# Distance Between Mist Eliminator Top And Vapor Outlet Nozzle For Vertical Separators

Dear All,

Besides defining the Low-Low (LLL), Low (LL), Normal (NLL), High (HLL) and High-High (HHLL) liquid level based on criteria such as retention time, surge requirements for normal process control and adequate disengagement space during events such as large liquid slugs entering the separator or foaming, it is also important to define the vapor outlet nozzle distance from the top of the mist elimination device.

The objective of providing a minimum distance between the mist elimination device and the vapor outlet nozzle is to prevent channeling by promoting equal velocities across the entire surface area of the mist elimination device.

Refer the sketch below for two separate configurations of mist eliminator and vapor outlet nozzle for vertical gas-liquid separators:

The vertical distance X4 is the minimum distance required between the mist eliminator top and the outlet nozzle and is given by:

X4 ≥ (D - d2) / 2 -------------(1)

Also

h ≥ d2 ------------------(2)

where:
X4 = vertical distance from mist eliminator top to vapor outlet nozzle as shown in sketch
D = Outside diameter of vessel
d2 = Outside diameter of vapor outlet nozzle

Some standards recommend that X4 should be a minimum of 12 inches even if the calculated value as per equation-1 is less than this value.

That is all for today folks and I would be happy to have comments and experiences from the "Cheresources" community members.

Regards,
Ankur.

Bobby Strain

Ankur,

It would also be helpful to include the source of this recommendation. Looks like it might come from a mist eliminator supplier. And the site probably has a lot more useful information.

Bobby

ankur2061

Ankur,

It would also be helpful to include the source of this recommendation. Looks like it might come from a mist eliminator supplier. And the site probably has a lot more useful information.

Bobby

The source is the GPSA Engineering Databook, 13th edition, SI units.

Regards,

Ankur.

ccjayesh

DEP 31220511 is silent about distance between mist pad and outlet nozzle. Minimum distance X3 is 0.15 D or 150mm.

jayesh

Bobby Strain

You can visit my website for vertical separator design. There are others, too. But use them with care. And always check the result with a reliable source.

Bobby

karamipoor

Hi & Good Day!

How can I calculate the pressure drop in vane & mist eleminator & demister?

Regard

ankur2061

Hi & Good Day!

How can I calculate the pressure drop in vane & mist eleminator & demister?

Regard

http://www.sciencedi...319610310001134

http://amacs.com/wp-...rochure-Web.pdf

http://www.civilica....SCCE07_149.html

http://courses.washi...-mist-elim..pdf

Regards,

Ankur

abhi_agrawa

Ankur,

Do you know why the angle between the top of mist eliminator and the vapor outlet nozzle is 45 degrees. Is it something that has been chosen and seems to work, so people stick with it or there is a reason.

Is there a guideline for the distance between inlet nozzle and the bottom of the mist eliminator as well?

Thanks,

And wish you a very happy new year.

Abhishek

ankur2061

nkur,

Do you know why the angle between the top of mist eliminator and the vapor outlet nozzle is 45 degrees. Is it something that has been chosen and seems to work, so people stick with it or there is a reason.

Is there a guideline for the distance between inlet nozzle and the bottom of the mist eliminator as well?

Thanks,

And wish you a very happy new year.

Abhishek

Abhishek,

I guess it is the later, a methodology based on established field practice. In "Chevron" standards they mention that a minimum 12 inches height should be maintained between the mist eliminator top and the vapor outlet nozzle. A trigonometric relation for a right angled triangle mentions the minimun distance between the mist eliminator top and the outlet nozzle as:

X4 = 0.707*hypotenuse where 0.707 is Sin(45 deg).

No there is no guideline for bottom of mist eliminator, since it is something which depends on the thickness of the mist eliminator pad. Mist eliminator pad thickness is based on other criteria which can be a separate discussion topic.

Regards,

Ankur.

abhi_agrawa

Ankur,

Thanks for the clarification.

My second query was for the vertical distance between feed nozzle and the bottom of the mist eliminator. I think that there should be some minimum requirements to ensure that the larger droplets separate due to gravity and do not load the mist eliminator.

Regards,

Abhishek

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