Karslake is a 300m-deep open pit around 2km long. The mine produces tens of thousands of tonnes per week of kaolin, an inert white mineral used in products such as paper, plastics and paints. Imerys recovers the kaolin by washing it from the rock face using high pressure water. The resulting mixture of water, kaolin and gravel is then pumped away for further processing.
Although the downstream drying and refining processes were already automated and controlled centrally, the actual mining operation was largely manual before the addition of the ABB equipment. "The new equipment allows the pit to run with a high level of automation," explains Mark Endean, Electrical Engineer for European Global Projects. "As well as improving energy efficiency and reducing staffing levels, the information we now have available from the pit is critical for improving the efficiency of downstream operations."
ABB has supplied the mine with seven variable speed drives for controlling the primary Gravel Pumps. Two 400kW units are housed in one new switch room, while five 315kW drives are housed in a second. ABB also supplied five UMC22 motor controllers for controlling the winches that raise and lower the Gravel Pump suction pipes in response to changes in the slurry level in the pit.
The immense versatility of the UMC22 controllers made them ideal as a standard solution for Imerys. Unlike other controllers, the UMC22 works with all the main fieldbus protocols. This allows it to fit easily into any application on any Imerys site, where the company uses both Devicenet and Profibus communications. Since it opted to use UMC22 units as standard earlier this year, Imerys has purchased a total of almost 40 controllers for use across a number of mines, including Karslake.
The controller can also operate as a standalone unit. The UMC22 can take on a wide range of predefined control functions and applications (such as Direct start or Star-Delta-start) that would otherwise be the job of a programmable controller PLC. "We can install it as a standalone unit in applications that haven’t yet been automated, knowing that we can integrate it into any future control scheme," says Endean. "Our philosophy is to increase automation across all our sites."
ABB is also the standard supplier of motors and VSDs to Imerys. But in the case of Karslake, Imerys took the unusual decision to buy complete ACS800 VSD packages direct from ABB, rather than adopting the conventional approach of employing separate panel builders. "This is an arduous duty and we needed efficient cooling on the drives," says Endean. "Because ABB supplied the whole package, we know we can go straight back to them if anything goes wrong.
"ABB also managed to house the drives and peripheral equipment in compact cabinets that the panel builders couldn’t match. We effectively bought ourselves some extra space," he adds. Space was an important consideration, since Imerys opted to house its new switch rooms in refurbished transport containers.
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