Thread Content
A packed tower is a mass transfer device that uses the packing inside the tower as the contact element between the gas and liquid phases. It has many advantages such as high throughput, high efficiency, low voltage drop, and low liquid retention. However, packing towers also fail quite often. How can they be diagnosed and repaired? Reason 1: Issues with the liquid distributor: 1. Unreasonable design; 2. Corrosion of the distributor leading to leakage; 3. Poor level of installation; 4. Exceeding operational limits; 5. Blockage of the distributor. Symptoms of the fault: Low efficiency of the entire tower, with the pressure drop being within acceptable limits as per the design specifications. Generally, it is possible to determine which distributor is having a problem based on the separation efficiency of each section of the tower. The low efficiency caused by 1, 3, and 4 can be improved by increasing the reflux. If the low efficiency is caused by 2 and 5, the distributor needs to be repaired. Solution: Improve the design and remanufacture the distributor ； Repair or replace the distributor ； Reinstall and adjust the levelness ； Adjust the density of the distribution holes ； Clear the blockage. Reason 2: Uneven gas distribution, usually due to the absence of a gas distributor at the vapor inlet at the bottom of the tower. Fault phenomenon: The overall efficiency of the tower is low, but the design error in the tower pressure drop is not significant. Generally, reducing the gas-phase load or increasing the reflux can significantly improve separation efficiency. Furthermore, foam entrainment is severe, and the pressure drop in the tower is high during high-load operation. Solution: Install an additional gas distributor. Reason 3: Leakage from the liquid collector. 1. The downcomer is too small or there is high inlet resistance, resulting in difficulty in liquid flow; as a result, the liquid leaks through the upcomer ； 2. Poor sealing, resulting in liquid leakage or splashing from the louver-type collector. Fault symptoms: Poor separation efficiency of the tower, high pressure drop, and low flux. Solution: 1. Increase the diameter of the downcomer or expand the size of its inlet ； 2. Improve the angle and size of the liquid barrier to prevent leakage. Reason 4: The liquid distributor was installed in the wrong position within the tower. Fault phenomenon: The separation efficiency is high when the tower operates at low load. However, the separation efficiency is poor under high-load operation. Solution: Reinstall the liquid distributor according to the design requirements. Reason 5: Quality issues with the packing installation: 1. The bulk packing is filled too loosely, resulting in large gaps between the structured packing trays or between them and the tower walls ； 2. Deformation or damage of the filler. Fault symptoms: 1. Low tower pressure drop and poor separation efficiency ； 2. The tower pressure drop is high, resulting in a low operating limit. When operating at low load, the tower has a high separation efficiency. Solution: Reinstall the tower packing according to the design requirements. Reason 6: The packing is blocked by materials, etc., causing the plastic packing to soften. Fault symptoms: High resistance, poor separation efficiency, and low operational limit. Solution: Clean or replace the packing. Reason 7: The packing is corroded. Fault phenomenon: The tower pressure drop fluctuates greatly, and the separation efficiency is very poor. Solution: Use corrosion-resistant materials and replace the packing. Reason 8: The porosity of the packing support openings is low. Fault phenomenon: Low separation efficiency of the tower under high-load operation. At low load operation, the tower has high separation efficiency. Solution: Replace the filler support with one that has a high enough porosity. Reason 9: The opening rate of the packing pressing plate is low. Fault symptoms: Under high-load operation, there is a high voltage drop, low efficiency, and a tendency to flooding; under low-load operation, the tower operates normally. Solution: Replace the packing plate with one that has a sufficiently high porosity. Reason 10: Fillers of different types or models are installed in the wrong positions within the tower. Fault phenomenon: Failure to reach the design load. Solution: Reinstall the tower packing according to the design requirements. Reason 11: Reboiler issue: 1. Accumulation of non-condensable gas on the heating medium side ； 2. Poor drainage of the condensate from the heating medium ； 3. The liquid seal is poor, resulting in air leakage ； 4. In heat-siphon reboilers, blockages, low liquid levels, or high pipe resistance can result in too low a circulation rate ； 5. In heat-siphon reboilers, an excessively high liquid level results in a too large circulation volume. Fault symptom: Insufficient heating capacity, preventing the tower from reaching normal operating load. Treatment method: 1. Discharge non-condensable gas ； 2. Take measures to ensure the smooth discharge of condensate ； 3. Improve the liquid seal ； 4. Remove blockages, increase the reboiler liquid level or lower its installation height ； 5. Increase the installation height of the reboiler, or add orifice plates and control valves at the inlet. Reason 12: Heat exchange issues with the tower top condenser: 1. There is non-condensable gas on the condensation side ； 2. Scaling on the cooling medium side ； 3. Low cooling water flow rate ； 4. Poor drainage of condensate. Fault symptom: Low heat transfer capacity of the condenser. Treatment method: 1. Discharge non-condensable gas ； 2. Remove dirt ； 3. Increase the cooling water flow rate ； 4. Increase the diameter of the condensate discharge pipe. Reason 13: The temperature control at the feed inlet and above is set too high. Fault symptoms: 1. The content of heavy components at the top of the tower is high, while the content of light components at the bottom of the tower is lower than the specified value. 2. The light component content in the tower bottom is high, while the heavy component content at the tower top is lower than the specified value. Solution: Adjust the control point temperature. Reason 14: The output of products at the top of the tower is too low, resulting in an imbalance in system materials. Fault phenomenon: The light component content in the product from the tower bottom is too high, while the heavy component content at the tower top is lower than the specified value. Solution: Increase the yield of product at the top of the tower. Reason 15: Excessive recovery of product at the top of the tower, resulting in an imbalance of materials in the system. Fault phenomenon: The content of heavy components at the top of the tower is high, while the content of light components at the bottom of the tower is lower than the specified value. Solution: Reduce the amount of product taken from the top of the tower. Reason 16: The control scheme for the 16 towers is unreasonable. Fault symptom: Large fluctuations in tower operation. Solution: Change the control scheme. Reason 17: The liquid level in the tower bottom vessel is too high, flooding the gas inlet and causing foam entrainment. Fault symptoms: High tower pressure drop, low separation efficiency, and prone to flooding. Solution: Use a pump to restore the normal liquid level and implement reliable liquid level monitoring measures. Reason 18: The middle distillates accumulate at a certain point in the tower. Fault phenomenon: The tower experiences periodic local flooding, resulting in unstable operation. Treatment method: Add a line to extract the middle distillate. Reason 19: Liquid-phase foaming. Fault symptoms: The designed load cannot be achieved; the separation efficiency is high at low load levels, and the tower pressure drop is higher than the theoretically calculated value. Solution: Add antifoaming agents to reduce fluctuations in the gas-liquid load inside the tower. Reason 20: Design error or inaccurate basic data. Fault phenomenon: The equipment, control, and operation are all normal, but it fails to meet the design requirements. Solution: Review the design plan and recalculate. Summary: The above are the common fault diagnosis and treatment methods for packed towers. Since there are many reasons for these faults, it is also necessary to be familiar with the general steps for diagnosing and dealing with them. If the situation is serious, the operation should be stopped immediately for inspection. If it is not serious, the operating data of the tower must be analyzed and compared with those of similar units. Inspect the upstream units and auxiliary equipment of the tower, such as pumps, heat exchangers, and related process pipelines. Cross-verify the gauge readings and analytical data, paying special attention to conducting tower material balance, heat balance, and phase balance analyses. If the fault is caused by the design, it is necessary to refer to the drawings, and then conduct fluid dynamics calculations this week to determine whether the tower is operating within its normal range. Finally, it is also necessary to perform simulation calculations for the actual mass transfer process in order to determine the tower efficiency.