Distillation systems are energy-intensive processes, and consequently contribute significantly to the greenhouse gases emissions (e.g. carbon dioxide (CO2). A simple model for the estimation Of CO2 emissions associated with operation of heat-integrated distillation systems as encountered in refineries is introduced. In conjunction with a shortcut distillation model, this model has been used to optimize the process conditions of an existing crude oil atmospheric tower unit aiming at minimization Of CO2 emissions. Simulation results indicate that the total CO2 emissions of the existing crude oil unit can be cut down by 22%, just by changing the process conditions accordingly, and that the gain in this respect can be doubled by integrating a gas turbine. In addition, emissions reduction is accompanied by substantial profit increase due to utility saving and/or export. (C) 2005 Elsevier Ltd. All rights reserved.