Thread Content
According to the \"Notice of the **State Administration of Work Safety on Publishing the List of Key Hazardous Chemical Processes Subject to Special Supervision\" (An Jian Zong Guan San [2009] No. 116) and the \"Notice of the **State Administration of Work Safety on Publishing the List of Key Hazardous Chemical Processes Subject to Special Supervision in the Second Batch and Making Adjustments to Some Typical Processes Among those in the First Batch\" (An Jian Zong Guan San [2013] No. 3), there are a total of 18 key hazardous chemical processes that are subject to special supervision. Today, we will provide a detailed introduction to several processing techniques and other methods. Oxidation process: Oxidation is the process of losing electrons in a chemical reaction involving electron transfer, that is, a process in which the oxidation number increases. The oxidation of most organic compounds involves the reactants gaining oxygen or losing hydrogen. A process involving oxidation reactions is an oxidation process. Common oxidizing agents include: air, oxygen, hydrogen peroxide, potassium chlorate, potassium permanganate, nitrates, etc. ▶Several typical oxidation processes: Oxidation of ethylene to ethylene oxide ； Oxidation of methanol to formaldehyde ； Oxidation of p-xylene to produce terephthalic acid ； Oxidation of cyclohexane to** ； Oxidation of natural gas to acetylene ； Oxidation of butene, butane, C4 fractions, or benzene to maleic anhydride ； Oxidation of o-xylene or naphthalene to phthalic anhydride ； Oxidation of p-chlorotoluene to prepare p-chlorobenzaldehyde (acid) ； Oxidation of toluene to prepare benzaldehyde (acid) ； Oxidation of p-nitrotoluene to prepare p-***formic acid ； **/Oxidation of alcohol mixtures to adipic acid ； Synthesis of glycolic acid by nitric acid oxidation of glyoxal ； Oxidation of butyraldehyde to butyric acid ； Ammonia oxidation to nitric acid, etc. ▶Process hazard characteristics: 1. The reaction raw materials and products are flammable and explosive ； 2. The composition of the reaction gas phase can easily reach the explosive limit, posing a risk of flash explosion ； 3. Some oxidizers pose a fire and explosion risk; substances such as potassium chlorate, potassium permanganate, and chromium anhydride are all oxidizers. Exposure to high temperatures, impact, friction, or contact with organic materials and acids can all lead to fires and explosions ； 4. Peroxides are likely to form in the product, resulting in poor chemical stability; it is prone to decomposition, combustion, or explosion under the effects of high temperatures, friction, or impact. ▶Key process parameters to be closely monitored include the temperature and pressure inside the oxidation reactor, the stirring speed in the oxidation reactor, the flow rate of the oxidant, the ratio of the reactants, the oxygen content in the gas phase, the peroxide content, etc. Basic requirements for safety control involve alarms and interlocks for the temperature and pressure of the reactor ； Proportional control of reaction materials, interlocks, and emergency shutdown power systems ； Emergency material cut-off system ； Emergency cooling system ； System for urgently introducing inert gas ； Gas phase oxygen content monitoring, alarm, and interlock ； Safety relief system ； Flammable and toxic gas detection and alarm devices, etc. ▶Recommendations for measures: Enterprises involved in oxidation processes should promptly engage professional agencies to conduct risk assessments of the reactions, and take appropriate actions based on the assessment results to ensure process safety. An interlock relationship is established between the temperature and pressure inside the oxidation reactor and the ratio and flow rate of the reactants, as well as with the inlet valve for the cooling water in the reactor’s jacket and the emergency cooling system. An emergency shutdown system is installed in the oxidation reactor, which automatically stops feeding material and triggers an emergency shutdown when the temperature inside the reactor exceeds the specified limits or when there is a malfunction in the mixing system. Equipped with safety devices such as safety valves and burst discs. ▶Event review: At around 16:00 on June 1, 1974, an explosion occurred in a cyclohexane air oxidation reactor at the British company Nypro, resulting in 28 deaths inside the plant, 36 injuries among the plant’s staff, and 53 injuries among people outside the plant. The economic losses amounted to $254.4 million. On May 26, 1990, an explosion occurred at a chemical plant in Itabashi Ward, Japan, resulting in 5 deaths and 17 injuries. The direct cause of the accident was a sudden explosion that occurred during the factory’s operation to produce benzoyl peroxide. Benzoyl peroxide is primarily used as a catalyst in plastic polymerization; it has highly reactive chemical properties and can explode upon slight impact or from sparks. At around 17:25 on April 9, 2009, an explosion and fire broke out in an oxidation reactor at a chemical plant that produced alkaline dyes during a material transfer operation, resulting in one person suffering serious injuries and direct economic losses of over 600,000 yuan. On April 25, 2016, an explosion occurred in the hydrogen peroxide production unit of Jiangxi Zhangjiang Chemical Co., Ltd. during trial production, resulting in 3 deaths, 1 person with minor injuries, and direct economic losses of around 15 million yuan. The direct cause of the accident was that, during the trial production preparation phase, the acidic oxidation working solution should have been alkaline. After initiating an emergency shutdown, the production supervisor attempted to recycle the defective working fluid by illegally releasing the oxidized working fluid into an acidic storage tank and adding phosphoric acid in an attempt to restore the oxidized working fluid to an acidic state. However, the hydrogen peroxide in the acidic storage tank decomposes rapidly under alkaline conditions, releasing heat and generating high-temperature and oxygen-rich combustion gases, which causes a sudden increase in pressure in the tank leading to an explosion; at the same time, this process ignites the oxidizing working fluid. Fluorination process: Fluorination is a reaction in which fluorine atoms are introduced into molecules, and the technological process involved in this fluorination reaction is known as the fluorination process. It is a highly exothermic reaction; the large amount of heat released can destroy the molecular structure of the reactants, even leading to fire and explosion. Fluorinating agents are usually fluorine gas, halogen fluorides, fluorides of inert elements, fluorides of high-valent metals, hydrogen fluoride, potassium fluoride, etc. ▶Direct fluorination: Fluorination of yellow phosphorus to produce phosphorus pentafluoride, etc. b. Fluorination using metal fluorides or hydrogen fluoride gas: Metal fluorides such as SbF3, AgF2, and CoF3 react with hydrocarbons to produce fluorinated hydrocarbons ； Hydrogen fluoride gas reacts with aluminum hydroxide to produce aluminum fluoride and other compounds. c. Displacement fluorination: Fluorination of trichloromethane to produce difluorochloromethane ； 2,4,6-Trifluoro-5-fluoropyrimidine and similar compounds are prepared from tetrachloropyrimidine and sodium fluoride. d. Preparation of other fluorides: Anhydrous hydrogen fluoride is produced by reacting concentrated sulfuric acid with calcium fluoride (fluorite), among others. ▶Process hazard characteristics: The reaction materials pose a fire and explosion risk ； The fluorination reaction is a highly exothermic reaction; if the heat generated by this reaction is not removed in a timely manner, it can lead to overheating and overpressure, thereby causing equipment explosion accidents ； Most fluorinating agents are highly corrosive and highly toxic; during production, storage, transportation, and use, they can pose dangers due to leaks, improper handling, accidental contact, and other accidents. ▶Key monitoring unit: Fluorinating agent storage and transportation unit ▶ Key process parameters to monitor: Temperature and pressure inside the fluorination reactor ； Stirring speed in the fluorination reactor ； Fluoride flow rate ； Additive flow rate ； Ratio of reactant components ； Fluoride concentration. ▶Basic requirements for safety control: Temperature and pressure inside the reactor, as well as alarms and interlocks related to reaction feed and emergency cooling systems ； Stabilization control system for stirring ； Safety relief system ； Flammable and toxic gas detection and alarm devices, etc. ▶Recommendations for measures: Enterprises involved in fluorination processes should promptly engage professional agencies to conduct risk assessments of the reactions, and take appropriate actions based on the assessment results to ensure process safety. During the fluorination reaction, it is necessary to strictly control factors such as fluoride concentration, feeding ratio, feed rate, and reaction temperature. Automatic proportional control devices and automatic interlock control devices should be installed when necessary. Interlocked control is established for the temperature and pressure inside the fluorination reactor, as well as for the stirring operation within the reactor, the flow rate of fluoride, and the inlet valve for the cooling water in the reactor’s jacket. An emergency shutdown system is installed in the fluorination reactor; it automatically stops feeding material and triggers an emergency shutdown when the temperature or pressure inside the reactor exceeds specified limits, or when there is a malfunction in the stirring system. Safety relief system. ▶Accident Review: On July 26, 2019, a hydrofluoric acid leak occurred at Xingguo Xingfu Chemical Co., Ltd. located in the industrial park of Xingguo County, Jiangxi Province. On July 27, when the Emergency Management Bureau of Xingguo County issued its second update on the handling of the leak, it stated that thanks to timely and appropriate measures taken at the scene, the leak was fully controlled, and no casualties resulted from the incident. On January 9, 2016, a hydrogen fluoride leakage and poisoning accident occurred in the perfluoroterephthalic acid workshop of Weifang Changxing Chemical Co., Ltd., resulting in 3 deaths and 1 injury. During the production of tetrafluoroparaxylene diol, hydrogen fluoride vapor is generated. Due to employees altering the production process in violation of regulations and the inadequate sealing of the feed lid on the reaction vessel, hydrogen fluoride leaked and spread, causing poisoning among the workers at the site and in adjacent workshops. On April 14, 2012, three explosions occurred in the vinylidene fluoride (VDF) production workshop of Inner Mongolia Sanaifu Marriott Fluorine Chemical Co., Ltd. The workshop building was severely damaged, multiple pieces of equipment were destroyed, and a large number of pipelines were broken, resulting in 1 death. At 10:40 a.m. on August 11, 2009, at Sinochem Modern Environmental Protection Chemicals (Xi’an) Co., Ltd. in the Jinghe Industrial Park of Gaoling County, Xi’an City, Shaanxi Province, a malfunction in the reactor used for producing tetrafluoroethane – a refrigerant that serves as a substitute for Freon – led to a gas leak (including more than 70 kilograms of hydrogen fluoride gas). As a result, 3 people were hospitalized, and dozens of others underwent various medical examinations in hospitals. Hydrogenation process: Hydrogenation is a reaction in which hydrogen atoms are added to organic compound molecules. The processes involved in hydrogenation reactions are referred to as the hydrogenation process, and they include the hydrogenation of unsaturated bonds, aromatic compounds, oxygen-containing compounds, nitrogen-containing compounds, and hydrolysis. ▶Typical processes: Hydrogenation of triple and double bonds in unsaturated alkynes and alkenes: Hydrogenation of cyclopentadiene to produce cyclopentene, etc. Aromatic hydrogenation: Hydrogenation of benzene to cyclohexane ； Phenol is hydrogenated to produce cyclohexanol and similar compounds. Oxide hydrogenation: Hydrogenation of carbon monoxide to produce methanol ； Hydrogenation of butyraldehyde to produce butanol ； Oleinaldehyde is hydrogenated to produce octanol and similar compounds. Hydrogenation of nitrogen-containing compounds: Hydrogenation of adiponitrile to produce adipamide ； ***Catalytic hydrogenation for the production of aniline, etc. Oil hydrogenation: Hydrocracking of distillates to produce naphtha, diesel, and residue oil ； Residue hydroprocessing ； Hydroreforming of vacuum distillate oil ； Catalytic (isomerization) dewaxing is used to produce low-viscosity diesel, lubricant base oils, etc. ▶Process hazard characteristics: The reaction materials are flammable and explosive; the explosion limit of hydrogen is 4%–75%, indicating a high level of flammability and explosivity ； Hydrogenation is a highly exothermic reaction; when hydrogen comes into contact with steel under high temperature and pressure, the carbon molecules in the steel react with hydrogen to form hydrocarbons, which reduces the strength of the steel components and leads to hydrogen embrittlement ； Explosions can easily occur during the catalyst regeneration and activation processes ； Unreacted hydrogen and other impurities in the exhaust gases from hydrogenation reactions can easily cause fires or explosions when released. ▶Key process parameters to monitor: hydrogen temperature and flow rate ； Coolant flow rate and outlet temperature ； Temperature and pressure inside the reactor ； Reactor sealing performance ； Ambient temperature ； System oxygen content ； Composition and concentration of the exhaust gas, etc. ▶Basic requirements for safety control: Based on high-performance industrial control computers and operating in control systems such as DCS/PLC/FCS, these systems enable complex, multi-variable, large-scale, and highly stable high-performance control of equipment and devices throughout the entire production process, building upon conventional control methods. The practical implementation of advanced control methods can improve the control effectiveness of the production process, enhance various control indicators, thereby increasing the economic benefits for enterprises and reducing energy consumption. Achieve automatic feeding and set up safety interlocks ； An automatic control system is used to record the device status and interlock protection conditions and status in real time, allowing the system to issue an automatic alarm in the event of any abnormalities ； Determine the maximum allowable hydrogen pressure for the process, and establish flow-limiting measures that must not be exceeded ； A dual-temperature control system is employed to monitor in real time that the temperature inside the reactor does not exceed the upper limit of the reaction temperature or the maximum temperature permitted by the system. An emergency cooling system (operating continuously) is provided to ensure that the reactor can be stopped quickly and cooled down in case of emergencies such as cooling water failures or power outages ； Regularly maintain and test the automatic production systems and safety interlock systems to ensure their reliability ； Implement lightning protection isolation measures. ▶Suggestion for measures: Each time the reactor is used, it should be checked for air tightness, and ventilation at the site should be improved to minimize the amount of flammable gas leakage and keep its concentration below the explosive limit ； Strictly control fire sources to prevent fires and explosions caused by flammable gases ； Regular maintenance and calibration of on-site alarm instruments ； Closely monitor key components such as the reactor, high-pressure heat exchangers, high-pressure air coolers, cyclohexane compressors, cyclohexane desulfurization towers, and the tail oil system; in the event of issues such as overheating, overpressure, or deviations from process parameters, immediate alarms should be triggered and prompt action taken ； During the shutdown of the plant, care should be taken to ensure complete and thorough release of hydrogen from high-pressure hydrogen-handling equipment, in order to prevent hydrogen embrittlement ； Strengthen the management of equipment to improve the intrinsic safety factor of the devices. Pay special attention to the areas where high-temperature hydrogen corrosion may occur. Upgrade the materials of equipment and pipelines that are severely corroded to ensure the intrinsical safety of such equipment ； Strengthen the drills for accident emergency plans, and regularly organize operators to study various accident response plans in order to improve employees’ ability to handle emergencies ； Strengthen fire and gas prevention management to ensure that fire and gas prevention facilities are in good condition and that fire access roads remain unobstructed ； The combustible gas alarm devices in the facility should be calibrated regularly. ▶Event review: At around 1:40 p.m. on January 15, 2020, a flash explosion occurred in the pre-hydrogenation unit of a reforming and hydrogenation plant operated by a petrochemical equipment company in Zhuhai, Guangdong, resulting in massive flames at the scene. At 4:06 p.m., the Publicity Department of the Zhuhai Municipal Party Committee announced that the open flames at the scene had been extinguished, and all indicators at the online environmental monitoring stations showed no abnormalities. At around 13:49 on May 3, 2018, a flash explosion occurred inside Hydrogenation Reactor No. 1 in the hydrogenation workshop of a chemical manufacturing company in Taixing City, during the process of removing catalysts from the reactor. The accident resulted in 1 death and direct economic losses of 1.446 million yuan. At 16:14 on March 12, 2018, an explosion occurred in vessel V501, the raw material buffer tank of a 600,000 tons per year diesel hydrotreating unit at a branch company in Jiujiang, resulting in 2 deaths, 1 person with minor burns, and direct economic losses of 3.38 million yuan. At 7:00 on March 22, 1987, an overpressure caused an explosion in the low-pressure separator of the hydrogenation unit at the Grangemouth refinery in the UK, which subsequently led to a large fire. The accident resulted in one death, severe damage to the equipment, and economic losses of $78.5 million.