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Analysis and treatment of water ingress in molecular sieve adsorbers. In many air separation units across the country, water ingress has occurred while these units were in operation within their circulating cooling water systems or during cleaning processes; in some cases, this led to the freezing and cracking of the plate units in the main heat exchangers. The author believes that the main cause of these failures is the neglect of the particularities of the oxygen production process during online cleaning or production, as well as the use of cleaning agents or water treatment methods that are not suitable for this process ； During online cleaning or operation, no effective measures have been taken to prevent water from entering the air separation equipment. The auxiliary oxygen production plant of Honghe Iron and Steel Co., Ltd. uses KDON-6500/6500 type air separation equipment manufactured by Kaifeng Air Separation Group Co., Ltd.; it came online on March 28, 2005. The circulating cooling water system operates on a closed-loop basis, with a circulation volume of 2535 m3/h, a water supply pressure of 0.35 MPa, and a water supply temperature of ≤35°C. The amount of fresh water added to the system is 25 m3/h. The new water is supplied by the water source station of Honghe Iron and Steel Co., Ltd. The treatment of circulating cooling water is carried out in collaboration with a water treatment chemicals manufacturer, who is responsible for monitoring water quality and determining the appropriate dosage of chemicals to be used. The main chemicals employed are scale inhibitors and biocides. 1 Symptoms of water-related problems: On August 25, 2005, the chemical manufacturer requested that 75 kg of biocidal and algaecidal agents as well as 50 kg of scale-inhibiting and release-control agents be added once per week. At 9:30 on August 31, 2005, the oxygen production water pump station added 50 kg of biocidal and algaecidal agents to the water system tanks. Due to the large number of novices among the operators and their lack of practical experience, they failed to pay attention to changes in the gas pressure entering the air separation unit. It was not until around 10:30 that the operators noticed that the gas pressure entering the unit had risen to 0.53 MPa; they immediately took measures to maintain pressure and release excess gas using the air compressor ； At 11:15, the operator on duty noticed that the pressure at the outlet of the air compressor was continuously rising. By 11:45, the pressure of the gas entering the air separation unit had risen to 0.53 MPa, while the volume of air processed dropped to 28,000 m3/h. The pressure throughout the air separation unit decreased, with the pressure in the upper tower falling to 49 kPa; as a result, the amount of gas flowing back as product decreased. Due to a lack of understanding of the equipment, the operator mistakenly thought that the switching valve of the molecular sieve purification system was not functioning. At 12:05, an experienced technician arrived at the site, reviewed the on-site records, and determined that the molecular sieve purification system contained water, prompting an immediate emergency shutdown of the air separation equipment. Inspection revealed that the No. 2 molecular sieve adsorber was severely contaminated with water; a large amount of water flowed out from the blow-off valve. It took over 30 minutes to drain water from this molecular sieve adsorber, and the water contained a significant amount of foam ； There is a large amount of foam accumulated on the surface of the water in the pool, reaching up to 20 cm high. 2 Causes of water carryover: Based on the foam generated in the tank and the occurrence of water carryover by the molecular sieve, it was determined that the cause was water quality issues. Due to the pharmaceutical manufacturers’ lack of familiarity with the processes involved in treating oxygenated water, large amounts of biocides and algaecides were added to the water at once. These chemicals reacted vigorously with the cooling water through hydrolysis, and since defoamers were not added in a timely manner, the hydrolysis products combined with surfactants to form large amounts of foam. The foam enters the air-cooled tower along with the circulating cooling water; once it has accumulated to a certain extent in the tower, it moves into the molecular sieve purification system together with the air, causing the molecular sieves to lose their adsorption capacity. As a result, water enters the air separation tower, leading to this water-inclusion incident. 3 Measures for dealing with water-related faults: After the air separation unit is shut down, the following actions should be taken: (1) Close the inlet guide vanes of the water-cooled air compressor to reduce the air flow, and maintain a pressure of 0.52 MPa behind the air compressor. (2) Use air activated by a water-free molecular sieve adsorber to activate and regenerate the molecular sieve in the water-containing 2nd molecular sieve adsorber; repeat this process of activation until the requirements of the process are met ； Then, use pure gas to thoroughly warm and thaw the entire air separation unit. Given that the molecular sieve retains water for a long time, which reduces its adsorption capacity, the activation and regeneration temperature of the molecular sieve is set at 200°C. At the same time, the overall activation and regeneration time as well as the gas flow rate are adjusted to increase the cold blowing time and the volume of gas used for cold blowing. After the molecular sieve is activated to meet the required standards (with a dew point of -60°C in air and a carbon dioxide content of ≤1×10‑6), and considering the possibility of water entering the main heat exchanger, the entire air separation tower is subjected to thorough drainage and heating. (3) Increase the amount of fresh water added to the tank, reduce the concentration of chemicals in the circulating cooling water, and simultaneously add antifoam agents to the tank to eliminate foam. (4) Install a trace water detector on the main gas outlet pipe of the molecular sieve purification system to monitor changes in trace water content in the air. After treatments such as molecular sieve activation and heating of the air separation tower, the air separation equipment was restarted and put into operation at 2:45 on September 7, 2005. At 20:50 on the same day, the equipment began to produce oxygen successfully, with an output of 6,450 m3/h and an oxygen purity of 99%. 7%. In this malfunction, due to the prolonged time during which the molecular sieve in the No. 2 molecular sieve adsorber was exposed to moisture, 1.8 tons of molecular sieve were added based on the results of its activation and regeneration. After restarting the air separation unit, the carbon dioxide concentration in the air exiting the No. 2 molecular sieve adsorber was kept within the range of 0.35–0.45×10-6, meeting the design standard of ≤1×10-6. During the normal operation of the air separation unit, the switching time is gradually restored to normal values in accordance with changes in carbon dioxide levels. It has been in operation for half a year now, and all parameters show normal values. 4. Experience Summary: After this water intrusion incident occurred, although appropriate and effective measures were taken, the air separation equipment was still forced to shut down for 8 days, resulting in significant economic losses. After reviewing the incident, some operational experiences were gained. (1) A professional water treatment manufacturer with experience in oxygenated water treatment must be selected. (2) Install one DN25mm discharge ball valve at the bottom of each molecular sieve adsorber to facilitate the inspection of its operation; strictly follow the technical operating procedures and regularly check the discharge condition of the adsorbers. (3) Strengthen staff skill training, improve operating procedures, and establish and refine various systems as well as emergency measures. (4) Existing problems: As it is a newly established facility, the capabilities for automatic control maintenance are relatively weak, resulting in an unreasonable switching procedure for the molecular sieve purification system. It is manifested as: when the opening degree of the adsorber pressurization valve is ≤23%, the pressure in the adsorber remains unchanged ； When the opening degree of the adsorber pressurization valve is ≥23%, the pressure in the adsorber rises rapidly, causing a quick drop in the pressure at the outlet of the air compressor as well as in the air cooling tower. This can lead to significant fluctuations in the operation of the air separation equipment, and it is also a major cause of water contamination in such equipment. If this valve is changed to online split-control, it can reduce fluctuations in the operating conditions of the air separation unit.