Turbo expanders
Equipment /Other-rotary

A Turbo Expander, Also Known As An Expansion Turbine, Is A Centrifugal Or Axial Flow Turbine Through Which A High Pressure Gas Is Expanded To Produce Work That Is Often Used To Drive A Compressor. Because Work Is Extracted From The Expanding High Pressure Gas, The Expansion Is Approximated By An Isentropic Process (I.E., A Constant Entropy Process) And The Low Pressure Exhaust Gas From The Turbine Is At A Very Low Temperature, -150 °C Or Less Depending Upon The Operating Pressure And Gas Properties. Partial Liquefaction Of The Expanded Gas Is Not Uncommon.



Turboexpanders Are Very Widely Used As Sources Of Refrigeration In Industrial Processes Such As The Extraction Of Ethane And Natural Gas Liquids (NGLs) From Natural Gas, The Liquefaction Of Gases (Such As Oxygen, Nitrogen, Helium, Argon And Krypton) And Other Low-Temperature Processes.


Turbo-Expander Systems Can Be Found At The Following Types Of Oil And Gas Facilities:
  • Liquefied Petroleum Gas (LPG)
  • Nitrogen Rejection
  • Natural Gas Liquids (NGL)
  • Fluid Catalytic Cracking (FCC)
  • Dew-Point Control (DPC)
  • Pressure Let-Down
  • Liquefied Natural Gas (LNG)


 

Turbo Expander Classification

 

Compressor-Loaded


The Compressor-Loaded Turbo-Expander Is The More Common Arrangement. After Separation Of The Heavy Liquid Hydrocarbon Components In A Separation Drum, The Gas Is Recompressed In The Machine’s Centrifugal Compressor.

Generator-Loaded


The Generator-Loaded Turbo-Expander Is Also Often Used In The Natural Gas Treatment Plant Or In Ethylene Plants. The Generator Brakes The Expansion Turbine. It Is Connected To The Grid And Allows Electricity Production. Different Designs Are Available, Including Either Planetary Gearbox Or Parallel Shaft Gearbox, With The Option Of An Asynchronous Or A Synchronous Generator.

Oil Brake


The Oil Brake Is Provided In Case The Expander Cold Production Is Relatively Low (Less Than 100 KW) And When The Process Gas Does Not Require Re-Compression.
 
 

Two Types Of Bearing Can Be Used In A Turbo Expander:


Oil Bearing:

Oil Bearings Use A Thin Layer Of Oil Between The Bearing Faces, Typically Sealed Around Or Under The Rotating Shaft. Oil Bearings Can Be Relatively Cheap Compared To Other Bearings With A Similar Load Rating.

Active Magnetic Bearing:

A Magnetic Bearing Is A Bearing That Supports A Load Using Magnetic Levitation. Magnetic Bearings Support Moving Parts Without Physical Contact Which Results In Very Low Friction And No Mechanical Wear. Magnetic Bearings Support The Highest Speeds Of All Kinds Of Bearing And Have No Maximum Relative Speed.