the effects of oxygen enrichment on clinker

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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 USSR 1. They found that upon the addition of oxygen that the flame shape became shorter

and brighter 2. Full commercial implementation of this technology in these countries was not enacted do to

problems with refractory life2. 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 increased 2. 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



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



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



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 aresmaller and some have ragged edges

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 sett ing 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

Clinker Crystal Size

Polished Surface Method

10

20

30

40

50

60

70

80

0 10000 20000 30000 40000 50000

O2 Enrichment Rate scfh

M i c r o n

Alite Length

Alite Width

Belite Width

Cement Strengths

1000

2000

3000

4000

5000

6000

7000

0 10000 20000 30000 40000


P S I

1 day cement strength 3 day cement strength

7 day cement strength 28 day cement strength



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.

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).

Concrete Strengths

3500

4000

4500

5000

5500

6000

6500

7000

0 10000 20000 30000 40000


P S I

7 day conc. Strength 28 day conc. Strength



O2 SCFH 0 25000 30000 35000 45000

Fe2O3 3.68 3.69 3.60 3.80 3.64SiO2 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 %retaine 48.00 50.76 49.74 53.48 60.00

Transmitted, plane-polarized light

Alite Avg Width(micro 24.8 28.6 26.9 25.7 29.0

Alite Avg Length 48.4 57.1 52.9 50.6 54.5

Alite Shapea

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

Belite Shapeb

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

Refractory In Belitec

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 Clinker Anal sis

Table #1

aAlite shape Index bBelite shape Index cRefractory 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



O2 SCFH 0 7350 23125 30972 35063 37500

Fe2O3 3.51 3.50 3.65 3.61 3.56 3.51SiO2 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 da cement stren t 1815 1820 1750 1817 1943 1560

3 da cement stren t 3493 3445 3430 3598 35407 day cement strengt 4427 4710 4725 4280 4238 4460

28 da cement stren 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 da conc. Stren t 5277 6310 5843

Table #2 Catskill Kiln Ox en Enrichment Test Cement & Concrete Anal sis

the effects of oxygen enrichment on clinker

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