O presente trabalho trata da modelagem de combustão em um queimador industrial de gás natural utilizando cadeias de reatores químicos idealizados. A partir de simulações de CFD e dados experimentais do ensaio denominado BERL 300 kW, sucessivas cadeias de reatores são propostas, baseando-se em premissas sobre as condições de temperatura e fluxo de massa entre as diversas regiões do escoamento reativo. O objetivo é obter uma cadeia de reatores que reproduza as emissões de NOx do ensaio. O erro relativo das emissões é de 98,23% na primeira cadeia, de 82,30% na segunda cadeia e de 1,54% na terceira cadeia. A partir da terceira cadeia de reatores proposta, considerada representativa do ensaio, realiza-se uma análise de sensibilidade e um estudo paramétrico, para avaliar a sensibilidade do modelo aos ajustes de segmentação de correntes e a capacidade de reproduzir os dados experimentais de emissão em condições de pré-aquecimento do ar de combustão e em operação fora do ponto de projeto. O modelo produz resultados satisfatórios para os casos de pré-aquecimento do ar até 110°C e para potências térmicas até 33% superiores ao ponto de projeto, não oferecendo bons resultados para as demais condições de operação. / This work shows the development and application of chemical reactor networks (CRN) to the modeling of a natural gas burner. The CRN development is based on experimental and CFD simulation results of the BERL 300 kW test. The CRN element arrangement, reactor volumes and flow splits are adjusted based on the best agreement with characteristic temperatures of the reactive flow, aiming to reproduce the experimental NOx emissions data. The relative error in the emissions predictions are 98,23% for the first CRN proposed, 82,30% for the second CRN and 1,54% for the third one. A sensitivity analysis and a parametric study of the third CRN are carried out to evaluate its sensitivity to the flow splits adjustments and its ability to predict emission with air preheat and turndown operation. The NOx emissions predicted by CRN are in good agreement until 110ºC preheating and for a turndown ratio of 1,33.

O presente trabalho trata da modelagem de combustão em um queimador industrial de gás natural utilizando cadeias de reatores químicos idealizados. A partir de simulações de CFD e dados experimentais do ensaio denominado BERL 300 kW, sucessivas cadeias de reatores são propostas, baseando-se em premissas sobre as condições de temperatura e fluxo de massa entre as diversas regiões do escoamento reativo. O objetivo é obter uma cadeia de reatores que reproduza as emissões de NOx do ensaio. O erro relativo das emissões é de 98,23% na primeira cadeia, de 82,30% na segunda cadeia e de 1,54% na terceira cadeia. A partir da terceira cadeia de reatores proposta, considerada representativa do ensaio, realiza-se uma análise de sensibilidade e um estudo paramétrico, para avaliar a sensibilidade do modelo aos ajustes de segmentação de correntes e a capacidade de reproduzir os dados experimentais de emissão em condições de pré-aquecimento do ar de combustão e em operação fora do ponto de projeto. O modelo produz resultados satisfatórios para os casos de pré-aquecimento do ar até 110°C e para potências térmicas até 33% superiores ao ponto de projeto, não oferecendo bons resultados para as demais condições de operação. / This work shows the development and application of chemical reactor networks (CRN) to the modeling of a natural gas burner. The CRN development is based on experimental and CFD simulation results of the BERL 300 kW test. The CRN element arrangement, reactor volumes and flow splits are adjusted based on the best agreement with characteristic temperatures of the reactive flow, aiming to reproduce the experimental NOx emissions data. The relative error in the emissions predictions are 98,23% for the first CRN proposed, 82,30% for the second CRN and 1,54% for the third one. A sensitivity analysis and a parametric study of the third CRN are carried out to evaluate its sensitivity to the flow splits adjustments and its ability to predict emission with air preheat and turndown operation. The NOx emissions predicted by CRN are in good agreement until 110ºC preheating and for a turndown ratio of 1,33.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / O aproveitamento do biogÃs e do gÃs natural (GN) com elevadas concentraÃÃes de diÃxido de carbono (CO2) e de sulfeto de hidrogÃnio (H2S), atravÃs de sistemas tÃrmicos de combustÃo convencionais, pode resultar em instabilidade de reaÃÃo ou, atÃ, apagamento da frente de chama, sob risco de avarias irreversÃveis para estrutura fÃsica dos equipamentos, devido aos Ãcidos corrosivos decorrentes da reaÃÃo. Ainda, altas concentraÃÃes desses contaminantes favorecem a ocorrÃncia de elevados Ãndices de gases poluentes nos produtos, a exemplo de monÃxido de carbono (CO) e hidrocarbonetos nÃo queimados (HC), dentre outros. Por essa razÃo, um estudo experimental foi realizado com base na aplicaÃÃo de uma tecnologia de combustÃo nÃo-convencional, a CombustÃo de FiltraÃÃo, a fim de lidar com esses combustÃveis de baixa qualidade. O aparato experimental empregado nessa pesquisa consiste de uma caldeira porosa de escoamento recÃproco, em que seu queimador à preenchido completamente por esferas cerÃmicas de alumina (Al2O3), formando uma matriz porosa inerte, que envolve os trocadores de calor da caldeira. O processo de queima de ambos os combustÃveis foi investigado sob condiÃÃes extremas de operaÃÃo, em termos de misturas ar-combustÃvel ultra-pobres. Como suporte para interpretaÃÃo dos fenÃmenos do processo, foi aplicado um modelo numÃrico de simulaÃÃo, que considera o mecanismo de oxidaÃÃo do metano em um meio poroso, adaptado para identificar os efeitos quÃmicos de uma alta concentraÃÃo de CO2 sobre a reaÃÃo. A influÃncia dos principais parÃmetros de operaÃÃo, razÃo de equivalÃncia e velocidade da mistura ar-combustÃvel, sob os produtos de combustÃo e sob a instabilidade de reaÃÃo foi estudada teÃrica e experimentalmente. Os resultados mostram excelente estabilidade operacional da caldeira com emissÃes ultra-baixas de CO e NOx, inferiores a 1 ppm para razÃes de equivalÃncia menores que 0,6, e com eficiÃncia de queima do H2S de mais de 99%. / The use of biogas and natural gas (GN) with high concentrations of carbon dioxide (CO2) and hydrogen sulfide (H2S) through conventional combustion thermal systems can result in reaction instability or flame front quenching, under risk of irreversible damages to the physical structure of a piece of equipments, due to corrosive acids remaining from reaction. Furthermore, high concentrations of these contaminants favor the occurrence of high pollutant levels in the products, like carbon monoxide (CO) and unburned hydrocarbon (HC), among others. Therefore, an experimental study was performed with basis on the application of a non conventional combustion technology, Filtration Combustion, in order to deal with these low-quality fuels. The experimental apparatus employed in this research consists of a reciprocal flow porous boiler, in which its burner is completely filled by ceramic spheres of alumina (Al2O3), forming an inert porous matrix, which involves boilerâs heat exchangers. The burning process of both the fuels was investigated under extreme operation conditions, in terms of ultra-lean fuel-air mixtures. As support for interpretation of the process phenomena, a numerical simulation model was applied, which takes in account the methane oxidation mechanism in a porous medium, adapted to identify the chemical effects of a high CO2-concentration on the reaction. The influence of the main operation parameters, equivalence ratio and gas flow velocity, on combustion products and on reaction stability was studied theoretically and experimentally. The results have shown excellent boiler operation stability with ultra-low emissions of NOx and CO, less than 1 ppm for equivalence ratios inferior to 0.6, and with the H2S-burning efficiency overcoming 99%.

Control of pollutants and emissions has become a major factor in the design of modern combustion systems. The “Liquid Hydrogen Fueled Aircraft - System Analysis” project funded in 2000 by the European Commission can be seen as such an initiative. Within the framework of this project, the Aachen University of Applied Sciences developed experimentally the “Micromix” hydrogen combustion principle and implemented it successfully in the Honeywell APU GTCP 36-300 gas turbine engine. Lowering the reaction temperature, eliminating hot spots from the reaction zone and keeping the time available for the formation of NOx to a minimum are the prime drivers towards NOx reduction. The “Micromix” hydrogen combustion principle meets those requirements by minimizing the flame temperature working at small equivalence ratios, improving the mixing by means of Jets In Cross-Flow and reducing the residence time in adopting a combustor geometry that provides a very large number of very small diffusion flames. In terms of pollutant emissions, compared to the unconverted APU, an essential reduction in emitted NOx was observed, stressing the potential of this innovative burning principle.<p>The objective of this thesis is to investigate the “Micromix” hydrogen combustion principle with the ultimate goal of an improved prediction during the design process. Due to the complex interrelation of chemical kinetics and flow dynamics, the “Micromixing” was analyzed first. Stereoscopic Particle Image Velocimetry was used to provide insight into the mixing process. A “simplified” set-up, that allowed to investigate the flow characteristics in great detail while retaining the same local characteristics of its “real” counterparts, was considered. The driving vortical structures were identified. To further investigate the physics involved and to extend the experimental results, numerical computations were carried out on the same “simplified” set-up as on a literature test case. In general, a number of physical issues were clarified. In particular, the interaction between the different vortical structures was looked into, and a kinematically consistent vortex model is proposed. After demonstrating the development of the mixing, the “cold flow” study was extended to a single injector. The double backward-facing step injector geometry was addressed experimentally and numerically. At design geometry, the flow appeared to behave single backward-facing like, with respect to the first gradation. In terms of varying step configurations, the flow was seen to be dependent on the periodic perturbation arising from the graded series of backward-facing steps. During the second part of the investigation, the “hot flow” was analyzed. Considering combustor similar operating conditions, a test burner was experimented on an atmospheric test rig. NOx emissions were traced by exhaust gas analysis for different working conditions. Particular flame patterns, such as a regular attached flame as well as lifted flames were observed. In parallel with the experimental work, numerical computations on a pair of opposite injectors, permitted to classify the combustion regime and the main factors involved in the NOx formation. Accordingly, NOx emission enhancing design changes are proposed. Finally, the demanding computational effort, worthy of acceptance for academic purposes, is found not agreeable as future design tool and improvements to speed up the design process are projected.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Ces travaux de thèse ont porté sur l'étude approfondie de catalyseurs à base d'argent et d'or dans la réduction catalytique sélective des NOx par C3H6. Pour le système Ag/Al2O3, nous avons réussi à fournir une explication rationnelle de l'origine de l'existence d'un optimum d'activité pour une teneur en Ag de l'ordre de 2 %pds reporté à plusieurs reprises. La caractérisation par NOx-TPD des catalyseurs Ag/Al2O3 a permis d'attribuer l'origine de cet optimum à la teneur maximale en Ag pour laquelle la dispersion quasi-atomique de l'argent est préservée. Nous avons aussi démontré pour la première fois que l'activité des catalyseurs Ag/Al2O3 dans la réduction des NOx par C3H6 en présence de H2 augmentait lorsque la densité surfacique en Ag diminuait. Ceci a été expliqué par l'augmentation du nombre de sites du support pouvant adsorber les NOx lorsque la teneur en Ag diminue. Le système catalytique Au/Al2O3 a été également étudié. En diminuant le nombre de sites d'or dans le réacteur, un effet promoteur de H2 a été mis en évidence pour la première fois pour ce système dans la réduction des NOx par C3H6. Cet effet promoteur était plus important lorsque la teneur en Au diminue. L'activité catalytique du système Au/Al2O3 a été optimisée par la cérine, le catalyseur présentant 1%pds en CeO2 et 0,5%pds en Au a montré la meilleure conversion des NOx. L'activité catalytique d'un système Au-Ag/Al2O3 a également été examinée mais trouvée moins intéressante que celles des systèmes monométalliques. La conversion des NOx en N2 en présence de H2 sur un catalyseur Ag/Al2O3 a pu être améliorée de prés de 30 % en déposant l'argent sur un support prétraité hydrothermalement. / This work provides further insights into C3H6-SCR on alumina supported silver and gold catalysts. The origin of the optimum loading of 2 wt% of Ag on Al2O3 in the C3H6-SCR of NOx was elucidated with the help of an original characterization method (NOx-TPD). The optimum loading was attributed to the maximum loading of silver on Al2O3 for which highly dispersed Ag species are preserved. Our study highlights for the first time that the H2-C3H6-SCR catalytic performance of Ag/Al2O3 samples improved in the 150-550 °C temperature domain as the Ag loading decreased well below 2 wt%. A detailed kinetic study of H2-C3H6-SCR was performed and led us to conclude that the unexpected higher catalytic performance of the Ag samples with the lower Ag surface densities was attributed to the higher concentration of active sites on the Al2O3 supporting oxide able to chemisorb NOx species. Regarding Au/Al2O3 catalysts, our work provides the first experimental evidence of an H2 effect in C3H6-SCR over Au/Al2O3 catalysts. This effect could only be observed when the number of Au catalytic sites in the reactor was decreased. The influence of the Au loading on the H2-C3H6-SCR was investigated. Au/CeO2-Al2O3 system was optimized with addition of ceria. Among the Au/CeO2-Al2O3 catalysts evaluated, the sample containing 0.5 wt% Au and 1 wt% CeO2 exhibited the best NOx conversion in C3H6-SCR at low temperature (from 150 °C). The catalytic activity of bimetallic Au-Ag /Al2O3 catalysts was investigated in C3H6-SCR and H2-C3H6-SCR. Finally, NOx conversion to N2 on Ag/Al2O3 in H2-C3H6-SCR could be improved substantially by nearly 30 % when silver is added on hydrothermally pretreated Al2O3 support.

Doctor Educationis / In summary, it has been shown during this study that bimetallic Fe and Mn containing catalysts can be prepared by wet impregnation and not by ion exchange because of the competition between two different metals at different oxidation number. Only a single metallic phase catalyst could be prepared successfully by using ion exchange. / South Africa

The scope of this thesis investigates value added by a turbocharger with an associated motor-generator unit to a diesel engine used by a commercial vehicle. A thermodynamic model of the engine was prepared in GT-SUITE software. Case studies were primary focused on a reduction of specific fuel consumption as well as a nitrogen oxides production using an energy recuperation of exhaust gas. Furthermore, there are described potential benefits of using an electric assistance in order to increase an exhaust gas temperature during a steady state engine operation. Additionally, there is an investigation of potential benefits of a turbocharger assistance in a transition engine mode operating during rapid acceleration of the vehicle. The results of individual analysis will be taken into account for a selection of turbocharger regarding specific engine implementation. The results of simulation suggest that it is possible to lower specific fuel consumption, production of nitrogen oxides, as well as accelerate turbocharger response.

The objective of the presented diploma thesis is reduction of nitrogen oxides from the flue gas stream on catalyst under non-standart conditions. Emphasis is places on the description of selected pollutants in flue gas (especially nitrogen oxides), legislative requirements for air protection and technologies for removal of nitrogen oxides, expecially methods of selective catalytic and non-catalytic reduction. The practical part is devoted to the reduction of nitrogen oxides by selective catalytic reduction on a pilot plant INTEQ II in the laboratory NETME Center. The subject of interest is the determination of the NOx reduction efficiency depend on the temperature for selected catalyst. The end of the practical part pursues with comparison of measurement results and their evaluation.

The topic of this thesis is the calculation of the steam-boiler. The begining of the thesis deals with stoichiometric calculations. In the second chapter is performed the heat balance of the boiler. In the fourth and fifth chapter are defined dimensions of the fire and is established the temperature of a combustion gas in the outlet from the fire. The fifth chapter includes the balance calculations of the particular heating surfaces of the steam-boiler. As a conclusion of the calculations of the steam-boiler is performed the total balance. In the last chapter are proposed the methods for a reduction of the quantity of NOx contained in the combustion gas.

Ce travail de recherche est consacré à l'étude des processus d'allumage et de stabilisation des flammes turbulentes en configuration aéronautique. Cette thèse, entièrement expérimentale, se base dans une première partie sur l'étude et la compréhension de l'effet des paramètres locaux (vitesse et concentration en combustible) et de l'historique du noyau de flamme au cours de sa propagation sur les statistiques d'allumage. Pour expliquer ces statistiques, des scénarios sont proposés et validés pour différentes configurations opératoires. La deuxième partie de la thèse est dédiée à l'amélioration de la stabilité des flammes kérosène/air par dopage en hydrogène. Nous avons montré qu'à même structure de flamme, l'amplitude des fluctuations de pression était abaissée par la présence d'hydrogène. / This research is dedicated to the study of turbulent flames ignition and stabilization processes in representatives' aircraft combustion chambers. This PHD thesis, fully experimental, is based on studying and understanding local parameters (velocity and fuel concentration) and historical effects of the flame kernel's environment during its propagation on ignition statistics. To explain this statistics, various scenarios arre proposed and discussed. In this way, we justify the existence of high and low efficiency areas thanks to a time development criterion of the flame kernel. The second part of this thesis is dedicated to flame stabilization improvment by using H2 enrichment. Turbulent kerosene/air flames have been doped in gaseous hydrogen. We demonstrate a reduction of pressure oscillations' amplitude for the same flame structure.