Modeling heat transfer and chemical reactions during pyrolysis of a single PCB particle

Pyrolysis is a promising approach for recovering both metal and non-metal components from waste printed circuit boards (PCBs). The behavior of a single PCB particle is fundamental to all practical applications. This study develops a pyrolysis model that integrates heat transfer and reaction kinetics for a single PCB particle. The heat transfer characteristics, chemical reaction properties, and the interaction between these processes are explored. The results indicate a strong correlation between temperature and reaction rate during pyrolysis. Endothermic reactions at the particle's outer layer significantly hinder the temperature rise, reducing the reaction rate. The reaction rate is influenced by both heat supply and reactant concentration. Specifically, during the intense reaction stage, the reaction rate at the outer surface of the particle is predominantly constrained by reactant concentration, while the reaction rate within the particle is primarily governed by the heat supply. Furthermore, the particle smaller than 0.75 mm is not restricted by internal heat transfer during fast pyrolysis. The lumped parameter method is unsuitable for fast pyrolysis, while its critical dimension for slow pyrolysis closely relates to the heating rate. At 600 °C and heating rates of 10, 15, and 20 °C/min, the critical particle sizes are 16.73 mm, 11.45 mm, and 9.27 mm, respectively. These insights offer valuable guidance for optimizing the pyrolysis process and enhancing energy utilization in PCB pyrolysis.