3.4 Onsite materials movement

The movement of overburden, ore and waste accounts for a significant proportion of energy use and operating costs on mine sites. Energy consumption is influenced by decisions that are made in mine design and asset selection and procurement and through day-to-day operating practices.

Many energy-efficiency strategies can improve the fuel efficiency of haul trucks through fleet optimisation and upgrades. There are also alternative material movement strategies to complement haul trucks, including in-pit mobile crushers, conveyor systems, overburden slushers, electric draglines, lighter haul trucks and diesel-electric trolley haul trucks. These opportunities are explored in this section.

Haul trucks

Trucks are used to haul overburden and ore from the pit to a dump site or stockpile or to the next stage of a mining process. Their use is scheduled in conjunction with other machinery, such as excavators, loaders and diggers, according to the site layout and production capacity.

Trucks use a significant amount of diesel and are expensive to purchase and maintain. Operating procedures influence energy use and maintenance costs. Truck velocity, especially cornering speeds and braking patterns, and road surface characteristics can affect tyre wear and replacement costs.

Many parameters can affect the efficiency of the fleet, such as:

  • mine plan and mine layout
  • speed, payload and cycle time
  • tyre wear and rolling resistance
  • age and maintenance of the vehicles
  • dump site design
  • idle time
  • engine operating parameters and transmission
  • shift patterns. Footnote 18

The main opportunities for improved energy performance in haul trucks include optimising payload management, implementing improved driver practices, benchmarking performance across the haul truck fleet, improving mine design, purchasing larger haul trucks and lightweighting tray liners, and considering technology options in asset selection and procurement.

Optimising payload management

Payload management ensures that each haul truck carries the optimal tonnage of material to increase fuel efficiency. In some cases, this approach can also reduce the number of trucks needed to complete tasks. The approach that has been taken at the Thiess Australian Mining Business Unit is outlined in Box 10.

Box 10: Optimising payload management at the Thiess Australian Mining Business Unit

Thiess has implemented payload management system improvements that have been estimated to save up to 117,300 GJ and 8,200 tonnes CO2-e of emissions per year across 12 Australian mine sites.

The opportunity to improve fuel efficiency and productivity through payload management was examined and progressed as part of an energy-efficiency assessment. An important part of the assessment was a review of data on payload performance.

The graph below shows the payload distribution for a particular class of dump truck. The payload is measured as the weight of material carried by the truck. If the truck is underloaded, more diesel is needed to transport the total payload. If the truck is overloaded, truck warranties may become void and maintenance costs increase due to additional wear and tear on the vehicle. The graph demonstrates the potential to reduce diesel use by having trucks more frequently loaded to the set target level. This type of analysis was used in the assessment to compare performance across sites and to identify specific actions to be taken on each site to improve energy efficiency.

Graph that shows the payload distribution for a particular class of dump truck

The following key initiatives were identified and implemented across all Thiess’ mining operations:

  • Daily payload data was downloaded and reviewed more frequently.
  • The actual versus targeted payload was communicated to operators more frequently.
  • Supervisors asked truck operators for payload data more frequently.
  • Senior management regularly reviewed payload performance.

The availability of timely and accurate data, clearly articulated targets and ongoing feedback have been central to achieving energy-efficiency and productivity improvements through changes to payload management.

Source: Department of Industry, Thiess’ Australian Mining Business Unit, Canberra, 2009, http://eex.gov.au/files/2014/06/Thiess-Australian-Mining-Business-Unit.pdf.

Implementing improved driver practices

improved driver practices, or eco-driving, refers to a system of driving in which the driver achieves optimal fuel economy. The system incorporates a range of driving behaviours, such as smoother driving (gentle acceleration and braking) and driving more slowly with less idling. The approach to operator training that has been adopted by Downer EDI Mining is outlined in Box 11.

Box 11: Downer EDI Mining: Operator training program

Operator training was identified as a potential energy-efficiency project during site-based workshops conducted as part of Downer EDI Mining’s assessments for the Energy Efficiency Opportunity program. The team reviewed proposals from a number of companies offering driver training services. Considerations that were taken into account included each company’s training approach, delivery mechanism, cost and alignment with the Downer EDI Mining company culture.

Individual meetings were held with personnel at the site level to obtain their support and to understand any concerns they may have had about the project. The benefits that the project could deliver were clearly communicated and linked to the priorities of each individual. They included

  • reducing fuel and maintenance costs—of primary interest to senior site managers
  • prolonging engine and tyre life—which appealed to the workshop and maintenance staff
  • greenhouse gas reductions and safety benefits—a priority for health, safety and environment representatives
  • the opportunity to promote the benefits of training—relevant to learning and development staff.

For the drivers, a key message was that ‘being hard on trucks is being hard on yourselves’.

Care was taken in setting up a trial and evaluating the outcomes to ensure that the findings were reliable, credible and consistent. Site management identified a number of concerns early in the trial. One was that reducing the speed at which trucks were driven would have an impact on productivity. No impact on productivity was found, but concerns such as these highlighted the importance of conducting the trial rigorously.

The project has been integrated into Downer EDI Mining’s equipment simulator training program and is delivering a fuel saving of approximately 2%. Many of the other benefits, including for maintenance and servicing, are still being evaluated. The training is being progressively rolled out to other mine operations through the learning and development department.

Source: Department of Industry, Business Case and Beyond case studies, http://eex.gov.au/case-study/downer-edi-mining-approach-to-energy-efficiency/.

Benchmarking performance across the haul truck fleet

Benchmarking provides a means to measure and identify best practices within a single organisation or across multiple organisations. Many variables can affect haul trucks’ energy efficiency, so simplistic performance indicators, such as litres of diesel per tonne moved, are often too blunt to provide useful insights into the factors that drive efficiency because they do not account for factors such as the distance travelled, the payload per cycle or other characteristics of an individual hauling task.

Calculations of theoretical energy efficiency might not reflect the level of performance that can realistically be achieved but can be a useful tool to track improvements in energy efficiency. The development of relevant theoretical benchmarks provides organisations with a practical energy-efficiency measurement tool that quantifies best practice and highlights areas where improvements can be made. The approach that Leighton Contractors adopted to address these challenges is described in Box 12.

Box 12: Application of the best truck ratio model at Leighton Contractors

Leighton Contractors developed a ‘best truck ratio’ (BTR) model to evaluate and benchmark the efficiency of fleet operations across a single site and multiple operations where the nature of the work varied greatly. The model provides an indication of how efficient Leighton’s fleet is in comparison with what is practically and realistically possible. It is providing a rigorous analytical tool that Leighton is using to support decision-making.

One of the factors that can affect the fuel consumption of haul trucks is the type and condition of the haul road. The figure below illustrates the use of the BTR model to analyse how road condition can change the rolling resistance of the haul trucks. A dry and hard-packed haul road keeps fuel costs and tyre wear to a minimum. Wet conditions can increase the rolling resistance experienced by the vehicle. In moving 20 million tonnes over a specific path, the BTR indicates that a wet hau road will result in the consumption of an additional 820,000 litres of diesel. This analysis can help fleet managers to determine the optimal use of haul trucks in wet conditions and can inform decisions on road design and maintenance.

Illustration that shows the use of the best truck ratio model

Source: Department of Industry, Analyses of diesel use for mine haul and transport operations, http://eex.gov.au/files/2014/06/Analyses-of-Diesel-Use-for-Mine-Haul-and-Transport-Operations.pdf.

Mine design

Many different factors influence mine design, and considerable effort is made to ensure that a site layout maximises productivity. Design decisions influence the initial location of haul roads, processing plant, dumps and transportation assets such as conveyors. Mine design is dynamic, and decisions are made throughout the life of the mine. An example that demonstrates the influence of the location of haul roads is outlined in Box 13.

Box 13: Minimising energy costs by reducing haul truck stops at the Fortescue Metals Group

As part of an energy-efficiency assessment at its Cloudbreak and Christmas Creek sites in the Western Australian Pilbara region, Fortescue Metals Group identified an opportunity to review the haul road design to enable trucks to achieve and maintain an optimal trip speed. A considerable fuel saving would result if the road design could allow the removal of stop signs, where that did not compromise safety.

The truck manufacturers were asked to do modelling for a fully loaded truck to accelerate from stationary for 100 metres and to advise the final speed at that distance. They were also asked to model the same truck operating at this same final speed, but using that speed for a distance of 1,000 metres, so that the steady-state fuel consumption could be calculated. In this way, the fuel saving as a result of the truck not having to stop was the difference between the two scenarios.

Evaluation of this opportunity revealed that Caterpillar 777 haul trucks could save an estimated 361 kL/year and Terex 3700 AC haul trucks could save 407 kL/year for each stop-sign intersection removed.

Source: Fortescue Metals Group—Opportunity F, EEO Opportunities Register, 2011, http://eex.gov.au/opportunities-register/fortescue-metals-group-ltd-opportunity-f/.

Purchasing larger haul trucks and lightweighting tray liners

Using larger haul trucks will typically reduce the number of trucks in a circuit and the amount of fuel needed to move equivalent tonnages. Similar outcomes can be achieved by lightweighting tray liners. These improvement options are illustrated in Box 14 and Box 15.

Box 14: Increasing the size of haul trucks at Homestead mine

The Homestead mine is owned by Norton Gold Fields Limited and is 35 km north-east of Kalgoorlie in Western Australia. Underground mining at Homestead was undertaken with underground trucks whose capacity was limited to 40 tonnes per load.

During the contract, the opportunity to increase to trucks capable of carrying 50 tonnes per load with similar burn rates was investigated and ultimately implemented for an estimated energy cost saving of $25,000/year.

Source: Norton Gold Fields Ltd—Opportunity B, EEO Opportunities Register, http://eex.gov.au/opportunities-register/norton-gold-fields-ltd-opportunity-b/.

Box 15: Reducing the weight of dump truck trays at Rio Tinto

Dump truck trays that are used across Rio Tinto mine sites are fitted with heavy-duty wear plates to make them last longer. Mine maintenance staff involved in an energy-efficiency assessment observed uneven wear in the tray liners. The trays have now been redesigned using thinner plate in low-wear sections. This has resulted in a weight reduction of approximately 10 tonnes/tray without affecting the trays’ longevity.

The benefits of this project are reduced diesel usage, reduced maintenance costs and increased payload capacity. The new tray liners will be progressively installed as new liners are needed. It is expected that an average 3.4% reduction in overall tray weight will be achieved.

Source: Rio Tinto Ltd—Opportunity K, EEO Opportunities Register, http://eex.gov.au/opportunities-register/rio-tinto-ltd-opportunity-k/.

Asset selection and procurement

Decisions on the selection and procurement of mine transportation options can significantly influence the energy intensity of mine operations. Some of the key improvement opportunities are as follows:

  • Use trolley trucks that use tram power lines to access or feed in electricity to enable energy to be recovered as the trolley trucks descend back into the mine.
  • ln-pit crushing conveyor (IPCC) systems are the most energy-efficient systems for hauling ore, overburden and waste from open-cut mines. Footnote 19 Innovations in IPCC system technologies in the past decade have resulted in IPCC systems being used at most types of open-cut mines. However, IPCC systems have significantly larger up-front costs compared to haul trucks.
  • Overburden slushers can be used instead of electric draglines. Slushers use two winches, one on each side of the open cut, to drag a large bucket across the overburden, then to the top of the mine. Existing draglines can be converted.
  • Use lightweight hybrid diesel-electric trucks, which are more fuel efficient and can recover energy through regenerative braking on descent into a mine.
  • Conveyor belt systems have been shown to be significantly more energy efficient in transporting materials than haul trucks, using about 20% of the energy required by heavy-duty trucks. Footnote 20 There is also scope to improve their performance through optimisation using simulation models and improved monitoring and management, as outlined in Box 16.

Box 16: Reducing conveyors’ run time at Port Hedland—Fortescue Metals Group Ltd

Conveyors at Port Hedland carry ore from train unloaders to stockpile stackers and then from stockpile recovery equipment out to ship loaders. During the port operations, conveyors would be left running with no load for long periods for a number of reasons, some necessary and some not.

It was suggested that conveyors should be limited to a period of 30 minutes running unloaded before being automatically shut down. Maintenance requirements can override this programming rule if necessary.

The port operations team agreed and implemented program changes that limit the unmanaged :no-load’ running periods. The port has several train unloader - conveyor circuits and several ship loading conveyor circuits, so the conveying system is designed into a set of ‘routes’ through the multitude of conveyor paths in the port. Any conveyor running unloaded that is not part of a scheduled route shut down after a very short controlled time. Conveyor segments within a scheduled route are allowed to run a little longer unloaded before they, too, are shut down by the program.

It is estimated that this project will deliver annual energy savings of $126,864/year at an investment return of less than two years.

Source: Fortescue Metals Group—Opportunity I, EEO Opportunities Register, http://eex.gov.au/opportunities-register/fortescue-metals-group-ltd-opportunity-i/.


Footnote 18
Department of Industry, Analyses of diesel use for mine haul and transport operations, Canberra, 2013, http://eex.gov.au/files/2014/06/Analyses-of-Diesel-Use-for-Mine-Haul-and-Transport-Operations.pdf.

Return to footnote 18 referrer

Footnote 19
D Tutton, W Streck, The application of in-pit crushing and conveying in large hard rock open pit mines, Independent Consultant Mining Engineers Germany 2009.

Return to footnote 19 referrer

Footnote 20
‘340 million tons of good reasons for climate protection’, ContiTech News, 2012.

Return to footnote 20 referrer

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