Electric power can offer important energy efficiency and environmental benefits over diesel engines in mining applications
By Len Eros
The mining industry has generally taken a conservative approach to the adoption of new technologies. But the many advantages of electric power, combined with the desire of many mine and quarry operators to achieve “zero emission” operations, is driving the development of a new generation of battery electric trucks, front end loaders, drill rigs and excavators.
These new generation battery electric vehicles (BEVs) are adopting even smarter and more advanced technology to make the transition from hybrid diesel-electric designs toward fully electric battery-driven derivatives.
Smarter converters, more compact motors, and more advanced batteries are bringing the performance of electric vehicles up to the level of their diesel counterparts, and in some areas are even surpassing them. Moreover, while diesel engines are the traditional standard for robust mining conditions, reducing the use of diesel fuel could have significant cost benefits for the industry. Currently as much as 40% of an underground mine’s energy outlay is spent on powering enormous ventilation systems that are designed to remove airborne contaminates such as dust, gases and heat, and to supply clean air. When diesel engine heat and exhaust contaminants are added to the mine atmosphere, the ventilation requirements go up and ventilation costs are significantly increased.
In addition to energy efficiency, environmental concerns are another important driver. In Australia, a new report by corporate consultants BDO predicts that within five years, diesel machinery will not be used in new underground mines, and existing underground mines will have begun to phase them out. According to BDO, this push will come from the financiers of new mines and potentially from government bodies too, who may even choose to ban diesel machines from new underground mines because of the health issues.
In contrast to diesel, using regenerative drives and electric motors can help mine operators achieve a reduction in their energy consumption, heat and gas emissions, and ventilation requirements. BEVs increase energy efficiency by using regenerative braking to convert kinetic energy, during deacceleration, and potential energy, when controlling downhill speed, into electrical energy, which is then stored in the batteries.
Furthermore, the efficiency of using electric energy to power equipment is much higher than the efficiency from using diesel, so the amount of heat that an electric vehicle produces is much less. Diesel engines can, at best, achieve around 45% efficiency, whereas electric powertrains can reach energy efficiency of 90% or more with relative ease. The result is a 30% to 50% reduction in the load the mobile equipment is putting on the ventilation system resulting in lower energy costs.
This makes BEVs especially suitable for deep mines where there are high ground temperatures and the working areas can be difficult to ventilate because of their extreme distance from the main fans. In these applications, the added heat load from a diesel-powered machine makes it difficult to mechanize the mining process without increasing the ventilation requirements. Using a BEV with much lower heat emissions can make mechanization feasible, creating a safer work environment without increased ventilation costs.
The conversion of diesel-powered vehicles to battery powered is well proven in many other industrial markets and has been shown to provide numerous benefits. In many cities around the world, battery-powered buses utilizing rapid charging systems are replacing diesel-powered buses. The reduced CO2 footprint lowered maintenance and power costs and increased user satisfaction continues to drive this conversion. In the automotive industry, the switch to EVs is in the early stages, but it is evident that it is gaining significant traction on a global level. The experience gained in these markets is directly applicable to the mining community and their conversion from diesel to BEVs.
These advances all drive down capital and operational expenditures, providing a substantial return on investment. Safety is also improved through increased mechanization as well as the removal of flammable diesel fuel from underground. At the same time, the health of those working in the mines is improved by the absence of diesel exhaust emissions.
Charging Power and Underground Infrastructure
Maintaining the battery energy levels in BEVs during operation is done either by battery pack swapping or by fast charging systems. For example, with load haul dump vehicles (LHDS), battery pack swapping has been successful when there is not time in the duty cycle for stopping to fast charge. An example of where fast charging is working well is an electric drill rig, which uses battery power to travel between work locations and then uses the in-place electrical grid power for drilling and recharging. Which of these battery charging methods is selected depends on the application as well as OEM preference, but both are being used successfully.
Currently, one of the most important considerations is the charging infrastructure. The ultimate objective is to make recharging and operating battery electric vehicles as simple and convenient as refueling and operating diesel vehicles. Because modern methods of underground mining require high levels of electrical power in the working areas, it’s possible to locate BEV charging stations close to the vehicles. But without careful consideration, it would be easy to end up with an array of incompatible charging stations throughout the mine.
In a recent development to meet the demands of particularly large mining vehicles, ABB is participating in defining a new combined charging system (CCS) standard in collaboration with automakers and other stakeholders as part of the Charging Interface Initiative (CharIN), the alliance that defines CCS charging standards. This will take charging capability up to 1 MW and even 2 MW.
Torque and Maintenance of BEVs
The electric drive is the core of the BEV propulsion system and enables sophisticated control of the vehicle. Advanced drives specifically designed for mobile equipment applications, such as ABB’s HES880, monitor wheel speed and closely regulate the torque transmitted by the drive wheels. The speed and torque control reduce wheel spin under adverse conditions and provide improved vehicle traction. When tire slip is eliminated the vehicle becomes easier to control and safer to operate. And there are significant cost savings when excessive tire wear is eliminated.
Many BEVs are designed without drive train gearboxes as they produce the required torque with the motors directly powering the drive wheels. Eliminating the gearboxes traditionally used in diesel-powered vehicles provides another reduction in maintenance and operating costs.
A BEV provides the opportunity to decouple the vehicle drive train from the hydraulic system. On diesel-powered vehicles the hydraulics are powered by the engine. But on a BEV, the hydraulics are powered by an electric motor and can be controlled to precisely meet the power demands of the system with resulting higher efficiencies and reduced wear.
Advances in Drives and Motor Design
Along with the converters, the electric motors are also undergoing new developments. Factors such as space limitations, the increasing power demands from larger machines and increasing energy efficiency requirements needed to prolong battery life are all driving motor innovation.
In applications where high power is needed but space is limited, a water-cooled motor can be a good solution. Water-cooled motors and drives are very power dense compared to air cooled, meaning there can be power rating increases of 25% to more than 50% from the same size motor. Both open and closed loop cooling systems are used.
Design improvements that increase motor efficiencies are also in constant development. Benefits from this include extending battery life, reducing motor heat rejection and increasing the power rating without increasing motor size. Permanent magnet (PM) motors are very efficient designs and recent improvements have reduced their cost and improved availability. Challenges exist with PM motors in some mobile equipment applications, but it’s an area of motor design receiving lots of attention.
Social and Environmental Impact
Diesel engines have constant vibration, high ambient temperatures and high noise levels. Electric vehicles (EVs), on the other hand, have significantly less noise and vibration and emit far less heat. These factors make it easier to operate, less fatiguing and less stressful for operators.
Switching to EVs improves the working environment in mines by removing diesel particulate and combustion gas emissions and reducing noise levels. At the same time, safety is improved by removing diesel fuel from the mine. In combination, low emissions, reduced noise and easier operation contribute to a healthier, safer and more pleasant work environment that ultimately helps reduce employee turnover.
To explore the advantages of electrification, in August 2018, Volvo Construction Equipment and its customer Skanska began testing the viability of its Electric Site concept at Skanska’s Vikan Kross quarry, near Gothenburg, Sweden. The system, which incorporates electric and autonomous Volvo machines, ran in a real production environment for 10 weeks — delivering an anticipated 95% reduction in carbon emissions and 25% reduction in total cost of operations.
New Standard for Sustainable Underground Mining
To set a new world standard for sustainable mining at great depth, LKAB, ABB, Epiroc, Combitech and the Volvo Group have joined forces in a partnership to start a unique testbed in the ore fields of northern Sweden. The project is studying the best ways to create an efficient autonomous production system that is both carbon-dioxide-free and with the highest safety levels.
The test bed project is called SUM (sustainable underground mining) and is located in LKAB’s underground mines in Kiruna and Malmberget, Sweden, as well as in a virtual mine. ABB is contributing to this project with solutions for underground electrification and an integrated platform for collaborative operations. The SUM project will lay the foundation for decisions to be made into the mid-2020s for one of Sweden’s largest ever industrial investments.
Optimized Electric Powertrain for Heavy Vehicles
An important new development for ABB is an optimized electric powertrain that enables heavy special and commercial vehicles, and especially mining vehicles, to transition to fully electric operation. The complete e-drivetrain solution includes the key elements — motor, drive and vehicle control unit — harmonized for maximum performance, reliability and energy efficiency. This approach enables ABB to work alongside vehicle OEMs to design a drive train that suits their specific application needs.
One of several customers to adopt this optimized electric powertrain is Epiroc, one of the world’s leading suppliers of underground mining and infrastructure equipment. A number of Epiroc’s second-generation battery-powered vehicles are using an ABB electric powertrain, including electric motors and HES880 Mobile Drives, for propulsion and auxiliary applications.
Many OEMs face the challenge that their drive-cycle and performance requirements vary greatly between applications such as drilling, loading and transporting materials. This can make it difficult for designers to identify the best choice in electric powertrains for their specific application. An over-specified e-drivetrain may cost more than necessary and carry a weight penalty. While an under-specified electric powertrain may not deliver the required power, could overheat and as a result will be unreliable with a reduced service life. When the OEM works with a single manufacture like ABB that provides a complete electric powertrain, there is a fast-track route to a solution that delivers both performance and total cost of ownership.
The electric mining vehicle revolution started to take off in 2016. The move to autonomous vehicles in both surface and underground mining operations is made much easier with BEVs whose control systems are highly compatible with autonomous vehicle control systems. The momentum will clearly continue to build as the energy-efficiency, environmental, financial and social benefits of electric power become ever more persuasive
Len Eros is the global mining manager for ABB Motion.