Thermodynamic viability of a new three step high temperature Cu-Cl cycle for hydrogen production

A new three step high temperature Cu-Cl thermochemical cycle for hydrogen production is presented. The performance of the proposed cycle is investigated through energy and exergy approaches. Furthermore, the effects of various parameters, such as the temperatures of the steps of the cycle and power plant efficiency, on various energy and exergy efficiencies are assessed with parametric studies. The results show that the exergy and energy efficiencies of the proposed cycle are 68.3% and 32.0%, respectively. In addition, the exergy analysis results reveal that the hydrogen production step has the maximum specific exergy destruction with a value of 150.9 kJ/mol. The results suggest that proposed cycle may provide enhanced options for high temperature thermochemical cycles by improving thermal management without causing a sudden temperature jump/fall between the hydrogen production step and other steps.     

Exergoeconomic analysis of a hybrid copper-chlorine cycle driven by geothermal energy for hydrogen production

In this study, we conduct an exergy, cost, energy and mass (EXCEM) analysis of a copper-chlorine thermochemical water splitting cycle driven by geothermal energy for hydrogen production. We also investigate and illustrate the relations between thermodynamic losses and capital costs. The results show that hydrogen cost is closely and directly related to the plant capacity and also exergy efficiency. Increasing economic viability and reducing the hydrogen production costs will help these cycles play a more critical role in switching to hydrogen economy.     

Thermodynamic performance assessment of boron based thermochemical water splitting cycle for renewable hydrogen production

The present study is related with the thermodynamic performance assessment of renewable hydrogen production through Boron thermochemical water splitting cycle. Therefore, all step efficiencies and overall cycle efficiency are calculated based on complete reaction. Additionally, a parametric study is conducted to determine the effect of the reference environment temperature on the overall cycle efficiency. In this regard, exergy efficiencies, exergy destruction rates and also inlet and outlet exergy rates of the cycle are calculated and presented for various reference temperatures. The exergy efficiency of the cycle is calculated as 0.4393 based on complete reaction and occurs at 298 K. This study has shown that Boron thermochemical water splitting cycle has a great potential due to cycle performance. As a result, Boron based thermochemical water splitting cycle can help achieve better environment and sustainability due to high exergetic efficiency. By the way, economic and technical issues of the storage and transportation of the hydrogen can find a proper solution if the hydrogen production reaction of the Boron thermochemical water splitting cycle takes place on-board of a vehicle.     

A specific exergy costing assessment of the integrated copper-chlorine cycle for hydrogen production

In this study the specific exergy costing (SPECO) approach is employed on a four-step integrated thermochemical copper-chlorine (Cu Cl) cycle for hydrogen production for a second-law based assessment purposes. The Cu–Cl cycle is considered as one of the most environmentally benign and sustainable options of producing hydrogen and is thus investigated in this study due to its potential of ensuring zero greenhouse gas (GHG) emissions. Several conceptual Cu–Cl cycles have been exergoeconomically examined previously, however this study aims at investigating the four-step integrated Cu–Cl cycle developed at the Clean Energy Research Laboratory (CERL) at the Ontario Tech University thereby contributing to the thermo/exergoeconomic assessments of the thermochemical hydrogen production. In this study, the cycle is first thermodynamically modeled and simulated in a process simulation software (Aspen Plus) through exergy and energy approaches. The basic principles of the SPECO methodology are applied to the system and exergetic cost balances are performed for each cycle component. The exergetic costing of each cycle stream is then performed based on the cost balance equations. The purchased equipment cost and the hourly levelized capital cost rates for each cycle component is also obtained. The exergoeconomic factor, relative cost difference and exergy destruction cost rate for various cycle components are also evaluated. Moreover, the effect of several parameters on the total and hourly levelized capital cost rates is analyzed by performing a comprehensive sensitivity analysis. Based on the analysis, the exergy cost, the unit or specific exergy cost, and the unit costs of hydrogen are evaluated to be 6407.55 $/h, 0.042 $/MJ, and 4.94 $/kg respectively.     

Exergoeconomic analysis of a new integrated copper-chlorine cycle for hydrogen production

In this study, an exergoeconomic analysis is performed on an integrated four-step thermochemical copper-chlorine cycle developed at the Ontario Tech. University through exergy, cost, energy, and mass (EXCEM) method. A thermodynamic model is first constructed in Aspen-plus (a process simulation software) to simulate and investigate the integrated cycle through exergy and energy analyses. The capital costs, thermodynamic loss rates, and the ratio of the thermodynamic loss rate to the capital cost of various system's components are also determined. Moreover, the average unit cost of hydrogen is evaluated and the influence of several system's parameters on the unit cost of hydrogen is analyzed. The results show that the cost of hydrogen is strongly dependent on the production capacity of the plant. Based on the analysis, our system generates hydrogen at an average unit cost of 5.54 $/kg with a plant capacity of 1619.3 kg/h considering both internal (operating and maintenance costs, etc.) and external (costs of various inputs, etc.) parameters.     

Thermodynamic assessment of geothermal energy use in hydrogen production

In this study, geothermal-based hydrogen production methods, and their technologies and application possibilities are discussed in detail. A high-temperature electrolysis (HTE) process coupled with and powered by a geothermal source is considered for a case study, and its thermodynamic analysis through energy and exergy is conducted for performance evaluation purposes. In this regard, overall energy and exergy efficiencies of the geothermal-based hydrogen production process for this HTE are found to be 87% and 86%, respectively.     

Study on an original cobalt-chlorine thermochemical cycle for nuclear hydrogen production

In this paper, a theoretical and experimental study on a novel cobalt-chlorine thermochemical cycle for hydrogen production is presented. The cobalt-chlorine cycle comprises a closed loop of four thermochemical reactions occurring at 700 °C that is a reaction temperature compatible with the present generation of high-temperature gas-cooled reactors. Firstly, a thermodynamic analysis was done for determining whether this cycle is attractive for hydrogen production in terms of both energy and exergy efficiencies. Following, proof-of-principle experiments were carried out at laboratory scale in a batch reactor at temperatures in the range from 550 °C to 950 °C and holding times between 1 h and 72 h. Experimental results complemented by the characterization of condensed compounds deposited on the reactor walls allowed confirm the reaction pathway of thermochemical reactions originally proposed, define the slowest step of the global process, and explain the beneficial effect of increasing the system pressure on the hydrogen yield. Even both performance assessment and proof-of-principle experimental results look like promising more research will be required in the future to confirm these preliminary findings. Finally, a modified version of the cobalt-chlorine cycle is proposed for enhancing the global kinetics, based on the experimental evidence found in the proof-of-principle tests.     

A comparative evaluation of three CuCl cycles for hydrogen production

The thermochemical CuCl cycle has received greater attention by numerous researchers during the past decade as a promising hydrogen production method because of some operational advantages. The present paper analyzes three different configurations of the CuCl thermochemical cycle, namely three, four and five step ones thermodynamically. Some comparative parametric studies are conducted in order to investigate the overall energy and exergy efficiencies of the cycles considered. The Aspen plus is the software tool employed for the modeling and simulation of the cycles. The energy and exergy efficiencies of the five-step CuCl cycle are found to be 38.8% and 70.2% while the three-step CuCl cycle has an energy efficiency of 39.6% and an exergy efficiency of 68.1%, respectively. On the other hand, the four-step CuCl cycle provides the highest energy and exergy efficiencies of 41.9% and 75.7%. A parametric study is also conducted to investigate the effect of varying ambient temperature on the exergy efficiencies of all three cycles. The present study results further reveal that the cycle performance can be enhanced by improving the thermal management and reducing the exergy destructions.     

Two-step hydrogen chloride cycle for sustainable hydrogen production: An energy and exergy assessment

In this study, we present the thermodynamic feasibility analysis of a two-step hydrogen chloride cycle for sustainable hydrogen production. Exergy approach in addition to conventional energy approach is utilized to study the performance of the cycle. Here, a solid oxide membrane for the gas phase electrolysis of hydrogen chloride is employed and the temperature change between the cycle steps is eliminated for better thermal management. Moreover, a parametric study is conducted to observe the cycle variation with certain parameters such as operating temperature, current density, and hydrogen production rate. The calculated results show that with the use of the current cycle, one can produce 1 kg/s of hydrogen with the consumption of 335.8 MW electricity and 29.2 MW of thermal energy. Additionally, two different definitions of energy and exergy efficiencies are introduced to investigate the difference between actual and ideal (theoretical) cycle performances. The proposed cycle can be effectively used to produce hydrogen using concentrated solar and nuclear waste heat at high temperatures.     

Thermodynamic analysis and experimental investigation of a unique photoelectrochemical hydrogen production system

In this study, we thermodynamically analyze and experimentally investigate a continuous type hybrid photoelectrochemical H₂ generation reactor. This system enhances solar spectrum use by employing photocatalysis and PV/T. Additionally, by replacing electron donors with electrodes to drive the photocatalysis, the potential of pollutant emissions are minimized. In this study, the present reactor is tested under electrolysis operation during which the present reactor is investigated under three different inlet mass flow rates (0.25, 0.50, and 0.75 g/s) and four different operating temperatures (20, 40, 60, and 80 °C). Some parametric studies are run by varying the environmental temperature between 0 and 40 °C. In addition, the impact of coating the membrane electrode assembly of the reactor with Cu₂O is investigated. The present results show that the highest energy and exergy efficiencies occur at the environmental temperature of 20 °C which is about 60% and 50%, respectively. The Cu₂O coated membrane gives a lot higher current readings, meaning that the coating makes the membrane more conductive and increases H₂ production by permitting ions at a higher rate.     

Development and assessment of a solar,wind and hydrogen hybrid trigeneration system

A solar-wind hybrid trigeneration system is proposed and analyzed thermodynamically through energy and exergy approaches in this paper. Hydrogen, electricity and heat are the useful products generated by the hybrid system. The system consists of a solar heliostat field, a wind turbine and a thermochemical copper-chlorine (Cu-Cl) cycle for hydrogen production linked with a hydrogen compression system. A solar heliostat field is employed as a source of thermal energy while the wind turbine is used to generate electricity. Electric power harvested by the wind turbine is supplied to the electrolyzer and compressors and provides an additional excess of electricity. Hydrogen produced by the thermochemical copper-chlorine (Cu-Cl) cycle is compressed in a hydrogen compression system for storage purposes. Both Aspen Plus 9.0 and EES are employed as software tools for the system modeling and simulation. The system is designed to achieve high hydrogen production rate of 455.1 kg/h. The overall energy and exergy efficiencies of the hybrid system are 49% and 48.2%, respectively. Some additional results about the system performance are obtained, presented and discussed in the paper.     

Parametric analysis and assessment of a coal gasification plant for hydrogen production

The purpose of this paper is to conduct a parametric study to show the best steam to carbon ratio that produces the maximum system performance of an integrated gasifier for hydrogen production. The study focuses on the energy and exergetic efficiency of the system and hydrogen production. The work is completed using computer simulation models in Engineering Equation Solver software package. This software is used for its extensive thermodynamic properties library. An equilibrium based model is used to determine the performance of the system. The data is presented in graphs which show the chemical composition in molar fractions of the syngas, the overall energy and exergy efficiency of the system, and the hydrogen production rates. A study of these parameters is conducted by varying the steam to carbon ratio entering the gasifier and the ambient temperature. It is observed that the higher the steam to carbon ratio that is achieved the more hydrogen and more power the plant is able to produce. Because of this, the exergy and energy efficiency of the system increases as the steam to carbon ratio increases as well. It is also observed that the system favors a lower ambient temperature for maximum exergy efficiency and hydrogen production.     

Assessment study of a four-step copper-chlorine cycle modified with flash vaporization process for hydrogen production

This paper develops a four-step copper-chlorine cycle for hydrogen production with conceptual modification through flash vaporization and evaluates its economic and environmental performances through exergy approach. The flash vaporization method is employed as a new approach for realizing the anolyte separation under vacuum conditions for reducing the thermal requirement of the anolyte separation step and consequently of the overall cycle. A flash vaporization is usually employed commercially for seawater desalination purposes. However, its utilization in a thermochemical hydrogen production process has not been considered previously which is really one of primary novelties of this investigation. The obtained results for the exergoeconomic and exergoenvironmental analyses of the conceptually modified cycle are also compared with those of the existing integrated cycle at the Ontario Tech University. The exergoeconomic analysis of the cycle has also been carried out for the cycle operating with and without waste heat recovery. In this regard, waste heat recovery from a steel furnace has been considered for supplying the required thermal energy for the hydrolysis step. The cost assessment of the cycle is carried out in the Aspen-plus. Compared with the existing cycle, the cycle with the proposed modification results in a lower unit cost of hydrogen. Moreover, a significant reduction in the unit cost of hydrogen is observed when waste heat recovery is considered for the modified cycle. The average unit hydrogen cost for the modified version of the cycle is evaluated to be 4.7 $/kg which reduces to 2 $/kg with incorporation of waste heat recovery. Furthermore, the overall environmental impact of the existing cycle can be potentially minimized by considering the proposed modification through flash vaporization.     

Thermodynamic and electrochemical analyses of a solid oxide electrolyzer for hydrogen production

In this paper, a modeling of the Solid Oxide Electrolysis Cell (SOEC), through energetic, exergetic and electrochemical modeling approaches, is conducted, and its performance, particularly through exergy efficiency, is analyzed under various operating conditions and state properties for optimum hydrogen production. In a comprehensively performed parametric study, at a single electrolysis cell scale, the effects of varying some operating conditions, such as temperature, pressure, steam molar fraction and the current density on the cell potential and hence the performance are investigated. In addition, at the electrolyzer system scale, the overall electrolyzer performance is investigated through energy and exergy efficiencies, in addition to the system's power density consumption, hydrogen production rate, heat exchange rates and exergy destruction parameters. The present results show that the overall solid oxide electrolyzer energy efficiency is 53%, while the exergy efficiency is 60%. The exergy destruction at a reduced operating temperature increases significantly. This may be overcome by the integration of this system with a source of steam production.     

Potential methods for geothermal-based hydrogen production

In this study, four potential methods are identified for geothermal-based hydrogen production, namely, (i) directly from the geothermal steam, (ii) through conventional water electrolysis using the electricity generated from geothermal power plant, (iii) using both geothermal heat and electricity for high temperature steam electrolysis and/or hybrid processes, (iv) using the heat available from geothermal resource in thermochemical processes to disassociate water into hydrogen and oxygen. Here we focus on relatively low-temperature thermochemical and hybrid cycles, due to their greater application possibility, and examine them as a potential option for hydrogen production using geothermal heat. We also present a brief thermodynamic analysis to assess their performance through energy and exergy efficiencies for comparison purposes. The results show that these cycles have good potential and become attractive due to the overall system efficiencies over 50%. The copper–chlorine cycle is identified as a highly promising cycle for geothermal hydrogen production. Furthermore, three types of industrial electrolysis methods, which are generally considered for hydrogen production currently, are also discussed and compared with the above mentioned cycles.     

Model development and analysis of a novel high-temperature electrolyser for gas phase electrolysis of hydrogen chloride for hydrogen production

In this study, a high temperature electrolyser for the gas phase electrolysis of hydrogen chloride for hydrogen production is proposed and assessed. A detailed electrochemical model is developed to study the J-E characteristics for the proposed electrolyser (a solid oxide electrolyser based on a proton conducting electrolyte). The developed model accounts for all major losses, namely activation, concentration and ohmic. Energy and exergy analyses are carried out, and the energy and exergy efficiencies of the proposed electrolyser are determined to be 41.1% and 39.0%, respectively. The simulation results show that at T = 1073 K, P = 100.325 kPa and J = 1000 A/m², 1.6 V is required to produce 1 mol of hydrogen. This is approximately 0.3 V less than the voltage required by a high temperature steam electrolyser (based on a proton conducting electrolyte) operating at same condition (T = 1073 K, P = 101.325 kPa and J = 1000 A/m²), suggesting that the proposed electrolyser offers a new option for high temperature electrolysis for hydrogen production, potentially with a low electrical energy requirement. The proposed electrolyser may be incorporated into thermochemical cycles for hydrogen production, like CuCl or chlorine cycles.     

Exergetic life cycle assessment of a hydrogen production process

Exergetic life cycle assessment (ExLCA) is applied with life cycle assessment (LCA) to a hydrogen production process. This comparative environmental study examines a nuclear-based hydrogen production via thermochemical water splitting using a copper–chlorine cycle. LCA, which is an analytical tool to identify, quantify and decrease the overall environmental impact of a system or a product, is extended to ExLCA. Exergy efficiencies and air pollution emissions are evaluated for all process steps, including the uranium processing, nuclear and hydrogen production plants. LCA results are presented in four categories: acidification potential, eutrophication potential, global warming potential and ozone depletion potential. A parametric study is performed for various plant lifetimes. The ExLCA results indicate that the greatest irreversibility is caused by uranium processing. The primary contributor of the life cycle irreversibility of the nuclear-based hydrogen production process is fuel (uranium) processing, for which the exergy efficiency is 26.7% and the exergy destruction is 2916.3 MJ. The lowest global warming potential per megajoule exergy of hydrogen is 5.65 g CO₂-eq achieved a plant capacity of 125,000 kg H₂/day. The corresponding value for a plant capacity of 62,500 kg H₂/day is 5.75 g CO₂-eq.     

Thermodynamic analysis of solar-based photocatalytic hydrogen sulphide dissociation for hydrogen production

The dissociation of gaseous hydrogen sulphide (H₂S) into its components is an energy intensive process. The process is studied in this paper with respect to the thermodynamic limits. The band gap of the catalyst and the nature of the solar radiation limit the proportion of incoming radiation that may be used for the reaction. The intensity of the incoming radiation and the reactor temperature are varied and the performance is studied. The exergy efficiency is determined as a function of the quantum efficiency of the photochemical process, and the catalyst band gap. It is shown that an optimum case exergy efficiency of up to 28% can be achieved for the process. With the current status of technology, an exergy efficiency value in the region of 0.4–1% is calculated, with a short-term improvement potential of up to 10%. Hydrogen sulfide has high energy content, but is not widely used due to its impact on environmental pollution. The proposed process in this paper is attractive as it allows that energy to be utilized, while degrading the highly toxic gas into less harmful products.     

Exergetic life cycle assessment of hydrogen production from renewables

Life cycle assessment is extended to exergetic life cycle assessment and used to evaluate the exergy efficiency, economic effectiveness and environmental impact of producing hydrogen using wind and solar energy in place of fossil fuels. The product hydrogen is considered a fuel for fuel cell vehicles and a substitute for gasoline. Fossil fuel technologies for producing hydrogen from natural gas and gasoline from crude oil are contrasted with options using renewable energy.     

Green methods for hydrogen production

This paper discusses environmentally benign and sustainable, as green, methods for hydrogen production and categorizes them based on the driving sources and applications. Some potential sources are electrical, thermal, biochemical, photonic, electro-thermal, photo-thermal, photo-electric, photo-biochemical, and thermal-biochemical. Such forms of energy can be derived from renewable sources, nuclear energy and from energy recovery processes for hydrogen production purposes. These processes are analyzed and assessed for comparison purposes. Various case studies are presented to highlight the importance of green hydrogen production methods and systems for practical applications.