Conceptual difference between mist entrainment and foam entrainment
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Dear sea friends, I have a question for everyone: I’m not sure whether mist entrainment and foam entrainment are the same thing If foaming occurs on the tray, is it a phenomenon of foam entrainment? Can mist entrainment cause foaming?
Foam entrainment is the phenomenon in plate distillation columns where rising vapor carries misty liquid droplets from one tray to the upper trays. Foam entrainment occurs when liquid enters the overflow tube; since the foam has not yet had time to separate completely from the liquid, it often enters the overflow tube along with the liquid and flows to the next tray in the tower. 【Mist entrainment is upward. Foam entrainment is downward. 】This is the fundamental difference.
Foam entrainment is liquid backmixing, while bubble entrainment is gas backmixing.
Can both of these cause flooding? There’s another question: does the foaming phenomenon on the tray constitute flooding?
Liquid flooding refers to the situation in a distillation column where, for various reasons, the liquid phase accumulates beyond the available space. Foaming can be divided into downcomer foaming, mist entrainment foaming, etc. Therefore, both mist entrainment and foam entrainment can lead to flooding.
Oh, so what causes that foaming phenomenon? We have a packed tower, and our supervisor suspects that foaming is occurring on the tray levels. But the instruments don’t show any changes; in fact, the pressure at the bottom of the tower rises intermittently
Foaming generally does not occur in packed towers; the packing can serve as a demister. Intermittent increases in pressure at the bottom of the tower are related to the output and reflux, as well as to the cooling water used in the condenser. Insufficient backflow pressure difference can cause intermittent backflow, or conditions such as air blockages in the product receiving tank can lead to intermittent increases in pressure.