Effects of Preheating and CO2 Dilution on Oxy-MILD Combustion of Natural Gas

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

Thermal Science ◽

10.2298/tsci180811347y ◽

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.

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

Energy & Fuels ◽

10.1021/ef501943v ◽

2015 ◽

Vol 29 (3) ◽

pp. 1987-1996 ◽

Cited By ~ 14

Author(s):

Shiying Cao ◽

Chun Zou ◽

Qingsong Han ◽

Yang Liu ◽

Di Wu ◽

...

Keyword(s):

Experimental Studies ◽

Formation Mechanisms ◽

Low Oxygen ◽

No Formation ◽

Mild Combustion ◽

Heated Air

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Experimental and Numerical Investigation of a MILD Combustion Chamber for Micro Gas Turbine Applications

Energies ◽

10.3390/en11123363 ◽

2018 ◽

Vol 11 (12) ◽

pp. 3363 ◽

Cited By ~ 4

Author(s):

Valentina Fortunato ◽

Andres Giraldo ◽

Mehdi Rouabah ◽

Rabia Nacereddine ◽

Michel Delanaye ◽

...

Keyword(s):

Combustion Chamber ◽

Gas Turbine ◽

Energy Production ◽

Kinetic Mechanism ◽

Combustion Model ◽

Low Oxygen ◽

Micro Gas Turbine ◽

Air Inlet ◽

Mild Combustion ◽

Stirred Reactor

In the field of energy production, cogeneration systems based on micro gas turbine cyclesappear particularly suitable to reach the goals of improving efficiency and reducing pollutants.Moderate and Intense Low-Oxygen Dilution (MILD) combustion represents a promising technologyto increase efficiency and to further reduce the emissions of those systems. The present work aims atdescribing the behavior of a combustion chamber for a micro gas turbine operating in MILD regime.The performances of the combustion chamber are discussed for two cases: methane and biogascombustion. The combustor performed very well in terms of emissions, especially CO and NOx,for various air inlet temperatures and air-to-fuel ratios, proving the benefits of MILD combustion.The chamber proved to be fuel flexible, since both ignition and stable combustion could be achievedby also burning biogas. Finally, the numerical model used to design the combustor was validatedagainst the experimental data collected. The model performs quite well both for methane and biogas.In particular, for methane the Partially Stirred Reactor (PaSR) combustion model proved to be thebest choice to predict both minor species, such as CO, more accurately and cases with lower reactivitythat were not possible to model using the Eddy Dissipation Concept (EDC). For the biogas, the mostappropriate kinetic mechanism to properly model the behavior of the chamber was selected

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Conceptual Approach to Combustor Nozzle and Reformer Characteristics for Micro-Gas Turbine with an On-Board Reforming System: A Novel Thermal and Low Emission Cycle

Sustainability ◽

10.3390/su122410558 ◽

2020 ◽

Vol 12 (24) ◽

pp. 10558

Author(s):

Jonghyun Kim ◽

Jungsoo Park

Keyword(s):

Gas Turbine ◽

Thermal Power ◽

Open Loop ◽

Inlet Temperature ◽

Outlet Temperature ◽

Low Oxygen ◽

Conceptual Approach ◽

Micro Gas Turbine ◽

Mild Combustion ◽

Heavy Duty Gas Turbine

In order to implement moderate or intensive low oxygen dilution (MILD) combustion, it is necessary to extend the flame stability and operating range. In the present study, the conceptual designs of a combustor single nozzle and reformer were numerically suggested for a micro-gas turbine with an on-board reformer. The target micro-gas turbine achieved a thermal power of 150 kW and a turbine inlet temperature (TIT) of 1200 K. Studies on a nozzle and reformer applying an open-loop concept have been separately conducted. For the nozzle concept, a single down-scaled nozzle was applied based on a reference nozzle for a heavy-duty gas turbine. The nozzle can achieve a good mixture with a high swirl with a splined swirl curve lower NOx emissions and smaller pressure drop in the combustor. The concept of the non-catalytic partial-oxidation reforming reformate was designed using the combustor outlet temperature (COT) of the exhaust gas. Feasible hydrogen yields were mapped through the reformer. Based on the hydrogen yields from the reformer, hydrogen was added to the nozzle to investigate its combustion behavior. By increasing the hydrogen addition and decreasing the O2 fraction, the OH concentrations were decreased and widely distributed similar to the fundamental characteristics of MILD combustion.

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Exact Navier-Stokes Solutions Including Swirl and Cross Flow

The Physics of Fluids ◽

10.1063/1.1762303 ◽

1967 ◽

Vol 10 (7) ◽

pp. 1438 ◽

Cited By ~ 8

Author(s):

Sheldon Weinbaum

Keyword(s):

Cross Flow ◽

Navier Stokes

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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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Iterative method for solving fully-coupled fluid solid systems

European Journal of Computational Mechanics ◽

10.13052/ejcm.19.653-670 ◽

2010 ◽

pp. 653-670

Author(s):

Elisabeth Longatte

Keyword(s):

Stokes Equations ◽

Cross Flow ◽

Elastic Cylinder ◽

Navier Stokes ◽

Arbitrary Lagrangian Eulerian ◽

Navier Stokes Equations ◽

Ale Formulation ◽

Volume Method ◽

Fully Coupled ◽

Solid System

This work is concerned with the modelling of the interaction of a fluid with a rigid or a flexible elastic cylinder in the presence of axial or cross-flow. A partitioned procedure is involved to perform the computation of the fully-coupled fluid solid system. The fluid flow is governed by the incompressible Navier-Stokes equations and modeled by using a fractional step scheme combined with a co-located finite volume method for space discretisation. The motion of the fluid domain is accounted for by a moving mesh strategy through an Arbitrary Lagrangian-Eulerian (ALE) formulation. Solid dyncamics is modeled by a finite element method in the linear elasticity framework and a fixed point method is used for the fluid solid system computation. In the present work two examples are presented to show the method robustness and efficiency.

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Large Eddy Simulation of Cross Flow in Pipe Junction

Volume 2: CFD and FSI ◽

10.1115/omae2018-77751 ◽

2018 ◽

Author(s):

Jiajun Chen ◽

Yue Sun ◽

Hang Zhang ◽

Dakui Feng ◽

Zhiguo Zhang

Keyword(s):

Large Eddy Simulation ◽

Stokes Equations ◽

Numerical Study ◽

Three Dimensional ◽

Cross Flow ◽

Exciting Force ◽

Navier Stokes ◽

Pipe Network ◽

Eddy Simulation ◽

Large Eddy

Mixing in pipe junctions can play an important role in exciting force and distribution of flow in pipe network. This paper investigated the cross pipe junction and proposed an improved plan, Y-shaped pipe junction. The numerical study of a three-dimensional pipe junction was performed for calculation and improved understanding of flow feature in pipe. The filtered Navier–Stokes equations were used to perform the large-eddy simulation of the unsteady incompressible flow in pipe. From the analysis of these results, it clearly appears that the vortex strength and velocity non-uniformity of centerline, can be reduced by Y-shaped junction. The Y-shaped junction not only has better flow characteristic, but also reduces head loss and exciting force. The results of the three-dimensional improvement analysis of junction can be used in the design of pipe network for industry.

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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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