1、 Definition of Leakage

In the operation of the distillation tower, the liquid does not flow down the tray step by step, but leaks directly to the lower layer through the tray openings (or liquid bypass caused by a malfunction in the downcomer), resulting in insufficient gas-liquid contact, a significant decrease in tower separation efficiency, and substandard product purity.

2、 Core cause of leakage

1. Low gas phase load

• The rising steam velocity inside the tower is insufficient to support the formation of a stable liquid layer on the tray, and the liquid leaks down from the sieve holes/float valve gaps;
• Typical scenarios: Low load operation of the device, sudden decrease in feed rate, and insufficient heating power of the reboiler.

2. Tower plate structure issues

• High tray opening rate: too many sieve holes/float valves, insufficient liquid retention;
• Blockage/Unreasonable design of downcomer: The cross-sectional area of the downcomer is too small and there is accumulation of debris, which causes the liquid to be unable to be discharged in a timely manner, resulting in overflow and leakage due to high liquid level;
• Installation deviation of tray: tray levelness exceeds the standard (≤ 3mm/m), weir height is inconsistent, and local liquid layer is too thick, causing leakage.

3. Abnormal operating conditions

• Excessive liquid load: sudden increase in feed rate, excessive reflux ratio, thickness of liquid layer on the tray exceeding the design upper limit, liquid leaking down from the edge or opening of the tray;
• System pressure fluctuations: Sudden changes in top/bottom pressure can cause unstable gas velocity and disrupt gas-liquid equilibrium;
• Changes in material properties: increase in feed viscosity, decrease in surface tension, deterioration of liquid flowability, and easy accumulation and leakage.

3、 Basis for judging leakage

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2. Decreased separation efficiency: the purity of the product at the top of the tower decreases, and the content of light components at the bottom of the tower increases;
3. Abnormal operating parameters: The tower pressure is stable, but the reflux ratio needs to continue to increase to maintain product quality, and the bottom temperature of the tower is too high;
4. On site observation: The vibration of the tower body has decreased, the condensation capacity of the condenser at the top of the tower has fluctuated, and the liquid level at the bottom of the tower has abnormally increased.

4、 Solution measures (sorted by priority)

1. Adjust operating parameters (quick effect)

• Improve gas phase load: increase the heating power of the reboiler, reduce the reflux ratio at the top of the tower, and increase the rising gas velocity;
• Stable liquid load: Control the feed rate and reflux ratio within the design range to avoid significant fluctuations;
• Adjust system pressure: maintain stable tower pressure and avoid sudden fluctuations in gas velocity.

2. Check and clean the components inside the tower

• Cleaning the downcomer: Remove the tray, remove scale and debris from the downcomer, and ensure liquid circulation;
• Correction of tray level: Adjust the tray level again to ensure consistent weir height and avoid local liquid layer thickness.

3. Optimize the tray structure (long-term solution)

• Adjust the perforation rate: replace the tray with a lower perforation rate to increase the liquid retention time;
• Improve the design of the downcomer: increase the cross-sectional area of the downcomer to enhance its liquid handling capacity;
• Change tray type: For systems prone to liquid leakage, the sieve plate can be replaced with a float valve tray or a guide sieve plate to enhance the stability of gas-liquid contact.

4. Control material properties

• Pre processing feed: removing solid impurities and viscous components from the feed, reducing material viscosity;
• Maintain feed temperature: Avoid excessively low feed temperature causing viscosity increase and affecting liquid flow.

5、 Preventive measures

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2. Control the operating load within 70% -110% of the design range to avoid long-term low load operation;
3. Regularly inspect and clean the components inside the tower to prevent scaling and blockage;
4. Buffer devices are installed in the feeding and reflux systems to reduce flow fluctuations;
5. Regularly calibrate instruments (such as flow, pressure, and temperature instruments) to ensure accurate monitoring of operating parameters.