Cenospheres are plausible intermediates in entrained flow gasification (EFG) of biogenic suspension fuels. However, their structure and reactivity remain poorly understood, limiting the accuracy of numerical simulations of entrained flow gasifiers.

The present study characterizes cenospheres from two experiments in a technical entrained flow gasifier using beech wood pyrolysis oil (PO) and char suspensions (slurry; POC) under intentionally low air ratios (0.35). Structural features and CO2 gasification kinetics are investigated, and mass transport effects under technically relevant conditions (1000 – 1500 °C, 10 bar CO2) are evaluated.

A broad particle size distribution of the cenospheres (100 – 800 µm) is identified. Micro computer tomography reveals internal macro-structures ranging from uniformly distributed porosity to a porous shell, with embedded char particles in POC cenospheres.

Micro- and mesoporosity are analyzed via argon physisorption. Only POC cenospheres show microporosity, which is assigned to the char particles. Structural ordering determined by X-ray diffraction (XRD) is stronger for smaller cenospheres. The evolution with increasing particle diameter differs between POC and PO cenospheres, with radial expansion of the graphene layers prevailing in POC cenospheres, while both radial expansion and graphene stacking vary in the structured domains in PO cenospheres.

Reaction kinetics in CO2 (5 – 20 bar, 810 – 850 °C) are determined in the differential fixed bed reactor for 200 – 400 and 600 – 800 µm fractions. The reaction rate increases with increasing temperature and CO2 partial pressure as described by the Arrhenius and the power law model (activation energy: 210 – 242 kJ/mol; reaction order: 0.2 – 0.3). Especially the mantle area-to-volume ratio of the stacked graphene layers derived from XRD and the mesopore surface area are found to impact the reaction rate.

Biochar performance in applications like soil amendment depends on properties including porosity, surface area, and pore structure, which are influenced by both process conditions and feedstock characteristics such as wood anatomy. However, their effects across micro- and nanometre length scales remain poorly understood. This study therefore investigates how feedstock and process conditions affect properties of pine wood biochar produced in industrially relevant pilot-scale continuous reactor for torrefaction (291–315°C, 6–12 min) and pyrolysis (350–400°C, 25 min). High-resolution X-ray microtomography combined with AI-assisted image analysis was used to quantify earlywood–latewood distribution, porosity, pore size, cell wall thickness, and micrometre-scale surface area, while N2 and CO2 sorption probed nanometre-scale structure. The wood microstructure was largely preserved across treatments, resulting in highly anisotropic pore networks. Porosity remained high (33–77%), primarily influenced by earlywood–latewood variability rather than temperature. From torrefaction to pyrolysis, cell wall thickness and pore diameter decreased, while microporosity (<∼0.7 nm) and accessible surface area increased significantly above 350°C. Discrepancies between N2 and CO2 measurements indicate differences in pore accessibility, likely associated with ultramicroporosity, pore constrictions and/or partially inaccessible pores. Water holding capacity ranged from 1.7 to 5.3 times dry weight, with highest average at 350°C, although differences were not significant. Combined use of microtomography and gas sorption provides a multiscale framework for linking biochar structure across micro- and nanometre scales to performance-relevant properties. These findings demonstrate that wood anatomy dominates over process conditions under mild thermal treatment, highlighting new possibilities for tailoring process design through consideration of wood anatomy.

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.

 Leaching pine bark with deionized water effectively reduced its total ash content by removing a portion of the inorganic elements, particularly the water-soluble potassium (K) and sodium (Na). As a result, biocarbon derived from leached pine bark contained lower levels of both ash and carbon, compared to biocarbon derived from untreated pine bark. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) confirmed that the content of total and individual inorganic elements in the leached bark biocarbon was considerably reduced relative to the untreated counterpart. X-ray diffraction (XRD) analysis identified calcium carbonate as the dominant mineral phase in both biocarbons; however, its peak intensity was notably weaker in the leached bark biocarbon, indicating a lower content of this mineral phase. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) revealed calcium-rich grains on the surface of the untreated bark biocarbon, which were largely absent in the leached bark biocarbon. Fourier transform infrared (FTIR) spectroscopy showed similar spectral profiles for both biocarbons, though the leached bark biocarbon exhibited reduced peak intensities corresponding to C=O and C–O–C stretching vibrations. This reduction is likely due to the removal of water-soluble extractives and polysaccharides during leaching, resulting in the formation of fewer oxygenated functional groups during carbonization and a reduced carbon content. 

Densified biochar particles emerge as a promising carbon-negative insulation solution for building constructions. Their effective thermal conductivity (ETC) is a critical parameter, but has not been systematically investigated in dependence of particle size, shape and packed bed porosity. The provided data sets allows the computation of a fully experiment-based ETC, using the approach from the article "Effective thermal conductivity of packed beds made of cubical particles" (10.1016/j.ijheatmasstransfer.2022.122994), as well as model-based ETC using the Zehner-Bauer-Schlünder approach.   Biochar particles of dried spruce bark chips were pyrolyzed in a pilot-scale rotary kiln reactor at around 350-400 °C with a residence time of ca. 45 min. Biochar particles were subsequently mixed with a binder and densified with a vacuum extruding process to a cylindrical shape before being crushed into smaller particles to eliminate the anisotropic pore structure and thermal conductivity inside individual particles.  The data includes measured data of particle thermal conductivity and heat capacity, using LFA 467HT from NETZSCH GmbH, Germany, and coin-shaped samples with diameters of 12.5±0.2 mm and thicknesses of 2.5±0.5 mm for the measurement. The particle size distributions were obtained from Camsizer from Microtrac Retsch GmbH, Germany. The particle shape, i.e. sphericity, was obtained from X-ray microtomography (XMT) using a Zeiss Xradia 510 Versa tomograpy and cylindrical packed beds with an inner diameter of 23 mm and a height of 18 mm. The tube voltage was 40 kV and a tube power of 3 W to reduce beam hardening artifacts. Each scan collected 1601 projections over a full 360° rotation. Image resolutions were adjusted based on the particle sizes, with voxel sizes of 5 μm for packed beds containing smaller particles of around 0.315 mm and 23 μm for all other samples. The number of particles in the samples ranged from about 70 to 200,000. The X-ray microtomography (XMT) raw data can be viewed using the open-source software Fiji (https://imagej.net/software/fiji).

In metallurgical processes, packed beds of biochar are subjected to thermal gradients and heterogeneous reactions. In addition, densified biochar particles emerge as a promising carbon-negative insulation solution for building constructions. This makes the effective thermal conductivity (ETC) a critical parameter, but the ETC of biochar particles has not been systematically investigated in dependence of particle size, shape and packed bed porosity. This work aims to partially fill this gap by using densified biochar from spruce bark. The ETC is derived from experiments under non-reactive conditions and numerical analysis including the Zehner–Bauer–Schlünder (ZBS) model. X-ray microtomography was used to quantify particle structure, including sphericity and void fraction. Thermal properties were measured experimentally, and ETC was determined for various particle size fractions between 0.315 and 6.3 mm. The smaller particle fractions exhibited similar bed porosities and ETCs, whereas the largest particle fraction (4-6.3 mm) showed slightly lower ETC and higher bed porosity. Analysis with the ZBS model revealed the need to include an additional thermal resistance in the gap between the irregular particles due to the imperfect contact of particles. The results highlight the importance of manipulating inter-particle thermal contacts in altering the ETC of packed beds of irregular particles.

Efficient biomass production through management like thinning is crucial for increasing the supply of renewable and carbon neutral feedstock. However, change in growth rates may alter feedstock properties and affect subsequent bioenergy conversion, material and chemical production. This study evaluated the effects of thinning treatments and stem diameter on the fuel, elemental, and structural composition of stemwood and bark from second-rotation poplar plantation (original stand: 1100 stumps ha−1). Two different thinning methods were applied: row thinning (removing all stems for every other row of plantation and reducing stump density to 550 stumps ha−1) and stem thinning (retaining only the single largest stem per stump). The results showed that thinning method and stem diameter affect fuel and lignocellulosic composition. Single-stem trees at high stump density had the best fuel traits, with low ash and high volatile matter to fixed carbon (VM/FC) ratios, reflecting reduced growth competition. Smaller stems contained more ash and VM/FC in bark. Carbon, hydrogen, and nitrogen contents were not affected by treatments. Single-stem trees had higher hemicelluloses and lower lignin, indicating more complete cell wall development, while crowded, multi-stem conditions increased lignin. Highest extractives were found in bark from low-density single-stem trees. Both total biomass and structural components yields were highest for single-stem trees without row thinning. It highlights the benefits of stem thinning. This study suggests that both quality and quantity of biomass from second-rotation poplar plantation can be influenced by thinning treatments and stem diameter, with potential implications for bioenergy and bio-based chemicals or fuels.

In biomass pyrolysis, final product selectivity is governed not only by major reaction conditions like temperature and heating rate but also by complex vapor–solid interactions and secondary reactions. Yet, the influence of internal flow configuration on pyrolysis vapor remains poorly understood in continuous pyrolysis systems. This study aims to evaluate how controlled vapor–solid interactions via changes in the vapor outlet port location affect the distribution and transformation of pyrolysis products. Experiments were performed in a continuous laboratory-scale auger reactor, processing pine bark at highest treatment temperatures (HTT) of 600, 700, and 800 °C. The reactor featured five independently heated zones and six selectable vapor outlet ports, enabling three vapor flow modes: parallel flow (PF, conventional cocurrent flow operation) and two counterflow (CF) configurations to systematically manipulate vapor–solid contact. Results showed that one of the CF configurations, where vapors passed through the coldest (the incoming) biomass zone before exiting, enhanced vapor condensation on incoming biomass and promoted secondary reactions, leading to up to a 15.5% relative increase in biochar yield compared to PF. The increase in biochar yield was accompanied by an increase in fixed carbon yield, and H2 and CH4 yields, indicating intensified thermal cracking and polymerization of pyrolysis vapors. In contrast, the CF configuration involving vapor recirculation without interaction with the coldest zone favored external condensation and achieved the highest bio-oil recovery. The PF configuration exhibited the lowest char yield and the highest unaccounted carbon fraction due to poor vapor condensation at elevated outlet temperatures. These findings demonstrate that the manipulation of vapor–solid interactions serves as a critical parameter for steering pyrolysis pathways toward targeted product enhancement, offering a scalable approach for optimizing biochar, gas, and bio-oil yields through in situ vapor recirculation.

The heat and mass transfer in packed bed reactors (PBRs) are strongly influenced by the random packing of particles, making a thorough understanding of the packed bed structure crucial for optimal reactor design. This study investigates the impact of particle shape irregularities and size distributions on packing and transport properties using X-ray microtomography (XMT) imaging. Key morphological parameters, including void fraction and tortuosity, are extracted and analyzed. Two pore network models (PNMs)- one using cylindrical throats and another based on dense graph approach- are compared, with the dense graph model more accurately reflecting empirical tortuosity distributions. Results reveal that in monodispersed beds, void fraction decreases for particle diameters below 2 mm, nearing theoretical minimums for spherical packings, while tortuosity aligns with established models despite particle sphericity ranging between 0.6 and 0.8. In contrast, highly polydispersed beds exhibit lower void fractions compared to monodispersed beds, yet their tortuosity distributions remain similar. Visualization indicates small particles fill voids without blocking flow paths, preventing substantial tortuosity increases. These findings enhance understanding of packed bed behavior and provide valuable insights for designing biochar-based PBRs.