Copper Chlorine Research Articles

Energy and exergy analyses of a new four-step copper–chlorine cycle for geothermal-based hydrogen production

Abstract In this paper, energy and exergy analyses of the geothermal-based hydrogen production via thermochemical water decomposition using a new, four-step copper–chlorine (Cu–Cl) cycle are conducted, and the respective cycle energy and exergy efficiencies are examined. Also, a parametric study is performed to investigate how each step of the cycle and its overall cycle performance are affected by reference environment temperatures, reaction temperatures, as well as energy efficiency of the geothermal power plant itself. As a result, overall energy and exergy efficiencies of the cycle are found to be 21.67% and 19.35%, respectively, for a reference case.

Heat recovery from molten CuCl in the Cu–Cl cycle of hydrogen production

The copper–chlorine (Cu–Cl) cycle of thermochemical hydrogen production requires heat recovery from molten CuCl at various points within the cycle. This paper examines the convective heat transfer between molten CuCl droplets and air in a counter-current spray flow heat exchanger. This direct contact heat exchanger is analyzed as a proposed new method of recovering heat from the solidified molten CuCl. Effective thermal management within the Cu–Cl cycle is crucial for achieving high thermal efficiency. The cycle’s efficiency is improved drastically when all heat released by the products of reactions is recycled internally. Recovering heat from molten CuCl is very challenging due to the phase transformations of molten CuCl, as it cools from liquid to different solid states. In this paper, a spray column direct contact heat exchanger is analyzed for the heat recovery process. A predictive model of heat transfer and droplet flow is developed and then solved numerically. The results indicate that full heat recovery is achieved with a heat exchanger diameter of 0.13 m, and heights of 0.6 and 0.8 m, for a 1 and 0.5 mm droplet diameter, respectively. Additional results are presented and discussed for heat recovery from molten CuCl in the thermochemical Cu–Cl cycle.

Nuclear-based hydrogen production with a thermochemical copper-chlorine cycle and supercritical water reactor: equipment scale-up and process simulation

SUMMARY Issues related to equipment scale-up and process simulation are described for a thermochemical cycle driven by nuclear heat from Canada's proposed Generation IV reactor (Super-Critical Water-Cooled Reactor; SCWR), which is a CANDU derivative using supercritical water cooling. The copper–chlorine (Cu-Cl) cycle has been identified by Atomic Energy of Canada Limited as the most promising cycle for thermochemical hydrogen production with SCWR. Water is decomposed into hydrogen and oxygen through intermediate Cu-Cl compounds. This article outlines the challenges and design issues of hydrogen production with a Cu-Cl cycle coupled to Canada's nuclear reactors. The processes are simulated using the Aspen Plus process simulation code, allowing the cycle efficiency and possible efficiency improvements to be examined. The results are useful to assist the development of a lab-scale cycle demonstration, which is currently being undertaken at the University of Ontario Institute of Technology in collaboration with numerous partners. Copyright © 2010 John Wiley & Sons, Ltd.

Kinetics study of the copper/hydrochloric acid reaction for thermochemical hydrogen production

The exothermic reaction of hydrochloric acid with particulate copper occurs during the hydrogen production step in the thermochemical copper–chlorine water splitting cycle. In this paper, this chemical reaction is modeled kinetically, and a parametric study is performed to determine the influences of particle size, temperature and molar ratios on the hydrogen conversion aspects. It is obtained that the residence time of copper particles varies between 10 and 100 s, depending on the operating conditions. The hydrogen conversion at equilibrium varies between 55% and 85%, depending on the reaction temperature. The heat flux at the particle surface, caused by the exothermic enthalpy of reaction, reaches over 3000 W/m 2 when the particle shrinks to 0.1% from its initial size. The estimated Biot number varies from 0.001 to 0.1, depending on the operating conditions and the accuracy of thermophysical data of the substances. A numerical algorithm is developed to solve the moving boundary Stefan problem with a chemical reaction that models the shrinking of copper particles in the hypothesis that the chemical reaction and heat transfer are decoupled. The model allows for the estimation of the temperature of a copper particle, assumed spherical, in the radial direction on the hypothesis of large Biot numbers. For small Biot numbers, the transient heat transfer equation results in a lumped capacitance model. In all cases, the particle decomposes in about 10–20s.

Diffusion of gaseous products through a particle surface layer in a fluidized bed reactor

This paper examines a solid conversion process during hydrolysis and decomposition of cupric chloride in a thermochemical copper–chlorine (Cu–Cl) cycle of hydrogen production. Reaction rate constants and the time required for complete solid conversion are determined by a shrinking-core model. Diffusion of gaseous reactant occurs through a film surrounding the particle, after which the reactant penetrates and diffuses through a layer of ash to the surface of the unreacted core. The shrinking-core model for spherical particles predicts the reaction of gaseous reactant with solid at the particle surface, and diffusion of gaseous products through the ash, back to the exterior surface of the solid. The hydrolysis reaction is also analyzed with respect to chemical equilibrium conversion and required heat input. Effects of varying operating parameters are examined, including the temperature, pressure, excess steam, inert gas and hydrogen chloride (HCl) in the steam. At a temperature of 375 °C, complete conversion of CuCl 2 can be achieved by controlling the excess steam, operating pressure and inert gas supply. Addition of HCl in the steam supply increases the excess steam requirement for conversion of cupric chloride solid, and the upper limit for HCl concentration increases with temperature and inert gas composition. The addition of inert gas may also reduce the excess steam requirement, thereby reducing the heat requirement. These new results have valuable utility for equipment scale-up in the thermochemical Cu–Cl cycle of hydrogen production.

Comparison of sulfur–iodine and copper–chlorine thermochemical hydrogen production cycles

Sulfur–iodine and copper–chlorine water splitting cycles are promising methods of thermochemical hydrogen production. In this paper, these two cycles are compared from the perspectives of heat quantity, heat grade, thermal efficiency, related engineering challenges, and hydrogen production cost. The heat quantity and grade required by each step of the cycles are evaluated and the thermal efficiencies are approximated from the heat requirements. It is found that the overall heat requirements of the two cycles do not have significant differences and the overall efficiencies of the two cycles are similar, between 37 and 54%, depending on the portion of heat recovery. The copper–chlorine cycle has the advantage of a lower maximum temperature of 803 K, which is 300 K lower than the maximum temperature of 1123 K in the sulfur–iodine cycle. This indicates that the copper–chlorine cycle can link more readily with various heat sources, such as grade Generation IV nuclear and fossil fuel power stations. It is also reported that the copper–chlorine cycle can have fewer challenges of equipment materials and product separation. A cost analysis shows that the copper–chlorine and sulfur–iodine cycles have similar hydrogen production costs, which are lower than steam-methane reforming, and conventional and high temperature electrolysis, due to less use of electricity, no carbon related charges and no methane requirement in the thermochemical cycles.

Design and reliability assessment of control systems for a nuclear-based hydrogen production plant with copper–chlorine thermochemical cycle

The thermochemical Copper–Chlorine (Cu–Cl) cycle is an emerging new method of nuclear-based hydrogen production. In the process, water is decomposed into hydrogen and oxygen through several physical and chemical processes. In this paper, a Distributed Control System (DCS) is designed for the thermochemical Cu–Cl cycle. The architecture and the communication networks of the DCS are discussed. Reliability of the DCS is assessed using fault trees. In the assessment, the impact of the malfunction of the actuators, sensors, controllers and communication networks on the overall system reliability is investigated. This provides key information for the selection of control system components, and determination of their inspection frequency and maintenance strategy. The hydrogen reactor unit, which is one of the major components in the thermochemical Cu–Cl cycle, is used to demonstrate the detailed design and analysis.

New Cu-Cl Thermochemical Cycle for Hydrogen Production with Reduced Excess Steam Requirements

The Cu-Cl (copper–chlorine) thermochemical cycles for hydrogen production are leading examples of water-splitting methods. In this article, the heat requirements of different types of Cu-Cl cycles with various numbers of steps are analyzed, and their thermal design features are discussed in terms of water requirements, heat quantity, and heat grade. A challenge arises from the excess steam quantity requirement in the hydrolysis of CuCl2. To address this challenge, a new type of Cu-Cl cycle is proposed in this article. It is found that the steam requirement can decrease by up to ten times, compared with conventional Cu-Cl cycles, and the heat grade of the hydrolysis step in the new cycle is significantly lowered from 375°C to 150°C. The engineering challenges of the new cycle are also discussed in the article.

On the synthesis of hydrogen producing alternative thermochemical cycles with electrochemical steps

Here we expand on our process systems engineering-based methodology for the initial evaluation of alternative thermochemical cycles for hydrogen production. A new identification algorithm is presented, which includes thermochemical cycles with electrochemical steps, referred to as hybrid cycles, in the reaction cluster search space. The resulting formulation is a mixed integer non-linear program, which we show can be solved as a set of mixed integer linear sub-problems using branch and bound. With a target base level, or theoretical maximum efficiency of 35%, as to be competitive with bottoming cycle based hydrogen production technologies, identified hybrid cycles are screened with an evaluation procedure based on heat pinch analysis. The strength of the expanded formulation is demonstrated with a case study for a hybrid copper–chlorine system. Results from our systematic evaluation suggest the proposed methodology is robust over a wide range of temperatures and candidate species. In this case study, we identify several hybrid cycles with estimated base efficiencies of up to 36%, exceeding our target efficiency.

Thermophysical properties of copper compounds in copper–chlorine thermochemical water splitting cycles

This paper examines the relevant thermophysical properties of compounds of copper that are used in thermochemical water splitting cycles. There are four variants of such Cu–Cl cycles that use heat and electricity to split the water molecule and produce H 2 and O 2. Since the energy input is mainly in the form of thermal energy, the Cu–Cl water splitting cycle is more efficient than water electrolysis, if the electricity generation efficiency for electrolysis is taken into account. Various chemicals are recycled within the plant, while the overall effect is splitting of the water molecule. The system includes several reactors, heat exchangers, a spray dryer, and an electrochemical cell. This paper identifies the available experimental data for properties of copper compounds relevant to the Cu–Cl cycle analysis and design (Cu 2OCl 2, CuO, CuCl 2, CuCl). It also develops new regression formulae to correlate the properties, which include: specific heat, enthalpy, entropy, Gibbs free energy, density, formation enthalpy and free energy. No past literature data are available for the viscosity and thermal conductivity of molten CuCl, so estimates are provided. The properties are evaluated at 1 bar and a range of temperatures from ambient to 675–1000 K, which are consistent with the operating conditions of the cycle. Updated calculations of chemical exergies are provided as follows: 21.08, 6.268, 82.474, and 75.0 kJ/mol for Cu 2OCl 2, CuO, CuCl 2 and CuCl, respectively. For molten CuCl, the estimated viscosity varies from 1.7 to 2.6 mPa s for the envisaged range of temperatures. A Riedel-like equation is proposed to correlate the vapor pressures with the temperature for molten CuCl.

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.

An exergy–cost–energy–mass analysis of a hybrid copper–chlorine thermochemical cycle for hydrogen production

An exergoeconomic assessment using exergy–cost–energy–mass (EXCEM) analysis is reported of a copper–chlorine (Cu–Cl) thermochemical water splitting cycle for hydrogen production. The quantitative relation is identified between capital costs and thermodynamic losses for devices in the cycle. A correlation detected in previous assessments, suggesting that devices in energy systems are configured so as to achieve an overall optimal design by appropriately balancing thermodynamic (exergy-based) and economic characteristics of the overall system and its components, is observed to apply for the Cu–Cl cycle. Exergetic cost allocations and various exergoeconomic performance parameters are determined for the overall cycle and its components. The results are expected to assist ongoing efforts to increase the economic viability and to reduce product costs of potential commercial versions of this process. The impacts of these results are anticipated to be significant since thermochemical water splitting with a copper–chlorine cycle is a promising process that could be linked with nuclear reactors to produce hydrogen with no greenhouse gases emissions, and thereby help mitigate numerous energy and environment concerns.

Exergoeconomic analysis of a thermochemical copper–chlorine cycle for hydrogen production using specific exergy cost (SPECO) method

The manner is investigated in which exergy-related parameters can be used to minimize the cost of a copper–chlorine (Cu–Cl) thermochemical cycle for hydrogen production. The iterative optimization technique presented requires a minimum of available data and provides effective assistance in optimizing thermal systems, particularly in dealing with complex systems and/or cases where conventional optimization techniques cannot be applied. The principles of thermoeconomics, as embodied in the specific exergy cost (SPECO) method, are used here to determine changes in the design parameters of the cycle that improve the cost effectiveness of the overall system. The methodology provides a reasonable approach for improving the cost effectiveness of the Cu–Cl cycle, despite the fact that it is still in development. It is found that the cost rate of exergy destruction varies between $1 and $15 per kilogram of hydrogen and the exergoeconomic factor between 0.5 and 0.02 as the cost of hydrogen rises from $20 to $140 per GJ of hydrogen energy. The hydrogen cost is inversely related to the exergoeconomic factor, plant capacity and exergy efficiency. The results are expected to assist ongoing efforts to increase the economic viability and to reduce product costs of potential commercial versions of this process. The impact of the results are anticipated to be significant since thermochemical water splitting with a copper–chlorine cycle is a promising process that could be linked with nuclear reactors to produce hydrogen with no greenhouse gases emissions, and thereby help mitigate numerous energy and environment concerns.

Equilibrium conversion in Cu–Cl cycle multiphase processes of hydrogen production

This paper performs a thermodynamic equilibrium analysis of individual steps within the copper–chlorine (Cu–Cl) thermochemical cycle of hydrogen production. The cycle has a maximum temperature of 550 °C and it involves four reaction steps – producing hydrogen, copper, hydrogen chloride and oxygen – and a cupric chloride drying step. In this paper, the chemical reaction steps of the cycle are analyzed to determine the effects of process variables on chemical equilibrium conversion. It is found that the hydrogen production reaction can occur as a two-phase gas–solid system, rather than three phases. The optimal conditions for hydrogen production occur at a temperature below 400 °C, at atmospheric pressure. The study also found that the ideal condition to minimize excess steam, and completely consume any chlorine formed during the reaction, is a temperature of 400 °C, at atmospheric pressure. The operating conditions for complete consumption of chlorine were identified by the equilibrium partial pressure of chlorine formed, during decomposition of cupric chloride solid (CuCl 2), and the equilibrium partial pressure of chlorine from the reverse chlorine consumption reaction. Furthermore, the ideal condition for the copper oxychloride decomposition reaction is a temperature around 500 °C, atmospheric pressure, which minimizes cuprous chloride (CuCl) vaporization.

Efficiency analysis of a hybrid copper–chlorine (Cu–Cl) cycle for nuclear-based hydrogen production

The role of the Cu–Cl cycle for thermochemical water decomposition, potentially driven by heat from a nuclear power generation station, in producing hydrogen in a sustainable way is investigated by examining efficiencies. The energy efficiency of the cycle is found to be 45% and the exergy efficiency 10%. The energy and exergy efficiencies of the cycle are observed to vary with temperatures of the reactions and reference-environment, and cycle heat losses. A parametric study is carried out considering several heat losses, reaction and reference-environment temperatures, and component-efficiency scenarios.

Advances in hydrogen production by thermochemical water decomposition: A review

Abstract Hydrogen demand as an energy currency is anticipated to rise significantly in the future, with the emergence of a hydrogen economy. Hydrogen production is a key component of a hydrogen economy. Several production processes are commercially available, while others are under development including thermochemical water decomposition, which has numerous advantages over other hydrogen production processes. Recent advances in hydrogen production by thermochemical water decomposition are reviewed here. Hydrogen production from non-fossil energy sources such as nuclear and solar is emphasized, as are efforts to lower the temperatures required in thermochemical cycles so as to expand the range of potential heat supplies. Limiting efficiencies are explained and the need to apply exergy analysis is illustrated. The copper–chlorine thermochemical cycle is considered as a case study. It is concluded that developments of improved processes for hydrogen production via thermochemical water decomposition are likely to continue, thermochemical hydrogen production using such non-fossil energy will likely become commercial, and improved efficiencies are expected to be obtained with advanced methodologies like exergy analysis. Although numerous advances have been made on sulphur–iodine cycles, the copper–chlorine cycle has significant potential due to its requirement for process heat at lower temperatures than most other thermochemical processes.

Comparison of different copper–chlorine thermochemical cycles for hydrogen production

Abstract Copper–chlorine thermochemical cycles for hydrogen production are very promising water splitting cycles. In this paper, different types of copper–chlorine cycles with various numbers of steps are compared. The factors that determine the number and effective grouping of steps are analyzed. It is found that the water requirement in the hydrolysis step is affected by a combination of drying and hydrolysis steps. It is also found that hydrogen can be produced either from electrolysis of cuprous chloride, or from chlorination of copper by hydrogen chloride, which indicates a potential combination of disproportionation and chlorination steps. The major engineering advantages and disadvantages of these cycle variations with different amounts of steps will be analyzed and discussed.

Fluid-particle mass transport of cupric chloride hydrolysis in a fluidized bed

This paper examines the mass transport phenomena of a hydrolysis reaction involving cupric chloride particles and superheated steam in a fluidized bed, as a part of the copper–chlorine thermochemical cycle for nuclear-based hydrogen production. The Gómez-Barea method was extended and utilized for the purpose of this study. A uniform reaction model (Volumetric Model; VM) and Shrinking Core Model (SCM) were used for limiting cases of the conversion processes. Using the solution procedures developed for each case, the effects of different parameters (such as the superficial gas velocity, bed inventory, and process temperature) were investigated in terms of the conversion of CuCl 2 particles and steam.

Energy and exergy analyses of the fluidized bed of a copper–chlorine cycle for nuclear-based hydrogen production via thermochemical water decomposition

Nuclear-based hydrogen production via thermochemical water decomposition using a copper–chlorine (Cu–Cl) cycle consists of a series of chemical reactions in which water is split into hydrogen and oxygen as the net result. This is accomplished through reactions involving intermediate copper and chlorine compounds, which are recycled. This cycle consists of three thermally driven reactions and one electrochemical reaction. The cycle involves five steps: (1) HCl(g) production using such equipment as a fluidized bed, (2) oxygen production, (3) copper(Cu) production, (4) drying, and (5) hydrogen production. A chemical reaction takes place in each step, except drying. In this study, the HCI(g) production step of the Cu–Cl cycle for hydrogen production as well as its operational and environmental conditions are defined, and a comprehensive thermodynamic analysis is performed, incorporating energy and exergy and considering relevant chemical reactions. The performance of the fluidized bed is evaluated through energy and exergy efficiencies, and various parametric studies on energetic and exergetic aspects with variable reaction and reference-environment temperatures are carried out.

The oxygen production step of a copper–chlorine thermochemical water decomposition cycle for hydrogen production: Energy and exergy analyses

In the copper–chlorine (Cu–Cl) thermochemical cycle water is decomposed into its constituents (oxygen and hydrogen) by a series of chemical reactions. The cycle involves five steps in which three thermally driven chemical reactions and one electrochemical reaction take place. Oxygen is produced during one of the main chemical reactions. In the present study, the O 2 production step is described with its operational and environmental conditions, and energy and exergy analyses are performed. The cycle is assumed driven using nuclear energy. Various parametric studies are carried out on energetic and exergetic aspects of the step, considering variable reaction and reference-environment temperatures. At a constant reference-environment temperature of 25 °C, the exergy destruction of the O 2 production step varies between 4500 and 23,000 kJ/kmol H 2 when the reaction temperature increases from 450 to 1000 °C. At a 500 °C reaction temperature and a 25 °C reference-environment temperature, the exergy destruction for this step is found to be 5300 kJ/kmol H 2. At a reaction temperature of 500 °C and a reference-environment temperature of 25 °C, the exergy efficiency of the step is determined to be 96% and to decrease with increasing reaction temperature and/or reference-environment temperature.