Dissertations / Theses on the topic 'Combustion diagnostics; Nitrogen oxide'

To fully utilize coal as a long-term energy source, pollution prevention technologies must be developed to mitigate the negative environmental and health impacts of coal combustion. NOₓ emissions are of particular concern due to their role in forming ground-level ozone, photochemical smog, fine particulates and acid rain. A systematic evaluation of near-flame aerodynamics was conducted to determine how burner operating parameters and oxygen partial pressure influence flame attachment and coal ignition, two properties essential for proper low NOₓ burner operation. A laboratory scale (17kW) 2m tall, 0.5m diameter electrically heated furnace and axial burner with adjustable secondary combustion air annuli and primary fuel jets were used in the study. Transport air oxygen partial pressure (PO₂), coal particle size distribution, primary and secondary jet velocity, and wall temperature were varied independently to determine the effect of each variable on flame attachment and NOₓ. NOₓ emissions from the furnace were similar to those from full-scale tangentially-fired boilers. The tendency for flame attachment increased with velocity ratio (Θ), wall temperature, PO₂, and coal fines. Θ's greater than 1 were required for stable combustion. Increasing Θ reduced flame standoff distances and NOₓ for always-detached flames. NOₓ increased with Θ for always-attached flames. Increasing PO₂ reduced NOₓ by up to 50% by promoting flame attachment. However both oxygen enrichment and increasing fines had little impact on NOₓ for always-attached and always-detached flames. Wall temperature and excess air in leakage were the dominant variables affecting NOₓ. Furnace exhaust oxygen levels increased when operating under a slight vacuum with corresponding increases in NOₓ. Emissions for detached flames increased with wall temperature 3 times faster than attached flames. Emissions data obtained from the furnace under slight positive furnace pressure increased linearly with wall temperature. A novel dual flame was produced at high Θ and reduced PO₂ consisting of one flame attached to the burner and one stabilized 18" below the burner. This configuration is similar to staged combustion but without separate over-fire air. Emissions from the dual flame were significantly below those observed from conventional Type-O attached and detached flames.

Le monoxyde d’azote (NO) est un polluant atmosphérique responsable d’effets nuisibles sur l’environnement et la santé. Afin de mieux contrôler ces émissions, il est indispensable de comprendre et de maîtriser leur formation,en particulier lors de la combustion à haute pression, domaine d’application industrielle (cas des turbines à gaz,des moteurs…). On distingue quatre voies principales de formation de NO : la voie thermique, la voie du NO précoce, la voie NNH et la voie N2O. L’objectif de cette thèse à caractère expérimentale est de compléter la base de données expérimentale déjà existante nécessaire à la compréhension et à l’identification de la contribution de chaque voie à la formation du NO à haute pression.Dans cette thèse, un dispositif de brûleurs à contre-courants a été utilisé pour étudier la structure de flammes laminaires, prémélangées à haute pression. Les profils de concentration de NO dans les flammes CH4/O2/N2 à différentes richesses (Фc =0,7-1,2) et différentes pressions (P=0,1-0,7 MPa) ont été mesurés par Fluorescence Induite par Laser. L’effet de l’ajout d’hydrogène (80%CH4/20%H2 : Application Hythane®) sur la formation de NO a également été étudié dans les flammes pauvres CH4/O2/N2. Le mécanisme cinétique GDF-Kin®3.0_NCN a été comparé aux mesures de NO disponibles dans la littérature ainsi qu’aux simulations des mécanismes cinétiques du Gaz Research Institute (version 2.11 et 3.0). Ces trois mécanismes ont été ensuite comparés aux mesures expérimentales réalisées dans ces travaux de thèse
The nitric oxide (NO) is a pollutant responsible of detrimental effects on the environment and health. To better control these emissions, it’s crucial to understand and to control their formation, in particular during the combustion process at high pressure, area of industrial applications (gas turbines, engines…).There are four major routes of the NO formation: the thermal route, the prompt-NO route, the NNH route and theN2O route. The aim of this experimental thesis is to complete the existing experimental database which isnecessary to the understanding and the identification of the contribution from each route to the NO formation at high pressure.In this thesis, a facility of two twin counter-flow burners was used to study the structure of the laminar, premixed flames at high pressure. Experimental NO concentration profiles have been measured in CH4/O2/N2 flames for arange of equivalence ratio (from 0.7 to 1.2) and pressures (from 0.1 to 0.7 MPa) by Laser Induced Fluorescence.The effect of adding hydrogen (80%CH4/20%H2: Hythane® application) on the NO formation has been also studied in lean CH4/O2/N2 flames. The GDF-Kin®3.0_NCN kinetic mechanism has been compared to experimental data from the literature and also compared to the simulations from the Gas Research Institute mechanisms (version 2.11 and 3.0). These three mechanisms have been finally compared to the experimental data from this thesis

Orientador: Waldir Antonio Bizzo
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Com a inovação tecnológica houve um aumento crescente no consumo de energia devido ao aumento das necessidades individuais e coletivas. Isso trouxe a necessidade de criar novas fontes de energia. A utilização intensiva de combustíveis fósseis tem causado o aumento da poluição ambiental e a degradação e escassez de recursos naturais não renováveis. A formação de gases poluentes, tais como oCO, COz, e os NOx, tem causado grande preocupação e contribuído para fenômenos como o aquecimento global ou formação de ozônio atmosférico. Com a crescente emissão desses gases e de compostos nocivos, as alternativas viáveis são as escolhas de combustíveis renováveis e a adoção de mecanismos minimizantes da formação. A formação de óxidos de nitrogênio, através do mecanismo de Zeldovich, é fornecida por altas temperaturas locais e disponibilidade de oxigênio. Estes fatores, por sua vez, sofTem influência da fluidodinâmica da combustão e a distribuição do tempo de residência. Este trabalho estudou a emissão e a formação de NOx e CO em uma câmara de combustão cilíndrica isolada termicamente, queimando GLP (gás liquefeito de petróleo) e etanol vaporizado. Foram utilizadas o mesmo tempo de residência, a mesma potência específica, temperaturas de saída dos gases de 1O00°C e 1175°C, e diversos números de rotação do queimador. Estes dados foram relacionados com a formação do oxido de nitrogênio na câmara de combustão. Em dois números de rotação específicos foram medidas o campo de temperatura e a distribuição de concentração de NOx, CO e O2, no interior da câmara de combustão
Abstract: The technological innovation caused a growing increase in the energy consumption because the individual and collective needs increased. Then it was necessary to create new energy sources. The intensive use of fossil fuels use has caused environmental pollution, besides degradation and shortage of natural resources. The generation of pollutant gases, such as CO, CO2, and NOx, has caused great concem and also has contributed to the global warming or generation of atmospheric ozone. To struggle with the rising emission ofthose gases, viable altematives are using renewable fuels and emission and formation minimization mechanisms. Nitrogen oxides formation, by the Zeldovich mechanism, occurs by high local temperatures and available oxygen. However, these factors are influenced by combustion fluid dynamics and residence time distribution. This work studied emission and formation of NOx and CO in a cylindrical combustion chamber, thermal insulated, buming LPG (Liquefied Petroleum Gas) and vaporized ethanol. In this equipment were used the same residence time, specific power, exit temperatures of gases 1000°C and 1175°C, and severa! swirl numbers at the bumer. These data were related to the nitrogen oxides formation in the combustion chamber. In two specific swirl numbers, the temperature field and the distribution of NOx, CO and O2 concentration were measured, inside the combustion chamber
Mestrado
Termica e Fluidos
Mestre em Engenharia Mecânica

La séquestration des fumées de dioxyde de carbone provenant des usines de production d'énergie par oxy-combustion est utilisée pour réduire considérablement les émissions de dioxyde de carbone. Des impuretés telles que les oxydes d’azote, de soufre, l’eau et l’oxygène sont présentes dans les fumées. Pour produire du dioxyde de carbone selon les spécifications requises pour le stockage, les fumées de combustion doivent être traitées. Au cours de toutes les étapes du processus de purification du dioxyde de carbone, les oxydes d’azote sont en présence d’oxygène et d’eau à l’état vapeur ou à l’état aqueux. Par conséquent, pour dimensionner l’unité de traitement du dioxyde de carbone, il est important de connaître l'évolution de la composition du mélange, et en particulier la formation d'acide nitrique et d'acide nitreux dans la phase aqueuse.Air Liquide et le LaTEP travaillent ensemble sur cette problématique depuis plusieurs années. Les travaux présentés dans ce manuscrit découlent de cette collaboration. Le but de la thèse est d’étudier d’une part, l’équilibre thermochimique et liquide vapeur du monoxyde d’azote en présence d’eau, de dioxyde de carbone et d’oxygène et d’autre part, la formation des acides nitreux et nitrique.Dans une première partie, une synthèse bibliographie des études sur les systèmesCO2-H2O et NOx-H2O a été réalisée, avec également une étude de la réaction d’oxydation du monoxyde d’azote en dioxyde d’azote. Dans une deuxième partie, le dispositif expérimental ainsi que les méthodes d’analyse mises en place ont été décrits. Pour finir, les résultats obtenus sont présentés et analysés. Les mesures obtenues par l’analyse de la phase aqueuse et un mécanisme réactionnel approprié permettent, notamment, d'estimer la concentration de tous les oxydes d'azote présents dans la phase aqueuse
The sequestration of carbon dioxide fumes from oxy-fuel combustion units is used to reduce significantly the carbon dioxide emissions in the atmosphere. Impurities like nitrogen oxides, sulfur oxides, water and oxygen can cause technical difficulties during the capture, the treatment, the transport and the storage steps of the carbon dioxide fumes. To produce carbon dioxide at specifications required for storage, the flue gas has to be treated. During all the steps of the carbon dioxide purification process, the nitrogen oxides are in the presence of residual oxygen and water in the vapor state or in the aqueous state. Consequently, to design the process, it is important to know the evolution of the composition of the mixture and in particular, the formation of nitric acid and nitrous acid in the aqueous phase and the distribution of the nitrogen oxides in the vapor phase.Air Liquide and the LaTEP are working together on this problematic for several years. The works presented in this manuscript derive from this collaboration. The aim of the thesis is to study on one hand the thermochemical and liquid vapor equilibrium of nitric oxide in the presence of water, carbon dioxide and oxygen and on the other hand the formation of nitrous and nitric acids.In the first part, a bibliography of the studies on CO2-H2O and NOx-H2O systems is made, with a study of the nitric oxide oxidation to nitrogen dioxide. In a second part, the experimental set-up as well as the methods of analysis of the aqueous and the gas phase put in place have been described. Finally, the results obtained are presented and analyzed in the last part of the manuscript. The measurements obtained by the analysis of the aqueous phase and an appropriate reaction mechanism make it possible to estimate the concentration of all the nitrogen oxides present in the aqueous phase

Doped ZnO nanoparticles were synthesized by three different methods – electrochemical deposition under oxidizing conditions (EDOC) , combustion method and wet chemical synthesis – for investigating the oxygen gas sensing response. Ga-doped ZnO was mostly synthesized but also In-doped ZnO was made. The samples were analyzed by XRD, SEM, EDX and TEM. Gas response curves are given alongside with Langmuir fitted curves and data for pure ZnO and Ga-doped ZnO. DFT quantum chemical investigation of cluster models ZnO nanoparticles were performed to evaluate defect effects and oxygen and nitrogen dioxide reactions with the ZnO surface. Defects were investigated by DOS and HOMO-LUMO plots , and are oxygen vacancy, zinc vacancy, zinc interstitial and gallium doping by replacing zinc with gallium. Oxygen and nitrogen dioxide reactions were investigated by computing Mulliken charges, bond lengths, DOS spectra and HOMO-LUMO plots.

A detailed study of NOT formation and destruction has been carried out on a pilot scale circulating fluidized bed combustor of cross-section 0.15 x 0.15 m and height 7.3 m. Coals of various ranks, including anthracite, bituminous, sub-bituminous and lignite, as well as one petroleum coke, were used in the study. Gas emissions in the flue gas and gas concentration profiles for 02, NOT, CO, CH4 and N20 inside the combustor were measured under various operating conditions. A multi-point gas sampling system was developed to accomplish the tasks. Parametric study of NOT emission shows that bed temperature and excess air ratio strongly influence NOT emissions. Increasing either parameter will increase NOT emission in the ranges studied. The effect of staged combustion on NOT emission in the pilot scale circulating fluidized bed combustion depends on the level at which the secondary air is introduced. A reduction of NOT emission was usually, but not always, observed when secondary air was introduced 3.4 m above the base. Limestone addition promotes NOT formation for high volatile bituminous coal due to the catalytic effect of limestone on oxidation of volatile-nitrogen. However, adding limestone during petroleum coke combustion reduced NOT emission. A relationship exists between fuel-nitrogen to NOT conversion and the volatile content of the fuel, with fuels of higher volatile content emitting more NO. Strong radial gas concentration gradients were found inside the combustor, with low concentration of oxygen and high concentrations of reducing gases near the wall where a relatively dense solid layer exists and the carbon concentration is usually high. This is consistent with the core-annulus hydrodynamic pattern often observed by earlier CFB investigators. NO concentration profiles also indicate that NO is mainly formed near the bottom of the reactor where volatile-nitrogen is released. At higher bed levels, competing reactions co-exist, including oxidation of char-N to NO and reduction of NO to nitrogen, mostly due to the char-NO reaction, and NO-CO reaction catalyzed by CaO. Based on the core-annulus flow pattern, a NO model was proposed in which 02 and CO concentration profiles were first calculated or fitted. Taking into account major hydrodynamic features of CFB and the most important reactions involving NO formation and reduction, the model correctly predicts the general qualitative trends in NO formation and reduction in a CFB combustor. Substantial N2O emissions were found in this study. Flue gas concentration ranged from 30 to 70 ppm for coals, and from 140 to 300 ppm for petroleum coke. Temperature and fuel type were found to be the most important operating parameters affecting N2O emissions, the N2O concentration decreasing with increasing temperature for the conditions studied. Excess air also significantly influenced the N20 level. Addition of limestone reduced N20 emissions. For the fuels tested in this study, there was no apparent correlation between N2O conversion and fuel properties. Both gas phase and gas-solid reactions are important in the formation and reduction of N20.

Thesis (M.S.)--Florida State University, 2003.
Advisor: Dr. Andrew A. Dzurik, Florida State University, FAMU-FSU College of Engineering, Dept. of Civil and Environmental Engineering. Title and description from dissertation home page (February 25, 2004). Includes bibliographical references.