Flotation is one of the most widely used processes in the mineral industry. It is possible to obtain good performance from a flotation plant, but it has proved difficult to obtain and sustain good performance. Flotation is a highly interactive process, with many factors affecting overall performance, therefore making stabilisation and optimisation of flotation plants often challenging.
Mintek has developed a suite of stabilisation and optimisation tools that can be used to enhance the performance of flotation circuits. The full range of flotation control strategies have been implemented on the StarCS platform.
- A stable flotation circuit with improved level control and disturbance rejection.
- Significantly faster start-up times with reduced losses.
- An optimised circuit with respect to concentrate flow rates, residence times, level setpoints, aeration rates and reagent addition selection.
- Reduction in grade variation.
- Improved recovery by approximately 1% or more.
Good level stabilisation control cannot be achieved by using controllers that only act locally. The FloatStar Level Stabiliser solves this problem, and is designed to provide the following benefits:
- Better level control and faster setpoint tracking,
- More effective disturbance rejection than with PID control, often eliminating disturbances completely.
- No propagation of disturbances from bank to bank.With PID control disturbances are usually magnified when they are passed to downstream banks.
- Faster settling times after start-ups.
- Improvement in the overall recovery of the flotation circuit, since poor level control reduces recovery.
1. FloatStar Flow Optimiser
The main goal of the FloatStar Flow Optimiser is to ensure that the entire flotation circuit operates at optimum conditions in order to obtain the following:
- correct grade.
- minimum amount of impurities.
- Internal flowrates.
Mass Pull Control
In order to obtain a constant mass pull off a flotation train, all of the cells that produce the final concentrate need to be set at the correct level and air setpoints as these affect the mass pull achieved. FloatStar Flow Optimiser makes use of multivariable techniques to achieve the desired mass pull rates off of these cells in the manner depicted by the image below:
Residence Time/Re-Circulating Load Controller
The mechanics of flotation shows that residence time changes have a direct impact on recovery. The FloatStar Flow Optimiser makes it possible to control the inferred flow and hence the residence time of a cell to setpoint.
Another example of effective circuit optimisation is the control of the tailings flowrate of the cleaning stages. The upstream level and air setpoints are manipulated in order to obtain the desired tailings flowrate.
2. Grade-Recovery Optimisation
The typical objective of a flotation circuit is to produce a concentrate grade of a specified quality, while providing the maximum recovery of the valuable mineral possible. The grade and recovery of the circuit will be influenced by, amongst other factors, the:
- Level setpoints.
- Aeration rates.
- Cell residence times.
- Reagent addition.
3. Reagent Optimiser
Reagents play an important role in froth flotation. They strongly affect the performance of the circuit, and are expensive. The selection of the reagent suite is a complex task, with multiple, often counter-intuitive, rules and calculations. The Reagent Optimiser aims to automate this process, providing consistent round-the-clock adjustments to the reagent suite tailored to the plant operating conditions.
The FloatStar Fault Detector is an online fault detection module that detects faults in sumps and flotation banks. It provides useful feedback regarding flotation and general level instrument performance.
The Fault Detector has three fault detection routines, and a general statistics/performance-monitoring package. It detects frozen level signals, spikes in signals, and tank overflows. The statistics module provides minimum value, maximum value, average value, standard deviation and instrument resolution information.
A performance monitor has been developed for situations that require control-loop performance evaluation. Currently the performance monitor:
- Calculates the performance under “Plant” and “FloatStar” control.
- Calculates the performance over a user-specified window-period.
- Automatically rejects situations where the MV (e.g. valve position) is at any of its limits.
- Additional rejection scenarios may be added.
- The utilisation (the percentage of data used) is determined.
- Base values may be set for the any given control -loop.
The FloatStar Dynamic Simulator is a tool for modelling almost any flotation process. The model is mechanistic and takes into account flotation due to true floatability and entrainment of the particles within the pulp. There are two modes in which the simulator may be used: true dynamic mode and steady state mode. With its flexible design, many objectives may be achieved.
The control of pH is required in many areas across the mining industry. One key area is in flotation reagent control systems. There are a number of difficulties in controlling pH:
- Non-linearity of the pH curve.
- Silting up of the basic feed-valve.
The FloatStar pH controller is designed to handle all of these control difficulties and consists of:
- An advanced multi-variable algorithm, including feedforward and feedback compensation.
- Non-linear compensation.
- Fault detection algorithms.