Dry Fog Dust Suppression System
What is Dry Fog?
Dry fog is a mist that where the droplets are so small that mist does not feel wet to touch.
The use of Dry Fog for dust suppression is based on the
concept of agglomeration. Dry Fog technology uses compressed air and water to
create micron sized droplets. When like-sized droplets and dust particles
collide, agglomeration occurs which results in larger particles that fall back
into the process by gravity because they are too heavy to remain suspended in
the air.
To achieve agglomeration at the dust source, equal amounts of like sized particles of water droplets and dust particles must exist and they must be contained in an enclosed area.
At the treatment point, fog droplets are used to blanket the
dust source and prevent the dust particles from escaping.
Advantages
- Highly efficient and effective at reducing fugitive dust and suppressing respirable dust
- Low water use
- No chemicals
- Minimises wetting and overall moisture content of the material
- Returns useable material to the product stream
- Ease of installation
- Low maintenance
- Flexible system configuration
The Technology
Dry Fog nozzles use a combination of focused compressed air and water and an external resonator to create an ultrasonic shock on the water particles to break them into a fine fog. They are commonly referred to as ultrasonic air atomising nozzles. The technology is illustrated in the following diagram.
The inlet water and air
pressures for air atomising nozzles are relatively low (1 bar water and 5 bar
air). These pressures can be easily adjusted to change the water droplet size and allow the fog to be 'drier' or 'wetter' depending on the
material, application or other factors.
It is all about droplet size
Droplet size is a key factor in the ability to suppress small (eg. less than 10 micron) dust particles. The table below lists the typical average droplet size for different fogging / misting technologies. Ultrasonic Dry Fog nozzles are significantly smaller than any other technology.
| Technology | Average Droplet Size |
| Ultrasonic Dry Fog Nozzles | 4 to 10 micron |
| Other Air Atomising Nozzles | 40 to 60 micron |
| High Pressure (>80 bar) Fog | 30 to 60 micron |
| Low Pressure (<15 bar) Misting including Fog Cannons | 100 to 200 micron |
The reason droplet size is so important is that airborne dust particles join with water droplets of the same size much more efficiently than different sized water droplets. This is due to the air stream that occurs at the surface of the dust particle and water droplet. The larger the particle/droplet the thicker the air stream and the further it protrudes from the surface. When there is a mismatch in particle/droplet sizes it is more difficult for the smaller particle/droplet to push through the air stream of the larger particle. The following image demonstrates this.
To effectively suppress PM10 dust particles you require water droplets smaller than 10 micron.
Maximising the total water surface area also improves dust suppression performance because there is more surface for the dust particles to impact. To maximise the total surface area you need to minimise the droplet size. Similarly the likelihood of collision is related to the number of droplets - the higher the number of droplets the higher the chance of a dust particle impacting a water droplet. Again reducing the droplet size dramatically increases the number of droplets.
The following table shows the number of droplets and their surface area for one litre of water.
| Droplet Size | Droplet Number | Droplet Surface Area |
| 10 micron | 1.9 trillion | 600 m2 |
| 30 micron | 71 billion | 200 m2 |
| 100 micron | 1.9 billion | 60 m2 |
| 300 micron | 71 million | 20 m2 |
| 1 mm | 1.9 million | 6 m2 |
To put this into an easy to understand image, 1 litre of 100 micron droplets has the surface area of a cricket pitch, and 10 micron droplets have the surface area of the whole cricket ground. And there are 1000 times as many 10 micron droplets in 1 litre of water than there 100 micron droplets.
The combination of more efficient dust suppression due to similar sized droplets and particles, larger surface area and much larger number of droplets makes Dry Fog exceptionally efficient at suppressing airborne dust.
Applications of Dry Fog
Dry Fog is a versatile dust suppression solution with applications across a wide range of industries. It is particularly effective at suppressing dust at conveyor transfer points, where bulk material movement often generates significant dust emissions. Other common applications include trippers, reclaimers, crushers, screens, ROM bins, truck dumps, railcar loading and unloading, ship loaders and unloaders, and ash silo discharge chutes.One of the key advantages of dry fogging is its ability to suppress dust while minimizing the moisture content added to bulk materials. This assists in preventing clogging of equipment due to sticky material.
The following illustrate some dry fog applications.
ROM Bins / Dump Hoppers
For ROM Bins / Dump Hoppers it is important to prefill the bins prior to dumping so the displaced air that normally is full of dust is prefilled with fog.
Conveyors & Transfer Points
The following images show that the transfer points are filled with fog so any air that escapes (eg travels with the conveyed material) is full of fog suppressing the dust.
Ship loading and unloading
For ship loading the fog is delivered around the discharge chute and the movement of the material carries the fog with it suppressing any dust. For ship unloading the hold is filled with fog to capture the dust generated when the grab picks up the material.
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Truck & Train Unloading
Why DSI Dry Fog?
DSI's low flow, ultrasonic nozzles create fog droplets 1-10μm in size which easily agglomerate to dust particles as small as PM2.5 and PM10. These ultra-fine fog droplets attach to similar size dust particles and drop them back into the process. As the particles agglomerate they also join and suppress the larger dust particles as well. When compared to alternative technologies, DSI Dry Fog's ultra-fine atomization can agglomerate to the widest range of particle sizes due to its small droplet size.Wet Earth uses the DSI Dry Fog System because it is a robust, proven solution that has been used since 1997 in over 50 countries.
The DSI nozzles produce the finest droplets and have large throw distances compared to similar solutions from other vendors. The DSI nozzle enclosures provide robust protection to the nozzles and their complete solution simplifies installation. DSI nozzles are manufactured in the US and solutions are manufactured in a combination of the US and Australia.
The solution design utilises the experience of DSI's engineers based in the US which ensure you get the best possible performance for your system.
Wet Earth DSI Dry Fog installations in Australia include:
- Whitehaven Daunia
- CS Energy Callide Power Station
- Jellingbah Coal
- Ora Banda Mining
- Peabody Wambo
- Fulton Hogan Eastern Creek
Other DSI Dry Fog installations in Australia include:
- BHP Port Hedland Operations
- Citic Pacific Sino Iron
- FMG Cloudbreak and Christmas Creek
- Newcrest Cadia And Telfer Operations
- Newmont Boddington Gold
- First Quantum Ravensthorpe
- Glencore George Fisher, Mt Isa, Hail Creek and Townsville Port
What about High Pressure Misting ?
High pressure misting is another approach to dust suppression, but it differs significantly from dry fog in both technology and effectiveness. High pressure misting systems use water at pressures typically greater than 80 bar and small orifice nozzles to generate larger droplets (usually in the 30 to 60 micron range). While these larger droplets can suppress visible dust, they are less effective at capturing the fine dust particles especially those smaller than 10 microns that pose the greatest health risks and are most likely to become airborne.
In contrast, dry fog systems use compressed air and water to create smaller sized droplets (3 to 6 micron) that are much better suited for binding with fine dust particles. This allows dry fog to achieve superior dust suppression, particularly for respirable dust that can travel offsite or be inhaled by workers. Additionally, dry fog systems require less water than high pressure misting systems to achieve the same dust suppression performance due to the larger surface area of the smaller droplets.
In contrast, dry fog systems use compressed air and water to create smaller sized droplets (3 to 6 micron) that are much better suited for binding with fine dust particles. This allows dry fog to achieve superior dust suppression, particularly for respirable dust that can travel offsite or be inhaled by workers. Additionally, dry fog systems require less water than high pressure misting systems to achieve the same dust suppression performance due to the larger surface area of the smaller droplets.
It is important for airborne dust suppression for water droplet sizes to
match dust particle sizes. A good discussion
of droplet size dust suppression performance and particle size travel
can be found on our Dust Control Theory page.
By choosing dry fogging over high pressure misting, industries benefit from improved dust control, reduced water usage, and lower operational costs, all while ensuring compliance with stringent health and safety regulations.
The DSI Dry Fog System
DSI Dry Fog systems allow for flexible configuration with pre-assembled modular components. The type of application, type of bulk material creating dust, and operating environments are considered when customizing your system.
Housed in protective enclosures, we supply
complete systems comprised of electrical controls, filtration, flow regulation,
supply lines and nozzle mounts. If required, we can supply all necessary
ancillary items including air compressors, air receiver stations, pumps, and
self-cleaning secondary filtration systems.
Key system components are described in more detail below.
DSI Dry Fog Nozzles
The DSI Dry Fog nozzle is the key element of the system converting the water into a dust suppressing fog. The nozzles are stainless steel and manufactured to exacting standards to ensure their performance. There are other ultrasonic air atomising nozzles available on the market, but most droplet sizes are well above the 1 to 10 micron size droplets that the DSI nozzles produce.
The following table provides an example of the droplet size distribution for the DSN-3 nozzle.
The following table lists the specifications for the range of DSI Dry Fog nozzles.
Universal Fogger Assembly
Ultrasonic air atomising nozzles are prone to damage due to
the thin wire that supports the resonator. The Universal Fogger Assembly
addresses this with the use of a robust enclosure for the nozzle as shown
below. The enclosure also combines air and water lines into a single
flexible hose from the supply enclosure.
Fogger Mounts
It is important to be able to install the nozzles so that they can be positioned and angled for optimum coverage. There are a range of Fogger Mounts that provide robust methods to position the Foggers so they are secure and easy to access.
Ball and Socket Mount
The Ball and Socket Mount allows the Fogger to be fitted
from the outside of transfer points and angled to provide best dust
suppression performance.
Angle Bracket Mount
The Angle Bracket Mount allows the Fogger to be connected to
most surfaces and allow the Fogger to be angled to the direction which provides best performance.
Fogging Manifolds
The Fogging Manifolds provide a multi-directional stainless-steel housing for the fog nozzles which are then connected through one conduit to the Multi-Function Modules. The Fogging Manifolds have the following features:
- Heavy duty steel casing
- Easily mounted
- Factory fitted internal manifolding, single connection to Multi-Function Modules for easy installation
- Unidirectional nozzle mounts allow adjustment of the fog direction to where it is needed
Fogging Solution Modules
There are a range of modules that can be included in a DSI Dry Fog solution which depend on the project size and layout.
The key functions of these modules are:
- Filtration - typically multiple levels with self-cleaning function
- Pressure control of water and air - to ensure the ideal performance of the atomising nozzles.
- Electronic control - interface to other site systems
- Distribution of the water and air to each nozzle
If you have a particular dust control application you would like to discuss or would like more information then please call us on +61 2 6062 3300 or send an email to sales@wetearth.com.au.
Does Dry Fog increase the moisture content of coal or iron ore?
Dry Fog does not increase the moisture content of the material. Due to the small droplet size it is very efficient at suppressing dust. For example one litre of water as dry fog will have over 2 trillion droplets and a total surface area of 600m2 (the size of a football ground). Due to this low moisture addition it can be used for materials where moisture addition would be a problem such as clinker and grain.
Frequently Asked Questions
What is the best dust suppression system for conveyor transfer points?
Dry Fog is the best dust suppression system for conveyor transfer points because it is the most effective at suppressing dust particles of all sizes due to its small droplet size. Solutions that pre-wet the material can also be very effective at preventing dust being generated at transfer points, but they can cause issues with blockages of crushers and screens and increase carryback.
How effective is Dry Fog at suppressing respirable dust and PM10?
Dry Fog is very effective at suppressing PM10 dust when setup correctly. Some providers guarantee at least 70% PM10 dust suppression with Dry Fog. It is the only technology can can product the less than 10 micron sized droplets that are required to effectively suppress PM10 dust particles.
Dry Fog is the best dust suppression system for conveyor transfer points because it is the most effective at suppressing dust particles of all sizes due to its small droplet size. Solutions that pre-wet the material can also be very effective at preventing dust being generated at transfer points, but they can cause issues with blockages of crushers and screens and increase carryback.
How effective is Dry Fog at suppressing respirable dust and PM10?
Dry Fog is very effective at suppressing PM10 dust when setup correctly. Some providers guarantee at least 70% PM10 dust suppression with Dry Fog. It is the only technology can can product the less than 10 micron sized droplets that are required to effectively suppress PM10 dust particles.
How does Dry Fog dust suppression compare with conventional water sprays?
Dry Fog is designed to suppress airborne dust. Conventional water sprays are designed to wet the material to prevent it becoming dusty. Where it is possible to prevent the material being dusty with water sprays you will get better dust control than trying to suppress it once it is airborne. There are many cases where it is not possible to wet the material before dust is emitted such as ROM Bins, hoppers, truck, train and ship loading and unloading. There are also cases where wetting the material may cause problems such as blockages or carry back. There are cases where a combination of solutions will get the best performance so it is not one or the other.
Dry Fog is designed to suppress airborne dust. Conventional water sprays are designed to wet the material to prevent it becoming dusty. Where it is possible to prevent the material being dusty with water sprays you will get better dust control than trying to suppress it once it is airborne. There are many cases where it is not possible to wet the material before dust is emitted such as ROM Bins, hoppers, truck, train and ship loading and unloading. There are also cases where wetting the material may cause problems such as blockages or carry back. There are cases where a combination of solutions will get the best performance so it is not one or the other.
What does a Dry Fog dust suppression system cost?
Dry Fog is a an expensive technology compared to conventional water spray due to the requirement for compressed air and the supporting equipment to ensure reliable, low maintenance, and effective solutions. As an example the nozzles are about ten times the cost of standard spray nozzles.
Which companies supply Dry Fog dust suppression systems in Australia?
There is only a small number of companies that supply Dry Fog dust suppression systems in Australia due to the relative complexity of the technology and getting it to perform effectively, reliably and with minimal maintenance.
Dry Fog is a an expensive technology compared to conventional water spray due to the requirement for compressed air and the supporting equipment to ensure reliable, low maintenance, and effective solutions. As an example the nozzles are about ten times the cost of standard spray nozzles.
Which companies supply Dry Fog dust suppression systems in Australia?
There is only a small number of companies that supply Dry Fog dust suppression systems in Australia due to the relative complexity of the technology and getting it to perform effectively, reliably and with minimal maintenance.
Does Dry Fog increase the moisture content of coal or iron ore?
Dry Fog does not increase the moisture content of the material. Due to the small droplet size it is very efficient at suppressing dust. For example one litre of water as dry fog will have over 2 trillion droplets and a total surface area of 600m2 (the size of a football ground). Due to this low moisture addition it can be used for materials where moisture addition would be a problem such as clinker and grain.
What is the difference between Dry Fog and high-pressure misting?
The key difference between Dry Fog and high-pressure fog / misting is the droplet size. The average droplet size of the smallest Dry Fog nozzle is 4 micron and for high pressure fog it is 40 micron. The smaller droplet means that Dry Fog has 1000 times the droplets and 10 times the surface area for a given volume of water which is much more effective at suppressing dust. The larger droplet size also means that high pressure fog only effectively suppresses visible dust where Dry Fog is effective at suppressing both visible and respirable dust (less than 10 micron). The technology to create the droplets is different with Dry Fog using ultrasonic air atomizing nozzles and high pressure fog using water at high pressure. Dry Fog requires compressed air which means that it has higher power requirements than high pressure fog.
How much water does a Dry Fog system consume?
Dry Fog system use very little water relative to any other technology. For example a large mine ROM bins using up to 25 litres per minute and large high speed transfer point using 3.5 litres per minute.
The key difference between Dry Fog and high-pressure fog / misting is the droplet size. The average droplet size of the smallest Dry Fog nozzle is 4 micron and for high pressure fog it is 40 micron. The smaller droplet means that Dry Fog has 1000 times the droplets and 10 times the surface area for a given volume of water which is much more effective at suppressing dust. The larger droplet size also means that high pressure fog only effectively suppresses visible dust where Dry Fog is effective at suppressing both visible and respirable dust (less than 10 micron). The technology to create the droplets is different with Dry Fog using ultrasonic air atomizing nozzles and high pressure fog using water at high pressure. Dry Fog requires compressed air which means that it has higher power requirements than high pressure fog.
How much water does a Dry Fog system consume?
Dry Fog system use very little water relative to any other technology. For example a large mine ROM bins using up to 25 litres per minute and large high speed transfer point using 3.5 litres per minute.
Can Dry Fog control respirable crystalline silica dust?
Dry Fog is very effective at suppressing respirable dust because its average droplet size (4 micron) is similar that to respirable dust (<10 micron) and you require similar sized water droplets and dust particles for effective dust suppression.
Dry Fog is very effective at suppressing respirable dust because its average droplet size (4 micron) is similar that to respirable dust (<10 micron) and you require similar sized water droplets and dust particles for effective dust suppression.
Is Dry Fog or dust extraction more effective for conveyor transfer points?
Dust extraction and Dry Fog work differently in how they control dust at conveyor transfer points. Dust extraction removes the dust which makes it better where the dust is a waste product. Dry Fog keeps the fines (dust particles) in the product stream making it better where the dust particles are part of the product. Dust extraction is generally a more complex and expensive solution and requires management of the extracted dust particles.
Dust extraction and Dry Fog work differently in how they control dust at conveyor transfer points. Dust extraction removes the dust which makes it better where the dust is a waste product. Dry Fog keeps the fines (dust particles) in the product stream making it better where the dust particles are part of the product. Dust extraction is generally a more complex and expensive solution and requires management of the extracted dust particles.
How much compressed air is required for Dry Fog dust suppression?
Dry Fog requires large volumes of compressed air. For example a large mine ROM bin can require up to 15m3/minute and a large high speed conveyor transfer point can require 2.5m3/minute.
Dry Fog requires large volumes of compressed air. For example a large mine ROM bin can require up to 15m3/minute and a large high speed conveyor transfer point can require 2.5m3/minute.
Can Dry Fog be installed on existing crushers, conveyors and transfer chutes?
Dry Fog can be easily retrofitted to existing crushers, conveyors and transfer points. The DSI Dry Fog system includes nozzle adaptors that make it easy to install in existing systems.
Dry Fog can be easily retrofitted to existing crushers, conveyors and transfer points. The DSI Dry Fog system includes nozzle adaptors that make it easy to install in existing systems.
What maintenance is required for a Dry Fog system?
The major maintenance is related to the water quality. If the water quality is good or managed effectively then this is significantly reduced. Low water quality requires automatic self cleaning filters and water conditioning to prevent blockages and the buildup of scale in the nozzles and fittings.
The major maintenance is related to the water quality. If the water quality is good or managed effectively then this is significantly reduced. Low water quality requires automatic self cleaning filters and water conditioning to prevent blockages and the buildup of scale in the nozzles and fittings.
Does Dry Fog work in open areas or windy conditions?
Dry Fog has very small droplets which are severely impacted by the wind. This is usually not a problem because for most applications the dust is generated and hence the fog is sprayed inside a enclosed area. This is also the case for most ROM bins as the majority of the dust is generated inside the bin which can be effectively fogged. In cases where the dust is generated in an open area then fixed or portable Wind Fences can be effective at reducing wind speeds to ensure the Dry Fog continues to be effective.
Dry Fog has very small droplets which are severely impacted by the wind. This is usually not a problem because for most applications the dust is generated and hence the fog is sprayed inside a enclosed area. This is also the case for most ROM bins as the majority of the dust is generated inside the bin which can be effectively fogged. In cases where the dust is generated in an open area then fixed or portable Wind Fences can be effective at reducing wind speeds to ensure the Dry Fog continues to be effective.
How do you calculate the number of Dry Fog nozzles required?
Calculating the number and size of Dry Fog nozzles for a particular application requires advice from an expert. Factors that effect the number of nozzles required for a transfer point include the dustiness of the material, conveyor tonnage rate, conveyor width, conveyor speed, shape of transfer point, exposure to wind, stilling box size and shape.
Calculating the number and size of Dry Fog nozzles for a particular application requires advice from an expert. Factors that effect the number of nozzles required for a transfer point include the dustiness of the material, conveyor tonnage rate, conveyor width, conveyor speed, shape of transfer point, exposure to wind, stilling box size and shape.