Electricity + Control December 2017

FLOW MEASUREMENT

Level 75 BAC is the same irrespective of the sur- face BAC outlet temperature. The relative humidity is between 45% and 60% during the baseline pe- riod. The relative humidity during the test days is similar to the relative humidity during the baseline period. To confirm this, measurements were also taken from the other inlet of the Level 75 BAC. The result of these measurements are shown in Figure 7 . In the second measurements, note that the temperature during the baseline period and test period are the same on Level 75 and the rela- tive humidity during the baseline and testing days is similar. This confirms that the measurements taken on the two inlets are correct. The average tem- perature increased from 31,9ºC (dry-bulb) during the baseline period to 32,1ºC (drybulb) during the testing period, while the average relative humidity decreased from 52.6% during the baseline peri- od to 49,1% during the testing period. At 31,9ºC and 52,6% relative humidity the average wet-bulb temperature is 24,2ºC during the baseline peri- od. During the testing period, the temperature was 32,1ºC (dry-bulb) with a relative humidity of 49,1%, which is an average wet-bulb temperature of 23,7ºC. The test shows that the effect on Lev- el 75 from the surface BAC flow control strategy is within the mine operational limits. The results also show that the dry-bulb temperature and rela- tive humidity increases to the same value at Level 75, irrespective of the outlet temperature of the surface BAC. The air is adiabatically compressed for 2,3 km and has been in contact with the rock face for an extended period of time. The air tem- perature is still below the industry standard of 27,5ºC wet-bulb. The daily average BAC flow was reduced by 80 l/s during the test. This equates to a daily average power demand reduction of 2,67 MW and an energy reduction of 64,08 MWh per day, for three days during the Eskom peak peri- od.The power reduction during the Eskom evening peak period was 3,75 MW and the energy saving for this period was 7,49 MWh. If these savings are achieved during the summer tariff period, the cost saving is R11,3 M. During the winter the BACs are already switched off and no savings is achieved.

Figure 6: Level 75 underground BAC first inlet temperature and relative humidity [2]. The solid grey and black lines show the baseline inlet drybulb temperature and test inlet dry-bulb temperature respectively on the primary axis. The dashed grey and black lines show the baseline relative humidity and test relative humidity respectively on the secondary axis.

Figure 7: Level 75 underground BAC second inlet temperature and relative humidity [2]. The solid grey and black lines show the baseline inlet dry-bulb temperature and test inlet dry-bulb temperature respectively on the primary axis. The dashed grey and black lines show the baseline relative humidity and test relative humidity respectively on the secondary axis.

Implementation Based on the test findings, it was concluded that

Figure 8: Implemented BAC flow control results show- ing the Baseline, November and December profiles.

Electricity + Control

DECEMBER 2017

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