Steam RDs discharging to atmospheric tank

Question

Steam RDs discharging to atmospheric tank

APIPapi (Chemical)

(OP)

17 Jul 23 23:02

I have 4 rupture disks from a section VIII div I vessel set @ 175 psig (8200lb/hr is WCDS) that discharge to an atmospheric tank. This tank has a large vent to atmosphere.

How do I determine if the atmospheric tank’s open ended vent to atmosphere is large enough?

LittleInch (Petroleum) · Answer 1 · 2023-07-17 23:13:30

By taking off the roof....

Or API 2000?

This really doesn't sound like a good idea to me. Rupture disk is a violent sudden flow rate.

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APIPapi (Chemical) · Answer 2 · 2023-07-17 23:18:13

I’ll take a look at api 2000 tomorrow! I was looking at Api 520 and ASME VIII, and didn’t know api 2000 existed.

This has been going on for over 10 years with rupture disks activating throughout. Just trying to see if there was any sound engineering basis for sending steam to a storage tank rather than to atmosphere.

Thank you!

georgeverghese (Chemical) · Answer 3 · 2023-07-18 04:27:59

Thumb rule is max operating pressure (MOP) on a vessel fitted with rupture discs is 80% of set pressure. Any higher and you risk blowing the RD.
An atmospheric tank acting as a vent knock out drum doesnt sound good at the outset - what is the design pressure of this "tank" ? An API650 tank has hardly any room to handle high pressure relief streams.

shvet (Petroleum) · Answer 4 · 2023-07-18 05:50:42

Quote (APIPapi)
Just trying to see if there was any sound engineering basis for sending steam to a storage tank rather than to atmosphere.

No, there was not. If liquid entrainment or noise were a reason then dedicated devices exist, more simple/reliable/cheap ones, for example
https://wright-austin.com/exhaust-heads/exhaust-he...

Looks like that steam is not steam during relief and vapor space of a storage tank is intended to serve as some secondary containment for hazardous fluid. It is recommended to study the relief scenario to find out a background of such design.

LittleInch (Petroleum) · Answer 5 · 2023-07-18 09:57:29

Well to start with RD / bursting disks just shouldn't be activating so solve that issue first....

Second issue is more the point. API 650 tanks are not normally capable of any significant over pressure ( inches of water column) and getting a very high velocity, very sudden injection of water vapour will almost certainly exceed its design pressure. API 2000 is not designed for such calculations really and how you calculate the instantaneous volume flow from an RD is not easy either.

Most RDs I know in steam just point upwards away from anywhere people are straight to atmosphere. Why these go via tank I have no idea.

So no, IMHO, there is no "sound engineering" why a 175psi steam release would go first int a tank designed for "atmospheric" pressure only. Unless it had no roof.

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Steam RDs discharging to atmospheric tank