Distillation systems consist of one or more distillation columns, in which a mixture is separated into higher-value products, and a heat exchanger network (HEN) that recovers and reuses heat within the system. For example, crude oil distillation systems comprise crude oil distillation units (CDU), in which crude oil is distilled into products for downstream processing, a HEN and a furnace. Heat-integrated distillation systems present complex interactions between the distillation columns and HEN. These interactions, together with the many degrees of freedom and process constraints, make it challenging to retrofit or modify the operating conditions of existing distillation processes to accommodate changes in process operating conditions. Retrofit designs aim to re-use existing equipment when process objectives change, for example to increase throughput, improve product quality, or reduce energy consumption or environmental impact. To achieve these retrofit objectives, operational, structural and/or flowsheet modifications to the overall system (distillation columns and HEN) may be considered, subject to specifications and system constraints. This work proposes an optimisation-based approach to retrofit design for the capacity expansion of heat-integrated distillation systems, with a particular focus on crude oil distillation systems. Existing retrofit approaches found in the open research literature consider operational optimisation, replacing column internals, adding preflash or prefractionation units and HEN retrofit to increase the capacity of existing systems. Constraints considered usually relate to the distillation column hydraulic limits, product quality specifications and heat exchanger performance (e.g. minimum temperature approach and, pressure drop). However, no existing methodologies consider these possible modifications simultaneously; thus, beneficial interactions between flowsheet modifications, operational changes, heat integration and equipment modifications may be missed. In this work, retrofit design solutions for crude oil distillation are developed using a stochastic optimisation framework implemented in MATLAB to optimise the system operating parameters and to propose flowsheet, column and HEN modifications. Within the framework, the optimiser can propose addition of a preflash unit, modifications to the CDU internals and changes to its operating conditions; the separation system is then simulated using Aspen HYSYS (via the MATLAB interface) and the hydraulic performance of the column is analysed using published hydraulic correlations. The optimiser also proposes modifications to the HEN (i.e. installed heat transfer area, HEN structure and operating conditions), which is then simulated to evaluate heating and cooling utility demand. Either simulated annealing and global search optimisation algorithms are applied to identify the optimal design and operating conditions that meet the production requirements and product specifications. Industrially relevant case studies demonstrate the effectiveness and benefits of using the proposed retrofit approach. The case studies illustrate that combined structural and operational modifications can be effectively and systematically identified to debottleneck an existing crude oil distillation system with a relatively short payback time, while simultaneously reducing energy consumption per barrel of crude oil processed.

Questions that were answered in the dissertation: Which process is suitable to desulphurize biogas knowing that chemical absorption will be used to separate CO2? Which absorption solvent is suitable to separate CO2 from concentrated gases such as biogas at atmospheric pressure? What properties of the selected solvent, namely aqueous diglycolamine (DGA), are already known? How to determine solvent properties such as equilibrium CO2 solubility under absorption and desorption conditions using simple, but robust apparatuses? What values do solvent properties such as density, viscosity and surface tension take at various DGA contents and CO2 loadings? How do primary alkanolamine content and CO2 loading influence solvent properties? What is the optimal DGA content in the solvent? What is the optimal desorption temperature at atmospheric pressure? How can equilibrium CO2 solubility in aqueous DGA solvents be simulated? What is the uncertainty in the results? How to debottleneck an absorber and increase its gas-treating capacity? How to determine the optimal lean loading of the absorption solvent? What are the characteristics of the absorption process that uses aqueous DGA as the solvent to separate CO2 from biogas and is more energy efficient and safer than the state-of-the-art processes? How to quantitatively compare the hazards of absorption solvents? What is the disposition of the German population towards hazards from biogas plants? What are the favourable and adverse environmental impacts of biomethane? / Fragen, die in der Dissertation beantwortet wurden: Welches Verfahren ist zur Entschwefelung von Biogas geeignet, wenn die chemische Absorption zur CO2-Abtrennung genutzt wird? Welches Absorptionsmittel ist geeignet, um CO2 aus konzentrierten Gasen, wie Biogas, bei atmosphärischem Druck abzutrennen? Welche Eigenschaften des ausgewählten Absorptionsmittels, wässriges Diglykolamin (DGA), sind bereits bekannt? Wie wird die CO2-Gleichgewichtsbeladung unter Absorptions- und Desorptionsbedingungen mit einfachen und robusten Laborapparaten bestimmt? Welche Werte nehmen die Absorptionsmitteleigenschaften wie Dichte, Viskosität und Oberflächenspannung bei verschiedenen DGA-Gehalten und CO2-Beladungen? Wie werden die Absorptionsmitteleigenschaften durch den Primäramin-Gehalt und die CO2-Beladung beeinflusst? Was ist der optimale DGA-Gehalt im Absorptionsmittel? Was ist die optimale Desorptionstemperatur bei atmosphärischem Druck? Wie wird die CO2-Gleichgewichtsbeladung im wässrigen DGA simuliert? Welche Ungenauigkeit ist zu erwarten? Wie wird eine Absorptionskolonne umgerüstet, um die Kapazität zu erweitern? Wie wird die optimale CO2-Beladung des Absorptionsmittels am Absorbereintritt (im unbeladenen Absorptionsmittel) bestimmt? Was sind die Prozesseigenschaften eines Absorptionsverfahrens, das wässriges DGA als Absorptionsmittel nutzt sowie energieeffizienter und sicherer als Verfahren auf dem Stand der Technik ist? Wie kann das Gefahrenpotenzial von Absorptionsmittel quantitativ verglichen werden? Wie werden Gefahren aus einer Biogasanlage durch die deutsche Bevölkerung wahrgenommen? Welche positive und negative Umweltauswirkung hat Biomethan?

Questions that were answered in the dissertation: Which process is suitable to desulphurize biogas knowing that chemical absorption will be used to separate CO2? Which absorption solvent is suitable to separate CO2 from concentrated gases such as biogas at atmospheric pressure? What properties of the selected solvent, namely aqueous diglycolamine (DGA), are already known? How to determine solvent properties such as equilibrium CO2 solubility under absorption and desorption conditions using simple, but robust apparatuses? What values do solvent properties such as density, viscosity and surface tension take at various DGA contents and CO2 loadings? How do primary alkanolamine content and CO2 loading influence solvent properties? What is the optimal DGA content in the solvent? What is the optimal desorption temperature at atmospheric pressure? How can equilibrium CO2 solubility in aqueous DGA solvents be simulated? What is the uncertainty in the results? How to debottleneck an absorber and increase its gas-treating capacity? How to determine the optimal lean loading of the absorption solvent? What are the characteristics of the absorption process that uses aqueous DGA as the solvent to separate CO2 from biogas and is more energy efficient and safer than the state-of-the-art processes? How to quantitatively compare the hazards of absorption solvents? What is the disposition of the German population towards hazards from biogas plants? What are the favourable and adverse environmental impacts of biomethane? / Fragen, die in der Dissertation beantwortet wurden: Welches Verfahren ist zur Entschwefelung von Biogas geeignet, wenn die chemische Absorption zur CO2-Abtrennung genutzt wird? Welches Absorptionsmittel ist geeignet, um CO2 aus konzentrierten Gasen, wie Biogas, bei atmosphärischem Druck abzutrennen? Welche Eigenschaften des ausgewählten Absorptionsmittels, wässriges Diglykolamin (DGA), sind bereits bekannt? Wie wird die CO2-Gleichgewichtsbeladung unter Absorptions- und Desorptionsbedingungen mit einfachen und robusten Laborapparaten bestimmt? Welche Werte nehmen die Absorptionsmitteleigenschaften wie Dichte, Viskosität und Oberflächenspannung bei verschiedenen DGA-Gehalten und CO2-Beladungen? Wie werden die Absorptionsmitteleigenschaften durch den Primäramin-Gehalt und die CO2-Beladung beeinflusst? Was ist der optimale DGA-Gehalt im Absorptionsmittel? Was ist die optimale Desorptionstemperatur bei atmosphärischem Druck? Wie wird die CO2-Gleichgewichtsbeladung im wässrigen DGA simuliert? Welche Ungenauigkeit ist zu erwarten? Wie wird eine Absorptionskolonne umgerüstet, um die Kapazität zu erweitern? Wie wird die optimale CO2-Beladung des Absorptionsmittels am Absorbereintritt (im unbeladenen Absorptionsmittel) bestimmt? Was sind die Prozesseigenschaften eines Absorptionsverfahrens, das wässriges DGA als Absorptionsmittel nutzt sowie energieeffizienter und sicherer als Verfahren auf dem Stand der Technik ist? Wie kann das Gefahrenpotenzial von Absorptionsmittel quantitativ verglichen werden? Wie werden Gefahren aus einer Biogasanlage durch die deutsche Bevölkerung wahrgenommen? Welche positive und negative Umweltauswirkung hat Biomethan?