Flow Of Nitrogen Through A Utility Hose?

[lastone]

Does anyone have a rule of thumb or an estimate of the flowrate of 70 psig N2 through about 100' of 3/4" utility hose? The hose/hoses will be connected to an empty reaction train sitting at 3-5 psig. I want to purge the reaction train to the flare to remove residual hydrocarbon, and I know how many reactor volumes I need to displace based on my current hydrocarbon concentration. I want a rough estimate of the time involved to do the purge, but I don't have a good feel for the flow through the hose. Using a few of the different calcs in Crane, I am coming up with something between 2500-5000 std-ft3/hr. Does this make any sense? I guess I could do a quick test with a large trash sack and stopwatch, but everbody has gone home. Any ideas?

 

[unclesyd]

7 volumes, but each volume has to be held for short peroid.

There is an excellent pamphlet put out by one of the gas companies concerning purging with N2. I can’t remember which one it was. The only thing I know it wasn’t Matheson gas, Maybe Linde or Airco or whoever they are now. I’ll look around and see if I still have it. There are also some textbooks that have your information.
Depending what you are purging to in the way of concentration it will take considerable more gas than you expect. I remember one particular problem with Cycohexane in a large reactor to get the level below the Tl value. It took 10 volume replacements to achieve this. The booklet said 7 volumes if the vessel is clean.
Heat Treating magazine had a very detailed article, with the required calculations, on purging large volume furnaces.

 

[pmureiko]

I'm not going to do flow calculations. You are a good enough engineer to do that.

I recommend using a safety factor for purging the reactor. Most systems are non-ideal and have deposits and deadspots that are hard to clear. In this case the lower flowrate and the higher volume replacements will help out.

The extra time and nitrogen used for a good purge are well worth preventing an explosion caused by doing the "minimum" purge.

 

[armonicman]

What you want to know is only the flow rate that you can obtain, don't you? . Well, with this conditions and a 100 feet 3/4" hose, you got a 1200 S ft^3/h flow rate. But don't be lazzy man! you can also calculate it!
Cheers

 

[pack12]

What you have is a long restricting orifice. The flow will go sonic very fast -- below 40 psia line pressure. Model the flow using restricting flow calculations.