L-L interface control

[shvet]

Dear forummembers

Is here anybody familiar with such L-L level control scheme? Is this method workable or not?

 

[pierreick]

Hi,
This is not going to work; you will carry forward light phase with heavy phase.
You must disconnect the light phase pipe.
Pierre

 

[LittleInch]

Err sorry, but where exactly is inflow as both pipes just flow out?

What are you trying to do?

Densities of liquids involved here?

Is valve open or closed?

Any level control or instrumentation?

Give us something more to work on here please.

 

[pierreick]

Little inch,
it is very clear ! this is a LL separator.
bottom valve is closed , open only to drain the separator.
Green is light phase , red is heavy phase .
The interface is controlled by the height of the inverse U pipe .
Pierre

 

[shvet]

Hi,
This is not going to work; you will carry forward light phase with heavy phase.
You must disconnect the light phase pipe.
Pierre

Disconnect from light liquid (green) and connect to vapor space (white). The same as for G-L level control? Am I correct?
What if the horizontal run of U-pipe will be oversized so velocity is almost 0? Will it help to avoid carryover?

 

[LittleInch]

Little inch,
it is very clear ! this is a LL separator.
bottom valve is closed , open only to drain the separator.
Green is light phase , red is heavy phase .
The interface is controlled by the height of the inverse U pipe .
Pierre

Not when there is no inflow it isn't.

But I agree it won't work because if there was more green stuff than shown, it would just flow out of the pipe on the left.

 

[pierreick]

Shvet.
Block the light line, no connection to the vapor space.
Only heavy phase going through the inverse u pipe. Of course the valve is closed.
Little lunch,
When liquid at rest, nothing special. the phase will separate.
Pierre

 

[shvet]

Shvet.
Block the light line, no connection to the vapor space.

If U-pipe is not connected to the separator then U-pipe elevation will have nothing to deal with L-L interface in the vessel. Am I correct?
The highest point of U-pipe can be 1 meter higher or 1 meter lower and this won't affect L-L level. Or I do not catch something?

@LittleInch
This is the classical continious 3-phase separator for chem industry. The difference (for me personally) is the weird methods to control L-L level. I have not met such U-pipe for L-L application and the contractor denies to provide a detailed comment.

As an example see the picture

 

[Compositepro]

The U-bend will not act as a Wier. It will act as a siphon. Even if it acted as a wier, it would not control interface level. It would behave the same as the other wier, controlling liquid level.

 

[LittleInch]

I'm very familiar with a 3 phase separator and this is not one.

I agree, the LL interface level control is not going to work.

 

[pierreick]

A description and explanation are given in Perry's chemical Engineer's handbook - page 15-26 -7th edition
To prevent siphoning effect the upper part of the inverse U should be connected to the vapor space/vent. No connection between the Inverse U leg and the light phase.
Pierre

 

[pierreick]

A schematic with equation.
In your case ZL is the height of the weir .
Pierre