Over the years, Quarry has featured many new processing plants. Several of these have featured prominently, either on the cover or notably positioned, comprising new features that were actively promoted. However, we rarely revisit these plants to see how the publicised features have panned out over time.
The December 2003 issue of Quarry carried an article covering a plant that had just been commissioned by Canberra Sand & Gravel at its quarry at Bungendore, NSW. Six years on, it seemed like a good time to have another look at this operation.
Canberra Sand & Gravel oversaw all aspects of the installation of the plant, with process flow information supplied by Rivergum Industries and Jonco Inc of Ames, Iowa, USA. The Bungendore deposit contains in excess of 30 per cent clay, some of it quite plastic, with a small portion of rock. The mining method six years ago was essentially a wet mining technique, and allowance was made for the plant to take a dry feed. Now, Canberra Sand & Gravel is mining from a different area, and all mining is currently done by a 36-tonne excavator and hauling is carried out by three 25-tonne off-road trucks. After wet screening, the sand size material falls into a sump. From there two 8? x 6? pumps feed two 30? cyclones. The cyclones are necessary for reduction of the -75 micron material. The product of the cyclones feeds the classifying tank.
The 48? x 12? classifying tank, as described in the original article, simulates a riverbed with material falling naturally into particle size ranges, over valve stations. The material can then be reblended to make product specs, provided the particle sizes exist in the original feed material. Canberra Sand & Gravel are predominantly making concrete sand. According to the quarry manager, Brian Humphries, this production is consistently around 280 tonnes per hour. This material goes to one of the largest screw washers in the country, a 54? x 34? double screw. The product of this screw is placed on a radial stacker. Their secondary product is a coarse bedding sand. The rising current classifiers are used, with fresh water input, to ensure the fines are pushed further down the tank (pictured on page 29). This material is sent to a 48? x 33? single screw washer. Brian advises this throughput is in the range of 20 to 25 tph.
While classifying tanks with three valves per station typically control two products, Canberra Sand & Gravel, through its experience and knowledge of the operation of the system, has been able to control a tertiary product, a fine brickies sand. The product of the third valve station and all overflow material from the two screws are fed to a fines processing section, consisting of a bank of small cyclones and a dewatering screen. The production of this finer material is processed at approximately 15 tph. They currently operate on a 12-hour day, five and half days a week.
Sand screws and classifying tanks have been in operation in Australia for a long time. The knowledge and expertise of running them has diminished over time. They are still one of the most efficient methods of washing and classifying sand. Canberra Sand & Gravel?s Bungendore Sands operation has been a successful partnership between an inquiring producer and a supplier that has been able to demonstrate how the equipment operated. Canberra Sand & Gravel has been able to set up a plant to satisfy its market and has the ability and expertise to make specialised sands to suit its clients? needs and the market?s growth in the future. It asked questions for a long period of time, visited other operations and talked to other producers using similar equipment. Once the decision was made to purchase this equipment, an enormous amount of time was spent in conjunction with Rivergum Industries and Jonco Inc resolving the operational issues necessary to ensure the plant ran correctly from the start.
Six years on, Canberra Sand & Gravel is one of the leaders in the field of efficient washing and classification of sand for construction aggregate. The plant is operating efficiently and the company has the expertise to control the process, allowing it to separate and reblend particle ranges, as required. It has the flexibility to change pits and mining methods, change feeds and specs to suit its markets. It has produced approximately 1.8 million tonnes of product in the last six years. The wear parts replacement on the classifying tanks and screw washers has been minimal, in that time. The other components would be typical for that volume of throughput.
Jim Hankins, managing director of Rivergum Industries, acknowledges Brian Humphries and Tom Trevillian of Canberra Sand & Gravel for their assistance in preparing this article