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8/13/2019 4. Thermal Radiation-TzxcUM
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Technische Universitt Mnchen
Oxy-Coal Flame Radiation Characteristics
Pedro Dias, M.Sc.
RELCOM Open Workshop
13thJune 2012
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Technische Universitt Mnchen
Content
1. Introduction
2. State of the art
3. RELCOM project
4. Summary
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Introduction
2.5 3 3.5 4 4.5 5 5.50
5000
10000
15000
Wavelength [m]
Intensity[W/(m
mSr)]
Air combustion
Oxyfuel 70% reci.
900C
1000C 1200C
600C
700C
800C
1100C
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Comparison between Oxyfuel and air combustion
Natural gas
70% wet recirculation
Gases participate more in radiation
Band overlapping behaviour changes
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Technische Universitt Mnchen
Two different approaches in literature:
Modified standard Weighted Sum of Grey Gases Model (WSGG)
3-4 equations for spectral modelling
Pros/Cons:
+ Standard model for gas radiation in CFD Software
- Accuracy when compared with other model
Implement more detailed Exponential Wide Band Model (EWB)
1 equation for each Wide Band
Pros/Cons:
+ Calculation of band overlapping more exact
- more equations than WSGG
- Implementation in CFD codes problematic
Modelling oxyfuel gas radiation state of the art
Introduction
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Technische Universitt Mnchen
IntroductionModelling single particle radiation
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Source: Modest 2003
Scattering depends on:
the shape of the particle (usually assumed as spherical),
the material of the particle (the complex index of refraction, m = n - ik),
its relative size (size parameterx = 2a/),
the clearance between particles (c/)
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IntroductionModelling particle clouds radiation
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Source: Modest 2003 and Tien et al 1987
Two approaches are used for particle clouds: The uniform size particles, is assumed that clouds consist of spheres that have the
same size
Nonuniform size particles, the cloud is described as a number of particles as a
function of radius.
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Technische Universitt Mnchen
Content
1. Introduction
2. State of art
3. Relcom project
4. Summary
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Technische Universitt Mnchen
Different solutions for WSGG
We canfind different approaches to change the WSGG for the oxyfuel gas
properties:
Khare 2008
Krishnamoorthy et al 2010
Johansson et al 2011
State of the art
29.06.2012 8
All of them have compared the results with more detailed models (SNB/EWB) for
validation.
The increase in the accuracy comparing with the original WSGG (Smith et al
1982) for oxyfuel combustion.
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Technische Universitt Mnchen
29.06.2012 9
State of the artDifferent solutions for WSGG
Source: Becher et al 2011
Deviation range over path length for WSGG model from Smith et
al. (1982) all combustion cases
Deviation range over path length for WSGG model from
Johansson et al. (2011) all combustion cases
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Technische Universitt Mnchen
29.06.2012 10
State of the artDifferent solutions for WSGG
Source: Becher et al 2011
Deviation of total emissivity for natural gas wet oxyfuel combustion
atmosphere at various temperatures for the WSGG model from Johansson et
al. (2011)
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Technische Universitt Mnchen
Min deviation Max
deviation
Recommended limits for improved
accuracy
WSGG (smith 1982) 32% 59% H2O/CO2 close to ratios
WSGG (Khare 2008) 13% 49% H2O/CO2 close to given ratios ( 0.3),
temperatures up to 800C, lower
pressure path length limit of 0.01 bar m
WSGG (Krishnamoorthy 2010) 32% 131% Lower pressure path length limit of 0.1
bar m, H2O/CO2 close to given ratios (
0:3)
WSGG (Johannsson et al 2011) 13% 21% Temperatures up to 800C, missing hot
lines in its reference model
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State of the artConclusions
Source: Becher et al 2011
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Technische Universitt Mnchen
29.06.2012 12
State of the art
Single particle combustion
Source: Bejarano et al 2008
The replacement of N2 by CO 2 causes, in average, a decrease by 200 K in
particle combustion temperature (exemplified for lignite coals)
To achieve the same combustion temperature as in N2 as bath gas, for the
bituminous volatiles and chars, the oxygen content has to be around 30%
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Technische Universitt Mnchen
29.06.2012 13
State of the art
Particle clouds combustion
Source: Wall et al 2009
Possible to observe that the increase in size rises significantly the gas emissivity
The increase in the size also rises the particle radiation
With the increase of size the emissivity approaches one
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Technische Universitt Mnchen
FTIR emission measurements in the 100 kW test rig to determine the spectral
radiation characteristics of oxy-pulverised coal flames
These spectral measurements will provide a detailed analysis of the changed gas
band radiation due to the changed ratio and higher concentrations of H2O and CO2in oxyfuel flames.
The influence of particle radiation under oxy-coal conditions will also be analyzed
These experimental results will be used to develop and validate radiation sub-
models
Relcom project
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Aims in task 1.2
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Technische Universitt Mnchen
Relcom project
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Plans for the measurements
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Relcom projectFirst measurements at the TUM combustion chamber
Oxy-coal flame
Lignite
65% dry
recirculation
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Technische Universitt Mnchen
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Relcom projectFirst measurements at the TUM combustion chamber
Oxy-coal flame
Lignite and
natural gas as
fuel Both are 65%
dry recirculation
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Technische Universitt Mnchen
Radiative characteristics of particle clouds is important for a full characterization of
oxy-coal flames
The data collection is important for the optimization of the CFD models for oxy-firing
Measurements in different facilities will help to understand influence of particle/gas
radiation contribution better
See the scalablity and the portability of the FTIR device
Summary
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Thank you for your attention
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References
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S. P. Khare. Heat Transfer in Air-Fired Pulverized Fuel Furnaces Retrotted to Oxy-Fuel Coal. PhD thesis, The
University of Newcastle, Newcastle, Australia, 2008.
G. Krishnamoorthy, M. Sami, S. Orsino, A. Perera, M. Shahnam, and E. D. Huckaby. Radiation modelling in oxy-fuel
combustion scenarios. International Journal of Computational Fluid Dynamics, 24(3):6982, 2010.
M. F. Modest. Radiative heat transfer. Academic Press, Amsterdam, 2nd edition, 2003. ISBN 0125031637.
T. Wall, Y. Liu, C. Spero, L. Ell iott, S. Khare, R. Rathnam, F. Zeenathal, B. Moghtaderi, B. Buhre, C. Sheng, R. Gupta,
T. Yamada, K. Makino, and J. Yu. An overview on oxyfuel coal combustion state of the art research and technology
development. Chemical Engineering Research and Design, 87(8):1003 1016, 2009.
C. Yin, L. C. R. Johansen, L. A. Rosendahl, and S. K. Kr. New weighted sum of gray gases model applicable to
computational uid dynamics (CFD) modeling of oxy-fuel combustion: Derivation, validation, and implementation.
Energy & Fuels, 24(12):62756282, 2010.
V. Becher, A. Goanta , H. Spliethoff. Validation of Spectral radiation models under oxyfuel conditions-Part C:
Validation of simplified models
V. Becher, H. Spliethoff. Spectral radiation measurements on oxy-fuel natural gas flames and flue-gases: Comparison
of air and oxy-fuel radiation. Proceedings of 1st Oxy-Fuel Combustion Conference Cottbus, Germany, 2009
P.A. Bejarano, Y.A. Levendis. Single-coal-particle combustion O2/N2 and O2/CO2 enviroments. Combustion and
Flame 153 (2008) 270-287
R. Johansson, B. Leckner, K. Andersson, and F. Johnsson. Account for variations in the H2O to CO2 molar ratio
when modelling gaseous radiative heat transfer with the weighted-sum-of-grey-gases model. Combustion and Flame,
158(5):893901, 2011.