char

…subsequent combustion of the residual char. Following ignition and combustion of the evolving volatile matter, oxygen diffuses to the surface of the particle and ignites the char. In some instances, ignition of volatile matter and char occurs simultaneously. The steps involved in char oxidation are as follows:

For thermodynamic and kinetic considerations, char is taken to be graphite, or pure carbon. In reality, however, coal char is a mixture of pure carbon and impurities with structural defects. Because impurities and defects can be catalytic in nature, the absolute reaction rate depends on their amount and nature—and also…