scholarly journals Numerical Investigation of the Effects of Swirling Hot Co-Flow on MILD Combustion of a Hydrogen–Methane Blend

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Seyed Mahmood Mousavi ◽  
Reza Kamali ◽  
Freshteh Sotoudeh ◽  
Nader Karimi ◽  
In-Seuck Jeung
Keyword(s):  
Flue Gas ◽  
Reactive Flow ◽  
Discrete Ordinates ◽  
Axial Distance ◽  
Low Oxygen ◽  
Radiation Model ◽  
Flow Temperature ◽  
Mild Combustion ◽  
Swirl Velocity ◽  
Fuel Nozzle

Abstract This paper examines the effects of swirl hot co-flow on the combustion behavior of a moderate or intense low oxygen dilution (MILD) burner fueled by a mixture of methane and hydrogen. Toward this goal, the realizable k-ɛ turbulence model, GRI. 2.11 reaction mechanism, and the discrete ordinates radiation model are incorporated into a computational modeling of the reactive flow. The numerical results are, first, favorably compared against the existing experimental data. Subsequently, a number of swirl co-flows are implemented, and structures of the resultant reactive flows are investigated systematically. The outcomes indicate that increasing the swirl velocity leads to the reduction of ignition delay and significantly enhances the reaction completion. The analysis of the spatial distribution of hydroxyl and formyl (OH and HCO) radicals reveals that swirling MILD combustion radially extends the reaction zone in comparison with the conventional MILD combustion. Yet, it reduces the length of the reactive region and allows for the occurrence of heat release in a shorter axial distance from the outlet fuel nozzle. Further, the addition of swirl reduces the production of carbon monoxide through its influences upon flow temperature and generation of formyl radical. However, it is found that swirling hot co-flow intensifies NOx emissions by strengthening of prompt and thermal mechanisms of NOx production. Reducing the temperature of the recycled flue gas is deemed to be an effective way of resolving this issue.

scholarly journals Numerical study of flame structure in the mild combustion regime

2015 ◽  
Vol 19 (1) ◽  
pp. 21-34 ◽  
Author(s):  
Amir Mardani ◽  
Sadegh Tabejamaat
Keyword(s):  
Fuel Injection ◽  
Numerical Study ◽  
Flame Structure ◽  
Combustion Regime ◽  
Low Oxygen ◽  
Mixing Rate ◽  
Jet Flame ◽  
Reduced Mechanism ◽  
Mild Combustion ◽  
O2 Concentration

In this paper, turbulent non-premixed CH4+H2 jet flame issuing into a hot and diluted co-flow air is studied numerically. This flame is under condition of the moderate or intense low-oxygen dilution (MILD) combustion regime and related to published experimental data. The modelling is carried out using the EDC model to describe turbulence-chemistry interaction. The DRM-22 reduced mechanism and the GRI2.11 full mechanism are used to represent the chemical reactions of H2/methane jet flame. The flame structure for various O2 levels and jet Reynolds numbers are investigated. The results show that the flame entrainment increases by a decrease in O2 concentration at air side or jet Reynolds number. Local extinction is seen in the upstream and close to the fuel injection nozzle at the shear layer. It leads to the higher flame entertainment in MILD regime. The turbulence kinetic energy decay at centre line of jet decreases by an increase in O2 concentration at hot Co-flow. Also, increase in jet Reynolds or O2 level increases the mixing rate and rate of reactions.

Premixed Moderate or Intense Low-Oxygen Dilution (MILD) Combustion from a Single Jet Burner in a Laboratory-Scale Furnace

2011 ◽  
Vol 25 (7) ◽  
pp. 2782-2793 ◽  
Author(s):  
Pengfei Li ◽  
Jianchun Mi ◽  
Bassam B. Dally ◽  
Richard A. Craig ◽  
Feifei Wang
Keyword(s):  
Laboratory Scale ◽  
Low Oxygen ◽  
Mild Combustion ◽  
Single Jet

scholarly journals Numerical study of hydrogen mild combustion

2009 ◽  
Vol 13 (3) ◽  
pp. 59-67 ◽  
Author(s):  
Enrico Mollica ◽  
Eugenio Giacomazzi ◽  
Marco di
Keyword(s):  
Numerical Study ◽  
Fluid Dynamic ◽  
Thermal Gradients ◽  
Radiation Model ◽  
Dynamic Simulations ◽  
Mild Combustion ◽  
Preheating Temperature ◽  
Nitric Oxide Emissions ◽  
Gas Recirculation ◽  
Good Agreement

In this article a combustor burning hydrogen and air in mild regime is numerically studied by means of computational fluid dynamic simulations. All the numerical results show a good agreement with experimental data. It is seen that the flow configuration is characterized by strong exhaust gas recirculation with high air preheating temperature. As a consequence, the reaction zone is found to be characteristically broad and the temperature and concentrations fields are sufficiently homogeneous and uniform, leading to a strong abatement of nitric oxide emissions. It is also observed that the reduction of thermal gradients is achieved mainly through the extension of combustion in the whole volume of the combustion chamber, so that a flame front no longer exists ('flameless oxidation'). The effect of preheating, further dilution provided by inner recirculation and of radiation model for the present hydrogen/air mild burner are analyzed.

Theoretical Study on Chemical-Kinetic Characteristics of Oxy-Coal Mild Combustion

2016 ◽  
Author(s):  
Ruochen Liu ◽  
Enke An ◽  
Kun Wu
Keyword(s):  
Activation Energy ◽  
Oxygen Concentration ◽  
Reaction Pathway ◽  
Chemical Kinetic ◽  
State Theory ◽  
Kinetic Characteristics ◽  
Low Oxygen ◽  
Elementary Reactions ◽  
Mild Combustion ◽  
Low Oxygen Concentration

The chemical-kinetic characteristics of oxy-coal MILD combustion under different initial temperature and oxygen concentration were studied numerically. Aromatic benzene was considered representative for coal molecule. A unique reaction pathway under low oxygen concentration was obtained, the activation energy and reaction rate constant of involved elementary reactions were calculated through classic transition state theory (TST). The results show that low oxygen concentration and high temperature is advantageous for thickening flame front as well as slowing down flame propagation; as oxygen concentration and temperature increase, the global activation energy increases with greater slope; the decomposition of C5H5 dominates under high oxygen concentration, while the decomposition and oxidation of C5H5 become equally important as oxygen concentration decreases, leading to a new pathway that the complexity of overall chemical reactions develops; the radical CH2CHO is easily trigged under low oxygen concentration, its decomposition reaction dominates in the unique pathway C5H5→C5H4O→c-C4H5CH2CHO→CH3 due to larger activation energy, where more CO escapes. The simulation results have theoretical referencing value, laying foundations for the further practical work.

Actuation Studies for Active Control of Mild Combustion for Gas Turbine Application

2014 ◽  
Author(s):  
Emilien Varea ◽  
Stephan Kruse ◽  
Heinz Pitsch ◽  
Thivaharan Albin ◽  
Dirk Abel
Keyword(s):  
Combustion Chamber ◽  
Gas Turbine ◽  
Active Control ◽  
Gas Turbines ◽  
Reverse Flow ◽  
Air Flow ◽  
Combustion Regime ◽  
Nox Emissions ◽  
Low Oxygen ◽  
Mild Combustion

MILD combustion (Moderate or Intense Low Oxygen Dilution) is a well known technique that can substantially reduce high temperature regions in burners and thereby reduce thermal NOx emissions. This technology has been successfully applied to conventional furnace systems and seems to be an auspicious concept for reducing NOx and CO emissions in stationary gas turbines. To achieve a flameless combustion regime, fast mixing of recirculated burnt gases with fresh air and fuel in the combustion chamber is needed. In the present study, the combustor concept is based on the reverse flow configuration with two concentrically arranged nozzles for fuel and air injections. The present work deals with the active control of MILD combustion for gas turbine applications. For this purpose, a new concept of air flow rate pulsation is introduced. The pulsating unit offers the possibility to vary the inlet pressure conditions with a high degree of freedom: amplitude, frequency and waveform. The influence of air flow pulsation on MILD combustion is analyzed in terms of NOx and CO emissions. Results under atmospheric pressure show a drastic decrease of NOx emissions, up to 55%, when the pulsating unit is active. CO emissions are maintained at a very low level so that flame extinction is not observed. To get more insights into the effects of pulsation on combustion characteristics, velocity fields in cold flow conditions are investigated. Results show a large radial transfer of flow when pulsation is activated, hence enhancing the mixing process. The flame behavior is analyzed by using OH* chemiluminescence. Images show a larger distributed reaction region over the combustion chamber for pulsation conditions, confirming the hypothesis of a better mixing between fresh and burnt gases.

Effect of Swirl and Wall Geometry on the Emissions of Advanced Gas Turbine Combustors

1994 ◽  
Author(s):  
Gerald J. Micklow ◽  
Karthikeyan Shivaraman
Keyword(s):  
Numerical Study ◽  
Substantial Effect ◽  
Pollutant Emissions ◽  
Reactive Flow ◽  
Fuel Distribution ◽  
Lean Combustion ◽  
Liquid Spray ◽  
Fuel Nozzle ◽  
Interface Geometry ◽  
Wall Geometry

A numerical study was performed to investigate the chemically reactive flow with liquid spray injection in a staged combustor concept for reducing pollutant emissions. The staged combustor consists of an airblast atomizer, a rich bum section, a converging connecting pipe, a quick mix zone, a diverging connecting pipe, and a lean combustion zone. For computational efficiency, the combustor was split into two subsystems, i.e. the fuel nozzle/rich burn section and the quick quench/lean bum section. The current study investigates the effect of wall geometry and swirl direction, i.e. co- or counter-rotating swirl, on fuel distribution, temperature distribution, and emissions for the fuel nozzle/rich bum section at a cruise condition. At an equivalence ratio of 1.9, the nozzle-combustor (dome) interface geometry was varied from a flat wall (normal to the combustor wall) to a sloped wall of 45 degrees. It is seen that the sloped wall with co-rotating swirl direction had a substantial effect on combustor performance and reducing pollutant emissions.

scholarly journals Assessment of chemical mechanism and chemical reaction sensitivity analysis for CH4/H2 flame under mild combustion environment

2020 ◽  
Vol 24 (3 Part B) ◽  
pp. 2101-2111
Author(s):  
Zhao Yang ◽  
Xiangsheng Li ◽  
Zhenlin Wang ◽  
Zhuangqi Wang
Keyword(s):  
Stokes Equations ◽  
Chemical Mechanism ◽  
Navier Stokes ◽  
Low Oxygen ◽  
Navier Stokes Equations ◽  
Chemical Mechanisms ◽  
Concept Model ◽  
Mild Combustion ◽  
Fluent Software ◽  
Combustion Environment

To analyze the performance of different chemical mechanisms on the prediction under moderate and intense low-oxygen dilution combustion environment, six different kinds of mechanisms were tested by solving the Reynolds averaged Navier- Stokes equations in a 2-D domain with the eddy dissipation concept model by FLUENT software. Temperature and the species concentration of OH, CO, and H2O were compared with the experiment data. The experiment results showed some similarities for each chemical mechanism as well as discrepancies. The comparison of CH4 oxidation route between the GRI2.11 and GRI3.0 mechanisms was made by Chemkin code. Reaction 95 and 147 were responsible for low temperature region for GRI2.11 mechanism at downstream area.

scholarly journals Determination of High Temperature Corrosion Rates of Steam Boiler Evaporators Using Continuous Measurements of Flue Gas Composition and Neural Networks

Energies ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 3134
Author(s):  
Tomasz Hardy ◽  
Sławomir Kakietek ◽  
Krzysztof Halawa ◽  
Krzysztof Mościcki ◽  
Tomasz Janda
Keyword(s):  
Neural Networks ◽  
High Temperature ◽  
Corrosion Rate ◽  
Flue Gas ◽  
Hard Coal ◽  
Steam Boiler ◽  
Gas Composition ◽  
Negative Consequences ◽  
Low Oxygen ◽  
Continuous Measurements

The use of low-emission combustion techniques in pulverized coal-fired (PC) boilers are usually associated with the formation of a reduced-gas atmosphere near evaporator walls. This increases the risk of high temperature (low oxygen) corrosion processes in coal-fired boilers. The identification of the dynamics and the locations of these processes, and minimizing negative consequences are essential for power plant operation. This paper presents the diagnostic system for determining corrosion risks, based on continuous measurements of flue gas composition in the boundary layer of the combustion chamber, and artificial intelligence techniques. Experience from the implementation of these measurements on the OP-230 hard coal-fired boiler, to identify the corrosion hazard of one of the evaporator walls, has been thoroughly described. The results obtained indicate that the continuous controlling of the concentrations of O2 and CO near the water wall, in combination with the use of neural networks, allows for the forecasting of the corrosion rate of the evaporator. The correlation between flue gas composition and corrosion rate has been demonstrated. At the same time, the analysis of the possibilities of significantly simplifying the measurement system by using neural networks was carried out.

Development of a “Solar Patch” Calculator to Evaluate Heliostat-Field Irradiance as a Boundary Condition in CFD Models

2010 ◽  
Author(s):  
Siri Sahib S. Khalsa ◽  
Clifford K. Ho
Keyword(s):  
Boundary Condition ◽  
Cfd Simulation ◽  
Time Of Day ◽  
Discrete Ordinates ◽  
Microsoft Excel ◽  
Radiation Model ◽  
Receiver Domain ◽  
Cfd Models ◽  
Multiple Beams ◽  
Computational Fluid Dynamics Cfd

A rigorous computational fluid dynamics (CFD) approach to calculating temperature distributions, radiative and convective losses, and flow fields in a cavity receiver irradiated by a heliostat field is typically limited to the receiver domain alone for computational reasons. A CFD simulation cannot realistically yield a precise solution that includes the details within the vast domain of an entire heliostat field in addition to the detailed processes and features within a cavity receiver. Instead, the incoming field irradiance can be represented as a boundary condition on the receiver domain. This paper describes a program, the Solar Patch Calculator, written in Microsoft Excel VBA to characterize multiple beams emanating from a “solar patch” located at the aperture of a cavity receiver, in order to represent the incoming irradiance from any field of heliostats as a boundary condition on the receiver domain. This program accounts for cosine losses; receiver location; heliostat reflectivity, areas and locations; field location; time of day and day of year. This paper also describes the implementation of the boundary conditions calculated by this program into a Discrete Ordinates radiation model using Ansys® FLUENT (www.fluent.com), and compares the results to experimental data and to results generated by the code DELSOL.

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