The first local 'OCS' optimising control system has been successfully installed at Impala Platinum Mine by Svedala South Africa, to optimise mill grind control. The company installed one unit successfully in January and has since extended the contract to include the other 14 Merensky lines.
"There is very little instrumentation on the milling circuits at this plant. Variability in the mill product grind and pulp density has been reduced significantly," says Rebecca Hope, Product Manager of Svedala's Cisa Products Division.
Svedala believes that systems such as these are setting new standards in process optimisation and are fast becoming a necessity, not luxuries for profitable operations. The present economic climate demands that every working unit must be utilised to maximise the potential of its equipment. Advanced process control techniques are among the most cost and time effective methods of improving metallurgical plant performance. Returns on investment typically range from 100 to 5000%.
This French designed system makes changes to process setpoints to achieve peak performance and Svedala says that it is distinguished from others by its soft sensor capabilities. (A soft sensor is a piece of software used to estimate values normally read by field instrumentation.)
The OCS application is developed on-site and set up to customer specification. It is a transparent system which allows ease of maintenance and good operator understanding. Control strategy is developed in conjunction with the plant team with input from the technical expertise that Svedala has built up over the last 10 years.
"We have had a system running since 1998 at Sadiola Hills in Mali and this has needed very little technical support and only minor changes to the control strategy," says Rebecca Hope. "This has been important for this area as it is so remote and the success of this system is that it paid for itself within six days." It is an expert system with embedded fuzzy logic which is able to identify problems and change boundaries to improve performance.
The OCS manipulates the many variables that influence each other in a processing circuit, allowing a number of problems and issues to be addressed at the same time ie the small frequent changes it makes allows stable operation of the circuit and a constant drive towards predetermined technical and economical goals.
The system at Impala scans the state of the process every 30 s and makes sure that it is running optimally. The installation required the involvement of every person on the plant from operators to senior management. Information from the operators had to be included in the entire control strategy.
Svedala's OCS system is running successfully worldwide in countries such as South America, Canada, Europe, the USA and North Africa.
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