GRINDING THROUGHPUT OPTIMISATION FOR MILL FEED STABILISATION
The MillStar Advanced Control System, a product from Mintek, has a comprehensive suite of control strategies that can be applied to provide an innovative control solution for almost any milling circuit configuration. The main goals are:
- Stabilise the mill feed
- Control product quality to the downstream processes
- Optimise throughput and grinding efficiency
- Provide a robust control solution.
Due to the complex nature of milling circuits, it is often found that conventional control does not address many of the common problems experienced. These include:
- Long process response times
- Multivariable interactions and disturbances
- Non-linear systems with varying dynamics
- Constraints on variables
- Lack of reliable process measurements.
- MillStar boasts a typical payback period of just a few months
- Maximised throughput
- More consistent feed to downstream processes therefore increased recovery
- Optimal use of mills
- Individual customisation
- Improved control of mill feed rate
- Better management of fine and coarse material, thereby preventing mill overloads
- Robust Control solution for effective milling
Milling Feed Control
The smooth operation of a milling circuit is difficult to achieve due to the varying nature of the feed material and the unfavourable dynamics between feeders and the weightometer. These dynamics degrade the performance of the PID controllers making feed optimisation more challenging. The MillStar Mill Feed Controller will compensate for the feed dynamics by modeling feeder responses, adapt for any model errors and adjust the feeder speeds in a desire
Milling operations need to operate close to the maximum mill power draw. The power-load relationship is highly non-linear and shifts around as the ore and steel load/liner changes. Traditional control and modeling techniques can therefore not be used. The MillStar Power Optimiser:
- Continuously “seeks” for the optimum mill operation by changing the solids feed or load setpoint.
- Uses the changes in the mill load and power to automatically detect whether the mill is overloaded or underloaded.
- Uses safety controllers to change the solids feed rate and feed water to prevent mill overloads.
- Estimates the power load curve and optimum load.
The MillStar Sump/Product Stabilisation focuses on:
- Taking into account multivariable interactions between input and output mill discharge variables.
- Controlling the sump level and cyclone overflow product size and/or density.
- Minimising flow variation to the downstream processes.
- Optimum usage or surge capacity of sumps, hoppers and conditioning tanks.
- Handling constraints of the sump level (to prevent pump surging and spillage) and cyclone density (to prevent pipeline chokes and pressure variations).
Mintek has developed a Model Predictive Controller (MPC) specifically for controlling milling circuits, with the following advanced features:
- Fully fledged multivariable controller that can efficiently eliminate interaction between variables.
- Explicitly handles limits on input and output variables to ensure all variables are kept within their allowed operating range.
- Very efficient in handling long time delays and slow-reacting processes.
- Special features to handle noise, integrators and model errors.