15103 nox formation - large natural gas boilder

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OBSER VATIO NS OF NO FORMATION IN TWO LARGE NATURAL GAS FIRED BOILERS

Verle V. Bland

Stone and Webster Engineering Corporation

7677 East Berry Avenue

Englewood, Colorado 80111

Phone: 303 741 7684

Email: [email protected]

John P. Guarco & Tom V. Eldredge

Todd C ombustion / John Zink Co.

2 Armstrong Roa d, 3 d Floor

Shelton, Connecticut 06484

Phone: 203 925 0380



A B S T R A C T

Nitrogen oxides NOx), a major source of ozone pollution, are

comprised of two major components; nitrogen oxide NO) and

nitrogen dioxide NO2). The formation of nitrogen dioxide NO2) in

combustion systems has attracted considerable attention over the last

several years because of relatively high levels of NO2 measured in

the exhaust of some combustors. The formation of NO2 has been

studied in small scale combustors, and reactions for the formation

and destruction of NO2 have been postulated. This paper describes

the results of measured NO2 and NO emissions on two 24 burner

natural gas fired boilers. For the first boiler, data was recorded over a

range of excess oxygen 02) levels and over-fire air OFA) settings.

Other staging methods, such as burner out of service BOOS)

operation and fuel bias ing were also investigated on the first boiler.

For the second boiler, data was recorded for a range of excess oxygen

02) levels, separated over-fire air SOFA) settings, and flue gas

recirculation FGR) levels. These results suggest that NO2 formation

is a strong function of OFA setting as well as a strong function of 02

level. This is consistent with published data from a laboratory scale

combustor, which found NO2 emissions to increase significantly as

the equivalence ratio was raised above one, to create a fuel rich

envi ronment near the flame. The presented data do not indicate that

NO2 formation was strongly affected by FGR levels. The presented

data also indicate that there may be an upper limit on the amount of

NO2 created in a fuel rich flame.

NOMENCLATURE

BNF - Burners not firing - no fuel, air doors closed.

BOOS - Burners out of service- no fuel, air doors open.

FGR - Flue gas recirculation.

NO, NO2 - Nitrogen oxide, nitrogen dioxide respectively.

NOx

-

Nitrogen oxides total).

02 - Excess oxygen.

OFA - Over-fire air.

SOFA - Separated over fire air, no FGR mixed with the OFA.

I N T R O D U C T I O N

The formation of nitrogen dioxide NO2) in combustion system

has attracted considerable attention over the last several year

because o f relatively high levels of NO2 measured in the exhaust o

practical combustors, such as gas turbines, natural gas furnaces

diesel and spark ignition engines, and laboratory combustion systems

Generally, in relatively unstaged commercial combustors,

NO

accounts for between 5 and 10 percent of total NOx emissions, wit

NO accounting for the remainder.

NO2

is more toxic than NO

therefore NO 2 emissions are of concern for unflued space heaters

NO2 emitted by combustors also has a direct impact on smo

formation; and if concentrations are high enough, NO2 can impart

coloration to the stack plume.

Under certain operating conditions for natural gas-fired furnace

the fraction of NOx that is NO2 can be significantly more than 1

percent. In order to understand why certain boiler operating setting

produce significant amounts of NO2, it is important to understand th

physical mechanisms by which NO2 is produced. Hori 1986

conducted chemical kinetics calculations using 29 gas phas

reactions, and found that NO2 was formed and destroyed by th

following reactions:

R e a c t i o n o f F o r m a t i o n

NO

+ HO2 =

NO2 + OH 1)

Reactions for Destruction

NO 2 +

H = NO + OH 2)

NO2 + O = NO + 02 3)

A study by Merrym an and Levy 1975) showed significa

NO 2 levels in the flame front followed by the apparent conversion o

Proceedings of2000 International Joint Power Generation Conference

Miami Beach, Florida, July 23-26, 2000

IJPGC2000-15103

1 Copyright (C) 2000 by ASME



NO2 back to NO in the near post flame region. At typical flame

temperatures the ratio of NO2/NOx should be negligibly small,

because the reaction rates for destruction are high, even at relatively

low temperatures. Therefore, NO: exists only as a trans ient species at

flame temperatures. However, studies have shown that rapid cooling

of hot combustion gas by mixing with cold air can result in

significant levels of NO2. Cernansky (1977) indicated that a possible

reason for the NO2 in practical combustors is the NO-NO2 conversion

during rapid quenching of turbulent eddies. Sano (1984) computed

NO

concentrations in the mix ing region of hot gas and cold air, and

maximum values of NO2 were found in the temperature range of 800

to 900°K. Hori (1986, 1988) conducted experiments on double

concentric jets and on a swirl burner, and claims that his

measurements prove that NOz can be formed by turbulent mixing of

hot combustion gases and cold air.

These findings may suggest that there are two effects resul ting

from the quenching. First, the NO2 formation reaction may occur

more readily, because quenching may result in a more abundant

supply of the HO2 radicals, because reactions, other than (1) above,

which use up HO2 do not proceed below a threshold temperature.

Secondly, quenching the hot combustion gases likely freezes the

NO2. That is, the destruct ion reactions, (2) and (3) above, do no t

proceed because the temperature is below a critical threshold value.

The most important result of this discussion is that it is known that

NO2 can result in practical combustors from quenching of hot

combustion gases.

Hori (1988) also observed two other results, which are

noteworthy. He found that the NOE/NO~ ratio was highest under fuel -

rich and fuel-lean extremes. Hori (1988) concluded that the relatively

high initial concentration of NO is the primary reason for increased

NO2 levels under fuel-lean conditions. Under fuel-rich conditions it

was concluded that the additional supply of radicals and unbumt

species (CO, H:, and hydrocarbons) result in higher levels of the HO2

radical which in turn results in higher levels of NO:.

C A S E S T U D Y 1

Uni t De s c r ipt ion

The first unit on which the magnitude of the NO2 phenomenon

has been investiga ted was a Babcock & Wilcox El Paso style,

opposed wall-fired, na tural circulation, forced draft design, rated to

supply steam to a 345 MW turbine generator. This unit is depicted in

Fig. 1. The combustion equipment was comprised of 24 bumers and

12 over-fire air (OFA) ports. Each wall had two elevations of six

burners below one elevation of six over-fire ports. Natural gas, the

primary fuel, is fired in the 24 TODD Combustion Dynaswirl-LNR

low NOx burners. These 24 burners using advanced steam atomizer

sprayer plates can also inject residual fuel oil, the secondary fuel. The

results, which form the subject of this paper, were obtained firing

natural gas only.

R e s u l t s a n d D i s c u s s i o n

As stated above, NO 2 and NO emissions were measured for a

range of excess oxygen (02) levels, over fire air settings, and flue gas

recirculation (FGR) levels. The data were taken with the unit

operated at 345 MW. The NOx and NO2 data were corrected to a 3%

02 level on a dry basis.

~'-a.

m

J

ca m ¢o~A m RUUe--UNm~ ~ JJO ;

Figure 1 - 345M W Bo iler

Figure 2 shows the effect of the flow through the OFA ports o

both NOx and NO2. As expected, opening the OFA ports was ver

effective at reducing overall NOx. It should be noted that the OF

ports were supplied with a combustion air/FG R mixture. The % OFA

flow represents the percentage of the total combust ion air/FG

mixture that was passed through the OFA ports.

45 8

40

35

30

~ 25

g 2o

z

15

10

5

j -

L ox o °o 2ppmo t

0 I I I I I

0 % 5 % 1 0 % 1 5 % 2 0 % 2 5 %

O F A %

1

0

3 0 %

Figure 2 - Effect of OFA Flow on NOx and NO2

5

¢

4 0

0

3 z




F i g u r e 3 s h o w s t h e e f f e c t s o f 0 2 o n t o t a l N O x a n d N O 2

emiss ions . I t shou ld be no ted tha t fo r the O2 tes t s the re were va r ious

l e v e l s o f O F A f l o w , w h i c h p r o v i d e d q u e n c h i n g o f t h e h o t c o m b u s t i o n

g a s e s . A s e x p e c t e d , l o w e r i n g t h e 0 2 l e v e l d e c r e a s e d t o t a l N O x

emiss ions .

4 5 -

40

3 5

~. 30-

e¢

O 25 -

Z

~

20

<

~

15

o

z

1 0

• . Ae.

I NOx ppmc • NO2 I

1.00

• • A • • •

- I [~ - , • - _

• Ll I I t I t

1.50 2.00 2.50 3.00

E x c e s s 02 . %

Figure 3 - Effect of O2 Level o n NOx and NO2

3.50

Figu re 4 shows tha t dec reas in g O2 leve l inc reased the NO2/NOx

r a t io . I t w a s e x p e c t e d t h a t t h e N O J N O x r a t i o w o u l d i n c r e a s e d u e to

the NO decreases , bu t a s shown in F ig . 3 , lower ing the 02 leve l a l so

ra ised the NO2/NOx ra t io because NO2 inc reased . Lower ing the O2

l e v e l c r e a t e d a m o r e f u e l - r i c h e n v i r o n m e n t w h i c h r e s u l t s i n m o r e

NO2, cons is ten t wi th Hor i ' s (1986 , 1988) f ind ings .

0.40

0 . 3 5

0 . 3 0

0.25

0 . 2 0

O

Z

0.15

0.10

0 . 0 5

0 . 0 0

' ' . . ~ . . , . , •

% . ' , . •

. 2 -

\

\ , ~ , . , , .

0.00 0.50 1.00 1.50 2.00 2.50 3.00

E x c e s s 02, %

Figure 4 - Effect of 02 Level and OF A % on NO2/NOx

F i g u r e 4 a l s o s h o w s t h e e f f e c t o f o p e n i n g t h e O F A p o r t s o n t h e

N O 2 /N O x r a t i o . W i t h t h e O F A d a m p e r s c l o s e d , t h e f r a c t i o n o f N O n

tha t was NO2 was le ss than 10 pe rcen t , bu t wi th 18-24 pe rcen t OFA

f l o w , t h e f r a c ti o n o f N O x t h a t w a s N O 2 w a s a p p r o x i m a t e l y 3 0

percen t . P r io r to ana ly s is o f the da ta , i t was e xpec ted tha t the

N O 2 /N O x r a t i o w o u l d i n c r e a s e a s N O d e c r e a s e d w h e n t h e O F A f l o w

w a s r a i s e d , ; b u t a s s h o w n i n F i g . 2 , r a i s i n g t h e O F A f l o w a l s o r a i s e d

the NO2/NOx ra t io because NO2 is inc reased , even though overa l l

N O x l e v e l s a r e r e d u c e d . T h e r e fo r e , O F A f l o w h a d a s i g n i f i c an t ef f e c t

o n l o w e r i n g t o ta l N O x e m i s s i o n s a n d o n i n c r e a s i n g N O 2 f o r m a t i o

O p e n i n g t h e O F A d a m p e r s h a d t w o e f f e c t s , o n e i t c r e a te d a f u e l r i c

e n v i r o n m e n t i n t h e f l a m e f r o n t a n d t h e n e a r - f l a m e r e g i o n . S e c o n d l

i t p r o v i d e d q u e n c h i n g o f t h e h o t c o m b u s t i o n g a s e s b y t h e m i x i n g o

t h e r e l a t i v e l y c o o l O F A f l o w . T h e r e f o re , t h e r e c o r d e d e f f e c t

o p e n i n g t h e O F A d a m p e r s o n i n c r e a s i n g N O 2 i s c o n s i s t e n t w i

H or i ' s (1986 , 1988) f ind ings .

W i t h t h e O F A p o r t s s e t t o d e l i v e r 1 8 -2 4 % O F A f l o w , f u r th e

s t a g i n g o f th e f u e l a n d a i r w a s i n v e s t i g a t e d . T h e t e c h n i q u e

i m p l e m e n t e d t o f u r t h e r s t a g e t h e b o i l e r w e r e b u r n e r o u t o f s e r v i c

( B O O S ) o p e r a t i o n (n o f u e l , b u r n e r a i r d o o r s o p e n ) , b u r n e r s n o t f i r i n

( B N F ) o p e r a t i o n ( n o f u e l, b u r n e r a i r d o o r s c l o s e d ) a n d f u e l b i a s i n g

F i g u r e 5 s h o w s t h e e f f e c t o f 0 2 o n N O x a n d N O 2 f o r m a t i o n w h e

t h e s e f u r t h e r s ta g i n g t e c h n iq u e s w e r e i m p l e m e n t e d . F i g u r e

i n d i c a t e s t h a t N O × a n d N O 2 f o r m a t i o n h a v e r e l a t i v e l y s i m i l a

r e a c t i o n s t o 0 2 w h e n f u r t h er s t a g i n g w a s i m p l e m e n t e d a s w h e

o p e r a t e d u n d e r t h e 1 8 - 2 4 % O F A o n l y b a s e l i n e c o n d i t i o n .

4 5 .

4O

35

•

3 0 -

o.

25

0

z

•

2 0 -

~ 1 5 -

z

10

r e ' # W

,~ BOOS/BNF NOx • FUEL BIAS NOx • 18-24%OFA NOx /

O BOOS/BNF NO2 Q FUEL BIAS NO2 z~ 18-24%OFA

NO2

°

~ ' $ . o o

5

C~b'° '~ - ~ . . . . ?

0

0.00 0.50 1.00 1.50 2.00 2.50 3.00

E x c e s s 02, %

3.50

Figure 5 - Effect of 02 L evel on NOx and NO2 with F urther

Staging.

0.50

0.45

0.40

0.35

x 0 . 3 0

o

0.25

0

Z 0.20

0.15

0.10

0.05

0.00

0.00

• BNF = FUEL BIAS & 18-24%OFA oBOO S }

&

A L 0

~ ' ~ . , . ~ o . ? . .

° % . . . .

0.50 1 (30 1.50 ZOO 2.50 3.00 3.50

E x c e s s 02 , %

Figure 6 - Ef fect of O= Leve l on NOzlNOx wi th Further

Staging.

F i g u r e 6 s h o w s t h e e f f e c t o f 0 2 o n N O 2 / N O x w h e n t h e s e f u r t h e

s t a g i n g te c h n i q u e s w e r e i m p l e m e n t e d . F i g u r e 6 i n d i c a t e s t h a t w h i l




BNF operation and fuel biasing did not increase the level of

NO2/NO~ as compared to the baseline condition, BOOS operation did

in fact increase the level of NO2/NO~ for a give O2, as compared to

the baseline condition,. This is indicated by the dashed line.

An important note should be inserted here regarding the

minimum levels of O2 for each curve. During this testing, as well as

all subsequent testing, the minimum O2 level for each operating

condition was dictated by the level of carbon monoxide (CO)

formation. The testing was conducted in such a way that the CO

generally remained in a controlled region of below 400 ppm. With

this in mind, Fig. 6 indicates that for BOOS operation, while the

curve of the NO2/NOx ratio as a function of 02 did increase, the

overall maximum level did not increase, the curve was just shifted

rightward along the O2 axis. This indicates that there may be a

maximum NOz/NOx level that is created while keeping CO under

control.

CASE STUDY #2

Unit Description

The second uni t investigated was a Babcock & Wilcox El

Paso style, opposed wall-fired, natural circulation, forced draft

design, rated to supply steam to a 325 MW turbine generator. The

unit is depicted in Fig. 7. The combustion equipment was comprised

of 24 burners and 8 separated over-fire air (SOFA) ports. SOFA

differs from OFA in that OFA has FGR mixed with the combustion

air flow, whereas with SOFA flow the SOFA air is separated from

the combustion air upstream of the FGR mixing station, therefore

there is no FGR in the SOFA flow. Each wall had three elevations of

four burners below one elevation of four SOFA ports. Natural gas,

the primary fuel, was fired in the (24) TODD Combustion Dynaswirl-

LNR low NOx burners. These 24 burners using advanced steam

atomizer sprayer plates can also inject residual fuel oil, the secondary

fuel. The results, which form the subject of this paper, were obtained

firing natural gas only.

Results and Discussion

As stated above, NO2 and NO emissions were measured for a

range of O2 levels, over fire air settings, and FGR levels. The data

were taken with the unit operated at 290 MW, except for a few tests

conducted at 212 MW. The NOx and NO2 data were corrected to a

3% 02 level on a dry basis.

Figure 8 shows the effect of the flow through the SOFA ports on

NOx emissions for various 02 and FGR levels. As expected, opening

the SOFA ports was very effective at reducing overall NOx. It should

be noted that the SOFA dampers were supplied with pure

combustion air, there was no FGR mixed with the SOFA flow. The

%SOFA flow represents the percentage of the total combustion air

that was passed through the SOFA ports. Figure 5 shows the effect of

opening the SOFA ports on NO2 formation. With the SOFA dampers

closed, the fraction of NOx that was NO2 was less than 10 percent,

but with 18 percent SOFA flow, the fraction of NO~ that was NO2

was approximately 30 percent. It is expected that the NO2/NO~ ratio

will increase because NO decreased as the SOFA flow was raised,

but as shown in Fig. 9, raising the SOFA flow also raises the

NO2/NOx ratio because NO2 is increased. Therefore, as with Cas

Study #1, SOFA flow has a signi ficant effect on lowering total NO

emissions and on increasing NO2 formation. Opening the SOF

dampers had the same two effects, one it created a fuel ric

environment in the flame front and the near-flame region. Secondly

it provided quenching of the hot combustion gases by the mix ing o

the relatively cool SOFA flow. Therefore, the effect of opening th

SOFA dampers on increasing NO2 is consistent with Hor i's (198

1988) findings. Comparing Figures 4 and 9, there was no noticeab

difference between the effects o f OFA or SOFA on NOJNOx.

70

£NClNA POW[R ~- -U ~I T NO 4

CALIF~NI&

OGW ~ rR,SCT NO IqB-477

F ig u r e 7 - 3 2 5 MW B o i le r

E -4 5 6

60

5O

~ 4o

=

30

2

20

10

0

• Econ. 02:1 .65 - 1.88% FGR: 24.7 - 25.8% |

J

Econ 02:2. 47 - 2,66% FGR: 22.8 -23.4

5 1 0 15

% SOFA F l o w

F ig u r e 8 - E f f e c t o f SO F A F lo w o n N O x

2




0 , 3 5

0 . 3

0 . 2 5

0 . 2

z

Oz 0.15

0 . 1

0 . 0 5

0

Effect if SOF A Only= Lowers NO

I e E c o n . O 2 : 1 . 6 5 - 1 , 8 8 % F G R : 2 4 . 7 - 2 5 . 8 %

A E c o n

0 2 : 2 . 4 7 - 2 . 6 6 % F G R : 2 2 . 8 - 2 3 . 4 %

5 1 0 1 5

% S O F A

F l o w

F i g u r e 9 - E f f e c t o f S OF A F l o w o n NOz /NOx

I

2 0

Figures 10 and 11 show the effects of 02 on total NOx and NO2

emissions. It should be noted that for the 02 tests there were various

levels of SOFA flow, which provided quenching of the hot

combustion gases. As expected, lowering the 02 level decreased total

NOx emissions. Figure 11 shows that decreasing 02 level increased

the NOE/NOx ratio. It is expected that the NO2/NOx ratio would

increase because NO decreases, but as shown in Fig. I l lowering the

02 level also raised the NOE/'NOx ratio because NO2 increased.

Lowering the 02 level creates a more fuel-rich envi ronment which

results in more NO2, consistent with Hori' s (I 986, 1988) findings.

50

4 5

4O

35

o 30

o. 25

ff

o

z 20

1 5

10

5

0

• SO FA: 17,5% FG R: 23 - 25.8%

IISO FA: 15.8 - 18.3% FG R: 15.1 - 15.8%

&S OFA : 10% FGR: 22,8 - 24.7%

0.5 1 1 .5 2 2 .5 3

E c o n o m i z e r 0 2 ( % )

F i gu re 1 0 - E f f ec t o f O2 l ev e l o n N O x

3.5

Figures 12 and 13 show the effects of FGR level on total NOx

and NO2 emissions respectively. As expected, raising the FGR level

lowers total NOx emissions, but there appears to be very little effect

on NO2 emissions. Some of the data presented in Fig. 13 appear to

show some small changes in NO2 as the FGR level is increased, bu t

the observed changes were essential ly within the accuracy range of

the instrument. The ratio of NO2/NO× was typically observed to

increase with increasing FGR level because NO2 essentially remained

constant while NO decreased, as presented in Fig. 14. This effect is

also shown in Fig. I 1 by comparing results for the firs t two data

series ( • and • symbols), which were collected at comparable

SOFA levels. Therefore, these data do not suggest a strong effect o

FGR on total NO2 emissions, since the change in NO2/NOx rat

observed is due to the affect of FGR on the NO emiss ions level.

0 . 3 5

0 . 3

0 . 2 5

0 . 2

z

z 0 .15

0.1

0 . 0 5

Effect i f 02 Only Increases NO

and NO2 remains constant

Effect if 0 2 On ly Inc re as es N O ~

e n d N O2 re m a i n s c ~ s t a n t & \ % ~

• SOFA: 17.5% FGR: 23- 28.6%

B- SO FA : 15.8 - 16,3% FGR : 15.1 - 15.8%

-~r SOFA: 10% FGR: 22.8 - 24.7%

0 0.5 1 1 .5 2 2 .5 3

E c o n o m i z e r 0 2 ( % )

F i gu re 1 1 - E f f ec t o f 0 2 l ev e l on N O21N Ox

3.5

70

60

5O

~ 4o

O 30

z

20

10

0

-a=-290 MW SOFA: 16.3% 02 :2.6 9 - 3 .06%

--11-212 MW SOFA : 1.4 - 1.8% 0 2:1 .56 - 1.75%

-11-212 MW SOFA: 9 .8 - 10.6% 0 2:1.4 5 - 1 ,64%

5 1 0 1 5 2 0 2 5 3 0

% FGR

Figure 12 - E f fect o f FGR leve l on NOx

1 0 -

3 5

o

Q.

O

z

8-

6

0

0

- e -29 0 MW SOFA: 16.3% 02 :2.89 - 3.06%

-11--212 MW SOFA: 1.4 - 1.8% 02 :1.56 -1.75 %

-i lk- 212 MW SOFA: 9.8 - 10.6% 02:1.4 5 - t .64%

-e- 315 MW SOFA: 19.8-21.4% 02:1,92-2.17%

5 10 15 20 25 30 35

% FGR

Figure 13 - E f fect o f FGR leve l on NO2




0.35

3 [

0.25

0.2

z 0.15

0.1

0.05

0

-A-2 90 MW SOFA: 16.3% 02 :2.89 - 3.06%

-e -2 12 MW SOFA: 1.4 - 1.8% 0 2:1 .56 - 1.76%

-11-212 MW SOFA: 9.8 - 10,6% 02: 1.4 5 - 1.64%

-4-- 315 MW SOFA: 19.8 - 21.4% 02:1.92 - 2.17%

A

0 5 10 15 20 25 30 35

% F G R

Figur e 14 - Ef fect of FGR lev el on NO2/NOx

C O N C L U S I O N S

Two la rge sca le na tu ra l gas f i red bo i le rs were inves t iga ted as to

t h e e f f e c t o f d i f f e r e n t o p e r a t i n g p a r a m e t e r s o n N O 2 f o r m a t i o n a n d

N O 2 /N O x r a t i o . T h e f i n d i n g s p r e s e n t ed s h o w t h a t O F A f l o w , w h e t h e r

m i x e d w i t h t h e F G R f l o w o r n o t , a n d e x c e s s 0 2 l e v e l b o t h h a v e

s i g n i f ic a n t e f fe c t s o n N O 2 f o r m a t i o n , d u e m a i n l y t o t h e l o c a l i z e d

e f f e ct s o f f u e l r i c h c o m b u s t i o n . O u r d a t a s h o w t h a t r a i s i n g t h e

O F A / S O F A f l o w s i g n i f i c a n t ly i n cr e a s e s N O 2 e m i s s i o n s a n d t h e

N O 2 /N O x r a t i o. O p e n i n g t h e O F A / S O F A d a m p e r s h a s t w o e f f e ct s ,

one i t c rea tes a fue l r ich env i ronment in the f lame f ron t and the nea r -

f l a m e r e g i o n . S e c o n d l y , i t p r o v i d e s q u e n c h i n g o f h o t c o m b u s t i o n

g a s es b y t h e m i x i n g o f r e l a t iv e l y co o l O F A / S O F A f l o w .

W h e n o p e r a t i n g a t 1 8 - 2 4 % O F A f l o w , f u r t h e r b i a s i n g

t e c h n i q u e s , s u c h a s B O O S , B N F a n d f u e l b i a s i n g , s h o w l i t t l e

n o t i c e a b l e d i f fe r e n c e i n e i t h e r t h e o v e r a l l N O x o r t h e N O 2 e m i s s i o n s .

H o w e v e r , B O O S o p e r a t i o n d i d t e n d t o f u r t h e r i n c re a s e t h e N O 2/ N O x

r a t io f o r a g i v e n 0 2 l e v e l , b u t t h e m a x i m u m v a l u e r e c o r d e d d i d n o t

i n c r e a s e . T h e c u r v e h a d j u s t s h i f t e d r i g h t w a r d a l o n g t h e e x c e s s 0 2

a x i s. T h i s i n d i c a t e s t h a t t h e r e m a y b e a n u p p e r l i m i t o n t h e a m o u n t

o f N O 2 c r e a t e d i n a f u e l r i c h f l a m e w h e n k e e p i n g C O u n d e r c o n t r o l.

L o w e r i n g t h e 0 2 l e v e l c r e a t e s a m o r e f u e l - r i c h e n v i r o n m e n t ,

w h i c h r e s u l ts i n m o r e N O 2 . T h e r e f o r e, t h e e f f e c ts o f o p e n i n g t h e

O F A / S O F A d a m p e r s a n d l o w e r i n g e x c e s s O2 b o t h w e r e o b s e r v e d to

inc rease NO2 emiss ions and the NO2/NOx ra t io , wh ich i s cons is ten t

wi th Hor i ' s (1986 , 1988) f ind ings .

T h e d a t a s u g g e s t t h at F G R h a s a n e g l i g i b l e e ff e c t o n N O 2

e m i s s i o n s . T h e N O 2 / N O x r a t i o i n c r e a s e s w i t h i n c r e a s i n g F G R

b e c a u s e o f t h e a f f ec t o f F G R o n r e d u c i n g N O e m i s s i o n s .

R E F E R E N C E S

Cernansk y , 1977 , N. P . , P ro~;ress in As t ron . and A eron . , Vo l . 53 ,

( B . T . Z i n n, E d . ) , p . 8 3 , A I A A

H o r i , M . , 19 8 6, E x p e r i m e n t a l S t u d y o f N i t r o g e n D i o x i d e

F o r m a t i o n i n C o m b u s t i o n S y s t e m s , T w e n t y F i r s t S y m p o s i u m

(In te rna t iona l ) on Com bus t ion , p . 1181-1188 , The Com bus t ion

Ins t i tu te

H o r i , M . , 1 9 8 8, N i t r o g e n D i o x i d e F o r m a t i o n b y th e M i x i n g o f

H o t C o m b u s t i o n G a s w i t h C o l d A i r , T w e n t y S e c o n d S y m p o s i u m

( I n t e r n a ti o n a l ) o n C o m b u s t i o n , p . 1 1 7 5 - 1 1 8 1 , T h e C o m b u s t i o

Ins t i tu te

M e r r y m a n , E . L . a n d L e v y , A . , 1 9 7 5 , F i f t e e n t h S y m p o s i u

( In te rna t iona l ) on Com bus t ion , p . 1073 , The Com bus t io n Ins t i tu te

Sano , T . , 1984 , Comb us t ion Sc ien ce and Tech no log y , 38 , 129


15103 nox formation - large natural gas boilder

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