Dust explosion is the main factor that leads to aluminum powder fire

image_pdfimage_print

The condition of dust explosion

Aluminum powder dust is very easy to cause fire explosion accident. When aluminum powder dust mixes with enough air and under the effect of certain combustion source, any of its superfine solid fuel dust will lead to explosion. Besides, the suspending aluminum powder combustible is entirely possible to cause diffusional secondary explosion. Usually, when the dust particle size is smaller, it will be easier to burn.

The international research results show that the factors that lead to the dust explosion combustion are mainly as follows: a. when the combustible dust is suspending in the air with a certain concentration, its surface molecule will fully contact with air and generate thermal decomposition or destructive distillation, thus it will form gas and discharge around the particles, eventually the explosive mixture will generate, which is the so-called dust cloud; b. enough air and oxidizing agent are required; c. the initial energy should be enough to cause dust explosion, for example, the combustion source or strong vibration and friction are needed as well as there is enough condition for corona and spark discharge, in which the energy that leads to corona and spark discharge should be equal or larger than the minimum ignition energy of combustible. Generally speaking, the accumulational dust will not cause explosion. However, when the suspended dust explosion occurs, the shock wave in the initial blast will raise the accumulational dust and form dust cloud, which will be ignited by the subsequent flame and lead to secondary explosion. As a result, huger explosion energy will produce and will aggravate the hazard degree of fire accident.

Mechanism of dust explosion

Aluminum metal powder is one of the materials that has dust explosion hazard. As it is inflammable under wet atmosphere as well as has small explosive limit and will cause large explosion hazard, it will lead to potential hazard in the aluminum powder production. Therefore, it will have profound historical significance in preventing the aluminum powder dust explosion by understanding the mechanism of aluminum powder.

buy aluminum powderAluminum powder dust explosion is a kind of momentary chain reaction and also belongs to gas-solid two-phase flow reaction. Its explosion process is complex and will be restricted by a number of factors.

Aluminum powder particle surface will obtain the energy from the combustion source by heat conduction and heat radiation, thus the surface temperature will rise sharply, which can accelerate the decomposition and evaporation of dust particles. Under this condition, the dust steam or decomposition gas will generate, which will be easy to cause ignition (gas phase ignition) after mixing with air. In addition, the dust particles will have melting gasification in susccession and will burst out tiny sparks that will become the ignition source of surrounding unburned dust and catch fire, thus it will expand the explosion range. This process is much more complex than gas explosion.

The hazard of aluminum powder dust explosion

The characteristics of aluminum powder dust explosion are as follows:

a. Although the dust explosion rate or the explosion pressure rising rate is smaller than explosion gas, it has longer burning time, will generate larger energy and will cause huger breakage degree.

b. The explosion induction period is very long. The dust explosion process is more complex than gas explosion, which includes the dust particle surface decomposition or evaporation stage as well as the combustion from surface to center, therefore, its induction period is much longer than gas.

c. It is possible to cause secondary explosion. As the shock wave that is generated in the initial dust explosion will raise the accumulational dust and suspend in the air, thus the mixture that reaches the explosion limit concentration range will form in the new space. Meanwhile, the flying sparks and radiant heat will become the ignition source and lead to secondary explosion. This kind of continuous explosion will cause severe damage.

Aluminum powder dust explosion belongs to explosive combustion, which will cause huge damage. When the dust in the air is premixed with a certain amount of air and reaches a certain concentration range, the explosion will happen once it is ignited. In terms of mechanism, dust explosion is considered to be a momentary process and as the explosion power may be very huge, it will cause huge damage. For example, it can destroy the whole building; as the air temperature that generated in the explosion will reach 2000 degrees Celsius to 3000 degrees Celsius and even higher as well as the heat of explosion gas will diffuse in a short moment, the nearby combustible materials will have high temperature and burn, thus it will cause aluminum fire and aggravate the breakage degree of explosion.