2 replies to this topic

[Bill B]

I am evaluating relief devices for a jacketed vessel. The vessel is designed to 15 psig MAWP and will be run normally with a 1 psi head. Both steam heating and water cooling will be done in the jacket, rated at 150 psig (steam pressure 50 psig). The vessel will be jacketed. I am evaluating fire case scenarios for both the jacket and vessel. I have a few fundamental questions that the forum constituents might answer:

1. Vessel - I assume a fire case is indeed a valid concern for the vessel? Some earlier posts by Phil had convinced me that for a heat exchanger, one should not be concerned about a fire scenario on the tube side. Not sure if the same logic applies here. From a practical perspective, is there an advantage of a relief valve over a RD?

2. Jacket - There are actually 3 sections. Please confirm this will require 3 separate RV's. I presume we could run an outlet pipe from the 3 sections to a common RV, but this would require a run of about 15 feet, which doesn't seem like a good practice. What have others normally done?

Thanks in advance.

[JoeWong]

Before we proceed, some additional information required.

i) The vessel is designed to 15 psig MAWP and will be run normally with a 1 psi head. Steam heating and water cooling will be done in the jacket, rated at 150 psig (steam pressure 50 psig).

Vessel good for 15 psig while jacket see steam pressure 50 psig. The vessel wall will experience net Dp of 50-1 = 49 psi > 15 psi ? I am sure i miss something here. Please help.


My appologize for mis-read the following. Ignore.
ii) Jacket - There are actually 3 sections....we could run an outlet pipe from the 3 sections to a common RV...

Can you connect three section together where CW meeting with Steam ? Or They are running in sequenece by drawing and purging ?

[JEBradley]

I havent directly re-read Phil's comment about dire scenario for heat exchangers, but I remember reading it and am pretty sure it was just for the exchanger itself and you should indeed consider the fire scenario for the vessel.

I looked at a similar setup a couple of years ago (but for a glass vessel). I found the worst case to be a malfunction in the heating system resulting in the maximum flow of heat transfer fluid - suprised me at first but when you think about it the system is designed for heat transfer so its well capable of transferring too much.

You asked about the practical differences between RD and valve - is RD 'Relief Disk'. If so theyre a good bit cheaper. Valves you can re-use though. Valves also give a more controlled release. Most of the time these days im seeing situations with the two in series - i hope someone else can give a good reason for this - I could think of a few but i won't say incase i mislead people.

Finally, I don't see there being any problem with relieving into a common header. I would try to keep the downstream length as short as possible but as long as it's adequately designed for. I believe there are certain standards legally limiting the length of explosion vents but not pressure relief.

Hope this might have helped