Solar Receiver-reactor Research Articles

Egg-tray-inspired concave foam structure on pore-scale space radiation regulation for enhancing photo-thermal-chemical synergistic conversion

Solar-to-fuel is an approach of converting concentrated solar high-temperature heat radiation to high-value chemical fuel, providing sustainable means for large-scale solar energy storage. However, the inefficient space radiation regulation and unclear photo-thermal-chemical multiphysics synergy limit solar to fuel conversion. To effectively improve photo-thermal-chemical conversion, here, we propose a novel idea of using an egg-tray-inspired concave structure in foam solar receiver-reactors for pore-scale space radiation regulation. The multiphysics field coupling model is accurately constructed to truly describe the complex radiation energy conversion process. Experimental and numerical results illustrate that, the proposed egg-tray-inspired concave structure can achieve the better radiation absorption and transmission, multi-field synergy and thermochemical conversion. The solar radiation absorption capacity can be increased by 7.05 %. The improvements reach a maximum efficiency of 3.17 % for photo-thermal conversion and 9.77 % for photo-chemical conversion. The excellent synergistic conversion of solar-to-fuel opens a new pathway towards accelerating energy transition and upgrading.

Exergy-based control strategy design and dynamic performance enhancement for parabolic trough solar receiver-reactor of methanol decomposition reaction

The parabolic trough solar receiver-reactors of methanol decomposition reaction (PTSRR-MDR) enable efficient hydrogen production with solar energy at users’ end. Solar fluctuations affect the solar-to-chemical efficiency, hydrogen yield and system stability, indicating the necessity for an appropriate control strategy. In this study, dynamic and thermodynamic models of PTSRR-MDR with Cu/ZnO/Al2O3 as catalyst were developed. Results of thermodynamic analysis show that an optimal flow rate exists for methanol to achieve the maximum solar-to-chemical exergy efficiency of the PTSRR-MDR. The temperature increases sharply and exceeds the catalyst sintering temperature when the methanol flow rate decreases under its optimal value. Then, control objectives to achieve the maximum efficiency are obtained with a temperature margin of 3 °C to guarantee the PTSRR-MDR safety. Control strategies based on Dynamic Matrix Control (DMC), Forward-Feedback Control (FFC) and Ramp Control (RC) were evaluated under dynamic simulations. Results show that strategies based on DMC, FFC, and RC increase the solar-to-chemical exergy efficiency from 14.76% to 16.31%, 16.28%, and 15.65%, respectively. The Integral Squared Error (ISE) of methanol conversion rate under three methods are 1.46, 0.32 and 5.28, respectively, indicating that strategy based on FFC is considered most suitable for PTSRR-MDR operation control.

Numerical study on novel parabolic trough solar receiver-reactors with double-channel structure catalyst particle packed beds by developing actual three-dimensional catalyst porosity distributions

Flow channel structure and operation strategy play important role in fixed packed bed based parabolic trough solar receiver-reactors (PTSRRs) for efficient hydrogen production. A horizontal separated double-channel structure with the countercurrent control strategy (H-DCS-CCS) and a vertical separated double-channel structure with the flow matching strategy (V-DCS-FMS) were proposed for better coupling of multiple physical fields in PTSRRs. A three-dimensional comprehensive numerical model was developed to simulate the complex optical-thermal-chemical process and real spatial pore structure characteristics of novel PTSRRs, based on a proposed coupling calculation procedure of actual three-dimensional catalyst porosity distributions. After validation, the effect mechanism of novel double-channel structures and operation strategies were further investigated. It was revealed that the H-DCS-CCS can significantly reduce the PTSRR maximum temperature, increasing the upper limit of the methanol conversion rate by 7.15%. The V-DCS-FMS can effectively improve the temperature uniformity and the reaction performance within tuned flow rate ratio ranges. This proposed novel concept could provide guidance for similar solar-driven thermochemical hydrogen production systems.

Comprehensive study on parabolic trough solar receiver-reactors via a novel efficient optical-thermal-chemical model of catalyst packed bed characteristics

The catalyst packed bed structure plays an important role in the promising solar-driven catalyst packed bed based thermochemical hydrogen production systems. However, corresponding accurate yet efficient numerical methods for characterizing and optimizing the catalyst packed bed structure as well as the whole complex solar-driven thermochemical process is still urgently needed. In this paper, a novel three-dimensional comprehensive model is proposed for the hydrogen production of methanol steam reforming reaction (MSRR) in parabolic trough solar receiver-reactors (PTSRR). A relatively realistic porosity distribution obtained by the discrete element method was combined with the optical-thermal-chemical coupling model. The proposed model was validated, proved to improve the accuracy of numerical predictions in a more efficient way. Moreover, it was effectively applied to tune the overall energy flow of the complex optical-thermal-chemical process of PTSRR-MSRRs for better performance, by optimizing the catalyst packed bed structure in aspects of catalyst sizes and packing methods. The results revealed that single packed beds of larger catalyst particles show better performance within the selected catalyst size range. The radial layered packing method of larger particle-to-particle diameter ratios can bring higher energy conversion efficiency and lower flow resistance, as compared to the single packing method and fully mixed packing method. This study could provide an efficient numerical modelling method and significant guidance for other similar solar-driven thermochemical applications of catalyst packed beds.

Study on solar-driven methanol steam reforming process in parabolic trough solar receiver-reactors by developing an optical-thermal-chemical model of realistic porosity distributions

The catalyst particle packing characteristics have a significant impact on improving the comprehensive energy conversion performance and economic benefits of sustainable solar-driven thermochemical hydrogen production systems. However, corresponding accurate and efficient numerical research tools or methods still need to be developed. In this paper, a three-dimensional comprehensive optical-thermal-chemical coupling model with catalyst particle packing characteristics is proposed for the parabolic trough solar receiver-reactor (PTSRR) of methanol steam reforming reaction (MSRR) for hydrogen production. This model is developed by combining a Monte Carlo ray tracing optical model, a computational fluid dynamics model, a MSRR comprehensive kinetic model with a Blender rigid body packing model. After validation, it was found from comparisons with previous studies that this model can represent relatively realistic catalyst porosity distributions of packed-bed reactors at a very low computational cost. Then, this model was applied to obtain the porosity of different PTSRR-MSRRs and optimize the catalyst size and shape, to achieve better comprehensive performance as well as economic benefits of higher overall efficiency and catalyst utilization efficiency. The results reveal that the PTSRR-MSRRs filled with cylinders and Raschig rings (R-PTSRR) can achieve similar high methanol conversion rate, while the R-PTSRR has more advantages with its lower average resistance coefficient and CO selectivity. After weighing the methanol conversion rate, the overall efficiency and the catalyst utilization efficiency, the optimum R-PTSRR is highly recommended. This study provides a useful option for rapid comprehensive analysis and optimization of similar solar-driven thermochemical conversion processes on catalyst particle packed beds.

A Conceptual Catalytic Receiver Reactor for Solar Thermal Sulfuric Acid Decomposition

The highest‐temperature step in iodine–sulfur and hybrid–sulfur thermochemical cycles for hydrogen generation is the sulfuric acid decomposition reaction. To efficiently utilize solar energy directly to operate this step, the development of a catalytic solar receiver reactor is essential. A cavity‐type reactor coupled to a solar dish and a numerical analysis of the reactor predicting the reaction conversion as a function of the solar absorption coefficient is presented in this study. The catalytic receiver reactor consists of a double‐walled quartz cylindrical tube to form the cavity and a flat quartz plate window for entry of the concentrated solar radiation. Two catalysts, Fe1.8Cr0.2O3 and Fe2O3/SiO2, are tested in the solar catalytic receiver reactor and SO2 yields of ≈40% and 38% are observed, respectively. Numerical analysis of the reactor is performed and a reaction conversion–absorption coefficient correlation is established. For the catalytic packed bed assuming absorption coefficient of 0.65, a steady‐state temperature of 1212 K is achieved, accomplishing an approximate theoretical efficiency of ≈56%. The numerical analysis suggests that by utilizing a material of construction with high absorption coefficient, significantly enhanced sulfuric acid decomposition can be achieved by the cavity‐type solar receiver reactor.

Performance analysis on the parabolic trough solar receiver-reactor of methanol decomposition reaction under off-design conditions and during dynamic processes

Parabolic Trough Solar Receiver-Reactor (PTSRR) of Methanol Decomposition Reaction process (MDR), which can achieve chemical storage and efficient utilization of solar energy, has gained increasing attention recently. To comprehensively study the performance of PTSRR of MDR under off-design conditions and during dynamic processes, a model of PTSRR-MDR is developed and validated. Detailed energy and exergy analysis model are developed to figure out the irreversibility distribution. Results indicate that exergy destructions caused by solar concentrating and thermochemical reaction processes limit the improvement of exergy efficiency, which account 39.32% and 18.32%, respectively, under 800 DNI. When DNI step decreases from 800 to 400 W m−2, the methanol conversion rate decreases from 90.0% to 40.9% in ∼400 s. The solar-to-chemical exergy efficiency increases from 16.39% to 32.80% immediately, then decreases to the lowest value in 30 s, and rises to 11.23%. The efficiency is lower than the stable value transiently because the exergy stored in solid phase is partly destructed when converted to chemical exergy. Then, dynamic performance under DNI step increase is studied. Due to thermal inertia, additional chemical energy and exergy are gained or lost, compared to the ideal process. The results may provide some guidance for further efficient operation control.

System and technoeconomic analysis of solar thermochemical hydrogen production

Hydrogen is a promising energy carrier that can be obtained from various feedstocks using renewable energy sources. Direct solar thermochemical hydrogen (STCH) production by water splitting can utilize the full spectrum of solar radiation and has the potential to achieve high solar energy conversion efficiencies. Currently STCH research areas focus on material discovery. This paper evaluates the performance of various STCH materials in the context of a system platform to assess techno-economic benefits and gaps in the path to STCH scale-up. To analyze the hydrogen production cost, a concentrating solar thermal (CST) system is introduced as a platform for integrating STCH materials and accommodating generalized thermochemical processes. The thermochemical process is based on a two-step STCH cycle using metal oxide that consists of a high temperature step for metal oxide reduction, followed by an oxidation step for water splitting at a lower temperature. A preferred configuration is to have the high temperature step occurring in a directly irradiated solar receiver reactor. To this end, we conceptualized a receiver design and associated solar field layout and investigated STCH operational boundaries, component costs and sensitivity parameters on the $2/kgH2 goal of hydrogen production. The study explored system-related variables and factors associated with scaling up. The CST platform allows more comprehensive studies that encompass aspects of STCH materials and systems such as cost, hydrogen productivity and replacement frequency, alongside other system components like heliostat field, tower, and potential receiver costs.

High performance solar receiver–reactor for hydrogen generation

This paper reports on the numerical analysis of a volumetric solar receiver-reactor for hydrogen production, using the 2-step reduction–oxidation cycle. A detailed parametric sweep covering hundreds of various parameter combinations is performed for a large solar reactor, using a transient physical model. We generate performance maps which are currently cost prohibitive via experimental or high–fidelity simulation studies. The following performance metrics are evaluated: solar to fuel efficiency, hydrogen yield, conversion extent and specific hydrogen yield. We show that the relations between the different performance metrics are complex, leading to different optimal points depending on the metric pursued. The daily hydrogen yield for a single reactor varied between 0.89 kg for an absorber thickness of 30 mm, and up to 1.04 kg for a 60 mm thick receiver, with solar to fuel efficiency values of 3.84% and 3.81% respectively. For a case with 45 mm thick receiver, an intermediate hydrogen yield of 0.94 kg is calculated, while exhibiting the highest efficiency (4.05%). The efficiency can be further increased to 5.86% by using a simple heat recovery system, and reach an upper limit of 21.16% with a more sophisticated heat recovery method.

Concentrating technologies with reactor integration and effect of process variables on solar assisted pyrolysis: A critical review

Solar pyrolysis shows promise as a technique to generate solar fuels in the context of the future economy besides mitigating emissions. The prior experiments were mainly demonstrated in an indoor environment using a solar simulator while recent studies have been established using natural solar radiation. An integrated solar receiver-reactor is likely to be employed to generate high-temperature for the conversion of feedstocks into valuable products. Undoubtedly, parabolic trough and parabolic dish with the integration of fixed bed batch reactor are the two-common type of concentrators that has been widely used by the researcher. The effectiveness of a solar pyrolysis process depends not only on the reactor configuration but also on the process variables. Temperature is the most crucial factor that dominant product yields. The current literature is scattered, vague, and difficult to understand the configuration of the system and operating parameters that affect the yield of solar products. In order to carry out an efficient solar pyrolysis reaction, the latest design and fabrication of different modes of experimental setup is presented. Moreover, operating factors that dominate the product quantity are elaborately discussed. A critical discussion, some challenges, and its probable solutions during scale-up of a pyrolysis system are also delivered.

Thermo-chemical water splitting: Selection of priority reversible redox reactions by multi-attribute decision making

Hydrogen is a top chemical and potential fuel. Its sustainable production from biomass or water splitting gains importance. Whereas sole thermal water splitting requires too high temperatures, thermo-chemical water splitting cycles offer a solution at moderate temperatures. Such cycles were investigated over the past decades, mostly by small-scale experiments and mainly to prove their concept without judgment of their practical, economic, environmental and cyclic performance. To facilitate the decision making and to guide future priority research, these multiple aspects can be combined in a global screening system that applies the improved Analytic Hierarchy Process (AHP) and grey relational TOPSIS, together with the use of linear and non-linear combination weighing. The assessment is quantitative and comprehensive, emphasizing the complex relationship between energy efficiency, conversion, recyclability, economy and environmental quality. The total index combines systematics and flexibility through its multi-objective and multi-level nature. The index helps users, system manufacturers, researchers and governments to select the most appropriate future schemes.Very high temperature reactions of e.g. metal-metal oxides, metal-metal hydroxides, perovskites or doped ceria were not included. At the required temperatures, concentrated solar energy is the evident heat source, although applicable temperatures should meet the mechanical and thermal constraints of the solar receiver-reactor construction materials. The experimental set-up that will be used for subsequent pilot-scale solar testing is briefly described. As a result of the multi-attribute assessment, 4 out of 24 oxidation/reduction reactions are selected for further laboratory or preferably pilot-scale application, including the MnFe2O4, MnO/NaMnO2 and ZnO/Fe3O4/ZnFe2O4 redox reactions.

Optical analysis of a solar thermochemical system with a rotating tower reflector and a receiver-reactor array.

We propose a concept of a rotating tower reflector (TR) in a beam-down optical system to alternate concentrated solar irradiation of an array of solar receiver-reactors, realizing multi-step solar thermochemical redox cycles. Optical and radiative characteristics of the proposed system are explored analytically and numerically by Monte-Carlo ray-tracing simulations. We study the effects of the system geometrical and optical parameters on the optical and radiative performance. TR axis is required to be tilted for accommodating the receiver-reactor array, resulting in reduced optical efficiency. We demonstrate that the annual optical efficiency of a baseline system with the receiver-reactor located south of the tower decreases from 46% to 37% for the axis tilt angle of TR increasing from 2° to 20°. The optical analysis conducted in this study provides a general formulation to enable predictions of required gain of thermal-to-chemical efficiency of the receiver-reactor array for obtaining improved overall solar-to-chemical efficiency of the solar thermochemical plant.

Parametric investigation of a volumetric solar receiver-reactor

Hydrogen production by solar-driven 2-step reduction–oxidation cycles has been successfully demonstrated in recent years. While the demonstrated efficiencies were quite low (up to 5.25% solar-to-fuel efficiency), there is a large potential for much higher efficiencies. This paper presents a detailed parametric investigation of a large scale (>100 kW) volumetric solar receiver-reactor, performed using a finite volume method model. The reactor temperature profile and extent of reduction are investigated by evaluating the effects of heat recovery, sweep gas mass flow, radiation flux and porosity. The current reactor concept is shown to have a temperature gradient across the absorber of 500–700 K, leading to a mean ceria reduction extent of 0.004–0.012, thus limiting the amount of hydrogen that can be generated to the order of several milligrams per cycle or less. It is also shown that heat recovery can reduce the temperature gradient across the absorber to 350 K, thus increasing the hydrogen generation significantly, up to four orders of magnitude higher than with no heat recovery (up to 5.25 g/cycle). The solar heat flux on the receiver can also significantly increase the hydrogen production and reduce the reduction step duration. Thus, the optimization of both design and operation of large volumetric reactors can increase the hydrogen generation rate significantly.

Methanol production using hydrogen from concentrated solar energy

Concentrated solar thermal technology is considered a very promising renewable energy technology due to its capability of producing heat and electricity and of its straightforward coupling to thermal storage devices. Conventionally, this approach is mostly used for power generation. When coupled with the right conversion process, it can be also used to produce methanol. Indeed methanol is a good alternative fuel for high compression ratio engines. Its high burning velocity and the large expansion occurring during combustion leads to higher efficiency compared to operation with conventional fuels. This study is focused on the system level modeling of methanol production using hydrogen and carbon monoxide produced with cerium oxide solar thermochemical cycle which is expected to be CO2 free. A techno-economic assessment of the overall process is done for the first time. The thermochemical redox cycle is operated in a solar receiver-reactor with concentrated solar heat to produce hydrogen and carbon monoxide as the main constituents of synthesis gas. Afterwards, the synthesis gas is turned into methanol whereas the methanol production process is CO2 free. The production pathway was modeled and simulations were carried out using process simulation software for MW-scale methanol production plant. The methanol production from synthesis gas utilizes plug-flow reactor. Optimum parameters of reactors are calculated. The solar methanol production plant is designed for the location Almeria, Spain. To assess the plant, economic analysis has been carried out. The results of the simulation show that it is possible to produce 27.81 million liter methanol with a 350 MWth solar tower plant. It is found out that to operate this plant at base case scenario, 880685 m2 of mirror's facets are needed with a solar tower height of 220 m. In this scenario a production cost of 1.14 €/l Methanol is predicted.

Numerical study on a novel parabolic trough solar receiver-reactor and a new control strategy for continuous and efficient hydrogen production

In this paper, a novel parabolic trough solar receiver-reactor is proposed for continuous and efficient hydrogen production via the methanol-steam reforming reaction. With a concentric through-type tube introduced for thermal energy storage, this novel system canbe effectively applied for better solar thermochemical energy conversion and management. The proposed novel system and the corresponding original system, as well as direct/indirect control strategies and parameter optimizations, were then fully investigated. This was numerically carried out by a proposed three-dimensional comprehensive model based on the finite volume method, combined with the Monte Carlo ray-tracing method and the comprehensive kinetic model of the methanol-steam reforming reaction. It is revealed that the proposed novel system has much better comprehensive characteristics and performance than that of the corresponding original system. These previously incompatible requirements, both an affordable temperature rise per unitreceiver-reactor length and a nearly complete methanol conversion rate, can be achieved simultaneously in this novel system. It is also found that the previously sensitive process of the methanol-steam reforming reaction can be controlled separately or jointly, by adjusting more control variables introduced in the novel system. Moreover, this novel system could also have great potential to be improved, by tuning corresponding key operating parameters such as the inlet temperature, the flowmodel and the concentric tube geometry. The energy distribution of the collected solar radiation and working temperature characteristics could also be further controlled or optimized. It could provide significant guidance for similar solar-driven thermochemical applications for continuous and efficient hydrogen production.

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).

Comprehensive study on novel parabolic trough solar receiver-reactors of gradually-varied porosity catalyst beds for hydrogen production

In this paper, novel parabolic trough solar receiver-reactors (PTSRR) of gradually-varied porosity catalyst beds are proposed for cost-efficient hydrogen production. A three-dimensional comprehensive model was developed for PTSRRs of the methanol-steam reforming reaction (MSRR) in porous Cu/ZnO/Al2O3 catalyst packed beds, by combining the finite volume method (FVM) and the Monte Carlo ray-tracing (MCRT) method with a MSRR comprehensive kinetic model. The validated model was applied to investigate different novel PTSRRs proposed, as well as the effects and mechanisms of different non-uniform porosity distributions, taking the methanol flow rate, the catalyst temperature limitation and the solar flux nonuniformity into account. It is revealed that the catalyst particles packed in the top part of the traditional absorber-reactor may not only have not fully played their roles but also influenced the multicomponent gas mixture fluid flow and heat transfer greatly. The non-uniform porosity catalyst bed gradually-increased from the bottom to the top better matches previously non-uniform temperature distributions and thus makes PTSRRs operated more safely, more efficiently yet lower cost of locally less packed catalyst mass. This comprehensive model and method offers a useful option of high potential for comprehensive analyses of the whole photo-thermal-chemical conversion process for different PTSRRs and realistic conditions.

Three-dimensional numerical study on a novel parabolic trough solar receiver-reactor of a locally-installed Kenics static mixer for efficient hydrogen production

In this paper, a novel parabolic trough solar receiver-reactor (PTSRR) system of a locally-installed Kenics static mixer (KSM) is proposed for efficient solar thermal hydrogen production. A three-dimensional comprehensive model was established for PTSRRs of the methanol-steam reforming reaction (MSRR) for hydrogen production, by combining the Finite Volume Method and the Monte Carlo ray-tracing method with a MSRR comprehensive kinetic model. The validated model was preliminarily applied to study the effects and mechanisms of the concentrated solar flux nonuniformity and the locally-installed KSM on PTSRR photo-thermal-chemical comprehensive characteristics and performance, taking the methanol flow rate and the catalyst sintering temperature limitation into account. With a preliminary optimization on the concentrated solar flux nonuniformity, the optical efficiency and the solar flux nonuniformity are improved by 6.58% and 30.42% respectively. It is further revealed that these PTSRRs of better concentrated solar flux density nonuniformity also have better thermal-chemical comprehensive characteristics and performance. Novel PTSRRs of the locally-installed KSM have better comprehensive characteristics and performance than corresponding original PTSRRs or even optimized PTSRRs, with a maximum increase in the methanol conversion rate of 6.92%. It thus will operate more safely and more efficiently, by the cost of a little more pump power to overcome corresponding larger flow resistance caused by the locally-installed KSM. From the mechanism, this kind of novel PTSRR of a locally-installed KSM provides a useful option of high potential for improving uniformities of a series of key field variables in the whole photo-thermal-chemical conversion process, and thus improves the comprehensive characteristics and performance of PTSRRs.

A comprehensive study on parabolic trough solar receiver-reactors of methanol-steam reforming reaction for hydrogen production

In this paper, a three-dimensional comprehensive model is firstly proposed for Parabolic Trough Solar Receiver-Reactors (PTSRR) of the Methanol-Steam Reforming Reaction process (MSRR) for hydrogen production. This PTSRR-MSRR comprehensive model is established by combining a comprehensive kinetic model of MSRR, a validated Monte Carlo Ray-Tracing (MCRT) optical model with a Computational Fluid Dynamics (CFD) model based on the Finite Volume Method (FVM), as well as useful comprehensive evaluation indicators. It is capable of comprehensively simulating and evaluating the whole complex photo-thermal-chemical conversion process of the entire PTSRR system, including the concentration, collection and conversion of photon energy, coupled heat transfers, fluid dynamics, multicomponent transports and methanol-steam reforming reactions. After validation, this comprehensive model was successfully used to determine the comprehensive characteristics and performance of different PTSRRs and realistic conditions. The effects and mechanisms of the solar time, the reflector geometric parameters, the inlet methanol molar flow rate, the reaction temperature limitation and the nonuniformity of the concentrated solar flux density distribution were discussed in detail. It is revealed that the reaction temperature limitation that should be smaller than the sintering temperature of Cu/ZnO/Al2O3 catalyst particles may only appear locally, which is mainly caused by the nonuniformity of the concentrated solar flux density distribution and the corresponding local peak solar flux density. For the mechanism of this kind of temperature limitation, different control strategies and optimizations were examined. Better comprehensive characteristics and performance of PTSRRs can be obtained, by making a reasonable tradeoff between the optical efficiency, the solar flux nonuniformity and the reflector surface curvature characteristics.

Solar–gliding arc plasma reactor for carbon dioxide decomposition: Design and characterization

The conversion of low-value feedstock such as carbon dioxide (CO2) into higher-value products using renewable energy, particularly solar, can help fulfill the increasing need for fuels and chemicals while mitigating environmental emissions. A direct solar receiver-reactor fitted with a gliding arc (glidarc) electrical discharge for potentially greater efficiency and continuous operation solar thermochemical synthesis is presented. The nonequilibrium plasma inside the reactor chamber leads to increased solar energy absorption by the gas-phase feedstock, potentially enhancing chemical conversion. Moreover, the reliance on electrical energy to sustain the plasma allows compensating for fluctuations in the solar radiation input. Two solar-glidarc reactor configurations are investigated and evaluated for the decomposition of CO2 at atmospheric pressure conditions, namely: axi-radial (AXR) and reverse-vortex (RVX) flow. The former provides greater control of residence time but presents limited solar-plasma interaction; whereas the latter allows for greater interaction, but requires higher flow rates to confine the plasma, lowering the residence time. Flow paths and residence times are evaluated via Computational Fluid Dynamics (CFD) models used to guide reactor design and operation. Evaluation of the plasma volume at different reactor orientations, aimed to mimic in-field operation, show that the AXR configuration leads to a larger plasma volume compared to that by the RVX design. Net-absorption tests, aimed to assess the extent of solar-plasma interaction, showed up to 18% net-absorption of solar radiation for the RVX configuration and 7% for the AXR one, compared to 0% in the absence of plasma. The AXR configuration, despite its lower absorption of solar energy, leads to greater CO2 homogeneous gas-phase decomposition (i.e. in the absence of any catalyst), of up to 4.5%, mainly due to its flexibility in operating with lower residence times. The results indicate solar-plasma direct-receiver reactors provide a compelling approach to solar thermochemical synthesis processes.