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Main Hazard Factors and Control Measures for Fine Chemical Reaction Kettles
Fine Chemical Production Enterprises and Reaction Kettle Hazards
A fine chemical production enterprise typically comprises several main production workshops and multiple auxiliary workshops, equipped with a number of reaction kettles and distillation columns. Overall, the facility features numerous pieces of equipment, numerous storage tanks, and a dense, crisscrossing network of pipelines. Structurally, the entire production system is composed of several production units. Each production unit is itself formed by combining one or more reaction kettles, condensers, and distillation columns. Analyzing the safety technical measures for reaction kettles within a unit system during operation, we can consider the simplest operational unit: one atmospheric pressure reaction kettle and one condenser handling liquid material transfer and an exothermic reaction. This allows for analysis of potential hazardous factors and the development of corresponding safety prevention measures and emergency response plans for sudden incidents.
Main Hazardous Factors in Fine Chemical Reaction Kettles
1. Charging Errors
Excessively fast charging speed, loss of control over the charging ratio, or incorrect charging sequence can all lead to a rapid exothermic reaction. If cooling cannot keep pace, heat accumulates, causing localized overheating and decomposition of the material. This can result in a rapid reaction, generating a large amount of hazardous gases and potentially causing an explosion.
2. Pipeline Leakage
During charging for an atmospheric pressure reaction, if the vent pipe is not open, pumping liquid material into the kettle can easily create positive pressure inside. This positive pressure can cause the material pipe connections to burst, leading to material leakage and potential personal injury from chemical burns. During discharge, if the material is discharged before being cooled to the specified temperature (generally required below 50°C), the high-temperature material can easily deteriorate and may splatter, scalding operators.
3. Excessive Heating Rate
Overly rapid heating of the material in the kettle, combined with a low cooling rate and poor condensation efficiency, can cause the material to boil, forming a gas-liquid mixture and generating pressure. Pressure relief may then occur through weak points like the vent pipe or vapor phase line, or through pressure relief systems like safety valves and rupture discs, potentially causing material ejection. If this ejection does not achieve rapid pressure relief, it may lead to an explosion of the kettle.
4. Hot Work during Maintenance
If electric welding, gas cutting, or other maintenance tasks are performed during the reaction process without effective preventive measures, or if sparks are generated from tightening bolts or impact from metal tools, encountering leaked flammable or explosive materials can potentially cause a fire or explosion accident.
Safety Technology for Reaction Kettles in Fine Chemicals
1. Heating Control Measures
For material heating systems where the reaction temperature is below 100°C, segmented heating using steam and hot water can be employed. To ensure the material does not deteriorate due to localized overheating, use medium-pressure steam for initial heating to approximately 60°C to improve production efficiency. Then, use 100°C boiling water for cyclic heat transfer to slowly raise the temperature to the process-specified level and maintain it for the reaction. This segmented heating approach prevents localized overheating and decomposition or violent vaporization of the material, which could lead to the formation of a gas-liquid mixture, material ejection, and explosion. It also promotes a more balanced reaction, improves yield, and reduces consumption costs.
2. Interlocked Cooling Measures
For exothermic reactions, heating is required in the initial stage, but the reaction itself releases heat, necessitating the rapid and effective removal of excess heat. The cooling systems typically used for reaction kettles are jacket cooling and coil cooling, utilizing circulating water or refrigerant as the coolant. Refrigerant provides faster cooling but at a higher cost. In the event of an abnormal reaction during production, particularly when temperature and pressure rise sharply, operators might evacuate the area quickly for their own safety, potentially failing to cut off the heat source or activate the cooling system effectively. Therefore, an emergency cooling interlock system should be installed at a remote location away from the operator's station. Ideally, located near the steam valve at the workshop's steam distribution header, this system should simultaneously close the steam valve, cut off the agitator power, and activate the cooling interlock. This implements measures to stop heating, cut power, halt agitation, and rapidly cool the system, controlling the incident in its early stages and preventing further escalation.
3. Interlocked Pressure Relief Measures
To ensure timely pressure relief in the event that materials inside the kettle generate gases due to a loss of temperature control, creating pressure, emergency pressure relief devices must be installed on atmospheric reaction equipment according to the specific reaction conditions. A safety valve must be installed on the top of the kettle. For processes that may involve relatively violent reactions, a rupture disc should be installed. The outlet of the rupture disc connection pipe must extend to a safe outdoor location or a ventilation duct intake. It must not point directly toward walkways or operating platforms, to prevent injury from material splashing. For processes involving dropwise addition reactions, the feed rate must be strictly controlled.
4. Closed Conveyance and Anti-Static Measures
The material conveying pipeline system should use steel or plastic pipes selected according to the material characteristics (as a rule, plastic pipes are not to be used, except in special circumstances). Regardless of the pipe type, flanges or bolts must be used for secure connections to prevent detachment and material leakage. Rubber sleeves must not be used to connect plastic pipes for conveying organic solvents. For steel pipes, electrostatic bonding (cross-bonding) must be performed for flange sections. If a pair of flanges has six or more bolts, electrostatic bonding may be omitted. For flanges with four or fewer bolts (including four), electrostatic bonding is required (normally, five bolts are not used for symmetry; if five are present, bonding is also required). Use 4 mm² copper core wire for electrostatic bonding leads. When plastic pipes are used to convey organic solvents or other materials prone to generating static electricity, proper electrostatic connection must be ensured. The method involves placing a thin copper wire inside the pipe. Specifically, a small steel nail should be welded at the metal pipe outlet, slightly inclined inward. The thin copper wire must be wound around this nail and secured, passed through the plastic pipe, and brought out at the other end, where it is also wound and secured at the pipe opening. Only this method ensures a path for static current and its timely transfer to the grounding system.
5. Labor Protection Measures
Install air blowers (supply fans) or exhaust fans at operator stations. This protects the operator's health and reduces the concentration of flammable gases at the station, preventing it from reaching explosive limits. To prevent leakage of gaseous materials from the kettle under pressure from spreading into the control room and harming personnel, an air blower (supply fan) should be installed for the control room. It should introduce fresh air from a high outdoor location into the control room, maintaining a slight positive pressure inside. Equipment emitting toxic or harmful gases should be located downwind of the local prevailing wind direction, facilitating gas dispersion or extraction and enabling operators to perform tasks rationally to reduce exposure to gas pollution.
6. Hot Work Safety Measures
The goal of safety technical measures for hot work management is twofold: first, to ensure no flammable materials are inside the equipment or pipelines involved in the hot work, and second, to ensure no combustible materials are in the surrounding area of the hot work. Achieving these two assurances requires a correct understanding of the importance of hot work management, enhanced safety awareness, and the diligent implementation of safety technical measures such as isolation, lockout/tagout, purging, cleaning, and ventilation. Furthermore, safety management procedures including initial review, re-inspection, approval, fire watch, site cleanup, and final inspection must be followed according to established protocols.
7. Other Safety Measures
All mechanical equipment must be effectively grounded, with a grounding resistance not exceeding 10 Ω. Electric motors must incorporate protective neutral conductor connection measures. Power transmission parts of gear reducers must be equipped with protective guards. Operator platforms must be stable, without shaking or holes. Protective railings must be over 1.05 meters high, with a maximum vertical spacing between rails of 0.35 meters. The installation height of equipment should be set to avoid contact with a person's head. For processes requiring batch feeding during operation, it is advisable to install valves and funnels on the manhole cover. The vent pipe from the condenser must be routed via a connecting pipe to the outdoors or a ventilation duct intake; it must not discharge directly towards walkways or operator work areas. Where conditions permit, emergency evacuation routes and full-process monitoring and alarm systems should be installed. Nitrogen protection measures must be implemented during shutdown procedures. Equipment where power or water supply failure could trigger an uncontrolled reaction must be equipped with a dual-circuit power supply and a dual-water source system.
Emergency Response Measures for Reaction Kettle Incidents in Fine Chemicals
1. Rapid Uncontrollable Rise in Production Temperature and Pressure
When the production temperature and pressure rise rapidly and become uncontrollable, immediately close all material inlet valves. Stop the agitator immediately. Quickly close the steam (or hot water) heating valve and open the cooling water (or chilled water) valve. Rapidly open the vent valve. If no vent valve is present or if temperature and pressure remain uncontrollable, quickly open the bottom discharge valve to dump the material. If the above measures are ineffective and discharging material through the bottom valve cannot be completed quickly, promptly notify all personnel in the area to evacuate the site.
2. Massive Leak of Toxic and Hazardous Substances
In the event of a massive leak of toxic and hazardous substances, immediately notify personnel nearby to evacuate the area swiftly upwind. Quickly don a positive pressure breathing apparatus and close (or secure) the leaking toxic/hazardous material valve. If the leaking valve cannot be closed, promptly notify facilities and personnel downwind (or in the surrounding area) to evacuate or take protective measures. Based on the substance's properties, apply appropriate agents for absorption, dilution, or other treatment. Finally, contain the leaked material and dispose of it properly.
3. Massive Leak of Flammable and Explosive Substances
In the event of a massive leak of flammable and explosive substances, quickly don a positive pressure breathing apparatus and close (or secure) the leaking flammable/explosive material valve. If the leaking valve cannot be closed, immediately notify personnel in the vicinity (especially downwind) to cease all open flames and operations that could generate sparks. Quickly halt other production or activities in the surrounding area. If possible, move the leaking flammable/explosive material to a safe area for handling. If the leaking gas is already on fire, do not rush to close the valve; monitor the situation carefully to prevent flashback and ensure gas concentration does not reach the explosive limit, which could cause an explosion.
4. Personal Injury Response
In case of personal injury, immediately identify the cause of poisoning for effective treatment.
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For inhalation poisoning: Quickly move the affected person to an upwind area with fresh air. If poisoning is severe, transport them to a hospital immediately for emergency treatment.
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For ingestion poisoning: Drink plenty of warm water to induce vomiting. Alternatively, administer milk or egg white for detoxification, or use other substances to promote purging.
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For skin exposure: Immediately remove contaminated clothing and rinse thoroughly with copious amounts of flowing water. Seek medical attention.
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If the victim stops breathing: Perform artificial respiration promptly.
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If the victim's heart stops beating: Perform cardiac compression immediately to restart the heart.
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For extensive skin burns: Immediately flush the burned areas with large quantities of clean water for about fifteen minutes. Take care to prevent hypothermia and frostbite injury. After rinsing, change into uncontaminated clothing and transport the victim to a hospital quickly for medical care.
Summary:
The reaction kettle is the most common equipment in fine chemical production plants and a typical piece of equipment within unit systems. It is a key focus for safety production supervision. Only by effectively managing the safety of every reaction kettle and each unit system, implementing corresponding safety interlock protection measures, and ensuring the installation of alarm interlock devices for human operational errors can the occurrence of accidents be reduced.
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