Fast pyrolysis of large coal particles in a novel hot plate reactor: Effects of the reaction atmosphere on the porous structure and char reactivity

Fast pyrolysis of large particles of coal semi-anthracite (SA) in a novel Hot Plate Reactor (HPR) was carried out. Advantages of gas flow control of the HPR were used to compare the effect of the reaction atmosphere on the fast pyrolysis process, mainly in aspects such as chemical and porous structure, also in char reactivity. The effects of the heating rate and the reaction atmosphere were evaluated through characterization of the surface of the char by using Fourier Transform Infrared (FTIR). When CO2 reaction atmosphere was used, evidence was found of thermoplastic effects, and such effects might have caused retention of aliphatic structures typical of volatile material. This shows that different processes apply to devolatilization of large coal particles compared to devolatilization under conventional combustion conditions. In addition, the possible presence of thermal annealing and graphitization of chars may explain their poor performance under combustion, due to carbonaceous structure chemical deactivation, which was stronger in those obtained under CO2 atmosphere than those obtained under N2 atmosphere. This allowed demonstrating that when it comes to large coal particles combustion, it is not advisable to assume as true the knowledge acquired during devolatilization under conventional combustion conditions.