Temperature variations in the oxygen carrier particles during their reduction and oxidation in a chemical-looping combustion system

A particle reaction model including mass and heat transfer has been developed to know the temperature variations produced inside the oxygen carrier particles during the cyclic reduction and oxidation reactions taking place in a Chemical-Looping Combustion (CLC) system. The reactions of the different oxygen carriers based on Cu, Co, Fe, Mn, and Ni during the reduction with fuel gas (CH4, CO, and H2) and oxidation (O2) have been considered. In these systems, the oxidation reaction is always exothermic with subsequent heat release; however, the reduction reaction can be exothermic or endothermic depending on the metal oxide and the fuel gas. The heat generated inside the oxygen carriers during the exothermic reactions increases the particle temperature, and could affect to the particle structure if the temperature increase is near to the melting point of the active materials. Several variables that affect to the reaction rate and to the heat transport process have been analyzed to know their effect on the internal particle temperature. For a given oxygen carrier and reaction, the maximum temperature of the particles depended mainly on the particle size, the reaction rate, and the external heat transfer resistance, being lower the effect of the oxygen carrier porosity, type of inert material, and metal oxide content. The highest temperature variations were reached for the oxidation reactions, with the maximum * Corresponding author: Tel.: +34-976-733977; fax: +34-976-733318. E-mail address: [email protected] (F. García-Labiano)