Larger quarries are increasingly looking for economical solutions to transporting aggregates from the face to the crushing circuit. A proposed curved rail running conveyor may yet provide an alternative to conventional transport by dump trucks and off-road vehicles.
Innovative operators in the quarrying business are constantly adapting to overcome the lean operating margins and environmental constraints at their sites. Now a new conveying technology from thyssenkrupp and the University of Newcastle relieves familiar challenges faced by larger quarry operations, including:
- Costly truck haulage from the face to the plant, especially where there is substantial elevation change.
- Concerns about diesel and dust emissions.
- Fugitive dust from conveyor transfer points.
- Mine layouts that are awkward or unfeasible for conventional trough conveyors.
This new belt conveying technology allows a conveyor to run in a single flight from pit to plant along the curve of the haul road, hairpins excepted. For many pit layouts where the haul road curve radii can be configured to about 100m or greater, mines will be able to run haul trucks adjacent to the conveying corridor, allowing for the flexibility of truck haulage alongside the extremely low cost per tonne of belt conveying.
The payback time for replacing the truck haulage by the curved conveyor can be less than a year in some cases, according to estimates by thyssenkrupp. Those estimates include the operating cost of feeding the conveyor from a mobile primary crusher sizing down to perhaps minus 200mm.
Rail running conveyor
This new type of curved conveyor is a “pipe conveyor” version of the “Rail Running Conveyor” (or RRC) technology now being commercialised in Australia under an exclusive agreement between thyssenkrupp and the University of Newcastle. The product is part of a new “platform technology” that combines the efficiency of rail transport with the continuous nature of belt conveying, and promises a “revolution” in overland, steep angle and pipe conveying, according to Luke Bennett, the national sales manager for strategic accounts at thyssenkrupp Industrial Solutions Australia.
The pipe conveyor version of the system is now ready to be deployed in a pilot installation at a quarry, ideally carrying the full output from a large tracked jaw crusher for a distance of up to one kilometre or through an elevation change of 50m to 100m. For this technology, testing and analysis point to:
- Capital expenditure (CAPEX) being about the same as a conventional trough conveyor of similar length, lift
and tonnage, and less than half of that for a conventional pipe conveyor in the same duty.
- Power consumption being about 40 per cent lower than a conventional pipe conveyor, even though most of the power requirement for the example above is needed for lifting the rock.
- Lower maintenance costs, because the transport mode eliminates almost all of the maintenance effort associated with the idlers, belt tracking and carry-back.
For some mine layouts, a planner might be considering costly trough conveyors on an elevated structure, such as that visible in the Google Earth image of a haulage route in a large limestone quarry (Figure 1). Due to the Rail Running Conveyor’s ability to negotiate very tight curves, the material could be carried by either trough or pipe RRC versions along the haul road, on a path indicated by the blue line. Even though the length of the RRC is greater than the direct, elevated route, the CAPEX cost per metre as well as the much lower maintenance intensity makes the curved RRC the lowest cost choice by far.
The RRC technology has been carefully developed over nearly a decade by TUNRA Bulk Solids at the University of Newcastle, and is covered by a number of international patents. Contemporaneously, thyssenkrupp’s heavy duty conveyor group created designs based on similar principles, and now the University of Newcastle and thyssenkrupp are collaborating to bring this product family to the industrial minerals industry.
To put this technology in context, it is worth remembering that conventional belt conveyors are constrained by well known inherent limitations, including:
- Intermediate transfer points, with their high maintenance requirements, which are often unavoidable because of limited horizontal and vertical curvability. Rail running pipe conveyors can curve much more tightly than conventional pipe conveyors, allowing transfer points to be eliminated in many cases.
- Idler rolls that are subject to multiple modes of failure all along the length of the conveyor. The failing idlers must be detected and replaced wherever they happen to be. Conventional pipe conveyors typically have more than twice as many idler rolls as a trough conveyor, increasing the idler-related maintenance demands.
- Energy loss that is caused by the belt/idler interaction which consumes as much as 50 per cent of the power, even in plant-scale pipe conveyors.
- Belt speed that is limited by several factors related to the fixed idlers, which drives up belt width and strength requirements.
“The Rail Running Conveyor system overcomes these limitations, allowing breakthrough performance improvements in each of these areas,” Martin Lurie, thyssenkrupp’s product lifecycle manager for rail running conveyors, said.
Figure 1. A Google Earth image of a haul road in a large limestone quarry. Material could be carried by either trough or pipe RRC versions along the haul road, on a path indicated by the blue line.
Benefits of cartage
Operators of large quarries are intimately familiar with the two core technologies that make up RRCs, namely belt conveyors and rail haulage. In RRCs, conventional fixed idlers carry a standard belt in the usual configuration near the head and tail of the conveyor, and the belt itself still carries all the tension. But between the head and tail, the belt rests securely in the cradles of slim, wheeled carts rolling on light rails.
In the trough version of a RRC, the loading point is exactly the same as in a conventional trough conveyor. The loaded belt travels a short distance from the load point by rolling on conventional idlers. Then the wheeled carts glide upwards on their rails to take over the load from the fixed idlers. Similarly – for the pipe belt version – the loading point and pipe formation is the same as a conventional pipe conveyor. For a short distance, the pipe belt moves through conventional pipe conveyor idler panels. Then the carts move up to take over from the fixed idlers. To keep the belt closed in its pipe form, the cradle of each cart has a circular bottom, and every two metres there is a fixed idler that presses down on the belt edge to keep the pipe closed, mounted in a frame above the carts.
Before reaching the head or tail, the cart train turns around independently of the belt, and a light wire rope keeps the carts moving through the turnaround. Automated inspection devices continuously monitor the condition of wheels and bearings at these turnaround locations, where deteriorating bearings or wheels can easily be exchanged. As with conventional rail systems, derailment is a possibility, but carts can be designed to be both resistant to and tolerant of derailments. Low cost automated derailment detection will allow the conveyor to be stopped should a derailment occur.
The very low losses in the RRC systems arise from the highly efficient wheel-on-rail interface. For context, rolling resistance in a haul truck is typically in the two to three per cent range. The measured rolling resistance for RRCs of about 0.4 per cent of the moving weight is comparable to that of light rail transport. This low level of rolling resistance contrasts to the best in class trough conveyors which are typically designed to handle rolling resistances about three times higher – at perhaps 1.2 per cent of the moving weight (DIN f of 0.012) – or to more typical trough conveyors designed to overcome rolling resistances five times higher – at about two (2.0) per cent of the moving weight. Conventional pipe conveyors have still much higher losses than conventional trough conveyors, with those conventional pipe conveyors operating in very cold conditions designed for rolling resistances of perhaps 4.5 per cent, or 10 times higher than a RRC.
An added feature of RRCs is that frictional losses don’t increase in cold operating conditions. This new low resistance paradigm translates directly into substantial CAPEX and operational expenditure (OPEX) savings. The CAPEX savings are due mainly to cost reductions for belt, drives and erection. For example, elevated gantries do not require walkways for idler maintenance, which allows enormous reductions in structural weight. The OPEX benefits come from lower power consumption, smaller maintenance crews, and lower costs from idler monitoring and replacement.
thyssenkrupp’s offices around the world have recently begun exploring suitable trial installations for the trough overland version of the RRC, with notable interest from major Australian mining companies. Now, Australian innovation and tax incentives may be available to industrial minerals and aggregates companies that partner with thyssenkrupp to build a pilot-scale system for demonstrating the pipe version of the RRC technology.
About the authors
Martin S Lurie is the product lifecycle manager for rail running conveyors for thyssenkrupp Industrial Solutions (USA).
Luke Bennett is the national sales manager for strategic accounts at thyssenkrupp Industrial Solutions (Australia).
Prof Craig A Wheeler is based in the School of Engineering (Mechanical Engineering) at the University of Newcastle, New South Wales.