What is the difference between flooding and tower flooding?

Liquid flooding: In practical operation, if both the gas and liquid loads are too high, the area of the downcomer is insufficient, and the gas velocity is high enough to prevent liquid from leaking through the valve openings. This results in a blockage of the liquid flow, causing the liquids on several layers of trays to merge together. This phenomenon is known as \"liquid flooding\" or \"tower flooding\". The relationship curve between the flow velocities of the gas and liquid phases at the onset of flooding is called the flooding line. When flooding is severe, liquid can emerge from the top of the tower. Foam formation can be prevented by increasing the cross-sectional area of the downcomer \"but this reduces the number of floating valves arranged on the tray, thereby decreasing the gas flow capacity\", controlling the reflux rate, and improving the tray design. Reference suggested: http://bbs.hcbbs.com/viewthread.php?tid=540240

In distillation operations, the liquid on the lower trays surges upward to the upper trays, disrupting the normal operation of the tower; this phenomenon is known as flooding. The cause of flooding is mainly due to the steam rising inside the tower at an excessive speed, exceeding the maximum allowable speed. Furthermore, in distillation operations, it is common to encounter a situation where the liquid load is too high, causing the liquid level in the overflow pipe to rise to such an extent that the liquids on the upper and lower trays become connected, thereby disrupting the normal operation of the tower; this is also a form of flooding. Both of the above phenomena are types of flooding, but they are caused by different reasons. During the distillation process, liquid gradually accumulates above a certain tray, eventually filling part of the tower section and obstructing the rising gas. This prevents proper mass and heat transfer between the gas and liquid phases, a condition known as tower flooding. Phenomenon: When the tower is flooded, the temperature at the top of the tower decreases, the liquid level in the reflux tank drops, while the liquid level and pressure at the bottom of the tower increase.

When the liquid flow rate on the tray is high, the upward velocity of the vapor is high, and the pressure drop across the tray is significant, the liquid cannot flow downward through the downcomer. As a result, the liquid continues to accumulate on the tray, and the liquid layer keeps rising until the entire space of the tray is filled with the gas-liquid mixture, leading to a phenomenon known as tray flooding. This completely destroys the multiple inverse internal contacts between gas and liquid, rendering distillation ineffective. There are many factors that can cause flooding, but the main ones include the following: (1) At high gas-liquid loads, the pressure drop of the gas as it passes through the tray is very large, which causes the downcomer to rise and reach the upper tray, leading to flooding. (2) When the liquid and gas loads on the tray are high and the liquid velocity is high, bubbles do not have enough time to separate, which increases the resistance to the flow of liquid through the downcomer. Alternatively, due to improper design, the area of the downcomer is too small, causing the liquid level inside it to rise and leading to flooding. (3) At very high gas velocities and small tray spacings, a large amount of liquid entrainment occurs, leading to an increasing amount of liquid flooding. {4) Overflowing caused by installation, maintenance, or other reasons. Foaming can be caused by issues such as a clogged downcomer or an inability to maintain a liquid seal, which allows air to enter. In simple terms, tower flooding occurs when the gas-phase load on the tower is too high, resulting in overheating and overpressure at the top of the tower.