Explosive dust environment, explosion-proof electrical equipment selection requirements and preventive measures

Explosive dust environment explosion-proof electrical equipment selection requirements and preventive measures

Dust explosion is mainly refers to the particle size less than 75um combustible dust, in a certain range of air suspension, reached the explosive limit concentration, in the open fire, high heat, static electricity under the ignition of the explosion. The power of this chemical reaction is amazing, will cause great harm to the lives of people around. And want to produce dust explosion need to have five conditions, respectively, is the source of ignition, combustible dust, oxygen, limited space, suspension. In order to prevent dust explosions in the case of more combustible dust, you need to take the correct cleanup of dust, eliminate all ignition sources (open flames, high heat, static electricity), explosion relief, explosion suppression and explosion isolation measures.

1 What are the formation factors of a dust explosion?

 Some dust concentration: high concentration, large spacing of dust particles, easy flame propagation

Oxygen content: Oxygen is the basis for the combustion of dust.

Adequate source of ignition

Must be in suspension: Increase gas-solid contact area and speed up reaction rate.

In a relatively confined space: it is in a confined space that the pressure and temperature can rise dramatically and then explode

2 dust explosion-proof electrical equipment requirements

1.1 Shell requirements

There are two main categories of dustproof shell, the first category for the 6 level of dust-tight shell, can completely prevent all the dust into the second category for the 5 level of dustproof shell, this shell than the dust-tight shell of the dust performance is slightly worse, but also able to prevent most of the dust into the normal operation of the equipment does not affect the whole. The entire dust shell for the prevention of dust explosion has a very important role,   Therefore, in the production of dust shell to be engraved on the surface of the Ex permanent mark, while the entire dust shell data information, warnings, etc. should be labeled to prevent the dust shell is destroyed.

1.2 Selection of electrical equipment materials

In order to prevent the entire dust shell cracked, as well as to ensure that the dust shell of the dustproof performance, in the choice of dust shell materials must be selected when the greater strength of the material, such as cast iron, steel and so on. If in some special circumstances the volume of the dust shell is less than 2L, this time you can choose plastic for the production of dust shell, but can not choose ordinary plastics, but to choose a better quality of industrial plastics, and to ensure that the thickness of the entire industrial plastics can not be too large, to prevent the impact of the normal construction of the situation, while the choice of industrial plastics, we must pay attention to the prevention of static electricity to ensure that the resistance of the entire industrial plastics is less than 10%. The resistance of the entire industrial plastic is less than 10Ω, but also in the process of fastening bolts set up metal buried seals, which can be conducive to the outflow of electrostatic discharge, to prevent static electricity caused by the phenomenon of dust explosion.

1.3 Maximum permissible surface temperature of dust enclosure

The use of dustproof shell effectively prevent the entry of dust, prevent the arc spark ignition of dust, but the heat of the electrical equipment will still lead to dust explosion, so we need to use a certain method to reduce the temperature of the entire electrical equipment, to prevent the heat of the electrical equipment caused by the dust explosion. In the surface temperature of electrical equipment to limit the work before, first of all, to have an understanding of the dust in the air, the ignition temperature of different dust there is a big difference, according to the ignition temperature of the dust to limit the heating temperature of the electrical equipment, can not blindly reduce the temperature of the entire shell of the electrical equipment. In the whole process of the work of the construction environment should be long-term cleaning of the dust, reduce the temperature of the dust in the whole environment, and at the same time to carry out regular cleaning of electrical equipment to prevent the phenomenon of dust accumulation.

If it is necessary to open the electrical equipment during the whole working process, it must be ensured that the temperature inside the electrical equipment is less than the maximum temperature limit set on the surface, to prevent dust explosion caused by the opening of the equipment.

3 dust explosion-proof electrical equipment how to select the type of

In the selection of dust-proof explosion-proof equipment before the first to understand the entire electrical equipment, dust-proof electrical equipment in the whole are marked with the ExtD logo, while its corresponding category for the ExtD can not replace the gas explosion-proof electrical dust explosion-proof electrical. Understand these data and then according to the specific construction environment with the dust category for the specific selection of electrical equipment, for example, in the case of high concentrations of dust material must be selected “dust-tight” shell, to prevent dust from entering the electrical equipment to cause an explosion. In some dust concentration is small, no dust cloud only dust layer of the place, for the dust shell can choose “dustproof” shell, so you can prevent the dust explosion phenomenon. Dust explosion-proof electrical types are ExtD shell protection type, ExiD intrinsically safe, ExmD pouring protection type, ExpD positive pressure protection type, while recognizing the signs of explosion-proof electrical equipment, the correct choice of explosion-proof electrical, such as ExtDA21IP65T135 ℃, Ex explosion-proof signs, tD shell protection type, A21A class equipment (flammable) 21 areas, IP56 Equipment protection level, T135 ℃ equipment maximum surface temperature.

After determining all the explosion-proof electrical equipment, the installation of equipment is also a very important part, only in accordance with the existing specifications to be installed, so as to be able to play the dust-proof electrical equipment should be effective, to ensure safe production, to prevent the phenomenon of dust explosions, to ensure that the lives and health of all staff safety.

4 prevention of dust explosion explosion other technical measures

4.1 The main explosion-proof measures taken from the production process equipment electrical selection and layout

To ensure the safety of the entire process of production must first do the reasonable design of the process, to avoid dust generated by the process, followed by the correct selection of electrical equipment, and then also on the entire production process of ignition control, to prevent open flames, for some electrical equipment to be grounded and automatic alarm and other settings, and finally to ensure that all the machinery and equipment can work properly.

4.2 Removal of dust accumulation to prevent explosion

Dust accumulation is one of the important reasons for the emergence of dust explosion, so be sure to do a good job in the entire workshop cleaning work, the air and equipment in the presence of dust clean up. Because dust can also produce flammable gases under certain conditions, so the use of wet methods can not completely eliminate the factors of dust explosion, in the cleanup of dust, try to choose the negative pressure adsorption method to remove all the dust, so that you can do a comprehensive cleanup without dead ends, to achieve a comprehensive cleanup of the working environment. Dust in the air more and more, the natural formation of sedimentation, and sedimentation is also the main cause of the explosion, so we must comprehensively remove the accumulation of dust.

4.3 Explosion venting, suppression and isolation measures

Eliminate the factors of dust explosion, to prevent the occurrence of dust explosion is certainly an important factor to ensure safe production, and in some cases, the factors of dust explosion has been formed can not be eliminated, this time you need to take a certain method of explosion range control, to prevent the emergence of a large area of the explosion, resulting in greater losses. And want to control the scope of the explosion there are three main methods.

The first method is the relief explosion, mainly through the installation of mechanical equipment or buildings on the box-type pressure relief fire extinguishers, this fire extinguisher can be in the event of a localized explosion, and the explosion of the flame mixing to achieve the effect of suppression of the explosion, so as to achieve the pressure relief to control the scope of the explosion;

The second method is to suppress the explosion, explosion suppression is mainly through the explosion suppression controller to play a role in the explosion suppression controller can be detected through two infrared probe on the dust explosion in the discovery of dust explosions in a timely manner to start the alarm measures, while cutting off the power supply, open the protection device, the entire explosion suppression controller is mainly through the control of the explosion effect to achieve the effect of protecting the safe production; the

The third method is explosion-proof, which is mainly realized through the explosion-proof door and other equipment to control the scope of dust explosion and prevent causing more harm.

The entire explosion relief, explosion suppression, explosion isolation of these three methods, can be done to a large extent for the entire dust explosion range of control, to prevent greater losses, to better ensure the smooth progress of the entire construction process, while using these three methods should also choose high-quality and reasonable equipment for installation, to avoid the use of poor-quality equipment.

4.4 Strengthening management, clarifying systems, adhering to implementation, carefully inspecting and improving staff quality

In the prevention of dust explosion to do human prevention and control supervision is very important, the first thing that needs to be done is to establish a clear system of responsibility for the work of each staff to carry out a reasonable layout, will be responsible for the implementation of the person, do a good job on a regular basis to check the layout, etc., and timely maintenance and replacement of equipment, etc., and secondly to establish a strict system of rewards and penalties for doing a good job for staff rewards, for those who have Work errors should be punished to fundamentally improve the safety of the entire work, and finally to all staff to carry out comprehensive training and assessment to ensure that all staff are able to do a safe production, to prevent serious accidents due to staff errors and explosions, to be held regularly, such as lectures, learning and so on, to ensure that each staff member can have sufficient channels for work skills learning and enhancement.