The developed water supply strategy was proven to be successful. However, a few recommendations can be made to optimise the strategy:
• It was observed that the water flow through the CBACs was slightly higher than the design water flow. Further research should be conducted to determine if an added benefit can be obtained and if water is wasted.
• The water flow through the CBACs can be controlled more efficiently by calculating the optimal critical flow where optimal heat transfer will take place. In other words, calculating the flow at which the best possible heat transfer between the water and air will be obtained. Furthermore, it should be ensured that the water flow through the CBAC is controlled effectively at this flow rate.
• One of the 100L hot dams should be converted into a dedicated return water dam.
Doing this will ensure that the return water does not mix with the hot service water.
20 22 24 26 28 30
Temperature [°C]
Location
102L east haulage temperatures
Baseline Actual
XC - Crosscuts
High pressure water supply strategy for mine bulk air coolers 100
Colder water will be sent to the refrigeration plants and decreased power consumption may be achieved as guide vanes of refrigeration plants will be cut back.
• It has been observed that BAC doors are open 62.6% of the time. Thus, the effects of the decreased air temperature will not be observed as effectively in the stopes/working areas. Therefore, it is necessary to develop a strategy to ensure that these doors are always kept closed.
Thus, scope can be identified to optimise the developed strategy to improve the holistic system.
High pressure water supply strategy for mine bulk air coolers 101
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Appendix A: Design specifications
Appendix A contains all the design inputs of the important components. All these inputs have been obtained from the manufacturer and/or from Mine A.
Table 13: Mine A’s CBAC specification database #1
Parameter Abbreviation Value Unit
Outside diameter Do 19.5 mm
Inner diameter Di 16 mm
Tube material – Copper HIFIN –
Tube coating – 92/8 lead/tin –
Number of tubes per row Nt 14 –
Number of tube rows Ntr 8 –
Total tubes N 112 –
Fin pitch Fp 3.8 mm
Fin thickness Ft 0.7 mm
Length of tube Lt 1 790 mm
Flow passage hydraulic diameter Dh 16 mm
Free flow to frontal area ratio 𝜎 0.9 –
Heat transfer area to total volume ratio 𝛼 12 –
Density of water 𝜌 1 000 kg/m3
Dynamic viscosity 𝜇 0.001052 Pa × s
Number of banks Banks 10 –
Table 14: Mine A’s CBAC specification database #2
CBACS specification sheet Unit
Location 102L 105L 109L 113L –
Number of CBACs per level 2 2 2 2 –
Design cooling duty per CBAC 2 000 2 000 2 000 2 000 kW Air
Design temperatures in [WB/DB] 29.5/34.5 29.5/34.5 29.5/34.5 29.5/34.5 °C Design temperatures out [WB/DB] 21.8/21.8 21.8/21.8 21.8/21.8 21.8/21.8 °C
Design flow 70 70 70 70 m3/s
Water
Design temperatures in/out 12/22 12/22 12/22 12/22 °C
Design flow 60 60 60 60 ℓ/s
High pressure water supply strategy for mine bulk air coolers 109 Table 15: Surface refrigeration plants’ specifications
Surface refrigeration plants
Description Unit Plant number
1 2 3 4
Make – Hitachi Hitachi Hitachi Hitachi
Model number – HM 25 A HM 25 A HM 25 A HM 25 A
Design refrigerant – R12 R12 R12 R12
Present refrigerant – R134A R134A R134A R134A
Compressor speed modified – Yes Yes Yes Yes
Lead/lag – Lag Lead Lead Lag
Serving –
Surface BAC and underground
services
Surface BAC and underground
services
Surface BAC and underground
services
Surface BAC and underground
services Evaporator
Design temperatures in/out °C 9.4/3 17.3/9.4 17.3/9.4 9.4/3
Design flow ℓ/s 350 350 350 350
Design duty kW 9 400 11 500 11 500 9 400
Derated duty kW 9 400 11 500 11 500 9 400
Condenser
Design temperatures in/out °C 27.5/31.5 27.5/32.2 27.5/32.2 27.5/31.5
Design flow ℓ/s 670 670 670 670
Design duty kW 11 220 13 300 13 300 11 220
Table 16: 71L refrigeration plant specifications #1 71L refrigeration plants
Description Unit Plant number
1 2 3 4
Make – Hitachi Hitachi Hitachi Hitachi
Model number – HM 20 A HM 20 A HM 23A HM 23A
Design refrigerant – R12 R12 R22 R22
Present refrigerant – R134A R134A R22 R22
Compressor speed modified – No No No No
Lead/lag – Lag Lead Lead Lag
Serving – Lower levels Lower levels 75L BAC 75L BAC
Evaporator
Design temperatures in/out °C 10.4/4 18/10.4 18/10.4 10.4/4
Design flow ℓ/s 120 120 240 240
Design duty kW 3 230 3 800 7 598 6 470
Derated duty kW 2 907 3 420 6 838 5 823
Condenser
Design temperatures in/out °C 44.9/41 49.4/44.9 52.9/45.9 45.9/42
Design flow ℓ/s 250 250 500 500
Design duty kW 4 430 5 000 8 090 9 448
High pressure water supply strategy for mine bulk air coolers 110 Table 17: 71L refrigeration plant specifications #2
71L refrigeration plants
Description Unit Plant number
5 6 7 8
Make – York York Hitachi Hitachi
Model number – TBC TBC HM 20 A HM 20 A
Design refrigerant – R12 R13 R14 R15
Present refrigerant – R134A R134A R134A R134A
Compressor speed modified – No No No Yes
Lead/lag – Lead Lag Lead Lag
Serving – Not working Not working Lower levels Lower levels
Evaporator
Design temperatures in/out °C 18.9/11.6 11.6/5.6 18/10.4 10.4/4
Design flow ℓ/s 126 126 120 120
Design duty kW 3 850 3 170 3 800 3 230
Derated duty kW 3 465 2 853 3 420 3 230
Condenser
Design temperatures in/out °C 57.2/52.8 52.6/48.9 49.4/44.9 44.9/41
Design flow ℓ/s 266 266 250 250
Design duty kW 4 900 4 125 5 000 4 430
Table 18: 100L refrigeration plants’ specifications 100L refrigeration plants
Description Unit Plant number
1 2 3
Make – Carrier Carrier Carrier
Design refrigerant – R12 R12 R12
Present refrigerant – R134A R134A R134A
Lead/lag – Parallel Parallel Standby
Serving – 100L BAC 100L BAC 100L BAC
Evaporator
Design temperatures in/out °C 14.4/6 14.4/6 14.4/6
Design flow ℓ/s 100 100 100
Design duty kW 3 520 3 520 3 520
Condenser
Design temperatures in/out °C 40.1/44.8 40.1/44.8 40.1/44.8
Design flow ℓ/s 225 225 225
Design duty kW 4 530 4 530 4 530
High pressure water supply strategy for mine bulk air coolers 111 Table 19: Dewatering pump specifications
Dewatering pumps Level Bed
no.
Serial no. Supplier Model Installed Installed motor capacity [kW]
29
1 4698351 Sulzer HPH 50-20 8+1 Mar-19 1 300
2 100297700 Sulzer HPH 50-20 8+1 Jul-19 1 300
4 590366 Sulzer HPH 50-20 8+1 Aug-19 1 300
5 100311667 Sulzer HPH 50-20 8+1 Oct-18 1 300
52
1 944968 Scamont HPH 50-20 8+1 Apr-19 1 300
2 100357385 Sulzer HPH 50-20 8+1 Jun-20 1 300
3 732581 Scamont HPH 50-20 8+1 Jul-19 1 300
4 100366982 Sulzer HPH 50-20 8+1 Sep-20 1 300
75
3 100369209 Sulzer HPH 50-20 9 Jul-20 1 300
4 100356938 Sulzer HPH 50-20 8 Mar-20 1 300
5 590358 Sulzer HPH 50-20 8+1 Dec-19 1 300
6 100366781 Sulzer HPH 50-20 8+1 Sep-20 1 300
100
1 100296986 Scamont HPH 58-25 8 Dec-18 2 600
3 100337384 Sulzer HPH 58-25 8 Mar-20 2 600
4 588681 Sulzer HPH 58-25 8 Aug-19 2 600
5 100326980 Scamont HPH 58-25 8 Aug-20 2 600
115
1 – – – – –
2 942690 Scamont HPH 58-29 5+2 Dec-18 2 500
3 Kus-115-P4 Sulzer HPH 58-25 5+2 Dec-19 2 500
4 100337379 Scamont HPH 58-25 5 Feb-20 2 500
High pressure water supply strategy for mine bulk air coolers 112 Table 20: Hot/cold water dam specifications
Hot/cold water dams
Description Unit Type Capacity Surface
Cold dam Mℓ Horizontal 5.3
Cold dam Mℓ Horizontal 3
Hot dam Mℓ Horizontal 2.24 Precool dam Mℓ Horizontal 2.5
29L
Cold dam Mℓ Horizontal 1.05 Hot dam Mℓ Horizontal 0.86 Hot dam Mℓ Horizontal 0.77
52L
Cold dam Mℓ Horizontal 1.96
Hot dam Mℓ Horizontal 1.1
Hot dam Mℓ Horizontal 1.24 71L
Cold dam Mℓ Horizontal 2.5
Cold dam Mℓ Horizontal 2
Cold dam Mℓ Horizontal 2
Hot dam Mℓ Horizontal 2.15 75L
Hot dam Mℓ Horizontal 2
Hot dam Mℓ Horizontal 2
92/94L
Cold dam Mℓ Raisebore 5
98/100L
Hot dam Mℓ Raisebore 4.8
Hot dam Mℓ Raisebore 4.8
Hot dam Mℓ Raisebore 4.8
115L
Hot dam Mℓ Horizontal 3
High pressure water supply strategy for mine bulk air coolers 113 Table 21: Water valves
Water valves
Location Purpose Size Control Type Quantity
Surface Water shut-off at cold dam – Manual Ball 1
Surface Recycling valve at BAC exit (to evaporator inlet) – Automated Ball 1 Surface Recycling valve at cold dam exit (to evaporator inlet) – Automated Ball 1
102L Water control 8" Automated Ball 2
105L Water control 8" Automated Ball 2
109L Water control 8" Automated Ball 2
113L Water control 8" Automated Ball 2
High pressure water supply strategy for mine bulk air coolers 114
Appendix B: Simulation verification
Appendix B discusses the verification data of Mine A’s simulation. The simulation was verified against a normal operating day. Calibration was done by using average operating conditions together with the data listed in Appendix A: Design specifications.
Table 22 shows the average percentage error between the actual and simulated results for a normal operating day for the chosen KPIs.
Table 22: Average percentage error between the actual and simulated results
KPI Actual Simulated Error [%]
CBAC inlet water flow [ℓ/s] 18.35 18.35 0.01
CBAC inlet water temperature [°C] 17.13 16.45 3.99
CBAC outlet air temperature [°C] 24.84 24.20 2.59
100L hot water dams’ level [%] 82.11 82.23 0.15
71L hot water dam level [%] 96.59 88.72 8.15
71L cold water dam level [%] 83.31 82.38 1.12
92L cold water dam level [%] 92.42 91.25 1.27
Pumping power consumption [kW] 13 203.93 13 469.83 2.01 Refrigeration power consumption [kW] 13 451.95 14 762.04 9.74
The average error between the simulated and actual results for the chosen KPIs was 3.22%, thus the simulation was deemed accurate. The graphs that follow depict a 24-hour profile that compares the actual and simulated results.
Figure 63 shows the inlet water flow of the CBAC. Verification resulted in a small error of 0.01%, which meant that the water flow through the cooling system was simulated correctly as water demands were utilised.
High pressure water supply strategy for mine bulk air coolers 115 Figure 63: CBAC inlet water flow verification
Figure 64 depicts the inlet water temperature of the CBAC. An error of 3.99% was observed between the actual and simulated results. In the simulation, the refrigeration plants controlled the outlet temperature at a given set point and the effects were instant, which explained the difference. This set point was constant in the simulation as seen in Figure 64. However, for the actual results, the refrigeration plants cooled the water and unforeseen factors caused the water to heat up or cool down slightly. Furthermore, cooling effects are not instant; it takes a certain amount of time before the effects are reached at the CBAC.
Figure 64: CBAC inlet water temperature verification 0
5 10 15 20 25 30 35 40
Water flow [ℓ/s]
Time [hh:mm]
CBAC inlet water flow
Actual Simulation
0 5 10 15 20 25
Temperature [°C]
Time [hh:mm]
CBAC inlet water temperature
Actual Simulation
High pressure water supply strategy for mine bulk air coolers 116
Figure 65 shows the outlet air temperature of the CBAC. An error of 2.59% was observed between the actual and simulation results. This error was relatively small, which meant that the outlet temperatures were simulated correctly. The small error seen at 19:30 was due to the simulation that switched off equipment instantly.
Figure 65: CBAC outlet air temperature verification
Figure 66 to Figure 69 show the hot and cold water dam levels. All the levels remained within the prescribed limits. Differences such as fluctuations were attributed to the difficult incorporation of human interface. The simulation used step controllers to control the dam levels between two given set points, whereas the actual results were dependent on control room operators to control the dam levels as they deem fit.
Figure 66: 100L hot water dams’ level verification 0
5 10 15 20 25 30 35
Temperature [°C]
Time [hh:mm]
CBAC outlet air temperature
Actual Simulation
0 20 40 60 80 100
Level [%]
Time [hh:mm]
100L hot water dams' level (average of dam 1, 2 & 3)
Actual Simulation
High pressure water supply strategy for mine bulk air coolers 117 Figure 67: 71L hot water dam level verification
Figure 68: 92L cold water dam level verification 0
20 40 60 80 100
Level [%]
Time [hh:mm]
71L hot water dam level
Actual Simulation
0 20 40 60 80 100
Level [%]
Time [hh:mm]
92L cold water dam level
Actual Simulation
High pressure water supply strategy for mine bulk air coolers 118 Figure 69: 71L cold water dam level verification
Figure 70 compares the actual and simulation pumping power consumption. An error of 2.01%
was observed, which was attributed to the simulation that used step and PI controllers to mimic human interface. However, each control room operator controlled the pumps differently.
Figure 70: Pumping power consumption verification
Figure 71 illustrates the refrigeration power consumption. An error of 9.74% was observed between the actual and simulated results. Again, the simulation controlled the refrigeration plants based on a given temperature set point whereas control room operators controlled the system as they deemed fit. However, the results obtained were still sufficient for verification.
0 20 40 60 80 100
Level [%]
Time [hh:mm]
71L cold water dam level
Actual Simulation
0 5 000 10 000 15 000 20 000 25 000 30 000
Power [kW]
Time [hh:mm]
Pumping power consumption
Actual Simulation