Solar Chemical Reactor Research Articles

Scale up analysis of a plasmon-enhanced ethylene oxide production process

Geometric modeling of hourly solar irradiance combined with Markov chain descriptions of cloud cover dynamics is shown to be an effective tool for the design and analysis of solar-assisted catalytic processes. A key finding of this study is that because of the large area needed to collect incoming irradiation, even at modest reactor operating temperatures, radiative thermal losses can greatly exceed the incoming solar irradiance — for the ethylene oxide process of this study, the most significant source of thermal power was found to be that released by the competing exothermic ethylene oxidation reaction. The net result of the radiative losses is that a fixed Earth-tangent solar chemical reactor, under representative annual weather and irradiance conditions, can only operate in the hours surrounding solar noon and would be idle on days between the fall and spring equinoxes. It is further shown that if a sun-tracking reactor configuration is used, the thermodynamic feasibility of the process improves considerably, even with no irradiance concentration. Significant gains are found for modest levels of solar irradiance concentration; however, while the illuminated catalyst surface area will decrease with increasing irradiance concentration for fixed production levels, the projected area of the concentrating system also will increase proportionally, offsetting the reactor performance gains.

Brinkman–Bénard convection in a box with temperature modulation

A bounded porous box saturated with Newtonian fluid and subjected to a sinusoidal temperature gradient has various practical applications, such as solar energy storage, groundwater remediation, food processing, and chemical reactors. We address the generalization of the classical Rayleigh–Bénard convection problem in a horizontal fluid layer in an infinitely large domain heated from below to a finite three-dimensional box. We also look into a more intricate form of the modulated Rayleigh–Bénard problem in which the temperature at the bottom boundary varies sinusoidally. The Rayleigh number quantifies the non-sinusoidal part of the temperature gradient, while the amplitude and frequency of modulation describe the sinusoidal one. The critical Rayleigh number is determined using linear and nonlinear stability analyses; for the latter, the energy method is used. There is a possibility of subcritical instabilities, as evidenced by the energy stability estimates being lower than the linear ones. Furthermore, eigenvalues are obtained as a function of aspect ratios, modulation amplitude, and frequency for varying Darcy numbers. Modulation amplitude more significantly triggers a change in flow patterns at the onset of convection compared to the effect of other parameters. Considering water-saturated porous media made up of different materials, we report the critical temperature difference between lower and upper surfaces required for the onset of convection. In addition, a comparison between such a temperature difference obtained from linear theory and the energy method is also provided in the same manner. It is observed that subharmonic instability occurs for all considered porous media packed densely or sparsely.

Thermal Performance Assessment of a Novel Hybrid Reactor for Solar Thermochemical Processes

Solar thermochemical conversion processes offer a promising pathway for converting sunlight into clean, sustainable, and carbon-neutral fuels. A solar chemical reactor is one of the most essential components that utilizes concentrated solar energy to drive chemical reactions. In this study, a novel hybrid solar reactor is designed, fabricated, and tested to assess its thermal performance for the purpose of studying the solar thermochemical conversion processes in Thailand for the first time. It was performed under different heating modes regarding solar heat and/or electrical heat, with the aim to support day-and-night operation and variations in solar radiation conditions. The reactor was experimentally tested under on-sun, off-sun, and hybrid conditions using air as a heat transfer fluid. As a result, with one kWth solar thermal power input absorbed, the solar reactor achieved high temperatures exceeding 500 °C from the hybrid system while the reactor absorption efficiency was found to be 4%. The reactor demonstrated the possibility and reliability of performing solar thermochemical conversion processes under day-and-night and unstable solar radiation conditions.

An impact of Richardson number on the inclined MHD mixed convective flow with heat and mass transfer

AbstractThe two‐dimensional mixed convective MHD flow with heat and mass transfer is investigated for its behavior with Dufour and Soret mechanisms over the porous sheet. The copper–alumina (Cu–Al2O3) hybrid nanoparticles are used in the base fluid water. The governing system of partial differential equations is converted into a system of ordinary differential equations via similarity transformations, obtaining the solution for velocity, temperature, and concentration fields in exponential form. The problem is demonstrated in the Darcy–Brinkman model, the impact of included parameters such as Richardson number, magnetic field, and Dufour numbers are studied for the obtained solution with the help of graphs. Increasing the magnetic field decreases both transverse and axial velocity profiles. Increasing the magnetic field and Richardson's number decreases the solution (Al2O3–H2O). Increasing the values magnetic field and Richardson's number decreases both transverse and axial velocity profiles. Increasing the values of the Dufour effect increases the axial and transverse velocity boundary layer. The magnetohydrodynamic hybrid nanofluid flow over porous media works efficiently in liquid cooling and, therefore, has significant applications in industrial heating and cooling systems, solar energy, magnetohydrodynamic flow meters and pumps, manufacturing, regenerative heat exchange, thermal energy storage, solar power collectors, geothermal recovery, and chemical catalytic reactors.

Impact of radiation on the MHD couple stress hybrid nanofluid flow over a porous sheet with viscous dissipation

The investigation is carried to observe the impact of radiation on the MHD couple stress hybrid nanofluid over porous sheet with dissipation. The water based MHD couple stress hybrid nanofluid flow due to porous shrinking sheet with thermal radiation and viscous dissipation has range of engineering applications dealing with energy distribution, solar energy storage, chemical reactors and polymer production. The flow problem is mathematically modelled into nonlinear partial differential equations, which are transformed into set of ordinary differential equations via similarity variable. The analytical solutions are derived in the form of hypergeometric functions. These results are in line with the existing classical results. The physical insights on the impact of MHD, mass transpiration, Eckert number, Couple stress, porosity and thermal radiation on velocity and temperature profiles are provided by means of graphs.

Thermochemical performance assessment of solar continuous methane-driven ZnO reduction for co-production of pure zinc and hydrogen-rich syngas

Converting renewable solar energy to dispatchable chemical products via solar-driven thermochemical processes is one of the best solutions for long-term solar energy storage and renewable fuel production. This study addresses the performance assessment of continuous methane-driven ZnO reduction, fully powered by renewable solar heat, for co-production of hydrogen-rich syngas and metallic Zn in a solar prototype consuming-bed chemical reactor. On-sun experiments were conducted under continuous ZnO and CH4 co-feeding to assess the effect of key parameters (inlet CH4/ZnO molar ratio: 1–1.5, temperature: 900–1000 °C, and ZnO feeding rate: 0.5–1.5 g/min) in order to maximize syngas and Zn yields, and reactor performance metrics. As a result, a rise in either the CH4/ZnO molar ratio or temperature enhanced the reaction extent but favored solid carbon formation, which downgraded syngas products quality, and consumed more solar energy input. Increasing ZnO feeding rate under a constant ZnO/CH4 molar ratio significantly promoted ZnO + CH4 reaction performance thanks to both hastened ZnO consumption rate (boosting products yield) and reduced solar energy consumption (improving solar conversion efficiency). However, excessively high ZnO feeding rate caused temporal ZnO accumulation in the reactor. Optimal operating conditions for on-sun continuous methane-driven ZnO reduction were identified (at ZnO feeding rate = 1.2 g/min, CH4/ZnO molar ratio = 1.5, and temperature = 950 °C), yielding total syngas yield of 12.3 mmol/gZnO, solid carbon formation down to 0.58 mmol/gZnO, ZnO conversion of 63.0%, methane conversion of 10.6%, energy upgrade factor of 1.08, and solar-to-fuel energy conversion efficiency of 5.3%. High-purity Zn particles with hexagonal morphologies were generated in continuous mode, demonstrating the proposed approach feasibility and reliability for simultaneous methane conversion to syngas and metallic Zn production in a single process.

Thermochemical solar-driven reduction of CO2 into separate streams of CO and O2 via an isothermal oxygen-conducting ceria membrane reactor

• Demonstration of single-step CO 2 thermolysis in a novel solar-driven membrane reactor. • In-situ separation of CO and O 2 via lattice oxygen transfer through ceria dense membrane. • Continuous and isothermal operation of the MIEC tubular membrane reactor at 1450–1550 °C. • Increasing the temperature, CO 2 concentration or flow rate enhanced CO and O 2 production rates. • The fuel production rate was up to 4.26 μmol/cm 2 /min at 1550 °C under pure CO 2 feeding. CO 2 single-step thermolysis was achieved using oxygen permeable MIEC (mixed ionic-electronic conducting) membranes made of ceria for separate production of CO on the feed side and O 2 on the sweep side. The CO 2 -dissociation reaction was driven by concentrated solar energy as a renewable thermal energy source and by applying a chemical potential gradient between both membrane sides. A continuous oxygen transfer across the membrane was achieved thanks to a flow of inert gas on the permeate side. This created the required oxygen partial pressure gradient and favored oxygen permeation via oxygen ion diffusion through the ceria membrane thickness. A novel solar chemical reactor integrating the reactive ceria membrane was designed and tested under real concentrated solar radiation, with operating temperatures up to 1550 °C. The reactive part of the tubular redox membrane was located inside a well-insulated cavity receiver for homogeneous heating, which was fed with a carrier argon flow on the sweep side to facilitate the transport and removal of the permeated oxygen. The dynamic response of the solar fuel production upon changing the operating conditions (temperature, CO 2 mole fraction, and feed gas flow rate) in the membrane reactor was investigated by quantifying the evolved gas production rates. Continuous CO 2 dissociation was achieved on the feed side inside the tubular membrane with in-situ spatial separation of O 2 and CO streams across the membrane. Reliable solar membrane reactor operation under real concentrated sunlight was successfully demonstrated for the first time, with stable and unprecedented CO production rates up to 0.071 μmol/cm 2 /s at 1550 °C and CO/O 2 ratio of 2.

Solar Photooxygenations for the Manufacturing of Fine Chemicals-Technologies and Applications.

Photooxygenation reactions involving singlet oxygen (1O2) are utilized industrially as a mild and sustainable access to oxygenated products. Due to the usage of organic dyes as photosensitizers, these transformations can be successfully conducted using natural sunlight. Modern solar chemical reactors enable outdoor operations on the demonstration (multigram) to technical (multikilogram) scales and have subsequently been employed for the manufacturing of fine chemicals such as fragrances or biologically active compounds. This review will highlight examples of solar photooxygenations for the manufacturing of industrially relevant target compounds and will discuss current challenges and opportunities of this sustainable methodology.

An ageing protocol for testing high temperature solar materials for thermochemical applications

Future's sustainable economy based on hydrogen will require large-scale hydrogen production processes in a CO2 emission-free way. Within this context, solar-driven thermochemical water splitting cycles have been proposed as a promising alternative for hydrogen mass production.Thermochemical processes require thermal and chemically stable reactor wall materials, which can withstand severe operating conditions, suitable for specific solar fuels production. Several unresolved issues are involved in predicting the effect of environmental degradation on the long-term performance of innovative materials for next generation solar chemical reactors to guarantee their reliability and durability under demanding working conditions.The research project ARROPAR-CEX involves a multidisciplinary team for studying novel receiver concepts and new materials, working under extreme conditions (in excess of 1000 kW/m2, and very high temperatures, typically above 1000 °C).The main objective of this work has been to develop and propose as candidate an accelerated ageing method for solar receiver’ materials, in order to estimate their degradation during lifetime under extreme solar operating conditions. A set of four selected ceramic materials have been submitted to these accelerated ageing test procedures and some preliminary conclusions on their suitability have been extracted.

Performance analysis and optimization of solar thermochemical reactor by diluting catalyst with encapsulated phase change material

Solar thermochemical reactor, which can produce solar fuel at low cost, suffers discontinuous low-efficiency performance due to solar radiation fluctuation caused by cloud passage. To achieve highly efficient steady and dynamic performance of solar chemical reactor with less catalyst, in this study, catalytic activity is adjusted by diluting catalyst with encapsulated phase change material. At first, two-dimensional model of solar parabolic trough receiver reactors diluted with encapsulated phase change material is established and validated. Then, effect of catalytic activity on performance of reactor is discussed. Afterwards, one-dimensional model is derived from two-dimensional model to train Back Propagation neural network for quick and precise performance prediction of reactor. Finally, optimal catalytic distribution is obtained by genetic algorithm and Back Propagation neural network, and steady and unsteady performance of reactor between uniform and optimal catalytic distribution are compared. The results show that when catalytic activity decreases from 1.0 to 0.2, steady methanol conversion efficiency and production rate of H2 are reduced by 8.4% and 9.9%, and reactor shows more stability under unsteady condition of solar radiation. One-dimensional model derived in present study is accurate enough and time-saving compared to two-dimensional model. And compared to reactor fully packed with catalyst, reactor with optimal catalytic distribution can achieve similar steady performance with 56% less of catalyst, but shows better stability under the fluctuation of solar radiation.

Design, simulation and experimental study of a directly-irradiated solar chemical reactor for hydrogen and syngas production from continuous solar-driven wood biomass gasification

The use of concentrated solar energy as the high-temperature heat source for the thermochemical gasification of biomass is a promising prospect for producing CO2-neutral chemical fuels (syngas). The solar process saves biomass resource because partial combustion of the feedstock is avoided, it increases the energy conversion efficiency because the calorific value of the feedstock is upgraded by the solar power input, and it also reduces the need for downstream gas cleaning and separation because the gas products are not contaminated by combustion by-products. A new concept of solar spouted bed reactor with continuous biomass injection was designed in order to enhance heat transfer in the reactor, to improve the gasification rates and gas yields by providing constant stirring of the particles, and to enable continuous operation. Thermal simulations of the prototype were performed to calculate temperature distributions and validate the reactor design at 1.5 kW scale. The reliable operation of the solar reactor based on this new design was also experimentally demonstrated under real solar irradiation using a parabolic dish concentrator. Wood particles were continuously gasified at temperatures ranging from 1100 °C to 1300 °C using either CO2 or steam as oxidizing agent. Carbon conversion rates over 94% and gas productions over 70 mmol/gbiomass were achieved. The energy contained in the biomass was upgraded thanks to the solar energy input by a factor of up to 1.21.

A drop-tube particle-entrained flow solar reactor applied to thermal methane splitting for hydrogen production

A solar chemical reactor with continuous particle feeding in a tubular absorber has been designed and tested for CO2-free hydrogen production from thermal methane decomposition. The entrained-flow reactor was operated on sun with carbon black particle injection in a stream of methane diluted in argon. The carbon particles are expected to act as a catalyst for the dissociation reaction and the indirect irradiation via an intermediate opaque tubular absorber results in a more uniform heating of the reactor volume and thus an easier reaction temperature control and determination. The effect of particle injection on the reactor performance was investigated as a function of the type of carbon black catalyst and characteristics, reaction temperature (1150–1400°C), total volumetric gas flow rate and methane content in the feed gas (10–40%). Key measured performance outputs were CH4 conversion and H2 yield, C2H2 outlet concentration, and solar-to-chemical reactor efficiency. The particle feeding did not drastically improve the methane decomposition rate and hydrogen yield, which can presumably be attributed to kinetic limitation due to short particle residence time in the high-temperature region. Likewise, the inlet methane mole fraction was not a primary influencing parameter. In contrast, the temperature and the gas flow rate strongly affected the methane decomposition rate.

Numerical modelling of flows in a solar-enhanced vortex gasifier: Part 1, comparison of turbulence models

The present paper reports the evaluation of performance of a series of turbulence models for an isothermal flow in a solar chemical reactor. This chemical reactor has similar swirling flow patterns to those in a solar–enhanced vortex gasifier (SVG) and measurements of velocity in this reactor are available in literature. Three turbulence models, namely, standard k–e model, baseline (BSL) Reynolds stress model, and shear–stress–transport (SST) model are used to simulate the flows in the solar chemical reactor. It is found that the predictions of the three models are in reasonable agreement with the experimental data, although none are entirely satisfactory, with the predictions of the SST model being slightly better than those of the other models. However, even the SST model is not able to predict the anisotropic Reynolds stresses in the flow. More detailed measurements of flow fields in SVG type reactors are required for further evaluation.

Development of a simulation-software for a hydrogen production process on a solar tower

A simulation and control model for a two-step thermo-chemical water splitting cycle using metal oxids for the generation of hydrogen with a solar tower system as heat source has been developed. The simulation and control model consists of three main parts, the simulation of the solar flux distribution on the receiver, of the temperatures in the driven reactor modules and the produced hydrogen in the metal oxide.The results of the three parts of the simulation model have been evaluated by comparing and validating them with experimental data from the Hydrosol 100kWth pilot plant at the Plataforma Solar de Almería (PSA) in Spain.With the overall model of the hydrogen production plant that was created, an evaluation of the two-step thermochemical cycle process in combination with a solar tower system was performed. The model was used to perform parametric studies for the development of the plant and the operation strategies. For this purpose, a provision in the overall model was integrated. The simulation helps to reduce the frequency of using the flux measurement system and can be used for the heliostat field control, in particular for the temperature control in the solar chemical reactor modules. Because of these promising results the overall system model is being extended to enable a use as a control model with controller for the temperature control of the two core reactions in the process.The central control variable of the process control was the operating temperatures for the hydrogen production and the regeneration of the two modules. The process control with its PI controller turned out suitable to compensate diurnal changes of solar input power as well as certain statistical fluctuation due to cloud passage. At the same time the limits of the operability and controllability of the process became clear in terms of the minimum of solar power needed and maximum acceptable gradients.With this experience an operating strategy, the basic parameters of the system in operation, especially the starting up and shutdown procedures, regular operation and the response to disturbances were selected and optimized. With this operation/control strategy such a complex system can be operated in the future on a commercial scale automatically. The obtained results can also be adapted for other solar chemical processes.

Morphological Characterization and Effective Thermal Conductivity of Dual-Scale Reticulated Porous Structures.

Reticulated porous ceramic (RPC) made of ceria are promising structures used in solar thermochemical redox cycles for splitting CO2 and H2O. They feature dual-scale porosity with mm-size pores for effective radiative heat transfer during reduction and µm-size pores within its struts for enhanced kinetics during oxidation. In this work, the detailed 3D digital representation of the complex dual-scale RPC is obtained using synchrotron submicrometer tomography and X-ray microtomography. Total and open porosity, pore size distribution, mean pore diameter, and specific surface area are extracted from the computer tomography (CT) scans. The 3D digital geometry is then applied in direct pore level simulations (DPLS) of Fourier’s law within the solid and the fluid phases for the accurate determination of the effective thermal conductivity at each porosity scale and combined, and for fluid-to-solid thermal conductivity from 10−5 to 1. Results are compared to predictions by analytical models for structures with a wide range of porosities 0.09–0.9 in both the strut’s µm-scale and bulk’s mm-scale. The morphological properties and effective thermal conductivity determined in this work serve as an input to volume-averaged models for the design and optimization of solar chemical reactors.

Numerical analysis of hydrogen production via methane steam reforming in porous media solar thermochemical reactor using concentrated solar irradiation as heat source

The calorific value of syngas can be greatly upgraded during the methane steam reforming process by using concentrated solar energy as heat source. In this study, the Monte Carlo Ray Tracing (MCRT) and Finite Volume Method (FVM) coupling method is developed to investigate the hydrogen production performance via methane steam reforming in porous media solar thermochemical reactor which includes the mass, momentum, energy and irradiative transfer equations as well as chemical reaction kinetics. The local thermal non-equilibrium (LTNE) model is used to provide more temperature information. The modified P1 approximation is adopted for solving the irradiative heat transfer equation. The MCRT method is used to calculate the sunlight concentration and transmission problems. The fluid phase energy equation and transport equations are solved by Fluent software. The solid phase energy equation, irradiative transfer equation and chemical reaction kinetics are programmed by user defined functions (UDFs). The numerical results indicate that concentrated solar irradiation on the fluid entrance surface of solar chemical reactor is highly uneven, and temperature distribution has significant influence on hydrogen production.

Numerical Investigation of a Metal-oxide Reduction Reactor for Thermochemical Energy Storage and Solar Fuel Production

The optimum design of a thermochemical reactor involves complex phenomena such as radiation heat and mass transfer, reaction kinetics, and fluid-solid interactions which makes the process to be cumbersome. The computational modelling using computational fluid dynamics (CFD) is an important tool to study, analyse, interpret and optimize such a complex system. The present study has developed a CFD model using Ansys-Fluent 14.0. The model employs the Eulerian-Lagrangian approach with the chemical reactions for a vertical axis thermochemical reactor for Zinc oxide reduction process. The conversion efficiency and temperature distributions for Zinc oxide reduction estimated by the CFD results have been validated with the published results by the PROMES CNRS laboratory (France) for a horizontal reactor design. The effect of particle size and gravity with a view to adapt it for a vertical beam-down solar concentrator have been analysed in the present study. It was observed that smaller particles provide higher surface area for enhanced heat transfer. Gravitational effects turned to be significant as the particle size increases. The model will assist in the effort of developing an efficient solar chemical reactor, for innovative thermochemical energy storage systems or fuel production, which will be tested at the Masdar Institute‘s beam down research facility.

Kinetic analysis of high-temperature solid–gas reactions by an inverse method applied to ZnO and SnO2 solar thermal dissociation

This study addresses the kinetic investigation of solid–gas reactions in a high-temperature solar chemical reactor. An inverse method was developed to identify the kinetics of metal oxide thermal dissociation as part of a two-step thermochemical redox cycle for solar splitting of H2O and CO2. This method was applied and further validated by studying ZnO and SnO2 solar thermal dissociation. A solar chemical reactor enabling continuous solid reactant processing was developed in which both the oxide reactant temperature at the front surface and the O2 concentration in the off gas were measured dynamically. The aim of the inverse method was to identify the intrinsic kinetics of the dissociation reaction using only the available experimental data.Different approaches were proposed and compared to investigate the kinetics of solid–gas reactions. The activation energy of the reaction was first estimated roughly using an iso-conversional model-free approach, which can be used as an initialization value for further refinement with the inverse method. The inverse method consists in identifying the reaction kinetics from only the online diagnosis of outlet O2 concentration and using a model enabling parameters fitting via an iterative process. Depending on the considered approach and assumptions for predicting the temperature profile within the reacting oxide rod (succession of stationary states assumption or unsteady state operation), the activation energy of the dissociation reaction was found to be 313±31kJ/mol for ZnO and 353±18kJ/mol for SnO2. Such a method may be implemented for the kinetic analysis of any kind of solid–gas reactions in high-temperature solar reactors.

CO2 and H2O reduction by solar thermochemical looping using SnO2/SnO redox reactions: Thermogravimetric analysis

The thermochemical dissociation of CO2 and H2O from reactive SnO nanopowders is studied via thermogravimetry analysis. SnO is first produced by solar thermal dissociation of SnO2 using concentrated solar radiation as the high-temperature energy source. The process targets the production of CO and H2 in separate reactions using SnO as the oxygen carrier and the syngas can be further processed to various synthetic liquid fuels. The global process thus converts and upgrades H2O and captured CO2 feedstock into solar chemical fuels from high-temperature solar heat only, since the intermediate oxide is not consumed but recycled in the overall process. The objective of the study was the kinetic characterization of the H2O and CO2 reduction reactions using reactive SnO nanopowders synthesized in a high-temperature solar chemical reactor. SnO conversion up to 88% was measured during H2O reduction at 973 K and an activation energy of 51 ± 7 kJ/mol was identified in the temperature range of 798-923 K. Regarding CO2 reduction, a higher temperature was required to reach similar SnO conversion (88% at 1073 K) and the activation energy was found to be 88 ± 7 kJ/mol in the range of 973-1173 K with a CO2 reaction order of 0.96. The SnO conversion and the reaction rate were improved when increasing the temperature or the reacting gas mole fraction. Using active SnO nanopowders thus allowed for efficient and rapid fuel production kinetics from H2O and CO2.

Thermogravimetry Analysis of CO2 and H2O Reduction from Solar Nanosized Zn Powder for Thermochemical Fuel Production

This study addresses the thermochemical production of CO and H2 as high-value solar fuels from CO2 and H2O using reactive Zn nanoparticles. A two-step thermochemical cycle was considered: Zn-rich nanopowder was first synthesized from solar thermal ZnO dissociation in a high-temperature solar chemical reactor and the reduced material was then used as an oxygen carrier during the CO2 and H2O reduction reactions. The kinetics of CO2 and H2O reduction was investigated by thermogravimetry to demonstrate that the solar-produced nanoparticles react efficiently with CO2 and H2O. Zn started to react from 513 K and almost complete Zn conversion (reaction extent over 95%) was achieved at 633–773 K in less than 5 min, thus confirming that the active Zn-rich nanopowder exhibits rapid fuel production kinetics during H2O and CO2 dissociation. The reaction mechanism was best described by a nucleation and growth model with an activation energy of 43 kJ/mol and an oxidant order of 0.8. The high reactivity of zinc was attri...