Residence Time in Vertical Vessel 3

[Victor4]

I am trying to calculate the residence time of an oil/water mixture with a flow rate of 250 gpm to pass through a vertical tank. Tank dimensions = 5ft-diameter and 10ft-height with 75% operating capacity.The oil/water mixture enters at the bottom of the tank and water exit at the same elevation while oil leaves from the top. So my question is how to calculate the residence time and does water head make any difference?
Any help is very appreciated.

 

[ajs1972]

This problem is related to densities of the fluids. Here, the equation:

t= (6.24 * viscosity of continuos phase in cP)/(density of liquid A - density of liquid B in lb/ft3)

The time (t) will be in hours.

Regards.

 

[Chance17]

For plug flow residence time = (physical volume)/ (flowing volume.
The flowing volume is assumed to be constant.
As the water level changes the physical volume for both oil & water changes.

The plug flow model is OK for bulk fluids.
If you are concerned about dissolved chemicals in either stream, the plug flow model may not be accurate -- al la CSTR models and residence time distributions.

 

[cloa]

Assuming its immiscible liquids and no foaming issue (some bioorganic oils are partly miscible), then its a separation speed issue. Relative densities are going to be an issue. So what's the density of the pure oil.

 

[Victor4]

First I would like to thank all of you for the valuable information. The density of oil is 34 API.

Ajs1972--Can you please give me the reference for the equation you have provided in the post.

Chance17--both the physical florate(water+oil level inside the tank) and flowing volume (inlet flow rate) is constant so should i use the PFR. But this is a separator not a reactor. And there are no chemicals involved.

cloa--this is a crude oil separation from water. They are almost immiscible liquids.

So should i use the formula provided by Ajs1972. But still i am not sure since i think it will involve the separation speed and the distance it is travelling. For example for horizontal separation tank it is tank volume/inlet flow rate =residence time. And for vertical tank it is suppose to be different thats what i think. So what you think guys.....

 

[ajs1972]

Hello Victor4:

The equation was taken from the book: "Unit Operations of Chemical Engineering" from Warren L. Mc. Cabe, Julian Smith and Peter Harriott.

In this book, it mentioned that the separation process is influenced by the densities of the sustances involved and the height of the outlets of tank. The flow velocities of the liquid doesn´t matter for the decanter design.

The tank can be vertical or horizontal, the important point is the height of the outlets of the tank.

Regards.