Exergy study of hydrogen cogeneration and seawater desalination coupled to the HTR-PM nuclear reactor

This work presents a novel integration system of the high-temperature gas-cooled reactor-pebble bed module project to a hydrogen production process using the iodine-sulfur cycle in cogeneration with seawater desalination. The current approach includes a Rankine cycle, a sulfur-iodine thermochemical cycle for hydrogen production and a multi-stage flash desalination process. The use of a catalyst that allows the H₂SO₄ decomposition reaction to being carried out at temperatures compatible with the nuclear reactor project is considered. The residual heat from the acid decomposition reactions is used to desalinate seawater through the multi-stage flash process. A chemical process simulator is used to create a computational model that allows estimates of global and local efficiencies of the proposed flow diagram. Some operating parameters were sized, and their influence on the efficiency is also reported. The proposed model for the sulfur-iodine cycle can produce 0.41 kg/s of hydrogen with partial energy and exergetic efficiency of 37.35% and 38.64%. The desalination process can process 40.70 kg/s with energy and exergy efficiencies of 58.78% and 82.66%, respectively. The higher exergy destruction share is obtained in the heat exchangers (36.55%), chemical reactors (16.56%) and separators (12.80%). The global system showed efficiencies of 40.13% and 52.04%, respectively.     

Investigation of the hydrogen production of a laser FUSION driver thorium breeder using various coolants

In this present work, hydrogen production and neutronic calculations of a Laser Inertial Confinement Fusion Fission Energy (LIFE) driven thorium breeder using various coolants have been investigated. In the neutronic calculations for fusion driver power of 500 MW_th has been examined with MCNP code. The 95 vol% Flibe or natural lithium 5 vol% TRISO coated ThC fuels have used in the neutronic calculations. Tritium breeding ratio (TBR) has been calculated as 1.08 and 1.19, respectively, for Flibe and natural lithium coolants. The energy multiplication values have been computed as 3.17 and 1.62, respectively, for these coolants. The burnup values with flibe and natural lithium have been obtained as 6 GWd/tM and 22 GWd/tM over 11 and 23 years, respectively. Also, the hydrogen production of a laser fusion driver thorium breeder using steam methane reforming (SMR), high temperature electrolysis (HTE) and sulfur-iodine (S–I) thermochemical water splitting processes have been performed. The highest hydrogen production values with flibe coolant of SMR method have been obtained as ~200 kg/s over 11 years.     

A study on the dynamic behavior of a sulfur trioxide decomposer for a nuclear hydrogen production

The sulfur–iodine thermochemical water-splitting cycle (S–I cycle) is one of the most promising technologies for mass H₂ production. The S–I cycle is generally divided into three sections, one of which involves a H₂SO₄ concentration and decomposition. In the sulfuric acid processing section (Section 2), H₂SO₄ is decomposed into H₂O and SO₃, and then the produced SO₃ is further decomposed into SO₂ and O₂, which takes place in a H₂SO₄ decomposer and a SO₃ decomposer, respectively. The SO₃ decomposition requires heat of a high temperature and this suggests a heat-exchanger type reactor. To understand the temperature profiles and chemical reactions through a SO₃ decomposer, a dynamic model was developed by considering the heat and material balances in partial differential forms. A model was used to size the decomposer to a proposed design basis and it was also applied to simulate the responses corresponding to the changes of the operation conditions such as increased or decreased flow rates.     

Pressure drop of packed bed vertical flow for multiphase hydrogen production

In this paper, fluid flow characteristics through a packed bed reactor are investigated. The packed bed is utilized in the hydrogen production step of the copper-chlorine (Cu-Cl) thermochemical cycle. The hydrogen reaction is given by 2Cu(s) + 2HCl(g) = 2CuCl(molten) + H₂(g) at 450 °C. Effectively controlling the pressure drop through the packed bed is important for increasing the system efficiency, since auxiliary pumps and other parasitic losses are affected by the pressure drop. Also, the chemical processes in the packed bed are affected by changes in pressure, temperature and heat transfer rates.Experimental results from a laboratory scale packed bed reactor, operating at ambient conditions, are presented and compared with analytical predictions, in terms of the pressure drop caused by fluid flow through the packing material. Three different packing materials, with various sphericities, are investigated with diameters of 450 μm, 4 mm, and 1 cm. The Ergun equation is shown to provide good agreement for flow conditions in the upper region of Reynolds numbers investigated (20 < Re_p < 150); however, lack of agreement is observed at lower Reynolds numbers (Re_p < 20). An analytical formulation for micro scale particles in a packed bed is developed based on the Stokes law for creeping flow. Good agreement is achieved with the corresponding experimental data. A new correction is also developed to connect the two flow regimes, as well as predict trends in the transition region. The results successfully demonstrate close agreement between the predictions and measured data.     

Progress of international hydrogen production network for the thermochemical Cu–Cl cycle

This paper presents recent advances by an international team which is developing the thermochemical copper–chlorine (Cu–Cl) cycle for hydrogen production. Development of the Cu–Cl cycle has been pursued by several countries within the framework of the Generation IV International Forum (GIF) for hydrogen production with the next generation of nuclear reactors. Due to its lower temperature requirements in comparison with other thermochemical cycles, the Cu–Cl cycle is particularly well matched with Canada's Generation IV reactor, SCWR (Super-Critical Water Reactor), as well as other heat sources such as solar energy or industrial waste heat. In this paper, recent developments of the Cu–Cl cycle are presented, specifically involving unit operation experiments, corrosion resistant materials and system integration.     

Overview of nuclear hydrogen production research through iodine sulfur process at INET

Thermochemical water-splitting cycle is a promising process to produce hydrogen using solar or nuclear energy. R&D on hydrogen production through iodine sulfur (IS) thermochemical cycle was initiated in 2005 at INET. Fundamental studies on the three reactions of IS cycle, i.e., Bunsen reaction, HI decomposition reaction, sulfuric acid decomposition reaction, and related techniques, such as separation, concentration and purification, were carried through. In Bunsen section, the reaction kinetics and separation characteristics of H₂SO₄ and HIx phases were studied. In HI section, Pt catalysts were loaded on different supporters by various methods and used for HI decomposition; and electro-electrodialysis(EED) was developed for concentration of HI acid. In sulfuric acid section, non-Pt catalysts were developed for SO₃ decomposition. Based on fundamental researches, a closed-loop test apparatus of 10 NL/h H₂ was designed and established. The current status of IS process research is summarized in this paper. In addition, R&D plan of IS process at INET is presented.     

Decomposition of hydrogen iodide via wood-based activated carbon catalysts for hydrogen production

In this study, the catalytic activity of wood-based catalysts produced by different activation methods was evaluated for the decomposition of hydrogen iodide (HI) as part of the sulfur-iodine hydrogen production process. The wood-based activated carbon catalysts showed strong improvement in the HI conversion compared to a blank, especially for carbon catalysts activated using H₃PO₄. Proximate analysis and ultimate analysis, XRD, BET, SEM, Boehm titration, TPD-MS, XPS were carried out to examine the characteristics of the catalysts. High carbon content (C_ad) seemed to favor high catalytic activity, while high ash content (A_ad) reduced catalytic activity of samples likely due to displacement of catalytically active material. Oxygen-containing groups were not directly responsible for catalytic activity. HI conversion increased as the surface area and pore diameter increased. Unsaturated carbon atoms maybe the main active constituent, therefore, low area density of oxygen [O] that was closely related to unsaturated carbon atoms was beneficial to HI conversion.     

A sulfur-iodine flowsheet using precipitation,electrodialysis, and membrane separation to produce hydrogen

The preliminary flowsheet of an electrodialysis cell (EDC) and membrane reactor (MR)-embedded SI cycle has been developed. The key components consisting of the preliminary flowsheet are as follows: a Bunsen reactor having a mutual separation function of sulfuric acid and hydriodic acid phases, a sulfuric acid refined column for the purification of the sulfuric acid solution, a HI_x-refined column for the purification of the hydriodic acid solution, an isothermal drum coupled to a multi-stage distillation column to concentrate the sulfuric acid solution, a sulfuric acid vaporizer, a sulfuric acid decomposer, a sulfur trioxide decomposer, a sulfuric acid recombination reactor, a condensed sulfuric acid solution and sulfur dioxide/oxygen gas mixture separator, a precipitator to recover excess iodine dissolved in the hydriodic acid solution, an electrodialysis cell to break through the azeotrope of the HI/I₂/H₂O ternary solution, a multi-stage distillation column to generate highly concentrated hydriodic acid vapor as a top product of the column, a membrane reactor to decompose hydrogen iodide and preferentially separate the hydrogen, and a hydrogen scrubber. The material and energy balance of each component was established based on a computer code simulation using Aspen Plus™. The thermal efficiency of the EDC and MR-embedded SI process has also been evaluated and predicted as 39.4%.     

Cost estimates for nuclear power in the UK

Current UK Government support for nuclear power has in part been informed by cost estimates that suggest that electricity from new nuclear power stations will be competitive with alternative low carbon generation options. The evidence and analysis presented in this paper suggests that the capital cost estimates for nuclear power that are being used to inform these projections rely on costs escalating over the pre-construction and construction phase of the new build programme at a level significantly below those that have been experienced by past US and European programmes. This paper applies observed construction time and cost escalation rates to the published estimates of capital costs for new nuclear plant in the UK and calculates the potential impact on levelised cost per unit of electricity produced. The results suggest that levelised cost may turn out to be significantly higher than expected which in turn has important implications for policy, both in general terms of the potential costs to consumers and more specifically for negotiations around the level of policy support and contractual arrangements offered to individual projects through the proposed contract for difference strike price.     

Hydrogen production from polystyrene pyrolysis and gasification: Characteristics and kinetics

Polystyrene (PS) pyrolysis and gasification have been examined in a semi-batch reactor at temperatures of 700, 800 and 900 °C. Characteristic differences between pyrolysis and gasification of polystyrene (PS) have been evaluated with specific performance focus on the evolution of syngas flow rate, evolution of hydrogen flow rate, evolution of output power, syngas yield, hydrogen yield, energy yield, apparent thermal efficiency and syngas quality. Behavior of PS under either pyrolysis or gasification processes is compared to that of char based sample, such as paper and cardboard. In contrast to char based materials, PS gasification yielded less syngas, hydrogen and energy than pyrolysis at 700 °C. However, the gasification of PS yielded more syngas, hydrogen and energy than pyrolysis at 900 °C temperature. Gasification of PS is affected by reactor temperature more than PS pyrolysis. Syngas, hydrogen and energy yield increased exponentially with temperature in case of gasification. However, syngas and energy yield increased linearly with temperature having rather a mild slope in the case of pyrolysis. Pyrolysis resulted in higher syngas quality at all temperatures. Kinetics of hydrogen evolution from the PS pyrolysis is introduced. The Coats and Redfern method was used to determine the kinetic parameters, activation energy (E_act), pre-exponential factor (A) and reaction order (n). The model used is the nth order chemical reaction model. Kinetic parameters have been determined for three slow heating rates, namely 8, 10 and 12 °C/min. The average values obtained from the three heating rate experiments were used to compare the model with the experimental data.     

Technical and economic evaluation of solar hydrogen production by supercritical water gasification of biomass in China

A novel thermochemical method for solar hydrogen production was proposed by state key laboratory of multiphase flow in power engineering (SKLMFPE) of Xi’an Jiaotong University. In this paper, a technical and economic evaluation of the new solar hydrogen production technology was conducted. Firstly, the advantages of this new solar hydrogen production process, compared with other processes, were assessed and thermodynamic analysis of the new process was carried out. The results show that biomass gasification in supercritical water driven by concentrating solar energy may be used to achieve high efficiency solar thermal decomposition of water and biomass for hydrogen production. Secondly, the hydrogen production cost was analyzed using the method of the total annual revenue requirement. The estimated hydrogen production cost was 38.46RMB/kg for the experimental demonstration system with a treatment capacity of 1 ton wet biomass per hour, and it would be decreased to 25.1 RMB/kg if the treatment capacity of wet biomass increased from 1 t/h to 10 t/h. A sensitivity analysis was also performed and influence of parameters on the hydrogen production cost was studied. The results from technical and economic evaluation show that supercritical water gasification of biomass driven by concentrated solar energy is a promising technology for hydrogen production and it is competitive compared to other solar hydrogen production technologies.     

Electrochemical mass transfer and entropy generation of cuprous chloride electrolysis

Diffusive mass transfer in an electrochemical cell, which produces hydrogen in a copper-chlorine cycle of thermochemical water decomposition, is investigated in this paper. A predictive model of entropy production for the electrochemical reaction of cuprous chloride and hydrochloric acid is developed. The effects of temperature and current density on entropy production are investigated with the new formulation. A comparative study is performed with respect to the relationships between current density and overpotential, using Tafel’s equation and a newly proposed method, based on the Nernst equation. The effects of ohmic and activation overpotentials on the thermodynamic irreversibilities in the electrolytic cell are also investigated. The impact of the charge transfer coefficient on the electrochemical reaction is also examined. The results of the new predictive formulation are compared successfully against Tafel’s model and past experimental data, in relation to measured electrochemistry data. The operating temperature of the electrochemical cell has a significant effect on the entropy generation. The ohmic resistance appears to have minimal effect on the electrolytic cell performance at high current densities. A significant effect of current density on overpotential was observed at low current densities (0-250 mA/cm²). The current density has a significant effect on entropy production between 0 and 400 mA/cm². The activation overpotential has the most significant effect on cell performance. Although the ohmic resistance has little effect at high current densities, the effects become significant at lower current densities.     

Thermochemical hydrogen production with a copper–chlorine cycle,II: Flashing and drying of aqueous cupric chloride

This paper examines the evaporative drying of aqueous cupric chloride (CuCl₂) droplets in the copper–chlorine (Cu–Cl) thermochemical cycle of hydrogen production. An aqueous CuCl₂ stream exiting from an electrochemical cell is preheated to 150 °C, before entering a flash evaporator to produce solid CuCl₂(s). New innovations of heat recovery aim to develop alternatives that reduce costs and improve efficiency of the evaporation process for CuCl₂ particle production. The liquid phase flashes due to a sudden pressure drop. Analytical solutions are developed for the cupric chloride spraying and drying processes, including empirical correlations for heat and mass transfer, based on a single droplet of aqueous CuCl₂ solution. The study shows that considerable drying can be accomplished through differentials of humidity alone. It also shows that benefits of flashing the solution to enhance drying are relatively minor, compared to the rate of evaporative drying in the spray drying process.