Evaluating the feasibility of integrating mine compressed air systems for energy savings
Abstract
The South African metals and mining industry is under pressure to increase their production output. While South Africa’s production trend has been decreasing, even though it is the third largest gold reserve, the global trend has been increasing. The rising cost to produce has forced these production rates to decrease. The rising production cost is coupled with the high electricity cost, which Eskom has been increasing steadily over the last few decades. As one of the industry’s highest expenditures, namely energy, increased, so has the importance of energy efficiency projects. The South African gold mining industry consumes approximately 15% of the total electricity generated by Eskom. The largest consumer of electricity on a mine is compressed air production. Compressed air production consumes 20% to 50% of a typical mine’s energy usage. Previous studies have investigated methods to reduce compressor energy consumption by reducing compressed air wastage on the supply and demand side. This included implementing pressure control schedules, auditing networks, and repairing leaks to minimise wastage. Experimenting with different compressor combinations also assisted in reducing the supply load. In some cases, compressors were found to have been over-specified for their networks, resulting in excess air being discharged into the atmosphere. To prevent compressors from blowing off, investigations into increasing network size through integration have been launched. These studies were based on mines with a wide range of compressors to choose from but with control philosophies limited to surface operations. The studies on integration that were based on simulations were those studies where factors such as infrastructure and pressure control prevented implementation. This research focuses on finding a cost-effective method to reduce compressor energy usage by integrating compressed air networks without impacting the flow or pressure negatively. Simulations will be used to verify the credibility of the methods before moving on to physical testing and implementation. The case study focused on two deep-level gold mine shafts and a processing plant supplied by two compressor houses and three compressors. The demand was reduced firstly by implementing proper control schedules, underground audits, and decreasing wastage. The compressor houses were then re-evaluated due to over-supply. Simulations were created to test the feasibility of integrating the two networks and were calibrated for an accuracy of 99.5%. The simulations proved that, with the proper control, only two compressors were required to provide both shafts with compressed air. The simulation was implemented on the network and resulted in a daily average power reduction of 1 160 kW. The total reduction was 1 450 kW when including the effect of the control schedules and underground audits, which equates to an approximate cost saving of R 7.37 million and R 11.19 million per annum, respectively. Thus, the study proved that it was possible to reduce compressor energy by integrating two compressed air systems; therefore, the set out objectives were met.
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