Influence of CO2 concentration on carbon capture using Zr-CaO

https://doi.org/10.3390/en14164822

“The effect of cyclic carbonation–decarbonation on the sorbent CO₂ uptake capacity at different CO₂ concentrations in the gas flow during carbonation is shown in Figure 2. The carbonation and decarbonation are performed at the temperatures indicated in Table 1. It is observed that the initial CO₂ uptake capacity of the sorbent slightly decreases from 10.7 to 10.2 mmol/g with the CO₂ concentration increase from 15 to 100 vol.%. Stoichiometric capacity of the sorbent is about 12.4 mmol/g. The CO₂ uptake capacity of the sorbent decreases with a rise in the cycle number attaining 9.2, 8.9, 8.2 and 7.7 mmol/g in the 25th cycle at 15, 30, 50 and 100 vol.% CO₂, respectively. The drop in the capacity value increases from 1.5 to 2.5 mmol/g with a rise in CO₂ concentration from 15 to 100 vol.%. The dependence of the sorbent CO₂ uptake capacity on the number of carbonation–decarbonation cycles attains saturation near the 25th cycle if the sorbent is carbonated in the atmosphere containing 15 vol.% CO₂. Thus, it can be concluded that the sorbent is more resistant to cyclic carbonation–decarbonation if carbonation occurs at lower CO₂ concentrations and low temperatures. In further experiments, carbonation is performed at 630 °C in the gas flow containing 15 vol.% CO₂ because such a concentration corresponds to the typical CO₂ content in the exhaust gases of coal-fired power plants and the indicated carbonation temperature corresponds to the average exhaust gases temperature [16].”

“Figure 2. The dependencies of the sorbent CO₂ uptake capacity on the number of carbonation–decarbonation cycles at different CO₂ concentrations in the gas flow upon carbonation. The insert shows the dependence of zirconium-undoped sorbent CO₂ uptake capacity on the number of carbonation–calcination cycles at 15 vol.% CO₂ in the gas flow upon carbonation.”

“It has been revealed that both cyclic carbonation–decarbonation and the rise in CO₂ concentration in the gas flow at carbonation lead to a decrease in the sorbent-specific surface area (Table 2). After 25 carbonation–decarbonation cycles, the specific surface area decreases by 3.7, 7.4, 15.2 and 20.3% in relation to the virgin sorbent-specific surface area value of 21.7 m²/g if carbonation occurs in the atmosphere containing 15, 30, 50 or 100 vol.% CO₂, respectively.”

“The rise in CO₂ concentration in the gas flow increases the carbonation intensity that results in densification of the CaCO₃ layer forming on the surface of CaO particles, which impedes the penetration of CO₂ deep into the CaO particles; therefore, a higher carbonation temperature is required to provide CO₂ penetration through the product layer, and a higher decarbonation temperature is also required to decompose the dense well-sintered product layer. The CaCO₃ sintering results in CaO particles’ growth with each subsequent carbonation–decarbonation cycle. The higher the CO₂ concentration, the more intense the CaO particles’ growth at carbonation, which is confirmed by the specific surface area measurements (Table 2).”

https://doi.org/10.3390/en14164822