Rapid pyrolysis of low rank coal: dynamic modeling and parameter analysis of a novel solid heat carrier in a co-current downer reactor

A novel co-current downer pyrolyzer was developed to enable high-temperature heat-carrying particles, preheated in a fluidized bed, to directly contact coal particles. This study clarifies the kinetics and parametric effects on coal-tar yields and properties during the fast pyrolysis of low-rank coal. Using the Friedman and Flynn-Wall-Ozawa methods and the Distributed Activation Energy Model (DAEM), apparent activation energy values were calculated across different conversion rates, ranging from 305.55 to 325.54 kJ/mol.The results indicate that the optimum temperature for coal-tar production is 580 °C. Favorable outcomes were observed with coal particle sizes between 0.18 mm and 0.25 mm. Larger particle sizes increase the intraparticle temperature gradient, resulting in more unreacted coal inside the reactor and lower product yields. Under optimized conditions, the tar yield reached 122% of that achieved by the chrome-gold method, with saturated and aromatic components in the tar comprising 23.52% and 44.65%, respectively.FT-IR analysis revealed that the intensity of O-H, C-O, and C=O groups varied with pyrolysis parameters. These findings confirm the feasibility of the rapid pyrolysis process for low-rank coal, supporting the production of high-quality coal tar and its industrial applications.