Compressor Fundamentals

• Compressor concepts
• Compressor


  Device that increases the pressure of a gas by reducing its volume
• Centrifugal Compressor


  • Increases gas velocity and then slows it down to increase pressure
  • Main internal components: Impeller (increases velocity of gas), Volute (slows down gas to convert kinetic energy to pressure)
• Axial Compressor


  • Main internal components: Rotating blades (draw in and speed up gas), Stationary blades (gas passes through, slows and increases pressure)
• Centrifugal Compressor - Single Stage

  1. Gas moves through impeller (creates low pressure, draws in more gas)

  2. In volute, gas expands and slows (pressure increases as gas slows down)

  3. Diffuser vanes designed to minimize radial thrust

  4. Gas slows as it flows between diffuser vanes, velocity converted into pressure, pressurized gas directed to discharge line
• Centrifugal Compressor - Multi-stage

  1. Gas enters impeller through suction line, pressure increased in volute

  2. Intercooler removes heat from compressed gas

  3. Second impeller and volute increase gas pressure more

  4. Gas cooled by second intercooler

  5. Third impeller and volute increase gas pressure again
• Axial Compressor


  • Inlet guide vanes (set of pivoting blades near suction line, control flow of gas into compressor)
  • Rotating blades accelerate gas (low pressure created in suction line, drawing more gas into compressor)
  • Stationary blades slow gas down and increase pressure
  • Process repeats through each stage until pressurized gas reaches discharge line
• Lubrication System


  Reduces friction between moving parts, provides continuous supply of clean oil at proper temperature
• Lubrication System


  Pump draws oil from reservoir, screen traps large solid particles, filter traps smaller particles, oil passes through cooler to maintain viscosity and lubricating capacity, oil flows to compressor to lubricate bearings and returns to reservoir
• Mechanical Seals


  • Rotating and stationary elements form a seal between shaft and housing
• Labyrinth Seals


  • Series of ridges create an intricate path that hinders leaks
• Seal Oil System


  Prevents gas leaks from casing along shaft
• Seal Oil System


  Oil pressure greater than gas pressure in compressor, some gas entrained in oil, gas separates from oil in oil reservoir and returns to compressor, oil returns to seal, head tank supplies oil if pump fails, check valve forces flow of oil to seal
• Radial Bearings


  • Support compressor shaft, prevent most perpendicular movement
• Thrust Bearings

  • Prevent axial movement, keep impellers or blades from hitting stationary parts