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Flowrate Of Butane And Propane Through Identical Positive Displacement

pump lpg butane propane postive displacement

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#1 N243

N243

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Posted 13 October 2019 - 07:21 AM

Hi everyone,

 

I'm a graduate process engineer looking over the Design and Operations aspect for an LPG Plant.

 

I have a question in regards to PD Pump flowrate and the fluid it's pumping.

 

We would be blending Propane and Butane via a vane-type positive displacement pump.

However, the flowrate of propane and butane will vary (Liquid Propane at 72 m³/hr and Liquid Butane at 36m³/hr) due to "thermodynamic phenomena of each compound."

 

I understand that positive displacement pumps will always give a fixed flowrate and differential pressure (wrt pump RPM), so I'm in doubt on how the thermodynamics of the fluid affects the flowrate? Should it not give the same amount of volumetric flowrate regardless?

 

 



#2 PingPong

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Posted 14 October 2019 - 06:14 AM

I understand that positive displacement pumps will always give a fixed flowrate and differential pressure (wrt pump RPM)
A PD pump delivers the same volumetric flowrate for a given speed. If you need a lower volume flow you would need to recycle part of the discharge fluid, or somehow reduce the pump speed.

 

It does not deliver a fixed differential pressure but merely delivers the fluid a the pressure of the discharge system, assuming that the pump casing and motor are strong enough.






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