Steam-Out Design 1

[codeeng]

I often challenge our Process Engineers regarding steam-out design criteria. Applying, say, full vacuum @ saturated steam temperature is not cost effective on large diameter, low pressure applications. Half vacuum is more appropriate, but what about temperature ? Is it really possible to reach sat. temp. under half vacuum ?

Appreciate your comments.

 

[EGT01]

Codeeng,

Assuming your reference to half vacuum means about 7.5 psia, that would correspond to water at about 180F.

So, if you have a vessel completely full of steam at 212F, 14.7 psia and completely blocked in, as the system temperature cools, steam condenses and the pressure is essentially equal to the vapor pressure of the condensed water. Once the system temperature cools to say an ambient temperature of 80F, you are down to an internal pressure of 0.5 psia. Might as well say full vacuum at that point.