Liquid flooding problem in distillation columns
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Why does the temperature difference in a distillation column decrease when flooding occurs? Why does the temperature at the top of the tower rise? Seek guidance from experts
This post was last edited by CHANGBAISHI on 2018-12-19 08:26. In a distillation column, flooding occurs when the liquid flowing downward is suspended by the rising gas. The normal operation of distillation relies on the rising gas overcoming the resistance created by the liquid flowing downward, thereby enabling mass and heat transfer to take place. As this resistance is overcome, the liquid becomes suspended (slugging), reducing the resistance of the liquid to the rising gas. The ability of rising gas to transfer mass and heat with the liquid decreases, and the temperature measured at the top of the tower rises compared to normal conditions. It is necessary to understand the mechanism behind flooding, avoid its occurrence, and address recovery after it happens. It’s meaningless to study the changes in various components after damage.
There are two types of flooding: one is when the air flow velocity is too high, causing the liquid to be carried away； Another scenario is the accumulation of liquid inside the downcomer; the liquid cannot pass completely through it, which causes the liquid level to rise and overflow from the distributor. The phenomenon you are referring to is the first type; it may be due to too low a reflux rate or too high an evaporation rate, which prevents effective mass and heat transfer between the liquid phase and the gas phase. As a result, the temperature difference throughout the tower is small, and the temperature at the top of the tower rises.
Foaming is a backflow of gas and liquid; the gas and liquid present above the tower can lower the temperature at the bottom of the tower and increase the reflux rate. It is necessary to resolve the foaming issue first, before controlling the rate of temperature increase