Experimental evaluation of chemical systems for CO2 capture by CaO in eutectic CaF2-CaCl2

Heidi S. Nygård; Maria Hansen; Yasen Alhaj-Saleh; Piotr Palimąka; Stanisław Pietrzyk; Espen Olsen; Heidi S. Nygård; Maria Hansen; Yasen Alhaj-Saleh; Piotr Palimąka; Stanisław Pietrzyk; Espen Olsen

doi:10.3934/energy.2019.5.619

AIMS Energy

2019, Volume 7, Issue 5: 619-633. doi: 10.3934/energy.2019.5.619

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Experimental evaluation of chemical systems for CO₂ capture by CaO in eutectic CaF₂-CaCl₂

1.
Faculty of Science and Technology, Norwegian University of Life Sciences (NMBU), N-1432 Ås, Norway
2.
AGH University of Science and Technology, Faculty of Non-Ferrous Metals, Kraków, Poland

Received: 04 June 2019 Accepted: 08 October 2019 Published: 15 October 2019

CO₂ capture by CaO in molten salts is a variant of calcium looping in which the active substances (CaO/CaCO₃) are dissolved or in a slurry with inorganic molten salts. One of the main advantages is the nonexistence of degradation in the reactivity between the active material and CO₂. Previous research has revealed good absorption and desorption characteristics with CaO contents up to 20 wt% in eutectic CaF₂-CaCl₂. The hypothesis is that the formed CaCO₃ continuously dissolves in the melt, leaving highly reactive CaO readily available for the incoming CO₂. In the present study, the CaO content is increased to 40 wt%, and the absorption characteristics is investigated with focus on the sorption capacity and CO₂ removal rate. The chemical system is also evaluated experimentally with regards to viscosity and solubility of the formed CaCO₃ during CO₂ absorption, with the aim of determining chemical upscaling limitations. The results show that the practical CaO content limit is 30 wt%, in which a sorption capacity of 20 g CO₂/100 g sorbent is observed, without any deterioration of the reaction kinetics. For 40 wt% CaO, the sorption capacity is higher, but on the expense of the CO₂ removal rate and CaO conversion. This is attributed to a significant increase in viscosity and the solubility limit of CaCO₃ being exceeded.
- CO₂ capture,
- calcium looping,
- molten salts,
- phase diagram,
- viscosity
Citation: Heidi S. Nygård, Maria Hansen, Yasen Alhaj-Saleh, Piotr Palimąka, Stanisław Pietrzyk, Espen Olsen. Experimental evaluation of chemical systems for CO2 capture by CaO in eutectic CaF2-CaCl2[J]. AIMS Energy, 2019, 7(5): 619-633. doi: 10.3934/energy.2019.5.619

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Abstract

CO₂ capture by CaO in molten salts is a variant of calcium looping in which the active substances (CaO/CaCO₃) are dissolved or in a slurry with inorganic molten salts. One of the main advantages is the nonexistence of degradation in the reactivity between the active material and CO₂. Previous research has revealed good absorption and desorption characteristics with CaO contents up to 20 wt% in eutectic CaF₂-CaCl₂. The hypothesis is that the formed CaCO₃ continuously dissolves in the melt, leaving highly reactive CaO readily available for the incoming CO₂. In the present study, the CaO content is increased to 40 wt%, and the absorption characteristics is investigated with focus on the sorption capacity and CO₂ removal rate. The chemical system is also evaluated experimentally with regards to viscosity and solubility of the formed CaCO₃ during CO₂ absorption, with the aim of determining chemical upscaling limitations. The results show that the practical CaO content limit is 30 wt%, in which a sorption capacity of 20 g CO₂/100 g sorbent is observed, without any deterioration of the reaction kinetics. For 40 wt% CaO, the sorption capacity is higher, but on the expense of the CO₂ removal rate and CaO conversion. This is attributed to a significant increase in viscosity and the solubility limit of CaCO₃ being exceeded.

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