Pillard Low NOx

Industrial operating experiences and Industrial operating experiences and burnerburner design optimisation design optimisation

using low NOusing low NOxx ROTAFLAMROTAFLAM burnersburnersin in cement kiln coalcement kiln coal combustioncombustion

Dr J-C. GAUTHIERPillard

13 Rue R. Teissere13272 Marseille Cedex 8 - [email protected]

Dr R. RIZZITechnologies Central Management - Combustion Department

via G. Camozzi, 124 24121 Bergamo, Italy

[email protected]

5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)

LOW NOx BURNER CONCEPT

The operating principle of a low NOx burner is based on a stepwise combustion which delays the mixing and input of fuel and air at appropriate stages to achieve a controlled combustion process.

The flame is ignited and stabilised as close as possible to the burner tip entraining a minimum of secondary air and mixing between primary air jets, which are properly designed to allowing the formation of the hot internal re-circulation zone.This results in a fuel rich flame and lower peak temperature.

The first generation of low NOx burners used the air staging principle. Nowadays, the new generations of low NOx burners use air staging technology but also specific fuel injection pointswhich help to reduce NOx emissions.


HISTORIC BACKGROUND

To date it can be considered that there are three burnergenerations for rotary kilns:

•• single circuit burnerssingle circuit burners using a long soft flame which was originally suitable for the long kilns as well in the wet as in the dry process;

•• multimulti--circuit burnerscircuit burners developed in order to reduce the primary air supply and to obtain a short, divergent with strong swirl flame suitable for firing pulverised coal; they were introduced in the 1970’s when the kilns became shorter with the use of PRS and PRC and the solid fuels were reused


Low Low NONOxx condition by partition of the primary aircondition by partition of the primary air

HISTORIC BACKGROUND

Until some years ago this type of burner represented the state of the art. The primary airprimary air was divided into a swirl and an axial divided into a swirl and an axial componentcomponent whose relative flow rates allow to modify the flame shape. They can be adjusted via damper. The coal stream was designed for low velocity and high coal concentrationhigh coal concentration.


HISTORIC BACKGROUND

The interior radial air flow was designed to expand the coal andstabilise the flame by generating an internal re-circulation zone. In this manner, it was possible to control the flame shape in conjunction with the constricting effect of the exterior axial air component.


HISTORIC BACKGROUND

• To reply to the increasing environmental needs, at the end of the 80’s a new burner generationa new burner generation was introduced characterised by a slightly longer but less divergent flames. From a combustion point of view the advantages concern:

- the formation of high temperature flames with reduced primary air using high velocities at the burner outlet

- the environmental pollution control by the reduction of NOx concentration.

The experience gained from low NOx burner technology permitted PILLARD to develop ROTAFLAM® burner in which a complete revision of the burner tip geometry was realised.


HISTORIC BACKGROUND

AxialAxial--swirlswirl--core air adjustment during burner operationcore air adjustment during burner operation

The burner includes axial, swirl, core primary air circuits and coal or pet coke circuit. The relative position of each pipe is relative position of each pipe is adjustableadjustable so as to be able to modify the flow rate of each stream and hence enable flame shaping to suit the kiln needs.


HISTORIC BACKGROUND

The revisions were :

• for flame stabilisation a perforated buffer plate was installed in the central part of the burner outlet cross section to induce in-flame flue gas re-circulation in order to guarantee flame stability at its root

• the pulverised fuel channel was relocated to the central part of the burner with respect to the radial and axial channels

• the radial and axial air channels were designed to convert the available pressure of the primary air supply to a maximum tip outlet velocity so as to maximise the momentum necessary for flame control while minimising the primary air flow


HISTORIC BACKGROUND

• the previously designed annular gap for the axial air channel was replaced by a number of slots. The purpose was to maintain perfect concentricity of the axial air channel and to promote the introduction of re-circulated combustion gases into the flame root, thus reducing the local free oxygen content

• an extended outer tube was added to handle the axial air component and thus to prevent premature mixing of the fuel and primary air mixture with hot secondary air.


BURNER GUIDELINESjust an example:

Burners without hot tube extension permit the secondary air secondary air swallowing into the flameswallowing into the flame which reduces the low reduces the low NONOxx performanceperformance

by the way:

Snowman formations enhance hurtful bowl effectsSnowman formations enhance hurtful bowl effects on the outside burner part reducingreducing at the same time thethe combustion efficiencycombustion efficiencyalong the flame axis.


CEMFLAMECEMFLAME, an European consortium of cement producers and associated research organisations, was formed with the purpose of funding research on a scale simulation of an industrial cement kiln. To this aim the effects of fuel type and burner design on NOxemissions have been studied.

It turned out the main main parameters affecting NOparameters affecting NOxx formationformation are:

•• location location of the pulverised coalof the pulverised coal circuitcircuit with respect to the primary air ones

•• air distributionair distribution and intensity of the related momentums, that is local mixing

• location of the ignition point and flame temperature which are directly connected to the locallocal oxygenoxygen concentrationconcentration

HISTORIC BACKGROUND


IN FIELD EXPERIENCES

In order to qualify the low NOx burner design concept, tests have been carried out in two Italcementi Group ’s cement plants (700 and 800 tpd) equipped with Lepol grid and housing two differentROTAFLAM burner prototypes.

In the first set of experiments the original burner (an indirect firedmono channel type firing 100 % petroleum coke) was replaced bya multi-channels low NOx ROTAFLAM burner.

In the second set of experiments a specific burner had been realised to test the effect of the pulverised fuel channel location on NOx emissions at the kiln back end. This ROTAFLAM burner, 100 % pet-coke burning, is characterised by three different ways of coal injection: standard, splitted and staged channels


IN FIELD EXPERIENCES (1st application)




ExperimentalExperimental kiln back endkiln back end total P.A.total P.A. remarksremarkscampaigncampaign deltadelta--NONOxx flow rateflow rate

(% vs. tube b.)(% vs. tube b.) (% (% stoichstoich.air).air)

commissioning 2828 17.5 slight higher heatslight higher heatconsumptionconsumption

1st optimisation 4545 12.5 no problem forno problem forsome weekssome weeks

2nd campaign 5454 11.4 few kiln operatingfew kiln operatingproblemsproblems

final set up 3535 13.6 burner designedburner designedas a compromiseas a compromise




Each point shows the average burner performance obtained with different burner geometry and set-up. Concept of the NONOxx dependence on heat input and burner designdependence on heat input and burner designis evident. SARCHE

ROTAFLAM burner

0

500

1000

1500

2000

2500

3000

3500

4000

1700 1800 1900 2000 2100 2200 2300

PET-COKE FLOW RATE at main burner (kg/h)

NO

x kiln

bac

k en

d (m

g/N

m3 @

0%

O2)

tip #6 different ax / sw

different tips

6

4

5

2

3

1

tip #6comm

tip #1tip #3

tip #7tip #5

tip #4tip #2


35 MW35 MWthth30 Gcal/h30 Gcal/h3.65 t/h pet coke3.65 t/h pet coke10 % total P. Air10 % total P. Air

IN FIELD EXPERIENCES (2nd application)





During the first experimental campaign using the standard standard channelchannel, the burner settings were adjusted to improve the clinker production whilst maintaining clinker quality. NONOx x reductionsreductions in in the order ofthe order of 30 % 30 % were obtainedwere obtained..

In the second experimental campaign the pulverised fuel was released by the splittedsplitted channelchannel. NOx emissions, flame temperature and clinker quality were similar to those obtained using the standard channel. The lack of NOThe lack of NOxx reduction could be explainedreduction could be explained..

In the third experimental campaign the combustioncombustion was stagedstaged(coal in the centre of the burner and in the standard channel).It seemsIt seems possible topossible to obtain lower NOobtain lower NOxx emissionsemissions if burner will be operated at a higher coal concentration.


IN FIELD EXPERIENCES (2nd application)BRONI

pet-coke: 25 - 26 MWth + 0.5 - 0.6 t/h in Lepolraw meal: 50 - 51 t/h

0

500

1000

1500

2000

2500

3000

3500

4000

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

OXYGEN kiln back end (%)

NO

x kiln

bac

k en

d (m

g/N

m3 @

3%

O2)

0

700

1400

2100

2800

3500

4200

4900

5600

CO

kiln

bac

k en

d (m

g/N

m3 @

3%

O2)

previous burner

Rotaflam burner -standard coal channel

NOx

CO



Splitted and staged tests have not given significant NOxreduction with respect to the use of the standard channel also because during the tests two parameters have been changed: the coal concentrationcoal concentration in the transport air and the burner burner positionposition inside the kiln.

The latter aspect is connected to the flame surroundingflame surrounding. In this condition it was evident that the well known phenomenon of flue gas back-circulation affected the NOx emissions. The effect of the re-circulation was proportionally higher with increasing the burner penetration even if a progressively larger kiln diameter kiln diameter affected with synergy the NOx reduction.


IN FIELD EXPERIENCES (2nd application) BRONI - ROTAFLAM burner


0

500

1000

1500

2000

2500

3000

3500

4000

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0

RATIO "coal / equivalent transport air" (kgpet/kgair)

NO

x kiln

bac

k en

d (m

g/N

m3 @

3 %

O2)

0

700

1400

2100

2800

3500

4200

4900

5600

CO

kiln

bac

k en

d (m

g/N

m3 @

3%

O2)

before the tests 2002 132 cm

standard coal 170 cm

standard coal 85 cm

standard coal 32 - 192 cm

splitted coal 228 cm



staged coal 199 cm

staged coal 147 cm

staged coal 85 cm

CO

NOx

STANDARD andSPLITTED COAL

STAGED COAL


IN FIELD EXPERIENCES (2nd application)BRONI - ROTAFLAM burner


0

500

1000

1500

2000

2500

3000

1.60 1.65 1.70 1.75 1.80 1.85 1.90 1.95 2.00 2.05 2.10 2.15 2.20 2.25 2.30 2.35 2.40

RATIO "coal / equivalent transport air" (kgpet / kgair)

NO

x kiln

bac

k en

d (m

g/N

m3 @

3%

O2)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

CO

kiln

bac

k en

d (m

g/N

m3

@ 3

% O

2)

burner at 23-85 cm

burner at 110 cm

burner at 170 cm


IN FIELD EXPERIENCES (1st application)SARCHE - ROTAFLAM burner (20-21 MWth)

pet-coke: 2.1-2.2 t/h + 0.6-0.7 t/h in LepolLepol grid velocity: 50-52 %

0

500

1000

1500

2000

2500

3000

3500

4000

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6OXYGEN kiln back end (%, wet)

NOx k

iln b

ack

end

(mg/

Nm3

@ 3

% O

2)

0

700

1400

2100

2800

3500

4200

4900

5600

CO k

iln b

ack

end

(mg/

Nm3 @

3%

O2)

main burner: 2 m travelled back

main burner: 1 m travelled back

main burner: totally inserted

CO

NOx




BURNER PERFORMANCES

NONOxx concentration is not the only pollutantconcentration is not the only pollutant to be taken into account. CO and SOCO and SO22 are likewise importantare likewise important from an emission control standpoint, but also in particular for guaranteeing high combustion efficiencies which in turn mean low heat consumption. NONOxx, CO and SO, CO and SO22 are each other dependent.are each other dependent.

PORTO EMPEDOCLE - Kiln #2ITC three-circuit burner

0

100

200

300

400

500

600

700

800

900

1000

0 1000 2000 3000 4000 5000 6000 7000

CO (ppm as measured)

NO

x (p

pm a

s m

easu

red)

0

50

100

150

200

250

300

350

400

450

500

SO2 (

ppm

as

mea

sure

d)

NOx

SO2


In the previous figures the CO concentrations are better correlated with the excess air than the coal / transport air ratio.

It can be noted that the “smoking point”“smoking point” (i.e. the oxygenconcentration at which the CO concentration begins to increase progressively) is very lowvery low.

This is due to an highhigh combustion combustion efficiencyefficiency permitted by theROTAFLAM ROTAFLAM burnerburner as a consequence of its particular flexibilityin guaranteeing the correct and optimum burner set-up suitablesuitablefor for satisfying different kiln operatingsatisfying different kiln operating conditions.conditions.

BURNER PERFORMANCES


LESSON LEARNED

•• NONOxx concentrationconcentration depends mainly on the coal / transport air ratio for a certain specific heat input and burner position

BRONI - New Pillard kiln burnerstandard coal tests

1.61.8

2

2.2

2.4

0.60.8

11.2

1.41.6

1.8

2

1,500

1,700

1,900

2,100

2,300

2,500

1,500

1,700

1,900

2,100

2,300

2,500

1.61.8

2

2.2

2.4

coal / transport air ratio (kg/kg)

0.60.8

11.2

1.41.6

1.8

2

Oxygenkiln back end (% )

1,500

1,700

1,900

2,100

2,300

2,500NOx kiln b.e.(m g/Nm 3 @ 3% O 2 )

1,500

1,700

1,900

2,100

2,300

2,500NOx kiln b.e.(m g/Nm 3 @ 3% O 2 )

NO x concentration2,500+2,400 to 2,5002,300 to 2,4002,200 to 2,3002,100 to 2,2002,000 to 2,1001,900 to 2,0001,800 to 1,9001,700 to 1,8001,600 to 1,7001,500 to 1,600

110 cm

170 cm

1.61.8

2

2.2

2.4

0.60.8

11.2

1.41.6

1.8

2

1,500

1,700

1,900

2,100

2,300

2,500

1,500

1,700

1,900

2,100

2,300

2,500

23-85 cm


LESSON LEARNED

•• CO CO andand SOSO22 concentrationsconcentrations are consistent with the available excess air and they can be controlled, to a certain extent, by an ad-hoc set-up of the outer air flows (axial and radial)

NAZARETH #1 - ROTAFLAM burner(axial air 6,750 Nm3/h)

-1000

-500

0

500

1000

1500

2000

2500

3000

3500

4000

0 1 2 3 4 5 6 7 8 9 10 11 12


NO

x kiln

bac

k en

d (m

g/N

m3 @

6%

O2)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

CO

kiln

bac

k en

d (m

g/N

m3 @

6%

O2)

meal 300-310 st/h; 150 MWth



radial air2,650 Nm3/h



CO

NOx


BURNER GUIDELINES

Swirl level Swirl level is a parameterdeeply affectingaffecting the flameflameandand the combustioncombustion. The greatdifference between a mono tube and a multi-circuit burneris evident so as for the swirlerintensity. It is a good toolgood tool forflame control and coating pro-tection butbut it is often misusedoften misused.Operators have opposing viewon appropriate flame shapes and they make too many and too many and frequent hurtful adjustmentsfrequent hurtful adjustments.

No swirl

Regular swirl

High swirl


LESSON LEARNED

NAZARETH #1 - 100% coal at main burnercommissioning ROTAFLAM burner

-1000

-500

0

500

1000

1500

2000

2500

3000

3500

4000

0 1 2 3 4 5 6 7 8 9 10 11 12


NOx k

iln b

.e. (

mg/

Nm3 @

6%

O2)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

CO k

iln b

.e. (

mg/

Nm3 @

6%

O2)

coal 15.8 t/h; meal 220 - 225 st/h coal 17.3 t/h; meal 240 - 280 st/h coal 15.7 t/h; meal 230 - 260 st/h coal 16.5 t/h; meal 240 - 255 st/h

axial air 5,600 Nm3/hradial air 3,300 Nm3/h

axial air 6,700 Nm3/hradial air 2,400 Nm3/h

NOx

CO


BURNER GUIDELINES

Mathematical modelling helpsMathematical modelling helps to studyto study the aerodynamic of the near field of the burner and to solveand to solve the relative problems.Figures show how the bowl effect (and consequently the expected wear problem) can be modified by shortening the hot outer tube and changing the axial air flow rate.


LESSONS LEARNED

• The flame surroundingflame surrounding, due to the burner penetrationburner penetration in the kiln, could produce an in-flame flue gas back-circulation whichin turn gives an efficient NOx reduction because the oxygenconcentration at the flame root is reduced, practically where the volatile matters are released and NOx are formed.



1.61.8

22.2

2.4

0.60.8

11.2

1.41.6

1.8

2

1,700

1,900

2,100

2,300

2,500

2,700

2,900

3,100

1,700

1,900

2,100

2,300

2,500

2,700

2,900

3,100

NOx kiln back end2,500+2,400 to 2,5002,300 to 2,4002,200 to 2,3002,100 to 2,2002,000 to 2,1001,900 to 2,0001,800 to 1,9001,700 to 1,8001,600 to 1,7001,500 to 1,600

1.61.8

22.2

2.4coal / transport air ratio (kg/kg)

0.60.8

11.2

1.41.6

1.8

2

Oxygenkiln back end (%)

1,700

1,900

2,100

2,300

2,500

2,700

2,900

3,100

NO x kiln b.e.(mg/Nm 3 @ 3% O 2

1,700

1,900

2,100

2,300

2,500

2,700

2,900

3,100 NO x kiln b.e.(mg/Nm 3 @ 3% O 2)

214 - 228 cm

131 - 132 cm


CONCLUSIONS

The above mentioned scheme confirms what has been found in other recent applications and it shows the common way for “reading” the kiln emissions

K ILN B U R N ER SC om pariso n am o ng d ifferent ap p lications

0

500

1000

1500

2000

2500

3000

3500

4000

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0

R AT IO "coal / equiva lent transp o rt a ir" (kg coal / kg air)

NO

x kiln

bac

k en

d (m

g/N

m3 @

6 %

O2)

0

600

1200

1800

2400

3000

3600

4200

4800

CO

kiln

bac

k en

d (m

g/N

m3 @

6%

O2)

P IC TO N 125 M W th m eal 220 - 235 t/h

N AZAR ETH #1 115 M W th m eal 215 - 225 t/h




G AUR IN #4 113 M W th m eal 325 - 335 t/h

BR O N I 25 M W th m eal 48 - 50 t/h 32 - 200 cm

BR O N I 25 M W th m eal 49 - 50 t/h 85 cm

C O

N O x


CONCLUSIONS

NONOxx formation depends on formation depends on different parametersdifferent parameters, a fewamong them are typical ofthe clinker process.Consequently manipulationof combustion process doescombustion process doesnot always producenot always produce the expected results on NONOxxcontrol.control.Therefore each kilneach kiln--burnerburnerarrangement has to be apartarrangement has to be apartconsideredconsidered and optimised.


Documents

Pillard Low NOx