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In modern chemical engineering, various derivative-free optimization (DFO) studies have been conducted to identify operating conditions that maximize energy efficiency for efficient operation of processes. Although DFO algorithm selection is an essential task that leads to successful designs, it is a nonintuitive task because of the uncertain performance of the algorithms. In particular, when the system evaluation cost or computational load is high (e.g., density functional theory and computational fluid dynamics), selecting an algorithm that quickly converges to the near-global optimum at the early stage of optimization is more important. In this study, we compare the optimization performance in the early stage of 12 algorithms. The performance of deterministic global search algorithms, global model-based search algorithms, metaheuristic algorithms, and Bayesian optimization is compared by applying benchmark problems and analyzed based on the problem types and number of variables. Furthermore, we apply all algorithms to the energy process optimization that maximizes the thermal efficiency of the steam methane reforming (SMR) process for hydrogen production. In this application, we have identified a hidden constraint based on real-world operations, and we are addressing it by using a penalty function. Bayesian optimizations explore the design space most efficiently by training infeasible regions. As a result, we have observed a substantial improvement in thermal efficiency of 12.9% compared to the base case and 7% improvement when compared to the lowest performing algorithm. [ABSTRACT FROM AUTHOR]

Steam methane reforming (SMR) is widely used in the hydrogen production industry; however, a significant amount of CO 2 is released during this process. Several efforts have been made to produce low-CO 2 hydrogen (blue hydrogen) via SMR; however, the proposed solutions are not applicable to small-scale plants. Therefore, this study proposes an on-site SMR process combined with a hollow fiber membrane module (HFMM) for CO 2 capture in small-scale plants. First, mathematical models for the on-site SMR process and HFMMs were developed, and their accuracy was validated with real-world data. Second, we designed and implemented the SMR–HFMM model based on different operating conditions and gas compositions at three potential CO 2 capture locations (dry syngas, PSA tail gas, and flue gas). The CO 2 capture performances at these three locations were compared using five performance indicators: stage cut, separation factor, CO 2 recovery rate, permeate composition, and retentate composition. Finally, to evaluate the integrated processes for each CO 2 capture location, feasible ranges of the number of HFMMs and the levelized cost of hydrogen (LCOH) were calculated. In the case of CO 2 captured in dry syngas, the number of HFMMs required to achieve a CO 2 purity of over 90% was calculated to be 10–25. Furthermore, despite additional HFMM installation, the LCOH was 0.8%–1.5% lower than that of the conventional on-site SMR process that is 7.07–7.13 USD/kgH 2. The proposed integrated SMR–HFMM process is a potential solution to the problem of CO 2 emissions in on-site SMR processes with a lower LCOH. Therefore, the findings of this study could be of significant importance in improving the environmental sustainability of hydrogen production in small-scale plants. [Display omitted] • Steam methane reforming (SMR) emits CO 2. • Conventional blue hydrogen production methods are not appropriate for on-site SMR plant. • Integration of on-site SMR with a hollow fiber membrane module (HFMM) for hydrogen production was proposed. • HFMM could capture CO 2 with high efficiency in a real on-site SMR plant. [ABSTRACT FROM AUTHOR]

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]

[Display omitted] • Oxy-fuel combustion-based blue hydrogen production process. • Integrates fossil fuel-based hydrogen production and electrolysis processes. • Proposed processes are SMR + SOEC and SMR + PEMEC. • SMR + SOEC shows highest thermal efficiency (85.2%) and exergy efficiency (80.5%) • SMR + SOEC shows lowest levelized cost of hydrogen and life cycle GHG emissions. Blue hydrogen is gaining attention as an intermediate step toward achieving eco-friendly green hydrogen production. However, the general blue hydrogen production requires an energy-intensive process for carbon capture and storage, resulting in low process efficiency. Additionally, the hydrogen production processes, steam methane reforming (SMR) and electrolysis, emits waste heat and byproduct oxygen, respectively. To solve these problems, this study proposes an oxy-fuel combustion-based blue hydrogen production process that integrates fossil fuel-based hydrogen production and electrolysis processes. The proposed processes are SMR + SOEC and SMR + PEMEC, whereas SMR, solid oxide electrolysis cell (SOEC), and proton exchange membrane electrolysis cell (PEMEC) are also examined for comparison. In the proposed processes, the oxygen produced by the electrolyzer is utilized for oxy-fuel combustion in the SMR process, and the resulting flue gas containing CO 2 and H 2 O is condensed to easily separate CO 2. Additionally, the waste heat from the SMR process is recovered to heat the feed water for the electrolyzer, thereby maximizing the process efficiency. Techno-economic, sensitivity, and greenhouse gas (GHG) analyses were conducted to evaluate the efficiency and feasibility of the proposed processes. The results show that SMR + SOEC demonstrated the highest thermal efficiency (85.2%) and exergy efficiency (80.5%), exceeding the efficiency of the SMR process (78.4% and 70.4% for thermal and exergy efficiencies, respectively). Furthermore, the SMR + SOEC process showed the lowest levelized cost of hydrogen of 6.21 USD/kgH 2. Lastly, the SMR + SOEC demonstrated the lowest life cycle GHG emissions. In conclusion, the proposed SMR + SOEC process is expected to be a suitable technology for the transition from gray to green hydrogen. [ABSTRACT FROM AUTHOR]

[Display omitted] • On-site hydrogen refueling stations require efficient catalysts/reactors. • Intrinsic kinetics of Ru catalysts were estimated using a parametric estimation. • New multistage (two- and three-stage) reactor designs were proposed. • Multistage reactors showed less temperature drop (better reactor stability). • Three-stage reactor can improve hydrogen production and conversion. In recent years, interest in the development of a hydrogen economy has increased, and the steam methane reforming (SMR) reaction, which yields so-called "gray" hydrogen, is expected to play a key role in hydrogen refueling stations (HRSs) in the interim before "green" hydrogen process is developed. For this purpose, compact and economical designs for small- to medium-scale SMR processes for HRSs are required. Herein, we investigated the intrinsic kinetics of a Ru-based catalyst using catalyst experiments and parametric estimation. In addition, reactor modelling was performed using a kinetic model with a special focus on multistage reactor configurations. The proposed reactor design showed an increase in the reactor energy supplied rate from 6.98 to 7.55 kW compared to the base case (single-stage reactor), and the conversion increased from 86.2% to 91.2%. Further, the drastic temperature drop owing to the strongly endothermic nature of the SMR reaction was reduced, and, thus, reactor stability was improved. The proposed novel design of a multistage reactor using a Ru-based catalyst will advance the development of the hydrogen economy. [ABSTRACT FROM AUTHOR]

Steam methane reforming (SMR) process is facing serious greenhouse effect problems because of the significant CO 2 emissions. To reduce pollution caused by gaseous emissions, desalination wastewater can be used because it contains highly concentrated useful mineral ions such as Ca2+, Mg2+, and Na+ , which react with carbonate ions. This study proposes a novel SMR process for carbon-neutral hydrogen production integrated with desalination wastewater-based CO 2 utilization. A process model for the design of a novel SMR process is proposed; it comprises the following steps: (1) SMR process for hydrogen production; and (2) desalination wastewater recovery for CO 2 utilization. In the process model, the CO 2 from the SMR process was captured using the Na+ ion, and the captured ionic CO 2 was carbonated using the Ca2+ and Mg2+ ions in desalination wastewater. The levelized cost of hydrogen (LCOH) was assessed to demonstrate the economic feasibility of the proposed process. Therefore, 94.5 % of the CO 2 from the SMR process was captured, and the conversion of MgCO 3 and CaCO 3 was determined to be 60 % and 99 %, respectively. In addition, the CO 2 emission via the proposed process was determined to be 0.016 kgCO 2 /kgH 2 , and the LCOH was calculated to be 2.6 USD/kgH 2. [Display omitted] • Steam reforming process was integrated with desalination wastewater process. • Feed stock restriction of the pollutant absorbent is possible to be solved. • Environmental contamination by desalination wastewater is prevented. • 94 % of CO 2 from the steam reforming process is capture and utilized. • Levelized cost of hydrogen production was 2.6 USD/kgH 2 by CO 2 and SO x utilization. [ABSTRACT FROM AUTHOR]

[Display omitted] • FNW CO 2 -based pyrolysis is integrated with the SMR to produce clean hydrogen. • The hydrogen production yield was increased by pyrolysis of FNW under CO 2. • The process was operated without external energy supply through energy optimization. • An environmental impact analysis was conducted for hydrogen production using FNW. Fishing net waste (FNW) represents more than half of marine debris, posing a substantial challenge to marine ecosystems. Conventional disposal methods, such as landfills and incineration, contribute to environmental pollution and overlook valuable material recovery. To address this issue, an innovative process that converts FNWs into high-purity hydrogen (H 2) through pyrolysis under CO 2 conditions, integrated with a natural gas (NG) reforming process, was proposed. The resulting gas undergoes a water–gas shift (WGS) reaction with NG-reforming syngas, amplifying H 2 production yield. High-purity H 2 is achieved through pressure swing adsorption (PSA). The high-temperature flue gas from pyrolysis oil combustion is utilized to generate electricity via the steam Rankine cycle (SRC) process. Furthermore, CO 2 in the flue gas is liquefied and stored through a carbon capture and storage (CCS) process. Techno-economic evaluation and life-cycle assessment (LCA) were performed to scrutinize the efficiency and feasibility of the proposed process. This study first demonstrated that the CO 2 -based waste fishing net pyrolysis integrated H 2 production process yielded 10.66 kmol h−1 of H 2 , providing a significant step toward sustainable H 2 production. Second, 87.13 % of wasted energy was recovered through the thermal integrated energy optimization of the waste fishing net and NG reforming process, and an additional 539.1 kW of electricity was generated through the SRC process, demonstrating high energy efficiency. Finally, although the levelized cost of hydrogen (LCOH) was slightly greater than that of the steam methane reforming (SMR) process, LCA revealed a significantly low greenhouse gas (GHG) index. Therefore, the proposed process serves as an eco-friendly approach to increase hydrogen production yield, which is a clean raw material with no carbon emissions, concurrently addressing the recycling of FNWs. [ABSTRACT FROM AUTHOR]