The Bullmoose coal mine is the smaller of two projects which were the basis for British Columbia’s massive $2.5-billion Northeast Coal Project. The relatively smooth startup at Bullmoose contrasted sharply with the nearby Quintette project which, because of its larger size, had more operational difficulties to overcome. Sizing Bullmoose at a manageable scale proved to be an astute move by Teck Corp., the mine operator. Like Quintette, it too has come under pressure to lower coal prices and reduce contract volumes. This strategy has reduced the heavy financial obligation associated with larger projects.
The mine and wash plant, with a rated capacity of 2.3 million tonnes of clean coal per year, cost a modest $275 million. Teck spread out the risk by taking on two partners: Lornex Mining Corp. (39%) and Nissho Iwai Canada (10%). There were no cost overruns with which to contend; and to use a Teck cliche, the project came in “on time and under budget.”
Mine construction took just over two years and commercial production started in November, 1983. Design production was achieved within the first three months of operation and Teck says contracted tonnages have been delivered ever since. Detailed engineering, along with specific procurement and expediting services for the coal plant, were provided by Phillips Barratt Kaiser Engineering of Vancouver.
The wash plant was designed to handle raw coal feed at 450 tonnes per hour. The plant can produce about 1.7 million tonnes of clean metallurgical coal and 600,000 tonnes of thermal coal annually.
Coal was formed millions of years ago by compaction of variously altered plant remains similar to those found in peat. It is readily combustible, contains more than 50% by weight and greater than 70% by volume of carbonaceous material including inherent moisture.
Differences in the kinds of plant materials (type), in degrees of metamorphism (rank) and in the range of impurity (grade) are used for coal classification.
There are five recoverable seams at Bullmoose and two major mineable areas — the South Fork and West Fork zones. The five seams vary in thickness from one metre to 4.9 m with a total combined thickness of 12.4 m. The two lower seams, A and B, contain less ash and are generally harder than the C, D or E seams. A massive sandstone parting, ranging in thickness from 0.5 to 2.0 m, separates into two smaller seams the A seam.
Pre-stripping and mining began at the north end of South Fork because there was less waste to remove and because this area is closer to the wash plant. Open-pit mining is carefully scheduled in order to provide a constant source of raw feed to the wash plant; a conventional truck and shovel system is used in the pit.
According to Fred Koch, mine manager at Bullmoose, waste-stripping currently averages 32,000-35,000 cu m per day and raw coal production is about 6,200 tonnes. Only B seam coal requires blasting. He says the mining method will change because the dip of the coal will change. The beds dip gently to the north at about six degrees but are considerably steeper at the south end of the deposit. Coal that exists near surface has been oxidized and is classified as thermal. Thermal coal is left in place unless it has to be mined in order to gain access to metallurgical coal. Thermal coal that was mined has been stockpiled except for a limited tonnage which is sold on a spot basis to Korea.
The interseam waste band varies in thickness from about 6 m between A and B seams to 24 m between D and E. This waste is drilled in one pass. The normal bench height, however, is 12 m. Drilling is done with Ingersoll- Rand rotary drills. Holes are loaded with a mixture of ammonium nitrate and fuel oil. This mixture is water- soluble and because of this, holes are pumped dry or lined with plastic. The anfo is occasionally boosted with aluminum to increase its explosive power.
P&H 2100 shovels equipped with 12.6-cu-m buckets mine most of the waste. A rotating laser is used to indicate the vertical position of the shovel relative to a fixed elevation. Knowing where the shovel is relative to the coal seam allows the shovel operator to mine close to the coal seam but minimizes mining into the seam. Waste that cannot be mined with a shovel is mined with Marion 3560 backhoes. The backhoes are equipped with a 12.3-m bucket. The use of backhoes allows removal of the waste immediately above the coal without placing heavy equipment directly on the seam. This practice reduces production of coal fines. The coal released with shovels and backhoes is loaded onto haulage trucks by Caterpillar 992 loaders.
Waste material is placed within the pit in mined-out areas and also on external waste dumps. These dumps are always close to active mining areas. The waste material consists of a mixture of sandstone, siltstone and mudstone.
Coal is blended in the pit by simultaneously introducing A and/or B seam coal with C,D and/or E. This is accomplished by dumping haulage trucks with A or B seam coal and reclaiming C,D and/or E coal from stockpiles with a front-end loader.
The coal from the pit and stockpiles passes over a 380×460-mm grizzly, with undersize collected in a 350-tonne bin. The coal is then fed by a variable spe ed apron feeder into a 3,350×7,300-mm rotary breaker, which is basically a large rotating drum with punch plates. The coal is tossed around in the drum and escapes through small holes (about two inches in diameter) to a conveyor.
The raw coal is reclaimed by variable speed vibratory feeders and conveyed to the wash plant at the rate of 450 tonnes per hour. The raw coal is then slurried and and sized at 0.5 mm using de-sliming sieve bends and vibrating screens.
The plus-0.5-mm material is combined with magnetite media and pumped to the heavy media coal recovery circuit. The large difference in specific gravity between rock and coal allows the use of gravity separation to produce clean coal. The coarse circuit includes a heavy media cyclone for separating coal and waste, four clean coal drains and rinse screens, two refuse drains and rinse screens and magnetic drums for magnetite recovery from the wash water.
The majority of the coal (75%) is coarse in nature. Wolf Nickel, preparation plant superintendent, noted that dual circuits were installed for cleaning coarse coal and that this allows maintenance to be done on one circuit while the other is operating. The plant, he stated, is designed to handle up to 33% of the feed as fine coal. The plant has a single fine coal circuit.
The minus-0.5-mm material, fine coal, is pumped to a 2-stage water- only cyclone circuit and the primary cyclone overflow is sized at 100-mesh with oversize reporting as clean coal. The undersize material reports to Denver flotation cells. Primary cyclone under-flow is fed to the secondary water-only cyclones which scavenge some missed coal and feed it back to the primary water-only circuit. Clean coal less than 0.5 mm is dewatered using disc filters. Fine coal centrifuges are installed to assist during high fines conditions.
Dewatered cleaned coal is conveyed to an eni Model 12.5 stoker-fired thermal dryer which is capable of reducing the moisture content to 6.5% from 14%. This dryer is fired by a stoker coal unit which produces a fluid bed drying action. Dried coal is then conveyed to a 5,000-tonne clean silo.
Instrument and equipment communication throughout the plant is provided by a programmable logic controller. Interlocking and relay logic associated with process equipment is performed by a computer program. As a result, the dryer and clean coal loadout system can be operated on a remote basis from the central control room. A detailed record of equipment annunciation and startup and shutdown times are provided on a continual basis by a printer. Equipment repair history and maintenance costs in each unit operation of the coal plant are stored in the computer.
Waste material from the plant (about 500,000 tonnes per year) is transported from the preparation plant by scrapers. A large portion of this material is used for construction of the tailings dam embankment and the remainder is disposed of in the coarse refuse dump. Fine refuse is transported as slurry to the tailings pond.
Clean coal is hauled by truck in specially designed trailers for on-highway hauling a distance of 35 km to the rail loadout. The loadout is 5 km from Tumbler Ridge, a community built specifically for northeast coal. From there it is either conveyed to two 11,000-tonne train loading silos or stockpiled. The loadout system uses pre-weigh bins and has been designed for a rate of 6,000 tonnes per hour. The system was supplied by Ramsey/Pebco. Under actual operating conditions a 98-car unit train can be continuously loaded with 9,000 tonnes in fewer than four hours.
Rail cars are sprayed with a latex solution to minimize dust losses en route to the port facility at Prince Rupert.
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