The First Step in Solar Hydrogen Production: Development of a Solar Thermal Reactor for the Reduction of Metal Oxide Particles

A solar thermal reactor has been designed to experimentally investigate promising paths for reducing metal oxide particles to reduced oxidation states (e.g. Fe2O3 to Fe3O4) utilizing concentrated solar energy. This reactor is windowless and is able to handle internal cavity temperatures in excess of 1700 K. It also has a quasi-continuous feed system that allows the particle residence times to be varied for particles between 0.044 mm and 1 mm in diameter. Furthermore, this reactor utilizes an instrumentation system for the measurement of temperature, particle residence time, particle mass flow rate, and solar flux. In an industrial setting, a large-scale metal oxide reactor would serve as the first step in a metal oxide solar thermal electro-chemical cycle. After the particles are reduced at elevated temperatures using concentrated solar energy, they are used in an electrolysis process to facilitate the production of hydrogen from water. In this process, the reduced metal oxide particles are reoxidized at the anode and hydrogen is liberated at the cathode. The presence of the metal oxide enables hydrogen to be produced with an ideal cell potential of 0.21 V, a potential substantially below the ideal value of 1.2 V for traditional water electrolysis

Multi-Tubular Reactor for Hydrogen Production: CFD Thermal Design and Experimental Testing

This study presents the Computational Fluid Dynamics (CFD) thermal design and experimental tests results for a multi-tubular solar reactor for hydrogen production based on the ferrite thermochemical cycle in a pilot plant in the Plataforma Solar de Almería (PSA). The methodology followed for the solar reactor design is described, as well as the experimental tests carried out during the testing campaign and characterization of the reactor. The CFD model developed for the thermal design of the solar reactor has been validated against the experimental measurements, with a temperature error ranging from 1% to around 10% depending on the location within the reactor. The thermal balance in the reactor (cavity and tubes) has been also solved by the CFD model, showing a 7.9% thermal efficiency of the reactor. CFD results also show the percentage of reacting media inside the tubes which achieve the required temperature for the endothermic reaction process, with 90% of the ferrite pellets inside the tubes above the required temperature of 900 C. The multi-tubular solar reactor designed with aid of CFD modelling and simulations has been built and operated successfullyFondo Europeo de Desarrollo Regional (FEDER) IPT- 2011-1323-920000Programa Operativo FEDER para Andalucía 2007–2013 RNM-612

Solar Furnace: Heliostat and Concentrator Design

In recent decades, solar energy has been shown as a viable, clean, and abundant alternative to fossil fuels. Many methods of solar energy collection are being researched, with solar thermal electrochemistry being one of the most promising. Solar thermal electrochemistry uses sunlight to heat a furnace to temperatures nearing 2000 K. At these temperatures, metallic oxides can be decomposed to metals and oxygen with minimal electrical work. Achieving these high temperatures requires a solar furnace that consists of a heliostat to track and reflect the sun’s rays into a concentrator, which then focuses the sunlight to a single point in a solar thermal chemical reactor. A system of louvers regulates the amount of sunlight entering the system. Our research focuses on the design and development of the solar furnace components; specifically, the design and construction of the heliostat structure, the heliostat control system, and the concentrator

Solar heated fluidized bed gasification system

A solar-powered fluidized bed gasification system for gasifying carbonaceous material is presented. The system includes a solar gasifier which is heated by fluidizing gas and steam. Energy to heat the gas and steam is supplied by a high heat capacity refractory honeycomb which surrounds the fluid bed reactor zone. The high heat capacity refractory honeycomb is heated by solar energy focused on the honeycomb by solar concentrator through solar window. The fluid bed reaction zone is also heated directly and uniformly by thermal contact of the high heat capacity ceramic honeycomb with the walls of the fluidized bed reactor. Provisions are also made for recovering and recycling catalysts used in the gasification process. Back-up furnace is provided for start-up procedures and for supplying heat to the fluid bed reaction zone when adequate supplies of solar energy are not available

Thermal Stress Analysis of Solar Thermochemical Reactor Using Concentrated Solar Radiation

Utilizing solar thermochemical reactor to convert exhaust gas into high-quality clean fuel by concentrated solar radiation is a valuable way to develop renewable energy. Due to the high working temperature, the issue of reactor damage occurs easily as found during the course of the experiment. In order to find out the reasons, some thermal stress simulation and analysis of solar thermochemical reactor were made in this article. The areas where thermal stress is concentrated were investigated in the contour simulation results. Based on the analysis, some suggestions for structural optimization for further research were formulated. Keywords: solar thermochemical, thermal stress, heat transfer and flow, reacto

Preliminary comparative assessment of land use for the Satellite Power System (SPS) and alternative electric energy technologies

A preliminary comparative assessment of land use for the satellite power system (SPS), other solar technologies, and alternative electric energy technologies was conducted. The alternative technologies are coal gasification/combined-cycle, coal fluidized-bed combustion (FBC), light water reactor (LWR), liquid metal fast breeder reactor (LMFBR), terrestrial photovoltaics (TPV), solar thermal electric (STE), and ocean thermal energy conversion (OTEC). The major issues of a land use assessment are the quantity, purpose, duration, location, and costs of the required land use. The phased methodology described treats the first four issues, but not the costs. Several past efforts are comparative or single technology assessment are reviewed briefly. The current state of knowledge about land use is described for each technology. Conclusions are drawn regarding deficiencies in the data on comparative land use and needs for further research

Heat Transfer Modeling and Analysis of Solar Thermo-chemical Reactor for Hydrogen Production from Water

AbstractA solar thermo-chemical reactor is modeled and analyzed for the solar thermal dissociation of zinc oxide into zinc and oxygen involved in the thermo-chemical cycle for hydrogen production. The reactor consists of a cavity surrounded by a rotating insulation layer made of alumina. The granular zinc oxide particles are fed into the cavity and are directly exposed to the solar radiation entering the cavity through a quartz window. A three dimensional numerical model coupling the multiphase particle dynamics in gravitational field, multiphase heat transfer, k-ɛ turbulence model, discrete ordinates radiation model, Arrhenius reaction rate model is developed. The cavity temperature and oxygen molar flow rate at the outlet of the reactor which is the indicator of the reaction rate has been validated with a 10kW reactor prototype. An energy balance study of thermal performance parameters including the various losses occurring from the reactor and efficiency is also done. The major losses were contributed by re-radiation (46%) and sensible heating of reactor components (35.5%), while the minor losses were contributed by convection by argon (1%) and conduction through insulation (2%).The thermal efficiency of the reactor is calculated to be 15.5%

Review of Reactors with Potential Use in Thermochemical Energy Storage in Concentrated Solar Power Plants

The aim of this study is to perform a review of the state-of-the-art of the reactors available in the literature, which are used for solid-gas reactions or thermal decomposition processes around 1000 ºC that could be further implemented for thermochemical energy storage in CSP (concentrated solar power) plants, specifically for SPT (solar power tower) technology. Both direct and indirect systems can be implemented, with direct and closed systems being the most studied ones. Among direct and closed systems, the most used configuration is the stacked bed reactor, with the fixed bed reactor being the most frequent option. Out of all of the reactors studied, almost 70% are used for solid-gas chemical reactions. Few data are available regarding solar efficiency in most of the processes, and the available information indicates relatively low values. Chemical reaction efficiencies show better values, especially in the case of a fluidized bed reactor for solid-gas chemical reactions, and fixed bed and rotary reactors for thermal decompositions.The work is partially funded by the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER) and ENE2015-64117-C5-2-R (MINECO/FEDER)). The authors would like to thank the Catalan Government for the quality accreditation given to their research groups GREA (2017 SGR 1537) and DIOPMA (2017 SGR 118). GREA and DIOPMA are certified agents TECNIO in the category of technology developers from the Government of Catalonia. Dr. Aran Solé would like to thank Ministerio de Economía y Competitividad de España for Grant Juan de la Cierva, FJCI-2015-25741

The Ammonia Looping System for Mid-Temperature Thermochemical Energy Storage

Thermochemical reactions have a great potential for energy storage and transport. Their application to solar energy is of utmost interest because the possibility of reaching high energy densities and seasonal storage capacity. In this work, thermochemical energy storage of Concentrated Solar Power (CSP) based on an ammonia looping (AL) system is analysed. The AL process for energy storage is based on the reversible reaction of ammonia to produce hydrogen and nitrogen. Concentrating solar energy is used to carry out the decomposition endothermic reaction at temperatures around 650 ºC, which fits in the range of currently commercial CSP plants with tower technology. The stored energy is released through the reverse exothermic reaction. Our work is focused on energy integration in the system modelled by pinch analysis to optimize the process performance and competitiveness. As result a novel configuration is derived which is able to recover high-temperature heat for electricity production with a thermal-to-electric efficiency up to 27 %. The current study shows a clear interest of the system from an energy integration perspective. Further research should be conducted to access the potential for commercial applications

Apparatus and method to keep the walls of a free-space reactor free from deposits of solid materials

An apparatus and method is disclosed for keeping interior walls of a reaction vessel free of undesirable deposits of solid materials in gas-to-solid reactions. The apparatus includes a movable cleaning head which is configured to be substantially complementary to the interior contour of the walls of the reaction vessel. The head ejects a stream of gas with a relatively high velocity into a narrow space between the head and the walls. The head is moved substantially continuously to at least intermittently blow the stream of gas to substantially the entire surface of the walls wherein undesirable solid deposition is likely to occur. The disclosed apparatus and process is particularly useful for keeping the walls of a free-space silane-gas-to-solid-silicon reactor free of undesirable silicon deposits