Speaker
Description
Biomass pyrolysis involves strongly coupled structural evolution and transport processes that govern heat and mass transfer, yet these processes remain insufficiently understood at the pore scale. In particular, the roles of pore-scale anisotropy and heterogeneity in controlling gas transport and reaction progression are often neglected in continuum-scale models. In this study, we present an image-based pore-scale framework to quantify the evolution of pore structure and transport properties in wood particles during staged pyrolysis, and to bridge these effects toward representative elementary volume (REV)–scale descriptions.
High-resolution X-ray computed tomography images acquired at multiple pyrolysis temperatures were used to reconstruct three-dimensional pore structures. Image-based pore network models (PNMs) were extracted that explicitly preserve the inherent anisotropy and heterogeneity of the biomass pore space. Structural descriptors, including pore size, coordination number, and orientation statistics, were quantified to characterize the temperature-dependent evolution of pore morphology and connectivity. The results reveal a contraction–enlargement duality: while the total number of micrometer-scale pores decreases due to solid-phase decomposition and pore collapse, the remaining pores enlarge and become increasingly aligned, leading to pronounced anisotropy in the pore network.
Pore-scale transport simulations were conducted on the extracted PNMs and subsequently upscaled to REV-scale transport properties. Although porosity remains an important control, permeability is shown to be strongly governed by coordination number and directional alignment, resulting in preferential transport along specific orientations. REV-scale conductance maps further demonstrate that anisotropy persists across scales: radial conductances migrate inward with increasing temperature, whereas azimuthal and elevation conductances remain spatially heterogeneous due to local structural variations.
By coupling REV-resolved transport properties with layer-resolved carbon loss, we show that pyrolysis progresses radially from the particle exterior toward the interior, while maintaining significant within-layer anisotropy in both reaction intensity and gas flux. The extracted REV-scale source terms and directional conductances provide physically grounded inputs for continuum-scale reactive transport models. Overall, this work highlights the critical role of pore-scale anisotropy in biomass pyrolysis and provides a multiscale pathway for predictive upscaling of thermochemical conversion processes.
| Country | China |
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