What are the effects of an underfilled tower and an overfilled tower, and what are the solutions?

Tower surging occurs when the temperature at the bottom of the tower is too high or the reflux is insufficient, causing a large amount of material to be pushed out from the top of the tower. This leads to the reflux tank becoming full, pressure rising, and even the safety valve opening. This treatment simply and immediately reduces the bottom temperature of the tower significantly. Remember not to add reflux in this situation; the reflux tank itself contains hot material, and adding more reflux will increase the pressure in the tower.

A full tower means that the entire interior of the tower is filled with liquid, leaving no room for heat exchange, which makes it difficult to operate. Try to export some of the materials from the bottom of the tower and send them first to the tank for rejection. Re-refine after the tower is balanced.

When the tower is filled to capacity, this phenomenon is known as flooding: during normal operation of the tray, a certain thickness of liquid layer is maintained on the trays to facilitate mass transfer with the gas. If, for some reason, the liquid fills the space between the tray plates, disrupting the normal operation of the tower, this phenomenon is known as flooding. When the liquid flow rate on the tray is high and the velocity of the rising gas is high, the amount of liquid carried by the gas to the upper tray increases significantly, causing the space between the trays to be filled with a gas-liquid mixture. Eventually, the entire tower gets filled with liquid. This type of flooding caused by an excessive amount of liquid entrainment is known as entrained flooding. It is also called a tower rammer. When the liquid in the downcomer cannot flow downward smoothly, it inevitably accumulates within the tube, causing the liquid level to rise and exceed the top of the overflow weir. The liquid then connects the two plates, leading to an accumulation of liquid on the tray, which gradually rises upward until the tower is filled with liquid. This phenomenon of flooding caused by a full downcomer is known as downcomer flooding.

Hello, may I understand it this way? Backflow is cold material. If the bottom temperature, which already has a high reflux rate, is increased at this time, a large amount of liquid will vaporize, thereby exacerbating the increase in tower pressure.

Hello, I’m a beginner and would like to ask some questions. According to you, is full tower and liquid flooding in the downcomer the same thing? A full tower means that the liquid phase fills the space between the tray plates; this is related to the flow of the liquid phase being blocked by the downcomer, right?

Backflow is not necessarily cold backflow; for example, in re-refining oil, it is drawn from the upper tray and sent back to the lower layer without going through any cooling or heat exchange process； Phasing, backflow, flooding, etc. – these concepts can be easily understood by studying carefully the book *Technical Questions and Answers on Catalytic Cracking Units*.

A full tower means liquid backflow, and there are two types of liquid backflow. In one case, an excessive amount of gas carries the liquid from the lower trays to the upper ones, and when droplets fill the upper trays, liquid backflow occurs. A condition that occurs when the amount of liquid falling is excessive, exceeding the flow rate through the downcomer, resulting in the plates being filled with liquid and causing liquid backflow. The tower-ramming we often talk about is the first case. The main solutions are to reduce the volume of gas entering the tower, lower the temperature, and in severe cases, reduce the reflux appropriately

The space between the trays is already filled with liquid; increasing the reflux at this point will only lead to a worse situation. It’s more serious with a full tower

Tower flooding is related to the gas phase load and the processing volume; generally, high moisture content in the feed material, excessive gas injection, and high processing load can all lead to tower flooding. This condition can cause the side-stream oil to change color and result in substandard products. The solution is to reduce the gas-liquid load

When the tower is filled to capacity, this phenomenon is known as flooding: during normal operation of the tray, a certain thickness of liquid layer is maintained on the trays to facilitate mass transfer with the gas. If, for some reason, the liquid fills the space between the tray plates, disrupting the normal operation of the tower, this phenomenon is known as flooding. When the liquid flow rate on the tray is high and the velocity of the rising gas is high, the amount of liquid carried by the gas to the upper tray increases significantly, causing the space between the trays to be filled with a gas-liquid mixture. Eventually, the entire tower gets filled with liquid. This type of flooding caused by an excessive amount of liquid entrainment is known as entrained flooding. It is also called a tower rammer. A flooded tower is far more serious than a full tower.