Dramatic reductions in energy use and environmental impact can be achieved with sandwich belt high-angle conveyors that serve as the vital link in any in-pit crushing and conveying (IPCC) system. These high-angle conveyors are not new, yet have not found wide use in IPCC systems where they can realise the greatest advantage.
Reduced energy consumption and environmental impact with IPCC systems were already realised in the 1970s. With the bulk material haulage limited to conventional open trough conveyors the most direct path out of the open pit was precluded, requiring low-angle spiral ramps and/or deep slots and/or tunnels through the high wall of the open pit. These excavations, to accommodate the low-angle limitations, represented undesirable impact on cost and on the environment. 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 pit, along the high wall – the shortest distance between the two end points.
Development of sandwich belt high-angle conveyors
Between 1979 and 1981 that study developed sandwich belt high-angle conveying systems that used 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 testing period (about one year) on the first large-scale prototype system, commercialisation began in 1983 at a USA major conveyor manufacturer, Continental Conveyor.
The first commercial installation was a 60° incline system, at a western USA coal mine, elevating 2,000 t/h 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 angle conveying system.
Sandwich belt system proves success in Serbian mine
In 1984 a copper mine in Serbia, already using pit perimeter crushing and conveying, decided to move its primary crusher deep into the pit and to use a sandwich belt high-angle conveying system to elevate the ore continuously, directly out of the pit, along the high wall to the pit perimeter where it then transferred to a conventional conveyor for the remaining haul to the plant. The system had impressive features including 2,000mm wide belts that elevated 250mm coarse ore, at 4,000 t/h, over six 15m high benches for a total 90m of net lift.
The system proved its worth in several notable ways:
* It reduced the truck fleet by 10 trucks, causing zero emissions to the air and greatly reducing traffic congestion in the pit
* It precluded the need for 4km of haulage ramps, 3.5km of which would be of constant ascent.
* Overall, it saved US$12 million per year
Meeting the challenges of today’s mining industry
The sandwich belt high-angle conveyor offers the link to optimisation of any IPCC system, yet that industry continues to struggle with the use of conventional conveyors and haul trucks to achieve the high angle function. The results are sluggish, low angle conveyor systems of limited flexibility requiring excessive manoeuvring time, excessive excavation, fill and re-handling to accommodate the low angle limitations.
The current alternative to conveyors is the fall back position of using 300 ton haul trucks at great operating and environmental cost. Recent studies have represented resurgence in interest in high-angle conveying and have demonstrated the technical and economical advantages along with the reduced environmental footprint.
High angle conveyor to the resue in Australian project
In 2008, a high capacity (8000 t/h) waste handling IPCC system at a Western Australian iron ore mine was limited in flexibility and mobility by the conventional conveyors that linked the in-pit crushing system with the out-of-pit waste rock and overburden spreading system. Broad, low-angle ramps had to be built ahead of these conventional crawler-mounted conveyors.
The additional material handled and re-handled became cost and time prohibitive.
The entire system, more than US$100 million worth of equipment was ultimately abandoned, parked until a solution could be found.
In 2011, Dos Santos International, through its Australian partnership with Cortex Industries, was contracted to develop the high angle solution, the vital link that would salvage the system.
Fig. 1 depicts the solution. The universal high-angle conveyor (UHAC), as dubbed by the customer, is a high capacity, mobile Dos Santos sandwich belt high-angle conveyor that can operate at various lift requirements, up to three benches (42m) and in both directions, elevating from the active pit to the spoiling surface and lowering to fill in mined out pits with the waste rock and overburden.
Using 2,600mm wide belts this system can easily handle the 350mm primary crushed product at the mine production requirement of 8000 t/h, compatible with the in-pit crushing and spoiling system. Fig. 2 depicts to scale, the sandwich cross-section and demonstrates the principle that large belts can easily handle large lumps.
A lost opportunity?
With the theory and basis fully developed by 1981 commercialisation began in 1983. Suitability for the rigours of IPCC applications was demonstrated in the 1990s by the
second commercial sale, a significant unit at a major Serbian copper mine. Yet despite the compelling advantages both technical and economic, the major IPCC system suppliers, consultants and mining companies continue to ignore the technology, foregoing the great potential for improved production and profits.
Joe Dos Santos is president of Dos Santos International www.dossantosintl.com