Variation of the Number of Heat Sources in Methane Dry Reforming: A Computational Fluid Dynamics Study

To overcome the weak point of the gas type heating (failure in heating uniformly and persistently), liquid type molten salt as a concentration of solar energy was considered as a heat source for dry reforming. This high-temperature molten salt flowing through the center of the tubular reactor supplies necessary heat. The dependence on the number of heat source of the hydrogen production was investigated under the assumption of the fixed volume of the catalyst bed. By changing these numbers, we numerically investigated the methane conversion and hydrogen flow rate to find the best performance. The results showed that the methane conversion performance and hydrogen flow rate improved in proportion to the number of heating tubes. For the one heat source, the reactor surrounded by a heat source rather than that located in the center is the best in terms of hydrogen yield. In addition, this study considered the case in which the system is divided into several smaller reactors of equal sizes and a constant amount of catalyst. In these reactors, we saw that the methane conversion and hydrogen flow rate were reduced. The results indicate that the installation of as many heating tubes as possible is preferable

An overview of water electrolysis technologies for green hydrogen production

Decarbonizing the planet is one of the major goals that countries around the world have set for 2050 to mitigate the effects of climate change. To achieve these goals, green hydrogen that can be produced from the electrolysis of water is an important key solution to tackle global decarbonization. Consequently, in recent years there is an increase in interest towards green hydrogen production through the electrolysis process for large-scale implementation of renewable energybased power plants and other industrial, and transportation applications. The main objective of this study was to provide a comprehensive review of various green hydrogen production technologies especially on water electrolysis. In this review, various water electrolysis technologies and their techno-commercial prospects including hydrogen production cost, along with recent developments in electrode materials, and their challenges were summarized. Further some of the most successful results also were described. Moreover this review aims to identify the gaps in water electrolysis research and development towards the techno-commercial perspective. In addition, some of the commercial electrolyzer performances and their limitations also were described along with possible solutions for cost-effective hydrogen production Finally, we outlined our ideas, and possible solutions for driving cost-effective green hydrogen production for commercial applications. This information will provide future research directions and a road map for the development/implementation of commercially viable green hydrogen projects. (C) 2022 The Author(s). Published by Elsevier Ltd

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

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

Removal of volatile organic compounds from air using activated carbon impregnated cellulose acetate electrospun mats

Volatile organic compounds (VOCs) are released from various sources and are unsafe for human health. Porous materials are promising candidates for the adsorption of VOCs owing to their increased ratio of surface area to volume. In this study, activated carbon (AC) impregnated cellulose acetate (CA) electrospun mats were synthesized using electrospinning for the removal of VOCs from the air mixture of ACs, and CA solution was electrospun at different proportions (5%, 10%, and 15%) in a single nozzle system. The different AC amounts in the electrospun mats were distributed within the AC fibers. The adsorption capacities were measured for acetone, benzene, and dichloromethane, using quartz crystal microbalance. The results elicited an increasing adsorption capacity trend as a function of the impregnation of ACs in the electrospun mats, while their capacities increased as a function of the AC concentration. Dichloromethane resulted in a faster adsorption process than acetone and benzene owing to its smaller molecular size. VOCs were desorbed with the N-2 gas purging, while VOCs were adsorbed at higher temperatures owing to the increased vapor pressures. The adsorption analysis using Dubinin-Astakhov equation showed that dichloromethane is more strongly adsorbed on mats

Concept for Temperature-Cascade Hydrogen Release from Organic Liquid Carriers Coupled with SOFC Power Generation

For a sustainable hydrogen economy, large-scale transportation and storage of hydrogen becomes increasingly important. Typically, hydrogen is compressed or liquified, but both processes are energy intensive. Liquid organic hydrogen carriers (LOHCs) present a potential solution for mitigating these challenges while making use of the existing fossil fuel transportation infrastructure. Here, we present a process intensification strategy for improved LOHC dehydrogenation and an example of clean power generation using solid oxide fuel cells. Four LOHC candidates???ammonia, biphenyl-diphenylmethane eutectic mixture, N-phenylcarbazole, and N-ethylcarbazole???have been compared as stand-alone and integrated systems using comprehensive process simulation. ???Temperature cascade??? dehydrogenation was shown to increase the energy generated per unit mass (kWh/kg LOHC) by 1.3???2 times in an integrated system compared to stand-alone LOHC systems, thus providing a possibility for a positive impact on a LOHC-based hydrogen supply chain. ?? 2020 The Author(s)Liquid organic hydrogen carriers (LOHCs) are a potentially safer alternative to conventional hydrogen storage processes. Here, Brigljevi?? et al. select four similar LOHC compounds and exploit differences in their physical chemistry, presenting the concept of a temperature-cascading process for a more energy-efficient dehydrogenation. ?? 2020 The Author(s

Scenario-Based Techno-Economic Analysis of Steam Methane Reforming Process for Hydrogen Production

Steam methane reforming (SMR) process is regarded as a viable option to satisfy the growing demand for hydrogen, mainly because of its capability for the mass production of hydrogen and the maturity of the technology. In this study, an economically optimal process configuration of SMR is proposed by investigating six scenarios with different design and operating conditions, including CO2 emission permits and CO2 capture and sale. Of the six scenarios, the process configuration involving CO2 capture and sale is the most economical, with an H-2 production cost of $1.80/kg-H-2. A wide range of economic analyses is performed to identify the tradeoffs and cost drivers of the SMR process in the economically optimal scenario. Depending on the CO2 selling price and the CO2 capture cost, the economic feasibility of the SMR-based H-2 production process can be further improved

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 Study of Employing a Catalytic Membrane Reactor for a Pressurized CO2 and Purified H2 Production in a Water Gas Shift Reaction

The effect of two important parameters of a catalytic membrane reactor (CMR), hydrogen selectivity and hydrogenpermeance, coupled with an Ar sweep flow and an operating pressure on the performance of a water gas shift reaction in a CMRhas been extensively studied using a one-dimensional reactor model and reaction kinetics. As an alternative pre-combustion CO2capture method, the feasibility of capturing a pressurized and concentrated CO2 in a retentate (a shell side of a CMR) andseparating a purified H2 in a permeate (a tube side of a CMR) simultaneously in a CMR was examined and a guideline for ahydrogen permeance, a hydrogen selectivity, an Ar sweep flow rate, and an operating pressure to achieve a simultaneous captureof a concentrate CO2 in a retentate and production of a purified H2 in a permeate is presented. For example, with an operatingpressure of 8 atm and Ar sweep gas for rate of 6.7 ?? 10-4 mols-1, a concentrated CO2 in a retentate (~90%) and a purified H2 in apermeate (~100%) was simultaneously obtained in a CMR fitted with a membrane with hydrogen permeance of 1 ?? 10-8 molm-2s-1Pa-1 and a hydrogen selectivity of 10000

Hydrogen selectivity and permeance effect on the water gas shift reaction (WGSR) in a membrane reactor

Simulated results are presented using a reaction rate equation and a one-dimensional reactor model for a water gas shift reaction (WGSR) in a membrane reactor (MR) with a feed stream obtained from coal gasifiers. CO conversion in a MR at 423-573 K was higher than equilibrium conversion at the same temperature. The effect of two important parameters of a membrane, hydrogen selectivity and hydrogen permeance, on MR performance was studied and hydrogen selectivity was favorable for enhanced CO conversion, reduced CO concentration, and enhanced fuel-cell grade hydrogen. Hydrogen permeance was also favorable for CO conversion enhancement in a MR due to an increased driving force between the shell side (retentate) and the tube side (permeate) of a membrane. The criteria of a hydrogen permeance of higher than 8x10(-8) mol m(-2)s(-1)Pa(-1) and a hydrogen selectivity of 100 were suggested to produce a fuel-cell grade hydrogen (CO concentration less than 50 ppm) in the permeate and a concentrated CO2 (more than 90%) in the retentate simultaneously in a MR