Combustion and explosion
What is combustion, or burning in other words?
Combustion is also called oxidation which means a chemical reaction that material combines with oxygen, and the material emits heat and light.Combustion needs oxygen to oxidize, however, additional energy for ignition is also necessary. There are several types of ignition energy such as flame, electric spark, frictional heat, heat of reaction and so on.
The reason materials get more burnable after drying is that the materials get more oxidizable because water or other liquid evaporate from the material.
On the other hand, combustion with rapid chemical reaction is called explosion.It is a phenomenon that caused by rapid chemical reaction, generates large amount of gas and heat with large sounds, sparks, and destruction, and occurs with burst caused by rapid increase of pressure inside.
One which propagate at supersonic speed with shock wave is called detonation, and one whom flame propagates at around sonic speed which is faster than several meters per second is called deflagration.
There are several types of explosion that we often hear in our industry as below.
1)About dust explosion
Even for materials like powder which cannot be said as burnable normally, when they are floating in air as dusts, each grain of them are in state which is very burnable, very oxidizable in other words.In such a state that huge number of small grains are floating, rapid chemical reactions easily triggered with a trivial ignition so that explosion occurred.
2)About steam explosion
When water contact to hot metal, one case is that the water decomposes into hydrogen and oxygen then explosion occurs by igniting the hydrogen, and another case is that water becomes steam with explosive speed and explosion occurs by sudden increase of its volume.
Steam explosion accident of hot blast furnace is one of the examples.