Solar Reforming Research Articles

Floating Carbon Nitride Composites for Practical Solar Reforming of Pre-Treated Wastes to Hydrogen Gas.

Solar reforming (SR) is a promising green-energy technology that can use sunlight to mitigate biomass and plastic waste while producing hydrogen gas at ambient pressure and temperature. However, practical challenges, including photocatalyst lifetime, recyclability, and low production rates in turbid waste suspensions, limit SR's industrial potential. By immobilizing SR catalyst materials (carbon nitride/platinum; CNx |Pt and carbon nitride/nickel phosphide; CNx |Ni2 P) on hollow glass microspheres (HGM), which act as floating supports enabling practical composite recycling, such limitations can be overcome. Substrates derived from plastic and biomass, including poly(ethylene terephthalate) (PET) and cellulose, are reformed by floating SR composites, which are reused for up to ten consecutive cycles under realistic, vertical simulated solar irradiation (AM1.5G), reaching activities of 1333 ± 240 µmolH2 m-2 h-1 on pre-treated PET. Floating SR composites are also advantageous in realistic waste where turbidity prevents light absorption by non-floating catalyst powders, achieving 338.1 ± 1.1µmolH2 m-2 h-1 using floating CNx versus non-detectable H2 production with non-floating CNx and a pre-treated PET bottle as substrate. Low Pt loadings (0.033 ± 0.0013% m/m) demonstrate consistent performance and recyclability, allowing efficient use of precious metals for SR hydrogen production from waste substrates at large areal scale (217 cm2 ), taking an important step toward practical SR implementation.

Demonstration and analysis of a steam reforming process driven with solar heat using molten salts as heat transfer fluid

Solar reforming of biogas or biomethane represents an example hydrogen production from the combination of renewable sources such as biomass and solar energy. Thanks to its relatively low-cost and flexibility, solar-reforming can represent a complementary source of hydrogen where/when the demand exceeds the green hydrogen availability from water electrolysis powered by PV or wind. Molten salts can be used as heat transfer fluid and heat storage medium in solar-driven steam reforming. The main units of the process have been developed at the pilot scale and experimentally tested in a molten salt experimental loop at ENEA-Casaccia research center: a molten salt heater and a molten salt membrane reformer. After experimental validation, techno-economic studies have been carried out to assess the solar reforming technology on commercial scale and exploitation opportunities have been analysed.

Exergy and exergoeconomic analyses of novel high-temperature proton exchange membrane fuel cell based combined cogeneration cycles, including methanol steam reformer integrated with catalytic combustor or parabolic trough solar collector

Based on high-temperature proton exchange membrane fuel cell, two new configurations of cogeneration systems including a methanol steam reformer and a Kalina cycle is presented to produce electrical power and hot water. In the first configuration, the heat required for methanol steam reforming reaction is provided by the integration of the reformer with a catalytic combustor while in the second configuration, a coupled parabolic trough solar collector with a heat storage tank is used. The performance of proposed cycles is investigated from the viewpoints of exergy, economics and environmental impact through a detailed parametric analysis. It is observed that under a basic operating condition, the overall exergy efficiency of the first configuration is 2.58% higher than that of the second one. The exergy destruction in the solar reformer utilized in the second configuration is 18% less than that in the reformer coupled with a catalytic combustor as used in the first configuration. Also, for different operating conditions, the second configuration shows a comparatively better exergoeconomic performance. Under the basic operating condition, the total unit product cost, and the specific CO2 emission for the second configuration are calculated as 23.95%, and 16.33% lower than those for the first configuration, respectively.

Cover Picture: Solar Reforming of Biomass with Homogeneous Carbon Dots (Angew. Chem. Int. Ed. 41/2020)

Cover Picture: Solar Reforming of Biomass with Homogeneous Carbon Dots (Angew. Chem. Int. Ed. 41/2020)

Solar Reforming of Biomass with Homogeneous Carbon Dots

AbstractA sunlight‐powered process is reported that employs carbon dots (CDs) as light absorbers for the conversion of lignocellulose into sustainable H2 fuel and organics. This photocatalytic system operates in pure and untreated sea water at benign pH (2–8) and ambient temperature and pressure. The CDs can be produced in a scalable synthesis directly from biomass itself and their solubility allows for good interactions with the insoluble biomass substrates. They also display excellent photophysical properties with a high fraction of long‐lived charge carriers and the availability of a reductive and an oxidative quenching pathway. The presented CD‐based biomass photoconversion system opens new avenues for sustainable, practical, and renewable fuel production through biomass valorization.

Solar Reforming of Biomass with Homogeneous Carbon Dots.

A sunlight‐powered process is reported that employs carbon dots (CDs) as light absorbers for the conversion of lignocellulose into sustainable H2 fuel and organics. This photocatalytic system operates in pure and untreated sea water at benign pH (2–8) and ambient temperature and pressure. The CDs can be produced in a scalable synthesis directly from biomass itself and their solubility allows for good interactions with the insoluble biomass substrates. They also display excellent photophysical properties with a high fraction of long‐lived charge carriers and the availability of a reductive and an oxidative quenching pathway. The presented CD‐based biomass photoconversion system opens new avenues for sustainable, practical, and renewable fuel production through biomass valorization.

Thermodynamic analysis of fuel cell combined cooling heating and power system integrated with solar reforming of natural gas

Hybrid natural gas combined cooling, heating, and power (CCHP) systems integrated with solar technologies offer the efficient use of distributed energy resources for reducing the use of fossil fuels and greenhouse gas emissions. This paper proposes a novel CCHP system, using the phosphoric acid fuel cell (PAFC) as the prime mover, integrated with the natural gas reforming with solar energy assistance. Their respective thermodynamic models are constructed for simulation of the system thermodynamic performance. The simulation results demonstrate that the energy efficiencies of the hybrid system with solar energy assistance are 55.12% for the heater mode and 66.77% for the chiller mode, while the exergy efficiencies are 32.87% and 31.59%, respectively. Similarly, when solar energy is not available, its energy efficiencies are 59.24% and 69.18%, while its exergy efficiencies are 40.09% and 39.01%, respectively. In the PAFC–CCHP hybrid system, the exergy efficiencies are key components in the overall efficiency, and the efficiencies with and without solar energy are 29.34% and 36.95%, respectively. Solar energy and exergy share is employed to analyze the solar energy contribution, and they are 36.1% and 35.6%, respectively. Meanwhile, the parametric analysis is also carried out to evaluate the effects of key parameters on the performance. The results show that increasing the reforming temperature, influenced by solar energy, improves the natural gas conversion and boosts the hydrogen concentration of the syngas fed into the PAFC, which increases the overall exergy efficiency. However, the effect of the reforming temperature is reduced when the reforming temperature is higher than 1073.15 K.

Efficiency assessment of solar redox reforming in comparison to conventional reforming

Solar redox reforming is a process that uses solar radiation to drive the production of syngas from natural gas. This approach caught attention in recent years, because of substantially lower reduction temperatures compared to other redox cycles. However, a detailed and profound comparison to conventional solar reforming has yet to be performed. We investigate a two-step redox cycle with iron oxide and ceria as candidates for redox materials. Process simulations were performed to study both steam and dry methane reforming. Conventional solar reforming of methane without a redox cycle, i.e. on an established catalyst was used as reference. We found the highest efficiency of a redox cycle to be that of steam methane reforming with iron oxide. Here the solar-to-fuel efficiency is 43.5% at an oxidation temperature of 873 K, a reduction temperature of 1190 K, a pressure of 3 MPa and a solar heat flux of 1000 kW/m2. In terms of efficiency, this process appears to be competitive with the reference process. In addition, production of high purity H2 or CO is a benefit, which redox reforming has over the conventional approach.

Ni/CeO2 Structured Catalysts for Solar Reforming of Spent Solvents

Spent solvents of the packaging industry are disposed of, thus representing economic, safety, and environmental issues. Steam reforming of these solvent streams can be an alternative, allowing their valorization to syngas. In this work, ceria supported nickel catalysts were deposed onto silicon carbide (SiC) honeycomb monoliths; these structured catalysts can be potentially used in solar steam reforming. Catalysts were characterized by SEM/EDS and tested in a lab-scale rig under conventional heating. Two spent solvent streams, coming from the distillation plant of the packaging industry Icimendue, were used as fuels. Catalytic tests have been carried out by changing the steam/carbon ratio, oxygen/carbon ratio, operating pressure, and fuel. The effect of the Ni content and the type of ceria were also studied. The best performances were obtained at low Ni content and by using micrometric rather than nanometric ceria as support. The structured catalysts showed good coking resistance, especially at H2O/C > 2, with oxygen addition furnishing a marginal improvement. On the contrary, oxygen feeding reduced the gas yield due to the formation of by-products being less reactive in reforming reactions. Performing the reforming process at high pressure the gas yield increased due to faster kinetics (higher reactants concentrations), higher contact times (slower flow rates), and process intensification. These results suggest that the proposed structured catalysts could be successfully applied in the solar reforming of spent solvents.

(Solar) Mixed Reforming of Methane: Potential and Limits in Utilizing CO2 as Feedstock for Syngas Production—A Thermodynamic Analysis

The reforming of natural gas with steam and CO2 is commonly referred to as mixed reforming and considered a promising route to utilize CO2 in the production of synthetic fuels and base chemicals such as methanol. In the present study, the mixed reforming reaction is assessed regarding its potential to effectively utilize CO2 in such processes based on simple thermodynamic models. Requirements for the mixed reforming reactions based on process considerations are defined. These are the avoidance of carbon formation in the reactor, high conversion of the valuable inlet streams CH4 and CO2 as well as a suitable syngas composition for subsequent synthesis. The syngas composition is evaluated based on the module M = ( z H 2 − z CO 2 ) / ( z CO 2 + z CO ) , which should assume a value close to 2. A large number of different configurations regarding CO2/H2O/CH4 at the reactor inlet, operating pressure and outlet temperature are simulated and evaluated according to the defined requirements. The results show that the actual potential of the mixed reforming reaction to utilize CO2 as feedstock for fuels and methanol is limited to approximately 0.35 CO2/CH4, which is significantly lower than suggested in literature. At 900 °C and 7 bar at the reactor outlet, which is seen suitable for solar reforming, a ratio of H2O/CH4 of 1.4 can be set and the resulting value of M is 1.92 (CO2/CO/H2 = 0.07/0.4/1).

ソーラー改質を伴うバイオエタノールPEM燃料電池による分散エネルギーシステムの開発 : 第1報-基本性能の見積もり

ソーラー改質を伴うバイオエタノールPEM燃料電池による分散エネルギーシステムの開発 : 第1報-基本性能の見積もり

Dynamic simulation and optimal heat management policy of a coupled solar reforming–heat storage process

This work is a first simplified approach on the exploitation of “direct” solar heat during on-sun operation, and stored solar-heat through thermochemical energy storage involving redox pair cycles during off-sun operation, for the production of solar hydrogen using concentrated solar energy. The coupling of the processes in a compact solar reforming–thermochemical heat storage system is conducted in terms of a lumped dynamic model; for the determination of the syngas composition in the reforming unit, thermodynamic equilibrium is assumed, while the required heat to facilitate the endothermic reforming reactions is provided by either solar heat (on-sun operation), or a combination of stored energy and an optimal linear profile of external heat provision (off-sun operation). The optimal heat management policy for the reduction or the oxidation step (during the solar heat storage and release process) ensures a steady H2 molar fraction for most of the operating time. It is revealed that the coupled scheme suggested is an in-principle viable option for sustainable H2 production, since reforming needs are entirely complemented by solar heat also supplying the required energy input for the storage unit, which in turn may provide almost 25% of the overall reforming energy needs under off-sun operation.

4-7 ソーラー改質用金属発泡体触媒デバイスのCO_2改質に関する速度論解析((2)太陽熱・未利用熱,Session 4 新エネルギー,研究発表(口頭発表))

4-7 ソーラー改質用金属発泡体触媒デバイスのCO_2改質に関する速度論解析((2)太陽熱・未利用熱,Session 4 新エネルギー,研究発表(口頭発表))

Model-based analysis of CO2 revalorization for di-methyl ether synthesis driven by solar catalytic reforming

The application of solar energy is investigated for the synthesis of di-methyl ether (DME) in a solar irradiated dry methane reformer (DMR). Solar radiations are concentrated onto a receiver and distributed to the reaction zone to provide necessary energy for syngas (CO and H2) generation. In order to maintain a H2/CO molar ratio of ‘1’, as required in DME synthesis, the produced syngas is processed via two alternative routes: solar reformer coupled in parallel with a non-solar reformer (SoR-NSoR) and solar reformer integrated with a water-gas shift reactor (SoR-WGS). It is found that steam methane reforming (SMR) is the most suitable methodology when coupled with a solar reformer due to high H2 content in the SMR syngas. Further performance analysis is conducted by simulating three days of operation under different insolation levels (high, medium and low irradiations). The simulation results showed that the SoR-WGS configuration produces the highest improvements of 18.7%, 32.2% and 20% in terms of methane, energy and CO2 emission intensity respectively. This enhanced process performance originates from the exothermic nature of the WGS process which helps in controlling the overall syngas composition, whereas the SoR-NSoR requires fossil based thermal energy to drive the NSoR process to similar control targets. This promising improvement of all metrics in SoR-WGS may stimulate in-depth techno-economic feasibility of this unique solar integration for DME and other synthetic fuels production.

Sensitivity analysis for a solar steam redox reformer

Interest in using renewable energy sources like solar energy for power production has grown because of the concern over CO2 emissions. One method of implementing solar energy for large scale power production is using hybrid solar fossil fuel power generation systems. Solar reforming has been shown to be a promising integration method with steam redox reforming to raise the chemical energy of the fuel. In this article, a sensitivity analysis for a solar steam redox reformer (proposed in Sheu and Ghoniem, 2016) with respect to different performance metrics is presented. Results show that the channel cross section, inlet gas temperature, and reformer pressure have the largest effect on the reactor performance. Furthermore, the analysis shows that the reduction kinetics can have a large effect on the calculated reactor performance and should be considered carefully. A reactor sizing analysis was also performed and results show that complete conversion can be achieved with a reasonable reactor size and that there is a tradeoff between conversion and cost/solar utilization efficiency. Moreover, a strategy for reactor design based on maximizing stand-alone performance as well as integration with a power cycle is discussed.

A solar thermochemical fuel production system integrated with fossil ​fuel heat recuperation

Thermochemical cycling (TC) is a promising means of converting solar energy and storing it in chemical fuels. Isothermal solar TC has the potential of achieving high solar-to-fuel efficiencies contingent on effective gas-phase heat recovery at high temperatures. We propose an approach of simultaneously recovering waste heat and unreacted gas species (e.g. H2O or CO2) downstream the isothermal TC reactor by taking advantage of endothermic reactions of certain fossil fuels (e.g. CH4). Such comprehensive utilization and the syngas produced enable a polygeneration system for simultaneous power and methanol production with the possibility of eliminating the self-generation power plant that is conventionally needed for methanol production. The scheme is proposed based on the type of splitting reaction in isothermal TC, and optimization of the polygeneration system is discussed with solar energy conversion efficiency as the objective. Fossil Fuel Consumption Rate of methanol production is about 22GJ/ton, lower than typical values in current industrial processes. Compared with direct solar reforming or direct combustion of the same amount of fossil fuels, this new approach features lower carbon emission per unit calorific value of fuel obtained due to the incorporation of the isothermal TC upstream.

Receiver reactor concept and model development for a solar steam redox reformer

As concern over the CO2 emissions associated with power production from traditional fossil fuels grows, there has been more interest in using renewable energy sources such as solar energy. However, there are many issues with using solar energy on a large scale including dispatchability and economically viable storage methods. A potential solution to these problems is using a hybrid solar-fossil fuel power generation system. Within such systems, solar reforming has been shown to be a promising integration method with steam redox reforming as an effective reforming process. In this article, a receiver reactor concept for a solar steam redox reformer is presented. The receiver-reactor consists of a dumbbell shape absorber system that has two distinct absorbers. This absorber system setup allows for the switching between reduction and oxidation steps without having to constantly change inlet streams to the reactor and is designed such that the inlet connections do not interfere with the solar window. In addition, at any point in time only one solar absorber is irradiated by the solar energy (during the reduction step). A computational model is developed to assess its performance. Simulations show that the receiver-reactor strongly absorbs the solar radiation and most of the radiative heat transfer occurs in the front half of the reactor. Moreover, results show that higher conductivity absorber materials yield smaller temperature variations not only within the reactor but also with time, and therefore are more suitable for long term reactor operation.

Available online Efficiency potential of indirectly heated solar reforming with different types of solar air receivers

In solar reforming, the heating value of natural gas is increased by utilization of concentrated solar radiation. Hence, it is a process for storing solar energy in a stable and transportable form that also permits further conversion into liquid fuels like methanol. This process has the potential to significantly decrease the natural gas consumption and the associated CO2-emissions of methanol production with only few open questions to be addressed prior to commercialization. In the medium and long term, it has the potential to generate methanol as an environmentally friendly fuel for both transport as well as flexible electricity production in combined cycle gas turbines, when biogas is used as reactant. In a previous study the high potential of indirectly heated solar reforming with solar air receivers was shown; however, the efficiency is limited when using state of the art open volumetric receivers. Therefore, different types of air receivers are implemented into an indirectly heated solar reforming process and the overall efficiency potential is assessed in the present study. The implemented receivers are an open volumetric cavity receiver, a closed volumetric cavity receiver and a tubular cavity receiver. The open volumetric cavity receiver and tubular cavity receiver achieve the best results due to their capability of operating efficiently at temperatures well above 700 °C. For these receivers peak efficiencies up to 29% and 27% respectively are predicted. As the utilization of an open volumetric cavity receiver constitutes an open heat transfer loop, the air return ratio together with air return temperature is identified as a major impact factor for overall efficiency. With an improved air return ratio, annual process efficiency of 18.4% is feasible. Considering its relative technical simplicity, this makes indirectly heated solar reforming a promising technology to efficiently provide renewable energy for methanol production and thereby diversify solar energy utilization.

Development of Cu foam-based Ni catalyst for solar thermal reforming of methane with carbon dioxide

Using solar energy to produce syngas via the endothermic reforming of methane has been extensively investigated at the laboratory- and pilot plant-scales as a promising method of storing solar energy. One of the challenges to scaling up this process in a tubular reformer is to improve the reactor's performance, which is limited by mass and heat transfer issues. High thermal conductivity Cu foam was therefore used as a substrate to improve the catalyst's thermal conductivity during solar reforming. We also developed a method to coat the foam with the catalytically active component NiMg3AlOx. The Cu foam-based NiMg3AlOx performs better than catalysts supported on SiSiC foam, which is currently used as a substrate for solar-reforming catalysts, at high gas hourly space velocity (≥400,000 mL/(g·h)) or at low reaction temperatures (≤ 720 °C). The presence of a γ-Al2O3 intermediate layer improves the adhesion between the catalyst and substrate as well as the catalytic activity.

Photocatalytic reforming of formic acid for hydrogen production in aqueous solutions containing cupric ions and TiO2 suspended nanoparticles under UV-simulated solar radiation

Hydrogen is the ideal candidate to fulfill the growing energy demand in a sustainable manner because of its high energy content and no emission of greenhouse gases from its combustion. Currently most of hydrogen generation techniques involve the employment of fossil fuels, with consequent production of toxic greenhouse gases. The possibility to produce hydrogen by means of photocatalytic processes using the solar radiation as energy source fits in perfectly with the switch to a more sustainable energy production. The solar photocatalytic hydrogen generation can be achieved by reforming organic substances contained in civil or industrial wastewaters. This could allow to combine water decontamination with production of an energy carrier starting from a renewable source, the solar radiation.Within this perspective, a novel nano-TiO2 photocatalytic system based on the solar reforming of formic acid in presence of cupric ions and chlorides has been investigated. The effect on hydrogen generation rate of the initial concentrations of formic acid, chloride and cupric ion, and pH values has been evaluated. For both formic acid and chloride ions, at least up to a starting concentration of 103mM, the higher the initial concentration, the higher the rate of hydrogen generation. Hydrogen production has turned out to be noticeably dependent on cupric ion concentration. An almost opposite behavior has been found varying the starting cupric ion concentration in the range 2.5–20mM, with the highest value of hydrogen production rate recorded for Cu(II) initial concentration equal to 5.0mM. The pH value has been identified to be a crucial parameter of the system. A decrease in hydrogen production has been also observed rising pH of the solution from 1.0 to 4.0. A characterization of the solid samples recovered at the end of the runs has been performed by X-ray Diffractometry. These experimental outcomes have been rationalized within a consistent reaction mechanism able to predict the system behavior under different operating conditions. This work opens the way to the development of new competitive processes able to use waste organic streams for hydrogen generation through photacatalytic system based on solar energy.