Periodic Reporting for period 1 - ABraytCSPfuture (Air-Brayton cycle concentrated solar power future plants via redox oxides-based structured thermochemical heat exchangers/thermal boosters)
Berichtszeitraum: 2022-11-01 bis 2024-02-29
The objectives of ABraytCSPfuture are to demonstrate an innovative, carbon-neutral way for implementing into air-operated CSP plants the much more efficient air-Brayton gas turbine cycle, increasing in parallel the plants’ TES capability by rendering their current sensible-only regenerative storage systems to hybrid sensible-Thermochemical storage (TCS) ones. Both will be achieved by exploiting reversible reduction/oxidation (redox) reaction schemes operating between the oxidized (MeOx) and reduced (MeOx-δ) form of a metal oxide. In the thermal reduction step, the higher-valence oxide state under supply of external heat releases oxygen and transforms to the lower-valence form. Exothermic oxidation of the reduced to the oxidized form via air establishes a cyclic, solar energy TCS process: the heat supplied to power an endothermic chemical reaction on-sun, can be recovered by the reverse, exothermic reaction taking place off-sun. Materials of choice are such of a perovskite structure, comprising low cost, abundant metals. The ambition is to demonstrate, for the first time ever and at a proof-of-concept level, this radically new idea by the development and operation of a first-of-its-kind, compact, dual-bed thermochemical reactor/heat exchanger, comprised of non-moving, flow-through porous ceramic structures based on such perovskite redox oxides, capable of transferring heat from a non-pressurized air stream to a pressurized one raising in parallel the temperature of the latter to levels required for gas turbine cycles. This “thermal boosting” will be achieved by performing the exothermic oxidation with pressurized air shifting its equilibrium to higher temperatures.
• A plethora of identified promising perovskite powder compositions was synthesized and investigated with respect to structural changes, oxygen uptake/release and redox reactions’ heat effects under cyclic redox operation.
• A CaMnO₃ powder synthesized via scalable solid state route was selected for long-term cycling tests under appropriately designed aging and oxidation protocols.
• Scalable manufacturing procedures were developed for producing robust porous structured ceramic honeycombs and foams entirely out of CaMnO3–based compositions, in diameters 10-65 mm and lengths 10-35 mm.
• Reactor modeling/operation simulation advanced computational tools are developed to design the dual-bed thermochemical unit and will be appropriately refined with experimentally measured thermophysical properties and reaction kinetics of the perovskite materials and structures developed.
• Comparative Life Cycle Analysis (LCA) studies are ongoing to determine the most impactful raw materials on the powder synthesis and porous monoliths production of shortlisted perovskite compositions in terms of criticality, supply risk likelihood, environmental and economic impact.
• A wide variety of sturdy, porous structured ceramic honeycombs and foams entirely out of CaMnO3 – based compositions have been produced, ranging in diameters from 10 to 65 mm and in lengths from 10 to 35 mm. To the best of the partners’ knowledge this is the first time that a systematic production of such a palette of structured redox perovskite ceramics is reported in the open literature.
• Rigid and thermally stable porous structured ceramic honeycombs of similar size made of industrial by-products were successfully prepared, to be tested as sensible-only heat storage media.
• Experiments with CaMnO3 honeycombs in specifically designed in-house test rigs demonstrated the ability of such structures to store and release heat due to the enthalpy of a reversible redox reaction. Such heat effects during oxidation could be clearly manifested as a measurable temperature rise of both the honeycomb specimen as well as of the air stream flowing through it. In “practical terms” it was demonstrated that an air stream becomes hotter when flowing through the (reduced) redox oxide and oxidizing it. Again, to the best of the partners’ knowledge, this is the first time that such operation is demonstrated.