Proper mine ventilation increases safety and can dramatically reduce costs
Ventilation is among the most important functions in a mining operation. Since ventilation directly affects the health and safety of employees working underground, mine owners take the regulation of air flow through a mine very seriously. Yet some may not realize how changes to ventilation practices can significantly – and positively – benefit the bottom line.
A paper titled “Review of Auxiliary Ventilation in Mine Planning and Design,” will be presented at the June 17-22, 2017, North American Mine Ventilation Symposium in Golden, Colorado. The paper by Pedram Rostami, a mining engineer with Stantec Consulting, summarizes common, yet less known, auxiliary ventilation planning and design approaches and solutions used in underground metal mines. Topics include ventilation ducting, auxiliary system arrangements, maintenance and approaches to cost savings.
An integral part of mine design
According to Kim Trapani, a ventilation and energy engineer at Stantec, factors that determine ventilation design include: the type of mine, its location, the regulations around how much ventilation is required (varies by jurisdiction), and the equipment being used. The latter is especially important because a mine that uses diesel equipment will require more ventilation to dilute the diesel fumes than one that uses electric vehicles.
The mine's location, and its rock conditions, can also be of prime significance when it comes to designing an effective ventilation strategy. For example the ventilation design of a mine under a lake created some challenging restrictions because the fresh air and exhaust shafts had to be installed at very specific locations. Stantec was therefore innovative in their ventilation design to permit sufficient fresh air flow throughout the mine.
At another mine, the ground surface was relatively unstable, so the use of larger-diameter raised vents was not possible. Instead, ventilation was limited to smaller-diameter openings. Stantec resorted to using the ramp opening for much of the exhaust air to flow, while the vent raise openings were dedicated for fresh air supply.
According to Trapani one of the biggest trends in mining ventilation is the switch from diesel-operated equipment to machinery with electric drives. This includes mining trucks and other underground equipment like jumbo drills. Electric machinery not only reduces particulate matter and so the fresh air requirements to otherwise dilute the diesel particulate matter, but also the heat losses generated by the machinery itself.
Trapani estimates that moving from diesel to electric-drive machinery can reduce a mine's ventilation requirements by anywhere from 35 to 50%. Because the electricity required to power the fan is not directly proportional to the flowrate, halving the air flow may result in significant reduction in the fan power. "Ventilation contributes to about 30 to 40% of the total energy operating costs in underground mines. So if you can reduce that by half, you're reducing your total operating costs significantly," she said.
Ventilation system design also include ventilation air heating and cooling. Conventional systems have typically been based on gas burners for provision of heating and refrigeration chillers for cooling. These are ofte big energy consumers on the mine site. Some mines in Canada have designed rock/ice heat exchange systems to cool/heat the ventilation air. Such systems exploit the seasonal cycles by cooling down the rock while warming up the air in winter, and warming up the rock while cooling down the air in summer. In such locations, properly designed systems can eliminate the use of external sources for heating or cooling of the mine’s ventilation air.
Another current trend in ventilation is the design of a smart ventilation network which allows air to flow only in the areas that it is required, a practice known as “ventilation on demand.” Sensors detect where people and machinery are working and direct air flow to those areas, while shutting off air to levels of the mine not being worked.
"Some mines that have implemented this approach have seen a 30% decrease in their energy consumption for ventilation," says Trapani. While economics are clearly a key incentive for mines to improve their ventilation systems, government-driven programs to reduce carbon emissions like cap and trade and carbon taxes can also move mines to make operational changes, of which ventilation can be an important part.
"Improving existing ventilation systems allow mines to decrease operating costs and comply with the carbon cap and trade, while minimizing the mine’s environmental footprint," says Trapani.
Kim Trapani, Ph.D, P.Eng., is a ventilation engineer at Stantec's Sudbury offices. Prior to joining Stantec, Trapani worked for MIRARCO as a research engineer developing solutions for deep and remote mines. Her specialty is natural ventilation heating and cooling solutions for mines in sub-arctic climates.
Pedram Rostami, Ph.D. is a mining engineer with diverse experience working at uranium, coal, and gold mines around the world. He has a master’s degree in mineral engineering and Ph.D. in mining engineering with emphasis on ventilation and cooling systems. He is based in Stantec’s Tempe, Arizona office.