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Introduction of explosion-proof electrical appliances for reaction kettle

By Thomas Huang December 7th, 2023 106 views

I General

In chemical production, the production equipment usually needs to be operated in flammable and explosive environments. Such equipment must comply with explosion-proof standards and utilize explosion-proof materials and techniques to avoid explosions caused by sparks, static electricity, high pressure, and high temperatures.

II Classification of explosive atmospheres

2.1 Gas Classification

 Working condition  Gas classification  Representative gas  Minimum detonation spark energy
 Mine underground  Ⅰ  methane  0.280mJ
 Factories outside the mine  ⅡA  Propane  0.180mJ
 ⅡB  Ethylene  0.060mJ
 ⅡC  Hydrogen  0.019mJ

2.2 Classification of hazardous media:

Taking explosive gases as an example, they are classified into three categories: IIA, IIB, and IIC. In comparison, IIA gases are the most difficult to ignite, and IIC gases are the most easily ignited.

2.3 Temperature groups of explosive media:

Again using explosive gases as an example, it is divided into six groups from T1 to T6. The T1 group of gases is the most difficult to ignite, T6 group of gases is the most easily ignited.
T1: gas ignition temperature t >450 ℃
T2: gas ignition temperature 300
T3: gas ignition temperature 200
T4:Gas ignition temperature 135
T5:Gas ignition temperature 100
T6:Gas ignition temperature 85

2.4 Classification of explosive hazardous areas:

Classification of explosive gas mixtures
The explosive gas environment is divided into Zone 0, Zone 1, and Zone 2, and their correspondence is as follows:
Zone 0: under normal circumstances, the explosive gas mixture continuous or long-term existence in the place (1000h/year or more);
Zone 1: in normal operation, explosive gas mixtures may occur in the place (10~1000h/year);
Zone 2: places where explosive gas mixtures are unlikely to occur during normal operation, and if they do occur, they occur occasionally and are present only for a short period. (below 10h/year).

III Requirements for equipment for use in specific explosive atmospheres

3.1 Equipment structure:

Explosion-proof equipment has a more rigorous structural design, including more hermetically sealed housings, explosion-proof junction boxes, explosion-proof electrical components, and so on. These special designs can ensure the safe operation of the equipment in explosive environments.

3.2 Operational safety:

Explosion-proof equipment is safer and more reliable in the operation process and can prevent sparks, arcs, and other situations that may cause explosions.

3.3 Marking:

Electrical equipment may be tested for a specific explosive atmosphere, in which case the relevant information should be recorded in the explosion-proof certificate of conformity and the electrical equipment should be marked accordingly.
Before using explosion-proof electrical equipment, be sure to check the nameplate of the equipment.

IV Explosion-proof electrical products are categorized according to their applications:

Lamps and lanterns:
There are three kinds of internal bulbs, tubes, and LEDs.
Electrical appliances: 
Operating columns, switches, buttons, distribution boxes, starters, and control cabinets.
Pipe fittings: 
Junction box, threading box, live joints, flexible connecting pipe
Safety barriers, meters, telephones.
Electric bell, fan, transformer, plug, ballast, heater, air conditioner.

V Application to stirred reactors

Whether or not to select electrical equipment for reactors with explosion-proof features is based on the actual environmental conditions of the place where the reactor is to be installed and used. 
In general, explosion-proof equipment is required where there is a potential risk of explosion.
The explosion-proof electrical appliances for reactors include:
Explosion-proof distribution boxes, explosion-proof control boxes, explosion-proof motors, and some independent explosion-proof electronic devices such as junction boxes (boxes), wiring boxes, meters, and so on. 
The following are introductions for  the most frequently used three devices: 
the explosion-proof power distribution box, explosion-proof control box, and explosion-proof motor.

VI Explosion-proof Distribution Boxes ( control carbinet)

6.1 Characteristics of the explosion-proof distribution box

photo of explosion-proof distribution box

6.1.1 Explosion-proof performance:

Explosion-proof distribution box has explosion-proof performance and can operate safely in an explosive environment. It adopts special materials and structural design, which can effectively prevent the diffusion of explosion sparks and ignition of surrounding combustible gases or dust, to protect the safety of equipment and personnel.

6.1.2 Protection level:

Explosion-proof distribution box usually has high protection level, such as IP65 or IP66, which can effectively prevent the intrusion of external substances such as dust, water vapor, and water splash, and improve the durability and reliability of the equipment.

6.1.3 Applicable environment:

The explosion-proof distribution box is suitable for flammable and explosive industrial environments, such as petrochemicals, coal mines, chemical engineering, and other places.
An ordinary distribution box is mainly applicable to general industrial places or civil buildings.

6.1.4 Design standard:

The design and manufacture of explosion-proof distribution boxes need to comply with specific explosion-proof standards and specifications, such as the international explosion-proof standard IEC60079 series.
However, ordinary distribution boxes follow the general design standards for electrical equipment.

6.1.5 Price:

Due to the special design and manufacturing requirements of explosion-proof distribution boxes, as well as their high protection performance, their price is usually higher than ordinary distribution boxes.

6.2 National standard specification requirements for explosion-proof distribution box (China)

According to the national standard GB3836-2010 "Explosion-proof Electrical Equipment for Explosive Environments", the design and manufacture of an explosion-proof distribution box need to follow the following specification requirements:

6.2.1 Explosion-proof type:

According to the hazard rating of the use environment, explosion-proof distribution boxes can be divided into intrinsically safe, explosion-proof, increased safety type, pressurization, and so on. The type selection of the explosion-proof distribution box is based on the specific working environment and its usage.

6.2.2 Explosion-proof grade:

The explosion-proof grade of the explosion-proof distribution box is divided into four grades: A, B, C, and D, of which grade A is the highest and grade D is the lowest.
The explosion-proof grade of the explosion-proof distribution box needs to be selected according to the hazardous degree of the combustible gas mixture in the environment.

6.2.3 Explosion-proof structure:

The design of the explosion-proof distribution box needs to take into account the arrangement and connection of electrical equipment, wires, connectors, and other components to prevent the sparks and arcs generated by the electrical equipment from triggering an explosion.

6.2.4 Working environment:

The design of the explosion-proof distribution box needs to take into account the influence of the working environment, such as high temperature, high humidity, corrosive gases, and so on, to ensure that it can work normally in all kinds of harsh environments.

6.2.5 Safety:

The design and manufacture of explosion-proof distribution boxes need to follow certain safety standards, such as protection against electric shock, fire, lightning, etc., to ensure their safety.

6.3 How to choose an explosion-proof distribution box

6.3.1 Select the explosion-proof distribution box by national standards:

When choosing an explosion-proof distribution box, you need to choose products that meet national explosion-proof standards and have relevant certifications.

6.3.2 Consider the weight and size of the equipment:

When selecting an explosion-proof distribution box, the size and weight of the equipment to be installed need to be considered. If the equipment is heavy or large, it may be necessary to select a larger or heavier explosion-proof distribution box.

6.3.3 Consider the operating environment:

The selection of an explosion-proof distribution box may vary in different environments. For example, in cold environments, it may be necessary to select an explosion-proof distribution box with better insulation.

6.3.4 Consider safety:

When selecting an explosion-proof distribution box, its safety needs to be considered. A safer Explosion-proof distribution box will usually provide more effective protection.
In general, the requirements of national standards for explosion-proof distribution boxes are the basis for ensuring their safety and effectiveness. These requirements need to be followed when selecting and using explosion-proof distribution boxes to ensure industrial safety.

VII Explosion-proof control box

7.1 Features of explosion-proof control box

7.1.1 Material of shell and special treatment

The material of the explosion-proof control box shell is high-strength metal. The shell is applying a special process. The shell surface uses high-pressure electrostatic spraying with strong adsorption plastic powder. 
The material has good corrosion resistance, bright and clean.

7.1.2 Increased safety shell

Modular structure and customized, with explosion-proof indicator, ammeter, voltmeter, buttons and transfer switches, and so on.

7.1.3 Flameproof enclosure

Built-in indicator lamps, ammeters, voltmeters, pushbuttons, change-over switches, relays, etc;

7.1.4 Customized Electrical Components Display

The internal electrical components can be arranged and assembled according to user requirements;

7.1.5 Wiring type

Can use steel pipe, explosion-proof flexible connecting pipe, or explosion-proof cable.

7.2 Types of explosion-proof control box and related uses

7.2.1 Wall-mounted explosion-proof control boxes

The wall-mounted explosion-proof control box is especially suitable for sites with high air cleanliness requirements, such as test laboratories, pharmaceutical company workshops, and so on.
 This type of explosion-proof control box is made of high-quality aluminum alloy, with heat-resistant, corrosion-resistant, and explosion-proof performance characteristics, and can be very good for maintaining electrical equipment and ensuring its normal operation.
In addition, this type of explosion-proof control box also has a compact structure, is easy to install, easy to use, has other characteristics, is durable, and has low maintenance costs.
photo of Wall-mounted explosion-proof control boxes

7.2.2 Vertical explosion-proof control box

Vertical explosion-proof control box for general industrial environment and chemical environment, such as chemical plants, oil and gas fields, natural gas extraction, and refineries.
 This kind of explosion-proof control box is made of carbon steel, and the surface is coated with antirust and anticorrosion paint, which can resist corrosive gases, high temperature, high pressure, and other factors in the environment.
They are also durable, sturdy, easy to assemble, and easy to maintain.
photo of Vertical explosion-proof control box

7.2.3 Explosion-proof control box with batteries

Explosion-proof control panels with batteries are suitable for use in areas that need to be left unmanned for long periods, such as hazardous areas, mainframe rooms, and substations.
photo of Explosion-proof control box with batteries  This type of explosion-proof control box has a battery pack and battery charging management system, which can provide sufficient power to ensure that the system is in a power outage or shut down the power premise of normal use.
It also has the advantages of anti-fouling, moisture-proof, explosion-proof, etc. It is mainly applicable to harsh environments to ensure the safety and stability of electrical equipment.

7.2.4 Real-time monitoring explosion-proof control box

Real-time monitoring of explosion-proof control boxes must be applied to real-time detection of the operating state of the equipment, such as industrial production automated assembly lines, water treatment plants, etc.
This type of explosion-proof control box internal structure is configured with a variety of sensors, detectors, and remote communication equipment, real-time collection, transmission, and analysis of machine data information, and remote operation of the equipment's running status.
Also has the advantages of being explosion-proof, corrosion-resistant, and highly stable, the electrical equipment can also be in a harsh environment for a long time.

VIII Explosion-proof motors

photo of explosion proof motors

8.1 Explosion-proof motors and ordinary motors in the labeling differences

The rated voltage, rated current, power, and speed of explosion-proof motors are the same as those of ordinary motors, but the explosion-proof motors have more explosion-proof symbols: Ex.
Explosion-proof motors generally must be equipped with an explosion-proof certificate when purchased. The explosion-proof certificate is generally issued by the competent authorities, you can verify the authenticity and validity of the network, for the relevant factories are also required to ensure that this certificate to ensure the safety of explosion-proof motors qualified type.

8.2 Explosion-proof motor labeling symbols significance of identification

Explosion-proof type + equipment category + (gas group) + temperature group explosion-proof.

8.3 Explosion-proof type standard:

China's explosion-proof grade standard is "GB3836.1-2000 Electrical equipment for the explosive gas environment", which will be supplemented or modified by the following explosion-proof type standards.
GB 3836.2 Electrical equipment for explosive gas environment Part 2: Flameproof enclosures "d".
GB 3836.3 Electrical equipment for explosive gas environments, Part 3: Increased safety type "e".
GB 3836.4 Electrical equipment for explosive gas environments Part 4: Intrinsic safety "i"
GB 3836.5 Electrical equipment for explosive gas environments, Part 5: Pressurization "p".
GB 3836.6 Electrical equipment for explosive atmospheres, Part 6: Oil-immersion "o".
GB 3836.7 Electrical equipment for explosive atmospheres Part 7: Powder filling "q"
GB 3836.9 Electrical equipment for explosive gas environments Part 9: Casting type "m"
GB 7957 Mining helmet lamps
The above standards and this standard do not apply to medical electrical equipment.

8.4 Examples:

The common symbol is "Exd Ⅰ / Ⅱ BT3".  
"Ex" is a common symbol, indicating explosive
"d" means that the second explosion-proof type is "explosion-proof type d".
"Ⅰ" or "Ⅱ" that the classification of electrical equipment, Ⅰ for coal mine electrical equipment, Ⅱ for other explosive atmospheres in addition to coal mine equipment. 
Among them, Ⅱ explosion-proof type "d" and intrinsically safe "i" electrical equipment are divided into Ⅱ A, Ⅱ B, and Ⅱ C." T3" indicates the temperature group.
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