In many mines, the ventilation requirements for diluting diesel exhaust are more than enough to dilute dust. A typical underground diesel engine (Deutz F6L714) will emit anywhere from 90 to 150 mg of respirable diesel particulates per cu m of air depending on the load/speed operating conditions. Many mines base their ventilation requirements on how much diesel equipment they have in their fleets. About 0.06 to 0.1 cu m per second of fresh air is typically supplied to a mine workplace for every kw of installed diesel power. A 2,000-ton- per-day gold mine with a fleet of diesel scoops and trucks, for example, may have a total installed diesel power of 475 kw and supply 70 cu m of fresh air per second to the mine workings.
But because of an increase in the use of electric/hydraulic and track- mounted equipment, dust is the dominant concern. Various companies have tried installing automatic doors at ore and waste passes to confine dusts, and water sprays are used in other mines to attempt to suppress dust. But water adds extra weight to the ore (which then has to be hoisted). Other disadvantages to using water are that it cannot remove fine dust once the dust is airborne and it causes fog in mines where rock temperatures are 4.5 degrees C to 7 degrees C. Water also tends to cause ore to clog up in a pass.
Desom Engineered Systems of Downsview, Ont., which specializes in solving ventilation design problems, is putting together a plan to try a baghouse/fan arrangement for a vertical orepass at Nerco’s Con mine, north of Yellowknife, N.W.T. The baghouse would collect the dry dust which would then be put back into the materials-handling system farther down stream in the process.
The environmental department of Hatch Associates Consulting Engineers also specialize in unusual ventilation problems.
When new mines establish their ventilation requirements, they usually turn to one of at least four fan manufacturers in Canada. These manufacturers usually build each fan to meet the requirements of a particular application. The major manufacturers of ventilation fans in Canada are Alphair Ventilating Systems of Winnipeg (formerly the fan division of Joy Technologies Canada), Canadian Blower/Canada Pumps of Kitchener, Ont., Novenco Canada of Cambridge, Ont., and Schauenburg Industries of North Bay, Ont.
Schauenburg is more than a fan manufacturer. A subsidiary of a large multi-national corporation based in West Germany, the company engineers, designs and manufactures underground mine ventilation systems as well as duct tubing, dust- collectors and scrubbers. General Manager Robert Davey says the company’s pioneering projects include: fully recycling dust collectors; the installation of ventilation ducting by cassette; and a completely integrated monitoring system. The company is also manufacturing an acid-based resin ducting which is more fire- resistant than conventional polyester flexible ducting. There are also several companies that specialize in installing ventilation systems. Simmons Ventilation of Lively, Ont., is one such company.
Usually the first decision facing ventilation engineers is whether to select a vane axial fan or a centrifugal-type fan. More often than not, the deciding factor is customer preference, according to Colin Harris of Novenco Canada. “It may be safe to say there is more maintenance required for an axial-type fan than a centrifugal fan, but there are several features that outweigh that higher cost,” Harris says. Customer preference is often based on familiarity with how a particular type of fan performs, knowledge of successful past performance and knowledge of problems with a particular type of fan. Denison Mines, for example, changed from axial fans to centrifugal fans when there was a turnover of ventilation personnel there about 10 years ago. “I can see mines going more and more toward the axial-type fan,” says Schauenburg’s Robert Davey. “They are more compact, more efficient and not as costly. But there are high static pressure applications for the centrifugal- type.” Schauenburg manufactures the Trimetal line of fans.
Once the type of fan has been selected, size and operating speeds are chosen (based on current and future ventilation requirements). Then it’s up to the manufacturing company to design and manufacture the fan. Engineers or technicians interested in taking a short course on designing ventilation systems should contact the Haileybury School of Mines.
The routing of mine air must also be controlled to protect miners against underground fires. That’s where mine doors, ventilation curtains, bulkheads, brattice curtains and regulators come in. There are several suppliers of this equipment in Canada. Overhead Door and M & I Door are major suppliers of ventilation doors.
Contributing significantly to mining costs in Canada is the cost of heating mine air in the winter. Propane, natural gas and even electric heaters are used. It is estimated that a mine spends about $2,000 per year for ever y cu m per second of air it supplies to a mine. That means some of the bigger mines can spend more than $1 million per year heating mine air. Much of that money is wasted when warm mine air is exhausted to the atmosphere without recovering its heat content.
Controlled recirculation has the potential of reclaiming some of that heat. But because of the dangers to health of recirculating dust and diesel exhaust-laden air back into the workplace, many provincial legislators specifically prohibit recirculation. However, the use of on-line ventilation-monitoring systems promises to make recirculation a safe, reliable alternative to high heating costs. The method has been used successfully in British coal mines and at least 25 South African metal mines. These installations use a system whereby recirculation is stopped in the event of a fire.
Prof Allan Hall of the Mining & Mineral Processing Dept. at the University of British Columbia estimates that a recirculation system, if installed at a cost of $100,000, could pay for itself in only one year by saving 10% of the cost of heating mine air. A test installation is needed to establish a model for future systems. “We are researching recirculation systems and we have proposals on the board for a couple of major mines,” Davey says. “The problem is to prove to the mining companies and to the government that the system is economic and safe.”
Old producing mines are faced with a different sort of ventilation problem. In these mines, where there can be many kilometers of underground workings, the problem involves designing a ventilation system around the labyrinth of mine workings. These problems often become so complex that they are impossible to solve without the help of a computer. CANMET (the Canada Centre for Mineral and Energy Technology) has developed a computer software program which can analyse various ventilation network options. It has been used to design the ventilation network for the lower
workings at the Ruttan mine in northern Manitoba, for example. The program runs on ibm-pc and compatible computers.
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