Kinetics of the carbonation reaction of an SrO-Al2O3 composite for thermochemical energy storage

Abstract

• The carbonation kinetics of a SrO-Al 2 O 3 composite has been investigated for TCES-CSP. • SrO has been stabilized using Al 2 O 3 as a sintering/agglomeration inhibitor. • The fast carbonation stage is well described by the contracting volume model. • The slow carbonation stage is well described by the Jander’s model. • Activation energy of the SrO-Al 2 O 3 carbonation reaction at the 900–1000 °C was estimated as 52 kJ/mol. In framework of the thermochemical energy storage (TCES) in concentrating solar power (CSP) applications, great attention is focused on the SrCO 3 /SrO system, which is characterized by remarkably high theoretical volumetric energy density (4 GJ m SrC O 3 - 3 ) and working temperatures (1200 °C). It has been shown that the incorporation of Al 2 O 3 in the SrO/SrCO 3 system can successfully hinder the sintering and agglomeration phenomena, thus improving the performances of the system. Aiming at providing useful information for the design, simulation and scale up of a reactor for the energy storage, besides the multicycle carbonation conversion, the evaluation of the reaction kinetics is crucial. Thus, in this work, the kinetics of the carbonation of a SrO-Al 2 O 3 composite (34%wt of Al 2 O 3 ) for TCES-CSP has been investigated for the first time using a two-stage kinetic model. In particular, tests have been performed in a thermogravimetric analyzer at operating conditions relevant for TCES, namely at 1 atm of CO 2 partial pressure within the temperature range of 900–1050 °C. The reaction rate, the intrinsic carbonation kinetic constant, the characteristic product layer thickness and their dependence on the temperature has been evaluated in the temperature range 900–1000 °C; the activation energy has been found to be 52 kJ mol −1 . Finally, comparison of the calculated conversion-time profiles, obtained from the applied kinetic models, with experimental data revealed a good agreement.