As per my "book knowledge" , in high pressure water based dry fog system, compressors are not required.

So there may be capital saving and subsequent maintenance & spares cost saving on compressors.

Regards, ■

Water for dust suppression in iron ore is best applied at low pressure (150 to 300 kPa). Low pressure means larger water droplets and less influence from drafts. High pressures give too much atomization and wetting of surrounding surfaces.

Over-wetting gives these systems a bad name. Best to add water in small increments (0.25%) until the maximum tolerable moisture content is reached. This is to prevent over-wetting, mud build-up and blockage.

Best application points are where the ore stream is opening up, in transfer chutes and at secondary and tertiary crushers. Conveyor belts need very effective scrapers and cleaners to avoid problems.

Use the Spraying Systems Company catalogue and select narrow-angle, flat pattern spray nozzles. These will allow you to aim the water at the ore stream without over-wetting.

Michael Reid. ■

These systems need to be rugged and simple, otherwise operators will not use them. If they promote blockages or clean-up problems, they will be turned off. The objective of low-pressure systems is to get dust to agglomerate and adhere to larger particles. Fog systems attempt to knock down fugitive dust once it is airborne. They are not as effective as the alternative and more troublesome, in my experience.

Whichever system you choose, you will need careful design to avoid problems with over-wetting. It is essential to stop spraying once ore-flow has stopped, for instance and to provide good belt cleaning.

Effective dust suppression with iron ore requires the total moisture content to be increased to about 4% for lump or about 7% for fines. If your system applies less than this, then you may not have good control of dust.

Michael Reid. ■

Fog systems can use compressed air for atomising or simply high pressure. The "alternative" I was referring to is the low pressure system.

Michael Reid. ■

In my experience, for iron ore systems, the low pressure systems are the ones which work -if they have been properly designed. All the fogging systems I have seen caused wetting of chutes and mud build-up and were very soon turned off. Low pressure minimises splashing and over-spray.

It is vital to address belt cleaning with properly designed scrapers and to position nozzles so that the spray pattern does not impinge on chute walls or on the edges of belts. Again, I stress that the best location for nozzles is where the ore stream is opening up, in transfer chutes. Spray behind the ore stream as well, if possible. It is important that you do not try to add too much water at any one point, build up the total moisture content gradually with small incremental additions.

Michael Reid. ■

Hello

I don't think it is a question of which system is better. HP systems will use more water and are a little less efficient. If in your process humidity of the material is not a problem then HP systems can be an option. I don't think you want to be wetting your iron ore pellets too much so atomizing may be the best solution. Where do you want to use this, at a truck dump station? If so this application works and the fogging system can turn on only when the trucks are dumping. If you want to use it on transfer points you may be creating more problems than solutions. Is your dust exposive and that is why you are trying to avoid dust collectors with explosion vents and all the complications what come with this? On transfer points the fogging has to be carried away by the material or you get a build up of water in the transfer point and as noted above belt cleaning quickly becomes an issue.

In cement we very rarely use fogging systems. Cement and water make paste and very hard one at that. The process for cement creation is a pyroprocess with very hot gasses so fogging is not an option. Water added into this stream evaporates to cool gas temperatures prior to arriving at the bag house. They could be used in the quarry but rarely are.

Atomizing systems are higher in capital cost and not always easy to justify when a project like fogging does not bring you increased production or ROR for the project.

On my last job we used atomizing. A company located in the US called Dust Solutions Inc. in South Carolina.

Liam ■

No system will work unless the air movement in the affected area is controlled. Compressed air systems in fact increases the air turbulence which in turn increases the dust emission. Apart from that, as Mr. Ganesh pointed out, the initial investment, operation and maintenance costs are high compared to high pressure water systems.

Genuine high pressure systems (50-70 Bar) makes very fine droplets and water addition very low (0.1-03 lpm per nozzle). A high pressure water dust suppression system with effective air containment can give very good results. Of course regular maintenance is key to effective functioning of any system whether it's air-water or high pressure water.

For more information on High Pressure Dust Suppression Systems, please contact Thejo Engineering Limited. (mail- marketing@thejo-engg.com)

Regards, ■

Originally Posted by mohandes

Still I would like to find a person with successful experience with high press system.

Meanwhile about cement industry I mean from the first step such as limestone crushing to clinker production.

People who had experience in cement industry, please tell me which system was better for you: dry fog atomizing or high pressure nozzles?

I am not sure you understand Mr Mohandes. I am from the cement industry. You can use a fogging system on the raw materials only. Cement production is a pyro process once the raw meal is mixed the temperature of the process is too hot to use water for dust suppression and is not practicle. We use high temperature bags in process bag houses. Water sprays are used in the downcommers to control/reduce temperature to protect the bags. All water is vaporized in this case. For all intensive purposes regarding your understanding clinker dust is basically cement powder so there is no way you would ever use a fogging system on it. In Joppa the power plant beside us who supplied coal to us used a fogging system on their transfer points.

If you want to talk to people with experience with HP systems as a vendor to put you in touch with some of their happy clients.

Good luck with your project ■

Originally Posted by mohandes

I would like to choose a fog system for dust control of crushing iron ore plant.

Which system is better:

Air atomizing or high pressure?

Dear Mohandes,

High Pressure System can be very relative. Cold Fog Systems deploys 1000 psi pressure & generate 1-15 micron droplets which are much finer than dry fog or other HP systems. This systems consumes 1/3 of water than air atomizers, 75% less electricity than compressed air aided systems.In fact CF Systems are quite different from available HP Systems in India which adds lot of moisture to the material. CF Systems adds 1/2 of DFDS on the material.

We have over 70+ installations working successfully in India . mail me for further details.

U.S Chakravorti

Ecodea P&C Pvt; Ltd.

mail.ecodea@gmail.com ■

Originally Posted by mohandes

I would like to choose a fog system for dust control of crushing iron ore plant.

Which system is better:

Air atomizing or high pressure?

Both of these will create a good fog. The reason to use a fog it to knock down the dust that is already in the air. To accomplish this, you need droplets that are less than 50 microns in diameter. This droplet can be achieved with high pressure water only and an atomizing nozzle or an air and water mix at lower pressure. Each system has drawbacks, and those must be evaluated based on your application and cost of types of maintenance. High pressure system pumps do require more maintenance, and the nozzles are very sensitive to plugging. A two fluid system introduces another fluid (air) and that brings all the maintenance of a compressor and air lines. I have seen both work and both be the most expensive in terms of maintenance.

I have always been a fan of applying low pressure water to the material stream before the dust becomes airborne. You then eliminate the potential for dust to be created, but the belt cleaners have to work harder and you use more water. ■