Since the industrial revolution to nowadays, many waste gases have been produced in iron-steel facilities. These gases increased the amount of energy consumption and risky by CO2 emissions. For these reasons, the useful waste gases, energy saving and decreased emissions technology are made. In this study, a collection of real operating data has been performed in an existing steam power plant using the useful waste gas that has occurred in iron and steel production facilities according to their nature, traditional and enhanced exergy analyses of it. The thermodynamic performance of the system is evaluated by improvement potential of the system components and by the interaction between the components. Useful waste gases produced in the facility consist of blast furnace gas, coke oven gas and converter gas. These gases are used for boosting the pressure and temperature of the circulation water by means of the heat of the exhaust gas produced by burning them at the steam-powered Rankine cycle's boiler and its subcomponents. The results of the study showed that the traditional and the enhanced exergy efficiencies of the system are respectively 60.7% and 83.7%. Potential improvement of the system and the interaction between the components are determined as 24.8% (low) and 74.5% (high). System components with improvement priority are condenser; combustion chamber, turbine, first super-heater and economizer at the traditional exergy analysis; whereas a combustion chamber, turbine, first superheater, economizer and second super-heater at the enhanced exergy analysis. Thus, as a similar result to those for all conversion thermal systems, combustion chamber is a component that always needs to be improved. (C) 2018 Elsevier Ltd. All rights reserved.