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Solid particles as heat absorptances and storage mediums promise enhanced energy storage densities in concentrated solar power/thermal (CSP/T) plants. Employment of metallurgical slags as a secondary precursor material for solid particle preparation is ecologically and economically beneficial. Although these processed wastes, comprised of several oxides, exhibit generally promising high-temperature properties, chemical scattering from batch to batch may result in distinct material and functional properties, which may be an obstacle for their utilization. In this study, a steelmaking slag, LiDonit (LD), produced using a unique controlled slag treatment with high reproducibility is investigated as a candidate material. The aforementioned subsequent unique slag treatment makes LD a very promising and distinguishable secondary raw material for high-temperature applications. The as-received microstructure, phase components, and chemical composition of the LD material were analyzed to understand its material properties and to assess its reproducibility. The as-received LD chunks were transferred into pellets by subsequent milling, gel-casting, and sintering stages to reveal the potential processing routes. The CSP/T-related properties of sintered pellets, such as high temperature stability, heat capacity, and solar absorptance, were also examined to reveal their potential use in CSP/T applications and expand application areas with high added value. [ABSTRACT FROM AUTHOR]

The use of solid particles as direct heat absorbance and storage media promises enhanced storage densities in concentrated solar power (CSP) technologies. The long-term optical performance of those particles, which aim to be operational over years, is crucial. Dry powder coating with a deep black Cu-Mn-oxide pigment in a resonant acoustic mixer and subsequent sintering was employed to improve the long-term optical performance of hematite-rich spherical particles, which aimed to replace the state-of-the-art bauxite proppants. Due to the specific reactivity of the hematite particles, a new strategy using an Al-modified composition of the initial deep black pigment was required. The Al modification diminishes cation diffusion into hematite, allowing the formation of spinel-type Fe-Mn-Cu-Al-oxide coatings with favorable long-term temperature and optical stability. The effect of chemical composition of the coating layer on the coating process mechanism was discussed and the need for an elongated sintering time was noticed to ensure the termination of stable spinel phase formation. The structural and optical measurements revealed the enhancement of the properties of hematite absorber particles through this new modified coating process. [ABSTRACT FROM AUTHOR]

The use of ceramic solid particle technology in TES-integrated CSP plants offers a high solar-to-electricity ratio and enhanced storage densities, thanks to their high operational temperatures and wide temperature ranges. Metallurgical slags with composition similar to that of the state-of-art bauxite particles can be used as a sustainable and economical secondary raw material to prepare solid particles. In this study, the as-received state and the high-temperature phase and microstructural changes of two fayalite slags from copper and lead production were elucidated by XRD and SEM/EDS methods in a comparative manner. Solid particles were prepared from slags by the oil dropping method, with subsequent heat treatment. Solar-thermal-application-related functional properties of slag particles, such as heat capacity, absorptance, and thermophysical properties, were evaluated by differential scanning calorimetry (DSC), spectrophotometer, heating microscope, and high-temperature compressive tests, respectively. Owing to the formation of more stable Fe-rich phase components and less amount of glassy phase, copper slag is found to be a more promising secondary resource than lead slag in terms of material and functional properties. [ABSTRACT FROM AUTHOR]

• Overall concept of centrifugal solar particle receiver-driven solid sulphur-based thermochemical cycle. • Commercial and composition-modified bauxite-based particles evaluated in non-solar-irradiated rigs. • Cu,Mn-modified bauxite particles showed high, stable SO 3 conversion for more than 1000 h. • Composition modification improved particles ' absorptance. • Thermomechanical properties of modified particles proved inferior to those of commercial ones. The present work is part of an approach targeted on demonstrating a concentrated solar energy-driven thermochemical cycle employing solid elemental sulphur as a chemical energy vector and a seasonal solar energy storage medium. In exploring the concept of coupling this cycle to a centrifugal particle solar receiver, bauxite-based particles, commercial and composition-modified, were tested and validated with respect to their suitability for simultaneous operation as solar energy harvesting media and sulphur trioxide splitting catalysts. Long-term catalytic activity tests exceeding 1000 h of operation at 850 °C, demonstrated that properly composition-modified bauxite particles were capable of achieving stable SO 3 conversion exceeding 70% (about 80% of equilibrium value under conditions studied) and exhibiting no or negligible loss of catalytic performance after this extended operation. In addition, such composition modification enhanced the particles' solar irradiation absorptance, which resulted in substantially higher than that of their commercial, non-modified bauxite counterparts. Commercial bauxite particles on the other hand, demonstrated much better mechanical strength, flowability, and attrition- and thermal shock resistance together with measurable, yet lower catalytic activity, which deteriorated with prolonged on-stream exposure. The combined results obtained advocate for the eventual selection of an "allothermal" cascaded sulphur trioxide splitting/sulphuric acid decomposition reactor, containing a non-moving catalytic bed that is heated indirectly by a moving bed of high-temperature (≥900 °C) non-modified commercial bauxite particles irradiated in the centrifugal solar particle receiver. [ABSTRACT FROM AUTHOR]