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In the cold winter months, to ensure the safe operation of chemical plants, anti-freezing and anti-condensation measures are crucial. To strictly prevent all freezing incidents, anti-freezing measures should also be carried out in accordance with the principles of \"prevention first, suppression second\", based on the characteristics of the installation. Strengthen the receipt, delivery, use, and management of items that are prone to freezing or solidifying; take preventive measures in advance using standard methods; conduct thorough inspections in accordance with regulations; and address freezing issues properly in order to ensure safe production. I. Antifreezing methods: Common antifreezing and anti-condensation methods used in chemical plants include evacuation, insulation, heat tracing, and circulation. In winter, to prevent freezing and condensation, one or more of these methods should be employed, taking into account the operating conditions of the equipment and pipelines, as well as the problems that have occurred during previous antifreezing efforts and the relevant experience gained. 1. Empty. Methods for draining anti-freezing and anti-condensation systems can be roughly divided into three categories. The first category involves draining equipment and pipelines that are operated intermittently or not in use for extended periods; this can be done by following these steps: (1) Close the relevant valves, and install blind flanges if necessary to prevent leaks inside the valves ； (2) Open the high-point vent valve and the low-point drain valve to empty the material inside the equipment ； (3) Purge and displace residual materials with nitrogen ； (4) Keep the normally open low-point drain valve open and inspect it regularly. Secondly, the facilities and pipelines inside the underground valve shafts are emptied; this applies mainly to fire-fighting equipment that does not have heating systems (such as water cannons and fire hydrants). The root valves in the valve shafts are closed, the water above the valves is drained through drain valves, and these drain valves are kept open, with the fire cannon nozzles pointed downward. Third, for temporarily used equipment, pipelines, or hoses, empty the medium inside them promptly after use and purge them with nitrogen ； If possible, it can be placed in a insulated building. 2. Heat preservation. From the perspective of frost prevention, insulation in chemical plants mainly involves the following three aspects: First, insulating materials are used to insulate equipment, pipelines, and their accessories. Before winter arrives, it is necessary to carefully examine this process based on problems that have occurred in previous years, and make necessary improvements. Special attention should be paid to the insulation of the ends of equipment and pipelines, as well as dead ends, where no heating is provided and frost prevention relies solely on the temperature of the materials themselves; it is essential to ensure that proper insulation is in place in these areas. Second, ensure that indoor spaces such as factories are well-insulated to keep them warm; check that the doors, windows, and door curtains in the factory are in good condition, and activate the heating system inside the factory promptly. Third, seal and insulate underground valve chambers; for such chambers, use plastic sheeting to ensure airtightness in advance, and apply insulation measures when necessary. http://p1.itc.cn/images01/20201211/4deb433be8fb433495c274624c36a27f.png3. Heat tracing. For winter anti-freezing purposes, common heat tracing media include hot water tracing, steam tracing, and electric tracing. Hot water tracing is suitable for situations where the operating temperature is not high or where high-temperature tracing media cannot be used. Steam tracing is generally used for tracing applications where the operating temperature of the medium inside the pipe is below 150°C. Electric trace heating is suitable not only for various situations requiring steam tracing, but also for pipelines carrying heat-sensitive media. It enables effective temperature control and prevents excessive heating of the pipelines. It is ideal for tracing pipelines or equipment located remotely from heat sources, as well as equipment with irregular shapes. The selection of the heating medium should take into account factors such as the properties of the material, required specifications, construction difficulties, and operating costs. Construction must be carried out in accordance with relevant standards, so as to achieve frost and condensation prevention while avoiding the emergence of new problems. 4. Loop. The use of cyclic anti-freezing and anti-condensation methods is primarily applied to equipment and pipelines that operate intermittently or are not in use for extended periods. This approach is used when other anti-freezing methods such as draining, insulation, or heat tracing are not employed, or when those methods are insufficient to meet the anti-freezing requirements. This method can be roughly divided into four approaches: The first is to circulate the material exiting the operating equipment back to the inlet of the standby equipment; this approach is commonly used to prevent freezing and condensation in standby equipment, such as through a bypass line adjacent to the check valve at the pump outlet, or by creating an opening in the valve core of the check valve. The second method involves connecting the equipment inlet pipeline to the equipment outlet pipeline through a bypass; this approach is often used to prevent freezing of the heat exchange inlet and outlet pipelines when they are not in use. A pipeline with a smaller diameter is connected in front of the inlet valve and behind the outlet valve of the heat exchanger, thereby allowing the fluid in the inlet and outlet pipelines to circulate. Third, carry out a small amount of circulation in normal operating mode; generally, it is advisable to close the outlet valves of the standby equipment as much as possible to reduce the volume of fluid circulation, thereby meeting the anti-freezing requirements. Fourth is the continuous or intermittent discharge of a small amount of medium; this method is mainly used in cases where it is not possible to install anti-freezing measures at the end of the circulation pipelines, such as in hose stations, drain pipelines and valves for storage tanks, drain valves at the lowest points of steam pipelines, and eye wash stations. II. Anti-freezing inspections: Anti-freezing inspections are an extremely important part of winter anti-freezing measures. Conducting such inspections on a regular basis allows for the timely detection and resolution of problems that arise during the anti-freezing process, thereby preventing further complications caused by freezing. The anti-freezing inspection primarily aims to assess the effectiveness of anti-freezing and anti-condensation measures, identify any gaps, and further improve these measures. The main inspection items and methods are as follows: 1. Regularly inspect the drainage function of the steam tracing pipelines’ traps. If abnormal drainage is detected, it should be investigated and addressed promptly. In cases where it is not possible to directly observe the drainage situation (such as when the water is directed to a drainage collection station), a temperature gun or direct touch of the trap body can be used for inspection (an inspection hole must be left available when insulation is in place). Generally, a temperature of over 30°C or a feeling of heat indicates normal operation; however, the sensation of heat does not necessarily confirm that drainage is functioning properly, especially in situations where water is sent to a drainage collection station, as heat conduction from nearby normal drainage pipelines can lead to misleading conclusions. 2. Use hot water for heating; use a flow indicator to check the flow of water, or use a temperature gun or touch the designated inspection points on the electric heating tape to verify that the temperature of the electric heating tape is normal ； When heat-traced hot water pipelines are collected together, experience should also be used to avoid interference from the heat conduction of adjacent normal hot water pipelines, which could affect inspection and judgment. 3. For electric heating elements with temperature indicators, it is necessary not only to check the temperature readings regularly, but also to use a thermometer or touch the designated inspection points on the heating element to prevent inaccurate temperature readings and ensure that the temperature of the heating element remains within the normal range. Electric heating elements without temperature indicators still require temperature monitoring. 4. Enclosed workshops should be equipped with thermometers; the sealing of doors and windows as well as the temperature of the heating system should be checked regularly, and the heating intensity in the room should be adjusted according to the indoor temperature ； Inspect the insulation and sealing of the valve chamber, and monitor its internal temperature if necessary. http://p7.itc.cn/images01/20201211/18b31535af3547f89628fdeb9328a034.png5. Regularly check whether there is any material flowing out or blockages due to freezing at the lowest points of the emptied equipment and pipelines; you can also use a wrench to tap on the pipelines to assess the situation. If a blockage due to freezing is detected, identify the source of the material promptly and take appropriate action. 6. Regularly inspect the anti-freezing circulation systems of equipment and pipelines; if there are flow indicators or sight glasses, check whether the indications are normal ； In the absence of flow indicators or sight glasses, a temperature gun or by touching the equipment itself or the relevant anti-freezing wiring can be used to determine the temperature; when it is difficult to make such judgments based on temperature, a listening rod can also be used to assess the flow of material within the equipment or pipelines. For materials that use a small amount of external circulation for anti-freezing, regularly check whether the external discharge volume is normal. 7. Instrument heating: Regularly check the sealing condition of the instrument heating box as well as the temperature inside it. Also, in accordance with the heating method used, inspect the instrument heating following the procedures mentioned above ； Additionally, a comparison can be made using on-site and remote instruments, and the normal readings of these instruments can be used as a reference to determine whether the instrument is frozen and blocked. 8. Whether used on a long-term basis or as spare equipment, rotating the machinery regularly is necessary to detect in advance any signs of freezing or blockage ； For equipment that cannot be rotated (such as canned pumps), in addition to ensuring proper anti-freezing circulation, a spot check should be conducted before starting; the temperature of areas prone to freezing (such as the rear part of the canned pump) should be measured, and only after everything is normal should the equipment be started. 9. For drain valves at the ends of gas (vapor) pipelines, drain valves at the lowest points of U-turns, and valves at hose stations, maintain an appropriate degree of opening or conduct regular drainage checks to prevent material from accumulating in low-lying areas and causing pipeline blockages due to freezing. 10. For instrument air, in addition to regularly draining water from the ends of the main pipelines and at their lowest points, it is also necessary to check the water content within them, in order to prevent water from accumulating and freezing inside the instruments, which could lead to malfunctioning of those instruments. 11. Regularly check the outlets of the drainage facilities to ensure that water is not flowing out or that there is no freezing blockage at the low-point drainage valves. If any issues are detected, clear them promptly and verify that the valves at the source are properly closed. 12. Regularly inspect the system’s vent and breathing exhaust ports, such as the storage tank’s breathing valve and flame arrester, emergency vent ports for pressure relief, the air compressor’s vent port, and the boiler’s safety valve vent port, to ensure that these vents remain unobstructed. 13. Regularly check the protective screens and filters at the inlet of outdoor fans, as well as those at the inlets of the cooling fans of motors and other equipment, to ensure that there is no freezing and blockage. Blockages are likely to occur if steam is released in the vicinity of such equipment or during snowy weather. 14. Regularly check whether the liquid in the outdoor water seal groove or liquid seal tank has frozen and caused blockages; address any abnormalities promptly to ensure its proper functioning. 15. In the event of a significant drop in temperature or at night, inspections should be intensified, and the amount of heat supplied, as well as the heating capacity of the facility and the flow rate of the anti-freezing system, should be adjusted according to the temperature conditions. A one-time solution is not sufficient to prevent freezing and blockages. III. During the thawing process for frozen blockages, handling should be carried out based on specific circumstances. Generally speaking, for equipment that is small and has short pipelines, as well as instruments and valves, steam can be used to blow on the surface of the frozen blockage in order to thaw it; if insulation is present, it must be removed first ； If the equipment affected by freezing is large and the pipelines are long, a temporary heating system (such as metal hoses) is often installed along with insulation to facilitate thawing gradually. For equipment, pipelines, instruments, and valves that are frozen and blocked and can be easily removed, they can be taken away and placed in a room with a higher temperature to thaw them out, depending on the circumstances. To avoid safety hazards such as the release of toxic and harmful gases or liquids that could cause injury or explosions during the treatment of frozen blockages, it is necessary to pay attention to the following points during this process: First, check whether there are any cracks or damages in the equipment, pipelines, and valves, as well as the operating status of these valves ； Second, it is necessary to isolate the relevant systems in advance ； Third, the operation must be carried out slowly, using low-temperature steam to dissolve the substance gradually, in order to prevent sudden heating from damaging frozen equipment, pipelines, and valves ； Fourth, consider the impact on instruments and process conditions after a sudden unblocking during the thawing process, and take preventive measures in advance. IV. Other matters 1. Drawing on past experience in preventing freezing, address any such issues that may arise by having ready available anti-freezing materials such as insulation materials, check valves, flexible hoses, temporary connectors, and anti-freezing gloves. 2. Take precautions in advance; start using and checking various anti-freezing measures before winter arrives, to provide enough time to address any anti-freezing issues and avoid situations where sudden drops in temperature prevent the implementation of such measures. 3. Adjust the heat supply in a timely manner to meet the anti-freezing requirements, while avoiding waste caused by excessive heat supply, as well as issues such as excessive process parameters and inaccurate instrument readings. 4. For material pipelines equipped with heating, there should be a defined direction for expansion, in order to prevent pressure buildup in the equipment or pipelines due to the expansion of the material when it is heated. If pressure gauges are installed, it is necessary to monitor their readings regularly. 5. When the material pipeline is in operation and flowing, the heat tracing pipeline heats the material pipeline it is meant to heat; if the flow of material in the pipeline stops, a thorough inspection should be carried out and the heat tracing intensity should be increased appropriately. 6. The heating temperature of the eye washer should be appropriate; excessive heating temperatures should be avoided to prevent additional injuries in emergency situations. 7. When hot water or steam heating needs to be temporarily shut down for maintenance purposes, care should be taken to prevent the heating pipes and the pipelines carrying the material being heated from freezing up. 8. For equipment equipped with heating systems that requires heat dissipation during operation, the insulation should be removed, the heating system should be turned down or disabled, in order to prevent the equipment from overheating. 9. For electric heating, attention should be paid to the load on the heating strip to prevent overload-induced shutdowns or fires ； For maintenance of electric trace heating, the power must be turned off first. During the maintenance period, measures to prevent freezing of the materials being heated must be considered. 10. If any abnormalities are detected in the steam tracing drainage system, such as water hammer, excessive or insufficient drainage volume, or inadequate heating from the tracing, prompt action should be taken to address them. 11. Adopt a circulating anti-freezing method; while meeting the anti-freezing requirements, minimize the circulation volume to avoid unnecessary waste caused by an excessive circulation volume. 12. Similar to fire valve shafts, when underground valves are closed, tools for opening the shaft covers and valves should be available to ensure they can be used promptly in emergency situations. 13. Promptly eliminate any leaks or drips at the site to prevent ice formation on the ground and in the air; if such situations occur, take action to address them immediately. 14. Conduct regular anti-freezing inspections to ensure their quality, while carrying out inspections focused on specific areas based on different times of day, temperature conditions, and the difficulty of preventing freezing. Safety must be considered at every step of chemical production, and extra attention should be paid to anti-freezing and anti-condensation measures in winter to prevent related accidents. This article is reproduced from China Hazardous Chemicals Logistics Network.