Compressed air system

Introduction

(Compressed air system)

-

-

Air inlet filter

Dryer Air filter Air receiver

After cooler and lubricant cooler

Lubricant/air separator

Filter, regulator and lubricator

Pressure/controller

Intake air filters Inter-stage coolers After coolers Air dryers Moisture drain traps Receivers

Air receiver

Intercooler

Air compressor

Piping

2

(Positive Displacement)

(Dynamics)

Types of compressor

Positive displacementDynamics

1) (Reciprocation Compressors)

2) (Rotary Compressors)

3) (Centrifugal Compressors)

3

=> =>

=> =>

=> =>

2 2

Reciprocating Compressors

(Rotary Compressors)

(Sliding Vane Compressors) (Vane)

Liquid Piston Compressors

Liquid piston

Two-Impeller Straight-Lobe

(Lobe) 2

straight lobe

(Screw Compressor)

2 (Helical)

(Centrifugal Compressors)

-

//

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)

(Assessment of compressor)

(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)

(Free Air Delivery, FAD)

P1 () P2

()

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

(Compressor efficiency)

Specific power consumption (kW/volume flow rate) Isothermal Volumetric Adiabatic Mechanical

(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

(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

(Air leak)

Energy waste: 20 30% of output Drop in system pressure Shorter equipment life

-

(Leak quantification method)

(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)

( )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]

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= = =

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

( 7 )

[/m3]

capacity

7.5-5.5 [kW/m3/min] (ANR) 0.13-0.18 [m3/min/kW] (ANR) 7.5 [kW]

( )

()

main source

(valves) flow meter

(pneumatic tool)

()

(pressure drop)

Meter Pressure (leak)

()

35 oc 25 oc 3.3%

()

1.

2.

3.

9

9 3 C 1%

9

9

After Cooler After Cooler

After Cooler

Air Dryer

Air Dryer

260.6

5151.5

1.03.00.3

15454.5

10303.0

Variable speed control [m3/min]

Constant speed control [m3/min]

[m3]

()

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]

()

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]

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 = =

( )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]

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

(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

=

5 %

6

2 6 3

2 Booster 7 11

()

2.

1.

3.

4.

5.

6.

7.