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A sulfur family chemical cycle having ammonia as the working fluid and reagent was developed as a cost-effective and efficient hydrogen production technology based on a solar thermochemical water-splitting cycle. The sulfur ammonia (SA) cycle is a renewable and sustainable process that is unique in that it is an all-fluid cycle (i.e., with no solids handling). It uses a moderate temperature solar plant with the solar receiver operating at 800°C. All electricity needed is generated internally from recovered heat. The plant would operate continuously with low cost storage and it is a good potential solar thermochemical hydrogen production cycle for reaching the DOE cost goals. Two approaches were considered for the hydrogen production step of the SA cycle: (1) photocatalytic, and (2) electrolytic oxidation of ammonium sulfite to ammonium sulfate in aqueous solutions. Also, two sub-cycles were evaluated for the oxygen evolution side of the SA cycle: (1) zinc sulfate/zinc oxide, and (2) potassium sulfate/potassium pyrosulfate. The laboratory testing and optimization of all the process steps for each version of the SA cycle were proven in the laboratory or have been fully demonstrated by others, but further optimization is still possible and needed. The solar configuration evolved to a 50 MW(thermal) central receiver system with a North heliostat field, a cavity receiver, and NaCl molten salt storage to allow continuous operation. The H2A economic model was used to optimize and trade-off SA cycle configurations. Parametric studies of chemical plant performance have indicated process efficiencies of ~20%. Although the current process efficiency is technically acceptable, an increased efficiency is needed if the DOE cost targets are to be reached. There are two interrelated areas in which there is the potential for significant efficiency improvements: electrolysis cell voltage and excessive water vaporization. Methods to significantly reduce water evaporation are proposed for future activities. Electrolysis membranes that permit higher temperatures and lower voltages are attainable. The oxygen half cycle will need further development and improvement.
22Structure and SO3 decomposition activity of CeVO4/SiO2 catalysts for solar thermochemical water splitting cycles
Structure and SO3 decomposition activity of CeVO4/SiO2 catalysts for solar thermochemical water splitting cycles
66Solar Hydrogen Production via a Samarium Oxide-Based Thermochemical Water Splitting Cycle
The computational thermodynamic analysis of a samarium oxide-based two-step solar thermochemical water splitting cycle is reported. The analysis is performed using HSC chemistry software and databases. The first (solar-based) step drives the thermal reduction of Sm2O3 into Sm and O2. The second (non-solar) step corresponds to the production of H2 via a water splitting reaction and the oxidation of Sm to Sm2O3. The equilibrium thermodynamic compositions related to the thermal reduction and water splitting steps are determined. The effect of oxygen partial pressure in the inert flushing gas on the thermal reduction temperature (TH) is examined. An analysis based on the second law of thermodynamics is performed to determine the cycle efficiency (ηcycle) and solar-to-fuel energy conversion efficiency (ηsolar−to−fuel) attainable with and without heat recuperation. The results indicate that ηcycle and ηsolar−to−fuel both increase with decreasing TH, due to the reduction in oxygen partial pressure in the inert flushing gas. Furthermore, the recuperation of heat for the operation of the cycle significantly improves the solar reactor efficiency. For instance, in the case where TH = 2280 K, ηcycle = 24.4% and ηsolar−to−fuel = 29.5% (without heat recuperation), while ηcycle = 31.3% and ηsolar−to−fuel = 37.8% (with 40% heat recuperation).
Read more17A dual-scale transport model of the porous ceria based on solar thermochemical cycle water splitting hydrogen production
A dual-scale transport model of the porous ceria based on solar thermochemical cycle water splitting hydrogen production
2Thermodynamic assessment of hydrogen production via solar thermochemical cycle based on MoO2/Mo by methane reduction
Inspired by the promising hydrogen production in the solar thermochemical (STC) cycle based on non-stoichiometric oxides and the operation temperature decreasing effect of methane reduction, a high-fuel-selectivity and CH4-introduced solar thermochemical cycle based on MoO2/Mo is studied. By performing HSC simulations, the energy upgradation and energy conversion potential under isothermal and non-isothermal operating conditions are compared. In the reduction step, MoO2:CH4 = 2 and 1020 K < Tred < 1600 K are found to be most favorable for syngas selectivity and methane conversion. Compared to the STC cycle without CH4, the introduction of methane yields a much higher hydrogen production, especially at the lower temperature range and atmospheric pressure. In the oxidation step, a moderately excessive water is beneficial for energy conversion whether in isothermal or non-isothermal operations, especially at H2O: Mo = 4. In the whole STC cycle, the maximum non-isothermal and isothermal efficiency can reach 0.417 and 0.391 respectively. In addition, the predicted efficiency of the second cycle is also as high as 0.454 at Tred = 1200 K and Toxi = 400 K, indicating that MoO2 could be a new and potential candidate for obtaining solar fuel by methane reduction.
Read more119Economic comparison of solar hydrogen generation by means of thermochemical cycles and electrolysis
Economic comparison of solar hydrogen generation by means of thermochemical cycles and electrolysis
36Applicability of an Equilibrium Model To Predict the Conversion of CO2 to CO via the Reduction and Oxidation of a Fixed Bed of Cerium Dioxide
Production of hydrogen and synthesis gas via solar thermochemical partial redox cycles is one route to renewable fuels and storage of solar energy. The efficiency at which these cycles produce fuel for candidate non-stoichiometric metal oxides and reactor concepts is normally evaluated from thermodynamic models that implicitly assume that the transport processes and reaction kinetics are rapid enough that the gas and solid attain chemical equilibrium. In this paper, we develop an equilibrium model of a fixed-bed reactor and demonstrate its applicability for reduction and oxidation of porous ceria (CeO2) particles with a volume-specific surface area of ∼106 m2 m–3 over a wide range of gas flow rates and reaction temperatures. The model predicts the measured rate of O2 production during reduction for mass-specific flow rates up to 900 mL min–1 gceria–1 and for temperatures from 740 to 1500 °C, and it predicts the measured rate of CO production during oxidation for flow rates up to 50 mL min–1 gceria–1 at 15...
Read more44.23 Solar Thermochemical Energy Conversion
4.23 Solar Thermochemical Energy Conversion
24Aluminum-doped strontium ferrites for a two-step solar thermochemical air separation cycle: Thermodynamic characterization and cycle analysis
Aluminum-doped strontium ferrites for a two-step solar thermochemical air separation cycle: Thermodynamic characterization and cycle analysis
Read moreHybrid Thermochemical Hydrogen Production
There exists a significant and growing need for clean, efficient, and large-scale hydrogen production. Using high temperature heat, thermochemical cycles can provide an energy-efficient route for hydrogen production. The Hybrid Sulfur process is a promising thermochemical watersplitting cycle with global-scale hydrogen production potential. The SO2-depolarized electrolyzer (SDE) is a critical component of the cycle. At the core of the electrolyzer is the membraneelectrode assembly, which consists of a solid electrolyte membrane sandwiched between two electrocatalyst layers. New electrocatalyst and membrane materials are being developed with the goals of improving the electrolyzer performance and extending the lifetime of the membrane-electrode assembly. A high-throughput methodology is being developed to screen potential candidates based on Pt and Au thin films prepared through physical vapor deposition. SO2 oxidation reaction kinetics are being analyzed for the novel catalysts and compared to the state-of-the-art, Pt/C. In addition, advanced polymer electrolyte membranes of polybenzimidazole (PBI) are utilized, which have shown superior performance in comparison to the state-of-the-art, Nafion®. These catalysts and membranes will be combined to produce high performance membrane-electrode assemblies.
Read more27Thermodynamic Analysis of the Use a Chemical Heat Pump to Link a Supercritical Water-Cooled Nuclear Reactor and a Thermochemical Water-Splitting Cycle for Hydrogen Production
Increases in the power generation efficiency of nuclear power plants (NPPs) are mainly limited by the permissible temperatures in nuclear reactors and the corresponding temperatures and pressures of the coolants in reactors. Coolant parameters are limited by the corrosion rates of materials and nuclear-reactor safety constraints. The advanced construction materials for the next generation of CANDU reactors, which employ supercritical water (SCW) as a coolant and heat carrier, permit improved “steam” parameters (outlet temperatures up to 625°C and pressures of about 25 MPa). An increase in the temperature of steam allows it to be utilized in thermochemical water splitting cycles to produce hydrogen. These methods are considered by many to be among the most efficient ways to produce hydrogen from water and to have advantages over traditional low-temperature water electrolysis. However, even lower temperature water splitting cycles (Cu-Cl, UT-3, etc.) require an intensive heat supply at temperatures higher than 550-600°C. A sufficient increase in the heat transfer from the nuclear reactor to a thermochemical water splitting cycle, without jeopardizing nuclear reactor safety, might be effectively achieved by application of a heat pump, which increases the temperature of the heat supplied by virtue of a cyclic process driven by mechanical or electrical work. Here, a high-temperature chemical heat pump, which employs the reversible catalytic methane conversion reaction, is proposed. The reaction shift from exothermic to endothermic and back is achieved by a change of the steam concentration in the reaction mixture. This heat pump, coupled with the second steam cycle of a SCW nuclear power generation plant on one side and a thermochemical water splitting cycle on the other, increases the temperature of the “nuclear” heat and, consequently, the intensity of heat transfer into the water splitting cycle. A comparative preliminary thermodynamic analysis is conducted of the combined system comprising a SCW nuclear power generation plant and a chemical heat pump, which provides high-temperature heat to a thermochemical water splitting cycle for hydrogen production. It is concluded that the proposed chemical heat pump permits the utilization efficiency of nuclear energy to be improved by at least 2% without jeopardizing nuclear reactor safety. Based on this analysis, further research appears to be merited on the proposed advanced design of a nuclear power generation plant combined with a chemical heat pump, and implementation in appropriate applications seems worthwhile.
Read moreHydrogen Production with High Temperature Solar Heat Thermochemical Cycle Using Dual-zone Reactor and CeO2/ZrO2 Foam Device
In this study, an artificial solar simulator composed of a 2.5 kW Xe-Arc lamp and mirror reflector was used to carry out the solar thermal two step thermochemical water decomposition cycle which can produce high efficiency continuous hydrogen production. Through various operating conditions, the change of hydrogen production due to the possibility of a dual-zone reactor and heat recovery were experimentally analyzed. Based on the reaction temperature of Thermal-Reduction step and Water-Decomposition step at 1,400°C and 1,000°C respectively, the hydrogen production decreased by 23.2% under the power off condition, and as a result of experiments using heat recovery technology, the hydrogen production increased by 33.8%. Therefore, when a thermochemical two-step water decomposition cycle is conducted using a dual-zone reactor with heat recovery, it is expected that the cycle can be operated twice over a certain period of time and the hydrogen production amount is increased by at least 53.5% compared to a single reactor.
Read more16Hydrogen production by water splitting with Mn3-xCoxO4 mixed oxides thermochemical cycles: A thermodynamic analysis
Hydrogen production by water splitting with Mn3-xCoxO4 mixed oxides thermochemical cycles: A thermodynamic analysis
26Hydrogen production by hup(-) mutant and wild-type strains of Rhodobacter capsulatus from dark fermentation effluent of sugar beet thick juice in batch and continuous photobioreactors.
Photofermentative production of hydrogen is a promising and sustainable process; however, it should be coupled to dark fermentation to become cost effective. In order to integrate dark fermentation and photofermentation, the suitability of dark fermenter effluents for the photofermentative hydrogen production must be demonstrated. In this study, thermophilic dark fermenter effluent (DFE) of sugar beet thick juice was used as a substrate in photofermentation process to compare wild-type and uptake hydrogenase-deficient (hup (-)) mutant strains of Rhodobacter capsulatus by means of hydrogen production and biomass growth. The tests were conducted in small-scale (50mL) batch and large-scale (4 L) continuous photobioreactors in indoor conditions under continuous illumination. In small scale batch conditions, maximum cell concentrations were 0.92 gdcw/L c and 1.50 gdcw/L c, hydrogen yields were 34% and 31%, hydrogen productivities were 0.49mmol/(L c·h) and 0.26mmol/(Lc·h), for hup (-) and wild-type cells, respectively. In large-scale continuous conditions, maximum cell concentrations were 1.44 gdcw/L c and 1.87 gdcw/L c, hydrogen yields were 48 and 46%, and hydrogen productivities were 1.01mmol/(L c·h) and 1.05mmol/(L c·h), for hup (-) and wild-type cells, respectively. Our results showed that Rhodobacter capsulatus hup (-) cells reached to a lower maximum cell concentration but their hydrogen yield and productivity were in the same range or superior compared to the wild-type cells in both batch and continuous operating modes. The maximum biomass concentration, yield and productivity of hydrogen were higher in continuous mode compared to the batch mode with both bacterial strains.
Read more120Life cycle assessment of nuclear-based hydrogen and ammonia production options: A comparative evaluation
Life cycle assessment of nuclear-based hydrogen and ammonia production options: A comparative evaluation
13Uranium thermochemical cycle used for hydrogen production
Uranium thermochemical cycle used for hydrogen production
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