The case study here presented deals with modernization of an industrial combined heat and power (CHP) plant located in a medium capacity steelworks industrial site. It is proposed to couple the existing power plant with a new gas turbine unit fired with Corex export gas. This fuel is a cold, low Btu by-product of the Corex process for pig iron production. The idea is to select the right distribution of heating surfaces in the heat recovery steam generator (HRSG) connected to a previously selected gas turbine and to the existing bottoming cycle in order to maximize the efficiency and economical profits of the whole plant. The study was performed using several simulation tools: a complete simulation of the system by means of engineering equation solver and a dedicated Fortran language code capable of performing all energy balances. For the correct design of the HRSG, a pinch analysis was applied. The whole set of simulation tools allowed comparing different solutions, of which the most promising ones are presented and discussed.