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.

The potential of recycling carbon fiber reinforced polymers (CFRP) as a sustainable solution for waste management is yet to be fully understood. This study reports on the evolution of mechanical, and chemical properties of reclaimed carbon fibers when recycled multiple times via pyrolysis and partial oxidation. The performed work aims at filling the knowledge gap related to repetitive recycling when moving towards a circular flow of resources. A recycling process existing at industrial scale is used to ensure the relevance and usefulness of the results in the current industry scene. Two sets of three identical model composites are recycled using distinct recycling parameters, and their properties are characterized at the end of each recycling cycle. Results show that recycling can lead to an increase in stiffness but can have a negative impact on strength of recovered fibers. Mechanical behaviour shows recovered fibers suitable for secondary applications with medium performance requirements after two recycling cycles. The findings highlight the importance of understanding the material properties evolution during recycling processes. This research contributes to the development of sustainable waste management strategies and a more environmentally friendly future.

Biocarbon is a potential alternative to fossil coal use in the industrial sector. Fluidized-bed technology, known for its exceptional thermal mixing and reactor integration capabilities, holds promise for large-scale biocarbon production. However, the successful implementation of this technology requires overcoming technical challenges such as high concentrations of potassium (K) and phosphorus (P) in forest-based biocarbon, which can limit its applicability in certain industrial processes.

The objective of this study was to identify the potential effects of biomass-bed material interactions that can affect the presence of these ash-forming elements in the resulting biocarbon. Laboratory-scale fluidized bed experiments were conducted in a weakly oxidizing atmosphere (86.2 % vol N2, 10 % vol CO2, and 3.8 % O2) at various temperatures and residence times. Pine bark, which is a low-cost Ca-K-rich biomass with a minor amount of P, was used as raw biomass. The experimental results were analyzed using scanning electron microscopy-energy-dispersive scanning electron microscopy (SEM-EDS) and thermodynamic equilibrium calculations (TECs), providing insights into the ash transformation process. Resulting biocarbon had a high carbon content (75–90 wt% d.b.), with mass yields ranging from 13 to 30 wt%. The K retention in the biocarbon after 400 s of conversion was between 67 % and 44 % at a bed temperature of 550–900 °C, whereas the P retention was between 58 % and 43 %. The results suggested that additional inorganic removal mechanisms, different from K and P volatilization, are present in fluidized bed reactors compared to other commercial pyrolysis technologies. This highlights fluidized bed reactors (FBRs) as a promising alternative for producing biocarbon with lower K and P levels. The findings of this study contribute to the development of the design and operational criteria for fluidized beds used in biocarbon production. In addition, the results strongly indicate that the interaction between the ash-forming elements and bed materials begins before the raw material fractions are completely converted, and further investigation is recommended.

According to the World Steel Association (WSA) data for 2023, 71.1% of steel production was ore-based through the BF-BOF route (blast furnace and basic oxygen furnace) and 28.6% was scrap-based through the electric arc furnace (EAF), resulting in a 7-9% contribution from the steel industry to global CO2 emissions. A major contribution comes from coke and coal use in the blast furnace (BF), a minor part is related to the use of coal at the EAF. Carbon is essential in metallurgical processes, and the question is how fossil coals presently used can be replaced by biogenic renewable carbon (so-called biocarbon). Reported research implies that biomass converted to charcoal (biocarbon) with properties resembling those of fossil coal can replace fossil coals as long as the content of elements causing process disturbances or affecting the steel quality, i.e. alkalis and phosphorus, are low enough. Research shows that biocarbon can replace fossil coals in BF ironmaking i.e. replace injection coal at the BF, coke breeze at the sinter plant, being part of a self-reducing residue of briquettes, and replacing fossil coal in the coke. The optimum ratio for efficient self-reduction and requirements on coke strength limits the maximum addition. It may be theoretically possible to replace around half of the fossil coals depending on the prerequisites at the specific steel plant. Together with carbon capture technologies (CCS/CCU), negative CO2 emissions might be possible. However, a huge amount of biocarbon demand is a hinder to the implementation, and fossil coals for coke making will still be required. Presently, several steel producers in Europe and globally aim for fossil-free steelmaking through hydrogen (H2) based direct reduction to produce carbon free DRI (H2-DRI). H2-DRI are melted in and EAF, submerged arc furnace (SAF) or other type of furnace. To make the process route fossil-free, renewable sources of carbon must be used to reduce in H2-DRI remaining iron oxides, foam the slag and dissolve carbon in the steel during the smelting step. The required biocarbon quantities are reasonable as a major part of the energy input at the EAF is renewable electricity. The conversion to fossil-free steelmaking makes understanding the functionality of biocarbon in the EAF process even more important, especially the effect of biocarbon properties on its contribution to reduction, slag foaming, and carburization, as well as methods to produce biocarbon from biomass of various quality.

Plasma-assisted entrained flow gasification (EFG) offers a potential solution to convert low-quality biomass and waste feedstocks into high-quality syngas. This study, therefore, evaluates the theoretical technical potential of steam plasma-assisted EFG using a novel Aspen Plus model (eGas), which integrates the simulation of thermodynamic plasma properties and dissociation phenomena into Aspen Plus. Simulation results show that increasing the electrification ratio (ELR) to 0.48, corresponding to full steam plasma gasification, raises the H2/CO ratio to 1.03—more than double that of oxygen-blown EFG—while improving carbon conversion efficiency (CCE) to 95 % and reducing syngas CO2 content by 79 %. The hydrogen-specific energy demand (HSED) reaches 181 MJ/kg H2, outperforming proton exchange membrane (PEM) electrolysis (198 MJ/kg H2) for H2 addition to syngas. Plasma power conversion efficiencies exceed 85 %. Validation against NASA CEA and Cantera confirms the model's accuracy. This highlights plasma-assisted EFG as a promising future technology for hydrogen-rich syngas production.

To address the impacts of climate change, it is imperative to significantly decrease anthropogenic greenhouse gas emissions. Biomass-based chemicals and fuels will play a crucial role in substituting fossil-based feedstocks and reducing emissions. Gasification-based biomass conversion processes with catalytic synthesis producing chemicals and fuels (Biomass-to-X, BtX) are an innovative and well-proven process route. Since biomass is a scarce resource, its efficient utilization by maximizing product yield is key. In this review, the electrification of BtX processes is presented and discussed as a technological option to enhance chemical and fuel production from biomass. Electrified processes show many advantages compared to BtX and electricity-based processes (Power-to-X, PtX). Electrification options are classified into direct and indirect processes. While indirect electrification comprises mostly the addition of H2 from water electrolysis (Power-and-Biomass-to-X, PBtX), direct electrification refers to power integration into specific processing steps by converting electricity into the required form of energy such as heat, electrochemical energy or plasma used (eBtX). After the in-depth review of state-of-the-art technologies, all technologies are discussed in terms of process performance, maturity, feasibility, plant location, land requirement, and dynamic operation. H2 addition in PBtX processes has been widely investigated in the literature with process simulations showing significantly increased carbon efficiency and product yield. Similar studies on direct electrification (eBtX) are limited in the literature due to low technological maturity. Further research is required on both, equipment level technology development, as well as process and system level, to compare process options and evaluate performance, economics, environmental impact and future legislation.

Oxygen-enriched air combustion of pulverized biomass fuel is an effective method to improve char combustion and improve flame stability. Moreover, understanding the impact of O2 addition is an important step toward oxyfuel combustion, one of the most promising technologies for bioenergy with carbon capture and storage (BECCS). Our previous studies focused on flow manipulation methods, e.g., swirling co-flow and acoustic forcing, to enhance particle dispersion during biomass combustion and gasification. This work aims to extend the understanding of the effect of different manipulation methods on oxygen-enriched combustion at different levels in a lab-scale entrained flow reactor. This methodology combines the analysis of visible flame characteristics, CO and NO gas emissions, and coarse particle emissions characterization with thermogravimetric analysis and particle size distribution by dynamic imaging. The results indicated that oxygen-enriched combustion leads to lower liftoff distance and higher flame brightness. Moreover, oxygen-enriched combustion presented coarse particle emissions with finer particle size distribution and lower carbon content. The acoustic forcing further decreased the flame liftoff and decreased CO emissions, increasing combustion efficiency under conditions with similar equivalence ratios and lower momentum flux at the secondary air.

Char conversion is a complex phenomenon that involves not only heterogeneous reactions but also external and internal heat and mass transfer. Reactor-scale simulations often use a point-particle approach (PP approach) as sub-models for char conversion because of its low computational cost. Despite a number of simplifications involved in the PP approach, there are very few studies that systematically investigate the inaccuracies of the PP approach. This study aims to compare and identify when and why the PP approach deviates from resolved-particle simulations (RP approach). Simulations have been carried out for CO2 gasification of a char particle under zone II conditions (i.e., pore diffusion control) using both PP and RP approaches. Results showed significant deviations between the two approaches for the effectiveness factor, gas compositions, particle temperature, and particle diameter. The most significant sources of inaccuracies in the PP approach are negligence of the non-uniform temperature inside the particle and the inability to accurately model external heat transfer. Under the conditions with low effectiveness factors, the errors of intra-particle processes were dominant while the errors of external processes became dominant when effectiveness factors were close to unity. Because it assumes uniform internal temperature, the models applying the PP approach always predict higher effectiveness factors than the RP approach, despite its accurate estimation of intra-particle mass diffusion effects. As a consequence, the PP approach failed to predict the particle size changes accurately. Meanwhile, no conventional term for external heat transfer could explain the inaccuracy, indicating the importance of other sources of errors such as 2D/3D asymmetry or penetration of external flows inside the particles.

Packed bed reactors play a crucial role in various industrial applications. This paper utilizes the Discrete Element Method (DEM), an efficient numerical technique for simulating the behavior of packed beds of particles as discrete phases. The focus is on generating densely packed particle beds. To ensure the model accuracy, specific DEM parameters were studied, including sub-step and rolling resistance. The analysis of the packed bed model extended to a detailed exploration of void fraction distribution along radial and vertical directions, considering the impact of wall interactions. Three different samples, spanning particle sizes from 0.3 mm to 6 mm, were used. Results indicated that the number of sub-steps significantly influences void fraction precision, a key criterion for comparing simulations with experimental results. Additionally, the study found that both loosely and densely packed beds of particles could be accurately represented by incorporating appropriate values for rolling friction. This value serves as an indicator of both inter-particle friction and friction between particles and the walls. An optimal rolling friction coefficient has been thereby suggested for the precise representation for the densely packed bed of spherical char particles.

Carbon fiber, despite its exceptional properties, remains underutilized due to monetary and environmental concerns. Concurrently, the imminent challenge associated with rising quantities of End-of-Life CFRP (carbon fiber reinforced polymer) demands the further development of recycling strategies. This study focuses on optimizing the recycling process parameters of pyrolysis and oxidation thermal treatment to maximize the retention of mechanical properties in the recycled fibers in the shortest process time. To assess the result of the pyrolysis, single fiber tensile tests were executed to measure strength and stiffness. Additionally, microscopy and spectroscopy studies were carried out to evaluate fiber geometry as well as surface quality. At the laboratory scale, experiments demonstrated that the combination of pyrolysis and oxidation yields clean, reusable fibers with mechanical properties suitable for secondary applications. The influence of various treatment parameters on the strength and stiffness of the recycled fibers was explored, establishing a clear correlation. The outcome is a set of optimized parameters that contribute to mechanical property retention, including a novel recycling method that allows for reduced processing times, as short as 10 min. This work paves the way for a more eco-friendly and cost-effective approach to harnessing the potential of carbon fiber in a wide range of applications while mitigating environmental concerns associated with landfill disposal.