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Reciprocating compressor
Reciprocating compressors compress gases via pistons moving inside cylinders. They have high pressure pulsations and can surge if not regulated properly. Flow rate in reciprocating compressors is regulated through variable clearance volumes, variable speed, bypass valves, or suction valve unloaders. Calculating intermediate pressures in multi-stage reciprocating compressors involves determining the common pressure ratio between stages using the overall pressure ratio and number of stages.
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Reciprocating compressor
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- 2. CompressorsCompressors HIGH LOWV. HIGH NONOYES 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
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- 9. RECIPROCATING COMPRESSORS: FLOW RATEREGULATION 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 CFCR CF = C CR = C 1 2 1 2
- 12. Point g suctionvalves 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 = Vag 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 Increasedsuction 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 Decreasedsuction 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 =
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- 24. Example 1 4Stages ReciprocatingAir 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 P3P4 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 ReciprocatingGas 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
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- 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 Gascompressor 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 =
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