1. CONTROL OF PARTICULATE CONTAMINANTS
1. Factors affecting Selection of Control
Equipment
2. Gas Particle Interaction – Working principle
3. Gravity Separators - Working principle
4. Centrifugal separators - Working principle
5. Fabric filters - Working principle
6. Particulate Scrubbers - Working principle
7. Electrostatic Precipitators - Working principle
2. Factors affecting Selection of Control Equipment
The following factors are considered for selecting a
particular air pollution control equipment.
• Environment
• Engineering
• Economic
Environmental :
• equipment location, availability space, ambient
conditions, availability of adequate utilities and
ancillary system facilities.
• Maximum allowable emissions.
• Contribution of air pollution control system to waste
water and solid waste.
• Contribution of air pollution control system to plant
noise levels.
3. Engineering:
• Design and performance characteristics of the
particular control system(size and weight)
• Pressure drop, reliability and dependability,
temperature limitation, maintenance
requirement.
• Contaminant characteristics(physical and
chemical) properties,concentration, particulate
shape and size distribution in the case of
particulates.
• Gas stream characteristics (volume, flow rate,
temperature, pressure, humidity, composition,
reactivity, corrosiveness and toxicity).
5. • PM stands for particulate matter - particle
pollution
• It is a mixture of solid particles and liquid
droplets found in the air - Some particles, such as
dust, dirt, soot, or smoke.
• Fine particulate matter (PM2.5) is an air pollutant
- when levels in air are high.
• PM2.5 are tiny particles in the air that reduce
visibility and cause the air to appear hazy when
levels are elevated.
• Exposure to such particles can affect both your
lungs and your heart.
6. Types of particulate matter
• Inhalable coarse particles - found near
roadways and dusty industries, they are larger
than 2.5 micrometers and smaller than 10
micrometers in diameter.
• Fine particles - found in smoke and haze, and
are 2.5 micrometers in diameter and smaller.
7. steps to Reduce Exposure to Indoor PM
• Vent all fuel-fired combustion appliances to the
outdoors (including stoves, heaters and furnaces)
• Install and use exhaust fans vented to the
outside when cooking.
• Avoid the use of unvented stoves, fireplaces or
space heaters indoors.
Measurement Method :
• The most accurate measurements is gravimetric
(weighing) method. Air is drawn through a
preweighed filter, and particles collect in the
filter.
8. Gas Particle Interaction –Working
principle - Gravity Separators
• Gravitational settling chambers used to remove large particles
usually > 50 µm from gas stream.
• Particles settle under gravitational force.
• This device consists of huge rectangular chambers in which
the velocity of the carrier gas is decreased so that particles in
the gas settle down by gravity.
• The gas stream polluted with particulates is allowed to enter
from one end..
• The horizontal velocity of the gas stream is kept low in order
to give sufficient time for the particle to settle by gravity.
• The particulates having higher density obey stoke’s law and
settle at the bottom of the chamber from where they are
removed ultimately.
• Several horizontal shelves or trays improve the collection
efficiency by shortening the settling path of the particles.
9. Advantages :
Low initial cost
Easy to design
Low pressure drop
low maintenance
cost
Disadvantages
Require large space
Less collection efficiency
Only larger size particles can be
collected
10. Cyclone separators
• A simple cyclone separator consists of a cylindrical shell,
conical base, dust hopper and an inlet. An out let for
discharging the particulates is present at the base of the
cone.
• Through an inlet, the dust laden gas enters tangentially.
where the gas receives a rotating motion and generates a
centrifugal force.
• Under the influence of the centrifugal force generated by
the spinning gas, the solid particulates are thrown to the
cyclone walls as the gas spirals upwards inside the cone.
• The particulates slide down the walls of the cone and into
the hopper and are discharged from the outlet.
• It can remove 10 to 50 µm particle size.
11.
12. Disadvantages:
• Requires large head room
• Less efficiency for smaller particles
• Sensitive to variable dust load and flow rate.
Advantages :
1. Low initial cost
2. Require less floor area
3. Simple construction and maintenance
13. Electrostatic precipitator
• Electrostatic precipitator are used in removal of fly ash dust particles
from electric utility boiler emissions.
• The dust laden gas is passed between oppositely charged
conductors.
• Then it becomes ionized as the voltage applies between the
conductors.
• As the dust laden gas is passed through those highly charged
electrodes, both negative and positive ions are formed.
• The ionized gas is further passed through the collecting units.
• Which consist of a set of vertical metal plates.
• Alternate plates are positively charged and earthed.
• As the alternate plates ate earthed high intensity electrostatic field
applies a force on oppositely charged dust particles and drives them
toward the grounded plates.
• The deposited dust particles are removed from the plates by giving
the shaking motion of the plates with the help of external means.
• The dust removed from the plates with the help of shaking motion is
collected in the dust hoppers.
14.
15. Advantages:
1.high collection efficiency
2. particles may be collected dry or wet
3. can be operated at high temperature.
4. Maintenance is normal
5. few moving parts
Disadvantages:
• High initial cost
• Require high voltage
• Collection efficiency reduce with time
• Space requirement is more
16. Centrifugal Separator
• The centrifugal separator features an inlet, outlet,
and separator. The separator produces a spinning
vortex, which leads to the filtration of solids from
liquids. The separated solids are collected at the
bottom of the separator, and they are removed
from there.
• centrifugal separator is the most effective
• least expensive method for PM control.
• More than 90% dust removal efficiency
17.
18. Fabric filter
• Fabric filter remove partcles upto 1μm. FFs are typically
referred to as baghouses.
• When the flue gas is allowed to pass through a fabric,
which filters out particulate matter.
• Dust laden gas or air enters the baghouse through hoppers
then it is directed into the baghouse compartment.
• The gas is drawn through the bags, either on the inside or
outside depending on cleaning method.
• A layer of dust accumulates on the filter media surface
until air can no longer move through it.
• When sufficient pressure drop occurs, the cleaning
process begins.
• When the compartment is clean, normal filtering resumes.
19.
20. Advantages
• Higher collection efficiency for smaller than 10
μm particle size.
• High removal yield for coarse and fine dust.
• Varying load does not influence pressure drop
and efficiency.
• Collected dust can possibly be re-used in the
process.
• Residual emissions are determined by incoming
concentrations.
• Relatively easy to use.
21. Disadvantages:
• High temperature gases need to be cooled
• High maintenance and fabric replacement cost
• Large size equipment
• Fabric is liable to chemical attack.
22. Particulate Scrubbers:
• Particulate scrubber is a low energy scrubber and is
the simplest wet scrubber used for particulate
control.
• A particulate scrubber is a scrubber in which a liquid
is mixed with the gas to collect solids.
• In particulate scrubbers, the liquid is dispersed into
the gas as a spray, and the liquid droplets are the
main collectors for the solid particles.
• It consists of an open vessel with one or more sets of
spray nozzles to distribute the scrubbing liquid.
• Typically, the gas stream enters at the bottom and
passes upward through the sprays.
23. • Devices called wet scrubbers trap suspended
particles by direct contact with a spray of water
or other liquid.
