Take The High Angle
Published by Jessica Casey,
Various articles that announce high angle conveying from opencast mines as ‘innovative’, ‘next phase’ and ‘new’ show that more research must be done. This method of conveying has been available for over 30 years but remains ignored by the IPCC equipment and systems providers.
For a company like Dos Santos International (DSI), it is increasingly frustrating to see these articles make their way to publications as a new technology when President and Owner, Joseph Dos Santos, has offered this option throughout his career. He is the inventor of the DSI Sandwich Belt High Angle Conveyor and has researched and spoken regularly on the subject of high angle conveying, and how it offers the vital and missing link to optimised IPCC systems.
Reduced energy consumption and environmental impact with IPCC systems was realised in the 1970s. With bulk material haulage limited to conventional open trough conveyors, this precluded the most direct path out of the opencast mine, requiring low angle spiral ramps and/or deep slots and/or tunnels through the mine high wall. These excavations, to accommodate the low angle limitations, represented undesirable impact on cost and on the environment, increasing the amount of environmental disturbance for the amount of ore recovered.
Against this backdrop, a major study in 1979 sought to develop high angle conveying systems that could continuously haul the mined bulk material directly out of the mine, along the high wall, “the shortest distance between the two end points.” Between 1979 and 1982, that study developed sandwich belt high angle conveying systems that utilised all conventional conveyor equipment, including smooth surfaced rubber belts that could be continuously scraped clean. These systems had all of the positive features of conventional conveyors, but overcame the angle limitation. By hugging the bulk material between two belts, the material’s internal friction could be developed to facilitate conveying at any high angle up to 90° (vertical).
After an intense, 1 year testing period on the first large scale prototype system, commercialisation began in 1983 with the installation of a 60 ° incline system at a Western US coal mine, elevating 2000 tph of coal to a train load out system. It did not take a long period of scrutiny and acceptance before this high angle conveyor found use in the most rugged requirements of an IPCC system. This was only the second commercial sale, and after more than 150 commercial installations, it remains arguably the most significant high conveying system.
In this case, a copper mine, already using mine perimeter crushing and conveying, decided to move its primary crusher deep into the mine and use a sandwich belt high angle conveying system to elevate the ore continuously, directly out of the mine, along the high wall to the mine perimeter where it then transferred to a conventional conveyor for the remaining haul to the plant. The system had significant features including 2000 mm wide belts that elevated 250 mm coarse ore at 4000 tph, over six 15 m high benches for a total of 90 m of lift. The system was able to reduce the truck haulage fleet by 10, 200 t trucks realising great cost savings, zero emission to the air and greatly reduced traffic congestion in the mine. They system operated successfully until 2002 when the mine shut down.
High angle conveyors
Suitability for IPCC systems has been demonstrated at all of the company’s sandwich belt high angle conveyors with a number of units handling very large ore and rock at very high rates. The most common concerns regarding sandwich belt high angle conveyor suitability for IPCC applications include:
- Can they handle very high tonnage rates?
- Are they suitable for continuous operation 24/7?
- Can they handle large, heavy, primary crushed ore and waste rock?
The various installations answer these concerns. Of these, the most important concern is third on the lists. The answer is this – large belts can handle large lumps, small belts can handle small lumps.
‘Large’ lump size is relative. 350 mm lumps are too large to handle at a sandwich belt of 1000 mm width, but not at a sandwich belt of 2600 mm width. Indeed, to have compatibility of belt width and material size, the material size is limited with regards to the trough depth. For predominantly lumpy material, the company limits the lump size to the depth of the trough. For occasionally lumpy material, less than 10% large lumps, the company increases the size criteria to 125% of the trough depth. This is to limit the separation of the belts, preserving a good covering of the bulk material and positive contact at the edges of the sandwich.
Sandwich belt high angle conveyors can and have conveyed very large oversize material from the sandwich entrance to the discharge. At a muck handling system, a 150 hp TBM cutter motor was unintentionally but successfully conveying from loading point to the discharge. There was some very minor damage, but the system continued to operate until a scheduled down time to make the minor repairs. It is not a question of what is the largest material that can be handled. The company’s criteria is to determine the material size that should be handled for reliable, trouble free operation with minimal wear and tear.
The only IPCC application to date in a copper mine shows that the 250 mm lumps are easily handled at the 2000 mm wide belts.
5 years after start up, the system had done the following:
- Reduced the truck fleet by 10.
- Precluded the need for 4 km of haulage ramps, 3.5 km of which would be of constant ascent.
- Saved US$12 million/yr.
Almost an IPCC application, another sandwich belt high angle conveyor elevates coarse (250 mm minus) gold ore from the primary jaw crusher to the next crushing stage. It is at the mine perimeter, not in the mine. Definitely and overreach on the lump size handled, this conveyor suffered some wear and tear consequences but remains in operation today more than 25 years later.
The vital elevating link of a self-unloading ship system handles a variety of materials, including 305 mm minus rock. The sandwich belt high angle conveyor lifts the material onto a boom conveyor that discharges the bulk cargo to shore. This system is right at the edge of the maximum lump criteria for occasionally lumpy material less than 10% lumps. Design reflected that the very coarse rock material is one of several commodities transported and the unloading conveyors do not operate continuously 24/7, rather there is much none-operating time at sea. This system replaced a massive apron type elevator that suffered very costly wear and tear.
The universal high angle conveyor (UHAC) is a prospective application in Western Australia. It is designed as the vital link to salvage an existing IPCC system that has proven sluggish due to its dependency on long, low angle conventional conveyors that link the IPCC system to the remote spoiling system. Operation of the present system proved impractical largely due to the extensive planning required, much non-productive movement, excavation and re-handling and grading work required to accommodate the present low angle link. Presently, the system sits idle awaiting the vital link that will free the rigid interdependency of the in-mine system and the remote spoiling system.
The UHAC promises salvation, providing a compact mobile link, capable of elevating or lowering the primary crushed 350 mm minus waste rock at 8000 tph. Designed with the emphasis on versatility the UHAC can operate in either direction (elevating or lowering the material) and at any level from tramming on grade to a 3 x 12 m bench operation. The UHAC offers the vital versatile link for surface spoiling (elevating) or back filling of the mined out mine (lowering).
Sandwich Belt High Angle Conveyors are suitable for IPCC applications for the following reasons:
- They can handle very high conveying rates.
- They are suitable for continuous 24/7 operation.
- High tonnage requirements are handled by wide belts that can easily handle large, primary crushed material.
- Conscientious design will ensure long life with minimal maintenance required.
This article was originally published in the July/August issue of World Coal. View the full issue here and register to receive your FREE trial of the magazine here.
Read the article online at: https://www.worldcoal.com/special-reports/23072020/take-the-high-angle/
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