Conceptual feasibility studies for cost-efficient and bi-functional methylcyclohexane dehydrogenation in a membrane reactor for H-2 storage and production

As the global trend towards transition to a "hydrogen society" continues to gain momentum, a lot of studies on alternative hydrogen (H-2) production methods are on the rise. Among them, methylcyclohexane (MCH) dehydrogenation in a membrane reactor (MR) is reported here as one possible candidate, affording its enhanced H-2 yield and a compact design. In this study, techno-economic analysis and carbon footprint analysis (CFA) of MCH dehydrogenation in an MR are carried out to investigate economic and environmental feasibility providing techno-economic and environmental guidelines for realizing it as mature technology. The economic parameters are determined through process simulation using Aspen Plus (R), and the unit H-2 production costs are obtained for a packed-bed reactor (PBR) and an MR in H-2 production capacities of 30, 100, 300, and 700 m(3) h(-1). The effects of each economic parameter on the unit H-2 production cost are identified through sensitivity analysis (SA) and scenario analysis is performed under various conditions to investigate the effects of technical parameters of the membrane, such as the H-2 production capacity, temperature, and H-2 permeance on the unit H-2 production costs. CFA is also performed to investigate the environmental feasibility of MCH dehydrogenation in an MR by considering CO2 emissions at each part

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

Feasibility study of power-to-gas as simultaneous renewable energy storage and CO2 utilization: Direction toward economic viability of synthetic methane production

According to an increase in concerns for environmental issues, the energy transition toward sustainable and alternative energy has received much attention. Synthetic methane, which is a fuel synthesized by the reaction of green hydrogen (H2) and carbon dioxide (CO2), is perceived as a promising alternative to fossil-fuel-based natural gas. A feasibility study of synthetic methane production focusing on green H2 production is conducted to investigate how to make the technology economically feasible. Cost estimation for methane production is performed by classifying various scenarios of H2 production based on water electrolysis technologies and renewable energy resources. The production costs of synthetic methane show diverse ranges following the considerations: 0.049-0.199, 0.059-0.215, and 0.154-0.273 $ kWh-1 for alkaline water electrolysis, polymer electrolyte membrane water electrolysis, and solid oxide water electrolysis, respectively. Moreover, sensitivity analysis discloses that parameters associated with green H2 production costs dominate the methane costs; therefore, predictive analysis demonstrates the economic outlook of synthetic methane production by applying learning-by-doing effects, future performance of electrolyzer, and renewable electricity costs. Consequently, we reveal the possibility of onshore wind electricity that can achieve economic feasibility with fully developed electrolysis systems for green H2 production at low electricity prices

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

Decision making with the deterministic judgment of urea production with various hydrogen sources: technical, economic, and environmental aspects

Demand for urea is gradually increasing, and is also focused on producing economical urea production; accordingly, urea production is concentrated on existing coal-fired power stations. However, coal-fired-power-station-based electricity production causes environmental pollution and urea production should be converted to renewable-energy-based production. Until now, renewable-energy-based urea production has been less economical than coal-fired-power-plant-based urea production, so various technical, economic, and environmental perspectives are needed. In particular, urea production can involve the unit urea production cost, considering various scenarios by the direct use of carbon dioxide and the indirect use of hydrogen through ammonia. In this work, unit urea production was estimated in consideration of the various type of hydrogen (grey, brown, blue, green, pink, and turquoise) and evaluated with respect to technical, economic, and environmental perspectives through an analytic hierarchy process with deterministic judgments

Electrified steam cracking for a carbon neutral ethylene production process: Techno-economic analysis, life cycle assessment, and analytic hierarchy process

Electrification is regarded as one of the solutions for decarbonization. To reduce the emissions of carbon dioxide from the steam cracking which is a conventional ethylene production process, the electrical heating furnace can be applied to the steam cracking called the electrified furnace. Here, to determine whether the electrified steam cracking is proper for carbon neutrality, the techno-economic analysis, life cycle assessment, and the analytic hierarchy process were implemented. The analysis was proceeded by the fourteen cases divided according to steam cracking, electrified steam cracking, and seven electricity generation methods. As a result, considering the technology development level, economic feasibility, and environmental impact, the best case was the steam cracking with hydropower, and the electrified steam cracking with hydropower, solar power, and wind power had high potential. As improving the technology development of the electrified furnace, the electrified steam cracking can be expected to become the proper ethylene production process to achieve carbon neutrality

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

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

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

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