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Flameless combustion technology has been developed over the past twenty years achieving low-NOx emissions and high energy efficiency for industrial applications. In the present work, three aspects of flameless combustion were examined based on a burner employing the Strong-Jet/Weak-Jet (SJ/WJ) configuration. In the first part of the work, a 3-D SJ/WJ physical model was developed in the Lagrangian perspective for an isothermal pair of free jets. The model was used to predict the WJ trajectory, identify important design/operation factors, and estimate the extent of mixing in the main combustion region (confluence region). The model was also validated with experimental data and showed excellent agreement over a wide range of flow conditions. In the second part of the work, a simplified chemical kinetic model was developed for the flameless combustion of natural gas. A detailed chemical reaction mechanism (GRI Mech 3.0) was successfully reduced to a skeletal chemical reaction mechanism under flameless combustion conditions by Principal Component Analysis, sensitivity analysis and reaction flow analysis. The skeletal mechanism was further simplified to a set of 2-D manifolds by Trajectory-Generated Low-Dimensional Manifolds (TGLDM) method. The set of 2-D manifolds was tested by the Batch Reactor (BR) and Perfect Stirred Reactor (PSR) models. From the BR model test, it was found that the chemical reaction rates were well represented by the 2-D manifolds. The effect of the physical perturbation, tested by PSR model, could be handled by the perpendicular projection instead of the orthogonal projection because both showed similar discrepancies with the skeletal mechanism. In the final part of the work, the steady-state Reynolds-Averaged Navier-Stokes (RANS) simulation was conducted for the turbulent flameless combustion in the SJ/WJ furnace, based on the Probability Density Function (PDF)/Mixing approach. The set of 2-D manifolds and Conditional Source-term Estimate (CSE) method were used for the combustion reaction and the estimation of the mean production/destruction rate, respectively. This CSE-TGLDM model provided good predictions of major species concentrations. However, the gas temperatures and CO concentrations were highly over-predicted. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2010-09-23 11:05:21.884

Flameless combustion in a 48 kW pilot scale furnace fired with natural gas is studied experimentally and computationally. The burner geometry involved a tunnel furnace with two separate feed streams --- one for a high momentum air jet and the other for a low momentum fuel jet. This burner configuration, called a Strong-Jet/Weak-Jet (SJWJ) burner, together with the jetto- jet interactions generate the flameless combustion mode with relatively uniform furnace gas temperature distributions and low NOX emissions. Experiments were carried out under laboratory conditions for turbulent reactive mixing in order to obtain local temperature and gas concentrations. The experimental findings were used to test the performance of CFD numerical models for turbulence, mixing and chemical reactions. For the SJWJ furnace operated in flameless combustion mode, 32 different flow cases were examined to assess the effects of the three main parameters (fuel/air momentum flux ratio, fuel/air nozzle separation distance and fuel injection angle) on the furnace wall temperature profile. Three specific flow configurations were selected for detailed near-field temperature measurements. The gas temperature distribution inside the combustion chamber was found to be relatively uniform, a characteristic of flameless combustion. Four flow configurations were studied to examine the effect of the fuel jet injection angle (0 degrees or 10 degrees) and fuel/air momentum flux ratio (0.0300 and 0.0426) on the mixing, combustion performance and NOX emissions. Gas compositions were measured in the flue gas and within the furnace at selected locations to estimate the concentrations of CO2 CO, CH4, O2, NO and NOX. The NOX concentrations in the flue gas were quite low, ranging from 7 - 13 ppm, another characteristic of flameless combustion. The combusting flow CFD calculations were carried out using the k-ε turbulence model and the eddy-dissipation model for methane-air-2-step reactions to predict the temperature and concentration field. The numerical results for gas temperature and compositions of CH4, O2 and CO2 generally showed good agreement with the experimental data. The predicted CO concentration profiles followed expected trends but the experimental data were generally underpredicted. The NOX concentrations were estimated through post-processing and these results were significantly underpredicted. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2008-04-04 11:25:25.455

Nowadays, in the field of energy production, particular attention must be paid to improving efficiency, reducing pollutants and fuel flexibility. To reach those goals, cogenerative systems represent an appealing solution. One of the most promising cogenerative systems available nowadays is the micro turbine, which provides reasonable electrical efficiency of about 30%, multi-fuel capability, low emission levels and heat recovery potential, and need minimum maintenance. Among the several options, micro gas turbines (mGT) are particularly interesting. Beside theuse of natural gas, other fuels like landfill gas, ethanol, industrial waste off-gases and other bio-based gases can be used. Moreover, it is possible to further improve the efficiencies and reduce the emissions for mGTs by paying particular attention at the design of the combustion chamber. To this goal, flameless combustion could be an interesting solution. Flameless combustion is able to provide high combustion efficiency with low NOx and soot emissions. The increasing interest in flameless combustion is motivated by its large fuel flexibility, representing a promising technology for low-calorific value fuels, high-calorific industrial wastes as well as in presence of hydrogen. Moreover, flameless combustion is very stableand noiseless, so it is suited for gas turbine applications where conventional operations may lead to significant thermo-acoustic instabilities (“humming”) and stresses. Flameless combustion needs the reactants to be preheated above their self-ignition temperature and enough inert combustion products to be entrained in the reaction region, in order to dilute the flame. As a result, the temperature field is more uniform than in traditional combustion systems, and it does not show high temperature peaks. Hence, NOx formation is suppressed as well as soot formation,due to the lean conditions, low temperatures and the large CO2 concentration in the exhausts.mGTs operating in flameless combustion regime represent a promising technology for the combined production of heat and power with increased efficiency, reduced pollutants emission and high fuel flexibility. The objective of the present Thesis is the design of a combustion chamber for amGT for residential applications. The design is performed employing CFD-tools. Thus, it is necessary to develop a reliable numerical model to use in the design process. Therefore, the first step of the Thesis consists in a series of validation studies, with the goal of selecting the most appropriate and reliable models to describe flameless combustion. The validation will be carried on three differenttest cases, which have different nominal powers and employ different gaseous fuels. The second part of the Thesis focuses on the design and optimization of the combustion chamber. Finally, the third part shows the experimental investigation of the aforementioned chamber.The study of those three cases shows that, to correctly predict the behavior of those systems, it is necessary to take into account both mixing and chemical kinetics. The best results have been obtained with the Eddy Dissipation Concept model, coupled with detailed kinetic schemes. As far as the NOx emissions are concerned, it is fundamental to include all the formation routes, i.e. thermal, prompt, via N2O and NNH route, to estimate properly the NOx production in flameless conditions.The aforementioned models have been used for the design and optimization of a combustion chamber for a mGT operating in flameless combustion regime. Both the design and the optimization have been carried out by means of CFD simulations and both are goal-oriented, meaning that they are carried out with the purpose of improving one or more performance indicators of the chamber, such as pollutants emissions, efficiency or pressure losses. The configuration that satisfies the criteria on the performance indicators has been built and investigated experimentally. The combustion chamber is stable and performs well in terms of emissions for a wide range of air inlet temperature and air-fuel equivalence ratio, lambda, values. Except for the condition closer to the stoichiometric one, both CO and NOx emissions are extremely low for all !and air inlet temperatures. Thechamber performs the best at its nominal operating condition, i.e. lambda = 3.5 and air inlet temperature 730 °C, In this case CO is 0 ppm and NOx is 5.6 ppm. The numerical model employed to describe the combustor performs quite well, except for the CO prediction, for all the conditions investigated. The final step of the present work is the application of a different kind of fuel, namely biogas. First the feasibility of such application has been evaluated using CFD calculations, and then the experimental evidence has been discussed. Due to a calibration error on the gas flow meter, it has not been possible to investigate the conditions of the design point (lambda = 3.5). Three other conditions have been examined,characterized by lower values of !closer to the stoichiometric conditions. Despite the relatively high values of NOx emissions due to the lower air excess and to the consequently higher temperatures, the combustion chamber has proven to be fuel flexible. Both ignition and stable combustion can be achieved also when biogas is burnt. Numerical simulations have also been performed; the results are in good agreement with the experimental evidence. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

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Den negativa miljöpåverkan från förbrukning av fossila bränslen ökar kravet på förnyelsebara energikällor. Biobränsle är ett speciellt lovande alternativ. Detta projekt vill visa på möjligheten att använda gas från biobränsleförgasning som förbränns utan synliga flammor i glassmältugnar. Med bättre teknik är det möjligt både att upprätthålla produktionen och reducera kväveoxidutsläppen med ekonomiska fördelar. Biobränslena bidrar inte till växthuseffekten. En del av hela projektet är de experiment som utfördes den 1 juni 2004 vid Kosta glasbruk. Experimenten tog 7 timmar och 50 minuter. Den viktigaste uppgiften i detta examensarbete är att utvärdera mass- och energibalanserna på den medströms fastbäddsförgasare som användes vid experimenten. / The negative environmental impact of the consumption of fossil fuels has led to an increased claim for a wider use of renewable energy sources. Biomass appears as a particularly promising option. This project demonstrates the possibility to heat glass furnaces with gas from biofuel gasification combusted without visible flames. By better technique you can both retain production and reduce nitrogenoxide emissions with economical benefit. The biofuel doesn’t contribute to the greenhouse effect. A part of the whole project is the experiments performed on June 1st 2004 in Kosta glass- factory, total 7 hours and 50 minutes. A major effort of this diploma work is to evaluate mass and energy balances of the down – draft fixed bed gasifier used in the experiments.

Idag värms glasugnar upp med antingen gasol eller olja, detta projekt vill visa på möjligheten att istället använda gas från biobränsleförgasning som förbränns utan synliga flammor. Detta skulle miljömässigt ge fördelarna att biobränslen inte bidrar till växthuseffekten och ge förutsättningar för att minska kväveoxidutsläppen genom bättre teknik än dagens. För att visa att det är möjligt att både behålla produktionen och reducera kväveoxiderna med förgasningsgas konstruerades en modell av ugnen och strömningsbilden studerades i vattenmodell. För att undersöka värmeöverföringen i ugnen behöver en eller flera kalorimetrar konstrueras för att kunna användas vid varma försök. Dimensionsberäkningar gjordes som visade att detta är möjligt med vissa typer av kalorimetrar. / Today glassfurnaces are heated with LPG or oil, this project will show the possibility to use gas from biofuel gasification combusted without visible flames. This would give the environmental benefits that biofuels don´t contribute to the greenhouse effect and reduce nitrogenoxide emissions by better technique than today. To prove the possibility to retain todays production and reduce nitrogenoxide emissions a model of the furnace was constructed and the flow field was studied using water model technique. To examine the heat transfer in the furnace one or more calorimeters need to be constructed to be used in hot experiments. Dimensioning calculations were made that showed that this is possible provided certain specific designs.

<p>Den negativa miljöpåverkan från förbrukning av fossila bränslen ökar kravet på förnyelsebara energikällor. Biobränsle är ett speciellt lovande alternativ. Detta projekt vill visa på möjligheten att använda gas från biobränsleförgasning som förbränns utan synliga flammor i glassmältugnar. Med bättre teknik är det möjligt både att upprätthålla produktionen och reducera kväveoxidutsläppen med ekonomiska fördelar. Biobränslena bidrar inte till växthuseffekten. En del av hela projektet är de experiment som utfördes den 1 juni 2004 vid Kosta glasbruk. Experimenten tog 7 timmar och 50 minuter. Den viktigaste uppgiften i detta examensarbete är att utvärdera mass- och energibalanserna på den medströms fastbäddsförgasare som användes vid experimenten.</p> / <p>The negative environmental impact of the consumption of fossil fuels has led to an increased claim for a wider use of renewable energy sources. Biomass appears as a particularly promising option. This project demonstrates the possibility to heat glass furnaces with gas from biofuel gasification combusted without visible flames. By better technique you can both retain production and reduce nitrogenoxide emissions with economical benefit. The biofuel doesn’t contribute to the greenhouse effect. A part of the whole project is the experiments performed on June 1st 2004 in Kosta glass- factory, total 7 hours and 50 minutes. A major effort of this diploma work is to evaluate mass and energy balances of the down – draft fixed bed gasifier used in the experiments.</p>

<p>Idag värms glasugnar upp med antingen gasol eller olja, detta projekt vill visa på möjligheten att istället använda gas från biobränsleförgasning som förbränns utan synliga flammor. Detta skulle miljömässigt ge fördelarna att biobränslen inte bidrar till växthuseffekten och ge förutsättningar för att minska kväveoxidutsläppen genom bättre teknik än dagens.</p><p>För att visa att det är möjligt att både behålla produktionen och reducera kväveoxiderna med förgasningsgas konstruerades en modell av ugnen och strömningsbilden studerades i vattenmodell. För att undersöka värmeöverföringen i ugnen behöver en eller flera kalorimetrar konstrueras för att kunna användas vid varma försök. Dimensionsberäkningar gjordes som visade att detta är möjligt med vissa typer av kalorimetrar.</p> / <p>Today glassfurnaces are heated with LPG or oil, this project will show the possibility to use gas from biofuel gasification combusted without visible flames. This would give the environmental benefits that biofuels don´t contribute to the greenhouse effect and reduce nitrogenoxide emissions by better technique than today.</p><p>To prove the possibility to retain todays production and reduce nitrogenoxide emissions a model of the furnace was constructed and the flow field was studied using water model technique.</p><p>To examine the heat transfer in the furnace one or more calorimeters need to be constructed to be used in hot experiments. Dimensioning calculations were made that showed that this is possible provided certain specific designs.</p>