Attrition-Driven Carbon and Mineral Matter Distribution during Biochar Production from Pine Bark in Fluidized Beds

High Resolution Image Download MS PowerPoint Slide During thermochemical conversion inside a fluidized bed, biomass and char particles experience physical breakup, commonly known as attrition. However, its consequences for the distribution of carbon and mineral matter among coarse biochar (referred to hereafter as biocarbon) particles, elutriated fines, and fines retained within the bed remain poorly quantified, despite its direct impact on product yields and properties. This study aims to fill this gap in the literature by devolatilizing pine bark in a lab-scale bubbling fluidized bed reactor at various temperatures, superficial gas velocities, and feed particle sizes. Coarse biocarbon, elutriated fines, and bed material were recovered and characterized for chemical compositions and physical properties. Increased porosity at higher temperatures resulted in greater susceptibility to fragmentation, thereby linking structural degradation with attrition. High gas velocity increased elutriated fines, while the coarse fraction exhibited lower pore volume, indicating the preferential fragmentation and removal of the most porous fragments as fines. A persistent fraction of unrecovered carbon was also identified within the bed, representing a hidden loss pathway that is often neglected in mass closure assessments. Major mineral matter elements exhibited retention levels significantly below 100% in the coarse biocarbon. Notably, phosphorus and calcium were consistently redistributed from the coarse fraction to fines but remained in intermediate bed-associated particles owing to their low volatility under the study conditions. Meanwhile, the increase in total ash, Na, and Al contents above feedstock levels indicates the contamination of coarse biocarbon and elutriated fines with bed material. These observations have direct implications for mass closure evaluation and downstream solids management. Overall, the results show that attrition affects not only fines generation but also carbon and mineral matter distributions. The observed effect can potentially be utilized as a tunable physical fractionation tool whose outcome is governed by the coupled effects of temperature, hydrodynamics, and feedstock properties.