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How Does Capacity Control Based On Speed Work For Recip Compressor?

compressor reciprocating capacity control capacity control compression positive displacement

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#1 zamakaze


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Posted 15 March 2023 - 03:10 AM

How does VFD speed control actually work in Reciprocating/Positive Displacement Compressor?
In case of reciprocating compressor, how does capacity control work with speed control. Since we don’t really measure capacity / flow, is the speed control done based on pressure?

For example lets assume a machine designed for 300 NM3/hr of gas with 3 bar suction pressure at full speed. In normal conditions, we get 300 NM3/hr supply from source at 3 bar and compressor happily compresses the gas working at full speed. Now lets say , the flow is reduced to 150 NM3/hr…in this case what will Compressor respond to? Is it the fact that suction pressure starts reducing as the Compressor initially at its full speed wants to move 300 NM3/hr? And as suction pressure reduces, the compressor speed is reduced to maintain same suction pressure which in turn reduces capacity of compressor? Is this correct understanding?

#2 sonu19921103


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Posted 18 March 2023 - 06:07 AM



There are a number of capacity control mechanisms for the recip compressor; some of them re listed below: -

  • Recycle (the gas from the compressor discharge is cooled and recycled back to the compressor on Suction pressure control).
  • VFD (The number of stokes is manipulated based on the compressor suction pressure).
  • Loaders and Unloaders (they kind of manipulate the volumteric eff of the compressor).

Best Regards

Sonu Singh

#3 breizh


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Posted 20 March 2023 - 12:28 AM


You may need to get a copy of the book in reference: a chapter is dedicated to reciprocating compressor and control.

Compression machinery for oil and gas   ELSEVIER 2019   ISBN: 978-0-12-814683-5







Good luck


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