Die Herleitung des Unterschieds zwischen globaler und lokaler Stöchiometriezahl für den Oxyfuel-Prozess hat gezeigt, dass gleiche lokale Stöchiometriezahlen bei variierendem Rezirkulationsanteil unterschiedliche globale Stöchiometriezahlen zur Folge haben. In dieser Arbeit wird vorgeschlagen, die Bezeichnung der Zustandspunkte im Oxyfuel-Prozess mit den Sauerstoffkonzentrationen am Brennkammereintritt bzw. -austritt zu verbinden. Für den Sauerstoffanteil am Brennkammereintritt (z.B. 30 vol.-%) und den Restsauerstoff am Brennkammerende (z.B. 4 vol.-%) folgt zum Bespiel die Bezeichnung Oxyfuel 30 mit 4 % Restsauerstoff. Diese Bezeichnung ist eindeutig und kann das Lambda – als Beschreibung der Stöchiometrie im konventionellen Betrieb – ablösen. Für eine Vielzahl an Punkten sind Verbrennungsversuche mit Trockenbraunkohle und Sauerstoff durchgeführt worden. Ein stabiler Betrieb der Versuchsanlage der TU Dresden wurde zwischen Oxyfuel 17 und Oxyfuel 33 erreicht. Die Untersuchungen haben nachgewiesen, dass die Rezirkulation des feuchten Abgases für die Verbrennung unkritisch ist. Die Schwefeldioxid-Emissionen sind abhängig von den variierenden Reaktionstemperaturen im Kennfeld, dem Restsauerstoff am Brennkammerende und der Rezirkulation des Abgases. Mit der Belagssondenmessung von Aschepartikeln im Abgasstrom wurde gezeigt, dass auch andere Komponenten (z.B. Chlor) im Oxyfuel-Prozess aufkonzentriert werden. Diese erhöhten Konzentrationen werden zu neuen Anforderungen in der Werkstoffauswahl führen. Für das Einschwingverhalten der Abgaszusammensetzung beim Umschalten von konventioneller Verbrennung zu Oxyfuel-Prozess-Fahrweise hat sich gezeigt, dass für diese Staubfeuerungs-Versuchsanlage ein einfaches Rührkesselmodell geeignet ist.

In dieser Arbeit werden unter der Nutzung von Simulationswerkzeugen und neu erstellten instationären Modellen von Kraftwerkskomponenten auf dem Sektor der Energieerzeugung mit fossilen Brennstoffen am Beispiel von Kohle, Betriebs- und Verhaltensweisen der Anlage untersucht und Optimierungsmöglichkeiten für die vorgegebenen Randbedingungen getestet.

Today, and for the foreseeable future, coal and other fossil fuels will provide a major portion of the energy services demanded by both developed and developing countries around the word. In order to reduce the emissions of carbon dioxide associated with combustion of coal for electricity generation, a wide range of carbon capture technologies are being developed. This thesis models the oxyfuel carbon capture process for pulverized coal and presents performance and cost estimates of this system in comparison to other low-carbon fossil fuel generators. Detailed process models for oxygen production, flue gas treatment, and carbon dioxide purification have been developed along with the calculation strategies necessary to employ these components in alternative oxyfuel system configurations for different types of coal-fired power plants. These new oxyfuel process models have been implemented in the widely-used Integrated Environmental Control Model (IECM) to facilitate systematic comparisons with other low-carbon options employing fossil fuels. Assumptions about uncertainties in the performance characteristics of gas separation processes and flue gas duct sealing technology, as well as plant utilization and financing parameters, were found to produce a wide range of cost estimates for oxyfuel systems. In case studies of a new 500 MW power plant burning sub-bituminous Powder River Basin coal, the estimated levelized cost of electricity (LCOE) 95% confidence interval (CI) was 86 to 150 [$/MWh] for an oxyfuel system producing a high-purity [99.5 mol% CO2] carbon dioxide product while capturing 90% of the flue gas carbon dioxide. For a CoCapture oxyfuel system capturing 100% of the flue gas CO2 together with all other flue gas constituents, the estimated LCOE 95% CI was 90 to 153 [$/MWh] (all costs in constant 2012 US Dollars). Using the IECM, an oxyfuel system for CO2 capture also was compared under uncertainty to an existing amine-based post-combustion capture system for a new 500 MW power plant, with both systems capturing 90% of the CO2 and producing a high-purity stream for pipeline transport to a geological sequestration site. The resulting distribution for the cost of CO2 avoided showed the oxyfuel-based system had a 95% CI of 44 to 126 [$/tonne CO2] while the amine-based system cost 95% CI ranged from 50 to 133 [$/tonne CO2]. The oxyfuel cost distribution had a longer tail toward more expensive configurations but over 70% of the distribution showed the oxyfuel-based system to be ~10[$/tonne CO2] lower in cost compared to the amine-based capture system. An evaluation of several low-carbon generation options fueled by coal and natural gas further considered both direct and indirect greenhouse gas emissions. This analysis showed oxyfuel to be economically competitive with all capture system considered, and also indicated oxyfuel to be the preferred carbon capture technology for minimizing overall carbon intensity. Combined, these results suggest that oxyfuel is a promising carbon capture technology, and the only one which offers the unique ability to capture all the combustion gases to become a truly zero emission coal plant. Realization of the latter option, however, is contingent on the development of new regulatory policies for underground injection of mixed flue gas streams that is outside the scope of this thesis.

Stainless steels were first developed in the early 20th century and have since then emerged as a very diverse class of engineering materials. Along with steels having new combinations of properties, there is a continuous development of new technologies allowing the material to be produced in a faster and more energy effcient manner. A prerequisite for new technologies to be adapted quicklyis a fundamental understanding of the microstructure evolution throughout theprocess chain. The first part of this thesis has been dedicated to the annealing and pickling processes from a process-microstructure perspective. In the second part the concept of utilising crystallographic texture as a way to attain microstructures with new combinations of properties has been evaluated. In the first part, annealing can be regarded as a high temperature oxidation process, resulting in chromium depletion that necessitate subsequent chemical pickling. Chemical pickling, on the other hand, is basically a wet-corrosion process and hence more difficult for highly corrosion-resistant grades. The chromium depleted layer was found to be enriched in austenite in case of duplex stainless steel UNS S32205 (Paper I) and this may inuence the pickling process. Proper pretreatment like shot-blasting dramatically increases the pickling rate because it provides the pickling acid with access to the chromium depleted layer (Paper II). Oxidation kinetics for S30400 in conditions relevant to strip annealing do not seem to be affected by the choice of air/oxygen as oxidiser even though the latter results in substantially higher water content (Paper III). This gives new possibilities regarding both cost savings and increased throughput. In the second part, the effect of crystallographic texture on resistance towards corrosion of S31603 in a solution of FeCl3 and AlCl3 in ethanol/glycerol and in 30 vol% H2SO4 is investigated. In the former, high density surfaces {1111} and {100} are less prone for pit nucleation, however the effect is relativelysmall. In H2SO4 pronounced crystallographic anisotropy is observed inwhich the corrosion rate increase in the order {111} &lt; {110} ≤ {100} (Paper IV).For corrosion at high temperatures, chromium diffusion is governed by randomhigh angle boundaries with ~20—55° misorientation. The possibilities to alter the texture in austenitic stainless steels by means of warm-rolling and annealing has been evaluated for S30403 and S31603. During warm-rolling, both steels develop the copper-type texture in contrast to the brass-type texture observedat room temperature. However only S30403 is prone to recrytallise cube texture during subsequent annealing (Paper V). / <p>QC 20150121</p>

Zugl.: Stuttgart, Univ., Diss., 2009

Die Herleitung des Unterschieds zwischen globaler und lokaler Stöchiometriezahl für den Oxyfuel-Prozess hat gezeigt, dass gleiche lokale Stöchiometriezahlen bei variierendem Rezirkulationsanteil unterschiedliche globale Stöchiometriezahlen zur Folge haben. In dieser Arbeit wird vorgeschlagen, die Bezeichnung der Zustandspunkte im Oxyfuel-Prozess mit den Sauerstoffkonzentrationen am Brennkammereintritt bzw. -austritt zu verbinden. Für den Sauerstoffanteil am Brennkammereintritt (z.B. 30 vol.-%) und den Restsauerstoff am Brennkammerende (z.B. 4 vol.-%) folgt zum Bespiel die Bezeichnung Oxyfuel 30 mit 4 % Restsauerstoff. Diese Bezeichnung ist eindeutig und kann das Lambda – als Beschreibung der Stöchiometrie im konventionellen Betrieb – ablösen. Für eine Vielzahl an Punkten sind Verbrennungsversuche mit Trockenbraunkohle und Sauerstoff durchgeführt worden. Ein stabiler Betrieb der Versuchsanlage der TU Dresden wurde zwischen Oxyfuel 17 und Oxyfuel 33 erreicht. Die Untersuchungen haben nachgewiesen, dass die Rezirkulation des feuchten Abgases für die Verbrennung unkritisch ist. Die Schwefeldioxid-Emissionen sind abhängig von den variierenden Reaktionstemperaturen im Kennfeld, dem Restsauerstoff am Brennkammerende und der Rezirkulation des Abgases. Mit der Belagssondenmessung von Aschepartikeln im Abgasstrom wurde gezeigt, dass auch andere Komponenten (z.B. Chlor) im Oxyfuel-Prozess aufkonzentriert werden. Diese erhöhten Konzentrationen werden zu neuen Anforderungen in der Werkstoffauswahl führen. Für das Einschwingverhalten der Abgaszusammensetzung beim Umschalten von konventioneller Verbrennung zu Oxyfuel-Prozess-Fahrweise hat sich gezeigt, dass für diese Staubfeuerungs-Versuchsanlage ein einfaches Rührkesselmodell geeignet ist.

Originally presented as the author's Thesis--Technische Hochschule Aachen, 2008. / Includes bibliographical references.

Le réchauffement climatique principalement dû aux émissions importantes de CO₂, gaz à effet de serre de référence, encourage les chercheurs à trouver des solutions pour lutter contre ce phénomène. Les techniques consistant à capter et stocker ou valoriser le CO₂ sont des solutions pertinentes, mais qui nécessitent d'avoir du CO₂ le plus pur possible. Parmi ces techniques, l'oxycombustion parait assez prometteuse pour produire du CO₂ en forte concentration. Toutefois, selon la nature du combustible et la pureté de l'oxygène, certains polluants peuvent apparaître tels que le CO et les NOx. Pour réaliser cette purification, la catalyse est un moyen efficace permettant de transformer simultanément le NO et le CO respectivement en N₂ et CO₂. L'objectif de cette étude est donc, de mettre au point des catalyseurs actifs pour la réduction des NOx en N₂ par le CO, dans un milieu oxydant et en présence d'eau. Deux types de catalyseurs ont été choisis : les métaux nobles (Pd, Pt, Rh) supportés et les oxydes de métaux de transition (Co, Cu, Al). Les résultats obtenus montrent que les catalyseurs à base de Pt sont plus performants et que leur activité catalytique augment pour les échantillons supportés sur un support neutre (SiO₂) ou réductible (TiO₂) que ce soit en présence ou en absence d'eau. Les oxydes mixtes de métaux de transition, obtenus par voie hydrotalcite, montre que la nature du cation bivalent joue un rôle important. Les oxydes mixtes Co-Cu ont montré une meilleure activité que les matériaux composés d'un seul de ces deux éléments. Cependant, l'ajout d'eau dans le flux réactionnel conduit à une baisse d'activité des catalyseurs contenant du Cu. / Global warming, mainly due to high CO₂ emissions, reference greenhouse gas, motivates researchers to find solutions to combat this phenomenon. The techniques of capturing and storing or reuse of CO₂ are revelant solutions, but which require a CO₂ as pure as possible. Among these techniques, oxyfuel combustion seems promising enough to produce CO₂ in high concentration. However, depending on the nature of the fuel and the oxygen purity, some pollutants may appear such as CO and NOx. To carry out this purification, catalysis is an effective means for simultaneously converting NO and CO respectively into N₂ and CO₂. The objective of this study is to develop active catalysts for NOx reduction in N₂ by CO, in oxidizing conditions and presence of water. Two types of catalysts were chosen : supported noble metals (Pd, Pt, Rh) and transition metal oxides (Co, Cu, Al). The results obtained show that the Pt-based catalysts were more efficient and that their catalytic activity increases for the samples supported on a neutral support (SiO₂) or reducible (TiO₂) whether in the presence or absence of water. The mixed oxides of transition metals, obtained by hydrotalcite, show that the nature of the bivalent cation plays an important role. Co-Cu mixed oxides showed better activity than materials composed of only one of these two elements. However, the addition of water to the reaction flow led to a decrease in activity of the Cu-containing catalysts.

O uso de combustíveis fósseis para a geração de energia, especificamente carvão mineral, ainda dominará a matriz energética mundial por algumas décadas. No Brasil, entretanto, apesar de sua vasta disponibilidade, o carvão mineral segue ocupando uma tímida posição na matriz. Ao mesmo tempo, há uma considerável geração de resíduos de biomassa oriundos de atividades agrícolas, que poderiam ser incorporados ao uso do carvão na geração termoelétrica de energia. Sobre o uso de combustíveis fósseis na geração termoelétrica e a consequente emissão de CO2, a ainda insipiente tecnologia de oxicombustão aparece como possibilidade de geração de emissões quase-zero de CO2. Diante disso, esta tese tem como objetivo estudar os aspectos envolvidos na adaptação da combustão em leito fluidizado borbulhante para a oxicombustão de carvão mineral e biomassa. Para tanto, inicialmente, realiza-se uma estimativa da possibilidade do uso de resíduos de biomassa, especificamente os provenientes da cadeia produtiva de madeira e casca de arroz, em sistemas de combustão no estado do Rio Grande do Sul. Estes combustíveis são, então, utilizados na combustão com ar atmosférico em planta piloto, com capacidade de 0,25 MWt de leito fluidizado borbulhante, para posterior comparação com a oxicombustão dos mesmos combustíveis. As comparações foram realizadas quanto ao balanço de massa balanço de energia e questões fluidodinâmicas. A influência dos principais parâmetros de processo na transição de combustão com ar atmosférico para a oxicombustão foi analisada quanto à possibilidade de minimizar a entrada de ar falso no sistema. A manutenção de pressões negativas mostrou-se indesejável na oxicombustão, especialmente quando é realizada a adaptação de plantas já existentes. Os resultados indicaram uma forte influência do ajuste da válvula de recirculação dos gases, da potência do ventilador e da vazão de gases no sistema na minimização da entrada de ar falso. A partir do ajuste das condições operacionais, foi possível a obtenção de uma concentração de 59,6% vol. de CO2 nos gases de combustão. / The fossil fuels use for energy generation, especially coal, will dominate the world energy matrix for decades. However, in Brazil, coal still occupies a timid position in spite of its extensive disponibility. At the same time, there is a considerable generation of wastes from agricultural activities that could be incorporated to coal as fuels on thermoelectric energy processes, in special for a decentralized system configuration. Yet, by considering the use of fossil fuels on thermoelectric generation and the consequent CO2 emission, there is the oxyfuel combustion technology that has appeared as an option for near-zear CO2 emissions by promoting its capture. From this perspective, this work has the objective of studying the aspects that involve the retrofit of bubbling fluidized bed combustion to oxyfuel combustion by using coal and biomass wastes as fuels. In this sense, an estimative of the use of biomass wastes, especially wood wastes and rice husk, on combustion systems in the State of Rio Grande do Sul is firstly proceeded. These fuels are used on air combustion in a 0,25 MWt bubbling fluidized bed pilot plant for comparison to oxyfuel combustion with the fuels used. Such comparisons where done by applying material balance, energy balance and fluid dynamics analysis. The influence of the main process parameters on the retrofit of air combustion to oxyfuel combustion were analyzed concerning the air leakage minimization. Negative pressure maintenance in key points of the system was shown as an undesirable issue when retrofitting. The results indicated a strong influence of the recycling valve adjustment, fan power and gases flow on the air leakage. From operational conditions adjustment, 59,6 vol.% CO2 concentration could be achieved in the gases.

O uso de combustíveis fósseis para a geração de energia, especificamente carvão mineral, ainda dominará a matriz energética mundial por algumas décadas. No Brasil, entretanto, apesar de sua vasta disponibilidade, o carvão mineral segue ocupando uma tímida posição na matriz. Ao mesmo tempo, há uma considerável geração de resíduos de biomassa oriundos de atividades agrícolas, que poderiam ser incorporados ao uso do carvão na geração termoelétrica de energia. Sobre o uso de combustíveis fósseis na geração termoelétrica e a consequente emissão de CO2, a ainda insipiente tecnologia de oxicombustão aparece como possibilidade de geração de emissões quase-zero de CO2. Diante disso, esta tese tem como objetivo estudar os aspectos envolvidos na adaptação da combustão em leito fluidizado borbulhante para a oxicombustão de carvão mineral e biomassa. Para tanto, inicialmente, realiza-se uma estimativa da possibilidade do uso de resíduos de biomassa, especificamente os provenientes da cadeia produtiva de madeira e casca de arroz, em sistemas de combustão no estado do Rio Grande do Sul. Estes combustíveis são, então, utilizados na combustão com ar atmosférico em planta piloto, com capacidade de 0,25 MWt de leito fluidizado borbulhante, para posterior comparação com a oxicombustão dos mesmos combustíveis. As comparações foram realizadas quanto ao balanço de massa balanço de energia e questões fluidodinâmicas. A influência dos principais parâmetros de processo na transição de combustão com ar atmosférico para a oxicombustão foi analisada quanto à possibilidade de minimizar a entrada de ar falso no sistema. A manutenção de pressões negativas mostrou-se indesejável na oxicombustão, especialmente quando é realizada a adaptação de plantas já existentes. Os resultados indicaram uma forte influência do ajuste da válvula de recirculação dos gases, da potência do ventilador e da vazão de gases no sistema na minimização da entrada de ar falso. A partir do ajuste das condições operacionais, foi possível a obtenção de uma concentração de 59,6% vol. de CO2 nos gases de combustão. / The fossil fuels use for energy generation, especially coal, will dominate the world energy matrix for decades. However, in Brazil, coal still occupies a timid position in spite of its extensive disponibility. At the same time, there is a considerable generation of wastes from agricultural activities that could be incorporated to coal as fuels on thermoelectric energy processes, in special for a decentralized system configuration. Yet, by considering the use of fossil fuels on thermoelectric generation and the consequent CO2 emission, there is the oxyfuel combustion technology that has appeared as an option for near-zear CO2 emissions by promoting its capture. From this perspective, this work has the objective of studying the aspects that involve the retrofit of bubbling fluidized bed combustion to oxyfuel combustion by using coal and biomass wastes as fuels. In this sense, an estimative of the use of biomass wastes, especially wood wastes and rice husk, on combustion systems in the State of Rio Grande do Sul is firstly proceeded. These fuels are used on air combustion in a 0,25 MWt bubbling fluidized bed pilot plant for comparison to oxyfuel combustion with the fuels used. Such comparisons where done by applying material balance, energy balance and fluid dynamics analysis. The influence of the main process parameters on the retrofit of air combustion to oxyfuel combustion were analyzed concerning the air leakage minimization. Negative pressure maintenance in key points of the system was shown as an undesirable issue when retrofitting. The results indicated a strong influence of the recycling valve adjustment, fan power and gases flow on the air leakage. From operational conditions adjustment, 59,6 vol.% CO2 concentration could be achieved in the gases.