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Condensate Formation Across Control Valve Pressure Drop

condensate formation control valve pressure drop

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#1 kengor10

kengor10

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Posted 03 February 2022 - 11:37 AM

New Engineer here, less than 1 year since graduating.

 

I'm designing an Upstream Central Processing Facility and Tank Battery along with a Gas Lift Compression system. My question is in regard to the Gas Lift Compression system. The gas leaving the processing facility will flow to three packaged reciprocating compressors working parallel. Following this the gas will then flow to three packaged reciprocating Booster compressors working in parallel before the gas is injected.

 

I am considering adding spillback/recycle valves external to the compressors to prevent a shutdown in the case of process upset downstream (i.e. excess gas volume and pressure). Due to the nature of the system the valves would need to operate under a high differential pressure roughly 900 PSI and 3000 PSI.

 

In part of my due diligence, I ran a HYSYS simulation reducing the gas pressure by 900 psi across a control valve. I generated 10 Barrels/day of liquid hydrocarbons. For the 3000 psi pressure differential case I generated substantially more liquid. Why am I generating liquid when reducing pressure? 

 

Any input on this Phenomena or my implementation of a spillback valve external to the packaged compressors is appreciated.

 

Thanks.



#2 Bobby Strain

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Posted 03 February 2022 - 12:26 PM

It's known as retrograde condensation. There is plenty hot gas at the compressor discharge to prevent condensation. But you need to consult with someone in your organization who has experience with this system.

 

Bobby



#3 SilverShaded

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Posted 11 February 2022 - 03:29 AM

Theres a lot that could be going on here and I would get an experienced person to look at it as mentioned above.  This is not a system i'm familiar with per se but i will comment on what might be happening. 

 

Much of what is happening will depend on the enthalpy changes occurring and as also mentioned above it's to do with enthalpy at/around or near the critical point of individual components and mixtures.  As you back away from the critical point there are sharp changes in enthalpy which can cause the retrogade condensation as mentioned above, even though pressure is lower.

 

Simulators (like hysys etc) are generally not great at getting enthalpy correct around or above the critical point and it is also impacted by which enthalpy method you are using.

 

Some simualtors actually have bugs in the Lee-Kesler enthalpy calculation which lead to incorrect answers as well.


Edited by SilverShaded, 11 February 2022 - 03:31 AM.





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