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Residence Time Distribution modeling of combustors through Chemical Reactor Network

Agizza, Maria Angela (2020)
Residence Time Distribution modeling of combustors through Chemical Reactor Network.
Technische Universität Darmstadt
doi: 10.25534/tuprints-00011777
Dissertation, Erstveröffentlichung

Kurzbeschreibung (Abstract)

The growing globalization and continuous industrial and urban development result in an ever-increasing energy demand for transportation and power generation. Therefore, providing sustainable and clean conversion processes is one of the most crucial challenges worldwide. By virtue of the high energy density of chemical fuels and the capability of satisfying strongly fluctuating energy demand, combustion dominates the global energy scenario. According to the crucial reasons listed above, its importance is not diminishing in the foreseeable future, despite the increasing share of renewable conversion sources. Hence, a continuous improvement of combustion devices, to increase their efficiency and reduce pollutants emission, is mandatory, and new combustion concepts must be explored and tested. Lean combustion fulfills the requirements of an efficient and clean combustion process, applicable to aviation gas turbines. As it results in higher temperatures of the combustor wall, this process is often coupled with effusion cooling of the combustor liner. This poses the problem of the interaction between a hot reactive environment and cold cooling air, which is not yet fully understood. This strategy needs further investigation because it could lead to high carbon monoxide emissions due to rapid and inhomogeneous cooling of pockets of reacting fluid. Oxyfuel combustion, instead, is a strategy applicable to stationary power plants. In this case, the substitution of air with a mixture comprising carbon dioxide and oxygen takes place. Such an approach represents a point of novelty with respect to standard combustion in air. Therefore, an improved understanding of the effect of excess CO2 in a reaction environment is crucial. Both outlined technologies present undeniable advantages, yet their possible drawbacks need to be understood and avoided, and a deeper knowledge is required to properly exploit their potential. To this aim, thorough experimental investigation in suitably designed close-to-reality configuration is mandatory, and ideally complemented by the modeling of the observed phenomena. A modeling strategy that well fits the idea of a strong synergy between experiments and modeling, is referred to as Chemical Reactor Network (CRN) modeling. This strategy proposes a simplified version of the flow field based on two extreme mixing possibilities. Such models give insight into the mixing and reactive features of a complex flow, as the ones encountered in practical combustion devices. To achieve a proper CRN model, it is possible to design and size it against the Residence Time Distribution (RTD) of a certain configuration. Even without further modeling, RTD data alone yields precious information on the mixing characteristic of the system under investigation. In the current work, Chemical Reactor Network modeling based on experimental Residence Time Distribution data is applied to two suitably designed close-to-reality configurations. They are representative of an aviation gas turbine combustor and a power generation furnace. These systems were designed to better understand the underlying phenomena while investigating new combustion concepts, such as lean combustion and oxyfuel combustion. CRN models are designed and tested in both situations. These models are developed based on zonal modeling of the flow field and on the Residence Time Distribution of the systems. In both cases, their performances are tested against experimental data available for both test-rigs regarding pollutants emissions. Additionally, they are employed to understand the impact of the operating conditions on the combustion process. This work states the importance of such simple and flexible tools in combustion research.

Typ des Eintrags: Dissertation
Erschienen: 2020
Autor(en): Agizza, Maria Angela
Art des Eintrags: Erstveröffentlichung
Titel: Residence Time Distribution modeling of combustors through Chemical Reactor Network
Sprache: Englisch
Referenten: Dreizler, Dr. Andreas ; Faravelli, Dr. Ing. Tiziano ; Sorrentino, Dr. Ing. Giancarlo
Publikationsjahr: 2020
Ort: Darmstadt
Datum der mündlichen Prüfung: 12 Juni 2019
DOI: 10.25534/tuprints-00011777
URL / URN: https://tuprints.ulb.tu-darmstadt.de/11777
Kurzbeschreibung (Abstract):

The growing globalization and continuous industrial and urban development result in an ever-increasing energy demand for transportation and power generation. Therefore, providing sustainable and clean conversion processes is one of the most crucial challenges worldwide. By virtue of the high energy density of chemical fuels and the capability of satisfying strongly fluctuating energy demand, combustion dominates the global energy scenario. According to the crucial reasons listed above, its importance is not diminishing in the foreseeable future, despite the increasing share of renewable conversion sources. Hence, a continuous improvement of combustion devices, to increase their efficiency and reduce pollutants emission, is mandatory, and new combustion concepts must be explored and tested. Lean combustion fulfills the requirements of an efficient and clean combustion process, applicable to aviation gas turbines. As it results in higher temperatures of the combustor wall, this process is often coupled with effusion cooling of the combustor liner. This poses the problem of the interaction between a hot reactive environment and cold cooling air, which is not yet fully understood. This strategy needs further investigation because it could lead to high carbon monoxide emissions due to rapid and inhomogeneous cooling of pockets of reacting fluid. Oxyfuel combustion, instead, is a strategy applicable to stationary power plants. In this case, the substitution of air with a mixture comprising carbon dioxide and oxygen takes place. Such an approach represents a point of novelty with respect to standard combustion in air. Therefore, an improved understanding of the effect of excess CO2 in a reaction environment is crucial. Both outlined technologies present undeniable advantages, yet their possible drawbacks need to be understood and avoided, and a deeper knowledge is required to properly exploit their potential. To this aim, thorough experimental investigation in suitably designed close-to-reality configuration is mandatory, and ideally complemented by the modeling of the observed phenomena. A modeling strategy that well fits the idea of a strong synergy between experiments and modeling, is referred to as Chemical Reactor Network (CRN) modeling. This strategy proposes a simplified version of the flow field based on two extreme mixing possibilities. Such models give insight into the mixing and reactive features of a complex flow, as the ones encountered in practical combustion devices. To achieve a proper CRN model, it is possible to design and size it against the Residence Time Distribution (RTD) of a certain configuration. Even without further modeling, RTD data alone yields precious information on the mixing characteristic of the system under investigation. In the current work, Chemical Reactor Network modeling based on experimental Residence Time Distribution data is applied to two suitably designed close-to-reality configurations. They are representative of an aviation gas turbine combustor and a power generation furnace. These systems were designed to better understand the underlying phenomena while investigating new combustion concepts, such as lean combustion and oxyfuel combustion. CRN models are designed and tested in both situations. These models are developed based on zonal modeling of the flow field and on the Residence Time Distribution of the systems. In both cases, their performances are tested against experimental data available for both test-rigs regarding pollutants emissions. Additionally, they are employed to understand the impact of the operating conditions on the combustion process. This work states the importance of such simple and flexible tools in combustion research.

Alternatives oder übersetztes Abstract:
Alternatives AbstractSprache

Sowohl die Zunahme des Luftverkehrs als auch des Energiebedarfs erfordern eine kontinuierliche Verbesserung von Verbrennungskraftmaschinen, um die Nachhaltigkeit des Verbrennungsprozesses sicherzustellen. Um die Verbrennungseffizienz zu erhöhen und die Schadstoffemissionen zu reduzieren werden neue Verbrennungskonzepte vorgeschlagen und getestet. Die magere Verbrennung erfüllt die Anforderungen eines effizienten und sauberen Verbrennungsprozesses für Luftfahrtgasturbinen. Sie ist oft mit einer Effusionskühlung der Brennkammerwände gekoppelt. Dabei ist die Wechselwirkung zwischen einer heißen Reaktionsumgebung und einer kalten Kühlluft noch nicht vollständig verstanden. Diese muss weiter untersucht werden, da aufgrund einer schnellen und inhomogenen Abkühlung von reagierenden Fluideinschlüssen hohe Kohlenmonoxidemissionen entstehen können. Die Oxyfuel-Verbrennung ist stattdessen eine Strategie, die für stationäre Kraftwerke anwendbar ist. In diesem Fall erfolgt eine Substitution von Luft durch ein Gemisch aus Kohlenstoffdioxid und Sauerstoff. Dies stellt eine Neuheit in Bezug auf die Standardverbrennung in Luft dar, wodurch ein besseres Verständnis der Auswirkungen von überschüssigem CO2 in einer Reaktionsumgebung entscheidend ist. Zu diesem Zweck ist eine gründliche experimentelle Untersuchung in einer entsprechend realitätsnahen Konfiguration erforderlich, die idealerweise durch die Modellierung der beobachteten Phänomene ergänzt wird. Eine Modellierungsstrategie, die gut zu der Idee einer starken Synergie zwischen Experimenten und Modellierung passt, wird als “Chemical Reactor Network” (CRN) Modellierung bezeichnet. Bei dieser Vorgehensweise wird eine vereinfachte Form des Strömungsfeldes betrachtet, basierend auf zwei extremen Mischungsmöglichkeiten. Diese Modelle werden häufig gegen die Verweilzeitverteilung einer bestimmten Konfiguration bemessen, welche bereits wertvolle Informationen über die Mischcharakteristik des untersuchten Systems liefert. In der vorliegenden Arbeit wird die CRN-Modellierung für zwei entsprechend realitätsnahe Umgebungen angewendet. Sie sind repräsentativ für die Brennkammer einer Luftfahrtgasturbine und einer Kraftwerkfeurung. Diese Konfigurationen wurden entworfen, um die zugrunde liegenden Phänomene besser zu verstehen und gleichzeitig neue Verbrennungskonzepte zu untersuchen, nämlich die magere Verbrennung bzw. die Oxyfuel-Verbrennung. Ein CRN-Modell wird jeweils für die beiden Situationen entwickelt und getestet. Diese basieren auf der zonalen Modellierung des Strömungsfeldes und der Verweilzeitverteilung der Systeme. Für beide Fälle wird die Leistungsfähigkeit anhand zur Verfügung stehender experimenteller Daten getestet. Außerdem werden sie verwendet um die Auswirkungen der Betriebsbedingungen auf den Verbrennungsprozess besser zu verstehen. In dieser Arbeit wird die Wichtigkeit solcher einfachen und flexiblen Werkzeuge für die Verbrennungsforschung aufgezeigt.

Deutsch

La crescente globalizzazione e il continuo sviluppo industriale e urbanistico sono alla base di un continuo incremento della richiesta energetica per il settore dei trasporti e della produzione di elettricità. Perciò, fornire processi di conversione energetica sostenibile e a ridotte emissioni di inquinanti è una delle piú grandi sfide a livello mondiale. Grazie alla elevata densità energetica dei combustibili e la flessibilità nel soddisfare richieste energetiche oscillanti, il processo di combustione domina lo scenario energetico globale e la sua importanza non diminuirà in breve tempo. Di conseguenza, il suo continuo miglioramento, al fine di aumentarne l’efficienza e ridurre le emissioni inquinanti, è di fondamentale importanza e nuove tecnologie devono essere proposte e testate. Un processo di combustione caratterizzato da condizioni magre soddisfa i requisiti di efficienza e ridotte emissioni, applicabile alle turbine a gas di tipo aeronautico. Un inconveniente di questo processo è l’aumento della temperatura di parete all’interno del combustore. Pertanto, la combustione magra è spesso accoppiata a un raffreddamento di tipo ad effusione del rivestimento della superficie del combustore. Ciò costringe a fronteggiare il problema della complessa interazione tra l’ambiente di reazione estremamente caldo e la corrente di aria fredda adibita al raffreddamento, che non è ancora pienamente compresa. Per questo motivo, ulteriori studi sono necessari in quanto una tale condizione operativa potrebbe portare alla produzione di elevate emissioni di monossido di carbonio come conseguenza di un rapido e disomogeneo raffreddamento di sacche di fluido reagente. D’altro canto, per quanto riguarda le grandi centrali elettriche, l’ossicombustione (Oxyfuel) rappresenta una valida strategia caratterizzata dalla sostituzione di aria con una miscela formata da anidride carbonica e ossigeno. Tale approccio costituisce una novità rispetto alle metodologie di combustione standard e, a tal riguardo, è quindi fondamentale ottenere una migliore comprensione degli effetti dovuti alla presenza di un eccesso di CO2 in un ambiente reagente. Le due tecnologie descritte hanno vantaggi innegabili. Tuttavia, gli eventuali inconvenienti che possono derivarne devono essere compresi ed evitati. È, pertanto, fondamentale perseguire approfondite indagini di tipo sperimentale in apparati il più possibile realistici, le quali devono inoltre essere affiancate e completate da modellazioni di tipo numerico dei diversi fenomeni osservati. In tale contesto, una strategia che ben si adatta all'idea di questa forte sinergia tra ricerca sperimentale e investigazione numerica è rappresentata dalla cosiddetta tecnica di modellazione “Chemical Reactor Network” (CRN, detto anche “modello a compartimenti”). Questo approccio propone una versione semplificata del campo di moto, basata sulle due possibilità estreme di miscelazione. Modelli di questo genere consentono di approfondire la comprensione delle proprietà reattive e di micelazione di campi di moto complicati, come quelli che caratterizzano i dispositivi di combustione reali. Questi modelli sono spesso dimensionati rispetto alla “Residence Time Distribution” (distribuzione del tempo di residenza) di una determinata configurazione. Questa quantità consente inoltre di ottenere preziose informazioni sulle caratteristiche di miscelazione del sistema in esame anche in assenza di modellazione dei dati. Nel presente lavoro, la metodologia basata sul modello a compartimenti viene applicata a due configurazioni, appositamente progettate per rispecchiare condizioni di funzionamento reali, rappresentate rispettivamente da un combustore di turbina a gas per aeromobili e un forno dedicato alla produzione di potenza. Questi sistemi sono stati realizzati per comprendere al meglio i fenomeni alla base dei nuovi approcci menzionati. In entrambi i casi, modelli di tipo CRN sono stati progettati e testati. Tali modelli sono sviluppati sulla base di una riproduzione di tipo zonale del campo di moto e della distribuzione dei tempi di residenza. I risultati ottenuti dai modelli sono confrontate con i set di dati sperimentali disponibili per entrambi gli impianti. Inoltre, i risultati ottenuti sono utilizzati per comprendere l'impatto che le condizioni operative esercitano sulla fase di combustione. Questo lavoro afferma l'importanza che tali semplici e flessibili strumenti rivestono per un’attività di ricerca relativa ai processi di combustione.

Italienisch
URN: urn:nbn:de:tuda-tuprints-117776
Zusätzliche Informationen:

Dissertation submitted for the double-degree Ph.D. "Dr. Ing. Maschinenbau" - Technische Universität Darmstadt "Dr. in Industrial Chemistry and Chemical Engineering" - Politecnico di Milano in the framework of the Marie Skłodowska-Curie Actions "CLEAN-Gas" Project.

Sachgruppe der Dewey Dezimalklassifikatin (DDC): 600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften und Maschinenbau
Fachbereich(e)/-gebiet(e): 16 Fachbereich Maschinenbau
16 Fachbereich Maschinenbau > Fachgebiet Reaktive Strömungen und Messtechnik (RSM)
Hinterlegungsdatum: 26 Mai 2020 07:21
Letzte Änderung: 01 Dez 2023 07:53
PPN:
Referenten: Dreizler, Dr. Andreas ; Faravelli, Dr. Ing. Tiziano ; Sorrentino, Dr. Ing. Giancarlo
Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: 12 Juni 2019
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