Reciprocating compressor - An Overview to Trainees

1. RECIPROCATING
COMPRESSORS
RECIPROCATING
COMPRESSORS

2. 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

3. Crosshead
Stuffing
Box
Packing
Discharge
Valves
Suction
Valves
PistonDistance
Piece
Con-rodCrank
Piston
Rod
Wiper
Rings

6. POWER ENDPOWER END

7. GAS
END
GAS
END
FIXED
CLEARANCE
VOLUME

8. VARIABLE
CLEARANCE
VOLUME

9. RECIPROCATING COMPRESSORS:
FLOW RATE REGULATION
RECIPROCATING COMPRESSORS:
FLOW RATE REGULATION
• VARIABLE CLEARANCE
• VARIABLE SPEED
• BYPASS
• SUCTION VALVE
UNLOADERS

10. CF CR
CF = C
CR = C
2
3
1
3
• VARIABLE CLEARANCE• VARIABLE CLEARANCE
C = Total Clearance Volume = CF + CR
Before operatingBefore operating

11. After operatingAfter operating
CF CR
CF = C
CR = C
1
2
1
2

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
VOLUME
AtAt
Point a suction valves closed
Point b discharge valves open
Point c discharge valves closed

13. Compression ratio
Pressure ratio )ABSOLUTE(
Pd
P s
=
Volumetric efficiency =
Va g
V cylinder a M
a g
=
= V cylinder
Vb M
C
v
b a
c
g
Pd
Ps c1M
b
b M
a M
=

14. C
v
Pd
Ps c1
M
b
a
c
g
Volumetric efficiency =
Va g
V cylinder a M
a g
=

15. C
v
Pd
Ps
M
b
a
c
g
Volumetric efficiency =
Va g
V cylinder a M
a g
=

16. v
Pd
Ps
M
C
g a
bc
Volumetric efficiency =
Va g
V cylinder a M
a g
=

17. If C Increased suction valves will open at
( g(
C
v
a
c
g
Pd
Ps
b
M
EV DECREASES
Q DECREASES
Volumetric efficiency =
Va g
V cylinder a M
a g
=

18. If C Decreased suction valves will open at
( d(
C
v
a
c bPd
Ps M g
EV INCREASES
Q INCREASES
Volumetric efficiency =
Va g
V cylinder a M
a g
=

19. •SUCTION VALVE
UNLOADERS
•SUCTION VALVE
UNLOADERS

20. STUFFING
BOX
RIDER
RINGS
RIDER
RINGS
PRESSURE
RINGS
PRESSURE
RINGS

21. WIPER
RINGS
WIPER
RINGS

22. T
R
TANGENTIAL RINGST
R RADIAL RINGS

23. RECIPROCATING
COMPRESSORS
INTERMEDIATE
PRESSURES
RECIPROCATING
COMPRESSORS
INTERMEDIATE
PRESSURES

24. Example 1
4Stages Reciprocating Air comp has
outlet pressure P4 = 80 barg
what are the intermediate pressures
P0
0barg
1st
stage
P1
2nd
stage
P2
3rd
stage
P3 P4
80
barg
4th
stage

25. P0
0barg
P1 P2 P3 P4
80
barg
1st
stage
2nd
stage
3rd
stage
4th
stage
R=
P1
P0
P4
P3
=
P3
P2
=
P2
P1
=
Assume
R is The equal Pressure Ratio between stages.
R=
4 P4
P0
RT=
P4
P0
BUT
RTR
=
4
AND RT= P4
P0
R = RT
4
Generally
R = RT
N

26. P4 = R * P3 = 3 * 27 = 81 bara = 80 barg
P0
0barg
P1 P2 P3 P4
80
barg
1st
stage
2nd
stage
3rd
stage
4th
stage
RT = P4 / P0 = (80 +1) / (0 +1) = 81/ 1 = 81
N 4
R = 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

27. Example 2
3Stages Reciprocating Gas compressor
has
Outlet pressure P3 = 127 barg
Inlet pressure P0 = 1 barg
what are the intermediate pressures
P0
1barg
1st
stage
P1
2nd
stage
P2
3rd stage
P3
127barg

28. P0
1barg
1st
stage
P1
2nd
stage
P2
3rd stage
P3
127barg
Assume
P3
P2
=
P1
P2
=R
P1
P0
=
RT
P3
P0
=
3
R
P3
P0
=BUT
3
R
P3
P0
=
R = RT
3 3
R = RT

29. P3 = R * P2 = 4 * 32 = 128 bara = 127 bar g
3
R = RT = 64 = 4
=
)127+1(
)1+1(
=
128
2 = 64
P1 = R * P0 = 4 * 2 = 8 bara = 7 bar g
P2 = R * P1 = 4 * 8 = 32 bara = 31 bar g
P3
P0
3
R=RT =

30. Example 2
3Stages Gas compressor has
Outlet pressure = 255 bar g
Inlet pressure = 3 bar g
What are the intermediate pressures
P0
3barg
1st
stage
P1
2nd
stage
P2
3rd stage
P3
255barg

31. P0
3barg
1st
stage
P1
2nd
stage
P2
3rd stage
P3
255barg
P3 = R * P2 = 4 * 64 = 256 bara = 255 bar g
3
R = RT = 64 = 4
=
)255+1(
)3+1(
=
256
4
= 64
P1 = R * P0 = 4 * 4 = 16 bara = 15 bar g
P2 = R * P1 = 4 * 16 = 64 bara = 63 bar g
P3
P0
3
R=RT =