Periodic Reporting for period 1 - ABraytCSPfuture (Air-Brayton cycle concentrated solar power future plants via redox oxides-based structured thermochemical heat exchangers/thermal boosters)
Periodo di rendicontazione: 2022-11-01 al 2024-02-29
Concentrated Solar Power (CSP) plants track the sun and concentrate its radiation by special mirrors converting solar energy to heat and via a power cycle to electricity. Heat can be stored at a much lower cost relative to that of electricity and used on-demand to produce it. For the eventual production of electricity, a receiver in the focal area of the radiation is used, in which a heat transfer fluid/HTF is solar-heated and then transfers its enthalpy to a heat engine via production of steam and operation of a conventional steam turbine (Rankine) power cycle. For 24/7 power supply, a thermal energy storage (TES) system to provide heat when sun is unavailable but demand for electricity remains, is a “must”. The temperature level of the stored heat is limited by the thermal resilience of the HTF, being currently ca. 560/450 oC for state-of-the-art molten salt or thermal oil heat storage units, respectively. Steam cycle limits the thermal-to-electric conversion efficiencies of CSP plants between 30 - 40%, thereby hampering CSP from becoming competitive to low cost PVs. By increasing the maximum cycle temperature to 850–1000oC efficiencies of 53% would be achievable in an air-Brayton/Rankine Combined Cycle giving CSP a unique competitive edge. Such efficiencies are non-reachable by either PVs or CSP plants operating with molten salts or thermal oils as HTF/storage media.
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.
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.
• Computational materials screening taking into consideration environmental, abundancy and cost aspects of raw materials, is employed to understand composition effects on the thermal and mechanical properties of perovskites and tune them via rational targeted doping.
• 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 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.
• CaMnO3 powder exhibited no redox performance deactivation in the course of 510 cycles between 300 and 1100oC and no compositional or phase alteration between the pristine and aged powder states. Based on the measurements of the heat effects of the oxidation reaction and of the heat capacity, values for calculated volumetric energy density as the sum of the sensible heat storage contribution and the redox thermochemical one for the pristine powder were determined to be between 467 and 476 kWh/m3. These values are more than double of those of current state-of-the-art sensible-storage materials used in CSP, namely molten salts that are of the order of 200 kWh/m3.
• 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.
• 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.