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• Carbonation reaction kinetics of limestone-based CaCO 3 /Al 2 O 3 mixture is estimated. • Numerical modelling of CaCO 3 based reactor for thermal storage application is performed. • The influence of operating parameters on the reactor's performance is examined. • The effect of incorporating graphite fin into the CaCO 3 reactor is studied. This study conducts kinetic analyses of the carbonation reaction of CaCO 3 (doped with Al 2 O 3) as well as parametric analyses of the performance of a thermochemical reactor, which can act as a thermal battery. Kinetic measurements of CO 2 release and absorption were carried out using thermogravimetric analysis (TGA) at 815, 830 and 845 °C on a CaCO 3 /Al 2 O 3 sample that had been previously cycled over 500 times. The rapid reaction kinetics revealed that the Avrami nucleation growth model with exponent 3 fits well to explain the carbonation reaction. The numerical study considered a cylindrical reactor with a height and diameter of 100 mm. According to numerical analysis, at an applied CO 2 pressure of 1 bar, increasing the thermal conductivity of the reactor bed from 1.33 to 5 W/m.K increases the rate of carbonation reaction by 74%. When the applied CO 2 pressure is increased from 1 to 2 bar, the performance of the reactor bed with thermal conductivity of 1.33 W/m.K improves by 42%; however, when the applied CO 2 pressure is increased from 2 to 3 bar, the performance improves by only 18%. Additionally, when the boundary temperature of the reactor was lowered by 30 °C, performance was enhanced by 43% at an applied CO 2 pressure of 1 bar. This study also examined the effect of using a graphite fin as a heat extraction system. The graphite fin allowed for more rapid heat extraction and increased the carbonation reaction by 44% in the reactor bed with poor thermal conductivity (1.33 W/m.K) but had no effect in the reactor with modest thermal conductivity of (5 W/m.K) due to its ability to already transfer heat effectively to the reactor shell. [ABSTRACT FROM AUTHOR]

The inherent nature concerning the intermittency of concentrating solar power (CSP) plants can be overcome by the integration of efficient thermal energy storage (TES) systems. Current CSP plants employ molten salts as TES materials although metal hydrides (MH) have proven to be more efficient due to their increased operating temperatures. Nonetheless, the heat exchange between the MH bed and the heat transfer medium used to operate a heat engine is a critical factor in the overall efficiency of the TES system. In this work, a computational study is carried out to investigate the performance of a magnesium hydride TES packed bed using a multiphase (boiling) medium instead of single-phase heat absorption methods. The boiling heat transfer behaviour is simulated by using the Eulerian two-fluid framework. The simulations are conducted at a transient state using SST- k -ω Reynolds-Averaged Navier-Stokes equations. It is observed that, unlike the single-phase heat collection method, the multiphase heat absorption method maintains a constant temperature in the heat transfer fluid throughout the reactor. Consequently, a higher temperature gradient is realised between the MH bed and heat transfer fluid (HTF), leading to improvements in the overall reaction rate of the hydrogenation process. • Performance enhancement of a magnesium hydride reactor due to multiphase heat absorption was studied. • Boiling heat transfer behaviour was simulated using Eulerian two-fluid framework. • The percentage of improvement in reactor performance was variable at different reacted fractions. • Dry out condition was critical in the reactor efficiency. [ABSTRACT FROM AUTHOR]

Metal hydrides are regarded as one of the most attractive options for thermal energy storage (TES) materials for concentrated solar thermal applications. Improved thermal performance of such systems is vitally determined by the effectiveness of heat exchange between the metal hydride and the heat transfer fluid (HTF). This paper presents a numerical study supported by experimental validation on a magnesium hydride reactor fitted with a helical coil heat exchanger for enhanced thermal performance. The model incorporates hydrogen absorption kinetics of ball-milled magnesium hydride, with titanium boride and expanded natural graphite additives obtained by Sievert's apparatus measurements and considers thermal diffusion within the reactor to the heat transfer fluid for a realistic representation of its operation. A detailed parametric analysis is carried out, and the outcomes are discussed, examining the ramifications of hydrogen supply pressure and its flow rate. The study identifies that the enhancement of thermal conductivity in magnesium hydride has an insignificant impact on current reactor performance. • 3-D validation of MgH 2 reactor with a helical coil heat exchanger was performed. • Reaction kinetics was found out by using Sievert's apparatus. • Effect of operating parameters on MH reactor performance was studied. • Addition of 20% ENG into MH reactor, under the study, proved ineffective. [ABSTRACT FROM AUTHOR]