Hi Janusz,

You should contact companies that supply dust collection equipment, such as Martin Engineering (get their website from the eDirectory).

Although I am not aware of an imperical study, I tend to think that multiple dust collection units are preferable -- even though this approach is more expensive. Single units, unless controlled to shut off at each transfer point when not required, tend to work even when a transfer point is not in use. This wastes money and lowers the efficiency of the unit. Individual or restricted joint use collectors can be controlled and maintained easier. Also, individual units have lower HP motors, which are easier to obtain and replace.

Good luck with your project. ■

Dear Janusz,

Unless your product is very fine, it may be possible to transfer your product without dust collection.

By controlling the granular flow velocity to more or less a constant between transfer elevations, you can vertually eliminate the gas dynamic gradients that create dust.

Dust becomes airborne, when a specific particle diameter is set in suspension from a specific applyied gas velocity. It will drop out of suspension as a function of time once the velocity drops below the critical suspension velocity.

So the trick is to analyze the chute geometry and propose a geometry that controls the conditions.

Conveyor Dynamics, Inc. (CDI) has developed a granular flow model (DEM) that can simulate most of these conditions (solids and gas dynamics created by the granular flow dynamics).

The caveate here is moisture. If little or no moisture is present and we are not talking micron particle sizes, then give us a chance to show what can be done.

This is becoming the mantra of coal fired power plants and mine operations where environmental considerations have gained the attention of operators.

Product degradation is also controlled.

PLease contact us for more information on such modeling and see our website.

Lawrence Nordell

Conveyor Dynamics, Inc.

ph 360-671-2200

fx 360-671-8450

email: nordell@conveyor-dynamics.com

website: www.conveyor-dynamics.com ■

Dear Janusz,

I agree with Lawrence Nordell that good transfer design is the place to start. Much of the fugitive dust from conveying systems could be reduced, even eliminated, by good design of enclosures, chutes and skirts. Skirts need to be well maintained to prevent spillage. Impact idler systems must be designed to stop spillage by avoiding deformation and keeping skirts in close contact with the belt.

Depending on the nature of your product, moisture can be used to agglomerate dust into larger particles. When the method is applied correctly, this is the best and least expensive form of dust control. It can be successful when used on its own, as in coal conveying, or used in combination with dust collection if high product moisture is unacceptable.

Unit dust collectors (so-called insertables) are an economical form of dust collection when transfer points are spaced far apart. A big disadvantage in that the collected dust is discharged back to the orestream and the amount of dust to be collected at the next transfer increases. Compressed air and electrical power need to be reticulated to them. Remote dust collectors are also often neglected and poorly maintained.

Depending on the scale and layout of the plant, a central, ducted dust collection system is more power efficient and easier to maintain (although ducting repairs may be an issue after a period). A central dust collector also gives you the option of using a wet scrubber instead of bagfilters (less capital cost).

Torit DCE are respected dust collector manufacturers in Europe. Send me an email if you want more details.

Good luck,

Michael Reid. ■

Possibly, you may be already knowing that there are two methods to minimise (prevent) dust emission at transfer points.

1) Dust suppression system. This is used if addition of few percentage of water is not objectionable for the material.

2) Dust extraction / collection system wherein dust is extracted from the air and is again fed back into conveying system

In general, one system of dust collection per transfer house or crusher house is widely used. For example, in a crusher house there may be number of dust generating points. To provide individual dust collection unit for each dust generating point would be difficult to install, interlock & maintain. Other consideration about number of units (say one, two or three) per transfer house will go by economy i.e. adopt such a number of units so that the total cost is minimum. I think I have clarified the issue ■

We have very good experience with so called spotfilters. A relatively small filter and fan is put on the discharge point. The collected dust on the filterbags is agglomerated and pneumatically cleaned with a puls jet system.

You only need: a hole in the discharge, a flange, power suplly and press air suplly.

For € 3.500,- you alreay might have a good solution.

Jur Lommerts

Jansen & Heuning Bulk Handling Systems

The Netherlands

tel: + 31 50 3126 448 ■