Numerical and Experimental Studies of NO Formation Mechanisms under Methane Moderate or Intense Low-Oxygen Dilution (MILD) Combustion without Heated Air

Oxy-moderate or intense low-oxygen dilution (MILD) combustion, which is a novel combination of oxy-fuel technology and MILD regime, is numerically studied in the present work. The effects of external preheating and CO2 dilution level on the combustion field, emission, and CO formation mechanisms are investigated in a recuperative laboratory-scale furnace with a recirculating cross-flow. Reynolds-averaged Navier–Stokes (RANS) equations with eddy dissipation concept (EDC) model are employed to perform a 3-D simulation of the combustion field and the turbulence–chemistry interactions. In addition, a well-stirred reactor (WSR) analysis is conducted to further examine the chemical kinetics of this combination when varying the target parameters. The simulations used the skeletal USC-Mech II, which has been shown to perform well in the oxy-fuel combustion modeling. Results show that with more preheating, the uniformity of temperature distribution is noticeably enhanced at the cost of higher CO emission. Also as inlet temperature increases, the concentration of minor species rises and CO formation through the main path (CH4→CH3→CH2O→HCO→CO→CO2) is strengthened, while heavier hydrocarbons path (C2H2→CO) is suppressed. Meanwhile, greater CO2 addition notably closes the gap between maximum and exhaust temperatures. In a highly CO2-diluted mixture, chain-branching reactions releasing CH2O are strengthened, while chain-terminating reactions are weakened. CH2O production through CH3O is accelerated compared with the straight conversion of methyl to formaldehyde. When diluting the oxidant, methylene CH2(s) plays a more influential role in CO formation than when pure oxygen is used, contributing to higher CO emission.

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A simplified approach for predicting NO formation in MILD combustion of CH4–H2 mixtures

Proceedings of the Combustion Institute ◽

10.1016/j.proci.2010.06.141 ◽

2011 ◽

Vol 33 (2) ◽

pp. 3343-3350 ◽

Cited By ~ 35

Author(s):

A. Parente ◽

C. Galletti ◽

L. Tognotti

Keyword(s):

Simplified Approach ◽

No Formation ◽

Mild Combustion

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Effects of hydrogen addition on structure and NO formation of highly CO-Rich syngas counterflow nonpremixed flames under MILD combustion regime

International Journal of Hydrogen Energy ◽

10.1016/j.ijhydene.2020.12.120 ◽

2021 ◽

Vol 46 (17) ◽

pp. 10518-10534

Author(s):

Namsu Kim ◽

Yongmo Kim ◽

Mohammad Nazri Mohd Jaafar ◽

Muhammad Roslan Rahim ◽

Mazlan Said

Keyword(s):

Combustion Regime ◽

Nonpremixed Flames ◽

Hydrogen Addition ◽

No Formation ◽

Mild Combustion

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Numerical study of flame structure in the mild combustion regime

Thermal Science ◽

10.2298/tsci120522091m ◽

2015 ◽

Vol 19 (1) ◽

pp. 21-34 ◽

Cited By ~ 7

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.

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

Energy & Fuels ◽

10.1021/ef200208d ◽

2011 ◽

Vol 25 (7) ◽

pp. 2782-2793 ◽

Cited By ~ 32

Author(s):

Pengfei Li ◽

Jianchun Mi ◽

Bassam B. Dally ◽

Richard A. Craig ◽

Feifei Wang

Keyword(s):

Laboratory Scale ◽

Low Oxygen ◽

Mild Combustion ◽

Single Jet

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The Mineral Chemistry of Chlorites and Its Relationship with Uranium Mineralization from Huangsha Uranium Mining Area in the Middle Nanling Range, SE China

Minerals ◽

10.3390/min9030199 ◽

2019 ◽

Vol 9 (3) ◽

pp. 199 ◽

Cited By ~ 3

Author(s):

Dehai Wu ◽

Jiayong Pan ◽

Fei Xia ◽

Guangwen Huang ◽

Jing Lai

Keyword(s):

Mining Area ◽

Uranium Mining ◽

Uranium Mineralization ◽

Formation Mechanisms ◽

Chemical Compositions ◽

Type I ◽

Low Oxygen ◽

Nanling Range ◽

The Relationship ◽

Uranium Mining Area

The Huangsha uranium mining area is located in the Qingzhangshan uranium-bearing complex granite of the Middle Nanling Range, Southeast China. This uranium mining area contains three uranium deposits (Liangsanzhai, Egongtang, and Shangjiao) and multiple uranium occurrences, showing favorable mineralization conditions and prospecting potential for uranium mineral resources. Chloritization is one of the most important alteration types and prospecting indicators in this mining area. This study aims to unravel the formation environment of chlorites and the relationship between chloritization and uranium mineralization, based on detailed field work and petrographic studies of the wallrock and ore samples from the Huangsha uranium mining area. An electron probe microanalyzer (EPMA) was used in this study to analyze the paragenetic association, morphology, and chemical compositions of chlorite, to classify chemical types and to calculate formation temperatures and n(Al)/n(Al + Mg + Fe) values of chlorite. The formation mechanism and the relationship with uranium mineralization of the uranium mining area are presented. Some conclusions from this study are: (1) There are five types of chlorites, including the chlorite formed by the alteration of biotite (type-I), by the metasomatism of feldspar with Fe–Mg hydrothermal fluids (type-II), chlorite vein/veinlet filling in fissures (type-III), chlorite closely associated with uranium minerals (type-IV), and chlorite transformed from clay minerals by adsorbing Mg- and Fe-components (type-V). (2) The chlorite in the Huangsha uranium mining area belongs to iron-rich chlorite and is mainly composed of chamosite, partly clinochlore, which are the products of multiple stages of hydrothermal action. The original rocks are derived from argillite, and their formation temperatures vary from 195.7 °C to 283.0 °C, with an average of 233.2 °C, suggesting they formed under a medium to low temperature conditions. (3) The chlorites were formed under reducing conditions with low oxygen fugacity and relatively high sulfur fugacity through two formation mechanisms: dissolution–precipitation and dissolution–migration–precipitation; (4) The chloritization provided the required environment for uranium mineralization, and promoted the activation, migration, and deposition of uranium.

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

ASME 2016 Power Conference ◽

10.1115/power2016-59032 ◽

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.

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Effects of preheating temperature and dilution level of oxidizer, fuel composition and strain rate on NO emission characteristics in the syngas moderate or intense low oxygen dilution (MILD) combustion

Fuel ◽

10.1016/j.fuel.2020.119118 ◽

2021 ◽

Vol 285 ◽

pp. 119118

Author(s):

E. Ebrahimi Fordoei ◽

Kiumars Mazaheri

Keyword(s):

Strain Rate ◽

Fuel Composition ◽

Emission Characteristics ◽

Low Oxygen ◽

No Emission ◽

Mild Combustion ◽

Preheating Temperature ◽

Dilution Level

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

Volume 4B: Combustion, Fuels and Emissions ◽

10.1115/gt2014-27138 ◽

2014 ◽

Cited By ~ 2

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.

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