The Energy Cost of Friction and Wear in Mining

By Benedette Cuffari, M.Sc.Jan 5 2018

Due to the growing increase in societal needs and many industrial activities, the global energy demand has been steadily increasing over the last 40 years, in which demand has nearly doubled. Despite the renewable energy sources currently available with the latest advances in technology, current industrial systems remain primarily dependent upon on utilizing non-renewable energy sources to obtain more than 80% of the total global energy demand. Even though non-renewable sources such as oil, coal and natural gas are valuable, these resources are major contributors of greenhouse gas (GHG) emissions.

Friction and Wear in Mining

Mining, a process of obtaining solid minerals from earth’s crust through different kinds of methods (such as open-pit mining, strip mining, quarrying and excavation) has been an integral part of human activity for thousands of years. While most of the mining activities throughout history have involved excavations for iron, gold, silver, copper, tin, lead, diamonds and coal, present-day excavations extend far beyond these elements to provide raw materials that ameliorate the security and quality of human life in the current industrial society. While there are several types and sizes of mines in the world that range from small surface quarries to large industrial underground mines recovering ores from several kilometers under the earth’s surface, all mines function by utilizing the basic mining processes.

Mining involves several steps including:

• Breaking
• Excavation
• Loading
• Hauling
• Transportation
• Mineral processing to reduce the size of the chunks
• The removal of gangue minerals to make a product of higher grade by various beneficiation processes (e.g. flotation and gravity separation)

Each of the aforementioned steps make the process of mining extremely energy intensive. In fact, it is estimated that the total global energy consumption of mining and mineral industries is between 4-7 % of the total global energy output. Along with the need for high energy consuming processes such as rock braking, crushing, loading, hauling, transportation, pumping and ventilation maintenance in underground mines, a large amount of energy consumption in mines is attributed to friction and wear losses.

Evaluating the Impacts of Friction and Wear in Mining

Researchers at the VTT Technical Research Center of Finland in collaboration with Tampere University of Technology, Finland and Argonne National Laboratory, USA have studied the global energy consumption due to friction and wear in the mining industry to determine the tribological and economic impacts on this industry.

Although rock excavation from quarries for civil engineering purposes is generally regarded as a mining process, it was excluded in the present study. The friction and wear rates of mechanical parts were estimated based on the data available from the literature belonging to four general cases, of which include:

1. A global average of mines in use today
2. A mine with today’s best commercially available technology
3. A mine with today’s most advanced technology based on the adaptation of the latest Research and development (R & D) achievements
4. A mine with best futuristic technology forecasted in the next 10 years

The results from the present study concluded that an astonishing 40 % [4.6 exajoule (EJ)] of the global energy consumption in mineral mining is used for overcoming friction. Additionally, 2 EJ of energy in mines is used to remanufacture and replace worn out parts, reserve and stock up the spare parts and equipment needed to wear failures. The results from this study have also concluded that friction and wear in mining contribute to 2.7% (970 million tons) of the world’s carbon dioxide (CO₂) emissions. The total global annual economic losses due to friction and wear losses are estimated to be 210,000 million Euros, of which 40% is distributed to overcoming friction while the rest of the 60% of losses are distributed in production of replacement parts and spare equipment (27%), maintenance work (26%) and lost production (7%).

The friction and wear losses in the mining industry could be reduced by 15% in the short term of 10 years, as well as by 30% in the long term (20 years) by improving the design of moving parts and surfaces. For example, the incorporation of liners, blades and plates, utilizing new materials with improved strength and hardness properties, as well as implementing more effective surface treatments, high performance surface coatings, new lubricants and lubricant additives.

Taking advantage of the currently available novel technologies to reduce friction and wear losses would save 31,100 million Euros, 280 terawatt hours (TWh) of energy and reduce 145 million tons of CO₂ emission in the short term (10 years) every year. In the next 20 years, it is estimated this would save 62,200 million Euros and 550 TWh of energy, as well as result in a reduction of 290 million tons of CO₂ emission annually. New technologies in the future to reduce friction losses and reducing wear in the equipment may further reduce the economical and electricity losses while also reducing the CO₂ gas emitted as a result of mining.

References:

1. “Global energy consumption due to friction and wear in the mining industry” K. Holmberg, P. Kivikyto-Reponen, et al. Tribology International. (2017). DOI: 10.1016/j.triboint.2017.05.010.

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