J. F. van Rensburg

Implementing DSM interventions on water reticulation systems of marginal deep level mines

South Africas steep electricity tariff increases have forced the mining industry to be more cost effective. One way is by implementing demand side management (DSM) projects. Energy saving priorities focused mainly on mines with large energy consumption and long “life-of-mine”. If paybacks are short enough, it should be a feasible investment to implement DSM projects. This could extend the “life-of-mine” of marginal mines. To assist with investigations, procedures are introduced to estimate the potential savings and required capital costs. These procedures were developed by analysing previous projects implemented by the CRCED PTA research group. Energy cost savings strategies are proposed for the dewatering-, refrigeration- and water distribution systems. A case study is used to show the benefit of the proposed procedures. Since capital investment on marginal mines is limited, breakdowns and equipment failures may be frequent. This may negatively influence saving and project paybacks.

Challenges faced during implementation of a compressed air energy savings project on a gold mine

Various challenges influence the implementation of an energy savings project on mine compressed air systems. These include, among others, operational changes, control limitations, industrial actions and installation delays. These challenges often lead to a project exceeding scheduled implementation time, exceeding the project budget and reduced quality of the achieved results. This study investigates and addresses the challenges faced during the implementation of a compressed air energy savings project on a gold mine. The study shows that although these problems have an impact on the implementation deliverables of the project, significant savings remain possible. An optimisation project is implemented on a gold mines compressed air network. Despite the challenges that occur during the implementation of the project, an average evening peak-clip saving of 2.61 MW is achieved during the projects consecutive three-month performance assessment period. The power saving produces an annual cost saving of RI.46 million, calculated with the aid of the 201412015 Eskom tariffs.

Business case for industrial DSM maintenance

The performance of industrial DSM projects often deteriorates without proper maintenance. Underperforming DSM projects waste money and increase the demand for electricity from Eskom. A solution to this problem is dedicated maintenance on industrial DSM projects. This ensures maximum performance and maximum electricity cost savings. In this paper, the business case for industrial DSM maintenance is presented. Results show that the benefits significantly outweigh the cost of DSM maintenance.

Automated control of mine dewatering pumps to reduce electricity cost

Deep gold mines use a vast amount of water for various purposes. After use, the water is pumped back to the surface. This process is energy intensive. Pump control is traditionally done with manual interventions. The purpose of this study is to investigate the effects of automated control on mine dewatering pumps. The benefits of pump automation include electricity cost savings through load shifting, as well as preventative maintenance and pump protection procedures. By automating pumps, the client will benefit from operating more cost effectively and realising electricity cost savings. A Demand Side Management (DSM) project was implemented in the form of a pump automation project to perform load shifting. The performance of the project was tested in manual control, manual scheduled control, manual scheduled surface control and auto control. In the case study the manual intervention achieved the highest electricity cost saving. To achieve this saving the system was exhausted to a point where columns and infrastructure started failing. The auto intervention achieved a lower electricity cost saving but was more sustainable. The auto intervention achieved a lower electricity cost saving when compared to the manual intervention. However, considering factors such as the damage to infrastructure after a period of manual control, the auto intervention proved the best balance for controlling mine dewatering pumps, to achieve electricity savings and system sustainability.

Reconfiguring mining compressed air networks for cost savings

The ever-growing human population, limited energy resources and the effect of greenhouse gas emissions have become major global concerns for the energy sector. This includes the electricity generation sector. This dilemma has caused electricity providers to revise their generation methods and created a major need for consumers to utilise electricity more efficiently. Demand Side Management (DSM) is one initiative developed for consumers to efficiently utilise electricity. Due to their high electricity consumption and availability of technical skills, mines are ideal targets for the implementation of DSM strategies. Therefore, the focus of this study was to investigate the possible implementation of DSM strategies on the compressed air networks of South African mines. The compressed air networks at South African mines are relatively old and inadequately maintained. This causes inefficient distribution and use of compressed air. This study will therefore focus on reconfiguring a mining compressed air network for electricity cost savings. Reconfiguring this network would entail interconnecting two shafts with a pipeline in order to distribute compressed air from one shaft to another. This proposed reconfiguring initiative was approved and implemented on a South African mines compressed air network. The results concluded that electricity cost savings can be achieved by reconfiguring mining compressed air networks.

Load management through the utilisation of VSDs on water transfer schemes

South Africa is a water scarce country and due to this, large water transfer schemes were built to supply major parts of the country with raw and potable water. These water transfer schemes are high energy consumers due to the large pumps utilised for distributing water over great distances against significant static heads. With the present electricity situation in the country, Eskom invested in, among others, Demand-Side Management (DSM) interventions to ease the load on the electrical grid during peak hours. A transfer schemes pump station that utilises Variable Speed Drive (VSD) technology for pump control was identified for a possible load management intervention. To develop an optimised control philosophy that utilises the VSD technology, tests were conducted on the pump station. Data gathered from these tests was used for the verification of a simulation model built to verify the proposed optimised control philosophy. After the proposed strategy was simulated and optimised, control and maintenance constraints limited the implementation of the control philosophy. The simulation however, indicated that an annual electricity cost savings of approximately R 3.3 million can be achieved. Due to the constraints, it was not possible to implement the load management initiative for a significant part of 2016. During periods when the pump station was operating at a reduced capacity, a 2.29 MW evening peak load reduction was achieved. This equates to a daily cost saving of R10 000 during the winter high demand season.

Improving existing DSM initiatives on mine refrigeration systems for sustainable performance

Mining is done at great depths in South Africa and the high virgin rock temperatures at these depths result in refrigeration systems being one of the largest electricity consumers on mines. The general operation, control and equipment stance of the refrigeration systems are, however, inefficient and overdesigned and, as a result, several demand-side management (DSM) initiatives have previously been implemented on mine refrigeration systems. Although significant electricity cost savings were realised from these initiatives, DSM project deterioration occurs over time thus eroding the viability of sustained electrical cost savings. It is therefore critical to identify the factors affecting the performance of DSM initiatives in order to develop a performance strategy that includes measures to improve the existing DSM initiatives on mine refrigeration systems for sustainable and optimised performance. The feasibility of such a strategy was proven using case studies. This was done by analysing the post-implementation effects of said strategy on two underperforming, deteriorating refrigeration systems situated at two separate gold mines with previously existing DSM initiatives. The studies showed that a sustainable average daily power saving of 1.8 MW was achieved during the course of 15 months for Mine A; with a sustainable average daily power saving of 1.62 MW over the course of 17 months for Mine B. As a result, the average electrical cost savings, according to the 2015/2016 Eskom electricity tariffs, amounted to R11.9 million for Mine A and R12.1 million for Mine B.

Verification procedures to ensure consistent energy metering

The majority of Energy Conservation Measures (ECM) implemented by South African Energy Service Companies (ESCOs), are funded by the Eskom Demand Side Management (DSM) initiative. In 2013 Eskom reported a total DSM savings of 595 MW. To measure this effect power usage data needs to be recorded. A slight variance with the accuracy of measurements will have a significant impact on the reported savings. It is therefore of critical importance to ensure consistent energy measurements throughout the life cycle of the ECM.A study was conducted in order to investigate how each step of the measurement process contributes towards the overall accuracy. Components investigated include instrumentation transformers, the Analogue Digital Conversion (ADC) process and the different signal processing techniques available. The study also investigated different power loggers and their impact on the overall accuracy. The study found that each component has the potential to affect the accuracy of the measurement. However, the most significant risk that affects the accuracy was not any specific component, but rather the process of installation and setup of the equipment. This prompted the development of a procedure to address the verification of measurements. The verification procedure consists of three main parts namely, Verify measurements of temporary power logger, Evaluation of data recorded and Verification of permanent power logger.

Maintenance procedure for improved sustainability of DSM pump load shifting projects

Mine dewatering systems are energy intensive and present ample opportunity for the implementation of electricity cost saving measures. One such electricity cost saving measure is the implementation of load shifting projects to shift pumping load from the peak periods to the off-peak periods of the Eskom Megaflex tariff structure. However, past experience has shown that the electricity cost savings generated by a pump load shifting project can deteriorate without proper maintenance. The major causes of the deterioration were therefore investigated with the aim of developing a maintenance procedure. The maintenance procedure consists of four sections: data loss prevention, mechanical failure prevention, control & instrumentation maintenance and control parameter optimisation. The developed maintenance procedure was implemented on the dewatering systems of South African gold mines. Results indicate that the application of the maintenance procedure resulted in both increased electricity cost savings and sustained performance.

The implementation of a Dynamic air Compressor Selector system in mines

Generation of compressed air represents 20% of the total electricity usage in the mining industry. There are significant costs associated with generating compressed air and maintaining a compressed air system. This paper focuses on the implementation of a novel dynamic air compressor selector. A Dynamic Compressor Selector (DCS) system was developed to reduce the electricity usage of a compressed air ring. The DCS is a system that combines demand- and supply-side management of a compressed air network. The DCS calculates a pressure set point for compressors and schedules them according to the demand of the end-users. This paper focuses on the DCS implementation process and problems encountered while implementing the DCS technology. The purpose of this study was to determine whether DCS can successfully be implemented on a mines compressed air system. The DCS was implemented at a platinum mine in South Africa where it was able to calculate pressure set points for the compressors. The supply of- and demand for compressed air was accurately matched resulting in lower overall compressed air usage. The DCS improved compressor scheduling and control whilst limiting compressor cycling. Improved compressor scheduling and control resulted in significant decreases in the electricity used to generate compressed air at the mine. Evening peak electric load reduction in excess of 3 MW were achieved.