API 650 tank Product Vapor pressure and storage query 1

[zamakaze]

I am trying to understand if I can send a hydrocarbon product to an API 650 tank which has max internal design of 2.5 psig.

Product is from Inlet Separator at 50 psig. Now when I model it I see that the vapor pressure of liquid from Separator is 50 psig. When I take it across LCV to the tank operating pressure of 0.5 psig, the vapor pressure of resulting liquid stream is 1 psig with the stream being 15% vapor fraction.

I am trying to understand the meaning of this? Does it mean that this flashed vapor will just be vented from tank outbreathing valve and I am safe to take this product in API 650 tank? Does this flashing of liquid create a problem and how?

Tank pressure is being maintained by fuel gas blanket at 15 mm wc or 0.5 psig

 

[1503-44]

Probably not a good idea.
Your condensate will almost all disappear from the tank by offgassing. You will retain only the small amounts of your stream components with vapor pressures less than 15 psia. Your blanket will be dispursed with the offgassing turbulence and won't stay in the tank. Tank vent valve must be large diameter and locked open. Might as well have an open tank. Why mix all that into the atmosphere? This method usually terminates with the high vapor pressure gasses being flared off. We are usually trying to avoid excess HC emissions. This is not helping.




--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

An API 650 tank is in theory up to 2.5 psig, but most are "atmospheric", i.e. about your 15mm w/c = 0.02 psi, no where near your 0.5...

Venting condensate flash gas is not usually done inside a tank as pressures can fluctuate and get it slightly wrong and your tank literally breaks apart or the roof comes off. So it's usually sent via a degassing drum which is a pressure vessel at something like 1 or 2 psi.

You say volume fraction at 1psi is only 15%, so it's not quite as volatile as Mr 44 is making out.

But is still doesn't make it a good idea.

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

 

[1503-44]

That can be relative to the size of the tank.

15% is still a relatively high potential loss of product.


--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

The environmental regulations in any country won't allow you to freely vent this off anymore so your tank pressure will be higher to send the vapour somewhere - a scrubber, a chiller unit, a flare, whatever, it all needs some pressure to send it there.

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

 

[MJCronin]

I support and agree with the wise comments above, but ... I am curious ..

Kamakaze states that he has "an API 650 tank which has max internal design of 2.5 psig" ... Does he have an actual record or nameplate of this design pressure, or ... is it something he was told, or does he assume all API-650 tanks are designed to this pressure ? ... are there any records at all ??

-- and, why are there no details of tank venting, tank relief device/vent size ?

MJCronin
Sr. Process Engineer

 

[georgeverghese]

You will need to set up a scheme to stabilise this stream and recover flashed light ends - it usually pays off soon. Flaring this flash gas through an LLP degassing drum may only be a stop gap solution till this recovery scheme is installed. Flame at the flare will be smoky and flare tip may get bunged up with carbon deposits, and soon the Govt HSE friendlies will knocking on your company CEO's door.

 

[1503-44]

Flaring the stuff is still more common than it should be in certain fields that yet do not have pipeline export capability, but most producers just want their money as fast as they can get it.


--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."