How Dry Fog Systems Work

Dry Fog systems use a unique sonic atomising nozzle that creates water particles at less than 10 microns in size (on average 4.91 micron) – smaller than any other water, mist or ‘fog’ sprays on the market. By a process of agglomeration, these water particles bind with like-sized, and greater, dust particles to form larger and larger particles which settle out under gravity. This allows Dry Fog to tackle respirable dust, defined as dust with an aerodynamic diameter 10 microns (PM10) and under in size, which is considered the most dangerous to health. PM10 dust is required to be monitored under Australian State and Territory Environmental Protection Authorities.

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Smaller airborne dust particles tend to migrate round larger water particles in a slipstream effect, meaning that they escape through the spray stream and remain in the atmosphere.

Dry Fog also uses far less water than other sprays as the smaller particles by nature have a much larger surface area. Dry Fog typically uses less than 1/3 of the water in comparison to a traditional water spray system, or x in comparison to high pressure misting. The agglomeration process is near instantaneous, Dry Fog water particles exit the nozzle with a slightly positive charge, generated dust usually has a slightly negative charge, and this aids the process.

 

 

 

 

 

The nozzle itself features a convergent/divergent venturi which accelerates air fed through the centre, this reflects off of a resonating chamber at the front of the nozzle which creates a sonic wave reflected back to the centre of the nozzle.Fog 2

Water is introduced at low pressure though ports inside the nozzle and away from the possibility of contamination from dirt build up. This water is vapourised and pushed outwards from the nozzle by the airstream, creating the small water particles which form the fog. The resonations at the chamber also creates an effective self-cleaning feature. There is a selection of four nozzle types to ensure that enough fog is generated to overwhelm the dust generated by each process.

 

MARC provides complete systems, not just nozzles. This is important since the systems include water filtering in order to protect the nozzles to prevent blockages, but also there are unique features that make these systems robust, flexible and expandable. MARC supplied Dry Fog systems, as provided by Dust Solutions Inc, are unique in the market in that they offer dual filtering systems, with an backwash and cartridge filter as standard, but also other options to cater for any type of water quality are available to make the system as close to maintenance free as possible. An air purge is run through the water lines at switch-off to atomise out all residual water and prevent any possibility of drop-out solid particulates out of suspension that could block the nozzle ports. Unique ‘blue block’ solenoid housings also allow multiple circuits to be fitted to a single cabinet, meaning systems such as shiploaders and hoppers, or ROM bins and apron feeders, can be treated from one cost effective panel. Multi-directional multiple nozzle manifolds or single nozzle ball and socket mountings are also unique features not found in other systems.

Dry Fog is an effective solution, with results showing as much as 90% dust reduction (ug/m3). Typical applications in the mining and bulk handling sectors include ROM bins, apron feeders, conveyor transfers, surge bins and open hoppers, longwall applications, train loaders and unloaders, stackers, reclaimers and shiploaders. Dry Fog adds less than 0.1% moisture to the product by volume, and can therefore be used with moisture sensitive products such as clinker and cement, bauxite and phosphate, as well as coal for power generation as there is little thermal penalty in comparison to using water sprays.

Dry Fog systems supplied by MARC Technologies are manufactured by Dust Solutions Inc,, who have been in business since 1985, and have an install base of over 500 projects worldwide. MARC have installed Dry Fog systems in a variety of mines in Australia, and have major clients such as BHP, First Quantum, Glencore, Newcrest, Newmont, Citic Pacific and many more.

 

 

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