Gas blowby from separator to tank

[antonioshaga]

Hi all,
I want to know gas blowby from upstream to the downstream- I have one scenario that now I'm working on. if trip on the pump can cause gas blowby from separator to the tank. I want to check is relive valve in the tank can handle gas blowby from separator or not. so what I want to ask is there any step should I follow to check gas blowby (how to check gas blowby).

thank you.

Regards,

Shaga

 

[LittleInch]

Gas blowby usually means gas going where it shouldn't, i.e. along a liquid only line.

Gas flowrate is then normally calculated as thought the level control valve for the liquid is fully open and the separatr full of gas at max operating pressure.

Often the flowrate is quite high, but everything depends on details.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MortenA]

@OP: its a wee bit unclear what you write

- As Littleinch says: Gas blow-by is gas going where its not intended to go (e.g. through a liquid line)
- Gas will only go from a higher pressure to a lower pressure so if your tank has a higher pressure than your separator then no
- BUT if if PAHH in your sep> SP of your PSV in your tank i would say yes
- Also if your need for pumping is due to hydrostatic head - it may be possible for gas to go to your tank (also through a tripped pump - at least if its a centrifugal pump)

You have to work through the various scenarias where P(sep)>SP of PSV in tank

Best regards, Morten

 

[georgeverghese]

What is the design pressure of your tank? API 650 tanks are hardly suitable for handling high pressure emergencies from upstream sources.

 

[LittleInch]

Given that Antonio has started 3 posts, but only actually replied to one of them, I'm not waiting on bated breath for the additional information we all need to help him further...

Surprise me Antonio!

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[SNORGY]

I think the best treatment of gas blow-by and related calculations is found in one of a myriad of publications by Emerson Process Management. I could probably find it through Google. Fisher (Emerson) Control Valve Handbook is pretty much all a person needs to handle most gas blow-by where the gas can be characterized as single phase ideal or non-ideal gas. It sort of still works pretty well for dense phase gas as long as you take a good cut at estimating Cp, Cp/Cv and pseudo-critical pressure and temperature (you would also want to use an EOS; for most gas blow-by calculations that I do, I use VDW - close enough - or RK, but if one wants to mess around with acentric factors etc. they can go to SRK or PR or BWR...). I have developed my own spreadsheet that draws upon all of this (I can select one of four cubic EOS's) and it generally agrees with Fisher's program and HYSYS within a percent or less. Compressibilities and densities agree quite well but the JT predictions (mine are VDW-based) are a bit off (~5%).