power savings by impeller replacements for main fan stations in the sa gold mining industry...
TRANSCRIPT
Power Savings by Impeller Replacements for Main Fan Stations in
the SA Gold Mining Industry
Presented by:• John-John Fourie
Agenda
• Introduction• Potential savings - Typical mine fan• Theory, Fan laws and Fan curves• Energy Saving Options• Drop-in Impeller Replacement• Conclusion
Introduction• Typically 250kW to 2.2MW per single fan can be
consumed• Potential financial savings significant • Intervention methods include centrifugal fan impellers
modifications
Potential savings - Typical Mine Fan
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Potential savings - Typical Mine Fan
Actual efficiency of 55% is much lower than the original,
selected efficiency of 80%
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Potential savings - Typical Mine Fan
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Pow
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Original dutyAir power = 540kWAbsorbed power = 620kWIn-efficiency lost = 80kW
Potential savings - Typical Mine Fan
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Original dutyAir power = 540kWAbsorbed power = 620kWIn-efficiency lost = 80kW
Actual dutyAir power = 360kWAbsorbed power = 660kWIn-efficiency lost = 300kW
Potential savings - Typical Mine Fan
• Efficiency achieved > 80% (from 60%) • Power Saved approximately 200 kW (per
fan)• Cost Saving R963 600 per annum (Based on
0.55c/kWh)
Potential savings - Typical Mine Fan
Theory – Basic Fan laws
1. Volume flow
2. Pressure
3. Power
Q – Volumetric flow rate (m3/s)P – Fan static pressure (Pa)kW – Absorbed power (kW)n – Fan operating speed (rpm)D – Impeller diameter (m)ρ – Air density (kg/m3)
Energy Savings Options
1. Inlet guide vanes (IGV’s)2. Speed control3. Impeller replacement
(1) Inlet Guide Vane (3) Impeller Replacement(2) Speed Control
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Energy Savings Options - Inlet Guide Vanes
60° rpm
90°
Duty 1
Duty 2
• Power consumption is related to volume flow• Volume flow reduction of 10% - 15% is power savings of 22% -
25%
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Energy Savings Options - Inlet Guide Vanes
60° rpm
90°
Duty 1
Duty 2
By altering the IGV opening from 90° to 60° a saving of ±150kW can be achieved.
Energy Savings Options - Speed control• Fixed speed reduction gearbox• Variable frequency drives (VFD’s)
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Energy Savings Options - Speed control
600rpm745rpm
Duty 1
Duty 2
𝑄2
𝑄1
∝(𝑛2𝑛1 )𝑃2
𝑃1
∝(𝑛2𝑛1 )2
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Energy Savings Options - Speed control
600rpm745rpm
Duty 1
Duty 2
By adjusting the fan speed from 745 rpm to 600 rpm a saving of ±300kW can be achieved.
𝑄2
𝑄1
∝(𝑛2𝑛1 )𝑃2
𝑃1
∝(𝑛2𝑛1 )2
Original inefficient paddle wheel impeller
Replaced high efficiency backward inclined impeller
Photo courtesy of FläktWoods Fans Hermit Crab concept
Impeller Replacement – Example
Impeller Replacement – Design constraints
• No change to fan casing and civils • Existing impeller should be stored• Re-evaluate fan shaft and bearing selection• Vibration signature of the fan
Impeller Replacement – Design Parameters
Impeller diameter
Impeller exit angle
Impeller width
• Impeller diameter• Impeller width• Impeller exit angle• Impeller blade profile• Number of blades
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Impeller Replacement – Impeller diameter
16% Change in impeller diameter,
results in 58% decrease in
absorbed power
Original Duty Impeller diameter 2610mm
New DutyImpeller diameter 2200mm
Impeller Replacement - Impeller width • Distance between the backplate and the shroud • Width is directly proportional to the volumetric flow• Width defines the volume capabilities• If altered check inlet cone arrangement
Increase in power due to increased impeller
width.
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Volume Flow (m3/s)
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Original DutyNew Duty
Impeller Replacement - Impeller exit angle• A larger blade exit angle reduces the exit shock losses• Backward curved impellers are typically more efficient than
radial type impellers• Changing the exit angle also impacts the static pressure
Impeller Replacement - Impeller blade profile
Blade aerodynamic profile:• Reducing drag and increasing lift• Reduced power at the same pressure and volume flow
Impeller Replacement - Number of blades• Increasing the number of blades increases the fan pressure• Increasing the blade numbers can result in secondary flow
losses and increased tip blockage
Impeller Replacement – Method of Analysis
1. Specify required static pressure and volume flow2. Start with a slightly decreased impeller diameter3. Increase impeller width by 100 mm to get a flatter head curve4. Decrease number of blades to get a reduced pressure curve5. Increase exit blade angle to get a reduced pressure curve6. Calculate efficiency using numerical methods (target eff. = 82%)7. Repeat steps 2 till 6 until desired curve is achieved
Finite Element Structural and fatigue analysis essential
Pres
sure
Flow
745 rpm
10°20°30°
Existing fan IGVsOld impeller/design resistanceOld impeller efficiencyNew resistanceNew impellerNew impeller efficiency
80%
70%75%
70%
75%
80%
745 rpm
Impeller Replacement – New fan curve
Original design duty @ 82%
NEW fan curve
Actual operating duty @ 65%
OLD fan curve
NEW fan duty @ 82%
Original mine system resistance
NEW mine system resistance
Impeller Replacement – Measured fan efficiency
Performance data:
• Volume flows 85 m3/s - 460 m3/s • Static pressures 1.6 kPa - 6.2 kPa.
• Old Fan efficiency 50% - 60% • New Fan Efficiency 75% - 80%.
• Possible Power Savings ~ 1 MWE
• Possible Cost Savings R5.6M pa (Megaflex)