Due to the very unusual ore characteristics at Nkomati the client elected to employ grinding methods that rely mostly on autogenous grinding (AG) in the mills (i.e. without the addition of steel grinding balls).
In this type of operation pebbles of unground ore are produced in the primary grinding mill and are used as grinding media in the secondary grinding process. Excess pebbles produced are fed to a pebble crushing circuit that in turn recycles the crushed product back to the primary grinding mill for further processing.
The Nkomati grinding circuit flowsheet (simplified)See large imageOperation of this type of circuit can be very cost effective because it requires no steel grinding media, the cost of which is a significant element in the operation of conventional grinding circuits. However, the operation of an autogenous grinding circuit is also more reliant on good control strategy as variations in the feed ore conditions have an influence on the stability and efficiency of the grinding process. Additional complications are the need to control the pebble storage bins to ensure sufficient quantity of pebbles used as grinding media and the requirement to handle and crush the excess pebbles produced. These considerations as well as FLSmidth being the supplier of the grinding mills were considered sound reasons for Nkomati to purchase an
ECS/ProcessExpert from FLSmidth.
See large image Implementation of the ECS/ProcessExpert at the Nkomati JV was completed in April 2010. Although formal evaluation will only commence later this year, to date the system has operated extremely well and shown to be very robust at a utilisation factor of 98%. This is considered to be a clear indication that operational staff at the mine has full confidence in the system achieving the objectives of the advanced process control. Mr. Danie Smit (Concentrator Manager at the 375kt Plant) says, “We’re certainly seeing a benefit from the expert system thus far and I’m confident it will contribute greatly in achieving our business plans. This project has been a success and it was the right decision to engage in this process.”
FLSmidth is confident that the ECS/ProcessExpert installation will continue to deliver benefits and improved plant performance well into the future. The plant continues to be supported via remote monitoring and support services that allow FLSmidth to monitor the health of the system and to make adjustments to control strategies to suit the dynamic operational conditions if necessary.
About ECS/ProcessExpert FLSmidth is known for its advanced
ECS/ProcessExpert control system and has delivered many such systems to the cement industry over the past more than 15 years. As FLSmidth continues to grow as a leading supplier in the minerals industry, the Automation Division now also offers leading edge control solutions to minerals processing plants.
FLSmidth ECS/ProcessExpert for Grinding Applications has been designed specifically with the following goals in mind:
• Circuit stability
• Circuit throughput optimisation
• Improved energy consumption
• Improved product quality
• Maximum equipment performance
and availability