Thermochemical storage of medium-temperature heat using MgO promoted with eutectic ternary mixture LiNO3-NaNO3-KNO3

Abstract

Decarbonation of MgCO3 is promising for thermochemical energy storage (TCES) at medium temperatures as it has appropriate reaction thermodynamics and low material cost. For approaching the problem of kinetic hindrance and severe reaction metastability, MgO was modified with the triple eutectic mixture LiNO3-NaNO3-KNO3 (Li0.30Na0.18K0.52NO3) to investigate the sorption/desorption properties, which were studied in detail for prospective conditions of a TCES system. The composites with various salt contents were comprehensively characterized by X-ray diffraction, N2 sorption, Scanning electron microscopy (SEM). The sorption behavior was tested at various salt contents, temperatures (290–360 °C) and CO2 pressures (50–100 kPa). The conversion of MgO to MgCO3 up to 0.65 and the CO2 uptake up to 16.2 mmol/g were found. The heat storage capacity reached 950 kJ/kg-composite and decreased down to 750 kJ/kg-composite after 20 carbonation/decarbonation cycles. The results obtained suggest an excellent performance of the material under the conditions that allow utilization of heat at T > 400 °C.