Research On The Minimum Ignition Temperature Of Combustible Dusts

In the dust manufacturing, processing and other projects, once the combustible dustdisperses and suspends in the air, then the ignition source exists, it is possible to explode. Inrecent years, with the continuous production process and dust usage is increasing year by year,dust explosion accidents occur from time to time, also the casualties of the accidents cannotbe underestimated. The minimum ignition temperature of dust as one of the characteristics ofthe dust explosion, it can not only measure the dust hazard, but also can provide an importantbasis for explosion-proof technology design and explosion-proof equipment selection.Therefore, studying the minimum ignition temperature of combustible dusts has veryimportant practical significance.A standard Godbert-Greenwald furnace apparatus was used to measure the minimumignition temperature of magnesium alloy dust, corn starch, sulfur dust, wood dust and coaldust. The effect of concentration, pressure, particle size, and humidity inert dust on theminimum ignition temperature of combustible dusts was also studied. The test results showthat:（1）Minimum ignition temperature decreases with the increasing of the dustconcentration, but when the concentration increased to a certain value, the minimum ignitiontemperature of dust is almost a constant, namely there is a sensitive concentration that at thisconcentration, the minimum ignition temperature of the combustible dust is the lowest. Andin this experiment, the sensitive concentration of magnesium alloy dust, corn starch, sulfurdust and coal dust is all1364g/m3, and the minimum ignition temperature of the four dusts isrespectively615℃,415℃,235℃,583℃; The sensitive concentration of wood dust is909g/m3, the minimum ignition temperature of it is474℃.（2）Diffusing pressure has influence on the minimum ignition temperature of combustible dust, with the increasing of the diffusing pressure, the minimum ignitiontemperature of combustible dusts first decreases then increases. When the diffusing pressureis0.03MPa, it is more advantageous for the combustion of magnesium alloy dust, corn starch,sulfur dust and coal dust, the ignition temperature is the lowest. When the diffusing pressureis0.02MPa, it is more advantageous for the combustion of wood powder. The ignitiontemperature of wood dust is the lowest under0.02MPa comparing to the ignition temperatureunder other diffusing pressure.（3）Once the concentration and diffusing pressure are constant, the minimum ignitiontemperature of combustible dust increases with increasing of the particle size，the effect ofparticle size on the minimum ignition temperature of dust is obvious. While the particlediameter of wood dust increasing from38μm to45μm, the minimum ignition temperatureincreases from474℃to541℃. The minimum ignition temperature of magnesium alloy dustincreases from545℃to615℃while the particle size increasing from45μm to75μm.（4）CaCO3and NH4H2PO4as inert medium can effectively inhibit the combustionreaction and make the minimum ignition temperature of combustible dust increase and theinhibition effect of NH4H2PO4on the dust combustion is stronger than CaCO3. In this test, theminimum ignition temperature of magnesium alloy dust increases with the increasing ofcalcium carbonate mass fraction and when the mass fraction reaches to52.4%, the inhibitioneffect is obviously and the minimum ignition temperature of magnesium alloy dust increasessignificantly. The minimum ignition temperature of coal dust increases significantly when themass fraction of inert medium up to23.1%.（5）The environmental humidity also has certain influence on the minimum ignitiontemperature of combustible dust. With the increasing of the environmental humidity, theminimum ignition temperature of dust increases. So high humidity can effectively suppressthe dust combustion. The effect of humidity on the wood dust is the largest. Corresponding tothe humidity of43%,57%and69%, the minimum ignition temperature of wood dust is474℃,523℃and552℃.