Europe’s competition situation in refining business is constantly severing. Additionally, EU’s Emission Trading System (ETS) will be considerably extended and strengthened in its Phase 3, which starts in 2013. This will cause an increase in costs from emission allowance purchases and in that way decrease refinery benefits. Thereof, further energy optimization appears being one of the most adequate measures to continue competitive operation of a refinery. This master thesis is focused on energy optimization of the FCC (Fluid Catalytic Cracking) plant at the refinery Petrobrazi. Thereto a first concept was already done in precedent studies; the aim of this master thesis is to evaluate the recommended ideas and to extend them by new conceptions and energy sources. An already existing Petro-SIM simulation of the FCC plant was modified and updated by including actual process data. Data extracted from the simulation were used for locating reasonable energy sources and additional possibilities of integration were elaborated. Those were evaluated both economically and from its’ technical viability. The technical feasibility study focuses on the dimensioning of the required equipment, space availability, detail consideration of the measures and emerging operation risks. The economical feasibility study of each project includes an invest cost estimate for the implementation measures and a calculation of the accruing revenues by saving both combustibles and emission allowances, together with a revenues’ sensitivity analysis. The project’s evaluation is done using dynamic capital budgeting methods and key performance indicators. Additionally, the measures’ impact on Solomon’s Energy Intensity Index® (EII®) was calculated. The EII® is one of the main key performance indicators in Solomon’s ‘Fuels Study’, which is used as a worldwide benchmarking tool for efficiency in the refining industry and serves as an efficient tool to reveal own weak points compared to refining industry average.