Operation and maintenance of packed tower equipment

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A packed tower is a common gas-liquid contact device, widely used in industries such as chemicals, petroleum, pharmaceuticals, and environmental protection. It achieves mass and heat transfer between gas and liquid by filling the tower with a packing layer of a certain height. The following provides a detailed introduction to the operation and maintenance of packed tower equipment. I. Installation of the packing 1.1 Preparations before installing the packing: A thin layer of oil covers the surface of the new packing; it is necessary to determine the properties of this oil and remove it before starting up the equipment. Carbon steel packing should be stored in a dry, enclosed area, and oil should not be removed from it in advance to prevent rust. New ceramic fillers and those that have been refilled should have any fragments removed from them; sometimes these fragments have to be taken out manually one by one. Bulk ceramic fillers are bound to get damaged during transportation, but larger pieces of broken filler can still be used. Their flux will decrease and the pressure drop will increase, but the separation efficiency will not decline. 1.2 Installation of bulk packing: Ceramic packing and non-carbon steel metal packing should be filled using the wet method whenever conditions permit. Using wet filling, after installing the support plates, water is filled into the tower, and the packing is gently poured into the water from above; the packing floats down in the water, with the water level being more than 1 meter above the packing. Wet filling can reduce filler damage and deformation. Wet filling also improves the uniformity of the bulk filler, reduces the filler usage by about 5%, increases the filler flux, and decreases the pressure drop. When using dry packing, the filler should always be poured from a certain height above the packing layer; when dry packing is employed in towers with large diameters, it is sometimes necessary for a person to stand on top of the packing layer to add the filler. It should be noted that people must not stand directly on the packing to prevent it from being compressed and deformed as well as from having uneven density; wooden planks can be placed on the packing to distribute the load. Whether using wet packing or dry packing, the filling should proceed from the tower wall toward the center to prevent bridging of the packing at the wall; the packing should not be compressed too tightly to avoid uneven density due to deformation. After the packing in each section has been installed, it is necessary to check whether the upper part of the packing is level; if there are any unevenities, they should be leveled out. 1.3 Installation of structured packing: For small towers with a diameter of less than 800 mm, structured packing is usually made in the form of complete discs that are inserted through flange holes. For towers with a diameter greater than 800 mm, the structured packing is usually divided into several pieces, which are inserted into the tower through manholes and arranged in a circular shape inside. Whether arranged as a single circle or in separate pieces, their diameter must be smaller than that of the tower; otherwise, they cannot be installed. The gap between the packing and the tower wall should be determined based on the type of anti-wall-flow ring used, and each packing manufacturer typically has its own standards. Typically, to prevent gas-liquid wall flow caused by the gap between the packing and the tower wall, a wall-flow prevention ring is installed in this gap. This baffle flow ring can be integrated with the packing or assembled separately inside the tower. II. Operation of the packed tower The operation of a packed tower is roughly the same as that of a plate tower. For more details: The main difference between the operation of a packed tower and a plate tower lies in ； Firstly, the packed tower should primarily ensure uniform liquid distribution, in order to prevent localized excessive flow over the packing from affecting the mass transfer efficiency ； Secondly, it is necessary to control pressure changes properly to avoid excessive gas phase variations that could cause damage to the packing pressure plates. III. Daily inspection of the packing tower: The daily inspections carried out by the operator on the packing tower should include the following items. Conduct regular inspections and cleanings, replace the showerheads or overflow pipes to ensure they are not clogged, damaged, or misaligned, so that the spraying mechanism can distribute the liquid evenly over the packing. The pressure and flow rate of the gas entering the tower must not be too high; otherwise, the packing will be disrupted or carried away, severely reducing the efficiency of contact between the gas and liquid phases. Control the inlet air temperature to prevent the plastic filler from softening or deteriorating, which could increase airflow resistance. The liquid entering the tower must not contain any impurities; if it is too dirty, it should be filtered to prevent these impurities from clogging the gaps in the packing. Conduct regular inspections, apply anti-corrosion measures, and clean the tower walls to prevent defects such as corrosion, erosion, and scaling. Regularly check the degree of corrosion on the grating; if it becomes thin due to corrosion, it should be replaced to prevent it from falling off. Regularly measure the thickness of the tower wall and check for any leaks in the tower; repair any issues found promptly. Check the liquid level regularly to ensure that the gas inlet is not submerged, thereby preventing vibrations and abnormal noises. Regularly monitor the settlement of the foundation and check whether the tower is tilting. Maintain the integrity of the tower’s paint, ensure there are no scratches on its surface, and keep it clean. Regularly open the drain valve to discharge the dirt and broken packing accumulated at the bottom of the tower. When out of use in winter, the liquid should be drained to prevent freezing. If the pressure drops suddenly, the possible cause at this time is a leak. If the pressure rises, possible causes are increased packing resistance or blockages in the equipment pipes. If the anti-corrosion layer and insulation layer are damaged, it is necessary to inspect the outdoor insulation equipment, paying special attention to areas where rainwater penetrates at temperatures below 100°C, areas where the insulation material has deteriorated, and areas that have been subjected to prolonged exposure to trace amounts of corrosive fluids. Inspection and patrol items and methods during the operation of packed tower equipment: Inspection item 1: Operating condition inspection methods: ① Check pressure gauges, thermometers, and flow meters; ② Examine equipment operation records. Judgment and explanation of problems: ① Sudden drop in pressure: Leakage in the tower section flanges or gaskets; ② Rise in pressure: Increased packing resistance or blockage in the equipment pipes. Inspection item 2: Material changes. Inspection methods: ① Visual inspection, ② Analysis of material components. Judgment and explanation of issues: ① Damage to internal components or operating conditions, ② Presence of foreign substances or impurities. Inspection Item 3: Corrosion and insulation layers. Inspection method: Visual inspection. Judgment and description of issues: For outdoor insulation equipment, check the areas where rainwater penetrates and the spots affected by corrosion. Inspection Item 4: Inspection method for auxiliary equipment: Visual inspection. Judgment and description of issues: ① Check whether the connection bolts at the pipe and valve station are loose or deformed; ② Check whether the pipe supports are deformed or loose; ③ Check whether the manholes are corroded or deformed, and whether they function properly. Inspection item 5: Foundation. Inspection method: Visual inspection, use of a level. Issues and explanations: If the foundation settles or develops cracks, it can cause the tower to tilt. Inspection item 6: Tower body. Inspection methods: ① Visual inspection, ② Inspection for foaming agents, ③ Gas detector inspection, ④ Thickness gauge inspection. Judgment and explanation of issues: Cracks and leaks are likely to occur at the tower body, flanges, joints, and support beams. IV. Diagnosis and Treatment of Common Faults in Packed Towers Failure of a packed tower to meet its design specifications is referred to as a fault. Failures in packed towers can be caused by a single factor or by multiple factors simultaneously. Once a failure occurs, it is necessary to identify the cause as quickly as possible in order to resolve the issue at the lowest cost. A fault diagnostician should have a thorough understanding of the design of the tower and its associated equipment, as well as related aspects; the more knowledge one has, the easier fault diagnosis becomes. Fault diagnosis should start with the simplest and most obvious aspects, and the following steps can be followed. If the fault is severe and affects safety, environmental protection, or prevents production from continuing, the machine should be stopped immediately to analyze and address the issue. If the fault is not severe, it should continue to operate while minimizing damage to safety, the environment, and profits. Data and various characteristic phenomena are collected during operation; without affecting production, certain operational changes are made to obtain more data and characteristics. If possible, a full reflux operation can also be carried out to provide analysis data for fault diagnosis. Analyze the past operation data of the tower, or compare it with similar units, to identify the similarities and differences. If the tower’s operation deteriorates, identify the time of the change as well as the differences before and after it, in order to determine the cause. Fault diagnosis should not be limited to the tower itself; the devices upstream of the tower as well as associated equipment such as pumps, heat exchangers, and pipelines should also be included in the analysis. Incorrect gauge readings and analysis data can lead to improper operation of the tower. Whenever a fault occurs, cross-analysis of the instrument readings and analysis data is conducted first, with particular attention paid to material balance, heat balance, and phase balance analyses in order to determine their accuracy. Some failures are caused by poor design. When checking for design-related faults, one should first examine the drawings to identify any obvious errors, and analyze whether such errors are the cause of the fault ； Secondly, fluid dynamics calculations must be carried out to determine whether there is any operation that exceeds the established limits in a certain area ； In addition, it is also necessary to perform simulation calculations on the actual mass transfer to assess the efficiency of the actual mass transfer process. Common faults and troubleshooting methods for packed towers: Fault symptom 1: Scaling on the working surface. Causes: ① Impurities present in the material being treated, ② Crystals precipitating within the material being treated, ③ Scaling caused by hard water, ④ Corrosion of the equipment, resulting in corrosion products ； Treatment methods: ① Improve filtration quality, ② Remove crystalline substances and scale, ③ Eliminate scale, ④ Take anti-corrosion measures. Fault symptom 2: Loss of sealing capability at the connection ； Causes: ① Looseness of the flange connection bolts, ② Local over-tightening of the bolts resulting in deformation, ③ Vibration of the equipment causing the bolts to loosen, ④ Fatigue damage to the gasket, ⑤ Corrosion of the washers by the medium, ⑥ Uneven lining on the flange surface, ⑦ Warping of the welded flange ； Treatment methods: ① Tighten the bolts, ② Replace the deformed bolts, ③ Eliminate vibrations and tighten the bolts, ④ Replace the deteriorated washers, ⑤ Replace with corrosion-resistant washers, ⑥ Machine the uneven flange, ⑦ Replace with a new flange. Fault symptom 3: Thinning of the tower thickness ； Cause: During operation, the equipment is subjected to corrosion, erosion, and friction by the medium. Solution: Use it under reduced pressure, repair the corroded parts, or replace it with a new one. Fault phenomenon 4: Local deformation of the tower. Causes: ① Local corrosion or overheating of the tower, which reduces the strength of the material and leads to deformation of the equipment ； ②The openings lack reinforcement, and weld stress concentration causes plastic deformation of the material ； ③When the operating pressure of a device under external pressure exceeds the critical pressure, the device becomes unstable and deforms. Treatment methods: ① Prevent local corrosion or overheating, ② Correct deformation or cut off the deformed area and weld in a patch, ③ Maintain normal operation. Fault phenomenon 5: Cracks appear in the tower. Causes: ① Increased local deformation; ② Internal stresses during welding; ③ Too small bending radius of the head transition arc; ④ Hydraulic impact; ⑤ Defects in the structural material; ⑥ Effects of vibration and temperature differences; ⑦ Stress corrosion. Treatment method: Repair the cracks. Fault phenomenon 6: Packing is present inside the condenser. Cause: The packing pressure plate has shifted. Treatment method: Fix the pressure plate properly. Fault phenomenon 7: Slow feeding. Cause: The feed filter is blocked. Treatment method: Disassemble and clean it