Fire Case or Non Fire Case 1

[shiplu48]

Hello,

I am facing difficulties for selecting Fire Case or Non Fire Case in PSV sizing.

I have a vessel that contains mixture of liquids including water. Water is the only compound that is to be vaporized.
The vessel is kept just below the saturated condition of water. When the temperature of the liquid is increased by
steam, water gets vaporized that causes over pressure scenario.

I am stuck with that is fire case is considered when there is source of external fire that is causing liquid to be
vaporized or any heat, not only from fire, causes liquid to be vaporized?

Help needed for this criteria!

Thanks.

 

[Latexman]

I hope you have a relief device mentor in your company.

Is any of the liquids in this "mixture of liquids" an NFPA Class I or II or IIIA flammable/combustible?
Is an NFPA Class I or II or IIIA flammable/combustible liquid stored near this vessel?
Does piping with an NFPA Class I or II or IIIA flammable/combustible liquid run above or near this vessel?
At any time (shutdown, start-up, maintenance, construction project, normal operation, abnormal operation, etc.) can an NFPA Class I or II or IIIA flammable/combustible liquid be at or near the area of this vessel?

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[shiplu48]

Dear Latexman,

Thanks for your reply.

First of all I don't have any relief device mentor in my company.

I have to deal with Ethylene Oxide and Propylene Oxide in my plant. Not in the vessel I had mentioned but on other vessels and pipelines.
Both have Flash Point less than 73°F; Boiling Point less than 100°F (Source Wikipedia).
So they fall into NFPA Class IA.

Thanks.
Shiplu48

 

[Latexman]

That's good to know. If you'll provide answers to the 4 questions asked above, advice on your question can be given.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[shiplu48]

Thank you Latexman.

I am clear that it is the fire case consideration for PSV sizing.
But vessel's design pressure and set pressure is 3.5 Barg.
Will fire case be applicable for this small designed pressure vessel?

Many Thanks
Shiplu48

 

[met11]

Fire case is considered when there is a fire. Excess heat case is considered when there could be excess heat (steam). Size for both if they're both applicable.

Whether fire case is applicable... you haven't provided nearly enough information. Are there inventories of burny stuff nearby that could pool and cause a prolonged fire? There's another thread on this subject:

http://www.eng-tips.com/viewthread.cfm?qid=414243

 

[georgeverghese]

It sounds like you have some source of heat generation within this vessel also, so in addition to external firecase, loss of internal heating controls should also be taken into account. In most cases, where automated safety shutoff devices are included to stop internal heat generation, it is possible to claim that these 2 cases are non coincidental(ie that you dont have to add the relief rates from both these sources to derive the total relief rate).

 

[shiplu48]

Dear met11 & georgeverghese,

Thanks for yours suggestion.

As per met11 query, there is no storage of burning liquid near the vessels or inside the process areas.

It seems to be several things and incidents are considered to consider a fire case PSV.

Many Thanks.

Shiplu48

 

[shiplu48]

Dear Latexman,

As per your last reply, followings are the answers of your questions-

1. Is any of the liquids in this "mixture of liquids" an NFPA Class I or II or IIIA flammable/combustible?
= Mixture of liquid contains no NFPA Class I or II or IIIA flammable/combustible liquid. (Another vessel contains NFPA Class IA flammable liquid for reaction purposes ).

2.Is an NFPA Class I or II or IIIA flammable/combustible liquid stored near this vessel?
= No.

3. Does piping with an NFPA Class I or II or IIIA flammable/combustible liquid run above or near this vessel?
= No. (Another previous mentioned vessel does - NFPA Class IA flammable liquid.)

4. At any time (shutdown, start-up, maintenance, construction project, normal operation, abnormal operation, etc.) can an NFPA Class I or II or IIIA flammable/combustible liquid be at or near the area of this vessel?
= No.

Sorry for late reply!

Many Thanks.
Shiplu48

 

[Latexman]

Sounds like a fire case is not very probable.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[shiplu48]

Thanks Latexman for your co-operation.

Regards
Shiplu48