Renewable synthesis fuels play a crucial role in enabling a circular economy. This study assesses the environmental impacts of power-to-hydrogen and biomass-to-hydrogen routes, considering four hydrogen storage options: hydrogen, ammonia, methane, and methanol with a function unit of 1 liter of a stored hydrogen-derived product. The assessment encompasses metrics such as carbon footprint, use of fossil and nuclear energy, ecosystem quality, human health impact, and water scarcity. The results reveal that the biomass-based route has a lesser impact on global warming potential (GWP), with the system involving chemical looping technology and using ammonia as the storage medium achieving a negative GWP of -7.55 kg CO₂eq. The power-based route outperforms the biomass-based route except for GWP which is influenced by the penetration of renewable energy. Liquid hydrogen is found to be suitable for the fossil fuel-based route, while methane and ammonia are favorable to the power-based and biomass-based routes, respectively.

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Efficient CO₂ utilization in the thermochemical conversion of biomass plays an important role in creating a future low-carbon economy. This study attempts to explore the CO₂-assisted chemical looping gasification and co-gasification process of lignocellulosic biomass components (hemicellulose, cellulose, and lignin) with iron oxide oxygen carriers using thermogravimetry and differential thermal analysis. Three different iron oxide oxygen carrier-to-biomass (O/B) ratios were taken into account to deeply understand the thermal degradation characteristics of individual components (O/B ratio: 0) and their blending with iron oxide oxygen carriers (O/B ratio: 0.5 and 1). Meanwhile, the reduction characteristics of three major biomass components were also investigated in terms of X-ray diffraction (XRD), synergistic interaction, and reduction degree. Experimental results suggest that the existence of iron oxide oxygen carriers could accelerate the reaction kinetics under the reactive CO₂ environment, arising from the competitive relationship between the direct reduction reaction by char in biomass and the Boudouard reaction at high temperatures (600–950 °C). Interestingly, the reoxidation behavior of the reduced iron oxide is observed at high temperatures, especially for lignin. Among all the tested biomass materials, their ability to reduce iron oxide oxygen carriers under the CO₂ atmosphere follows the order of biomass mixture (1:1:1 wt%)>lignin>xylan>cellulose. Moreover, the findings indicate that significant synergistic interaction exists during the CO₂-assisted chemical looping co-gasification process.

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Because of their compact structure, ease of processing and higher heat transfer coefficient, curved-tube heat exchangers are widely applied in various industry applications, such as nuclear power systems, solar-powered engineering, aircraft engine cooling systems and refrigeration and cryogenic systems. Accurate knowledge about the heat transfer characteristics of the supercritical fluids in the tube is critical to the design and optimization of a curved-tube heat exchanger. The available literature indicates that the flow of supercritical fluids flowing in curved tubes affected by the dual effects of the buoyancy force and centrifugal force is more complex compared to straight tubes. Therefore, to obtain insight into their unique characteristics and further research progress, this paper presents a comprehensive review of available experimental and numerical research works on fluids at supercritical pressure flowing in curved tubes. Overall, the secondary flow caused by the curvature enhances the heat transfer and delays the heat transfer deterioration, but it also causes a non-uniform heat transfer distribution along the circumferential direction, and the strengthening performance of the curved tube is damaged. Compared with the more mature theories regarding straight tubes, the flow structure, the coupling mechanism of buoyancy and centrifugal force, and the general heat transfer correlation of supercritical fluids in a curved tube still urgently need to be further studied. Most importantly, studies on the suppression of heat transfer oscillations and heat transfer inhomogeneities specific to curved tubes are scarce. Considering the current status and shortcomings of existing studies, some study topics for supercritical fluids in a curved tube are proposed@en