Analysing mine energy management considering utility demand
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This dissertation was completed using an article-based format. Article 1 has been submitted to the Journal of Energy in Southern Africa and Article 2 to Sustainable Energy Technologies and Assessments. In the past, the cost of electricity was not as significant as it is today. Therefore, it was not common practice for mining companies to take peak time-of-use tariffs into account for their shift schedules. The literature indicates a need for the analysis of mine energy management, focusing on utility demand. Mines have numerous utilities with varying power demands, which are mostly based on mining operation. Mining operation often varies from one day to the next despite the schedule being fixed, as this schedule is dependent on people. The schedules are dependent on people in that the underground workers use utilities for purposes that the schedules and shifts describe. This leads to variability in that different utilities have different purposes which align with the specific work done by underground mining personnel. The overall study was conducted on the mining operation system of a South African platinum mine consisting of various mining shafts, focusing on the power demand of utilities in general and the compressed air system in particular. The overall study was conducted on the mining operation system of a South African platinum mine consisting of various mining shafts, focusing on the power demand of utilities in general and the compressed air system in particular. Article 1 Throughout literature, no study has been reported where an entire mine was holistically analysed regarding utility power demand, using a top-down approach. Therefore, the objective of the study reported on in Article 1 was to analyse an entire mining operation system with the notion of integrating load management with shift changes. This was achieved by analysing the power demand of the utilities, mine operational schedules and their interconnectedness. The study indicated a potential power reduction of the studied system. The power demand reduction was statistically estimated using the average power demand reductions from existing studies that were conducted on mines. The demand reductions were applied to the power demand of the utilities when specific shifts at the shafts aligned. Firstly, a maximum savings scenario was determined. The resulting operation schedule change was estimated to result in a 1.3% reduction in the total electricity costs of the mine. Furthermore, system operational improvements were simulated and had a potential total reduction effect of 8.4%, which was primarily attributed to a reduction in compressor power demand. The implications (large adjustments in shaft operations and shifts starting at difficult times) of the proposed schedule adjustments (that entails adjusting shift starting times at different shafts on the mine to align with other shafts on the same mining system, and to account for higher cost time-of-use times) necessitated the simulation of a realistic scenario. This was necessitated because drastic adjustments in shaft operations are not necessarily feasible and shifts start at improbable times according to shift descriptions. The realistic scenario showed an electricity cost reduction of 0.7% resulting from only schedule adjustments. The realistic schedule adjustment, however, revealed possibilities for further system operational improvements. When these operational improvements were simulated on the relevant utilities, the effect was a potential total reduction of 7.6%. The operational improvements continuously used in this study include, as also previously described, the average reduction found from numerous studies on various utilities. This includes load shifts on pumping systems, peak clips on ventilation fans, improved control of compressors and refrigeration system utilities and it includes load shifts and improved scheduling of winders. This is just some of the power demand reductions included to achieve operational improvement. Article 1 identified the need for further analyses of the relevant utilities. The compressor system was found to demand between 20% and 55% of utility power supplied to a mine based on literature and analysis of the case study system. It was, therefore, necessary to analyse this utility with regards to its performance, power demand and air supply. Article 2 Mine compressed air systems are difficult to analyse due to their inefficiency and complexity. No clear method exists that can be used to characterise the total performance of the supply side system regarding air supply and utility power demand. Moreover, a simplified and unbiased performance measuring method was lacking in the literature. The objective of the study reported on in Article 2 was therefore to develop a simplified method that used a single metric (specific energy) to characterise the performance of a compressed air system relative to the compressed air supply and compressor power consumption. This metric required minimal data and can be used as a guide to improve performance. A compressed air system was analysed before and after project implementation, using the simplified method. The projects included control optimisation, underlying compressor system improvement and energy efficiency projects. The simplified method gave a good indication of performance changes resulting from the abovementioned projects on the compressed air system, with an improvement of 6% on the average total specific energy, from 104 to 98 Wh/m³. The non-drilling shift specific energy of the system decreased from 103 to 94 Wh/m³, which constitutes a 9% improvement. The reduction in specific energy corresponds with an 8% reduction in power demand with only a 0.4% reduction in supplied flow. This study showed the possibility of characterising the performance of complex compressed air systems using a simplified metric. It can also be used to verify whether supply side initiatives were effective.
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