Comparative study of mine dewatering control systems
Deep-level mines use a series of dams and pumps known as a dewatering system to remove water from underground. The dewatering process can be automated and then controlled on different levels in the control system: programmable logic controllers (PLCs), supervisory control and data acquisition (SCADA), or third-party control software interacting with the SCADA. Based on personal industry experience, automation engineers often have preferences or bias towards the use of certain levels of control in control systems, but these preferences are not always based on comparative knowledge of all three control systems. Investigation of literature revealed mathematical techniques aimed at optimising pumping schedules and studies using a single control system for pumping optimisation. Experimental studies comparing the three control systems used for dewatering process control were not found. In order to experimentally compare the control systems, a scoring evaluation method was developed. After verification and validation of the accuracy of mathematical modelling and simulation of the dewatering process, the method is applied to facilitate the comparison. The comparison methodology incorporates the control systems' features and control performance. The features are identified as beneficial to the control of dewatering systems, and includes aspects such as alarm handling capability and a built-in simulation/testing environment. Control performance is assessed from simulation results, and takes into account electrical operating cost, dam levels controlled within limits and frequency of pump starts. The developed methodology was applied on three case studies provided by deep-level gold mines from a mining group in South Africa. For the case studies, PLC control uses a similar control algorithm to SCADA control, except for the fact that SCADA control considers the downstream dam level. In its state at the time of comparison, this control algorithm did not allow for customisation, whereas third-party control software did. It was found that control of complex dewatering systems could be better optimised using control systems offering the capability of incorporating more complex/site-specific logic in the control algorithm. Complex dewatering systems require a non-generic approach. For simple dewatering systems, higher complexity control systems are not strictly required, but might offer the advantage of more advanced features which aid in the implementation and use of the control system. For the mining group providing the case studies, third-party control software showed to be the optimal choice of control system to use. This is followed by SCADA control and then PLC control. Furthermore, it was found that the mines' SCADA control algorithm as developed by the case studies' mine is likely to cause unnecessary starting and stopping of pumps. This leads to increased frequency of pump maintenance and preventable expenditure. The findings are directly applicable to dewatering systems using the same control algorithms as in the study. The developed methodology can be applied to any dewatering system, or system containing at least one dam and pump.
- Engineering