Thermochemical Cycle For Hydrogen Production Research Articles

Modeling of a direct solar receiver reactor for decomposition of sulfuric acid in thermochemical hydrogen production cycles

Hydrogen production thermochemical cycles, based on the recirculation of sulfur-based compounds, are among the best suited processes to produce hydrogen using concentrated solar power. The sulfuric acid decomposition section is common to each sulfur-based cycle and represents one of the fundamental steps. A novel direct solar receiver-reactor concept is conceived, conceptually designed and simulated. A detailed transport phenomena model, including mass, energy and momentum balance expressions as well as suitable decomposition kinetics, is described adopting a finite volume approach. A single unit reactor is simulated with an inlet flow rate of 0.28 kg/s (corresponding to a production of approximately 11 kgH2/h in a Hybrid Sulfur process) and a direct solar irradiation at a constant power of 143 kW/m2. Results, obtained for the high temperature catalytic decomposition of SO3 into SO2 and O2, demonstrate the effectiveness of the proposed concept, operating at pressures of 14 bar. A maximum temperature of 879 °C is achieved in the reactor body, with a corresponding average SO2 mass fraction of 27.8%. The overall pressure drop value is 1.7 bar. The reactor allows the SO3 decomposition into SO2 and O2 to be realized effectively, requiring an external high temperature solar power input of 123.6 kJ/molSO2 (i.e. 123.6 kJ/molH2).

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.

Enhanced CANDU reactor with heat upgrade for combined power and hydrogen production

Nuclear energy is considered a key alternative to overcome the environmental issues caused by fossil fuels. It offers opportunities with an improved operating efficiency and safety for producing power, synthetic fuels, delivering process heat and for multigeneration applications. The high-temperature nuclear reactors, although possess great potential for integration with thermochemical water-splitting cycles for hydrogen production, are not yet commercially established. Current nuclear reactor designs providing heat at relatively low temperature can be utilized to produce hydrogen using thermochemical cycles if the temperature of their thermal heat is increased. In this paper, a hybrid chemical-mechanical heat pump system is proposed for upgrading the heat of the Enhanced CANDU (EC6) reactor design to the quality required for the copper-chlorine (Cu–Cl) hybrid thermochemical water splitting cycle operating at 550–600 °C. A modification to the heat pump is proposed to bring the heat to temperature higher than 650 °C with operating coefficient of performance estimated as 0.65.

A novel three-step GeO2/GeO thermochemical water splitting cycle for solar hydrogen production

This investigation reports the thermodynamic exploration of a novel three-step GeO2/GeO water splitting (WS) cycle. The thermodynamic computations were performed by using the data obtained from HSC Chemistry thermodynamic software. Numerous process parameters allied with the GeO2/GeO WS cycle were estimated by drifting the thermal reduction (TH) and water splitting temperature (TL). The entire analysis was divided into two section: a) equilibrium analysis and b) efficiency analysis. The equilibrium analysis was useful to determine the TH and TL required for the initiation of the thermal reduction (TR) of GeO2 and re-oxidation of GeO via WS reaction. Furthermore, the influence of PO2 on the TH required for the comprehensive dissociation of GeO2 into GeO and O2 was also studied. The efficiency analysis was conducted by drifting the TH and TL in the range of 2080 to 1280 K and 500–1000 K, respectively. Obtained results indicate that the minimum Q˙solar−cycle=624.3kW and maximum ηsolar−to−fuel=45.7% in case of the GeO2/GeO WS cycle can be attained when the TR of GeO2 was carried out at 1280 K and the WS reaction was performed at 1000 K. This ηsolar−to−fuel=45.7% was observed to be higher than the SnO2/SnO WS cycle (39.3%) and lower than the ZnO/Zn WS cycle (49.3%). The Q˙solar−cycle can be further decreased to 463.9 kW and the ηsolar−to−fuel can be upsurged up to 61.5% by applying 50% heat recuperation.

Thermodynamic assessment of a lab-scale experimental copper-chlorine cycle for sustainable hydrogen production

An integrated lab-scale copper-chlorine (Cu-Cl) thermochemical cycle for hydrogen production at the University of Ontario Institute of Technology (UOIT) is presented and analyzed in this paper. In a practical operation of the Cu-Cl cycle, besides the main steps of hydrolysis, thermolysis, electrolysis and drying, the oxidized anolyte (consumed anolyte at the electrolyzer cell) needs to be recycled to be concentrated sufficiently for the electro-chemical process. Recycling of the oxidized anolyte through the separation processes is achieved by distillation of anolyte, drying unit, separation cell, pressure swing distillation and CuCl2 concentrator. This study examines the thermodynamic performance of all unit operations in the lab-scale Cu-Cl cycle. A process simulation model with Aspen Plus is used to assess the system by energy and exergy analyses. For the specific system design characteristics, the cycle is capable of producing 100 L/h of hydrogen. From the simulation results, the overall energy and exergy efficiencies of the lab-scale Cu-Cl cycle are determined to be 11.6% and 34.9%, respectively. Furthermore, after the thermolysis and hydrolysis reactors, the quench cell and CuCl2 concentrator have the highest exergy losses with thermal energy transferred through CuCl solidification and water vaporization phase-change processes at relatively high temperature. Additional results of the processes are presented and discussed.

High temperature electrolysis of hydrogen bromide gas for hydrogen production using solid oxide membrane electrolyzer

Using solid oxide membrane, this paper presents the theoretical modeling of the high temperature electrolysis of hydrogen bromide gas for hydrogen production. The electrolysis of hydrogen halides such as hydrogen bromide is an attractive process, which can be coupled to hybrid thermochemical cycles. The high temperature electrolyzer model developed in the present study includes concentration, ohmic, and activation losses. Exergy efficiency, as well as energy efficiency parameters, are used to express the thermodynamic performance of the electrolyzer. Moreover, a detailed parametric study is performed to observe the effects of various parameters such as current density and operating temperature on the overall system behavior. The results show that in order to produce 1 mol of hydrogen, 1.1 V of the applied potential is required, which is approximately 0.8 V less compared to high temperature steam electrolysis under same conditions (current density of 1000 A/m2 and temperature of 1073 K). Furthermore, it is found that with the use of the presented electrolyzer, one can achieve energy and exergy efficiencies of about 56.7% and 53.8%, respectively. The results presented in this study suggest that, by employing the proposed electrolyzer, two-step thermochemical cycle for hydrogen production may become more attractive especially for nuclear- and concentrated solar-to-hydrogen conversion applications.

Exergy and cost analyses of waste heat recovery from furnace cement slag for clean hydrogen production

This paper examines the performance and viability of a cement slag waste heat recovery system combined with a thermochemical copper-chlorine cycle for hydrogen production combined with hydrogen compression and a reheat Rankine cycle. The waste heat from the cement slag is recovered as a heat source for high-temperature reactions in the copper-chlorine cycle. The clean hydrogen production from waste heat recovery is examined with respect to both energy and exergy efficiencies. The integrated system is simulated and modeled in Aspen Plus. The multigeneration system utilizes the industrial waste heat and significantly reduces operating costs from the waste heat recovery. The overall energy efficiency of the integrated system is obtained as 32.5% while the corresponding exergy efficiency becomes 31.8%.

Investigation of Heat Extraction Methods from Cuprous Chloride for Improving the Efficiency of the Thermochemical Copper-Chlorine Cycle

In order to improve the efficiency of the thermochemical copper-chlorine cycle (Cu-Cl) for hydrogen production, a quench cell configuration for the quenching of cuprous chloride (CuCl) is being investigated. Initial testing has been performed in water to determine whether the molten cuprous chloride can be cooled enough to be quenched in hydrochloric acid (HCl (aq)). Quenching in HCl (aq) would reduce the number of components in the overall cycle, simplifying it and potentially making it more cost effective. A thermal camera was used to experimentally obtain the heat loss as the CuCl falls through the heat exchanger and into the quench cell. In addition, a FlowSense 2M shadow imaging camera was used to observe the behavior of the CuCl droplets interacting with the quench solution. It was observed that the CuCl droplet disintegrating into dust like particles as it enters the water pool and vapour was generated hence the temperature at the surface of the droplet as it entered the liquid water exceeded 100 °C.

First-principles investigation of BiVO3 for thermochemical water splitting

Thermochemical water splitting is a promising clean method of hydrogen production of high relevance in a society heavily reliant on fossil fuels. Using evolutionary methods and density functional theory, we predict the structure and electronic properties of BiVO3. We build on previous literature to develop a framework to evaluate the thermodynamics of thermochemical water splitting cycles for hydrogen production. We use these results to consider the feasibility of BiVO3 as a catalyst for thermochemical water splitting. We show that for BiVO3, both the thermal reduction and gas splitting reactions are thermodynamically favorable under typical temperature conditions. We predict that thermochemical water splitting cycles employing BiVO3 as a catalyst produce hydrogen yields comparable to those of commonly used catalysts.

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.

Catalytic performance of semi-coke on hydrogen iodide decomposition in sulfur-iodine thermochemical cycle for carbon dioxide-free hydrogen production

Sulfur-iodine thermochemical water splitting cycle is a promising and carbon dioxide-free method for hydrogen production. Among the reactions in this cycle, hydrogen iodide catalytic decomposition is the rate-determining step. In this study, catalytic reactivity test combined with characterizations of nitrogen physisorption, X-Ray diffraction, and Raman spectroscopy provide evidences that hydrofluoric acid modified semi-coke is a promising catalyst candidate for hydrogen iodide decomposition because of its high active and low cost. The raw semi-coke enhanced the hydrogen iodide conversion rate. After modification of hydrofluoric acid, the catalytic activity of semi-coke increased largely. Semi-coke modified by 40 wt% hydrofluoric acid showed better performance than commercial activated carbon catalyst. Combine the characterization results and catalytic reactivity, the graphitic edge carbon atoms in semi-coke are the active sites for hydrogen iodide decomposition. This finding pointed out the direction of carbon material catalyst design for hydrogen iodide decomposition.

Experimental assessment of the cyclability of the Mn2O3/MnO thermochemical cycle for solar hydrogen production

Abstract The cyclability of Mn2O3/MnO thermochemical cycle for solar hydrogen production has been experimentally evaluated. The results of three consecutive cycles show a stable hydrogen production per mass of initial solid that is in agreement with the maximum expected amount according to the stoichiometry of the process. The characterization of the material recovered after each cycle shows a mixture of different manganese oxide phases that are completely converted into MnO in the subsequent thermal reduction, maintaining the productivity of the cycles. Based on that, a modification of the thermochemical cycle scheme is proposed taking into account the differences observed between the first cycle and the following ones. MnO2/MnO thermochemical cycle appears as a promising alternative, working in the same temperature range but with a theoretical hydrogen production per unit mass of solid manganese oxide almost twice than that obtained with the conventional Mn2O3/MnO cycle. Finally, the results of exergy efficiency of the complete cycle give new insights into the commercial possibilities of the cycle for hydrogen production, demonstrating the sustainable cyclability of the process regarding the manganese containing materials at lower temperatures than those theoretically reported in literature and consequently with higher exergy efficiencies that the common values associated to this cycle.

Catalyst Screening and Development for HI Decomposition in Sulfur-iodine Thermochemical Cycle for Hydrogen Production

The intrinsic activities of six important transition metals for HI decomposition were identified by kinetic study. Ru showed high activity and a low apparent activation barrier, indicating a good activity at low temperature. Ru/AC (Ru clusters supported on activated carbon) was designed and proved to be a highly active, cost-effective, and long-term durable catalyst for HI decomposition. The present work could contribute to catalyst development for the industrialization of the sulfur-iodine thermochemical cycle for hydrogen production.

Corrosion behavior analyses of metallic membranes in hydrogen iodide environment for iodine-sulfur thermochemical cycle of hydrogen production

HI decomposition in Iodine-Sulfur (IS) thermochemical process for hydrogen production is one of the critical steps, which suffers from low equilibrium conversion as well as highly corrosive environment. Corrosion-resistant metal membrane reactor is proposed to be a process intensification tool, which can enable efficient HI decomposition by enhancing the equilibrium conversion value. Here we report corrosion resistance studies on tantalum, niobium and palladium membranes, along with their comparative evaluation. Thin layer each of tantalum, palladium and niobium was coated on tubular alumina support of length 250 mm and 10 mm OD using DC sputter deposition technique. Small pieces of the coated tubes were subject to immersion coupon tests in HI-water environment (57 wt% HI in water) at a temperature of 125–130 °C under reflux environment, and simulated HI decomposition environment at 450 °C. The unexposed and exposed cut pieces were analyzed using scanning electron microscope (SEM), energy dispersive X-ray (EDX) and secondary ion mass spectrometer (SIMS). The extent of leaching of metal into liquid HI was quantified using inductively coupled plasma-mass spectrometer (ICP-MS). Findings confirmed that tantalum is the most resistant membrane material in HI environment (liquid and gas) followed by niobium and palladium.

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.

Experimental density-composition data and thermal expansion coefficient of HI-I2-H2O solution

In thermochemical water-splitting iodine-sulfur cycle for hydrogen production, basic physico-chemical data of HI-H2O-I2 (HIx) solution are very important. Detailed and systematic studies on density/coefficient of thermal expansion (CTE) are in great need. In this work, the density values of 53 HIx samples with different compositions are measured at atmospheric pressure and temperatures ranging from 20 to 90 °C. HIx solution's density varies dramatically when changing HI or I2 contents. Increasing either HI or I2 concentration will cause increase of density. When heated, HIx's density decreases because of thermal expansion. With the help of density-temperature curves, the CTE values are calculated for HIx solutions of different compositions. It is found that increase of either I2/HI or H2O/HI will bring rise of HIx's CTE. Although the CTE value is relatively small, it is very sensitive to the change of composition. In the range of this work, the HIx's CTE value changes within 5.45E-4/ºC to 9.17E-4/ºC. Polynomial regression is conducted to model the relationship between CTE and the composition. The obtained approximate quadratic polynomial model has good accuracy to reproduce most of the experimental CTE values within a deviation of ±5%.

R&D status in thermochemical water-splitting hydrogen production iodine-sulfur process at JAEA

The IS process is the most deeply investigated thermochemical water-splitting hydrogen production cycle. It is in a process engineering stage in JAEA to use industrial materials for components. Important engineering tasks are verification of integrity of the total process and stability of hydrogen production in harsh environment. A test facility using corrosion-resistant materials was constructed. The hydrogen production ability was 100 L/h. Operation tests of each section were conducted to confirm basic functions of reactors and separators, etc. Then, a trial operation for integration of the sections was successfully conducted to produce hydrogen of about 10 L/h for 8 hours.

Numerical modeling of a bayonet heat exchanger-based reactor for sulfuric acid decomposition in thermochemical hydrogen production processes

Sulfur-based thermochemical hydrogen production cycles represent one of the most appealing options to produce hydrogen from water on a large scale. The Hybrid Sulfur is one of the most advanced thermochemical cycles. The high temperature section of the process, common to all sulfur-based cycles, operates the sulfuric acid thermal decomposition reaction at temperatures on the order of 800 °C. The paper shows and discusses the modeling results obtained for a bayonet heat exchanger based high temperature reactor that decomposes the sulfur compounds into sulfur dioxide and oxygen. A detailed transport phenomena model, including suitable decomposition kinetics, has been set up using a finite volume numerical approach. A preliminary configuration of the reactor, established based on process simulation results and on the initial reactor prototype developed at Sandia National Laboratory, has been examined and simulated. Results, obtained for a reactor driven by thermal power provided by helium flow, demonstrate the effective decomposition performance at maximum temperatures on the order of 800 °C and pressures of 14 bar. For a laminar flow configuration a sulfur dioxide production yield of about 28 wt% (with sulfur trioxide reduction from 69 wt% to approximately 33 wt%) has been achieved, representing decomposition rates practically equal to the corresponding equilibrium values. Limited pressure drops of approximately 2500 Pa have also been achieved in the sulfur mixture region.

Solar hydrogen production via sulphur based thermochemical water-splitting

The first technical developments on thermochemical cycles for hydrogen production are based on the use of sulphur as a redox material. After the oil crises of the 1970s, high temperature (over 1200K) heat from nuclear very high temperature reactors (VHTRs) was considered as a promising energy vector to produce fuels for the transport sector. The chemical reactions to convert water into hydrogen must fit to this heat source. As metal-oxide based cycles need higher temperature levels they were not taken into account at that time. The development of the sulphur cycles lost momentum during the 1980s because of cheap fossil fuels. But in the beginning of the 2000s they came back into the focus with the intention to reduce CO2 emissions. At that time their coupling to heat from concentrated solar radiation in large scale was developed. The interest from the nuclear energy side faded again when the interest in VHTRs lost momentum. In parallel concentrated solar technologies were not implemented fast enough. The developments were mainly achieved by research institutions that concentrated more on the metal-oxide technologies. However, sulphur based cycles remain very promising because the necessary temperature is low compared to metal-oxide cycles and sulphur and sulphuric acid are amongst the most important chemical products offering a high potential of synergies with other processes. The present analysis gives an overview on recent developments and the state-of-the-art of this type of cycles, has a look on the most important performance parameters involved, and gives an outlook on further potential and necessary developments.

A new integrated heat pump option for heat upgrading in Cu-Cl cycle for hydrogen production

A potential cascaded vapor compression heat pump is proposed to address the high temperature heat demand in the copper chlorine (Cu-Cl) thermochemical cycle for hydrogen production. The configuration studied is a cuprous chloride CuCl vapor compression heat pump cascaded with a biphenyl (C6H5)2 heat pump. Such cascaded heat pumps is meant to upgrade heat from nuclear power plants with a heat input temperature of approximately 300°C or industrial waste heat to meet the Cu2OCl2 decomposition reactor heat demand. Energy and exergy analyses are performed to understand the performance of the heat pump. It is determined that the CuCl-biphenyl heat pump exhibits a high coefficient of performance for certain operating conditions relating to the compressor isentropic efficiency and the excess CuCl feed temperature. The base energetic and exergetic coefficient of performances of the CuCl-biphenyl heat pump are 1.76 and 1.15 respectively.