Ion transport membranes (ITM) have been studied as a promising air separation unit (ASU) technology for oxy-fuel combustion owing to their high oxygen permeability. Even though the power consumption of the ITM is lower than that of cryogenic ASU, it still consumes a high proportion of the overall system power. In this study, a numerical analysis of the ITM system has been conducted using Aspen Plus (R) to determine the optimal system design for minimizing the power consumption to separate oxygen from air. Since the oxygen permeation through the ITM is driven by the oxygen partial pressure gradient between feed and permeation side, three ITM systems that have different pressure gradients across the membrane have been presented and their performances compared. The effects of the contributing parameters, such as thickness, pressure, temperature, and air flow rate on the oxygen permeation rate have been investigated. ITM performances of the counter and parallel flow configurations have been compared. The system that operates under atmospheric pressure at the feed channel and under vacuum pressure at the permeate channel yields the lowest power consumption for obtaining the same oxygen permeation rate among other pressure conditions.