The Siemens Industrial Solutions and Services Group (I&S) has received an order from Equinox Copper Ventures Ltd. of Zambia to equip two ore-grinding mills for the Lumwana copper project with gearless “Simine Mill GD” drive systems. The “frozen charge shaker” function will be used here in ore-grinding mills for the first time. It will enable controlled detachment of frozen (i.e. hardened) charges stuck in the mill shell. Manual loosen of the sticking charge will no longer be necessary. The documentation for the drive systems will be produced with the help of the “eWD” electronic documentation system. This means that all the relevant information will be available online and it will facilitate maintenance and also the rectification of faults. The contract is worth approximately 15 million euros and the ore-crushing mills are scheduled to start operating approx. end of 2007.
The Lumwana copper mining district is around 220 kilometers to the west of the Copperbelt in the north-western province of the African state of Zambia. In this region, copper deposits have been found which can be extracted by open-cast mining. The reserves are estimated to amount approx 1.6 million tones of copper. In addition, the extraction of gold, cobalt and uranium is planned. For grinding of the ore, an SAG (Semi Autogenous Grinding) mill and a ball mill will be used.
For the two ore-grinding mills, Siemens is supplying gearless ring motor drive systems supplied with power via cycloconverters. The SAG mill has a diameter of 38 feet (11.6 meters) and will be equipped with a 18 megawatts drive system. The 26 foot mill (8 meters) will have a drive output of 16 megawatts. The drive systems are based on “Simine Mill GD”, a solution developed especially for ore-grinding mills. The variable-speed drives are controlled with the patented transvector control principle. The operating point of a drive can thus be adjusted easily and precisely to changing requirements. Soft stopping and re-starting are functions which reduce wear and, due to the lack of any gears, the cost of maintenance and repairs is considerably lower than is the case with conventional drives. Shorter down times and longer servicing intervals increase availability. Moreover, gearless drives are more efficient and work using less energy. This reduces the operating costs.
The “frozen charge shaker” will be used for the very first time for the ore-grinding mills envisaged for Zambia. The procedure developed by Siemens is used for controlled detachment of frozen (hardened) charge stuck to the inner wall of the mill shell: defined forward and reverse movements of the mill loosen the sediment. The frozen charge no longer has to be detached by hand in the tube. This shortens down times and increases availability. Damage to the mill resulting from uncontrolled dropping material is avoided.
“eWD” (electronic Web-based Documentation) will ensure that all the plant documents will be available centrally in the operator control and visualization system. All the relevant documents will be kept in electronic form at a central location. A context-sensitive link-up to the operator control and visualization system with automatic links to documents will provide the operating personnel with an up-to-date general overview at all times. The integrated search engine will ensure that important information can be found very quickly. The documentation can be updated easily and flexibly supplemented – also by adding the documents of other project partners.