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Compressors - Training sessions

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Compressors - An Overview to Trainees

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Compressors - Training sessions

  2. 2. WHAT IS A COMPRESSOR? A device used for pumping compressible fluids. i.e. Air , gas and Steam
  3. 3. Compressor is a mechanical device that increases the pressure by reducing volume. Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas. Liquids are relatively incompressible, the main action of a pump is to pressurize and transport liquids
  4. 4. COMPRESSOR PRESSURE RATIO GAS Suction Pressure = Ps Suction Temperature = Ts Suction Velocity = Us GAS Discharge Pressure = Pd Discharge Temperature = Td Discharge Velocity = Ud Compressor = Black Box to increase Gas Pressure
  5. 5. a) Principle of operation b) Type of construction c) Staging d) Service duty e) Lubricated/ non lubricated Compressor Classification Based on
  6. 6. Types of Compressors • Reciprocating • Rotary • Centrifugal • Axial
  7. 7. Rotary Compressors  Screw  Sliding Vane  Twin Lobe  Liquid Ring
  8. 8. Selection of compressors
  9. 9. Parameters for selection of compressor- Application:  Gas handled:  Gas analysis:  Flow rate:  Suction Pressure :  Suction Temperature:  Mol wt. of Gas:  Compressibility  Discharge Pressure:  Drive System:
  10. 10. NOCL Private & confidential Selection of compressor
  11. 11. Typical Reciprocating Compressor
  12. 12. Centrifugal Compressor
  14. 14. Cut-view of Screw Compressor
  16. 16. Reciprocating Compressor
  17. 17. NOCL Private & confidential Centrifugal Compressor
  18. 18. NOCL Private & confidential
  19. 19. Casing Diaphragm Impellers Sealing Elements Balancing drum Bearings Parts of centrifugal compressor
  20. 20. Casing: It is the housing of the compressor, in which all components were intacted. There are two types of casing 1. Horizontal Split 2. Vertical Split Horizontal Split: Centrifugal compressors with horizontal split casings typically permit internal of around 700psi (70 bars) with flow rate of around 300,000 Nm3/hr at low pressure.
  21. 21. Vertical split or Barrel type compressor Above 700psi horizontal split casing lose their sealing capability, resulting in an increased in potential for the escape of process gas. Hence vertical casing is more preferred for high pressure application. Based on the nozzle arrangement: Straight through: It is the general arrangement of compressor. In which the casing consisting of two nozzles, one is inlet and the other one is outlet. gas enters at the inlet nozzle passes through one or more stages of compression and leave through the discharge nozzle in to the piping system.
  22. 22. NOCL Private & confidential
  23. 23. Impeller: Impeller is the heart of the compressor. In which the mechanical energy (rotary motion) of the rotor is converted in to kinetic energy of the process fluid (compressing fluid There are three types of impellers Open impeller Semi open impeller Closed impeller Open impellers have the vanes positioned radial direction and have no enclosing covers on either front or back side. Semi open impellers have the vanes positioned in a radial or backward leaning direction and have a cover on the back side with extended to the periphery of the vanes. Closed impellers have enclosed cover on both front and back side. this is the most common type in large processing compressors. The blades are usually backward leaning and in some special cases radial curved vanes
  24. 24. Diaphragm: It is the stationary component of the centrifugal compressor. It consisting of two parts one is the diffuser and the return guide vanes. Normally around 2/3 of kinetic of gas is converted in to pressure energy in the impeller itself and the remaining 1/3 of energy conversion is takes place in the diffuser as shown below.
  25. 25. Cross section view of Diaphragm
  26. 26. After conversion of kinetic energy in to pressure energy in the diffuser the gas pass through the return guide vanes. The function of return guide vanes is to guide the gas to the next stage of impeller with laminar flow.
  27. 27. NOCL Private & confidential
  28. 28. Radial Bearing: Radial bearing of the centrifugal compressor are force lubricated. For the ease of maintenance the bearing are horizontal split with replaceable Babbitt lined pads. Number of pad in the radial bearing is depending upon the speed and load condition of the compressor.
  29. 29. Thrust bearing: The main purpose of the bearing is to take the thrust load produced in the rotor. Tilting pad is the most common type of bearing used in centrifugal compressor. Flat land, tapper land , kingsbury and Michel bearings are used by most of the manufacture , the selection of bearing is depend up the thrust load produced by the rotor.
  30. 30. Sealing system Types 1.Liquid film seals 2.Labyrinth Type seals 3.Mechanical seals 4.Injection &Extraction seals 5.Dry gas seals
  31. 31. 1. Liquid film seals: This system is used when the gas medium is poisonous, inflammable and expensive and no external leakage is permitted. The principle of this sealing is that high pressure oil is injected in between a set of close clearance seal rings mounted on shaft ends. The seal rings are free floating type with white metalled bore. The oil leakage through LP side is recirculated through the oil system and HP leakage is recovered by automatic traps are re-used after separating dissolved gases.
  32. 32. This system is employed for gases like Air, Nitrogen. The amount of gas leaking to ambient is reduced by selecting adequate number of labyrinth fins. Some of the developments in a labyrinth type seals are stepped type seals, honey comb type and turbine type. LABYRINTH SEALS
  33. 33. In this type of seals the carbon-rings forming part of stator part is kept in continuous contact with a rotating collar. The contact surfaces are lubricated either by a cool buffer gas or lubricating oil. These seals are very effective means of providing shaft sealings. Mechanical Seals
  34. 34. For gases like oxygen, raw gas and other explosive, corrosive, media the sealing has to be perfect and where sealing medium like oil cannot be used, the above sealing system is selected. The principle of this sealing is that vacuum is created by a ejector at the shaft ends which sucks the gases and thus prevents any outward leakage of the contained gas. INJECTION EXTRACTION SEALS
  35. 35. Today the preferred choice is the dry-running, gas-lubricated seal over conventional seals. A gas-lubricated mechanical seal necessarily needs a gas supply system to ensure pressurizations of the seal with clean process gas or external gas. Dry gas seals
  36. 36. NOCL Private & confidential
  37. 37. Single seal arrangement Single seal is used for the compressors, which have lower sealing pressures and where a small leakage of gas medium can be tolerated. The single seal is particularly advantageous as they occupy less space at compressor ends.
  38. 38. Double arrangement A double arrangement is a sealing system, which reliably prevents product gas escaping to the surroundings. It involves feeding a buffer gas, e.g. nitrogen, between the seals at a higher pressure than the product pressure.
  39. 39. Any questions?