Dear Mr. Delbruck,

Although I've only seen stacked conveyors in a salt mine (a 4 system stack), the use of stacking for an overland system is quite feasible.

Potential problems include:

(1) Contamination of product on the lower conveyor due to spillage from the top conveyor, if carrying two different materials.

(2) Requirement for a heavy-duty framework that is capable of supporting both systems.

(3) Requirement for a specialized take-up arrangement for the top conveyor (unless the top conveyor's discharge is substantially ahead of the lower conveyor's).

(4) Requirement for a specialized discharge arrangement (unless the top conveyor's discharge is substantially ahead of the lower conveyor's).

(5) Increased maintenance costs, as it is more difficult to work on the two systems.

(6) Potential for damage to the lower system if the upper conveyor's belt should break.

Benefits include:

(1) Space savings (normally not an issue for overland systems).

(2) Construction savings (less footings required and reduced tunneling costs, if needed).

General Comment:

As this would be an unusual approach, specialized engineering is required. As such, you should employ a reputable firm for the design work - such as Larry Nordell's company, which has a history of getting involved with unique applications and is well qualified. (You can contact them through this website.)

Regards, ■

Sorry I sat on this all day and have no recent or know of active installations to contribute. I can comment on past knowledge.

THis has already been successfully done as David noted. My knowledge is from a long since retired installation. THis was applied to the predecessor to the 12.2 km incline for Selby in the UK. I forget the name of the mine or the design construction firm.

I consulted to the design firm, in 1990, on other projects and was amazed this was a well kept secret. They made a mockup of the piggyback design. I do not know where the firm is today. This was about 15 years ago. I could probably go back to our archives. I would be a bit of work.

THe belt is a little under, but close to the Selby specifications which, from memory, is 1600mm wide. I believe this system was closer to an ST-5000 N/mm than Selby's ST-7000 N/mm



Good maintenance access, handling of idler changeout, detection of failed bearings, idler and belt fire control, belt changeout, cleanup access, make the sparks place their electrical conduits and instruments away from maintenance access. Corrosion from ground water is another factors.

You must also develop a tunnel which provides proper vertical and horizontal ground support. ■

I believe there is a Stacked Overland System in Gladstone, Queensland, Australia that was commissioned late last year.

The Conveyor runs from the Plant to the Port facility, it has 2 belts running on top of each other in the one conveyor structure.

One belt takes the raw material from the Port to the Plant, it’s then processed and the second belt takes it back the Port for Shipping.

Unsure of the stats but there are others in the Forum from that area that may be able to help further. ■

You should also investigate the capasule opipeline system developed by the folks at

<www.Pneutrans.net>

This system relies on technology that has been in use for a century or more and is very dependable etc. Just to relieve your concern I do not represent them.

lzaharis ■

Further info Re Gladstone

System is installed at Comalco Alumina Refinery [CAR] , Gladstone, Queensland, Australia,

Bechtel were the Engineers, United KG installed the conveyor system and SMH installed the belts.

I believe there are 2 stacked systems installed, one at about 4 klms centres which feeds onto another at about 2 klm centres.

One belt carry’s Bauxite into the plant from the Wharf and the other carry’s Alumina out from the Plant to the Wharf for shipping.

Width is approx 1050 mm, unsure of the rating, one is HR.

Hope this helps. ■

Hi Bruce,

Gary James, who often subscibes to this forum was involved in the design.

Shane ■

Dear Mr. A. Delbruck,

Conveyors have regular installation in enclosed gallery or tunnel of say 2.5m head room. Thus two conveyors can certainly be installed one over the other, if one decides for the same. However, I draw your attention to the following aspects which may be of use to you :

1) Case-1 : If total conveying route is not very long then both conveyors can be placed in common vertical plane one above the other. The lower conveyor can have take-up arrangement as usual. But upper conveyor can only have take-up at tail end or the upper conveyor is to be further elevated at take-up location, where again counterweight is not advisable to install in the space so created. The lower conveyor can directly rest on ground whereas upper conveyor will have a portal type of enclosure spanning over the underneath conveyor. The supporting floor to upper conveyor should be of chequered plate and enclosed for full width. The transfer point of two conveyors will also need specialised arrangement.

2) Case-2 : You have got a very long conveying route and you only want to make it one above the other in tunnel portion. Both the conveyors are on ground prior to tunnel and after tunnel. This can be achieved as below :

- Terminate one conveyor prior to tunnel and elevate it at head end.

- Put small length cross conveyor to transfer the material received from this conveyor on to the upper conveyor in tunnel. Similar thing to be done at outer end of tunnel to put both the conveyors on ground.

- If you don’t want to have this transfer points then one conveyor will need curvature in horizontal plane to come over the other conveyor prior to entering in the tunnel. It will again have horizontal curvature after tunnel to bring it to the ground level.

- In my opinion two junctions one prior to tunnel and one after tunnel will result into easier arrangement because horizontal curvatures will require long length for them to run parallel at ground level.

Regards,

Ishwar G Mulani.

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

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

I have been to CAR Gladstone and seen the stacked belt conveyor. I beleive that QAL Gladstone has the same??

I would not like to change the idlers - top belt is really close to the roof/covers and both have large and heavy rolls in not soo easy to get to locations. Designers need to consider maintenace and safety - as people have to live with these for 20+ years.

At one end, the top conveyor is fed from above (of course) and the conveyor underneath goes to a discharge further away.

At the other end of the run, there is an interesting transfer - need a bit of height to make it all work.

For your tunnel, U may wish to fully support your conveyor from the roof..this will allow a grader blade to sweep the floor clean/clear under the bottom belt.

Cheers

James ■

Dear sir

We have erected 300 m long double conveyors for coal handling system of a captive power plant in India. Both conveyors are having separate galleries with common trestles.

In underground tunnel also these can be provided. Top conveyor can be hanged from roof and bottom will be floor supported.

Feasibility of such system can be established only after knowing feed and discharge point layout.

A R SINGH

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