Representatives of two Sudbury research organizations — MIRARCO Mining Innovation and the Centre for Excellence in Mining Innovation (CEMI) — brought delegates at the Energy and Mines conference in Toronto up to speed on the projects they’re working on to reduce energy consumption and introduce environmentally-friendly technologies.
Speaking on the “Journey to the 40 Per Cent Mine,” Dean Millar, director of energy, renewables and carbon management at MIRARCO, highlighted two case studies from the Sudbury Basin for which current energy use was analyzed and a basket of initiatives proposed to more than halve consumption by 2040.
The mine in the first case study presented was found to consume 72 per cent of its energy use on ventilation, “so that was an obvious place to target to bring consumption down,” said Millar.
The MIRARCO team found that a switch to low-friction, well-insulated ventilation ducting and variable speed auxiliary fans would bring energy consumption down to 87.5 per cent of the current level.
A further reduction to 70 per cent was deemed possible by pumping warm water from the depths of the mine to heat sub-zero mine ventilation air in winter. The so-called ice stope technology has been in use at Vale’s Frood-Stobie complex for decades and totally eliminates the use of natural gas for heating ventilation air. In addition to warming the ventilation air, the process creates snow and ice, which collects in a void and is used in summer to cool the air. Adopting ice stope technology would bring energy consumption down to 70 per cent of the current level.
Switching to battery-electric power for the mine’s fleet of loaders removes a substantial amount of diesel from underground and reduces ventilation requirements enough to bring energy consumption down to 40 per cent target.
Glencore’s Nickel Rim South Mine in Sudbury started production in 2010 with a ventilation-on-demand system that accounts for only 33 per cent of the operation’s energy usage. Reducing energy consumption at the mine to 40 per cent of current usage is, therefore, more of a challenge, but still possible, said Millar.
The first technology proposed is an air recirculation system that would scrub and possibly cool air instead of exhausting all of it to surface. “It requires an upgrade in legislation to make it a reality, but it’s technically very feasible, especially if you remove diesel engines from the sub-surface,” said Millar.
Hydraulic air compression is a century-old technology that produces compressed air very economically. The technology was used at the Ragged Chutes air plant in Cobalt to supply 29 silver mines with compressed air and could be adapted for use at Nickel Rim and other mines, said Millar.
“That technology in combination with the latest and greatest energy efficient crushers and grinding units underground would allow us to take just the valuable minerals up the shaft rather than all of the ore.”
Also proposed is a natural heat exchange system in use at Creighton Mine, where a ventilation air flows through a large pile of broken rock over the intake collar. The rock absorbs heat in summer. When winter arrives, the cold air passing through the rock is warmed up, preventing icing as the air passes through the intake system.
“This completely offsets any natural gas use,” said Millar. “Other mines have big piles of rock as well. It just takes imagination to re-engineer them.”
Turning to renewables, Millar proposes wind energy and the use of floating photovoltaic panels over a mine’s tailings pond. Electricity from these sources can power batch processes such as backfill production or charge batteries used to power underground mining equipment.
Damien Duff, vice-president of geoscience and geotechnical R & D at CEMI, provided an overview of the Ultra Deep Mining Network (UDMN), a $46-million research initiative aimed at addressing challenges with deep mining.
UDMN energy reduction research projects focus on deep mine cooling and electrification of underground equipment.
McGill University researchers, for example, are focused on two projects. One seeks to optimize the design of freeze plants used in mines with ground water challenges. The other is investigating the potential for exploiting geothermal resources.
In Sudbury, a Laurentian University team is studying the use of wind energy to power refrigeration plants on surface and new designs to optimize ice stope technology. Other studies are focusing on the optimization of the natural heat exchange system in use at Creighton Mine and the potential for using liquid air for underground cooling and as a source of energy for underground equipment.
“Liquid air expands (when allowed to do so) at a very significant rate and to a very significant volume – some 700 times in terms of volumetric expansion,” said Duff. “Can that do mechanical work? It absolutely can. Can it drive turbines, which in turn drive ventilation fans that not only move air, but also cool it? We believe that’s the case. Can that same technology help to drive LHD equipment or utility vehicles in an underground mine? Absolutely. The technology is already proven at a smaller scale.”
Another project under way addresses the potential for battery-powered production equipment.
“There is a whole range of costs associated with the current way we move equipment in our underground mines, not only in terms of dollars and cents, but also in terms of the well-being of our workforce,” said Duff.
In addition to the ill effects of diesel exhaust, there’s the heat issue, which is already a problem in deep underground mines.
“If you’ve ever stood in an area where an LHD is operating, you’ll know exactly how much heat these machines are capable of generating,” said Duff.
