1. Analysis of radial-flow packed beds for thermal energy storage Josh D. McTigue Alexander J. White 9 th June 2016 Department of Engineering, University of Cambridge

2. Summary Previous work on axial-flow packed beds Description of radial-flow packed beds Comparison of radial-flow and axial-flow stores Thermo-economic optimisation

3. HOT STORE (500 C)COLD STORE (-150 C) MaterialHeat Capacity J / Kg K Energy Density MJ / m 3 Heat Capacity J / Kg K Energy Density MJ / m 3 Al 2 O 3 1070 56054095 Fe 2 O 3 850 585500125 SiO 2 1020 36057075 Typical Storage Densities Hydro(500m drop)5 MJ / m 3 CAES(100 bar)36 MJ / m 3

4. Previous work – axial-flow packed beds [1] A. J. White, “Loss analysis of thermal reservoirs for electrical energy storage schemes,” Applied Energy, vol. 88, pp. 4150– 4159, Nov. 2011 [2] A. White, J. McTigue, and C. Markides, “Wave propagation and thermodynamic losses in packed-bed thermal reservoirs for energy storage,” Applied Energy, vol. 130, pp. 648–657, 2014.

5. Previous work – segmented stores [3] J. MacNaghten, J. S. Howes, and R. G. Hunt, “Improved heat storage apparatus,” Patent no. EP/2689207/2011, 2011. [4] J. McTigue and A. J. White, “Segmented packed beds for improved thermal energy storage performance,” IET Renewable Power Generation, 2016. Accepted

6. Previous work – integration with PTES [5] A. White, G. Parks, and C. N. Markides, “Thermodynamic analysis of pumped thermal electricity storage,” Applied Thermal Engineering, vol. 53, pp. 291–298, May 2013. [6] J. D. McTigue, A. J. White, and C. N. Markides, “Parametric studies and optimisation of pumped thermal electricity storage,” Applied Energy, vol. 137, pp. 800–811, Sept. 2015.

7. Radial-flow packed beds [7] L. Bradley, “Regenerative stove,” 1942. US Patent 2,272,108. [8] R. Daschner, S. Binder, and M. Mocker, “Pebble bed regenerator and storage system for high temperature use,” Applied Energy, vol. 109, pp. 394–401, Sept. 2013.

8. Radial-flow thermal fronts [2] A. White, J. McTigue, and C. Markides, “Wave propagation and thermodynamic losses in packed-bed thermal reservoirs for energy storage,” Applied Energy, vol. 130, pp. 648–657, 2014.

9. Radial-flow thermal fronts [2] A. White, J. McTigue, and C. Markides, “Wave propagation and thermodynamic losses in packed-bed thermal reservoirs for energy storage,” Applied Energy, vol. 130, pp. 648–657, 2014.

10. Radial-flow availability losses

11. Radial-flow availability losses - comparison

12. RADIAL AXIAL

13. Radial-flow availability losses - comparison RADIAL AXIAL

14. Radial-flow availability losses - comparison RADIAL AXIAL

15. Optimisation involves minimising Availability losses: Capital cost per availability output: Optimisation objectives

16. Packed bed capital costs CostValue k PV (£/m 3 bar)200 k pack (£/m 3 )1400 k ins (£/m 3 )1950

17. Optimisation parameters

18. Optimisation results – cold store

19. CONCLUSIONS A number of packed bed technologies have been investigated Radial-flow stores have comparable performance to axial-flow stores Radial-flow stores are typically more expensive due to larger volume requirements

20. Acknowledgements Dr. White and Dr. Markides Cambridge University Engineering Department St. Catharine’s College, University of Cambridge EPSRC Isentropic Ltd.