I am very curious about how the fog works with fine cement? is your claim to this product correct? ■

I agree. Fogging systems become useless in the slightest draft of air, even the entrained air in material transfer chutes. It is too late to try to knock down fugitive dust once it is airborne.

The best use of dust suppression water is to increase the moisture content of the material and bind dust particles to larger ones.

Irrigation style water cannons can be used for capping stockpiles or dusty open ground. Fogging will not work in the open air.

Michael Reid. ■

Dear Mr. Braz,

We are a mechanical engineering company who specialise in dust suppression in the bulk materials industry (transfer points, crushers etc. etc.).

In many areas of the Bulk Material Industry, combating of dust still represents a large problem. The NALTEC ® - System, developed by us, conquers these problems in a simple way.

Special nozzles generate an artificial fog that binds the dust particles and guides them back onto the material.

For more information please refer to our website www.buwip.de.

Kind regards

Silke Dykes

Export Manager

B+W GmbH

https://edir.bulk-online.com/profile...e-produkte.htm ■

I first became aware of a "Fog Cannon" concept in the early 90's. The original documentation I have on file is from a German company in Regensburg whos equipment was developed using an axial blower with a ring of hydraulically powered high pressure nozzles. This equipment was employed in frost prevention, humidification, evaporative cooling, odour control as well as for dust control application. The process is well proven. ■

Dust is dust. If it is at rest and immobile it is not a problem for anyone.

Once movement occurs the scene changes.

Any movement induces surrounding air to move. Its this air movement that moves the dust. When you walk you move/displace air. A conveyor belt running empty induces air to move through what we know as and term "friction". I have measured airflow INTO empty silos/bins in association with the operation of empty belts and when you have big belts it can be a lot of air. Add material to the empty belt and you change the effective friction factor. The more coarse the material, then, proportionately more air is moved in sympathy. So its not difficult to realise a significant problem will occur at following transfer point/s. Air is induced to enter and pass through any ensuing transfer point enclosure. Within the transfer, material separation and segregation occurs and the material stream "swallows" a volume of air. Within the transfer, or at the impact point on the following equipment, this "air of aeration" is violently expelled. This high velocity expelled air transports the finer particulate fractions (dust) out of the material stream. This is the dust fraction that we all see exiting transfers as "fugitive emissions".

The solution. Simple. Control air movement and the dust will be under control.

When you're determining ventilation requirements for a dust collection system it is essential to objectively take into account air flow induction into transfers as well as environmental issues. Our duct system design process utilises a modelling process progressively developed since the mid 70's that specificallly takes all these variables into account.

In 1975 I adopted the term "Ore Conditioning" to describe moisture adding for the minimisation of dust levels within bulk material streams. My direct involvement in pioneering this technique in the Pilbara iron ore region of West Australia was to combat the industries dust emission problems. Today ore conditioning is widely used and now recognised as benchmark practice.

It is important to recognise that dust emissions can be fully "extinguished" at specific moisture levels. The key is to accurately determine this point and avoid other material handling issues. This we do.

Fogging, as an emission control method, is another proven process, however, it can have some negatives. Especially where it is applied in the open. As has been indicated earlier in this thread it does has its limitations. Conversely it can be very effective when correctly applied. As L Nordell has intimated earlier in this thread, material that emulates the characteristics of cement dust can and will coat everything in the vicinity. So if the dust is cementious in character fogging would not be best practice.

Contrary to M Reid's negative comment, "Fogging" can be beneficially applied in the open under conditions of minimal wind so this option should never be overlooked.

Be cautious. Not all "fog systems" as are labelled "foggers, etc." actually produce fog size droplets! The term is often missapplied. In essence, the only equipment that generates effective fog sized droplets or aerosols, are nozzles that employ high frequncy vibration to achieve consistent droplet fragmentation in the sub micron range and generate effective fog. Simple hydraulic nozzles do not produce "Fog".

It is also important to recognise that it is possible to design into new plant both passive and active "dust controls" that can embrace "foggers" as a complimentary control philosophy. Similarly, the advantages of "soft transfers" can also be harnessed where applicable. Amongst other fugitive emission control activities, this we do.

Conveyor belt "carry back" is another "dust issue" that is given inadequate attention. Mechanical belt cleaners can only remove a portion (commonly < 80%) of the contaminants from the conveyor belt carcass. So the return strand of all conveyors are continual sources of fugitive dust emissions and often overlooked, especially in modelling scenarios.

When it comes to dust control, it is essential to focus on ALL the contributors and then carefully and objectively determine priorities for action. This is a service that we provide. It's an Audit process. We audit your process for compliance with what is known today as global best practice and model the emissions across the plant to provide a "complete" picture, the BIG picture together with a relevant action plan.

If you would like more assistance with this very broad specialty subject, we would be pleased to help. ■

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jamesc@DuctMonkey.net ■