keep in mind in the
selection of proper equipment is:
 Quantity of gas to be treated and its variation
with time
 Nature of particulate matter
 Concentration of particulate matter
 Temperature and pressure of gas stream
 Nature of gas stream (i.e. solubility, corrosivity,
ignitability, etc.)
 Desired quality of treated effluent

5. Introduction
• Objectives of control equipment
 Prevention of nuisance
 Prevention of physical damage to property
 Recovery of valuable waste product
 Minimization of economic losses
• Efficiency of separating device
η = (quantity of particulates collected
from gas)/(quantity of particulates
present initially)

6. Filters
• Filters (or) fabric filters,
also called as fabric
collectors/ cloth filters/
bag filters/ bag house.
• Fabric collectors use
filtration to separate
particulates from
polluted gas streams.

7. Filters
• Polluted gases enter the bag
house and pass through
fabric bags that act as filters.
• The bags can be of woven,
cotton, synthetic or glass-
fibre material in either a
tube or envelope shape.
• In this system, the entered
gas allowed to pass through
these bags, which filters out
the particulate matter and
allows the gas to escape.

8. Fabric filters
• Small particles are
retained on the fabric,
later on when the dust
mat will be formed.
• Frequently the bags/ filter
material should be
cleaned or replaced.
• Small particles can retain
in the bags.
• Fabric filters can remove
particle of size about
1µm.

9. Fabric filters
• Fabric filters are 99 % efficient in removing
particles of size 1µm to 10µm
• The factors affecting efficiency is:
 Improper selection of filter media
 Temperature of gaseous stream
 Particle size of particulate matter

10. Fabric filters
Advantages
• Higher collection efficiency
• It collects particles smaller than 10µm
• Requires normal power consumption
Disadvantages
• High temperature gases need to be cooled
• High initial and maintenance cost
• High fabric replacement cost
• Large size equipment
• Fabric is liable to chemical attack

11. Fabric filters
Applications
• Metallurgical industry
• Foundries
• Cement industry
• Ceramic industry
• Flour mills
• Brick works

12. Electrostatic precipitators
• Electrostatic precipitator is a device that
removes suspended dust particles from a gas
or exhaust by applying a high-voltage
electrostatic charge and collecting the
particles on charged plates
• Electrostatic precipitators can remove
particles of size less than 1µm
• Efficiency – 95 to 99%

13. Electrostatic precipitators
• In this method two electrodes are
fitted inside a chamber.
• When high voltage is applied an
electric discharge takes place in
between these two plates as a
result a strong electromagnetic
field will be created.
• The air in the strong
electromagnetic field get ionised.
• The ionised air consists of ions
and free electrons.

14. Electrostatic precipitators

15. Electrostatic precipitators
• If the polluted gas allowed to pass through the
strong electromagnetic filed, the particulate
matter get negatively charged and attracted to
positively charged electrodes.
• Therefore, the particulate matter settle down
on the surfaces of electrode plates.
• These can be dislodged by vibrating the
electrodes.

16. Electrostatic precipitators

17. Electrostatic precipitators
Components of ESP
• A Source of high voltage
• Electrode plates
• Inlet and outlet for the gas
• A hopper for disposal of
collected gases
• A cleaning system
• An outer casing to form an
enclosure around the
electrodes

18. Electrostatic precipitator
Advantages
• Particles may be collected wet or dry
• Even small particles can be removed
• They can be operated at high temperatures up to 450 ˚C
• Maintenance is nominal
Disadvantages
• Higher initial costs
• Sensitive to variable dust loadings and flow rates
• Collection efficiency reduces with time

19. Electrostatic precipitator
Applications
• Cement factories
• Pulp and paper industries
• Steel plants
• Non-ferrous metal industry
• Chemical industry
• Petroleum industry
• Power plants

20. Scrubbers
• Scrubbers are also called as wet collectors.
• Scrubbers utilise liquids (generally water) to
assist in the removal of particulates from the
carrier gas stream.
• In wet collectors, the particulate matter is
agglomerated with water and then separated
from the gas with water.
• Scrubbers can separate particles even smaller
than 0.2µm.

21. Spray towers
• Spray tower is the simplest
type of wet scrubber.
• In this scrubber, gas is
passed counter current to
falling drops of liquid from
a series of nozzles.
• The impingement and
interception of particles
with liquid droplets cause
settlement of particles
along with liquid droplets.
• Spray towers are used to
separate coarser particles.

22. Cyclone scrubbers
• Cyclone scrubbers are
another types of wet
collectors.
• High pressure nozzle
sprays located inside the
chamber generate a fine
spray that intercepts
particles entrained in the
swirling gases.
• The particulate matter is
thrown on to the walls by
centrifugal action and then
drained to the bottom.

23. Scrubbers/ wet collectors
Advantages
• Simultaneously remove particulates as well as
gaseous pollutants
• Hot gases can be cooled down
• Corrosive gases can be recovered and neutralised
Disadvantages
• Lot of waste water produced
• Maintenance cost is high

24. Choice of equipment
1. Particulate size
2. Particulate loading
3. Required efficiency
4. Properties carrier gas: Composition,
Temperature, Pressure, Viscosity, Density,
Humidity, ignitability, reactivity, electrical
property, etc.
5. flow characteristics of carrier gas
6. Capital and operating cost of equipment
7. Ease of maintenance and reliability

25. Economic aspects

26. THANK YOU