13 :2-l 'B'l iOS 9!33 32-lO .-\LCO FrEL TECH @ OO-l t 014 

Reduction of NOx Emissions 

from Cement Kiln/Calciner 

through the Use of the 

NOxOUT® Process 

By W.H. Sun, M.J. Bisnett, and D.W. Kirk, Narco Fuel Tach and 

H.E. Stauch and J. Hille, Ash Grove Cement Company 

ABSTRACT 

Post-combustion urea injection has proven to be an 

effective method in controlling NO;r; from various combustion. sources. This process, a selective non-catalytic 

reduction process known as NOxOU'J"', has been successfully demonstrated in a cement kiln I calciner 

operated by Ash Graue Cement. Testing was done 

under ten different kiln I calciner operating conditions. 

Usinc three to four injectors, NOx was efficiently 

reduced from 350 to 600 pounds per hour (3.5 to 

6. 0 lb I ton of clinker) to less than l 00 pounds per hour 

(1.0 lb I ton of clinker). This calculates to a NOx 

reduction of >80% for most cases. Chemical utiliza· 

tion was greater than 50%. A high degree of mi:r:ing 

and a long residence time at an appropriate tempera· 

ture present in the preheater tower contributed to these 

excellent results. An average ammonia slip was four 

ppm above a baseline level at normalized stoichio· 

metric ratio of 1. 

Based on this demonstration, cement kiln I calciners 

have been identified as an ideal application for the 

NOxOUT Process. NOx was efficiently and effectively 

reduced with minimal by-product emissions and 

uirtually no effect on plant operations. 

INfRODUCTION 

The oxides of nitrogen (NOx) affect the environment 

by contributing to acid rain, ground level ozone, and 

photochemical smog. The Clean Air Act Amendments 

CCAA) of 1990 address the control ofNOx emissions 

in Titles I (non-attainment) and IV (acid rain) and 

state regulators are required to submit plans (SIPs) 

to comply with the CAA. In addition to fossil-fuel fired 

utility boilers, which are the major source, industrial 

sources ofNOx such tts process heaters, incinerators 

and kilns may be regulated depending on their emis· 

sion rate and the level of attainment of the National 

Ambient Air Qualilty Standards in the area of these 

sources. 

NOx emissions from cement kilns are significant (>1000 

TPY) due to the process requirements. In a cement kiln, 

gas temperature is raised above 2700°F to form 

"clinker". This heat is provided by burners whose peak 

flame temperatures can exceed 3000°F. Since NOx formation during combustion increases with temperature 

and oxygen content, NOx concentrations resulting from 

such high temperature process can exceed 1000 ppm. The 

thermodynamic equilibrium concentration of NOx at 

3000QF and 1% oxygen with natural gas is 1500 ppm. In 

addition, NOx emission increases with nitrogen content 

in the fuel termE~d, fuel-NOx. The NOx generation from 

fuel bound nitrogen is also sensitive to oxygen content in 

the flame zone. 

Utilizing its sensitivity to oxygen content, NOx emission 

can be reduced through combustion modification. While 

maintaining the flame temperatlll."e, combustion air can 

be staged to provide a slightly fuel-rich condition at the 

flame zone. At 3000°F, the equilibrium NOx concentration decreases to 500 ppm at the stoichiometric condition and even lower under oxygen-starved conditions. 

Additional air is injected downstream of the peak temperature zone to complete the combustion. A combustion 

modification is an effective method to control NOx but 

the extent of NOx control is limited because a high 

temperature zone, which generates NOx, must still be 

provided for the process. 

SNCR Process 

Selective non-catalytic NOx reduction (SNCR) processes 

have effectively controlled NOx em.issions in various type: 

of boilers firing all types of fossil fuel or waste-fueL 1.2.• 

Unlike combustion modifications. ammonia' or ureas is 

injected in the post-combustion zone, typically at temperatures between 1600 and 2200°F. Therefore, the 

process does not affect the burner operations. The levei 

ofNOx removal depends on the res.~;ent feedrate and car. 

range from 30 to 70%. Some critical process parameter~ 

are temperature, residence time, mixing between th~ 

reagent and flue gas, and uncontrolled NOx level. 

Presented at the International Specialty Conference on Wastll Combustion in Boilers and Industrial Fvrnaees, 

sponsored by A'r & Waste Managemen! Association, Kansas City, Missouri, Apri/21. 1994 
•• 

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A leading SNCR process that injects stabilized urea 

to control NOx is the NOxOUT Process, marketed by 

Nalco Fuel Tech. In the process, NOxOUT·A, a stabi· 

lized urea solution, is injected into a furn!lce and 

reacts with NOx in the gas phase to produce molecular nitrogen, water, and C02

• 

Urea+ Nitrogen+ Oxygen-.> Nitrogen +Carbon +Water 

Oxide Dioxide 

A dime~ionless parameter that describes the reagent 

flowrate 1s the normalized stoichiometric ratio (NSR). 

This ratio is defined as an actual molar ratio of urea 

to inlet NOx divided by the stoichiometric molar ratio. The reagent utilization is the ratio ofNOx reduction and NSR. 

Nalco Fuel Tech expanded the technology by devel· 

oping chemical injection hardware, widening the 

applicable temperature range, and process control 

expertise required for commercial applications. The 

design of a system is guided by a computational £1 uid 

dynamics (CFD) and chemical kinetic (CKM) models, in addition to results from field measurements. 

These co~puter models determine the ideal temperature reg~on for chemical reaction and the optimum 

injection strategy to distribute the reagent. The 

NOxOUT Process also provides effective load following capabilities through control of reagent concentration. multilevel injection, droplet size and spray 

patterns, and the introduction of chemicals at selected 

injector locations. There are substantial benefits 

gained from the application of the NOxOUT Proce$S 

compared to first generation NOx control technolo· 

gies, such as ammonia injection. These benefits are 

briefly SWlllnarized below: 

• Use of non-toxic, non-hazardous chemicals 

• Potentially lower capital cost due to the lack of 

large system compressors and elimination of 

anhydrous ammonia storage, handling, and safety 

equipment 

• Lower operating costs resulting primarily from 

minimization of gas (steam or compres:sed air) 

requirements 

• Inherently more effective control of spray patterns 

and chemical distribution for better mixing with 

the use of liquid rather than gas-based reagents, 

thereby resulting in better chemical utilization 

• Chemical enhancers which can be used to improve 

control of potential by-product generation while 

reducing NOx over an expanded temperature range 

There are over 100 commercial applications of the 

NOxOUT Process in the world and over 200 short· 

:erm test applications. Recently, the NOxOUT 

Process has been demonstrated at a cement plant 

operated by Ash Grove Cement in Seattle. 

CE:l\IIENT KILN/CALCINER 

Ash Grove Cement in Seattle operates a calcinerlkiln 

that processes about 160 tons of solids per hour to 

produce -100 tons of clinker. This unit is an energy 

efficient design that consists of a kiln and a preheater/ 

precalciner. The preheater tower, as shown in Figure 

1, is made up of five cyclones and a calciner. The plant 

is equipped with an elaborate feed system, a finishing mill, and storage silos. The entire plant is well 

instrumented and automated. 

Combustion products flow countercurrent to solid 

flow. Hot flue gas is generated with a burner firing 

natural gas or coal at one end of a kiln. Gas flows 

through a slightly inclined rotating kiln to a calciner. 

Inside the kiln, lime, silica, and clay undergo reac· 

tions to form clinker which is subsequently milled to 

produce cement. The calciner is at the bottom of a 

preheater tower and is about 60 feet high and l4 feet 

in diameter. To further improve fuel efficiency, gas or 

coal in an amount of 5 to 10% of total heat input is 

injected into the calciner. Flue gas enters at the bottom of the calciner and flows upwards carrying solids dropped from the bottom of cyclone #4. Solids are 

calcined and exit to cyclone #5. Solids are separated 

from the gas, dropped through a bottom chute to the 

bottom of the calciner, and then flow into the kiln. 

Flue gas exits cyclone #5 into cyclone #4 and continues upwards to eventually reach cyclone #1. Finely 

groWld solids of limestone, silica, clay and iron mill 

scale are fed into cyclone #2 and flow downwards 

through the cyclones. Flue gas enters the bottom of 

the calciner at about 2100°F and cools to 550°F at 

the top of cyclone #1. Flue gas then flows through a 

raw mill, a cyclone, and a baghouse before exiting to 

the atmosphere. 

Flue gas is analyzed at several locations: kiln exit, 

preheater e:cit, and stack. NOx, CO, and 0 2 are monitored at the kiln exit while CO and 0 1 are measured 

at the preheater exit. At the stack, NO:"' SOx, CO, 

and 0 2 are measured. Opacity and flue gas flowrate 

are also measured at the stack. The stack emission 

limits for the plant are 422 pounds per hour (pph) of 

NOx, o38 pph of CO, and 40 pph of SO •. Emissions of 

so2 are well controlled from reactionS between lime 

and S02 to form CaS04 in the preheater/calciner and 

a raw mill. When the raw mill needs servicing, 

sodium bicarbonate is injected before the baghouse 

to control SO. emissions. Particulates are well con· 

trolled by the baghouse indicated by low opacity. NOx, 

however, can be higher than the limit when firing 

with gas in the kiln. NOx emission decreases below 

the limit when fired with coaL However, NOx still 

may exceed the limit with coal if the kiln needs to 

operate at higher than typical kiln temperature to 

process material that is "hard to bum". It was desir· 
. 09 ·· 21 : 95 13 : :! 6 "Bl iOS 983 32-1 0 AL O FL"EL TECH 

----~----------~~~~~~----~~ 141 006 / 01-1 

.. 

0 

0 

0 

0 

Feed 

Calciner 

fuel 

Kiln 

i ·----------··· ····· ···-To coal mi!ls 

------- ----~ on sheet 3 

Preheater ' 

··············--------- To raw mill 

on sheet 1 fan 

Figure 1 - Cement kilnlcalcin.er 

?!:1111 air !Upply 11:: I ~ tE lnji:C!Org 

I I L.rChamocal maturing : I f1::; 

r --------,:liJmp:; ~ .._ n~o~ 

~ $ ~~=~ L------!:..~ 'n41ne n:ua1er 1l Fl~orcu alkln Pllm:l 

I 

Plant W819f-------+ 8 

Figure 2 - NOxOUT equipment layout 

able, therefore, to test the NOxOUT Process to determine its effectiveness in NOx control under all 

operating conditions and to establish its effect on 

other emissions and plant operations. 

NOxOUT EQUIPMENT AND INJECTION 

LOCATIONS 

The chemical and water pumping equipment were 

delivered and used in a 20 ft. trailer. The reagent, 

NOxOUT-A, was delivered and stored in a 4500 gallon insulated tanker trailer. The equipment consisted 

of a chemical recirculation module with an in-line 

Kiln 

fuel 

o a a a 

To clinker storage 

chemical heater, chemical metering pumps, water 

pumps, chemical distribution panels, and sufficient 

number and type of injectors to test several spray 

patterns. Inside the trailer, metered NOxOUT-Aflow 

and water were mixed with a static mixer before flow~ 

ing to the distribution panel. On this panel, liquid 

tlowrate to each injector was controlled with a needle 

valve and atomizing air pressure was controlled with 

an air regulator. NOxOUT equipment layout is shown 

in Figure 2. 

Observation ports at the cnlciner were modified to 

accommodate NFT injectors. Three ports at the top 

of the calciner, t hree ports halfway up the calciner, 

and four ports at the bottom of the calciner were used 

to inject NOxOUT-A. Gas temperature was also measured through these ports using a suction pyrometer. 

RESULTS AND DISCUSSIONS 

The performance of the NOxOUT Process was 

optimized through a series of tests at kilnlcalciner 

operating conditions listed in Table 1. Solid feedrate 

was steady at 160 tons per hour and kiln was fired 

with natural gas. These conditions covered a wide 

operating range of fuel firing and excess air conditions. At each operating condition, tests were carried 

out to achieve effective chemical distribution by vary· 

ing the following parameters: air and liquid flowrates, 

type of injector tip, injection level, and treatment rate. 

Effective chemical distribution is achieved when a 

sufficient amount of chemical is distributed in a 

region where temperature and residence time are 
·---· 13 : 28 'B'l i08 983 32-10 ~-~LCO FrEL TECH 08 01-1 

Table 1 - Tested Kiln/Calciner Conditions 

Fuel to Heat Input to Praheater Uncontrolled 

calclner calclner oxygen(%) NOx (pph) 

gas 5% 1.8-2.1 415-455 

2" gas 9% 2-2.2 420-520 

3' gas 5% 2-2.2 42o-520 I 

4 gas 5% 2.2 500-550 

5 I gas 5% 2.2- 2.4 350-400 

6 gas 5% 2.4-2.7 45o-530 I 

7 gas s•;. 2.3-2.5 45C-500 

e coal 9% 2.3-2.7 460-550 

9 coal 5% 2.6-2.9 340-500 

10 coa I 9% 2.~ 2 41 0-426 

• Raw mill was off snd soeflum blt:aroaiiBtB injscrlon wA$ on 

from several operating conditions showed NOx reduction was lower by 20% at NSR 1.5 when oxygen 

increased from 2% to 2.6%. Even at this reduced efficiency, the reduction was still high: -50% at NSR 1. 

NOxOUT-A injection through three different elevations in the calciner showed similar reductions, indicating that process requirements are satisfied as long 

as the reagent i.s injected in the calciner. Baseline 

NOx varied from 350 pph for condition 5 to 550 pph 

for condition 4. This variation in the baseline had 

negligible impact on NOx reduction which remained 

at -60% at NSR 1. 

The NOxOU'l' Process, like any other chemical reaction, requires good mixing between the reagent and 

NOx and appropriate temperature and residence 

time. In this kiJnlcalciner application, the reagent was 

well mixed with the flue gas due to highly turbulent 

flows in the calciner and cyclone preheater and an 

appropriate placement and use ofNFTinjectors. Gas 

temperature of about 1530°F is at the lower end of 

the process temperature window. However, high CO 

concentration from coal or gas oxidation inside the 

calciner shifted the required process temperature to 

a lower temperature.

6 The calciner temperatures, 

therefore, became more optimum as the result of 

elevated CO concentration. The available reaction 

time at this temperature exceeded 1 second in the 

calciner and another 1-2 seconds in cyclone #5. This 

reaction time of 2-3 seconds is higher than reaction 

times of 0.5 U> l second in other applications. As the 

available reaction time increases, the required 

temperature shifts U> a lower temperature and NOx 

reduction efficiency increases.

6 This combination of 

long residence time, good mixing, and an appropriate reaction temperature (a result of elevated CO 

and long residence time) gave excellent process 

performance. 

A typical heat input to the calciner was about 5% of 

the total heat input to the kilnlcalciner. Increasing 

this heat input had a negligible effect on NOx reduction when gas was injected into the calciner. Changing the calciner fuel from gas to coal or decreasing 

the coal feedrate decreased the reductions. This 

decrease was likely caused by an increase in oxygen 

concentration that accompanied coal injection. When 

coal is injected into the calciner, air carries pulverized coal from a mill to the calciner. This additional 

air increased preheater oxygen from 2 to 2.5% for gas 

U> 2.4 to 3.3% for coal. High oxygen preheater condition with gas as the calciner fuel was virtually the 

same as the coal fired cases with high 0 2• Similarly, 

improvement in reduction with increasing coal 

feedrate is because of reduced preheater oxygen. As 

indicated in Table 1, oxygen was the highest at 2.8-

3.3% under 5% coal and 2.6-2.7% with 9% coal 

feedrate. 

BY-PRODUCT EMISSIONS 

SNCR processes can release unreacted ammonia, 

known as "ammonia slip", and increase CO above 

baseline levels. A part of the NOxOUT Process technology is a method and know-how to minimize byproduct emissions. During this test, NOxOUT-A injection increased concentrations of co and so2 in 

stack gas. This increase was related to oxygen concentration at the preheater exit and can be minimized 

by injecting through the bottom ports, operating the 

calciner at oxygen greater than 2.3%, or by limiting 

the NOxOUT-A flowrate to less than NSR of 0. 7. 

co 

The CO emissions exiting the preheater were higher 

than from the kiln. At the kiln exit, CO was typically 

less than 0.02% while the pre heater exit gas contained 

between 0.08 and 0.1 %. This CO increase in preheater 

is the result of gas or coal firing in the calciner in 

addition to oxidation of organics in the raw mix. The 

temperature in the calciner is 1500 to 1550°F and 

oxygen concentration is typically less than 1%. Such 

condition delays combustion of gas or coal resulting 

in an elevated CO emission. 

In Figure 6, CO at the stack corrected to 10% oxygen 

is plotted against preheater exit oxygen concentration for several chemical injection rates (NSR) and 

without injection. The best fit curves through each 

set of data are also presented in the figure. The stack 

CO emission increased with decreasing preheater 

exit oxygen and with increasing NSR. This CO 

increase was negligible at preheater oxygen concen· 

tration greater than 2.4% and at NSR less than 0.7. 

When the reagent was injected through the bottom 
--· 13 : 28 '5'1 i 08 983 32.!0 ~.-\LCO F'l'EL TECH ~008 0l.l 

Table 1 - Tested Kiln/Calciner Conditions 

Fuel to Heat Input to Preheater Uncontrolled 

calclner calc:lner oxygen(%) NOx (pph) 

gas 5% 1.8-2.1 415-455 

! 2. gas 9% ~-2.2 420-520 

3" gas 5% 2- 2.2 420-520 I 

4 gas 5% 2.2 500-550 

5 gas 5% 2.2-2.4 350-400 

6 gas 5% 2.4-2.7 450-530 I 

7 gas 5% 2.3-2.5 45o-500 

e coal 9% 2.3-2.7 48()-550 

9 coal 5% 2.6-2.9 34CJ-500 

10 coal 9% 2.C>-2.2 410-426 

• Raw mill was off sna $Odium 1:1/caroonate lnjectJo•, was 01) 

from several opera tin~ conditions showed NOx reduction was lower by 20% at NSR 1.5 when oxygen 

increased from 2% to 2.6%. Even at this reduced efficiency, the reduction was still high: -50% at NSR 1. 

NOxOUT-A injection through three different eleva· 

tions in the calciner showed similar reductions, indicating that process requirements are satisfied as long 

as the rea~ent is injected in the calciner. Baseline 

NOx varied from 350 pph for condition 5 to 550 pph 

for condition 4. Thls variation in the baseline had 

negligible impact on NOx reduction which remained 

at -60% at NSR 1. 

The NOxOUT Process, like any other chemical reaction, requires good mixing between the reagent and 

NOx and appropriate temperature and residence 

time. In this kiln/calciner application, the reagent was 

well mixed with the flue gas due to highly turbulent 

flows in the calciner and cyclone preheater and an 

appropriate placement and use ofNFT injectors. Gas 

temperature of about 1530°F is at the lower end of 

the process temperature window. However, high CO 

concentration from coal or gas oxidation inside the 

c:alciner shifted the required process temperature to 

a lower temperature.6 The calciner temperatures, 

therefore, became more optimum as the result of 

elevated CO concentration. The available reaction 

time at this temperature exceeded 1 second in the 

calciner and another 1-2 seconds in cyclone #5. This 

reaction time of 2-3 seconds is higher than reaction 

times of 0.5 to 1 second in other applications. As the 

available reaction time increases, the required 

temperature shifts to a lower temperature and NOx 

reduction efficiency increases.

6 This combination of 

long residence time, good mixing, and an appropri· 

ate reaction temperature (a result of elevated CO 

and long residence time) gave excellent process 

performance. 

A typical heat input to the calciner was about 5% of 

the total heat input to the kilnlcalciner. Increasing 

this heat input had a negligible effect on NOx reduction when gas was injected into the calciner. Chang· 

ing the calciner fuel from gas to coal or decreasing 

the coal f~edrate decreased the reductions. This 

decrease was likely caused by an increase in oxygen 

concentration that accompanied coal injection. When 

coal is injected into the calciner, air carries pulverized coal from a mill to the calciner. This additional 

air increased preheater oxygen from 2 to 2.5% for gas 

to 2.4 to 3.3% for coal. High oxygen preheater condition with gas as the calciner fuel was virtually the 

same as the coal fired cases with high 0 2

. Similarly, 

improvement in reduction with increasing coal 

feedrate is because of reduced preheater oxygen. As 

indicated in Table 1, oxygen was the highest at 2.8-

3.3% under 5% coal and 2 .6- 2. 7% with 9% coal 

feedrate. 

BY-PRODUCT EMISSIONS 

SNCR processes can release unreacted ammonia, 

known as "ammonia slip", and increase CO above 

baseline levels. A part of the NOxOUT Process technology is a method and know-how to minimize byproduct emissions. During this test, NOxOUT·A injection increased concentrations of co and so2 in 

stack gas. This increase was related to oxygen concentration at the pre heater exit and can be minimized 

by injecting through the bottom ports, operating the 

calciner at oxygen greater than 2.3%, or by limiting 

the NOxOUT-A flowrate io less than NSR of 0. 7. 

co 

The CO emissions exiting the preheater were higher 

than from the kiln. At the kiln exit, CO was typically 

less than 0.02% while the preheater exit gas contained 

between 0.08 and 0.1 %. This CO increase in preheater 

is the result of gas or coal firing in the calciner in 

addition to oxidation of organics in the raw mix. The 

temperature in the calciner is 1500 to 1550<>F and 

oxygen concentration is typically less than 1%. Such 

condition delays combustion of gas or coal resulting 

in an elevated CO emission. 

In Figure 6, CO at the stack corrected to 10% oxygen 

is plotted against preheater exit oxygen concentra· 

tion for several chemical injection rates (NSR) and 

without injection. The best fit curves through each 

set of data are also presented in the figure. The stack 

CO emission increased with decreasing preheater 

exit oxygen and with increasing NSR. This CO 

increase was negligible at preheater oxygen concen· 

tration greater than 2.4% and at NSR less than 0.7. 

When the reagent was injected through the bottom 
• 09 : 21 : 95 13 : 2!3 '5'1 708 983 32.!0 

1~0r---------------------------------~ 

0 

):1 1400 Q 

£ 1200 , 

~ 

~ 1000 

8 

~ BOO 

g &00 

~ 400 iii 

' ... ... 

0 M -- 0 0 - _ .. ~ • • ..... 4J= .... -4"t'':llt,.. 

200 "=s---~2.~o-----:-2'-s-------:"3"":-o----.J3s 

P•e~&G1er oxygen. '4 

NSI'I- 0 0.3·0.7 0.8·1.1 1.3·1.1. 6·1.8 2.0·2.4 

--... .;,.. .. -->-- - - • 

Figure G -Effect of NO~OU'I!A injection on. atack 

co 

60 

0 

~ so 

~ 

'2 

~ 

~ 

' ,. 

' -- ~ ,_ ... . ......... -- .... ... ,_ .. __ ,_ ' "': ::: .. ' . ..._:.., ::.:.-- ' 0 ··.:. · .. ···,-· ·--·--- · -· 

'• .. ~ ... 

. - · >·:~·.~ -~&: ~~ ·- [ 

Q. 

~ 

·- --... ~·tor..,.,..~ .... "'~ .:· :: .. i . 0 " ' 0 .•. ..... ......... ~ 

~ 0 

\.6 1.8 2.0 2.2 2.4 2.6 2.1! 3.0 

Pre eat~r ox ~en. ,-, 

NSFI- 0 0.3·0.7 OJ!-1.1 1.3·1 4 1.6-i.S 2.0.2.4 --iii- ........ .... o .. ........ • ... 

Figure 7 -Effect of prehea.ter orygen on a tack SO 1 

ports, CO was about the same as the baseline levels 

atNSR L 

The NOxOUT chemistry requires oxygen and appropriate temperature to react with NOx. At low 0= or 

at low temperatures, CO generated from the urea 

decomposition oxi~es to C02 at a slower rate. In 

addition, combustion of gas, coal, or CO is delayed 

with a reduced 0 2 concentration caused by the 

NOxOUT reactions that consume 0~. Both of these 

paths are likely to have contributed to -the CO increase 

with NOxOUT injection at 0 2 less than 2.3%. A$ in· 

jection location moved to a higher temperature 

region (the bottom level), the rate of CO oxidation 

increased, which gave lower CO than the middle or 

top ports. Therefore, the NOxOUT-A injection into 

high temperature zones and/or increased oxygen can 

prevent a CO increase above a baseline level. 

S02 

Emissions ofS02 increased with decreasing preheater 

exit oxygen concentration. Concentration of SO~ 

\:\.LCO FrEL TECH 

corrected to 10% 0 2 was about 20 ppm at >2.4% 0 2, 

but increased to 36 ppm at lower 0 2• This increase is 

likely to be the result of very low oxygen and high 

CO concentrations which decrease the rate of sulfur 

capture by lime. In high temperature applications 

described in literature, the rate of sulfur capture with 

lime or limestone decreased as excess oxygen decreased close to stoichiometric condition. 7 

NOxOUT injection increased S02 with increasing 

NSR and decreasing 0 2• In Figure 7, 802 during in· 

jection was higher than baseline conditions but only 

at less than 2.3% oxygen. This oxygen level is also 

the level where CO started to increase. The SO. 

increase was the least when the reagent was injected 

through the bottom level ports. This correspondence 

between so2 and co supports the role of high co 

and low 0 2 concentrations in reducing the SO~ capture efficiency. 

~ 

Flue gas was analyzed for ammonia at the preheater 

exit. Many samples were obtained and analyzed 

during injection and baseline condition. The results, 

however, were erratic, ranging from 5 ppm to 20 ppm 

during injection and between 2 and 9 ppm with an 

average of6.5 ppm during baseline conditions. At NSR 

of 1, average of 7 data points were 10.4 ppm of 

ammonia. Further ammonia sampling and analysis 

is needed to validate these results. 

ECONOMIC ANALYSIS 

The cost to maintain NOx emissions to less than the 

limit of 422lblhr will depend on the firing rate in the 

kiln to process a raw material mix to manufacture a 

certain type of clinker. Raw material variations and 

the product requirements change the firing rate which 

in tum affects the NOx levels such that the required 

NOxOUT-A feedrate will change constantly. In 

Figure 8, the average daily NOx emissions in pounds 

per hour for June, 1993, varit:!d from 300 pph to 700 

pph. Using this as a basis, the reagent cost for a ton 

of clinker was estimated as shown in Figure 9. This 

cost varied even more and ranged from no chemical 

feed to $0.50/ton of clinker. An average chemical cost 

for June, 1993 would have been $0.18 per ton of 

clinker. In addition to high chen1ical utilization, the 

NOxOUT Process is cost-effective because the chemical is injected only when necessary and the bulk of 

the operating cost is the chemical. 

The capital cost of the process for this cement kiln! 

calciner was estimated to be SO.OS per ton of clinker 

on a 15-year life, 85% average plant capacity of 
•••. -.0~9 · 2~1~· 9~5-~~~1~3ii2il9••'a'iilill-il, til)o- 9i1Sil.)- 3111i!.!. -!ill(•l ____ ..,..:\.._A~ _ .. C_l _P:EL TECH 

800,--------------------------------~ 

&0 

NO, 11111 • 42~ POll 

1 3 ! 7 9 ',1 13 ~ 5 17 , ~ 21 23 25 27 29 

OSy! (JUr\6, 1993) 

Figure 8 -AJJerage daily NO:r emissions 

100 tonlhr normal output. The capital cost incbdes 

equipment, engineering, installation (estimate), 

license fee , service cont.ract, start-up, optimization 

and training. 

CONCLUSIONS 

A short-term testing of the NOxOUT Process on a 

cement kiln/calciner has demonstrated that the 

process is highly effective and efficient. At NSR of 

1.5, NOx reduction was as high as 80% and chemical 

utilizations were typically higher than 50%. High 

degree of mixing and a long residence time at appropriate temperature contributed to the excellent 

process performance. The current limit of 422 pounds 

per hour was maintained under various kiln/calciner 

operating conditions with less than 40 gph of 

NOxOUT-A or NSR of less thar. 0.5. As for byproducts, SO. and CO were unchanged from baseline 

levels at NSRless tho.n 0. 7. At higher flowrates, these 

emissions also !"emained near baseline levels when 

preheater oxygen concentration was greater than 

2.3%. However, both SO~ and CO increased slightly 

wit.h increasing chem.ical injection rate at lower oxygen. Ammonia measurement at the exit uf the 

preheater was erratic but ranged about 6 ppm under 

basel~-:le condition and 10 ppm during chemical 

injection at NSR of 1. 

The NOxOUT Process was easily installed, tested, 

and removed. using existinr, ports and available 

resources without e plant outage. The plant operation was unaffected during the NOxODT testing. A 

commercial system should also be easily s.de.pted t.o 

plant operations and easily maintained.. 

An economic analysis using June, 1993 as an example 

showed that the average operating cost would be $0.18 

per ton of clinker to meet the current limit of 

1 3 5 7 9 11 13 15 17 19 ~ 23 2$ 

Oay6 (June. ~ 0~3) 

Figure 9 -Reagent C011f in $/ton of clinker 

422 pph. \Vith the capital cost of $0.08 per ton, the 

NOxOUT Proces$ is a cost-effective and flexible 

system to meet the current NOx requirement as well 

as any futl;.!'e lower limits. 

REFERENCES 

1. Hofmann, J .E., Johnson, R.A., Schumacher, P.D., 

Sload, A., Afonso, R., "Post-Combustion NOx Con· 

trol for Coal-Fired Utility Boilers," EPRIIEPA Joint 

Symposium on Stationary Combustion NOx 

Centro!, Miami Beach, FL, May, 1993. 

2. Shore, D.E., Buening, H.J., Prodan, D.A., Teetz, 

R.D., Muzio, L.J., Quartucy, G.C., Sun, W.H., 

Carm.ignani, P.G., Stallings, J.W., O'SulliYan, R.C., 

''Urea SNCR Demonstration at Long Island Lighting Company's Port Jefferson Unit 3," EPRIIEPA 

Joint Symposium on Stationary Combustion :t\Ox 

Control, ~1iami Beach, FL, May, 1993. 

3. Hofmann, J.E., iubanese, V.M., and Stamatakis, 

P., "NOx Control for Waste Combustors," Air & 

Waste Management Association Annual Meeting, 

Denve:, CO. June. 1993. 

4. lJ.S. Patent 3,900.544, Lyon, R.K., August, 1975. 

5. U.S. Patent 4,208,386, Aranci, J.K, Muzio, L.J., 

and Satter, J.G., June, 1980. 

6. Sun, W.H., Stamatak.is, P., Hofmann, J .E., "Reaction Kinetics of Selective Non-Catalytic NOx 

Reduction with Urea," 205th American Chemical 

Society :Vleeting, DiYision of Fuel Chemistry, 

Denver, CO, March, 1993. 

7. Steuch, H.E., Johansen, \ Z, "SO, Emissions from 

Cement Kilns," Proceedings of Rock Products 

International Seminar, Decem~er, 1990.