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In a jet engine air and oil are mixed during removal from the bearing chamber. Before the oil can be recycled back into the system it must be separated from the air. This is accomplished through use of a de-aerator and breather. The oil air mixture enters the de-aerator first. The de-aerator is a vertical cylinder in which the air and oil enter from the top of the system. Gravity then pulls the oil down as it circulates along the outer wall of the de-aerator. The air is forced out through a top hole and sent to the breather where any oil droplets which remain are furthered separated. A pedestal is located near the bottom of the de-aerator. The pedestal creates a gap between itself and the de-aerator wall. Ideally this gap should be large enough to allow oil to flow through the gap without pooling on the pedestal, but small enough so that air does not flow through the gap. The oil will pool up on the pedestal and reduce the efficiency of the system. In this research, a 30° conical pedestal with a gap of 10.7% was tested. The results showed that the pedestal gap of 10.7% is too large and allows air to flow through the gap. The maximum water was 8.5% and the average water thickness was 5.11%. After studying both the previous experimental data and current CFD data, it is recommended further testing be conducted on pedestal gaps between 8.5% and 9.5%. / Master of Science

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Large scale nonlinear programming (NLP) has proven to be an effective framework for obtaining profit gains through optimal process design and operations in chemical engineering. While the classical SQP and Interior Point methods have been successfully applied to solve many optimization problems, the focus of both academia and industry on larger and more complicated problems requires further development of numerical algorithms which can provide improved computational efficiency. The primary purpose of this dissertation is to develop effective problem formulations and an advanced numerical algorithms for efficient solution of these challenging problems. As problem sizes increase, there is a need for tailored algorithms that can exploit problem specific structure. Furthermore, computer chip manufacturers are no longer focusing on increased clock-speeds, but rather on hyperthreading and multi-core architectures. Therefore, to see continued performance improvement, we must focus on algorithms that can exploit emerging parallel computing architectures. In this dissertation, we develop an advanced parallel solution strategy for nonlinear programming problems with block-angular structure. The effectiveness of this and modern off-the-shelf tools are demonstrated on a wide range of problem classes. Here, we treat optimal design, optimal operation, dynamic optimization, and parameter estimation. Two case studies (air separation units and heat-integrated columns) are investigated to deal with design under uncertainty with rigorous models. For optimal operation, this dissertation takes cryogenic air separation units as a primary case study and focuses on formulations for handling uncertain product demands, contractual constraints on customer satisfaction levels, and variable power pricing. Multiperiod formulations provide operating plans that consider inventory to meet customer demands and improve profits. In the area of dynamic optimization, optimal reference trajectories are determined for load changes in an air separation process. A multiscenario programming formulation is again used, this time with large-scale discretized dynamic models. Finally, to emphasize a different decomposition approach, we address a problem with significant spatial complexity. Unknown water demands within a large scale city-wide distribution network are estimated. This problem provides a different decomposition mechanism than the multiscenario or multiperiod problems; nevertheless, our parallel approach provides effective speedup.

[pt] Diante da crise energética e de mercado a Cogeração se apresenta oportuna tanto para a produção de energias elétrica e térmica quanto para a redução dos custos operacionais de produção de uma empresa. Um sistema de cogeração integrado e adaptado ao processo de uma Planta Criogênica de Separação de Ar, que tem a energia elétrica como insumo básico, pois o ar não tem custo, pode se mostrar viável, com considerável redução nos custos operacionais da planta. Um estudo termoeconômico, englobando uma análise da Primeira e Segunda Lei da Termodinâmica, e uma análise Econômica, foi necessário não apenas para demonstrar esta viabilidade, mas também para propor as modificações no processo Criogênico de Separação de Ar, assim como, para definir o melhor sistema de Cogeração a ser integrado à planta típica T-240 NA MPL3. Os resultados da Análise Termodinâmica das modificações foram bem satisfatórios. As eficiências de Segunda Lei - Exergéticas - dos equipamentos envolvidos nas modificações da planta melhoraram, e o seu consumo de energia elétrica foi reduzido em 12 porcento. Foram propostos para integrar a planta 4 (Quatro) Sistemas de Cogeração a partir dos Ciclos Clássicos: Rankine, Brayton, Combinado e Otto. Estes Sistemas foram analisados inicialmente pelas Primeira e Segunda Leis da Termodinâmica e finalmente foram analisados economicamente. Termoeconomicamente, o Sistema de Cogeração a partir do Ciclo Combinado foi o que melhor se apresentou para integrar o processo Criogênico de Separação de Ar da planta. Neste Sistema houve um maior equilíbrio entre as demandas térmica e elétrica, acarretando a eficiência de Segunda Lei - Exergética - mais alta. Este Sistema teve, também, a maior Receita Operacional e embora o seu Investimento Adicional tenha sido um pouco maior, este acréscimo compensou, pois apresentou os menores Tempo e Taxa Interna de Retorno. Apesar do Sistema de Cogeração a partir do Ciclo Combinado se apresentar viável, os resultados devem ser considerados, apenas, como preliminares, pois são provenientes da primeira interação Termoeconômica. Outras interações devem ser realizadas visando a melhoria deste Sistema, para viabilizar cada vez mais a Cogeração em Plantas Criogênicas de Separação de Ar. / [en] The energy shortage and the cogeneration market present a unique opportunity for energy cost reduction of an industry by simultaneously making use of electric and thermal energy generated with the same fuel. This thesis analyzes an integrated cogeneration system adapted to an air separation criogenic plant which has electric energy as a basic input, besides the available and costless air from the atmosphere. It has been shown to be feasible with the big savings inthe operational cost of the plant. A thermal and economic study, carried on by using the first and second Law of thermodynamics demonstrated the economic feasibility of the cogeneration system, and proposed modifications to be done in the studied criogenic plant, a typical T240- NA MPL3 plant. The thermodynamic analysis showed that the second law efficiency of the processes could be improved, together with a 12 percent electric energy consumption reduction. Four cogeneration schemes were analyzed with both the first and second laws of thermodynamics and, then, the economic analysis was performed. Rankine, Brayton, OTTO and combined gas-steam basic cycles were used in this analysis. The combined gas-steam cycle was shown to be more economically feasible than others. Thermal and electric loads were well balanced, resulting in a higher second law efficiency. Although the initial investiment for the modification was higher, the savings resulted to be higher, turning into a high rate of return of the investment. This analysis was judged to be preliminary. More precise results require a deepers analysis with more detailed information.

Cryogenic air separation units (ASUs) are the most widely used technology for industrialscale production of large amounts of high-purity air components. These are highly energyintensive processes, which have motivated the development of demand response strategies to adapt their operation in response to the increased volatility of the energy market. The startup of ASUs warrants particular consideration within this context. ASUs are tightly integrated, thermally and materially, and have slow dynamics. These result in startup times on the order of hours to a day, during which electricity is consumed with limited revenue generation. In the current environment of electricity price deregulation, it may be economically advantageous for ASUs to shut down during periods of high electricity pricing, increasing the occurrences of startups. This presents a promising research opportunity, especially because ASU startup has received relatively little attention in the literature. This thesis investigates the optimal startup of ASUs using dynamic optimization. First, this thesis focuses on startup model development for the multiproduct ASU. Startup model development requires accounting for discontinuities present at startup. Four main discontinuities are considered: stage liquid flow discontinuity, stage vapor flow discontinuities, flow liquid out of sumps and reboilers, and opening and closing valves. Other types of discontinuities accounted for include the change in the number of phases of streams. These discontinuities are approximated with smoothing formulations, using mostly hyperbolic tangent functions, to allow application of gradient-based optimization. The modeling approach was assessed through three case studies: dynamic simulation of a successful startup, dynamic simulation of a failed startup, and dynamic optimization using a least-squares minimization formulation. Following startup model development, this thesis investigates the development of a framework for optimizing ASU startups using readily interpretable metrics of time and economics. For economics, cumulative profit over the startup horizon is considered. Two events are tracked for the definition of time metrics: time taken to obtain product purities and time to obtain steady-state product flows. Novel approaches are proposed for quantifying these time metrics, which are used as objective functions and in formulating constraints. The / Thesis / Doctor of Philosophy (PhD)

I detta examensarbete presenteras en ny metod för att göra schemaläggningsbeslut inom processindustrin och samtidigt ta hänsyn till det dynamiska beteendet hos processen. En modell av en luftsepareringsanläggning som producerar kvävgas och utnyttjar ett rörligt elpris användes för att exemplifiera denna metod. Modellen omfattade en kryogenisk destillationskolonn med en integrerad återloppskokare /kondensator, en multiströms värmeväxlare, en kompressor, två turbiner och en kondensator. Den innehöll 5079 ekvationer och 437 differentiella variabler. Dynamisk optimering användes för att approximera det dynamiska beteendet hos processen vid skiftningar mellan olika driftpunkter. Den registrerade data utnyttjades sedan för att identifiera en reducerad modell som fångade det transienta beteendet hos relevanta processvariabler. Den reducerade modellen bestod av 525 ekvationer och 67 differentiella variabler. Den identifierade modellen visade på god matchning mellan relevanta processvariabler i de simulerade övergångarna och den reducerade modellen. Den reducerade modellen användes för att optimera schemaläggningen av luftsepareringsprocessen så att elkostnaden över en tredagars period minimerades. De optimala resultaten visade på en minskning av kostnaden på 2.6 % jämfört med en konstant produktionstakt. Schemat implementerades och simulerades i den fullt dynamiska modellen över de första 24 timmarna för att jämföra relevanta processvariabler med den reducerade modellen. Resultaten visade på god matchning mellan de båda modellerna. Detta examensarbete visar att en exakt reducerade modell kan användas för att snabbt hitta ett optimalt schema över ett större processystem. Detta genom att kraftigt minska systemets storlek utan att offra noggrannhet av det dynamiska beteendet. / A novel framework for making plant scheduling decisions while considering the plant process dynamics is presented in this thesis. A model of an air separation unit built to supply nitrogen gas and subject to time-varying electricity prices was used to illustrate this framework. The model includes a cryogenic distillation column with an integrated reboiler/condenser, a multi-stream heat exchanger, a compressor, two turbines, and a liquefier. It consisted of 5079 equations and 437 differential variables. The dynamic behavior of the process during operating point transitions was determined using dynamic optimization. This data were used to establish a reduced order dynamic model of the system which captures the transient behavior of relevant process variables. The reduced order model consisted of 525 equations and 67 differential variables. The identified model showed a good fit between the relevant process variables in the simulated transitions and the reduced order model. The air separation unit process schedule was optimized using the reduced order model to minimize electricity cost over a three day time horizon. The optimal result showed a 2.6 % reduction in electricity cost compared to a flat production rate. The optimal schedule was implemented and simulated in the full dynamic model for the first 24 hours to compare the relevant process variables to the reduced model predictions. The result displayed good match between the reduced model and the full dynamic model. This thesis shows that an accurate reduced order dynamic model can be used for quickly finding the optimal schedule of large process systems. This by greatly reducing the size and complexity of the system without sacrificing accuracy of the dynamic behavior. Furthermore, it also shows the economic benefits of the integrating scheduling and control to count for the dynamic behavior of the system.

In der vorliegenden Arbeit wird eine simulationsbasierte Methodik zur Energie- und Kostenoptimierung der Kühlung von Rechenzentren mit Kalt-/Warmluft-Separation vorgestellt. Dabei wird die spezifische Charakteristik der Luftseparation für einen wesentlich einfacheren und schnelleren Simulationsansatz genutzt, als das mit herkömmlichen, strömungsmechanischen Methoden möglich ist. Außerdem wird der Energiebedarf des Lufttransports – einschließlich der IT-Ventilatoren – in der Optimierung berücksichtigt. Beispielhaft entwickelte Komponentenmodelle umfassen die IT-Systeme und alle für die Kühlung relevanten Anlagen in einer dem aktuellen Stand der Technik entsprechenden Ausführung. Die besonders wichtigen Aspekte Freikühlbetrieb und Verdunstungskühlung werden berücksichtigt. Anhand verschiedener Konfigurationen eines Modellrechenzentrums wird beispielhaft die Minimierung der jährlichen verbrauchsgebunden Kosten durch Anpassung von Temperatursoll- werten und anderen Parametern der Regelung demonstriert; bestehendes Einsparpotenzial wird quantifiziert. Da die Kalt-/Warmluft-Separation in modernen Installationen mit hoher Leistungsdichte auch Auswirkungen auf bauliche Anforderungen hat, wird ein für diesen Anwendungsfall optimiertes Gebäudekonzept vorgeschlagen und praktisch untersucht, das sich insbesondere durch Vorteile hinsichtlich Energieeffizienz, Flexibilität und Betriebssicherheit auszeichnet.:1 Einleitung 1.1 Motivation 1.2 Kategorisierung von Rechenzentren 1.3 Effizienzmetriken für Rechenzentren 1.4 Wissenschaftlicher Beitrag und Abgrenzung 2 Luftgekühlte IT-Systeme: Anforderungen und Trends 2.1 Anforderungen an das Raumklima 2.1.1 Lufttemperatur 2.1.2 Luftfeuchte 2.1.3 Luftzustand im Warmgang 2.1.4 Schalldruckpegel und Schadgase 2.1.5 Betriebsabläufe und Personal 2.2 Kühllasten 2.2.1 Leistungsbedarf der IT-Systeme 2.2.2 Lastgänge und Teillastbetrieb der IT-Systeme 2.2.3 Flächenspezifische Kühllasten 2.3 Leckströme 2.4 Entwicklungstendenzen 3 Rechenzentrumskühlung: Übliche Lösungen und Optimierungskonzepte 3.1 Anlagenkonzepte zur Entwärmung von Rechenzentren 3.1.1 Freie Kühlung 3.1.2 Maschinelle Kälteerzeugung 3.1.3 Umluftkühlung von Rechnerräumen 3.2 Umluftkühlung mit Separation von Kalt- und Warmluft 3.2.1 Konzept 3.2.2 Umsetzung 3.2.3 Regelung der Umluftkühlgeräte 3.2.4 Effizienzoptimierung durch Anhebung der Lufttemperatur 3.2.5 Betriebssicherheit 3.3 Modellbasierte Untersuchungen in der Literatur 3.4 Zwischenfazit 4 Modellbildung 4.1 Struktur des Modells und Ablauf der Simulation 4.2 Annahmen und Randbedingungen 4.3 Modellierung der IT-Systeme 4.3.1 Testsysteme und -software 4.3.2 Testaufbau und Messung der relevanten physikalischen Größen 4.3.3 Drehzahl der internen Ventilatoren 4.3.4 Leistungsaufnahme der internen Ventilatoren 4.3.5 Luftvolumenstrom 4.3.6 Leistungsaufnahme der IT-Systeme ohne Lüfter 4.3.7 Ausblastemperatur 4.4 Modellierung der Kühlsysteme 4.4.1 Pumpen, Rohrnetz und Ventilatoren 4.4.2 Wärmeübertrager 4.4.3 Umluftkühlgeräte 4.4.4 Pufferspeicher 4.4.5 Kältemaschinen 4.4.6 Rückkühlwerke 4.4.7 Freie Kühlung 4.5 Regelstrategien, Sollwertvorgaben und Lastprofile 4.5.1 Kaltluft 4.5.2 Kaltwasser 4.5.3 Kühlwasser 4.5.4 Kälteerzeuger 4.5.5 Lastprofil der IT-Systeme 4.5.6 Wetterdaten 4.5.7 Standortspezifische Kosten für sonstige Betriebsstoffe 4.6 Validierung der Simulationsumgebung 4.6.1 Stichprobenartige experimentelle Prüfung der ULKG-Modellierung 4.6.2 Stichprobenartige experimentelle Prüfung der Modellierung der Kälteerzeugung 4.6.3 Plausibilitätskontrolle und Modellgrenzen 4.7 Zwischenfazit 5 Variantenuntersuchungen und Ableitung von Empfehlungen 5.1 Konfiguration und ausgewählte Betriebspunkte des Modellrechenzentrums 5.2 Optimierung des Jahresenergiebedarfs mit konstanten Kühlmedientemperaturen 5.2.1 Jahresenergiebedarf des Modell-RZs und Optimierung nach Best Practices 5.2.2 Bestimmung der optimalen (konstanten) ULKG-Ausblastemperatur 5.2.3 Einfluss von Last und Typ der IT-Systeme 5.2.4 Einfluss von Standortfaktoren 5.2.5 Einsparpotenzial Pumpenenergie 5.3 Optimierung mit variablen Kühlmedientemperaturen, RKW trocken 5.3.1 Dynamische Sollwertschiebung der Luft- und Kaltwassertemperaturen 5.3.2 Sollwertschiebung der Kühlwassertemperaturen im Kältemaschinenbetrieb 5.3.3 Kombination der Optimierungen und Übertragung auf andere Standorte 5.4 Optimierung mit variablen Kühlmedientemperaturen, RKW benetzt 5.4.1 Dynamische Sollwertschiebung der Luft- und Kaltwassertemperaturen 5.4.2 Optimierung eines modifizierten Modells ohne Kältemaschinen 5.4.3 Betriebssicherheit der Konfiguration ohne Kältemaschinen 5.4.4 Optimierung der Betriebssicherheit durch Eisspeicher 5.5 Zwischenfazit 6 Vorstellung und Diskussion eines neuen Gebäudekonzepts für Rechenzentren 6.1 Gebäudekonzepte und Anforderungen an Sicherheit, Effizienz und Flexibilität 6.1.1 Limitierungen klassischer Konstruktionsprinzipien 6.1.2 Alternative Konzepte für Umluftkühlung in Rechenzentren 6.1.3 Rechenzentren mit Installationsgeschoss statt Doppelboden 6.2 Plenum statt Doppelboden: Konzept und Umsetzung 6.2.1 Aufgabenstellung und konzeptionelle Anforderungen 6.2.2 Lösung mit dem Plenums-Konzept 6.2.3 Anforderungen an die Regelung der Umluftkühlgeräte 6.3 Experimentelle Leistungsbestimmung und Optimierung 6.3.1 Testaufbau und Messung der relevanten physikalischen Größen 6.3.2 Regelung von Luftvolumenstrom und -Temperatur bei konstanter Last 6.3.3 Optimierung der Kaskadenschaltung der Umluftkühlgeräte bei Lastwechseln 6.3.4 Optimierung der Betriebssicherheit der Umluftkühlung bei Stromausfällen 6.3.5 Ermittlung der Leistungsgrenzen 6.4 Zwischenfazit und weiteres Optimierungspotenzial 7 Zusammenfassung und Ausblick

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