3rd Oxyfuel Combustion Conference, Ponferrada, Spain, 2013

Evaluation of Global Reaction Mechanisms Evaluation of Global Reaction Mechanisms

for CFD Modelling of Oxy-Fuel Combustion

Fredrik Normann

Chalmers University of TechnologyChalmers University of Technology

BackgroundBackground

Purpose To obtain information for development of commercial oxy-fuel boilers

Progress of work Chalmers 100 kW oxy-fuel unitProgress of work Chalmers 100 kW oxy fuel unitOxy-CFB combustionSeries of experimental and modelling studies

Content of work Combustion issuesEmissions (NOx and SOx)Heat transferHeat transfer

Present presentation Evaluation of reduced reaction mechanisms for CH oxidation in CFD simulations

Fredrik Normann

Computational Fluid DynamicsComputational Fluid Dynamics

Complex GeometriesComplex GeometriesComplex Turbulent Flames

Simplified reaction mechanisms

Limited generalizability

Source: www.hightech.fiApplicability to oxy-fuel combustion with

high CO2 concentration?

Fredrik Normann

Global Reaction MechanismsAir Oxy-fuel

JL 3-step 4-step 6-step

Global Reaction Mechanisms

x x x x

x x xFuelOxidation

x x x x

x x xIntermediatesOxidation

x

x

Oxidation

Radicalx

Jones & Lindstedt, Leiser et al

2007Glarborg

et al 2009Frassoldatiet al 2009

Radical Formation

1988 2007 et al, 2009 et al 2009

Fredrik Normann

Mixing (turbulence)

Temperature (heat transfer)(heat transfer)

GeometryBoundary ConditionsValidation

Reaction Mechanism

Burner and Boiler Optimization

Fredrik Normann

Mapping of 100 kW Oxy-Propane FlameMapping of 100 kW Oxy Propane Flame

Fredrik Normann

Temperature MeasurementsTemperature Measurements

• Contour map created entirely from measurement data

• Six measurement positions

• Temperature and Concentration Profiles

Fredrik Normann

3D CFD Model• Sub-models:

k-ε Realizable turbulence d l

3D CFD Model

modelEddy Dissipation ConceptDiscrete Ordinates model with a WSGG model forwith a WSGG model for oxy-fuel conditions (grey)

• Flame shapeFlame shapeJL predicts a wider and shorter flame than the oxy-fuel derived mechanisms

• Concentration of COJL and 3-step yield the

di ti hi h tpredictions which are most in line with measured data

Generation of 1D-ModelGeneration of 1D Model

• Traced a “particle” from the fuel inlet throughout the furnace

• Recorded O2 concentration and temperature

Fredrik Normann

Fredrik Normann

Comparison – CO concentration • The propane-fired Chalmers

100 kW OF27 flame

Comparison CO concentration

• Includes comparison with a detailed scheme

• Path-line data from CFD calculations is used in the PFR model

TemperatureO2 concentration

• Large discrepancies between the global models.

Comparison - Reaction Dynamics Fuel Oxidation CO Oxidation

Comparison Reaction Dynamics

Fredrik Normann

ConclusionConclusion

• There is a significant improvement potential for global oxy fuel• There is a significant improvement potential for global oxy-fuel reaction mechanisms and, thus, a need to develop a refined global reaction mechanism.

• Simply adjusting the reaction parameters to compensate for quantitative errors (such as over-predicted CO concentration or

b ti t t ) l d t i th ti d icombustion temperature) may lead to errors in the reaction dynamics

• A qualitatively incorrect behavior reduces the generic nature and li bilit f th h iapplicability of the mechanism.

Fredrik Normann

3rd Oxyfuel Combustion Conference, Ponferrada, Spain, 2013

Evaluation of Global Reaction Mechanisms Evaluation of Global Reaction Mechanisms

for CFD Modelling of Oxy-Fuel Combustion

Fredrik Normann

Chalmers University of TechnologyChalmers University of Technologyhttp://www.chalmers.se/en/projects/Pages/forbrannings

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