Jon,

Drop me an email and I will send some relevant papers on the subject wiith respect to transfer chutes and how we control dust emissions, spillage, belt wear, liner wear, and coal particle fragmentation around them using DEM and CFD technologies. I can send a series of granluar flow animations - picture worth a thousand words.

Lawrence Nordell

Conveyor Dynamics, Inc. ■

Hello Jon,

There are a number of service companies in your area that can help. Try contacting Vulcanisers International (at the old BTR plant north of Liverpool) or a belt manufacturer, such as Fenner in the Hull area for information.

Companies such as Conveyor Dynamics, Martin Engineering, and Benetech can also provide assistance.

Good luck with your project and certification. ■

Hello Jon,

There are two methods to minimize dust emission in surrounding environment.

1) Dust extraction system :

As an example, this is like domestic vacuum cleaners wherein air is extracted at dust generation area, dust separated and clean air is discharged in to atmosphere. Example is only for simple explanation, however, dust extraction systems are of much larger size, in specialized form and designed for continuous operation round the clock.

2) Dust suppression system :

The dust suppression system applies fine spray of water or water mixed with chemical. The spray wets the particles and the particles settle down due to heavier weight. Dust suppression is often preferred however, its limitations are:

- Addition of water / moisture, can be objectionable for certain material.

- One avoids to add water / moisture before crushing / before screening, because it may interfere with the crushing / screening operation.

The dust suppression is also used to prevent dust being carried by air / wind from stock-pile surfaces. In this, water is sprayed on stock pile surfaces at regular time intervals, automatically.

Both the above systems have been extensively used in India in many coal-based power stations (around 150 power stations).

There are manufacturers of both these systems in UK. You can contact them and seek their suggestions / recommendations / literature.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyor.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 5882916 ■

A 3rd Method of Dust Emission Control:

PREVENTION: don't generate the dust and you don't have to extract or suppress it. Properly designed chute transfers, using engineering physics of solids granular flow and gas dynamics turbulence, will minimize dust emission levels and overall maintenance. Chute designs can be compared and differences quantified which exhibit lowest gas velocities to warranty dust leves by particle size.

Why spend unnecessary monies on collection and suppression?

Lawrence Nordell

Conveyor Dynamics, Inc.

website & contacts: www.conveyor-dynamics.com ■

Getting to the root cause is the key to dust supression. Introducing any outside agency into the system may complicate airflows and complicate the problems. Good transfer design is the key. Also look at carryback, which often create as much dust as the transfer. Good luck. ■

A response to Glenn Segrs comment:

Belt carryback occurs from: a) poor belt cleaner adjustment, b) poor belt cleaner selection, c) distressed belt surface such as a cracked / irregular and broken surface, or d) adhesive muck which cannot be cleaned by normal means.

a & b) is a mindless fix

c) belt surface distress is often caused by excessive impact damage to the belt at the load transfer point. This type of damage can be avoided by proper chute design. The surface of the belt can then be cleaned by conventional means. Carryback is eliminated.

d) use special devices such as high pressure / low volume water knife.

Lawrence Nordell ■

The most benefit from dust suppression comes from water addition to the material stream in small increments at points where the material stream is changing direction (at a transfer) or where it is being crushed or other places where the stream is opening up. The dust adheres to wet larger lumps and is retained in the material stream. Fine dust, once airborne, is difficult to knock down with fine water droplets. Fine sprays are easily dispersed by the drafts inside chutes and will wet the sides of the chutes, edges of belts etc. and cause problems. Coarse, low pressure, narrow angle sprays are able to be aimed precisely to avoid overspray. Proper design of the hardware is essential to prevent dribble.

Chemicals additions provide no benefit, in my experience, except where used to consolidate haul roads or to cap stockpiles.

Michael Reid. ■

Dear Jon,

please have a look to our www.vsr-industrietechnik.de

We are an international manufacturer of dust suppression systems.

Please don't hesitate to contact me directly

email:schlabach@vsr-industrietechnik.de ■

Gulf conveyors, www.thegulfgroup.com.au have a patented sytem called GCAT. It uses the principles of controlling the acceleration, velocity and angles of impact and incorporating air stilling and airflow control methodology to reduce dust generation to very acceptable levels.

GCAT has ben very successful with coal and alumina in Australia.

Bag filters are not used and there is no power input into the system. No maintenance is required. Look at the website or contact me to find out more. ■

Glenn,

May I suggest you research your comments on Gulf's bauxite (alumina?) successes to see if they are accurate claims. Your coments suggest Gulf can(have) predict(ed) the particle/granular physics of velocity, accleration, directional vectors and impact forces throughout the chute system. Are you sure about this? Ask them to demostrate full chute flow mechanics comparing predictions verses measurements.

Larry ■

Jon, our Foundations III book covers most aspects of this subject. It is available by contacting Gini at 309-594-2384 ext 429 in the USA. ■

Hi Jon

A very interesting string of responses. I note your query is headed Dust Suppression. To me this suggests you have a prediposition to active dust suppression techniques.. after the dust has become airborne.

Remember without airflow to entrain the dust the fine particulate referred to as dust is just that... benign dust. Control the air movement then dust is controlled.

So step by step remembering coal is no different form any other bulk solid commodity when it comes to fugitive emission control.

1) Condition the material stream (with water) to maximise agglomeration of the fine particulate to coarser particulate. Moisture content from the materials handling perspective is quite critical so accurate controls are required. Lump size and PSD are also very important.

2) Control air movement through the transfer... logically.. by minimising the amount of air entering, minimising the effective width (exposed material surface) of the material stream and deploy passive air movement controls to minimise airflow induction through the transfer and ensure the transfer has minimal appertures that will allow air to ENTER the ore path.. encapsulation is vital. Don't over-throttle the air flow otherwise dust laden air may start venting via the least line of resistance under the head pulley with the return strand. Remember anything that moves creates sympathetic air movement.

3) Employ active fog suppression (if necessary) in the upper regions of the air path.. yes AIR path

4) Ensure there are no pressurised pockets present in the transfer where the dust laden air can become trapped and exhausted under the skirts

5) Employ both passive and active dust controls in the lower regions of the transfer and through the exit skirt enclosure on the receiving conveyor as required

6) Take particular notice of belt carryback. We have done a lot of research on this and have found in some larger materials handling complexes return belt cleaning is the main key to successful fugitive emission control. Belts wear and as they get older the damaged covers result in increased carryback and increased fugitive emissions.

7) Dont overlook spillage to the top side of the return strand. This often becomes a major emission cause with the normally clean side of the belt becoming heavily contaminated.... not so noticable with coal as the belt is also black.

Not simple is it?.. and as every transfer is invariably different in some way a different set of rules apply every time.

Our speciality is this very business having assisted the major international players in coal, iron ore, gold, etc. over the last three decades so if I can help any further don't hesitate to drop me a line.

Best wishes for 2004

www.tandt.com.au ■

Since you have an established plant and money constraints, your best solution is dust suppression sprays. Look at my previous post in this thread. Apply only SMALL amounts of water at each application point to bring the free moisture content up to the maximum you figure you can tolerate. Fit controls so that when material flow stops, so does water, without dribble. Fit controls to adjust the water pressure and flow so that you can adjust things if you have trouble.

Good luck,

Michael Reid. ■

Gents,

I am interested in dust suppresion - coal and other products.

We burn low grade coal and handle it via

rail unloader - dump stn

belt convs to overhead gallery with travelling tripper

FEL reclaim to hoppers

Hoppers > belt feeder> convs. to mill raw coal bin.

Belt conv. have dust collection at transfers.

Dump stn. has nothing > but capability for future dust collection system.

Main (environmental) dust issues with coal handling are;

Tripper discharge to empty stockpile - large fall height

FEL reclaiming to hopper

Truck traffic in area of stockpiles

For the dump stn, it is inside a shed..issues are personell - localised dust and smell.

We have had severe water retrictions due to drought but these are now lifted...but we are not using water - we can as we can tolerate some moisture to the mill circuit

I have heard of "gum" applications at transfers and stockpiles to seal piles.

I would like to tap into your experiences and receive your opnions and comments.

Thanks

James Morrish ■