A modified pore evolution particle model applied to CaCO3 decomposition and CaO sintering during calcium looping CO2 cycles

The calcium looping of calcium-based carbonation/calcination cyclic reaction is an efficient decarbonization technology that can be applied to post-combustion carbon capture, solar thermal storage, and enhanced methane reforming hydrogen. The pore structure generated during the calcination stage greatly affects adsorption performance. Hence, the change of pore structure is crucial during the calcination. Existing models related to pore structure still need to be further improved regarding pore formation mechanisms. In this paper, a modified pore evolution model is proposed. The modified pore evolution model contains the kinetic equation, the CO2 diffusion equation, and the vacancy aggregates equation. The modified model considers the possibility of spontaneous pore formation in the mechanism, which can better fit the experimental results and provide higher simulation accuracy. The model reveals the diffusion of CO2 within the particles during decomposition, and spatiotemporal evolutionary properties of pore parameters. The pore change trend is the most obvious when the initial pores are mainly 3 nm mesopores. The pore evolution is relatively stable when the initial pores are mainly 25 nm mesopores. Besides, the particles experience significant pore migration during the sintering stage when the temperature reaches 1273 K. At 1073 K, the maximum pore size occurring during pore evolution did not exceed 40 nm. The model estimates a maximum pore size of more than 60 nm at 1273 K. The modified model can aid in a deeper comprehension of how the pore structure changes throughout the calcination process.