Foaming/flooding distillation

Foam Flooding. In enhanced oil recovery, the process in which a foam is made to flow through an underground reservoir. The foam, which may be either generated on the surface and injected or generated in situ, is used to increase the drive fluid viscosity and improve its sweep efficiency. In refinery distillation and fractionation towers, the occurrence of foams which can carry fiquid into regions of the towers intended for vapour. 

Equation 1 above stales that a tray will become less efficient due to incipient jet flood when the pressure drop per tray, expressed in inches of liquid, equals 22% to 25% of the tray spacing. The inches of liquid term assumes the liquid is deaerated. Of course, the liquid in the downcomers and on the tray decks is closer to a froth than to a flat liquid. The more highly aerated the liquid is (i.e. the more foamlike it becomes), the greater will be the depth of liquid corresponding to a measured external pressure drop. Hence, liquids which foam in distillation columns (such as dirty amine and ethane-rich fractionators) reach their incipient jet flood point at pressure drops below the 20% indicated in Equation 1. 

Note that no derating was used here. The previous flood calculation was derated because of the foaming tendency at high pressure. This is not taken into account in the interpolation, which is based on data at lower pressure. On the other hand, the pressure drop criterion used applies specifically for high-pressure distillations, and should therefore contain any nseded derating. 

Fig. 2-4. Examples of typical scan profiles obtained for various problems met on distillation columns, respectively from up and left to bottom and right normal column, collapsed tray, flooding, entrainment, weeping and foaming (IAEA, 2002).

A common example of foam formation in the bottom of a fractionator inducing flooding occurs in a crude preflash tower. In this case, stable foam accumulates in the bottom of the column as a consequence of the "flow improver" chemicals added to crude oil. These chemicals reduce pressure drop in the crude pipelines. Once the foam level rises to the feed inlet nozzle, the trays flood and black distillate is produced. Please see Chapter 18 (Preflash Towers). 

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