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# Min Purge Rates For Open To Atms Tank

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### #1 v8landy

v8landy

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Posted 14 January 2008 - 02:40 PM

Hi

I am looking for some guidance for the nitrogen usage/requiremnt to purge a tank (5m^3).

The tank is dual purpose, 1 as a knock down pot should the RD burst, 2 (reason for question) a tank source of nitrogen (inert gas) to replace the vacuum in the tank linked for the RD, when the vacuum is broken.

We would require the vacuum break approx every 4 hours, so we have 4 hours to purge the tank for next cycle.

Is it just as simple as to say tank is 5m^3 = 177 ft^3

therfore if I wanted the tank purged and ready in 2 hours (4 hours between opperations)

(177 ft^3 / 2hrs)60 = 1.48 CFM N2 purge rate (cubic feet per minute) ????????

### #2 v8landy

v8landy

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Posted 14 January 2008 - 02:59 PM

I have used an equation that works out number of purges, and from this it equated to 3.5 to ensure full purge.

From this I would then assume by tank volume to be 3.5 time greater than actual i.e. 615.96 ft^3

i.e (619.5/2hr)/60 mins = 5.12 CFM

???????????

### #3 proinwv

proinwv

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Posted 14 January 2008 - 04:45 PM

I am not sure that I understand the details of your application...I am a mere mechanical engineer.

However, there are two general comments that I will make regarding this subject.

1. For a critical application, in order to prove a purge, the appropriate instrumentation need be in place to sample the gas.

2. In practice many use the mehtod in which some multiple of the tank volume is supplied. That is say 5 or 8 volumes swept through the space. Your 3.5 factor may also be valid. Check this source out:
http://www4.us.airli...sp?0&OID=-14860

Also use the search feature on this site as I am sure that this has been discussed previously and other gas suppliers besides airliquide probably have similar information.

### #4 proinwv

proinwv

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Posted 14 January 2008 - 07:26 PM

OOOPS

I see that link is no longer active, but I did print it out previously and it was in the public domain, and I saved it so go to this document....  PURGE_WITH_NITROGEN.doc   218KB   283 downloads