Modern Mining January 2018

DIAMONDS

achievement, including an average 5 % effi- ciency improvement through the use of IE3‑rated Top Premium electric motors – which deliver an almost constant efficiency in the 75-100 % load range. Energy savings on all conveyor drives and pumps will be further enhanced through controlling them with vari- able speed drives (VSDs). Standardisation on LED lighting in and around the plant is another energy saver, while all motor control centres (MCCs) are equipped with multi-step, low-voltage power factor cor- rection units, enhancing their ability to manage current load and reducing the risk associated with medium-voltage units. Powering the mills with a medium-voltage VSD drive motor com- bination makes for more efficient control of the load and torque required. The leaner infrastructure comprising the new plant is well reflected in the drastic reduc- tion in the sheer volume of equipment in operation. The number of conveyor belts has been reduced from 151 in the old plant to just 22 – cutting the distance covered by these belts from 15 km to 3 km. There is now less need to pump slimes due to the new design that allows slimes to be gravity fed to the tailings dams, and the number of pumps is down from 121 to only nine. With the slimming down of conveyors and other equipment, the number of

‘Cullinan Heritage’ – worth over US$35 mil- lion, and a 122,5 carat blue diamond worth almost US$28 million. Dippenaar expects the plant ramp-up and optimisation into early 2018 to give clarity on the economic level of recovery of the fine dia- monds, which are the small stones of minus 5 Diamond Trading Company (DTC) sieve size; they constitute only a small percentage of over- all value, however. The plant’s comminution improvements will contribute to the mine’s strategic aim of improving its recovery rates and better grades. Despite the much-reduced footprint of only 5 ha – just a fifth of its predecessor’s – the new plant will deliver even more punch. Its process- ing capacity of over 6 Mt/a is an improvement on the old plant’s 5,3 Mt, and will initially comprise 4 Mt ROM and the remainder from tailings. The ROM treatment will deliver 2 Mct a year, with 0,2 Mct coming from the tailings. The new design, more modern technology and reduced size have significantly improved the energy efficiency of the material flow and lowered operating costs. Overall, a 6 % saving in the maximum electricity demand costs has been achieved, following new 88 kV take-off from Eskom, and the plant as a whole will be 12 %more energy efficient per tonne processed. There are a range of contributors to this

Clean product leaves the mill section where

autogenous (AG) milling is employed for the +25 mm material.

The new design, more modern technology and reduced size have significantly improved the energy efficiency of the material flow and lowered operating costs.

January 2018  MODERN MINING  59