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Negative pressure ventilation to keep your plant away from dust explosion

Article Source:Admin Popularity: 1548  Published: 2015/4/15 

I believe 2014 Kunshan-Metal Company That alarmed the whole nation of "dust explosion" event, we all can remember it! This caused 146 deaths and a direct economic loss of 351 million yuan of large accidents, the explosion so that the number of families lost their loved ones, this explosion make this larger enterprise instant bankruptcy, the explosion so that the number of people being responsible legal action, painful price, bloody lessons must be borne in mind, let's look at dust storm is about how to produce

1. generation condition

Dust explosion conditions are generally three:

(1) to the appropriate concentration of combustible dust suspended in the air, forming a cloud of dust is often said;

Where was fine state of solid material are called dust. You can burn and dust called a combustible dust explosion; floating dust in the air is called suspended dust; settling on a solid wall of dust called deposition of dust.

Explosive dust: metal (such as magnesium, aluminum); coal; grain (such as wheat, starch); feed (such as blood meal, fish meal); agricultural products (such as cotton, tobacco); forest products (such as paper powder, wood powder); synthetic materials (e.g., plastics, dyes).

Some factories produce dust generated in the process, especially some dust generated organic process, under certain conditions can burn explosion accident.

(2) there is sufficient air and oxidant;

(3) sources of ignition or intense vibration and friction.

Principle 2 explosion

Tend to be more prone to dust explosion roughly aluminum, zinc, ferrosilicon powder, magnesium, iron, aluminum processing abrasive powder, plastic powder, organic synthesis intermediates pharmaceuticals, wheat flour, sugar, wood chips, dyes, bakelite gray, milk powder, tea powder, tobacco dust, grime, dust and other plant fibers. These materials are prone to dust explosions burn because there are strong reducing agent H, C, N, S and other elements are present, when they coexist with peroxide and explosive dust, they decompose, produced by the oxidation reaction a large amount of gas, or gas amount is small, but the release of a large amount of combustion heat. For example, aluminum powder in a carbon dioxide atmosphere in there as long as the risk of explosion.

Physical and chemical properties and environmental conditions of dust explosion difficulty with dust related. Heat of combustion is generally believed that the greater the likely explosion of matter, such as coal dust, carbon, sulfur and so on. Oxidation rate of substances that can explode, such as magnesium, aluminum, ferrous oxide, dyes and the like. Easily charged dust is also very easy to cause an explosion, such as synthetic resin powder, fiber dust, starch and the like. These adverse conductive material and machine due to static electricity generated by friction or air build up, when it reaches a certain amount, it will discharge spark, constitute the source of fire explosion.

Typically there is unlikely to cause an explosion of dust soil, sand, iron oxide, abrasive materials, cement, silica dust and similar combustion dust. Dust and chemical properties of such materials is relatively stable, so you will not burn. But if such oil mist and dust generated in CO, CH4, gas and the like combustible gases, but also prone to explosion.

Dust explosion visual development formed by the following three steps: The first step is the suspension of dust quickly dry distillation or gasification at heat sources to produce a combustible gas; the second step is a combustible gas is mixed with air and combustion; s three steps dust released by burning calories to heat conduction and flame radiation way to pass close to or suspension of dust blowing up there, the dust after the combustion cycle heat of vaporization to continue. With successive conducted each cycle, the reaction speeds up, through intense burning, the final form of explosion. This explosive reaction and explosion flame speed, explosion wave velocity, explosion pressure will continue to accelerate and increase, and was a great leap forward.

3 Features hazards edit this section

3.1 Factors

Physical and chemical properties

Combustion greater thermal mass, then the danger of dust explosion greater, such as coal, carbon, sulfur dust; more easily oxidized substance, the more explosive dust thereof, such as magnesium, ferrous oxide, dyes and the like; more easily charged dust more easily this explosion. Dust in the production process, due to collide with each other, friction and other effects, is not easy to dissipate static electricity, resulting in the accumulation of static electricity, when reaches a certain value, then static discharge. Electrostatic discharge spark can cause fire and explosion. Dust explosion also contains volatile matter related thereto. When pulverized coal in less than 10% volatile matter, it is no longer the explosion occurred, and therefore no coke dust explosion hazard.

Particle size

Surface adsorption of dust in the air of oxygen, the finer particles, the more oxygen adsorption and thus more prone to explosion, and that the lower the ignition point, the lower the lower explosive limit. With the decrease of the diameter of the dust particles, not only increases the chemical activity, but also easy to bring static electricity.

Dust Levels

Combustible gas phase intended, dust explosions have a certain concentration range, there are upper and lower limits of the points. But in general most of the information lists only the lower explosion limit of dust, because of the high ceiling dust explosion.

3.2 Explosive Features

(1) The most important feature is the multiple explosions of dust explosion.

The first explosion blast, put dust deposited on the device or on the ground to blow up there, a short time after the explosion in the central area of ​​the explosion will be a negative pressure surrounding the fresh air will come in from outside to inside to fill, and it raises the a dust, causing secondary explosions. When the second explosion, dust concentration will be higher.

(2) The minimum ignition energy required for high dust explosion, usually in the tens mJ or more.

(3) Compared with the flammable gas explosion, dust explosion pressure rise more slowly, high pressure continues for a long time, the energy released is large, strong damage.

3.3 The main hazards

(1) has a strong destructive. Range of dust explosion involving a wide, coal, chemical, pharmaceutical processing, wood processing, food and feed processing and other sectors have occurred.

(2) prone to secondary explosions. The first blast of the explosion is deposited on the device or on the ground of dust blowing up there, in the central area of ​​the explosion a short time after the explosion will be a negative pressure surrounding the fresh air will come in from outside to inside to fill, a so-called "return wind ", and it raises the dust mixed in under the first explosion ignited embers caused the second explosion. When the second explosion, the dust concentration is generally much higher than when the first explosion, secondary explosions so much more powerful than the first secondary. For example, a sulfur flour mill, grinding machine internal explosion, the blast wave along the gas pipeline from the mill spread to a cyclone, a second explosion occurred in the cyclone, after the blast wave produced by the explosion in the cyclone The cracks propagate to the workshop, he raised the settlement process equipment in the building and sulfur dust, and exploded.

(3) can produce toxic gases. A carbon monoxide; the other is the explosives (such as plastic) decomposition of toxic gas itself. Gas generation tends to cause a lot of livestock poisoning casualties after the explosion, must pay full attention.

4 Precautions

Such as the use of effective ventilation, non-smoking and fire operations. Pressure relief valve is provided in the device housing or other device used in explosion containment systems. Dust explosion hazard for the plant, must be in strict accordance with explosion-proof technical level design, and provided separately ventilated, dust exhaust system. Always wet cleaning shop floor and equipment to prevent dust and aggregation. Ensure that the system should have a good tightness of the closed container or pipe filled with combustible dust if necessary nitrogen, carbon dioxide and other gases, in order to reduce the content of oxygen, inhibit dust explosion.

Xia Wei Yi fan, which use air convection, the principle of negative pressure ventilation ventilation cooling, the indoor poor (odor, heat, smoke, dust, etc.) quickly exhausted to the outside, so that the interior pressure lower than outdoors, while the role of the atmospheric pressure , the outdoor fresh air from the rapid inflow of indoor installation opposite windows negative pressure exhaust fan, ventilation frequency of up to 60 times per hour (100M2 workshop), thus creating a comfortable working environment fresh and clean air. In some metallurgy, coal, chemical, electroplating, polishing, food processing and other industries generate combustible dust workplace, often occur dust filled environment, therefore, the choice of better ventilation, to improve equipment and workshop environment, to ensure the production only the safe operation of great significance. My company production of ventilation cooling equipment - suction fan, allowing you to shop dust, smoke, odors swept away! Suction fan fully reflects the high efficiency, low energy, environmental protection, cost, wide range of other top-five advantage, has become the brand of choice for many enterprises ventilation. ]

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