Two-phase separation

[EZeng]

When designing a two phase horizontal separator, what is the minimum retention time required in order to have good separation?
what measures can compensate for a short retention time, due to size limitation?

 

[pierreick]

Hi,
I guess it's a liquid- liquid separator!
a)Can you perform a lab test? This is the best way to get relevant data. Use a graduated flask and a stopwatch.
b)Coalescer.
Pierre

 

[LittleInch]

Depends on how mixed the two phases are and what level of separation you want.

I would aim for min 1 minute in the liquid phase to allow gases to emerge.

Meshes, demister coalescers, use of chemicals can help.

So can entry devices like the famous schoepentoeter inlet device

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

See retention time

https://petrowiki.spe.org/Separator_sizing

Mind your pressures and temperatures, especially as related to how they affect velocities. That's where time enters the equations.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[EZeng]

Thanks,
(for some reason I can't seem to find the specific reply to each response, so I'll reply in one post)
The process is separation of n-Butane (gas) from water (liquid).
about 10 bara and 80 °C (though the pressure and temperature can vary).
flow ratio is about 8%[sub]vol[/sub] gas in mostly liquid flow.
The assumed bubble size is about 0.1 mm.
I am looking for ways to improve separation and avoid bubble running with the liquid.
I did a preliminary sizing of a horizontal separator, but need to reduce the retention time, as i am limited with size.
In order to compensate for the short retention time, I assume that some sort of a coalescer is needed, maybe in addition to flow manipulation (buffles).
I would appreciate any input on the options and how each contributes to the separation.

Thanks,

 

[GD2]

OP, I am not a process engineer, however, I will try to respond within the limit of my process knowledge.
Use Stokes Law to calculate the rising velocity of the bubble.
For the horizontal vessel, the residence time below the low level will be that, that will allow the minimum bubble size to travel the distance between the vessel bottom and the low liquid level.

GDD
Canada

 

[LittleInch]

So this is basically a degassing vessel?

Why 10 bar?

You might be better off with a vertical separator and trays. What you have is fizzy water. The bigger the bubble and lower the pressure works best.

But this is a specialist area and there are many guides and design issues. Vendors often have good designs specific to your requirements.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

There can be many reasons for gas carryunder. Show us a level sketch showing internals and dimensions, all levels, residence time between levels etc

 

[LittleInch]

To be honest, you're probably better off asking a different question with loads more detail in the chemical plant design forum.

You need to give people some idea of flowrates, and what level of separation you're looking for. Plus what is your size limit.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.