This work leverages the advantages of exergy over energy in portraying the thermody-namic performance of heat exchanger network components to propose innovative ap-proaches for optimizing thermal integration systems. Heat integration, achieved through the interconnection of heat sources and sinks, can be implemented either via direct heat exchange between streams or indirectly through an intermediate medium. The first methodology developed in this thesis focuses on the latter, allowing the inter-mediate streams to mix wherever beneficial. The mixing of streams with different tem-peratures can be optimally used for enhancing the heat integration. Using exergy in-stead of energy as the basis for formulating optimization objectives has proven highly effective. Applying this approach to an industrial case study resulted in a heat recov-ery improvement of 18.2 % and a utility demand reduction of 28.8 %. Furthermore, the design of flexible heat exchanger networks was explored. A model was formulated to identify the optimal configuration of bypasses for operating the network efficiently over a predefined set of operating points. In a case study, it was demonstrated that optimization based on exergy not only reduced the total exergy de-struction of the system by an order of approximately 30 % but also simplified designs by eliminating unnecessary bypasses. Additionally, two alternative bypass configura-tions were investigated for the same case study. It was highlighted that alternative con-trol configurations cannot be compared based on energy analysis, whereas exergy pro-vided a solid basis for comparing different designs by unveiling the actual thermody-namic inefficiencies of the system components. The thesis also delves into industrial-urban symbiosis within the context of heat inte-gration. A building energy model was proposed for calculating the heat demand at district scale. A novel exergy-based key performance indicator was tailored to evaluate the performance of the buildings by accounting for both quantity and quality of the energy required for heating purposes. An exergy mismatch index was introduced to quantify the discrepancies between the exergy supplied by district heating networks and that required by buildings connected to them. Finally, a methodology was pro-posed to integrate the developed methods for the heat exchanger network synthesis with intermediate circuits, the design and optimization of bypass configurations and a multi-period model of district heating systems. The methodologies and findings in this thesis will benefit future researchers, heat integration planners, system operators and policy makers by providing insights for decision-making on heat integration systems in both industrial and industrial-urban applications.
Bahar Saeb Gilani (Thu,) studied this question.