Reciprocating compressor

RECIPROCATING COMPRESSORS


CompressorsCompressors

HIGH LOWV. HIGH

NO NOYES

YESNO YES

LOW HIGH V. HIGH

YES NO NO

Pressure PPressure P

Flow Rate QFlow Rate Q

S .R .VS .R .V

EfficiencyEfficiency

Maint. costMaint. cost

PulsationPulsation

SurgingSurging

Reciprocating Centrifugal Axial

V. HIGH LOW LOW

LOW HIGH V. HIGH

Crosshead

Stuffing

Box

Packing

Discharge Valves

Suction Valves

PistonDistance Piece

Con-rodCrank

Piston Rod

Wiper

Rings

POWER END POWER END

GASEND

GASEND

FIXED CLEARANCE

VOLUME

VARIABLECLEARANCE

VOLUME

RECIPROCATING COMPRESSORS:FLOW RATE REGULATION

RECIPROCATING COMPRESSORS:FLOW RATE REGULATION

• VARIABLE CLEARANCE

• VARIABLE SPEED

• BYPASS

• SUCTION VALVE

UNLOADERS

CF CR

CF = C

CR = C

23

13

• VARIABLE CLEARANCE• VARIABLE CLEARANCE

C = Total Clearance Volume = CF + CR

Before operating Before operating

After operating After operating

CF CR

CF = C

CR = C

12

12

Point g suction valves open

C = Clearance volume

C

v

b

a

c

g

Pd

Ps c1M

EFFECT OF CLEARANCE VOLUME

EFFECT OF CLEARANCE VOLUMEAtAt

Point a suction valves closed

Point b discharge valves open

Point c discharge valves closed

Compression ratio

Pressure ratio )ABSOLUTE(P d

P s=

Volumetric efficiency =V a g

V cylinder a M

a g=

= V cylinder

V b M

C

vb a

c

g

Pd

Ps c1M

b

b M

a M =

C

v

Pd

Ps c1M

b

a

c

g


V cylinder a M

a g=

C

v

Pd

PsM

b

a

c

g


V cylinder a M

a g=

v

Pd

Ps M

C

g a

bc


V cylinder a M

a g=

If C Increased suction valves will open at ( g (

C

va

c

g

Pd

Ps

b

M

EV DECREASES

Q DECREASES


V cylinder a M

a g=

If C Decreased suction valves will open at ( d (

C

va

c bPd

Ps M g

EV INCREASES

Q INCREASES


V cylinder a M

a g=

•SUCTION VALVE

UNLOADERS

•SUCTION VALVE

UNLOADERS

STUFFING BOX

RIDER RINGSRIDER RINGS

PRESSURE RINGS

PRESSURE RINGS

WIPER RINGS

WIPER RINGS

T

R

TANGENTIAL RINGST

R RADIAL RINGS


INTERMEDIATEPRESSURES


INTERMEDIATEPRESSURES

Example 1

4 Stages Reciprocating Air comp has outlet pressure P4 = 80 barg

what are the intermediate pressures

P0

0 barg

1st

stage

P1

2nd stage

P2

3rd stage

P3 P4

80 barg

4th stage

P0

0 barg

P1 P2 P3 P4

80 barg

1st

stage2nd

stage3rd

stage

4th stage

R =P1

P0

P4

P3=

P3

P2=

P2

P1=

Assume

R is The equal Pressure Ratio between stages.

R = 4 P4

P0RT =

P4

P0BUT

RTR =

4

AND RT = P4

P0

R = RT4

Generally

R = RTN

P4 = R * P3 = 3 * 27 = 81 bara = 80 barg

P0

0 barg

P1 P2 P3 P4

80 barg

1st

stage2nd

stage3rd

stage

4th stage

RT = P4 / P0 = (80 +1) / (0 +1) = 81/ 1 = 81

N 4R = RT = 81 = 3

P1 = R * P0 = 3 * 1 = 3 bara = 2 barg

P2 = R * P1 = 3 * 3 = 9 bara = 8 barg

P3 = R * P2 = 3 * 9 = 27 bara = 26 barg

Example 2

3 Stages Reciprocating Gas compressor has Outlet pressure P3 = 127 barg Inlet pressure P0 = 1 barg

what are the intermediate pressures

P0

1 barg

1st

stage

P1

2nd stage

P2

3rd stage

P3

127 barg

P0

1 barg

1st

stage

P1

2nd stage

P2

3rd stage

P3

127 barg

Assume

P3

P2=P1

P2=R

P1

P0

=

RTP3

P0

=3

RP3

P0

=BUT

3R

P3

P0

=

R = RT3 3

R = RT

P3 = R * P2 = 4 * 32 = 128 bara = 127 bar g

3R = RT = 64 = 4

=)127+ 1(

)1+1(=

1282 = 64

P1 = R * P0 = 4 * 2 = 8 bara = 7 bar g

P2 = R * P1 = 4 * 8 = 32 bara = 31 bar g

P3

P0

3R=RT =

Example 2

3 Stages Gas compressor has Outlet pressure = 255 bar gInlet pressure = 3 bar g

What are the intermediate pressures

P0

3 barg

1st

stage

P1

2nd stage

P2

3rd stage

P3

255 barg

P0

3 barg

1st

stageP1

2nd stage

P2

3rd stage

P3

255 barg

P3 = R * P2 = 4 * 64 = 256 bara = 255 bar g

3R = RT = 64 = 4

=)255+ 1(

)3+1(=

2564 = 64

P1 = R * P0 = 4 * 4 = 16 bara = 15 bar g

P2 = R * P1 = 4 * 16 = 64 bara = 63 bar g

P3

P0

3R=RT =

Engineering

Reciprocating compressor