For many years, there has been debate in the extractive industry globally about whether product from the face to the stockpile would be more efficient and less expensive if it were transported by conveyor rather than by wheel loaders and dump trucks. The advantages and savings have been argued as follows:
- Reduced costs on the operation and maintenance of loaders and trucks.
- Reduced handling of the material, ie the material is fed direct to the crushing and screening circuit.
- Reduced labour costs.
- Higher production capacity.
- Greater flexibility of mobile link conveyors, ie utilised as link/stockpiling conveyors.
- Greater fuel efficiency in comparison with loading of trucks.
The following case studies indicate that perhaps the “truth” of the matter falls somewhere in-between – that linking conveyors can complement, if not outright replace, a load and haul fleet. Nonetheless, the utilisation of linking conveyors in the right locations and in the right circumstances might mean the load and haul fleet can be diverted to other tasks within the quarry.
The case studies cited below are about Telestack mobile conveyor products, which are distributed in Australia by Tricon Equipment (east coast) and OPS Screening & Crushing Equipment (west coast). They all focus specifically on the performance of Telestack plant and equipment in pits across three countries.
Caliché in Chile
Before the Telestack conveyors, ACF Minera was using truck and wheel loaders to stockpile caliché at a mine site near the port city of Antofogasto, in Chile, 1100km north of Santiago. This method was expensive and inefficient but limited the leaching capabilities and leaching quality of the application.
As the wheel loader drove up the stockpile, the material was compacted, which did not allow for an effective leaching process. The caliché also became contaminated, due to oil leaks and spillages. Stockpiling in this way meant the operator’s leaching rates were not achieved as the compacted and larger material (not crushed) limited the percolation and infiltration of the sea water leaching within the stockpile.
With the assistance of Telestack, ACF Minera subsequently installed seven mobile link conveyors (five of a fixed length and two telescopic links) and a radial telescopic stacker. The automatic stockpiling system and range of mobile links covered a distance of more than 300 metres from the crusher to the discharge point.
The Telestack equipment was fed directly from a Kleemann 162 mobile crusher, which in turn was fed 0-600mm ROM material from the mine with 150-tonne Komatsu trucks. The caliché was discharged from the trucks via the semi-mobile platform into the crusher and discharged at 1500 tonnes per hour as 0-250mm material.
The operator used the mobility of these links to create a 300m x 150m heap leach level pad. When it started the procedure, ACF Minera set up all seven link conveyors with the stacker at the end of the system. As the first stockpile of the material is completed, the operator, using the telescopic technology on the two TS 1524 tracked telescopic conveyors (the sixth and seventh mobile links), retracts the stacker backwards in 10m increments.
The TS 1524 telescopic link conveyors are always feeding the stacker to ensure the 10m increments are maintained for the flat stockpile that is required for the heap leach process. As the stacker continues to move backwards to build the level pad, the operator removes each of the 43m fixed length conveyors from the system.
The TS 1542 radial telescopic stacker automatically stockpiles the material from the link conveyors with a “custom-designed” stockpiling program to ensure the stockpile is flat for the leach heaping process up to a 10m height.
As the operator sprays the sea water over the caliché during the heap leaching process, the liquid can percolate easily through the material and offer a high quality leaching procedure, which leads to a higher quality product.
Limestone in Austria
At a Leube GmbH quarry near Salzburg, in Austria, two TT643 mobile link conveyors were employed to replace an excavator that was loading feed directly into trucks. The trucks were transporting material down a mountain approximately one kilometre from the crushing plant for processing. This method was high cost in terms of fuel, operators, and machinery maintenance, and an inefficient way to transport limestone to the plant.
The two TT643 mobile link conveyors have become an integral part of the new plant arrangement, in which they are fed directly from a Kleemann 140 mobile crusher. The ease of movement on these tracked machines allows for total manoeuvrability on-site which ensures each part of the site can be reached and a greater flow of material can be produced to feed the fixed field conveyor.
The mobile link conveyors are being utilised to transport the crushed limestone from the Kleemann crusher directly into the field conveyor on-site, which is directly feeding the cement plant a kilometre away. This method has greatly reduced costs on the operation and maintenance of the trucks that were previously used on-site. Leube GmbH also availed itself of Telestack’s customised options, which included an increase in the discharge height of the link conveyors from almost five to seven metres. This enables the stockpiling of material in the event of the failure of the fixed field conveyor.
Other features included galvanised dust covers, tail shaft rotation monitors, remote control and an upgraded electrical specification to link the mobile conveyors to all sections of the plant for monitoring and control.
“We are extremely happy with the purchases of these two mobile link conveyors,” Leube mining manager Johannes Thesis said. “The flexibility and mobility of the link conveyors ensures that our production targets are met and maintained as we reach all sections of the site with ease.”
Leube subsequently ordered three more machines for one of its other locations, where the TT643 Transtack link conveyors are being fed from a Hazemag single roller crusher.
Slate in Wales
At Penryn Quarry, in Bethesada, in northern Wales, the quarry operator increased the size of the blast area within the quarry, therefore leading to a greater haulage distance for the wheel loader to travel each time. This increased fuel, maintenance and labour costs for the wheel loader, which raised the costs per tonne of the finished product. With the price of fuel increasing, it was clear that the loading shovel solution was no longer viable for the operator.
The solution was to install a TT443 Transtack link conveyor and a TS 624 tracked telescopic link/stockpiling conveyor, which would be fed by a Kleemann MC 122 crusher. The TT443 can move around the blast area with the mobile crusher to ensure all of the blast material is easily “picked up” without moving or extending the large hopper on the overland conveyor.
The movement of the TT443 Transtrack is by diesel engine, complete with dog-lead remote control. When the unit is in position, the diesel engine is shut off and the conveyor belt receives its power from a generator installed on the MC 122. This greatly reduces the operating costs and fuel consumption of the TT443, which has an output of 400 tph.
The TS 624 tracked telescopic conveyor, which can create a conical stockpile up to 1400 tonnes high, further increases the flexibility of the operations. It feeds directly into the large hopper onto the overland conveyor into the screening plant. The combination of the mobility and telescopic feature of this unit allows increased flexibility for the operator as the inner conveyor can be easily extended or retracted depending on the position of the conveyor or crusher.
The TS 624’s features minimise set-up time and increase production rates. Using this unit at the discharge point ensures the operator can move it easily without disrupting the TT443, the crusher or the excavator, which in turn reduces labour costs.
Since the installation of the units, the operator has reduced its reliance on the wheel loader. The haulage of the material with the loader has been entirely eliminated and allowed it to be deployed in other parts of the quarry as required.
Penryn Quarry estimates that with the new conveyor system, it has been able to reduce production, labour, costs and handling of the material and increase its production rates up to 400 tph. Further, the quarry now enjoys more mobility and flexibility within the blast area.
Source: Tricon Equipment