Effective strategies for preventing hazardous accidents in reaction vessels in fine chemical enterprises

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　　Overview of Huatianmou’s experts in lean production management: Fine chemical manufacturing enterprises have several main production workshops as well as multiple auxiliary workshops, and are equipped with a number of reaction vessels and distillation towers. Overall, there are many devices and storage tanks, with a dense network of pipelines stretching 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 reaction vessel during operation in a unit system: Taking a constant-pressure reaction vessel 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. 　　Analysis of a Typical Case: On June 2, 2012, a fire broke out during the testing of a new manufacturing process at a company’s facility designed to produce 1,000 tons of hydroquinone per year. The accident resulted in 2 deaths, 1 person with serious injuries, and 1 person with minor injuries, causing direct economic losses of around 4 million yuan. 　　Direct cause: Methanol and phenol were added to the reactor, and after oxygen was introduced, an explosive mixture of methanol and oxygen-rich gas formed inside the reactor. During the stirring process, the stirring speed increased, which accelerated the accumulation of static electricity within the reactor. Although the reactor was equipped with static electricity dissipation devices, the static electricity generated during this accelerated stirring could not be dissipated in time, leading to localized accumulation of static electricity and ultimately causing a fire in the reactor. 　　Indirect reasons: First, the technical processes did not meet the requirements for conducting experiments in production facilities; no risk assessment was carried out prior to the experiments, and no specific experimental plan, operating procedures, or emergency response plans were established for this experiment ； The technology developed by Hu Yucai has only been successful in laboratory tests; it has not been approved by any authority, and thus does not meet the requirements for testing in production facilities. Secondly, it violates the relevant regulations on safety permits for hazardous chemical construction projects: instead of using the mature process provided by Beijing Tubin New Silicon Technology Co., Ltd., whose setup plan had been approved, the company purchased a laboratory-based process to conduct experiments with this new process in its production facilities. Third, the equipment and facilities of the project have not been fully installed; during experiments, the necessary remote control safety systems are not in use, such as those for centralized monitoring, control, and alarm of pressure, temperature, liquid level, and flow rate, as well as automatic control mechanisms like interlock control of the feed amount into the reactor, interlocks between the reactor’s pressure and temperature and the oxygen supply valves, and interlocks with the cooling water valves. 　　Main hazards of reaction vessels in fine chemical industry 1. Incorrect feeding An excessive feeding rate, loss of control over the feeding ratio, or incorrect feeding sequence can all lead to rapid exothermic reactions. If cooling is not carried out simultaneously, heat will accumulate, causing the material to decompose locally. This results in rapid reactions and the generation of large amounts of hazardous 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 and burns that can cause injury to people. During unloading, if the material in 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. Excessive heating rate
Due to an excessively rapid heating rate, low cooling rate, and poor condensation effect, the materials inside the kettle may boil, resulting in a mixture of vapor and liquid phases. This generates pressure, which is then relieved through weak points such as vent pipes and vapor lines, as well as pressure relief systems including safety valves and rupture discs. If the blanking process fails to achieve rapid pressure relief, it may lead to an explosion of the reactor vessel. 　　4. Maintenance involving open flames: If welding, gas cutting, or other maintenance tasks are carried out inside the reactor while there are no effective preventive measures in place, or if sparks are generated from tightening bolts or striking metal objects, this could lead to fires or explosions in the presence of flammable and explosive materials that may be present. 　　Safety technologies for reaction vessels in fine chemical industry 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, steam is first used to heat the materials to around 60°C at a moderate rate, thereby improving production efficiency; thereafter, boiling water at 100°C is used for heat transfer, allowing the temperature to rise slowly to the value specified by the process requirements, after which the temperature is maintained during the reaction. Such segmented heating not only improves production efficiency but also prevents the material from decomposing or vaporizing intensely due to localized high temperatures, which could otherwise lead to the formation of a vapor-liquid mixture and subsequent material explosion. It also facilitates a more uniform reaction of the material, increasing yield while reducing consumption costs. 　　2. Cascade 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 station. 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 shutdown, cessation of mixing, and rapid cooling, thereby containing the accident at an early stage and preventing it from spreading further. 　　3. Sequential explosion relief measures 　To prevent pressure buildup caused by gas generation due to uncontrolled temperature of the material in the reactor, 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 material conveying pipeline systems, steel pipes or plastic pipes should be selected based on the properties of the materials (it is generally specified that plastic pipes cannot be used, except in special cases). Regardless of the type of pipeline, it should be securely 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’s sake, 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 using plastic pipes to transport organic solvents or other materials that are prone to generating static electricity, it is necessary to ensure proper static electricity connection; this is achieved by 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 then wrapped around and secured at that opening as well. 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 　　Installing blowers or exhaust fans at the operation stations not only protects the health of the operators but also reduces the concentration of flammable gases in those areas, preventing them from reaching explosive levels. 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 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 prevailing wind direction in the area, to facilitate the dispersion or removal of these gases and to enable operators to carry out their tasks properly, thereby reducing the risk of gas-related pollution. 　　6. Safety measures for maintenance work involving open flames 　　The objective of the safety technical measures for managing work with open flames 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 these two guarantees, it is essential to properly recognize the importance of fire management, enhance safety awareness, and effectively implement safety technical measures such as isolation, separation, displacement, cleaning, and ventilation. Additionally, safety management procedures such as preliminary review, reinspection, approval, supervision, cleanup, and acceptance must be followed. 　　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. 　　Emergency response measures for unexpected incidents in reaction vessels in fine chemical industry 1. Uncontrolled rapid increase in production temperature and pressure 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 still cannot be controlled, quickly 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. Massive leakage of toxic and harmful substances 　In the event of a massive leakage of toxic and harmful substances, it is necessary to immediately inform those around and urge them to evacuate the area quickly 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 impossible to close the valves controlling toxic and harmful substances, promptly notify units and personnel downwind (or in the surrounding areas) to evacuate or take preventive measures. Additionally, based on the characteristics of the substance, spray treatment agents to absorb and dilute it. Finally, the leakage is contained and properly disposed of. 　　3. Massive leakage of flammable and explosive substances In the event of a massive leakage of such substances, it is necessary to quickly put on a positive-pressure respirator and close (or seal tightly) the valves through which the substances are leaking ； If it is not possible to close the valves for controlling the leak of flammable and explosive substances, immediately inform the people in the surrounding area (especially those downwind) to stop using open flames and carrying out any operations that may generate sparks, and also halt other production or operational activities in the vicinity. Where possible, transfer the leaked flammable and explosive substances to a safe location for handling. When the gas leak has already caught fire, one should not rush to close the valves; it is necessary to monitor the situation to prevent backfire and explosions caused by the gas concentration reaching its explosive limit. 　　4. When someone is injured, the cause of poisoning must be determined immediately.
When someone is injured, it is necessary to promptly identify the cause of poisoning and take effective measures to address 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 case of skin-induced poisoning, immediately remove contaminated clothing and rinse the affected area with plenty of running water; then seek medical attention ； When the poisoned person stops breathing, perform artificial respiration promptly ； 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. It is important to avoid exposure to cold that could cause further injury; after changing into clean clothing, the affected person should be taken to the hospital as soon as possible. 　　Summary The reaction kettle is the most commonly used equipment in fine chemical manufacturing enterprises, as well as the most typical type of equipment in unit systems; it is a key focus for safety production supervision. Only by ensuring the proper operation of each reactor and every unit system in terms of safety, by implementing appropriate safety interlock measures, and by putting in place warning interlocks to prevent human error, can accidents be reduced.