1. The Effects of Oxygen Enrichment on Clinker, Cement and Concrete Quality
Frederick Hommel
St. Lawrence Cement, Catskill, NY
ABSTRACT
From 1/19-2/27/2000 the Catskill plant with the assistance of Air Products personal ran a trial test on
enriching the kiln combustion air with pure oxygen to improve production and quality. This paper gives an
overview of this test and describes how this effected the clinker, cement and concrete quality.
INTRODUCTION
Enriching combustion air with oxygen to improve clinker production was first suggested back in 19031.
During the 1940’s commercial attempts at enriching combustion air in blast and rotary kilns were tested in
Germany and the USSR1. They found that upon the addition of oxygen that the flame shape became shorter
and brighter2. Full commercial implementation of this technology in these countries was not enacted do to
problems with refractory life 2. Commercial attempts in wet kiln were conducted in the early 6o’s by Union
Carbide at Southwestern Cement’s Victorville, CA wet kiln. They found that a 1 to 2.3% oxygen enrichment
level increase clinker production by 5% and specific fuel consumption decreased by 7%. Increasing clinker
production beyond 5% was limited by their clinker cooler capacity. After modifying their clinker cooler they
were able to increase the oxygen enrichment to 4% which increased production rates to 35% and decreased
specific fuel consumption by 15% 2. In addition to the production increases and decreases in fuel
consumption it was indicated that cement clinker quality improved. Particularly they found that the free CaO
content decreased and the concentration of C3S increased2. The use of oxygen enrichment of the kiln
combustion air since the 60’s has been limited do to the high cost of oxygen. However in resent years the
value of clinker has increased while the cost of oxygen has remained stagnate, making the use of oxygen
enrichment again a possibility. The possibility of increasing clinker production and improving cement
quality by oxygen enrichment was the main reason for trying this technology at the Catskill Plant.
St. Lawrence Cement owns the Catskill Plant that is located on the banks of the majestic Hudson River
approximately 100 miles north of New York City. The Catskill plant contains a single long wet kiln with an
annual clinker production of 520000 metric tons. The kiln is 550 feet long 18x17 feet in diameter with an F L
Schmidt grate cooler. The fuel is a mixture of coal and petroleum coke and is blown into the kiln by the
direct-fired method. Currently the pet coke substitution rate for coal is around 12%. Wasted kiln dust is
recycled back into the kiln by a dust scoop system located just after the chain section. The burning
process, raw and finish grinding is semi-automated with the operation being handled from a central control
room.
From 1/19-2/27/2000 the Catskill Plant conducted a trial test to oxygen enrich the kiln combustion gas. The
goal of this test was to see at least a 10% increase in production and a 10% decrease in specific energy
consumption with improved cement quality via a oxygen enrichment in the range of 1 to 4%. The plan was to
increase feed and speed while the volume of kiln gases decreased. Data showing how this process would
change clinker, cement and concrete quality was very limited and so would be also investigated. Air
Products provided the engineering and equipment needed to run the test. They worked side-by-side with
our operators in the control room to develope operating ranges for the kiln operating parameters. For the
trial period we were to pay Air Products $0.15/100 scf oxygen and $6.00/ton for clinker which exceeded our
normal clinker production.
INSTALLATION
The outside installation consisted of a 9000-gallon tank of liquid oxygen with 8 ambient vaporizers located
near the kiln (see Figure 1). Oxygen from this tank went to a controlling regulator which feed oxygen into a
flow-controlling device located on the kiln deck. From this regulator, oxygen was injected into a stainless

2. steel lance that was located approximately 12 inches behind the nose of the coal pipe and was positioned
towards the load quadrant of the kiln (see Figure 2). Heat generated by the injection of oxygen would
radiate towards the load while the main body of the flame would act as a shield protecting the refractory and
it’s coating from the intense flame generated by the oxygen enrichment. A safety interlock system was in
place to guarantee that if there were a loss in fuel the oxygen enrichment would be shutoff automatically.
Standard Oxygen Enriched Firehood
Flame Section of Flame
Burner
Fuel
Clinke
Oxygen r
Lance Oxygen
Load Clinker Load
Front View Side View
Figure 1. View of a Typical Liquid Oxygen Figure 2. Diagram of oxygen enrichment in
Storage System in the rotary kiln
QUALITY OBSERVATIONS
Oxygen enrichment did effect the clinker quality. Clinker density increased and became harder to grind with
increasing oxygen. Alites in general became larger and more rounded with increasing oxygen and some of
the more rounded alites had a slight fringe around them (Graph 1). The large alites tended to be less reactive
to 1% Nital etching solution and turned brown, however there was areas of very small crystals which were
very reactive and changed to dark brown to blue. Alites remained bright under plane-polarized light and the
birefringence improved slightly at 25000 scfh but decreased at higher oxygen levels. Belites tended to
decrease in size and appear to be slightly more ragged with increasing oxygen, however they were very
reactive to the 1% Nital solution and turned blue in this etching solution (see Figures3-7 & Table#1). Most
of the belites had a fine twin lamellae structure and had a color of clear to pale yellow under transmitted
light. Under plane polarized light the belites with no oxygen enrichment had a higher percentage of higher
order color. Many clinkers throughout the test had very large nests of belites. The matrix surrounding the
alite and belite crystals remained well differentiated for the entire test, however at times the distance
between crystals were very narrow especially at the higher oxygen levels.

3. Figure 3 Clinker taken on 1-8-2000, no oxygen Figure 4 clinker taken on 1-20-2000, oxygen
enrichment, alites and belites have sharp edges enrichment rates at 25000 scfh, some crystals are
slightly larger, both alites and belite continue to have
sharp edging

4. Figure 5 clinker taken on 2-1-2000, oxygen figure 6 clinker taken on 2-3-2000, oxygen
enrichment rate at 30000 scfh, alites are larger and enrichment rate at 350000 scfh, alites are large and
more rounded, belites are large and some have rounded, belites are large with some ragged edges,
ragged edges liquid phase poor

5. Figure 7 clinker taken on 2-24-2000, oxygen
enrichment rate at 40000 scfh, alites are very large,
rounded and some have a belite fringe, belites are
smaller and some have ragged edges
Clinker Crystal Size
Polished Surface Method
80
70
60
Alite Length
Microns
50
Alite Width
40
Belite Width
30
20
10
0 10000 20000 30000 40000 50000
O2 Enrichment Rate scfh
Graph 1
7 and 28 day cement strengths improved and setting times lengthen until the oxygen level exceeded 30000
scfh. After exceeding the 30000 scfh the 7 and 28-day cement strengths decreased and the setting time
shorten slightly. Water demand as measured by the Normal consistency test and cement cube flow stayed
about the same throughout the test (see Table2 & Graph2).
Graph 2
Cement Strengths
7000
6000
5000
PSI
4000
3000
2000
1000 O2 Enrichment Rate scfh
0 10000 20000 30000 40000
1 day cement strength 3 day cement strength
7 day cement strength 28 day cement strength

6. Concrete tests were fewer in number than the cement testing however they showed similar results to 28-day
cement strengths. The 28-day concrete strengths improved with increasing oxygen enrichment until the
oxygen level exceeded 30000 scfh. At 30000 scfh the 28-day strength decline. 7-day concrete strength did
not improve but stayed the same (see graph3). Water demand as measured by the slump increased slightly
higher upon the addition of oxygen, but then remained the same as oxygen increased.
Concrete Strengths
7000
6500
6000
5500
PSI
5000
4500
4000
3500
0 10000 20000 30000 40000
O2 Enrichment Rate scfh
7 day conc. Strength 28 day conc. Strength
Graph 3
BRICK & COATING OBSERVATIONS
During the test maintaining a good coating was not a problem. After the trial test was completed the kiln
was shutdown for our annual maintenance overhaul. The brick in the burning zone did not show signs of
glazing which might be expected if excessive heat was produced. The brick however showed rounding of
corners which is more indicative of material wear. The kiln was shutdown during the early part of the test do
to a coal mill fire. At the time of that shutdown a ring was found at 106 ft with no coating between 80 and 100
ft. The Chemistry of the ring showed that it was regular coating with slightly higher SO3 and K2O. At the
end of the test there was no ring and the coating was very good to the 90ft. Normally at a major shutdown
there is a mud ring at the kiln feed inlet but this time there was none.
KILN OPERATION OBSERVATION
With the addition of the oxygen we expected to see the flame shorten and become brighter like an acetylene
torch, however with our kiln that did not appear. Only the flame nearest to the oxygen lance increased in
brightness. Kiln burning zone temperatures and secondary air did increase with additional oxygen but
material and backend temperatures remained constant. The kiln draft decreased and the kiln amps increased
as oxygen levels increased. Kiln operators adjusted the speed of the kiln by monitoring the heat profile, as
the kiln got hotter they increased the speed. We did experience some persistence problems with maintaining
constant fuel in the kiln. Wet coal gave us problems in the coal mill and so we experienced several times
when the fuel and oxygen enrichment had to be shutdown. To maintain the heat profile, kiln operators
tended to over burn the kiln. Another problem experienced during the test was that the oxygen lance would
warp if it were not removed quickly enough when the oxygen was discontinued.
ENVIRONMENTAL OBSERVATIONS
When the trial test was started it was thought that the NOx levels might increase. However after looking at
the Nox readings the conclusion is that there was no change (see graph 4).

7. O2 trial at Catskill plant
ppm NOx
1000
900
800
700
ppm NOx
600
500
400
300
200
100
0
1/4/00
1/6/00
1/8/00
1/10/00
1/12/00
1/14/00
1/16/00
1/18/00
1/20/00
1/22/00
1/24/00
1/26/00
1/28/00
1/30/00
2/1/00
2/3/00
2/5/00
2/7/00
2/9/00
2/11/00
2/13/00
2/15/00
2/17/00
2/19/00
2/21/00
2/23/00
2/25/00
2/27/00
ppm NOx STDEV ppm NOx O2 SCFH*f
Graph 4
SUMMARY OF TEST
The clinker microstructure and visual inspection of the kiln indicate that the flame did not get shorter but
remained a long flame. The clinker was over burned, but with increasing oxygen the kiln refractory was
easier to coat. The kiln refractory was not damaged by excessive heat caused by the injecting of oxygen in
the combustion gases. Coal mill problems increased instability within the kiln and frequent changes in
oxygen enrichment also increased variations in clinker microstructure. Clinker and cement quality improved
with some oxygen enrichment but decreased after a certain point. This exact point needs to be determined
when the kiln is operating steadily and the tendency to over burn is minimized. Oxygen enrichment had no
over all effect on raising NOx emission levels. Clinker production increased about 9% and the heat
consumption decreased about 5% by the end of the test. Lowering the heat consumption was hampered do
to a very high kiln feed moisture caused by poor weather conditions and lack of chain in the kiln. It is
projected that enriching the combustion gases with oxygen will increase clinker production by 9% and save
the plant $1.7 million per year.
REFERENCES
1. “Use of Oxygen in Cement Clinker Burning”, Zement Kalk Gips, Vol. 4, 140-145, 1967.
2. “Oxygen Enrichment of Combustion Air in Rotary Kilns”, Regional Fall Meeting General Technical
Committee, Portland Cement Association, Miami Beach, 1961.

8. Table #1 Clinker Analysis
O2 SCFH 0 25000 30000 35000 45000
Fe2O3 3.68 3.69 3.60 3.80 3.64
SiO2 22.47 23.04 22.87 22.45 23.00
Al2O3 4.14 3.83 3.96 4.17 4.03
CaO 65.72 66.20 65.92 65.76 67.08
MgO 1.60 1.60 1.62 1.67 1.69
SO3 0.37 0.34 0.39 0.35 0.17
Na2O 0.23 0.23 0.23 0.23 0.22
K2O 0.61 0.49 0.59 0.59 0.30
TiO2 0.23 0.22 0.23 0.23 0.23
P2O5 0.21 0.22 0.20 0.21 0.22
Total Alki 0.63 0.48 0.61 0.61 0.42
Free Lime 0.13 0.12 0.18 0.18 0.04
C3S 60.72 60.41 59.82 60.65 62.90
C2S 18.70 20.58 20.54 18.69 18.58
C3A 5.90 5.05 5.55 5.79 5.72
C4AF 11.19 11.23 10.95 11.56 11.08
Li. Phase 21.58 20.69 20.87 21.96 21.22
L.S.F 92.96 92.02 92.12 92.95 93.10
Si Ratio 2.72 2.91 2.87 2.67 2.83
Al Ratio 1.24 1.16 1.22 1.21 1.23
CL density 1168.8 1267.8 1248.1 1248.9 1259.8
Grindability %retained 200 48.00 50.76 49.74 53.48 60.00
Transmitted, plane-polarized light
Alite Avg Width(microns) 24.8 28.6 26.9 25.7 29.0
Alite Avg Length 48.4 57.1 52.9 50.6 54.5
a
Alite Shape 2.0 2.5 2.7 2.9 4.0
Alite Birefring 0.0081 0.0085 0.0076 0.0075 0.0086
Belite Size 35.5 42.6 35.2 33.9 35.0
b
Belite Shape 1.0 1.5 1.3 1.7 3.0
Belite Color 1.3 1.3 1.2 1.2 2.1
Ohno Strength Index 6210 6210 6188 6121 5940
c
Refractory In Belite 2.8 3.0 2.2 2.1 2.0
Polished Surface Method
Alite Width 28.7 32.1 32.7 29.0 39.2
Alite Length 57.0 62.1 60.1 57.6 77.5
Belite Width 37.2 39.6 36.8 34.5 33.3
Table #1
a b c
Alite shape Index Belite shape Index Refractory in Belite Index
1 Sharp edges 1 Sharp circular 1 None
2 Some rounding of edges 2 Circular with slight ragged edges 2 Trace
3 Rounded edges 3 Circular with some ragged edges 3 Some
4 Very Rounded edges 4 Many with very ragged edges 4 A lot

9. Table #2 Catskill Kiln Oxygen Enrichment Test Cement & Concrete Analysis
O2 SCFH 0 7350 23125 30972 35063 37500
Fe2O3 3.51 3.50 3.65 3.61 3.56 3.51
SiO2 21.61 21.30 21.12 21.14 21.48 21.21
Al2O3 3.89 3.84 3.81 3.81 3.96 3.79
CaO 64.28 64.22 63.38 63.65 64.06 64.31
MgO 1.65 1.66 1.61 1.60 1.63 1.61
SO2 2.54 2.57 2.65 2.56 2.67 2.50
Na2O 0.23 0.23 0.23 0.23 0.23 0.23
K2O 0.58 0.51 0.59 0.58 0.62 0.51
TiO2 0.22 0.22 0.22 0.21 0.22 0.22
P2O5 0.20 0.21 0.20 0.18 0.20 0.21
Total Alki 0.61 0.57 0.61 0.61 0.64 0.57
Free Lime 0.30 0.30 0.20 0.28 0.38 0.34
C3S 56.2 58.5 56.3 57.7 55.3 60.0
C2S 19.7 17.0 18.2 17.2 19.9 15.6
C3A 5.47 5.40 5.05 5.02 5.59 5.25
C4AF 10.68 10.65 11.09 11.00 10.83 10.68
Blaine 3745 3720 3770 3680 3843 3760
325 mesh 93.02 93.58 93.95 93.23 92.75 91.35
NC 24.3 24.9 24.5 24.3 24.4 24.3
Vicat Intial Set 190 255 218 172 180 240
Vicat Final Set 281 330 300 253 293 315
Cement Cube Flow 116 119 110 116 116 114
1 day cement strength 1815 1820 1750 1817 1943 1560
3 day cement strength 3493 3445 3430 3598 3540
7 day cement strength 4427 4710 4725 4280 4238 4460
28 day cement strength 6213 6780 6323 6080
Concrete
Slump 3.8 3.5 3.5
Unit Weight 149.8 152.9 150.6
7 day conc. Strength 4063 3950 4133
28 day conc. Strength 5277 6310 5843