"
Explosion-proof electrical equipment is a kind of safety electrical equipment, which is widely used in explosion hazard places in petrochemical and other industries. Reasonable and correct selection, installation, overhaul and maintenance of explosion-proof electrical equipment is an important part of avoiding explosion accidents. This article briefly describes the explosion-proof principle, the selection of explosion-proof electrical equipment, and the requirements of standards and specifications for your reference.
"
In the production process of petrochemical plants, there are a large number of leakage potential performance of explosive mixtures, in order to ensure the safety of personnel and production, explosion-proof instruments and equipment should be reasonably selected.
In 2019, the Ministry of Emergency Management promulgated Document No. 78 "Guidelines for the Investigation and Management of Potential Safety Hazards", in 2017 the Work Safety Supervision Bureau issued Document No. 121 "Criteria for Determining Major Safety Hazards", and in 2020 promulgated the "Three-year Action Implementation Plan for Special Rectification of Hazardous Chemicals Safety".
These laws and regulations have put forward clear requirements: explosion-proof electrical equipment should be installed and used in explosion hazard places in accordance with the requirements of national standards. The explosion-proof level of electrical equipment should meet the explosion-proof requirements of the corresponding area.
This includes electrical equipment and instrumentation equipment.
The above requirements are the terms that constitute the determination of major hidden dangers, and are strictly implemented in the engineering design and project implementation. This fully shows that the importance of explosion protection should be paid special attention in engineering design and project implementation!
Petrochemical plant features
All places involving the production, processing, handling, storage and transportation of explosive substances may form an explosive atmosphere, and the leakage of explosive substances will inevitably occur in the production fields of petroleum, chemical industry, coal, etc., and form an explosive dangerous place in the air.
According to the information:
Ø Under coal mines, 2/3 of the premises are called explosive hazardous places;
Ø About 60~80% of the oil production sites and refineries are explosive hazardous places (explosion hazard areas);
Ø In the chemical industry, more than 80% of the production workshops are explosive hazardous places (explosion hazard areas).
Sources:
Safety Supervision Manager No. 3 [2017] No. 121 "Judgment Standards for Major Production Safety Accidents in Chemical and Hazardous Chemicals Production and Business Units (Trial)"
12. Explosion-proof electrical equipment is not installed and used in explosion hazard places in accordance with national standards.
In general, the selection principle of explosion-proof electrical equipment:
The selection principle of explosion-proof electrical equipment is safe, reliable, economical and reasonable.
Explosion-proof electrical equipment shall be selected according to the class of the explosion hazard area and the type, grade and group of explosive hazardous substances.
AQ 3009-2007 Safety Code for Electrical Explosion Protection in Hazardous Locations
5. Selection of explosion-proof electrical equipment in explosion hazard places
5.1 Selection principles
Selection principle of explosion-proof electrical equipment:
a) The selection principle of explosion-proof electrical equipment is safe, reliable, economical and reasonable.
b) Explosion-proof electrical equipment shall be selected according to the class of the explosion hazard area and the type, grade and group of the explosion hazardous substance.
Relevant standards:
GB 50058, GB 3836, AQ 3009, GB 12476, GB 25286, IEC 60079, API RP 505, etc.
Extended reading:
1. Confirm the zoning, classification, grading and grouping of hazardous areas
Electrical sparks and temperature in electrical instrumentation are the main sources of ignition that produce an explosion. The ignition characteristics of different explosive substances vary. In order to make explosion protection measures more targeted, it is necessary to divide the hazardous area of explosive gas atmospheres and classify, classify, classify, and group explosive gas substances/mixtures.
Zoning: Determine the safety (degree) requirements for electrical equipment according to the likelihood (probability) of the occurrence of an explosive atmosphere.
Classification, grading, grouping: According to the type and characteristics of the gas/dust, the class and group of explosion-proof electrical equipment shall not be lower than the class and group of combustible substances in this explosive atmosphere.
Examples of different ignition characteristics of explosive gaseous substances are shown in Table 1.
2. Confirm the zoning of explosive hazardous environments
An explosion hazard area is an area where explosive mixtures occur or are expected to occur in quantities sufficient to require precautions for the construction, installation and use of electrical equipment.
Under atmospheric conditions, the mixture of gases or vapor combustible substances and air ignites and can maintain an environment in which combustion propagates on its own, which is an explosive gas environment.
Under atmospheric conditions, the mixture formed by combustible dust and air is ignited, and the combustion can maintain an environment where combustion spreads on its own, which is an explosive dust environment.
GB 50058-2014 Code for Design of Electrical Installations in Explosion Hazardous Environments
2.0.12 爆炸危险区域 hazardous area
Areas where explosive mixtures occur or are expected to occur in quantities sufficient to require precautions for the construction, installation and use of electrical equipment.
2.0.10 爆炸性气体环境 explosive gas atmosphere
Under atmospheric conditions, a mixture of gases or vapors combustible with air ignites to maintain an environment in which combustion propagates on its own.
2.0.24 爆炸性粉尘环境 explosive dust atmosphere
Under atmospheric conditions, the mixture formed by combustible dust and air is ignited, and the environment in which combustion spreads on its own can be maintained.
3. Confirm the protection level of the partition and device
The selection of the level of protection of electrical equipment in explosive atmospheres is generally determined by the classification of hazardous areas.
The selection shall be in accordance with Table 5.2.2-1:
GB 50058-2014 Code for Design of Electrical Installations in Explosion Hazardous Environments
5.2.2 The relationship between the classification of hazardous areas and the protection level of electrical equipment shall comply with the following provisions:
1 The selection of the protection level of electrical equipment in explosive atmospheres shall be in accordance with the provisions of Table 5.2.2-1.
4. Confirm the protection level (EPL) of electrical equipment and the explosion-proof type of electrical equipment
The relationship between the electrical equipment protection level (EPL) and the explosion-proof type of electrical equipment of commonly used explosion-proof instruments shall be in accordance with the following table:
Note: (1) The electrical equipment of the increased safety type "e" used in Zone 1 is limited to the electrical equipment defined in Note A in Table 3 of GB/T 3836.15-2017.
5. Confirm the classification and grading
The class and group of explosion-proof electrical equipment shall not be lower than that of the explosive gas mixture in the explosive atmosphere. The relationship between the classification of gases, vapors or dusts and the category of electrical equipment shall be in accordance with the provisions of Table 5.2.3-1:
GB 50058-2014 Code for Design of Electrical Installations in Explosion Hazardous Environments
5.2.3 The class and group of explosion-proof electrical equipment shall not be lower than the class and group of explosive gas mixture in the explosive gas atmosphere, and shall comply with the following requirements:
1 The relationship between the classification of gases, vapors or dusts and the category of electrical equipment shall be in accordance with the provisions of Table 5.2.3-1. When there is an explosive mixture formed by more than two flammable substances, explosion-proof equipment should be selected according to the level and group of the mixed explosive mixture.
Explosion-proof equipment marked as suitable for specific gases and vapors shall not be used in other gas environments without identification.
6. Confirm the grouping
The class and group of explosion-proof electrical equipment shall not be lower than that of the explosive gas mixture in the explosive atmosphere.
The relationship between the temperature group, the maximum surface temperature and the ignition temperature of gas and vapor of Class II electrical equipment shall be in accordance with the provisions of Table 5.2.3-2.
The maximum surface temperature of Class III electrical equipment shall be determined by the minimum ignition temperature of the relevant dust minus the safety margin.
Electrical equipment used in explosive dust atmospheres will be directly marked with the maximum surface temperature of the equipment, and the temperature group will no longer be divided.
Content basis:
GB 50058-2014 Code for Design of Electrical Installations in Explosion Hazardous Environments
5.2.3 The class and group of explosion-proof electrical equipment shall not be lower than the class and group of explosive gas mixture in the explosive gas atmosphere, and shall comply with the following requirements:
2 The relationship between the temperature group, the maximum surface temperature and the ignition temperature of gas and vapor of Class II electrical equipment shall be in accordance with the provisions of Table 5.2.3-2.
General Code for Electrical Engineering in Explosive Atmospheres (Draft for Comments)
3.1.4 The class and group of explosion-proof electrical equipment shall not be lower than the class and group of flammable substances in the explosive atmosphere, and shall comply with the following requirements:
3 The maximum surface temperature of Class III electrical equipment shall be determined by the minimum ignition temperature of the relevant dust minus the safety margin.
Explanation of Provisions,
Paragraph 3 is modified on the basis of Article 5.6.3.1 of "Explosive Atmospheres Part 15: Design, Selection and Installation of Electrical Installations" GB/T 3836.15-2017, and this general specification only gives the principle of determining the maximum surface temperature of Class III electrical equipment, and the specific method can be found in the above standard. Electrical equipment used in explosive dust atmospheres will be directly marked with the maximum surface temperature of the equipment, and the temperature group will no longer be divided. For example, for electrical equipment with explosive dust atmospheres in explosive dust atmospheres class III.C "ia" (EPL Da), the maximum surface temperature below 1200 °C can be expressed as Ex ia III.C T1200 °C Da or Ex ia III.C T1200 °C IP20.
Temperature group or maximum surface temperature is one of the basic parameters of the safety performance of explosion-proof equipment, is the most basic requirement of explosion-proof electrical design, practice has proved that the correct selection of temperature group or maximum surface temperature can reduce or eliminate the possibility of electrical equipment as a source of ignition for the conditions that cause explosions.
Examples of Explosive Gas Classification and Grouping:
7. Consciousness cognition
8. Confirm the explosion-proof type and technical measures
Seek to eliminate one or more of the three elements of the explosion so that the risk of explosion is reduced to an acceptable level.
9. Check the explosion-proof signs for explosive gas atmospheres
GB 3836.1-2010 Explosive atmospheres – Part 1: General requirements for equipment
29.14 Examples of Signs
Flameproof enclosure "d" (EPL Mb) for coal mines prone to gas:
Ex d I. Mb or Ex db I.
Flameproof enclosure Ex element "d" (EPL Gb) with intrinsically safe "i" (EPL Ga) output circuit for use in Class C explosive gas atmospheres except for coal mine gas gases (symbol "U" after the explosion-proof certificate is compiled):
Ex d[ia Ga] II.C Gb or Ex db [ia] II.C.
Electrical equipment using increased safety type "e" (EPL Gb) and positive pressure housing type "px" (EPL Gb), with a maximum surface temperature of 125 °C, is used in explosive gas atmospheres with an ignition temperature higher than 125 °C, except for coal mines prone to gas, and the specific conditions for safe use are indicated in the explosion-proof certificate (the symbol "X" is added after the explosion-proof certificate is compiled):
Ex e px II.C 125°C(T4)Gb or Ex eb pxb II.C 125°C(T4)
Electrical equipment for coal mines using separator housings "d" (EPL Mb and Gb) and increased safety type "e" (EPL Mb and Gb) and explosive gas atmospheres with ignition temperatures higher than 200°C for Class B gases except coal mines prone to gas generation:
Ex de I. Mb or Ex db eb I.
Ex de II.B T3 Gb or Ex db eb II.B T3
Flameproof enclosure electrical equipment "d" (EPL Gb) for use in atmospheres with only ammonia explosive gases, except in coal mines prone to gas generation:
Ex d II. Ammonia (NH3) Gb or Ex db II. Ammonia (NH3)
For explosive dust atmospheres with conductive dust, Class III.C encapsulated electrical equipment "ma" (EPL Da) with a maximum surface temperature of less than 120°C:
Ex and III.C T120°C Da 或 Ex and III.C T120°C IP68
For electrical equipment in explosive dust atmospheres with conductive dust, class III.C "ia" (EPL Da) with a maximum surface temperature of less than 120°C:
Ex ia III.C T120°C Da or Ex ia III.C T120°C IP20
For use in electrical equipment with explosive dust atmospheres class III.C "p" (EPL Db) with conductive dust, with a maximum surface temperature of less than 120°C:
Ex p III.C T120°C Db or Ex pb III.C T120°C IP65
For use in electrical equipment with explosive dust atmospheres class III.C "t" (EPL Db) with conductive dust, the maximum surface temperature is less than 225°C, and when tested with a 500mm dust layer, it is below 320°C:
Ex t III.C T225°C T500 320°C Db or Ex tb III.C T225°C T500 320°C IP65
In short, if you want to figure out the explosion-proof design principles and the following problems, there will be no big problem in the selection.