Energy Resource Efficient Industrial Energy Supply Systems For Decarbonization: Adaption of Mixed-Integer Design and Operation Optimization Models for Discretized Heat Recovery

Climate change calls for immediate action in all sectors. Industrial energy supply causes roughly one third of global primary energy consumption and greenhouse gas emissions in the same order of magnitude. Addressing decarbonization goals without taking measures to increase energy efficiency
beforehand e.g., through using available excess heat potentials, leads to increased operational expenditures and keeps end energy usage at an unnecessarily high level. Optimization of heat integration via methods of heat exchanger network synthesis (HENS) as well as design and operation optimization (DOO) based on mixed-integer linear programming (MILP)
formulations proved to support energy mangers, plant operators and decision makers when evaluating new and adapted concepts for increased energy efficiency in industrial production and energy supply systems. HENS addresses the question of optimal heat integration within energy supply systems for known heating and cooling requirements. It thereby proved to be a valuable method for identification of exergetically optimal utilization of excess heat potentials in energy supply systems. In contrast, DOO seeks to optimize the structure and the energy flows in energy supply and distribution systems to satisfy predefined process demands, such as heat at given temperature levels, power, or fuel demands. Simultaneous optimization of heat exchanger network design and supply system design and operation proved to be a demanding task, due to highly non-linear models. This paper introduces a simple MILP component model, that combines some of the advantages of commonly used HENS formulations, with those of state-of-the-art DOO formulations. It allows for utilization and provision of available heat flows in predefined temperature stages within a superstructure of an industrial energy supply system. By considering different cooling and heating requirements, as well as excess heat potentials, the optimal heat flow in the energy supply system can be determined. In future work, this approach can easily be extended for commonly used features in HENS-formulations, such as forbidden or restricted matches
of streams and calculation of necessary heat exchanger areas. To showcase the capabilities of the proposed formulation a case study based on a generalized energy supply model of a pharmaceutical production facility was conducted. It shows that applying cascaded usage of thermal energy, as modeled with this new formulation, the primary energy consumption of a commonly used process in pharmaceutical production can be reduced by 5.7 to 15.5%, compared to the
traditional modeling approach used in the reference scenarios.