HIGH TEMPERATURE CAPTURE OF CARBON DIOXIDE: CHARACTERISTICS OF THE REVERSIBLE REACTION BETWEEN CaO(s) and CO2(g)

Abstract

The reversible reaction between CaO(s) and CO₂(g) may ultimately find application in a high temperature process to control CO₂ emissions from advanced power generation processes. At appropriate temperature and pressure combinations, CO₂(g) is removed from the gas phase and captured as CaC₃(s). At higher temperature and/or lower pressure, the reaction is reversed to produce a gas stream having high CO₂(g) concentration suitable for use or ultimate disposal. Both the calcination and carbonation reactions have been studied in an electrobalance reactor as a function of temperature, pressure, and gas composition. Multicycle tests have provided preliminary information on sorbent durability. Solid structural property characteristics have been measured as a supplement to the reaction studies. Rapid and complete calcination of CaCO₃ can be achieved at temperatures as low as 750°C under one atmosphere of N2. Higher pressure reduces the calcination rate while the presence of CO₂ in the calcination atmosphere requires the use of higher temperature. Mild calcination conditions produce a CaO product which is most reactive during the carbonation phase. Carbonation is characterized by a rapid initial reaction rate followed by an abrupt transition to a quite slow rate. Significant reduction in CO₂ capacity between the first and second carbonation cycles, ranging from 15% under favorable reaction conditions to more than 30% at severe conditions, was found. However, the capacity loss tended to moderate as the number of cycles increased.