Risk Analysis of Fire and Explosion in Acetic Acid Production and Its Fire Safety Countermeasures

Acetic acid is an important basic organic chemical raw material, mainly used in the preparation of vinyl acetate monomer (VCM), acetate fiber, polyvinyl alcohol, acetate, etc., in dyes, spices, medicines, pesticides and adhesives. A wide range of uses is one of the basic organic chemical products that have developed rapidly in recent years. In 2008, China's acetic acid production capacity has reached about 3.3 million tons. With the development of science and technology, the scale of acetic acid production is becoming larger and more complex, and the potential fire and explosion hazard in the production process is also increasing. Therefore, the evaluation and analysis of fire and explosion risk during the acetic acid production process is of great practical significance for improving production safety and economic benefits.

First, the acetic acid production process and the fire and explosion hazard of the reaction device

At present, acetic acid production at home and abroad mainly adopts methanol low-pressure oxo process production process, using carbon monoxide and methanol as raw materials, under a certain temperature and pressure conditions, with the action of catalyst and accelerator, low-pressure carbonyl synthesis of acetic acid. The main reaction materials in the acetic acid production process, carbon monoxide and methanol, have explosion ranges of 61.5 and 30.5, respectively. The explosion range is quite wide and the explosion risk is very high. They are all flammable, explosive and explosive. The acetic acid production reaction device is an integrated system designed or selected for achieving specific process performance and capable of organically combining various production equipments of various performances, and the production reaction device has the following dangerous characteristics:

(1) The continuity of production of acetic acid reaction equipment, the concentration of operation and the automatic control of the whole process, eliminating many intermediate storage links, and the failure of each link on the production line will have a major impact on the overall situation.

(2) With the development of modern science and technology and the continuous maturity of the production process principle, acetic acid production tends to become larger and larger, the reaction device is centralized, and a large number of chemical substances are in the process state. Caused a major accident, posing a serious threat to the safety of the country and people's lives and property. For example, in the process of producing acetic acid from acetic acid, accidents caused by carbon monoxide leakage caused by casualties have been more common in the past.

(3) Most of the acetic acid production process is closed. A large number of processing processes are in closed reactor tanks and pipelines. The internal conditions are difficult to observe directly. The entire production situation is transmitted from the sensor and transmitter to the control center. Various pressure, flow and temperature signals on the instrumentation are reflected, which puts higher safety requirements on operation and monitoring work.

(4) There are many side reactions in the production of acetic acid. Some mechanisms are not fully understood. Once the production conditions are out of control, serious accidents may occur. There are many interference factors affecting the various process parameters of acetic acid production, and the preset parameter values ​​are prone to offset, even in the process of automatic adjustment, the phenomenon of runaway will occur. At the same time, due to the difference in quality of employees and poor ergonomics design, it often causes misuse, such as mistaking the meter and opening the wrong valve.

2. Analysis of fire and explosion types in the production process of acetic acid

The main dangers in the acetic acid production process are fire and explosion, and the types of fire and explosion mainly include leakage type and reaction uncontrolled type.

(1) Leak-type fire and explosion. Leakage type fire and explosion refers to a fire, explosion caused by a container, machinery or equipment that processes, stores or transports combustible materials for some reason to cause flammable substances to leak into the outside or combustion-promoting substances into the equipment. The most common process in the production of acetic acid is the leakage of carbon monoxide gas. The main causes of leakage are: leakage caused by the deterioration of equipment material properties, leakage caused by equipment defects, and leakage caused by human factors, such as misuse, illegal operation, equipment operation. Poor maintenance and so on.

(2) Responding to an uncontrolled fire and explosion. The uncontrolled fire explosion is caused by the fact that the exothermic rate of the chemical reaction in the acetic acid production process exceeds the heat dissipation rate, resulting in heat accumulation in the system, an increase in temperature, an increase in the reaction rate, and a condensation of the reaction product, causing the reaction process to be out of control and causing a fire and explosion accident. In the reaction process of methanol low pressure carbonylation to produce acetic acid, if the raw materials are too much or the feed rate is too fast, the materials are not pure, etc., the violent reaction may be triggered, and the heat in the reaction tank is sharply increased. The failure of refrigeration equipment, insufficient cooling, agitator failure, uneven agitation, etc., are the main reasons for the unfavorable heat dissipation during the production of acetic acid.

There are many ways of fire and explosion accidents during the acetic acid production reaction. According to the analysis of the accident tree, in the case of multiple basic causes, the leakage of combustible materials in the reactor and the air are mixed to reach the explosion limit, and the reactor cooling is unfavorable. The most important factors, followed by equipment material performance degradation, equipment defects and other human factors lead to leakage of combustible materials, again caused by open fire, high temperature, static sparks, electrical sparks, impact sparks, lightning strikes and other causes.

Third, the fire safety countermeasures in the production process of acetic acid enterprises

(1) Principles of fire safety measures. According to the results of the analysis of the risk of fire and explosion in the acetic acid production process, the principle of “ensure key hazardous parts and control important basic cause events” should be adopted. The acetic acid reactor unit must be given priority safety protection, and sufficient human and material resources should be invested to strengthen safety. Implementation of the measures. At the same time, it is necessary to strictly control the most important basic cause events such as the reactor cooling failure, which can cause the occurrence of fire and explosion accidents in the acetic acid reactor unit, and the basic performance of the equipment in the process unit, equipment defects, open flames, impact sparks, etc. The cause events are strengthened and controlled according to their importance, and they are taken into account. In addition, the safety monitoring of the acetic acid reactor process unit should be strengthened, and strict work permit management systems and operating procedures should be developed and implemented to prevent fire and explosion accidents.

(2) Fire safety design requirements. In order to protect the safety of people and property, in the safety design of fire protection and explosion-proof of acetic acid enterprises, the principle of “prevention first, anti-disintegration” should be implemented, and firefighting should be strictly followed in accordance with “Code for Fire Protection of Building Design” and “Code for Designing Fire Safety of Petrochemical Enterprises”. The requirements of technical standards and regulations, targeted fire prevention, explosion-proof measures to prevent and reduce fire hazards. For example, the total surface of the acetic acid plant should be arranged according to the production process of the plant and the production characteristics of each component and the fire hazard, combined with the topography, wind direction and other conditions, according to the functional division; the acetic acid production equipment and pipeline should be based on the internal materials. Fire and explosion hazard and operating conditions, set the appropriate instrument, alarm signal, automatic interlock protection system or emergency stop measures; acetic acid production enterprises should also set up fire-fighting facilities and equipment suitable for the materials they produce, store and transport, for full-time Used by firefighters and post operators.

(3) Fire safety operation measures. First, prevent the leakage of combustible materials. For equipment purchased in the acetic acid production process, qualified products produced by qualified manufacturers must be selected. During the production reaction, it is necessary to prevent leakage of CO gas and methanol liquid caused by failure of the safety accessories of the reactor, valve failure and tank damage. Second, we must strictly control the fire source. Open flames are strictly forbidden in the tank area. The liquid material in the process pipeline must control the flow rate. It is forbidden to use mechanical equipment and tools that are prone to sparks. The electrical facilities must be explosion-proof. The process unit should be installed in strict accordance with the requirements of the regulations. All equipment and pipelines should be equipped with static electricity. Ground. Third, we must ensure the cooling effect. It is necessary to regularly check the various flowmeters, regulating valves, analyzers, pressure gauges, thermometers and other instruments and accessories of the calibration reaction system to ensure that they are in good condition. For the operation of the refrigeration system in the production reaction process, it is necessary to strengthen inspection and maintenance, and at the same time, there should be a refrigeration backup system to ensure the safety of refrigeration in the production of the process unit.

(4) Fire safety management measures. Due to the complexity of the acetic acid production process, operators are more likely to make mistakes. Therefore, enterprises must configure scientific and reliable automatic control systems in strict accordance with relevant national standards and industry standards, and develop practical and feasible fire safety management systems and operational procedures. To eliminate and reduce the possibility of fire and explosion accidents caused by human error. In accordance with the relevant regulations of the state, province, city and industry authorities, it is necessary to equip with the necessary safety and health monitoring equipment and on-site first-aid equipment, and it is advisable to set up an ambulance station or a health center near the factory to facilitate timely and effective injury to the injured. Treatment. In addition, education and training on the operational skills, safety protection and emergency response of operators should be strengthened. In particular, the operators of the acetic acid reaction section should be subject to strict fire safety training. They must be certified by fire safety training and be certified to be familiar with the acetic acid production process. They have a high degree of responsibility and have the ability to prevent and treat fires during the production of acetic acid. The ability to explode dangerous situations and promptly respond to and promptly deal with emergencies.

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