THE EFFECT OF RESIDENCE TIME

ON SNCR PROCESSES

L. J. Muzio

T. A. Montgomery

G. C. Quartucy

Fossil Energy Research Corp.

D. P. Teixeira

Pacific Gas and Electric Company

presented at

EPRIIEPA 1993 Joint Symposium

on Stationary Combustion NOx Control

Bal Harbor, Florida

May 24-27, 1993
THE EFFECT OF RESIDENCE TIME

ON SNCR PROCESSES

L. J. Muzio

T.~.Montgo~ery

G. C. Quartucy

Fossil Energy Research Corp.

23342 C South Pointe

Laguna Hills, C~ 92653

D. P. Teixeira

Pacific Gas and Electric Company

3401 Crow Canyon Rd.

San Ramon, C~ 94583

Abstract

pilot-scale experimental study was perfor~ed to determine the effect of residence

ti~e on SNCR processes. Test results showed that residence times less than 250 msec

adversely impact process performance. Further, the test results showed that NO

re~oval was faster with either anhydrous or aqueous a~onia injection than with

aqueous urea injection. The results also showed that short residence times can lead to

higher N20 emissions since N20 reduction reactions do not have sufficient time to

reduce N20. Che~cal kinetic calculations were in qualitative agreement with the pilotscale test results.

Introduction

Interest in the use of selective non catalytic NOx reduction (SNCR) is increasing within

the utility industry. This has resulted in a variety of applications where the SNCR

te~perature window occurs both in the main radiant furnace and within the furnace

convective sections. When the temperature window is in the convective sections,

chemical injection is limited to the cavities between convective tube banks. Depending

on the specific furnace design, residence times in these convective cavities can range

fro~ 30 to 100 milliseconds. These short cavity residence times, coupled with steep

te~perature gradients, can limit potential NOx removal performance.

While an extensive amount of pilot- and bench-scale work has been done on SNCR

processes, most of this work has addressed process parameters including SNCR

chemical type, amount of chemical, temperature, initial NOx levels, and additives.

Little work has focused explicitly on the effect of residence ti~es. Sun, et al., used
chemical kinetic calculations to investigate residence time effects (1). In this work, it was

shown that residence time was most important as the temperature decreased below the

temperature for peak NOx removal; on the high temperature side of the temperature

window, it was less important since reaction rates increase exponentially with

temperature.

The current study was undertaken to experimentally study the effect of residence time

on SNCR processes. This work was done in support of an SNCR demonstration at

PG&E's Morro Bay power plant (2). For this full-scale demonstration, SNCR chemical

injection was into the convective section cavities. Since residence times within the

convective cavities were on the order of 35 milliseconds at full load, it was decided that

a pilot-scale study of residence time would be beneficial in interpreting the full-scale

data.

The objectives of the present study were to experimentally determine the effect of

residence time on SNCR processes and to determine the differences in rates of NOx

removal between anhydrous ammonia (NH3), aqueous ammonia (NH.40H) and

aqueous urea.

When addressing SNCR residence time effects, three characteristic times need to be

considered:

• mixing of the SNCR chemical with the combustion products

• evaporation and release of reactive nitrogen compounds (for aqueous solutions)

• chemical reaction times

In any experimental approach, it is difficult to separate each of the above characteristic

times. For the current study, an effort was made to keep the mixing as constant as

possible between the various chemicals. In this way, residence time effects can be

attributed to evaporation and release of reactive nitrogen compounds and chemical

reaction times.

During the current experimental study, the following parameters were investigated:

SNCR Chemicals: anhydrous NH3, aqueous ammonia (NH40H),

aqueous urea (NH2CONH2)

Residence Time: 33 - 500 msec

Temperature: 1500 - 2100°F

Chemical Injection Rate (N/NO molar): 0-2

Aqueous Solution Concentration: 0-1.67 gmol N/liter.

Again, the primary objective was to define residence time effects on SNCR performance.

To support the experimental results, a limited amount of chemical kinetic calculations

were performed. The calculations were done using a PC version of CHEMKIN (3) along

with the Bowman and Miller mechanism for nitrogen chemistry (4).
Pilot-Scale Facility

A schematic of the pilot-scale facility used for the current tests is shown in Figure l.

The pilot-scale combustor fires natural gas doped with NH3 to control the initial NO

level. The combustion section is water cooled and partially refractory lined. The test

section is refractory lined, 6 in. in diameter and 8 feet long. At the firing rates used for

these tests, the residence time in the test section is nominally 0.5 seconds; the

temperature drop along the test section is nominally 450°F/sec (250°F for the 0.5 second

residence time through the test section). Fifteen ports are spaced along the length of the

test section which provides a residence time resolution of about 30 milliseconds.

SNCR chemicals used for the current study were gaseous ammonia (NH3), and aqueous

ammonia (NH40H) and aqueous urea (NH2CONH2) solutions. The SNCR solutions

were injected into the combustion products at the throat of a venturi section located just

upstream of the test section. A small air assist atomizer was used to inject the

chemicals. For the case of gaseous NH3, the NH3 was mixed with the atomizing air; no

liquid solution was used in this case. The atomizer was fabricated into a water cooled

holder and located at the center of the venturi throat. The spray was directed

downward (Le., co-flowing with the combustion products). The solutions were

pumped with variable speed peristaltic pumps and metered with rotameters. In order

to maintain a constant thermal environment in the test section when aqueous solutions

were used, the total amount of liquid injection was held constant at nominally 1

liter/hr. By diluting a concentrated reagent solution with distilled water, the amount of

chemical reagent was varied, while the total liquid flow rate was maintained. At a

N /NO ratio of 2.0, the solution concentrations were 0.833 mole % nitrogen per liter (i.e.,

2.5 wt% for urea and 1.4 wt% for ammonium hydroxide).

Gas samples were taken at the sampling ports along the test section using a hot watercooled probe and transported to a series of gas analyzers (NOjNOx, N20, CO, C02,

and 02). NH3 concentration measurements were made by scrubbing a gas sample

through impingers containing dilute sulfuric acid followed by analysis with a specific

ion electrode.

Experimental Results

The results first compare the effect of residence time on NO reduction for the three

chemicals. Subsequently, the effect of residence time on byproduct emissions (e.g.,

NH3, N20) are discussed.

NO Reduction

The effect of residence time on NO reduction for anhydrous ammonia (NH3)g, NI!40H

and aqueous urea is shown in Figure 2 for chemical injection temperatures of 1600°F,

1750°F and 1850°F and 2000°F. This figure shows data collected at nominal 30 msecond
intervals along the combustor test section. During this test series, the combustor was

operated at a constant combustion product flow rate. The overall residence time in the

test section decreased from 0.47 seconds at 1600°F to 0.4 seconds at a temperature of

2000°F. The initial NO level was 125 ppm and the aqueous solutions had a

concentration of 0.833 gmol N/liter. The chemicals were injected at a rate

corresponding to a N/NO molar ratio of 2.0.

Itshould be noted that the temperature referred to throughout the paper is a suction

pyrometer temperature measurement obtained at the first sampling port downstream of

the injection point. At this point, the aqueous solutions have had a chance to partially

vaporize and mixing with the main combustion product flow is nearly complete. This

was felt to be a more representative temperature than the temperature entering the

injection venturi since the concentrations of the aqueous solutions used for these

experiments were more dilute than those utilized at full scale. (The maximum urea

concentration was nominally 5 wt% and the maximum NH40H concentration was

nominally 2.8 wt%.)

A number of observations can be made from the data shown in Figure 2. First, at a

temperature of 1850°F, residence times in excess of 150 mseconds are generally needed

for the reaction to be substantially completed, regardless of the chemical utilized. As

the temperature decreases, the reaction rates decrease. At temperatures below 1750°F,

minimum required residence times approach 250 mseconds.

As mentioned above, the experiments contain three characteristic times: mixing,

evaporation/decomposition, and reaction. Insight into evaporation effects can be

gained by comparing the results in Figure 2 for anhydrous ammonia, NH3(g), and

aqueous ammonia, NH.40H (1). For these two cases, the primary differences are

expected to be the evaporation of the N1f40H and the release of the NH3 to the gas

phase. As seen in Figure 2, at 1600°F and 1750°F, gaseous NH3 removes NO faster than

aqueous ammonia. At a temperature of 1850°F, which is on the high temperature side

of the SNCR temperature window for ammonia, the NO removal rates are comparable

for the first 100 msec. Higher removals are ultimately attained with aqueous ammonia.

This higher overall removal with aqueous ammonia can be attributed to either 1) the

somewhat slower release of the chemical with more NH3 reaching the cooler region of

the test section; or 2) continued evaporation of the aqueous phase beyond sample port

number 1 (33 mseconds) resulting in some cooling of the gases in the test section.

At the two lower temperatures shown in Figure 2, aqueous urea reacts much slower

than either anhydrous or aqueous ammonia. At 1850°F, NO removal rates become

more comparable for all three chemicals. This is due to two effects. First, since 1850°F is

above the peak temperature for NO removal using ammonia, with reactions oxidizing

NH3 to NO beginning to playa more important role, the net affect is an overall decrease

in the NO removal rates. Secondly, at higher temperatures, the evaporation and

chemical decomposition rates will increase. At the same time, 1850°F is near the

optimum temperature for NO removal with urea, when NO removal rates should be

highest.
At a higher temperature of 1850°F, it can be seen that the NH3 emissions with aqueous

ammonia decrease much more rapidly than at 1750°F. Again, the NH3 profile with

aqueous urea is different. At this higher temperature, there is no delay in the

appearance of NH3. However, with urea, the NH3 decay is much slower than with

aqueous ammonia injection. Also, as at 1750°F, the maximum NH3 concentration with

urea injection was only 150 ppm, slightly over one half of the injected nitrogen.

N20 Emissions

NzO is also a product of SNCR process, with urea producing higher NzO levels than

ammonia injection (5). NzO profiles were also measured along the length of the test

section during the course of the experiments. Figure 6 shows the NzO concentrations as

a function of residence time for each chemical. In Figure 7, the NzO concentrations have

been normalized by the NO reduction, which can also be interpreted as the fraction of

NO converted to NzO. Consistent with previous studies, urea produces higher levels of

NzO than either aqueous or anhydrous ammonia.

The residence time effects on NZO concentrations are quite interesting. At temperatures

below 1750°F, the ammonia injection results show increasing NzO concentrations with

increasing residence time. As the temperature increases above 1750°F, a peak in the

NzO concentration is observed. This peak occurs at a residence time of nominally 150-

200 mseconds at 1850°F and 75 mseconds at 2000°F. As residence times increase, NZO

concentrations decrease due to destruction reactions. Even at 1750°F, NzO

concentrations at residence times in excess of 250 mseconds are lower than those

measured at 1600°F. This indicates that NzO destruction reactions are important even at

these temperatures.

Somewhat similar trends are seen with urea injection (Figure 6c) except the overall NzO

levels are higher. At temperatures of 1600°F, 1750°F, and 1850°F, NzO levels are seen to

increase monotonically with both residence time and temperature. At a temperature of

2000°F, NzO levels peak at a residence time of 200 mseconds and then begin to decrease

as NzO destruction reactions predominate.

The normalized NzO profiles show similar trends (Figure 7). With ammonia injection,

the normalized N zO levels are under 10%. At higher temperatures, normalized NzO

levels decrease with increasing residence times. With urea injection at long residence

times, normalized NzO concentrations increased from 15% to near 40% with increasing

temperatures. More importantly, at high temperatures and short residence times, NzO

levels approached 60% of the NO reduction. From a practical standpoint, this suggests

that for applications with short residence times (e.g., injection in convective cavities),

NzO levels may be enhanced. In fact, the residence time effect seen in Figure 7c with

urea injection explains the relatively high NzO production observed during the PG&E

Morro Bay SNCR demonstration(Z).
At 2000°F, the temperature is beyond the SNCR temperature window for ammonia, at

an initial NO level of 125 ppm, and additional NO is formed along the combustor

(Figure 2d).

The data for temperatures of 1750°F and 1850°F shown in Figure 2 have been

normalized and replotted in Figure 3. In Figure 3, the NO is shown as the fractional

removal of NO along the test section. Figure 3 shows that anhydrous ammonia reacts

slightly faster than aqueous ammonia which reacts slightly faster than urea. For

instance, at 1750°F, 75% of the reaction is complete in nominally 150 mseconds with the

ammonium chemicals, whereas 220 mseconds is needed for urea. At 1850°F, reaction

rates are faster on a normalized basis, with 75% of the reaction completed in about 100

mseconds with the ammonium compounds. In comparison, aqueous urea requires

about 180 mseconds to complete the same 75% of the reaction.

To better compare the effect of residence time and temperature, the data in Figure 2 for

urea and ammonia have been cross-plotted as a function of temperature in Figure 4.

With ammonia injection, a marked decrease in NO reduction occurs at residence times

less than 110 mseconds. Also, consistent with previous pilot-scale studies, peak NO

removals occur at 1750°F, at long residence times. For aqueous urea injection, residence

times less than 280 mseconds have a marked effect on performance. Again, this is likely

related to the temperature gradient in the combustor (450°F/sec), and the slower release

of reactive nitrogen compounds from the urea solution. Also, the data in Figure 4 show

peak NO removals for a long residence time at 1850°F with urea, nominally 100°F

higher than for ammonia.

NH3 Emissions

During this study, NH3 concentrations were measured along the test section for each of

the three chemicals at a temperature of 1750°F. At a temperature of 1850°F, NH3

profiles were obtained along the test section for aqueous ammonia and aqueous urea.

The NH3 profiles are shown in Figure 5. At 1750°F, the NH3 profiles for anhydrous and

aqueous ammonia are comparable, with anhydrous ammonia showing a somewhat

faster decay than aqueous ammonia. The NH3 profile with aqueous urea injection at

1750°F is markedly different. First, there is a distinct delay in the formation of

ammonia, with maximum NH3 concentrations occurring after 100 mseconds. This is

consistent with a more gradual release of reactive nitrogen compounds to the gas phase

with urea injection. With urea, it can be speculated that the aqueous solution must

evaporate to near saturation before substantial decomposition of the urea occurs

releasing reactive nitrogen compounds to the gas phase. Secondly, at 1750°F, peak NH3

concentrations are only 100 ppm, whereas 250 ppm of reactive nitrogen is being injected

as urea. These lower measured concentrations of NH3 would be consistent with a urea

decomposition mechanism producing NH3 and HNCO (Le., NH2CONH2 --> NH3 +

HNCO).
Chemical Kinetic Calculations

To support the pilot-scale tests, chemical kinetic calculations were performed using a

PC version of CHEMKIN(3) and the Miller Bowman mechanism for nitrogen

chemistry(4). The calculations were performed over a temperature range from 1500-

2100°F, for an initial NO level of 125 ppm and NINO molar ratio of 2. The calculations

also incorporated a temperature gradient of 450°FI second. Calculations were made for

both ammonia (NH3) and urea. The urea calculations assumed that the urea

decomposed instantaneously to NH3 + HNCO.

The calculated histories of NO are shown in Figure 8 for both ammonia and urea. The

calculated NO profiles are in qualitative agreement, although the absolute levels of NO

removal are higher than observed experimentally. With NH3 injection, calculations

show some NO removal even up to an injection temperature of 2100°F; whereas

experimentally, additional NO was formed above 2000°F. This could be due to the

"injection temperature" which was defined for the experiments. Recall, the injection

temperature for the experiments was measured at a point 33 mseconds below the point

of injection. Thus, some of the injected ammonia experienced higher temperatures

during the mixing process. This effect would be expected to be more important at the

higher injection temperatures.

Likewise, with urea injection, the calculated NO removals are higher than measured

experimentally. Again, this may be attributed in part to the mixing and evaporation

process which experimentally is more gradual than the assumed instantaneous release

of NH3 + HNCO assumed for the calculations.

The calculated N20 profiles versus time are shown in Figure 9 for urea injection. Figure

9a shows the calculated N20 concentrations versus residence time and Figure 9b shows

the time histories of the N20 concentration normalized by the NO removal. These

calculated N20 profiles can be compared to the experimental profiles in Figures 6c and

7c. The N20 profiles are in good qualitative agreement with the experiments. The

calculated N20 profiles further support the observation that short residence times can

lead to enhanced levels of N20 emissions from SNCR processes. In fact, consistent with

the experiments, the calculations show that at residence times between 50 and 100

mseconds over 50% of the NO reduced can be converted to N20.

Conclusions

The results of the present study have shown the importance of residence time for SNCR

processes. Specifically:

• The tests showed that for all chemicals tested, residence times on the order of 250

mseconds were required to substantially complete 80% of the NO removal. This

residence time will vary somewhat for full-scale application, since mixing and
evaporation times will be dependent on site-specific factors which may differ

from the pilot-scale.

• For short residence time applications (t<100 mseconds), it is necessary to inject at

higher temperatures where evaporation and reaction rates are increased. Even at

higher temperatures, residence times can still impact SNCR performance.

• The tests also showed that gaseous ammonia and aqueous ammonia (NI-40H)

reacted more rapidly than urea. For instance, with ammonia, peak removals

occurred at a temperature of 1750°F while for urea, peak removals occurred at

1850°F. The table below shows the residence times required to complete 50% of

the NO removal observed at the combustor exit.

Chemical

NH.tOH

Urea

Temperature

Time for 50% of the

Overall Removal

70 mseconds

110 mseconds

• At residence times below 100 mseconds and temperatures greater than 1850°F,

NzO levels can be relatively high for urea injection. For these conditions, NzO

destruction reactions, which are relatively slow, have not had sufficient time to

reduce NzO.

References

1. Sun, W. H., et al., "Post Combustion NOx Reduction with Urea: Theory and

Practice," presented at the Seventh Annual International Pittsburgh Coal

Conference (September 1990).

2. Teixeira, D. P., et al., "Selective Non catalytic Reduction (SNCR) Demonstration

in a Natural Gas Fired Boiler," 1993 Joint Symposium on Stationary Combustion

NOx Control.

3. Kee, R. J., et al., CHEMKIN: A General-Purpose, Problem-Independent,

Transportable FORTRAN Chemical Kinetics Code Package, SANDIA Report

SAND80-8003, reprinted July 1987. '

4. Miller, J. A., Bowman, C. T., "Mechanism and Modeling of Nitrogen Chemistry in

Combustion." Progress in Energy and Combustion Science, 15,287 (1989).

5. Muzio, L. J., et al., ''NzO Formation in SNCR Reduction Processes," EPA/EPRI 1991

Joint Symposium on Stationary Combustion NOx Control (March 1991).
....-WATER JACKET

INSULATION

COOUNG COILS

(6 TOTAL)

PCUEO..JS H20

REAGENT

ATOMIZING

AIR

MAIN

AIR

NH3

NAT.

GAS

Figure 1. Pilot Scale Combustor Facility
0.1 0.2 0.3 0.4 0.5

0.00 L....;I000.10.....10...........L...................-.10......."""-......................10......................""""-1......J......

0.0

1.00

0 NH3 (g)

E 0.80 11 NH40H (I) c.

c.

-E 0 Urea (I) c.

c.

6 0.60

z

lIII

:E

.: 0.40

-

0

Z

lIII

c 0.20

-

Residence Time, seconds

0.1 0.2 0.3 0.4 0.5

0.00

0.0

1.00

0 NH3 (g)

E 0.80 11 NH40H (I) c.

c.

-E 0 Urea (I) c.

c.

6 0.60

z

iii

.:=

0.40

-

0

Z

lIII

c 0.20

;:

Residence Time, seconds

b) 17500 F

Figure 2. Effect of Residence Time and Chemical on NOx on Reduction

(NOj =125 ppm; NINO =2.0)
0.1 0.2 0.3 0.4 0.5

0.00 L...o -"" ....L. -"" .....

0.0

1.00

0 NH3 (g)

E 0.80 IJ. NH40H (I) c.

c.

-E

c. 0 Urea (I)

c.

6 0.60

z

III

.:

c 0.40

-

0

Z

III

c 0.20

-

Residence Time, seconds

o Urea (I)

o NH3 (g)

0.2 0.3 0.4 0.5

--0--:::::0---0-10

is IJ. A

0.1

1.60

1.40

E

c.

c.

- 1.20 E

c.

c.

6 1.00

z

0.80

c

- 0.60

0

z

iii 0.40 c

:;::

0.20

0.00

0.0

Residence Time, seconds

d) 20000 F

Figure 2. (Continued) Effect of Residence Time and Chemical on NOx on Reduction

(NOi =125 ppm; NINO =2.0)
0.1 0.2 0.3 0.4 0.5

0.2

0.2

0.0 B-__......--Io........-...Io-......-...--r..-...Io-__.I.-.I--Io.......__...&...__.......--Io.....

0.0

1.0

0 NH3 (g)

0.8 11 NH40H (I)

CI Urea (I)

~~ 0.6

00

z 0.4

0.0

0.0 0.1 0.2 0.3 0.4 0.5

Residence Time, seconds

a) 17500 F

1.0

0 NH3 (g)

0.8

li. NH40H (I)

0 Urea (I)

~: 0.6

0.4

Residence Time, seconds

Figure 3. Normalized NO profiles versus Residence Times

(NOi =125 ppml NINO =2.0)
1.2

.; 1.0

.-

s::::

0 0.8

Z

.....

-; 0.6

s::::

g- 0.4

Z

0.2

RESIDENCE TIME. msec

--0-- 33

110

ts 280

• 420

0.0 L...-.....L.._I...-...J-----'-....L...----'--..L...----'--'---.........-.r.-----'

1500 1600 1700 1800 1900 2000 2100

TEMPERATURE, of

a) Ammonia

~-----C---n----- 1:: 0

0.8

<'CS

s::::

g 0.6

Z

.....

0.4

--

o

z

0.2

RESIDENCE TIME. msec

c 33

-0-- 110

ts 280

• 420

0.0 '---..........----'""---.........---I._................_ ................_"'---.....L..--JL.....---'

1500160017001800 190020002100

TEMPERATURE, of

b) Urea

Figure 4. Effect of Temperature and Residence Time on NO Reduction

with a) Anhydrous NH3• and b) Aqueous Urea

(NOj = 125 ppm, NINO = 2.0)
o 50

250

0 NH3 (9)

/:i NH40H (I) 200

0 Urea (I)

E

Co 150 Co

en

M 100

z

=

o

0.0 0.1

. I

0.2 0.3 0.4 0.5

Residence Time, seconds

0.1 0.2 0.4 0.5

oL... .-..J.........._....s:...:::::;::I:::i:::::;;tEc~ .......................J

0.0

250

/:i NH40H (I)

0 Urea (I) 200

E

c. 150

c.

Ii

en

M 100 =z

50

Residence Time, seconds

b) 18500 F

Figure 5. NH3 Profiles along the Combustor

(NINO = 2.0; NOi = 125 ppm)
10 0 1600 of

8 t:. 1750 of

E

0. 6 Cl 1850 of 0.

0 4 <> 2000 of N

z

2

0

o~o- 0.1 0.2 0.3 0.4 -0.5

Residence Time, seconds

a) NH3 (g)

10 0 1600 OF

8 t:. 1750 .oF

E

0. 6 0 1850 OF

0.

6 4 <> 2000 OF N

z

2

0

0.0 0.1 0.2 0.3 0.4 0.5

Residence Time, seconds

b) Aqueous Ammonia (NH4OH)

20

0 1600 of

15 t:. 1750 .oF

E

0.

0. 0 1850 OF 10

0

N <> 2000 of z

5

0

0.0 0.1 0.2 0.3 0.4 0.5

Residence Time, seconds

C) Aqueous Urea

Figure 6. N20 Concentration Versus Residence Time

(NOi = 125 ppm; NINO = 2.0)
0.5 0 1600 of

0.4 tJ. 1750 *F 0

z

<1 0.3 0 1850 of

-

0 0.2 N

z

0.1

0.0

0.0 0.1 0.2 0.3 0.4 0.5

Residence Time, seconds

a) NH3 (g)

0.5 I T I I :

. 0 1600 of

0.4 - - 0

z tJ. 1750 *F

<l 0.3 - - - 0 1850 of

0

N 0.2 - z

0.1 - ~r-1 "I" ...,

0.0

0.0 0.1 0.2 0.3 0.4 0.5

Residence Time, seconds

b) Aqueous Ammonia (NH4OH)

1.0 0 1600 of

0.8 tJ. 1750 *F 0

z

<l 0.6 0 1850 of

-

0 0.4 N <» 2000 OF

z

0.2

0.0

0.0 0.1 0.2 0.3 0.4 0.5

Residence Time, seconds

C) Aqueous Urea

Figure 7. Normalized N20 Profiles versus Residence Time

(NOj =125 ppm, NINO =2.0)
c 25

o 50

o 100

6 200

• 500

RESIDENCE TIME. msec

0.0 L.-........_L.-........._L.-........___JL...-........----l_........---I._........---J

1500 1600 1700 1800 19002000 2100

TEMPERATURE, of

a) Ammonia

ctl

c 0.4

0.2

o

z

:=- 0.8

ctl

--

c

o 0.6

Z

-

-~

1.0

RESIDENCE TIME. msec

0.8

ctl C 25

c 0 50 - 0.6 0

Z 0 100

--

ctl 6 200

c 0.4

- • 500 -

0

Z

0.2

0.0 L.-........_.L..-........_.L-........___JL...-....I----lL...-........---lL...-.....I...----l

1500 1600 1700 1800 190020002100

TEMPERATURE, of

b) Urea

Figure 8. Calculated Effect of Temperature and Time on NO Removal

(NOj =125 ppm, NINO =2.0)
200 300 400 500

RESIDENCE TIME, msec

100

5

25

TEMPERATURE. of

0 1500

20

6 1700

E [] 1800 Co 15 Co 0 1900-

0

C\l

Z 2100 •

10

a) N20 Concentration, ppm

60

TEMPERATURE of

50 0 1500

.. 1700

<f!. 40 [J 1800

6

z • 1900

0 30 N

Z • 2100

20

10

RESIDENCE TIME, msec

Figure 9. Calculated N20 Profiles

(Urea, NINO = 2.0; NOj =125 ppm)
0.1 0.2 0.3 0.4 0.5

0.2

0.0 r'I-......-...-................................-.._.........."'---...-.._...................................

0.0

0.2

0.0

0.0 0.1 0.2 0.3 0.4 0.5

Residence Time, seconds

a) 17500 F

1.0

0 NH3 (g)

0.8

6. NH40H (I)

[J Urea (I)

~: 0.6

0.4

1.0

0 NH3 (g)

0.8 6. NH40H (I)

[J Urea (I)

r

0.6

z

I I

.. _~ 0.4 --

Residence Time, seconds

b) 18500 F

Figure 3. Normalized NO profiles versus Residence Times

(NOi = 125 ppml NINO = 2.0)
1.2

-ttl

:: 1.0

c:

0 0.8

Z

-;0.6--

c:

g- 0.4

Z

0.2

RESIDENCE TIME. msec

---0-- 33

110

ts _280.

• 420

0.0 1...-.........---"_.............._01...--'-----'-_""'-........_""'"---'-----'

1500 1600 1700 1800 1900 2000 2100

TEMPERATURE, of

a) Ammonia

1.0 ....---r----r-"'T"""---r--..--....,....-,.......-r----,.-~"""T"---,

....

~----_a_--_---- C

_ 0.8

eu

;::

c:

g 0.6

Z

::::::..

0.4

--

o

z

0.2

RESIDENCE TIME. msec

c 33

---0-- 110

A 280

• 420

0.0 L..--'--.....I._..............._""'"--...L----I_...L.........._.J....,..........---I

1500 1600 1700 1800 190020002100

TEMPERATURE, of

b) Urea

Figure 4. Effect of Temperature and Residence Time on NO Reduction

with a) Anhydrous NH3' and b) Aqueous Urea

(NOj =125 ppm, NINO =2.0)
o NH3 (g)

[J Urea (I)

o 50

100

200

150

e

c.

c.

-~-

UJ

(')

:%:

Z

o

0.0 0.1 0.2 0.3 0.4 0.5

Residence Time, seconds

0.1 0.2 0.3 0.4 0.5

o L.............L...............~::::i:J:::i::i:tI:c::::=;a....................J

0.0

250

A NH40H (I)

[J Urea (I) 200

e

c. 150 c.

UJ

(') 100 :z::

z

50

Residence Time, seconds

b) 18500 F

Figure 5. NH3 Profiles along the Combustor

(NINO = 2.0; NOi = 125 ppm)
10 0 1600 of

8 A 1750 of

E

c. 6 [J 1850 of c.

0 4 0 2000 of N

z

2

0

-0:0---- ---0:1- - ---0:2------- - - -0:3-- - --- - 0.4 0.5

Residence Time, seconds

a) NHS (9)

10 0 1600 of

8 l:!t. 1750 *F

E

c. 6 [J 1850 of

c.

0 4 0 2000 of

N

z

2

0

0.0 0.1 0.2 0.3 0.4 0.5

Residence Time, seconds

b) Aqueous Ammonia (NH40H)

20

0 1600 of

15 6 1750 *F

E

c.

c. [J 1850 of 10

0

N 0 2000 of z 5

0

0.0 0.1 0.2 0.3 0.4 0.5

Residence Time, seconds

C) Aqueous Urea

Figure 6. N20 Concentration Versus Residence Time

(NOj = 125 ppm; NINO = 2.0)
0.5 0 1600 of

0.4 Ii. 1750 "F 0

z

<l 0.3 [J 1850 of

-

0 0.2 N

z

0.1

------- --- - - -- - - -- -

0.0

0.0 0.1 0.2 0.3 0.4 0.5

Residence Time, seconds

a) NH3 (g)

0.5 I I I I

I- 0 1600 of

0.4 · 0

z Ii. 1750 "F

<l 0.3 · - [J 1850 of

0 0.2 N · z

0.1 l:-

~.A:::I 1""'1 · -""" FI 'T -,

0.0

0.0 0.1 0.2 0.3 0.4 0.5

Residence Time, seconds

b) Aqueous Ammonia (NH40H)

1.0 0 1600 of

0.8 Ii. 1750 "F 0

z

<l 0.6 0 1850 of

-

0 0.4 N <> 2000 of

z

0.2

0.0

0.0 0.1 0.2 0.3 0.4 0.5

Residence Time, seconds

C) Aqueous Urea

Figure 7. Normalized N20 Profiles versus Residence Time

(NOj = 125 ppm, NINO = 2.0)
::::::- 0.8

as

-

0' 0.6

Z - - -..-.,-----------------------

- ----------- ---

as

l: 0.4

--

o

z

0.2

RESIDENCE TIME. msec

c 25

o 50

o 100

---- -

6 200

• 500

0.0 L..........L-.......I_.........--'-_....&..........L._........--L-----''--.........--L-----I

1500 1600 1700 1800 1900 2000 2100

TEMPERATURE, of

a) Ammonia

1.0

RESIDENCE TIME. msec

::::::- 0.8

C'll c 25

-l: 0 50

- 0.6 0

Z 0 100

--

as 6 200

l: 0.4

- • 500 -

0

Z

0.2

0.0 L...-........_ .........&..........I_.........--I._....&............._ ............L._L..-......I

1500 1600 1700 1800 1900 2000 2100

TEMPERATURE, of

b) Urea

Figure 8. Calculated Effect of Temperature and Time on NO Removal

(NOj =125 ppm, NINO =2.0)
200 300 400 500

RESIDENCE TIME, msec

100

5

25

TEMPERATURE, of

0 1500

20

6 1700

E D 1800

c. 15 c. _.- --- --- - ----

-.-----

0

C\I

Z 2100 •

10

a) N20 Concentration, ppm

60

TEMPERATURE OF

50 0 1500

.. 1700

40 c 1800

6

:z • 1900

0 30 ('\I

:z • 2100

20

10

RESIDENCE TIME, msec

Figure~. Calculated N20 Profiles

(Urea, NINO = 2.0; NOj = 125 ppm)