ThermoChemical Storage systems (TCS) are gaining attention for long term-thermal energy storage applications. Those systems can successfully increase the electricity generation flexibility in CSP (Concentrated Solar Power) plants or optimize the heat recovery and storage in energy-intensive industries (EII) as well. CaO/CaCO3 based systems are currently broadly investigated for thermochemical storage, either natural or synthetic materials. Among these, CaO/Mayenite (Ca12Al14O33) sorbents are considered very promising. CaO/Mayenite (Ca12Al14O33) based material was developed according to two different synthesis methods. The first one consisted in a one-step sol-gel method where aluminium precursor and pure CaO are weighted to obtain the exact weight ratio of 75/25 (CaO/Ca12Al14O33). In the second one, a two-step method was adopted: pure Mayenite was preliminarily synthetized by one step sol-gel method and CaO/Mayenite was obtained by direct wet mixing with pure CaO. Samples obtained were characterized by XRD, SEM, TGA, nitrogen physisorption, Raman spectroscopy and thermal stability was tested over 40 charging/discharging cycles in TGA. Raman spectra revealed free oxygen O2− presence in the structure of Mayenite and in CaO-Mayenite samples as well, lying at 1128 cm-1. Thermal properties such as thermal conductivity, heat capacity and volumetric energy density storage have been determined. The thermal conductivity found were 0.377 ± 0.004 (W/mK) for A; 0.101 ± 0.006 (W/mK) for B and for Mayenite 1.16 ± 2.7 10−4 (W/mK). It was found that two step method led to a better performing material in terms of carbonation reaction reactivity, and hence thermal storage. This material showed 50 % carbonation reaction conversion value at 40th cycle, corresponding to 0.250 g CO2/g dry sample, which is 4 times higher than CaO conversion. At 40th cycle, moderate sintering effect is remarked, with 2.3 % conversion drop, indicating that Mayenite insertion effectively acts as spacer. Volumetric storage energy density Sd has been determined for both samples and compared to CaO at increasing cycle number. Sample B storage density was effectively even at 40th cycle with 0.69 GJ/m3, thus about 3.5 times higher than CaO.
Thermochemical heat storage through CaO-Mayenite/CaCO3 system: Thermal performances comparison for two synthesis methods
Spadoni A.;Sau S.;Corsaro N.;Lanchi M.;Tizzoni A. C.;Veca E.;Falconieri M.;Della Seta L.;De Girolamo Del Mauro A.;Turchetti L.;Mansi E.;Liberatore R.
2023-01-01
Abstract
ThermoChemical Storage systems (TCS) are gaining attention for long term-thermal energy storage applications. Those systems can successfully increase the electricity generation flexibility in CSP (Concentrated Solar Power) plants or optimize the heat recovery and storage in energy-intensive industries (EII) as well. CaO/CaCO3 based systems are currently broadly investigated for thermochemical storage, either natural or synthetic materials. Among these, CaO/Mayenite (Ca12Al14O33) sorbents are considered very promising. CaO/Mayenite (Ca12Al14O33) based material was developed according to two different synthesis methods. The first one consisted in a one-step sol-gel method where aluminium precursor and pure CaO are weighted to obtain the exact weight ratio of 75/25 (CaO/Ca12Al14O33). In the second one, a two-step method was adopted: pure Mayenite was preliminarily synthetized by one step sol-gel method and CaO/Mayenite was obtained by direct wet mixing with pure CaO. Samples obtained were characterized by XRD, SEM, TGA, nitrogen physisorption, Raman spectroscopy and thermal stability was tested over 40 charging/discharging cycles in TGA. Raman spectra revealed free oxygen O2− presence in the structure of Mayenite and in CaO-Mayenite samples as well, lying at 1128 cm-1. Thermal properties such as thermal conductivity, heat capacity and volumetric energy density storage have been determined. The thermal conductivity found were 0.377 ± 0.004 (W/mK) for A; 0.101 ± 0.006 (W/mK) for B and for Mayenite 1.16 ± 2.7 10−4 (W/mK). It was found that two step method led to a better performing material in terms of carbonation reaction reactivity, and hence thermal storage. This material showed 50 % carbonation reaction conversion value at 40th cycle, corresponding to 0.250 g CO2/g dry sample, which is 4 times higher than CaO conversion. At 40th cycle, moderate sintering effect is remarked, with 2.3 % conversion drop, indicating that Mayenite insertion effectively acts as spacer. Volumetric storage energy density Sd has been determined for both samples and compared to CaO at increasing cycle number. Sample B storage density was effectively even at 40th cycle with 0.69 GJ/m3, thus about 3.5 times higher than CaO.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
