As a consequence of growing energy demand and expanded use of fossil fuels, CO2 level in the atmosphere has risen in the last couple of centuries. The principal effect of these anthropologic emissions of greenhouse gases is global warming. In the last years, there has been much effort on finding a long term solution to this problem, mostly based on clean power technologies. In order to reduce green-house gas emissions different technologies to capture CO2 are under investigation. One of the most promising technologies is oxy-combustion using ITM (ion transport membranes) used in air separation units or integrated directly in reactors. This work presents a model for the integration of dense oxygen membrane modules in air separation units. An axially resolved model for the distribution of oxygen concentration is developed, incorporating a model of the oxygen flux across membrane surface and its dependency on the local conditions, which satisfies the conservation equations of mass and energy. The oxygen flux model is based on accurate experimental measurements and incorporates the effects of chemistry at the surface and diffusion in the bulk material, as well as heat and mass transport on the feed and sweep side. (C) 2015 Elsevier Ltd. All rights reserved.