Chimney trays are used for proper distribution of gas for the internals of its upper part, collection and mixing of liquid for exit or internal reflux and liquid holdup. In columns containing acne or grids, especially in vacuum towers where pressure drop is critical, proper design of these trays is necessary to create uniform gas distribution while minimizing pressure drop. If trays are used on top of a chimney tray, gas distribution is not important, as the pressure drop of the trays normally evens out the steam flow. Chimney tray should be used in the following cases:
• Considerable holdup of liquid is required, such as where water settling is required.
• When leakage cannot be tolerated for process reasons, including in water washing sections where leakage into amine or caustic solutions is unacceptable.
