Chemical Engineering Interview Question:

How do you design a vapor-liquid separator or a flash drum?

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The size of a vapor-liquid separator should be dictated by the anticipated flow rate of vapor and liquid from the vessel. 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).

At the vapor outlet, provide a de-entraining mesh section within the vessel such that the vapor must pass through that mesh before it can leave the vessel. Depending upon how much liquid flow you expect, the liquid outlet line should probably have a level control valve.
Submitted by: Administrator