Thermochemical batteries using metal carbonates: A review of heat storage and extraction

Reversible sorption of carbon dioxide in Ca–Mg–Fe systems for thermochemical energy storage applications

“…8,13,61 Operating at 750 °C allows for overcoming the challenges of high-temperature systems identified in a recently published review article. 7 Also, the optimal operating temperature of a large-scale Stirling engine (40 kW) is about 700 °C; therefore, the Ca : Mg : Fe system is a suitable TCES material for applications using a heat-to-power engine, such as a TCB. 7,11 Considering −146 kJ mol −1 , the enthalpy of the exothermic absorption of CO 2 in the 2CaO·Fe 2 O 3 ·MgO, and 312 g mol −1 the molar mass of the material, the maximum energy density of the system is 468 kJ kg −1 .…”

“…7 Also, the optimal operating temperature of a large-scale Stirling engine (40 kW) is about 700 °C; therefore, the Ca : Mg : Fe system is a suitable TCES material for applications using a heat-to-power engine, such as a TCB. 7,11 Considering −146 kJ mol −1 , the enthalpy of the exothermic absorption of CO 2 in the 2CaO·Fe 2 O 3 ·MgO, and 312 g mol −1 the molar mass of the material, the maximum energy density of the system is 468 kJ kg −1 . Taking into account the stable capacity over cycles to be 0.9, this value drops to 421 kJ kg −1 , which is nearly the double of the energy density of pure CaCO 3 system, which has a capacity drop to 0.15 over time (249 kJ kg −1 ).…”

“…6 TCES relates to materials that undergo reversible endo- and exothermic gas sorption reactions, allowing for the storage of thermal energy and its release in the form of heat, respectively, as defined by eqn (1) where M is an alkaline-earth metal. 7 Particularly, cheap and abundant calcium carbonate operates at 900 °C and has high energy density (∼1.7 MJ kg −1 ). 7–10 For example, a 100 MW CSP plant would require ∼6250 t of CaCO 3 , considering 40% efficiency, to back up the power production for 12 h.MCO 3 + Δ H ⇌ MO + CO 2 …”

“…7 Particularly, cheap and abundant calcium carbonate operates at 900 °C and has high energy density (∼1.7 MJ kg −1 ). 7–10 For example, a 100 MW CSP plant would require ∼6250 t of CaCO 3 , considering 40% efficiency, to back up the power production for 12 h.MCO 3 + Δ H ⇌ MO + CO 2 …”

“…Beyond application in CSP plants, TCES using metal carbonates can be implemented into thermochemical batteries (TCB) at smaller scales to run heat-to-power engines. 7 A recent study highlighted the challenges associated with the high operating temperatures (<900 °C) of calcium carbonate, especially concerning engineering aspects and longevity of storage capacity. 11 The bimetallic carbonate, dolomite (CaMg(CO 3 ) 2 ), operates at lower temperatures (<600 °C) and also has potential for TCES applications.…”