graymont seeks to install dust-control equipment

Graymont Western Canada is planning to undertake a $2.5 million project to enhance dust control measures at the company’s Exshaw plant, located just east of the hamlet.

Exshaw plant production superintendent Wayne Hingley said Graymont approached Alberta Environment in December seeking permission to install a total of three baghouses, a device that traps and collects dust in large fabric bags, on the plant’s stone crushing, screening and conveying systems.

While Hingley said it is not possible for Graymont to collect all of the dust it produces during plant operations, he added the baghouses would significantly decrease the amount of dust it produces over time.

“When you are crushing stone there is always going to be some emissions, but that is where putting in the right dust-collection system and maintaining it should help a lot,” Hingley said.

At this point, the Graymont board has approved the project and the expenditure, but the company is waiting for approval from the province before moving ahead with construction.

Hingley said Graymont has confidence Alberta Environment will look favourably on the proposal, as it is not tied to production, but controlling emissions. Hingley added construction would begin once approval is obtained and he expects the work would be completed by the end of the year.

The company is also planning to install dust collectors on the conveyors and storage silos used for the plant’s finished products, such as quicklime and hydrated lime.

The proposed baghouses will complement previous dust control measures at the Graymont plant that include replacing the Kiln No. 2 wet scrubber – an older, less effective dust control technology – with a baghouse, a sweeper, paved roads, a wash station and vacuum for trucks leaving the plant, windscreens, spraying water on the crusher and planting vegetation to reduce the amount of dust that the wind picks up from the open ground.

The baghouses, however, are expected to have the greatest effect on dust emissions, which has been tracked for the past few years by an ambient dust monitor operating east of the plant.

“This is probably one of the big steps for us but we feel this will have a significant impact on dust emissions,” he said.

Along with dust produced during the initial stages of rock crushing, screening and conveying, Graymont plant also produces lime kiln dust (LKD), a byproduct of burning limestone in the plant’s kilns.

LKD is incorporated into the finished materials, bought by Lafarge North America as an additive for its ready-mix cement and incorporated into cement manufactured at the Lafarge Exshaw plant. The remaining LKD is sent to the Class III Francis Cooke Landfill.

Each year, Hingley said, Graymont is sending less and less LKD to the landfill.

In 2011, for example, the plant hauled about 1,000 tonnes of LKD to the landfill, which is down from previous years amounts of 3,000 to 4,000 tonnes.

Burning natural gas over coal does help to reduce the amount of LKD, as coal ash increases the amount of LKD the plant produces.

Graymont is also working with the Municipal District of Bighorn on a project to amend treated sewage sludge – also referred to as biosolids – with waste lime dust to create a compost that can be used in quarry reclamation.

The dust collection project stemmed from priorities identified by the plant’s dust team comprised of front-line staff, equipment operators, supervisors and plant management, established as part of the 2010 operating permit renewal process.

“Through that process we committed to reviewing and improving our dust mitigation measures at the plant,” he said.

“We identified a few locations mainly in our crushing, screening and stone handling systems that we felt were our highest priority targets for addressing dust emission systems.”