Liquid Knockout
Liquid Knockout
(OP)
I need to program some liquid knockout calculations into a piece of software I am writing to simulate fluid passing through a compressor. I am looking for either a library that performs liquid knockout calculations, or for a good source on how liquid knockout is calculated for gas mixtures. If you know of where either of these are, or where I might try looking, th help would be greatly appreciated.
Evan
Evan





RE: Liquid Knockout
RE: Liquid Knockout
This is a few months late, but perhaps it will still be useful.
The size of a flash drum (or knock-out pot, or vapor-liquid separator) 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).
For the maximum vapor velocity (which will set the drum's diameter), use the Souders-Brown equation:
Vmax = (k) [ (dL - dV) / dV ]0.5
where:
Vmax = maximum vapor velocity, ft/sec
dL = liquid density, lb/ft3
dV = vapor density, lb/ft3
k = 0.35 (when the drum includes a de-entraining mesh pad)
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 section 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.
Milton Beychok
(Contact me at www.air-dispersion.com)
.