Inert particle tracking of flow fields for selective tar enhancement in a fixed-bed reactor with internals

This study introduces an innovative inert particle tracking method to directly visualize and regulate volatile flow patterns within a fixed-bed coal pyrolysis reactor equipped with internal baffles. Unlike conventional studies focusing solely on product yields, we employed coal-quartz co-pyrolysis coupled with colorimetric analysis of quartz to map real-time volatile transport. Results demonstrated that internals redirected volatiles from the hot reactor wall toward the cooler core, significantly altering temperature profiles and reaction pathways. This controlled flow field suppressed secondary cracking and promoted condensation of heavy tar components in the low-temperature zone, thereby increasing total tar yield by approximately 8.5%, and enhancing light tar fraction content to 74.42%. Notably, the flow redirection also improved gas fuel quality by reducing H2 content and increasing CH4 proportion, raising the higher heating value (HHV) from 20.60 MJ/Nm3 (in the reactor without internals, A1) to 21.69 MJ/Nm3 (in the reactor with internals, B1). Kinetic analysis via TG-FTIR-GC/MS indicated dominant volatile release at ~500 °C, with activation energies ranging from 67–306 kJ/mol. This work provides a visually validated strategy for reactor design that selectively enhances tar yield and quality, offering a scalable pathway for efficient conversion of low-rank coal.