Carbon capture and storage is a concept to reduce greenhouse gas emissions of energy production from fossil fuels. In oxy-fuel combustion, the fuel is burned in a mixture of oxygen and recycled flue gas. This generates CO2-rich flue gas from which the CO2 is easily separated and compressed. Foster Wheeler Power Group is developing the existing design tools and process models of air-fired circulating fluidized bed boilers to implement specific features of oxycombustion. The validation data is produced from bench-scale and pilot-scale experiments at the VTT, Technical Research Centre of Finland. A three-dimensional circulating fluidized bed (CFB) furnace model is developed and applied by Lappeenranta University of Technology for predicting the effects of oxycombustion in full scale units. This paper presents concept Studies and initial 3D modeling results based on a 460 MW, supercritical CFB power plant at Lagisza, and pilot-scale studies with flue gas recirculation demonstrating real oxygen combustion conditions.