Located near Steelpoort on the Eastern Limb of the Bushveld Igneous Complex, bordering Mpumalanga and the Northern Province, the Modikwa Platinum mine forms part of the Anglo Platinum (Amplats) Group’s current expansion programme. Amplats is the world’s leading primary producer of platinum group metals (PGMs) and accounts for more than half of South Africa’s 73% contribution to world primary supplies. The expansion programme is aimed at increasing Amplats annual production of platinum from the 2001 level of 2,1 million ounces to 3,5 million ounces by 2006.
The Modikwa expansion is a joint venture between ARM Mining Consortium and Anglo Platinum Group. It was approved in February 2000, with a R1,8 billion (real 2003 terms) budget with full production expected in 2004. The fully operational plant is expected to utilise its maximum design capacity of 200 000 milled tons per month, 162 000 ounces of platinum per annum and 146 000 ounces of palladium per annum.
The Modikwa Project is committed to the introduction and implementation of the most advanced technology and systems available to achieve maximum cost effectiveness and optimal exploitation of its mineral interests for the benefit of local and foreign stakeholders and to ensure world-class performance to optimise this investment - Modikwa is designed to be a high production, continuous operations mine, the concentrator plant having 57 km of pipelines, 500 motors and 257 pumps. It was a requirement from the onset that the plant's concentrator has a high level of automated process control enabled by the Adroit supervisory control and data acquisition (scada) software. Some of the processes that are being controlled include ROM ball milling, the separate treatment of chrome and silicate fraction and an automated process control lab.
Why Adroit?
When the Modikwa put the scada system up to tender for the new plant in 2000, Adroit offered the entire prerequisite, world-class functionality at a highly competitive price. Adroit's local development and manufacturing account for its superior cost advantage. The Adroit scada is robust, a feature that is of high priority to Modikwa, as it aims to deliver value to its stakeholders by eliminating the costs associated with plant downtime and to optimise the plants usage to achieve maximum value from their investment. "We have had very good service from Adroit: everyone from the sales engineer to the support team," comments Danie Oosthuizen, senior technician.
How the system works
The Adroit scada HMI is used to visualise the entire plant operation and to set certain parameters for process control within the plant, including level, flow, temperature and density control. As ore is conveyed from underground the Adroit scada monitors the bin and silo levels while the transported tonnage of the raw material are recorded and totallised. The running of the conveyor system to the silos and the crusher are displayed visually using the Adroit mimics. "The Adroit graphics are of a much better quality than other packages. The resolution is very good and the mimics are clear," says Johan Viljoen, plant engineer. Modikwa were not required to use any scripting and created the entire project, including all the mimics, with the standard tools provided by the Adroit package. One of the salient features of the plant is the high level of automated process control, delivered by the PLC system assisted by the scada HMI. Ore is fed into the primary mill. From the primary milling, the ore is right sized through the classification process where the control system ensures that it is separated into primary silicate or chromite rich fractions.
The Adroit system also monitors the running status, amps, mill feed and load to ensure optimal performance and usage of the equipment. At the flotation cell section, the scada monitors valve positions, levels, airflow and the running status. Reagents are fed into the milling and flotation process to enhance the flotation process. Adroit manages the mixing sequences and levels of airflow to ensure that flammable gas that accumulates at this stage is purged from the tanks. In the final concentrate phase, filters press the slurry to reduce the water content to 12%. The Adroit scada monitors operations and measures the tons travelling over the final conveyor belt and the bin levels before it is transported to one of the Anglo Platinum smelters either in Polokwane or Rustenburg.
It is Modikwa's intention to ensure a world-class safety record both above and below ground. Future expansion of the Adroit scada system includes installation into the underground environment to optimise safety, visibility and control. Due to the enormous size of the operation, three sets of Siemens' S7400 PLCs perform most of the control functions for the plant. The PLCs are uniquely configured for hot standby, with each PLC having two CPUs that monitor each other. In addition, the plants two scada systems monitor the CPUs and each other, switching automatically to the standby CPU if the operational unit should go down, thereby ensuring the redundancy of the CPUs, network and scada and required availability of the plant.
Modikwa is currently running Adroit Version 5.0 on a Windows 2000 operating system. Over 10 000 tags are currently in use with the capacity for unlimited access points that would accommodate the possible future expansion of the plant to almost double its size. An Ethernet network connects the scadas and PLCs to the Profibus ASI equipment in the field. The scada servers are comprised of rack mounted Intel PCs located in the PLC room, adjacent to the control room. The system uses an industrial SQL server database that accumulates data directly from the PLCs and other vendor packages, namely Robotic Process Control Lab, Instream Analysers, Particle size analysers and FloatStar system. The control room consists of three workstations each comprised of monitor, keyboard and mouse. View nodes provide remote plant visibility to all supervisors and managers who receive the same extensive visibility as the control room operators in their respective offices on their desktop computers. "Adroit offers a very powerful report system that generates reports directly off the system," says Viljoen. They also plan to install Opus Report Writing and Analysis software for greater flexibility and customisation in report generation for the rest of the mine.
Key benefits
Due to the continuous operation of the plant, Modikwa required superior response time from the scada, which Adroit was able to provide through customised, on-site development of drivers to ensure that their needs were met. No field starts are performed in the plant. This is due to the fact that Modikwa elected to improve efficiency and reduce costs by doing away with much of the extra wiring and panels associated with field starts. By using a communications cable to the on-site control room, all stops and starts can be controlled from one central point that has complete visualisation of the entire plant operations. Safe lockout facilities are provided in all MCCs with indications on the scada. Adroit also allows users the flexibility of being able to add and remove tags online which is both a cost and time-saving advantage for Modikwa as it progresses through the various phases of expansion.
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