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MOELLER CONTROLS DUNE DREDGING

Control panels based on Moeller technology have been installed in dredge mining plants at Richards Bay Minerals, a key part of RBM's expansion towards a target of two megatons of minerals output per year.

The panels were designed at Moeller Electric's Johannesburg engineering department, and assembled in Richards Bay by authorised panel-builder Magnol Electrical.

They comprise Moeller moulded case circuit breakers, contactors and overload protection devices housed in Moeller polycarbonate enclosures to provide flameproof protection to IP65 standard.

Ranked today as the largest single producer of titanium products in the world, Richards Bay Minerals began operations in 1977 with one dredge mining plant and two furnaces, producing 400 000 t/year of titania slag.

There are now four dredge mining plants and four furnaces producing 1Mt of titania slag and 550 000 tons of pig iron per year.

RBM uses a dredge mining technique pioneered in Holland and Australia to extract the heavy minerals ilmenite, rutile and zircon (about 5% in volume) from the sand.

Dune sand is bulldozed to create very large artificial freshwater ponds some 200 metres in diameter, on each of which floats a dredger and concentrator plant.

Burrowing into the mining faces of the dunes, the dredgers advance at a rate of two to three metres per day, undermining the sand faces to collapse them into the ponds and form a slurry which is then sucked up and pumped to the floating concentrator.

At this point, the heavy minerals are separated from the sand using a gravity process and stockpiled as heavy mineral concentrate for transportation to the smelter site.

Moeller components have been used in RBM control panels from the start, traversing the continuous and often rapid advances in technology and protocols over three decades.

According to Moeller Electric's branch manager in Durban, Bradley Whitaker, control and automation panel design for the dredge mining plants is now moving towards the American protocol deviceNet, with which Moeller Electric products are fully compatible.

"Our components are mainly used for the controlling and protection functions, with the bulk of our supply comprising switchgear; that is contactors, motor protective breakers and timers for start-up and shut-down," Whitaker explained.

"All these products are deviceNet compatible, allowing complete automation of the dredge mining plant and the monitoring of operations from a single control desk," he said.

"Each dredger is controlled by third-party automation devices which include touch panels for entering and programming the position data, scanning the operating hours and monitoring service intervals.

"Dredger pumps are also controlled by Moeller's switchgear to ensure reliable running of the plant throughout the year," Whitaker added.

Higher level automation is used to control the dredger's position and speed, and to monitor the rate of material flow through the pumps.

Whitaker said that Magnol Electrical was currently working on new panels comprising cubic motor control centres incorporating Moeller switchgear, and refurbishment of various panels on the minerals separation plant.

When dredger upgrades are complete, further work is planned for the tails recovery plant.

PHOTOGRAPH SHOWS: dredge mining at Richards Bay Minerals

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