Main reasons for flooding

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Foaming in tower equipment and its causes: At the onset of foaming, the pressure drop in the tower increases sharply, and its efficiency drops significantly. Subsequently, the operation of the tower was disrupted. The main factors that contribute to flooding are as follows: a. Backflow of liquid in the downcomer back to the upper tray. Due to the resistance exerted by the tray on the rising gas flow, the pressure above the lower tray is higher than that above the upper tray. Only when the static head corresponding to the height of the foam in the downcomer is sufficient to overcome this pressure difference can the liquid flow downward. When the liquid flow rate remains constant while the gas flow rate increases, the pressure difference between the lower and upper plates also increases, causing the liquid level in the downcomer to rise. If the gas flow rate is increased to such an extent that the liquid in the downcomer rises to the top of the weir, the liquid in the tube can no longer flow downward; instead, it begins to flow back upward toward the upper tray, causing liquid to accumulate on that tray. Additionally, as liquid is continuously fed into the tower from outside during operation, eventually the entire tower will be filled with liquid. This results in flooding. If the gas flow rate remains constant while the liquid flow rate increases, the resistance to the flow of liquid through the downcomer rises, and the liquid layer on the plate thickens, which increases the pressure difference between the upper and lower sides of the plate. All these factors cause the liquid level in the downcomer to rise, leading to flooding. b. Excess foam carried to the upper plate – The foam carried by the airflow to the upper plate can cause the liquid layer on the plate to thicken; under normal conditions, however, this increase is not significant. At a certain liquid flow rate, if the gas flow rate is increased to a certain level, the thickening of the liquid layer becomes significant (more liquid accumulates on the plate, and more bubbles appear and grow larger). The droplets carried away by the airflow through the thickened liquid layer increase further. This excessive entrainment of liquid foam reduces the distance between the top of the foam layer and the bottom of the upper plate. The entrainment of liquid foam continues to increase, with large droplets easily being ejected onto the upper plate; foam can also rise to that plate, until ultimately the entire tower is filled with liquid. Of the two reasons mentioned above that lead to flooding, excessive entrainment of liquid foam is the more common one.