Copper-chlorine Cycle Research Articles

Investigation of the flash vaporization technique as a novel anolyte separation method in a copper-chlorine thermochemical cycle for sustainable hydrogen production

Thermochemical water-splitting processes are a promising alternative to the conventional hydrogen production technologies. In this regard, the thermochemical copper-chlorine cycle is amongst the clean hydrogen production processes that have shown immense promise to achieve commercialization in the long term future through several investigations reported in the open literature. A primary reason for this is its moderate temperature requirements which can be harnessed through a wide variety of sources such as waste heat or solar thermal energy. More specifically, the four-step variant of the copper-chlorine cycle has exhibited the highest efficiencies compared to its three and five-step versions. However, certain aspects of the cycle need further attention. One such aspect is the fourth and the final step of the cycle – the anolyte separation step which ensures the complete replenishment of all chemical compounds within the cycle. The anolyte is a homogeneous solution that constitutes water, hydrochloric acid, copper (II) chloride, and copper (I) chloride. The existing methodology for the separation of all these chemicals considers a multi-step drying process that takes place at ambient pressure and temperatures over 100°C. These conditions have been concluded to contribute to lowering the energy efficiency and increasing the cost rate of hydrogen through various studies previously conducted and published by the authors. In this regard, the authors have investigated an alternative technique for the anolyte separation process – the flash vaporization method where the partial separation of various chemical species can be achieved under vacuum conditions resulting in lower required temperatures and ultimately making the anolyte separation process relatively less energy intensive. Thus, this paper develops a stand-alone experimental set-up to investigate the flash vaporization process on a lab scale to determine its feasibility and potential to be a replacement for the existing approach of anolyte separation in a four-step copper-chlorine thermochemical cycle. The experiments are conducted under a wide variety of conditions and the obtained results are quite promising. Further, this study also considers the development of an empirical model to enable an analytical quantitative prediction of the separated anolyte solution.

Thermodynamic performance assessment of the four-step copper-chlorine cycle in hydrogen production and compression

Rapidly increasing global energy demands requires sustainable alternatives to conventional fossil fuels. Hydrogen emerges as a promising energy carrier due to its high energy density and minimal environmental impact, mainly when produced via thermochemical cycles like the Copper Chlorine (CuCl), which makes use of low-grade waste thermal energy for hydrogen production in an environmentally friendly manner. This study integrates hydrogen production using the Cu-Cl cycle and hydrogen compression systems crucial for establishing robust hydrogen infrastructure. Following hydrogen generation, the study examines the thermodynamic analysis of compressing hydrogen to higher pressures. Parametric variations in compression, including inlet and outlet pressures and the number of stages, are analyzed to optimize energy efficiency and exergy performance. Energy efficiency of around 47.05% is obtained for the 4-step Cu-Cl cycle. The integrated step showed a notably high exergy efficiency of 98.48%. Other key findings include a 35% increase in energy efficiency with five compression stages for an inlet pressure increment from 15 to 30 bars, and a 12% efficiency decrease when varying outlet pressure from 500 to 800 bars. Exergy efficiency shows a 17% improvement with increased compression stages under constant inlet pressure but a 4% decline when varying outlet pressure with a five-stage configuration. These findings highlight the critical role of efficient compression systems in enhancing hydrogen storage and distribution for sustainable energy applications.

Assessment of hydrogen production potential of APEX fusion blanket via cobalt-chlorine and copper-chlorine cycles

In this paper, the neutronic and hydrogen production performances of the advanced power extraction fusion reactor (APEX) have been investigated by using TRISO thorium fuel. With this study, TRISO-coated nuclear fuel was first used in the APEX fusion reactor. In this calculation, firstly, the neutronic performances for 10 % ThC + 90 % FLiBe and various 6Li enrichment ratios have been computed with MCNP. Secondly, the potential of hydrogen production of the hydrogen unit, which contains cobalt-chlorine cycle and copper-chlorine cycle, integrated with the advanced power extraction fusion reactor has been performed. The tritium breeding ratio has changed between 1.09 and 1.15 among 7.5 % and 90 % 6Li enrichment ratios for 10 % ThC + 90 % FliBe. The energy multiplication factors have been obtained as 1.2727 and 1.3209, respectively, among 7.5 % and 90 % 6Li enrichment ratios. The thermal power, its ratio, and the hydrogen production amount have been calculated depends on the energy multiplication factor for various 6Li enrichment ratios and each considered cycle. The results showed that hydrogen production quantity increases with a rising 6Li enrichment ratio for both cycles. The highest produced hydrogen amount was obtained as 12.74 kg/s via the Cu-Cl cycle, whereas hydrogen production with the Co-Cl cycle has been computed as 6.79 kg/s in the cases of 10 % ThC fuel ratio and 90 % 6Li enrichment ratio.

A comparative exergoenvironmental assessment of thermochemical copper-chlorine cycles for sustainable hydrogen production

Hydrogen is one of the highly promising clean solutions to address the concerns of energy security in the future given the rapid rate of depletion of naturally occurring hydrocarbon sources. However, it is of immense importance that hydrogen is obtained through sources that ensure sustainability. Thermochemical water-splitting processes are among such routes of hydrogen production that are both sustainable and environmentally benign. Thus, this study focuses on assessing the copper-chlorine thermochemical cycles that are among the more promising cycles of the chlorine family in terms of efficiency and cost-effectiveness. Moreover, this study considers a comparative exergoenvironmental evaluation of the four variants of the copper-chlorine cycle that vary in the number and the nature of steps. A comparison in this regard is carried out between the various steps of each cycle in terms of the component-associated environmental impact rates and environmental impact rates of energy transfer as well as the overall environmental impacts of all cycles. In addition, a comparison of the global warming potential of hydrogen synthesized through utilizing various electricity sources is also performed. Based on our evaluations, hydrolysis and electrolysis are the common steps in the five-step cycle, the four-step cycle, and the three-step cycle configuration 1 yielding the highest component-associated environmental impact rates and environmental impact rates of energy transfer, respectively. Conversely, in the three-step cycle configuration 2, the electrolysis and thermal decomposition steps yield the highest corresponding values, respectively. In addition, the three-step cycle configuration 2 (4,869 mPts/h) and the five-step cycle (3,194 mPts/h) have the highest and the lowest component-associated environmental impact rates, respectively while the five-step (530,694 mPts/h) and the four-step (248,050 mPts/h) cycles result in the highest and the lowest environmental impact rates of energy transfer, respectively.

Electricity and hydrogen production by integrating two kinds of fuel cells with copper chlorine thermo-chemical cycle

An innovative cogeneration system based on a solid oxide fuel cell (SOFC) and copper chlorine cycle is being investigated. Instead of directly making electricity by any thermodynamic cycle or thermoelectric generator, the waste heat from SOFC should be used to make hydrogen through the copper-chlorine cycle (Cu–Cl). A portable polymer exchange membrane fuel cell (PEMFC) has been suggested due to its compatibility with portable and non-portable applications. The obtained results reveal that increasing the current density of SOFC results in higher methane consumption, output power, overpotentials, and hydrogen production. Furthermore, temperature variation does not have as much influence on power generation and efficiency as current density, where the system efficiency, when operating at 0.7 A/cm2 and SOFC operating temperature of 900–1200 K, varies between 40.4 % and 46.3 %. Regarding the methane flow rate, as it increases, the output power increases as well, but the efficiency falls. The system's greatest power output is 677.5 kW and occurs at a methane flow rate of 2.13 mol/s, although the system efficiency is just 39.7 % at that point. Most importantly, SOFC generates nearly 65 % of the total power, while PEMFC generates around 35 %. Therefore, the percentage of additional power that PEMFC can produce is around 55 %.

A review of the integration of the copper-chlorine cycle with other systems for hydrogen production

There are different methods for hydrogen production, among which thermo-chemical cycles are particularly important. One of the most common thermochemical cycles is the copper-chlorine cycle. In this cycle, the water electrolysis process takes place during a thermo-chemical reaction, and copper chlorine is used as a thermochemical reaction intermediate. This cycle requires two factors to produce hydrogen: A heat source with a temperature of about 520 oC and electricity. For this reason, it is possible to use the hot waste gases of industries or parabolic through collector and heliostat field to provide its heat. To supply electricity for this cycle, various alternatives from the power grid and wind turbine to heat recovery in cycles that use low-temperature energy sources are considered. In this article, the integration of the copper-chlorine cycle with power generation systems has been discussed and investigated from the perspective of energy, exergy, and economics. This review is divided into two general parts using renewable and non-renewable resources. At the beginning of this article, various methods of hydrogen production focusing on the copper-chlorine cycle have been briefly discussed. In the following, the way this cycle works is explained along with energy, exergy, and economic equations, and the research done in this direction is explained. Finally, a strategy for how to integrate the copper-chlorine cycle with other systems is described. Studying this article, in addition to giving a better attitude in the field of integrating this cycle with other plants, is similar to a guideline for using the cycle along with other systems for better productivity. The conducted investigations showed that the recovery of hot industrial exhaust gas as a source of heat for the Cu-Cl cycle has a high potential for saving energy consumption and reducing environmental pollutants. To produce the required electricity, it is recommended to use cycles that work with a low-temperature energy source, such as the organic Rankine cycle and Kalina cycles. Also, if renewable energy sources are used, it is recommended to use parabolic through collectors and heliostats to produce the required heat. As in the case of non-renewable energy sources, cycles with low-temperature energy sources can be used.

Techno economic analysis of efficient and environmentally friendly methods for hydrogen, power, and heat production using chemical looping combustion integrating plastic waste gasification and thermochemical copper chlorine cycles

Fossil fuels harm the environment and deplete resources. This study presents eco-friendly systems producing power, hydrogen, and heat with minimal pollution. Non-fossil sources like plastic waste solve waste issues and provide valuable energy. Thermochemical water splitting is another clean method for sustainable hydrogen production. The proposed systems employ chemical looping combustion in conjunction with PWG (plastic waste gasification) and thermochemical cycle of Cu–Cl (copper-chlorine), leveraging thermal integration between the CLC (chemical looping combustion) and subsequent processes. Comprehensive process simulations using Aspen Plus have been conducted for systems. The results indicated that the most desirable operational conditions for CLC occur when the molar ratio of oxygen carrier to fuel is 2.6. Under these conditions, there is no methane present in the fuel reactor products. Additionally, the thermal and exergy efficiencies of the CLC-PWG and CLC-CuCl cycles are determined to be 77.08/67.62 % and 66.11/61.1 % respectively, and the most irreversibility component for both systems is associated with the air reactor, with a value of 375 kW. Moreover, the hydrogen production rate in the CLC-PWG cycle is higher than in the CLC-CuCl cycle, with 105.6 kg/h compared to 34.6 kg/h, and the estimated lower minimum sale price for hydrogen is 2.8 USD/kg for CLC-PWG.

Heat utilized pressure swing distillation (PSD) process for the separation of the maximum boiling azeotrope HCl and Water in the Cu-Cl Cycle

The four-step copper-chlorine cycle is utilized for hydrogen production from water. Intermediate copper and chlorine compounds facilitate the process, while all other reactants are regenerated and recycled, forming a closed-loop system. Hydrolysis of CuCl2, leading to the formation of Cu2OCl2 and dilute HCl, is a crucial step that uses a large excess of steam to ensure completion of reaction leading to the formation of dilute hydrochloric acid which needs to be recycled for the electrolysis reaction, requiring removal of the azeotrope between HCl and water. This study explores the utilization of pressure swing distillation (PSD) for concentrating HCl above azeotropic composition. Separation of the aqueous mixture of HCl and water using PSD is optimized using a sequential iterative optimization technique, focusing on process intensification. Integration of a simple heat-utilized FE-Process results in a reduction of TAC and energy cost (4.27% TAC and 7.20% energy cost) compared to the process without heat integration. A higher feed composition of HCl (8 mol %) leads to savings of ∼ 38.75% in TAC and a reduction of 53.06% in CO2 emissions compared to a lower feed composition (2.53 mol % HCl). The heat-utilized FE-Process with a higher feed composition is more economically viable for the separation of HCl and water.

Performance analysis of a small lead-cooled fast reactor coupled with a copper-chloride cycle hydrogen production system

Hydrogen is widely acknowledged as a pivotal energy carrier in the global transition towards sustainable energy. One promising approach to hydrogen production is method copper-chlorine cycle powered by nuclear energy. This article presents an innovative integrated system for small lead-cooled fast reactors that are coupled with a copper-chlorine cycle. To assess the performance of the entire system with regards to energy, exergy, and economics, comprehensive modeling, simulation, and analysis are conducted using the simulation tool Simulink. Furthermore, a comprehensive examination of key operating parameters was conducted to explore their impact on the system. The obtained results demonstrate the energy efficiency of system is 21.3 % and the exergy efficiency of system is 40.9 %. The overall system based on the small LFR can produce high-pressure compressed hydrogen gas at a rate of 2.34 g/s and generate 53.9 kW of electricity. According to the study, the levelized cost of energy production is determined to be $0.04252/kW·h. The specific energy cost is primarily influenced by equipment investment, including the costs associated with operating and maintaining the system. Notably, the small lead-cooled fast reactor and the copper-chlorine cycle plant represent the major capital investments within the system. This study provides valuable insights and serves as a significant reference for the future engineering applications of lead-cooled fast reactors coupled with copper-chlorine cycle hydrogen systems.

Hydrogen production using hybrid six-step copper-chlorine thermochemical cycle: Energy and exergy analyses

The hybrid thermochemical copper-chlorine (Cu–Cl) cycle for water splitting, developed as a novel approach to produce green hydrogen, has gained greater attention. A series of close-loop reactions makes the process environmentally friendly. A newly developed hybrid six-step Cu–Cl cycle consists of thermochemical, electrochemical, and a unit operation of spray drying. The present paper analyzes the configuration of the six-step Cu–Cl cycle thermodynamically. Studies on many factors are carried out to determine the cycle's total energy and exergy efficiency. The modeling and simulation of the six-step process was done by Aspen Plus. The six-step cycle was found to have an energy and exergy efficiency of 38.94 % and 52.74 %, respectively. The effect on exergetic efficiency with ambient temperature and cycle temperature variation was also investigated. The enhancement in the effectiveness of six steps Cu–Cl cycle could be possible from the current study analysis using thermal recovery and minimizing exergy destructions.

Sustainability assessment of hydrogen production based on nuclear energy

Hydrogen is expected to be a key energy carrier in the global energy transition. A promising method of hydrogen production is water electrolysis powered by nuclear energy. This energy source can also be used in other hydrogen production technologies, such as copper-chlorine cycle. Proper comparison of various hydrogen production methods from the sustainability perspective requires the use of analysis in a global balance boundary. The paper presents a comparison of sustainability of various hydrogen generation methods, with emphasis on the methods exploiting nuclear energy. Instead of local energy efficiency, the index of Thermo-Ecological Cost (TEC) is proposed. TEC is a measure of the depletion of non-renewable resources burdening the production of a given product. Other criteria used in the assessment are: availability of energy supply (capacity factor), cumulative greenhouse gas emissions and resources to production ratio. In addition, water electrolysis and copper-chlorine cycle have been considered cogeneration processes, providing oxygen as a useful by-product. Taking into account all the criteria suggests that obtaining hydrogen with the use of nuclear technologies will provide a fair, long-term compromise compared to other hydrogen generation technologies.

Waste heat recovery potential in the thermochemical copper–chlorine cycle for hydrogen production: Development of an efficient and cost-effective heat exchanger network

With the finite nature of fossil fuel resources and related environmental issues, it is necessary to replace fossil-fuel-based hydrogen production methods with more sustainable ones. For the clean production of hydrogen, the copper-chlorine (Cu–Cl) thermochemical cycle is a favorable choice. However, internal waste heat recovery of the cycle is essential to improve the efficacy of the system. In this paper, the waste heat recovery potential of the four-step Cu–Cl cycle is investigated, to support the design of a new cost-effective and high-performance heat exchanger network. Pinch analysis is executed to find the optimum rates of cold and hot utilities for this cycle. Three heat exchanger network cases are investigated which include case 1, without heat recovery; case 2, with 16 heat exchangers; and case 3, with 11 heat exchangers. The effect of varying design parameters on the energy system's efficiency and cost-related parameters are also explored here. Based on the pinch analysis results, the minimum heating and cooling and the maximum recoverable heat, on a normalized basis, are 333.3 kJ/mol H2, 76.9 kJ/mol H2, and 134.4 kJ/mol H2, respectively. Moreover, for cases 1, 2, and 3 the thermal efficiencies are calculated as 33.3%, 41.1%, and 40.5%, respectively. Additionally, it is observed that, when the thermal energy of the cycle is supplied from a solar power tower plant, the levelized cost of hydrogen for case 1 is 9.6 $/kg H2, for case 2 is 7.9 $/kg H2, and for case 3 is 7.8 $/kg H2.

A comparative exergoenvironmental evaluation of chlorine-based thermochemical processes for hydrogen production

Environmental impact assessment of energy generation processes is essential to evaluate their contributions toward the global carbon footprint. Even though hydrogen is a non-carbonaceous energy source, the pathways undertaken for its production can have harmful environmental implications. Thus, this study focuses on investigating the exergoenvironmental performances of the copper-chlorine, iron-chlorine, and magnesium-chlorine thermochemical hydrogen generation processes. This study also performs a comparative exergoenvironmental analysis of the three processes. The performances of the various processes are examined based on of the environmental impact rates of exergy destruction, component-related environmental impact rates, cumulative environmental impact rates, and exergoenvironmental factors. The global warming potentials of the thermochemical cycles are also evaluated and compared for various electricity sources to obtain hydrogen. The modeling and simulation of each process are performed using Aspen-plus by considering various heat recovery approaches for thermal management. The results suggest that the environmental impact rates of exergy destruction are relatively much higher compared to the environmental impact rates associated with the components for all processes. Furthermore, the hydrolysis step yields the highest component-associated environment impact rate for all thermochemical cycles considered (Fe–Cl: 3497 mPts/h, Cu–Cl: 1997 mPt/h, and Mg–Cl: 910 mPts/h). Moreover, the magnesium-chlorine cycle results in the highest environmental impact rate of exergy destruction (650,328 mPts/h) while the iron-chlorine cycle has the highest component-related environmental impact rate (5219 mPts/h) among the three cycles. In addition, the global warming potential of the magnesium-chlorine cycle is relatively higher compared to the copper-chlorine cycle for several electricity sources.

Evaluation and comparison of hydrogen production potential of the LIFE fusion reactor by using copper–chlorine (Cu–Cl), cobalt–chlorine (Co–Cl) and sulfur–iodine (S–I) cycles

In this paper, the hydrogen production and neutronic analysis of the Laser Inertial Confinement Fusion-Fission Engine (LIFE) fusion reactor have been analyzed. The potential of hydrogen production from unit integrated of the reactor with three different hydrogen production methods which has copper-chlorine (Cu–Cl) cycle, cobalt-chlorine (Co–Cl) cycle and sulfur-iodine (S–I) cycle have been investigated. Neutronic performance analysis for various parameters was calculated statically by using Monte Carlo N-Particle Nuclear Code and determined optimum reactor operation conditions. The hydrogen production potential for all conditions was investigated as statically. And also, the production potential with determining optimum conditions was performed over operation plant. Tristructural isotropic (TRISO) coated thorium carbide (ThC) was used as fuel of LIFE fusion reactor. Natural lithium and FLiNaBe (LiF + NaF + BeF2) were used first and second coolant, respectively. In the statistical analysis, effects of ThC fuel ratio, 1st and 2nd coolant zone thicknesses were examined. As a consequence of the neutronic analysis, tritium breeding values and energy multiplication values (M) was attained and according to M values, hydrogen production amount, required thermal power and thermal power ratios were acquired. Among the used hydrogen production methods, Cu–Cl cycle produced the highest hydrogen amount, while the Co–Cl cycle has the lowest H2 amount. At the end of the reactor operation time for determining optimum conditions, the produced hydrogen amounts are 9.00, 4.80 and 7.36 kg/s for Cu–Cl, Co–Cl and S–I cycles, respectively.

Heat transfer characteristics and design aspects of thermolysis reactor in copper-chlorine thermochemical water splitting cycle

Thermolysis of copper oxychloride is the highest temperature reaction step of Copper–Chlorine cycle which forms cuprous chloride and oxygen gas as products. In the present study, important design aspects of thermolysis reactor have been investigated experimentally and a mathematical model has been developed to understand the effect of critical parameters on conversion. Experiments were conducted in tubular reactors with three different diameters of 25 mm, 50 mm and 100 mm to study the effect of reactor geometry on heat transfer and conversion. Modelling of batch thermolysis reactor has been carried out using governing heat transport equations coupled with reaction kinetics and validated against experimental data. As per the experimental and modelling results, enhancement in conversion could be achieved with increasing aspect ratio and heat transfer. The studies provide clear insights into the design and scale-up of thermolysis reactor to address the issues of low conversion observed during the multi-step thermal decomposition reaction.

Exergoeconomic performance evaluation of three, four, and five-step thermochemical copper-chlorine cycles for hydrogen production

Thermochemical water-splitting processes are among the most promising options for producing sustainable and green hydrogen due to being extremely environmentally benign. Being extensively investigated in the literature, the thermochemical copper-chlorine cycle has demonstrated much promise in this regard as one of the most efficient options for thermochemically obtaining hydrogen. Thus, this study focuses on investigating the exergoeconomic performances of the different variants of the copper-chlorine cycle including the three-, four-, and five-step versions. All cycles are modeled and simulated in Aspen-plus software by considering a recovery of thermal energy from industrial waste flue gases in addition to internal heat recovery. Moreover, a hydrogen production capacity of 668 kg/h is considered for all cycles. The Specific Exergy Costing methodology is employed to study the exergoeconomic performance of each cycle. All cycles are initially examined in terms of the cost rates of energy transfer and hourly levelized cost rates for each step. The cycle variants are further examined through a comparative assessment of several performance parameters including hydrogen cost rates, overall cost rates of energy transfer, and overall hourly levelized cost rates. According to the performed analyses, the three-step variant of the cycle that constitutes a high-temperature electrolysis process produces hydrogen at the lowest cost rate (0.83 $/kg) while the four-step cycle produces hydrogen at the highest cost rate (1.82 $/kg). Furthermore, the hydrolysis step is found to have the highest hourly levelized cost rates for all variants of the cycle. Several factors that impact the hydrogen cost rate are also examined comprehensively. In addition, the extent to which the hydrogen cost rate is sensitive to those factors is discussed.

Novel thermoelectric generator heat exchanger for indirect heat recovery from molten CuCl in the thermochemical Cu–Cl cycle of hydrogen production

The looming threat of global warming has elicited efforts to develop reliable sustainable energy resources. Hydrogen as a clean fuel is deemed a potential solution to the problem of storage of power from renewable energy technologies. Among current thermochemical hydrogen generation methods, the thermochemical copper-chlorine (Cu–Cl) cycle is of high interest owing to lower temperature requirements. Present study investigates a novel heat exchanger comprising a thermoelectric generator (TEG) to recover heat from high temperature molten CuCl exiting the thermolysis reactor. Employing casting/extrusion method, the performance of the proposed heat exchanger is numerically examined using COMSOL Multiphysics. Results indicate that maximum generated power could exceed 40 W at the matching current of 4.5 A. Maximum energy conversion efficiency yields to 7.1%. Results demonstrate that TEG performance boosts with increasing the inlet Re number, particularly at the hot end. For the molten CuCl chamber, findings denote that there is a 36% discrepancy between highest and lowest Re numbers. Similarly, the highest efficiency value pertains to the case with the highest inlet velocity. Moreover, the highest temperature difference between inlet and outlet of the cooling water is about 28 °C and 10 °C for the lowest and highest inlet Re numbers, respectively. Average deviation from anticipated friction factor and Nusselt number are 0.31% and 12.62%, respectively.

A novel clean hydrogen production system combining cascading solar spectral radiation and copper-chlorine cycle: Modeling and analysis

In this work, a novel integrated hydrogen production system was proposed. A detailed analysis of the efficiency limit, energy requirement, and parametric impact was theoretically performed. The system combined cascading solar spectral radiation with a copper-chlorine thermochemical cycle, which effectively converted different grades of solar energy to clean hydrogen. The process of a four-step copper-chlorine cycle was simulated to obtain the energy demands using Aspen Plus software. A model for cascading utilization of solar spectral radiation was developed to select the optimal segmented wavelengths and investigate the effects of parameters on the system efficiency. The system designs integrated with other solar cells were also optimized using this model. Among the parameters, the segmented wavelengths were the key parameters that determined the amount of solar energy converted to heat and electricity. The theoretical calculations and simulations were used to determine the performance of this new hydrogen production system. Efficiency analysis demonstrated that the proposed system achieved an ideal efficiency of 68.20%, exceeding the theoretical limit of the single-junction photovoltaic-electrolysis water system. The efficiency of the actual design was 43.44%, higher than the systems without a spectrum splitting module. This study provides an efficient method for realizing high efficiency and high-grade solar energy cascading utilization for producing clean hydrogen energy.

A Comparative Assessment of Thermodynamic and Exergoeconomic Performances of Three Thermochemical Water-Splitting Cycles of Chlorine Family for Hydrogen Production

Hydrogen production processes utilizing hydrocarbon-based sources as feedstocks have severe environmental implications (when not incorporating carbon capturing and storage technology) in addition to resulting in depletion of non-sustainable naturally occurring fuel sources. In this regard, thermochemical water-splitting is an extremely environmentally benign pathway for obtaining sustainable hydrogen. Thus, this paper studies and comparatively evaluates three different thermochemical cycles of the chlorine family for hydrogen production which include iron-chlorine, copper-chlorine, and magnesium-chlorine cycles. Each cycle is first modeled and simulated in Aspen-plus and then analyzed from thermodynamic and exergoeconomic viewpoints. A thermodynamic and exergoeconomic performance comparison of the three thermochemical cycles is further performed in terms of their overall efficiencies, net heat input and rejection rates, exergy destruction rates, unit costs of hydrogen, hourly levelized cost rates, and cost rates of exergy destruction. All cycles are modeled and simulated by considering the incorporation of waste heat recovery from a steel plant and internal heat recovery within each cycle to improve the process efficiencies by reducing the overall thermal energy consumption. According to the performed analyses, the copper-chlorine cycle has the highest energy (79.7%) and exergy (81.1%) efficiencies followed by the iron-chlorine cycle (energy and exergy efficiencies of 48.8% and 49.6%, respectively) with the magnesium-chlorine cycle exhibiting the lowest overall energy (19.8%) and exergy (20.2%) efficiencies. Moreover, the iron-chlorine cycle demonstrates the lowest unit cost of hydrogen (0.7 $/kg) followed by the copper-chlorine cycle (4 $/kg) with the magnesium-chlorine cycle exhibiting an extremely high unit hydrogen cost (8.9 $/kg). This study also identifies certain key factors that largely impact the cost of hydrogen and comprehensively discusses the influence and extent of each factor on the cost of hydrogen.

Transient Thermo-Fluid Analysis of Free Falling CuCl and AgCl Droplets with Liquid-to-Solid Phase Change

Hydrogen extraction from nature is a time-consuming and energy-intensive procedure. Most of the current methods of extracting H2 are not eco-friendly, and the thermochemical copper-chlorine (Cu-Cl) cycle is a promising alternative since the ingredients are continuously recycled within the cycle without discharging pollutants into the atmosphere. In this study, the heat recovered from molten cuprous chloride (CuCl) salt produced in one of the reactors and quenched in a water bath is analyzed numerically to determine the amount of thermal energy that can be recovered and improve the efficiency of the Cu-Cl cycle. The quenching cell is simulated in an inert atmosphere since CuCl is highly reactive in the presence of oxygen. The interactions of various diameters of CuCl droplets within nitrogen (N2) are numerically modeled in COMSOL Multiphysics. Silver chloride (AgCl) is also used in this study to validate the phase-change process. It was discovered in this study that during the free fall, the outer surface of the molten droplets solidifies, and the phase change of droplets slowly propagates radially inwards, which slows down the energy dissipation. It was also determined that the average internal temperature of the droplet does not change substantially with droplet diameter or quenching height. Based on this study, the net energy recovered after quenching was calculated to be around 23 kJ during 1 kg of H2 production.