DEVELOPMENT OF AN INCLINED SLOPE SOLAR REACTOR TECHNOLOGIES FOR TWO-STEP SOLAR THERMOCHEMICAL CYCLES BASED ON REDOX-ACTIVE MATERIALS

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1 DEVELOPMENT OF AN INCLINED SLOPE SOLAR REACTOR TECHNOLOGIES FOR TWO-STEP SOLAR THERMOCHEMICAL CYCLES BASED ON REDOX-ACTIVE MATERIALS PETER G. LOUTZENHISER SOLAR FUELS AND TECHNOLOGY LABORATORY GEORGE W. WOODRUFF SCHOOL OF MECHANICAL ENGINEERING

2 PROMOTES SOLAR THERMOCHEMICAL STORAGE

3 SOLAR THERMOCHEMICAL REACTOR DEVELOPMENT IS IMPORTANT TOO! Redox-active materials development Thermochemical reactor development? Cation substitution to tune MIEC materials for Increased redox capacitance Faster kinetics from increased oxygen mobility Optimized thermodynamics Thermochemical reactors must also be designed for Optimal absorption of concentrated solar irradiation Specific solar concentrating facilities Redox-active materials and residence times

4 SOLAR THERMOCHEMICAL REACTOR DESIGN CRITERIA WITHIN THE PROMOTES PROJECT FOR SOLAR THERMOCHEMICAL HEAT STORAGE Use redox-active particles in a continuous/semi-continuous flow reactor: Particles are easier to heat and move and continuous feed reduces the reactor size. Heat particles to greater than 1000 C: Ideal for integration with an Air Brayton cycle. Operate under partial vacuum: Allows for increased thermal reduction (Le Chatelier s principle) without operating with an inert gas and mitigating the associated sensible heat and O 2 separation losses. Directly irradiate particles: The transmission losses through a window are smaller than the entropy production due to transferring heat across an absorber plate/tube to the particles for indirect irradiation at these temperatures. Maximize absorption (receiver) efficiency: Little opportunity to vary spectral properties at > 1000 C to reduce emissions, necessitating a cavity-type system NOT A DESIGN CRITERION Solid-to-solid heat recovery: The heat is being used in the Air Brayton cycle through a counter-flow direct exchange reactor and is being directly converted to work.

5 SOLAR THERMOCHEMICAL REACTOR CONCEPT: SOLAR RECEIVER/REDUCER/REACTOR (SR3) Solar Thermochemical INclined Granular flow Reactor (STINGR) Schrader et al, Solar Energy 150 (2017) Efficient thermal reduction within solar thermochemical reactor: Direct solar irradiation Continuous on-sun operation Matched incident solar power to rate of sensible and chemical energy storage Reactor cavity designed to mitigate radiative losses through window and promote direct irradiation along inclined plane Reactor evacuated to promote low partial O 2, sealed with quartz window to introduce concentrated solar irradiation Combination of frictional and collisional effects of particles produce thin granular flow, increased particle residence times

6 COMMUNICATION BETWEEN SOLAR THERMOCHEMICAL REACTOR AND MATERIAL DESIGNERS WAS (IS) KEY Factors in materials design and synthesis: Thermodynamics and kinetics Particle sizes Shape Scaling Cost Communication Effects on the thermochemical reactor design to control residence times: Ability to flow Ability to heat and thermally reduce Ability to cycle

7 COMMUNICATION BETWEEN SOLAR THERMOCHEMICAL REACTOR AND MATERIAL DESIGNERS WAS (IS) KEY Factors in materials design and synthesis: Thermodynamics and kinetics Particle sizes Shape Scaling Cost Communication Effects on the thermochemical reactor design to control residence times: Ability to flow Ability to heat and thermally reduce Ability to cycle

8 PARTICLE FLOW CHARACTERIZATION Velocity profile determine for a range of slopes for empirical parameters factoring in slope roughness, and particle size and shape Particle imaging velocimetry Velocity field Streamlines Tilt flow rig at room temperature

9 HEAT TRANSFER MODELING Temperature distribution Steady-state Radiative heat transfer: Monte Carlo directional intensities and exchange from high flux solar simulator in the bed accounting for spectral properties, and Rosseland approximation for granular bed Bed: 1-D particle flow and 3-D conduction 1D transfer through cavity walls Conversion distribution of Co 3 O 4 Schrader et al, Solar Energy 150 (2017)

10 FABRICATION OF A LABORATORY-SCALE STINGR Demonstrated under vacuum at ~120 mbar Inert Material Composition Size Distributi on Angle of Repose CarboAccucast ID50 75 % Al 2 O 3, 11 % SiO 2, and other metal oxides µm 27 o

11 CONCLUSIONS AND THE PATH FORWARD CONCLUSIONS The design of solar thermochemical technical requires close interactions with materials engineers and scientists developing novel redox-active materials with inputs from all team members The culmination of these interactions has resulted in a solar receiver/reducer/reactor (SINGR) developed within the PROMOTES project to thermally reduce CaAl 0.2 Mn 0.8 O 3-δ with preliminary experiments already performed THE PATH FORWARD Numerous engineering challenges need to be addressed that were not possible given the timeframe and scope of the PROMOTES project: Particle flow characterization at high temperatures (radiative turbulence) Development of particle feedthroughs that facilitate particle vacuum within the SR3 but allow different pressures throughout the system Thorough characterization and validation of models for subsequent scale-up of solar reactors with a ranges solar concentrating facilities (secondary concentrator development) Development of feeding technologies to address solar transients by regulating flows into and out of the reactors [Engage controls people]

12 ACKNOWLEDGEMENTS Funding: U.S. Department of Energy SunSHOT initiative under Award No. DE-FOA (PROMOTES project in ELEMENTS) and the National Science Foundation Graduate Research Fellowship under Grant No. DGE Georgia Tech: Evan Bush, Robert Gill, Alex Muroyama, Garrett Scheiber, Andrew Schrader, and Sheldon Jeter Visiting ETH Zurich students (Aldo Steinfeld): Karl-Philipp Schlichtung and Gianmarco De Dominicis SNL: Andrea Ambrosini, Sean Babiniec, Cliff Ho, and Jim Miller ASU: Ellen Stechel and Nathan Johnson KSU: Haney Al-Ansary