Redox cycles with doped calcium manganites for high-temperature thermochemical energy storage in concentrating solar power

Redox cycles with reducible perovskite oxides of the form ABO₃ can provide thermochemical energy storage (TCES) with higher energy density and storage temperatures than molten-salt systems for large-scale energy storage in concentrating solar power (CSP). Perovskites from earth abundant cations are desirable for cost-effective solutions, but such materials must demonstrate appropriate thermodynamics for high specific TCES and favorable kinetics for heat-driven reduction and exothermic re-oxidation. This dissertation explores the thermodynamics and kinetics of doped CaMnO_3-δ particles for TCES redox cycles where particles are heated and reduced in N₂ (P_\text{O2} \approx 10^-4 bar) to high temperatures (700 to 1000^\circC) in a solid-particle solar receiver. Chemical and sensible energy stored in the reduced perovskite particles is released as needed to a supercritical CO₂ power cycle via re-oxidation and cooling of the material. Thermodynamics of Ca_1-xSr_xMnO_3-δ ($x=0.05$ and $0.1$) and CaCr_yMn_1-yO_3-δ ($y=0.05$ and $0.1$) are characterized through thermogravimetric analysis and calorimetry. Results indicate Ca_1-xSr_xMnO_3-δ compositions can store over 200 kJ kg^-1 more specific energy storage compared to inert particulate TES media for T \ge 900^\circC; the specific energy storage potential of Ca_0.9Sr_0.1MnO_3-δ at T=900^\circC and P_\text{O2}=10^-4 bar is 706 kJ kg^-1. Challenges are expected achieving these high values of energy storage in a transport-limited receiver with low residence time for CSP. Redox kinetics are explored in a packed bed reactor with rapid heating capabilities. Results in isothermal tests show that oxidation is significantly faster than reduction. Modeling of packed bed experiments indicate that reduction at T \ge 800^\circC is limited by build-up of oxygen in the gas phase and equilibrium thermodynamics between the solid and gas phases. Long-term redox cycling tests, which simulate a nominal TCES cycle, demonstrate excellent chemical stability for all materials. A standard deviation of 1.9\% on the extent of reduction over 1000 cycles was observed for Ca_0.9Sr_0.1MnO_3-δ. Modeling efforts of the packed bed experiments allow for characterization of redox kinetics, to be implemented in computational models for system component design. One of the most promising compositions, Ca_0.9Sr_0.1MnO_3-δ, is implemented in a 1-D receiver model to explore designs and operating conditions for perovskite-based energy storage systems.

Name thesis:degree_name

Doctor of Philosophy (Ph.D.)

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor dc:publisher

Colorado School of Mines. Arthur Lakes Library

Year dc:date.issued

2018

Author dc:creator

• Imponenti, Luca

Advisor dc:contributor.advisor

• Jackson, Gregory

Committee members dc:contributor.committeemember

• O'Hayre, Ryan P.
• Kee, R. J.
• Braun, Robert J.

• concentrated solar power
• redox cycles
• calcium manganite
• thermochemical energy storage
• perovskite

Statement dc:rights

• Copyright of the original work is retained by the author.

Language dc:language.iso

eng, English

Identifier

T 8625

OAI identifier oai:identifier

oai:repository.mines.edu:11124/172807