Combustion in an O-2/CO2 atmosphere is a very promising technology, although the process of desulfurization using CaCO3 raises many doubts. An increase in CO2 concentration up to 95% blocks calcination and, thus, the bonding of SO2. The issues related to the conversion of combustible matter are addressed in a paper entitled Combustible Matter Conversion in an Oxy-fuel Circulating Fluidized-Bed (CFB) Environment (Czakiert, T.; Muskala, W.; Jankowska, S.; Krawczyk, G.; Borecki, P.; Jesionowski, L.; Nowak, W. Energy Fuels 2012, 26, 5437-5445). That publication discusses the problems of flue gas desulfurization using CaCO3 and CaCO3 modified by the use of a CO(NH2)(2) addition. The main objective of this study was to determine the possibility of using modified limestone in the flue gas desulfurization process during combustion in the O-2/CO2 atmosphere.