Dust settles at Bracalba Quarry

Brisbane CityWorks operates three sites in south east Queensland: Pine Mountain Road Material Recycling Facility and the Mount Coot-tha and Bracalba Quarries.

The company's Bracalba Quarry commenced operations in the early 1990s and supplies road base, concrete and asphalt aggregates, and decomposed granite fill from the site.

With production exceeding 600,000tpa, the quarry prides itself on its high productivity and advanced production methods. Regular site surveys and evaluations ensure that quarrying and crushing operations maintain the company's high standards. As part of the company's regular reviews, the quarry's manager, together with the maintenance and project manager, sought input from a number of dust suppression specialists to review the way the crushing plant dealt with dust and assessed the advice received.

While the traditional water spray dust suppression system was working well, their assessment indicated that further improvement was possible from more modern technologies. As a result a scope of works was written around the plant's dust suppression needs using filtration technology. The quarry looked at water nozzles, water fogging and extractive filtration. While all are good systems, they felt that water fogging was an unproven technology, whereas the company has filtration systems in other plants. They also thought standardising on the filtration method with the other plants was a beneficial move for the future.

Other criteria considered included ease and cost of maintenance and the life expectancy of the equipment. The quarry was looking for equipment with a reasonable life and that was well built. The maturity of the technology was also an important factor. Deciding on the final choice of equipment was the hardest as there was not much between them. All the suppliers put forward very professional submissions, with sound engineering principles and solid construction behind them.

The final decision was based on a combination of factors: cost versus value, waterproof, longer lasting filter bags and sturdy construction.

The Dust Services Australia-designed and installed system extracts 4-5t of .75 micron dust an hour from the screening and crushing plant. The collector uses 121 x 5m-long snap cuff-style bags that filter 36,000m3 an hour. The dust is either returned to the plant's final discharge or gets mixed with products at a metered rate. The ducting fitted is of heavy wall construction with flanged bends. The ducting was all made by Dust Services Australia and installed with only one Saturday's downtime to the plant.

The system is fitted with a PLC controller that monitors the pressure of the collector and adjusts the pulse to suit the dust loading of the filter bags. This automatic monitoring and continuous adjustment can extend filter life by up to two years. The information is stored on the controller and is downloaded at each service. Converted to graphs, it shows dust loading peaks and how many pulses the collector has completed to let users schedule a filter change in advance.