Trolley-assisted haul trucks - Technical requirements and benefits

In this second article, of our three part series we take a deeper dive into the technical aspects, as well as who is doing it and why, and benefits. 

Haul trucks, which transport the ore or waste from the rock face to the dump point, use the most energy out of the underground mining fleet. In open-pit mining operations, the operational cost of transporting the ore and waste from the mine to the crushing plant, stockpiles and waste areas can reach up to 50% of the total cost of operation of the mine area.

The trolley assist system is a configuration that allows maintaining electrical supply to the propel motors of the extraction trucks from the electric grid of the mine, by engaging the truck on the trolley lines as shown in the illustration below. Among the benefits provided using the trolley system is the increase of speed on travel up trajectories, which produces an increase of material transported, and fuel savings and reduction in the carbon footprint of the transport operations.

Trolley-assisted haul truck manufacturers and mines they operate in

Trolley-assisted haul trucks are used in different parts of the world. The buzz of reducing Scope 1 carbon emissions is the talk of town. Many mining companies are trying their best to commit to the cause and head start in reducing Scope 1 emissions. This has also opened more opportunities for haul truck manufacturers such as Komatsu, Hitachi, Liebherr and BELAZ to ride on that wave. There are different trolley-assisted haul truck manufacturers, and they operate in different surface mines. The table below summarizes the key players. 

What are the technical requirements for the truck?

Longer haulage distances and steeper grades state a challenge for more powerful transporting systems. The optimum loading target for shovels is three passes per truckload. The payload requirements need a huge power source (around 2200 kW) that must be efficiently used. Keeping haul trucks as small as possible is also desired, so power consumption goes to ore transport only. These conditions make electronic packaging a fundamental part in haul truck. design not only because of the small room left to place an adequate power source driver, extreme environmental conditions must be considered too. Size and capacity are not the only necessities that have to be satisfied. There are other operational and environmental requirements:

• Very high reliability: 24 months Mean Time Between Failure (MTBF)
• Continuous operation: with >95% electrical availability
• Reduced maintenance: no brushes, filters, or regular lubrication.
• High shock and vibration limits: 2g in all directions
• Operation between –40 °C and +55 °C 
• Forced air cooling with unfiltered air and very high dust levels (including coal, ore, salt, conductive and corrosive materials)

What are the benefits of trolley-assist haulage?

Longer hauls and steeper grades present an opportunity for trolley assisted haulage. Typical truck payload requires a huge power source (around 2,200 kW) that has to be efficiently used. Keeping the gross vehicle weight for haul trucks as low as possible is also important, so power consumption is limited to just ore transport. Every ton added to the truck itself is one less ton of ore the truck can haul. Most mines are located in remote areas (deserts, high mountains, etc.) and the trucks have to contend with extreme environmental conditions. These parameters make electronic packaging a fundamental component in haul truck design because of the small space left to place adequate power source drivers. Aside from the obvious reduction in fuel cost, further advantages have been realized with modern systems, including:

• Increased production capacity of the mine and a reduced number of trucks due to higher speed of the trucks on a trolley system (better fleet utilization);
• Greater accessibility in the deeper parts of the mine. The trucks under trolley power are able to achieve high-er gradients and operate at full load for longer periods;
• Reduction of maintenance costs on the trucks, particularly on the diesel engine, which would normally suffer the greatest wear while operating at full load only while on the ramp;
• Increased availability and decreased life cycle costs for the diesel engine (less operating hours);
• Ability to handle a wide range of line voltages;
• Ability to run on the line at any speed and payload; and
• Environmental improvements (lower emissions and less noise).

Conclusions 

Trolley is an essential step in the decarbonization process which can be implemented today to make significant reductions in GHG emissions and certainly will be a part of zero emission mining going forward. Trolley Assist will require a robust implementation plan but the rewards are huge. This has been a technology that has been available for many years on many truck sizes. Yet mining companies have been reluctant to adopt this in spite of (some of them) having excellent conditions – meaning long uphill hauls on ramps that are quite static. Especially in deep copper pits the fuel consumption reduction and speed increase are impressive. Main reason given is usually the reduced flexibility. Trolley has lots of advantages, but you need to consider the total cycle.

Find out more about trolley-assist haul road construction and maintenance and how GRT can provide you with dust control solutions for trolley-assist haul roads in part three of the article series. 

Part 1 – An introduction to trolley-assist haulage systems

Part 3 – Trolley-assisted haul roads construction and maintenance

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