Exergoeconomic analysis of the power generation system using blast furnace and coke oven gas in a Brazilian steel mill

The rational use of energy has become a priority for all industries in Brazil, mainly after the energy rationing in 2001. Methodologies to quantify and improve the performance of plants that consume and generate electricity and thermal energy are being used to reach this goal. Exergoeconomic analysis provides a complete diagnosis of a plant, both in exergetic and in monetary values. This study shows the methodology used to assess the power generation system of the Companhia Siderúrgica Tubarão (CST). 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. Use of the Theory of Exergetic Cost allowed determination of monetary and exergetic costs. Moreover, indicators such as cost variation, relative cost variation, and exergoeconomic factors were calculated to determine the influence of each component in the make-up of plant costs and to find the best way of decreasing generation costs of energy and process steam.