In-situ study on the evolution of biochar–coal blended agglomerates during co-gasification

Introducing biomass derived biochar into coal gasification provides a practical route for incorporating renewable carbon into existing high temperature conversion systems. The influence of the biochar to coal blending ratio on particle-scale evolution remains insufficiently resolved. In this study, agglomerates containing 10–50 wt% biochar were prepared from slurry droplets and gasified in 40 % H 2 O/60 % N 2 atmosphere using a single particle laser ignition platform and in situ dual camera visualization. All agglomerates underwent swelling, shrinkage, fragmentation-dominated evolution, and residual ash melting and coalescence. As the biochar content increased, the maximum swelling ratio decreased from 1.58 to 1.24. The peak apparent average surface temperature decreased from 1670 to 1535 °C, and the residual ash volume ratio decreased from 0.191 to 0.129. The time for 95 % cumulative sub-particle generation increased from 13.4 to 18.2 s. The peak normalized generation rate and mean sub-particle size decreased from 10.99 to 8.97 %/s and from 32.4 to 25.4 μm, respectively. A fragmentation mode factor, based on body localization and relative sub-particle size, decreased from 0.623 to 0.448, indicating a transition from localized to distributed peripheral fragmentation. The biochar content was correlated with agglomerate swelling, sub-particle generation, peripheral fragmentation, and residual ash evolution. The quantified relationships between biochar content and agglomerate evolution provide particle-scale guidance for evaluating biochar blending in entrained flow co-gasification and support the modeling of sub-particle release and ash residue formation.