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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.
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.
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
take note
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:
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:
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:
ENERGY + ENVIROFICIENCY: FOCUS ON VALVES + ACTUATORS
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, 6th ed. Upper Saddle River.
Pearson Education Inc. 2006.
[3] Zucker RD. Gas Dynamics, 2nd 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.
Plant pressure
Time in hour
Low pressure side
500.00
450.00
400.00
350.00
300.00
250.00
200.00
150.00
100.00
50.00
0.00
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Pressure in kPa
Actual
consumption
Baseline
Time in hours
45000.00
40000.00
35000.00
30000.00
25000.00
20000.00
15000.00
10000.00
5000.00
0.00
Power in kW
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
• 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.
39 February ‘16 Electricity+Control