Anti-freezing and anti-condensation methods and precautions for chemical plants in winter

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Methods and precautions for anti-freezing and anti-condensation in chemical plants during winter. I. Methods of anti-freezing and anti-condensation: Common methods used in chemical plants to prevent freezing and condensation include draining, insulation, heat tracing, and circulation. Anti-freezing and anti-condensation measures in winter should be determined based on the operating conditions of the equipment and pipelines. 1. Empty. Methods for draining systems to prevent freezing and condensation can be roughly divided into three categories. First, for equipment and pipelines that operate intermittently or are not in use for extended periods, drainage can be carried out following these steps: (1) Close the relevant valves; if necessary, install blind flanges to prevent leaks inside the valves; (2) Open the high-point vent valves and low-point drain valves to remove the contents from the equipment ； (3) Purge and displace residual materials with nitrogen ； (4) Keep the normally open low-point drain valve open and inspect it regularly. II. The facilities and pipelines inside the underground valve chamber are emptied, primarily those fire-fighting equipment that does not have heating systems (such as water cannons and fire hydrants). The root valves in the valve chamber are closed, and the water above the valves is drained through the drain valves; these drain valves are kept open, with the fire cannon nozzles pointed downward. III. For equipment, pipelines, or hoses used temporarily, empty the contents within them promptly after use and purge them thoroughly with nitrogen ； If possible, it can be placed in a temperature-controlled facility. 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 past problems and make improvements; 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 materials, to ensure that proper insulation is in place. II. Ensure that indoor spaces such as factories are well-insulated to keep them warm; check that the doors, windows, and shutters in the factory are in good condition, and activate the heating system inside the factory promptly. III. Seal and insulate underground valve chambers; for such chambers, ensure a tight seal using plastic sheeting first, and apply insulation measures if necessary. 3. 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 when the operating temperature of the medium inside the pipe is below 150°C. Electric heating 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 supply point, 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 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: First, the material exiting the operating equipment is returned to the inlet of the standby equipment for recycling; 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. II. Connect the equipment inlet pipeline to the equipment outlet pipeline via a bypass. This method is commonly used to prevent freezing in inactive heat exchanger inlet and outlet pipelines. Smaller-diameter pipelines are connected before the inlet valve and after the outlet valve of the heat exchanger, allowing the medium in the inlet and outlet pipelines to circulate. III. Under normal operating mode, carry out a small number of cycles; 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. IV. 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 at hose stations, drain pipelines and valves of storage tanks, drain valves at the lowest points of steam pipelines, and eye wash stations. II. Precautions 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. Plan ahead by putting various anti-freezing measures into use and checking them before winter arrives, to provide sufficient time to address any anti-freezing issues and avoid situations where sudden drops in temperature prevent these measures from being implemented. 3. Adjust the heat tracing capacity in a timely manner; this should not only meet the needs of freeze prevention, but also prevent waste caused by excessive heat tracing, exceeding of process parameters, and inaccurate instrument readings. 4. For material pipelines with trace heating, there must be a designated expansion direction to prevent situations where heating-induced expansion of the material causes overpressure in equipment or pipelines. For pipelines equipped with pressure gauges, it is necessary to monitor the pressure levels accordingly. 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 within 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; it is necessary to avoid excessive heating temperatures that could cause additional harm 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 freezing and blockages in the heating pipes as well as in the pipelines carrying the materials that are being heated. 8. For equipment equipped with heating systems that requires heat dissipation during operation, the insulation should be removed, the heating system should be adjusted to a lower level, or it should be turned off, in order to prevent the equipment from overheating. 9. When using electric heat tracing, attention should be paid to the load on the tracing wire to prevent overload-induced shutdowns or fires ； When maintaining electric heat tracing, the power supply must be turned off first, and 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 cyclic anti-freezing method; while meeting the anti-freezing requirements, minimize the circulation volume to prevent unnecessary waste caused by excessive circulation. 12. Similar to fire valve wells, when underground valves are closed, tools for opening the manhole covers and valves should be readily available for immediate use in emergency situations. 13. Eliminate any leaks or spills on site promptly 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.