This case study simulates a mining compressed air network to ensure minimum shaft pressure of 580 kPa during increased production. Using Flownex, three scenarios with current and forecasted air consumption were modeled. Results show the existing system suffices for one year, after which an additional compressor at the North shaft is required to maintain pressure.
CHALLENGE
Compressed air is used widely in mining for the operation of pneumatic equipment. Due to the constant variation in demand during production and constant expansion in mining area, the pressurized system needs to maintain acceptable pneumatic delivery pressures in the various shafts.
BENEFITS
The Flownex simulation will verify whether the compressed air network can maintain the required minimum shaft pressures when the production figures increase in the future expansion of the mining activities.
SOLUTION
The steady-state simulation of a compressed air network used in the mining industry is demonstrated in this example. The forecasted production figures were used to ensure that the compressed air network will be able to supply all the shafts with the minimum pressure of 580 kPa when the production is increased. It was seen that the current layout is adequate for the next year after which an additional compressor is needed at the North shaft compressor house.
SYSTEM DESCRIPTION
The layout of the compressed air network is shown in Figure 1.
The network consists of five shafts located about two kilometers from each other. Compressors A to D are located in a compressor house near South shaft and compressor E in a compressor house near North shaft. All the shafts have different production levels and thus require different amounts of compressed air. The minimum pressure needed at the shafts to maintain production is 580 kPa.
OBJECTIVE OF SIMULATION
The objective of the simulation is to model the steady-state operation of the current compressed air network using the current production figures. The investigation must then establish whether the compressed air network can maintain the required minimum shaft pressures when the production figures increase in the future expansion of the mining activities.
The production figures can be converted to air consumption per shaft as shown in Table 1.
Table 1: Current and forecasted air consumption per shaft.
Shaft |
Current air consumption -2006 (kg/s) |
Forecasted air consumption - 2007 (kg/s) |
Forecasted air consumption - 2008 (kg/s) |
|---|---|---|---|
| South | 3.36 | 4.15 | 5.5 |
| West | 2.0 | 2.5 | 3.5 |
| North | 12.12 | 10 | 8 |
| Middle | 3.78 | 6 | 10 |
| East | 7.56 | 7.56 | 7.56 |
FLOWNEX MODEL
The Flownex model of the system is shown in Figure 2.
All the pipes are assigned a roughness of 45 μm and all the pipe lengths are increased with ten percent to account for secondary losses. Due to a lack of compressor performance characteristics the compressors are modeled in a simple manner by assigning a fix mass flow through a pipe. A pipe with a check valve is then used to simulate the compressor blow off set pressure. Table 2 shows the compressor specifications and mass flow rates that are calculated at nominal conditions (Atmospheric Pressure: 89.4 kPa, Ambient Temperature: 20 ºC, Air density: 1.06 kg/m³).
Table 2: Compressor specifications and flow rates.
Comp Nr. |
Pressure setpoint (kPa) |
Rated volume flow rate at nominal conditions (m³/hr) |
Mass flow rate at nominal conditions (kg/s) |
|---|---|---|---|
A |
620 |
8500 |
2.51 |
B |
620 |
25600 |
7.56 |
C |
620 |
25600 |
7.56 |
D |
620 |
8500 |
2.51 |
E |
620 |
48750 |
14.39 |
DESCRIPTION OF SIMULATION
Three different scenarios are simulated:
Simulation of the current network, using 2006 production figures.
Simulation of the current network, using 2007 production figures.
Simulation of the current network, using 2008 production figures. (An additional compressor can be added at the North shaft compressor house).
RESULTS
Table 3 compares the Flownex results for the different scenarios.
Table 3: Comparison between the different scenarios.
Parameter |
Units |
Scenario 1 |
Scenario 2 |
Scenario 3 |
Pressure at South shaft |
kPa |
617.89 |
617.13 |
615.71 |
Pressure at West shaft |
kPa |
609.15 |
607.15 |
603.86 |
Pressure at North shaft |
kPa |
600.97 |
601.44 |
601.92 |
Pressure at Middle shaft |
kPa |
605.50 |
602.39 |
598.57 |
Pressure at East shaft |
kPa |
592.43 |
589.70 |
587.06 |
Compressor blow off * |
% |
16.50 |
12.50 |
6.69 |
* Blow off is the percentage of supplied mass flow that is being blown off i.e. excess air.
All the pressures are above the required 580 kPa at the shafts. In scenario 3, the current installed compressors were not able to supply enough compressed air, and an 8500 m³/hr compressor was added to the North shaft compressor house.
CONCLUSION
The steady-state simulation of a compressed air network used in the mining industry is demonstrated in this example. The forecasted production figures were used to ensure that the compressed air network will be able to supply all the shafts with the minimum pressure of 580 kPa when the production is increased. It was seen that the current layout is adequate for the next year after which an additional compressor is needed at the North shaft compressor house.