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Coal dust suspended in air is explosive—coal dust has far more surface area per unit weight than lumps of coal, and is more susceptible to spontaneous combustion. However, five elements are needed for an explosion to occur: oxygen, an ignition source, coal dust, dispersion of the coal dust, and confinement of the dust. [4]
Lab demonstration with burning lycopodium powder. A dust explosion is the rapid combustion of fine particles suspended in the air within an enclosed location. Dust explosions can occur where any dispersed powdered combustible material is present in high-enough concentrations in the atmosphere or other oxidizing gaseous medium, such as pure oxygen.
Damp is the collective name given to all gases (other than air) found in coal mines in Great Britain and North America. [1]As well as firedamp, other damps include blackdamp (nonbreathable mixture of carbon dioxide, water vapour and other gases); whitedamp (carbon monoxide and other gases produced by combustion); poisonous, explosive stinkdamp (hydrogen sulfide), with its characteristic rotten ...
Since any breathable atmosphere contains oxygen, and a safety lamp's raison d'être is to operate in an atmosphere also containing fuel (firedamp or coal dust), the element which must be blocked is heat. The key to manufacturing a successful safety lamp is to control the transfer of heat while still allowing air (the necessary oxidant) to enter ...
In addition to wood, combustible dusts include metals, especially magnesium, titanium and aluminum, as well as other carbon-based dusts. [19] There are at least 140 known substances that produce combustible dust. [20]: 38 [21] While the particles in a combustible dusts may be of any size, normally they have a diameter of less than 420 μm.
The creation of sparks from metals is based on the pyrophoricity of small metal particles, and pyrophoric alloys are made for this purpose. [2] Practical applications include the sparking mechanisms in lighters and various toys, using ferrocerium; starting fires without matches, using a firesteel; the flintlock mechanism in firearms; and spark testing ferrous metals.
The pressure of the magma builds until the blockage is blasted out in an explosive eruption through the weakest point in the cone, usually the crater. (However, in the case of the eruption of Mount St. Helens , the pressure was released on the side of the volcano, rather than the crater. [ 3 ] ).
Coal is ground to the size of a fine grain, mixed with air and burned in the flue gas flow. Biomass and other materials can also be added to the mixture. Coal contains mineral matter which is converted to ash during combustion. The ash is removed as bottom ash and fly ash. The bottom ash is removed at the furnace bottom.