COMO a Computational Fluid

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COMO: A Computational FluidDynamics Model For PredictingBoiler Flow And Combustion

Authors:S.A. Dudek

Z. Chen A.N. Sayre

Babcock & Wilcox PowerGenera on Group, Inc.Barberton, Ohio, U.S.A.

Presented to:

33rd Interna onal TechnicalConference on Coal U liza on& Fuel Systems

Date: June 1-5, 2008

Loca on:Clearwater, Florida, U.S.A.

Technical PaperBR-1810


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Babcock & Wilcox Power Generation Group 1

COMO: A Computational Fluid Dynamics Model For Predicting Boiler Flow And Combustion

S.A. Dudek, Z. Chen and A.N. SayreBabcock & Wilcox Power Generation Group, Inc.

Barberton, Ohio, U.S.A

Presented at:33rd International Technical Conference on Coal Utilization & Fuel Systems

Clearwater, Florida, U.S.A.June 1-5, 2008

BR-1810

AbstractThis paper describes a computational uid dynamics and

combustion model that simulates the numerous interacting processes that occur within a boiler burning pulverizedcoal and operating at steady state. The processes modeledinclude three-dimensional turbulent gas ow, particle mo -tion, heterogeneous and homogeneous chemical reactions,and radiative and convective heat transfer.

The model is routinely used as a cost-effective tool toassist in the design of boiler equipment and in the diagno-sis and resolution of boiler operating problems. It is useful

because the effects of modifying operational parametersor the physical arrangement of equipment can be quicklyevaluated.

A recently completed simulation for a pulverized coal-red boiler demonstrates the models capabilities and its role

in the design process. Individual burner and over re air portsub-models were created to generate ow boundary condi -tions for the furnace model. Boiler simulations were usedto more fully optimize the over re air arrangement, produc -ing improved mixing, a more uniform gas ow distribution

within the furnace, and a more uniform distribution of gastemperature heading into the convection pass.

IntroductionThe use of a computational uid dynamics (CFD) model

provides detailed boiler equipment performance predictionsthat cannot be obtained solely through experience, traditional

performance predictions, or eld measurements. Experi -ence and traditional performance predictions are not able to

predict the three-dimensional distributions of the ow eld,

gas species, and temperature throughout a boiler as a modelcan. Field measurements provide actual performance data

but are limited to a few locations from which interpretationsmust be made. Additionally, it is typically not practical toevaluate multiple hardware design options (such as pressure

part changes) using eld measurements.These are some of the reasons why CFD has become more

prevalent in the power generation industry. With tighteremission limits, it is important to utilize all available tools

to maximize the effectiveness of combustion equipment.As one of these tools, modeling provides complementaryinformation to an engineering design team to help bridge thegap between previous experience and a new design. It canaccelerate the evaluation of design parameters, allowing amore thorough examination of the design space, which im -

proves con dence in the nal design. Design optimizationis more likely when modeling results are used in conjunctionwith experience, traditional performance predictions, and

eld measurements.Babcock & Wilcox Power Generation Group, Inc.,

an operating group of The Babcock & Wilcox Company(B&W), has a unique CFD modeling capability within thefossil power generation industry. The substantial investmentin CFD modeling made by B&W over the past twenty- veyears has resulted in the COmbustion MOdel, COMO SM,which is general-purpose ow and combustion modelingsoftware. COMO is an advanced, mature design tool that isroutinely used to analyze and assist in the design of complexcon gurations, from concept burner designs and staged low-

NO x combustion systems to windbox and selective catalyticreduction (SCR) systems. The diversity of the COMO mod -eling software has been proven through unique applicationssuch as large-particle ash capture, cyclone furnaces, coal


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2 Babcock & Wilcox Power Generation Group

gasi cation, and oxy-combustion, as well as for stoker-red power boilers, Kraft process recovery boilers, and the

full spectrum of pulverized-coal boilers: tangentially- red,single-wall- red, and opposed-wall- red.

COMO has been successfully used over many years forthe modeling of gas ow and combustion within boilers r -ing pulverized coal. During the last decade, it has producedhundreds of simulations for more than 50 coal- red boilers.

The main strength of the model is its ability to comparerelative changes in combustion effectiveness between dif-ferent scenarios. Combustion effectiveness is evaluated

based on mixing uniformity, gas temperature distribution,oxygen distribution, and carbon monoxide distribution andconcentration at the furnace and model exits.

This paper describes the capabilities of the COMO mod -eling software and provides an example of its use for a 600MW, opposed-wall, pulverized coal- red boiler.

Model descriptionB&Ws computational uid dynamics and combustion

modeling software, COMO, simulates the numerous interact -ing processes that occur within a combustion system burning

pulverized coal and operating at steady state (Fiveland, etal., 1984; Fiveland, 1996; LaRue, et al., 2006; Sarv, et al.,2008). The processes modeled include three-dimensionalturbulent gas ow, particle motion, heterogeneous andhomogeneous chemical reactions, and radiative and con -vective heat transfer. The capabilities of the program aresummarized schematically in Figure 1 and are described inthe sections below.

The COMO modeling software uses the nite-volumemethod with a body- tted unstructured mesh containing

a mixture of element shapes for geometric exibility. Ac -curacy of the solution is enhanced without overwhelmingcomputer resources by using local mesh re nement, eitheron speci c volumetric regions or through the use of solution-adaptive mesh re nement in regions of high gradients (e.g.,turbulent jets, diffusion ames, etc.).

Gas fow To obtain the three-dimensional steady-stategas ow distribution, the density- (or Favre-) averaged

Navier-Stokes equations (Cebeci and Smith, 1974) aresolved using the SIMPLE algorithm (Patankar, 1980). Astandard k- model (Launder and Spalding, 1974) is used forturbulence closure. The gaseous products from the coal andthe aerodynamic drag of the particles are included as sourcesin the mass and momentum balances of the gas phase.

Particle fow Dilute particle ow can be representedwith either an Eulerian or Lagrangian model, or both mod -els can be used simultaneously. Typically, for a pulverizedcoal boiler, the smaller particles are transported with the gas

ow without slip and are therefore modeled in an Eulerianfashion. The larger particles will not necessarily follow thegas ow and are treated in a Lagrangian fashion.

For the Eulerian particle model, the Favre-averaged gastransport equations are modi ed to include dilute particle

ow (Crowe and Smoot, 1979).The Lagrangian particle model (Crowe, 1979) calculates

particle aerodynamics and turbulent dispersion for the pul -verized coal particles transported through the boiler. Thecontinuous distribution of particle sizes produced by the pul -verizer is modeled by a small number of discrete particle bins(typically between ten and twenty). The dense distributionof particles leaving the burner are modeled by a prescribednumber of particle streams (typically many thousands), witheach stream characterized by an initial position, particle size,mass ow rate, velocity, and temperature. The ight historyof each stream through the furnace is determined by grav -ity, the aerodynamic drag force from the furnace gas, andturbulent dispersion. A stochastic particle dispersion model(Milojevic, 1990) is used to simulate the effect of turbulent

uctuations in the gas velocity on the instantaneous motion

of the particle.As coal particles are heated by radiation and convec -tion, they are modeled as sequentially undergoing drying,devolatilization, and char oxidation. The particle diameter isassumed constant during the drying stage. During devolatil -ization, the particle diameter is modeled as increasing pro -

portionally (using an empirical swelling factor) to the extentof devolatilization. During char oxidation, it is assumed thatthe char density remains constant while the particle diameteris reduced through a burning mode. Weight loss and densityvariations affect the gravitational and aerodynamic forceson each particle. Moisture, volatile species and char com -

bustion products that evolve from the particles during ight

are added to the conservation equations of the gas speciesto ensure overall material and energy balances.

Conserved species Conservation equations aresolved for each gas species and each elemental species ofeach Eulerian particle size group. Source terms in theseequations are produced from homogeneous and heteroge-neous reactions.

Heterogeneous chemistry Combustion processesthat convert the coal to ash encompass three stages: drying,devolatilization, and char oxidation. These processes aremodeled by several global chemical reactions:

Fig. 1 Capabilities of COMO for pulverized coal- redboilers.


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Wet Coal Dry Coal + H 2O

Dry Coal Volatile Gas + Char

Char + O 2 CO + CO 2 + H 2O + Ash

As the coal particle absorbs heat by radiation and convec -tion, the moisture in the particle evaporates, leaving driedcoal. A further increase in the coal temperature causes pyro -lytic reactions that form volatile gases and char. The volatilecomposition depends on the coal elemental composition,

but typically includes species such as CH 4, SO 2, CO 2, andH2O. Coal devolatilization is modeled using two competingchemical reactions (Kobayashi, et al., 1977), with the volatileyields depending on coal composition (Neoh and Gannon,1984). Combustion of the char proceeds at an effective ratedetermined from the apparent chemical kinetic rate and therate of oxygen diffusion to the surface of the char particle.Char combustion produces gaseous products CO and CO 2,leaving inert ash and unburned carbon.

Homogeneous chemistry Combustion of the volatilegas is characterized as a two-step process. In the rst step,volatile gases are assumed to react with oxygen to formcarbon monoxide and water:

Volatiles + O 2 CO + H 2O

This reaction is very fast and the combustion rate is con -trolled by the rate of turbulent mixing, as predicted by theeddy dissipation model (Magnussen and Hjertager, 1976),which is used to calculate the volatile reaction rate.

The second step involves the moist oxidation of CO:

CO + (1/2) O 2 CO 2

The combustion rate for this step is limited by theminimum of the global reaction kinetic rate (Howard, etal., 1972) and the rate of turbulent mixing (Magnussen andHjertager, 1976).

Energy The energy balance includes convection andradiation, and it accounts for the gas phase, the particles (Eu -lerian, Lagrangian, or both), the walls, and the tube banks.The discrete ordinates method (Fiveland, 1988) is used tosolve the radiative transport equation for an absorbing, scat -tering medium in an enclosure. Radiation properties of the

participating gases (CO 2, H 2O, CO, SO 2) are calculated withEdwards Exponential-Wide-Band model (Edwards, 1976),and absorption and scattering by particles are calculated withMie Theory (Van De Hulst, 1957).

The gas energy balance is achieved using the inlet en -thalpy de ned for the incoming air streams and the Eulerian

particles as well as gaseous products (water vapor, volatilesand char combustion products) from the Lagrangian par -ticles. Gases exchange heat by radiation and convectionwith the walls and entrained particles. The Eulerian particletemperature is identical to the gas temperature, and energy

sinks and sources associated with the Eulerian particles areincluded in the uid energy balance equation.

The Lagrangian particle energy balance is solved sepa -rately but is coupled with the gas phase. Particles exchangeheat with the gas phase by radiation and convection. Particleconvective heat transfer with the gas is dependent upon therelative velocity between the particle and the gas, with theheat transfer coef cient including the effect of mass transferfrom the particle (the blowing effect). The thermodynamiceffects of heterogeneous reactions are also included in theenergy balance equation.

Boundary conditions are applied for radiation and con -vection heat transfer to the furnace membrane walls andtube banks of the convection pass, and for conduction heattransfer through ash deposits and tube walls to the water orsteam inside the tubes. Surface temperature and heat ux arecalculated from a balance of energy for each surface element.Convective heat transfer to tube banks is calculated usingcorrelations for turbulent cross ow over tube bundles, whileradiative heat transfer to tube banks is modeled by addinga contribution to the absorption and scattering coef cientsin the tube regions. Tube banks are treated as a continuumsince it is computationally expensive to resolve individualtubes within the boiler mesh.

Nitrogen oxides (NO x ) model COMO containsa global NO x model that can predict both the formationand reduction of NO x. During devolatilization, fuel-boundnitrogen is assumed to form HCN and NH 3. These speciesreact with the ue gas and are either oxidized to form NO x or reduced to form N 2 (de Sote, 1975). The formation anddestruction of thermal NO x is described by the modi edZeldovich mechanism (Bowman, 1975). Nitrogen releasedfrom the burning of char is assumed to form N 2 and NO.

Because the concentrations of NO x pollutants are typicallyseveral orders of magnitude lower than that of the othercombustion species, the pollutant solution mechanism can

be de-coupled from the combustion solution and solved afterthe combustion solution is converged.

Advanced models The above sections describe theCOMO sub-models that are used for the pulverized coal

boiler application described in this paper. However, themodeling software also contains a number of advancedmodels. These include: a realizable k- model for tur -

bulence (Shih, et al., 1995); the eddy dissipation conceptmodel for homogeneous reactions (Magnussen, 1981); theChemical Percolation Devolatilization (CPD) model for

coal devolatilization (Fletcher, et al., 1990); the CBK modelfor heterogeneous char reactions (Hurt, et al., 1998); a sootmodel for pulverized coal combustion (Brown and Fletcher,1998); and a combustion model for char-ash deposits on thefurnace walls.

Additional model development is ongoing in many areasto more accurately model boiler performance. For example,incorporation of a reduced NO x mechanism is in progress,which is expected to better describe the formation and de-struction of NO x and to better predict NO x emissions fromutility boilers.


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Model application for a pulverized coal-fred boiler

The COMO modeling software is routinely used tosimulate the ow and combustion within pulverized coal-

red boilers. As an example of its use, a model has beengenerated for a wall- red, pulverized coal radiant boiler

ring bituminous coal, with a nominal full load generatingcapacity of 600 MW, operating at steady state.

Boiler description The furnace is 60 ft wide, 51 ftdeep, and approximately 167 ft tall. There are 3 elevationsof B&W Dual-Register burners on both the front and rearwalls, each row with 7 burners, for a total of 42 burners.Six pulverizers supply coal and primary air to the burners,with each pulverizer serving seven burners at a particularelevation. The existing over re air (OFA) system, small andoutdated by todays standards, consists of single-zone non-swirling ports, located on the front and rear walls above thetop burner elevation. The boiler geometry was discretizedusing a homogeneous hexahedral mesh, in a similar mannerto the mesh shown in Figure 2 (which is for the proposed

combustion system).Objective To help the customer reduce NO x emissions,B&W is installing a new low-NO x combustion system con -sisting of forty-two B&W DRB-4Z Ultra Low-NO x burnersin combination with an OFA system using ten B&W Dual-Zone NO x ports. The new burners will be custom designedto t in the existing burner locations, and the OFA ports will

be at the same elevation as the current OFA system.Modeling has been used to study the combustion perfor -

mance of the existing unit and the proposed low-NO x combustion system. Modi cations in the proposed OFA systemarrangement and operation were evaluated by comparing themixing effectiveness of each variation.

Case summary The COMO modeling software wasused to create steady-state simulations of the ow, heattransfer, and combustion processes within the boiler for thecurrent con guration as well as the proposed B&W low-

NO x combustion system, both operating at full load withall burners in service.

Input to the model included the coal and air ow rates,the ultimate analysis of the coal, rate parameters for coaldevolatilization and char oxidation, wall and tube bank heattransfer conductance, and pressure loss coef cients for thetube banks. Some of these values are shown in Table 1.

Current confguration and operation For the currentcon guration model, the operating conditions and coalanalysis corresponded to recent plant operation. The plant-measured values for primary air, coal ow, and over re airwere used, and the burner secondary air was back-calculatedusing the measured excess O 2 level. The burner-zone stoi -chiometric ratio was 1.06, with 12% of the secondary airsupplying the OFA ports. Further details of the operatingconditions for this case are shown in Table 1. The boilercomputational mesh for the current con guration containedapproximately 476,000 elements, which included additionalre nement in the burner and OFA port regions.

Including the detailed burner geometry within the fur -nace model would result in an excessive number of meshelements. Therefore, the furnace model began at the burnerthroat, and the velocity distribution at the burner exit wasmapped to the burner inlets in the furnace model. To deter -mine the velocity distribution at the throat, a COMO owmodel of a single dual-register burner was run, as shown inFigure 3. For the current single-zone OFA ports, a uniformvelocity pro le was assumed.

Fig. 2 Computational mesh on boiler surface for proposedlow NOx combustion system. Full mesh and enlarged viewof OFA ports (upper inset) and burner (lower inset).

Table 1 . Modeling Operating Conditions: Combustion Air and Fuel Summary600 MW Utility Boiler

Furnace Excess Air (% Theo Air) 16.6 19.0Burner Zone Stoichiometry 1.06 0.90Primary Air Flowrate (kpph) 1141 1180Primary Air / Coal Mixture Temp (F) 165 150Burner Secondary Air Flowrate (kpph) 3139 2586

(% Total SA) 88.20 68.06OFA Port Secondary Air Flowrate (kpph) 420.00 1213.50

(% Total SA) 11.80 31.94Secondary A ir Tem perature (F) 525 579

Coal Rank High-Vol Bit C High-Vol Bit CCoal Flow Rate (kpph) 559.100 572.200Primary Air / Pulverized Coal Ratio (lbm / lbm) 2.041 2.062Temperature (F) 165.3 150.0

Ultimate Analysis (As Received) (wt %) Ash 20.37 21.78 Moisture 9.94 8.93 Carbon 54.24 54.21 Hydrogen 3.80 4.04 Nitrogen 1.14 1.00 Sulfur 0.76 0.76 Oxygen 9.75 9.28

Proximate Analysis Ash 20.37 21.78 Moisture 9.94 8.93 Volatiles 34.37 33.76 Fixed Carbon 35.32 35.53

Dry, Ash-Free Volatile Matter 49.32 48.72Heating Value (Btu/lbm) 9611 9502

ProposedLow-NOxCombustion Air and Fuel Summary

CurrentConfiguration


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Proposed confguration and operation For the pro - posed low-NO x combustion system, the forty-two burnerswere replaced (in the identical locations) with B&W DRB-4Z burners. At the OFA elevation, ten dual-zone OFA portsreplaced the original system. Five ports were used on eachwall to provide full coverage across the entire cross-sectionof the boiler. To generate the maximum mixing, these portswere slightly offset from the burner columns and the interior

ports were directly opposed on the front and rear walls. The ports were not equally spaced because of structural steelobstructions. Based on intermediate modeling results thatshowed elevated CO concentrations near the front of theleft sidewall and the rear of the right sidewall, the leftmostfront-wall port and rightmost rear-wall port were each placedslightly closer to the side walls than their counterparts on theopposing wall. The boiler computational mesh for this casecontained approximately 557,000 elements, which includedadditional re nement in the burner and OFA port regions,as shown in Figure 2.

The model was run at the proposed operation for full-loadwith all burners in service. The burner-zone stoichiometricratio was 0.90, and furnace excess air was 19%, with 32%of the secondary air supplying the OFA ports. Furtherdetails of the operating conditions for this case are shownin Table 1.

The B&W DRB-4Z burners have been modeled often andas a result a correlation has been previously developed thatspeci es the velocity distribution in each zone for prescribed

burner settings. This correlation was used in these modelsto de ne the velocity distribution at the burner inlets of thefurnace model. The individual OFA ports were modeled,as shown in Figure 4. The port exit velocity distributionfrom each model was then mapped to the port inlets in thefurnace model.

Results and discussion The gas ow distributionwithin the boiler is shown in Figure 5 for both cases. Forthe current con guration and operation, the burner and OFA

ow both meet midway between the front and rear of thefurnace, forming a column of high-speed upward owing

gas. However, the jets from the OFA ports do not penetratefar enough into the furnace to break up this gas stream. Forthe proposed con guration and operation, because of the

burner characteristics and the lower secondary-air ow rate per burner, there is less mass channeled up the center of thefurnace. Furthermore, any upward- owing gas is mixedmore fully by the OFA air jets, which penetrate much furtherthan the jets from the current OFA system.

Fig. 3 Flow results for a single dual-register burner in a600 MW utility boiler (clockwise swirl). Top: streamlines(green: primary air; blue: inner-zone secondary air; red:outer-zone secondary air). Bottom: gas speed contours.

Fig. 4 Flow results for a single dual-zone over re airport in a 600 MW utility boiler (clockwise swirl). Top:streamlines (green: inner-zone air; blue: outer-zone air).Bottom: gas speed contours.


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The gas temperature distribution within the boiler isshown in Figure 6. Because of the inadequate penetrationand coverage of the OFA ports for the current con guration,the hot combustion gases from the burner zone are convecteddirectly to the upper furnace without mixing with the coolerover re air. This causes temperatures in the upper-furnacethat are greater than those predicted for the proposed con gu -ration and operation, as seen in Table 2. The uneven mixingalso leads to a higher-temperature bias toward the right sideas the gas leaves the furnace. The enhanced mixing abilityof the OFA system of the proposed combustion system haswidespread positive implications for the combustion process.The high-temperature gases convected upward from the

burner zone are mixed well with the over re air, resultingin a more uniform and symmetric temperature distributionheading into the convection pass, as seen in Figure 6, whichleads to better heat transfer in the region.

The carbon monoxide concentration within the boiler isshown in Figure 7. For the current con guration and opera -tion, the inadequate penetration of the OFA ports allowshigh CO concentrations to persist in the center of the unit,high into the upper furnace. In addition, the lack of cross-sectional coverage of the OFA system results in elevated COlevels along the side walls in the upper furnace, including theconvection pass. The ow-weighted average of CO concen -tration at the furnace exit (shown in Table 2) is 1420 ppm,which is consistent with gas measurements taken at similarunits. The CO has been reduced to 237 ppm at the modelexit, and further reduction would be expected prior to anymeasurements taken at the economizer outlet or stack.

The CO concentration distribution for the proposed com -

bustion system also displays improvement over the currentcon guration. Although there is more CO generated in thelower furnace since the burners are run at a lower stoichio-metric ratio (0.9 vs 1.06) to most effectively reduce NO x, theOFA system mostly con nes the high concentrations of COto the lower furnace. There is minimal CO that is convectedup the center of the furnace, and the good cross-sectionalcoverage of the OFA system signi cantly reduces the COlevels along the side walls. The ow-weighted averages ofCO concentration shown in Table 2 quantify the improved

performance: 293 ppm at the furnace exit and 81 ppm atthe model exit.

The global NO x model predictions for both simulationsare shown in Table 2. For this unit, these provide a qualita -tive comparison between the cases, but cannot be used as aquantitative indicator of expected NO x emissions.

In summary, the results presented show that the currentOFA system does not provide suf cient jet penetration orcross-sectional coverage to accomplish adequate mixing.On the other hand, the OFA con guration of the proposed

low-NO x combustion system provides signi cant improve -ments in jet penetration and cross-sectional coverage. Thisresults in improved mixing over the current OFA system andimproved combustion performance.

Concluding remarksB&Ws computational uid dynamics and combustion

modeling software, COMO, has been developed to simulatethe numerous interacting processes that occur within a boiler

burning pulverized coal and operating at steady state. To

Fig. 5 COMO modeling predictions gas speed contoursat various elevations and vertical planes on a 600 MWutility boiler.

Fig. 6 COMO modeling predictions gas temperaturecontours at various elevations and vertical planes on a 600MW utility boiler.


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demonstrate its use as a tool in the design process, the modelwas applied to a 600 MW opposed-wall, pulverized coal-

red boiler, for both the current con guration and operationand the proposed con guration and operation. The resultsclearly demonstrated the superior mixing performance ofthe OFA arrangement for the proposed low-NO x combustionsystem, resulting in more uniform conditions heading intothe convection pass, as well as lower levels of CO. It isexpected that this system will meet the customers need for

NOx reduction, and after the proposed combustion systemis installed, modeling results will be compared with eldmeasurements.

AcknowledgementsThe authors wish to acknowledge Al LaRue and Wane

Goss for their contributions to the example boiler modelingwork shown here.

Fig. 7 COMO modeling predictions carbon monoxideconcentration contours at various elevations and verticalplanes on a 600 MW utility boiler.

ReferencesBowman, C.T., Kinetics of Pollutant Formation and

Destruction in Combustion, Progress in Energy and Com - bustion Science, Vol. 1, pp. 33-45, 1975.

Brown, A.L., and Fletcher, T.H., Modeling Soot De -rived from Pulverized Coal, Energy & Fuels, Vol. 12, pp.745-757, 1998.

Cebeci, T., and Smith, A.M.O., Analysis of TurbulentBoundary Layers, Applied Mathematics and Mechanics,Vol. 15, Academic Press, New York, 1974.

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Crowe, C.T., and Smoot, L.D., Multicomponent Con -servation Equations, Pulverized Coal Combustion andGasi cation, edited by L.D. Smoot and D.T. Pratt, PlenumPress, New York, 1979.

de Sote, G.G., Overall Reaction Rates of NO and N2Formation from Fuel Nitrogen, 15th International Sympo -sium on Combustion, The Combustion Institute, Pittsburgh,

p. 1093, 1975.Edwards, D.K., Molecular Gas Band Radiation, Ad -

vances in Heat Transfer, Vol. 12, edited by T.F. Irvine, Jr.and J. P. Hartnett, Academic Press, New York, pp. 115-193,1976.

Fiveland, W.A., Cornelius, D.K., and Oberjohn, W.J.,COMO: A Numerical Model for Predicting Furnace Per -

formance in Axisymmetric Geometries, ASME Paper No.84-HT-103, 1984.

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Table 2 . COMO Modeling Predictions: Flow-Weighted Average for Temperature,Carbon Monoxide, and Nitric Oxide at Various Planes

600 MW Utility Boiler

Arch (F) 2775 2746Furnace Exit * (F) 2464 2384Model Exit ** (F) 1574 1554

Furnace Exit * (ppm, dry) 1420 293Model Exit ** (ppm, dry) 237 81

Furnace Exit * (ppm, dry, 3% O2) 263 214

* The furnace exit is at the upstream portion of the secondary superheater inletbank, which is approximately the plane extending vertically from the arch.

Proposed B&WLow-NOx SystemFlow-Averaged Quantities

Gas Temperature

** The model exit is slightly downstream of the reheat superheater outlet bank.

Carbon Monoxide Concentration

Nitric Oxide (NO) Concentration

CurrentConfiguration


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LaRue, A., Rowley, D., Sarv, H., Kahle, W., and Sayre,A., B&Ws AireJet Burner for Low NOx Emissions,Presented at the Power-Gen International Conference, Or -lando, FL, November 2006.

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Magnussen, B.F., and Hjertager, B.H., On Mathemati -cal Modeling of Turbulent Combustion, 16th Symposium(International) on Combustion, The Combustion Institute,Pittsburgh, pp. 719-729, 1976.

Milojevic, D., Lagrangian Stochastic-Deterministic(LSD) Predictions of Particle Dispersion in Turbulence,Journal of Particles and Particle Systems Characterization,Vol. 7, pp. 181-190, 1990.

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Sarv, H., LaRue, A., Sayre, A.N., Maringo, G.J., Vara -gani, R., and Levesque, S., Selective Use of Oxygen andIn-Furnace Combustion Techniques For NOx Reduction InCoal Burning Cyclone Furnaces, To be Presented at the33rd International Technical Conference on Coal Utilization& Fuel Systems, Clearwater, FL, June 2008.

Shih, T.-H., Liou, W.W., Shabbir, A., Yang, Z., and Zhu,J., A New k- Eddy-Viscosity Model for High Reynolds

Number Turbulent Flows - Model Development and Valida -tion, Computers Fluids, 24(3), pp. 227-238, 1995.

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Wessel, R.A., and Fiveland, W.A., Pulverized CoalCombustion Model with Finite-Rate Carbon MonoxideOxidation, presented to the American Flame ResearchCommittee, Pittsburgh, October 4-6, 1988.


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COMO a Computational Fluid

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