This document discusses several technologies for dust suppression systems in coal handling plants. It begins by describing current wet dust suppression systems used in many power plants that have issues meeting health and safety standards. It then examines ultrasonic dust suppression systems that use micron-sized water droplets, light scattering property-based systems that measure dust concentration using light reflection, and sound-based systems that detect dust using sound waves. The document concludes by stating that while current systems could be improved by modifying the ultrasonics or using other technologies based on light or sound, these alternatives may be more effective at controlling smaller respirable dust particles.

1. Present Day
Dust Suppression Systems
A CASE STUDY
BY PRASHANT MEHROTRA &MUKESH DUBEY
DEPARTMENT OF MECHANICAL ENGINEERING
G.B.TECHNICAL UNIVERISTY
JHANSI
The literature study of modern day dust suppression system reveals
that many thermal power plants use coal as their fuel. To handle the
coal, each power station is equipped with a coal handling plant. The
coal has to be sized, processed, and handled which should be done
effectively and efficiently. While working in the coal handling plant
the major factor which reduces staff efficiency is the working
environment i.e. a dusty atmosphere. Lots of care is always taken to
reduce dust emission.
Generally all systems used in power station coal handling plants are
wet dust suppression systems. In this paper the reasons for failure of
these type of dust suppression system are discussed. The remedy for
the improvement of this system is also given in this paper. The
existing system can be easily modified by using ultrasonic system.
The spray discharge should be proportional with dust emission. The
solenoid valve should be open with proportion with quantity of dust
generation.
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2. The Dust Suppression System is meant to suppress the coal dust
generated during transfer of coal at feed/discharge points of
conveyors in various transfer towers. There are several existing
methods of controlling dust but many are ineffective, costly and have
detrimental effects on plant and machinery. An effective system for
the control of fugitive dust in industry should meet the following
objectives.
1. Must be efficient to meet Health & Safety requirements.
2. Be practical and simple in operation.
3. Have low initial cost.
4. Have low operating costs.
5. No adverse effects on product quality or plant and machinery
should be created.
But the system used in the plant is not meeting the entire
requirement, especially it does not meet Health & Safety
requirements.
OPERATING PRINCIPLE:-
Auto control or manual control governs the system. It has to be
insured that main tank is filled with water. The water is pumped by
feed water pump from main tank to feed water tank and at the same
time metering pump doses proper quantity of chemical. The feed
water pump operation is controlled by float switch automatically.
The pump picks up at low level and stopped at high level. The
interlock with low level of main tank will not allow to pickup the feed
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3. water pump. The metering pump will stop the operation by sensing
low chemicals in tank. After insuring proper level the solution pumps
will start. If the pressure increase the pressure relief valve keeps the
system in recalculation. The sensing system for controlling spray at
proper header ensures spraying solution if conveyor is running with
coal. And will not allow spraying solution if conveyors are running
empty.The solenoid valve headers are energized if conveyor is
running with coal. If all or some of the solenoid valves are not
energized the system will realize pressure through pressure relief
valve, which protects the system. A solenoid valve is provided with
bypass line, which operates when none of the spray header solenoid
valves are operative.
Nozzle:-
The design of the system is based on a very unique device which can
produce a very dense fog of 1 - 10 micron size water droplets which
literally blanket the dust source and keep the dust particles from
becoming airborne. It does this at low cost, both from a capital and a
maintenance standpoint, while achieving all of the goals stated
above for an ideal dust suppression system. The fogger is an air
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4. driven acoustic oscillator for fogging liquids by passing them through
a field of high frequency sound waves. This is accomplished by
compressing air upstream of a specially designed converge section of
the fogger. To further enhance the fogging capabilities, a resonating
chamber in the path of the air stream reflects the air stream back at
itself to amplify and complement the primary shock wave. Once this
standing shock wave is generated, water is delivered through annular
orifices where it is first sheared into relatively small droplets. These
small droplets are then carried by the primary air stream into the
intense shock wave where the sound energy is converted into work
by exploding the droplets into thousands of micron size droplets.
After having done its work, the air then escapes around the
resonating chamber and carries the droplets downstream in a soft,
low velocity fog. The design of this fogger has obvious benefits
regarding the control of respirable dust.
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5. Alternate TechnologiesFor Effective
Dust Suppression
A CASE STUDY
BY MAKARAND JOSHI
DEPARTMENT OF MECHANICAL ENGINEERING
R.G.TECHNICAL UNIVERISTY
ITM UNIVERSE GWALIOR
INTRODUCTION:-The existing system is not effective on respirable
dust.Typical water droplet sizes are 200 to 600 microns, which are
much greater than the respirable dust. And it does not operate on
the emission quantity.The spray of the system should be operated on
emission quantity.
Thus, water sprays can be improved by increasing pressure or by
designing nozzles which produce smaller droplets.And also
developing the control system which sense quantity of dust. Most of
the improvements in this direction already have been made. The
problem with this approach, and one, which prevents much
additional improvement, is that introduction of very small water
droplets into an atmosphere.Hence arises the need for alternate dust
suppression tehnologies.
ULTRASONIC DUST SUPPRESSION SYSTEMS:-
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6. This system uses water and compressed air to produce micron sized
droplets that are able to suppress respirable dust without adding any
detectable moisture to the process. Ideal for spray curtains to
contain dust within hoppers. Generally the system consists of three
main parts. These are as follows.
1. Air compressor units.
2. Spray headers with pipe lines & pumping system.
3. Control units with electrical systems.
The theory behind the Ultrasonic Atomizing System is based on
research considering a water droplet from a spray that is about to
impinge on a dust particle. The probability of impaction increases as
the size of the water spray droplet decreases. This explains why
conventional hydraulic water sprays are not effective onrespirable
dust. With typical diameters of 200-600 microns the droplets are
much larger than the dusts they are attempting to suppress.
Nozzles mounted on or above screen areas will suppress dust clouds
due to the particulates being encouraged to become air-bourne
through natural vibration and fall of the conveying bulk.
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7. LIGHT SCATTERING PROPERTY BASED SUPPRESSION
SYSTEMS:-
When air-borne dusts or suspended particulate are irradiated with
light, the light is scattered in all directions. The intensity of light
scattered at any particular angle depends on the wavelength of the
light and the size, volatility, and mass concentration of the dust or
suspended particles
Both theory and experiment indicate that at a scattering angle of
around 200 to 300, the size and volatility of respirable coal dusts
have a negligible impact on the measured intensity so that this
intensity is directly proportional to the mass concentration of the
dust. At an angle of 150, equal concentrations of either
respirablecoal dust or diesel particulate matter (DPM) yield equal
intensities of scattered light. At larger angles, the intensities from
DPM are significantly greater.
Specific angles in the range of 150 to 300
offer significant promise for respirable dust or DPM measurement
and, possibly, for determination of mass fractions of dust/DPM
mixture.
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8. DUST SUPPRESSION SYSTEMS BASED ON SOUND:-
The sound generator generates sound beam. The stainless steel
reflector on the other side reflects the sound beam. The receiver
who is built with sound generator receives the reflected sound
beam. The dust particles absorb some of the energy of sound beam
and also deflect sound beam. The sound signal received is inversely
proportional to the dust emission.
CONCLUSION:-The existing system is failing due to very low
working pressure. In addition to this the control of the system is not
depend on the quantity of dust emission.
Using ultrasonic spray method existing system can be modified with
less effort.And the other two systems based on light and sound are
more effective on dust particles of smaller range compared to
ultrasonic so they are likely to be more prominently used in the
future because it is a cost effective time reducing method.
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9. SYSTEMS FOR DUST CONTROL IN
THERMAL POWER PLANT
A CASE STUDY
BY ANKUSH KUMAR & SUMIT
CHAKRABORTY
DEPARTMENT OF MECHANICAL ENGINEERING
NIT HAZRATBAL,SRINAGAR
ABSTRACT:-Theaim of the work is to propose measures and
device methods to reduce and prevent dust at Coal Handling plant
(CHP) of a coal fired thermal power plant. This paper discusses
qualitative methods for preventing dust including design of a wet
centrifugal dust collector.
Since wet dust suppression system uses optimum amount of water
for suppressing dust, therefuse of dust collector which discharges
dust in the form of slurry is very elegant approach to control dust at
large scale. Every thermal power plant is equipped of a large CHP
where coal is handled. Such plants consume large quantity of water
in order to suppress dust properly which is undesirable. Therefore
use of dust collector units at particular places of CHP plant where
dust particles are airborne is highly recommended, since it
discharges dust in the form of slurry.
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10. STAGES FOR DUST CONTROL IN POWER PLANT:-
Stage 1:-When
coal is transported
from wagon tippler to reclaimer large amount of dust is generated
and addition of moisture is most efficient technique as water acts as
a binding solvent.Diverging nozzles are used for moisture addition.
Stage 2:-This is the reclaiming stage.Here water can be futile so wind
plays an important role as storage area is large.So here blocking wind
speed is concentrated upon to prevent dust from being airborne.So
wind shields or wind forests are used.
Stage 3:-Reclaimer piles up coal at a large area for storage.At this
stage surface compaction method is used for dust suppression.6-12%
water solution of very good binding substance prevents dust from
being airborne.Moisture is supplied for controlled flow of solution
over coal pile and suppress dust without affecting coal quality.
Stage4:-Here dust particle is as low as 1-10 microns.Dust collector is
used to reduce concentration as low as 1% in the concerned area.It
discharges dust in concentrated form to reduce water intake.At this
stage coal is transferred from coal stack through conveyor to relay
section.
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11. Stage 5:-Last stage is unloading from relay to boiler section.Usual
amount of moisture is added for moisture removal since dust is in
small amount here.
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12. 12

13. The above fig is an important device for dust collection at each and
every level of a thermal power plant.It is a centrifugal dust
collector.
Centrifugal collectors use cyclonic action to
separate dust particles from the gas stream. In a typical cyclone, the
dust gas stream enters at an angle and is spun rapidly.
The centrifugal force created by the circular flow throws the dust
particles toward the wall of the cyclone. After striking the wall, these
particles fall into a hopper located underneath.
This device uses the principle of dynamic precipitation technique in
which very high suction pressure suck the dusty air and allow
tocentrifuge through it. Centrifugal action separates dust from fresh
air and fresh air is allowed to escape from other end of dust
collector.
The dust collector has a small tank full of water which has two valves.
These two springs loaded valves are operated to allow passage of
concentrated dust and automatic filling of fresh water using sensors.
The dust collector uses automatic discharge technique and hence
save time for manual operations for discharging and refilling. Also
discharge is recycled in order to have minimum water wastage. This
centrifugal dust collector is very efficient and requires minimum
amount of water since it discharges dust in concentrated form.
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14. cONCLUSION:-A wet centrifugal dust collector with automatic
discharge can reduce airborne dust particles and minimize water
wastage. Also other methods of dust collection reduce dust and
water wastage as discussed earlier.
This has great impact not only at workplace but also in environment.
Proper implementation of dust suppression and prevention methods
reduces health hazards of workers, employees and people residing
nearby. Since current situation demands eco-friendly methods of
dust suppression without much water wastage, above mentioned
ergonomic designs are noteworthy.
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