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With fuel and energy costs rising, and mining companies looking for more environmentally friendly solutions, it might just be the right time to go electric, writes Leon Louw.

The popularity of electric and hybrid engines is growing across all sectors, not just automotive. In underground mining, the debate surrounding electric, diesel-driven and hybrid equipment has been going on for decades.

While surface mining has made impressive strides in the area, underground has been slower to make the change. However, the current focus on technology and modernisation across all sectors, particularly in the context of Industry 4.0 – the so-called fourth industrial revolution – has revitalised this debate, and focus is slowly turning towards electric and hybrid options.

One of the biggest problems with switching from time-tested diesel-driven equipment to a new electric fleet is the significant capital investment required. In an economy dealing with lowered commodity prices, procurement managers are feeling the pressure. However, 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.

Safety first
One of the primary benefits of electric equipment over traditional diesel-driven machines is the increased safety. Since the first fleet of diesel driven equipment was sent down underground mines in the early 1900s, thousands (if not millions) of miners have inhaled huge quantities of harmful diesel particulate matter (DPM), gases and odours.

But this was at a time when diesel was cheap and there were no viable alternatives. Mine workers continued toiling in gas filled stopes, and some paid the ultimate price. Numerous studies have shown that long-term exposure to combustion-related fine particulate pollution, including DPM, is an important risk factor for cardiopulmonary and lung cancer mortality (Pope 2002). The use of diesel-powered equipment by the underground mining community has increased over the past several decades, and despite technological advancements such as Tier 4 engines, which reduce the amount of pollutants released into the atmosphere, gases and DPM remain hazardous.

In the US, for example, about 150 units of diesel equipment were operating in underground coal mines in 1974 and by 1995 that number had reached 3 000 units, according to the Mine Safety and Health Administration (MSHA). A similar trend was seen in underground metal/non-metal mines (M/NM), also in the US, where the use of diesel equipment first started in 1936 and by 2001 there were more than 4 000 units operating in underground M/NM mines.

Although diesel emissions and the health impacts have been the subject of many studies, globally and in South Africa, diesel-driven equipment still dominates the underground mining environment. However, fuel and energy costs are rising and mining companies seek more environmentally friendly solutions, so it might just be the right time to go electric.

More than one study has found that mining operations could save up to 70% of their operational expenditure when using electric equipment instead of a diesel-driven fleet. If you consider the total cost of ownership, including operator, tyres and so on, the potential cost saving offered by electric equipment could result in a total cost reduction of around 10%.

Potential benefits
According to the report Electric Vehicles for Construction, Agriculture and Mining 2017-2027, the market for electric vehicles (including hybrids) for the construction, agriculture and mining sectors will reach USD81-billion by 2027.

South African OEM Bell Equipment, which manufactures both surface and underground articulated dump trucks (ADTs), and sell a Rockscaler for clearing loose overhanging rocks underground after a blast – is also looking at electric and hybrid drive machines, according to the company’s ADT product marketing manager Tristan du Pisanie.

Du Pisanie identifies two enormous potential benefits of using electric technology underground. “Firstly, it does not produce problematic exhaust gases so the ventilation requirement underground is less. Secondly, 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 benefits cooling requirements,” he says.

Despite these benefits, diesel engines are the traditional method of earthmoving and they work very well. Du Pisanie says that a diesel engine’s major strength compared to electric is that the energy density of diesel fuel is very high. “Storing a shift's worth of energy is a lot more compact and cost effective for a diesel machine than an electric machine,” he says.

According to Kevin Reynders, managing director at Rham Equipment, diesel engines offer underground miners ample flexibility in their stoping or development ends. Rham has a full range of underground roofbolters, electrical/hydrostatic belt drives, LHDs, utility vehicles, dump trucks and face drills that are completely compatible with diesel engines, electric motors and hybrid options.

Marc de Chalain, business development manager, Africa for OEM Joy Global, agrees. “Diesel equipment offers a high-level of mobility and flexibility when compared to electrical equipment.” However, he points out, this comes at the price of burning diesel, which causes heat and creates emissions underground. “As a result, mines have to invest in extensive cooling and ventilation systems.”

Joy Global manufactures a full range of underground, electrically powered and flameproof coal equipment that includes continuous miners, shuttle cars, battery haulers, flexible conveyor trains and roof bolters. In addition, the company also builds a full range of diesel non-flameproof equipment including LHDs, ADTs and jumbo and production drill rigs.

De Chalain adds that electrical powered equipment is typically easier to flameproof, making it easier to use in coal applications, which is the company’s primary application area.

Counting the costs
But if the benefits are so potentially significant, why have electric and hybrid drive machines not taken over the underground equipment market? Du Pisanie identifies cost as the major constraint. “Both electric and hybrid systems tend to be expensive, but the mine operator's main priority is to ensure that they have the most commercially profitable solution. Both electric and hybrid have benefits not available from more traditional solutions, but these benefits need to outweigh the costs.”

The second factor that has delayed the development of electric and hybrid solutions is energy storage. Although modern batteries are much better than those from 20 years ago, they still have some limitations. For example, they are heavy, charge more slowly than would be ideal and are more expensive than diesel. The energy density is also not as high as most people would like it to be, as well as being much lower than diesel, although it is improving every year.

While another possibility for well-established haulage tunnels is running the machines off electric lines, this solution will not work in new expansion areas, limiting its application.

According to Reynders, a massive underground power supply configuration is required to accommodate electrical or hybrid-powered machines, and the additional power source will have come in the form of gully boxes, power points and substations, as diesel is not required for these vehicles.

The limitations on mobility created by the tethering of electrical machines make haulage units a challenge. Electrically powered equipment is usually best suited for use in continuous miners, drills and roof bolters, as they move extremely slowly. “However, to employ an electrical drive on an LHD travelling hundreds of metres is impractical for cable handling,” says De Chalain.

The best of both worlds
While hybrid machines operate in different ways; most have a fully mechanical drivetrain – engine, gearbox, driveshafts and wheels – and an electric motor. This motor runs off a battery pack and provides additional power when the operator calls for maximum power, and then also provides braking force when the operator wants to slow down. When braking, the motor turns into a generator and charges the battery pack.

“Hybrids offer benefits in efficiency by assisting a diesel engine with an electric motor when peak power is required,” says Du Pisanie. “In a hybrid the electric motor becomes a generator and charges battery packs, the generator serves to slow the machine down. It also works harnessing energy when excavator booms are lowered or when stopping an excavator during swinging.” Similarly operating hydraulic solutions allow for the use of a smaller and more efficient engine.

Advantages of battery versus diesel
  • Instant power
  • No diesel particulate matter (DPM) problem
  • Lower noise
  • Lower operating temperatures
  • Less mine ventilation required
  • Less machine maintenance
  • No diesel fuel handling or storage
  • Fully proportional traction speed and hydraulics
  • Whisper pump with less noise and uses less power
  • Regenerative braking
  • Advanced proximity ready

While the extent of hybrid systems’ benefits depends on the type of application in which the machines run, they can harness energy that is normally lost, such as the energy from vehicle braking, which is normally dissipated as heat, for feeding back.

One example of this is Joy Global’s ‘switched reluctance’ (SR) hybrid drive, which captures and stores regenerated braking energy in its underground LHDs (load, haul, dump machines) and distributes it back into the systems powering the machines’ main motions. “It’s really just a mechanism of controlling an electric motor without brushes. It’s literally about how, and how fast, you energise the poles and how you change that around that determines whether you’re going to have the rotor being driven or the rotor driving,” says De Chalain. “The beauty of that is it allows us to regenerate energy into the system.”

According to De Chalain, hybrids offer a good compromise between diesel and electrically driven equipment by providing diesel-like mobility and flexibility. “At Joy, we have found that about 30% less fuel is burned when using a hybrid system, which of course results in lower heat and less emissions,” he says.

The hybrid LHD delivers its best benefits when employed in a production application over short haul distances. This allows their high torque delivery to create an acceleration advantage over mechanical units, while still delivering a significant fuel saving. The shorter cycle times mean higher production and therefore lower cost per ton.

And while integration of the SR technology into Joy’s underground equipment is a relatively new development, De Chalain points out that the product itself has over 20 years of development and testing aboveground in the company’s wheel loaders. It has also been transitioned from the P&H generation II wheel loaders into the design of its new 2650CX hybrid rope shovel for surface mining.

Despite the numerous benefits to using electric and hybrid technology, De Chalain says it remains challenging to develop these solutions. Hybrid units need to generate and store electrical energy, which is difficult and can be achieved in a variety of ways. Joy Global, for example, has successfully developed kinetic energy storage systems (KESS) for both surface and underground applications.

Underground applications have the added challenge of scaling energy storage systems to fit into a low-profile package suitably sized for underground mining. According to De Chalain, one of the advantages of Joy Global having transitioned the technology from its wheel loaders to other machines in its portfolio is that the same drive packages are used for the control panels across all sizes of motors, just scaled by the number of drive packages used.

Eye to the future
And hybrid and electric technology are not the only options on the table. Hydrogen-fuelled equipment is another exiting new development. South African platinum giant Impala Platinum (Implats) recently announced its intention to convert some of its underground diesel-driven machines to hydrogen. Du Pisanie is a huge fan of hydrogen-fuelled technology, but warns that the challenges are even greater for hydrogen than electric and hybrid.

“Production of hydrogen is very energy intensive. The most common method is electrolysis and if the electricity used is from a fossil fuel-powered power station, then the carbon footprint of the process is very big indeed,” he says. “The distribution network for hydrogen also needs to be set up for it to become a viable option. In addition, the energy density of hydrogen as a fuel is very low, so a very big tank is needed to allow a hydrogen-powered vehicle to be driven a practical distance,” adds Du Pisanie.

While hydrogen is used as a fuel in internal combustion engines, the more exciting option is fuel cells, which were first developed for travel in space. These cells take hydrogen and use it to generate electricity for running an electric motor, with water as the by-product. But while fuel cells are more cost effective every year, they are still quite expensive.

In March 2016 Implats, in partnership with the University of the Western Cape (UWC), unveiled its prototype hydrogen fuel cell forklift and refuelling station at its Impala Platinum Refineries in Springs, outside Johannesburg. The three-year project – the first of its kind in South Africa – was a collaboration between Impala Platinum Refineries, Hydrogen South Africa (HySA) Systems, the UWC and the Department of Science and Technology. Implats plans to use hydrogen fuel cell technology as its main source of energy for material handling and underground mining equipment.

According to Fahmida Smith, fuel cell coordinator at Impala Platinum Refineries, fuel cells have several advantages over diesel as a power source. “Underground mining equipment that uses diesel releases carcinogenic DPM. A hydrogen fuel cell system, on the other hand, releases only water. Even if you use a carbon-based methane-rich stream that releases some carbon dioxide emissions, they will be significantly reduced. There will also be no sulphur oxides nor nitrogen oxides – or at least extremely low levels – as well as zero carbon monoxide and zero particulates. From both a health and an environmental perspective this is a major improvement,” she explains.

Smith acknowledges the disadvantages to using hydrogen as a power source and cost is foremost. “The technology is highly advanced and because it is still so new, the initial capital expenditure is very high, much like solar power was when it was first introduced to the market.” However, she points out that, as with latest technology, the cost of implementation will decrease as deployment increases. “If we look at the cost of the equipment when we first started with this initiative a few years ago compared to now when we are looking at implementing it, we have already seen at least a reduction in capital cost of 15% to 20%.”

However, the potential safety concerns of having hydrogen – an extremely light and highly volatile gas – underground can be circumvented by using methanol water rather than hydrogen for underground refuelling. This also has the effect of reducing cost, since the same system currently used to get diesel underground for refuelling can be used for methanol water. This will also help with change management for a company switching from diesel to hydrogen as a power source, since operators do not need to learn an entirely new system.

And there are advantages to using fuel cells beyond environmental and health impacts. With fuel cell technology, the exit temperature at the fuel cell on an LHD is roughly half of that on a diesel vehicle, which reduces ventilation problems and excess heat.

“Stationary hydrogen fuel cells also offer excellent efficiency – for every kilowatt of energy you produce, you produce an equivalent amount of heat, and if you recover that heat it not only additionally lowers costs, but also lowers the carbon footprint,” says Smith.

Click below to read the June 2017 issue of Mining Mirror.