Search Results (1,111)

Understanding the fluid dynamics of fluidized beds loaded with biomass pellets is of significant value for the design of wood waste gasifiers. In the present study, cylindrical wood pellets are loaded into a lab-scale cold gasifier unit at 2.5 vol% and 7.5 vol% concentrations and studied at superficial air velocities of 0.25, 0.282, and 0.344 m/s (corresponding to 80, 90, and 110 SCFM). Measurements of bubbles, sand particles, and biomass pellets are taken at a 45 cm height from the distributor plate, and at 9, 12, 15, 18, and 21 cm radial positions from the column wall by employing the CREC-GS-Optiprobes, a valuable integrated fiber optic-laser tool system. A new data processing methodology is established using laser signals that are reflected from the outer surface of aluminum-foil-wrapped cylindrical wood pellets. In addition, a new algorithm is implemented to distinguish pellet-reflected signals from those of bubbles and emulsion-phase particles. On this basis, for the first time, a Phenomenological Probabilistic Predictive Model (PPPM), is considered to predict Bubble Axial Chords (BACs) and Bubble Rise Velocities (BRVs), in a sand fluidized bed loaded with biomass pellets. This is accomplished within a set band of values accounting for three standard deviations from their means or including 85.9% of the bubbles measured. Thus, it is demonstrated that the PPPM is adequate to establish the constrained random motion of bubbles in sand fluidized beds, under the influence of uniformly distributed biomass pellets. It is anticipated that the findings of the present study will be of significant value for the design of sand biomass gasifiers of different scales. Full article

Improving the thermal utilisation of organic production waste to generate energy is integral to solving one of the most pressing issues of our time: transitioning away from fossil fuels. In this context, the thermal utilisation of organic waste, particularly sewage sludge (SS) and lignin-containing by-products from the biochemical industry, is of considerable scientific and practical interest. This study provides a thorough analysis of the co-combustion processes involving SS, lignin-based pellets and briquettes, and their mixtures with various component ratios. The aim of the work is to evaluate the fuel properties, thermokinetic characteristics, and potential for synergistic interactions during joint fuel combustion, considering the mechanical impact on lignin during granulation. The aim is to optimise conditions for the thermal utilisation of industrial waste. The study employed standard analytical methods: the thermophysical properties of the fuels were determined; morphological analysis of the particle surface was conducted using scanning electron microscopy; and X-ray fluorescence analysis was performed to identify the inorganic oxide phase. It has been established that lignin briquettes have the highest lower heating value, exceeding that of lignin pellets and sewage sludge by 7% and 27%, respectively. Thermogravimetric analysis (TGA) in an oxidising atmosphere (air, heating rate of 10 °C/min) made it possible to determine the following key combustion parameters: the ignition temperature of the coke residue (T_i); the temperature at which oxidation is complete (T_b); the maximum combustion rate (R_max); and the combustion efficiency index (Q). The ignition temperature of the coke residue was 262.1 °C for SS, 291.8 °C for lignin pellets, and 290.0 °C for lignin briquettes. Analysis of co-combustion revealed non-linear behaviour in the thermograms, indicating synergistic effects, which are manifested by a decrease in the maximum combustion rate compared to the additive prediction, particularly in mixtures with a moderate lignin content (25–50%). It was established that the main synergistic interactions between the mixture components occurred during moisture evaporation and the combustion of coke residue. These results are valuable for designing and operating power plants that focus on co-combusting industrial organic waste, and they contribute to the development of thermal utilisation technologies within closed production cycles. Full article

Urban tree-management operations generate substantial amounts of woody biomass that often remain underutilized despite their potential value as a local renewable fuel. This study investigates the possibility of using woodchips and sawdust delivered from municipal tree-cutting activities as boiler fuel, with a specific focus on how fuel moisture, particle size, and natural-fiber packaging influence combustion performance and emission characteristics. In collaboration with a municipal greenery-cutting company, representative batches of biomass were collected, characterized through proximate and ultimate analyses, and combusted in a small-scale boiler. Unlike conventional densification routes (pelletization/briquetting), the proposed approach uses combustible natural-fiber packaging to create modular ‘macro-pellets’ from minimally processed urban residues. The study quantifies how this low-energy packaging concept affects emissions and boiler efficiency relative to loose chips/sawdust at two moisture levels. The results demonstrate that packaging the fuel in jute bags markedly improved performance for both woodchips and sawdust by stabilizing the fuel bed, enhancing air distribution, and reducing emissions of incomplete combustion products. Boiler efficiency increased from approximately 60% for raw unpackaged fuels to 71–75% for the dried and jute-packaged variants. The findings highlight that simple preprocessing steps—drying and packaging in natural-fiber bags—can substantially enhance the energy recovery potential of urban green waste, offering a practical pathway for integrating municipal biomass residues into a sustainable fuel. Full article

Pellets produced from raw or torrefied shredded logging residues have been investigated in the study. The research material came from pine and spruce stands in Poland, Slovakia, Czechia and Hungary. Torrefaction temperatures (T_t) of 250, 300, and 400 °C were applied. Before pressure agglomeration, 3% wheat flour was added to the torrefaction material as a binding agent. Pellets with a diameter of 8 mm were produced at constant humidity, compaction pressure (P) of 140 or 180 MPa and agglomeration temperature (T_a) of 100, 120 or 140 °C. The produced pellets were assessed for their physicomechanical parameters (density, radial compressive strength, compression ratio, modulus of elasticity), chemical parameters (extractive compounds, cellulose, lignin) and energy parameters (ash content, elemental composition, calorific value). The results were subjected to basic statistical analysis and multi-way ANOVA. The produced pellets varied in physical, mechanical, chemical and energy properties. A significant effect of torrefaction temperature, agglomeration temperature and compaction pressure on the results was observed. In terms of physicomechanical parameters, the best pellets were produced from the raw material, while in terms of energy parameters, those produced from the torrefied material were superior. Pellets of satisfactory quality produced from torrefied logging residues could be obtained at T_t = 250 °C, T_a = 120 °C and P = 180 MPa. Pellets with specific density of approximately 1.1 g·cm⁻³, radial compressive strength of 3–3.5 MPa, modulus of elasticity of 60–80 MPa and calorific value of 20.3–23.8 MJ·kg⁻¹ were produced in the process. Full article

The use of activated carbon (AC) in environmental applications, particularly for water and air purification, is highly valued due to its excellent microstructural and adsorption properties. However, its powdered form presents significant challenges in industrial applications, such as difficulty in handling and potential environmental risks due to its tendency to disperse easily. To overcome these issues, converting activated carbon into a more industrially viable form, such as pellets, is crucial. In this study, pelletizing AC within a crosslinked polyvinyl alcohol–diglycidyl ether of bisphenol A (PVA–DGEBA) matrix enabled the production of structurally stable cylindrical pellets through the formation of a robust three-dimensional polymeric network. This approach required minimal binder usage and facilitated processing at relatively low temperatures, effectively overcoming common disintegration issues associated with traditional pelletization methods reliant on linear polymer binders and compression-based techniques. The resulting pellets exhibited methylene blue (MB) adsorption (q max ~14.8 mg/g of pellet), which is about 50% of the initial AC’s adsorption capability, and retained structural integrity across multiple aqueous cycles. They also remained stable in methanol, ethanol and acetone by showing no observable disintegration, which highlights their excellent stability. Comprehensive characterizations, including hardness tests, swelling behavior, and various structural evaluations, revealed a mechanical strength of 3.37 ± 0.46 MPa and an adsorption volume of ~250 cm³/g through Brunauer–Emmett–Teller analysis, confirming effective crosslinking and the adsorption capabilities of the pellets. This eco-friendly and stable pelletization strategy demonstrated great potential for low-temperature pelletizing of AC, ensuring advanced applications in wastewater treatment even under pressurized conditions, presenting a significant improvement over the traditional method. Full article

Hydrogen-based direct reduction (H-DR) represents an environmentally benign and energy-efficient alternative in ironmaking that has significant industrial potential. This study reviews the current status of H-DR shaft furnaces and accompanying hydrogen-rich reforming technologies (steam and autothermal reforming), assessing the three dominant numerical frameworks used to analyze these processes: (i) porous medium continuum models, (ii) the Eulerian two-fluid model (TFMs), and (iii) coupled computational fluid dynamics (CFD)–discrete element method (DEM) models. The respective trade-offs in terms of computational cost and model accuracy are critically compared. Recent progress is evaluated from an engineering standpoint in four key areas: optimization of the pellet bed structure and gas distribution, thermal control of the reduction zone, sensitivity analysis of operating parameters, and industrial-scale model validation. Current limitations in predictive accuracy, computational efficiency, and plant-level transferability are identified, and possible mitigation strategies are discussed. Looking forward, high-fidelity multi-physics coupling, advanced mesoscale descriptions, AI-accelerated surrogate models, and rigorous uncertainty quantification can facilitate effective scalable and intelligent application of hydrogen-based shaft furnace simulations. Full article

The paper presents research on the compaction process of oak sawdust as a proposal for the management of post-production waste. The variable input parameters whose influence was studied were the particle size of the sawdust, the compaction force, the temperature of the compaction process, and the moisture content of the sawdust. The results obtained were used to determine the density of the briquette and the value of its Young’s modulus obtained from each test sample. The interaction between the input parameters as variables in the tests and the determined values of density and Young’s modulus was analyzed using ANOVA. The highest density value was recorded for the lowest particle size, the highest compaction force and compaction temperature, and a moisture content of 9%. The highest Young’s modulus E value was recorded for a moisture content of 9%, a compaction force of 25 kN, a temperature of 25 °C, and a particle size of S < 1 mm. Variance analysis enabled the optimal selection of compaction process parameters, where the main criterion in general terms was to minimize the energy consumption of the compaction process. The best mechanical properties of the briquette can be obtained for process settings of F = 5 kN, M = 20%, T = 25 °C, S = 2.5–5 mm. Full article

The presented research focuses on assessing the impact of the geometry of the compaction channel on the quality of pellets produced from giant miscanthus, silphium, and sida. Geometry refers to parameters such as L, D, α, and the diameter of the channel, as well the height of the compacting cone. Our analysis covered the pressure compaction process of monocotyledonous and dicotyledonous perennials, considered a valuable source of biomass for energy purposes. These species are the subject of processing research; they are promising, easy to grow and, crucially, non-invasive. The results of the research indicated the optimal configurations for each plant. For miscanthus: D = 12 mm, α = 10°, L = 13 mm, and compaction pressure P = 245 MPa; for D = 10 mm, α = 10°, L = 22 mm, and P = 185 MPa. For silphium: D = 12 mm, α = 20°, L = 21 mm, P = 50 MPa, and for D = 10 mm: α = 20°, L = 26 - 27 mm, and P = 42 MPa. For Virginia mallow: D = 12 mm, α = 10°, L = 5 mm, and P = 237 MPa, or with a diameter of 10 mm: α = 30°, L = 23 mm, and P = 58 MPa. Full article

The objective of this study was to establish the kinetic of gasification reactions involved in chemical looping gasification (CLG) using pelletized biomass as solid fuel. However, significant limitations have been found in obtaining such kinetics using a traditional methodology from a large number of tests in a thermogravimetric analyzer (TGA) for pelleted biomass. A novel methodology is presented in this article, namely: (i) the determination of the intrinsic gasification rate for several biomasses; (ii) the determination of the gasification rate of pelletized biomass under selected operating conditions; (iii) the development and validation of a reaction model for pelletized biomass considering the determined intrinsic kinetics and gas diffusion in the biomass particles; and (iv) obtaining an apparent kinetics from data calculated with the developed model, which will be easy to implement in the modeling of gasifiers. To evaluate the applicability of this methodology, it was demonstrated with three different types of biomasses: pine forest residue (PFR), industrial wood pellets (IWP), and wheat straw pellets (WSP). The intrinsic kinetics was derived from tests with powdered char under several operating conditions: reacting temperature (1073–1223 K), concentration of gasifying agent (10–40 vol.% H₂O or CO₂), and concentration of gasification product (0–40 vol.% H₂ or CO). The evolution of the char conversion with the reacting time was predicted using a model involving three different regimes: (I) deactivation at the beginning; (II) uniform progress in the main middle part following a n-order model; and (III) catalytic activation as complete conversion is approached. The second regime was included for all biomasses, being 1, 0.4, and zero-order for WSP, IWP, and PFR, respectively. However, the third regime was observed for PFR and IWP, and the first regime only for IWP. The intrinsic kinetics was successfully used in a theoretical model to properly predict the gasification rate of pelletized biomass, and, eventually, to determine an apparent gasification kinetics as simple as possible in order to be easily implemented in future gasifier modeling works. Full article

The creation of bioenergy based on the biomass wood pellet industry, which accounts for the majority of the global biomass supply, is one of the most common and important ways to utilize waste wood, wood dust, and other byproducts of wood manufacturing, known as forestry residues. Pellet production processes might greatly benefit from fast monitoring systems that may allow for at least a semi-quantitative measurement of crucial parameters such as lignin and cellulose. The determination of lignin and cellulose is complicated and time-consuming because it usually requires time-demanding and labor-intensive sample preparation. This, however, might be a crucial problem. In this context, the application of Raman spectroscopic techniques is considered a promising approach, as it enables rapid, reliable, and label-free analysis of wood pellets, providing information about the chemical composition of the biomass, specifically lignin and cellulose. The purpose of this article is to report on the application of Raman spectroscopy exemplified by the detection of the lignin/cellulose ratio. In our methodological approach, we integrated the area under the selected Raman bands to avoid a large scatter of data when only the intensities of the bands were used. Moreover, the acquired Raman spectra displayed very strong signals from both substances, which contributes to the feasibility of the analysis even with a portable instrument. This study is expected to be of assistance in situations when the monitoring of the chemical changes and the quick inspection of pellets are required in near real time, online, and in situ. Full article

The increasing global demand for cleaner transportation has intensified the importance of efficient AdBlue^® (AUS32) production, a key chemical in selective catalytic reduction (SCR) systems that reduces nitrogen oxides (NOx) emissions from diesel engines. This work presents a computational fluid dynamics (CFD) simulation study of the urea–water mixing process within a high shear mixer (HSM), aiming to enhance the sustainability of AdBlue^® manufacturing. The model evaluates the hydrodynamic characteristics critical to optimising the dissolution of urea pellets in deionised water, which conventionally requires significant preheating. Experimental validation was conducted by comparing pressure drop simulation results with operational data from an active industrial facility in the United Kingdom. Therefore, this study validates the CFD model against an industrial two-stage Rotor–stator under real operating conditions. The computational framework combines a refined mesh with the k-ω SST turbulent model to resolve flow structures and capture near-wall effects and shear stress transport in complex flow domains. The results reveal opportunities for process optimisation, particularly in reducing thermal energy input without compromising solubility, thus offering a more sustainable pathway for AdBlue^® production. The main contribution of this work is to close existing gaps in industrial practice and propose and computationally validate strategies to improve the numerical design of HSM for solid dissolution. Full article

Climate change and the impacts related to nonbiodegradable synthetic materials highlight the need for sustainable alternatives. Biopolymers from renewable sources show great potential for producing hydrogels, which are three-dimensionally crosslinked materials with high water absorption. In this work, super-absorbent biodegradable hydrogels were produced via single-step reactive extrusion using mixtures of starch, gelatin, cellulose, and xanthan gum, with glycerol as a plasticizer, and citric acid as a crosslinking agent. Pelleted hydrogels were obtained with water absorption between 290% and 363%. Reactive extrusion promoted the formation of new ester and amide bonds, confirmed by FT-IR. Citric acid was effective as a crosslinker, and higher citric acid content (3%) produced samples with greater swelling, supported by the porous internal structure observed. Preliminary agricultural tests showed that the formulation with the highest citric acid content, when added to soil at 5%, significantly increased water-holding capacity and resulted in the highest germination rate of maize seeds. Overall, the extrusion process proved efficient, scalable, and environmentally friendly for producing biodegradable hydrogels for agricultural applications. Full article

This work investigates the influence of spark plasma sintering (SPS) parameters on the microstructure and mechanical properties of consolidated aluminum powders processed by high-energy ball milling under an air atmosphere. Sintering was performed under vacuum at various temperatures ranging from 550 °C to 625 °C and under pressures between 50 and 100 MPa. The particle size, crystallite size, and microstructure of the powders and the consolidated pellets were analyzed using laser granulometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Archimedes’ density measurements. Mechanical properties were evaluated via Vickers microhardness, nanoindentation, and tribological testing. For comparison, unmilled aluminum powders were also consolidated and characterized. After 46 h of milling, the aluminum crystallite size was reduced from 74 nm to 68 nm. The sample’s density increased with higher sintering temperature and pressure. The aluminum sintered at 600 °C and 100 MPa after 46 h of milling exhibited the highest microhardness (187.5 HV). Nanoindentation tests were conducted to characterize different microstructural regions formed after SPS, revealing two distinct zones: one hard and one soft. The tribology results revealed that the SPS-consolidated samples of milled powders exhibited a reduction of 50% in specific wear rate and a reduction of 20% in the coefficient of friction compared to the SPS-sintered samples of unmilled powders. Full article

Lignocellulosic biomass wastes are renewable carbon resources that can be available for conversion into biofuels. There is a growing interest in utilizing a broader range of alternative biomass feedstocks such as agri-crop residues aside from the traditional forest-origin wood residues for fuel pellet production. However, crop residues typically have low and inconsistent fuel quality. This paper investigated the effectiveness of the combined steam explosion and water leaching pretreatment techniques to upgrade the fuel properties of wheat straw. The experimental treatments involved auto-catalyzed steam explosion and acid-catalyzed steam with and without subsequent water leaching. Using steam explosion catalyzed by dilute H₂SO₄ at a low concentration of 0.5 wt%, results showed the highest ash, Si, and Ca removal efficiencies of 82.2%, 91.1%, and 74.3%, respectively. Moreover, there was significant improvement in fuel quality in terms of fuel ratio (0.34) and calorific value HHV (21.9 MJ/kg), as well as a pronounced increase in the comprehensive combustibility index at the devolatization stage, indicating better combustion characteristics. Overall, the results demonstrate that with adequate pretreatment, the quality of agri-pellets derived from wheat straw could potentially be on par with wood pellets that are utilized for heat and power generation and residential heating. To mitigate the dry matter loss due to steam explosion, future studies shall consider using the process effluent to produce biofuel. Full article

Water scarcity is an increasingly critical global issue, particularly in arid regions like Morocco. Innovative approaches, such as the use of alternative water sources like landfill leachate, offer promising solutions. In this study, phosphate washing sludge was used to treat landfill leachate with the aim of producing irrigation-quality water and recovering nitrogen from the resulting sediment. A total of 40 L of raw leachate was treated with three concentrations of phosphate washing sludge (25%, 37%, and 50%). This volume was processed at the laboratory scale as a proof of concept for potential larger-scale applications. After 24 to 36 h of mixing and agitation, the mixture underwent sedimentation, yielding clear supernatants and nitrogen-rich sludge pellets. These pellets showed a significant increase in organic matter content, from 6.4% to 13.5%, representing an enhancement of 110.9%, thus demonstrating partial leachate depollution and organic matter enrichment. Microbiological analyses revealed a 98.9% reduction in fecal streptococci. The supernatants met irrigation water standards in terms of pH and electrical conductivity, and phytotoxicity tests on maize seeds confirmed their suitability for irrigation. Additionally, the recovered nitrogen-rich sediment presents a valuable input for composting and soil amendment. Full article