May 22, 2017
Ventilation currently represents around 50% of underground metal mines’ overall energy costs. Producers are looking to go deeper and still remain economic, while also eliminating fine diesel particulate matter from the underground work environment. Couple these aims with the need to achieve clean-energy targets and it’s clear that there are a myriad of drivers for the introduction of battery-powered vehicles that are engineered for life underground.
“Interest is coming from two sources,” says Jani Vilenius, director of research and technology development, PA Rock Drills and Technologies, at Sandvik Mining and Rock Technology, one of the first OEMs to introduce a battery-propelled drill rig. “Battery technology is being applied more widely in other industries and, for that reason, its applicability in mining is also being questioned, creating a technology push.
“On the other hand, future mining conditions are going to be even tougher than today, creating the need for greener and more efficient technologies. Battery cell production has ramped up in recent years to be ready for the automotive and green-energy industries. The mining industry has acknowledged that an improved work environment with better air quality, plus the application of new battery technologies, may enable an increase in the productivity of underground units, giving the ingredients for a new way of mining.”
Batteries of some sort or design have been around in mining for decades. However, with advances in chemistry and associated technologies such as DC motors and charging technologies, what exists now are batteries that are much more suitable for the underground mining environment.
There are three types currently in use:
• Lead acid;
• Sodium-nickel chloride; and
• Lithium ion: a subcategory that includes lithium iron phosphate (LFP), lithium titanate (LTO) and lithium nickel-manganese-cobalt (NMC).
Each has its strengths and weaknesses based on the specific application.
Traditional lead-acid batteries have been used in mining for a long time, mainly in soft-rock applications such as coal, salt and potash. However, their widespread use has been stunted by their large size and heavy weight, limited energy and power capacity, limited cyclic life of the batteries and questionable safety credentials.
Many modern battery technologies are now still being pilot tested, but others have been accepted by the industry and market interest is increasing. These include different lithium ion (Li-ion) formulations and sodium-nickel chloride technology. Li-ion technologies include several chemistry alternatives; the most attractive for mining applications include LTO, LFP and NMC.
“Fast rechargeable LTO batteries seem favourable for loading and hauling products as they give the possibility for rapid charging, cyclic longevity and superior intrinsic safety features,” explains Vilenius. “Sodium-nickel chloride batteries also seem favourable for mining due to their high safety level and excellent volumetric energy density, providing sufficient operation time and range.”
US-based OEM MacLean Engineering launched its Fleet Electrification programme in 2015, based on NMC battery technology. The effort resulted in three completed builds in 2016—two battery-powered underground Bolters and one battery-powered Boom Truck.
Anthony Griffiths, MacLean’s product manager, explains: “The [NMC] chemistry that we have chosen for powering our fleet has easily doubled and, in some cases, tripled the total life cycle and number of charging cycles that a traditional lead-acid battery can provide.”
Sandvik has two battery technologies in use at the moment. “No single technology can today fulfil the needs of different applications, so application needs to drive technology selection,” says Vilenius.
“However, our number one selection criterion is safety. For applications needing lower power and higher energy-capacity-per-volume, sodium-nickel chemistry is used. For high power, LTO chemistry is used.”
Vilenius acknowledges that there is a continuous need for higher-energy capacity batteries, but no promising solutions are available in the near future. “Battery technology selection is a multivariable question with technical and financial aspects,” he says. “If some of the current high-energy alternatives were chosen, good properties such as safety would be compromised.”
Currently, the vast majority of underground mining equipment is powered by diesel. However, every major miner in the world is evaluating the use of battery-powered machines. Several have projects underway to deploy battery-based equipment for large-scale production operations and these will help drive broader market acceptance. “Mining executives are telling us that they know the industry is moving away from diesel and toward zero-emission equipment for underground use,” says Kasaba. “The tipping point for the entire industry will be driven by success stories from soon-to-be-announced large-scale deployments. “We believe that by 2020 all RFPs [request for proposals] for underground operations will request only zero-emission equipment and any remaining diesel equipment will be phased out soon thereafter.”