How do chemical plants prevent freezing and condensation?

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Common anti-freezing 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 anti-freezing 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 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 chambers are emptied, mainly those fire-fighting systems that do not have heating capabilities (such as water cannons and fire hydrants). The root valves in these valve chambers are closed, and the water above the valves is drained using drain valves; 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. Thermal insulation. 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, and of on-site pressure gauges that rely solely on the temperature of the materials themselves for frost prevention, to ensure proper insulation. Second, ensure that indoor spaces such as factories are well-insulated; check to confirm 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 heating 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 heat tracing 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 the goals of preventing freezing and condensation 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 evacuation, 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 element 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 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. Image 2: Antifreeze Inspection. Image: Antifreeze inspection is an extremely important part of winter antifreeze protection efforts. Conducting regular antifreeze inspections allows for the timely detection and resolution of any issues that arise during this 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 drain water is collected at a drainage recovery station), a temperature gun or touch can be used to check the valve body of the drain valve (an inspection hole must be left for this purpose 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. This is especially true in situations where the drain water is collected at a drainage recovery station, as heat conduction from nearby normal drainage pipelines can lead to incorrect assessments. 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 collecting heat-traced hot water pipelines together, it is also necessary to avoid, based on experience, 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. 5. Regularly check whether there is any material flowing out or freezing 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 blockage is detected, promptly identify the source of the material 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 trace heating: Regularly check the sealing condition of the instrument trace heating box and the temperature inside it. Additionally, depending on the type of trace heating used, inspect the instrument trace heating in accordance with the aforementioned procedures ； 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 shielded 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 back seat of the shielded 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 valve at the source is 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 nets 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 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 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 volume of fluid used in anti-freezing systems, should be adjusted according to the temperature conditions. A one-time solution is not sufficient to prevent freezing and blockages. Image 3: Treatment of freezing blockages. During the thawing process, it is necessary to take into account 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 blockages in order to thaw them; 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 measures 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 accidents such as the release of toxic and harmful gases or liquids that could cause injury or explosions during the treatment of freezing blockages, the following points should be taken into consideration 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 the 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 following a sudden unblocking during the thawing process, and take preventive measures in advance. Image 4: Other matters. Image 1: Drawing on past experience in preventing freezing, address any such issues that may arise; prepare 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 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 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 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 as appropriate. 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 tracing must be temporarily shut down for maintenance purposes, care should be taken to prevent freezing and blockage of the tracing pipes as well as the material pipelines being traced. 8. For equipment with trace heating that requires heat dissipation during operation, the insulation should be removed, the trace heating should be turned down or disabled 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 should 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 dealt with 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.