Tank venting requirements for explosion case 1

[barilko]

Can anyone direct me to a code or method which defines the sizing requirements for large storage tank vents for an explosion case?
I am being asked to confirm if the atmospheric vents on a large storage tank would allow venting or if the tank would fail catastrophically.

 

[TD2K]

I'd talk to Fike or someone who works in that area.

Emergency relief vents sized per API 2000 are not intended to relieve an internal explosion.

 

[MJCronin]

barilko,

TD2K is right....

If you want a vessel that is designed for a large surge in pressure (read explosion) you are beyond the capabilities of a simple flat bottomed tank. (API-650 or 620 design)

You should consider liquid storage in several smaller ASME code rated pressure vessels equipped with apprpriately sized rupture discs.

Large, flat bottomed tanks have barely enough strength to sustain the liquid head and cannot sustain an explosion generated pressure surge.

MJC

 

[farshi]

hi.
the large tank of liquid is not design for releasing gas
for explosion case,the psv line is design for release of high pressure case,and nitrogen pressure control or atmospheric breathing is necessary for tank.
your truly,
farshi

amir farshi
farshia@nioc-ripi.org

http://www.nioc-ripi.org

 

[saidsaz]

is explosion a scenario in ur case ? i heard of fire case , blocked dicharge , rupture of bottom manway ,line but not explosion ...can u please describe your system ?

thnx

 

[barilko]

Sorry for not keeping up to date on this....

The tank is used for surge storage of liquid sulphur.

A deluge system is in place for fire prevention.

If a fire occurs the deluge system will dump water into the tank creating steam. The concern is that the roof vents are inadequately sized to allow relief of the steam and when the tank overpressures, because there is no 'frangible' roof connection, the whole tank will lift creating a wave of molten sulphur.

Can you point me to a code section which deals with this?

 

[Whe]

Hi, Barilko,

ASME B&PVC VIII:1 clause UG 133 and AS 1210-1997 clause 8.6 (p.276) give some guidance.

I guess you'd want to at LEAST prevent splash/spray of sulphur and calculate the maximum possible volume of steam created from a mass/energy balance.

 

[butelja]

BARILKO,

The system that you have described using liquid water on a molten sulfur tank is extremely dangerous. Deluge is fine on the outside of the tank, but not inside. Don't attempt to size the vent for this case, avoid it by not creating the problem. Usually either steam or nitrogen is used for snuffing out any fires in a sulfur storage tank. Additionally, it is common to use a nitrogen blanketing system at all times to avoid the fire hazard all together.

 

[barilko]

Butelja,
Do you have any experience retrofitting large tanks for blanketing? I'm not sure how easy (read $$$$) this would be as the atmospheric vents are fairly large.

 

[TD2K]

I'm not sure what you mean Barilko. If you are putting on gas blanketing, you will need to install pressure and vacuum vent valves on the atmospheric vents (I assume they are now just open connections). API 2000 goes through how these are sized for normal and emergency venting/breathing though molten sulfur is not exactly the main focus of that document but the principles apply. The vents themselves aren't that expensive.

You'll need to play around with the sizing to get a valve and setting that will pass enough gas volume to avoid an overpressure or vacuum situation on the tank since tanks are usually pretty low design pressures and you need a reasonable 'overpressure' above the vent's set point to achieve significant flow rates. Shand and Jurs or Protectoseal are a couple of companies that sell these vents and have a good catalog.

For gas blanketing, companies like Anderson Greewood have valves to keep positive pressure on the tank.

 

[CHD01]

If I read your concerns correctly, Barilko, you need to address 2 problems. First - what is the relieving pressure in the tank based on your worst case of the water deluge flashing to steam; second - you need to determine if the resultant tank internal pressure is great enough to cause the tank to lift above grade pulling what ever tank anchors may be installed from the concrete base (if there is one).

The first case can be solved for the equilbrium internal pressure using equations similar that for computing required receiver tank volumes for plant compressed air systems. The second one requires modeling of the anchor system to determine whether the concrete or the anachor bolts or the tank fails - a bit more complex.

I have a personal spreadsheet that addresses all of these concerns and calculates the required anchor design or the dunnage required if you want to do it that way. What I mean by dunnage are steel beams braced and mounted as part of the flat bottom to reinfoprce it against being lifted.

If you analyze all of the above (in addition to calculating the required relief flowrate and the required vent size) then I believe you will answer your question.

Regards,

The more you learn, the less you are certain of.