Slow and Rapid Pyrolysis of Coal

Abstract

Coal is a heterogeneous, mainly organic, material which decomposes upon exposure to high temperatures. This process is called pyrolysis. Coal pyrolysis is the most important aspect of coal behaviour because it occurs in all major coal conversion processes. Upon pyrolysis coal is divided into a hydrogen-rich volatile fraction, consisting of gases, vapors, and tar-components, and a carbon-rich solid residue. Moreover, for certain coals decomposition can result in a temporary softening of the solid material. The pyrolysis process consists of a very complex set of reactions involving the formation of radicals. The overall decomposition of coal is open to manipulation by a variety of experimental conditions. Due to the nature of the coal conversion processes distinction should be made between slow Cheating rate < 1 K/s) and rapid Cheating rate > 1000 K/s) pyrolysis of coal. In this chapter the experimental techniques used to study the chemical an the physical changes which occur upon slow and rapid pyrolysis of coal are reviewed. Relevant experimental results are described. The influence of experimental conditions on the yield and composition of the volatile fraction, liberated upon coal pyrolysis, is considered. Some models, which describe the overall process of coal pyrolysis, are given. Finally, this chapter is concluded with a study on the thermal stability of aromatic model compounds, relevant in coal pyrolysis, to elucidate the nature and to describe the extent of primary and secondary reactions.