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I have a vessel 50% full of ammonia at outdoor temperature of 20F - 100F depending on time of year. This vessel will be evacuated with a compressor and the vapor will be discharged into an ammonia storage tank. The compressor is capable of pulling enough of a vacuum to evacuate the vessel once the liquid has been evaporated.

The question is when the compressor begins to pull on the vessel and flash the ammonia, is there a situation (size of compressor, volume of vessel) where I can achieve a vacuum before all of the liquid has 'boiled off'? Or will all liquid ammonia vaporize prior to any vacuum being pulled on the vessel?

With small volumes in large vessels (such as 200 gallons of NH3 in a 25,000 gallon vessel), using the same process, the ammonia appears to completely flash off before any drop in pressure (the vapor pressure at its respective temperature) is detected.

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  • $\begingroup$ The pressure won't start dropping significantly as long as the temperature is maintained, until all the liquid has evaporated. $\endgroup$ – Chet Miller Oct 16 '20 at 18:48
  • $\begingroup$ Thank you - the reason this is important here is because the compressor cannot handle liquid. $\endgroup$ – ARinLA Oct 16 '20 at 18:52
  • $\begingroup$ it would also seem the evaporation would absorb heat - if any effect at all, this should serve to lower the temperature of the liquid NH3 slightly keeping the temperature at or below ambient. $\endgroup$ – ARinLA Oct 16 '20 at 18:57

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