Characteristics of a Methane Jet Flame in Elevated Pressure and Oxy-Fuel Atmosphere Using Large Eddy Simulation with Tabulated Chemistry

ABSTRACT

The pressurized oxy-fuel combustion is a promising CO₂ capture technology for its further reduction of CO₂ capture cost. In order to study the combustion behaviors of hydrocarbons under different pressures and atmospheres, a methane/air jet flame is used as the simulation target, with modifications on its oxidizer species and operating pressure. A Large Eddy Simulation (LES) with a tabulated chemistry model is employed, whose lookup tables are constructed by using a 2-D counterflow diffusion flame under different atmosphere and pressure conditions. The original flame with detailed experimental data is used for the validation of the model accuracy, and the simulation results show good agreement with the experiments. The detailed profiles of the temperature, species, and mixture fraction are analyzed. Compared with the air-fired, the flame in the oxy atmosphere is shorter and thinner. Important species and radicals are compared. The comparison shows that under elevated pressure, the differences caused by oxy atmosphere is similar to those found under atmospheric pressure. With the elevation of pressure from 0.1 MPa to 1.5 MPa, the flame height becomes smaller while the radial width is larger near the inlet, which can be observed in both air-fired and oxy-fired conditions. Under elevated pressures, the flame temperature changes slightly, but CO production increases noticeably in the fuel-rich regions.

Graphical abstract

KEYWORDS:

• Tabulated chemistry
• Large-Eddy Simulation
• oxy-fuel combustion
• pressurized combustion

Highlights

1. Pressurize oxy-fuel methane flames are characterized detailly by Large Eddy Simulation with tabulated chemistry.

2. Oxy-fuel atmosphere leads to smaller flame height and flame width.

3. Oxy-fuel atmosphere produces more CO and H₂O, but the temperature is slightly lower.

4. With the elevation of pressure, the flame height becomes smaller while the radial width is larger near the inlet.

5. At elevated pressure, the temperature changes slightly, but the CO production increases noticeably in the fuel-rich regions.

Nomenclature

Abbreviation

CCS	=	Carbon Capture and Storage
ASU	=	Air Separation Unit
CPU	=	Compression Purification Unit
LES	=	Large Eddy Simulation
FGM	=	Flamelet Generated Manifolds
RANS	=	Reynolds Average Navier-Stokes
SGS	=	Sub-Grid-Scale
CFD	=	Computational Fluid Dynamics
PDF	=	Probability Density Function
FVM	=	Finite Volume Method
TVD	=	Total Variation Diminishing

Symbols

$\rho$	=	Density
$u$	=	Velocity
$p$	=	Pressure
$\tau$	=	Shear stress tensor
$D_{eff}$	=	Effective diffusivity
$D$	=	Diffusivity
$D_t$	=	Turbulent diffusivity
$S{c}_t$	=	Turbulent Schmidt number
Z	=	Mixture fraction
$\widetilde{Z^{{ }^{\prime \prime }2}}$	=	Mixture fraction variance
$C_g$	=	Constant for mixture fraction generation terms
$C_{d,Zv}$	=	Constant for mixture fraction dissipation terms
$\chi$	=	Scalar dissipation rate
$a$	=	Strain rate
T	=	Temperature
$D_T$	=	Temperature diffusivity
${\omega }_i$	=	Chemical source term
$h_i$	=	Specific enthalpy
$c_p$	=	Specific isobaric heat capacity
$\mathrm{\Gamma }$	=	Gamma function
$\delta$	=	Dirac function

Acknowledgments

Financial support of this work by National Key Research and Development Plan (No.2016YFB0600802) and National Nature Science Foundation of China (No. 51776040) are gratefully acknowledged.

Additional information

Funding

This work was supported by the National Key Research and Development Plan [No.2016YFB0600802]; National Nature Science Foundation of China [No. 51776040].