N2 Purge Velocity
N2 Purge Velocity
This is my first post to the forum so please excuse if this thread is in the wrong spot.
I am currently in a summer internship as a process engineer. One of my projects is to install N2 purge rotameters on Cl2 PSV piping.
Here is some additonal info on the process. For our process Cl2 needs to be in a vapor form, so we have two chlorine vaporizers with the same relief design. Cl2 is very aggressive and we continuously have to send PSV's & PSE's out for PM. Each vaporizor has two PSV's, one that relieves to an emergency vent header line and the other relievs to ATM. The reason we have two PSV is when one is out for PM we still have one and service. Only one is in service at a time, normally the one that relieves to the EVS. We continously have issues when it rains and when the one to ATM is in service; water will back in and sit on top of the PSE. We have a small run of bypass piping with a FO to prevent pressure from building between the PSV and PSE causing an insufficient dP across the PSE (vessel could exceed MAWP) and also the PSE could fail inward causing material to enter the vaporizer(NOT GOOD!). If there is any small leak of Cl2, the mix with it and water is very aggresive and corrode the PSE. Another problem is when the one to the vent header is in service; if the vent header gets backed up then whatever is in there will back in and sit on our PSE, again causing corrosion.
Ok, so finally my quesiton. I am putting N2 purge rotameters on the vent stacks to prevent moisture from sitting on the PSE supplying it with a slight N2 sweep. What should be my N2 purge velocity?
Also I am putting a similar N2 purge on the vent header to sweep the material away, preventing it from sitting on the PSE as mentioned before. Same purge velocity??
I took a similar application in the plant where there is a N2 purge on a vent header. With the flow set at 6CFM, I calculated a velocity of only .2 ft/sec or ~12 ft/min. That seemed pretty low to me.
Any thoughts on this matter is much appreciated.
Thanks in advance,
Matt, GEAUX TIGERS!