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Technical Application Battery electric vehicles are changing the face of mining
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Battery electric vehicles are changing the face of mining

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Health and cost savings considerations are driving an increasing move towards electric battery-driven vehicles and machinery in underground and opencast mining operations.

Battery powered mining vehicles were introduced in the 1980s, but it is only in recent years that large-scale adoption of the technology is being considered. A recent news report states that the market for underground mining machines is still in the beginning stages of a paradigm shift that will ultimately see battery-powered equipment make its diesel competition obsolete. The tipping point where everyone has decided that, in future, they will use battery-driven zero emissions equipment underground has not yet been reached. It is anticipated that all major mining companies will only purchase zero-emission equipment for underground [4].

Battery technology is ideally suited for underground mining and the speed of adoption will be driven by the mines’ comfort level with the technology and the OEMs’ ability to deliver a solid product that will operate for a full shift [4].

The broad range of benefits driving the battery electric vehicle transition are:

  • Elimination of diesel fine particular matter and other exhaust gas components in the underground environment, requiring less ventilation and therefore lower costs, as well as improved health for miners.
  • The efficiency of conversion from electric energy to wheel drives is much higher than the conversion efficiency from diesel to wheel drive, so the amount of heat that an electric vehicle produces is much less. This results in reduced ventilation requirements (30 to 50% less) and lower associated energy costs.
  • Diesel engines consume air, which increases the ventilation requirement. BEVs do not consume air.
  • Elimination of diesel fuel costs, a variable quantity.
  • Reduced maintenance costs (some 25% fewer parts on EV propulsion versus diesel propulsion systems).
  • Less noise, vibration and heat for miners operating the equipment underground.

In addition to these advantages, there is an increasing move towards automation of mine machinery, and the use of remotely controlled mining robots, which favour the use of electric drives and battery-driven vehicles.

Most underground mining operations currently use diesel-powered trackless mobile machines. BEVs are far more energy efficient than their internal combustion engine counterparts. As an additional benefit, they can further increase efficiency by using regenerative braking to convert kinetic energy into potential energy, which can then be re-used when accelerating. Mining operations could save a considerable amount of their operational expenditure when using electric equipment instead of a diesel-driven fleet [6]. Battery-powered machines, unlike their power cord-tethered or trolley-connected cousins, have an unlimited range of motion, the freedom to work in development areas without outlets, and few exposed fragile parts.

Fig. 1: The battery powered Scooptram (Atlas Copco).

Cost issues

One of the biggest problems with switching from diesel-driven equipment to a new electric fleet is the significant capital investment required. In an economy dealing with lowered commodity prices, this places pressure on new purchases. While most mines have slowed down on their spending, the long-term benefits of investing in a clean, green and modern range of electrically driven underground equipment may outweigh the short-term cash outlay. Directly driven mine machinery (ie power from an AC feed) has advantages, but there is a serious disadvantage in areas where mobility is required. It is these areas specifically where battery driven and hybrid units come to the fore [3].

With the cost of batteries and other storage systems being driven down by other sectors, the cost of converting to BEVs in underground mines is reducing. In addition, the electric vehicle market is developing and producing batteries with increased energy density and of the size and shape suitable for low profile mining traction units. The cost of batteries specifically designed for transport is decreasing rapidly, and charging regimes have been developed which allow rapid recharge of batteries. A further development is the use of hybrid mining propulsion units, which can be adapted to a wide variety of underground operations.

BEV equipment range

Most people are aware of BEVs being used for transport in underground mines, but the range is being expanded to other vehicles and machinery as well. It is estimated that 80% of the fuel burned in an underground mine is burned by loaders or trucks [3]. Since these machines are commonly used in underground mining operations, they were the first obvious choice for conversion to battery operation, and most of the mining BEVs today fall in this category. BEVs are confined to personnel transport, load haul dumpers (LHDs) and trucks, but there are several companies intending to extend the battery-powered option over the full range of equipment powered by diesel engines [5].

Load haul dumpers

Tried and tested, operational and available, battery-powered load haul dumpers (LHDs) primarily face one obstacle to widespread use in underground mining. Both manufacturers and academics say the equipment is largely proven, but its market share will remain limited until the perception improves [4]. A few examples are:

  • Scooptram loader: A front-end loader produced by Atlas Copco. The performance matches that of the company’s diesel-powered version. It is powered by a 165 kWh, 630 V DC LiFePO4 battery.
  • Artisan’s 3-mt 153: This LHD offers a total power of 214 kW. It is powered by a 600 V DC 88 kWh lithium-ion phosphate battery. The unit is claimed to outperform the equivalent sized diesel powered unit.
  • The GE Fairchild: It is powered by a 240 V, 930 Ah (214,8 kWh) battery.

Fig. 2: A battery powered load haul dumper (Artisan).

Battery powered haul trucks

  • GE and others are offering battery powered underground haulage trucks, which are similar to LHDs but are used for ore haulage only.

Battery powered shield haulers

These are used to move heavy shields used in long wall coal mining between sites. There are several suppliers.

Battery tramming: drills and other equipment

Tramming is the movement of machinery from one site to another. Usually accomplished using diesel engines, units using battery-driven motors are now available to perform the function. The battery unit has several other advantages over diesel:

  • The battery can be recharged during drilling.
  • The battery can boost the mine AC supply during drilling.
  • The unit can recharge when tramming downhill.

The Sandvik DD422iE is an example of a battery tramming driller. The unit is powered by a 160 kW battery and is claimed to be more energy efficient than the diesel version.

Personnel carriers (PC)

These are light vehicles designed to transport people and light equipment in the mine. There is a wide variety of battery powered versions, but all are designed for steep gradients and rough roads, and the batteries are required to withstand this type of abuse. The batteries were originally automotive or small industrial types, and required several hours to recharge. More modern designs use LiFePO4 batteries for safety reasons. The PC is not expected to have a high duty cycle and is suited to slow charge methods. Designs may change with the advent of cheaper batteries for normal electric vehicles. The battery-powered mine personnel carrier has been in use for many years.

Future battery powered ranges

MacLean’s fleet electrification programme aims to offer customers a battery tramming/operating option on all units across the company’s product range. GE also aims to produce battery-powered options for all of its diesel-powered mining equipment in the future. It is expected that other mining equipment manufacturers will follow suit.

Fig. 3: The DD422iE tramming driller (Sandvik).

Hybrid solutions

Hybrid diesel/battery electric propulsion systems are quite common in mine vehicles, offering a reduction in fuel consumption as well as better controls over the operation of the vehicle. Most hybrid versions also make use of regenerative energy recovery. There is a wide variety of hybrid configurations in use, making use of both batteries and supercapacitors [7].

Regenerative energy recovery

Regenerative braking is a well-known technique of converting kinetic energy into electricity. In an EV or train, for instance, the movement is slowed down by reversing the motor to act as a generator. Regenerative braking is used extensively in mining BEVs, especially those operating on a fixed route with significant gradients. Where a BEV is operated over a fixed route, the regenerative energy could be calculated accurately, which would allow accurate sizing of the battery and recharge cycles.

Battery technology

Battery-driven mine equipment has been around for almost 30 years. Earlier models used valve regulated lead acid batteries but the technology of choice today seems to be lithium ion phosphate. Technologies in use include:

  • Lead acid: Lead acid industrial batteries are an established technology, mainly the VRLA or valve regulated variety. Advantages are lower cost compared to other technologies, but power density is lower and rapid recharge is usually not possible. The technology is falling out of favour except for smaller applications where weight is not critical.
  • Lithium ion phosphate (LiFePO4): A well-developed technology offering a very rugged battery with a long service life and a reasonably short recharge time. LiFePo4 batteries have the least probability of bursting into flame of all the lithium-based batteries, and are chosen for this reason.
  • Lithium titanate: A high performance battery offering a very short recharge time (15 minutes) and long cycle life. The battery was primarily developed for the mobile battery market, and is offered by one of the suppliers of LHDs. The single-battery quick recharge system removes the need for backup batteries and a dedicated swap, service and recharging area, which reduces cost.
  • Sodium metal halide (NaMx): These batteries are an emerging technology with performance and longevity comparable to those of lithium ion (Li-ion) batteries, yet require less capital. NaMx technology has been considered for mass transit and industrial applications. One supplier uses a proprietary sodium nickel chloride battery.

The biggest concern with BEVs is the capacity of the battery and the ability to work a complete shift without a recharge. Capacities depend on the type of BEV and prospective usage cycle, and range from four to eight hours. With a battery swap-out during the shift break, the four-hour capacity unit could manage an eight-hour shift of continuous operation. Development of batteries is expected to extend this time.

Fig. 4: Sodium nickel chloride battery mounted on an LHD (Saminco).

Charging regimes 

To maintain most units in an operational state requires two sets of batteries: one in the vehicle and one on charge [2]. Units using lead acid (LA) batteries used three sets per BEV, two on the unit (one operational and one spare) and one on charge. This was because LA batteries took eight hours to recharge. More advanced units can recharge in less time than it takes the battery to discharge and only two batteries are required per unit. The charging regime may be adapted if the BEV is not operational on a 24-hour basis.

Onboard charging

In this system, the charger is associated with the BEV, and charge is accomplished by connection to an AC source. The disadvantage of this method is that extra weight is placed on the BEV. This system is used in tramming vehicles where connection to an AC source during operation is available, and where battery swap out is not used.

Offboard charging

In this method, the charger is located at a special charging station and DC is fed to the BEV. The disadvantage is that the BEV is out of service during the charge process. This process only applies to BEVs that run a single shift or multiple shifts with breaks in between, and where swap-out is not anticipated. The battery must be able to power the BEV for the whole shift.

Offboard swap charging

In this method, a spare battery is charged offboard and swapped out with a discharged battery at specific times or at the prompting of a charge monitoring system. The battery must have a discharge time longer than the charge time.

Hybrid charging

This system is a combination of onboard and offboard. The onboard charger is used for slow charging of the battery, and the offboard when a rapid or boost charge is required.

Diesel-free mines

The diesel-free mine option is being considered by several mining companies. Goldcorp, a gold producer based in Vancouver, Canada, recently announced plans to build the world’s first diesel-free hard rock mine near Chapleau, Ontario. Going diesel-free is an ambitious goal. A typical mine can have dozens of diesel engines across its heavy equipment fleet. Going electric means enormous up-front cost, and massive retraining. This means embracing the reality that, until recently, the technology to create a diesel-free mine was barely a realistic possibility, but has been made possible by developments in the battery storage sector [5].

References

[1] L Louw: “Time to go electric” Mining Africa online, 16 May 2017.
[2] J Burke: “GMSG recommended practices for battery electric vehicles in underground mines”,  2016.
[3] S Jensen: “Battery powered underground mining equipment”, OEM off highway, 13 September 2016.
[4] J Morton: “More battery powered options for LHDs”.
[5] S Lister: “Mclean EV series to support development of world’s first 100% diesel free hard rock mine”, www.mcleanengineering.com
[6] T Ronkeinen: “Why electric mining vehicles are starting to take off”, www.ABBconversations.com
[7] J Wang, et al: “A comprehensive overview of hybrid construction machinery”, Advances in Mechanical Engineering, 2016.

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