CO2 Capture Performance of Calcium-Based Sorbents in a Pressurized Carbonation/Calcination Loop

Calcium-based sorbents have applicable potential in a high-temperature process to control carbon dioxide (CO2) emissions from power generation. However, studies showed that the CO2 capture capacity of calcium-based sorbents decreased sharply with an increase in the number of calcination/carbonation reaction cycles. To improve the CO2 capture capacity, studies were focused on the effect of the reaction pressure together with the temperature on CaO conversion because elevated pressure may increase the carbonation rate of CaO according to the CO2-CaO reaction. The carbonation reaction was studied in a pressurized thermogravimetric analyzer, and the multicycle tests were carried out in an atmospheric calcination/pressurized carbonation reactor system to provide preliminary information about sorbent durability in pressurized carbonation. Pore structure characteristics were measured as a supplement to the reaction study. High carbonation reaction rate and conversion were observed under pressurized carbonation. When the CO2 partial pressure was much higher than the equilibrium partial pressure of CO2 at the carbonation temperature, the reaction rate increased and high conversion was obtained as the carbonation temperature increased. However, the effect of sintering at high temperature was serious, and a decline in conversion was observed with an increase in the number of cycles. The effect of the carbonation temperature and pressure on the CO2-CaO reaction was ultimately reflected in the effect on the microstructure of the sorbents. A combination of optimum carbonation temperature and pressure was obtained via the experiments, where the calcined limestone presented the highest Brunauer-Emmett-Teller surface area and pore volume, which was the ideal microstructure suitable for CO2 capture.