3 replies to this topic

[zawielski]

We're designing large (1MM gal+) batch fermentors for a biomass alternate fuel plant. Between batches the fermentors are cleaned in place (CIP) by washing with a hot (~180 °F) caustic solution. They are then rinsed with a cool (~90 °F) water solution. I understand that the caustic CIP solution could cause a vacuum in the tank by reacting with residual CO2 left from fermentation. I am more concerned, though about the cooling effect of the 90 °F rinse following the hot CIP causing a vacuum and collapsing the tank. Is there a good way to calculate/estimate the cooling effect ans sizing needed for the vacuum relief?

[mav9rick]

This is an interesting problem and one that is not usually faced in in pressure vessels because we are able to design the pressure vessel for full vacuum to avoid the vacuum relief contingency.
Can you please provide the following information:
1) Design pressure of your tank. Both positive and negative
2) maximum quench water flowrate
3) A possible sketch of the spray system for water inside the tank
4) size of tank
5) any insulation?

Although it may not be possible to accurately estimate how quick the steam generated in the CIP stage is condensed in the cooling phase, we may be able to take a conservative approach and based on contact condensation heat transfer coefficients and calculate a rate of condensation.

Please provide the above info so I can look into this further

[mcecasf]

Hi there, I have a similar issue, with smaller tanks.

 

Between 20 and 170 m3.  Some tanks chilled water jacketed, some just insulated.  Depending on which are of our factory, rinse flowrates vary and CIP temperature vary but principle is the same, looking for a method rather than an answer for a specific case (we have had an issue with a tank imploding due to blocked vent, and another one that is creaking a bit! - rather than just blanket "make all teh vents bigger" I want to have some form of basis of design...)

 

All are "atmospheric" tanks (i.e. not pressure or vacuum rated).

 

Hot CIP followed by cold rinse = vaccum risk

 

How do I size the vent? (other than making it "bloody big") - OK so I don't have an expensive valve to size as the tank is open to atmosphere anyway, but I don't want a HUGE vent as there are implications on tank top layout, vent cleaning (food product, don't want muck in the vent) etc etc.

 

Any help appreciated!

[mcecasf]

If anyone finds this in future, see this thread on eng-tips:

http://www.eng-tips.....cfm?qid=329825