3 replies to this topic

[jprocess]

Dear All,
I have read lots of books and articles about 2 and 3 phase separators.Most of them are based on gravity settling concepts but as you know today modern separators use special internals like mesh and pads for optomization of separation and reduction of the size of separators.How can i enter the effects of these internals when i design a separator?
Regards.

[Sandeep01]

You seem to be asking for proprietary data, which will not be available in the public domain. You could, of course, contact potential vendors seeking their assistance, which they would normally provide.

Regards
Sandeep

[mbeychok]

jprocess:

You have posted three questions in this forum today, all of which related to the design of phase separators. I am going to respond to your question about the effect of mesh pads in phase separators and specifically for vertical, 2-phase (vapor and liquid) separators:

A vapor-liquid separator drum is a vertical vessel into which a liquid and vapor mixture (or a flashing liquid) is fed and wherein the liquid is separated by gravity, falls to the bottom of the vessel, and is withdrawn. The vapor travels upward at a design velocity which minimizes the entrainment of any liquid droplets in the vapor as it exits the top of the vessel.

The size a vapor-liquid separator drum (or knock-out pot, or flash drum, or compressor suction drum) should be dictated by the anticipated flow rate of vapor and liquid from the drum. The following sizing methodology is based on the assumption that those flow rates are known.

Use a vertical pressure vessel with a length-to-diameter ratio of about 3 to 4, and size the vessel to provide about 5 minutes of liquid inventory between the normal liquid level and the bottom of the vessel (with the normal liquid level being at about the vessel's half-full level).

Calculate the vessel diameter by the Souders-Brown equation to determine the maximum allowable vapor velocity:

V = (k) [ (dL - dV) / dV ]^0.5

In metric units:

where:
V = maximum allowable vapor velocity, m/sec
dL = liquid density, kg/m³
dV = vapor density, kg/m³
k = 0.107 m/s (when the drum includes a de-entraining mesh pad)

Then A, the cross-sectional area of the drum, in m² = (vapor flow rate, in m³s) / (vapor velocity V, in m/s)

and D, the drum diameter, in m = ( 4 A / 3.1416 )^0.5

The GPSA Engineering Data Book recommends the following k values for vertical drums with horizontal mesh pads (at the denoted operating pressures):

0 barg: 0.107 m/s
7 barg: 0.107 m/s
21 barg: 0.101 m/s
42 barg: 0.092 m/s
63 barg: 0.083 m/s
105 barg: 0.065 m/s

GPSA Notes:
1. K = 0.107 at 7 barg; subtract 0.003 for every 7 bar above 7 barg
2. For glycol or amine solutions, multiply above K values by 0.6 – 0.8.
3. Typically use one-half of the above K values for approximate sizing of vertical separators without mesh pads.
4. For compressor suction scrubbers and expander inlet separators, multiply K by 0.7 – 0.8

In USA units:

where:
V = maximum allowable vapor velocity, ft/sec
dL = liquid density, lb/ft³
dV = vapor density, lb/ft³
k = 0.35 ft/s (when the drum includes a de-entraining mesh pad)

Then A, the cross-sectional area of the drum, in ft² = (vapor flow rate, in ft³/s) / (vapor velocity V, in ft/s)
and D, the drum diameter, in ft = ( 4 A / 3.1416 ) ^0.5

The GPSA Engineering Data Book recommends the following k values for vertical drums with horizontal mesh pads (at the denoted operating pressures):

0 psig: 0.35 ft/s
100 psig: 0.35 ft/s
300 psig: 0.33 ft/s
600 psig: 0.30 ft/s
900 psig: 0.27 ft/s
1500 psig: 0.21 ft/s

GPSA Notes:
1. K = 0.35 at 100 psig; subtract 0.01 for every 100 psi above 100 psig
2. For glycol or amine solutions, multiply above K values by 0.6 – 0.8.
3. Typically use one-half of the above K values for approximate sizing of vertical separators without mesh pads.
4. For compressor suction scrubbers and expander inlet separators, multiply K by 0.7 – 0.8

The drum should have a vapor outlet at the top, liquid outlet at the bottom, and feed inlet at somewhat above the half-full level. At the vapor outlet, provide a de-entraining mesh pad within the drum such that the vapor must pass through that mesh before it can leave the drum. Depending upon how much liquid flow you expect, the liquid outlet line should probably have a level control valve.

As for the mechanical design of the drum (i.e., materials of construction, wall thickness, corrosion allowance, etc.), use the same methodology as for any pressure vessel.

Note that the GPSA values of k are for vertical drums with horizontal mesh pads, and that the GPSA recommends that those values be divided by 2 if the drum has no mesh pads.

[Technocrat]

dear jprocess,

for more information on mist eliminators and coalescers and help from the vendors please visit www.koch-ottoyork.com.

DEMISTER is a registered trademark of KOCH-OTTO YORK and should not be used freely. you should call it wire mesh type mist eliminator and not a DEMISTER.

regards.