In addition to taking measures to eliminate flammable and explosive gases, steam leaks, and dust flying, it is also necessary to control fire sources in places where flammable and explosive materials are produced, used, and stored. Among them, a reasonable explosion risk environment zone classification and explosion-proof electrical equipment selection is a key issue in factories and enterprises that manufacture and use chemical dangerous goods. China, like other industrial countries, has formulated environmental codes for the classification of fire and explosion hazardous environments and specifications and regulations for electrical equipment, and has provided scientific evidence for the regional division of fire and explosion hazardous environments and the selection of electrical equipment. 1 Division of Explosion Hazardous Areas If an oil refinery or one of its installations has flammable substances as its raw materials and products, it is extremely uneconomical for the entire plant or installation to be identified as an explosion hazardous location. Obviously, it is also unreasonable. The emergence of flammable substances has created a potentially explosive environment. The so-called potential means that they do not appear at all times, and some have a high frequency and some have a low frequency. In this case, there are dangerous places and dangerous places. Therefore, it is necessary to carry out a "place classification" of these dangerous places. The purpose of classification is to use the principle of statistics to classify the degree of danger of a site according to the frequency of the gas environment and the length of existence of the gas environment in the site so that different explosion protection measures can be used according to the type of the hazardous area. 1.1 Finding and Identifying Hazards Sources of explosive gas atmospheres exist in the workplace where flammable gases, vapours or mists form flammable gas mixtures with air. Therefore, it is necessary to determine whether flammable substances are present in the relevant premises. In the chemical production enterprises, the equipment (such as tanks, pumps, pipelines, containers, etc.) in each chemical operation unit has, in its interior, materials capable of forming a flammable gas environment, it shall be deemed as a release source, which may pose a danger Site; If the equipment contains flammable materials but does not release into the environment (such as all welded pipes, etc.), it should not be considered as a source of release, and it will not form a hazardous location. In the classification of sites, the level of release source should be determined first according to the frequency and duration of release of flammable substances. According to the design criteria of the electric equipment in explosion and fire hazardous environment 92), the regulations are divided into three levels: 1.1.1 Continuous release source The release source that is expected to be released for a long period of time or frequently released in a short time. It can be classified as a continuous release source like the following: surfaces of flammable liquids in fixed overhead tanks not covered with inert gas; surfaces of flammable liquids such as oil and water separators that come in direct contact with the space; often Or free vents and other orifices for the long-term release of vapors of flammable or flammable liquids into space. 1.1.2 Primary Release Source The release source that is expected to operate during normal operation or occasionally released. Similar to the following circumstances, can be classified as the first release source: in the normal operation will release flammable substances of the pump, compressor and valve seal; in normal operation, will release flammable materials to the space, installed in Drainage system for containers containing flammable liquids; sampling points for flammable materials released into space during normal operation. 1.1.3 The secondary release source is not expected to release during normal operation, even if it is released only as an occasionally released release source. Similar to the following cases, it can be classified as a second-level release source: In the normal operation, the seals of pumps, compressors, and valves that release flammable substances cannot occur; flanges, connectors, and pipelines that cannot release flammable substances during normal operation Fittings; Safety valves, vents, and other orifices that cannot release flammable substances into space during normal operation; Sample points that cannot release flammable substances into space during normal operation. 1.1.4 Multi-level release source The release source consisting of the above two or three levels of release sources is called a multi-level release source. 1.2 Division of Explosion Hazard Zones The division of explosion hazard zones is based on the frequency and duration of the occurrence of explosive mixtures. According to the design specifications of electrical installations for explosive and fire hazardous environments, the explosion is first divided according to the explosion hazard zone classification map and the level of the release source. Hazardous area: The area where there is a continuous release source can be classified as zone 0; the zone where the primary release source is present can be zoned as zone 1; the zone where the secondary release source is present can be zoned as zone 2. Secondly, the regional division should be adjusted according to the ventilation conditions: when the ventilation is good, the level of the explosion danger zone should be reduced; when the ventilation is poor, the level of the explosion danger zone should be improved; and the local mechanical ventilation is more effective in reducing the concentration of the explosive gas mixture than natural ventilation and general mechanical ventilation. When effective, local mechanical ventilation can be used to reduce the level of explosive hazards; in obstacles, pits, and dead ends, the level of explosion hazards should be increased locally; using barriers such as embankments or walls to limit explosive gas mixtures that are heavier than air Diffusion can narrow the scope of explosive danger zones. In the production plant, Zone 0 is extremely individual, and most of them belong to Zone 2. When dividing the explosion hazard zone in the design, reasonable measures should be taken to minimize Zone 1. 2 Range of Explosive Gas Environmental Hazardous Areas Range of Explosive Gas Environmental Hazard Areas should be in accordance with the scope of the 2.1 explosion hazardous area should be based on the level and location of the release source, the nature of flammable substances, ventilation conditions, obstacles and production conditions, operating experience , Comprehensively determined by comparison of technology and economy. 2.2 Within the building, the scope of the explosion hazard zone should be delineated by the plant as a unit. However, according to the specific conditions of production, when the space inside the workshop is large and the flammable material released from the release source is of low quality, the internal space of the workshop may be used. Delimit the scope of the explosion hazard and meet the following requirements: 2.2.1 When the building has flammable substances that are heavier than air, the number of ventilation changes in the workshop shall not be less than 2 times/h, and ventilation shall not be affected. Obstruction; the concentration of explosive gas formed by the air with an internal volume of 1 m inside the factory floor and the flammable substances released into the workshop shall be less than the lower explosion limit. 2.2.2 When the building has flammable substances that are lighter than air, the volume of air within the height of 1m below the plane of the flat roof of the building or within 2m below the highest point of the dome and inclined roof, and flammable release into the building The concentration of the explosive gas mixture formed by the substance should be less than the lower explosion limit. In the actual application process, the situation described above should also be conceived: the maximum amount of flammable substances released into the plant should be calculated as 3 times the release amount of 1 hour, excluding the release amount due to a catastrophic accident; Explosive gases with a relative density of less than or equal to 0.75 are defined as lighter than air; explosive gases with a relative density greater than 0.75 are defined as gases heavier than air. 2.2.3 When flammable substances may be released in large quantities and diffuse beyond 15m, the area of ​​the explosion hazard zone shall be divided into additional 2 zones. 2.2.4 In the event that the material operating temperature is higher than the flash point of the flammable liquid, the range of the explosion danger zone may be appropriately reduced when the flammable liquid may leak. Determine the level and scope of the explosion hazard zone should comply with the relevant regulations, and should be based on the release of flammable substances, gas or vapor release rate (release source geometry, release rate, concentration, flammability liquid volatility, Liquid temperature, flash point) relative density of released gas or vapor, lower explosion limit, and local climate and topography, etc., combined with practical experience. The increase and decrease of these quantities are directly related to the size of the explosion risk area. The factors defined by these quantities are more complicated. Therefore, the parameters listed above for the size of the impact range are only adopted by the IEC (International Electrotechnical Commission) regulations, which have so far been only a principle and no specific dimensions can be followed. Since the conditions, processes, equipment, instruments, ventilation arrangements, etc. of the actual production equipment are all different, proper design must be properly selected in combination with actual conditions to ensure safety. After the explosion hazardous area is divided, a “division map of explosion hazard area†should be drawn for the result to serve as the selection basis for the electrical equipment within the area. 3 Principles of Type Selection of Electrical Equipment for Explosive Gas Environments The scope of explosive hazards refers to the range of areas where the explosion danger concentration may form under normal circumstances, rather than the scope of accidents. Within this area, appropriate anti-explosion electrical equipment should be installed; outside of the explosion hazardous area, non-anti-explosive electrical equipment can be installed. However, it is not possible to use open flames or other sources of fire as the basis for operations in this area, because electrical equipment is different from other sources of ignition. The selection of explosion-proof electrical equipment must follow the following principles. 3.1 Principles for selection of equipment Selection of explosion-proof electrical equipment must be compatible with the risk of explosive mixtures. The degree of danger of a so-called explosive mixture refers to the group of explosive levels and ignition temperature of an explosive mixture. The selected explosion-proof electrical equipment must be compatible with the detonation level, group, and level of the hazardous area of ​​the explosive mixture. Otherwise, the safety cannot be guaranteed. In addition, if there are two or more explosive substances with different levels of danger in the same area, the explosion-proof structure must be selected to suit the explosion level and natural temperature level with the highest degree of danger. In non-hazardous areas, ordinary electrical equipment is generally used. However, when a container containing explosive substances is placed in a non-hazardous area, there is a possibility of danger in abnormal situations. For example, due to the container corroded by hazardous substances, or due to the operator's misuse of the release of dangerous substances, or due to abnormal reactions to the formation of high temperature and pressure, so that the device, the container is damaged and leaked explosive substances. Therefore, the possibility of accidental danger must be considered. 3.2 Selecting the appropriate type of explosion protection The explosion protection structure must be suitable for use in hazardous areas. What kind of hazardous area must be used in what kind of explosion-proof structure. Explosion-proof performance is due to different structures, so you must choose the type of explosion-proof according to the type of explosive substances, the type of equipment, the degree of danger of the installation site. 3.3 Adapt to environmental conditions The explosion-proof performance mentioned in this article is based on the standard environment as a basic condition. Explosion-proof equipment is divided into "indoor use" and "outdoor use". The equipment used indoors is used outdoors and the ambient temperature of 40 feet is not suitable. Outdoor use of equipment to adapt to the open-air environment requires the prevention of sun, rain and sand and other measures. In addition, some devices are used in corrosive or toxic environments, high temperature, high pressure, or low temperature environments. When selecting explosion-proof devices, special requirements for these special environments should be considered. 3.4 To facilitate maintenance The maintenance and repair of explosion-proof electrical equipment during use is extremely important. Choose the structure of the explosion-proof electrical equipment as simple as possible, at the same time pay attention to convenient management, short maintenance time, low cost, but also to do a good job of normal storage of spare parts and spare parts. 3.5 Should pay attention to the economic benefits When using explosion-proof electrical equipment, not only to consider the purchase and sale price, but also to conduct a comprehensive analysis and balance of the reliability, life, operating costs, energy consumption and maintenance of electrical equipment, in order to select the most economical and appropriate explosion-proof electrical equipment. 4 Conclusion In the environment that can form explosion hazardous areas, in addition to focusing on the division of explosion hazardous areas, the selection of explosion-proof electrical equipment and other content, there are many other requirements, such as the design and installation of lightning protection facilities, electrostatic protection equipment Special factors such as design and installation. At the same time, the division of hazardous areas in explosive dust environments and the selection of explosion-proof electrical equipment cannot be ignored either. The content described in the article is purely a part of my understanding of the specification, and it is hoped that it will provide for the division of explosion hazardous areas of production companies and the selection of explosion-proof electrical equipment. The “Highly-skilled Talents Training Model†and the open curriculum system based on the work process system are adopted to support the paid and top-paying talents, and the “Chemical Machinery Installation and Construction†and “Chemical Production Device Maintenance†courses with professional characteristics have been developed. The establishment of a practical training environment that can serve the outside world has achieved remarkable results. The profession will be further oriented to employment and will serve the purpose of serving the production and construction of the petrochemical industry in Jilin Province. We will train and train high-skilled personnel for the application of chemical machinery installation and maintenance jobs. Equipment installation and maintenance technician level curriculum content, teaching conditions, teaching methods and organizational models. Why You Need A
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