The rational use of energy became a priority for all industries in Brazil after the energetic rationing in 2001. The aim of this work is to assess a proposal of a power generation system for Companhia Siderurgica Tubarao, a steel mill plant. The current system is based on a regenerative Rankine cycle using two gases from steel production-blast furnace gas (BFG) and coke oven gas (COG)-to generate electric power and occasionally steam for the process. The proposed system is a combined cycle comprising two gas turbines, two heat recovery steam generators (HRSGs), and a steam turbine. The fuel for the gas turbines is BFG, and the supplementary firing of HRSG uses COG. The proposed HRSGs work at three pressure levels. The system was assessed by means of two thermoeconomic methodologies, Theory of Exergetic Cost and Thermoeconomic Functional Analysis; exergetic and monetary costs of power production were calculated and compared to the respective values of the current system. (c) 2006 Elsevier Ltd. All rights reserved.