The thermoplastic characteristics of a packed bed of coal with different particle sizes were investigated in carbonization. The dilatation of the packed bed of coal was examined using a dilatometer, and the amount of volatile matter released from the coal particles was evaluated using a thermogravimetric meter. As a result, the total dilatation (TD) of a coal bed with an average diameter of 67 µm was 127%, and that with an average diameter of 60.5 µm was 80%. We revealed that its particle size affects the swelling of the packed bed of coal. The release behavior of volatile matter (i.e., temperature and the amount of the releases) was different depending on the particle size. Therefore, the release rate and amount of volatile matter depend on the coal particle sizes, and the particle size of coal particles affects the swelling behavior of the packed bed of coal.

The swelling of a packed bed of coal during carbonization was numerically investigated. The coal particles were assumed to be spheres capable of swelling. When falling particles of the same size, the height of the packed bed was determined by the particle size, and during swelling of particles of the same size, the height of the packed bed was also determined by the particle size. However, the height of the packed bed with different particle sizes was lower than that of the packed bed with particles of the same size. This was owing to the densifying of the smaller particles between the larger particles. When the swelling ratio of the particles in the differently packed beds was 25%, no difference in dilatation was observed. By fitting the numerical solutions and previous experimental data, the difference in the swelling ratio between the smaller and larger particles was 16.8%.