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Accurate prediction of gas-solid flow hydrodynamics is key for the design, optimization, and scale-up of a circulating fluidized bed (CFB) reactor. Computational fluid dynamics (CFD) simulation with two-dimensional (2D) domain has been routinely used, considering the computational costs involved in three-dimensional (3D) simulations. This work evaluated the prediction capability of 2D and 3D gas-solid flow simulation in the lab-scale CFB riser section. The difference between 2D and 3D CFD simulation predictions was assessed and discussed in detail, considering several flow variables (superficial gas velocity, solid circulation rate, and secondary air injection). The transient Eulerian-Eulerian multiphase model was used. CFD simulation results were validated through an in-house experiment. The comparison between the experimental data and both computational domains shows that the 3D simulation can accurately predict the axial solid holdup profile. The CFD simulation comparison considering several flow conditions clearly indicated the limitation of the 2D simulation to accurately predict key hydrodynamic features, such as high solid holdup near the riser exit and riser bottom dense region. The accuracy of 2D and 3D simulations was further assessed using root-mean-square error calculation. Results indicated that the 3D simulation predicts flow behavior with higher accuracy than the 2D simulation. [ABSTRACT FROM AUTHOR]

Summary: Techno‐economic viability studies of employing a membrane reactor (MR) equipped with H2 separation membranes for methane steam reforming (MSR) were carried out for H2 production in Korea using HYSYS®, a well‐known chemical process simulator, including economic analysis based on itemized cost estimation and sensitivity analysis (SA). With the reaction kinetics for MSR reported by Xu and Froment, the effect of a wide range of H2 selectivity (10‐10,000) on the performance in an MR was investigated in this study. Because of the equilibrium shift owing to the Le Chatelier's principle, great performance of enhancement of methane conversion (XCH4) and H2 yield and reaction temperature reduction was observed in an MR compared with a packed‐bed reactor (PBR). A window of a H2 selectivity from 100 to 300 is proposed as a new criterion for better MR performance of MSR depending on potential applications from in‐depth analysis of XCH4 and H2 yield enhancements, a H2 purity, and temperature reduction. In addition, economic analysis to evaluate the feasibility of an MR technology for MSR was carried out focusing on a levelized cost of H2 based on itemized cost estimation of capital and operating costs as well as SA. Techno‐economic assessment showed 36.7% cost reduction in an MR compared with a PBR and revealed that this MR technology can be possibly opted for a cost‐competitive H2 production process for MSR. [ABSTRACT FROM AUTHOR]

An advanced solid reducing agent, i.e., a CaO/SiO2 composite has been optimized to improve the hydrogen fluoride (HF; a green house gas) elimination in semiconductor-based industrial applications. To avoid the Ca(OH)2 formation and enhance the HF removal efficiency of CaO, the hydrophobic properties of silica (SiO2) have used as a catalyst materials to enhance the stability of CaO/SiO2 solid reducing agent in the present investigation. The novel composite structure based on CaO/SiO2 was prepared using various concentrations of hydrophobic nano-silica sol and Ca(OH)2. The composite was characterized by contact angle goniometry, thermogravimetry analysis, and scanning electron microscopy. The water contact angle of the CaO/SiO2 composites significantly increased with increasing SiO2 content. In particular, angles of 61.6°, 73.7°, 84.8°, and 84.9° were obtained for SiO2 concentrations of 20, 40, 60, and 80 wt.%, respectively. These results suggest that the hydrophobic nature of the composites was improved with the addition of 60 and 80 wt.% of SiO2. Moreover, the surface properties were measured using the nitrogen Brunauer-Emmett-Teller method for obtaining the weight ratios (wt.%) and calcinations times. The determined specific surface areas (SSAs) were 16.19, 27.25, 32.86, and 40.56 m2/g for 80:20, 60:40, 40:60, and 20:80 CaO/SiO2 composites, respectively. From the water contact angle and SSA analysis, the optimum hydrophobic nature of CaO/SiO2 composites for HF removal was achieved at a weight ratio of 40:60 (Ca(OH)2/SiO2) at the calcination temperature of 650 °C. The perfluorinated compound (PFC) removal rate is 80 and 88% for a common regenerative catalytic system (RCS) catalyst and the CaO/SiO2 reaction-enhanced (RE)-RCS catalyst, respectively. In addition, higher amount of HF elimination is successfully achieved using CaO/SiO2 solid reducing agent. During the RE-RCS process, SiO2 acts as a catalyst to prevent the formation of Ca(OH)2 when CaO is exposed to water. [ABSTRACT FROM AUTHOR]

As environmental pollution worsens, many strategies are emerging to reduce CO 2 in various chemical processes. The practical strategy of byproduct hydrogen utilization in propane dehydrogenation is also being reviewed a lot. In this work, a comprehensive analysis was conducted for propane dehydrogenation process design integrated with membrane reactor and solid oxide fuel cell. Especially, membrane reactor and sequential reactor were used to increase the yield of the process. All assessments were investigated based on Aspen Plus®, which is commercial software for process simulation. Levelized cost of electricity was derived through itemized cost estimation. The 2.81 $ kWh-1 of levelized cost of electricity was revealed through itemized cost estimation; it is higher than industrial electricity in general. Therefore, various scenarios were conducted to reduce the levelized cost of electricity compared to industrial electricity price on sale, currently. The optimistic case (1.20 $ kWh-1) can be priced close to industrial electricity price through 100 % of propane recycling rate and − 20 % of reduction in the price of the influential factors. For life cycle assessment, the environmental impact of global warming potential was assessed as 4.93 kg CO 2 eq MJ-1 of CO 2 emissions. Various scenarios had been proposed to reduce CO 2 as with the economic assessment. Under pessimistic, realistic, and optimistic conditions, the results of global warming potential were 5.61, 4.93, and 4.25 kg CO 2 eq MJ-1, respectively. The comprehensive analysis will be presented as guidelines for the actual use of byproduct hydrogen. • Comprehensive analysis was conducted for the proposed process. • Levelized cost of electricity was derived as 2.81 $ kWh-1 for the process. • Economic and environmental assessment was conducted based on process modeling. • Global warming potential was estimated as 4.93 kg CO 2 eq MJ-1 for the process. [ABSTRACT FROM AUTHOR]

COX-free hydrogen production from ammonia decomposition in a membrane reactor (MR) for PEM fuel cells was studied using a commercial chemical process simulator, Aspen HYSYS®. With process simulation models validated by previously reported kinetics and experimental data, the effect of key operating parameters such as H2 permeance, He sweep gas flow, and operating temperature was investigated to compare the performance of an MR and a conventional packed-bed reactor (PBR). Higher ammonia conversions and H2 yields were obtained in an MR than ones in a PBR. It was also found that He sweep gas flow was favorable for XNH3 enhancement in an MR with a critical value (5 kmol h-1), above which no further effect was observed. A higher H2 permeance led to an increased H2 yield and H2 yield enhancement in an MR with the reverse effect of operating temperature on the enhancement. In addition, lower operating temperature resulted in higher XNH3 enhancement and H2 yield enhancement as well as NG cost savings in a MR compared to a conventional PBR. [ABSTRACT FROM AUTHOR]

Abstract: Conceptual design using multi‐bed series reactors consisting of catalysts and adsorbent beds was performed for a new SF6 abatement and utilization technology free of toxic chemicals to reduce SF6 emissions and produce valuable products like CaF2 and CaSO4 simultaneously. With process simulation studies using Aspen HYSYS®, comparative studies for a single‐bed reactor (SR‐1), a two‐bed series reactor (SR‐2), and a three‐bed series reactor (SR‐3) revealed that more CaF2 and CaSO4 were produced in multi‐bed series reactors compared to a SR‐1 (SR‐3 > SR‐2 > SR‐1) possibly due to sorption‐enhanced hydrolysis. In addition, lower operating temperatures were observed in multi‐bed series reactors (TSR1 > TSR2 > TSR3) showing the positive effect of using multi‐bed series reactors for a simultaneous SF6 abatement and utilization technology. [ABSTRACT FROM AUTHOR]

In this paper, a multi-stage catalyst-adsorbent reactor consisting of a series of catalyst and adsorbent beds is proposed for an effective tetrafluoromethane (CF4) abatement and conversion of corrosive hydrogen fluoride (HF) to CaF2, a useful chemical. Experimentally, enhanced CF4 conversions were observed in multi-stage catalyst-adsorbent reactors compared to a zero-stage reactor (catalyst bed only) confirming sorption-enhanced CF4 hydrolysis due to selective removal of HF during reaction. In addition, some useful design guidelines to select the number of stages and a proper time to replace adsorbents are presented. To develop a process simulation model to represent experimental data, Aspen HYSYS®, a commercial process simulator, was used providing a proper model to match experimental data quite reasonably. Based on experimental and simulative studies, a three- or four-stage catalyst-adsorbent reactor is recommended for CF4 abatement considering both reactor performance and capital/operating expenditures. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A preliminary techno-economic analysis combining process simulation and economic analysis has been carried out to assess the feasibility of employing a new CF4 abatement and utilization process without HF effluent, where CaO was employed to convert produced HF into CaF2, a useful chemical. Moreover, the effect of employing multi-bed series reactors compared with a single-bed reactor on CaF2 production was analyzed using Aspen HYSYS® based on material and energy balances from process flow diagrams for three systems, a single-bed reactor (S-1), a two-bed series reactor (S-2), and a three-bed series reactor (S-3). From economic analysis to estimate annual operating cost savings for three systems, it was found that multi-bed series reactors (S-2 and S-3) performed better than a single-bed reactor (S-1) due to equilibrium shift by Le Chatelier's principle leading to reduced operating temperatures to produce the same amount of CaF2 as S-1. Consequently, annual cost savings of about 7 to 13% were obtained in S-2 and S-3 compared to S-1 and this can serve as a useful guideline for the efficient system design. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Alkaline water electrolysis has been in the spotlight for green H 2 production using electricity generated from renewable energy because of its high technology readiness level and low investment. However, commercialization of alkaline water electrolysis is challenging because of the low current density. Therefore, a techno-economic and environmental assessment was conducted for green H 2 production by alkaline water electrolysis with experimental data from the advanced alkaline water electrolysis system of the Korea Institute of Energy Research (KIER) to identify the potential of this technology. Based on techno-economic analysis results, the stack cost and unit electricity price must be below 0.035 $ kWh−1 and 406 $ kW−1, respectively, to make this technology cost-competitive compared to the conventional H 2 production method (< 2 $ kgH 2 −1). Furthermore, CO 2 emissions of 30.7, 17.4, 7.04, and 3.12 kgCO 2-eq kgH 2 −1 were obtained for the current, 2030, 2050, and renewable Korean electricity mix scenarios, respectively, indicating that both scenarios (Korean electricity mix in 2050 and renewable) have lower CO 2 emissions than the conventional H 2 production method (11.5 kgCO 2-eq kgH 2 −1). In addition, environmental impact reductions of 89.8%, 83.6%, 65.9%, and 91.0% for CO 2 emissions, stratospheric ozone depletion, fine particulate matter formation, and fossil resource scarcity, respectively, were obtained for the renewable scenario compared to the current Korean electricity mix. Therefore, the electricity source has significant effects on the economic feasibility and environmental impacts for green H 2 production. [Display omitted] • TEA was performed to calculate unit H2 production based on experimental data. • Life cycle assessment was conducted to evaluate environmental impacts for green H2 production. • Economic and environmental guidelines can be provided. [ABSTRACT FROM AUTHOR]

[Display omitted] • Double DWCs are proposed for light olefin purification. • AI-based PI controller tuning is proposed to control double DWCs. • The AI-based PI tuning is compared to ZN, CC, and Aspen recommendation PI tuning. • The AI-based one outperforms all in terms of stability, cost, and CO 2 emissions. This study investigates the light olefin separation using dual dividing wall columns (DWCs) and compares various proportional-integral (PI) controller tuning methods. A novel process-conscious reinforcement learning (RL) approach, utilizing Deep Deterministic Policy Gradient (DDPG), is developed by incorporating domain-specific knowledge into the reward function to ensure compliance with critical process variables and product purity. The DDPG-based PI tuning is evaluated against traditional methods such as Aspen's recommended initial tuning, Ziegler-Nichols (ZN), and Cohen-Coon (CC). The result shows that the DDPG method significantly enhances control stability and accuracy, reducing error by factors of 11.9, 2.3, and 1.6 compared to Aspen, ZN, and CC, respectively. Additionally, DDPG demonstrates superior energy efficiency, consuming 13% less energy than the next best method. It also reduces purification costs by up to 13.5% and CO 2 emissions by 20% compared to other methods. This study highlights the potential of integrating advanced RL techniques into industrial process control, delivering substantial improvements in stability, energy efficiency, economic, and environmental performance. [ABSTRACT FROM AUTHOR]

• Powerfulness of molten salt as a heat source in methane dry reforming. • A tortuous type reactor, a frustum reactor and reactors immersed in molten salt. • Small reduction of methane conversion for tortuous reactor. • Better when smaller feed inlet radius of frustum reactor. • Better when smaller number of catalyst beds immersed in molten salt. A numerical study of the dry reforming of methane is discussed by applying molten salt as the heat source. A tortuous array of reactors, a reactor with frustum shape and a change in the number of reformer beds immersed in the molten salt are studied. The first observation is that the temperature of the heat source does not drop significantly between the inlet and outlet. This property naturally leads to a methane conversion that is proportional to the length when the catalyst volume is fixed. For a tortuous shape with 12 reactors in series, 0.4 m long each, neither the molten salt temperature nor the methane conversion differed significantly between the first and last reactors. Compared to the gas-type heat source, the molten salt turns out to be a very powerful energy carrier. In addition, we briefly discuss the frustum reactor and the variation in the number of reformer beds immersed in molten salt keeping the amount of catalyst fixed. In general, for the frustum reactor the conversion increases as the radius of the feed input becomes smaller. Finally, the CH 4 conversion decreases as the number of reformer bed increases for the variation of the number of reformer beds. [ABSTRACT FROM AUTHOR]

• A comprehensive CFD-economic model was developed to study NH 3 -CH 4 cofiring. • NH 3 addition into the fuel mixture results in a significant decrease in CO 2. • At high levels of NH 3 in the fuel mixture, NO decreases due to the DeNO X process. • As NH 3 content in the fuel mixture increases, there is a notable rise in N 2 O level. • Cofiring is cost-effective vs. CH 4 derived from landfill gas and H 2 methanation. In recent years, there has been a growing emphasis on the co-firing of conventional fossil fuels with carbon-free alternatives to mitigate CO 2 emissions. In the current study, a computational fluid dynamics (CFD) simulation was carried out to investigate the co-combustion of ammonia and methane in a combustion furnace located at the University of Lisbon. To examine the interaction between turbulence and chemistry, the Eddy Dissipation Concept (EDC) model was utilized. The fuel mixture consisted of methane and ammonia, ranging from 100 % methane combustion to 100 % ammonia combustion. The fuel proportions were determined based on their respective calorific values, ensuring an equivalent thermal input to the furnace. Subsequently, the CFD results were analyzed from an economic perspective. The research findings revealed that ammonia-methane cofiring led to a noteworthy reduction in CO 2 emissions compared to pure methane combustion. However, an increase in NO x emissions during ammonia combustion was observed. Interestingly, as the proportion of ammonia in the fuel mixture increased, the NO and NO 2 emissions decreased, while the amount of N 2 O increased. Based on the economic analysis results, the lowest annual cost (1922 USD y−1) was observed from the use of 100 % CH 4 fuel, primarily due to the relatively lower CH 4 cost compared to the NH 3 and NO x reduction system. However, as the NH 3 -contained fuel was considered, the annual cost increased with the NH 3 contained percentage, reaching the highest annual cost (5811 USD y−1) in the case of 100 % NH 3 -contained fuel. Among the economic parameters examined, the cost of NH 3 emerged as the most influential factor affecting the annual cost in the co-firing system. Furthermore, the co-firing system proved to be an economically viable option when considering CH 4 sourced from landfill gas and the renewable H 2 methanation process. [ABSTRACT FROM AUTHOR]

Ammonia emerges as a promising substitute for traditional fuels, offering a potential reduction in fossil fuel consumption and the associated emissions. Given its weak reactivity, an effective strategy to harness the potential of ammonia involves cofiring it with methane, to establish a self-sustaining combustion process. The understanding of heat release rate (HRR) in the cofiring process of ammonia and methane is crucial for burner design. This study introduces novel HRR indicators through a machine learning-based approach, focusing on species significantly contributing to HRR. Kinetic analysis is carried out utilizing a one-dimensional freely propagating flame model, applying a mechanism including 59 species and 356 reactions. Domain knowledge-based feature selection narrows down the search space, enhancing computational efficiency during HRR indicator identification. A random forest model is then employed to identify radical/radical combinations and their respective reaction orders, representing HRR optimally based on mean decrease impurity. The proposed HRR markers are [CH 4 ]0·76[OH]1.08, [HCO]0·65[NO]0.24, [CH 3 ]0.65[O]0.63, [NH 2 ][O]0.59, and [NH 3 ]0·93[OH]0.96. The root mean square error for each marker was extracted and compared with literature data, demonstrating higher reliability of the proposed indicators over those previously suggested. Additionally, the paper concludes with a discussion of the feasibility of measuring these markers from an experimental perspective. [Display omitted] • Thorough kinetic analysis of focusing on key HRR contributors. • Pioneering ML for crucial HRR indicator identification in ammonia-methane cofiring. • Domain-based feature selection streamlines HRR marker identification for efficiency. • Proposed 5 HRR markers that are superior in accuracy compared to existing markers. [ABSTRACT FROM AUTHOR]