WESTRAY: CURRAGH’S COAL MINE

Jerry Bell is a mechanical engineer who, for the past 16 years, has worked on the construction of coal-fired electric generating plants in Canada. Today he’s in charge of another such project, in Trenton, N.S. Budgeted at $252 million, the Trenton No. 6 unit, as it is called, is the eighth 150-MW, coal-fired unit Nova Scotia Power (nsp) has constructed since 1970.

With 20 years of experience, nsp knows what snags to look for in such an undertaking, and it has assembled a team to take full advantage of that experience. “Generally, about four to five years elapse from the time a work order is issued to the time we are operating at design capacity,” Bell told The Northern Miner Magazine at the Trenton site. That compares very favorably with similar-sized plants in other provinces and beats, hands-down, lead times required for either larger-scale hydro-powered or nuclear-powered generating stations.

But all that experience with public utilities has not prepared Bell for the task of co-ordinating his work with a privately owned mining company which depends on federal loan guarantees and (limited) interest equalization payments for financing.

In mid-April, the Trenton facility was about half finished — ahead of schedule and under budget. But despite the good performance by the 300 or so workers on site, Bell was not at ease. And with good reason. The $140-million mine being built nearby by Westray Coal, which is to supply 700,000 tonnes per year to No. 6, received full financing following our visit. Westray is a division of Curragh Resources of Toronto; and was to have financed the project on a stand alone basis pending loan guarantees from the federal government. Delays in securing those guarantees had been causing unease among nsp managers.

Just nine kilometres south of Trenton No. 6, across the East River from Stellarton (population: 5,200), Westray development got off to a good start in 1988 but has since been delayed by federal government indecision. Today, Brampton, Ont.-based mine contractor Canadian Mine Development has a skeleton crew of 5 at the site working underground one shift a day. The site is equipped to accommodate 50 miners, good for three shifts per day.

A lease to begin mining, approval for constructing a coal washing plant and other surface facilities, and an industrial discharge permit were issued by the Nova Scotia government in 1989. Since then, about $23 million has been spent clearing and leveling the site in preparation for production, which should reach a rate of 195 tonnes per hour (one million tonnes per year) by 1993. Also completed are holding ponds for settling fines out of mine water, the beginning of two 5.5×4.5-metre declines, and an underground slope conveyor which will bring development muck (and later coal) to surface.

Demand for electricity in Nova Scotia is growing by more than 3.5% per year and at an estimated capital cost of $1,680 for every kw it will produce, Trenton No. 6 is an integral component in nsp’s plan to meet that demand at a relatively low cost. The company is also building a fluidized bed plant boiler in Cape Breton to run on high-sulphur coal of marine origin. Although similar to No. 6 in electrical output and sulphur dioxide exhaust, the fluidized bed plant will require almost double the capital outlay. Trenton No. 6 will cost less because of the feed-coal quality, which, with an average sulphur content of only 0.7%, obviates the need for expensive coal-burning technology or exhaust gas scrubbing. About 60% of No. 6’s operating cost will be comprised of payments to Curragh for its coal. Trenton No. 6 is expected to generate electricity for 25 to 30 years.

Demand for electricity in the New Glasgow area comes mainly from a pulp and paper mill and a Michelin Tires plant. The Westray mine itself will be a major consumer of electricity (about 10% of Unit No. 6’s capacity). But if the Trenton No. 6 does not come on-stream on schedule, it does not mean that Nova Scotians will face brown-outs and electricity rationing. Nsp could burn costlier and less efficient alternative fuels.

Nsp plans to begin firing the Trenton No. 6 on coal on Aug. 15, 1991. “We’ve never brought a unit into production behind schedule or over budget,” Bell said. This particular unit was designed and built specifically to burn coal from the Foord seam, the 6.5-metre-thick unit of Bituminous a coal Westray plans to mine. (It can also burn other fuels but less efficiently.) Deposited originally in a non-marine environment, the coal has a low sulphur content (0.7%) and a relatively high thermal energy content (12,000 British Thermal Units, or btus, per lb). Babcock & Wilcox Canada of Cambridge, Ont. designed the boiler and Lodge Cotterell (Dresser Industries) of Toronto designed the precipitator (which removes ash from the exhaust gases) at Trenton No. 6 and have guaranteed nsp certain performance characteristics. Babcock & Wilcox is confident the boiler can meet these specifications because the design emerged from knowledge of the specific characteristics of the coal in the Foord seam.

“The plant cannot operate to its full potential without that particular coal,” plant manager Dennis Martin said. And with only a small crew at the mine compared with a full crew of 300, Bell is slightly on edge.

At the mine, twin 5.5×4.5-metre declines, critical to the project’s success, are being driven at a grade of 23%. Designed to intersect the Foord Seam at a depth of 335 metres, they had advanced about 225 metres at the time of our visit (17% of the total design length). Advance rates slowed considerably in early 1990 as the company, pending financing, cut back the mine contractors’ development crews to one shift per day. The funding was expected to be completed about one week after our visit. “We have to average eight metres per day (four metres in each decline) to meet our target,” Phillips said. Detailed geotechnical engineering by Golder Associates dictates the type of ground support (6-ft split-set bolts, steel ribs or shotcrete). Canadian Mine Development transformed two drill jumbos into a roof-bolting jumbo and a shotcrete jumbo. Muck is hauled from the face in 8-cu-yd ST8 Wagner scooptrams, dumped into a crawler-mounted rock-breaker and whisked to surface on a 1.2-metre-wide conveyor belt purchased from a New Brunswick potash mine at a cost 90% lower than that of a new belt. A short crosscut connecting the two declines was excavated a distance of about 150 metres down the declines to shorten the tramming distance from the face of the other decline.

Unlike engineering a thermal generating station, engineering a mine requires flexibility. A last-minute change in the orientation of the two declines, for example, could save Curragh’s bacon with respect to the development schedule. The layout was altered to intersect coal earlier. Although the new design results in longer tunnels (1,300 metres each) before continuous mining machines can take over, that earlier development in coal should give nsp the first fuel to fire Trenton No. 6 on schedule next summer. Phillips expects to supply 300,000 tonnes of coal in 1991 as a result of the change in decline layout. “You only have one chance to make a good impression,” Phillips said. “And we plan to do that by bringing the mine in on schedule and on budget.”

In full production by 1993, the mine is to have five active mining blocks, each with its own coal characteristics and its own continuous mining machine. This built-in flexibility should produce premium products, tailored to clients’ needs. The continuous mining machines will operate in a full retreat mining system, advancing the full extent of a block before retreating toward the escapeway. About 35% of the coal seam will be mined. The back will be allowed to collapse as mining retreats. Since 80% of the mine’s 47-million-tonne reserves lie between 450 and 600 metres below surface, surface subsidence should not occur (as was the case recently in Glace Bay, N.S.). Continuous mining machines will be purchased off-the-shelf (no new technology) every three months or so to
allow for a steady increase in production and operator training. “We’ll be looking for competitive bids on machines of the same quality as those manufactured by Joy,” Phillips said, “They are recognized as the leaders in the field.” Shuttle cars will transport coal from the face to the conveyor system and conventional 2-boom electric/hydraulic drill jumbos and load-haul-dump machines will be dedicated to development. None of this equipment has been selected and virtually every major equipment manufacturer is anxious to bid on the project.

The coal-washing process was designed following extensive computer simulations using British Coal’s “Coalwash” program and Kilborn Ltd.’s “Separation Performance Program.” The washing plant has been designed to allow flexibility in run-of-mine ash content and coal fines (material less than minus 28 mesh). Coarse coal, plus six millimetres, will be cleaned in a 2-stage, 3-product heavy medium drum separator. Small coal, 6mmx0.6mm will be cleaned in a single-stage heavy medium cyclone. Fine coal, 0.6mmx0mm will be removed by wet screening from the larger size coal, thickened, filtered and thermally dried. Dried fine coal will then be discharged onto the product coal conveyor. The plant will operate on a closed water circuit with make-up water being provided from underground. All coal will be recovered; there is no need for a tailings pond. Water content of the final product will be key to profitability. For every 1% increase in water content, the coal loses 150 btus per lb. Since the contract with nsp is sensitive to btu content, Kilborn has recommended Westray install coal-fired rotary drum dryers. “It’s easier to dry coarse coal and we’ve been pessimistic in our predictions of how much fines we’ll generate,” Phillips said, “so it will be better for us if we get less than what we’ve predicted.”

Phillips is no stranger to the development of underground coal mines. He worked for the Coal Board in the United Kingdom before coming to Canada 15 years ago to join Coleman Collieries and later Luscar, the second-largest domestic coal miner. At that company’s Cardinal River mine in Alberta, he was mine manager for several years. He became involved in the Westray project about three years ago, working on a 6-volume, “bankable” feasibility study for Placer Development when it had a property option in 1987. Today, Phillips owns a house within walking distance of the Westray mine. Tony Petrina, now chairman and chief executive officer of Placer Dome, recommended the coal project to Placer’s board of directors in 1987, but the company declined for reasons other than economics. Placer had amalgamated with Dome Mines. “So a new coal mine in the first year of the new gold mining company would not have looked good to investors,” Phillips said.

Suncor, the oil company that owned the Westray property until 1987, couldn’t afford to develop the property. Oil prices had collapsed and the company was withdrawing from the mining business. Curragh’s chairman, Clifford Frame (twice The Northern Miner’s Mining Man of the Year), recognized the potential of the project. He negotiated a deal with nsp which saves the $125-million cost of building a scrubber by using Westray’s low- sulphur coal.

The biggest risk remains financing. Although the 20-year minable reserves were calculated from only 46 drill holes, its accuracy is not in doubt. Coal has been mined in the New Glasgow area for years. Fourteen million tonnes were extracted from the same seam Curragh will mine and 56 million tonnes came from five other seams in the same geological sequence. Previous mining in the Foord seam took place on the west side of the East River. The Westray mine is in a virgin part of the same seam.

Nor is the mine and mill design considered risky. “We’ve hired the best structural geologist, the best geotechnical consultants and the best consultants in the country to design our washing plant,” Phillips said. And Westray is not building a Cadillac mine either. Much of the equipment purchased is used, so glitches due to unproven technology should not occur. That’s not to say the mine will be free of problems. Since moisture content is key, dust from surface stockpiles may annoy local residents. Also, the number and orientation of faults in the mining blocks have not been fully defined and the potential for spontaneous combustion underground has not been clearly assessed. However, the mining method and layout is flexible, and the development schedule take into account possible faulting.

Then of course, there is nsp. Bell and Martin seem satisfied Westray will come through on its promise to supply coal to Trenton No. 6 on Aug. 15, 1991, as promised. “They seem to be smart businessmen,” nsp’s Martin said. “They’re looking at all their options.”

Under the 15-year contract, payments to Curragh will be made according to the btu content of the coal shipped to the plant by rail. “If they come in at 12,000 btus per lb., they’re off to the races,” Bell said. Phillips agrees.