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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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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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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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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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Content

1. Introduction

2. State of art

3. Relcom project

4. Summary

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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

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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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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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29.06.2012 10

State of the artDifferent solutions for WSGG


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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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



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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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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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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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Relcom project

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Plans for the measurements


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29.06.2012 17

Relcom projectFirst measurements at the TUM combustion chamber

Oxy-coal flame

Lignite

65% dry

recirculation


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29.06.2012 18

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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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.

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