Electricity + Control December 2017

FLOW MEASUREMENT

Dr. Hendrik Brand is a registered professional engineer and holds a PhD in mechanical engineering from the North-West University. Prof M. Kleingeld is a registered professional engineer and holds a PhD in mechanical engineering. He is currently a lecturer at the North-West University’s Centre for Research and Continued Engineering Development (CRCED) in Pretoria. Dr. P. Maré holds a PhD in mechanical engi- neering from the North-West University. Dr Abraham J. Schutte is a registered professional engineer and holds a PhD in mechanical engineering from the North- West University. gold mining industry. PhD thesis, Mechanical engineering, Potchefstroom: North-West Uni- versity, 2014. [3] Du Plessis, GE. A variable water flow strategy for energy savings in large cooling systems. PhD Thesis, Mechanical engineering, Potchef- stroom: North-West University, 2013. [4] Oberholzer, KJ. Reconfiguring mine cooling auxiliaries for optimal operation. Master’s dis- sertation, Mechanical engineering, Potchef- stroom: North-West University, 2015. [5] Stanton, DJ. Development and testing of an underground remote refrigeration plant. PhD thesis, Mechanical engineering, Potchef- stroom: North-West University. 2004. [6] Van Greunen, D. Energy efficiency through var- iable speed drive control on a cascading mine cooling system. Master’s dissertaion, Mechan- ical engineering, Potchefstroom: North-West University, 2014. [7] Moropa, TS, Cost savings on mine surface cooling systems. Master’s dissertation, Me- chanical engineering, Potchefstroom: North- West University, 2017. [8] Den Boef, M. Assessment of the national DSM potential in mine underground services. PhD thesis, Mechanical engineering, Potchef- stroom: North-West University, 2003.

the wet-bulb temperature of the underground air remains within the acceptable limits and that the surface BAC flow control strategy can be im- plemented. This was done on Mine B and two months’ (November & December) results from the performance assessment period ( Figure 8 ) which shows that a 4,2 MW peak clip was achieved dur- ing the Eskom evening peak period. Since the flow was also controlled based on the enthalpy during the day, November realised an average power saving of 2,46 MW throughout the day.This was however only feasible during Novem- ber. The atmospheric air enthalpy increased during December resulting in the same BAC loads as the baseline. Further opportunities exist to also control the BAC water flow rate during other months of the year. Should this be done during all the months excluding the winter period, a saving of R11,4 M would be achieved. Conclusion It is important to consider all factors when investi- gating mine ventilation. The BAC reduces the tem- perature and absolute humidity at the inlet of the mine. The effect on the underground wetbulb tem- perature is negligible when the BAC flow is con- trolled based on the enthalpy. By switching off the BAC from 18:00 to 20:00, the wet-bulb tempera- ture is not negatively affected and compares fa- vourably with the baseline wet-bulb temperature. Testing this strategy on Mine A showed a possible average peak demand saving of 3,75 MW and dai- ly energy saving of 64,08 MWh. This would result in a cost saving of R11,3 M if implemented during the summer tariff months. During two months of the performance assessment period on Mine B, an average daily Eskom evening peak power sav- ing of 4,20 MW and daily average energy saving of 59,04 MWh was achieved. This would result in a cost saving of R11,4 M if implemented in the sum- mer tariff months.This verified the reduced energy consumption of the BAC flow control strategy. References [1] Vosloo, J; Liebenberg, L and Velleman, D. Case study: Energy savings for a deep-mine water reticulation system. Applied Energy, Vol. 92. [2] Brand, HG. An integrated sustainability frame- work for environmental impact reduction in the

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DECEMBER 2017