Flashing

[wfn217]

We will have a vessel containing a suspension of solids in water at 340 F (103 psig). We want to depressurize the tank to 1 atmosphere. This will cause 13.5% of the water to flash. We are concerned about losing solids out the vent due to the vigorous flashing. What is the best way to depressurize the tank?

 

[ash9144]

Assuming you can't cool the contents first, the best way to vent the tank is slowly. Don't open the valve completely initially

 

[djack77494]

If you want to do a design on the depressurizing step, then depressure at such a rate so as to NOT generate so much entrainment that the liquid droplets won't settle back down before reaching the outlet nozzle.

As you depressure, a portion of your liquid will flash. The generated vapor flows upward in your vessel to the outlet nozzle. If it is flowing fast, it can carry small liquid droplets with it, which is what you hope to avoid.

Knowing your vessel's geometry, you can use the Sauder-Brown Equation to get to a permissible vapor flowrate. Then depressure so that the calculated rate is not exceeded.
Doug

 

[25362]

Parts of the following link may be of some help:

http://www.spiraxsarco.com/resources/steam-engineering-tutorials/condensate-recovery/flash-steam.asp