The document discusses a dust suppression system used in a raw material handling plant. It describes how dust is generated during material transfer processes and the need for dust control. It then explains the major components of a wet spray and dry fog dust suppression system, including different types of nozzles, nozzle maintenance, and performance testing. The key types of nozzles discussed are hydraulic, air atomizing, and ultrasonic nozzles and their varying abilities to produce different sized water droplets for dust control applications.
2. Content
o Raw Material Handling plant
o Dust generation
o Necessity of dust control
o Dust Suppression system
• Types of Dust Suppression system
• Types of atomization
• Types of Nozzles
• Major Components of System
• Nozzle Maintenance and Performance testing
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.
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.
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 Suppression System
• The Dust Suppression System is meant to suppress the row material dust generated during transfer of
Row material at feed/discharge points of conveyors in various transfer towers.
1. Wet Spray System
2. Dry Fog Dust Suppression System
• 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.
13. Wet Spray System
• Probably the oldest and most often used method of dust control at Material Handling part or mineral
processing operations is the use of wet spray systems.
• Wet dust control systems use spray nozzles to apply humidity, water, and/or chemicals to: The dust
source to prevent the dust from becoming airborne. Airborne dust particles to suppress (capture or
knock down) dust and minimize the distance it travels.
• In essence, as the fines are wetted each dust particle's weight increases, thus decreasing its ability
to become airborne.
• As groups of particles become heavier, it becomes more difficult for the surrounding air to carry them
off.
14. Wet Systems are used For:
Dust prevention: Humidity/moisture content in the material is
increased to prevent dust from becoming airborne.
Dust suppression/capture: Humidity/moisture is added to the air to
capture dust particles that are already airborne.
• Most operations require both prevention and suppression to effectively control dust.
• It is important to understand the differences between prevention and suppression systems to ensure
proper spray nozzle specification and operation.
18. Wet spray system,
• The keys to effective wet spray dust control are proper application of moisture, careful nozzle location,
controlling droplet size, choosing the best spray pattern and spray nozzle type, and proper maintenance
of equipment.
• Surface wetting affected by droplet size and impact velocity.
• Surface wetting can be increased by reducing the droplet diameter and increasing the number of
droplets and by increasing the impact velocity (by increasing the system’s operating pressure).
• Typical size of droplets produces is in the 200 to 600 μm range to create a light rain effect. Which is
much grater than respirable dust so, not effective for respirable dust.
19. Controlling Droplets Size
• If the droplet diameter is much greater than the diameter of
the dust particle, the dust particle simply follows the air
stream lines around the droplet.
• If the water droplet is of a size comparable to that of the dust
particle, contact occurs as the dust particle follows the
stream lines and collides with the droplet.
• For optimal agglomeration, the particle and water droplet
sizes should be roughly equivalent.
• The probability of impaction also increases as the size of the
water spray droplets decreases, because as the size of the
droplets decreases, the number of droplets increases.
20. • Water droplets of size 200 to 500 μm are use full for airborne dust prevention system during bulk material
handling.
• In contrast, for airborne dust suppression, where the goal is to knock down existing dust in the air, the water
droplets should be in similar size ranges to the dust particles. To achieve this goal, droplets in the range of 10
to 150 μm have been shown to be most effective.
• Atomization is the process of generating
fine droplets by forcing liquid through a nozzle,
which is accomplished by one of two methods.
1. Hydraulic Atomization
2. Air Atomization
21. Hydraulic or airless atomization
• Hydraulic or airless atomization controls droplet size by forcing the liquid through a known orifice
diameter at a specific pressure.
• This method utilizes high liquid pressures and produces relatively small- to medium-sized droplets in
uniformly distributed fan, full cone, or hollow cone spray patterns.
• Hydraulic fine spray nozzles are preferred in most areas because operating costs are lower since
compressed air is not required.
• Spray Pattern depends on angle ground in to tip of nozzle and flow rate depends on pressure
generated by pump.
22. a) Full cone Nozzle
• Hydraulic full cone nozzles produce a solid cone-shaped spray pattern with a round impact area that
provides high velocity over a distance.
• They produce medium to large droplet sizes over a wide range of pressures and flows. They are
normally used when the sprays need to be located further away from the dust source.
Hydraulic Full Cone Nozzle
Hydraulic atomizing Nozzle
24. b) Hydraulic hollow cone Nozzles
• Hollow-cone nozzles, produce a circular ring of water. Drops are generally smaller than other nozzle
types and are used in locations where dust is widely dispersed. Reduced clogging is an added benefit
of hollow-cone nozzles because its orifice is larger than other nozzle types.
• Spiral sprays are used when greater water flow is needed, resulting in less clogging due to the large
orifices.
• Whirl Chamber produces uniform Pattern and smaller droplets while spiral spray has less pattern
uniformity and larger droplets.
Hollow cone whirl chamber nozzleHollow cone spiral nozzle
Hydraulic atomizing Nozzle
25. c) Hydraulic flat fan Nozzles
• Hydraulic flat fan nozzles produce relatively large droplets over a wide range of flows and spray
angles and are normally located in narrow enclosed spaces.
• These nozzles are useful for wet dust prevention systems. Flat fan nozzles are available in three
different designs: tapered, even, and deflected.
Hydraulic Flat Fan Nozzle
Hydraulic atomizing Nozzle
26.
27. Dry Fog Dust Suppression / Air atomization
• Dry Fog Dust Suppression System uses air atomizing Nozzle some time also called two fluid nozzle
because they inject compressed air in to water stream to achieve atomization.
• This system uses plain water and compressed air to produce micron sized droplets and uniform distribution
that are able to suppress respirable dust without adding any detectable moisture to the process.
• Air atomization nozzle generating a dense fog of 1-10 micron size droplets can be used to envelop and
smother dust particles at their source and prevent them from becoming airborne.
• Wet Spray system produces droplet size 200 to 600 microns not able to suppress respirable dust (<10
micron), but dry fog nozzle can be use to suppress very fine dust,
• The unique feature of such dry fog type Dust Suppression over other types of Systems is that the moisture
added is hardly a maximum of 0.1% and around half of it evaporates, thus the moisture retention in the
final material is always less than 0.1%.
28. a) Internal mix Nozzle
• Internal mix nozzles use an air cap that mixes the liquid and air streams internally to produce a
completely atomized spray.
• With an internal mix nozzle, the atomization air pressure acts against the liquid pressure to provide
additional liquid flow rate control. a change in air flow will affect the liquid flow.
• Internal mix nozzles can produce either round or flat spray patterns. Internal mixing should be
preferred when water without solid matter are to be atomized.
Air atomizing Nozzle
Round
Spray
Wide - Angle
Spray
Flat
Spray
Air Caps
29. b) External mix Nozzle
• External mix nozzles use an air cap that mixes the liquid and air streams outside of the nozzle.
• With an external mix nozzle, the liquid pressure is unaffected by the atomization air pressure and
flow rates can be easily controlled. External mix nozzles produce flat and round spray patterns.
• External mixing is particularly suited for atomizing viscous liquids which are prone to impurities and
therefore tend to cause clogging of the nozzle. Low liquid pressures are used with this type of nozzle
due to its design.
Air atomizing Nozzle
Round
Spray
Flat
Spray
Air Caps
30. Ultrasonic atomizing Nozzle
• The Ultrasonic Atomizing Nozzle takes the form of a whistle using compressed air which accelerates through a
converge section and expands to a diverge section into a resonator chamber. This produces a powerful sonic
shockwave.
• Water or other liquids delivered to this sonic area are shattered into droplets. Droplets produced by sonic
atomization are small and relatively uniform in size, in the order of 10 micron, with a Low Mass and low
forward velocity. The nozzles have a large orifice and low liquid pressure which are prevent nozzle from wear
and blockage.
31. Droplet Size
• Above figure shows relative drop size for various types of nozzles. It can be seen that air atomizing
nozzles produce the smallest drop sizes followed by hydraulic fine spray, hollow cone, flat fan and full
cone nozzles.
• Air and ultrasonic atomizing nozzles produce very small drops and are commonly used to capture small
dust particles in enclosed areas.
• Droplet will be small if pressure is high, low flow rate and low surface tension.
34. Major Components
1. Proportioner units: It includes feed water pump, feed water tank. The water required for the system
is supply by feed water pump. Compressed air is supply by compressor.
2. Spray Headers With Pipe Lines Pumping System: It includes Pumps, Isolation Valves, Spray
Nozzles, Pipe lines.
3. Control Units With Electrical Systems: It includes Sensing units and control panel. Material flow
is sense by under belt switch.
• Other components like solenoid valves, level switch, Motor, Filter, Pressure gauge, Pressure relief
valve etc.
Under Belt Switch
36. Pumping
Unit
From Water Tank
Main Water
Header
Manual
Valve
Solenoid
Operating
valve
Bypass Valve
Pressure
Gauge
Compressor
Air
Main Air
Header
Manual
Valve
Solenoid
Operating
valve
Bypass Valve
Pressure
Gauge
Nozzle1
Nozzle1
Feedback From Belt
Running in Load
Feedback From Belt
Running in Load
Recalculation of water
if belts are off
Feedback From tank level
switch
Typical Flow chart of Dust Suppression system
WaterHeader
AirHeader
37. Nozzle Location
• Due to the unique characteristics of each application, there are no hard and fast rules for specifically
locating spray nozzles in dust control applications; however, the following guidelines will contribute
to spray system efficiency.
• It should be accessible for maintenance.
• It Should not be in the path of flying material. It should be locate for best mixing.
• It should be upstream of the transfer point where dust emissions are being created.
• For airborne dust prevention, the nozzles should be located at an optimum target distance from the
material - far enough to provide the coverage required but close enough so that air currents do
not carry the droplets away from their intended target.
• For airborne dust suppression, nozzles should be located to provide maximum time for the water
droplets to interact with the airborne dust.
38. Nozzle Maintenance
• Maintenance of Nozzle will depend on application specifications, the water quality used, and nozzle
material.
• Nozzles require maintenance, regular inspection, cleaning, and even replacement to preserve material
quality.
oErosion and wear: gradual removal of material from the surfaces of the nozzle orifice
o Corrosion: Environment effect and water quality
o Clogging: Unwanted dirt blocking the inside of orifice
o Improper reassembly: Misaligned gaskets, over-tightening, or other repositioning problems can result
in leakage.
o Accidental Damage: Scratching through the use of improper tools during installation or cleaning
39. Performance testing of Spray equipment
• Analysis or measurements
oVisual inspection consists of simply observing the dust-producing area to determine if the spray
system is effectively controlling the dust condition.
oDust particle monitoring equipment is available that will quantify the dust loading in the problem
area.
• Flow Rate
oThe flow rate of each nozzle should be checked periodically by reading the flow meter or
collecting the spray in a container.
• Spray Pressure and Pattern
oPressure at nozzle manifold should be check using properly calibrated pressure gauge. Visual
inspection of spray pattern.
• Nozzle alignment
oTo provide uniform coverage, nozzles should be oriented correctly
