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An energy source transition is necessary to realize carbon neutrality, emphasizing the importance of a hydrogen economy. The transportation sector accounted for 27% of annual carbon emissions in 2019, highlighting the increasing importance of transitioning to hydrogen vehicles and establishing hydrogen refueling stations (HRSs). In particular, HRSs need to be prioritized for deploying hydrogen vehicles and developing hydrogen supply chains. Thus, research on HRS is important for achieving carbon neutrality in the transportation sector. In this study, we improved the efficiency and scaled up the capacity of an on-site HRS (based on steam methane reforming with a hydrogen production rate of 30 Nm3/h) in Seoul, Korea. This HRS was a prototype with low efficiency and capacity. Its efficiency was increased through thermodynamic analysis and heat exchanger network synthesis. Furthermore, the process was scaled up from 30 Nm3/h to 150 Nm3/h to meet future hydrogen demand. The results of exergy analysis indicated that the exergy destruction in the reforming reactor and heat exchanger accounted for 58.1% and 19.8%, respectively, of the total exergy destruction. Thus, the process was improved by modifying the heat exchanger network to reduce the exergy losses in these units. Consequently, the thermal and exergy efficiencies were increased from 75.7% to 78.6% and from 68.1% to 70.4%, respectively. The improved process was constructed and operated to demonstrate its performance. The operational and simulation data were similar, within the acceptable error ranges. This study provides guidelines for the design and installation of low-carbon on-site HRSs. [Display omitted] • The capacity of hydrogen refueling station (HRS) was expanded from 30 to 150 Nm3/h. • Efficiency of on-site HRS was improved through exergy analysis. • Simulation data was validated with real operation data of the implemented process. • The fuel consumption and CO 2 emission were reduced. • This study provides design and efficiency improvement guidelines for on-site HRSs. [ABSTRACT FROM AUTHOR]

In this study, a novel hollow fiber nanofiltration (HFNF) was investigated for treating real Cijengkol river water in Indonesia. Ultrafiltration (UF) pretreatment was performed to evaluate the effect of UF on the HFNF performance. The water quality of the raw water and permeate of the UF, HFNF, and UF-HFNF hybrid was first characterized. UF could remove only solids, while both nanofiltration (NF) and the UF-NF hybrid achieved a high removal efficiency for impurities in river water, meeting the standards for drinking water quality. However, severe organic fouling occurred in the HFNF membranes. To effectively control organic fouling, various cleaning methods were investigated, and then the analyses of gel permeation chromatography (GPC) and fluorescence excitation emission matrix (FEEM) were conducted on backwashing wastewater to identify the cleaning mechanism. First, hydraulic flushing and backwashing were evaluated, and both methods achieved higher than 90% efficiency particularly for high-molecular-weight organic foulants (>1000 Da). However, the cleaning efficiency decreased during long-term operation because of the low removal efficiency of low-molecular-weight (LMW) organics. Hence, chemically enhanced backwashing (CEBW) (i.e., 5 ppm and 10 ppm NaOCl) was employed to enhance the cleaning efficiency. The results showed that membrane fouling was easily controlled by CEBW with 95% removal efficiency. To reduce the usage of chemicals, CO 2 scouring, and CO 2 nucleation backwashing were also examined. CO 2 nucleation backwashing exhibited a better efficiency than CO 2 scouring because of the additional effect of CO 2 nucleation on the HFNF membrane surface. Interestingly, a relatively high removal efficiency for fulvic acid-like organic fouling was observed in both CEBW and CO 2 nucleation backwashing, whereas tryptophan and tyrosine-like proteins, soluble microbial products (SMPs), and humic-like organics were hardly removed by acidic condition (pH < 6.5) or high shear force, leading to a low cleaning efficiency of CO 2 nucleation backwashing. [Display omitted] • Indonesia river water was treated by novel hollow fiber nanofiltration membrane. • The dominant membrane fouling was due to low molecular weight organic fouling. • Periodical hydraulic backwashing and CO 2 scouring can replace pretreatment. • Hydraulic backwashing removes only high molecular weight organic foulants. • Chemical and CO 2 backwashing can remove low molecular weight organic fouling. [ABSTRACT FROM AUTHOR]

Currently, hydrogen is produced primarily through steam methane reforming, a gray hydrogen production process that generates CO 2 as a by-product. Thus, it is crucial to optimize the process thermal efficiency with minimizing CO 2 generation in a hydrogen production process. This study focuses on the multi-objective optimization of low-carbon hydrogen production process, considering both process thermal efficiency maximization and CO 2 emission minimization. To this end, a hybrid deep neural network model is developed to increase the robustness of the multi-objective optimization. The developed hybrid deep neural network model is incorporated into a proposed multi-objective particle swarm optimization algorithm that performs Pareto dominance-based multi-objective optimization. In experiments conducted, Pareto-optimal solutions with thermal efficiency distribution between 77.5 and 87.0% and CO 2 emissions between 577.9 and 597.6 t/y were obtained. Furthermore, the Pareto-optimal front was analyzed to provide various representative solutions to assist decision-makers. The findings of this study can enable efficient and flexible process operations according to various requirements. [Display omitted] • Low-carbon hydrogen production from an on-site steam methane reforming process. • Multi-objective optimization of thermal efficiency and CO 2 emission simultaneously. • Multi-objective particle swarm optimization for Pareto dominance-based optimization. [ABSTRACT FROM AUTHOR]

In the transition of the global energy paradigm toward decarbonization, hydrogen is expected to play a crucial role as an energy vector. To enhance the sustainability of hydrogen as an energy source, it is important to reduce costs and carbon emissions in the hydrogen production. Among various hydrogen production technologies, the autothermal reforming (ATR)-based blue hydrogen production method can stand out as a promising option in terms of both economic and environmental considerations. However, there are several bottlenecks: (i) ATR requires an air separation unit that increases the cost burden, and (ii) conventional amine-based carbon capture method consumes a significant amount of energy. To address these bottlenecks, this study proposes a novel cryogenic carbon capture process for ATR-based blue hydrogen production. In the proposed process, air separation unit are utilized not only for oxygen production but also for carbon capture. The compressed air from the air separation unit provides cooling energy to the mixture gas, leading to solidification and separation of carbon dioxide. Despite imposing an additional burden on the air separation unit, it significantly reduces the energy and cost associated with carbon capture. Consequently, there exists a trade-off relationship between the increased load on the air separation unit and the decreased load in carbon capture. This trade-off was evaluated by comparing it with the conventional absorption-based carbon capture process in terms of energy and economic aspects. The proposed process exhibits a 36.4% reduction in total energy consumption, with a particularly approximately 49.5% decrease in the energy consumed for carbon capture (0.278 kW h/kg-CO 2). The economic performance indicates an 11% decrease in the levelized cost of hydrogen (1.62$/kg-H 2), and a 45.3% decrease in CO 2 avoidance cost (40.1$/kg-CO 2). The captured solid CO 2 can offer advantages during storage and transportation. Furthermore, the potential utilization of cooling energy of solid CO 2 from an end-user perspective is expected to contribute to the establishment of a new industrial value chain. [Display omitted] • A novel cryogenic CO 2 capture process is proposed for ATR hydrogen production. • The proposed process imposes a slight burden on the ASU but simplifies CO 2 capture. • In terms of overall H 2 production, an energy saving of 36.4% was achieved. • LCOH and CO 2 avoidance cost are 1.62$/kg-H 2 and 40$/kg-CO 2 , respectively. • The economic viability variations across diverse carbon scenarios were evaluated. [ABSTRACT FROM AUTHOR]