6 replies to this topic

[aider94]

I have a question about heat exchanger shell and tube PSV device considering blocked outlet case.

The question is more of fluid dynamics than of PSV. Consider that shell design pressure is as high as a source of pressure and on the shell outlet, we have a valve. If we have normal flow and a valve is closed during normal operation, will the pressure rise and rise and exceed design pressure? 

If does I assume that I need PSV designed for all source stream flow.

Sorry for a newbie question.

Regards,
Jakub
 

[latexman]

It depends on what is moving the fluid.  A centrifugal pump?  Maybe, it depends on the dead head pressure.  Is that higher than the shell design pressure?  A positive displacement pump?  Yes.  A fixed pressure reservoir?  Maybe.  Is reservoir pressure higher than shell design pressure.

[Art Montemayor]

In addition to Latexman's comments, I would add the question: is the shell fluid being heated by a tubeside fluid?  if so, can the shell side be subjected to vaporization and high vapor pressures? 

 

The data given is much too general to make detailed, accurate comments.  The problem with studying the safety risks and over pressure possibilities is that not enough thought has been given by the O.P. as to the possible hazards related to the operation.   More thinking and studying of the unit operation is required.  By doing in-depth study of the operation, positive learnings are obtained.  Our Forum comments are meant to stimulate your thinking in that direction.

[aider94]

Heat exchanger details - it`s inert gas chiller
shell side design parameters: 24 barg, (-45)/120 degC - cooling gas

tube side design parameters: 3,5 barg, (-25)/120 degC - inert gas

There are valves on inlet and outlets on both sides of HX.

[diogovalente]

To answer this question the information regarding the pressure source is necessary. Do you have this information?

[ryn376]

Also, is it important to consider flashing of a fluid above it's normal boiling point when going to atmosphere (e.g. the fluid such as water could be sub-cooled at relief of 150 psig and 300 F, but super-heated at atmospheric pressure)?

[SawsanAli311]

Hi ryn,
If ur source pressure is a vessel having the same design pressure as the shell side of your exchanger and if the exchanger is in the same circuit downstream the vessel (locked open valves) then the psv on the source separator would be sufficient to cover the blocked outlet scenario ( if sized correctly)
However, considering that the tube side design pressure is less than 10/13 of the design pressure of shell side, it if very important to ensure that the tubes are tested and designed considering them being at their low pressure while the shell side at the design pressure in order to ensure they don’t fail because of the wide difference in pressure.
Note: conventionally, high pressure is tube side and a psv for tube rupture would be installed on the shell low pressure side in case 10/13 rule applies