vapour collapse

[kingkong1]

Can anybody advise me on vapour collapse during cooling in a reactor, ie after a distillation when cooling is initiated. We are currently using nitrogen to sweep through the reactor and keep air out. However it is feared that we may not be using enough nitrogen. Any tips on how I can calculate the volume of nitrogen required to keep air out?
Many thanks.

 

[epoisses]

Kingkong you can either spend a full afternoon (during your busy shutdown) calculating this, or you can quickly send an operator with breathing air up the reactor to measure the O2% inside and compare with the max limit you want to apply. I would recommend the latter.

If you're not in a shutdown, I guess there must be guidelines for the exit velocity of N2 through the outlet, but I have no numbers available.

 

[gerhardl]

Purging or blanketing with nitrogen is fairly common.

Check if this solution is possible, or am I stating the obvious?:

If your reactor to be protected can be closed, and fed nitrogen through pipeline and valves, you could have a nitrogen source at high pressure in a separate vessel, a shutdown valve, a checkvalve to prevent backflow, a pressure reducing valve station with PSV, possibly a new checkvalve and an on/off valve for inlet to your reaction tank.

Provided correct arrangement and pressures the necessary amount will be drawn into the tank when steam collapses.

If necessary you could purge by having a controlled outlet of nitrogen from the ractor, maintaining a slight overpressure inside, feeding in extra nitrogen as before.

The presure reducing station capacity (volume/time) during a possibly 'sudden steam collapse' (is this actually the situation?) inside your reactor: have to be measured directly or by measured temperature and pressure curve over time inside vessel against actual steam table.

You could also guesstimate aginst the given tank volume, nitrogen feeding pressure and pressure reduction capacity. (Like: I need xNm3 in not less than y seconds).

Note: beware of allowed operating under- and overpressure for closed tanks. They tend to collapse very fast by underpressure, especially by sudden steam collapsing,and shold be protected by bursting discs or other type of protection....

 

[StoneCold]

Kingkong1
My guess is by the language you use (distillation in a reactor) that this is a batch process. If that is correct then just have a pressure gauge connected to the reactor during shutdown. If you want to keep O2 out then keep the pressure in the reactor/column above atmospheric. If you cool it down the first time and the pressure goes to zero gauge or below, increase the flow by adding larger lines or a larger pressure regulator.

 

[kingkong1]

Thanks for your opinions guys. I had intentions of actully calculating the volumes of Nitrogen required, but as you have all suggested, the experimental method is the way to go. I will try this, I am planning on going for a worst case scenario and then applying this to the other vessels on site. By worst case I would take a solvent with the lowest specific heat capacity, and I would only put a minimal volume in the reactor, this should give me max cooling rates.
Any comments on this approach?