Optimising Energy Usage in Mining Operations

Mining is inherently energy-intensive. The extraction and processing of minerals demands substantial power, contributing significantly to global energy consumption and associated greenhouse gas emissions.

This case study delves into the typical energy consumption patterns within mining operations, pinpointing the major energy-consuming processes, exploring the financial implications of energy use, and outlining strategies for optimisation. These strategies encompass improved operational efficiencies, the integration of renewable energy sources, and the potential transition to electric vehicle fleets.

Energy Consumption Patterns in Mining:

A mine site, whether sprawling across the surface or burrowing deep underground, functions as a complex system requiring energy input for a multitude of processes. These include the initial ore extraction involving drilling, blasting, loading, and hauling vast quantities of rock. Following extraction, the ore undergoes comminution – the energy-intensive process of crushing and grinding it into smaller sizes, preparing it for further processing. Mineral processing itself, which separates the valuable minerals from the waste rock, utilises various techniques like flotation, leaching, and smelting, each with its energy demands.

The movement of materials, both ore and waste rock, across the mine site, often over considerable distances, requires substantial energy for trucks, conveyors, and other transport systems.

Underground mines face the added challenge of ventilation, requiring powerful systems to supply fresh air and remove hazardous gases, a significant energy drain. Beyond these core processes, energy is also needed for water pumping and management, essential for dewatering, supplying process water, and managing wastewater.

Heating, ventilation, and air conditioning (HVAC) for buildings, including offices, workshops, and accommodation, along with lighting for both surface and underground operations, contribute to the overall energy footprint. Finally, ancillary services, such as workshops, maintenance facilities, and administrative offices, add to the total energy consumption.

Major Energy Consumers within a Mine:

Within this complex energy ecosystem, certain processes stand out as particularly demanding. Comminution, the crushing and grinding of ore, often claims the largest share of energy consumption, sometimes exceeding 50% of the total. This is due to the immense forces required to break down rock.

Example Energy Consumption at a Conventional Surface Mine (from ‘Unlocking the energy productivity value proposition’)

For underground mines, ventilation represents another significant energy consumer. Maintaining adequate airflow in deep, confined spaces necessitates powerful ventilation systems that run continuously. Material handling, the movement of massive volumes of ore and waste, especially over long distances, requires substantial energy input for the large trucks, conveyors, and other equipment involved. Mineral processing, depending on the specific minerals being extracted and the methods used, can also be a major energy consumer. While office and residential infrastructure contribute to the overall energy picture, their consumption is typically much lower than the core mining operations.

Strategies for Energy Usage Reduction:

Mining operations can implement a range of strategies to reduce their energy consumption. Process optimisation plays a crucial role. Improving the efficiency of comminution circuits, optimising blasting practices to reduce the number of trips required, and minimising haulage distances can all contribute to energy savings. Upgrading equipment to newer, more energy-efficient models can also make a significant difference. Retrofitting existing equipment is also being explored with companies such as EPSA converting their Cat truck fleet from diesel to electric as the tests indicated the total cost of ownership of the electric trucks would be less than 50% of a diesel truck.

Energy recovery, such as utilising waste heat for other purposes like preheating process water or even generating electricity, offers further opportunities for reducing energy waste. Implementing demand-side management strategies, which focus on reducing energy consumption during peak periods, can also lower costs. A great example of this is at Boliden’s Garpenberg mine in Sweden that implemented Ventilation on Demand (VoD) technology from ABB to reduce their fan energy consumption by ~40%.

Example demand for ventilation fans (courtesy of Costa, 2019)

For underground mines, optimising airflow and using more efficient fans can improve the efficiency of ventilation systems. Finally, the increasing adoption of automation and digital technologies allows for the optimisation of processes and the reduction of energy waste through more precise control and monitoring.

Optimisation of the Mine:

Many mines often overlook the ability to make significant changes with current assets in the short term. A lot of focus, investment and effort is placed on the longer term replacement of assets and/or infrastructure. This should be pursued, but the short term opportunities should also be pursued with equal vigour. In many cases, these short term initiatives create improved company processes and housekeeping that magnify when the longer term investments come online.

It’s key for mines to identify these areas of opportunity, quantify and prioritise them, breaking each into individual projects with clearly defined objectives. This site review and roadmap can be completed in a short period of time by MTS specialists to help kick start these initiatives.

Leveraging existing technology in the review and initiatives gives facts to quantity and justify any changes, establish benchmarks, as well monitor improvements over time to ensure success.

MTS has worked with many mines to help them execute their short term initiatives, typically acting as an extension of their internal teams. These have yielded significant results including a site in Europe that improved efficiencies by utilising existing technology. This not only reduced their fuel consumption by $2.1m/year and carbon emission by 3,200 Tons/year, but also resulted in a 6% productivity gain.

Other common areas for gains include streamlined haulage cycles, improved blasting and fragmentation efficiency, reduction of required assets to make plan, reduction of fuel consumption, amongst others.

The Role of Renewable Energy:

Renewable energy sources, such as solar and wind, offer a compelling pathway for reducing reliance on fossil fuels and lowering energy costs, especially for mines located in regions with abundant solar or wind resources. Solar photovoltaic (PV) systems can be deployed at mine sites to generate electricity for a variety of uses, from powering buildings and lighting to contributing to process loads. In sunny regions, solar can become a substantial component of the energy mix. B2 Gold at their Fekola Mine in Mali constructed a hybrid power plant in 2021 using a combination of a 30MW Solar PV plant and Heavy Fuel Oil (HFO) for power generation and 15 MWh battery capacity. This resulted in them reducing their HFO burn by 13,000,000 liters/year, as well as reducing their carbon footprint by 39,000 tons per year. It has been so successful that B2 Gold has just finished expanding the Solar PV to 52 MW total and battery capacity to 27.7 MWh total!

B2 Gold Extensive Solar PV hybrid plant at Fekola Mine in Mali

Wind turbines can also be used to generate electricity, particularly in areas characterised by consistent and strong winds. Hybrid systems, combining solar and wind power, often coupled with battery storage, can provide a more reliable and consistent source of renewable energy. The feasibility of renewable energy integration depends on several factors, including the availability of the resource, proximity to existing grid infrastructure, and the specific energy demands of the mine. While renewables may not entirely replace conventional energy sources, they can significantly offset a portion of the load and reduce dependence on fossil fuels.

Electric vs. Diesel-Powered Haul Trucks:

The transition from diesel-powered haul trucks to electric trucks holds the promise of significant reductions in greenhouse gas emissions and operating costs. However, this transition also presents challenges. The widespread adoption of electric trucks would substantially increase the mine’s electricity demand, requiring significant investment in grid infrastructure or on-site power generation capacity.

Battery technology, including battery capacity, charging infrastructure, and battery lifespan, are key considerations. Furthermore, the initial capital cost of electric trucks is currently higher than that of their diesel counterparts. While the shift to electric trucks is a promising development, careful planning and substantial investment are necessary to ensure a reliable and cost-effective implementation. This has not put off major players though with companies such as Fortescue Metals Group signing a historic US $2.8 billion deal with Liebherr to deploy 360 autonomous battery-electric haul trucks (alongside electric excavators and dozers), replacing two-thirds of its fleet. And in the underground space companies such as South32 has recently commissioned a fleet of Sandvik equipment at their Hermosa Critical Minerals project in Arizona, USA.

Hybrid solutions such as the use of Diesel-Electric trucks and trolley lines have seen an increase in popularity particularly in the ultra class sizes. These offer a halfway house solution leveraging fixed power plants and onboard systems to reduce overall costs and carbon emissions. Liberherr and Caterpillar released their new take on the trolley assist technology with Liebherr’s Power Rail technology and Caterpillar’s Dynamic Energy Transfer (DET) system that BHP will be trialling. It aims to make the trolley-assist/charging technology more applicable across sites where traditional systems may not be suitable.

Liebherr’s Power Rail Technology

Surface vs. Underground Mine Energy Consumption:

Underground mines typically exhibit higher energy consumption per ton of ore extracted compared to surface mines. This difference primarily stems from the need for extensive ventilation systems in underground environments, more complex material handling systems necessitated by confined spaces, and the often greater depths of underground operations. Surface mines, while consuming large amounts of energy for material handling, generally do not face the same ventilation demands.

Seasonal Variations in Energy Use:

Energy consumption in mining can fluctuate seasonally. In colder climates, more energy is required for heating, while in hotter climates, air conditioning loads increase. Seasonal variations in the availability of solar and wind resources must also be taken into account when planning for renewable energy integration.

Fleets of trucks commonly line up and idle over activities like shift change, lunch etc.

Further Considerations:

Ongoing research and development efforts are focused on improving the energy efficiency of comminution, which presents a significant opportunity for energy savings. The integration of sophisticated energy management systems can help mines monitor and optimise energy consumption in real-time. Finally, engaging with local communities and stakeholders is essential for ensuring the sustainable development of mining projects, including responsible energy management practices.

Conclusion:

Optimising energy usage is not just a matter of environmental responsibility; it is also crucial for the long-term sustainability and profitability of mining operations. By implementing energy-efficient technologies, integrating renewable energy sources, and exploring the transition to electric vehicles, mines can significantly reduce their environmental footprint while also improving their bottom line. Continued research and development, coupled with supportive policies, will be instrumental in driving further improvements in energy efficiency within the mining sector.