Post Combustion NOx Reduction with Urea: 

Theory and Practice 

Seventh Annual International 

Pittsburgh Coal Conference 

September 1 0-14, 1990 

William H. Sun, John E. Hofmann 

Nalco Fuel Tech 

Naperville, Illinois 

Reinhard Pachaly 

Fuel Tech, GmbH 

Mulheim, FAG 
Post Combustion NOx Reduction with Urea: Theory and Practice 

William H. sun, John E. Hofmann 

Abstract 

Nalco Fuel Tech 

Naperville, Illinois, U.S.A. 

Reinhard Pachaly 

Fuel Tech, GmbH 

Mulheim, FRG 

The NOxOUT Process has ·proven to be effective in controlling NOx 

emissions from various combustion sources when chemicals are 

injected at temperatures between 750 ~ 1100 °c and their 

distributions optimized. High levels of NOx reduction and low 

byproduct emissions have been achieved by using urea and other 

chemicals, along with the use of multi-level injection techniques. 

The factor which limits the process application at temperatures 

above 1100 °c has been determined through a chemical kinetic model. 

The model is based on the CHEMKIN subroutine package and uses 

published reaction parameters and thermodynamic data. This factor, 

referred to as 'Critical NOx', is affected strongly by temperature 

but weakly by excess oxygen concentration. It is also affected by 

baseline NOx concentration at temperatures above 1050 °c. Through 

this study, conditions under which NOx can be reduced at 

temperatures as high as 1200 °C and beyond have been defined. 

Experimental results from a laboratory combustor and industrial and 

utility boilers support this finding. 

Introduction 

The oxides of nitrogen (NOx) contribute to smog, ground level ozone 

formation, and acid precipitation which can severely damage 

vegetation, marine life and various man-made structures (1]. Manmade NOX emissions are mostly from both mobile and stationary 

combustl.on of fossil fuel. To control mobile sources, engine 

designs were modified, and automobiles have been equipped with 

catalytic converters. As for stationary sources, tighter 

regulations have and are being promulgated on utility and 

industrial boilers and incinerators. Various techniques have been 

employed to control NOx, and they can be categorized into three 

areas: 

(1) Fuel Cleaning or Low Nitrogen Fuel 

(2) Combustion Modification 

(3) Post Combustion control 

The first method lowers NOx by limiting contribution from fuel 

sources. NO is formed from oxidation of fuel bound nitrogen, 

termed fuel N6x, and from oxidation of atmospheric nitrogen, termed 

thermal NOx· By removing fuel bound nitrogen from fuel or burning 
fuel with low nitrogen, i.~. natural gas, fuel NOX is limited. 

Combustion modification reduces NOx emission by lim1ting thermal 

and fuel NOx· By lowering combustion temperature through flue gas 

recirculation and by limiting oxygen for N2 oxidation through 

staged combustion, thermal NOx is controlled. Staged combustion 

also lowers the conversion of fuel bound nitrogen to NOx· Unlike 

previous methods which limit the formation of NOx, the third 

method, post combustion control, reduces NOx after the formation is 

completed. In this method, two categories exist: catalytic and 

noncatalytic. Catalytic reduction deals with reaction of NOx with 

ammonia on various metal catalysts at temperatures between 300 -

500 °c [2]. The noncatalytic method consists of injecting either 

ammonia or urea where flue gas temperature ranges between 850 - 1100 °c. Ammonia injection is an Exxon process and has been called 

the Thermal DeNOx Process [ 3, 4] while the urea injection was 

patented by EPRI [5,6]. Nalco Fuel Tech is EPRI's exclusive 

licensing agent, and the technology is being marketed as NOxOUT 

Process. The NO OUT Process has been in development for several 

years by Fuel Tee~, Inc., and several articles have been published 

dealing with various facets including process demonstration results 

[7-11]. 

NOXOUT Kinetic Model 

As a part of the development effort, a chemical kinetic model has 

been developed to understand the basic chemistry, to determine 

important factors and to define the limits of process capability. 

This model describes an ideal plug flow, i.e., no temperature or 

species concentration gradient in radial direction and no backmixing. Species concentrations with this type of flow are 

described by a set of ordinary differential equations. The number 

of equations depends on the number of species being modelled, and 

the equations are interrelated through reaction rates. Enthalpy 

equations are neglected in the model. Instead, measured or 

estimated temperature profile is a model input. Reaction rates, 

density, and thermodynamic information are supplied by a library of 

gas-phase subroutines called CHEMKIN developed at the Sandia 

National Laboratories (12]. This package of subroutines compiles 

user supplied reaction set and thermodynamic data file. The 

resulting set of differential equations are integrated 

simultaneously using a numerical integrator called LSODE [ 13) • 

This solver was developed at the Lawrence Livermore National 

Laboratory and has shown to be most efficient in solving combustion 

problems ( 14]. Initial condition for the calculation was the 

equilibrium concentrations of species at temperature and excess o2 

as measured. Measured NOx concentration is also an input. 

Equilibrium concentration was calculated using a program called 

STANJAN developed at Stanford University [15]. The components of 

the NOxOUT Kinetic Model are shown in figure 1. 

The reaction set is adopted from the work of Miller and Bowman 

( 16) • From these elementary radical reactions, only the ones which 

do not react with hydrocarbons were selected. The wet co oxidation 
reactions, ammonia oxidation reactions, and HCN oxidation reactions 

make up the set. Urea decomposition is modelled as a rapid and one 

step breakdown to NH3 and HNCO. Experimental results by eaton and 

Siebers [17] show a quantitative conversion of urea to NH3 and HNCO 

at high temperatures. The final reaction set consists of over 90 

reactions describing interactions among 31 species. The major 

pathway of urea breakdown and reaction with NOx is shown in figure 

2. 

Model Validation 

With the developed model, results from a pilot scale combustor are 

compared with model results. A schematic of the pilot combustor 

and the analytical setup is shown in figure 3. The test zone of 

the combustor was kept isothermal by electrical heating. The 

residence time at this zone was approximately o.s second. This is 

the average residence time between the injection point and the end 

of the isothermal zone. Temperature was varied from 850 °c to 1100 

0 c. Baseline NOx value and treatment rate were kept constant at 

200 ppm and at NSR of 2, respectively. NSR is defined as the 

actual mole ratio of urea to NOx divided by the theoretical 

stoichiometric ratio, which is o.s for the reaction between urea 

and NOx. Chemicals were injected with an air atomized nozzle, 

which creates a spray of fine droplets. The initial condition was 

the measured baseline NOx and the equilibrium concentration at the 

measured temperature. Tne comparison of the model and experimental 

results is shown in figure 4. The available reaction times for 

injected chemicals are less than the residence time because 

reaction starts after droplet evaporates. Because of this delay, 

calculation results from reaction times of 0.1, 0.2, 0.4, and 0.6 

seconds are compared to the experimental results. As shown, the 

trend and the shape of the experimental results are well modelled. 

In addition, all the experimental points fall within the calculated 

lines with reaction times of 0.1 and 0.4 seconds. 

Temperature Window 

A range of temperature where significant NOx reductions are 

obtained is called the temperature window as indicated on figure 4. 

Within this window, the NOx versus temperature curve consists of 

three zones: left side, right side and plateau. This shape is a 

result of chemical kinetics. At temperatures lower than this 

window, reaction initiating hydroxyl radical concentrations and 

reaction rates are low. These two factors slow the breakdown of 

NH3 and HNCO. NOx reduction therefore requires longer reaction 

time than is typically available in most commercial combustion 

systems. At the left side of the curve, NO decreases with 

increasing temperature because reaction rates and'oa concentration 

increase with temperature, which in turn, increases NOx reduction. 

Residence time limits the NO reduction at this zone. At the 

plateau, reaction rates and oR concentration are optimum for NOx 

reduction. A temperature variation at this zone has only a small 

effect on NOx. A further increase in temperature beyond the 
plateau zone decreases NOx reduction. At the right side, the 

oxidation reactions of NH3 and HNCO to NO become a significant 

path for injected chemical and compete with Aox reduction reactions 

for reagent. These oxidation reactions increase with temperature 

and OH concentration and thus NOx reduction decreases with 

increasing temperature at the right side. A further increase in 

temperature beyond the right side increases NOx above a baseline 

NOx. Although the reduction is less than the maximum, operation at 

the right side is practiced and recommended since byproduct 

emissions decrease with increasing temperature. 

Treatment Rate 

Increasing NSR has a diminishing return in NOx reduction. In 

figure 5, model results of NOx concentration as a function of NSR 

are presented for several temperatures. NOx decreases with 

increasing NSR for those calculations within the temperature 

window; at higher temperatures, increasing NSR increases NOx· At 

temperatures between 900 and 1200 °c, NOx reaches a lower limit at 

an NSR of about 2. A further increase from NSR of 2 increased NOx 

for 1200 °c case but had no effect on other cases. 

Residence Time 

The temperature window becomes wider with an increase in residence 

time. As shown in figure 6, the window is only 150 °c wide for a 

0.1 second case but the window increases to 300 °c for one second 

residence time case. This widening resulted from shifting of the 

left side of the NOx versus temperature curve to a lower 

temperature. At this side, NOx reduction is limited because of 

slow reaction rates and low OH radical concentrations. Therefore, 

a longer reaction time increases NOx reduction. The plateau zone 

where NOx reduction is maximized widened from 50 °c at 0.1 second 

to 150 °c at 1 second. At this plateau region, NOx was reduced by 

only a few ppm when residence time increased from o.a to 1.0 second 

indicating that the reactions are essentially complete at one 

second and that the lowest achievable NOx concentration has been 

reached. The right side is unaffected by residence time. 

Baseline NOx 

NOx reductions were calculated at baseline NOx levels of 100, 200, 

and sao ppm and at temperatures between 750 - 1300 °c. In figures 

7a, b, and c, NOX concentrations.versus residence times are plotted 

for three basel~nes and at 1000, 1100, and 1200 °c, respectively. 

NSR was kept constant at 2 for all cases. The residence time 

needed· to reach a steady state condition was shortest at 1200 °C; 

the baseline values did not affect the time to reach a steady state 

value at a temperature. As for the controlled NOx level, starting 

from 100, 200, or 500 ppm resulted in the same reduced NOx of about 

30 ppm at 1000 °c. The controlled levels were higher for the 500 

ppm baseline case than the 200 ppm case by 15 ppm at 1100 °C and 

100 ppm at 1200 °c. 
As shown in figure 7c, NOx increases with chemical injection for 

a baseline of 100 ppm with temperature at 1200 °C. However, when 

the baseline is 500 ppm, a significant reduction can be achieved. 

This illustrates that higher NOx baselines shift the right side of 

the NOx reduction versus temperature curve toward higher 

temperatures. A plot of the NOx reduction curve for three baseline 

NOx levels, as shown in figure a, clearly shows the widening of 

temperature window. 

Critical NOX 

In figure 6, the curve which represent the reduced NOx 

concentrations at 1 second residence time and at temperatures 

between 900 and 1300 °c is the lowest achievable NOx concentration 

curve. As discussed earlier, increases in residence time or NSR do 

not lower NOx below this curve. At temperatures below 900 °c, 

calculations with 10 seconds of residence time and several NSRs 

were performed to determine the lowest achievable concentration. 

This minimum achievable NOx concentration through urea injection, 

is termed as 'Critical NO ', as first indicated by Fenimore for the 

Thermal DeNOx process. ~n figure 9, critical NOx concentrations 

are plotted as a function of temperature for three baseline NO 

levels. The baseline level affects the reduced concentration, bul 

only at temperatures above 1050 °C. The critical NOx concentration 

therefore is a function of baseline NOx only at temperatures above 

1050 °c as shown in figure 9. 

The critical NOx is affected strongly by temperature and baseline 

NOx. This critical NOx concentration is less than 40 ppm at a 

temperature of 1050 °C and even lower at temperatures below 1000 

0 c. These low levels usually do not limit the process application. 

Critical NOx concentration increases rapidly as temperature 

increases beyond 1050 °c, and therefore, the process application is 

limited at high temperatures. However, as long as baseline NOx is 

above the critical NOx, the reduction should be achieved. 

Laboratory· and Field Verification 

The model study has indicated that critical NOx limits the 

achievable NOx concentration regardless of treatment rate or 

residence time. The left side of the temperature window shifts to 

a lower temperature with an increase in residence time while the 

right side shifts to a higher temperature when starting with a 

higher baseline NOx concentration. This finding is verified in 

this section througn experimental results. 

case 1. 

During a process demonstration at an ethylene cracker, NOx 

reduction was limited regardless of the NOxOUT Process parameters. The cracker unit operated steadily at a temperature of 
approximately 1050 °c. When the unit operated at a higher NO 

baseline, NOx reduction increased, but the lowest achievable NO~ concentration remained the same, as shown in figure 10. Increasing 

NSR or other methods to optimize chemical distribution had no 

effect on .the minimum controlled NOx. This showed the existence of 

critical NOx which is unaffected by NSR, chemical distribution, or 

baseline NOx. 

case 2. 

The NO level decreases with increasing NSR as long as gas tempera~ure at the injection point is within the temperature 

window. At temperatures above 1100 °c, the model, however, 

calculated a NOx increase when NSR is increased beyond the level 

where the minimum NOx has been achieved. Testing at a 160 MWe 

tower boiler firing oil and at a 19 MWe stoker fired boiler burning 

wood waste verified this phenomenon of NOx increase as indicated by 

the model. As shown in figure 11, NOx was reduced to the minimum 

concentration at NSR of 3. 5. A further increase was counter 

productive as NOx increased slightly with NSR. Gas temperature at 

the injection location was greater than 1150 °c. A testing at a 

stoker unit also showed an increase in NOx when NSR increased 

beyond the treatment rate where minimum NOx was achieved, as shown 

in figure 12. Gas temperature for this case was in excess of 1100 

°C at the injection location. This behavior was only seen for 

those applications where gas temperatures were higher than 1100 °c. 

case 3. 

The temperature window for NOx reduction widens by shifting the 

left side of the curve to a lower temperature with an increase in 

residence time. Testings at municipal solid waste combustors 

showed that high NOx reductions were achieved as shown in figure 13 

[11]. Ammonia emissions were limited to less than 20 ppm. Gas 

temperatures at injection level for these testings were 900 - 950 

0 c, and available residence times in this temperature range were in 

excess of 1 second. This type of performance was not seen from 

utility boilers where residence time is very limited. 

case 4. 

An increase.in NOx baseline shifts the right side of the curve to 

a higher temperature. To verify this, a pilot scale combustor was 

operated at 1200 °c and NOx baseline was increased from 150 to 750 

ppm. At baseline NOx below about 200 ppm, NOx increased with urea 

injection, while at higher than 200 ppm, NOx decreased as shown in 

figure 14. A comparison with an ammonia injection showed that urea 

is more effective in reducing NOx at these high temperatures than 

ammonia. 
conclusions 

The reaction kinetic model has proven to be a valuable tool in the 

development of the N0¥0UT Process. Model predictions with respect 

to the temperature w1ndow for reaction, the effect of residence 

time, and the phenomenon of critical NOx, which limits NOx 

reduction at the high end of the temperature window, have all been 

verified in laboratory and field tests. The temperature window has 

been shown to be defined primarily by residence time at the low 

temperature (left) side and by baseline NOx at the high temperature (right) side of the window. 

The model is now used to define temperature/residence time 

requirements for specific applications and to predict maximum 

achievable NOx reduction. The model has also shown that the NOxOUT 

Process can oe applied at higher temperatures than previously 

thought applicable provided that the initial NOx baseline is 

sufficiently high. An example of such an application is the 

utility "cyclone" boiler which is used to burn coals of generally 

low quality. These boilers typically have furnace exit 

temperatures of 1200-1250 °C. These temperatures would normally 

have been said to be outside the temperature window for urea. 

However, NOx produced in these boilers are high in concentration. 

This level of NOx which is about 1000 ppm is substantially above 

the critical NO concentration at 1250 °C. Thus a significant 

amount of NOx re8uction should be achievable by urea injection into 

the upper furnace of these boilers. 

References 

1. Mohnen, V.A., "The Challenge of Acid Rain", Scientific 

American, Vol. 259, No. 2, p.JO, August, 1988 

2. Benson, c. E., Chittick, G. D., and Wilson R. P., Selective 

catalytic NO Reduction Technology for Cogeneration Plants, 

Arthur o. Lit~le Report, Prepared for New England Cogeneration 

Association, November 1988. 

J. Lyon, R.K., u.s. Patent 3,900,559, 1975. 

4. Lyon, R.K., "Thermal DeNOx: Controlling Nitrogen oxides 

Emissions by a Noncatalytic Process", Environ. Sci. Techno!., 

Vol. 21, No. J, p.2Jl, 1987. 

5. Arand, J.K., and Muzio, L.J., u.s. Patent 4,208,386, 1980. 

6. Arand, J.K., Muzio, L.J., Teixeira, D.P., u.s. Patent 

4,325,924, 1982. 

7. Epperly, W.R., Broderick, R.G., and Peter-Hoblyn, J.D., 

"Control of Nitrogen oxide Emissions from Stationary Sources", 

American Power Conference, April 20, 1988, Chicago, IL 

a. Epperly, W.R., Hofmann, J.E., "The NOXOUT Process for 

Reduction of Nitrogen oxides", Presented at the a1st A.P.C.A. 

Annual Meeting, Dallas, Texas, June, 1988. 

9 . Hofmann, J. E. , von Bergmann, J. , Bokenbr ink, D. , and He in, K. , "NOx Control in a Brown coal-Fired Utility Boiler", EPRI/EPA 

Symposium on Stationary Combustion NOx Control, March a, 1989 

10. Epperly, W.R., Hofmann, J.E., "Control of Ammonia and Carbon 
Monoxide Emissions in SNCR Technologies", Prepared for AIChE 

1989 summer National Meeting, August 20, 1989. 

11. Hofmann, J. E. , Luftg lass, B. K. , sun, w. H. , Ferraro, F. A. , Porter, T.J., Pachaly, R., "NOx Control for Municipal waste 

Combustors", Present~d at Air & Waste Management Association 

Annual Meeting, Pittsburgh, PA., June, 1990. 

12 Kee, R.J., Miller, J .A., Jefferson, T .H., "CHEMKIN: A General 

Purpose, Problem-Independent, Transportable, Fortran Chemical 

Kinetics Code Package", Sandia Laboratories Report #SANDS0-

8003, Livermore, CA, 1980. 

13 Hindmarsh, A.C., "ODEPACK, A Systematized Collection of ODE 

Solvers", Scientific Computing, R.S. stepleman et al. (eds.), 

Vol.l of IMACS Transactions on Scientific computation, p.ss, 

North-Holland, Amsterdam, 1983. 

14 Radhakrishnan, K., "A Comparison of the Efficiency of 

Numerical Methods for Integrating Chemical Kinetic Rate 

Equations", 1984. 

15 Reynold, w.c., STANJAN, Copyright Stanford University, 1987. 

16 Miller, J.A., Bowman, C.T., "Mechanism and Modeling of 

Nitrogen Chemistry in Combustion", Fall Meeting of the Western 

States Section/The Combustion Institute, Dana Point, 

California, October, 1988. 

17 Caton, J .A., Siebers, D.L., "Comparison of Nitric Oxide 

Removal by cyanuric Acid and by Ammonia", Fall Meeting of the 

Western states Section/The Combustion Institute, Dana Point, 

California, October, 1988. 
I NOxOUT Kinetic Modelj 

Thermodynamic Data Reaction Set 

~ / 

CHEMKIN ~---

+ 

Initial Condition __,...Plug Flow Model • ~ LSOOE 

i 

Results 

Fig. l 

POST COMBUSTION NOx REDUCTION 

with UREA 

Urea 

/~ ... HNCO NH3 

I I 

I i 

NCO ' ' NH2, 

//'1 I --------- NO ~ I "'---"'-..,_ ... / . ', I ~ 

NO r ~ NO 

I N20 ! 

~N2/ Fig. 2 
I PILOT SCALE COMBUSTOR I 

INJECTOR 

\ CHEMICALBURNER 

ZONE 

ELECTRICALLY HEATED 

NOx - 1 DRYER CHILLER 

~~ Ji---~=--t_J N20 

Fig. 3 

Effect of Temperature on NOx Reduction 

Urea Injection, NSA = 1.8-2.3, NOxl = ,.. 200ppm 

Comparl.on of MOdel vs. Experimental 

250~--------------------------------------------~ 

200 

-

~ 150 

a. 

a. 

-)( 

0100 

z 

50 

: TEMPERATURE .._. WINDOW ____... 

0.2 sec 

0~----~--------------------------------~----~ 600 700 800 900 1.000 1,100 1,200 1,300 

Temperature (C) 

Fig. 4 
350 

300 

250 

~200 Q_ 

!h 

X 

0 150 z 

100 

50 

0 

0 

Effect of NSR on NOx Reduction 

0.5 

R .. idenc:a Time 11 1 sec, NOxl = 200 ppm 

NOXOUT Kinetic Modet 

1 5 2 

NSA 

2.5 

Fig. 5 

3 

1300C 

1200C 

800C 

11 00 c 

1000C 

900C 

Effect of Residence Time on NOx Reduction 

NSR = 2, NOxl = 200 ppm 

NOxOUT Kinetic Model 

3.5 

300 ~------------------------------------------------. 

250 

-200 

E 

a. 

.3; 150 

X 

0 

z 100 

50 

BOO 900 1.000 1,100 1,200 1,300 1,400 

Temperature (C) 

0.1 0.2 0.4 0.6 0.8 1.0 

---£:,-- - ... o...... - _.,._ - -.. ----.. - _,_.,_ __ 

Fig. 6 
{'\ 

Effect of Baseline NOx 

NSA = 2, Temperatura= 1000 C 

NOxOUT Kinetic Modet 

~~--------------------------------------------~ 

500 f-

-400f-· 

~ 

a.. 

9:,300-

x 

0 

z 200 r: 

100 ~-~----~-- --~-~~--~--~~--~----------~~ 

0~--------------------------------------------~ 0 

600 

500 ~ 

-400 ~-. 

~ 

a.. 

fh300 ~ 

X 

0 

z 200 ~ 

.. ~- ~ 

100 I--

0 

0 

0.1 0.2 0.3 

Time (second) 

Fig. 7a 

Effect of Baseline NOx 

NSA:: 2, Temperatura= 1100 C 

NOXOUT Kinetic Model 

0.05 0.1 

Time (second) 

0.15 

Fig. 7b 

0.4 0.5 

0.2 
f 

Effect of Baseline NOx 

NSR = 2. TemperatuN = 1200 C 

NOxOUT Kinetic MOdel 

~r----------------------------------------------

500 f-

........... 400 .__. 

~ 

a. 

~300 .... ···. 

)( ······································ ... . ························································· 0 

z 200 ~. ·--------------------·---·-------------------------------·-------------

100 ~ 

0~--------------------------------------------~ 0 0.05 0.1 0.15 0.2 

Time (second) 

Fig. 7c 

Effect of Baseline NOxon Temperature Window 

NSA = 2, Realdence Time = 1 sec. 

NOxOUT Kinetic Model 

100-----------------------------------------------

........... 50 .'#, 

-

c: 

0 

13 

,----------

BaselineNOx 

SOOPPM 

~ 0~----------------------------~--~--------~ 1:l 

Q) 

a: 

)( 

0 

', 

• 200PPM 

z (50) 

100PPM 

(100) L.-----....:......----__:_----------~---__..:....---------------..~ 

700 800 900 1,000 1,100 1,200 1,300 1,400 

Temperature (C) 

Fig. 8 
.l Critical NOx Concentration 

3% ExCHa OXygen 

NOxOUT Kinetic Model 500.-----------------------------------------

400 ~ 

X 

0 200 r--

z 

100 r--

NOxi::z500 PPM 1 

( 

r , • 

r .·· 

NOxi= 100 PPM 

oL-------==========~--------------~----~ 700 800 900 1,000 1.100 1.200 1,300 

Temperature (degrees C) 

Fig. 9 

NOx REDUCTION AT ETHYLENE CRACKER 

Temperature - approximately 1 050 C 

1.400 

100~----------------------------------------

-90 

N 

0 

?ft. 80 

('I) 

~ 

~ 70. 

~ 

a. 

a. 60 

X 

0 

z 50 

Reduction Limited by Critical NOx 

Independent of Initial Baseline 

~~------~------------------------------~ 0 5 10 15 20 25 

NSR. 

Fig. 10 
f"', ' l 

NOx Reduction at High Temperature 

160 MWe 011 Fired Tower Boiler 

240 ~ 

~ [~ Gas Temperature at Injection Point: 

~200 l ~~-------------------~--------------~B 

>1150 c 

0 

z 

-

~ 

180 ~ 

160 ~ 

0 

240 

220 

200 

8: 180

1 

-X 

0160 

z 

140 

120 

2 3 4 5 

NSR 

Fig. 11 

NOx Reduction at High Temperature 

19 MWe Wood Waete Stoker Fired Boiler 

Gas Temperature at Injection Point: > 11 00 C 

6 

100~------~--------~------~--------~------~ 0 0.5 1.5 2 2.5 

NSR 

Pig. 12 
(\ 

Comparison of NOxOUT Performance from MWC's 

so------------------------------------~---------------

60 -

c: 

j 

d 40 

z 

j 

20 

c 

0~------~------~------~--------~------~------~ 0 

60 

40 

.....-. 

#. 

20 

-

c: 0 0 

n 

::l (20) 

"C 

Q) 

a: (40) )( 

0 

z (60) 

(80) 

(100) 

0 

0.5 1 1 5 2 

Normattzec:J Stoichiometnc Aatro (NSR) 

A B C 

• --·*-·-· ····0·· 

Fig. 13 

Effect of Baseline on NOx Reduction 

RHult from Pilot Scale Combuator, NSA = 2 

Gas Temperature at Injection Point: 1200 C 

Urea Injection-------... 

--- --- -----. --- --- .--

~------

..•• •• '-Ammcnl&lnieclien 

,' 

,' 

... 

200 400 600 

Baseline NOx (PPM) 

Fig. 14 

2.5 3 

--~ 

800