Solar-driven Processes Research Articles

Kinetic model implementation in raceway pond reactors with hydrodynamic and radiation fields

Vertical mixing plays a critical role in solar-driven processes using raceway pond reactors (RPRs). However, incorporating the time history of radiation for each fluid element is still an open issue. This work aims to develop an effective methodology using Computational Fluid Dynamics (CFD) tools that couples hydrodynamics and radiation fields into kinetic models of biomass growth or cell lysis enhanced from radiation. First, three methodologies to assess vertical mixing were investigated. It was found that, under typical RPR flow conditions, the velocity in the direction of solar light incidence can maintain particles in constant motion and a near-homogenous particle distribution. In addition, two RPR applications were studied regarding radiation influence analysis: the production of microalgae and an innovative approach for waste activated sludge (WAS) pre-treatment, fostering biogas production. Regarding microalgae production, coupling the biokinetic models with CFD data enables the development of a cost-effective computational methodology to describe the growth of microalgae cultures accounting for hydrodynamics and radiation fields. This work was successful in introducing hydrodynamics and radiation conditions in models to design and optimise RPRs. Reduced geometries based in 2D and Periodic Boundary Conditions were used for CFD simulations to make it feasible for RPRs design purposes.

Recent advances in copper kesterite thin film photocathodes for hydrogen production via water splitting: A review

The increasing scarcity of fossil fuels has made it crucial to investigate alternative, clean, and renewable power sources. Hydrogen, the simplest element on the planet can act as an energy carrier and can be a promising solution for this quest of carbon-free energy alternates. The practical implementation of cost-effective, efficient, and stable production of hydrogen fuel from water presents a significant challenge. Researchers around the globe have been actively exploring photoelectrochemical (PEC) water-splitting methods for large-scale commercialization of hydrogen production through solar-driven processes. Among these methods, the use of semiconductor photoelectrodes (PEs) is considered highly efficient. In this review, of the effectiveness and stability of the PEs, we describe the recent progress of copper-based chalcogenides for hydrogen generation by water splitting using solar energy. It is anticipated that this report will provide insightful guidance to study the low-cost materials for solar to chemical fuel energy conversion.

Photocatalytic conversion of cellulose into C5 oligosaccharides

Cellulose is made up of linear polymers of glucose monomers that could be a crucial source for valuable chemicals and sustainable liquid fuels. Cellulose is however, very stable and its conversion to a useful fuel or platform chemical products remains a significant challenge (Kimura et al 2015 Sci. Rep. 5 16266; Xia et al 2016 Nat. Commun. 7 11162). Photocatalysis is a versatile technology which has demonstrated potential for solar driven processes such as water splitting or solar fuels production and has also been applied to the degradation of pollutants in air and water and for the production of useful products from biomass. Here, we focus on the products that are produced from cellulose (a glucose (C6) based polymer) photocatalysis that compliment hydrogen production. Probing the initial steps via UV-TiO2 photocatalysis, we remarkably find that an array of oligosaccharides containing only five (C5) carbon units is initially produced. As the process continues, C6 oligo oligosaccharides grow to dominate. The photocatalytic process is generally not viewed as a controllable synthetic process; however, these findings show, on the contrary that photocatalysis at semiconductor surfaces can achieve novel reaction pathways yielding new products.

Ozonation Vs sequential solar driven processes as simultaneous tertiary and quaternary treatments of urban wastewater: A life cycle assessment comparison

Solar driven advanced oxidation processes (S-AOPs) have been successfully investigated in the last years as tertiary and quaternary treatment of urban wastewater for simultaneous inactivation of microorganisms and removal of contaminants of emerging concern (CECs), respectively. However, the lack of data about the comparison with consolidated technologies, including also the evaluation of their impact on the environment, has contributed to humper their application at full scale so far. In this study, the environmental impact of a new S-AOP, namely sequential treatment (ST) with sunlight/H2O2 and solar photo-Fenton (SPF) at neutral pH (using Ethylenediamine-N, N′-disuccinic acid (EDDS) as chelating agent) operated at pilot scale in a raceway pond reactor, was compared to a pilot scale ozonation (O3) treatment unit in terms of simultaneous bacteria inactivation and CECs removal, through a Life Cycle Assessment (LCA). Different urban wastewater treatment plant (UWWTP) sizes and scenarios (namely effluent disposal and reuse) were evaluated. While the reuse scenario resulted in a higher impact compared to the disposal scenario in the construction/deconstruction phase, due to the more stringent limits that resulted in longer treatment time and a higher consumption of raw materials, the positive impact on water resources saving compared to disposal makes the reuse scenario a more sustainable solution. Despite O3 disinfection by-products were taken into account, ST resulted in a higher toxicity to human health (0.27·10−9 DALYs Vs 2.11 10−9 DALYs, respectively) due to the higher residual concentration of the target CECs. However, it is noteworthy that both values are significantly lower than the acceptable DALYs value (≤10−6). Chemicals, energy, groundwater consumption and residual CECs can affect resources 1125 and 1874 times more for O3 treatment than for the ST, for disposal and reuse scenarios, respectively. The total impact of O3 on the human health was 13 and 19 times higher compared to ST, for disposal and reuse scenarios, respectively, due to the higher energy and chemical consumption. According to the LCA results, ST resulted in a better overall environmental performance compared to O3 and it is a more sustainable and attractive solution in particular for small UWWTPs.

Recent progress in membrane distillation configurations powered by renewable energy sources and waste heat

Membrane distillation (MD) is a promising process for high-quality water reclamation mainly due to its high capacity to retain non-volatile components and operate without the need for hydraulic pressure. However, its low energy efficiency limits its widespread use. With that in mind, this paper critically summarizes the different engineered configurations of membrane distillation coupled with renewable energy sources and waste heat, namely: solar, geothermal, and waste heat, to overcome the limitations associated with low energy efficiency commonly reported. From all sources, solar-driven processes are preferred due to the greater technological maturity related to flat plate collectors (FPCs), evacuated tube collectors (ETCs), compound parabolic concentrators (CPCs), salt-gradient solar ponds (SGSPs), and solar stills. The integration with renewable energy sources represents one of the leading solutions for energy consumption, proving to be a decisive choice for the system's economic viability. The summarized studies suggest membrane distillation's potential to be economically competitive with the classical membrane separation process (ultrafiltration, nanofiltration, and reverse osmosis) when waste heat is considered for wastewater treatment. Even under these conditions, alternative energy sources have a few shortcomings to be investigated in future studies, such as short periods of solar radiation and the intermittence of waste heat sources. These factors still represent obstacles to an uninterrupted and large-scale operation of membrane distillation and must be overcome in a near future. Even so, successful case studies on full-scale systems that integrate membrane distillation and solar energy sources suggest the process's potential for widespread use in the near term.

A continuous photo-Fenton-like process using persulfate salts for the degradation of acetaminophen under solar irradiation at circumneutral pH

The demand for sustainable and feasible water treatment technologies (WTT) increases with the growing realization of the magnitude of the damage that our indiscriminate wastewater disposal strategy has caused the Environment. Considering the increasing costs of energy, the development of solar-driven processes is key to ensuring the economic feasibility of WTT for industries of all sizes. In this direction, this paper reports the development of a photo-Fenton-like system based on the persulfate ion and the use of solar irradiation as its coactivator for use in continuous processes. Using acetaminophen as model contaminant (C0 = 5 ppm), we showed that under optimal conditions and circumneutral pH (pH ∼5.6), a removal of 94% was achievable with a residence time of 3.3 min. Economically, this translates into a collector area per order of 11.4 m2/(m3 order), in line with the best numbers found in the literature. We showed that this was achieved due to the improved concentration of sulfate radicals, SO4•−, formed in the system, when compared to the same process carried out in a small-scale batch reactor. Our results, obtained under controlled conditions using a solar simulator, were validated under natural sunlight, confirming the feasibility of our proposed intensification strategy.

Effect of Functionalized Benzene Derivatives as Potential Hole Scavengers for BiVO4 and rGO-BiVO4 Photoelectrocatalytic Hydrogen Evolution.

Sustainable hydrogen production is one of the main challenges today in the transition to a green and sustainable economy. Photocatalytic hydrogen production is one of the most promising technologies, amongst which BiVO4-based processes are highly attractive due to their suitable band gap for solar-driven processes. However, the performance of BiVO4 alone in this role is often unsatisfactory. Herein we report the improvement of BiVO4 performance with reduced graphene oxide (rGO) as a co-catalyst for the photoelectrochemical water splitting (PEC-WS) in the presence of simple functionalized benzene derivatives (SFBDs), i.e., phenol (PH), benzoic acid (BA), salicylic acid (SA), and 5-aminosalicylic acid (5-ASA) as potential photogenerated hole scavengers from contaminated wastewaters. Linear sweep voltammetry and chronoamperometry, along with electrochemical impedance spectroscopy were utilized to elucidate PEC-WS performance under illumination. rGO has remarkably improved the performance of BiVO4 in this role by decreasing photogenerated charge recombination. In addition, 5-ASA greatly improved current densities. After 120 min under LED illumination, 0.53 μmol of H2 was produced. The type and concentration of SFBDs can have significant and at times opposite effects on the PEC-WS performance of both BiVO4 and rGO-BiVO4.

Solar Driven Gas Phase Advanced Oxidation Processes for Methane Removal - Challenges and Perspectives.

Methane (CH4 ) is a potent greenhouse gas and the second highest contributor to global warming. CH4 emissions are still growing at an alarmingly high pace. To limit global warming to 1.5 °C, one of the most effective strategies is to reduce rapidly the CH4 emissions by developing large-scale methane removal methods. The purpose of this perspective paper is threefold. (1) To highlight the technology gap dealing with low concentration CH4 (at many emission sources and in the atmosphere). (2) To analyze the challenges and prospects of solar-driven gas phase advanced oxidation processes for CH4 removal. And (3) to propose some ideas, which may help to develop solar-driven gas phase advanced oxidation processes and make them deployable at a climate significant scale.

Temperature-controlled nanomosaics of AuCu bimetallic structure towards smart light management

Gold–copper nanostructures are promising in solar-driven processes because of their optical, photocatalytic and photoelectrochemical properties, especially those which result from the synergy between the two metals. Increasing interest in their internal structure, such as the composition or distribution of the Au and Cu as well as the size and shape of the nanoparticles, have developed to define their physicochemical properties.In this work, we present the influence of thermal treatment in temperature ranges from 100 to 600 °C on the formation process of bimetallic AuCu structures and their properties. AuCu materials were placed on nanostructured titanium foil substrates that were fabricated using electrochemical anodisation and chemical etching. Thin layers of AuCu mixture, as well as Au and Cu, were sputtered on the obtained Ti nanodimples. The materials were then annealed in a rapid thermal annealing furnace in an air atmosphere. Thermal treatment strongly affected the morphology and optical properties of the fabricated materials. AuCu NPs formed at 400 °C in titanium dimples. The material exhibits absorption of visible light in the range from c.a. 400 to 700 nm. The characterisation of the chemical nature of the samples was determined using X-ray photoelectron spectroscopy. In addition, X-ray diffraction and Raman spectroscopy defined composition and crystallinity. Based on photoelectrochemical studies carried out with the use of linear voltammetry in 0.1 M NaOH, it is possible to distinguish two types of interactions of light with the materials such as photogenerated charge accumulation and electron–hole pair separation. A 10AuCu electrode annealed at 300 °C achieved the highest current registered under illumination at − 0.17 V vs. Ag/AgCl/0.1 M KCl. The value was 11 times higher than for a non-annealed structure.

AuCu Nanostructures Active in the Visible Light – Optical and Photoelectrochemical Properties

Nowadays, due to global warming and increasing environmental pollution, intensified research on materials for energy harvesting from renewable sources is being carried on. Solar energy is one of the most abundant energy resources that can be converted into electric energy. Here, we demonstate that AuCu bimetallic nanostructures placed on structured titanium foil can be applied in solar driven processes [1, 2].The electrode material is fabricated via Ti foil anodization process, chemical etching, thin AuCu layer (10 nm) magnetron sputtering and rapid thermal treatment at 600°C in varius atmospheres (air, vacuum, argon, hydrogen). AuCu nanoparticles are obtained only for annealing in air, while in argon and hydrogen porous structures and nanoplates are formed, respectively. UV-vis spectroscopy and X-ray diffraction studies of marterials indicate that the shape of the reflectance spectra differ significantly due to the changes in material morphology as well as its structure. The reflectance band minima are located at 380 nm and 750 nm for electrode material annealed in air and hydrogen, respectivetly. Moreover, sample thermally treated in air exhibits wide absorbance band from 300 to 1000 nm, whereas the one annealed in hydrogen from 500 to 1000 nm. Linear voltammetry measurements in dark and under light illumination were carried out in 0.1M NaOH solution in order to evaluate the photoactivity. The highest photocurrent in visible light is obtained for AuCu electrode annealed in hydrogen (5 times higher than in air), however, under Uv-vis light for electrode processed in air.All in all, thermal treatment in various atmospheres has a great impact on morphology, optical and photoelectrochemical activity of AuCu structures placed on Ti support material. We believe that presented results provide new opportunities in designing advanced photoactive materials.Research is financed by National Science Centre (Poland): Grant no. 2019/35/N/ST5/02604.[1] W. Lipińska, K. Grochowska, J. Ryl, J. Karczewski, K. Siuzdak, Influence of Annealing Atmosphere on Photoelectrochemical Activity of TiO2 Nanotubes Modified with AuCu Nanoparticles, ACS Applied Materials and Interfaces, 13 (2021) 52967–52977, DOI: 10.1021/acsami.1c16271[2] W. Lipińska, K. Grochowska, J. Karczewski, J. Ryl, A. Cenian, K. Siuzdak, Thermally tuneable optical and electrochemical properties of Au-Cu nanomosaic formed over the host titanium dimples, Chemical Engineering Journal, 399 (2020) 125673–125685, DOI: 10.1016/j.cej.2020.125673 Figure 1

Dehydrogenase-Functionalized Interfaced Materials in Electroenzymatic and Photoelectroenzymatic CO2 Reduction

The simultaneous extenuation of emitted CO2 conversion to chemicals and fuels has purposely motivated researchers toward adapting electrochemical techniques associated with gas diffusion electrodes by using enzyme formate dehydrogenase (FDH). Herein, an in-depth analysis on the background of electroenzymatic CO2 reduction in connection with the nature of binding of FDH on the electrode surface for interfacial direct electron transfer (DET) and mediated electron transfer (MET) are discussed. Types of bioelectrodes with a dehydrogenase enzyme and adapted techniques for their fabrication are emphasized along with new FDH enzymes and their possible effect on CO2 reduction efficacy. Solar-driven photoelectroenzymatic CO2 reduction has emerged as a promising strategy, which is discussed in terms of the rate of CO2 conversion in photoelectrochemical (PEC) cells, enzyme-interfaced materials, NADH regeneration, the role of synthetic photoelectrode materials, and diffusional electron mediators. Advanced applications of electroenzymatic CO2-reduction-driven fuels and their effect are assessed to offer future directions of interfaced materials for electroenzymatic and solar-driven processes.

XPS of the surface chemical environment of CsMAFAPbBrI trication-mixed halide perovskite film

Perovskite-based materials have been considered as the most promising materials in several solar-driven processes, especially photovoltaics. Some features such as high sunlight harvesting and improved carrier transport have been highlighted to have an impact on the efficiency of the above topics, but limited studies have pointed out their surface composition, which mainly influence the above abilities. As a starting point to recognize the surface environment and chemical states of these materials, x-ray photoelectron spectroscopy measurements were performed. Trication-mixed halide perovskite films based on Cs0.08MA0.18FA0.78PbBr0.42I2.58 were prepared by a one step process and deposited on an indium tin oxide substrate by spin-coating. Survey spectra, Pb 4f, I 3d, Br 3d, Cs 3d, C 1s, N 1s, Pb 4d, and Pb 5d core levels, and valence band spectra were measured for the semiconductor sample. Results exhibit symmetrical peaks, indicating that a homogenous solid solution was achieved. Main chemical states of this kind of perovskites such as Cs-Br and Pb-I species are also shown. We deduced that the later signals are associated with the [PbI6]4− octahedra existing in the perovskite lattice, while the former one is related to Cs+ bounded to [PbBr6]4− units on the perovskite surface. Interestingly, the NR4+ signal was also identified, associated with the presence of methylammonium and formamidinium cations.

Fresh-cut wastewater reclamation: Techno-Economical assessment of solar driven processes at pilot plant scale

Up-scaling of solar processes for water purification is a key challenge for their implementation at industrial scale on the agro-food sector. Benefits of using flow-tubular reactors provided with Compound Parabolic Collector mirrors have been previously demonstrated, nevertheless some techno-economic aspects still being unknown.This study shows a comparative analysis of the treatment efficiency of H2O2/solar, Fe3+-EDDHA/solar and Fe3+-EDDHA/H2O2/solar as novel processes for treating synthetic fresh-cut wastewater (SFCWW) containing 100 NTU of turbidity. The highest treatment capability was obtained with Fe3+-EDDHA/H2O2/solar (2.5/20 mg/L-Fe3+-EDDHA/H2O2), attaining the fastest microbial inactivation kinetics (>5-log of Escherichia coli O157:H7 and Salmonella enteritidis) and organic microcontaminants (OMCs) degradation (36 % of 5 OMCs) in 60 and 120 min, respectively.Treated SFCWW by Fe3+-EDDHA/H2O2/solar process fits microbiological quality established in water reuse guidelines for irrigation, no bacterial reactivation after 24 h post-treatment, no significant ecotoxicity and treatment cost was estimated as 1.10 (only disinfection) and 2.10 €/m3 (simultaneous disinfection and decontamination).

An overview of solar decarbonization processes, reacting oxide materials, and thermochemical reactors for hydrogen and syngas production

Solar decarbonization processes are related to the different thermochemical conversion pathways of hydrocarbon feedstocks for solar fuels production using concentrated solar energy as the external source of high-temperature process heat. The main investigated routes aim to convert gaseous and solid feedstocks (methane, coal, biomass …) into hydrogen and syngas via solar cracking/pyrolysis, reforming/gasification, and two-step chemical looping processes using metal oxides as oxygen carriers, further associated with thermochemical H2O/CO2 splitting cycles. They can also be combined with metallurgical processes for production of energy-intensive metals via solar carbothermal reduction of metal oxides. Syngas can be further converted to liquid fuels while the produced metals can be used as energy storage media or commodities. Overall, such solar-driven processes allow for improvements of conversion yields, elimination of fossil fuel or partial feedstock combustion as heat source and associated CO2 emissions, and storage of intermittent solar energy in storable and dispatchable chemical fuels, thereby outperforming the conventional processes. The different solar thermochemical pathways for hydrogen and syngas production from gaseous and solid carbonaceous feedstocks are presented, along with their possible combination with chemical looping or metallurgical processes. The considered routes encompass the cracking/pyrolysis (producing solid carbon and hydrogen) and the reforming/gasification (producing syngas). They are further extended to chemical looping processes involving redox materials as well as metallurgical processes when metal production is targeted. This review provides a broad overview of the solar decarbonization pathways based on solid or gaseous hydrocarbons for their conversion into clean hydrogen, syngas or metals. The involved metal oxides and oxygen carrier materials as well as the solar reactors developed to operate each decarbonization route are further described.

Dynamic simulation and control of solar biomass gasification for hydrogen-rich syngas production during allothermal and hybrid solar/autothermal operation

Solar biomass steam gasification using concentrated sunlight offers an efficient means of storing intermittent solar energy into renewable solar fuels while upgrading the carbonaceous feedstock. Such solar-driven (allothermal) processes have demonstrated the ability and the effectiveness for the production of high quality hydrogen-rich syngas, but they suffer from inherent barriers related to the variability of solar energy caused by cloud passages and shut off at night. The concept of hybrid solar/autothermal gasification appears promising to meet the requirement for stable and continuous operation under fluctuating or intermittent solar irradiation. To date, dynamic modelling to simulate coupled solar/combustion heating and steam gasification using real solar irradiation data has never been proposed and could be used to predict the annual performance of large-scale solar gasification plants. In this study, a dynamic mathematical model of a scaled-up solar gasification reactor was developed. The model was composed of a system of differential equations that were derived from unsteady mass and energy conservation equations. After an experimental validation step with the results from a lab-scale solar reactor, the dynamic model was applied at large scale to determine the reactor temperature and syngas production evolution during continuous day and night operation in both solar-only (allothermal) and hybrid solar/autothermal modes. Different reactants feeding management strategies were proposed and compared with the aim of achieving enhanced syngas productivity and optimized use of solar energy during solar-aided steam gasification. It was shown that the hybrid mode with partial oxy-combustion of the feedstock and dynamic feeding control results in the most stable process operation upon fluctuating solar power input, while ensuring continuous production of H2 and CO at night and during cloudy periods.

Water Disinfection in Rural Areas Demands Unconventional Solar Technologies.

Providing access to safe drinking water is a prerequisite for protecting public health. Vast improvements in drinking water quality have been witnessed during the last century, particularly in urban areas, thanks to the successful implementation of large, centralized water treatment plants and the distribution of treated water via underground networks of pipes. Nevertheless, infection by waterborne pathogens through the consumption of biologically unsafe drinking water remains one of the most significant causes of morbidity and mortality in developing rural areas. In these areas, the construction of centralized water treatment and distribution systems is impractical due to high capital costs and lack of existing infrastructure. Improving drinking water quality in developing rural areas demands a paradigm shift to unconventional, innovative water disinfection strategies that are low cost and simple to implement and maintain, while also requiring minimal infrastructure. The implementation of point-of-use (POU) disinfection techniques at the household- or community-scale is the most promising intervention strategy for producing immediate health benefits in the most vulnerable rural populations. Among POU techniques, solar-driven processes are considered particularly instrumental to this strategy, as developing rural areas that lack safe drinking water typically receive higher than average surface sunlight irradiation. Materials that can efficiently harvest sunlight to produce disinfecting agents are pivotal for surpassing the disinfection performance of conventional POU techniques. In this account, we highlight recent advances in materials and processes that can harness sunlight to disinfect water. We describe the physicochemical properties and molecular disinfection mechanisms for four categories of disinfectants that can be generated by harvesting sunlight: heat, germicidal UV radiation, strong oxidants, and mild oxidants. Our recent work in developing materials-based solar disinfection technologies is discussed in detail, with particular focus on the materials' mechanistic functions and their modes of action for inactivation of three common types of waterborne pathogens (i.e., bacteria, virus, and protozoa). We conclude that different solar disinfection technologies should be applied depending on the source water quality and target pathogen due to significant variations on susceptibility of microbial components to disparate disinfectants. In addition, we expect that ample research opportunities exist on reactor design and process engineering for scale-up and improved performance of these solar materials, while accounting for the infrastructure demand and capital input. Although the practical implementation of new treatment techniques will face social and economic challenges that cannot be overlooked, novel technologies such as these can play a pivotal role in reducing water borne disease burden in rural communities in the developing world.

Green Bioplastics as Part of a Circular Bioeconomy

The rapid accumulation of plastic waste is driving international demand for renewable plastics with superior qualities (e.g., full biodegradability to CO2 without harmful byproducts), as part of an expanding circular bioeconomy. Higher plants, microalgae, and cyanobacteria can drive solar-driven processes for the production of feedstocks that can be used to produce a wide variety of biodegradable plastics, as well as bioplastic-based infrastructure that can act as a long-term carbon sink. The plastic types produced, their chemical synthesis, scaled-up biorefinery concepts (e.g., plant-based methane-to-bioplastic production and co-product streams), bioplastic properties, and uses are summarized, together with the current regulatory framework and the key barriers and opportunities.

New Route for Valorization of Oil Mill Wastes: Isolation of Humic-Like Substances to be Employed in Solar-Driven Processes for Pollutants Removal.

The valorization of olive oil mill solid wastes (OMW) has been addressed by considering it as a possible source of humic-like substances (HLSs), to be used as auxiliary substances for photo-Fenton, employing caffeine as a target pollutant to test the efficiency of this approach. The OMW-HLS isolation encompassed the OMW basic hydrolysis, followed by ultrafiltration and drying. OMW-HLS structural features have been investigated by means of laser light scattering, fluorescence, size exclusion chromatography, and thermogravimetric analysis; moreover, the capability of OMW-HLS to generate reactive species under irradiation has been investigated using spin-trap electronic paramagnetic resonance. The caffeine degradation by means of photo-Fenton process driven at pH = 5 was significantly increased by the addition of 10 mg/L of OMW-HLS. Under the mechanistic point of view, it could be hypothesized that singlet oxygen is not playing a relevant role, whereas other oxidants (mainly OH• radicals) can be considered as the key species in promoting caffeine degradation.

Design and Characterization of a Novel Upward Flow Reactor for the Study of High-Temperature Thermal Reduction for Solar-Driven Processes

The design and characterization of an upward flow reactor (UFR) coupled to a high flux solar simulator (HFSS) under vacuum is presented. The UFR was designed to rapidly heat solid samples with concentrated irradiation to temperatures greater than 1000 °C at heating rates in excess of 50 K/s. Such conditions are ideal for examining high-temperature thermal reduction kinetics of reduction/oxidation-active materials by temporally monitoring O2 evolution. A steady-state, computational fluid dynamics (CFD) model was employed in the design to minimize the formation of eddies and recirculation, and lag and dispersion were characterized through a suite of O2 tracer experiments using deconvolution and the continuously stirred tank reactors (CSTR) in series models. A transient, CFD and heat transfer model of the UFR was combined with Monte Carlo ray tracing (MCRT) to determine radiative heat fluxes on the sample from the HFSS to model spatial and temporal sample temperatures. The modeled temperatures were compared with those measured within the sample during an experiment in which Co3O4 was thermally reduced to CoO and O2. The measured temperatures within the bed were bounded by the average top and bottom modeled bed temperatures for the duration of the experiment. Small variances in the shape of the modeled versus experimental temperatures were due to contact resistance between the thermocouple and particles in the bed and changes in the spectral absorptivity and emissivity as the Co3O4 was reduced to CoO and O2.

Solar-driven pyrolysis and gasification of low-grade carbonaceous materials

Three low-grade carbonaceous materials from biomass (Scenedesmus algae and wheat straw) and waste treatment (sewage sludge) have been selected as feedstock for solar-driven thermochemical processes. Solar-driven pyrolysis and gasification measurements were conducted directly irradiating the samples in a 7 kWe high flux solar simulator and the released gases H2, CO, CO2 and CH4 and the sample temperature were continuously monitored.Solar-driven experiments showed that H2 and CO evolved as important product gases demonstrating the high quality of syngas production for the three feedstocks. Straw is the more suitable feedstock for solar-driven processes due to the high gas production yields. Comparing the solar-driven experiments, gasification generates higher percentage of syngas (mix of CO and H2) respect to total gas produced (sum of H2, CO, CO2 and CH4) than pyrolysis. Thus, solar-driven gasification generates better quality of syngas production than pyrolysis.