Canada's “Rock to Road” Magazine

September/October 2007 Issue

• High capacity B.C. quarry targets U.S. concrete markets
• Contractor digs deep for returning troops
• Green sand recycling program pays big dividends for Edmonton
• 2008 Buyers Guide

For a copy of the issue that contains these articles with colour photos, click here.

High capacity B.C. quarry targets U.S. concrete markets

By Andy Bateman, Engineering Editor

     Still in its first year of operation, Polaris Minerals Corporation’s new quarry has major concrete aggregate customers in San Francisco and B.C’s Lower Mainland, with more sure to follow.
     Located at the northern end of Vancouver Island on Broughton Strait, the Orca Quarry is some four kilometres west of Port McNeill and went into operation in February 2007. Herb Wilson, senior vice president and chief operating officer, explains the quarry is permitted to produce six million tonnes of sand and gravel annually and, with the expectation of strong demand for its concrete aggregates, every aspect of the process has been designed with high capacity in mind. In the short time since Orca’s opening, those demand expectations have already been met with the frequent arrival of 70 000-tonne capacity Panamax class bulk carriers bound for San Francisco and barges on the shorter run to the Lower Mainland.
     Plant capacity numbers certainly reflect the design goals, with Wilson reporting peak and operating average throughput rates of 1500 tonnes/h and 1200 tonnes/h, respectively. Four finished product stockpiles, two for sand and two for gravel, each have about 125 000 tonnes gross and 44 000 tonnes live capacity to ensure adequate inventories for rapid vessel loading. Aggregates drawn from these huge stockpiles are conveyed to ships or barges by a 5000 tonnes/h capacity reclaim and conveying system and loaded by a single quadrant shiploader of similar capacity. (See “Shiploader installation goes like clockwork”, Aggregates & Roadbuilding December 2006).
     Orca’s processing plant separates material into three concrete aggregates; coarse gravel, fine gravel and concrete sand, and consists of primary screening with a crushing circuit, secondary screening, washing and sand classification, product storage stockpiles and a product reclaim system. Downstream of the sand classification system, a sophisticated silt recovery and water recirculation system eliminates the need for settling ponds and minimises the requirement for process make up water.
     Like any aggregate operation, good reserves are essential for Orca’s long-term success, where “good” is measured in terms of quantity, quality and location. Orca scores high on all three counts. The new plant is currently processing the East Cluxewe deposit, the first of three here, containing reserves of 121 million tonnes of high-quality sand and gravel. This deposit contains about 70 per cent sand and 30 per cent gravel and, as most of the gravel is already naturally sized at 25 mm or smaller, only about 12 per cent of the pit run has to be crushed. That is good news for customers, as concrete containing aggregates with a high percentage of natural rounds means concrete with excellent mixing, pumping and finishing characteristics.
     Production begins with scrub removal, followed by the stripping and storage of a thin layer of overburden for later rehabilitation. In a rare application for these machines, both primary loading and hauling are then completed by scrapers. The deposit is generally loose enough for the two Caterpillar 637G scrapers to self-load, though their design provides for push pull loading or standard push loading by dozer if required. The loaded scrapers then discharge over a relocatable drive over hopper, under which two belt feeders equipped with Torspec variable speed drives maintain a steady flow of pit run onto the plant feed conveyor belt.
     Pit run arriving at the processing plant is stockpiled in a plant feed surge pile with 90 000 tonnes gross and 28 000 tonnes live capacity to provide several shifts of running without recharge if necessary. Material drawn from the surge pile is first screened on a pair of Metso 6x20 double-deck dry screens fitted with 50 mm and 25 mm cloths on the upper and lower decks, respectively. All material larger than 25 mm is directed to a Metso HP 400 cone crusher, while material smaller than 25 mm is conveyed to two Metso 8x24 double-deck washing screens fitted with 12.5 mm and 4.75 mm cloths on the upper and lower decks, respectively. Material sized at 25 mm x 12.5 mm retained on the top deck is stockpiled as large gravel while 12.5 mm x 4.75 mm material is stockpiled as small gravel.
     Meanwhile, sand slurry (minus 4.75 mm material and water) passing the bottom deck of the wet screens discharges into a sump and pumped from there to a bank of four McLanahan LPT VD 21 dewatering screens. Finished sand product retained on each dewatering screen is conveyed to sand stockpiles one and two, while fine material and water passing through the screens is pumped up to LPT S 830 cyclone separators mounted above each screen. Cyclone underflow containing recoverable sand fractions discharges back onto the dewatering screen, falling on top of the bed of material already on the screen to increase sand recovery. At the same time, overflow from each cyclone containing water and silt (very fine sand less than 75 microns in size) is directed to a 18.3 m diameter McLanahan high-rate thickener via a gravity flume. Inside the thickener, anionic flocculent is added to encourage the fine particles to clump together and so accelerate the separation of fines and water. Fines accumulate on the thickener bottom while clear water overflowing from the top is recycled back to the operation’s process water supply tanks. Settled fines are recovered from the bottom of the thickener and pumped to a conditioning tank, where cationic flocculent is added to disperse the fines before the fines and water mixture is fed to a pair of 3 m wide Phoenix belt filter presses. The presses squeeze excess water out of the slurry and the resulting silt cake is hauled back to the pit for storage.
     Wilson emphasises that the overall plant design construction and operation has been a team effort, and in particular points to the contribution of the local workforce: “From the beginning, local people have been closely involved and are among the best I’ve ever worked with. One example that comes to mind was our electrical contractor who, on his own initiative, decided to install thousands of metres of electrical cable one Sunday when other trades were not working. This gave our plant completion a huge boost and was part of the reason we were able to begin production on schedule. With construction completed, our commitment to the local workforce continues under an agreement with two first nations in which half the workforce is first nations. To help achieve this, we have provided over 6000 hours of employee job training in operations, health and safety, first aid and mine rescue.”
     Major suppliers to the construction project included Metso Minerals, who completed the detailed design of the plant from the raw feed conveyor to the finished stockpile conveyors. The McLanahan Corporation was subcontractor to Metso Minerals for the dewatering screens, thickener and conditioning tank. Structural steel was fabricated on Vancouver Island and trucked to the site, while the product stackers were built by U.S. based Swift Manufacturing. ORCA and its contractors completed foundations, reclaim tunnels and the load out system. The 1.37 m wide, 1.5 km long load out conveyor system was supplied by Continental Conveyor & Equipment Company through their west coast agent and installed by Orca employees.
     The Orca operation provides some interesting additional examples of efficient plant and process design. Its mobile equipment fleet, for example, is relatively small compared to many other aggregate operations of similar capacity and includes, besides the two scrapers, just a Caterpillar D8T dozer, a 980H wheel loader, and an IT 38 G Series II Integrated Tool Carrier. This small fleet demonstrates the application of two established materials handling practices: once material has been picked up, minimise the number of times it is dumped, reloaded and hauled by mobile equipment. Secondly, when moving material between two fixed points, conveyors provide a lower operating cost per tonne than a loader and truck fleet of similar capacity. The Orca feasibility study mining plan identified that four scrapers would be needed to achieve maximum design capacity and the company anticipates adding a third unit in the spring of 2008.
     At the front end of the process, the use of scrapers replaces a possibly bigger fleet of primary loader(s) and haul trucks. During the process, the connection of all process stages by conveyor or slurry line eliminates the need for intra-plant material transfer by loader or truck. Finally, all finished products leave the operation via the shiploading conveyor.
     The availability of electricity at reasonable cost is also an important component of the economics of an aggregate operation. In general, operations will install mains power where practicable as the cost per tonne of power from diesel driven portable generators is usually significantly higher than mains power in the long run. At Orca, mains power is provided through a 25kV line of BC Hydro, with one connection providing power for the shiploader and the other for the rest of the processing plant. Transformers step the power down from 25 kV to 4160 volts or 600 volts as necessary.
     Polaris’ approach to community relations and the environment was recognised in a 2007 award from the Prospectors and Developers Association of Canada. The award recognised Polaris for “establishing excellent community relations and environmental practices during the exploration and subsequent construction of its Orca Quarry near Port McNeill on Vancouver Island. The company set up partnerships with First Nations communities that have enabled bands to have an equity stake in the operation, and two of the largest quarries of their kind in Canada have been successfully permitted with the support and cooperation of the local community.”
     The Award also recognised the company’s environmental approach, noting that, “Polaris has also exceeded expectations in its attention to the protection of the environment. For example, the processing plant at the Orca Quarry will feature a closed circuit water recycling system to ensure that no process water will be discharged into the environment. The system includes a filtering process that eliminates the use of settling ponds, minimizes silt handling and clean-up costs and allows for the silt to be used to beneficiate the soils during reclamation.”

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Contractor digs deep for returning troops

By Andy Bateman, Engineering Editor

     An infrastructure upgrade project at a Canadian Forces Base places unusual demands on excavation and sewer installation equipment.

    The months of July and August 2007 saw soldiers based at Canadian Forces Base (CFB) Petawawa returning from their mission in Afghanistan. Those returning to the Married Quarters at the base found significant construction activity, with an infrastructure upgrade project underway to replace aging water and other services. For its contractor, the project’s deep excavations have posed some unusual challenges requiring significant digging, lifting and pulling capacity.
     CFB Petawawa is described as one of Canada’s leading military bases, closely linked to its host community of the Town of Petawawa, as well as the City of Pembroke and the sixteen other municipalities that make up Renfrew County. Established in 1905, personnel numbers for the base include 5,100 military, 7,700 family members and 1,000 civilian employees for a total of 13,800. Of these, approximately 6,000 live in local communities of the Ottawa Valley, with the majority living between Deep River and Pembroke.
     Contract PA045511 provides for extensive infrastructure upgrades to the Married Quarters (MQ) at the base, some of which date back to the 1950’s. Officially described as the Parental Marriage Quarters Municipal Upgrade, the contract is valued at $1.77 million and includes full replacement of sanitary sewers, storm sewers and water mains, as well as service replacement to each unit on Moreuil Wood Blvd., Dieppe St., Liri Ave. and Ortona Ave. (War historians will recognise that street names at CFB Petawawa are named after famous conflicts). Following pipeline installation, surface work has included road reconstruction, asphalt paving and sidewalks and is on target for completion in November 2007 after a July 5th 2007 start. Construction conditions are typical of the area, with loose sandy soil and generally dry working. At shallow depths, these conditions make for easy digging, but it has been a different story in some locations due to excavation depths of up to 10 m and large diameter storm sewer installation.
     To tackle the deep excavation work, contractor R.G.T. Clouthier Construction Ltd. put the company’s new Liebherr 954 excavator into service and reports good results. Besides excavating duty, the excavator has had the necessary capacity to handle heavy items such as double trench boxes as well as the reach to place pipe bedding, cover material and 6 m long sections of storm sewer pipe.
     Occasionally, more lifting power in the shape of a 90 tonnes capacity Liebherr LTM1090 mobile crane has been necessary to deal with the installation of heavy precast concrete pipe sections. A Hanson STC 6000 precast concrete stormceptor (storm interceptor), for instance, weighed in at 12 tonnes and was lifted with the LTM1090 set well back from the edge of the deep excavation to ensure a safe and uneventful lift.
     R.G.T. Clouthier Construction Ltd. is Pembroke Ontario and activities of this vertically integrated business include heavy civil, as well as municipal and road construction. The aggregates side of the business includes aggregate production and delivery, custom crushing, screening and asphalt and concrete recycling with some 10 company owned pits and 10 leased pits. The group’s affiliated companies include Valley Crushing and the Pembroke Machine Shop.

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Green sand recycling program pays big dividends for Edmonton

     An award-winning processing system for decontaminating and recycling winter street sand rather than disposal in a landfill is being used by the City of Edmonton to save millions of tax dollars while generating significant environmental benefits.
     Depending on the severity of winter, approximately 165 000 tonnes of sand and salt are spread on the city’s 15 000 lane-km of paved roadways as traction aids to keep traffic moving and stopping safely. Roughly 70 per cent of these materials are subsequently picked up each spring through street sweeping operations. Historically, only about 25 per cent of the street sand has been recycled, usually by blending the recovered sand with new sand. Most of the remaining street sweepings, containing sand, salt, clay, leaves soil and other debris were deposited in a Class 3 (unlined) landfill.
     In 2001, it was determined that the street sweepings exceeded new stricter Alberta Environment guidelines for salt contamination by five to 10 times the permissible levels and, as such, had to be disposed of in the city’s Class 2 (lined) Clover Bar landfill facility. That year, more than 115 000 tonnes of winter street sweepings were recovered – an amount equal to 50 per cent of the total weight of contaminated materials delivered to the Clover Bar facility in an average year. It was clear to city officials that landfilling of winter street sweepings would have a negative impact not only on the life of Clover Bar and the city’s finances, it also accelerated the depletion of valuable, non-renewable sand resources.
     Due to high construction demand in the past 20 years, all of the local sand deposits have been depleted. Edmonton’s nearest sources of raw sand are currently more than 100 km from the city limits. According to Barry Belcourt, director of roadway maintenance for Edmonton, the city was spending up to $3 million annually buying sand for its winter sanding operations. A less costly and more environmentally acceptable alternative to existing practices had to be found.
     In 2003, the City of Edmonton’s Transportation and Streets Department established, in partnership with the Edmonton Waste Management Centre of Excellence (EWMCE), a two-year pilot project to determine the feasibility of reclaiming and recycling winter sand. The goal was to produce a cost-effective, environmentally acceptable product that was as clean as the original material while meeting the city’s gradation specs for street sand. The pilot project was partially funded by a grant from the Federation of Canadian Municipalities’ Green Fund. EWMCE is a North American leader in developing, commercializing and providing training in sustainable waste management technologies.
     Through its contract partner, Sand Recycling Ltd., of Edmonton, a research and development program was carried out in 2004 at the Clover Bar landfill site using a portable spread of newly-purchased screening and washing equipment. The Sand Recycling team, led by John Mundy, formerly general supervisor, Technical Services and Gravel Operations with the City of Edmonton’s Transportation and Streets Department and now the private company’s operations manager, started the pilot project with 70 000 tonnes of contaminated street sweepings. The recycling target was 65 to 75 per cent of reusable sand. After experimenting with several different concepts and equipment configurations, Sand Recycling developed a five-phase wet processing system. A dry processing alternative was rejected at the outset due to the high cost of the equipment as well as concerns regarding fugitive dust emissions from the processing operations.
     Following completion of the pilot project’s in September 2004, the results revealed an 80 per cent clean sand recovery rate from the street sweepings, 10 per cent clean fine sand, 4.5 per cent contaminated fine sand, 4 per cent litter, and 1.5 per cent oversize gravel for reuse by the city’s aggregate recycling program.

     Physical testing of the recovered sand by the city’s laboratory did not indicate any difference between the recycled and virgin winter sand. Chemical analysis also indicated that most of the contaminants (salt, hydrocarbons, heavy metals, etc.) contained in the fine sludge could be removed for disposal in a Class II landfill. The success of the project exceeded the city’s expectations by a substantial margin and clearly showed that Sand Recycling’s process could recover and decontaminate street sand to new sand specs at a cost well below market value for new sand. Based on the technical and economic success of the initial stage of the pilot, the city and EWMCE entered into a six-year agreement to recycle more than 900 000 tonnes of street sweepings in Edmonton.
     The pilot project was expanded in 2005 to process some 115 000 tonnes of street sweepings. A number of modifications were made to improve the efficiency of process system and to further reduce the quantity of litter and contaminated material directed to the landfill.
     In 2006, Sand Recycling relocated its spread of portable equipment to Edmonton’s Poundmaker Snow Storage facilities in the city’s west end. Here, the plant produced approximately 120 000 tonnes of recycled street sand from approximately 150 000 tonnes of sweepings.
     According to John Mundy, this is believed to be the largest street sand recycling program in the world. The success of the project is generating annual savings of more than $3 million for the city while reducing some 700 000 km of truck haulage from outlying sand pits. Fewer trucks on the road hauling sand is lowering greenhouse gas emissions by up to 1400 tonnes per year. In addition, street sweepings are now being collected from neighboring municipalities including the County of Strathcona, the City of Fort Saskatchewan and the City of St. Albert.
     The revolutionary street sand recycling program has recognized by the Transportation Association of Canada (Environmental Achievement Award) and by the American Public Works Association - Alberta Chapter (Technical Innovation Award, Project of the Year). It is also a key component in Edmonton’s EcoVision program to protect the environment.
     During Aggregates & Roadbuilding’s recent visit to Sand Recycling’s operations at the Poundmaker site, the plant was running at full capacity processing a record amount of street sweepings. Last winter’s severe weather saw 180 000 tonnes of street sand and salt spread on city’s streets and parking lots to deal with the icy road conditions. More than 140 000 tonnes were subsequently picked up during the sweeping operations in April, May and June.
     The plant normally produces 1200 to 1400 tonnes of clean, decontaminated street sand per day. Mundy states that the plant operates 11 hours a day, seven days a week. The target is to run the plant 110 days a year to produce around 150 000 tonnes of recycled street sand.
     The continuous processing operation begins with recovering the street sweepings from a stockpile using a 3 m3 New Holland LW170 wheel loader. The loader dumps the material into a 1.5 m dia. x 4.2 m long McCloskey 14R trommel screen, fitted with 25 mm openings, which separates the sand and miscellaneous debris from large litter. A second, larger New Holland LW230 wheel loader equipped with a 3.6 m3 bucket, transports the sand and small size litter discharged from the trommel to an ELRUS 7.6 m3 capacity variable speed grizzly feeder. The material is conveyed from the feeder onto an ELRUS 7x16 triple-deck screen with 25 mm, 15.8 mm and 10 mm openings on the top deck, middle and bottom decks, respectively.
     The top deck is used to remove litter such as leaves, twigs, wood, plastic and metallic fragments including coins, keys and other small objects. The plus 10 mm material retained on the second and third decks are taken off and stockpiled for the city’s aggregate recycling program. The minus 10 mm bottom deck throughs are conveyed to a pair of Ortner Series 4000 material classifiers which wash and separate the coarse and fine particles. Each machine is powered by a 15 hp electric motor and has a capacity ranging from 108 to 190 tonnes/h. Sand Recycling has configured each machine to achieve an output at the lower range of the 4000’s capacity due to the unique nature of the application.
     The operating principal of the Ortner 4000 is fairly straightforward. Material is fed to a slowly revolving pan on an incline and vibrated at high speed. The high-speed vibration separates the various sizes of material with the fines and water rising to the top and flowing over the pan’s edge to the discharge. The coarser particles sink to the bottom. The rotating pan carries the settled particles up the machine and out of the water, where a stationary plow diverts the dewatered material to a center discharge spout. The driving and vibrating mechanism is mounted under the pan, preventing any contamination with the water and processed material, thus increasing the life of the components. It is possible to vary the angle, speed, and vibrations of the pan. This, claims the manufacturer, gives the Ortner a wide range of flexibility and increases its capacity and efficiency. Another advantage of the Ortner is its relatively low water usage compared with a conventional sand screw.
     The overflow with the 300 micron material goes to a slurry box for further processing while the clean sand is conveyed to two 6x12 Sizetec VDS410-4 intensive dewater screens that reduce the moisture content to approximately 10 per cent. The sand is stockpiled for additional drying by both gravity and air. At the end of the 30 to 60-day drying cycle, the moisture content of the stockpiled sand is less than 5 per cent.
     The slurry box material is pumped to four 254 mm diameter Krebs model DSF10LB hydrocyclones that remove 75 per cent of the water. The remaining solids are discharged onto a 4x10 Sizetec fine sand dewatering screen. The resulting material is sold to mudjacking contractors or used as fillcrete.
     The plus 80 micron material goes to a Terex Finlay Siltmaster 45. The Siltmaster, with the aid of a flocculent, allows the continuous removal of clay and silt from waste water before it is discharged into the two seepage bays. Each bay holds 300 tonnes of solids. Approximately 150 tonnes of the material is removed daily by wheel loader to an adjacent field where it is air dried to achieve a moisture content of about 30 per cent. The material is then sold as landfill cover. Virtually all of the 4.1 million l of water used per day in the street sand recycling process system is recycled.
     Mundy estimates the cost of buying new sand and landfilling the street sweepings was approximately $70/tonne. The winter street sand recycling program has reduced costs dramatically to between $15 and $18 per tonne. Other snow belt areas across western Canada faced have indicated interest in the processing system. He adds that Sand Recycling is exploring marketing opportunities to extend the company’s operations to these communities.
     Key personnel involved in Sand Recycling’s winter sand recycling project are business manager Phil Haug and operations supervisor Jason Mundy who is responsible for the day-to-day production activities.

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September-October 2007 issue

Aggregates and Roadbuilding Magazine
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