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.