Primary techniques for NOx containment in a ... - Prime Glass

Designing low NOx combustion systems for end port glass melting furnaces using an integrated CFD based approach

Author(s)

Affiliation

1

Primary techniques for NOx containment in a sustainable glass industry The achievements of the Prime Glass Project

Sauro Pasini, Sandro Merlini, Lucia Giovannini – rjc soft

LIFE12 ENV/IT/001020 - PRIME GLASS Prime Glass Conference

Rapallo (Genova – Italy) – March 30th 2017

Outline

• NOx formation/destruction chemistry

• Modelling approach and calibration

• Case studies



rjcsoft®

Time

Temperature Turbulence

The fire triangle The phenomena involved

High temperature furnaces: a complex environment rjc soft®

Large boilers & glass furnaces have similar environments



The pollutants of interest

N2 NOx

NITROGEN OXIDES

CO

CARBON OXIDE

NOx formation/destruction mechanismsNOx formation mechanisms for CH4 combustion

REDUCING ATMOSPHERE

OXYCYANOGEN(OCN,HNCO)

NOX

N2

FRAGMENTSHYDROCARBON

CH, CH2

NITRICCOMPOUNDS

SPECIE AMMONIACALI

(NH3, NH2, NH, N)

CYANOGEN(HCN, CN)

HYDROCARBONFRAGMENTS

CH, CH2

NOX

N2

N2O

H

AIR FUEL

A

B

F

F

E

B

D

B D

G

G B

B

BC

B

B

AMMONIACAL SPECIES

(NH3, NH2, NH, N)

THERMALNOX

PROMPTNOX

FUELNOX

OXIDISING ATMOSPHERE



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NOx reduction options

Reduce the temperature

“Oxidise without oxidising”

Flue gas recirculation

Staging, OFA, Burner Out Of Service, …

Reburning

Lean Reburning



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Low NOx Burners

Outline



• Case studies



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Under contract from Enel, RJC has completed the development of a code capable of managing any typical configuration of boilers and furnaces (opposite wall fired or tangentially fired boilers, glass furnaces, …), any fuel or combustion environment (gas, oil, coal, biomass, reducing environment, oxy-firing, gasification), providing detailed information on fluid flow, heat transfer, combustion efficiency, pollutant emissions, …

An integrated CFD based approach: the IPSE Code

The prediction of NOx emissions under reducing conditions requires the capability of using a complex chemistry: hundreds of radical species and thousands of reactions.

Being the option to incorporate detailed reaction kinetics directly in a 3D CFD code unfeasible, in 2000, together with University of Pisa, the Reactor Network Model was developed, based on the rezoning of the computational volume in a series of simple chemical reactors.



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The CFD + RNA Modeling Methodology

Reactor Network Analysis (RNA), is a post-processing tools to estimate combustion emissions.

RNA generates an equivalent network of reactor elements extracted from the results of CFD simulations by an automatic zoning algorithm.

Detailed reaction mechanisms are applied over the reactor network and a more accurate calculation of the combustion yields is performed.



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R1302

R4909

R32900R123524

R2218

R91143

R6951

R8927

R5264

R10344

R7774

R11752

Reaction progress is calculated with DSMOKE, a CHEMKIN like software

Detailed kinetic mechanism by Milan Polytechnic researchers:

A series of hierarchical reaction blocks are disposed, starting from the basic CO/H2 oxidation mechanisms.

Hydrocarbon Combustion Mechanism involves about 200 species and more then 3000 reactions.

Nitrogen sub-mechanism involves about 200 reactions and 40 species.

Detailed Reaction Chemistry Computation



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Inlet Air

Burners

Outlet GlassMeltedLoadDog-House

INLET/OUTLET DUCTS

VAULT

GAS/GUN - BURNERS

GLASS MELTED LOAD“DOG HOUSE”

Calibration: “End-Port” Glass Melting Furnace (2001)The first calibration of the model for glass furnaces was performed by Enel in 2001, together with Stara Glass. In those test campaigns Enel verified the capabilities of the software methodology in this new environment.



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0 5 10 15 20 25 30 351500155016001650170017501800185019001950200020502100

10 MW furnace

measurements CFD simulation

Tem

pera

ture

(°C

)

measurement positions

CFD simulation against “in flame” measurements



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1,0 1,2 1,4 1,6 1,8 2,0800

900

1000

1100

1200

1300

1400

1500

1600

1700

1800

measured values predicted by RNA (CFD with kinetics)

NO

2 [ m

g/N

m3 @

8%

O2 ]

O2 in exhaust (% dry vol.)

NOx predicted from Reactor Network Model



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This integrated methodology well performed for glass melting furnaces, resulting in a good agreement between measured and calculated values of temperature and chemical species.

This concept is not restricted to the NOx calculation, it can be used also for any other species for which a detailed reaction scheme is available.

This approach is also a reasonable trade-off between the complexities of the phenomena occurring in reactive flow fields and the engineering demands for addressing the design of practical combustion systems.

Some considerations for glass furnaces



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Outline



• Case studies



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Some low-NOx technologies for EP glass furnaces

In the following a preliminary evaluation of the possible efficiencies of typical low NOxconfigurations applied to glass furnaces has been performed

1 – Baseline (& low NOx burner) 2 - Flue Gas Recirculation

Flue Gas

4 – Over Fire Air

Air

5 – Lean Reburning Gas

3 – Burner Out Of Service

x

x



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Base case: temperature and chemical speciesHorizontal section 18 cm above burners

Mean O2 at exit ~ 2% Mean NOx at exit ~ 850 mg/Nm3

Temperature 800-2000 °C

Oxygen0-12%

NOx0-0.6% w/w



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Base case: temperature and chemical speciesVertical section 60 cm from entrance


Oxygen0-12%

NOx0-0.6% w/w



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Base case: temperature and chemical species


Oxygen0-12%

NOx0-0.6% w/w

Vertical section in the middle of the entrance



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Burner modification: ongoing activity (IFRF data)

Fuel input: 0.5 MW

Combustion Air

o Temperature: 1100° C

o Angle: 20°

o Velocity: 10 m/s

Gas firing modes: Underport, Overport, Sideport, Parallel sideport.

Fuel injection modes: Normal, Annular, Swirled.

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UP 16° 125 m/s

OP 20° 125 m/s

NOx reduction efficienciesBurner modification: IFRF experimental data rjc

soft®

NOx



UP 16° 125 m/s OP 20° 125 m/s

Burner modification: IFRF experimental data

Burner geometry and operative conditions are important parameters to be analyzed.Modelling activity ongoing together with prof. Pourkashanian at Sheffield University

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Flue Gas Recirculation: fundamental concepts



External FGR has already shown its potential in many high temperature process applications. Diluted combustion has both a thermal effect, dampening temperature peaks, and a chemical one, reducing flame burning velocity (no effect on CO emissions), with a more pronounced effect for intense flames.

Soft flame Tight flame

CO Iso-surfaces Tight flame

Gas- und Warme-Institute FGR testing results in a semi-industrial test rig.

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FGR: O2 concentration at the inlet

Base Case, No FGR Base Case, low FGRBase Case, uniform FGR



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NOx 0-06% w/w

∆NOx = -19 %∆NOx = -14 %

FGR: NOx concentration

Base Case, No FGR Base Case, low FGRBase Case, uniform FGR



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50,00%

55,00%

60,00%

65,00%

70,00%

75,00%

80,00%

85,00%

90,00%

95,00%

100,00%

Base 21% uniform 21% low

NOx Emissions, %

FGR: reduction efficiency

∆NOx = -14 %∆NOx = -19 %

Flue gas recirculation can reduce NOx linearly, of the same entity of FGR fraction for the “low” configuration



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Burner out of service: comparison with base caseTemperature 800-2000 °C NOx 0-06% w/w

Base Case Burner out of service Base Case Burner out of service



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NOx 0-0.6% w/w Base Case



Burner out of service

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Burner out of service: comparison with base case

Burner out of service: reduction efficiency

50,00%

55,00%

60,00%

65,00%

70,00%

75,00%

80,00%

85,00%

90,00%

95,00%

100,00%

Base BOOS

NOx Emissions, %

∆NOx = -12 %

Burner Out Of Service can reduce NOx due to the staging of the fuel achieved in the main burner zone



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Fuel staging: comparison with base caseTemperature 800-2000 °C NOx 0-0.6% w/w

Base Case Staging Base Case Staging



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Fuel staging: comparison with base caseNOx 0-0.6% w/w Base Case

Fuel Staging



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50%

55%

60%

65%

70%

75%

80%

85%

90%

95%

100%

Base Br. 3 Br. 2 Br.1

NOx Emissions, %Fuel staging: NOx reduction efficiencies

∆NOx

-17 %

-25 % -25 %



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The integrated methodology developed can be efficiently used to calculate NOx reduction efficiencies corresponding to different configurations of the combustion system

Comparison with experimental data has shown good correspondence, on average, between reductions predicted and measured, even if these preliminary calculations have been performed with a not well detailed grid.

Combustion modification is an interesting option to adopt in glass furnaces to reduce NOx, before seeking for expensive flue gas cleaning technologies. The preliminary results obtained confirm the validity of the extensive know-how already developed for p.p. boilers:

Flue gas recirculation can reduce NOx linearly, of the same entity of FGR fraction

Burner Out Of Service has shown a 10 to 15% reduction due to fuel/air staging

Lean reburning realized moving one of the three gas burners to the side wall, has shown a NOx reduction efficiency of about 25%

Some final considerations for glass furnaces



rjcsoft®

Primary combustion modifications offer a lot of different options, as function of furnace characteristics, baseline NOx emissions, expected reduction efficiencies, investment costs, …. , and glass furnaces are favored over power station boilers, due to the much larger residence times

Designing combustion modifications is the same as sewing a tailor’s dress.

The methodology developed can easily allow any combination of the above mentioned technologies, proving very effective in supporting the definition of the optimal strategy to be adopted as function of the specific case.

Some final considerations for glass furnaces



rjcsoft®

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Primary techniques for NOx containment in a ... - Prime Glass