Search Results (971)

Sustainable fertilizer technologies are essential to address nutrient losses, environmental pollution, and inefficiencies associated with conventional urea application. In this study, humic acid–functionalized starch (St–HA) gel coatings were developed and optimized via a Wurster fluidized-bed system to produce controlled-release urea granules, with an additional carnauba wax outer layer to further extend nutrient release duration. The coating formulation was synthesized through in situ crosslinking of tapioca starch with humic acid using N,N′-methylenebisacrylamide and potassium persulfate, yielding a cohesive film. A central composite rotatable design (CCRD) was employed to investigate the influence of atomizing air pressure, fluidizing air flow rate, fluidized-bed temperature, and spray rate on coating performance. Comprehensive characterization; including FTIR, XRD, rheological analysis, thermogravimetric studies, water retention, biodegradability, and surface abrasion, confirmed chemical crosslinking, structural stability, and mechanical robustness of the coatings. Nitrogen release analysis in both water and soil demonstrated a substantial extension of release longevity from less than 2 days (uncoated) to 18–20 days for St–HA-coated urea, and up to 28 days with the additional wax coating. Coated granules exhibited low abrasion (8–24%), high water-retention capacity, and 68% biodegradation in 60 days, ensuring environmental compatibility. The findings establish St–HA/wax hybrid coatings as a viable, eco-friendly strategy for controlled-release fertilizers, integrating renewable feedstocks with scalable industrial processing for precision nutrient management. Full article

Biomass combustion, as a key technology for achieving a low-carbon transformation of the energy system, faces multiple challenges in its efficient and clean utilization, including the high heterogeneity of fuels, the complex multi-scale coupling of the combustion process, and the attainment of ultra-low emissions. Traditional research methods have significant disconnections between microscopic mechanism understanding, macroscopic performance prediction of reactors, and end-of-pipe pollution control, which restricts the improvement of system performance. This review presents recent advances in advanced numerical simulation, pollutant control strategies, and bioenergy with carbon capture and storage (BECCS) pathways targeting ultra-low emissions in biomass combustion. This work synthesizes progress across three interconnected domains. First, methodologies are examined for integrating detailed chemical kinetics, particle-scale models, and reactor-scale simulations to develop high-fidelity predictive tools. Second, low-nitrogen combustion and synergistic pollutant control strategies for primary furnace types (e.g., grate, fluidized bed) are evaluated, alongside process optimization from fuel pretreatment to flue gas purification. Third, the potential for integrated design of biomass energy systems with carbon capture is assessed, emphasizing that system efficiency hinges on holistic “fuel-combustion-capture” chain optimization rather than isolated unit improvements. Future research directions are highlighted, including the development of physics-informed AI modeling paradigms, deeper co-design of multiple processes, and the establishment of robust life-cycle assessment frameworks. This review aims to provide a structured reference to inform both fundamental research and the practical development of next-generation clean biomass combustion technologies. Full article

This study employs a Computational Fluid Dynamics (CFD) approach based on the Two-Fluid Model (TFM) to investigate the CO₂ capture characteristics in a bubbling fluidized bed reactor using potassium carbonate (K₂CO₃) as the sorbent. The simulations are conducted at five superficial gas velocities ranging from 1.5 to 3.5 times the minimum bubbling velocity (u_mb = 0.26 m/s), with a particle diameter of 0.4 mm, particle density of 2300 kg/m³, and an initial solid volume fraction of 0.55. The gas mixture consists of CO₂, H₂O, and N₂ at a molar ratio of 0.1:0.1:0.8 and a temperature of 343 K. First, the numerical simulation was validated against experimental data reported in the literature, confirming its accuracy in quantitatively describing the adsorption process. Subsequently, the distributions of CO₂ concentration and adsorption reaction rate in both the bubble phase and the emulsion phase were analyzed under different superficial gas velocities. The simulation results indicate that CO₂ concentration and adsorption reaction rate in both phases decrease along the bed height. Compared to the emulsion phase, the bubble phase exhibits higher CO₂ concentration and gas temperature but a lower adsorption reaction rate. As the gas velocity increases, CO₂ concentration rises in both the bubble and emulsion phases, accompanied by an increase in the proportion of the bubble phase, and a higher CO₂ concentration at the reactor outlet. Further comparison of CO₂ concentrations in the bubble and emulsion phases at the upper part of the bed with the outlet concentration reveals that the outlet CO₂ primarily originates from the unadsorbed portion within the bubble phase, while the contribution from unadsorbed CO₂ in the emulsion phase is almost negligible. Full article

To address global carbon reduction demands, oxy-fuel combustion in circulating fluidized beds (oxy-CFB) has emerged as a highly promising carbon capture technology, offering extensive fuel flexibility and facilitating bioenergy with carbon capture and storage (BECCS). However, its commercialization is hindered by significant energy penalties and complex scale-up challenges. This review comprehensively analyzes the fundamental multiphase mechanisms, heat transfer behaviors, and multi-pollutant emission characteristics of oxy-CFB systems, drawing upon multiscale modeling advancements and operational data from pilot to 30 MW_th industrial demonstrations. Replacing air with an O₂/CO₂/H₂O mixture fundamentally alters gas–solid hydrodynamics and char conversion pathways, necessitating active fluidization state re-specification. Despite shifting optimal desulfurization temperatures and introducing recarbonation risks, the technology demonstrates inherent advantages in synergistic pollutant control, including the complete elimination of thermal NO_x. While atmospheric oxy-CFB is technically viable, transitioning to pressurized operation is critical to minimizing system efficiency penalties. Furthermore, integrating oxygen carrier-aided combustion (OCAC) and developing advanced predictive control strategies are essential to managing multi-module thermal inertia and enabling rapid dynamic responsiveness for modern power grids. Full article

Calculation of heat transfer in granular materials is an important task for many applications, from thermal management in electronics to exploring celestial soils. Usually, an effective thermal-conductivity model is employed to predict heat flux in unstructured granular media, such as a packed bed. However, a more advanced approach, the discrete element method (DEM), can capture the complex effects of mechanical loading and material mixtures on thermal transport coefficients, which traditional models struggle with. Pivotal for this approach is knowing the heat transfer coefficient between two adjacent particles. Currently, in most DEM-capable software, only particles in direct surface contact are considered to have non-zero heat conduction. We propose considering particles that are close to each other but don’t have a contact area with a non-zero surface area. We perform numerical modeling of the conductive heat transfer coefficient between equal spherical particles separated by media, assuming the fluid’s thermal conductivity is at least an order of magnitude lower. We use numerical solutions of differential equations to account for both thermal resistance within particles and through the gap between them. We found a simple generalized correlation for the heat transfer coefficient between particles and a general formula for the angular distribution of heat flux density across the particle surface. By employing a non-dimensional approach, the obtained formulas are constructed using non-dimensional parameters: the ratio of the particle’s thermal conductivity to that of the medium, and the ratio of the gap width between particles to their radius. The resulting formula is simple and convenient for DEM heat transfer calculations in packed and fluidized beds. Full article

An electrical heating fluidized-bed thermal energy storage (EH-FB-TES) system is proposed for integration with a coal-fired power plant (CFPP) for deep peak shaving (DPS) due to its high energy storage density and extensive heat exchange performance. The primary objective of this study is to evaluate the thermodynamic performance and economic feasibility of the integrated EH-FB-TES system, specifically focusing on identifying the optimal coupling and heat recovery strategies for enhanced deep peak shaving performance. Since EH-FB-TES uses air flow for fluidization in the heating storage process, its coupling with the CFPP differs from other TES technologies, and the associated thermodynamic performance and cost are thereby analyzed. The results show that, in EH-FB-TES, the heat release efficiency is predominantly constrained by thermal losses. To increase the energy utilization efficiency, a two-stage heat recovery strategy is proposed to release the stored energy in the integration. The first stage is to heat up the feedwater extracted from the deaerator and the second one is to heat up the condensate water. The analyses also show that the selection of reinjection positions for the heated medium from EH-FB-TES greatly influences the system performance. Returning the stored thermal energy to heat up feedwater can effectively increase the output of the unit, while directly generating steam can be beneficial for coal saving. The integrated system achieves a maximum equivalent round-trip efficiency of 32.9% under 20 MW/800 °C conditions. An economic analysis reveals that, compared with other energy storage methods, EH-FB-TES can realize a relatively high energy storage density with a rather low cost. Under the present DPS compensation policy, for a 315 MW subcritical CFPP integrated with a 50 MW EH-FB-TES system, when heat storage is 8 h, heat release is 4 h per day, and the plant operates 100 days per year, the estimated static and dynamic payback periods are 3.06 years and 3.67 years, respectively. The integration of CFPP with EH-FB-TES could be promising for meeting DSP requirements. Full article

The aim of this research was to experimentally analyze the influence of drying method, temperature, and drying time on moisture content (MC), elemental composition (percentages of C, H, N, S, and O), and protein and fat content in sunflower seeds, as well as to apply and compare different existing machine learning regression models for moisture content prediction. The study was conducted on three sunflower hybrids (Sumiko, Pioneer, and Agromatic Lidea) using conduction, vacuum, and fluidized bed drying at temperatures from 50 to 80 °C and durations from 15 to 60 min. The results showed that temperature and time are the main controllable parameters of drying, while drying methods and hybrid also significantly influence the process. In moisture content modelling, artificial neural networks (ANN) achieved the best predictive performance (R² = 0.97; RMSE = 0.46), while SVR models showed slightly weaker but still high accuracy. The results indicate that machine learning models can be useful tools for predicting moisture content based on drying parameters and may support improved monitoring and management of the sunflower seed drying process. Full article

This study experimentally investigated the movement, combustion, and potassium (K) and chlorine (Cl) migration behaviors of three biomass types: densified wood pellets (heavy), corn straw (lightweight), and wheat straw (lightweight, friable). The experiments were conducted under conditions representative of industrial coal-fired circulating fluidized bed (CFB) boilers, with a temperature range of 850–950 °C and a fluidization velocity of 6–8 m/s. Results show that densified wood pellets sink into the dense-phase zone and release volatiles slowly, in about 50 s. As the volatiles are nearly fully released, the pellets fracture multiple times along their length, eventually forming nearly spherical particles. Their movement and combustion processes closely resemble those of coal, making them suitable for direct co-firing in coal-fired CFB boilers. Conversely, corn straw and wheat straw exhibit low density, high volatile release rates (2 and 10 times that of wood pellets, respectively), rapid char fragmentation and abrasion, and high inherent K and Cl content (with >50% of K and >90% of Cl released). These properties lead to particle segregation, shortened gas-phase combustion time, an upward shift in heat release distribution, and potential risks such as high-temperature KCl corrosion, HCl dew point corrosion, ash slagging, and bed agglomeration. Therefore, untreated corn straw and wheat straw are unsuitable for co-firing in conventional coal-fired CFB boilers. This study provides essential data and engineering guidance: strict quality control is necessary for wood pellets to prevent Cl contamination, while pretreatment is mandatory for straw fuels. These findings offer practical insights for implementing diverse biomass co-firing strategies in coal-fired CFB boilers. Full article

The foundry industry produces over 66 million tons of mixed casting waste sand, containing toxic and harmful substances such as phenols and aldehydes, every year, which has caused serious soil pollution, water source pollution, and large amounts of CO₂ emissions. Green resource recycling and utilization are urgently needed. The hot method circulating fluidized bed furnace is currently the mainstream technology for the regeneration of casting waste sand. However, traditional equipment has a series of key technical bottlenecks, such as VOC (volatile organic compound) emissions, low yield of fine sand, poor stability of phase change sand, and uneven fluidization, which directly limit the effectiveness, large-scale promotion, and application of waste sand regeneration. This study, based on a self-designed experimental prototype, constructed models with different hood densities and inlet air velocity parameters. A CFD-DEM coupled model, combined with two turbulence models, was used for numerical simulations and experimental validation, and the optimal combination of fluidization parameters was determined. The study confirmed that the k–ω SST model is more suitable for precise simulation of such gas–solid two-phase flows. The research revealed quantitative relationships between key parameters and sand particle fluidization states, addressing the core problem of uneven fluidization in conventional bubbling furnaces and providing important guidance for the optimized design of new thermal cycle bubbling furnaces. It has significant engineering value for promoting the efficient resource utilization of foundry waste sand and the green and sustainable development of the industry. Full article

Erosion is widely encountered in circulating fluidized bed (CFB) boilers. Investigations into erosion mechanisms and mitigation strategies are essential for improving the operational reliability and reducing economic losses. This paper presents a bibliometric analysis and review of recent progress in erosion-related studies for CFB boilers, identifying three main research hotspots: CFD-based erosion prediction from flow dynamics, anti-wear coatings from materials science that consider chemical corrosion, and boiler design adaptations for biomass. Building upon classical studies on solid particle erosion mechanisms and accounting for the high-temperature and reactive chemical environments characteristic of CFB boilers, the erosion mechanisms in CFB boilers are systematically summarized. It is revealed that particle flow parameters dominate the erosion process, coupled with chemical corrosion. Subsequently, the application of computational fluid dynamics (CFD) methods to erosion prediction and mitigation in CFB boilers is reviewed, and the characteristics of various anti-wear techniques are discussed. It is found that CFD can serve as an effective tool for the design of anti-wear techniques; however, the design must account not only for erosion resistance but also for the resulting impacts on boiler heat transfer and thermal inertia. Finally, perspectives and future research directions for erosion studies in CFB boilers are outlined. Full article

With global plastic production creating immense environmental pressure and conventional recycling methods facing limitations, advanced chemical recycling techniques are crucial. This paper presents details of the design, construction, and operation of two fluidized reactors: a laboratory-scale (LS) reactor and a large-scale laboratory reactor (LSLR) for the catalytic pyrolysis of mixed plastic waste. A waste stream simulating municipal collection, consisting of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polystyrene (PS), was processed using a custom Ni/γ-Al₂O₃ catalyst and an industrial G-0110 catalyst in a two-stage system. The large-scale reactor demonstrated high efficiency, achieving a 90% yield of valuable pyrolysis oil and waxes, a 2% yield of syngas, and an 8% yield of solid residue containing mainly carbon at operating temperatures between 400 and 453 °C. The resulting liquid and wax fractions contained a rich mixture of aliphatic and aromatic hydrocarbons (such as styrene, indene, benzoic acid, toluene, and cumene), confirming their potential as a feedstock for the chemical industry. These results establish that two-stage catalytic pyrolysis in a fluidized bed reactor is a highly effective and promising technology for upcycling mixed plastic waste into valuable resources. Full article

The cement industry seeks alternative raw materials to lower its environmental impact, and biomass ash represents a potential material for construction applications. This study evaluates biomass ashes (BMA) produced from grate and fluidized bed combustion, as well as co-combustion with coal, focusing on their chemical, mineralogical, and physical characteristics. The results reveal a substantial variability in BMA composition, influenced primarily by the fuel type and combustion method. This heterogeneity critically affects the reactivity and overall suitability of the BMA for use in construction materials. It was found that none of the 23 analyzed samples met the requirements of EN 450-1. This outcome is largely attributable to the combustion process and to sampling from the bottom part of the boiler, which typically yields material with properties outside the limits of the standard. Even when assessed directly against the specific limit values of EN 450-1, the ashes did not comply without further processing or modification. Despite these limitations, BMA show potential for use in accordance with EN 197-1, which permits the incorporation of up to 5 wt.% minor additional constituents. However, their practical application under this framework requires validation through tests performed on hydrated cement. These findings underline both the limitations and the promise of BMA as a supplementary cementitious material (SCMs) in sustainable construction. Full article

Parboiling improves rice-milling performance and consumer acceptance; however, drying parboiled rice can be energy intensive and highly sensitive to drying conditions, making it costly for processors. High head rice yield (HRY) and whiteness index (WI) are essential for commercial value because they reduce breakage and improve visual quality. In the United States, parboiled rice is typically dried in a two-stage process using rotary drum and crossflow dryers, but the high temperature condition of rotary drums can increase energy demand and compromise rice quality. This study evaluated the drying kinetics, effective moisture diffusivity (D_eff), energy consumption, and quality for three common cultivars (CLL 18, RT 7521, and Titan) using four methods: natural air drying (NAD), two-pass hot air oven drying (OO), two-pass fluidized bed drying (FBD), and a hybrid of oven and fluidized bed method (OFBD). Moisture content (MC) was monitored during drying until 12.5% (w.b.) to understand the drying kinetics. FBD achieved the fastest drying, reducing Titan MC from 38.24% to 13.79% (w.b.) in 60 min (two passes). It also produced highest D_eff across cultivars and consumed less energy (1.6599 kWh) as compared to OFBD (1.6733 kWh) and OO (1.68 kWh). Among nine thin-layer models explored, the logarithmic model provided the best fit, and Midilli–Küçük and Verma et al. models performed better in specific cases. NAD produced a higher quality of HRY (Titan: 65.33 ± 2.07%) and WI (RT 7521: 63.99 ± 0.25) than FBD but required 7–10 days to reach the target moisture content, limiting industrial applicability. Results from this study show that drying method and rice cultivars significantly influenced parboiled rice quality, and FBD offered efficient drying without compromising parboiled rice quality. Full article

Biochar activation is critical for producing high-performance adsorbents; however, conventional activation methods are energy-intensive and difficult to control, particularly when air is used as an activating agent. This study investigates CO₂–air co-activation in a laboratory-scale fluidized bed reactor as an energy-efficient alternative. Experiments were conducted at 750–850 °C under varying gas flow rates with a constant CO₂/O₂ ratio. Optimal properties were achieved at 800 °C and 0.2–0.3 L/min CO₂, yielding a maximum BET surface area of 479 m²/g, a micropore contribution of 42%, and controlled carbon conversion (~25–35% yield). Aspen Plus equilibrium simulations also confirm that CO₂-only activation remains endothermic (heat duty up to +0.07 kW), air-only activation becomes strongly exothermic (down to −0.13 kW), while the CO₂–air mixture exhibits near-thermoneutral to mildly exothermic behavior (+0.13 to −0.10 kW), thereby reducing external energy demand potentially by approximately 60–70% compared with CO₂-only activation and significantly improving process stability. These results demonstrate that CO₂–air co-activation offers a practical route to produce high-quality activated biochar with controlled porosity and improved energy efficiency. Full article

This paper examines the study of an advanced design for a continuously operating fluidized bed reactor applied to sunflower husk torrefaction in a superheated steam environment, which is simulated in a cold model of the reactor. The simulated reactor has a diameter of 0.3 m and contains six vertical baffles installed along the reactor walls, providing loop-like movement of crushed husk particles from the reactor loading point to the reactor biomass unloading point. The residence time of crushed sunflower husk biomass particles in the reactor was studied by introducing colored biomass particles into the bed; these particles had the same mass and size as the undyed material. According to modeling results, replacing superheated steam with room-temperature air in the “cold” model may not lead to significant changes in the hydrodynamics of the fluidized bed or their effect on particle mixing. Experiments were conducted at an air velocity of 0.6 m/s relative to the cross-section of the empty apparatus, which is 3.5-fold greater than the minimum fluidization velocity. Samples were collected at the reactor outlet and dissolved in distilled water. The transparency of the resulting solution was measured using a KFK-3 photometer, and the amount of colored substance in each sample was determined accordingly. The most probable average residence time of biomass particles in the cold model amounted to 6–8 min at a Peclet number of 47. To ensure full operation of the torrefaction reactor under ideal plug-flow conditions, the reactor must be equipped with 24 baffles. The residence time of biomass particles required for optimal operation of the reactor was estimated to 24–32 min, which may be sufficient to produce biochar with a high calorific value, suitable for co-firing with coal. Full article