This study explores the production of biocarbon from forest biomass through pyrolysis in fluidized bed reactors, emphasizing the relationship between the operating conditions, ash behavior, and physicochemical properties of the resulting solid biocarbon. Fluidized bed reactors offer distinct advantages for biocarbon production, including efficient heat transfer, isothermal operation, and scalability. These characteristics make them particularly suitable for integration into existing energy infrastructures.

A key strategy investigated in this study is the use of a weakly oxidizing atmosphere composed of recycled flue gases from combustion processes as the fluidization medium. This approach enables heat integration with fluidized bed boilers and reduces the need for external inert gases, thereby lowering operational costs and improving the overall energy efficiency and circularity of the system. The impact of this atmosphere on biocarbon yield and composition was studied in detail, particularly regarding its influence on the behavior of ash-forming elements and textural properties.

Special attention is given to the transformation and retention of ash-forming elements, such as potassium and phosphorus, which affect the suitability of biocarbon for industrial applications. The experimental and modeling results show that fluidized bed conditions favor the selective removal and distribution of these elements. Analytical techniques, including inductively coupled plasma (ICP), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and thermodynamic equilibrium calculations (TECs), were used to assess the mechanisms of ash transformation.

In parallel, the evolution of particle properties, such as size, density, porosity, and surface area, was evaluated under different conversion regimes. Structural degradation owing to attrition and fragmentation was found to play significant roles in carbon retention and fines generation. Preliminary pilot-scale tests conducted with a different woody feedstock showed trends similar to those observed at the laboratory scale when comparable devolatilization severities were applied, reinforcing the transferability of key process–property relationships.

Overall, these findings support the development of integrated and sustainable fluidized bed systems for biocarbon production, offering practical pathways to reduce fossil carbon use and improve resource efficiency in biomass valorization processes.