How do chemical plants prevent freezing and condensation in winter?

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How do chemical plants prevent freezing and condensation in winter? Anti-freezing and anti-condensation measures in chemical plants during winter are essential means to ensure safe production. To prevent any freezing or condensation incidents, these measures should be carried out in accordance with the principle of \"prevention first, suppression second\", taking into account the characteristics of the facilities. 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 appropriately, so as to ensure safe production. I. Anti-freezing methods
Common anti-freezing and anti-condensation methods used in chemical plants include draining, thermal insulation, trace heating, and circulation. In winter, the choice of one or more of these methods should be based on the operating conditions of equipment and pipelines, as well as past problems and experiences encountered during previous anti-freezing efforts. 1. Drain. Methods for draining anti-freezing and anti-condensation systems can be roughly divided into three categories. The first category involves the drainage of 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, and the water above the valves is drained using drain valves, which are kept open at all times, 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 improvements accordingly. Special attention should be paid to the insulation of the ends of equipment and pipelines, as well as dead ends, where no heat tracing is available and frost prevention relies solely on the temperature of the fluids flowing through them; it is important to ensure that proper insulation is in place in these areas. Second, ensure that indoor spaces such as factories are well-insulated to keep out heat; 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. 3. Heat tracing. For winter anti-freezing, 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 heat tracing is suitable not only for various situations involving steam heat tracing but also for pipelines carrying thermosensitive media; it enables effective temperature control to prevent the pipes from overheating. It is appropriate for heating pipelines or equipment that are dispersed or located far from the source of heat supply, 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 recycle the material exiting the operating equipment back to the inlet of the standby equipment for circulation; 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 enabling circulation of the fluid in the inlet and outlet pipelines. 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 situations where it is not possible to install anti-freezing measures at the end of circulating 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-freeze inspections
Anti-freeze inspections are a crucial component of winter anti-freeze efforts. Conducting these inspections regularly helps to promptly identify and address any issues that arise during the anti-freeze process, thereby effectively preventing further occurrences of freezing-related blockages. 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 when insulation is in place). Generally, a temperature of over 30°C or a feeling of heat indicates normal operation; however, a warm sensation obtained through touch does not necessarily mean that the drainage is functioning properly, especially in situations where the 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 the 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 level 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. 5. Regularly check whether there is any material flowing out or freezing and blockage at the low points of the emptied equipment and pipelines; alternatively, use a wrench to tap on the pipelines to assess the situation. If freezing and blockage 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 device 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 device 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 aforementioned procedures ； Additionally, a comparison can be made between on-site and remotely transmitted instruments; by referring to the normal indicator values of the instruments, it is possible to determine whether an instrument has become frozen or blocked. 8. Whether it is equipment used long-term or kept as a backup, it should be periodically cranked to detect in advance whether any freezing or blockage has occurred ； For equipment that cannot be cranked (such as canned motor pumps), in addition to performing anti-freeze circulation checks, a trial start should be conducted prior to normal operation. The temperature of freeze-prone areas (such as the rear housing of canned motor pumps) must be measured; only after ensuring normal temperatures can the equipment be started. 9. For drain valves at the ends of pneumatic/hydraulic pipelines, drain valves at the low points of U-bends, valves at hose stations, etc., maintain them at a moderate opening or conduct regular drainage inspections to prevent materials from accumulating at low points, which could lead to freezing and blockage of the pipelines. 10. For instrument air, in addition to regularly draining water from the ends and low points of the main pipeline, its moisture content should also be monitored to prevent water accumulation and freezing inside the instruments, which could lead to malfunction of their regulation functions. 11. Regularly check whether water is flowing out of or if there is any freezing blockage at the outlets of drained consumption facilities and at the low-point drain valves. Upon discovering any issues, promptly clear them and verify whether the root valves are tightly 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 whether there is any freezing or blockage in the protective screens and filters at the inlets of outdoor fan motors, as well as in the cooling and heat-dissipation fans. Blockages are likely to occur if there is steam emission around such equipment or during snowy weather. 14. Regularly check whether the liquid in outdoor water seals or liquid seal tanks has frozen and caused blockages; address any abnormalities promptly to ensure their proper functionality. 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 factory buildings 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. Treatment of freezing blockages: During the thawing process, measures should be taken based on the specific circumstances. Generally, for equipment that is small and has short pipelines, as well as instruments and valves, steam can be used to blow on the surface affected by freezing to dissolve the blockage; in cases where insulation is present, it must be removed first ； If the frozen equipment is large and the pipelines are long, a common approach is to lay temporary tracing (such as using metal flex hoses) and insulation to gradually thaw them. For equipment, pipelines, instruments, and valves that are frozen and stuck, if it is possible to remove them, they can be taken away and placed in a room with a higher temperature in order to thaw. To prevent safety accidents such as the ejection of toxic and harmful gases or liquids that could injure people, or explosions during the thawing process, the following points should be observed: First, inspect the frozen equipment, pipelines, and valves for any cracks or damage, as well as check the on/off status of the valves ； Second, it is necessary to isolate the relevant systems beforehand ； 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 following 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. Be proactive by putting various anti-freezing measures into use and checking them in advance before winter arrives, to allow enough time to address any anti-freezing issues and prevent sudden temperature drops from preventing 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 exceeded 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 intended 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 and becoming blocked. 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. When using electric heating, attention should be paid to the load on the heating strip to prevent overload-induced shutdowns or fires ； To carry out maintenance on electric heat tracing, the power supply must be turned off first; during the maintenance period, measures must be taken to prevent the materials being heated from freezing. 10. If any abnormalities are detected in the steam tracing steam traps, 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 occurrences do happen, they must be addressed immediately. 14. Conduct regular anti-freezing inspections to ensure their quality, while carrying out inspections focusing on key areas depending on different times, temperature conditions, and the difficulty of preventing freezing.