SrO-Al2O3 composites for thermochemical energy storage: carbonation kinetics

Among possible alternatives, the reversible dissociation/carbonation of metal carbonates, carried out in fluidized bed reactors, is of paramount relevance for thermochemical energy storage (TCES) in concentrating solar power (CSP) plants. In this framework the SrCO3/SrO system is receiving great research interest due to its high energy density (4 GJ m-3) and working temperatures (up to 1200 °C). In analogy to the more investigated CaCO3/CaO couple, one of the main problems of SrO is that particle sintering causes a dramatic drop of its reactivity over multiple carbonation/calcination cycles. In this context, it has been shown that Al2O3 can be successfully used as sintering and agglomeration inhibitor to improve the performances of the SrO/SrCO3 system. Besides the multicycle carbonation conversion, also the carbonation kinetics is crucial for the reactor design, especially during the scale-up of thermal processes from laboratory to real scale. However, no studies are available on the kinetic modelling of the SrO carbonation reaction under operating conditions typical of TCES-CSP applications. In this work, the gas-solid kinetics of SrO carbonation has been investigated in thermogravimetric equipment. In particular, tests have been performed using an SrO-Al2O3 composite containing 34%wt of Al2O3, which has been previously proved to be stable from both the reactive and mechanical point of view. Then, two different kinetic models, for the fast and slow stages of the carbonation reaction, have been applied to analyze the experimental data, thus obtaining useful information for design and optimization of the SrO carbonation reactor.