Abstract
The MgO-CO2 working pair has been regarded as prospective for thermochemical energy storage (TCES) due to its relatively high heat storage capacity, low cost, and wide availability. This study is aimed at the optimization of the molar salt content, α, for the MgO modified with the eutectic mixture of LiNO3 and KNO3 (Li0.42K0.58NO3) which was earlier shown to provide high conversion, Δx, in heat-storage/release processes at 300–400 °C. The composites that have different salt content were prepared and carbonation kinetics was investigated under various conditions (carbonation temperature, Tcarb., is 290–360 °C and CO2 pressure, P(CO2), is 50–101 kPa). Significant accelerating effect was revealed at α ≥ 0.05, and the Δx value was maximized at α = 0.10–0.20. The largest conversion of 0.70 was detected at α = 0.10 and Tcarb. = 350 °C that corresponds to the specific useful heat (Qcomp.) is 1.63 MJ/kg-composite. However, the salt content of 0.20 ensures the high conversion, Δx = 0.63–0.67 and Qcomp. = 1.18–1.25 MJ/kg-composite in the whole temperature range between 290 and 350 °C. The (LiK)NO3/MgO composite with an optimal salt content of 0.20 exhibits reasonable durability through cyclic experiment at 330 °C, namely, the stabilized reacted conversion Δx = 0.34 (Qcomp. = 0.64 MJ/kg-composite). The studied (Li0.42K0.58)NO3 promoted MgO-CO2 working pair has good potential as thermochemical storage material of middle temperature heat (300–400 °C).
Highlights
Storage of thermal energy by means of chemical reactions with high heat effect, or thermochemical energy storage (TCES), is a promising approach to convert primary energy source due to high thermal energy storage capacity and long-term storage at ambient temperature without insulation [1,2,3]
We have optimized the salt content keeping in mind, first of all,of dynamic features the MgO
Optimized the salt content keeping in mind, first of all, dynamic features of the MgO carbonation reaction
Summary
Storage of thermal energy by means of chemical reactions with high heat effect, or thermochemical energy storage (TCES), is a promising approach to convert primary energy source due to high thermal energy storage capacity and long-term storage at ambient temperature without insulation [1,2,3]. Chemical reactions that can be neatly applied to TCES at medium temperatures (200–500 ◦ C) to store heat from industrial and renewable (e.g., solar energy) sources are not numerous. They are dehydration of Mg(OH)2 [5], Ca(OH)2 [6], dehydrogenation of MgH2 and that were extensively studied for TCES at medium temperatures. They are dehydration of some other hydrides [7].
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