Q&A on Purification Technology [027]

The phenomenon of liquid flowing back inside the tower is called flooding, and when flooding occurs, the pressure difference in the tower increases significantly. To avoid flooding, it is first necessary to control an appropriate liquid/gas ratio and space velocity. At the same time, it is necessary to prevent the liquid from foaming, improve the purity of the absorbent, and ensure that the tower plates are clean and free of contaminants.

In a distillation column or absorption tower, the gas and liquid phases flow in opposite directions. When the flow velocities of both phases are low, the flow of one phase is not affected by the other. As the flow velocities increase, some liquid droplets can be carried upward by the rising gas stream to the upper tray, resulting in foaming. The liquid phase can also carry some bubbles into the downcomer; this phenomenon of entrainment intensifies as the flow velocities increase, and in severe cases it can lead to blockages in the flow channels and reverse flow of liquid within the column. This phenomenon is known as flooding. Measures to prevent flooding by a sharp increase in tower pressure difference: (1) Control an appropriate liquid-to-gas ratio ； (2) Control the appropriate load ； (3) Ensure the liquid is clean and does not easily foam ； (4) Ensure the tray is clean and free of contaminants.

In a distillation column, when the liquid phase accumulates beyond the available space for various reasons, this phenomenon is known as flooding. Foaming can be classified into downcomer foaming, mist entrainment foaming, etc. 1. Try to increase the cross-sectional area of the downcomer, but this will reduce the opening area of the tray; improve the structure of the tray. 2. Reduce the pressure drop across the tray; ensure that the amount of liquid returning is not too large.

It occurs in distillation columns when, for various reasons, the liquid phase accumulates beyond the available space. Solutions: 1. Reduce the gas-phase load by lowering the feed rate, feed temperature, vacuum level, etc. 2. Reducing the liquid phase load can decrease the external reflux flow (by lowering the reflux ratio), and increasing the side-stream extraction can reduce the internal reflux flow and the liquid accumulation in the packing.

On the tray, the liquid from the upper tray flows down to the lower tray through the overflow pipe. As it moves downward, it must overcome various resistances, which requires a certain level of liquid to be maintained in the overflow pipe; as a result, the overflow resistance increases and the liquid level rises accordingly. When this increased level prevents the liquid from flowing from the upper tray to the lower tray through the overflow pipe, this phenomenon is known as flooding. Causes of flooding: excessive amount of rising gas and high gas temperature, too large a feed rate to the tower, blockage of trays or overflow pipes, and improper design or manufacturing of the trays. Addressing the above issues appropriately can prevent flooding.

The phenomenon of liquid flowing back inside the tower is called flooding, and when flooding occurs, the pressure difference in the tower increases significantly. To avoid flooding, it is first necessary to control an appropriate liquid/gas ratio and space velocity. At the same time, it is necessary to prevent the liquid from foaming, improve the purity of the absorbent, and ensure that the tower plates are clean and free of contaminants.

The phenomenon of liquid flowing back inside the tower is called flooding, and when flooding occurs, the pressure difference in the tower increases significantly. To avoid flooding, it is first necessary to control an appropriate liquid/gas ratio and space velocity. At the same time, it is necessary to prevent the liquid from foaming, improve the purity of the absorbent, and ensure that the tower plates are clean and free of contaminants.

The phenomenon of liquid flowing back inside the tower is called flooding. Control the appropriate vapor-liquid ratio and space velocity

In a distillation column or absorption tower, the gas and liquid phases flow in opposite directions. When the flow velocities of both phases are low, the flow of one phase is not affected by the other. As the flow velocities increase, some liquid droplets can be carried upward by the rising gas stream to the upper tray, resulting in foaming. The liquid phase can also carry some bubbles into the downcomer; this phenomenon of entrainment intensifies as the flow velocities increase, and in severe cases it can lead to blockages in the flow channels and reverse flow of liquid within the column. This phenomenon is known as flooding. Flooding is the limit of counterflow between the gas and liquid phases. When flooding occurs, the pressure difference and liquid level in the tower fluctuate: when the tower pressure difference rises sharply, the liquid level at the bottom of the tower drops ； And when the pressure difference drops suddenly, the liquid level rises sharply ； At the same time, the pressure in the tower will also fluctuate ； The purity of the product will decrease. Measures to prevent flooding: (1) Control an appropriate liquid-to-gas ratio ； (2) Control the appropriate load ； (3) Ensure the liquid is clean and does not easily foam ； (4) Ensure the tray is clean and free of contaminants.

In the counter-current movement of the gas, liquid, and solid phases, when the rising gas encounters excessive resistance, it supports the descending liquid droplets and thereby carries them away; this phenomenon is known as flooding. Try to increase the cross-sectional area of the downcomer, but this will reduce the opening area of the tray plates ； Improve the tray structure to reduce the tray pressure drop ； The control of the liquid return flow rate should not be too high.