Kinetic investigation and numerical modelling of CaCO3/Al2O3 reactor for high-temperature thermal energy storage application

This study conducts kinetic analyses of the carbonation reaction of CaCO3 (doped with Al2O3) as well as parametric analyses of the performance of a thermochemical reactor, which can act as a thermal battery. Kinetic measurements of CO2 release and absorption were carried out using thermogravimetric analysis (TGA) at 815, 830 and 845 degrees C on a CaCO3/Al2O3 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 CO2 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 CO2 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 CO2 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 degrees C, performance was enhanced by 43% at an applied CO2 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.

Automated summary

This study conducted kinetic and parametric analyses of the carbonation reaction of CaCO3 with Al2O3 as well as the performance of a thermochemical reactor. The results revealed the rapid reaction kinetics of the carbonation reaction and provided a suitable model to explain the growth of carbonation. Numerical analysis showed that increasing the thermal conductivity of the reactor bed and reducing the boundary temperature can greatly improve the reactor's performance.