Basedon the requirements of CO₂ transportation and storage, non-condensable gases, such as O₂, N₂ and Ar should be removed from the CO₂-stream captured from an oxy-fuel combustion process. For a purification process, impurities have great impacts on the design, operation and optimization through their impacts on the thermodynamic properties of CO₂-streams. Study results show that the increments of impurities will make the energy consumption of purification increase; and make CO₂ purity of separation product and CO₂ recovery rate decrease. In addition, under the same operating conditions, energy consumptions have different sensitivities to the variation of the impurity mole fraction of feed fluids. The isothermal compression work is more sensitive to the variation of SO₂; while the isentropic compression work is more sensitive to the variation of Ar. In the flash system, the energy consumption of condensation in is more sensitive to the variation of Ar; but in the distillation system, the energy consumption of condensation is more sensitive to the variation of SO₂, and CO₂ purity of separation is more sensitive to the variation of SO₂. © 2008 Elsevier Ltd. All rights reserved.