compressed air system
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Compressed air system
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Introduction
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(Compressed air system)
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Air inlet filter
Dryer Air filter Air receiver
After cooler and lubricant cooler
Lubricant/air separator
Filter, regulator and lubricator
Pressure/controller
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Intake air filters Inter-stage coolers After coolers Air dryers Moisture drain traps Receivers
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Air receiver
Intercooler
Air compressor
Piping
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2
(Positive Displacement)
(Dynamics)
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Types of compressor
Positive displacementDynamics
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1) (Reciprocation Compressors)
2) (Rotary Compressors)
3) (Centrifugal Compressors)
3
=> =>
=> =>
=> =>
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2 2
Reciprocating Compressors
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(Rotary Compressors)
(Sliding Vane Compressors) (Vane)
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Liquid Piston Compressors
Liquid piston
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Two-Impeller Straight-Lobe
(Lobe) 2
straight lobe
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(Screw Compressor)
2 (Helical)
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(Centrifugal Compressors)
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//
0.10 0.18 kW/cfm0.15 0.25 kW/cfm0.30 0.45 kW/cfm
(1 50 bar)
(1 15 bar)
(1 100 bar)
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(Assessment of compressor)
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(Actual flow: Free Air Delivery, FAD)
2 1
o
P P VQP T= [Nm3/min]
= Final pressure after filling [kg/cm2 a]= Initial pressure after bleeding [kg/cm2 a]= Atmospheric pressure [kg/cm2 a]= Storage volume [m3] including receiver, after cooler, and delivery piping= Time take to build up pressure P2 [min]
2P
1PoP
VT
T2 FAD (273+T1)/(273+T2)
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(Free Air Delivery, FAD)
P1 () P2
()
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ExampleTheoretical compressor capacity : 14.75 m3/min @ 7 kg/cm2Receiver volume : 7.79 m3Additional hold up volume,Pipe, Water cooler, etc., : 0.4974 m3Total volume : 8.322 m3Initial pressure P1 : 0.5 kg/cm2Final pressure P2 : 7.03 kg/cm2Atmospheric pressure Po : 1.026 kg/cm2 a
2 1
o
P P VQP T=
Compressor output [m3/min]
7.03 0.5 8.322 13.171.026 4.021
= = m3/min
10.69% less than theoretical capacity
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(Compressor efficiency)
Specific power consumption (kW/volume flow rate) Isothermal Volumetric Adiabatic Mechanical
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(Isothermal efficiency)
1 1 ln [ ]36.7rIsothermal power P Q kW=
Isothermal efficiency = Actual measured input powerIsothermal power
P1 = Absolute intake pressure [kg/cm2]Q1 = Free air delivery [m3/hr]r = Pressure ratio, P2/P1
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(Volumetric efficiency)
Volumetric efficiency = Free air delivery [m3/min]Compressor displacement
2
4DCompressor displacement L S x n=
D = Cylinder bore [m]L = Cylinder stroke [m]S = Compressor speed [rpm]x = 1 for single acting and 2 for double acting cylindersn = Number of cylinders
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(Air leak)
Energy waste: 20 30% of output Drop in system pressure Shorter equipment life
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(Leak quantification method)
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(Leak quantification method)
[ ] 11 2
% 100tLeakaget t
= +t1 = on load time [min]t2 = off load time [min] 5%
3 1
1 2
[ / min] Q tSystem leakage mt t= +
Q = Free Air Delivery (FAD)
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( )1 21 2
%[ ]
Leakage xt dt HEnergy waste kWh
t t= +
(Leak quantification method)
t1 = On load time [sec]t2 = Off load time [sec]x = On load power [kW]d = Off load power [kW]H = Operating hour [h]
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Compressor capacity (m3/minute) = 35 Cut in pressure, kg/cm2 = 6.8Cut out pressure, kg/cm2 = 7.5 Load kW drawn = 188 kWUnload kW drawn = 54 kWAverage Load time = 1.5 minAverage Unload time = 10.5 min
Example
1
1 2
1.5[%] 100 100 12.5%1.5 10.5
tLeakaget t
= = =+ +
3% 0.125 35 4.375 / minSystem leakage Leakage Q m= = =
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Example
( )1 21 2
%[ ]
Leakage xt dt HEnergy waste kWh
t t= +
( )( )
0.125 188 1.5 60 54 10.5 60 81.5 10.5 60
70.75 kWh
+ = + =
Assume operating time = 8 hours
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( 7 )
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[/m3]
capacity
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7.5-5.5 [kW/m3/min] (ANR) 0.13-0.18 [m3/min/kW] (ANR) 7.5 [kW]
( )
()
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main source
(valves) flow meter
(pneumatic tool)
()
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(pressure drop)
Meter Pressure (leak)
()
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35 oc 25 oc 3.3%
()
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1.
2.
3.
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9
9 3 C 1%
9
9
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After Cooler After Cooler
After Cooler
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Air Dryer
Air Dryer
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260.6
5151.5
1.03.00.3
15454.5
10303.0
Variable speed control [m3/min]
Constant speed control [m3/min]
[m3]
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()
Size of pressure tank og o
A Q PP P = +
A = factor [min] (usually give A = 1.5 for 6 10 bar)Q = capacity of air compressor [m3/min] (FAD)Pg = pressure gauge [bar]Po = ambient pressure [bar]
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()
Size of pressure tank 3 og o
Q PP P = +
A = factor [min] = 3Q = capacity of air compressor [m3/min] (FAD)Pg = pressure gauge [bar]Po = ambient pressure [bar]
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Example
25 m3/min 7 bar
Q = 25 m3/minPo = 1.013 barPg + Po = 7 + 1.013 = 8.013 bar
Size of pressure tank 3 og o
Q PP P = +
33 25 1.013 9.58.013
m = =
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( )o d oP V C tP
= Size of pressure tank
( )( )o d o
Size of tank Pt
P V C=
Vd = [m3/min]t = [min]P = [bar]
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Example 30 m3/min 6 bar g
Size of tank = 9.5 m3P = 7 6 bar = 1 barQ = 25 m3/minPo = 1.013 barVd = 30 m3/min
( )( )o d o
Size of tank Pt
P V C=
( )9.5 1 1.9 min
1.013 30 25t = =
Overload 5 m3/min 1.9
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(Power of air compressor in theory)
T1 = inlet temperature [K]P1 = ambient pressure [bar]P2 = absolute working pressure [bar]k = gas constant for air k = 1.4R = universal gas constant [R = 0.287 kJ/kg.K]
1
1 2
1
[ / ] 11
kk
compkRT PW kJ kgk P
=
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5 %
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6
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2 6 3
2 Booster 7 11
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