The theory behind the function of a fog cannon is that it uses different mechanisms of removing dust from the air and dropping it to the ground. It does so through misting of water droplets which bind and suppress airborne dust particles and coalesces them achieving dust suppression.
Exposure to airborne dust compromises occupational and non-occupational health and safety. If not dealt with at the source, respirable dust particles settle in the deepest paths of the lungs resulting in dust-related lung diseases which are fatal.
In this article we evaluate how a fog cannon is used for dust suppression, in the process highlighting droplet formation mechanisms and theories, the shortcomings of these theories, challenges faced when using a fog cannon, GRT automatic dosing units, why GRT automated dosing units should be the first choice and for which GRT applications.
How is a fog cannon used for dust suppression?
The series of steps depicts how a fog cannon is used for airborne dust suppression, the systems at work, atomic mist creation, binding of dust particles and coalescence leading to dust suppression. The steps are as follows:
- Choose a fog cannon with adequate air volume and power from matching fan.
- Keep metrological factors such as wind speed and wind direction in check.
- Place fog cannon strategically for adequate coverage of the area.
- Pipeline system sends water to the ends of multiple spray nozzles.
- High-pressure atomization system atomizes water into a mist.
- Atomized mist is blown, spreading a fog of fine droplets in the air.
- Misty droplets absorb, gather and precipitate dust particles in the range.
- Dust suppression happens when dust particles are brought to the ground.
What droplet formation mechanisms does a fog cannon use?
There are different types of droplet formation mechanisms that a fog cannon uses but their founding principle is based on particle size disintegration into an atomized mist. Droplet formation mechanisms contribute to dispersing the similar atomic mist size droplets from the nozzles to match the airborne dust particle size distribution.
Through a special high-pressure atomization system and a double-tube annular spray ring, water and/or surfactant is atomized into a fine mist particles with particle sizes in the micron range. The dust suppression mechanisms used by a fog cannon work on the following aerosol mist fundamentals:
- Bulk liquid is disintegrated into small droplets by internal and/or external forces.
- If disruptive forces exceed liquid surface tension, atomization into droplets occurs.
- The initial atomization is called primary atomization (pa).
- A population of larger droplets produced in pa may be unstable.
- Secondary atomization (sa) occurs when critical droplet size is exceeded.
- The final droplet size distribution is determined by the liquid properties in pa and sa.
What theories govern the science and engineering of droplets?
Different theories have been proposed for explaining the science and engineering of droplets. Listed below are some of the popular theories worth reading and exploring. These are:
- Dripping mechanism.
- Rayleigh mechanism.
- Weber theory.
- Ohnesorge criteria.
- Castleman hypothesis.
- Taylor mechanisms.
What challenges are faced when using a fog cannon?
Droplets sizes produced by pressure atomization are proportional to the square root of the initial thickness of the sheets or the initial diameter of the ligaments from which the droplets are formed. In reality, there are some R&D challenges to using a fog cannon for dust suppression which leads us to these important factors to consider. The challenges faced with using a fog cannon for dust suppression include:
- Sensitivity to water with minimal Total Suspended Solids/Total Dissolved Solids.
- Nozzle abrasion which increases droplet size and affects spray profile.
- Fan blades become coated in accretion.
- High pressure pumps wear out rapidly.
- Caking/Bearding occurs on nozzles.
- Corrosion occurs.
- Motors fail.
What are GRT automated dosing units?
There are GRT’s superior dust suppression units that improve on the challenges faced by fog cannons. These units are deisgned to dose GRT’s unique dust capturing technologies into the water being sprayed. This makes water work! So instead of just producing a fog or mist that shields the dust, it actually captures the particles, drawing them into the water droplets 12 times more effectively than water alone.
They can range from simple hand-operated pumps to fully automated dosing units applicable in mining and quarrying. So, how do they work?
- GRT’s dosing units inject GRT products into the flow stream of water.
- This happens at standpipe or hydrant fill points.
- GRT’s recommended dosage rates are used.
- Calibration is done to the rate of flow in the water supply pipe.
Why choose GRT automated dosing units for dust suppression?
The units are tailor-made for each customer to suit their individual needs and ensure accurate dosing of the product with the following options:
- Solar-powered, generator or mains power compatible.
- Manual, remote control, automated start.
- Permanently fixed, mobile skids/bunds, truck, miner or drill-mounted units available.
- Can be dual purposed to also dose different GRT products.
- Complement the different chemical technologies that suppress dust at its source.
- Enables safe working environment for workers and communities.
- Provide accurate dosing at low dosage rates.
- Deal with chemical incompatibility of water with dust
- Optimise the chemical and physical performance of dust suppression system.
We summarise fog cannon dust suppression focusing on the science, components, advantages and disadvantages in our previous article. If not effectively managed, dust affects the business operation, progressively impacts on the health of workers and neighbouring communities. Over and above using effective dust suppression systems helps you minimize wastage of resources and achieve the purpose of your dust suppression plan. Given the challenges faced with using fog cannon dust suppressions systems, GRT offers its automated dosing units and chemical additives as viable and effective alternatives to dealing with dust at its source. There is a clear advantage of using both GRT automated dosing units and GRT products which can work in synergy with the availability of fog cannons. Where fog cannons experience limitations, GRT automated dosing units and products pick up the slack and provide the superior option.
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Fog Cannon Dust Suppression. Retrieved 25/08/21.
Fog Cannons. Retrieved 25/08/21.
Fog Cannon. Retrieved 25/08/21.
Fog Cannons. Retrieved 25/08/21.