School of Mechanical & Mining Engineering

The majority of open pit mines in Australia currently operate using discontinuous shovel/truck systems. These systems are favoured as they enable; (i) mining capacity to be progressively scaled up over the life of a mine; (ii) the use of narrow benches that defer the high costs of stripping, and (iii) flexibility to rapidly adapt mine plans in the face of uncertainties caused by changing commodity prices or unexpected variability in ore grades. However, shovel/truck systems are labour intensive and depend on international prices of inputs such as fuel and tyres. In recent years, a number of mining companies have turned to continuous mining systems. This include FMG in the Pilbara, where continuous mining machines having rotating drums fitted with picks are used to mine iron ore, and BMA and Rio Tinto in the Bowen Basin where in-pit-crusher conveyors are used to transport overburden.
 
In-Pit Crusher Conveyor (IPCC) systems use shovels or hydraulic excavators to load a small fleet of trucks or to directly load a mobile (or semi-mobile) crusher station located within the mine pit. Crushed material is then transported via an overland conveyor or grasshopper conveyors to its final destination. IPCC systems offer higher productivity since they require fewer operators and maintenance personnel. They also offer a significantly reduced carbon footprint since electrically powered conveyors are inherently more efficient than trucks at transporting material.      
 
Given their promise, why are not more mining companies seriously examining IPCC systems? The University of Queensland have identified a number of barriers to implementation. These include:
 
  • Orebody characteristics: The hardness of waste rock associated with an orebody determines the type of crusher that should be applied. Hardrock mines require larger, heavier gyratory crushers, whereas soft rock applications are better suited to lighter weight sizers. These latter are better suited to mobile applications. The geometry of the orebody is also an important factor. Coal and iron ore, for example, typically occur in shallow-dipping stratified deposits. Thus mining benches can be designed to be long and straight, facilitating the use of an overland conveyor and minimising expensive crusher repositions. Deep gold and copper applications, however, require a high vertical rate of mining that in turn require crusher repositioning to be more frequent.  
  • Operational reliability: A shovel/truck system has an inherent level of redundancy. If one unit is out of service, the mine will not lose all production. IPCC systems, however, can be viewed as series-connected systems. If one element is out of service, the mine loses total production. In addition, stoppages do not just occur for reasons of maintenance. Many operational delays also result in loss of production. The criticality of IPCC components means that a different philosophy needs to be adopted towards maintenance and operations. Activities need to be planned according to a “campaign” strategy, whereby a “mini-shutdowns are programmed at regular intervals to perform all necessary maintenance and inspections. 
  • High capital cost: Currently, IPCC systems are application specific. As such, they are engineered and constructed for a specific purpose. Engineering, procurement, construction and management (EPCM) processes are expensive, and mining companies would like to be able to purchase system components off-the-shelf. In addition, in the early years of a mine’s life, stripping ratios are typically lower and less mining capacity is required. A mine does not want to over-invest in capacity in the early years of operation.   
  • Mine planning: Direct shovel loading of mobile IPCCs can require a large amount of real estate resulting in wide benches. This has the effect of decreasing the effective working angle pit walls and increasing the smallest mining unit (SMU), the minimum block size to be mined. The former has the effect of bringing forward stripping costs, whilst the latter is detrimental if there is variability in ore grades that will effectively reduce head grade or metallurgical recovery. In addition, application of semi-mobile crushers requires crusher stations to be constructed at different depth intervals of a mine. In effect, this requires a mining approach that can be described as “deep-then-wide”, whereby the mine must first excavate a deep slot in order to provide sufficient time for construction of the next crusher station, followed by mining out horizontal benches to the pit limit. This approach is often non-optimal when calculating the net present value of discounted cash flows.

Associated Research Centre

CRCMining

Staff

Professor Peter Knights
Professor Ross McAree
Associate Professor Mehmet Kizil
Dr Micah Nehring

For further information please contact Professor Peter Knights.


Current Research

So what research is The University of Queensland conducting related to IPCC systems for surface mines? The School of Mechanical and Mining Engineering is growing a critical mass of researchers in this area. Our work can be classified as follows: 

Shovel/IPCC loading simulation: Prof Ross McAree and his colleagues in the Smart Machines Group have conducted a number of studies investigating automated loading by shovels to mobile IPCC systems. Prof. Knights and his team have also conducted computer simulations to estimate the productivity of dragline-hopper-crusher systems.

Systems selection for deep gold operations: Mr Munirud Dean, a PhD student, is currently investigating the suitability of IPCC systems for deep gold applications. His approach revolves around the development of a two-stage filtering process consisting of a “coarse” filter to reject alternative designs and a “fine” filter that seeks to model the financial impact of remaining alternatives in more detail.

Mine planning: A mining student is currently investigating the Net Present Value impact of adopting “deep-then-wide” strategies for repositioning crusher stations in deep open pit gold operations for his final year honours project.

Operational reliability: Mr Juan Londono used reliability software to model the availability and utilisation of IPCC systems having a redundant, parallel conveyor and stacker system. The study was conducted for a surface coal mine in Central Queensland and indicated an increase in systems availability of between 9 - 12%.  Another mechanical engineering student recently completed his final year project analysing transfer chute design for the Clermont IPCC system. Work is also underway by an international student project to investigate the feasibility of applying a “campaign” maintenance strategy to mobile equipment.

In addition, two students with extensive industry experience will shortly commence research higher degree studies related to IPCC systems. One study will investigate IPCC systems for stripping coal overburden and the other will examine transition points between shovel/truck and IPCC operations in deep pit.