Hi James,

I don’t think that curved chutes are necessarily the answer to all problems with ore handling, in much the same way that there is no belt cleaner that is universally suited to every application.

The coal installation you refer to impressed me when I saw it. The ore appeared to be very well controlled and there was no evidence of spillage. The belts, however, were deeply troughed and were showing idler junction cracking.

I am aware of sites handling sticky ores where curved chutes have proven successful, and others where they have been problematic and unpopular. The problems can be wide and varied, and the list could be added to.

Some of the problems were:

•Unexpected and unacceptably high chute wear, leading to extensive trials of wear materials, some of which were poorly conceived.

•Excessive spillage associated with surges in ore flow. Curved chutes provide no damping in comparison with some more conventional designs.

•Blockage, initiated in the discharge end of the chute and caused by the accretion of colloidal sized particles segregating from the main ore stream. This problem is similar to the formation of scale in fluid systems, and differs from the effects that can be related to the bulk properties of the ore. I have not seen any in-depth analysis of this effect in the literature. It sounds a bit like your rhino-horns.

•Excessive cleanout frequency due to the small internal volume of the chute in relation to the volume of the internal accretions.

•Difficulty in removing accretions due to their hardness.

In some cases, the curved chutes were removed and replaced with more conventional designs. In others, solutions were devised that provided some relief from the principal problem, such as wear or cleanout, but which compromised other things like belt wear.

Like I said, I don’t think that there is a universal solution, but being aware of some potential problems can sometimes be helpful. ■

One thing we are using the hood and spoon designed chutes (Inertial Flow Technology by Martin Engineering) is to reduce dusting in load zones that have long drops. As material leaves the head pulley and spreads out air is pulled in. This is called induced air.

The IFT consists of four parts, Head chute enclosure to reduce induced air, a hood to prevent the material from spreading out, a curved chute called a spoon to receive the load, and dust curtains in the stilling area to reduce dust from the exit area of the load zone.

This is in our Foundations III book. Please contact Martin Engineering for a copy. 309-594-2385 ext 429 ■

Curved Hood & Spoon Chute(CH&SC) Applications for Belt Conveyor Transfer Stations:

CH&SC's are in their infancy. Modern granular flow models will, in the future, guide the industry in CH&SC applications as the granular internal properties library of information becomes known and granular models apply the lab measured rheologies.

Yes, CH&SC do not fit all applications. Large and/or dry granular particles flow well in CH&SC. Wet and fine grain sizes (with a p50 < 0.5mm) may not. Internal water surface tension between many fine particles, such as clays and concentrates, can significantly increase the granular strength properties in shear, cohesion, and adhesion. This appears to us as "sticky material". These properties need to be defined to provide the engineering parameters for accurate prediction of flow behavior.

Discrete Element Method (DEM) modeling can incorporate these physical properties and yield accurate prediction of flow mechanics.

There are axioms of design that are often not followed with respect to fine and wet or for coarse products . For fine and wet product, chute flow slopes and internal wall angles should: 1) keep the contact vertical slopes and valley angles steep > 70 degrees, and internal wall included angles > 120 degrees; for coarse product 3) impingment angles between product and wall should be less than 30 degrees.

One needs to obtain the working history of sucessful and unsucessful claims of performance before advising.

Too many wise chefs with a different recipe can soil the intended broth.

Lawrence Nordell

Conveyor Dynamics, Inc.

email: nordell@conveyor-dynamics.com

website: www.conveyor-dynamics.com ■

Dear BKD & J. Morrison,

To be fair to the industry of curved chute (CH&SC) design methods you should specify the science required to expect an accurate outcome such as:

1. Lab testing of strength and time (rate) dependent rheology that can be added to DEM - have the lab demonstrate science of rheology measurements

2. Determine if lab can deliver proper parameters - moisture and fines is not always so easy - J&J shear test with moisture driven off and then added in lab may produce bogus results as Prof Roberts has noted.

3. Model flow physics in Discrete Element Method (DEM) noting not all DEM models can produce the rheology of wet fines or even approximate its behavior or, as an alternative, build a representative physical model such as promoted by Mr. Donecker

4. DEM should be capable of a size range of 10-20:1 large:small - do you believe all DEM particles of the same size gives meaningful results?

5. DEM should be capable of modeling non-round material shapes to synthesize granular shear strength - what is the use of having all particle of a spherical shape - the world of granular materials are not all marbles and bearings

6. DEM should be able to identify wear intensity on liners and belt by degree, location and expected life

7. DEM should be able to quantify comminution damage to granular product in chutes of any confiuration

Do the two companies BKD recommended have these skills? I see no publications from them about their applied mechanics skills and their relevant applications of theory and practice.

Caveat Emptor!

Lawrence Nordell

Conveyor Dynamics, Inc.

website: www.conveyor-dynamics.com ■

Larry, James & Others,

I believe I was one of the originators of the curved chute concepts, installing our first chutes back in around 1985 in the Queensland (Australia) coal industry - but I would be interested to hear of anyone designing & installing them on large conveyors earlier than this.

Interestingly, I am now a conveyor engineer (on contract) with Gladstone Port Authority - where there many such chutes as James mentioned in his initial post. We now run these up to 6,000 tph and 5.1 m/sec and looking at going higher. These chutes do a very good job on coal.

These chutes are very expensive to design & install (relative to standard chutes), so you need to be experiencing very high wear, dust, noise, attrition rates etc. to justify the cost. Of course, a proper life cycle costing may show them justified for other installtions. When conveyors ran at 500 tph & 3 m/s with generous head chutes & high transfers & low wear rates, it wasn't justified - different story today.

I have seem them attempted in coal wash plants where there is high clay contents - but with little success. You can usually keep the product momentum there to wash or wipe off any clay which wants to stick to the chute OK while you are operating - but it is the startup lead-in flow and the tail-out which causes all the problems - mainly on the bottom chute. If you can pull the lower curved section of chute out of the way during these times - you may have a chance of success. (The top curve often is missed by the flow during start-up & tail-out, unless you have a really tight curve so it is not such an issue) Or, you can try to ensure there is no lead-in or tail-out flow - only full flow - not easy but not impossible.

Can DEM modelling handle sticky clay mixed in with the product Larry ? ■

Yes after a fashion.

First, participants must agree upon the rheology model. Cohesion, adhesion, time dependent strain rate yield criterion, etc. as a funtion of the other physical parameters.

Second, clients must agree to the cost of testing to collect the necessary rheological coefficients. This may or may not be possible. Wethered materials, of differing surface moisture levels and significant micron partical sizing class, may not be easily reproducable in the lab for extended moisture and micron size sensitivities. This dilemma leads to added and maybe unacceptable testing costs.

Third, simple phenomenalogical or emperical models may be adaptable to a reasonable degree by synthesizing field results to the DEM emperical model or visa versa as the reviewer choses. Here less lab testing is required, and more model sensitivity is prescribed. This third choice is the cheapest but least attestable to the real world. Bottom line is it works on a case-by-case basis.

Fourth, usually the client is in the Big Hurry, has limited time, limited funds, and/or not acquainted/doubtful of the process to get the details required.

Fifth, if the product is big rock and separately wet clay, then a curved spoon may not be the answer. DEM can give you the hint if this is so.

There are other factors, but I just do my blah blah and audience eyes go to half mast.

Dale, glad to meet up with you. Have heard the many stories of your successes, plights, rip-off artists, plargarists, and so on. I am often in OZ and the Queensland territory. It would be an honor to get together. I will keep you informed when this may be possible. Email me through the web contact if this is possible.

Hoping for a good future,

Lawrence Nordell

Conveyor Dynamics, Inc.

Web: www.conveyor-dynamics.com ■

Thanks for the invite. Who is us?

I did receive you email and will respond. I have been traveling.

As you may note, we differ in our design approach:

1. Best approach - you have something that works and can be copied

2. Second best approach - have good analytic tools to guide a design by sensitivity analysis and being able to tune from examples

3. Third approach - estimate from prior experience which may be a stretch of associations giving rise to concerns for which the educated searchs far and wide for closer associations than are at hand.

4. Worst approach - suck-it-and-see -- this is the best approach for those wanting to learn by others mistakes

Regards,

Lawrence Nordell

Conveyor Dynamics, Inc.

www.conveyor-dynamics.com ■

HI Ken,

Corrosion Engineering USA) manufactures a alumina ceramic rubber composite.

One curved chute installation using rubber/ceramic, I am famliar with, is Los Pelambres in Chile installed in 2000. It transports >7000 t/h (design rate = 8700 t/h) of primary crusher copper ore at 6m/s through three . The ceramic/rubber is(was) not use on high impact zones, mainly on the side walls.

See our website for a reference of the geometry.

I am not familiar with the term "tight as a drum" wrt the subject liners.

Lawrence Nordell

Conveyor Dynamics, Inc.

web: www.conveyor-dynamics.com ■

Hi all.

Our experience with wet and sticky material in convencional chutes (Rectangular cross section) was very bad, many obstruction and we need to put water in the chute for to avoid the begining the block of the chute. This water has a cost because the chute is in a inlet of one dryer and our consuption of the natural gas was very hight. The humidity in the material is 30% but this measure is before the chute, with additon more water more gas we need. The layout has one belt with 1,1 mts/seg; 48" wide belt; 300 TPH; and use the deflector in the discharge chute of the belt and the material fall free almost 6 mts to impact in inlet dryer chute.

Our solution was to increase the belt velocity at 1,7 mts/seg, use the parabolic movement of the material when out the head pulley conveyor and move the head pulley conveyor 600 mm rear at the initial position and to move all the material without touch the wall of the discharge chute. The initial chute angle was 57° when check the original angle found the 65° then change to original angle and check the velocity when the material impact to inlet chute, and increase the resultant velocity and use curve cross section inlet chute with liner abrasion resisting. The result was very excellent , never more addition of the water in the inlet chute and our gas comsuption is very lower than before the modification. ■