4 replies to this topic

[mastergii]

Hello,

 

I'm working with separators. The operating pressure will determine to what extent light hydrocarbons vaporize, right?

 

What happens if i decrease or increase the operating pressure? Will a pressure decrease affect the gas density and velocity? In which manner?

 

Hopefully some of you can help me understand.

 

Thank you

[Dacs]

While it's true that the operating pressure will dictate the extent of degassing in your vessel, there's the consideration of residence time to allow the fluid to have ample time to separate the light ends from your stream.

 

I dunno how density and velocity would matter in this system, but normally separators (at least the ones I came across with) are operated with pressures as low as practical to have better separation of the feed.

[mastergii]

So if I changed the operating pressure from 20 bar to 15 bar, what kind of effect would I experience?

[Dacs]

If you change your OP from 20 to 15 barA, you'd expect more light ends flashing off your stream (higher vapor and lower liquid products) and depending on the composition, you may experience temperature depression (to some extent).

 

May you share what you're trying to do?

[Art Montemayor]

Mastergii:

 

As Dacs has explained, if you reduce the operating pressure of the separator you are operating, you normally would expect existing lighter components to flash off with more ease --- HOWEVER, this assumes that you are flashing within the separator.  You are over-generalizing what you explain.  If your system pressure (which would include other equipment both upstream and downstream were to be reduced in pressure, the effect of more light components flashing off may not be noticed at the separator because the flashing (or evaporation) might have taken place further upstream.  We don’t know what you are doing – or trying to explain – and it becomes difficult (if not impossible) to give you a concise and correct response because we lack a full, detailed explanation of your system and operation.

 

There is a difference between the operation of a flash drum and a vapor - liquid separator.  A flash drum is the incorporation of a vapor-liquid separator in conjunction with a throttling device.  A vapor-liquid separator is nothing more than a sophisticated “wide spot” in the line that facilitates the separation of a gas phase from a liquid phase.  The liquid might (or might not) be in the saturated state.  There is no throttling (adiabatic, isenthalpic process) in a pure vapor-liquid separator.  I am mentioning these basic definitions because a LOT of students are continuing to getting mixed up in understanding the basic Unit Operations of both of these processes.  (This kind of puts a bad light on those presently teaching Unit Operations in universities.)  For a good explanation on a flashing operation, read the paper offered by Breizh in the following current thread: http://www.cheresour...848-flash-drum/

 

As Dacs requests, we may help you further if you share a detailed description of what you're trying to do?  A sketch would be a great help also.