Limiting Droplet Size For Separator Design According to GPSA Proposed K factors

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A gas liquid separator is used for bulk separation and mist eliminator i.e. vane type, mesh type, cyclone type) are used to promote liquid drop coalescence and separation from gas. Souder-Brown equation has been widely used in Oil and gas industry to size a gas liquid separator with and without mist eliminator.

Generally the K factor as proposed in GPSA has been used by many engineers. Following figure tabulate the K factor may be used for horizontal, vertical, vertical scrubber and others separator for special services.

On the other hand, there are no indication of the liquid droplet size can be removed. The following is intended to studies the limiting droplet size based on the K factor used for horizontal, vertical and vertical scrubber. In some event, it may be a useful information especially when there is droplet size limitation of downstream equipment i.e compressor.

For a droplet in free fall (gravity action), the droplet terminal velocity is as follow :

By arranging in the Souders-Brown equation :

And the K factor is as follow :

The drag coefficient (C') can be read from the following figure.

(Click to view large image)

where Re is Reynolds number as follow :

Basis

For a vapor and liquid with the following condition and properties :

• Pressure = Atmosphere
• Temperature = 40 degC
• Molecular Weight = 20-40
• Compressibility factor = 0.9
• Liquid density = 500 - 850 kg/m3
• K factor for horizontal separator is 0.06 -0.075 m/s
• K factor for vertical separator is 0.025-0.055 m/s
• K factor for vertical scrubber is 0.018 -0.039 m/s

Results
The limiting liquid droplet size are

Horizontal separator without mist eliminator : 350 -540 micron
Vertical separator without mist eliminator : 160 -400 micron
Vertical scrubber without mist eliminator : 125-290 micron


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