Search Results (79)

To improve the flexibility of coal-fired power units and support renewable energy integration, molten salt thermal storage has been widely considered a promising retrofit option. However, under unified operating conditions, the comparative effects of different heat-release pathways and steam extraction ratios on flexibility, full-cycle thermodynamic performance, and economic performance have not been sufficiently clarified. In this study, a thermodynamic model of a 600 MW subcritical coal-fired power unit coupled with a two-tank molten salt thermal storage system was established in Ebsilon and validated against the design heat-balance data under typical load conditions, with maximum relative deviations of 0.06% for power output, 0.95% for main steam flow rate, and 1.24% for heat consumption rate. Three representative heat-release pathways were comparatively investigated under identical heat-storage conditions, with steam extraction ratios ranging from 2% to 18%. The results show that increasing the extraction ratio raises the thermal storage capacity from 9.762 to 84.636 MWh and enhances the downward peak-shaving capability, but weakens the full-cycle thermodynamic performance. Among the three schemes, Scheme 2 exhibits the strongest upward peak-shaving performance, with upward peak-shaving energy increasing from 2.893 to 24.395 MWh, and also yields the highest annual net profit (0.546–4.342 million CNY). Scheme 3 exhibits the best full-cycle thermal and exergy efficiencies, with full-cycle thermal efficiency of 42.76–41.56% and full-cycle exergy efficiency of 38.34–37.27%. In addition, Schemes 1 and 2 show significantly higher round-trip efficiencies than Scheme 3, with Scheme 2 becoming more advantageous at higher extraction ratios. Scheme 1 exhibits the shortest static payback period (7.12–7.63 years) and the highest internal rate of return (12.77–11.65%). These results indicate that the three schemes have distinct advantages in peak-shaving performance, full-cycle thermodynamic performance, and economic performance, and provide a comparative basis for engineering selection and parameter optimization of molten-salt-based flexibility retrofits in coal-fired power units. Full article

In this paper, we investigate the multi-scale dynamics of a singularly perturbed Rosenzweig–MacArthur model with a generalist predator and identify dynamical phenomena, including equilibrium bifurcations, supercritical or subcritical singular Hopf bifurcations, canard explosion bifurcations and homoclinic bifurcations. Specifically, the system exhibits a globally stable node, a headless canard cycle evolving into a homoclinic cycle, a headed canard cycle encompassing either a headless canard cycle or a homoclinic cycle, and so on. Notably, near the boundary equilibrium, these cycles exhibit a diminutive beard-shaped structure whenever it aligns with the transcritical non-normally hyperbolic point. The numerical simulations confirm the occurrence of a canard explosion, relaxation oscillation, and an inverse canard explosion phenomena not previously reported in singularly perturbed systems with both a transcritical point and a canard point. In brief, our results demonstrate that the generalist predation can cause richer bifurcations and dynamics. Full article

During the operation of nuclear power plants, nuclear fuel undergoes significant compositional changes. After several cycles of use, the fuel must be removed and stored. Currently, spent fuel is stored mainly in pools or casks, and it is necessary to demonstrate the subcriticality of these systems. Spent nuclear fuel has a complex composition, and because computational codes are typically validated using fresh-fuel experiments, subcriticality assessments are usually performed conservatively with fresh-fuel compositions. These approaches demonstrate subcriticality but are very conservative and can lead to storage system designs that are more expensive or have reduced capacity. This paper focuses on the validation of computational codes using nuclear power plant critical start-up tests (referred to as reactor criticals). These tests include spent fuel and are well documented, allowing them to serve as validation experiments. Codes validated using reactor criticals can be applied to systems containing spent fuel calculation if sufficient similarity is demonstrated. Similarity is evaluated using the SCALE TSUNAMI-IP module, which is widely used for this purpose. Based on a database containing dozens of reactor criticals and similarity analyses, we developed a methodology for demonstrating the subcriticality of spent-fuel storage systems. Full article

Biopolymers from renewable sources are increasingly explored to reduce the carbon footprint of materials and mitigate plastic pollution. This review synthesizes the last five years of progress across the biopolymer value chain, comparing plant, microbial/fermentation, fungal, and marine/algal resources and critically assessing greener extraction and fractionation routes (ultrasound and microwave intensification, subcritical water, supercritical CO₂ with co-solvents, ionic liquids, deep eutectic solvents including natural deep eutectic solvents, and enzymatic or bio-mediated processes). We emphasize yield-selectivity trade-offs, scalability, energy demand, and solvent recovery. Downstream, we summarize purification and performance tuning via crosslinking, derivatization, blending/plasticization, and nanocomposites, and we map advanced characterization to targeted functional properties to bridge processing choices with end-use performance. Applications are organized across food and agriculture, biomedical and pharmaceutical technologies, packaging, and cosmetics, with cross-cutting attention to safety and regulatory compliance, quality-by-design, techno-economics, and life-cycle assessment. Key bottlenecks are feedstock variability, viscosity and recyclability limitations of designer solvents, and persistent gaps in barrier and thermal properties versus petrochemical benchmarks, compounded by uneven composting and recycling infrastructure. Promising directions include low-viscosity or switchable solvents, data- and artificial intelligence (AI)-guided process optimization, engineered biopolymers, and circular end-of-life strategies that align material design with realistic recovery routes. Full article

The paper presents a comparative economic and environmental assessment of high-temperature steam turbine technologies (subcritical, supercritical, ultra-supercritical, and advanced ultra-supercritical cycles) within the energy transition. The research employs a model-based analysis to evaluate the cost of electricity production across countries with divergent environmental, social and governance (ESG) strategies, reflected in their carbon pricing mechanisms. The developed model estimates the economic feasibility and optimal timing for the transition to high-efficiency technologies, based on the projected fuel cost dynamics. Within the framework of the model, the optimal energy transition timings for implementing advanced ultra-supercritical steam turbine technologies were established: 2031 for the energy transition model in the Russian Federation (a country with developing ESG principles) and 2018 for the model in the Czech Republic (a country with an emerging ESG strategy). The results indicate that while carbon pricing mechanisms influence economic feasibility, hydrocarbon fuel costs remain the predominant factor. The study concludes that the enhancement of conventional generation technologies aligns with all three pillars of the ESG framework and facilitates the transition to a sustainable development model for the energy sector and the national economy. Full article

In line with the circular economy approach and the pursuit of sustainable solutions for spent coffee grounds, this study investigates the valorization of spent coffee grounds as a source of cellulose-based enzyme immobilization carriers. Considering that global coffee consumption generates approximately 6.9 million tonnes of spent coffee grounds annually, their disposal represents both an environmental challenge and an opportunity for value-added applications. A multistep extraction process, including Soxhlet extraction followed by sequential subcritical extraction with ethanol and water, and alkaline treatment, led to the production of cellulose-enriched carriers. The carriers obtained were characterized by their morphology, porosity and surface properties and subsequently used for the two lipases immobilization, Burkholderia cepacia (BCL) and Pseudomonas fluorescens (PFL), using three techniques: adsorption and covalent binding via direct and indirect methods. The immobilized lipases were analyzed for key biochemical and operational properties and compared with each other and with their free enzymes. Based on their stability, catalytic activity, and reusability, the lipases immobilized by adsorption were identified as the most efficient biocatalysts. These immobilized enzymes were then used in two selected reactions to demonstrate their practical utility: cocoa butter substitute synthesis using PFL and the enzymatic pretreatment of wastewater from the oil processing industry using BCL. Both immobilized lipases showed excellent catalytic performance and maintained their high activity over four consecutive reuse cycles. Full article

Concentrated solar power technology offers an effective pathway for large-scale renewable electricity generation in areas with abundant solar resources. This study develops and evaluates a cascaded multigeneration system that integrates a solar power tower with a subcritical-CO₂ Brayton cycle, a bottoming Rankine cycle, and a multi-effect distillation unit designed for Mediterranean conditions. The system achieves a maximum net power output of 23.48 MW and a freshwater production rate of 14.25 kg/s during peak summer conditions. The analysis reveals that high solar availability enables CO₂ mitigation of up to 27,434.55 kg-CO₂/h, thereby emphasizing the strong environmental benefits of the proposed system. The integrated Sb-CO₂–Rankine–Desalination configuration attains overall thermal efficiencies of 0.39–0.43, while exergy efficiencies reach 0.58 and 0.73 for the Sb-CO2 and Rankine subsystems, respectively. Sensitivity analysis further confirms the strong pressure dependence of the Sb-CO₂ cycle, with an optimum operation condition around 10 bar and 1100 °C, whereas the Rankine cycle exhibits a steady efficiency enhancement with increasing pressure. The proposed system achieves a simple payback period of 15.3 years, demonstrating its economic feasibility under Mediterranean climatic conditions. Full article

To fully recover abundant waste heat and reduce the operation cost in liquid-cooled data centers, a Carnot battery consisting of a heat pump (HP) and organic Rankine cycle (ORC) is proposed. Due to the existence of different cycle states for HPs and ORCs, four different cycle combinations are considered. To evaluate and compare their performances, thermo-economic models are developed. Under the design conditions, the optimal working fluid combinations are first determined for each battery. On this basis, thermodynamic and economic performances of the four batteries are analyzed in detail. The results indicate that the system consisting of a subcritical HP/transcritical ORC achieves the highest round-trip efficiency at 76%. Notably, the round-trip efficiency of the system can exceed 100% at low ORC condensing temperatures. Additionally, the system cost is about 767–796 USD/kW∙h, depending on the cycle combinations. Furthermore, the effects of operating parameters on system performances are also investigated. Finally, with the objective of maximum round-trip efficiency, key parameters of four batteries are optimized. The results reveal that the system with a subcritical HP/subcritical ORC attains a maximum round-trip efficiency of 83% after optimization. These research results contribute to the development of green data centers and the reduction of power costs. Full article

The recycling of carbon-fiber reinforced polymers (CFRPs) presents significant challenges due to their thermosetting matrix, which complicates end-of-life management and often results in energy-intensive disposal or significant waste accumulation. Despite advancements in recycling methods, knowledge gaps remain regarding their sustainability and economic viability. This study undertakes a comprehensive Life Cycle Assessment and Environmental Life Cycle Costing analysis of four key recycling techniques: mechanical recycling, pyrolysis, solvolysis, and high-voltage fragmentation (HVF). By using the SimaPro software, this study identifies mechanical recycling and HVF as the most sustainable options, with the lowest cumulative energy demand (CED) of 5.82 MJ/kg and 4.97 MJ/kg and global warming potential (GWP) of 0.218 kg CO₂eq and 0.0796 kg CO₂eq, respectively. In contrast, pyrolysis imposes the highest environmental burdens, requiring 66.3 MJ/kg and emitting 2.84 kg CO₂eq. Subcritical solvolysis shows more balanced environmental impacts compared to its supercritical counterpart. Cost analysis reveals that for mechanical recycling and pyrolysis, material costs are negligible or zero. In contrast, solvolysis and HVF incur material costs primarily due to the need for deionized water. Regarding energy costs, pyrolysis stands out as the most expensive method due to its high energy demands, followed closely by solvolysis with supercritical water. Full article

It is challenging to handle heavy-metal-rich plants that grow in contaminated soil. The role of heavy metals in biomass on the physicochemical structure and electrochemical properties of their derived carbon has not been considered in previous research. In this study, Cu-ion hybrid nanoporous carbon (CHNC) is prepared from Cu content-contaminated biomass through subcritical hydrocharization (HTC) coupling pyrolytic activation processes. The CHNCs are used as advanced electrode material for energy storage applications, exhibiting an impressively ultrahigh capacitance of 562 F g⁻¹ at a current density of 1 A g⁻¹ (CHNC-700-4-25), excellent energy density of 26.15 W h kg⁻¹, and only 7.59% capacitance loss after enduring 10,000 cycles at a current density of 10 A g⁻¹, making CHNCs rank in the forefront of previously known carbon-based supercapacitor materials. These comprehensive characterizations demonstrate that copper ions introduce new electrochemically active sites and enhance the conductivity and charge transport performance of the electrode material, elevating the specific capacitance of CHNC from 463 to 562 F g⁻¹. These findings offer valuable insights into the effective energy storage application of heavy-metal-contaminated biomass wastes. Full article

This study explores the use of a passive control technique to mitigate aeroelastic effects on a wing operating near the ground. An aeroelastic model, based on a typical airfoil section, equipped with a nonlinear tuned vibration absorber (NLTVA), is established to study the interactions between the airfoil’s dynamics, aerodynamics, and the nonlinear energy dissipation mechanisms. Geometric nonlinearity is incorporated into the airfoil’s dynamics to account for possible large wing deflection and rotation. The flow is modeled based on the nonlinear unsteady discrete vortex method with the ground effect simulated using the mirror image method. Stability analyses are conducted to study the influence of NLTVA parameters on flutter mitigation and the bifurcation behavior of the airfoil near the ground. The numerical results demonstrate that the NLTVA effectively delays the onset of flutter and promotes a supercritical bifurcation in the presence of ground effect. Optimally tuning the NLTVA’s linear parameters significantly increases flutter speed, while selecting the optimal nonlinear parameter is key to preventing subcritical behavior near the ground and reducing the amplitude of post-flutter limit cycle oscillations. Overall, this study highlights the potential of the NLTVA in enhancing the aeroelastic stability of flying vehicles with highly flexible wings, especially under the influence of ground effects during takeoff and landing. Full article

Grape stalks (GSs) from winemaking were submitted to a green process to valorise its lignocellulosic biomass that applied subcritical water extraction (SWE) at 170 °C and 180 °C to obtain active extracts and cellulose-enriched fractions. The sum of the total phenolic content of the soluble extract and the solid residue fractions from the SWE exceeded that of the GS, which suggests the generation of compounds with antioxidant properties through SWE. All SWE fractions showed high antioxidant power. The increased temperature promoted the extraction of polyphenolic compounds, enhancing the antioxidant power of both extracts and solid residues. These solid residue fractions were bleached with alkaline hydrogen peroxide solutions (4 and 8% v/v) to purify cellulose. After two bleaching cycles, no notable delignification progress was observed, as the bleaching yield or whiteness index did not significantly change in the further cycles. The first bleaching cycle led to a significant reduction in the lignin content at both SWE temperatures. The cellulose purity was higher in the samples obtained at 170 °C and bleached with 4% alkaline hydrogen peroxide. SWE at 180 °C led to greater cellulose oxidation during the bleaching step regardless of the hydrogen peroxide concentration. Full article

Of the three types of waste generated in beer processing, brewer’s spent grain (BSG) is the most abundant and has a high potential for valorization. In this work, defatted BSG (DB) was subjected to an extraction process with subcritical water at different temperatures to obtain extracts rich in phenols and the cellulosic fractions, which were also purified by using hydrogen peroxide (H₂O₂). The results showed that the dry extracts obtained at 170 °C were richer in phenolics (24 mg Gallic Acid Equivalent (GAE) g⁻¹ DB), but with lower antioxidant capacity (71 mg DB·mg⁻¹ 2,2-diphenyl-1-pikryl-hydrazyl). This extract also showed the highest antibacterial potential against L. innocua (80 mg·mL⁻¹) and E. coli (140 mg·mL⁻¹) than those obtained at lower temperatures. The purification of cellulose from the treated residues, using hydrogen peroxide, revealed that DB is a limited source of cellulose material since the bleached fractions showed low yields (20–25%) and low cellulose purity (42–71%), even after four bleaching cycles (1 h) at pH 12 and 8% H₂O₂. Despite this, the subcritical water extraction method highlights the potential of a simple process as a technological option to convert underutilized side streams like beer bagasse into added-value, potential ingredients for innovative food and pharmaceutical applications. Full article

This paper proposes, for the first time, the research concept of comparing energy and economy between transcritical cycle high-temperature heat pumps and subcritical cycle high-temperature heat pumps with new refrigerants. Experiments and simulations are conducted to compare the system performance and economy of two heat pumps, and the effects of different factors on the performance of two heat pumps are analyzed. The results show that R744/R1234yf (90/10) and R515-1 are the preferred refrigerants for transcritical cycle heat pumps and subcritical cycle heat pumps, respectively. The COP of the R744/R1234yf (90/10) transcritical heat pump is generally higher than that of the R515B-1 subcritical heat pump, and compared to the R515B-1 subcritical heat pump, the cost recovery period of the R744/R1234yf (90/10) transcritical heat pump is about 9–15 years. Therefore, it is recommended that users who use heat pumps for a long time choose transcritical cycle heat pumps. Meanwhile, with the change of evaporation temperature, the system COP of the R515B-1 subcritical heat pump and R744/R1234yf (90/10) transcritical heat pump increases by 61.11% and 65.91%, respectively. In addition, the optimal charge amount for the R515B-1 subcritical heat pump is 81.8% of that of the R744/R1234yf (90/10) transcritical heat pump. Full article

Almond skin (AS) is an agro-industrial residue from almond processing that has a high potential for valorisation. In this study, subcritical water extraction (SWE) was applied at two temperatures (160 and 180 °C) to obtain phenolic-rich extracts (water-soluble fraction) and cellulose fibres (insoluble fraction) from AS. The extraction conditions affected the composition and properties of both valorised fractions. The dry extracts obtained at 180 °C were richer in phenolics (161 vs. 101 mg GAE. g⁻¹ defatted almond skin (DAS)), with greater antioxidant potential (1.063 vs. 1.490 mg DAS.mg⁻¹ DPPH) and showed greater antibacterial effect (lower MIC values) against L. innocua (34 vs. 90 mg·mL⁻¹) and E. coli (48 vs. 90 mg·mL⁻¹) than those obtained at 160 °C, despite the lower total solid yield (21 vs. 29%) obtained in the SWE process. The purification of cellulose from the SWE residues, using hydrogen peroxide (H₂O₂), revealed that AS is not a good source of cellulose material since the bleached fractions showed low yields (20–21%) and low cellulose purity (40–50%), even after four bleaching cycles (1 h) at pH 12 and 8% H₂O₂. Nevertheless, the application of a green, scalable, and toxic solvent-free SWE process was highly useful for obtaining AS bioactive extracts for different food, cosmetic, or pharmaceutical applications. Full article