Large coal piles stored for long periods are liable to undergo self-heating due to the chemisorption of oxygen and low-temperature oxidation. In extreme conditions self-ignition and eruption of fires may occur. It has been reported that the emission of carbon dioxide, which is the main gaseous product, is accompanied by small but appreciable amounts of carbon monoxide, low molecular weight hydrocarbons and molecular hydrogen. The presence of these gases appreciably lowers the temperature of self-ignition and increases the risk of fires. The mechanism and the nature of the side reactions responsible for the emission of these gases are not well understood. A study of the different parameters which affect these emissions has been performed. The results indicate that the emission of the saturated hydrocarbons occurs via two different paths: (i) a fast process which is dependent on the concentration of oxygen; and (ii) a slow process which occurs also in an inert atmosphere. The emission of unsaturated products such as ethylene is an oxidation-correlated process (which resembles the molecular hydrogen emission) and terminates after all the oxygen has been consumed.
- atmospheric conditions
- coal storage