Thread Content
Common anti-freezing methods: The common anti-freezing and anti-condensation methods used in chemical plants include evacuation, insulation, heat tracing, and circulation. To prevent freezing and condensation in winter, 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. Methods for draining anti-freezing and anti-condensation systems can be roughly divided into three categories: For equipment that operates intermittently on the ground or is not in use for extended periods, as well as pipelines, the drainage process can be carried out following these steps: Close the relevant valves, and install blind flanges if necessary to prevent leaks inside the valves ； Open the high-point vent valve and the low-point drain valve to empty the material inside the equipment ； Purge with nitrogen to displace residual material ； Keep the normally open low-point drain valve open and inspect it regularly. The facilities and pipelines in the underground valve chamber are emptied, mainly referring to fire-fighting equipment without heating systems (such as water cannons and fire hydrants). The root valves are closed inside the valve chamber, and the water above the valves is drained through drain valves; these drain valves should remain open. The fire cannon nozzles should be directed downward. For those equipped with built-in return mechanisms, this step is not necessary. Temporarily used equipment, pipelines, or hoses should be emptied. After use, the medium contained within such equipment, pipelines, or hoses must be emptied promptly, and they should be cleaned using nitrogen ； If possible, it can be placed in a insulated building. From the perspective of frost prevention, insulation in chemical plants mainly involves three aspects: insulating equipment, pipelines, and their accessories with thermal insulation materials. 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 important to ensure that proper insulation is in place in these areas. 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. Sealing and insulation of underground valve chambers: For valve chambers, plastic sheeting should be used to ensure airtightness in advance, and insulation measures should be taken if necessary. For winter anti-freezing purposes, common heat tracing media include hot water tracing, steam tracing, electric tracing, and circulating heat media. Hot water tracing is suitable for use in situations where the operating temperature is not high, or when it is not possible to use high-temperature tracing media. Hot water tracing uses hot water at temperatures of 80 to 90 degrees as a heat source, and heat is transferred through tracing pipes to warm the instruments and equipment that require heating. Due to the relatively low temperature of the hot water used in this method, it can hardly be utilized for preventing condensation; it is only suitable for keeping instrument systems from freezing, acting in a similar manner to heating systems. Hot water has a relatively low temperature, so strict requirements are placed on the entire instrument heating system. It is essential to ensure that the insulation of the whole system is adequate, with no exposed pipes or valves. The installation of the heat tracing tubes must be carried out in a strict and standardized manner; the U-shaped bends in these tubes inside the insulation box should be numerous enough to enhance heat transfer. Hot water tracing requires a pressure pump for pressurization, and a separate hot water tracing system must be installed, resulting in significant engineering workload. Although hot water heating requires less energy, its complex setup results in limited use in small and medium-sized enterprises; only some large state-owned enterprises have well-developed hot water heating systems in place. Steam tracing: External steam tracing pipes are a commonly used tracing method in petrochemical plants both domestically and internationally. The heat released by the heat tracing tube is used, in part, to compensate for the heat loss of the fluid inside the main pipe, while the rest is lost to the surrounding environment through the insulation layer outside the tube. When a rigid insulated prefabricated shell is used, a space is created between the main pipe and the heating tubes; this allows the heat generated by these heating tubes to nearly fully compensate for the heat losses of the main pipe. As a result, this type of heating system requires less energy, making it more economical. Steam tracing is generally used for tracing applications where the operating temperature of the medium inside the pipe is below 150°C. Electric heating tracing has been widely used as an effective method for pipeline insulation and anti-freezing. Its working principle is to release a certain amount of heat through the heating medium, and to compensate for the heat loss in the pipeline being heated through direct or indirect heat exchange, thereby meeting the requirements for temperature elevation, heat retention, or anti-freezing to ensure normal operation. Circulating heat media are widely used in the petroleum, chemical, and heat treatment industries. As a heat carrier, its operating temperature can be precisely controlled, making it particularly suitable for large-scale heat conversion and heat transfer, such as heat transfer oils. 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 frost and condensation prevention while avoiding the emergence of new problems. 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: recycling 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. It involves connecting the device’s inlet pipeline to its outlet pipeline through a bypass. This method 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. Under normal operating mode, with a small number of cycles, it is generally 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. Small amounts of medium are discharged continuously or intermittently. This method is primarily used in situations where it is not possible to install anti-freezing measures at the end of circular pipelines, such as in hose stations, tank drain pipelines and valves, steam pipeline low-point drain valves, eyewash stations, etc. Key points of anti-freezing inspection: Anti-freezing inspection is an extremely important part of winter anti-freezing measures. Conducting regular anti-freezing inspections allows for the timely detection and resolution of issues that arise during this process, thereby effectively 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 it is routed to a drain recovery 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 is considered normal, but such a warm sensation does not necessarily indicate proper drainage function. This is especially true in situations where the drainage is sent to a drain recovery station, as heat conduction from nearby normal drainage pipelines can lead to misleading inspection results. 2. Use hot water for heating; use a flow indicator to check the flow of water, or employ a temperature gun or touch the designated inspection point on the electric heating tape to verify that its temperature is within the normal range ； 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 equipment itself or the relevant anti-freezing wires 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 aforementioned procedures ； Additionally, a comparison can be made using on-site and remote sensors, and the normal readings of these sensors can be used as a reference to determine whether the sensor is frozen or 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 carried out 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-shaped bends, 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 the lowest points, it is also necessary to check the dew point to prevent excessive moisture content from causing the instruments to freeze, which could lead to malfunctioning of the control systems. 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 found, 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 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 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. Anti-freezing and anti-condensation plan: To ensure the safe, stable, and smooth operation of the instruments in various units throughout the winter, and to guarantee the proper functioning of these production units during that period, the instrument management team has formulated this work plan for preventing freezing and condensation of instruments in winter, in line with the company’s guidelines.