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O2 Releasing Reactivity of Ceramics for Rotary-Type Solar Reactor With Two-Step H2O Splitting

[+] Author Affiliations
Yutaka Tamaura, Hiroshi Kaneko

Tokyo Institute of Technology, Tokyo, Japan

Paper No. ES2009-90421, pp. 497-505; 9 pages
doi:10.1115/ES2009-90421
From:
  • ASME 2009 3rd International Conference on Energy Sustainability collocated with the Heat Transfer and InterPACK09 Conferences
  • ASME 2009 3rd International Conference on Energy Sustainability, Volume 2
  • San Francisco, California, USA, July 19–23, 2009
  • Conference Sponsors: Advanced Energy Systems Division and Solar Energy Division
  • ISBN: 978-0-7918-4890-6 | eISBN: 978-0-7918-3851-8
  • Copyright © 2009 by ASME

abstract

The relationship among the factors determining the thermal efficiency to convert concentrated solar thermal energy to chemical energy by the O2 -releasing reaction of the reactive ceramics in the tow-step water splitting process has been studied for the development of rotary-type solar reactors. The α O2 -releasing reaction which has been discovered in the present study for Ni-ferrite (NiFe2 O4 ) has a high chemical reaction rate (k = 0.50 mol sec−1 /m2 ). From calculation with the heat transfer equation in terms of heat transfer through the cavity wall with thckness, d (m), and heat absorption by the endothermic process of the O2 -releasing reaction with rate constant, k (mol sec−1 /m2 ), it is cralified that the heat flux of 2000 kW/m2 can be absorbed by the α O2 -releasing reaction using the cavity wall with the thickness, d = 0.00036 m and thermal conductivity, λ = 70 WK−1 m−1 . The heat loss in the temperature swing (ΔT = 300K) for the two step water splitting of O2 releasing step (TH = 1773K) and H2 generation step (TL = 1473K) is only 8.3% for the α O2 -releasing reaction. However, the O2 releasing reaction of NiFe2 O4 in the β region where the reaction rate constant is around 0.0001 mol sec−1 /m2 , the heat flux of the concentrated solar energy to be used for conversion to chemical energy becomes very low around 300 kW/m2 ; the heat loss by the temperature swing in the two step water splitting is 87%. It is concluded that the α O2 -releasing reaction can be used for the rotary-type solar reactor to convert the concentrated solar thermal energy to chemical energy with a high efficiency.

Copyright © 2009 by ASME

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