Numerical modelling of ceria undergoing reduction in a particle-gas counter-flow: Effects of chemical kinetics under isothermal conditions
- Authors: Li, Sha , Wheeler, Vincent , Kumar, Apurv , Lipinski, Wojciech
- Date: 2020
- Type: Text , Journal article
- Relation: Chemical Engineering Science Vol. 218, no. (Jun 2020), p. 14
- Full Text: false
- Reviewed:
- Description: A numerical model is employed to simulate a single tube reactor featuring a downward particle flow counter to an upward inert gas flow for ceria reduction in the dilute flow regime. The coupled phenomena of mass and momentum transfer as well as chemical kinetics are simulated assuming isothermal operation for the reactor. The model predicts the reduction extent under varying reaction kinetics as well as design and operational choices. The reduction extent is found to increase with the reaction rate constant until achieving the thermodynamic upper limit at a certain critical value. This critical rate constant signifies a transition from a chemical kinetics limited conversion to a gas advection limited conversion. The effect of the reactor length and the particle size on reaction extent is studied for a range of realistic cases. An empirical correlation is developed to quantify the effects of particle and gas flow rates on reduction extent at both slow and fast kinetics. The present work offers insights to help guide reactor design and operation towards achieving the maximum reduction extent. (C) 2020 Elsevier Ltd. All rights reserved.
Thermodynamic guiding principles for designing nonstoichiometric redox materials for solar thermochemical fuel production : ceria, perovskites, and beyond
- Authors: Li, Sha , Wheeler, Vincent , Kumar, Apurv , Venkataraman, Mahesh , Muhich, Chrisopher
- Date: 2022
- Type: Text , Journal article
- Relation: Energy Technology Vol. 10, no. 1 (2022), p.
- Full Text: false
- Reviewed:
- Description: Two-step solar thermochemical water splitting is a promising pathway for renewable fuel production due to its potential for high thermal efficiency via full-spectrum sunlight utilization. Such a promise critically relies on simultaneous innovation in the redox materials and the reactor systems. Most prior efforts on material design are focused on improving the fuel yield at lower reduction temperatures. However, developing materials with both high fuel output and efficiency remains a key challenge, requiring a rigorous understanding of the effects of material thermodynamic properties. Herein, a generic thermodynamic framework is described to decipher the material effects by studying both the state-of-the-art and hypothetical materials within a counterflow reactor system. A global efficiency map is presented for redox materials, revealing inevitable tradeoffs among competing factors such as thermal losses, sweep gas and oxidizer demand, solid preheating, and reduction enthalpy. The choice of the most efficient material is closely linked to the system conditions. Ceria-based materials outperform perovskites under most scenarios, and the optimal hypothetical materials tend to favor higher reduction enthalpies and entropies than existing materials. This work offers a valuable material design roadmap to identify solutions toward efficient solar fuel production. © 2021 Wiley-VCH GmbH. **Please note that there are multiple authors for this article therefore only the name of the first 5 including Federation University Australia affiliate “Apurv Kumar” is provided in this record**