If you are concerned about breakage of your product ask the supplier to arrange a trial of your material in his machine. It's the only sure way. ■

Talk to suppiers of pneumatic conveying equipment about an "air lift". It is commonly used to gently lift fine materials to similar heights. It is essentially a column of the material, fluidised with compressed air, which overflows at the top.

Michael Reid. ■

Originally Posted by Michael Reid

It is essentially a column of the material, fluidised with compressed air, which overflows at the top.

Michael Reid.

Sounds like something I used to have on a tank of tropical fish to power a filter unit. ■

Yes, fascinating to watch.

I have seen it work with raw alumina in carbon bake off-gas scrubbing systems, (dosing alumina into the airstream to react with fluorides).

Michael Reid. ■

I'm not sure about using fluidised compressed air to move any materials that are really friable or prone to breakage or materials that cannot endure the friction or heat that is generated when using air to move anything.

For that you need what the question originally called for - a disc and a cable or chain. When you have discs the product is contained between the discs and you're not risking separation or product degradation as you would in the uncontrolled atmosphere affected by air - fluidised, compressed or not.

Cable is better than chain for a variety of reasons: it's stronger so it'll last longer; it can be coated or jacketed - chain can't; chain accumulates gunk which is difficult to clean - this is why you use dental floss - you have to get to where the toothbrush can't get to; chain links have been known to twist and stop the conveying process - sometimes even breaking inside the tube.

Pneumatics are absolutely the wrong approach to move friable materials. Air breaks product at the sweeps and although air can ultimately move products faster that same speed beats up friable materials, separates blends and compromises the integrity of the product as it traverses the system.

The cost of operation is tenfold compared to a mechanical tubular drag system. The horsepower to move the product pneumatically might be 50 HP compared to a tubular disc & cable system using 5 HP.

Finally, your inlets and discharges are key to preserving the material in its whole and original state. If your inlets are not accepting materials at the appropriate speed the product may endure being sheared during entry into your system. And the same is true when it is being discharged - the height it is being dropped from will affect how it ends up at the end of the process.

In short: Friable Product should not be moved using pneumatic or vacuum systems because this material needs to be controlled to avoid degradation, separation and friction from beginning to end. ■

karlseidel,

I think you have misunderstood. Michael Reid was talking about a simple vertical lift device powered by air, not a lean phase pneumatic conveying system which is clearly likely to damage the product. Of course, there's always a dense phase system to reduce product damage.

By the way, are the cables used in these tubular conveyors really stronger than chains? ■

I too am puzzled by the response that a rope is better than a chain. If the chain is continuous, i.e. like an anchor chain, there is no build up of dust. Usually if it is a steel rope and disks, it is an aeromechanical conveyor trying to be a tube chain conveyor, typically, under these circumstances, the rope will snap because it is not strong enough to transmit the forces required.

We have installed many tube chain conveyors across the British Isles with good results and good plant availablility. We are the UK agents for Schrage Rohrkettensystem GmbH who are probably Europe's leading manufacturer of tube chain conveyors, I believe that there is an agent covering Belgium, but if not, check www.schrage.de for contact. (my apology if I am not supposed to post a web link)

Regarging the handling of delicate powders, they are generally very good for this, although as advised above, a trial would probably be sensible. Schrage have an extensive test hall and would offer this to you should it be deemed necessary ■