(200f) Carbonation Kinetics of Sro By CO2 for Solar Thermochemical Energy Storage

Concentrated solar power (CSP) is one promising method of converting clean solar thermal energy into electricity which avoids the use of fossil fuels.  Thermal energy storage (TES) in conjunction with CSP can increase the utilization of solar energy by enabling plant operators to generate electricity beyond normal on-sun hours. Thermochemical energy storage (TCES) is an emerging type of TES system based on a reversible reaction that offers higher energy density than latent or sensible energy storage. Thermochemical energy storage of on-sun thermal energy is achieved when a reactive system absorbs thermal energy and proceeds with a reversible chemical reaction. In a time of off-sun power demand, the reverse reaction is then initiated and energy is released, thus recovering thermal energy for use in a power cycle.  One such reactive system is the reversible carbonation/decomposition of SrO/SrCO₃, which occurs ca. 1200°C.  Such high quality heat is suitable for high efficiency, combined cycle power generation, which has the potential to translate into more competitive solar electricity prices.

In order to accurately predict the rate of heat generation from a TCES system and improve the CO₂ capture capacity of SrO, it is important to understand the mechanism of strontium oxide carbonation and the kinetic expressions describing the reversible reaction, which has not been studied. To investigate this mechanism, SrO carbonation kinetics have been studied by means of thermogravimetric analysis (TGA). In order to better describe the reaction mechanism, the influence of intensive variables such as reaction temperature and CO₂ partial pressure were investigated. Carbonation was performed at several temperatures (900-1200°C) and partial pressures of CO₂ (0.1 to 1 bar).  The effects of different initial mass (20-60 mg) and sample size (25 – 106 µm) has also been investigated.   

The carbonation reaction progression can be divided into three stages: an initial induction period; a rapid kinetically-controlled carbonation stage; and finally a sluggish diffusion-controlled regime. Our research aims to present the kinetic model developed to explain the experimental data and compare the heat generation rates to the current state of the art TES systems.