Hi Lyle,

Chamfering the corners will help but it is not the root cause of your problems. I would have to look at the design but the key to handling what is a very cohesive material is flow control and in particular ensuring that any deflection of the bauxite is done at very shallow angles such no part of the ore stream can slow down. For build up to be occuring in the corners suggest that the intercept angles are too high somewhere in the upper chute configuration and this could come down to;

> the trajectory calculation done as part of the design

> The design and/or shape of the deflector (presuming there is one)

> The positioning of the deflector relative to the head pulley either as a consequence of the trajectory calculation or for other reasons.

It is a very tough assignment to give a graduate student to look at given that designing chutes that will handle such cohesive materials such as bauxite is extremely difficult. Once you have the flow control issues addressed such that there is no build up or blockages, the next challenge is managing the wear as bauxite can be highly abrasive.

By the way given your liners are alumina, what do you intend filling the corners in with if this is what you initially do. If you in fill wilh alumina the corner pieces must have the same compression and therefore abrasion resistance as the flat tiles sections otherwise they will quickly erode away and build up will not only re-occur but the build up patterns will be different.

Cheers

Colin Benjamin

Gulf Conveyor Systems P/L

colin.benjamin@gcsm.com.au

www.conveyorsystemstechnology.com ■

Hi Lyle

I was a vacation student at QAL many years ago too. After which I spent a good many years working on bauxite both at Weipa and in various engineering offices within Comalco.

I am wondering if there has been a sudden change that has brought about a new problem or if this is something that has been going on for a long time?

There was always talk of shipping Andoom run of mine (ROM) ore directly to Gladstone one day. Is this happening, or is the ore all washed at Weipa in the Beneficiation Plant before shipment?

Cheers ■

Originally Posted by Lyle C

Hello,

I am a vacation engineering student working on an alumina refinery in Queensland, Australia. Our bauxite transfer chutes are blocking up frequently and causing much pain.

The corners have been identified as a major contributor. The bauxite catches in the sharp corners and then rapidly builds up upon itself. The current lining is alumina ceramic tiles.

We are considering chamfering the corners just with a tile or perhaps getting curved tiles fired.

Has anybody had a similar issue or any suggestions.

Many thanks,

Lyle Campbell

The easy way would be to just weld some small angle iron lengths

at each corner if any exposed steel exists in the corners of the chute

to weld it or use round bar stock welded in several places(strip welds)

along the bar stock at the corners to eliminate any material

building up in the corners, where it eliminates the space with the angle

iron or bar stock protruding into the flow. ■

Unfortunately the recommendations in the last post will increase the liklihood of build up. With cohesive materials it is essential that all surfaces are very smooth, low friction. What is easy does not always solve the problem. Like Peter Donecker I have had quite a lot of experience with transfer chutes handling bauxite

Cheers

Colin Benjamin ■

Hello Lyle,

Would you be interested in a DEM simulation of your problem showing the effects you are proposing and other corrective concepts?

I offer free of charge to simulate the problem. I only ask to be allowed publication of the results to show interested parties what can be done today with DEM modeling using non round geometries integrated with cohesion properties that mimic your results. You chute behavior should give sufficient calibration to demonstrate cause, effect, and simulation of proposed corrective actions.

This may invite others to offer the same, from other points of view and other tools. I think the industry will have a clearer picture of the maturity of todays technologies. We offer to clock the time to complete said project and allow open debate on your observation of the results.

Maybe others will offer in-kind support of your problem and solutions. ■

Hi Larry,

Lyle is a vacation student who heads back to university to complete his studies in a couple of weeks just by way of clarification. To do this exercise for what is almost certainly a division of Rio Tinto's Alcan subsidiary means it has to be done professionally and thoroughly and given the issues this requires a site visit and a great deal more information if a proper solution is the outcome required. If it needs to be done, it needs to paid for as far as I am concerned.

If what you want is to do an exercise on a known problem with a transfer then by all means find an application that has serious problems and invite others with their DEM software to do DEM models and see if they, through their DEM, create a model that shows there is a problem and compare their outputs to yours. For my part all I need is enough information to do a trajectory calculation and detailed drawings of the chute to identify where the issues are likely to occur and this, compared to doing a DEM model is pretty quick. The only problem is I don't have any pretty pictures to show for my work, only sketches. I do not create scale models of a transfer unless I feel there is a need and then only when I want to compare the flow of what I have created to what is currently in place or if I want to do various what if evaluations because the material variability or the complexity of the design.

Cheers

Colin Benjamin

Gulf Conveyor Systems P/L

www.conveyorsystemstechnology.com ■

Originally Posted by donecker

Hi Lyle

I was a vacation student at QAL many years ago too. After which I spent a good many years working on bauxite both at Weipa and in various engineering offices within Comalco.

I am wondering if there has been a sudden change that has brought about a new problem or if this is something that has been going on for a long time?

There was always talk of shipping Andoom run of mine (ROM) ore directly to Gladstone one day. Is this happening, or is the ore all washed at Weipa in the Beneficiation Plant before shipment?

Cheers

Precisely. There has to be a process change to get persistent blockages on a chute that worked before. Include missing liners etc as process changes. ■

Hi Lyle,

UHDPE will not last with Bauxite so it is not an option. Based on what you have said the angles in the chute are the problem. I know you have said that re-design is not an option but it is the only real solution. I would also believe controlling moisture levels would be critical. If the material gets over a certain mosuisture level then blockages would occur much quicker. If liners are what you can only look at then youshould stick to ceramics but be careful of the in fill corner tiles specification relative to the flat tiles as I already indicated. The chute will still block but it may take a bit more time

Cheers

Colin Benjamin

Gulf Conveyor Systems P/L

colin.benjamin@gcsm.com.au

www.conveyorsystemstechnology.com ■

Hi Lyle,

That comment made me chuckle. The too wet/too dry debate will forever rage in bauxite handling circles. The fact is that bauxite, as with other materials, exhibits a 'sticky range'. The exact moisture levels for that range depend on the amount of ultrafines in the ore as well as the ore sizing. In your case, that level will be low, as the ore is washed. It will also depend on the amount of handling, as the surface of the pisolites will release ultrafines as it is handled.

So rather than a point in the middle, it is really a question of operating either below or above the sticky range at all points in the process. Or, very careful application of water at key points to provide lubrication. Water control in bauxite processing is very important and often poorly controlled. I have a set of slides that I have presented as a talk about this a few times that illustrate the importance of water control and the chaos that can ensue if it is done badly.

The abrasivity of washed bauxite should be less than that of raw ore, particularly from the Weipa deposit (as opposed to the Andoom deposit, further to the north) , as the quartz in the interstitial clays will have been removed, and that is the main hard mineral. You should be able to gauge the wear level from the chute in any case.

Looking at that design, I would definitely want to see chamfers incorporated to eliminate the 90 degree corners.

There are some other tricks that could be applicable in your particular situation, but some of them depend on an intimate knowledge of bauxite behaviour and also the position of the chute in the process.

Since you seem to be dependent on second hand information, it may be hard to ascertain, but it would be interesting to know if the initial accumulations in the corners are of material finer than the bulk ore.

Cheers, ■

Hi

I have dealt with limestone/clay and in Gladstone - not with bauxite.

Moisture content is important - can get a critical range - but how to manage it is the question

Have you stopped the running and looked at the chute buildups as they progresses to a full scale blockage...I reckon that they are building up from the bottom spoon section.

I can see a clean wall section on the right side.....is this impact from feeder conveyor. Can aslo see build up of fines on steep wall liners on the left..meaning very sticky.

My rough experince from handling sticky clay was - keep the speed up, low angles of incidence with walls/chutes, less contact with chutes/liners the better.

Fillet plates in the corner will help - you will need 200mm leg at least..but I think that the bottom section is the problem.

Are there better transfer chute examples on site at QAL - so you can make a performance comparison??

Cheers

James ■

Dear Lyle,

We all believe that 45 degree corner chamfers will help a lot. In lieu of making the change in the short time, I recommend to cut the bottom two rows of tile and chute steel back plane support, only in the center section. This will lower the surface drag that leads to blockage. It might not be enough, but, if you are on the edge of go or no-go, then this may do it. ■

To clear the chute very quickly and without any damage or further modification, I have trained and QAL have in their assets a product called Cardox which is a 'Non Explosive- Explosive'(a crazy analogy) in that it uses a pressurized tube of CO2 in a high pressure breaking system. This product tube/s is placed into drilled holes in the buildup and actually lifts the product at the separation layer on the chute liner plate surface, and there is minimal vibration that is because it uses gas to lift and break up the compacted adhered material and also helps dry the product per-se`. It is also useful on tiled chutes and there is no structural damage. The maximum registered vibration at 500mm at 53,000psi during the activation of 2 tubes is <0.2mm/s/s. There are qualified trained operators at QAL who can perform the task whenever it becomes necessary. It only takes a few minutes preparation and the activation is instantaneous with excellent results. They were to also use the Cardox process in buildup within the calcification tanks and to break the slaby product when it blocks as they rake it into the crushing machinery at the draw-down points under the tanks.

As for the design of the chute, it will always block as the product builds up in an over vertical fashion and there must be a solution/s but I have found from home testing that the product will even stick to Teflon which says a lot for its tenacity.

Check with the QAL AME Mr. Geoff Rhode for more information. ■