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, 51147 Köln, Germany
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
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).
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
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, 81 829 837, 2007. 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).
DLR.de Chart 6 Tests Scale Evolution (single-oxide or cascaded testing) TGA Lab-scale furnace test rig Solar receivers
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 1200 100 99 t=1 hr 1000 98 97 96 95 T redox =? o C t=1 hr T plateau oxidation 800 600 400 Temperature ( o C) 94 Me x O y oxidized Air Ar Me x O y reduced 200 93 Me x O y : T plateau reduction > T redox > T plateau oxidation 92 0 0 100 200 300 400 500 600 700 800 900 Time (min) Reaction T red ( o C) Max. wt. loss ( %) 2 BaO 2 + ΔH 2 BaO + O 2 690 9.45 2 Co 3 O 4 + ΔH 6 CoO + O 2 870 6.64 6 Mn 2 O 3 + ΔH 4 Mn 3 O 4 + O 2 950 3.38 4 CuO + ΔH 2 Cu 2 O + O 2 1030 10.01
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 800-1000 o C (950 o C). As powder, coated on honeycombs/ foams or shaped in foams. 102 102 Co Co 3 O 4 -loaded Cordierite foam o C/min; long-term cycling 3 O 4 powder, 30 cycles: 985-785 o C, 5 o 101 101 100 100 99 99 98 97 98 96 97 95 96 94 95 93 6.69 % -2000 92 94 200 91 93 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 92 0 0 400500 800 1000 1200 Time (min) 1500 1600 2000 2400 2500 2800 Time (min) 1200 1000 1000 800 1000 0 800 600 0-1000 400 Temperature ( o C) Temperature ( o C) ( o C) Agrafiotis, Roeb, Schmücker, Sattler, Solar Energy, Parts I, II, III (2014), (2015).
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 ( 780-690 o C)!! Very narrow temperature range ( 690-750 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. 101 100 99 98 97 96 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 95 0 0 100 200 300 400 500 600 700 800 900 1000 Time (min) 1200 1000 800 600 400 200 Temperature ( o C)
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 2 202.5 895 875 6 Mn 2 O 3 + ΔH 4 Mn 3 O 4 + O 2 31.9 950 720 101 100 Wt loss: 1.35 % Wt re-gain: 0.6 % 1200 99 98 97 96 95 94 93 La SrFeO 3 800 400 Temperature 92 0 0 100 200 300 400 500 600 Time (min) Temperature ( o C) Favourable Ts for oxidation but entire cascade needs T > 950 o C during reduction
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 ) 1000 800 600 400 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 50 40 30 20 O2 O2 concentration concentration (% (% in in air) air) 200 10 0 0 0 200 400 600 800 1000 Time Time (min) (min)
DLR.de Chart 12 Solar furnace test rig: Receiver storage modules assembly; 1 st tests: T along non-coated storage module (sensible-only storage)
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
DLR.de Chart 14 Comparative performance of SiC receivers tested 1500 1400 Receiver: SiSiC honeycomb Receiver: SiSiC foams Air Flow: 190 slm 1300 1200 Receiver: ReSiC honeycomb 1100 1000 Temperature ( o C) 900 800 700 600 500 400 300 T1 T2 T3 200 T4 T5 T6 100 T7 T9 T8 0 0 100 200 300 400 Time (min) T1 T3 T4 T5 T6 T7 T9 T8 0 100 200 300 400 0 50 100 150 200 250 Time (min) Time (min) T1 T3 T4 T5 T6 T7 T9 T8 Tcamera T3 1030 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
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.
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 300194: 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).
DLR.de Chart 17 > Thank you for your attention! christos.agrafiotis@dlr.de martin.roeb@dlr.de christian.sattler@dlr.de