Pressure Relief Valves

Why?

What happens if the vent is plugged? Where will the gas go then. The PSV is for the protection of the vessel itself. When we mfg skid packages that have vessels on them we always note that if the P&ID does not list a PSV attached to the vessel, the customer is responsible to ensure one is down stream. Stephen

Thanks, Stephen for your expediate reply. Hours after I posted this question, ABSA, (Alberta Boiler Safety Association) sent out an information bulletin. These sour gas scrubbers are a non-code vessel, and a recent incident indicates that they are in service without PSV's and that the client is allowing them to to be put into service without garunteeing the integrity of the system.

This bulletin can be viewd and printed off from this address;

http://www.absa.ca/IBIndex/IB09-007.pdf

This re-iterates why I was asking this question, and unfortinately the answer was given after an incident. Luckily no one was injured.

No. Scrubbers operate at atmospheric pressure, so it's unnecessary.

As an engineer DVader, its not likely you have had to witness the catastrophy of an incident in the field, Safety is important, especially when dealing with H2S in excess of 25% or more. Yes you are right in saying they work at atmospheric pressure but they are also flowing at an increased rate through a pressure line, creation of blockage thru waxing is possible, as well as operator error. A PSV is an essential, I believe that this needs to be addressed by the local governing authority. Here in Alberta we have had several incidents involving these non-code vessels involved in the operation of sour gas scrubbing. One that resulted in a worker being hurt.

A psv in these cases would have let the vessel vent off the build up of pressure, and the incident would have been avoided.

I asked this question of wether or not to have PSV installed and the answer is I keep finding in my search for a code reason is not there, although the safety aspect of it is definitely there.

Thank you all for your input.

It depends upon the results of the HazOp Study.