The electric dream
If you’ve been following the news in the mining industry recently, you would have noticed the growing number of announcements about investment by mining companies and suppliers in battery-electric vehicles, particularly for underground mines. For example, BHP is trialling Voltra eCruisers—a battery-converted Toyota Landcruiser—at Olympic Dam, Nouveau Monde Graphite in Canada is moving towards a fully-electric mine, and the new Artisan 40t battery-electric underground hauler is being trialled at Kirkland Lake Gold Mine in Ontario, also in Canada. A number of mines are successfully using trolley-assisted (pantograph) haulers—but such systems limit the flexibility of the haulage system and require fixed infrastructure.
This renewed focus on battery-electric haulage is not surprising considering the billions of dollars of investment going into battery-electric cars, buses, and trucks in the automotive industry; the rapid improvements in the batteries themselves; and the potential for significant savings from electric haulage through reduction in emissions (hence ventilation costs), shorter haul-cycle times (through lighter, constant torque, electric drive units), and significant reduction in maintenance and energy costs (an electric car has around 20 moving parts in the drive chain compared to over 2000 in an internal combustion car).
Mining3 has been actively researching electric haulage for the mining industry for a number of years. One of the major shortfalls for battery technology in mining applications is the need to operate equipment on a 24/7 basis. Combined with the high energy demand and energy density of batteries (constraining space and weight), batteries either need to be swapped out quickly and regularly or somehow re-charged ‘on-the-fly’ if they are to become practical for mining operations.
Attempts to create swappable battery packs for load, haul, dump vehicles (LHDs) have led to occupational health and safety and battery-pack management issues. Perhaps this is one reason why early proposals by car manufacturers to do the same for electric cars have failed to gain acceptance. So, the other obvious path for the mining industry is to develop methods to quickly charge electric vehicles on-the-fly.
The public transport industry has been leading the push and development of wireless charging systems. These systems are based on the principle of resonant inductive coupling where a primary coil—located under the road surface and supplied with a high-frequency power source—transfers power to a secondary coil mounted under the chassis of the above vehicle. The two coils form part of tuned circuits such that energy is induced from the primary coil to the secondary coil. The efficiency of energy transfer in commercial installations is reported between 80-85 per cent at distances between coils of up to 40cm.
Recently, Mining3 has been exploring a novel transportation system based on small, 15t capacity, autonomous electric haulers that are powered and recharged via a wireless power system embedded in the haul road along the route of the haulers. The system is designed to provide the flexibility of conventional haul trucks and the efficiency of belt conveyors.
Preliminary economic analysis which considered capital and operating costs over a 15-year period indicated a 35 per cent decrease in cost per tonne using for a 16Mtpa operation compared to a conventional truck haulage operation. The cost reduction was due to the combined effect of a 45 per cent saving in energy cost, a 60 per cent reduction in labour cost, and a 30 per cent reduction in maintenance cost. The capital cost was however 5 per cent higher than the conventional truck haulage case with the same modelling parameters.
A further case study of the impact on pit design using smaller footprint trucks capable of driving up steeper ramps also indicated a 23 per cent increase in resource utilisation over the design using conventional 90t-class trucks.
Our studies are indicating that, for some types of mining operations (both underground and open pit), smaller can be better and wireless power has the potential to enable this.
Putting some meat onto the bones of an idea, a proof-of-concept autonomous electric hauler was constructed by five Bachelor of Engineering (Honours)/Master of Engineering (BE (Hons)/ME) University of Queensland students in the first half of 2018 during their semester-long industry placement*. The students were given some guidelines for the design but the freedom to explore and innovate. The Mining3 team was really proud that the students were able to work together as a self-driven team, presenting and demonstrating an induction-powered autonomous 100kg hauler at a recent Mining3 Members technical meeting. The ‘baby’ hauler is now being used to explore different configurations of relocatable, induction power transfer systems, and testing against theoretical models.
We’re fortunate that a lot of investment already exists in the automotive industry to improve battery, induction, and drive-chain technologies. The mining industry can leverage from this. Mining3 research will continue on developing a flexible, economically viable, inductive coupling system to suit mining operations.
The dream may indeed be a reality in the near future.