3.6 Air, water and ancillary equipment

Air ventilation

Relatively low-cost energy savings can be achieved through maintenance improvements in ventilation systems. For example, fan impellers or blades should be cleaned regularly to avoid fouling in dusty environments, which causes static pressure losses.

Energy-efficiency savings can also be achieved by ensuring that air ventilation supply matches demand Since ventilation is a major health and safety issue, most mines run air ventilation systems harder than necessary. Mine ventilation systems are also subject to changing system characteristic curves as the workings move. This means that a system that is initially optimised will deviate from the optimum over time.

For underground mines, air ventilation is a significant area of energy usage. Energy savings can be achieved by ensuring that air ventilation supply matches demand (Box 19 and Box 20), minimising energy use in air and water flows and reducing the area required to be cooled. Often fan and pumping energy losses are high due to the long distances air and chilled water must be moved. Localised systems using the latest high-efficiency air conditioners, fans and pumps can be more efficient.

Box 19: Minimising ventilation fan operation to reduce energy use and defer major capital expenditure at Newmont’s Jundee mine

At Newmont’s Jundee underground operations, which are 520 km north of Kalgoorlie in Western Australia, detailed investigation and energy analysis have highlighted opportunities to turn off ventilation in non-operational parts of the mine.

The project is projected to reduce load requirements by 1,400 MWh/year. Beyond the energy saving, however, the project has meant that a capital upgrade to the ventilation system can be deferred by around two years. This is a major benefit, particularly at a time of significant capita constraints.

Source: Department of Industry, Business Case and Beyond case studies, 2011, http://eex.gov.au/case-study/newmont-asia-pacific-business-case-and-beyond/.

Box 20: Reducing ventilation restrictions at Northgate Australian Ventures Corporation Pty Ltd

Unnecessary restrictions to ventilation airflow in underground mines waste the power required to deliver that flow. Reducing those restrictions not only increases ventilation airflow rate but also improves the air quality in the mines.

Depending on the fan curve, this will also generally reduce power somewhat. Slowing rotational speed of the prime mover (the fan or pump) to return airflow rate to the original level decreases energy consumption further.

Northgate Australian Ventures Corporation Pty Ltd found that an estimated 1,470 GJ in potential savings from the implementation of this opportunity was possible at its Stawell, Victoria, goldmine.

Source: Northgate Australian Ventures Corporation Pty Ltd—Opportunity G, EEO Opportunities Register, 2012–13, http://eex.gov.au/opportunities-register/northgate-australian-ventures-corporation-pty-ltd-opportunity-g/.

The energy-water nexus

On a mine site, water is involved in many different activities, including extracting and processing ore, suppressing dust, cooling, washing, and transporting waste as tailings.

Therefore, ensuring that there is a consistent supply of water, in terms of both quantity and quality, is critical. This can be particularly challenging on mine sites where there is water scarcity, high climate variability or competing users, where production is set to increase, or where any combination of those factors applies.

The University of Queensland examined the trade-off between water and energy savings as part of the Australian Coal Association Research Program (ACARP). Footnote 26 ACARP developed a model that allowed the nexus between energy and water use to be examined.

Sometimes sites can make water and energy savings simultaneously. For example, the use of additives in dust suppression requires road water trucks to be used less frequently. However, at other times reducing water and energy use are competing objectives and so trade-offs between the two must be made. For example, treating water can reduce the volume of high-quality water withdrawn or purchased by a site, but also increases energy used on site. Therefore, any attempt to solve a water problem without considering the associated energy impacts will simply be shifting problems, rather than providing a genuine solution.

While every site is different, the ACARP report highlights just how important it is that decisions about energy and water use be made on a site-by-site basis. This should be kept in mind when considering the energy-efficiency opportunities discussed in Box 21.

Where dewatering is required, the energy efficiency of pumping systems can be optimised by using efficient motors and pumps, using smooth pipes with a large diameter, and running the pumps continuously at low speed instead of for short periods at high flow. In open-cut mines, rather than pumping water from the bottom of the mine up to the top, the water can be put into dust-suppression water tankers at the bottom to be used as spray water while the trucks are driven uphill (tankers usually spray while being driven downhill).

Box 21: Reducing friction head losses to process water line at the Wonnerup mine

The Cristal Mining Wonnerup mine, which is near Busselton in Western Australia, excavates mineral-rich sand and processes it to separate the target minerals such as titanium, monazite and zircon as a heavy mineral concentrate. The sand is above the watertable, so dry mining techniques are used to excavate it, after which it is transported into the primary screening plant and then the secondary screening plant, which is regularly moved to always be adjacent to the excavation area The primary screening plant uses a large volume of water to separate and remove large rocks and debris. The target materials are then pumped as slurry to the concentrator plant, which can be 400-1,500 metres away. The water used in the pumped slurry is recycled, being pumped from the concentrator back via the water cleaning circuit and production water storage facility to the primary and secondary screening plant.

An opportunity was identified at the mine to:

  • increase the diameter of the high-density polyethylene pipeline from 280 mm to 315 mm to reduce friction head losses, which allows the installation of a smaller motor, thereby reducing the energy required
  • change the 110 kW motor to an available spare 90 kW motor (possible because of the reduction in friction losses).

This opportunity was initially identified during energy-efficiency opportunity identification workshops for a mine at Gwindinup, which has now ceased mining. At Gwindinup, the project was not financially attractive due to implementation costs and the relatively short remaining life of the mine.

Cristal’s mine planning is designed around the relocation and reuse of mine infrastructure, which in this case was to be moved to its new Wonnerup mine. This energy-efficiency opportunity was re-evaluated and the pipe change was implemented during the initial development at Wonnerup.

When fully implemented, this innovation will reduce the risk of line failure, which reduces the risk of environmental incidents and increases reliability and production run times. It will also reduce annual maintenance costs for the pump and allow for a reduction in the energy load due to a reduction in the pump head of about 18 metres.

The project will reduce energy consumption by 600 GJ, resulting in a net reduction of greenhouse gas emissions of 150 tonnes CO2-e per year. It has a capital cost of $30,000, producing annual energy and maintenance savings of $26,000 and a payback period of 1.2 years.

Opportunities in ancillary equipment

Further energy-efficiency opportunities can be achieved by implementing improvements in specific technologies, such as motors, pumps (Box 22), fans (Box 23), lighting (Box 24) and air compressor systems. These systems consume a significant amount of energy in mining and mineral processing.

Box 22: Modifications to pump controls at Mount Isa Mines

A pump is required for water delivery to head tanks, which are filling stations for the water trucks used for dust suppression at Mount Isa Mines’ Black Star open-cut copper mine. The existing pump control is an externally mounted box in an area subject to a high number of lightning strikes.

This project will disconnect the pump and remove a hired diesel generator, attach mains power, provide lightning protection for the motor control centre with a full earthing system, and provide dual redundancy in the soft-start unit and the ability to power washing at targeted times. This project is expected to deliver annual energy savings of $270,300 for a simple payback of less than two years.

Source: Glencore Investment Pty Ltd—Opportunity G, EEO Opportunities Register, 2012–13, http://eex.gov.au/opportunities-register/glencore-investment-pty-ltd-opportunity-g/.

Box 23: Fan replacements at Barrick’s Kalgoorlie mine

A project was implemented to replace the single primary vent fan at Barrick Pty Ltd’s Kalgoorlie goldmine with multiple lower rated fans. This resulted in one 530-kVV fan being replaced with three 37-kVV fans.

Post-implementation measurements showed energy savings of 15,000 GJ with a better than two-year payback.

Source: Barrick (Australia Pacific Holdings) Pty Ltd, EEO Opportunities Register, 2011–12, http://eex.gov.au/opportunities-register/barrick-australia-pacific-holdings-pty-ltd-opportunity-e/.

Box 24: Automating mobile lighting equipment at Thiess

Thiess runs 24-hour mining operations, so good lighting is essential to support safe and efficient work practices. Due to the geographical spread and changing location of operations, diesel-powered mobile lighting units are used.

Workshop personnel identified an energy-efficiency opportunity that involved fitting automated systems to the lighting plants to ensure that they operated only in low-light conditions.

The estimated diesel saving is 165,000 litres/year (6,400 GJ/year), with an investment return of less than two years. Other benefits from the project include a reduction in operator labour time and light vehicle diesel use (as people no longer need to travel on the site to turn the lighting units on and off), improved safety, and reduced maintenance and longer operational life of the lighting units.

Source: Department of Industry, Thiess Australian Mining Business Unit case study, http://eex.gov.au/files/2014/06/Thiess-Australian-Mining-Business-Unit.pdf.

Footnotes

Footnote 26
A Woodley, G Keir, E Roux, D Barrett, J White, S Vink, Modelling the water energy and economic nexus, ACARP research report C21033, Australian Coal Research Limited, February 2014.

Return to footnote 26 referrer

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