Electricity + Control February 2016

ENERGY + ENVIROFICIENCY: FOCUS ON VALVES + ACTUATORS

This was 5 725 tons less than the average 197 453 tons of air per month consumed before the ring was split. This saving is a combination of the air saved as a result of a reduced line pressure leading to smaller line friction losses as well as the reduced amount of air lost through air leaks. Figure 8 shows the pressure profile of the low pressure side after the control valves were installed and commissioned.

within the output pressure set point range. The reduced output means less power is required and this will result in significant electrical energy savings. This saving can clearly be seen in the results of the case study. References [1] Hughes A, Howells MI, Trikam A, Kenny AR, van Es D. A study of demand side management potential in South African industries. Energize. Sept. 2006. [2] Mott RL. Applied fluid mechanics, 6 th ed. Upper Saddle River. Pearson Education Inc. 2006. [3] Zucker RD. Gas Dynamics, 2 nd ed. Hoboken. John Wiley & Sons. 2002. [4] Plint MA, Boswirth L. Fluid mechanics: A laboratory course, London. Charles Griffin & Company Ltd. 1978. [5] Cerci Y, Cengel YA, Turner HT. Reducing the cost of compressed air in industrial facilities. Thermodynamics and the Design, Analy- sis and Improvement of Energy Systems.

Low pressure side

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Figure 8: Low pressure at the plants.

The reduced energy consumption, which can be calculated from the area under the actual power profile of Figure 9 , is clearly evident. This saving was achieved through a reduction in pressure on the low pressure side of 80 kPa. Figure 9 shows the actual average power consumption, after project implementation, over a period of one month, against the original power baseline before the project was implemented. The average daily energy efficiency saving achieved was 43,2 MWh.

• Energy, like water, should be seen as a resource to be nurtured. • Every opportunity to improve energy efficiency must be taken. • Compressed air systems use large amounts of energy and are prime targets for improved efficiency.

take note

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Rudi Joubert, HPR, is a registered professional engineer. He holds a Masters degree in electrical engineering and is enrolled for PhD studies at North-West University. E-mail: rjoubert@researchtoolbox.com

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Dr Johann van Rensburg is a registered professional engineer and holds a PhD in electrical engineering from the North-West University. He is a senior lecturer at the North-West University. E-mail: 10728023@nwu.ac.za

Figure 9: Actual power profile vs. baseline.

Conclusion Evaluation of the compressed air system at a gold mine showed that it is possible to reduce the pressure and air flow in certain sections of the mine. This was accomplished by installing automatic pressure reducing control valves in the compressed air delivery line. When these valves are signalled to reduce the downstream pressure, they cause the upstream pressure to increase. The increased upstream pressure will cause the compressors to reduce their output to stay

Dr Ruaan Pelzer holds a PhD in mechanical engineering from the North-West University. He is a senior lecturer at

the North-West University. Email: rpelzer@rems2.com

February ‘16 Electricity+Control

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