Safety technical measures for reaction vessels in fine chemical enterprises

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Fine chemical manufacturing enterprises have several main production workshops and multiple auxiliary workshops, as well as several sets of reactors and distillation columns. Overall, there are many devices and storage tanks, with a dense network of pipelines extending in all directions ； Structurally, the entire production system is composed of several production units. Each production unit is composed of one or more reactors, condensers, and distillation towers. Safety technical measures for the reactor in the unit system during operation: Taking a constant-pressure reactor used for transporting liquid materials and carrying out exothermic reactions, along with a condenser, as the simplest operating unit, this approach analyzes the potential hazardous factors, and formulates corresponding safety precautions as well as emergency response measures for unexpected situations. I. Analysis of major hazardous factors: 1. Incorrect feeding: An excessive feeding speed, loss of control over the feeding ratio, or incorrect feeding sequence can all lead to rapid exothermic reactions. If cooling cannot keep up, heat will accumulate, causing the material to decompose locally. This results in rapid reactions and the generation of large amounts of harmful gases, which can lead to explosion accidents. 2. Pipeline leakage: During feeding, in the case of reactions at atmospheric pressure, if the vent pipe is not open, pumping liquid material into the reactor can create positive pressure inside the reactor. This may lead to cracks at the connections of the material pipes, resulting in leaks of the material and causing burns as a result of personal injury. During unloading, if the material inside the tank is unloaded before it has cooled to the specified temperature (usually below 50°C), the material at a higher temperature is prone to deterioration, and it can also cause the material to splash and burn the operators. 3. Rapid temperature rise: In the reactor, a too fast heating rate combined with a low cooling rate leads to poor condensation, which can cause the material to boil and form a mixture of vapor and liquid. This generates pressure, which is then released through weak points such as vent pipes and vapor lines, as well as through pressure relief systems like safety valves and burst discs. If the blanking process fails to achieve rapid pressure relief, it may lead to an explosion of the reactor vessel. 4. Welding and cutting during maintenance: If welding, gas cutting, or other maintenance tasks are carried out inside the tank while the materials are still reacting, without appropriate safety measures in place, or if sparks are generated from tightening bolts or striking metal objects, this could lead to fires or explosions if flammable or explosive materials are present. II. Safety technical countermeasures: 1. Heating control measures: For heating systems used with materials whose reaction temperature is below 100°C, steam and hot water can be used for staged heating. To prevent the materials from deteriorating due to localized overheating, the materials are first heated to around 60°C using steam at a moderate rate, thereby improving production efficiency; thereafter, boiling water at 100°C is used for heat transfer to gradually raise the temperature to the value specified by the process, after which the temperature is maintained during the reaction. This segmented heating method not only improves production efficiency, but also prevents local overheating of the material, which could lead to decomposition or rapid vaporization. This, in turn, avoids the formation of a vapor-liquid mixture that might cause material blowout or explosion. Additionally, it ensures uniform reaction of the material, thereby increasing yield and reducing consumption costs. 2. Chain cooling measures: For exothermic reactions, heating is required in the initial stage of the reaction, but heat is released during the reaction process; therefore, it is necessary to transfer the excess heat quickly and effectively. The cooling systems used in reactors under normal operation are mainly jacket cooling and coil cooling, with circulating water and refrigerant being the primary cooling fluids used. Coolant has a fast cooling speed but high costs. In the event of abnormal reactions during the production process, especially when temperature and pressure rise sharply, operators will evacuate the operation site quickly to ensure their own safety; as a result, they are unable to shut off the heat source effectively or activate the cooling system. To this end, an emergency cooling interlock system should be installed at a remote location outside the operating area. It is best to be near the steam valve of the workshop’s steam distribution cylinder; by closing that steam valve and cutting off the power supply to the mixer, the cooling interlock system can be activated. This allows for measures such as insulation, power disconnection, cessation of mixing, and rapid cooling, in order to contain the accident at an early stage and prevent it from spreading further. 3. Chain venting measures: To prevent pressure buildup caused by gases generated when the temperature inside the reactor gets out of control, it is necessary to have mechanisms for rapid pressure release. Emergency pressure relief devices should also be installed in reactors operating at atmospheric pressure, depending on the specific conditions of the reaction. A safety valve should be installed at the top of the kettle, and a burst disc should be installed for processes that may involve relatively intense reactions. The outlet of the connecting pipe for the blast disc must extend to a safe location outdoors or to the exhaust duct opening; it must not point directly at roads or operation platforms, in order to prevent material splashes from injuring people. For processes involving a dropwise addition, the addition rate must be strictly controlled. 4. Anti-static measures for closed conveying: For the material conveying pipeline system, steel pipes or plastic pipes should be selected based on the properties of the materials (it is generally stipulated that plastic pipes cannot be used, except in special cases). Regardless of the type of pipeline, it should be firmly connected using flanges or bolts to prevent leakage of materials. Plastic pipes cannot be connected using rubber sleeves to transport organic solvents. Proper static bonding must be carried out on the flange portion of the steel pipe. If a pair of flanges has six bolts or more, static bonding is not required; however, if there are four bolts or fewer, static bonding is necessary (for symmetry reasons, normally there are not five bolts, but if there are five, bonding is still required). For static bypass wires, 4 square millimeter copper core wire should be used. When transporting organic solvents or other materials prone to static electricity, plastic pipes must be properly grounded. The grounding method involves installing thin copper wires inside the pipes. The specific method involves welding a small steel nail at the outlet of the metal tube and tilting it slightly inward; a thin copper coin must be wrapped around this steel nail and secured, passed through the plastic tube, emerging from the other end where it is also wrapped around and secured. Only in this way can it be ensured that a circuit for generating static current is formed, and that static electricity is promptly transferred to the grounding system. 5. Labor protection measures: Install blowers or exhaust fans at the operation stations, which not only protects the health of the operators but also reduces the concentration of flammable gases at those stations, preventing them from reaching the explosive limit. To prevent gas materials inside the kettle from leaking under pressure and spreading to the control room to harm the operators, a blower should be installed in the control room. Fresh outdoor air at high altitude is introduced into the control room, keeping it in a slightly positive pressure state. Equipment that emits toxic and harmful gases should be located downwind of the local prevailing wind direction, to facilitate the dispersion or removal of these gases, as well as to enable operators to carry out their tasks properly and reduce the risk of gas-related pollution. 6. Safety measures for welding and hot work: The objective of the safety technical measures for managing welding and hot work is to ensure two things: first, that there are no flammable materials inside the equipment and pipelines used for such work; second, that there are no combustible materials in the area surrounding those equipment and pipelines. To achieve the two guarantees, it is essential to correctly recognize the importance of hot work management, enhance safety awareness, and earnestly implement safety technical measures such as cutoff, isolation, replacement, cleaning, and ventilation. Additionally, safety management measures including preliminary review, re-examination, approval, supervision, cleanup, and acceptance must be carried out in accordance with established procedures. 7. Other safety measures: Mechanical equipment must be properly grounded, with the grounding resistance not exceeding 10Ω ； The electric motor must have measures to connect to the neutral wire ； The transmission part of the reducer must be equipped with a protective cover ； The control panel must be stable and not wobble, and it must have no openings ； The protective railing must be at least 1.05 meters high, and the spacing between the upper and lower parts of the railing must not exceed 0.35 meters ； The height at which the device is above the ground should be such that it does not collide with human heads. For situations where materials need to be added in batches during operation, it is advisable to install valves and funnels on the manhole cover ； The vent pipe of the condenser should be connected to the outside through a conduit or to an exhaust outlet; it must not be directed directly at passages or areas where operators are present ； Where applicable, emergency evacuation routes and comprehensive monitoring and alarm systems should also be installed ； Nitrogen protection measures must be taken during the parking process. Equipment that could experience uncontrolled reactions due to power or water outages should have a dual-circuit, dual-water-source system. III. Emergency response measures for sudden incidents 1. When the production temperature and pressure rise rapidly and cannot be controlled, all material inlet valves must be closed immediately ； Stop stirring immediately ； Quickly close the steam (or hot water) heating valve, and open the cooling water (or chilled water) cooling valve ； Quickly open the vent valve ； When there is no vent valve and temperature and pressure remain uncontrollable, promptly open the discharge valve at the bottom of the equipment to discard the material ； If the above measures prove ineffective and it is not possible to discharge material through the bottom discharge valve in a short time, immediately inform the personnel on duty to evacuate the site. 2. In the event of a large-scale leakage of toxic and harmful substances, immediately inform those around to evacuate the area swiftly towards the upwind direction ； Quickly put on a positive-pressure respirator and close (or seal tightly) the valves for toxic and harmful leaks ； When it is not possible to shut off the valves for toxic and harmful substances, promptly inform the units and personnel in the downwind direction (or surrounding areas) to evacuate or take preventive measures, and apply treatment agents according to the properties of the substances in order to absorb and dilute them. Finally, contain the leakage and take appropriate action to deal with it. 3. In the event of a large-scale leakage of flammable and explosive substances, quickly put on a positive-pressure respirator and close (or seal tightly) the valves related to the leakage ； When it is impossible to close the valves leaking flammable and explosive substances, immediately notify people in the vicinity (especially those downwind) to cease any open flames, as well as any production or operations that may generate sparks. Other nearby production activities or operations should also be halted promptly. Where possible, the leaked flammable and explosive materials should be moved to a safe area for handling. When the gas leak has already caught fire, one should not rush to close the valves; it is necessary to stay vigilant to prevent backfire and explosions caused by the gas concentration reaching its explosive limit ； 4. In case of personnel injury, promptly determine the cause of poisoning and take effective measures to handle it ； In the event of poisoning caused by inhalation, quickly move the poisoned person to an area with fresh air upwind. In cases of severe poisoning, rush to the hospital for emergency treatment ； In cases of poisoning caused by ingestion, drink an adequate amount of warm water to induce vomiting, or administer milk or egg white as a antidote, or use other substances to induce excretion ； In cases of poisoning caused by the skin, immediately remove contaminated clothing, rinse with plenty of flowing water, and seek medical attention ； When the poisoned person stops breathing, perform artificial respiration immediately ； When the victim’s heart stops beating, immediate artificial chest compressions must be carried out to restart it ； When a person’s skin is severely burned over a large area, the affected area should be immediately washed with plenty of clean water for about 15 minutes. Care should be taken to avoid exposure to cold, which could cause further damage; after changing into clean clothing, the person should be taken to the hospital as soon as possible. The reaction kettle is the most commonly used equipment in fine chemical manufacturing enterprises, as well as the most typical device in unit systems; it is a key focus of safety production supervision. It is only by ensuring the safe operation of each reactor and each unit system, implementing appropriate safety interlock measures, installing warning interlocks against human error, that can the intrinsic safety of the equipment be achieved.