5 replies to this topic

[Moh.Abdelhameed]

Dear Gents,

  I want to size flare Knockout drum;however, we still in the beginning of the project so we don't have accurate value for the liquid hydrocarbon.  I came encounter to some forums where they propose use 10% of vapor as a liquid carryover as first guess then re-check the flare KO drum dimension after implementing the flare mode. I just want to know is there any reference (code,standards,company RC) for this value (10%) ?? 

 

Thanks in advance.

[Bobby Strain]

You can't size the drum until you have appropriate data.

 

Bobby

[Pilesar]

Flare knockouts are typically designed for 300 to 600 microns liquid carryover. Size the KO drum for the vapor phase with this criteria. Then check how much liquid this size drum would handle and adjust the dimensions if needed. That may be enough to get you a placeholder for a cost estimate or site layout. As long as the KO drum is large enough, you may not have to rework it later so be generous if you must size it early in the project. Refine the design basis before you confirm a final design.

[fallah]

 

  I want to size flare Knockout drum;however, we still in the beginning of the project so we don't have accurate value for the liquid hydrocarbon.  I came encounter to some forums where they propose use 10% of vapor as a liquid carryover as first guess then re-check the flare KO drum dimension after implementing the flare mode. I just want to know is there any reference (code,standards,company RC) for this value (10%) ?? 

 

 

Hi,

 

The value of 10% as liquid carry over could mostly be a rough estimation for the gaseous process fluid; hence for the plants is mostly handling liquid process fluid, more precise evaluation could be performed for such estimation...

[Bobby Strain]

What's the rush?

 

Bobby

[Sharma Varun]

As highlighted by others:

 

- Flare KOD is mainly sized for separation based on liquid droplet size criteria (typically 300 to 600 microns, lower the droplet size higher the required diameter).

- Flare KOD is also sized to take care of the condensate separated during vapor relief or liquid accompanied with the vapor relief case. Normally 5 to 10% liquid estimation is good enough to arrive at cases where no valid liquid relief case exists. As far as reference or codes are required, refer API 521 which specifies design liquid as a minimum of 2 wt% of maximum gas flow.

 

Thus you must first study all relief scenarios if no liquid relief is there follow 10% rule or follow other hold up requirements (apart from height required for liq. vapor disengagement) clearly written in API 521.

Edited by Sharma Varun, 27 May 2020 - 03:53 AM.