A new hot mix asphalt plant is in pole position to take advantage of the development boom in British Columbia’s Lower Mainland.

Officially described as “Columbia Bitulithic’s Port Kells asphalt facility,” the plant is located some 35 km south east of Vancouver, on the south side of the Fraser River and close to Golden Ears Bridge project. The new set up includes a new stationary drum mix plant, high capacity raw material storage, multiple feed bins, bag house, finished product storage, control tower and truck load out, together with a batch tower transferred from Columbia Bitulithic’s decommissioned Coquitlam plant. Add extensive air and water quality protection measures as well as noise reducing equipment to that list for an impressive example of modern hot mix asphalt production technology.

Larry Howorth, the company’s general manager of asphalt plants in the Greater Vancouver Area, explains that the new location was selected to take advantage of current and projected growth south east and east of Vancouver. “The plant is well positioned to meet the increased demand for asphalt in Surrey, Langley and Abbotsford south of the Fraser River as well as Maple Ridge north of the Fraser on completion of the Golden Ears Bridge in 2009. Having both drum and batch capacity provides full market coverage. High volume contracts can be supplied from the drum plant while smaller volume retail business or specialty mixes can be supplied from the batch plant. The batch plant also provides winter operating flexibility. Here in Vancouver we tend to keep our plants open pretty well all year round, shutting down only a few weeks for winter repairs.  On many of those winter days, the batch plant comes in very handy for mixing smaller loads of the various mixes, including cold mix, which is best produced in a batch plant for safety reasons.”
    
In operation, aggregates arriving on site are stored in one of six storage bays, each with a capacity of 5000 tonnes. Reclaimed Asphalt Pavement (RAP) will be stored separately in a 2500 tonnes capacity bay. Material is recovered from these bays by wheel loader to charge a bank of eight cold feed bins or four RAP feed bins. Cold feed and RAP are conveyed to the plant separately, with both conveyor systems incorporating a 4x10 scalping screen to pre screen all feed material. Asphalt cement is pumped to the plant from one of three 120 tonnes capacity tanks. The hot mix plant itself teams an Astec Double Barrel drum mixer with a Phoenix Talon PT100 burner to provide a nominal aggregate drying capacity of 363 tonnes/h. Within the drum, feed aggregates are dried and superheated in the rotating inner dryer drum of the plant. The heated aggregates then discharge into the stationary outer shell of the plant where RAP, other additives and asphalt cement are added as required, with mixing provided by paddles on the outside face of the rotating inner drum. The resulting asphalt mixture is transferred via a drag conveyor and a silo top conveyor system into four product silos, each having a rated capacity of 270 tonnes, giving a total of 1080 tonnes of finished product storage. Underneath the product silos are two 41.2 m long Pacific Industrial scales, with each scale served by two silos. After loading, trucks pull forward to the end of the scale where the driver collects a ticket from a remote printer and heads for the job site.

General plant superintendent Reynold Amey explains the thinking behind some key design aspects of the new operation. “Having eight cold feed bins compared to the four to six of many plants allows the mixing of an increased variety of aggregates. Some of these may be the same size though from a different location and therefore necessitating a separate mix design. This mix design flexibility is expected to become increasingly important as aggregate supply tightens and sources are changed more often. By the same token, having four recycle feed bins where most plants have only one or two will allow increased RAP usage through improved control of recycled asphalt cement and rock being added to new mix. This makes good business sense, as higher RAP content means significant cost savings from reduced virgin asphalt cement and aggregate demand. Stockpile covers are provided for RAP, sand and 7 mm minus materials, that is, feed materials containing fine sized fractions. These covers keep stockpiles dry, resulting in lower drying costs. At the same time, the covers also help control fugitive dust emissions, an area that is attracting increased regulatory scrutiny in addition to odours and noise. On that note, the Greater Vancouver Regional District (GVRD) required the entire site to be paved to reduce dust emissions, a good practice in any case to eliminate mud tracking or stockpile contamination in wet weather.”

The extensive list of environmental protection measures continues. The asphalt cement (A/C) tanks are fully contained (along with a 6000 gallon diesel tank) and their vertical rather than traditional horizontal mounting conserves much needed space. Oil flow to the plant is controlled by air actuated valves on the A/C tanks, while vent condensers on the top of the each tank cool the exiting gases so that hydrocarbons in the gas stream are condensed and drain back down into the tank.

On the plant, variable frequency drives on both the burner blower and the baghouse exhaust fan result in both electrical savings and a significant reduction in the noise generated by each component. As a result, it is possible to stand on the burner platform and carry on a conversation at normal volume with the burner firing at full capacity.

Both odours and volatile organic compounds (VOC) emissions are minimized with the Double Barrel technology. The exhaust system that evacuates steam and products of combustion from the inner drum also evacuates steam and hydrocarbons from the mixing chamber. These are pulled back through the aggregate dropout holes and into the flame for incineration.

The air emissions permit that Columbia Bitulithic was required to obtain from the GVRD included the company’s own request for a permit that would authorize a maximum of 47 tonnes of total emissions per year. By comparison, the Port Kells plant replaces two older plants that are currently authorized to emit up to 330 tonnes per year and current air emissions in the GVRD are in the order of 3.4 million tonnes per year, not including carbon dioxide. The plant will be fired by natural gas, with low sulphur diesel fuel as back up in accordance with the air quality permit.

The baghouse is fitted with micro-denier capped Nomex bags providing much higher dust collection efficiency than standard bags. As a result, the baghouse is expected to emit less than 20mg/m3 of aggregate dust, or 50 per cent less than the current maximum outlet concentration requirement of 40mg/m3.

The plant’s silo-top blue smoke package is designed to minimize odours and the escape of hydrocarbons associated with the filling of the product storage silos. Instead, captured hydrocarbons are ducted back to the dryer burner where they are injected into the flame for incineration.

Surface runoff from the whole operation is directed to an oil/water separator, sediment pond, and water treatment system that chemically precipitates out and captures suspended solids, and includes a specially modified 12.2 m cargo container for the flocculent system. All run off water discharged from the site must be four times cleaner than the nearby Fraser River is today.

Close attention has also been paid to the production process, with mix production automated by a PC based control system instead of panel mounted, push button control systems, thereby bringing all of the plant’s controls onto one computer screen. This system, together with closed circuit cameras at key process points, give the plant operator close control over mix selection, production and storage. During truck loading, the long scales mean that both tare and gross weights can be measured live, as even trucks with pup boxes are fully on the scale throughout the loading cycle. One scale is designated for internal customers and the other for external customers to provide faster service and trucking cost savings for all customers.

Now hidden, the plant’s design and location also necessitated significant foundation works. Seismic (earthquake) concerns meant engineering for and placement of a total of 56 piles, some of which had to be driven to a depth of 33.6 m to support major plant components such as the silos, liquid AC tank farm, slat conveyor and drum mixer. The pile cap (concrete foundation constructed atop the piles) for the silos is 15.25 m. x 12.2 m x 1.22 m thick while a 225 tonnes capacity crawler was required to lift the silos themselves onto the foundation base plates. Despite these challenges, it took only 16 months from the beginning of the rezoning application to project completion and plant start up, with an actual plant construction period of just seven months.

Columbia Bitulithic is a division of Lafarge Canada Inc.