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centrifugal compressors overview
Centrifugal compressors work by imparting kinetic energy to a gas stream using an impeller, converting the dynamic energy into increased static pressure. They have advantages like high throughput capacity and efficiency over a wide operating range, but also disadvantages like discharge pressure limitations. Key components include impellers, diffusers, volutes, casings, shafts, bearings, and seals. Surge, a dangerous condition where flow reverses rapidly, must be controlled. Compressors can operate alone or in multi-stage arrangements with intercoolers. Common drivers are steam turbines, electric motors, and gas turbines.
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centrifugal compressors overview
- 1. Centrifugal Compressors A basicoverview Presented By : Muhammad Junaid
- 2. Contents Theory of compression Purposeof compression Understanding of key terms Kinetic theory of gases Compressibility Methods of compression Types of compressors Centrifugal compressors Advantages and disadvantages Basic construction Understanding compressor curves Basic operation Compressor arrangements Maintenance
- 3. Theory of compression Compression Processof increasing the pressure of a fluid in order to make it travel to another place Compressor Mechanical equipment that is used to increase the pressure of a compressible fluid. Why compressors are required Increase temperature and pressure of gas for certain reactions to take place. Liquefaction of gases for storage purposes Refrigeration effect Pressurized air is used for measuring and control Applications in industry In every field of life. Purpose of compression
- 4. Absolute Pressure Understanding ofkey terms Theory of compression
- 5. Theory of compression Capacityof a compressor Understanding of key terms Volume of gas handled in a unit time. Its units are cubic feet per minute Capacity is always measured at compressor suction flange. SCFM and ACFM
- 6. Theory of compression PressureRatio (R) Understanding of key terms
- 7. Theory of compression Efficiency Understandingof key terms
- 8. Theory of compression Stateand state functions Understanding of key terms
- 9. Theory of compression Theaverage kinetic energy of the molecules does not change with time. The average kinetic energy of the molecules is proportional to absolute temperature. Kinetic theory of gases
- 10. Theory of compression Lawof Conservation of Energy
- 11. Theory of compression Trapquantities of gas, reduce the volume, push the compressed gas out of the enclosure. Trap gas, carry it without volume change to the discharge opening. Compress the gas by backflow from discharge system, then push the compressed gas out of the enclosure Compress by the mechanical action rotating impellers or bladed rotors that impart velocity and pressure Entrain the gas in a high velocity jet of the same or another gas and convert the high velocity of the mixture into pressure in a diffuser. Methods of compression
- 12. Theory of compression Methodsof compression
- 13. Theory of compression Methodsof compression
- 14. Theory of compression Methodsof compression
- 15. Types of compressors Continuousand intermittent Compressors can be subdivided into two broad groups based on compression mode. Intermittent This compression is cyclic in nature. A specific quantity of gas is ingested by the compressor, acted upon and discharged, before the cycle is repeated. Continuous The compression mode in which gas is moved into the compressor, acted upon, moved through compressor, and discharged without interruption of the flow at any point in the process.
- 16. Types of compressors Compressors Positivedisplacement Dynamic Reciprocating Rotary Centrifugal Axial Single acting Double acting Diaphragm Lobe Screw Vane Liquid ring Scroll Ejector
- 17. Types of compressors Applicationsof compressors
- 19. Centrifugal Compressors Working Principle Theworking principle is based upon imparting kinetic energy to a fluid stream and conversion of this dynamic energy into static energy, i.e., from velocity into pressure. The specific compression energy transmitted to the gas by the impeller is called "head." The discharge pressure of a turbo compressor, which is affected by gas inlet conditions, is a function of head.
- 20. Centrifugal Compressors Less efficientfor small volumes. Discharge pressure limitation. Effect of gas density and temperature. Problem of surge phenomenon. Discharge flow is relatively free of pulsation. Mechanical design permits high through puts, capacity limitation is rarely a problem. Centrifugal Compressors are capable efficient performance over a wide range of pressure and capacities even at constant speed operation. These are relatively small, occupy less space, operate with minimum attention and quieter. Less contamination due to lubricants. Disadvantages Advantages
- 21. Centrifugal Compressors Major componentsof a centrifugal compressor include: Impeller The part of centrifugal compressor that moves the gas is the impeller. As the impeller rotates, it moves the gas toward the outer rim of the impeller and its velocity increases. Diffuser As the gas leaves impeller, it flows into a passage-way called the diffuser. The diffuser being larger in volume, the velocity of gas decreases and its pressure increases Volute Gas passes from diffuser into the volute. In the volute, the conversion of velocity energy to pressure energy continues. Casing It is the outer cover of a centrifugal compressor which contains inlet and discharge nozzles. Construction
- 22. Centrifugal Compressors A centrifugalcompressor has two main type of parts; Rotor assembly Main shaft Impellers Thrust runner Disc spacer Balance drum Stationary parts Casing Nozzles Volutes Bearings Shaft seals Construction
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- 24. Centrifugal Compressors Impellers The impellersadd energy (velocity) to the gas. There are three types of impellers Open impeller Semi closed impeller Closed impeller Construction
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- 31. Centrifugal Compressors Volute anddiffuser Construction
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- 35. Centrifugal Compressors Radial bearinglubrication Construction
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- 38. Centrifugal Compressors Thrust bearinglubrication Construction
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- 40. Centrifugal Compressors Shaft endseals Construction
- 41. Centrifugal Compressors Non contacttype mechanical seal Construction
- 42. Centrifugal Compressors Mechanical oilseals Construction
- 43. Centrifugal Compressors Dry gasseal Construction
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- 45. Centrifugal Compressors Inter stageseals Construction
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- 48. Centrifugal Compressors Understanding CompressorCurves Single speed compressor drive with suction and discharge pressure control P1 Source P3 Destination C
- 49. Centrifugal Compressors Understanding CompressorCurves Flow Head Stone wall Surge Compressor curve System curve Operating point
- 50. Centrifugal Compressors Incoming flowto compressor decreases Understanding Compressor Curves Flow Head Stone wall Surge
- 51. Centrifugal Compressors Incoming flowto compressor decreases below surge limit Understanding Compressor Curves Flow Head Surge control pointSurge Stone wall
- 52. Centrifugal Compressors Gas DemandIncreases Understanding Compressor Curves Flow Head Stone wall Surge
- 53. Centrifugal Compressors Understanding CompressorCurves Variable speed compressor drive with speed controller
- 54. Flow Head minimum speed maximum speed surgelimit stonewall or choke limit Centrifugal Compressors Understanding Compressor curves
- 55. Flow Head Centrifugal Compressors Understanding Compressorcurves Incoming flow to compressor decreases Surge Line Stone wall N1 N2 N3 N4 Nmin
- 56. Flow Head Centrifugal Compressors Understanding Compressorcurves Incoming flow to compressor decreases below surge limit Surge Line Stone wall N1 N2 N3 N4 Nmin SCL
- 57. Flow Head Centrifugal Compressors Understanding Compressorcurves Gas demand increases Surge Line Stone wall N1 N2 N3 N4 Nmin
- 58. Flow Head Centrifugal Compressors Understanding Compressorcurves Gas MW increases Surge Line Stone wall Nmax Nmin Nmax Nmin
- 59. Centrifugal Compressors Start upSequence All jobs completed and blinds removed All instrument calibrated and in service System Purging Lube oil Circulation Cooling water circulation System pressurization Sealing system Start up Basic Operation
- 60. Centrifugal Compressors Proper Oillubrication Basic Operation
- 61. Centrifugal Compressors Bad Oilviscosity Basic Operation
- 62. Centrifugal Compressors Lube Oilsystem Basic Operation
- 63. Centrifugal Compressors Lube Oiltank Basic Operation
- 64. Centrifugal Compressors Instrumentation onLO tank Basic Operation
- 65. Centrifugal Compressors Lube OilPump Basic Operation
- 66. Centrifugal Compressors Lube OilCooler Basic Operation
- 67. Centrifugal Compressors Lube OilFilter Basic Operation
- 68. Centrifugal Compressors Lube OilCirculation Basic Operation
- 69. Centrifugal Compressors Start upProcedure Open suction valve Open discharge valve (discharge check valve closed). Open bypass or vent valve Start and bring up to speed Close bypass or vent Place bypass or vent on automatic control Basic Operation
- 70. Centrifugal Compressors Basic Operation Startup Procedure
- 71. Centrifugal Compressors Thermodynamic condition Acompressor's efficiency is reflected by its thermodynamic performance Evaluation of performance requires acquisition of the following data. Suction and discharge pressures of each stage Suction and discharge. temperatures of each stage Volume flow Density Operating speed Power consumption Cooling water Flow rate, Fouling Basic Operation
- 72. Centrifugal Compressors Mechanical condition Themost critical components of a compressor are the rotor, its bearings and seals. Monitoring of mechanical compressor functions, therefore, will center around the behavior of these components. The following data allow assessment of the mechanical condition: Radial vibration Shaft position Bearing temperature Lube-oil supply pressure and temperature Seal-oil supply temperature, and differential pressure between oil supply and reference gas Seal buffer-gas pressures and differential pressures Compressor speed (with variable speed driver) Basic Operation
- 73. Centrifugal Compressors Common Problems DirtyIntercoolers - Increased gas temperature reduces the density into the compression stage. Hot Coolant - Increased gas temperature reduces the gas density into the compression stage. Dirty Inlet Filter - Reduces the pressure into the first stage. Driver Input Speed - The ability for a centrifugal compressor stage to make pressure falls as the square of the stage speed. A reduction in the driver input speed can dramatically affect the total machine ratio. Discharge valve closure - Discharge valve closure decreased the flow through the compressor hence increase the pressure and causes surging . Suction valve closure- Suction valve closure or suction vent opening causes pressure drop in suction reducing flow and surging the machine. Inter stage vent malfunction- In a multistage compressor if inter stage vent valve malfunction and opens the down stream stage will surge. Change in gas composition. If the gas composition change it effects the pressure thus the compressor can go into surge at the same speed Recycle valve malfunction. Recycle valves are normally open during reduced flow operation. if closes by accident or malfunction it will surge the compressor. Basic Operation
- 74. Centrifugal Compressors Basic Operation Whatword strikes fear in the heart of centrifugal compressor operators? SURGE!
- 75. Centrifugal Compressors Surging Flow reversesin 20 to 50 milliseconds Surge cycles at a rate of 0.3 s to 3 s per cycle Compressor vibrates Temperature rises “Whooshing” noise or “Clanking” noise Trips may occur Conventional instruments and human operators may fail to recognize surge Basic Operation
- 76. • Rapid flowoscillations • Thrust reversals • Potential damage • Rapid pressure oscillations with process instability • Rising temperatures inside compressor FLOW PRESSURE TIME (sec.) 1 2 3 TEMPERATURE TIME (sec.) 1 2 3 TIME (sec.) 1 2 3 Centrifugal Compressors Trend of major process parameters during surge
- 77. Qs, vol Pd Machine shutdown noflow, no pressure • Electro motor is started • Machine accelerates to nominal speed • Compressor reaches performance curve • Note: Flow goes up faster because pressure is the integral of flow • Pressure builds • Resistance goes up • Compressor “rides” the curve • Pd = Pv + Rlosses A • Compressor reaches surge point A • Compressor looses its ability to make pressure • Suddenly Pd drops and thus Pv > Pd • Plane goes to stall - Compressor surges B • Because Pv > Pd the flow reverses • Compressor operating point goes to point B C • Result of flow reversal is that pressure goes down • Pressure goes down => less negative flow • Operating point goes to point C D • System pressure is going down • Compressor is again able to overcome Pv • Compressor “jumps” back to performance curve and goes to point D • Forward flow is re-established Pd Pv Rlosses Pd = Compressor discharge pressure Pv = Vessel pressure Rlosses = Resistance losses over pipe • Compressor starts to build pressure • Compressor “rides” curve towards surge • Point A is reached • The surge cycle is complete • From A to B 20 - 50 ms Drop into surge • From C to D 20 - 120 ms Jump out of surge • A-B-C-D-A 0.3 - 3 seconds Surge cycle Centrifugal Compressors Surge representation on compressor curves
- 78. Centrifugal Compressors Unstable flowand pressure Damage in sequence with increasing severity to seals, bearings, impellers, shaft Increased seal clearances and leakage Lower energy efficiency Reduced compressor life Some surge consequences
- 79. Centrifugal Compressors Surge Factors leadingto onset of surge Startup Shutdown Operation at reduced throughput Operation at heavy throughput with: - Trips - Power loss - Operator errors - Process upsets - Load changes - Gas composition changes - Cooler problems - Filter or strainer problems - Driver problems Surge is not limited to times of reduced throughput. Surge can occur at full operation
- 80. Qs, vol Rc stable zone ofoperation adding control margins Actual available operating zone Centrifugal Compressors Anti surge control
- 81. OUTPUT INPUT Suction Flow Anti-Surge Valve SuctionTemperature Suction Pressure Discharge Pressure Anti-surge Controller Discharge Temperature
- 82. OUTPUT INPUT Suction Flow Anti-Surge Valve SuctionTemperature Suction Pressure Discharge Pressure Anti-surge Controller Discharge Temperature
- 83. Centrifugal Compressors Single stagecompressor Compressor arrangements
- 84. Centrifugal Compressors Single stagecompressor with internally split flow Compressor arrangements
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- 86. Centrifugal Compressors Multistage compressorwith single intercooler Compressor arrangements
- 87. Centrifugal Compressors Multistage compressorwith double intercooler Compressor arrangements
- 88. Centrifugal Compressors Multistage compressorwith double inlet Compressor arrangements
- 89. Centrifugal Compressors Multistage compressorwith side streams Compressor arrangements
- 90. Centrifugal Compressors Commonly useddrivers for a centrifugal compressor are: Steam Turbine Electric motor Induction Synchronous Gas Turbine Expander Compressor drivers
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