EMISSIONS CONTROL 

t-

~--

~ 

t f:- I SNCR emission control 

by Joe Horton, Suwannee 

American Cement/Votorantim 

Cimentos North America, 

AI Linero, Florida Department 

of Environmental Protection, 

& F MacGregor Miller, Cement 

Etc, Inc 

P limc,ry f'-lOx control measures alone 

do not alw~1.ys achiev-e the most 

stringent regulatory targ~ts for 

abatement or exacerbate process problems 

from s:ulphur cycles. So, end-of-pip~ 

au-gmentation is needed. Providing .good 

accounts and reviews of using cornbined 

measures is important The lndust1y has 

concerns regarding ammonia slippage 

a_nd consequent emission. Operators also 

a. wait contirmation of the extent tb wh1ch 

.successf-ul industrial demonstrc_tions can 

imrried1atety be repliCated elsewhere. We 

need certainty of simu!taneous!y achieving 

NOx r·eductions, vvhiie avoiding excessive 

CO or 50 2 emiss1ons and/or undue 

process p~oblems. 

SCR has potentral expense-and 

technH:al difficulties associated vvith 

catalyst fouling _and replacement, and 

scrubbing methods have no lo-ng-term 

conclusive demonstrations. Hence. 

SNCR fs tavouredlil, Ammonia, urea, 

or other nitrogen compounds (such ascyanuric acid, PJ'ridine, and ammonium 

acetate) are inje<:t.ed to the kiln system 

Use of SNCR to control emissions of oxide-s of nitrogen from cement 

plants: this was the topic of the first prize winning paper at this year's IEEE 

Conference. ICR is delighted to offer the following extracts from this work, 

augmented by material from another recent 5tudy - from which more is 

to appear m a future article that concentrates on allematives to the SNCR 

method, now described in some detaJ/ below. 

1 

Various techniques to avoid or abate NOx emission~ Pnmary measurf!s 

• Fl<itne cooling (for example. waler addition) 

• LOV·.i-NO~ burners (vvhlch arc not always successful) 

~ Staged combustion in secondaryJprecalciner firing systems. or mid-kiln firing in 

long kilns 

• ,1\~ineralised clinker production 

Secondary 'end-of-pipe' measures 

• Selective C:otalytiC..Reduction, or 'SCR' (involving an1mcnia and a bas·e-rnctal 

catalys-t .at em cppropria.te temp~raturc, lo read and form water arid gaseous 

ni~rogen) 

• Gas sGubbing with an oxidi:.ing additive such as ozone or hydrogen peroxide 

• Selective Non-Catalytic RcducltDn, or 'SNCR' (injectipn of ammonra or its 

-::ompounds to preheaters -Of perhaps at rnfd-kiJn, at c,ppropriate COnditions or 

temperature, e-tc). 

Sorne ca..n be applied s.imnltancously_ 

;:;t <1ppropriate tempernture -and oxygen 

concentrations- (and potentially also CO 

concentrnticms). The selection of reagents 

is proces-s and telllperature spedfjc: at 

h1gher temper-atures, ·urea decornposes to 

produce·amrnonia, which reduces NOx. 

For reason-s of test safety, simplicity and 

by-product formatiOn. ammonia and 

F1gure 2: ammonia and urea-dissociation and reduction pathways 

urea have b-een pr·eterred_ {9) Ammonia 

has typically_ p~rfQrmed best in -early kiln 

applications. in Europe (see box ·story). 

Cy:;inuric 

+OH +NO 

Add ...:----:....: HNCO ~ 

! "- NCO 

_,_ __ _,.,' HNCO "~ 

NH,~O, +OH o~-NO NH:~: N_z 

~0 •Ny"P' Ammoni::~ ',-----~ NH-a --...._ _ / .,._ NNH/ 

Oc'(;omp<.:>sition 

!'r.oc-es_.; 

~•-l'.H't~ t-', if<•!"lf'l••, i"tn!>•,;rm;. hWF/i."i/ R<;<;'..lF(fJ l,<JJiOri!(Ot)' 

CJ~pa'I,"t'-~fit -:Jf M<;:h~>:Jc~l i.'f'f.'ntci"PG_?, To!'?(;<; c\&Ai U11NNS!:',I 

Theory of reduction 

In SNCR f.!l, NO reacts with ammonia: 

(1) 2NH3 + 2NO +% 0 2 _____,.. 2N 2 + 3H 20 

lt urea is used. the reaction is: 

(2) CO(NH2)2 +2ND + y, 02 -· 2 N2 + 

C02 + 2H20 

B-oth react'rons ·form innocuous nilrogen. 

acco1npanied by water. The reagents are 

most conveni-ently Introduced a~ a water 

solution. 

Reagents used 

SNCR with .ammonia and urea. may l?.ke 

.several paths. 
EMISSIONS CONTROL 

European experience 

SNCR was demonstrated in a preheater 

kHn with both ammonia and urea_ These 

were injected to the gas riser duct as 

shown in the Rgure, with a molar ratio of 

reagent to N02 of 1:1 (7). About 70 per 

cent reduction in emissions was observed 

with ammonia and about 35 per cent with 

SNCR is used in 18 European suspension 

preheater or precalciner kilns, tvvo Swedish, 

one Swiss and the rest German. l

41 The· 

mpst common reagent is 25 per cent 

ammonia water.£5.61 NOx reduction rates 

vary from 10 per cent to 50 per cent with 

an NH3:N02 molar ratio of 0.5-0.9, NOx 

emissions are then 2.4-3.8\b/t of clinker. 

urea. There was no major increase in ammonia emissions and 

greater NOx reductions were obserted with excess reagent, 

although there was· then increasing ammonia slip. 

Two dry-process cyclone pre heater/ 

precaldner kilns in Sweden achieve 80 per cent to 85 per cent 

reductl.on (emission at 11b/t of clinker) at an NH3:N02 molar 

ratio of 1-1.1. {5,6] One reason for this remarkable result is 

Early application of SNCR at Hokirn 

Albert Scheuer of the VDZ reported on 148 SNCR trials 

involving five different kiln systems~ three with cyclone 

preheaters and two with grates .. A 25 per cent molar 

concentration of NH3 in water was the main reagent, with 

some additional te~ts using ammonium sulphate and urea. 

NOx reductions with ammonia solution ranged from 15 

per"C:erit to 75 per c:ent, with reagent effectiveness strongly 

influenced by temperature. Maximum NOx reduction occurred 

at 980"( (1795"F)'. NH3 escape occurred below 900"C {165(YF) 

and when NOx concentration fluctuated. NH3 utilisation 

decreased·significantly with increasing NH3:NO molar ratio 

and with decreasing NOx concentration, suggesting that SNCR 

offers les.s promise at low NOx emissions levels. [2,3) 

the use of multiple injection points (12 in al!) that ensure a 

long enough retention time for the reaction to take place. The 

optimum temperature is said to be 900-1100'C (1650-2Q1o·F). 

Results sUg-gest that some .tests may have been carried out at 

below-optimum tempe~atures. 

FLSmidth tested SNCR on a preheaterJprecaldner kilnm, 

injecting ammonia to the lower preheater cyclone, with 

favourable temperatures. Emissions reductions averaged 40 per 

cent, but reductions above 90 per cent were obtained when 

the Injection rate was 10-20 per cent above stoichiometric. 

Operating experience has identified some concerns with 

build-up of ammonium btsulphite or bisulphate scale, which is 

significant for·sulphur-containing fuels. 

The reactions are the same as those 

for SCR, but the temperature window 

is critiCal without a catalyst. If the 

temperature is too low, unreacted 

reagent will remain, referred to as 'slip'. 

Alternatively, if the temperature is too 

high, some or all of the nitrogen present 

in the reagent may be oXidised to NOx. 

The traditional optimum temperature 

range to avoid either of these undesirable 

outcomes for ammonia Is about 1600-

205"0"F (870-1 t20'C): however several 

factors may shift this window. For urea the 

temperature range is slightly higher, with 

optimal efficiency theoretically around 

1000'C. Tests in other industries show 

that the lowest effective temperature 

range falls to about 700~C (1300"F) when 

hydrogen is cidded simultaneousJylBJ in 

'enhanced SNCR', although high sulphur 

levels may interfere. 

In preheater/calciner kiln systems, the 

relevant temperatures occur at the upper 

end ofthe rotating kiln, in the gas riser 

duct and in the lowest preheater cyclones. 

The effiCiency of reduction depends upon 

temperature, concentrations of oxygen 

and carbon monoxide and residence 

time. as well as upon ammonia and 

NOx concentrations. This contra?ts with 

SCR, where a dedicated reactor proVides 

controlled temperature and residence 

time, aimlng to avoid ammonia slip a,nd 

optimise reagent consumption, Concepts 

for applying SNCR in long kilns are being 

considered {see box out below). 

With urea, the same temperature 

.~'profile problems exist as for ammonia, 

along wtth a couple of new ones)11l 

Urea decomposes under the proper 

conditions to give carbon dioxide, as in 

Equation 2. If oxygen is deficient, carbon 

monoxi~e. m-;yTo~·~-;:~.~~~~~Th~-~-;;:1··-

roTes -of carbon monoxide are discussed 

later: suffice_ it tQ say .that it can hinder 

t/ie N6~ ~~ductig_~_~.a~.~f!..J_n sO~e 

crrCuhlStances~-a-~.? -·~-~~!]!p~er. A"d dTtlo nally, 

during dissociation of urea to -NH2·· tne urea competes for the OH radicals needed 

for NO, reduction as well .as for'the 

burr-lout of CO. These two competing 

reactions lead to more unreacted CO. Jn 

theory thFrprOhleffi Should" be eq~·~i·ly· 

In a long kiln, the appropriate temperature window occurs at mid-kiln and 

continuous injection of reage.Jits has not yet been achieved. Mid-kiln fir'ing 

technology might be applied, though solid ammonium or urea salts cannot be used 

directly because of rapid decomposition. Injection inside used vehicle tyres has 

been proposed, but not yet evaluated. Fue! Tech lnc is currently evaluating dry dust 

or pellet injectfon methods.f9l 

With mixing air fans to enhance gas turbulence in the system, improved mixing 

of gases containing NOx and ammonia may also otfer possibilities. Chain gas 

temperatures are generally in the range 1500-1600~F (815-870~C) and mid-kiln 

injection systems are usually down-kiln somewhat, at higher temperatures. There 

is a good poss.fbility that the correct temperature range can be achieved if mixing 

is enhanced and volatilisation or decomposition is suitably delayed. In addition, 

reagents could arrive via. traditional dust return scoops. !twill clearly be necessary 

to mix NOx with the reagent before this decomposes. 
}:,gure 3; fet~ttveefl=et:liveness of ammOnia and urea tn reducing NOx in cement kilns 

100 

' E 

I 

Ammoni~ 1. ,.- - -'I I ~ 80 

~ 0 

u 

e v ~"' / 

I 

1 5 60 z I /\ J 

r 

-

900"( (1650"F), whereas 

urea achieves almost no 

reduction. 

Some proprietary 

SNCR variants for deNOx will be outlined 

further in a coming 

ltR article 'B.iOso!Jds 

lrriedion Technology 

(BSJ) and Aqueous Urea 

Technology (Noxoui't').' 40 

850 900 950 1000 1050 1100 

Temperature ln "C 

vexing for ammonia, but appears much 

more prevalent for urea. ~dditionally, the 

presence of the localise:d_ CO -genercit\onfr'Om urea dissoci~tion may further retard 

the consumption of NH2 intermediates in 

the reaction, giving loy.;_e_re_tfideflcy ~_i_tJ:l 

insufficient oxygen,_?.='_:!tel~iiJlY_~~-~-~~~'llhe ___ ~jln-cafclner region. Also, a by-product 

o·f the u·;-ea-reaci10f1~n particular, is 

nitrous oxide (N 20). a serious greenhouse 

gas, Y.Jith effects mNe than 300 times as 

strong as carbon dioxide. 

The advantages of urea are primarily 

in handling and safety. It has a much 

lower vapour pressure than ammonia, 

and can be easily handled with fevver 

concerns for leaks or spills. However, 

as discussed. ~~~_o_nia appears to be 

a much more effective reagent for use 

in SNCR, especially considering the 

'tn-)nimal oxyg~n -content and temperature 

windows_ in kiln-calciner regions. As 

!Hustrated ln Figure 3, urea is also slightly 

less efficient than ammonia, even at its 

optimum temperature.l4 · '10) Ammonia 

appears to have a maximum efficlei1C)f at 

about 950'C (1740'F), where about 9o 

per ce;;rQf-H1e··No; may be reacted for 

optimum oxygen and carbon monoxide 

concentrations. Urea, on the other hand, 

has a maximum efficiency of ahout 80 

per cent at 990"~ __ (1815GF). Ammonia carl 

achieve almost 70 per cent efficiency at 

Results of fuli 

scale cement 

plant 51\lCR tests 

The following discussion outlines results 

of SNCR testlng carried out at five 

cement plants. At one plant (Pianl D). 

thls included both urea and ammonia 

injection. DLJe to the temperature 

dependenc€"shown in Figure 3, Plants 

A, 0, and E were tested entirely with 

ammonia or a Combination of both. Plants 

B and C tested with urea for the reasons 

noted (safety and ease of handling). Ba~ed 

on the res-ults and condus-tons from the 

tests, Plant A installed a permanent SNCR 

system in March 2005 -and has been 

operating to date with ammonia only. 

Burnability effects 

The overall level of NOx 

from the burning zone will 

be a function of clinker 

composition· and kiln feed 

fineness, particularly the 

quartz and calcite fractions, 

all other things -being equaL 

Table 1 shows the relative 

contrfbutions of feed chemistry 

to kiln NOx; no data is 

currently available on the 

coarse quartz and caldte 

contributions. As. judged by 

LSF and slli<;:a ratio, Plant B is 

by farthe hardest-to-burn mix 

here~ reflected in a high level 

of lbs NO)t clinker. 

EMISSIONS CONTROL 

Plant A 

A four-stage preca!ciner facility with no 

bypass and maximum clinker production 

level around 120stph. There ls a separate 

line calciner and tertiary air can be 

introduced at three locations to -estabfish 

and (Ontrol staged combustion. Tertiary 

air can be introduced either to the calciner 

for combustion, the calciner burner as 

primary air for Tuel, or further along ·,n the 

process in the caklner ducting for burnout 

of CO following the re-ducing zone of 

staged combustion. 

Thls plant a:lso beneflt-s from a low 

feed alkali and sulphur content, assisting 

culciner operation under reducin_g 

conditions; despite this, it is preferable 

to operate with oxidising -conditions to 

avoid build-ups, with attendant increases 

in prehea.ter pressure drop and output 

limitation due to ID fan lirhitations. 

The plant therefore performed -5NCR 

testing without maxfmising its low-NO)( 

calciner capability. P!ant A \.vas tested 

with ammonia, injected after the calciner 

hopper, but before the bottom stage 

cycione (see Figure 4). This location 

was then fitted with a permanent SNCR 

system with four nozzles at 90' intervals 

Figt,Jre 4: SNCR injection location at Plant A 

transecting the ducting. The 

retentiOn time from the 

cakiner to this location is 

in ihe order of nearly three 

seconds, giving sufficient 

time for the burnout of 

ca!clner coal. 

Here, 'theoretical NOx 

reduction' is the number 

of lbs/h reduction of NO 
EMISSIONS CONTROL 

PlantA NO • Red.lction 

I 

p ........ ~~-""' 

............. 1~~-

-· ... ---~ .. rooi!nol ......... 

~Figure 5~ SNCR results at Plant A 

[expressed as N02] at 100 per cent 

efficiency, and the ratio of actual reduction 

to NSR is the efficiency of the SNCR 

process. Thus, 100 per cent efficiency 

implies complete reaction of ·eve'ry mole of 

NO with One mole of NH3-, and -an NSR of 

one would result in complete removal cif 

all NO;.; present at the injection location. 

ln practice it is usua.lly very difficult to 

achieve near theoretical reductions, but 

Plant A did achieve very ·high efficiencies 

of ammonia utilisation. Figure 5 Shows 

the res-ults, ·including with the maximum 

theoretical redUction, a;; well as results 

obtained from an equipment supplier 

during tests on a kiln system of similar s!ze 

and designL10J. 

Comparison of the reduction levels 

to theoretical limits and to results from 

previously testing, show this to be a highly 

successful installation. The mechanisms 

responsible for this success are discussed 

later. 

One other outcome was the formation 

of an ammonia cyc\e within the roller 

mill system. Plant A does not monitor 

"'·•·"' -·· 

"" Q ~""-"~Jl..,..,.i»)<l .. <O,l 

___ ,._.~ .. -~ .. '"""'t~"" 

ammonia continuously, but a Fourier 

Transform Infrared Analysis (FTIR) gas 

analyser unit was placed on the stack to 

observe NH3 emiSsions for part ·of the 

test pe-riod. The raw mill was stopped 

ffllce while monitoring, and ammonia was 

detected at the stack during each of these 

occurrences. Data are shown in Figure 6: 

At the first raw mill stop, no ammonia 

was injected. On the second instance, 

injection vvas occurring -..vhen the raw mill 

iriitlally went down but was stopped part 

way through the outage. The injection 

rate did not appear to be correlated with 

the stack ammonia level, which in both 

cases peaked at about 50ppm (v/v), 

The ammonia s-eemed to be caught 

in an internal cycle in the kiln/raw mill 

system. 'vVhen the raw mill v~as removed 

from the process during outages, the 

scrubbing offered by the raw meal was 

eliminated and ammonia escaped through 

the stack Several kiln feed samples 

from various test periods were sent for 

evaluation of ammonia concentration, 

to determine the possible enrichment of 

feed with ammonia. Results, when above 

the detection limit; s-how an increase ln 

ammonia concentration over baseiine 

conditions_. However, due to the relatively 

low -ammonia concentrations and the hlgh 

detection limit for the method, .definitive 

conclusions were nOt poSsible~ An 

ammonia cyde was present. in part due 

to the highly soluble nature of ammonia. 

Unrea-cted ammonia condenses on to 

moist partidP..s in the raw mill (17 per 

cent moisture in mill feed). As the volatile 

ammonia encounters higher temperatures 

within the mill and/or preheater, it 

evaporates.back int6 the gas stream to 

repeat the process-. This .cycle continues 

until the raw mill is stopped, removing the 

scrubbing effect, whereupon the ammonia 

escapes· out the stack. 

Plant B 

A four-.Stage pretalcin~r. with maximum 

produdiph level of approximately 19otph 

of clinker; with tertia'Y air recovi:?ry.·from 

the cooler for use in ca!ciner combustion 

and an alkali bypass used for·sulphur and 

alkalis present in raw materials and kiln 

fuel. During testing, the plant operated 

at aroL:~nd 180tph. of clinker, with 

approximately 5-10 per cent-of main stack 

floV\1 bypassed through a separate stack. 

After the bypas~ takeoff, kiln exit gas 

travels throUgh a riser dud before tertiary 

air is introduced at one location only, and 

during testing the duct was· fixed at 100 

per cent open. Following the tertiary air 

arrival, the kiln riser abruptly stops and is 

diverted tangentially into the calciner, with 

four fuel firin-g locations, Following the 

caldner, exhitUst gases arrive imniediately 

at the lowest cydone. Retention time from 

calciner to cyclone is in the order of 0.'2 

seconds to 0.8 seconds- at the most. 

SNCR testing was carried· out wlth urea 

reagent. injected at four locations. 

1. Ri.ser duct, a-fter the alkali byp_ass 

takeoff, but befO're the tertiary air duct 

(two nozzleS) 

2. ·Gas exit of the lowest stage cyclone 

(two nozzles) 

3. The· same location as (1), but with fournozzles 

4. In the riser duct, after the tertiary air 

duct, but before the· caldner. 

Figure 7 shows the system layout. The 

average results 'for the four locations and 

a graph of the results are given in Table 3 

and Figure 8. 

The results arc similar to reduction levels 
EMISSIONS CONTROL 

i ... 

! ~ jf,:~:\R:I,<::; ! ] ,,. 

:i 

" . f;,;;~":'lJ!t t!~Ji~~lJ' 

achieved in tests by an equipment supplier 

on a similar sized calciner (5000tpd)l"l0l. 

The Ideal location was in .the lower 

portion of the riser duct prior to· tertiary 

air introduction, due to several factors. 

The sele~.:tion of urea reagent forced 

higher temperature profiles for increased 

reduction efficiency. Location 2, the 

gas exit after the lowest cyclone, ha.d 

conditions very similar to those used at 

Plant A: temperature around 1550~F. 

sufficient oxygen (1-2 p~::r cent). CO at 

1-000-2000ppm, and sufficient r·etention 

time for the reaction. However, with urea 

the reaction did not achieve comparable 

efficiency, As previously discussed, 

the dissociation and reaction of urea 

is-improved by a higher temperature 

profile w~th sufficient oxygen present 

and perhap-s. !onger retention tfme. ln 

Plant B, the temperature was the most 

significant factor-affecting. effidency. This 

led to the highest temperature injection 

location (riser duct location prior to the 

introduction of tlie 'colder' 

tertiary air) being the most 

partly due to mixing occurring as a result 

of waH effects_ However, with the noztles 

-selected and tested, little difference was 

noted between the use of one, two, three, 

or tour nozzles at the same flow rates, 

caJiing into question the hypothesis of a 

lack of mixing between reagent and-gas 

-stream~ Fluid -dynaf!:ll£_mliing.:etft:.<ttS may 

be more ette&·~lth ammonia re~ient 

one Other-n~bk diffe~~~;·"-

between results at P_lants A.and _B was 

the observed increase in CO from Plant 

8, especially with_.reagent inj€(tian·at 

~ocations with !~wver oxygen content. As 

[x~viously discussed, urea can create CO 

in its dissociation into NH3 , but may also 

interfer€ with the OH radical and retard 

burnout of CO to C02 more rapidly than 

ammonia. Perhaps the creation of NH3 

from urea results in dissociation of urea 

and creates denser localised areas of CO, 

which can interfere \.vith the oxygenenhanced NH2 /NO interaction. 

Amrnonia s.!ip was not monitored at 

Plant B, but a pronounced t:letached 

plume was noted dudng testing, despite 

low levels of 502 in the stack. This, 

coupled V'Jith the overall low level of 

efficiency for NOx removal. suggests that 

Plant B would achieve only limited NOx 

reduction with lhe SNCR system as tested; 

-however some improvements learned 

~f~~IT!Other tests may be. possible. 

· Ther-f-is a.ri.Jriteresting explarlation fOr 

the relatively inefficient NO~ removal 

from Plant B (and Plant C) relative to 

the other plants. Plants B and Care 

caldner kilns, where the rtser duct is the 

most efficient location for injection. This 

V<~o.uld be expected to deal efficiently 

with NOx from the burning ;::one, but 

Ftgure 7: Plant B ca:Jcfner configuration 

effident location, still resulting 

in much lower efficiency than in 

Plant A. 

j Kiln B:lt Gas 

K'!n Ff'e-d 

Additionally, Plant B's caldner 

cross section is much larger 

than at Plant A. As noted from 

Rose, Alder and Erpeldingf10] 

a measurable reduction in 

SNCR efficiency is observed as 

the cross sectional size of the 

injection location increase-s. 

This is partially attributed to a 

reduction in mixing capabilities 

at the injection location from 

both the reagent and the NOx 

ln the gas stream. It may also be 

' ' r--Q 

y------l 

. o"~----n lnjer:1ion 

•"'I -¥ Localion 

•+-·······~1 hljeclion ~------1 Ter!iaryAir I UJC.11ion ' '-~="---'--·-~--~---"' .---~~ ~-----11-\ ByPass i 

\T---.,. 
F1gure 8: SNCR Results- Plant B 

P1a01tB NO • Redocloo 

0,1l 

- /tlrt<DI>co:; ...... l), .... __ "'-"_1>_>! 

o'"""''"'~-~"'"'--~~ .. lllo .. IW<IPJI..-.. Il•""-...,,,.._,p,Duor 

car~-~~~!?_d!~~~!~~9X~~~~~!~tep ln_th': __ _ 

calciiler, as the injection pOi lit is up.Str_eam; 

No direct measurements of NO,: and flow 

combined were taken __ up.s-tream of the 

Injection site, ~ __ no direct ·ll}~a?Yf~memtof 

the effic1ency Can be·off.ered fn t~rm.S:of 

NSR. For comparison purpos~S, the':NSR 

listed a·ssumes that a_ll ~Q~J~·-g~~-~~!~ 

·-~-·1-..... -... e.~ ........ ,......~Jo.ot~..-.l-4--o<-•l'l'o .... ol 

-n.-~-~-""' 

the dlstiilct.advantages asSociated wlth 

mmg.-arnmonia:ra,th'e·r·fua]i -urea, as the 

apti'm~m tf!nlperature is: lower. 

Plant C 

,A two string preheater tower with 

{):ne string:·equlpped w·lth a calciner 

and the ;othe.r Without. The 

strings. 

time, yielded 

elevated co levels 

post-ca!dner and 

through the lower 

preheater stage. In 

addition, residual 

carbonaceous 

material in raw 

meal is believed 

to contribute 

to elevated CO 

levels throughout 

preheater and calciner 

SNCR testing was carried out lVith urea 

injection to each string. Calciner injection 

locations were: 

1. lower portion o-f the caldner (two 

nozzles) 

2. up·per portion of lhe calciner (two 

nozzles) 

3. gas exit of the lowest cyclone after 

calciner (two nozzles). 

Preheater·string injection locations vvere: 

1. lower portlon of the riser duct (two 

noZzles) 

2. uper .portion of the riser duct {two 

nozzles). 

A combination of locations was also 

tested -wlth the upper portion of the 

preheater s-tring riser and the upper 

portion of the calciner. Rgure 9 shows the 

plant layout. The avera-ge results for the 

locations and a graph of the results are 

given in Table 4 and Figure 10. 

In -general Plant C reduction efficiencies 

were very low, with rnlnimal decrease 

In NOx emissions despite high NSR. As 

discussed, the choice of urea as reagent 

probably damaged efficiency of the 

i rom the burnintt~?-~e_, _that ·hOne· Pfthis tak'ine.r ~rin-g- has mQc:h 

latSE:dhf.o~:ghput,- re¢eiVirlg 

appfoxirililtely 80~85 per ·Cerit 

figure 9: Plant C configuration 

is reduced ir:i the caltin"er, .ana thatthecalci~~r _g;_e_~~~!~s ~o fUrl:her NOx·:·b.f 

course -"these are~;:;Q(~~IT~f_"a5sU0-Ptions,---

as· the-5~1~0-~~r~9~rif0?,~!~0~~1~9~}brmosrfu:els, __ so _thai__ the :?-N~_ -~ffld_er\:cy 

determir1~d at u:;;: ~~s-~-~~-;-pt~bab!i .. a·rtificialiY 10W,· ;1~d~ th>e j~age~t-did ·n9t 

have ~he __ ?er~f~:~f!Y:?JJb1":@~i9~----­

locatiqnJ9._r~_?.0: :~i_th _l)J_.9·~·-'geb~rated 

further_ __ Qack in th_e_ ~roGess" in -the_. ·ca!dner . .. ~s;;ce th~- rise; d~ct [;;c3.11Gl1-Wa5- ______ _c -

optimum for thes-e kilns despite Jh~-fa,t;t 

that ca.lclner fuel NOx vi.as·m~_t:;trea:te.d, 

1 !_ ~ppe_~~~-!b.§_t ___ R9_s!~~~~~~~t _J .9_e~!:~n 

wa?_§ijpo __ lo_w_ __ ~--!~_n::p~e~':"!We, -.or_~Up~q·. 

high a CO .. level, ~obe·effedjve_v~tth 

tb~.~Y-~~-~-r~~g;~t 'Again, ih-is;:sJlbwS 

~f the gas- ·and material ·flow. 

MaximU(Jl production level is 

·?tpproXimateJy .215tph of- clinker. 

There ls_ an p.Jkilli bypass, used, 

fOr sufphu'r ar1d .alkalis present in 

fuel and rav·{ materials. Tertiary 

iidrbm the. coOler i.S inthJ.duc'ed 

pr!or'.to ±he caldiier in that 

strl.ng of the tower. During 

- t~?ting, the plant operated at 

around 206tph of clinker. The 

pettoke fuel was·.u:se·d in both 

main ·burn~r ahd talcfner, and as 

a re:.ult bf !Pw volatile content 

: iihd limited C:ak:inet retentiOn 
EMISSIONS CONTROL 

F1 ure 10: SNCR results Plant C 

Plant C NO·• Redudlon 

·-

~ 

:I 

:I 

I 

I 

I '-.... ,-

/ ·- - "'""'"'" I 

·~ I 

/ .. = I 

·~e-;l~~-~----~-K'~-~-~--~~~~~~~r~-~-~~-·._: __ --~-.L._ __________________________________ • __ ··_··----~ 

~,~~-----·--~·~:--~~----------------------------------------------------~ "' "' ..• HO :l..r:<l l.~ , . 

calciner would have been greatly reduced 

by the calciner with its inherent reducing 

zone as operated durin·g tests. Since 

these principles of staged combustio·n are 

present in the calciner and quite effective 

at Plant C for reducing 

r_eduction was more 

effective in the upper 

portions. ·of the riser, 

which was_ unusual, 

given the reagent. With 

\)tea temperature was 

evidently th-e dorrilnant 

factor controlling 

effiCiency, However, 

temperatures in this riser 

duct .may- not-increase. in 

the upper portions, but 

it is presumed that CO 

present at the ki!h irilet 

ft'orri uncombusted ·fuel 

deCreases in the upper 

portion of the- riser. This may contribute to 

increased efficiency for the upper portfon 

of the riser. 

Plant D 

A tvvo-strlng preheater kiln without 

calciner, maximum clinke:r production level 

approximately 11 Otph. Alkali bypass used 

both for sulphur and alkalis present in the 

raw materials and 'fueL During testing; 

the plant operated with an hourly clinker 

production of around 105tph. The fuel 

used during testing was petcoke, SNCR 

testing was carried out with both u1·ea and 

ammonia. Jnjeclion locations were selected 

in the upper and lower portions of the 

comnlon r!ser duct. (ln kilns without 

cakiners, the optimum temperature will 

usually be found i-n the riser duct). 

1. Lower portion of the riser with urea 

(four nozzles) 

2. Upper portion of the riser with urea 

(three nozzles) 

3. Upper portion of the riser with 

ammonia (three nozzles). 

NSR. As stated earlier, independent 

measurements have shown that a great 

deal of NOx here Is generated in the 

tower (fuel and feed NOx), subsequent 

to the injection site. As previously 

discussed this makes it very difficult to 

calculate the overall NSR and efficiency, 

:as injection locations prior to the calciner 

do not reduce NOx generated within 

kfln NOx, the effectiveness 

of the Low-NOx calciner 

should be maximised, 

Ftgure 11: Plant D :eonfiguratfon 

the cakiner and the molar rate of NOx 

flow frorn the kiln is not easily known. 

ln Plant C, kiln and calciner operation do 

quite an effective job at reducing burning 

zone thenna! NO~ generation. so that 

lnjectJon zones prior to the calciner have 

two d'1sadvantages. First they wll! have 

only limited a111ounts of NO/( present to 

reduce: when compared to overall rates of 

NOx reduction, it will appear to have very 

limited efficiency, but in reality SNCR may 

be effectively reducing the limited NO;.; 

present at the injec:tion location. Secondly, 

NOx reduced by SNCR prior to the 

with subsequent SNCR 

reduction. The choke and 

location of testing should 

mOst likely have focused 

on post calciner injection. 

since there is a [ow NOx 

level in ga5 enter'mg the 

caloner and significant 

generation of NOx from 

ceJciner fuel, Plant C's 

size may have contributed 

some inefficiency, being the 

lar_g·est tested. 

In the preheater string, 

Kiln Feel:! 
Rgure 12: SNCR results Plant D 

-----~~" 

··r·------------------~·L·~-----c----------~,~-·~·~···~·~--~~---~-~·--··~ .. ~·---------.. --:1 

//' ,..,~ -

~~~--~-~~1~-----~~------'-'-------------------------------cl ;; " 

;~~ f---~-~~;'·-·--~">--~--------------------------------------------------il /·~ • •• I . ... / 

·---·-- F1gure 13: P!ant D urea versus ammanra 

/ 

--.-

J 

i 

- ~ ----- :~. --~_£~·~~--:~:~---~-·----------

/ 

/ 

;?·:~/ 

/' 

.• ____ , __ ·---~-- ·-----

Figure 't1 shows the plant tafout: Tabl'e- 5 

and Figure 12 give the -average resul~ for 

the locations. 

Plant D experienced·the·iT)ost.effident 

reductions of any plant te$d With urea. 

This plant has low riser duct CO and 

suffident temperature for the highly 

temperature sensitive urea reaction. 

Also; no fuel is burned -subsequent to 

the injectior:~ location, so no chance of 

additional fuf'i! NO~: fe>:rmation exists. 

Fe-ed NOx, of course, could still form. 

This was also the only 

plant tD test both with 

urea and ammonia_ 

Results ln the same 

location showed marked 

improvement for 

ammonia, with almost 

theoretical reductions 

in NO~ result-ed. Rgure 

13 shows results of the 

sc.me injection location 

with the same number of 

nozzles for urea versus ammonia. 

Results show the effioency advantages 

of ammonia over urea, as \<\'ell as the 

possible influence of siz_e and wa.ll effects 

that could be present in smaller crosssectlona! injection locations. 

PlantE 

A small preheat-er kiin with maximum 

dinker production of approximately 30tph. 

There is no alkali bypass despite- the fact 

that 100 per cent petcoke was -ftred and 

there are high S03 concentrations in 

clinker {2.52 per cent 503). SNCR testing 

was carried out with arnmonl.a at injection 

locations throughout the riser duct. as 

follows: 

1. lower portion of the ri~er {t-.·.·o nozzles) 

2. lo-•.-;er portion ot the riser (one nozzle) 

3. middle portion of riser (two nozzles} 

4_ middle portion of riser (one nozzle) 

5. upper portion of the rlser (tv,ro nozzles) 

6. upper portion o·f the riser ione nozzle). 

Figure 14 shoWs the plant layout. The 

average results tor the locations are given 

in Table 6 and Figure 15. 

Plant £. with low CO and high oxygen 

throughout the kiln inlet and riser 

duct, expenenced very effJCtent NO~ 

reduction. The lov..-er porUons of the 

riser duct with higher temperature wer-e 

Fi~re 14: PJant E conhgurabon 
EMISSIONS CONTROL 

Figure 15; SNCR results Plant 'E 

Plant D NO' Rt)ducliOfl 

·~-·~- >< ,~,.. ...... ,_~>'~"""'r' u.---"'O<iy • --·~=loo:J.C>nl:f £ >Oll<o..R .... :-• --~~ - ~-~-~·-"'~ ~ <-;~>o ... ~- 0 '---1~0.U,O 

the most efficlent reductiOn locations .. 

CO and oxygen levels are fairly uniform 

throughout the riser so the higher 

temperature provided higher reductions, 

but even at lower temperatures exiting 

the riser duct, redUction efficiencies were 

quite hJgh. As with Plant D the absence of 

a cakiner or pbst kiln burner NO~ source 

niakes evaluatiOn of NSR and SNCR 

efficiency accurate arid reliable. 

Plant D was also by far the smallest kiln 

tested and exhibited very high efficiencies 

for NOx reduction. These results suggest 

that, after all, there may be som:e vqlidity 

in considering the possibJ·e influence 

of mixing and wa\1 effects on SNCR 

efficiency. 

Conclusions 

Reagent 

VVith regard to reagent selection, 

ammonia solutiOn is seemingly always 

favoured ·In cement manufacturing for 

reduction efficiencies. In research by D. 

Kupper and l. Brentrupm, it was noted 

that ammonia water was much more 

-effective at reducing NOxemissions than 

urea solution. In particular, ammonia has 

greater reaction efficiency through the 

normaJ temperature window ptes_ent in 

the preheater or calciner. Additionally the 

increase of CO is much more prevalent 

with use of urea, especially when used 

in injection locations vitth low oxygen or 

high CO. It appears that dissociation of 

urea results in additional CO that then 

may compete for the OH radical pool for 

the oxidat1on to C02 . Figure 16 shows 

the marked increase in CO from injection 

of urea in Plant B in the high CO region 

after the c.alciner. 

This localised increase in CO with 

dissociation of urea to NH3 may be one 

reason why urea achieves lower efficiency 

in the tests. This increase in CO competes 

for the limited supply of OH radicalS, and 

n-ot only for burnout of the CO; these 

same radicals are needed tor the NH3-

to-NH20H intermediate, fundamental 

for reduction of NOx. In the low oxygen 

environment of 

preheat~_rs and caldners, 

there is limited oxygen 

·present to g_enerate 

the·se OH radicals. 

ThiS was also noted in 

research by Steuchl11l, 

which showed increased 

stack :concentrations of 

CO; The CO incr~ase 

was minimised with 

oxygen concentrations 

greater than 2.4 per cent 

and at NSR injection ratlo of less than 

0,7, Additionally, urea indicated a strong 

dependence on temperatures in the range 

of 1600 to 170trF for effective reduction. 

Ammonia was shown to react with NOx 

with high effidenQes at temperatures as 

low as 1500'F, giving many more useful 

potential injection lo_catioris than urea. 

Plant size versus reduction 

A correlation between plant size and 

reduction efficiency was· noted. This 

agreed with previous findingsf10,12J 

that larger plants had lower efficiencies 

than smaller.- The fallowing figure shows 

the best resUltS achiE-ved from all five 

plants, and the· thre.e plants with outputs 

from 600-300Dtpd have much higher 

efficiencies than the two larger facilities. 

Intuitively it seems to make ·sense that 

large gas flows with larger cross sectional 

areas would result In less miXing and direct 

c:o·ntact between NH3 and NOw However, 

testing condu~ed at several of the· plants 

Shows that the addition of more injector 

nozzles in the same location traversing 

the ducting did not increase effidency. 

Under the first assumption the increase 

in injection locations with the same flow 

should have overcome the presumed lack 

o.f mixing and increased efficiency noted. 

Figvre 18 shows testing conducted at the 

same location with varying number of 

nozzles for Plant B. 

No change was noted with four versus 

two nozzles .. Howevet', the correlation 

between size and reduction efficiency 

is evident and may instead rely on fluid 

dynamic mixing differences experienced 

br on stratification present as size 

increases. Additionally the influence of 

wall effects Which exert a slowing effect 

on the te'nninal velocity of particles, 

may increase the lam'1nar character of 

flow, and could impact the efficiency 

of reactton between the reagent and 
EMISSIONS CONTROL 

F1gure 16: CO increase in Plant B 

Figure 17: il!l plants NO~~. reduction and plant size 

figure 18: Plant B results with d1fferent nozzle configurations 

::+1 ____________________ ~/'~~----c-·~-~·~-------------------------~ 

~:1 ===,,;';:,;=-:;~~;,_,~-~:========~-~-"' : 

I ,v "'~----J"~------~"o_ _________________________________________ .,~ •• ~.""-

·~+l ___ /7~1~-"~0~0~-~~~,~~~~---·-__ -_-__ -_-_-_-_._-_-_-_-_· ______________________ _c 

r· 0 o 

.. ·-· .. '" '" 

NOx present ln the gas stream. Ctttaly.tlc 

effects of Iron Compounds ha:ve also 

been- shown to aid NOx decomposition: 

wall effects may enhance interaction 

between such potential catalysts and gas 

stream components; this will be discussed 

subsequently_ Complex conceptual fluid 

dynamic modelling of injection locations 

would be required to further examine the 

influEnce of Wall effects: and is bey_ond the 

scope of this paper. 

Sulphur cycle effects on 

SNCR reaction 

The presence of sulphur and chlorine 

were "OTiginally thought to be potentially 

troublesome to the SNCR reaction due 

to the propensity of ammonia to interact 

with sulphates .and chlorides. However, 

the stability of ammonium salts was 

known to be low in the high temperature 

profile of the injection locations, and 

with the volatility of the ammonia, it 

was expected to readily volatilise even 

if trctnsitorily -combine-d with sulphate or 

chloricje. lt was not known. however, if 

this would develop a· cyde with sulphur 

or even chloi"ine l

13,14l that might impair 

reaction of NH-3 with NO~ as 1t circulated. 

It appears that the presence of sulphur 

has little effect on the use of ammonia 

as a reagent. PlantE, which fired 100 

per c.ent.petcoke, had high 502 in the 

injection area, high dinker 503 and yet 

experiehced some of the highest reduction 

efficiencies. This has fed to the perhaps 

intUitive conclusion that the presence of 

sulphur, all other things equal, has no 

apparent detrimental impact on the SNCR 

reaction. 

Catalytic reactions from kiln feed 

The correlatiori between iron content in 

the kiln feed and researchers have noted 

an increase In the reduction efficiency of 

SNCR reaction.L1 5, 16llt was observed that 

Plant A, D and E, whkh had higher iron 

perc~ntage in klln feed than Plant Band 

C. h-c.d rhuch higher SNCR efficiei'ndes, 

It should a!so be noted that these plants. 

als-o used ammonia instead of urea and 

are the smaller sized of the five plants. 

The presence of some catalytic reduction 

with ammonia either in the inje-ction 

location or at higher portions of the 

tower at lower temperatures cannot be 

discounted. The SCR reaction can occur at 

temperatures from 570"F and 8406

F and 

this temperature range is present at the 
1.2-,----------:.-----, 

-II- w/o CO 

0.8 

0 

z 

;::::: 0.6-

0 

z 

0.4 

0.2 

--+- 100 ppm CO 

~ 1000ppmCO 

-+- sooo ppm co 

Horoogeneous Case 

Quench Rate= -260C/sec 

o~~~~~~~~~~ 

600 700 800 900. iQOO 1100.1200 

Tempera!llie(G} 

Figure 3. Effect Qf CQ On,$.t:'{fR ¥14 rurutl:~~_fqr hOmOgeneqUs ~ditions with 

NOi = 500 P~-~/NDi ':;;:::,1.5~_:_and-.a_thermalquencll rate of260K/sec. 

Figure 19; Effect of CO on SNCR 

top Of pre heater toviers-~ so i:efentibii>tfliie: 

n the area of greater'th.::in 1 0-.secOndS -at 

this temperature -are exper!Emced. rn,:ci.IIJb.e 

preheater towers. Despite-the·ab?e~~- · 

of a traditional catalyst s,uqh.:as:-.q~!d:e~ .. 

of titanium and vanadiu'm, the,:influ·~n,ce: 

of increased NO'X. reductio'n py .t_at_a:l¥tl:t 

mechanisms_ cannot be_.-dis¢Q_i:!ri±¢d- rrP.PJ 

the testing- conducteil 

CO effect -on SNCR reactiOn·-, 

CO was ·shown· to ha>/ebol:h•••~o.>nd\i'" 

and negative impa:ct <on.lh''·'~·ed.tJc!ign 

t!X·'ob;n\fliSt, .. a high GO atmosphere with 

lftil~;o~;y~en,•or ·J.!)_su_ff)crie?t mixirtg of 

t.<l'-!i<~~·qs ,sr'o~ltllechaili :re·action of 

•b,;Jr~(Jutqf c:oan.cl the ·continuing 

/tq*'i~.n,:ol'x<<oi<;als when -both Oxygen 

ln approXimately 

(1 I 

(2) 

(3) 

(4). 

of NOx with th~,(~~~~~ ~:ii~~··~;r;:~~~6:;, ,,,)~~~~"'~;~;::~~1~= 

and the N 

of (0 to C02 

the reaction of 

the radical pool ~~t:i~:it:;~;~~~~ 

the -rise_r 

SiZ¢ frl 

EMISSIONS CONTROL 

and construction of preheater towers. 

available raw materials or fuels. However, 

it does appear that three key approaches 

for SNCR NOx reduction are identified 

and one or more should b-e achievable 

at most locations, to approach desired 

efficiencies. 

The first approach to riser duct 

reducti.on -of kiln NO>: relies on the 

tradittona! reduction techniques., requiring 

high temperature, sufficient oxygen and 

low CO_ In most cases these conditions 

should be available ln ca!ciner systems, 

and for preheater·ki!ns it is the only 

option. However, lf suffiCient oxygen is 

not present in the riser or kiln exit. due t6 

carryover of unbUrned fuel or' insufficient 

oxygen from the kiln itself, then efficiency 

for this reduction Will 5Uffer. Additionally, 

this location upstream of the calciner will 

only reduce kiln NOx, which is pr-esumed 

to be the majority of the NOx formed, 

and will not reduce NO>< subsequently 

generated in the caldner from fuel of feed 

nitrogen. 

The :Second approach for SNCR 

reduction is to use a post calciner location. 

Jn most situations tem~ratures are 

lower In these regions than in the riser 

duct. and choosing a spot with adequate 

oxygen and small amounts of CO will 

lead to greatest efficiency. ln calciners 

with limited retention time for burnout of 

CO, such a locatfon may not exist or may 

even be at the exit of the lowest cyclone. 

However for most new calciner designs, a 

location should be available in the burnout 

zone wlth sufficient oxygen, CO and 

temperature. D.ependlng on fwel usage 

arid its associated volatility, a location prior 

to the lowest -cyclone should be sufficient. 

The other distiilct "advantage of postcalclner injection is the reduction of total 

NOx produced from both combustion 

zones. While it is' assumed that most 

stack NO:.: is produced vra the thermal 

NOx mechanism in the kiln, calculations 

·at Plant A showed apprOximately 20 

per cent NOx generation in the calciner. 

Frbm studies conducted at Plant C, the 

majOrity of Nox generation again occurs 

1n the calciner. Th.1s NOx generatlon was 

also noted by Tokheiml1Bl in studies of 

the impact of staged cor'nbustion on NO-x 

reQuction, where it was noted that 30 to 

40 _per cent of the total NOx was· caltiner 

generated, A riser duct iiljediOn location, 

sacrifices the ability to reduce NOx from 

this source. 
EMISSIONS CONTROL 

F1gure 20: Pl11nt A molar NOx ba!am:e 

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

\ ~-- ~ \ ...._ __ 

I 

I 

\ 

" ..... __ 

Another benefit of the post~calciner 

injection is the use of inherent staged 

caldner combustion for initial reduction 

of kiln NOx. via staged ~ombustlon design 

arid Operation~ This redu_ction mechanism 

will be present integral to the Operation of 

the calciner and should be used to reduce 

as much kiln- generate-d NOx as possible, 

with SNCR treating the residual unreduced 

NOx or newly created calciner NO_){" This 

aHows for accurate NSR calculations and 

reduction efficiencies from SNCR to be 

calculated. 

To illustrate this point, a tOtal NOx 

balance calculated for PIJnt A is shown 

in the fol~owing ftgure. Cohcentrations of 

NOx at the kiln inlet are known, as wei! 

as estimated flows from C02 balances. 

Molar rates of NOx as N02 are given for 

NOx from the kiln burning zone as we\! 

as NQx generated in the. calciner. lt was 

estimated that approximately 40 per cent 

of fuel nitrogen was converted to NOx.-

The reducing zone created in the calciner, 

even with the kiln operated in an oxidised 

state, reduces around 45 per cent of both 

NOx from the kiln and NOx from calciner 

p::;::~wr•c:·oa:;r~::-.·. 1 

fueL The reducing capacity of staged 

combustion can be increased by the 

presence ot CO; however during testing 

this 45 per ·cent reduction was achieved 

with at least two per cent oxygen at the 

kiln· exit Finally the molar ratio of the 

Nbx expressed as N02 is given at the exit 

of the system or the stack. 

If two separate scenarios are evaluated 

with injection locations in the riser duct 

and in the upper portions of the calciner 

with the same NSR and reduction 

efficiency, the following is observed. 

The post ca.lciner location will cause 

correspon'dingly greate-r overall stack NO~ 

reduction. due to the reduction of both 

fuel NOx from the caldner and thermal 

NOx from the kiln. Also, the calciner 

reducing conditions de-stroy more of the 

burning zone thermal NO~. Table 7 shows 

the theoretical reductions based on a 0.7 

NSR at the actual location of reductlon 

(molar rate of NH3 divided by molar 

rate of NOx at the location of injection). 

the overall 1'-JSR (molar rate of NH 3 

divided by the uncontrolled molar rate 

of NOx at the stack) and a 75 per cent 

efficiency of reduction at each location . 

The overall efficiency of NOx reduction 

is the reduction of the l.mcontrolled NOx 

versus the theOretical reduction of NOx 

achieved at each location. Thes'e results 

are achievable with ammonia at Plants A, 

D and E, as irlustrated in Table 7. 

The results demonstrate that -even 

though each location was- assigned a 0.7 

NSR, to actually achieve this NSR jn a 

kiln riser with high exit oxygen requires: 

much more reagent In addition, even 

though the riser location reduces the NO:.:: 

wlth 75 p_er cent efficiency, this results 

in an overall 41 per cent reduction from 

uncontrolled NOx levels .at the stack-. 

As stated earlier, this is because this 

location has no opportunity to reduce 

NOx .generated irom cakiner fuel. For the 

riser duct location to achieve the same 

reduction~ as_ the post caldner location, 

a localised NSR rate of 0 865 (185gph) 

wOuld have to be used. Thus, we see 

the advantages ofuslng SNCR at a postcalciner location, This relationship of 

red.uction would further be ·-exagge_rated 

if the kiln were run with lower excess 

oxygen and had loy.ier levels of klln exit 

NOx. The presence of unburne-d tyres or 

·other lump fuel introduced at the kiln ex·1t 

could lead to this -situatiOn. In these cases, 

injection points at the calclner exit would 

be the only acceptable location for SNCR. 

As for preheater kilns, this issue is avoided 

as no additional fuel or ther.mal NOx is 

ge·nerated- past the burning zOne. Lastly, 

we have not seen a:ny ·ability fo~ ammonia 

or urea to remain unreacted and circulat,:; 

pci.:st the calciner, if injected in the rlser 

duct. 

The thlrd approach is to adopt multiple 

injection points for ammonia -and/or 

urea. Junker[5J at the Slite cement plant 

in Sweden achieved excellent suCcess 

with techniques including the use of 

12 injection points, redudng the NOx 

emissiOns to about 11b/t of clinker. 

References 

[1] Kupper. D. and L. Brentrup; ''SNCR 

technology for NOxreduction in the 

cement indust1y"; Krupp Polysius. 

Germany; March 1992; pp. 4-8. 

[2] Penta Engineering Corporation Report 

on NO>: Formation and Variability in 

Portland Cement Kiln Systems Potential 

Control Techniques and Their Feasibility 

and Cost Effectiveness. Penta Project No-. 
EMISSIONS CONTROL 

971212_ Prepared for the Portland Cement Assodation. PCA 

R&D Serial No. 2227. Skokie, IL. 1999. 

[3] Scheuer, A., Non-cataJytic reduction of NO with NH3 ln 

the cement burning· p'roc¢_!?S. -Z!;ment-Kalk-.Gip.s, Nci. 3/1990, 

VV1esbaden. Germany. 

[4] Campbell, LM .. O.K. StOne, and GS ShareeL Sourceb-ook: 

NO';( Control Technology Data: U.S. EPA, Air and Energy 

Engineering Research LaboratOry. _'EPA-600-/2-91-029~ July 

r991. 

t5J Junker, P., Member of the Techni_gd Working Group, 

Swedish Environmental pr~feCtion Agency, Ui.nsstyre1sen 

Gotland, S-62185 Visby, Sweden 

[6J Euro-pean lnlegra:te.d pOllution Prevention and Control 

Bureau (ElPPCB). Reference :DOcuinent on Best Available 

Techniqu-es in the Cement ,:U,d-Uine Manufacturing Industries. 

World Trade Center, Seville_. Spain. March 2000. 

f7l Yee. G.M. Suggested Co,n~l M~asure fOr the Control of 

Emissions of Oxides of NitrOgen fr:pm Ceirlent Kilns. Presented 

to the State of CalifornJC\ •. Alr-Resourc_es_BOard for Discussion 

on October 21, 1981. 

[8] Haas, GA Selective NMcell)!ytic ~ed~ction tSNCR): 

Experience with the EXXO:n Thefri'1ZI DeNO~ Process. Presented 

at the NO:.: Control V t:Onferen~e. ··toundl of Industrial Boi~er 

0-.•.:ners. Long Beach, CA.-_Februilry10~'11, 1992. 

!91 Lin, M.L. MJ. Knenfeirl~·fue1 Tech Inc.. "Cement Kiln 

NO:.: Reduction Experi_enc_e_ ~s!ng_·_tne~NOxD~ Process," 

proceedings o·f the 2000 lr:'Jfem.atjo:nai_JO,int Powe.r Generation 

Conference, Miami Beech, EL,)yly;23S26, 20.00. 

[10] Rose, D., K. Alde;r;·:ahd:b .. :·;;Ei-pddihg·.;··jlNOx Abatement 

with the SNCR- Proce.ss:in Kiln :~n_t5-.with Staged· 

Combustion": kn;pp POJys)uS-,. 'Seckt.i'rt{Gefnlany 

[11] Steuch, H.E., J. HifieT WJ';.. -Sun.-MJ.--Blsnett, and D.W. 

Kirk: "Reduction of N{)x £missjons_,frQm a·Dry Process 

Pre heater Kiln with Caltin~r Tt}_(Ough the- Use of .the Urea 

Based SNCR Process''; 1995.'!E£E Cement Industry Technical 

Conference; XXXVI C_ofift:{t'eliC~:·Hec_ord;·Se:n Juan, PR; June 

1995;p. 466 

(12] Schmidt A, 'The ·ModUlar PDi_f5ius Caldner Concept- A 

Solution far All Ap~liCationS:b,Y:-<;:Orr\binatlon .... ECR'\ Seminar; 

Experiences with Precaki!ler: :KilnS; ·semburg Gerrriany. 

November 2004. 

[13] Ritzmann, H~. "'Kr{!istaUre·:in {?rehofe_nsystemt:nM ,.Zement.:. 

Kalk-Gips 24 (1971), p . .338 

[14} Sprung, S., "-DEJS V¢rhal.t~n-·:.des'·?Cllyrefels be.im Brennen 

von Zementklinker", l'98inq~stfieZe.itur.g89 (1955), Nr. 96. 

p, 124 

[151 Zamansky. V.M._. V.\1. LiSslariski, a.'ld HM. Maly. 

~Promotion -of SNC'R oy:s.f.X:iiUri_-Ltompounds," Energy and 

Environmental Research cOfPO_fiipon. ·18 :Mason, bv!ne, CA 

926i8 

[16] Yang. R. T., and K::-T _Li ·_:··~·~ialytlc Decomposition of Nitric 

Oxide on Sodium Ferrite·~_, Jryq.:Eng; '(:~em . .-·R¢s. DeY., Vol. 21, 

No.1.1982, p. 407. 

[17] Brouwer. L M.P. H~ap;_ :o:w~- .Pershirig,-ahd PJ. Smith, 

Proc. Combust. lnst. 26;2.117-212~ (1996) 

(18] Tokhe;m, L, -The Impact of Staged Combustion on th~ 

Op--eration of a Precaldne:r C:ement'!(J!n", PhD Thesis, T-ekmark 

Colle-ge. Porsgrunn Norway._~-~·