June 18, 2007

Phase Separator - Design Improvement

Phase Separator Design Based on My Experience


Recently when I was working on some problem of a phase separator in which Toluene water system is handled with some amount of acetic acid, I had some great experience which I thought I should share with all of you. The Idea was to reduce the acetic acid in the water phase, which anyway cannot be reduced by separation becasue its inherent solubility in water is very high or practically unlimited. Therefore, even though plant people were trying to reduce it by changing the locaion of Interface layer, My focus was on the better separation for water & toluene and increasing its capacity.

Are you convinced that by changing the location of interface layer you can reduce the loss of a completely miscible component???????????????????


Phase separators are basically horizontal or vertical vessels, can be used for separation of two or more liquids (generally industry uses only two due to lack of knowledge for better design in general). Separation is based on the gravity difference principle, so greater the diffeerence in densities better & faster is the separation.

Here is simple drawing representing general design.

You can read the theory & design in Coulson & Richardson for better understanding of above.


Now the capacity in terms of better & faster separation depends on the settling velocity of dispersed phase (Water) in the continuous phase (Toluene in this case). If the actual velocity coming from the pipe (as shown above) is more than the settling velocity which is generally of the order of 0.01 or less m/sec than naturally the toluene will also go to bottom phase. This is usually the case where actual velocities are much higher than the required one in actual plant operation & design both. Therefore, we generally operate a phase separator at much lower capacity than what it is capable of.


I have found that it is better to provide a nozzle plate at the end of inlet pipe in order to reduce the velocity. this plate should be in the horizontal plane & its width can be based on separator diameter or size. For my case I can accomodate a 4-6" wide plate with a length of ~800 mm minimum. This with an hole dia of 0.5" on each side i.e width and length can have ~128 holes.

Compared to an inlet pipe of 4" in size it can have double cross sectional area reducing the inlet velocity to half of the original design value.

Imagingly I can increase the capacity of this separator by 100% to double.

Here is a picture of what it will look like.

Enjoy using this Idea for increasing the capacity of your phase separator. Send me your comments if any.

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