United States
Environmental Protection
Agency
Industrial Environmental
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-84-075 Sept. 1984
Project  Summary
Combustion   Modification  Tests
on  a  Subscale  Cement  Kiln  for
NOX  Reduction
W.A. Carter and R.C. Benson
  Field tests were conducted on a
subscale rotary cement kiln to evaluate
the effect of various combustion
modifications on  gaseous emissions.
The test program was conducted with a
research  kiln donated by a cement
company. The test unit was 8.2 m (27
ft) long and 0.38 m (15  in.) inside
diameter and will  produce 68 kg (150
Ib) of clinker per hour. A coal burner was
designed and built for the test program,
and the kiln was reworked to incorporate
heated secondary  air and flue gas
recirculation (FGR).  The effect on NO
emissions of FGR, diluted primary air,
primary/secondary air ratio, burner tip
velocity, and secondary air temperature
were  evaluated.  The  most effective
combustion modification for coal firing
was determined to be dilution of
primary air with inert gas which reduced
NO by nearly 40 percent when the
primary-air oxygen concentration was
reduced to 12 percent.
  This Project Summary was developed
by EPA's Industrial Environmental
Research Laboratory. Research Triangle
Park. NC, to announce key findings of
the research project that is fully
documented in a separate report of the
same  title (see Project Report ordering
information at back).


Introduction
  KVB has reported  on previous EPA-
sponsored sub- and full-scale cement kiln
combustion modification tests  that
evaluated the effects on NO* emission of
several types of modifications including air
preheat, fuel injection velocity, and
oxygen content of the primary combustion
air stream. Tests in a combustion tunnel
simulating kiln conditions showed dilution
of the primary air stream with an inert
gas, altered fuel injection velocity, and
combustion air preheat to be most
effective in lowering the NO emission
level.
 This report summarizes results of tests
of a subscale rotary cement kiln firing
natural gas and pulverized coal. The kiln
was modified to incorporate flue gas
recirculation (FGR) and combustion air
preheat. A coal burner wasfabricated and
installed in the kiln. The FGR system was
designed to inject flue gas into the
secondary combustion air stream or into
a tertiary air stream in the burner.
 The  overall objective of the contract,
under which the work reported here was
conducted, was to  investigate advanced
combustion modification concepts  re-
quiring relatively minor hardware modifi-
cations that could be used by operators
and/or manufacturers of  industrial
process equipment to reduce NOX emis-
sions. Another objective was to investigate
the feasibility of these modifications to be
readily adopted by  equipment manufac-
turers  and operators.
 The  specific object of the test program
reported here  was to evaluate FGR,
vitiated primary air, primary/secondary
air ratio, temperature of combustion  air,
and coal-carrier air velocity as they affect
emission of NOX in a subscale rotary
cement kiln provided by a major cement
manufacturer. The test results were to be
compared with previous laboratory-scale
tests and recommendations formulated
for tests at larger scale.
 The  initial  phase  of testing was
conducted with natural gas fuel to define

-------
kiln operation over a range of operating
variables; e.g., excess air, primary-to-
secondary-air ratio, and combustion air
preheat. When the performance of  the
kiln was documented with natural  gas
fuel, firing was changed to coal. Kiln NO
emissions were evaluated as a function
of combustion air temperature, primary
air velocity, primary-to-secondary-air
ratio,  FGR rate, and primary (carrier) air
oxygen content.


Previous Work
  The present program is a  follow-on
study, intended to build on the results of
an  earlier program in a laboratory
combustion tunnel. The objective of the
earlier effort was to determine the effect
of burner parameters on near-flame NO
levels for both natural gas and coal fuels.
This laboratory effort  determined  that
combustion  air preheat, fuel  injection
velocity,  and  oxygen  content of  the
primary combustion air stream have first-
order effects on  NO levels. These
parameters were  then  selected  for
implementation on the  subscale kiln.


Program Approach
  During the  earlier program, several
subscale test facilities  were visited and
evaluated. A test program was presented
to the operators of these facilities, and
estimates  of test costs were  received
from  each. The  selected subscale kiln
offered the  most operational flexibility
and opportunity for the maximum data at
minimum cost.
  Prior to the  subscale tests, KVB
conducted laboratory  tests in a kiln-
simulation furnace to define key param-
eters  influencing NO formation in  the
near-burner region. The data gained from
this program were used to design  the
subscale test plan.
  A coal burner and feed system were
built and installed at the test site, and the
kiln was modified to incorporate combus-
tion air preheat and flue gas recirculation.
The initial portion of the test program was
conducted firing natural gas to define kiln
operation over  a range  of operating
variables;  e.g., excess  air, primary-to-
secondary-air ratio, and combustion air
preheat.
  When the performance of the kiln was
documented with natural gas fuel, firing
was changed to coal. Kiln NO emissions
were evaluated as a function of combus-
tion air temperature, primary air velocity,
primary-to-secondary-air ratio, tertiary
air injection FGR rate,  and primary-air
oxygen content.
  Tables 1 and 2 summarize the signifi-
cant results obtained from the  test
program for natural gas and coal firing,
respectively.

Conclusions
  The following conclusions were made
from the field tests and the analyses of
the data:

   The subscale tests corroborated
    laboratory  combustion tunnel test
    results. Combustion tunnel tests
    indicated that reducing the  coal
    carrier  air oxygen content  was a
    promising method of NO reduction,
    and the subscale tests verified this.
    Figure  1 compares the data taken
    during the laboratory program with
    those from the subscale kiln tests.
    The data trends are similar: the kiln
    was more sensitive to carrier-gas
    oxygen content  probably  due  to
    higher  secondary air preheat tem-
    perature.
   The subscale kiln tests showed that
    NO emissions are quite sensitive to
    kiln operating 02 level. Figure 2
    shows the effect of kiln oxygen level
    on NO emissions for 1100F (593C)
    secondary air temperature.  This
    figure  shows that  a 1-percent
    reduction in Oa level results in a NO
    reduction of about 63 ppm.
   Flue gas recirculation  (FGR)  was
    found to be more effective with gas
    firing  than with  coal firing. Gas
    firing  reduced  NO by about 20
    percent from the baseline condition
    at  a FGR rate of 34 percent.  Coal
    firing reduced NO by only 7 percent
    from the baseline with 21 percent
    FGR.
   Diluting coal carrier air with an inert
    gas reduced NO by about 30 percent
    from baseline conditions. Diluting
    the primary air (coal carrier gas) was
    found  to be  the  most effective
    combustion modification.
   Further evaluation of the dilution of
    coal carrier air in larger scale  kilns
    should provide valuable information.

-------
Table 1.    Summary of Test Results: Gas Firing - Subscale Cement Kiln*

                               SA Temp
Test Series"
                           i Primary
                             Air
                                     %FGR
                                   Fuel
                                   MW
                         Firing Rate
                         (W6 Btu/hr)
                    Kiln Exit
                       Oz
                    <%. dry)
                    NO fppmv, @
                    3% Oz, dry)
                             Maximum %
                      COz   NO Reduction
                    (%, dry) from Baseline
PA/SA Variation   Baseline
(20/80J
PA/SA Variation  Baseline
(33/67)
SA Temp.
Variation
FOR
Baseline
Baseline
1100    867
 900    756
 600    589
 300    422
Amb.
1200    922
 600    589
 300    422
Amb.
1000    811
 900    756
 800    700
 700    644
Amb.
1168    904
                             19.1
                            33.0
14.6
28.0
           0
          21.6
          28.6
          32.6
          33.8
                                              0.21
                                              0.21
0.19
0.19
                           (0.70)
                           (0.70)
(0.64)
(0.64)
                                                                    2.0
                      2.0
2.0
2.0
640
600
400
243
228
300
194
180
170

404
419
364
350
212
340
163
135
110
100
                                                                                          11.2
                                                                                          11.5
14.2
15.8
                                                                                                                     64.4
                                                                                                                     43.3
                                                                                                                     47.5
                                                                                                                     70.6
*AII CO data for the nominal Oz's listed are less than 200 ppmv.
*PA = Primary Air; SA = Secondary Air; FOR = Flue Gas Recirculation.
Table 2.    Summary of Test Results: Coal Firing - Subscale Cement Kiln
Date
(1982)
7/27
7/27
8/04
7/29
8/12
8/12
8/12
8/12
8/12
8/11
7/29
8/04
8/04
8/04
8/04
8/10
8/10
8/10
8/12
8/12
8/12
SA Temp."
F
1099
1003
1145
1167
1162
1158
1166
1169
1161
1187
1167
1153
1130
1144
1160
1140
1160
1140
1160
1160
1160
(K)
(866)
(816)
(892)
(904)
(901)
(899)
(903)
(905)
(900)
(915)
(904)
(896)
(883)
(891)
(900)
(889)
(900)
(889)
(900)
(894)
(900)
PA Velocity"
fpm
3338
3338
3338
3232
2950
2504
2285
2128
2504
2915
3232
3268
3440
3390
3440
3120
2890
3120
2500
2500
2500
(m/s)
(17)
(17)
(17)
(16.4)
(15)
(12.7)
(11.6)
(10.8)
(12.7)
(14.8)
(16.4)
(16.6)
(17.5)
(17.2)
(17.5)
(15.8)
(21.7)
(15.8)
(12.7)
112,7)
(12.7)
%PA
28.4
27.9
29.4
25.8
21.0
19.3
17.1
16.2
9.3
22.2
25.4
29.8
30.1
29.7
30.1
22.5
21.7
22.5
19.3
18.4
19.7
Avg. Oz
(%)
3.5
3.7
3.8
3.6
3.7
3.6
4.1
5.3
4.3
3.6
3.6
4.1
5.4
5.0
5.6
2.9
3.7
2.3
5.0
4.0
3.8
Avg. NO
Avg. CO fppm corrected COz
(ppm) to 3% Oz. dry) (%)
25 753
35 794
559 826
125 848
148 806
396 643
303
963
293
608
136
268
452
79
167
481
104
550
188
87
708
773
711
775
822
848
847
836
788
727
700
613
771
635
440 544
16.4
15.4
14.6
15.4
15.5
17.8
15.3
15.5
17.6
15.1
15.8
14.6
13.8
16.4
13.7
15.3
13.5
16.2
17.5
17.9
17.6
Comments

Evaluate the effect of SA temperature on NO
emissions; PA = constant Oz = constant.




Velocity variation; varied primary air flow.
SA &P was relatively constant.





PA/SA variation tests. Varied PA flow and SA
flow at constant Oz.


Baseline for series to evaluate FGR.
19% FGR*
21% FGR
Baseline for PA dilution tests\
18% O2 in PA >
12% Oz in PA 1
Baseline for PA dilution tests)
15%OzinPA }
12% Oz in PA )



O%FGR



High PA
Velocity

Low PA.
Velocity
*SA = Secondary Air; PA = Primary Air; FGR = Flue Gas Recirculation.

-------
   1000
    900
    800
    700
    600
<5  50
   400
 
    300
    200
     too
                                              Subscale Kiln
                                                Results
                                                      Laboratory Tunnel
                                                           Results
Western Bituminous Coal
Coal Nitrogen Content = 1.1%
Kiln Exit O2 = 4.0%
Combustion Air Temperature = 894 K (1150F)
               \
      A
I
              2.5
              7.5     10     12.5     15    17.5

              Primary Air Oxygen Content, %, dry
                                                                 20
                                          22.5   25
 Figure 1.   Effect of primary-air oxygen content on NO emissions.

-------
      1200
      1100
      1000
       900
       800
       700
       600
       500
       400
       300
       200
       700
                 I      I      I      I      I      I
               Western Bituminous Coal
               Secondary Air Temperature = 567 K (1100F)
                                     I
I
                                     456

                                    Kiln Exit Oa %, dry
                           9     10
Figure 2.   Effect of kiln oxygen level on NO emissions.
   W. A. Carter andR. C. Benson are with KVB, Inc., Irvine, CA 92714.
   Robert E. Hall is the EPA Project Officer (see below).
   The complete report, entitled "Combustion Modification Tests on a Subscale
     Cement Kiln for /VO Reduction," (Order No. PB 84-223 502; Cost: $10.00,
     subject to change) will be available only from:
          National Technical Information Service
          5285 Port Royal Road
          Springfield, VA 22161
          Telephone: 703-487-4650
   The EPA Project Officer can be contacted at:
          Industrial Environmental Research Laboratory
          U.S. Environmental Protection Agency
          Research Triangle Park, NC27711
                                                                 frl). S. GOVERNMENT PRINTING OFFICE: 1984/759-102/10659

-------

-------
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
                             1'  ^PUTtCTlOK   AGfcjvCY
                 C H i c a b u  1 L  b 0 6 o a

-------