The road to energy savings
With fuel being the biggest operating cost in the mining industry, finding greater energy efficiencies is critical for improved productivity. Twenty-five per cent of Australia’s diesel is consumed by the mining industry, mostly for electricity generation and powering the heavy machinery involved in material transportation.
Haul trucks (often over-sized mega-trucks) are used to move overburden and ore from the pit to a stockpile or processing stage, or to a haul-train for further transportation by rail.
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, braking patterns and road surface characteristics all affect tyre wear and replacement costs.
In open-cut mining, many factors affect the efficiency of the fleet:
- mine plan and 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.
Various measures can be put in place to address these factors and optimise hauling efficiency in existing truck fleets and mines:
Manage payload levels. This ensures that each haul truck carries the optimum load size to increase fuel efficiency. In some cases, this approach can also reduce the number of trucks required to complete tasks. For example, Thiess put in payload management systems which brought energy efficiencies that save up to 117,300 GJ and 8200 tCO2e (tonnes of CO2 equivalent) emissions per year.
Improve driver practices. The ‘eco-driving’ system incorporates a range of techniques such as smoother driving and driving more slowly with less idling. Fortescue Metals Group quantified the energy costs associated with stopping haul trucks unnecessarily, which equated to 361 kL (13,935 GJ) of diesel per annum for its Caterpillar 777 fleet and 407 kL (15,710 GJ) of diesel per annum for its Terex 3700 AC fleet for a single stop-sign-per-payload cycle.
Use larger haul trucks, where appropriate. Jellinbah Resources Pty Ltd operates the Jellinbah East Mine in the Bowen Basin of central Queensland. The purchase of larger coal trucks will reduce the number of vehicles in a circuit. This will lower the number of trips to the pit, cutting fuel use by almost 152,000 L or around 5,860 GJ per year.
Measure and analyse haul truck energy use. Downer EDI Mining developed performance indicators that use an equivalent flat haul calculation to account for elevation changes on a specific mine route. The indicators provide a more consistent measure of true energy performance, enabling the company to track energy intensity over time. The Commodore open-cut coal mine in southeast Queensland has been used as the pilot site for energy efficiency improvements. Energy intensity of the mine improved by 18.2% over five years.
Benchmark and compare performance. Leighton Contractors developed a best-truck ratio model to evaluate and benchmark the efficiency of fleet operations across a single site and multiple operations, where the nature of the work undertaken varied greatly. This model provides a rigorous analytical tool which Leighton is using to support the decision-making processes.
Consider energy efficiency when upgrading haulage systems
Although larger haul trucks reduce the number of trips required, there are other situations where smaller vehicles will be more suitable. For example, lightweight hybrid diesel-electric trucks are more fuel efficient and can recover energy through regenerative braking on descent into a mine.
Trolley trucks are vehicles which use tram power-lines to access or feed in electricity which can be recovered as they descend back into the mine. Rio Tinto at Rössing Uranium in Namibia has invested in an overhead wire system for haul trucks with diesel-electric units that can draw power like a trolley bus. This dramatically reduces fuel consumption, with a payload of 182 t down from 350 L an hour to 25 L an hour. Although it consumes electricity, overall energy savings of up to 30% can be achieved.
Complementing haul trucks with other systems
It’s worth considering some of the other less fuel-intensive methods available for onsite mineral transportation:
Conveyor belt systems. These 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. There is also scope to improve their performance through optimisation using simulation models and improved monitoring and management.
In-pit-crushing-conveyor (IPCC) systems. These are the most energy efficient means of hauling ore, overburden and waste from open-cut mines. IPCC systems do have significantly larger upfront costs however compared to haul trucks, but technological advances in the last decade have brought IPCC systems into widespread use in today’s open-cut mining operations.
Improve the efficiency of existing draglines. Electric motors can be upgraded, the ropes and motors strengthened and the bucket and rigging configuration revised to decrease the weight of the system whilst increasing the weight it can carry.
Overburden slushers to replace electric draglines. An overburden slusher uses two winches, one on each side of the open cut, to drag a large bucket across overburden, then to the top of a mine. Existing draglines can be converted to this method.
Conveyor belts. Across horizontal distances, and where practical, conveyor belts are significantly more energy efficient than trucking on gravel roads.
For much more information on energy efficiency practices available to the industry, see the Opportunities - Mining page.