Thanks very much for this thread.

I spoke to a Chinese who was obsessed with his observation that in a vacuum there would be no air to hold the particles in suspension. Although reasonably true it was an impurely theoretical standpoint. If there is a fine powder how can there be a vacuum? What, no voids? However the flawed theory should not stand in the way. Baghouses attempt partial vacuum in attempts to coax fugitive particles onto the filter cloth. In doing so the airstream disturbance is perpetuated. Although the analogy to throwing petrol on a fire is a little extreme the similarities are there. Fines are the fuel, air is the oxygen and air disturbance is the ignition source.

Fines are the root issue. Fines cannot be confined in an envelope of coarser lumps or if they could they would need disturbing through air. Off target. Air disturbance is created by moving the material through air. Ethereal as it may sound the air shouldn't be asked to run along at the same speed as the fines and then stop very suddenly when the material has fallen to rest somewhere. There is no point in trying to envelope fines, if they are present, because that would create even more dust. Moving the air alongside the flowing material is difficult. Pneumatic conveying steps pipes to lessen the speed of expanding air. This would mean enclosing the conveyor in two directions and impose structural nightmares. A more achievable dust limitation exercise is to strictly limit the surrounding air. That is what we try to do already, or should try. Improving enclosures to reduce the available air while still affording service access is one step along the way.

There were some pretty clean plants around before my time and there are some real pigsties being built with all the latest technology. There is a trade-off between engineering tenacity and budget. Always was: always will be. Good engineering principles in this exercise are the selection of what the learned manufacturers of dust control equipment have at their disposal coupled with an understanding of the Owner's situation. If there was a life changing better dust control system we'd all be using it. ■

Dear Colin,

This is very interesting topic for me.

Nowadays I have involved in a case for generation of dust in a bin as the belt conveyor discharge material in the bin.

Dust generation reason: the bulk material enter the bin and occupy a volume so the same volume of air should discharge. This volume of air will take some dust out.

The simplest way as I have seen before is the installation of a bin mounted bagfilter on top of the bin.

However I would like to know is there any way to prevent dust generation when the bin fills with a belt conveyor? ■

However as you know most of the dust creates during bulk falling down and hitting the bottom of the bin, isn't it?

what is your idea for the above dust? ■

Greetings all.

I recently conducted some research on this very issue. The fuels supervisor at a plant and I knew that dust followed airflows, and if you could control your air through engineering, you could minimize your dust. With that in mind, we attempted to quantify the airflows. Various standards have been adopted in industry, and we endeavored to find the best methodology to calculate airflows. Using the reality of the applications as the baseline, we compared each methodology to find the best correlation. Once we found the best method for calculating air, we altered the chutes to minimize said air. While we could not eliminate all of the air, and associated dust, we prevented a large part of it. We were then able to instal a small dust collector to agglomerate the rest. Ultimately, we were able to maximize control and minimize capitol investment.

We will post our paper to this forum after we have presented it at Coal Handling in St Louis Thursday of this week. Keep an eye on this thread for the update as we make them. ■

Originally Posted by Colin Benjamin

I have witnessed large coal dump trucks dump large volumes of coal into a hopper without any dust escaping the hopper enclosure, and in all cases without the introduction of any dust collection or dust suppression system, simply through flow control using basic engineering principles.

Would you please explain how was the hopper which doesn't generate dust!? ■

Originally Posted by mohandes

Would you please explain how was the hopper which doesn't generate dust!?

Quite right. Are you talking about the truck driving out of the device? If you enclose the tip, slow down the air with baffles so that the dust settles somewhere: you have to ask what sort of throughput is achieved? Dust will usually settle onto the truck and get blown off as soon as it reaches escape velocity.

Dust is something we have to live against. Mother nature is a bitch! What can escape will escape. I've read the Martin book (Foundations) back to front; inside out and upside down and it tells me that if a product contains dust the dust will show itself, wherever it can. We can limit many sources of that dust generation, depending on available budget, but in the end there will always be some dust, unless we assume the levels of dust exclusion demanded when handling e.g. hydrogen gas carrying plutonium dust. (Been there: done that.)

When it comes to bulk handling dust is just one aspect. There are proprietary belt cleaners, idlers and belts which we are obliged to rely on. Fugitive dust is just another facet we must contend with and without quantum leaps from dust control equipment suppliers we must use what we have. Any such leap would knock holes into the filter bag replacement market and would be sure to be copied by competitors almost as soon as it hit the tracks. If you made a good living supplying replacement filter elements would you blow your foot off? ■

We have a solution to the material handling problem - dust fallout while transferring, dry, granular, free-running products. This system has no internal moving parts and uses no utilities.

The DSH System is installed under a feed point where it can be suspended above the target and kept at operating level.

A small degree of natural agitation as the hopper is filled helps exclude air from the material being transferred. At the point of loading, or transferral, the DSH System concentrates the discharge of dry goods as a tight solid column through free air into any target repository. Loading can be continuous without plant interruption.

Comment made by Associate Professor Peter Wypych, University of Woollongong, Australia - "The DSH Systems Ltd dusdt suppression hopper can achieve major reductions in fugitive dust emissions and also dust explosion hazards. It will be a very useful tool for many bulk handling engineers and technicians."

Please contact Ian Walton, CEO - ian@dshsystems.com

Please visit our web site and see our gallery and installation map - www.dshsystems.com ■

Originally Posted by Daniel Marshall

Greetings all.

I recently conducted some research on this very issue. The fuels supervisor at a plant and I knew that dust followed airflows, and if you could control your air through engineering, you could minimize your dust. With that in mind, we attempted to quantify the airflows. Various standards have been adopted in industry, and we endeavored to find the best methodology to calculate airflows. Using the reality of the applications as the baseline, we compared each methodology to find the best correlation. Once we found the best method for calculating air, we altered the chutes to minimize said air. While we could not eliminate all of the air, and associated dust, we prevented a large part of it. We were then able to instal a small dust collector to agglomerate the rest. Ultimately, we were able to maximize control and minimize capitol investment.

We will post our paper to this forum after we have presented it at Coal Handling in St Louis Thursday of this week. Keep an eye on this thread for the update as we make them.

Here is the paper.

http://www.martin-eng.com/sites/defa...st-and-air.pdf ■

Originally Posted by Colin Benjamin

Hi Daniel,

Thanks for the paper. Conceptually I have no arguments but I am surprised you still needed a bag house or dust collection system. We have been using this concept for 15 years now and have never had to use a dust collection system save for when we are managing alumina that has been either aerated using air slides, in other words has been substantially bulked up with air to allow it to flow down low angle slopes (usually while it is hot and before it goes onto a conveyor belt) or where we did not have the geometry to put in a optimised chute design. For all other materials and applications dust control at the transfer point has been relatively easy to achieve. The one thing that usually presents a problem is cleaning and therefore material carry over due to scrapers but that is a separate story.

Cheers and good luck

Colin Benjamin

Gulf Conveyor Systems Pty Ltd

www.conveyorsystemstechnology.com

New construction can account for air, but most thins older than 20 years do not.

In this case, the chute geometry was limited by the building geometry. The chutes were very compact and they were not allowing the air to be settled. This is the case in most applications that I see. The chutes were designed without air control in mind, so concessions to dust had to be made after the fact.

Whether collectors are sized or chutes designed, the target air flows must still be designed to. This paper addresses the methodologies used to compute the airflow.

Thank you for the time you took to read this. Any feedback from an experienced bulk handler is always good. ■