Chemodynamical Analysis of Metal-rich High-eccentricity Stars in the Milky Way's Disk

We present a chemodynamical analysis of 11,562 metal-rich, high-eccentricity halo-like main-sequence (MS) stars, which has been referred to as the Splash or Splashed Disk, selected from Sloan Digital Sky Survey (SDSS) and Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). When divided into two groups, a low-[$\alpha$/Fe] population (LAP) and a high-[$\alpha$/Fe] population (HAP), based on kinematics and chemistry, we find that they exhibit very distinct properties, indicative of different origins. From a detailed analysis of their orbital inclinations, we suggest that the HAP arises from a large fraction (~ 90%) of heated disk stars and a small fraction (~ 10%) of in situ stars from a starburst population, likely induced by interaction of the Milky Way with Gaia Sausage/Enceladus (GSE) or other early merger. The LAP comprises about half accreted stars from the GSE and half formed by the GSE-induced starburst. Our findings further imply that the Splash stars in our sample originated from at least three different mechanisms - accretion, disk heating, and a merger induced starburst

An assessment of drag models in eulerian???eulerian cfd simulation of gas???solid flow hydrodynamics in circulating fluidized bed riser

Accurate prediction of the hydrodynamic profile is important for circulating fluidized bed (CFB) reactor design and scale-up. Multiphase computational fluid dynamics (CFD) simulation with interphase momentum exchange is key to accurately predict the gas-solid profile along the height of the riser. The present work deals with the assessment of six different drag model capability to accurately predict the riser section axial solid holdup distribution in bench scale circulating fluidized bed. The difference between six drag model predictions were validated against the experiment data. Two-dimensional geometry, transient solver and Eulerian???Eulerian multiphase models were used. Six drag model simulation predictions were discussed with respect to axial and radial profile. The comparison between CFD simulation and experimental data shows that the Syamlal-O???Brien, Gidaspow, Wen-Yu and Huilin-Gidaspow drag models were successfully able to predict the riser upper section solid holdup distribution with better accuracy, however unable to predict the solid holdup transition region. On the other hand, the Gibilaro model and Helland drag model were successfully able to predict the bottom dense region, but the upper section solid holdup distribution was overpredicted. The CFD simulation comparison of different drag model has clearly shown the limitation of the drag model to accurately predict overall axial heterogeneity with accuracy. ?? 2020 by the authors. Licensee MDPI, Basel, Switzerland

When Bigger Is Not Greener: Ensuring the Sustainability of Power- to-Gas Hydrogen on a National Scale

As the prices of photovoltaics and wind turbines continue to decrease, more renewable electricity-generating capacity is installed globally. While this is considered an integral part of a sustainable energy future by many nations, it also poses a significant strain on current electricity grids due to the inherent output variability of renewable electricity. This work addresses the challenge of renewable electricity surplus (RES) utilization with target-scaling of centralized power-to-gas (PtG) hydrogen production. Using the Republic of Korea as a case study, due to its ambitious plan of 2030 green hydrogen production capacity of 0.97 million tons year-1, we combine predictions of future, season-averaged RES with a detailed conceptual process simulation for green H2 production via polymer electrolyte membrane (PEM) electrolysis combined with a desalination plant in six distinct scale cases (0.5-8.5 GW). It is demonstrated that at scales of 0.5 to 1.75 GW the RES is optimally utilized, and PtG hydrogen can therefore outperform conventional hydrogen production both environmentally (650-2210 Mton CO2 not emitted per year) and economically (16-30% levelized cost reduction). Beyond these scales, the PtG benefits sharply drop, and thus it is answered how much of the planned green hydrogen target can realistically be if on an industrial scale

Feasibility of offshore wind turbines for linkage with onshore green hydrogen demands: A comparative economic analysis

Imprudent fossil fuel use for getting energy caused serious environmental problems making us necessary to seeking for alternative energy sources which are renewable and sustainable. Using wind energy is currently considered as one of feasible renewable energy sources, however, the problem of noise pollution from the sweep of turbine blades should be solved. As a feasible solution for the noise pollution problem, the construction of wind farms offshore is currently considered. In addition, many factors can change the onshore wind speed, while offshore wind has a higher wind speed and consistency, which leads to higher energy efficiency. However, the remained intermittency of wind energy makes storage media such as H-2 necessary, thus, the construction of an offshore wind base H-2 production system can be required for protecting the energy security. In this study, a comparative economic analysis is conducted to verify feasible equipment placements of offshore wind-based H-2 production systems in various possible cases with different electrolyzer types, wind speeds, and offshore distances. An optimization study for 4 case scenarios with different regions, offshore lengths, and kinds of electrolyzers, was preliminarily conducted to find several placements that are economically optimal in common. For the optimization, a mixed-integer programming tool in Python was used, and as a result, three absolutely economical placements were selected. Then, the comparative economic analysis with considering the selected three cases was conducted indicating the most feasible placement according to the considered offshore length and wind speed, and costs ranged from 1.64 to 4.46 $ kgH(2)(-1). From the optimal cases for considered regions (Ulsan, Magallanes), the system using alkaline electrolyzer can achieve the feasible prices for both regions, while using other types stay in ranges of the current green H-2 produced by electrolysis

The Urban Museum as a Creative Tourism Attraction: London Museum Lates Visitor Motivation

The urban museum has become a multi-functional institution that transcends the functional display of artifacts. The museum has become, in cities, a hybrid institution that keeps its doors open late to support a wide variety of special events. This study explored London’s “Museum Lates” programs and event characteristics, theoretical views of museums as cultural and creative tourism attractions. Furthermore, the study applied the contextual model of learning to understand visitor attendance motivations. The authors employed an interpretive approach using interviews with two types of participants: event visitors and event coordinators. The findings suggest that attendees possess personal, physical, and socio-cultural motivations for participating in “Museum Lates” events. The characteristics of late events—extraordinary quality and evening-time atmosphere—produce different effects from those of current museum exhibitions held during regular operating hours. “Museum Lates” events can contribute to achieving cultural sustainability, adding a cultural construct to the traditional three pillars of sustainability

Comparative feasibility studies of H-2 supply scenarios for methanol as a carbon-neutral H-2 carrier at various scales and distances

Hydrogen (H-2) energy has come to the fore as a significant role of chemical industry in achieving a sustainable energy sector under serious environmental problems. Therefore, research for using H-2 as an energy carrier has been actively conducted. However, H-2 has very low volumetric energy density making it require conversion to other forms to acquire higher volumetric energy density. In this paper, the promising compound methanol (MeOH) was considered as a H-2 carrier owing to carbon-neutral in environmental terms. The two main overall H-2 supply scenarios were considered. The first case covers the use of MeOH produced from various types of H-2 (from steam methane reforming (SMR), coal gasification (CG), and water electrolysis (WE)), indirectly, and CO2 electrolysis, directly, as a H-2 carrier, further converted to H-2 at desired locations. The second case covers the conversion of MeOH from four production pathways into H-2 followed by the transportation of the produced H-2 via various H-2 transportation methods such as compressed H-2 (CH2), liquefied H-2 (LH2), liquid organic hydrogen carrier (LOHC), and ammonia (NH3). In this work, diverse H-2 supply scenarios considering various MeOH production methods, capacities, pathways, and distances were analyzed with unit H-2 supply cost via economic analysis. (c) 2021 Elsevier Ltd. All rights reserved

Materializing International Trade of Decarbonized Hydrogen Through Optimization in Both Economic and Environmental Aspects

As deviations in H-2 production capacity by countries become a considerable barrier to the realization of the global H-2 economy, international trade between countries with abundant resources and those with limited resources is required. In line with this trend, numerous supply chains between several countries have been planned, and associated studies have been conducted. However, the study which treats international overseas H-2 trade chains considering numerous major importing and exporting countries has rarely been conducted before. In this study, a comprehensive optimization for the overseas H-2 supply chain considering the three major importing countries including Korea, Japan, and Germany was conducted with mixed-integer linear programming considering both economic and environmental aspects simultaneously. Through the optimization study, the most feasible H-2 supply chains for each importing country could be verified according to years and case scenarios. Blue H-2 from Qatar turns out to be the most feasible supply chain for Japan in 2030, while green H-2 from South Africa is the most feasible one for other importing countries. In 2040, green H-2 from South Africa and Australia becomes the best one for Asian importers, and Australia finally dominates all the supplies after 2050. In the case of Germany, green H-2 from Spain is considered the best after 2040. Depending on the scenario, the difference in the selected countries and supply amounts is not significant, though the costs are varied. Ammonia turns out to be the most feasible carrier for H-2, and the total cost including the carbon tax ranges from 2.15 to 3.43 $ kgH(2)(-1), which is a range from the current green H-2 to the blue H-2 price

Comparative Economic Optimization for an Overseas Hydrogen Supply Chain Using Mixed-Integer Linear Programming

As environmental problems become serious, many countries have been striving to change fossil-based energy to renewable and sustainable hydrogen energy. However, there are large capacity differences for each country's hydrogen production, making hydrogen trading necessary. Although extensive research has investigated hydrogen technologies and economics, to the best of our knowledge, no study has examined the optimization of the overall hydrogen supply chain, from overseas supply to domestic consumption, considering various feasibility scenarios. This is a case study on the hydrogen supply chain for South Korea, which is expected to be one of the major hydrogen-importing countries, considering the decarbonized hydrogen requirements of the importing country and the production capacities of exporting countries over two decades. This study's optimized results for a hydrogen supply chain via mixed-integer linear programming reveal that it is most feasible for South Korea to import blue hydrogen from Qatar and Russia and green hydrogen from UAE and India, using liquefied hydrogen in the near term. This is because of the significantly lesser resource prices compared to other countries. The share of blue hydrogen supply dominates in the near term, while the green hydrogen supply is expected to gradually prevail over blue hydrogen due to an exponential drop in the renewable electricity price. With the price drop of green hydrogen, green hydrogen purchases from other countries in tandem with the UAE are predicted, rather than the blue hydrogen supply, considering that long-term demand will exceed the UAE's predicted capacity

Carbon dioxide removal from the oceans: Carbon dioxide emission and techno-economic analyses of producing renewable synthetic methane

The capture of carbon dioxide from ocean water and utilizing the captured carbon as a stock for carbon-neutral renewable methane production may reduce a considerable amount of carbon in the atmosphere. However, given the lack of comprehensive analyses to reveal the potential, the examination proceeded through techno-economic and carbon dioxide emission analyses with several possible options of carbon dioxide extraction, location, electricity sources, and transport media. Through the economic analysis, the unit methane supply costs range from 3.5 to 7.5 $ kgCH4- 1 according to the different options, and the majority of the total cost is found to be the electrolysis for generating hydrogen. The results of the emission analysis indicate cumulative emissions of the considered pathways which are highly negative values of around -80,000 tonCO2 y-1 due to the utilization of carbon by extraction. However, the utilization of synthesized methane in the natural gas power plant makes the final cumulative emission amount become highly positive values of more than 70,000 tonCO2 y-1. Here, the required capture rates in the power plant are suggested for the respective pathways to achieve carbon neutrality. A capture rate of 54.44 % is required for the pathway using column and OTEC, while 77.62 % is required for the pathway using BPMED and PV. Thus, given that it could be verified that the suggested pathways are competitive in the environmental aspect if the carbon capture in the utilization plant is possible, which can take advantage of the rate less than the common existing rate, a significant reduction in the cost, especially the levelized cost of electricity, will be crucial for the pathways to attaining competitiveness in the economic aspect as well