1,721,008 research outputs found
The Role of Ammonia in Decarbonization: A Techno-economic Assessment of NH3 as H2 Carrier and NH3 as Energy Vector
No full textNH3 is increasingly recognized as a versatile and promising energy vector in the transition towards a sustainable energy future. By utilizing renewable electricity to power the Haber-Bosch process for ammonia synthesis, green ammonia production eliminates or significantly reduces greenhouse gas emissions compared to conventional fossil-based NH3 production pathways. As a clean and sustainable alternative to conventional ammonia, green NH3 offers multiple benefits, including serving as a carbon-free fuel for transportation, providing a means of storing and transporting renewable energy, and enabling the production of carbon-neutral fertilizers and chemicals. In this framework, this work discusses the potential of NH3 as both H2 carrier and energy vector through a detailed techno-economic assessment. For each stage of the value chain, both fixed and operating costs are highlighted, to understand where to focus research efforts for future process intensification
Investigating Mixed Refrigerant Solidification in Hydrogen Liquefaction Processes
No full textWithin hydrogen liquefaction cycles, refrigerant mixtures reach highly critical conditions, with temperatures approaching the solidification temperatures of the pure components. To ensure the feasibility of the hydrogen liquefaction process, it is necessary to verify that such mixtures do not solidify under specified temperature and pressure conditions. This verification is carried out through the minimization of Gibbs free energy by simulating a RGibbs reactor in Aspen Plus® V11. For a given refrigerant mixture, comprising light hydrocarbons, hydrogen and nitrogen, the solidification temperature is determined as a function of pressure. The solidification curve is plotted for four mixed refrigerants that have been utilized in the literature for the precooling section of the hydrogen liquefaction process. The composition of the mixed refrigerant greatly affects the minimum temperature at which a refrigerant can be safely used without incurring solid precipitation, which varies between 60 K and 100 K. This work provides a guide for selecting the appropriate mixed refrigerant composition and operating conditions, with the aim to enhance the efficiency, reliability, and safety of hydrogen liquefaction technologies
Role of Tumor Vessels’ Features in Determining Risk of Bleeding in Meningiomas: Which Came First, the Chicken or the Egg?
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Energy and economic assessment of LH2, NH3, TOL/MCH and H0-DBT/H18-DBT for large-scale hydrogen transport
Full text linkThe transport of hydrogen from regions rich in renewable energy resources, where green hydrogen can be produced at a low cost, to countries with high energy demand, but limited resources, requires its conversion into a "hydrogen carrier", a substance capable of efficiently storing it. Techno-economic analyses are carried out on the value chains of ammonia (NH3), liquefied hydrogen (LH2), toluene/methylcyclohexane (TOL/MCH), and dibenzyltoluene/perhydro-dibenzyltoluene (H0-DBT/H18-DBT) for H2 transportation. A case study is examined in which hydrogen is transported from North Africa to Italy. The value chain includes H2 conversion into a carrier, storage, maritime transport, distribution, and reconversion back to H2. The conversion and reconversion processes correspond to liquefaction and regasification for LH2, synthesis and cracking for NH3, and hydrogenation and dehydrogenation for TOL/MCH and H0-DBT/H18-DBT. NH3 emerges as the most cost-effective and energy-efficient carrier when hydrogen is delivered to a hydrogen valley to serve nearby industries. The synthesis of ammonia, starting from green hydrogen, stands out as the primary cost driver of the value chain, followed by the ammonia cracking process. Ammonia cracking is the main source of energy inefficiency, highlighting the advantage of using ammonia directly where possible to avoid this step. For H2 application in the road transport sector, which involves its distribution to multiple refuelling stations operating at high pressure, LH2 is the most cost-effective and energy efficient carrier, provided that reconversion to hydrogen occurs at the refuelling stations. In this value chain, the liquefaction process represents the main cost driver and source of energy inefficiency
Green vs fossil-based energy vectors: A comparative techno-economic analysis of green ammonia and LNG value chains
Full text linkThis study conducts a comparative techno-economic assessment on the value chains of ammonia, as a green energy vector, and Liquefied Natural Gas (LNG), representing the benchmark energy vector, for long-distance energy transportation from Middle East to Europe. The value chain involves production from resources, conversion to an energy vector, storage and transport and reconversion of the energy vector to a suitable fuel. For comparison purposes, an electric power output of 400 MW is assumed to be produced by a power plant that utilizes either green or fossil fuels delivered to it. The adopted parameter for this comparison is the Levelized Cost of Energy (LCoE). Greenhouse gas emissions are economically penalized through the Social Cost of Carbon (SCC). Considering a SCC of 0.100 euro/kg, the LCoE of the LNG value chain is 59.19 euro/MWh, while that of ammonia is 231.71 euro/MWh. Since the cost of producing green hydrogen and purified natural gas strongly affects the results, a sensitivity analysis is performed to assess the impact of the assumed values. The SCC required to break even the LCoE of the two value chains is: 0.183 euro/MWh when considering the most favorable scenario for the green energy vector (low green hydrogen and high purified natural gas production costs) and 1.731 euro/kg when considering the most unfavorable one. This study highlights the cost-effectiveness of LNG in the current economic and regulatory landscape. However, the break-even range for the SCC indicates the potential for green ammonia to gain economic viability under higher carbon pricing scenarios
Hydrogen Liquefaction: a Systematic Approach to its Thermodynamic Modeling
Full text linkIn the present work, a thermodynamic approach capable of describing the hydrogen behavior during its cooling and liquefaction is proposed both for the case of catalytic ortho to para conversion occurring inside dedicated reactors and for the case of continuous conversion inside heat exchangers where the catalyst is packed on the hydrogen side. The state-of-the-art Equation of State to describe the properties of normal-, para- and ortho-hydrogen is the Helmholtz free energy explicit equation. However, it can only describe pure components and not mixtures. The novelty of the proposed approach is that it is based on the widespread Peng Robinson Equation of State and that it allows to accurately describe the calorimetric and volumetric properties of the different forms of hydrogen and their mixtures. Furthermore, it can be easily implemented in the Aspen Plus® process simulator, resulting to be useful in view of design and optimization of the hydrogen liquefaction process
Comparative Analysis of Conventional and Novel Low-Temperature and Hybrid Technologies for Carbon Dioxide Removal from Natural Gas
No full textNatural gas production is expected to increase, leading to the exploitation of low-quality reserves that contain high levels of acid gases, such as carbon dioxide. The aim of this work is to compare various innovative and conventional technologies for the removal of CO2 from natural gas, considered as a binary mixture of methane and carbon dioxide, with CO2 contents ranging from 10 to 70 mol%. The processes are simulated using Aspen Plus® V9.0 and compared in terms of energy consumption, which is evaluated through the net equivalent methane method. The results show that novel low-temperature and hybrid technologies, which combine distillation and physical absorption, are the most energy-efficient for CO2 removal from natural gas with high acid gas contents, while conventional physical absorption processes are optimal for natural gas with low to moderate acid gas contents
Animal husbandry at Arslantepe from the 5TH to the 1ST millennium BCE. An isotope approach
No full textThis study integrates isotopic analyses of 279 animal (domestic and wild) skeletal remains from the site of Arslantepe (Eastern Anatolia). The O, C and N isotopic analyses provide multiple information on husbandry strategies and on climatic variation from Late Chalcolithic to Iron Age (4700-712 BCE). Significantly, the study indicates that goats and sheep are the species that give the best information in terms of variation of climatic conditions. Pigs and cattle give complementary information mainly related to breading practices. This is because they are obliged drinkers, needing to be watered in the driest periods. Our analyses point out that, even when the climate was more arid, water sources were always present in the area. Cattle isotope values also indicate that fertilization of fields was already practiced during the Chalcolithic and that, in the period of stable occupation of the site, agriculture and stock farming were carried out in the same fields. This information, combined with the historical events and characters of the settlement in the different investigated periods, provide an invaluable and new point of view on the influence that political, social, and economic dynamics and organization had on the strategies of animal economy
Postoperative acute cerebellar swelling after pineal surgery: pathogenesis and treatment
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