The present contribution focuses on the carbonate looping process, i.e., post-combustion CO2 capture by means of CaO containing solid sorbents in a system of two circulating fluidized bed reactors. Material and energy balances were performed using the ASPEN PLUS (TM) software. Two different modeling approaches are applied to the carbonator. First, the entire active fraction of CaO is assumed to be converted; second, the CO absorption efficiency in the circulating fluidized bed is calculated using an analytical 1D model for fast fluidization. The absorption of SO2 by CaO is taken into account. The overall plant efficiency depends on the mass flows of fresh limestone and circulating CaO. The process is shown to be economically feasible, having low energy penalties in comparison with other CO2 capture technologies and it seems to be suited for retro-fitting existing power plants.