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The problem of energy use is one of the challenges of modern society. It is connected not only with the generation of harmful emission but also with the use of other associated resources. Energy efficiency in industry is one of the cleanest energy sources due to not generating energy. Current work proposes an approach for reducing primary energy use and harmful emissions at the oil refinery via thermodynamic analysis of process and energy streams and definition of an energy recovery potential. The proposed approach is based on the systematic reduction of energy consumption by an energy audit, a detailed process and units simulation, improved energy recovery and identifying the most reliable and economically viable process changes. It includes the heat and utility exchanger network analysis by grid diagram to find an energy gap and main drawbacks. The case study represents an application of the proposed method at the hydrocracking unit, where a considerable potential for energy efficiency was identified and utilised. The retrofit option was developed to show how debottlenecking and process changes contributes to overall operational efficiency. As a result, the energy consumption was cut by 54% and the economic efficiency of the proposed process changes confirmed by the discounted payback period of 9.5 months, excluding the time for the detailed design, equipment purchase, installation and start-up. Environmental results demonstrate the annual saving of 18,915 tons of carbon dioxide. Due to the slowing down of global economic growth, more attention should be paid to the modernisation of existing process plants. It may speed up the transition to an environmentally friendly economy and help solving global problems.