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Pressure Gradient Through Vacuum Distillation Tower


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#1 fineleric

fineleric

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Posted 24 April 2018 - 11:08 AM

Dear professional engineers,

 

1- In distillation towers the amount of temperature increases from bottom to top. But what about the pressure? Is it constant through the tower?

2- In a batch ethylene glycol vacuum distillation tower, at the first the pressure is uniform through the tower. But near the end of the process, the pressure in lower parts of the tower increases while at the top the same pressure conditions exists. Do you know what is the problem?



#2 Saml

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Posted 24 April 2018 - 09:05 PM

In every distillation tower, the liquid falls by gravity and the gas flows up because of pressure gradient.

Pressure (absolute) is lower at the top by two reasons:

 

1) Height. Gas has density, and there is more pressure in the bottom than in the top. May be that at the end the gas is denser. Also, be sure that you are measuring absolute pressure, not vacuum relative to air. Otherwise you will have to take into account outside air density as well. At first you may have water (MW=18) and you could even see that the pressure relative to atmospheric(MW=29) is even higher at the top than at the bottom while at the end, with mostly glycol, you have the reverse.

 

2) Friction thru the internals. See if RhoxV^2 of the gases are higher at the end than at the beginning.






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