Hybrid sensible/thermochemical storage of solar energy in cascades of redox-oxide-pair-based porous ceramics

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1 DLR.de Chart 1 Hybrid sensible/thermochemical storage of solar energy in cascades of redox-oxide-pair-based porous ceramics Christos Agrafiotis, Andreas Becker, Lamark deoliveira, Martin Roeb, Christian Sattler Institute of Solar Research DLR/ Deutsches Zentrum für Luft- und Raumfahrt/ German Aerospace Center Linder Höhe, Köln, Germany

2 DLR.de Chart 2 Outline: Solar Energy Storage in air-operated Solar (Tower) Thermal Power Plants (STPPs) ThermoChemical Storage (TCS) principles and redox oxide pairs Some new ideas on redox-oxidebased porous ceramics for TCS in STPPs From laboratory to solar testing Conclusions, current and future work

3 DLR.de Chart 3 Air-operated CSP Plants (Solar Tower Jülich/STJ) HTF: Air at atmospheric pressure, heated up to about 700ºC and then powering a steam generator. Sensible heat storage : TES by temperature increase (cp T) Latent heat storage : TES by phase transition ( h sl ) Thermochemical storage : TES by chemical reaction ( h R ) 7m x 7m x 6m S. Zunft, et al.:solarpaces, (2009); (2010); JSEE (2011); Energy Procedia, (2014).

4 DLR.de Chart 4 > 14 ECERS, Toledo, Spain > Agrafiotis, Becker, deoliveira, Roeb, Sattler > June 21-25, 2015 From TES with sensible heat to hybrid sensible-thermochemical storage with redox oxides MO 2x+1 MO + xo 2 Increase the volumetric storage density instead of the storage volume: coat with/ make of honeycombs with redox oxide General Atomics: GA C27137: THERMOCHEMICAL HEAT STORAGE FOR CONCENTRATED SOLAR POWER THERMOCHEMICAL SYSTEM REACTOR DESIGN FOR THERMAL ENERGY STORAGE ; Phase II Final Report, 2011

5 DLR.de Chart 5 Cascaded ThermoChemical Storage (CTCS) A cascade of different redox oxide materials can be combined with various porous structures along as well across the reactor/heat exchanger. HTF flow when discharging F. Dinter, M. Geyer, R. Tamme, Springer-Verlag, Berlin, (1991); Michels and Pitz-Paal, Solar Energy, , TCS reactor/heat exchanger with spatial variation of functional materials and porosity in three dimensions, (C. Agrafiotis and R. Pitz-Paal, Patent Application Filed 2013).

6 DLR.de Chart 6 Tests Scale Evolution (single-oxide or cascaded testing) TGA Lab-scale furnace test rig Solar receivers

7 DLR.de Chart 7 > 14 ECERS, Toledo, Spain > Agrafiotis, Becker, deoliveira, Roeb, Sattler > June 21-25, 2015 TGA (DSC) rig: Cyclic reduction oxidation protocol weight change (vs. stoichiometric) = f(t) 101 T plateau reduction t=1 hr T redox =? o C t=1 hr T plateau oxidation Temperature ( o C) 94 Me x O y oxidized Air Ar Me x O y reduced Me x O y : T plateau reduction > T redox > T plateau oxidation Time (min) Reaction T red ( o C) Max. wt. loss ( %) 2 BaO 2 + ΔH 2 BaO + O Co 3 O 4 + ΔH 6 CoO + O Mn 2 O 3 + ΔH 4 Mn 3 O 4 + O CuO + ΔH 2 Cu 2 O + O

8 DLR.de Chart 8 TGA: Co 3 O 4 /CoO Co 3 O 4 can operate in a quantitative, cyclic and fully reversible reduction/ oxidation mode within o C (950 o C). As powder, coated on honeycombs/ foams or shaped in foams Co Co 3 O 4 -loaded Cordierite foam o C/min; long-term cycling 3 O 4 powder, 30 cycles: o C, 5 o % Co 3 O 4 made foams, cycles 1-30 Foam, 30 Coating ppi, powder No 1 Temperature Cycles 1-30: Coated cordierite foam 3, loading 64% (overall); calculated per mass of loaded powder 90 Temperature Time (min) Time (min) Temperature ( o C) Temperature ( o C) ( o C) Agrafiotis, Roeb, Schmücker, Sattler, Solar Energy, Parts I, II, III (2014), (2015).

9 DLR.de Chart 9 TGA: Mn 2 O 3 /Mn 3 O 4 Mn 2 O 3 : reduction fast, stoichiometric; but large temperature gap between reduction ( 950 o C) - oxidation ( o C)!! Very narrow temperature range ( o C) within which Mn 2 O 3 reoxidation is significant. Mn 2 O 3 re-oxidation is slow and needs extended dwell at the optimum temperature (range) for completion. Can be also achieved with slow rates and no dwell as shown below Mn, 10 o 2 O 3 C/min T rdxn = 950 = 950 o C o C T ox = = 780 o C o C T dwell oxidation : 900 o C 750 o C 720 o C 690 o C 650 o C T = 1000 o C T = 1000 o C T = 870 o C Wt loss: 3.68 % Wt loss: 3.70 % Wt re-gain: 3.51 % Temperature Time (min) Temperature ( o C)

10 DLR.de Chart 10 TGA: Other oxides CuO/Cu 2 O: reduction temperature very close to m.p. of Cu 2 O (shrinkage and sintering); could not work reproducibly even for few (5 cycles). BaO 2 /BaO: BaO reacts with CO 2 present in air to BaCO 3 Perovskites: loose/gain (little) weight continuously with T (perhaps plus in a cascade but H also very low): Reaction ΔH (kj/mol) T red ( o C) T ox ( o C) 2 Co 3 O 4 + ΔH 6 CoO + O Mn 2 O 3 + ΔH 4 Mn 3 O 4 + O Wt loss: 1.35 % Wt re-gain: 0.6 % La SrFeO Temperature Time (min) Temperature ( o C) Favourable Ts for oxidation but entire cascade needs T > 950 o C during reduction

11 DLR.de Chart 11 Furnace test rig: Visualization of Hybrid Sensible-TCS vs. Sensible-only storage effect 1200 Coated vs. non-coated honeycombs Co 3 O 4 -Coated honeycombs 60 Temperature Temperature (C ) (C ) Air flow rate = 5000 sccm Temperature at reaction zone end: Coated 5000 sccm honeycombs Non-coated 2500 sccm honeycombs O370 sccm 2 concentration Total Co 3 O 4 coated mass = 98 g O 2 concentration 5000 sccm 2500 sccm Difference between Sensible 370 sccm and Thermchemical effect O2 O2 concentration concentration (% (% in in air) air) Time Time (min) (min)

12 DLR.de Chart 12 Solar furnace test rig: Receiver storage modules assembly; 1 st tests: T along non-coated storage module (sensible-only storage)

13 DLR.de Chart 13 Comparative testing of storage module and (SiC) receiver types (190 slm) 3 Cordierite foams 30 ppi; L = 12 cm SiSiC honeycomb 90 cpsi; Schunk Weight 1404 g Length = 15 cm 3 SiSiC foams 10 ppi; ERBICOL Weight 246 g Length = 12 cm ReSiC honeycomb 90 cpsi; Stobbe TC Weight 584 g Length = 10 cm 1 Cordierite honeycomb 400 cpsi L = 12 cm

14 DLR.de Chart 14 Comparative performance of SiC receivers tested Receiver: SiSiC honeycomb Receiver: SiSiC foams Air Flow: 190 slm Receiver: ReSiC honeycomb Temperature ( o C) T1 T2 T3 200 T4 T5 T6 100 T7 T9 T Time (min) T1 T3 T4 T5 T6 T7 T9 T Time (min) Time (min) T1 T3 T4 T5 T6 T7 T9 T8 Tcamera T o C T3 930 o C T3 930 o C T5 975 o C T5 915 o C T5 875 o C T6 725 o C T6 755 o C T6 775 o C

15 DLR.de Chart 15 Conclusions: The construction modularity of the current state-of-the-art storage system in airoperated STPPs provides for implementation of concepts like cascades of different redox oxide materials and spatial variation of solid material porosity in three dimensions, to enhance utilization of heat transfer fluid and storage of its enthalpy. However: limited variety of redox oxides available within the particular temperature range. Co 3 O 4 : the most reliable, demonstrating full, quantitative cyclability within a narrow temperature range ( model system ). Mn 2 O 3 : low cooling rates required for oxidation; large temperature gap between reduction/oxidation temperature. This disadvantage though, can be rendered to benefit within a cascaded structure. Relatively high reduction temperatures of both Co 3 O 4 (T red 895 o C) and Mn 2 O 3 (T red 950 o C). Could be achieved in the solar furnace with currently available SiSiC honeycomb receivers: capability of solar-heating incoming air to 1050 o C, and two cordierite foams downstream ( 8 cm) to 950 o C demonstrated.

16 DLR.de Chart 16 Acknowledgements: To EU for financing this work under the MARIE CURIE ACTION Intra- European Fellowships (IEF) Call: FP7- PEOPLE-2011-IEF, Grant : Thermochemical Storage of Solar Heat via Advanced Reactors/Heat exchangers based on Ceramic Foams (STOLARFOAM) To DLR Programmdirektion Energie (PD-E) for funding through Project Thermochemical storage for CSPapplications based on Redox- Reactions from materials to processes (REDOXSTORE).

17 DLR.de Chart 17 > Thank you for your attention!