basic compressor knowledge

8/22/2019 Basic Compressor Knowledge

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Basic compressor knowledge


2/87

The Process Of Gas

Compressors

kinds of gas compressors

principle of reciprocating compressors

Effect of clearance

Multilevel compress with intercoolers


3/87

Types of gas compressors

There are two general types compressors

Reciprocating compressor

For high pressures and low-volume flow

rates..

Rotative compressor

For lower pressures and high-volume flow

rates.


4/87


Air compressor


5/87


Reciprocating compressor


6/87


Refrigerator compressor

Motor

Compressor


7/87



Motor

Compressor


8/87




9/87


Icebox compressor


10/87


Centrifugal rotative compressor


11/87


Centrifugal rotative compressor


12/87


Axis flow rotative compressor


13/87


Wc

H1

H2

Q?

V

p

P1 1

P2 2


14/87


v

p

P1 1

P22T 2s2n

s

T

P1

1P2

2s

2n

2T


15/87


1.The principle

Notice that there will be a difference between the work

necessary to compress the gas from states 1 to state

2 and the total work of process.

Wcs>Wcn>WcT


16/87


2.The work of compressor

Adiabatic compressor

11

)(1

1

1

21112212,

k

k

gscp

pTRk

kvpvpk

khhw


17/87

9-2. The principle of reciprocating

compressors


Isothermal compressor

1

21

1

21, lnln

p

pTR

v

vTRw ggTc


18/87

9-2. The principle of reciprocating

compressors


Polytropic compressor

11

)(1

1

1

211122,

n

n

gncp

pTR

n

nvpvp

n

nw


19/87



Tns

Tns

Tcncsc

vvv

TTT

www

,2,2,2

,2,2,2

,,,


20/87

Effective Absolute pressure

atmospheric

pressure

absolute

pressure

effectivepressure

total pressure

pressure = 0


21/87

Effect of clearance

Wc

V

p

P1 1

P2 2

H1

H2

4

3

1.Clearance

f

g


22/87

Effect of clearance

Wc

V

p

P1 1

P2 2

H1

H2

4

3

1.Clearance

f

g


23/87

Effect of clearance

2.The work of compressor Polytropic compressor

1)(1

11

11

1

1

2411

1

4

344

1

1

211

343112,

n

n

n

n

n

n

gfgfnc

p

pVVp

n

n

p

pVp

n

n

p

pVp

n

n

w


24/87

Effect of clearance

2.The work of compressor Polytropic compressor

)1(1

11

1

1

1

1

21,

nn

g

n

n

nc

TmRn

n

ppVp

nnw


25/87


1.SystemCooling water

Low pressure gas

1st-stage

compression

2nd-stage

compression

Intercooler

High pressure gas

1223


26/87


2.Diagram

V

p

P1

1

P2

2

3

e

g

f2

3

Pm

3T


27/87



2)()(1

1)(1

1)(1

1

2

3

1

1

2

1

1

2

32

1

1

21

,,

'

n

n

n

n

g

n

n

gn

n

g

hclcc

p

p

p

p

TRn

n

p

pTR

n

n

p

pTR

n

n

www


28/87


312 pppp m

2

3

1

2

pp

pp


m

m

m

m

p

p

p

p

p

p

p

p 1

12

3

1

2

..........


29/87



)1(1

1

1

n

n

gc TRn

nmw


30/87

Absolute pressure8 bar

Atmospheric pressure

1 bar

Effective pressure

7 bar

Effective pressure

The effective pressure is the differencebetween absolute pressure and

atmospheric pressure

It is the pressure available to deliver work


31/87

Free Air Delivery

Free Air Delivery :

is the measured real

delivered volume of air

(in l/s or m/min or cfm)at the same conditions of

pressure and temperature

at the air inlet


32/87

Free Air Delivery

FAD is not equal to the displacement

volume of the compressor element,

because internal losses in the element

(leaks to air inlet)

FAD is independent from the ambient

conditions (temperature & pressure)


33/87

Compression principle

1

Volume

Pressure


34/87


1

Volume

Pressure2

Compression


35/87


1

3

Volume

PressureDischarge 2

Compression


36/87


1

3

4

Volume

PressureDischarge

Pressurereduction

2

Compression


37/87


1

3

4

Volume

PressureDischarge

Suction

Pressurereduction

2

Compression


38/87


1

3

4

Volume

Pressure

Suction Volume

Stroke Volume

Discharge

Suction

Pressurereduction

2

Compression


39/87

Screw Compressor

Introduced in 1958 by Atlas Copco

Male and female rotors move towards

each other, while the volume between

them and the housing decreases.


40/87

Screw Compressor Screw profile improved in 1966

Symmetrical screw was changed in an

asymmetrical helical profile

10% more efficiency


41/87


Compressionstart

Compression

Suction

Deli

very


42/87

Pressure Ratio

Each screw element has a fixed,integrated pressure ratio

This depends on :

length of the rotors Pitch of the screw

form of the discharge port

Best efficiency is reached when thepressure ratio is adapted to the required

working pressure


43/87

Advantages screw compressor

High shaft speeds and large flow rate :

gives small exterior dimensions

Simple and strong design :

no valves and seals reliable and

maintenance friendly

small dirt particles improve the sealing and

the efficiency almost pulsation free air


44/87

Advantages screw compressor

Low wear :

guaranteed long life time and constant

capacity

life time is determined by the bearing wear

Absolute oil free design possible

No inertia forces

vibration free operation

high speeds possible

big power possible


45/87

Disadvantages screw compressor

Lower efficiency because of internal leaks

High quality bearing of the rotors required

rotor clearances are small

axial bearings needed

Higher noise level (high frequency)

High quality finishing of the rotors required

expansion of rotors through heat results in

blocked elements


46/87

Oil injected screw compressors


47/87


Oil is used for :

Cooling : compression heat is absorbed by

the oil

Lubrication of rotors, bearings, gears

Sealing between rotors and rotor and

housing

Corrosion protection of the internal metalparts


48/87


Oil is injected in the bottom of the rotor housing,

on the bearings and gears


49/87


Only one rotor is driven, this rotor then

drives the other one :

old XAS 90 : female driven rotor

all other compressors : male driven rotor

When required a gear box or drive belt

brings the compressor element to the

correct speed


50/87

Oil Free screw compressor

No oil is injected in the air Complete separation of oil used for

lubrication of bearings and gears

An external synchronizing gear is usedto synchronize the rotors

no contact between rotors and housing

Pressure ratio is limited by thetemperature difference between the

intake and the discharge


51/87

Oil Free screw compressor

Synchronizing Gear

Seal rings

Oil gallery

Water jacket cooling


52/87

Comparison

Separate oil system

with oil pump

No oil separators

required Compression of

gasses is possible

Special coating onthe rotors

Water jacket cooling

Integrated oil system

without oil pump

Oil separators

needed Not suitable for oil

aggressive gasses

No coating on therotors

Oil cooling

Oil Free Oil Injected


53/87

Comparison

Seal rings on the

shafts

Synchronization

gears High speed, high

noise

High temperature Max. pressure ratio

is low (1:4)

No internal sealing

One rotor drives the

other

Lower noise due tolower speed and oil

Low temperature due

to oil cooling High pressure ratio

possible (1:13)

Oil Free Oil Injected


54/87

Compressor regulating system


55/87

Compressor running condition

Four major running conditions : NO-LOAD

Machine started, minimal pressure build-up

UNLOADReceiver tank pressurized, no air

consumption

LOAD

Receiver tank pressurized and airconsumption

BLOW-DOWN

Machine stopped, blow-off of air pressure


56/87

Compressor systems

Four major components :

Air system

Oil system

Regulating system

Electrical system


57/87

Air filterCompressorElement(AFCE)(with

vacuator valve VV, Safety Cartridge SC and

vacuum indicator VI)

Unloading Valve (UV)

Compressor Element (CE)

Temperature Switch (TS)

Check Valve (CV)

Air Receiver(AR)

Non Return Valve

Minimum Pressure Valve(MPV)

Air Outlet Valve (AOV)

Air system


58/87

Air filter

Filtration of the inlet air in 3 stages :

centrifugal dust separation

paper filter element

safety cartridge (optional)

Vacuum indicator gives an indication

when the pressure drop over the filter

element is too high filter element needs

to be replaced


59/87

Air filterAir inlet Centrifugal separation

Dust

Filter element

to compressor element

Vacuum indicator


60/87

Unloading valve

Opens and closes the air inlet to the

compressor element.

Open position at load condition

=> Air consumption

Closed position at no load condition

=> No air consumption.

Control of the valve by regulatingpressure.


61/87

Compressor element

Oil is injected in the air and compressed

to the pressure as set by the regulating

valve.


62/87

Compressor element


63/87

Compressor element

Oil

Oil

Air/Oil

Air inlet


64/87

Air receiver / Separator

Air/Oil

Centrifugal separation

Separator element

Air outlet

Mi i l / l


65/87

Minimum pressure valve / nozzle

Guarantees a minimum pressure in the oil

separator (approx. 3.5 bar)

Minimum pressure is required toguarantee an continuous oil supply to the

element.

N l / Mi i l


66/87

Nozzle / Minimum pressure valveMINIMUM PRESSURE VALVE

NOZZLE

Oil filt


67/87

Oil filter

Dirty Oil Filtered Oil

By-pass valve


68/87

Compressor element

Oil

Oil

Air/Oil

Greasing to the bearings

Air inlet


69/87

Regulating system

Unloading valve

Speed regulator

Blow-down valve

Safety valve

Regulating system (Series 6)


70/87

Regulating system (Series 6)

Regulating Valve

Unloading Valve

Speed Regulator

Safety Valve


71/87

Unloading valve

Opens and closes the air inlet to the

compressor element.

Open position at load condition

=> Air requirements

Closed position at no load condition

=> No air requirements


72/87

Unloading valveRegulating pressure Air inlet

Vent Hole


73/87

Unloading valveLOAD UNLOAD

Re

gulatingpressure

Air inlet


74/87

Blow-down valve

Blows off the air receiver pressure oncethe compressor has shut-down

=> this to depressurize the receiver tank

Integrated in the unloading valve

Blow down valve


75/87

Blow-down valve

blow-down

valve

Receiver pressure

blow-off hole

Air inlet


76/87

Blow-down valveLOAD / UNLOAD BLOW-DOWN

Receiver pressure

Receiver pressure return

after shut-down

Blow-off

receiver pressure


77/87

Safety valve

Blows off the air receiver pressure oncethis pressure raises above the design

pressure.


78/87

Electrical system

Battery voltage : 12 or 24 V Starting system

cuts-out starter motor when engine is running

avoids cranking when receiver tank ispressurized

Safety shut-downs

Instrument indications

S f h d


79/87

Safety shut-downs

Compressor : Compressor element outlet temperature

Engine :

Coolant temperature Coolant level

Oil pressure

Fuel level Emergency stop

S f t h t d


80/87

Safety shut-downs

All safety shut-downs are Normal Closedswitches

Fail safe as a loose wire will result in a shut-

down

Good electrical contacts are important

PARTS OF SERVICE COMPRESSOR


81/87

PARTS OF SERVICE COMPRESSOR

Air treatment options

Lubricator Aftercooler

Water separator

Fine filters PD / QD

Re-heater



82/87


Aft l W t t


83/87

Aftercooler - Water separator

The aftercooler is a heat exchanger,which cools the hot compressed air to

precipitate the water that otherwise would

condensate in the air hose.

The outlet temperature is ambient + 7C.

It is followed by a water separator that

separate the condensate and drains it

Used for : sandblasting, fibre optic cable

steering, pipe cleaning

Aft l W t t


84/87

Aftercooler - Water separator

Water separator

Aftercooler

Fi filt PD / QD


85/87


PD filter will separate oil and solidparticles.

QD filter or carbon filter will separate oil

and water vapour. Air becomes technically oil free.

Only 0.003 ppm oil is available in the air

outlet

Fi filt PD / QD


86/87


PD filter

QD filter

R h t


87/87

Re-heater

The re-heater is a heat exchanger, whichwarms up the compressor outlet air to

ambient + 60C.

The water and oil will be vaporized resulting

in hot and dry air, this avoids condensate

problems.

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