10 replies to this topic

[Julien123456789]

Dear All,

Could you please tell me what is pressure at the end of discharge line of PSV in critical condition ? (sketch attached)

If  I can subtract pressure drop caused by gas movement, I got the pressure at this point > 1 bar (ATM).

It looks like weird ! 

 

Thank you in advance,

 

Julien

Attached Files

•  Query.png   11.08KB   8 downloads

Edited by Julien123456789, 21 April 2016 - 11:18 AM.

[fallah]

 

Could you please tell me what is pressure at the end of discharge line of PSV in critical condition ? (sketch attached)

If  I can subtract pressure drop caused by gas movement, I got the pressure at this point > 1 bar (ATM).

It looks like weird ! 

 

Julien,

 

The pressure at the end of the discharge line with the conditions you mentioned would be a little bit lower than 3.5 bara. Then there would be a pressure discontinuity at the end of discharge line toward atmospheric pressure and the energy of this pressure will be dissipated as noise and vibration...
 

Edited by fallah, 21 April 2016 - 12:14 PM.

[shantanuk100]

Hi Julien,

 

It is as Fallah has said.

You would be releasing it at close to 3.5 bara.

But since the ambient atmospheric conditions are at 1 bara, that gap in pressure is energy which has to dissipate in some form, as heat, noise, etc.

 

Regards,

Shantanu

[Julien123456789]

Thank you so much Mr. Fallah and Shantank,

Your explanation are very clear for me, I got it.

In reality, is it recommended implementing a solution when PSV works in critical condition ?

However, If I can not find a relevant solution for reducing effects in critical conditions, what should I do in this case ? 

I let it be or absolutely I need to change my design ?

 

 

Julien

[breizh]

Hi Julien ,

What is the problem with Critical pressure ?

 

Consider the document attached  7-2

 

Breizh

[shantanuk100]

@Julien,

 

Yes. It is fine to have supercritical PSVs, but make sure the sizing is done as per Supercritical sizing criteria and formulae and not the subcritical ones.

 

Criticality is just an indicator of phase unison, so the valve doesn't know or get affected by this except that the pressure for relief changes due to change in sizing criteria post criticality. All the valve is bothered with is pressure, temperature, flow, and material parameters based on which we decide the relief pressure.

 

Regards,

Shantanu

[Julien123456789]

Thank you so much Mr. Breizh for your very good document.

I am trying to get it.

 

 

Julien

[Julien123456789]

Thank you Shantanuk for your comment.

Could you please explain me more why you talked about super-critical here ? and Why is it better than critical condition ?

As things I interpreted from your explanation, It means that I would accept the situation when PSV works in critical condition ?

The only thing is to inform vendor for a relevant material of PSV in case of application.

Don't I need to investigate a solution to avoid critical condition if posssible, Ex : reducing line size for increasing back pressure, etc. ?

 

Julien

[shantanuk100]

Julien,

 

Supercritical just means the fluid is in a condition past the critical point.

It doesn't mean that the supercritical condition is better than critical condition.

It also doesn't mean that valves in critical condition are better or valves in super critical are better, since both the conditions are encountered in daily life and both are necessary.

 

You don't need to specifically investigate it yourself. It is good if you mention the critical conditions to the vendor if you have accurate data, but otherwise also, they usually have fluid databases and are capable of getting the data if you ask them. 

 

Regards,

Shantanu

Edited by shantanuk100, 22 April 2016 - 04:39 AM.

[shantanuk100]

Also, if you wish to learn more on supercritical valve sizing, go through the following articles.

They are quite informative.

 

Files:

 

http://people.clarks...gn/reliefv2.pdf

http://files.engineering.com/download.aspx?folder=ada4fce7-83f0-46c3-8491-cc4e7ef765de&file=Designing_Pressure_Safety_Valves_in_Supercritical_Service.pdf

 

Links:

 

http://www.processec...critical Region

http://www.hydrocarb...cal-fluids.html

http://www.valveuser...eam-boilers.htm

 

Regards,

Shantanu

[Julien123456789]

Many Thanks Shantanuk !!