Session: 06-04: CSP Receivers and Reactors III

Paper Number: 169851

169851 - Reduced Order Modeling of a Fluidized-Bed Solar Receiver for Perovskite-Based Thermochemical Energy Storage 

Abstract: 

Perovskite oxides from earth abundant elements have the potential to store and release high-temperature heat from concentrated solar energy through reversible reduction/oxidation (redox) cycles. These redox cycles can achieve higher specific energies than inert oxides for temperature ranges that are relevant to drive efficient supercritical CO₂ cycles or chemical process for solar fuel production. The total energy of one noteworthy perovskite, Ca_0.9Sr_0.1MnO_3-δ, for storage cycles between T_C = 500 °C and T_H = 950 °C can exceed 850 kJ kg⁻¹ [1] while inert alumina/silica can provide 600 kJ kg⁻¹ over the same temperature range. Capturing the high specific thermochemical energy storage in the perovskites through central solar receivers requires receiver/reactor designs that sustain high rates of heat transfer into the perovskite material to drive the endothermic reduction. This work examines an indirect fluidized-bed particle receiver that uses an upward-flowing, fluidizing sweep gas with low O₂ partial pressure to facilitate reduction of downward-flowing Ca_0.9Sr_0.1MnO_3-δ for thermochemical energy storage in a concentrating solar plant. A reduced-order, vertically discretized model of the fluidized bed receiver/reactor predicts how changing particle properties and adjusting operating conditions - such as solar wall fluxes, particle mass fluxes, and fluidizing gas velocities - impact receiver efficiency and the partitioning of thermal and chemical energy in the reduced perovskite particles.

This reduced order model solves the 1-D conservation equations, including mass, species, momentum, and energy balances of the gas and solid particle phases as well as the receiver walls along the height of the reactor using the finite volume approach. The model implements empirical heat transfer correlations derived from narrow-channel fluidized bed heat transfer experiments [2]. Kinetics and thermodynamics calculations of a low-cost perovskite oxide Ca_0.9Sr_0.1MnO_3-δ are derived from packed-bed cyclic redox studies [3]. A baseline case was established with an inlet particle mass flux of 10 kg m^-2 s^-1, particle diameter of 320 μm, an inlet O₂ mole fraction of 0.01, and an average wall solar flux of 200 kW m^-2. The baseline case results show that fluidized bed receiver heats the perovskite particles to an acceptable temperature (T_s = 1019 ºC) and the high particle-wall heat transfer coefficient maintains a receiver solar efficiency of η_solar = 85.7% with a maximum wall temperature T_w,max = 1167 ºC. Such a wall temperature can be readily sustained with sintered SiC  walls as used in this study. For this case, the fraction of 15% of the total energy stored was in chemical energy as the extent of reduction was limited to δ = 0.16 due to the increase in O₂ partial pressure throughout the reactor due to the reduction reaction. 

Parametric studies explored variation in operating conditions including external wall solar fluxes up to 260 kW m^-2 at which T_w,max = 1355 ºC and the extent of reduction increases to δ = 0.21. Different particle fluxes from 6 to 10 kg m^-2 s^-1 indicate that lowering particle inlet flux leads to higher perovskite δ due to the longer residence time of solid particles within the bed but at the expense of higher maximum wall temperature (T_w,max = 1448 ºC) , which exceeds the limits for SiC material.  These design tradeoffs indicate that an indirect fluidized bed particle receiver may be feasible with SiC walls and adequate particle and gas flows.

References

[1] Imponenti L, Albrecht KJ, Kharait R, Sanders MD, Jackson GS. Redox cycles with doped calcium manganites for thermochemical energy storage to 1000 °C. Applied Energy. 2018;230:1-18.

[2] Brewster KJ, Fosheim JR, Arthur-Arhin WJ, Schubert KE, Chen-Glasser M, Billman JE, et al. Particle-wall heat transfer in narrow-channel bubbling fluidized beds for thermal energy storage. International Journal of Heat and Mass Transfer. 2024;224:125276.

[3] Albrecht KJ. Multiscale Modeling and Experimental Interpretation of Perovskite  Oxide Materials in Thermochemical Energy Storage and Conversion for Application in Concentrating Solar Power [Dissertation]. Golden, CO: Colorado School of Mines; 2016.

Presenting Author: Armin Asadi Colorado School of Mines

Presenting Author Biography: Armin Asadi is a PhD student in Mechanical Engineering at the Colorado School of Mines.