Coal is a type of sedimentary rock that forms when decaying plant matter is compressed over thousands of years. The most common type of coal is called anthracite. It is formed when pressure and heat turn the decaying plant material into a hard, black substance. Anthracite has a higher energy content than other forms of coal, making it an important fuel source.
In the coal industry, the expression free expansion number (FEN) is used to describe the number at which coal will expand without breaking. FEN directly relates to the coals incipient plasticity, which is a measure of the coals ability to be compressed and then reform. A higher FEN number indicates higher incipient plasticity, meaning the coal will deform and absorb more energy before failing.
The FEN of coal can be determined by measuring its expansion and delivery under a compressive force. This is measured in millimeters with a coal dilatometer and the speed at which the coal deforms is also monitored. The FEN is expressed as the millimeter expansion point of the coal when it can no longer deform without cracking. The higher the FEN, the more energy is needed to deform the coal and ultimately break it.
In addition to its use in the coal industry, FEN is also important for assessing how combustible a coal is. Specifically, the FEN is used to determine the fluidity of coal in a boiler. Fluidized coal burns more efficiently and with less ash than the same coal which is not fluidized. A higher FEN indicates that the coal is more fluid when under pressure, allowing it to be more evenly distributed in a boiler and therefore, provide a more efficient and clean burn.
In conclusion, the FEN of a coal is determined by measuring its expansion, delivery and millimetes under a compressive force. A higher FEN indicates more energy is needed to deform the coal and ultimately break it, as well as more efficient and clean burning in a boiler.
