3 replies to this topic

[venkyravula]

In sizing a horizontal knockout drum how much ullage space has to be maintained and what is the criteria for choosing of L/D ratio to be 2.5 to 5 in sizing horizontal separator.

[ankur2061]

By ullage space I presume that you mean the vapor space above the liquid level. This is strictly dependent on the application. For example, if you are expecting large liquid slugs alon with vapor which can happen in case of an emergency flaring scenario, the flare knockout drum is required to be sized with 50% ullage as you call it. Similarly an application for a separator which also acts as a slug catcher such as the one installed at the end of a gas-condensate pipeline would reuire a large ullage space to handle the liquid slugs and also for effective gas-liquid separation.

The L/D ratio of a minimum 2.5 ensures enough residence time in the separator for effective gas-liquid separation in terms of the gas being able to bubble out of the liquid due to pressure drop as well as enough time for liquid droplets to coalesce and form bigger droplets which can then disengage from the vapor and fall to the bottom of the separator by gravity. The key word here is residence time for effective gas-liquid separation due to longer lengths of the separator.

Hope this helps.

Regards,
Ankur.

[venkyravula]

Thank you so much Mr.Ankur...

Am doing sizing for a knockout drum which only liquid flow is there and there is no gas flow into KOD just it acts like a surge drum.. How much ullage space i have to maintain. i got the values as 900mm ID X 2200S/S lenght through some Spread sheet.. LAHH i maintaind is 800 mm. 100 mm is suitable for this condition suppose there is no slug condition in the flow.

[DB Shah]

check this
http://www.cheresour...ge-drum-sizing/