chemical engineering research and design 86 (2008) 1216–1222 Contents lists available at ScienceDirect Chemical Engineering Research and Design journal homepage: www.elsevier.com/locate/cherd Dynamic modeling of a volumetric solar reactor for volatile metal oxide reduction Patrice Charvin a,* , Stéphane Abanades a , Pierre Neveu a , Florent Lemont b , Gilles Flamant a a PROcesses, Materials and Solar Energy Laboratory (PROMES – CNRS/UPR 8521) PROMES Laboratory, 7 rue du four solaire, 66120 Odeillo, Font Romeu, France b Commissariat à l’Energie Atomique, Rhône Valley Research Center, BP 17171, 30207 Bagnols sur Cèze, France abstract The study deals with a dynamic modeling of a solar thermochemical reactor operating continuously to simulate its behavior during transient periods. This reactor is devoted to the thermal reduction of volatile metal oxides which are involved in water-splitting cycles for hydrogen production. Unsteady mass and energy balances are solved to determine the evolution of the reactor temperature and of the outlet gas composition versus time. The kinetics of the chemical reaction is considered in the specific case of zinc oxide dissociation for which reliable data are available. For the chosen reactor design, the thermal inertia of the reactor materials has a weak influence on zinc production during short solar flux interruptions. Energy losses by conduction through reactor walls are the highest at small scale (ranging between 30% and 40% at 1kW scale), whereas radiative losses through the aperture become predominant at large scale (50MW scale) and greatly depend on the solar concentration ratio. Then, simulations show that a minimum concentration ratio of 2500 is necessary to reach a sufficient temperature (above 2000K) allowing efficient ZnO dissociation. © 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. Keywords: Dynamic modeling; Thermochemical cycle; Water-splitting; Solar energy; Zinc oxide 1. Introduction The development of renewable energies and the production of sustainable energy carriers is a major challenge to ensure mankind development and energy surety with the respect of environment. Hydrogen is a promising energy carrier and could be the solution to store and transport solar energy in a chemical form. Water-splitting achieved by the mean of multi-step thermochemical cycles is an environmentally friendly route to produce hydrogen without any fossil fuel consumption and greenhouse gas emission. Short thermo- chemical cycles (two or three chemical steps) based on metal oxide redox pairs have been highlighted as the most efficient processes to convert solar energy into hydrogen (Bilgen and Bilgen, 1982; Perkins and Weimer, 2004; Abanades et al., 2006). The dissociation of water is performed at medium tem- perature using a metal or a reduced oxide. This active ∗ Corresponding author. Tel.: +33 4 68 30 77 31; fax: +33 4 68 30 29 40. E-mail address: patrice.charvin@promes.cnrs.fr (P. Charvin). Received 24 January 2008; Accepted 17 May 2008 intermediate must be previously prepared from the stable oxide by thermal reduction. The endothermic reduction of the oxide must be carried out in a high-temperature reactor heated by concentrated solar energy. The only energy input of the cycle is supplied to the solar reactor which is the key point of the whole process achieving solar energy absorption and conversion into chemi- cals. Its large scale extrapolation must be kept in mind during the design of the solar reactor. Solar energy can be absorbed directly by a solid reactant or used in an indirect heating configuration leading to two reac- tor concepts. For the latter configuration, a vertical tubular reactor can be heated with concentrated solar energy absorbed by the external surface of the wall (Perkins and Weimer, 2004). The solid reactant introduced at the top falls in the tube and absorbs IR radiations emitted by the internal surface of the high-temperature tube. Temperature of particles increases 0263-8762/$ – see front matter © 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.cherd.2008.05.009