 |
Description  |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to the manufacture of cement clinker in
long rotary kilns. In particular, the invention relates to the method and
apparatus for the manufacture of cement clinker in conventional long wet
or dry rotary kilns wherein blast-furnace slag is added at the input-end
of kiln with a stream of feedstock material containing lime such that as
the stream of feedstock and blast-furnace slag moves toward the heat at
the heat-end of the kiln, the blast-furnace slag is melted and defused
into the feedstock material to form cement clinkers.
2. State of the Art
As stated in U.S. Pat. No. 5,156,676, the literature is replete with
processes by which the calcining and clinkering of cement ingredients can
be accomplished. The typical process using a rotary kiln, either wet or
dry, is well known. Cement raw materials such as limestone, clay and sand,
or the like, are finely ground and intimately mixed to provide a
substantially homogeneous mixture at the input or feed-end of the kiln.
The kiln is tipped downwardly at an angle such that the heat-end of the
kiln is below the feed-end. The kiln has generally four operating zones
including a precalcining zone, a calcining zone, a clinkering zone, and a
cooling zone. Conventional fuel is combined with preheated air and
injected into the kiln at the heat-end. Fuels such as natural gas, oil or
powdered coal are conventionally employed in cement manufacturing
processes.
As the finely divided cement raw materials pass into the rotating kiln at
the feed-end thereof, the materials are heated from near ambient
temperature to about 538.degree. C. (1000.degree. F.) in the precalcining
zone. In this zone, the heat of the combustion gases from the calcining
zone is used to raise the temperature of the raw materials. Additionally,
in the kiln, chain systems or the like may be attached to the interior of
the kiln and are employed to improve the efficiency of heat exchange
between the gases and raw materials.
The temperature of the raw materials is increased from about 538.degree. C.
to about 1093.degree. C.(1000.degree. F. to about 2000.degree. F.) as they
pass through the calcining zone and in this zone CaCO.sub.3 iS decomposed
with the evolution of CO.sub.2.
Calcined material at the temperature of about 1093.degree. C. (2000.degree.
F.) then passes into the clinkering or burning zone where the temperature
is raised to about 1500.degree. C. (2732.degree. F.). It is in this zone
that the primary raw materials are converted into the typical cement
compounds such as tricalcium silicate, dicalcium silicate, tricalcium
aluminate, and tetracalcium-aluminoferrite. The cement clinkers then leave
the clinkering zone where the clinkers are cooled and thereafter processed
further such as by grinding.
Further, the use of ground blast-furnace slag as a cementitious material
dates back to 1774. In the production of iron, the blast furnace is
continuously charged from the top with iron oxide sources, fluxing stone,
and fuel. Two products are obtained from the furnace: molten iron that
collects in the bottom of the furnace and liquid iron blast-furnace slag
floating on the pool of iron. Both are periodically tapped from the
furnace at a temperature of about 1500.degree. C. (2732.degree. F.). The
slag consists primarily of silica and alumina combined with calcium and
magnesium oxides from the fluxing stone. Cementitious activity of this
slag for use in mortar or concrete is determined by its composition and
the rate at which the molten material is cooled when it comes from the
furnace.
Further, in the production of steel, a similar process occurs wherein
liquid steel slag floats on the pool of steel. Again, the steel slag
consists primarily of silica and alumina combined with calcium and
magnesium oxides. Disposing of both the steel slag and the blast-furnace
slag poses a major disposal problem for the manufacturer thereof because
of the amount of materials involved.
Both the steel slag and the blast-furnace slag is composed of particles
that are very hard. The blast-furnace slag, when used, has always been in
a finely powdered or granulated form, which means that a great deal of
energy must be used to grind and pulverize the slag into the finely
powdered form or to granulate it. Such a process is disclosed in U.S. Pat.
No. 2,600,515 in which a blast-furnace slag, in a finely powdered mixture
with limestone, is fed in rotary cement kilns and is introduced directly
into the flame of the kiln. The slag powder is blown in at the same time
and by the same channels as the fuel, namely, pulverized coal, heavy oil
or gas. This process has several disadvantages. One of the most
significant disadvantages is that enormous amounts of energy are required
to pulverize and dry the material so that it could be blown into the
furnace.
Many of the chemical compounds in steel slag and blast-furnace slag are
common to cement chemical compounds and their heat of formation is already
been accomplished in their respective processes. The American Concrete
Institute defines blast-furnace slag as follows:
blast-furnace slag--the nonmetallic product, consisting essentially of
silicates and aluminosilicates of calcium and other bases, that is
developed in a molten condition simultaneously with iron in a blast
furnace.
1. air-cooled blast-furnace slag is the material resulting from
solidification of molten blast-furnace slag under atmospheric conditions:
subsequent cooling may be accelerated by application of water to the
solidified surface.
2. expanded blast-furnace slag is the lightweight, cellular material
obtained by controlled processing of molten blast-furnace slag with water,
or water and other agents, such as steam or compressed air, or both.
3. granulated blast-furnace slag is the glassy, granular material formed
when molten blast-furnace slag is rapidly chilled, as by immersion in
water.
In the present case, the term "blast-furnace slag" will be used hereafter
to designate only "air-cooled blast-furnace slag" and not expanded or
granulated blast-furnace slag unless otherwise stated.
These products, with the addition of CaO, can be converted to 3CaO
.SiO.sub.2 (C.sub.3 S), 2CaO SiO.sub.2 (C.sub.2 S), 2CaO . Fe.sub.2
O.sub.3 (C.sub.2 F), 4CaO Al.sub.2 O.sub.3 . Fe.sub.2 O.sub.3 (C.sub.4
AF), 3CaO . Al.sub.2 O.sub.3 (C.sub.3 A) in the burning zone of the rotary
kiln.
Experience has shown blast-furnace slag has no deleterious effect on the
operation of a cement rotary kiln. Emission of volatile materials from the
rotary kiln is improved because the slag has previously been heat treated
and most volatile materials have been removed, i.e. carbon dioxide,
carbon, volatile organics, and the like. However, as stated in the prior
art, fine grinding or comminution or pulverization of the slag is
required, thus adding an expensive step to the cement-making process.
Also, granulated slag is also very expensive to form.
SUMMARY OF THE INVENTION
Because it has long been recognized that many of the chemicals and chemical
compounds in blast-furnace slag are common to cement making materials and
because blast-furnace slag is available in large quantities, it would be
advantageous to be able to use the blast-furnace slag in the cement-making
process if it could be used in a much coarser state than the pulverized or
granulated state now required and if it could be added to the feedstock
materials being fed to the kiln at the feed-end of the kiln instead of the
heat-end thereof.
The present invention provides such use of blast-furnace slat and provides
a method and apparatus for utilization of various blast-furnace process
slags that have been crushed and screened to provide a coarse state with a
predominant particle size having diameters up to 2" with the coarse
blast-furnace slag being fed into the input-end of the kiln with the
feedstock materials, thereby obtaining all of the advantages of the prior
art use of blast-furnace slag without the disadvantage of the requirements
to provide granulation of the slag or fine grinding, pulverizing or
comminution of the slag and introducing the fine blast-furnace slag into
the heat-end of the kiln.
As stated previously, Applicant's experience has shown blast-furnace slag
to have no deleterious effect on the operation of a cement rotary kiln.
Emission of volatile materials from the rotary kiln is improved because
the blast-furnace slag has previously been heat-treated and most volatile
materials have been removed, i.e. carbon dioxide, carbon, volatile
organics, and the like. Because of the previous history of the
blast-furnace slag, the required blast-furnace slag chemistry has already
been achieved during the iron making process thus conserving energy in the
cement making process. Thus there are a number of advantages of the use of
this slag. First, as stated earlier, no fine grinding, pulverizing or
comminution of the slag is required. Large quantities of coarse slag
(defined herein as blast-furnace slag having predominant particle sizes
that are substantially up to 2" in diameter) can be incorporated into the
cement clinker composition with only minor chemical changes to the regular
material feed to the rotary kiln. Crushing and screening is required only
for slag particles in excess of 2" in diameter.
Second, no drying of the slag is required. Inherent moisture normally runs
1% to 6%. In the wet process rotary kiln system, substantial moisture
reduction and savings are realized. In the dry process rotary kiln system,
it is not required that the blast-furnace slag be dried.
Third, no plugging of the kiln has been experienced due to mud ring or
clinker buildup. In both the wet and the dry process rotary kilns, the
coarse blast-furnace slag has a cleaning effect on material buildup as it
moves through the kiln.
Fourth, the coarse blast-furnace slag can be utilized as part of the
initial feedstock and is introduced into the kiln at the feed-end thereof.
The blast-furnace slag and wet or dry feedstock may be injected into the
feed-end of the rotary kiln as separate materials and may be injected
together at the feed-end of the kiln without prior blending.
Fifth, only slight chemical changes in the feedstock composition are
required for the normal feedstock to accommodate the blast-furnace slag.
This usually means the feedstock must be richer in lime content.
Six, the coarse blast-furnace slag chemical compound structure transforms
to the desired cement clinker structure during the heat treatment within
the rotary kiln by diffusion.
Seventh, substantial energy savings are realized when the blast-furnace
slag is utilized because of the low temperature at which the blast-furnace
slag melts and because no grinding or pulverizing of the blast-furnace
slag is required.
Eight, cement clinker production increases are almost proportional to the
amount of blast-furnace slag utilized.
Ninth, the environmental condition of the rotary kiln process improves
because of the low volatile content of the blast-furnace slag.
Tenth, recycling of the blast-furnace slag improves the environment because
it provides an important use for the large quantities of blast-furnace
slag available and avoids any so-called problems with disposal of the
blast-furnace slag.
Eleventh, the cost of cement production is substantially reduced because of
the energy savings, and the plentiful supply of low cost blast-furnace
slag.
Thus, it is an object to the present invention to provide an improved
method and apparatus for operating a rotary kiln for the production of
cement clinker using coarse blast-furnace slag, a by-product of the
iron-making processes.
It is another object to the present invention to introduce the coarse
blast-furnace slag into a cement-making rotary kiln at the feed-end
thereof.
It is still another object of the present invention to use coarse
blast-furnace slag having predominant particle sizes that are
substantially 2" in diameter or less.
Thus, the present invention relates to a method of cement clinker
manufacture using an elongated rotary cement kiln having a feed-end and a
heat-end, the heat-end being tilted downwardly with respect to the
feed-end, the method comprising the steps of directing heat from a heat
source into the heat-end of the kiln, introducing a stream of feedstock
material containing lime into the feed-end of the kiln such that the
stream of feedstock material moves toward the heat at the heat-end of the
kiln, and adding a predetermined amount of crushed and screened
blast-furnace slag to the stream of feedstock material at the feed-end of
the kiln such that as the stream of feedstock material and blast-furnace
slag moves toward the heat-end of the kiln, the blast-furnace slag is
melted by the heat and diffused into the feedstock material to form cement
clinkers.
The invention also relates to apparatus for forming cement clinkers
comprising a rotary cement kiln having a feed-end and a heat-end, the
heat-end being tilted downwardly with respect to the feed-end, a heat
source at the heat-end for heating the interior of the rotary kiln, and
conveying means for introducing a stream of feedstock material containing
lime and blast-furnace slag into the feed-end of the rotary kiln such that
as the stream of feedstock material and blast-furnace slag move toward the
heat-end of the kiln, the blast-furnace slag is diffused by the heat into
the feedstock material to form cement clinker.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other more detailed objects of the present invention will be more
fully disclosed in the following DETAILED DESCRIPTION OF THE DRAWINGS in
which:
FIG. 1 is a basic diagrammatic representation of a rotary kiln system of
the present invention for forming cement clinkers in which the feedstock
material and the blast-furnace slag are fed together into the input-end of
the rotary kilns;
FIG. 2 is a diagrammatic representation of the feedstock material and the
blast-furnace slag being feed separately into the inlet-end of the rotary
kiln.
FIG. 3 is a flow chart representation of the process in which the feedstock
material and the blast-furnace slag are fed into the input-end of the kiln
in a combined mixture; and
FIG. 4 is a flow chart representation of an alternate process in which the
feedstock material and the blast-furnace slag are fed separately into the
input or feed-end of the rotary kiln.
DETAILED DESCRIPTION OF THE DRAWINGS
The present invention allows crushed and screened raw blast-furnace slag to
be added to the kiln feed as a separate component at the feed-end of the
rotary cement kiln in various particle sizes wherein the predominant
particle size is up to a maximum of 2" in diameter. The term "raw"
blast-furnace slag, as used herein, means blast-furnace slag that is
unprocessed in any manner except for crushing and screening of the
blast-furnace-slag that is in a solid state. Most blast-furnace slag has
particles below 2" in diameter. However, some of it is over 2" in diameter
and thus a crushing and screening process is required to achieve only the
desired predominant particle size that is substantially 2" in diameter or
less. No fine grinding, pulverizing or comminution of blast-furnace slag
is required by the present invention. The invention provides a method of
utilization of various blast-furnace slags in a much coarser state than
previously recognized in rotary cement kiln processes which allows the
elements in the chemical compounds of the blast-furnace slag, i.e.,
silicates, and aluminosilicates of calcium, and the like, to become an
integral part of the cement clinker. As understood by those skilled in the
art, the chemistry of the slag must be understood and controlled as part
of the overall ingredients of the cement and thus the quantity of the
blast-furnace slag being added to the feedstock must be balanced with the
feedstock materials and their chemical compounds.
In a laboratory furnace burn test of 100% blast-furnace slag, the melting
point of the blast-furnace slag was determined and is the key to its use
in a cement kiln. As can be seen in Table I, the melting point was
determined to be 2552.degree. F./1400.degree. C. for blast-furnace slag
which allows the blast-furnace slag to be added to the feed-end of the
kiln in fairly large particle sizes, the predominant particle size being
up to 2" in diameter.
TABLE I
______________________________________
LAB FURNACE BURN
EFFECTS ON SLAG
Slightly
Temp. Interval None Sticky Melts
______________________________________
Start
800 C. 15 Min. X
1000 C. 15 Min. X
1100 C. 15 Min. X
1200 C. 15 Min. X
1300 C. 15 Min. X
1385 C. 15 Min. X
1395 C. 15 Min. X
1400 C. 15 Min. X
______________________________________
Table I illustrates the effects on blast-furnace slag when heated to
various temperatures. The tests set forth in Table I were run 15 minutes
at each temperature with slag size approximating 3/8" particles. As a
result of the tests, it has been determined that the slag will not thicken
slurry in the chain section of the rotary kiln, cause mud rings or
increase dust loss because of particle size. Further, it will reduce
moisture content as much as 2.2% or more depending upon the quantity of
blast-furnace slag. The blast-furnace slag begins to melt and combine with
other raw materials somewhere between the calcination zone and the burning
zone in the rotary kiln. Because of the low melting point, it is not
necessary to grind, pulverize or comminute this material such as in the
prior art which requires 80% of the material to pass through a 200-mesh
screen for a chemical combination with other ingredients. The formation of
silicates and aluminosilicates of calcium and other bases which are
similar to cement clinker compounds, if not the same, have already been
accomplished in the blast-furnace slag during the steel-making process.
These compounds, with the addition of CaO, can be converted to
2CaO.SiO.sub.2 (C.sub.2 S), 3CaO.SiO.sub.2 (C.sub.3 S), 2CaO.Fe.sub.2
O.sub.3 (C.sub.2 F), 3CaO.Al.sub.2 O.sub.3 (C.sub.3 A), and 4CaO. Al.sub.2
O.sub.3 Fe.sub.2 O.sub.3 (C.sub.4 AF) with very little additional heat.
These are the major chemical compounds of cement clinker.
The apparatus of the present invention is illustrated in FIG. 1. The
apparatus 10 includes the rotary kiln 12 supported in a well-known manner
by flanges 14 that rotate with the kiln. The kiln has a feed-end 16 and a
heat-end or burning zone 18. The heat-end 18 is tilted downwardly with
respect to the feed-end 16 as is well known in the art. A fuel source 20
creates a flame 22 in the heat-end 18 of the rotary kiln 12 to provide a
temperature of approximately 1500.degree. C. (2732.degree. F.). Cement raw
materials or feedstock such as limestone, clay, sand and the like is
carried by a variable speed conveyor belt 24 to the rotary kiln 12. If a
wet slurp is used, the variable speed conveyor belt 24 will convey the
feedstock to a grinder 26 and from the grinder 26 to the feed-end 16 of
the rotary kiln 12. The feedstock moves in a stream 28 through the
rotating kiln 12 toward the flame 22. The well-known chemical processes
take place within the kiln 12 and the cement clinker 30 exits the heat-end
18 of kiln 12 for further processing. Pollution control devices 32 and 34,
well known in the art, are at the heat-end and feed-end, respectively, of
the kiln 12. At the heat-end 18, out of the pollution control device 32,
waste gases 38 are expelled to atmosphere and reclaimed waste products 40
are recovered.
At the feed-end 16, the pollution control equipment 34 removes the waste
gases 36 which are expelled and reclaims the waste products at 42.
In the present invention, the blast-furnace slag 44 is carried by a
conveying device 46, such as a variable speed conveyor belt, to the
feedstock material 48 that is being fed through a dust hopper 56 (FIG. 2)
at the feed-end 16 of the rotary kiln 12. A controller 25 controls the
speed of the conveyor belts 24 and 46 so that the proper proportion of
blast-furnace slag 44 is provided relative to the feedstock depending upon
the chemical compositions thereof. Such control is well known in the art
and will not be discussed in detail.
FIG. 2 is a diagrammatic representation of the apparatus for providing a
separate feed of the blast-furnace slag and the feedstock into the
input-end of the rotary kiln 12. In FIG. 2, it can be seen that the
blast-furnace slag 50 is dropped into a hopper 52 and carried upwardly by
a conveying system 54 where it is deposited at 55 so as to pass through
the dust hopper 56 to the input-end 16 of the rotating kiln 12. The feed
of the material to the input-end of the kiln can be done in any well-known
manner. In like manner, the feedstock material 58 is dropped into a hopper
60 where it is carried upwardly by conveyor means 62 and dropped at 64
into the hopper 56 for feeding into the input-end 16 of the rotary kiln
12. Either the apparatus of FIG. 1 or FIG. 2 produces the desired results.
Table II sets forth the results of the chemical analysis of a sample of
blast-furnace slag taken from a blast-furnace slag stockpile at random. Of
course, the chemical analysis of blast-furnace slag may vary from the
values in Table II depending upon the slag.
TABLE II
______________________________________
BLAST-FURNACE SLAG
ELEMENTS BLAST-FURNACE SLAG
______________________________________
SiO2 35.76
Al2O3 9.42
Fe2O3 0.63
CaO 40.01
MgO 8.55
SO3 2.70
P2O5 0.00
TlO2 0.00
Na2O 0.32
K2O 0.57
______________________________________
It can be seen that the blast-furnace slag composition is suitable for the
manufacture of cement.
Table III illustrates the typical mix calculations for a feedstock having
0% blast-furnace slag, 89.67% limestone, 4.42% shale, 4.92% sand, and
0.99% shale.
TABLE III
______________________________________
TYPE I LA MIX CALCULATION - 0% SLAG
______________________________________
LS SHALE SAND ORE
______________________________________
SiO2 8.25 49.25 90.00 0.81
Al2O3 2.31 18.60 3.24 0.28
Fe2O3 1.30 5.79 1.90 96.17
CaO 47.60 3.30 0.51 0.51
MgO 0.46 1.25 0.07 0.70
SO3 0.90 3.37 0.13 0.11
P2O5 0.00 0.00 0.00 0.00
TiO2 0.00 0.00 0.00 0.00
Na2O 0.10 0.73 0.03 0.03
K2O 0.50 3.10 0.31 0.04
______________________________________
CLINKER ANALYSIS
SLURRY CLINKER
______________________________________
SiO2 14.01 21.78
Al2O3 3.06 4.75
Fe2O3 2.46 3.83
CaO 42.86 66.62
MgO 0.48 0.74
SO3 0.96 0.75
P2O5 0.00 0.21
TiO2 0.00 0.21
Na2O 0.12 0.19
K2O 0.60 0.50
TOTAL 99.59
S/R 2.42
A/F 1.35
C3S 63.33
C2S 14.66
C3A 7.22
C4AF 11.65
______________________________________
Table IV illustrates a test mix calculation having 5% blast-furnace, slag,
86.11% limestone, 4.14% shale, 3.76% sand, and 0.97% mill scale.
TABLE IV
______________________________________
TYPE I WITH 5% BLAST FURNACE SLAG ADDED
______________________________________
ELE- MIDL. PHILLIPS
MILL B-F
MENTS LS SHALE SAND SCALE SLAG
______________________________________
SiO2 8.25 49.25 90.00 0.81 35.76
Al2O3 2.31 18.60 3.24 0.28 9.42
Fe2O3 1.30 5.79 1.90 96.17 0.63
CaO 47.60 3.30 0.51 0.51 40.01.
MgO 0.46 1.25 0.07 0.70 8.55
SO3 0.90 3.37 0.13 0.11 2.70
P2O5 0.00 0.00 0.00 0.00 0.00
TiO2 0.00 0.00 0.00 0.00 0.00
Na2O 0.10 0.73 0.03 0.03 0.32
K2O 0.50 3.10 0.31 0.04 0.57
______________________________________
CLINKER ANALYSIS
SLURRY CLINKER
______________________________________
SiO2 13.19 21.38
Al2O3 3.04 4.98
Fe2O3 2.51 3.76
CaO 43.36 66.33
MgO 0.48 1.14
SO3 0.97 0.70
P2O5 0.00 0.22
TiO2 0.00 0.22
Na2O 0.12 0.12
K2O 0.60 0.50
TOTAL 99.47
S/R 2.33
A/F 1.44
C3S 63.76
C2S 13.20
C3A 8.00
C4AF 11.44
______________________________________
Table V illustrates a test mix calculation having 10% blast-furnace slag,
82.66% limestone, 2.94% shale, 3.32% sand, and 1.08% mill scale.
TABLE V
______________________________________
TYPE I WITH 10% BLAST-FURNACE SLAG ADDED
______________________________________
ELE- MIDL. PHILLIPS
MILL B-F
MENTS LS SHALE SAND SCALE SLAG
______________________________________
SiO2 8.25 49.25 90.00 0.81 35.76
Al2O3 2.31 18.60 3.24 0.28 9.42
Fe2O3 1.30 5.79 1.90 96.17 0.63
CaO 47.60 3.30 0.51 0.51 40.01
MgO 0.46 1.25 0.07 0.70 8.55
SO3 0.90 3.37 0.13 0.11 2.70
P2O5 0.00 0.00 0.00 0.00 0.00
TiO2 0.00 0.00 0.00 0.00 0.00
Na2O 0.10 0.73 0.03 0.03 0.32
K2O 0.50 3.10 0.31 0.04 0.57
______________________________________
CLINKER ANALYSIS
SLURRY CLINKER
______________________________________
SiO2 12.52 21.30
Al2O3 2.85 4.98
Fe2O3 2.61 3.76
CaO 43.85 66.09
MgO 0.47 1.53
SO3 0.94 0.70
P2O5 0.00 0.22
TiO2 0.00 0.22
Na2O 0.12 0.24
K2O 0.57 0.50
TOTAL 99.54
S/R 2.32
A/F 1.44
C3S 63.39
C2S 13.25
C3A 8.00
C4AF 11.44
______________________________________
Table VI illustrates a test mix calculation having 15% blast-furnace slag,
74.22% limestone, 1.68% shale, 2.93% sand, and 1.16% mill scale.
TABLE VI
______________________________________
TYPE I WITH 15% BLAST-FURNACE SLAG ADDED
______________________________________
ELE- MIDL. PHILLIPS
MILL B-F
MENTS LS SHALE SAND SCALE SLAG
______________________________________
SiO2 8.25 49.25 90.00 0.81 35.76
Al2O3 2.31 18.60 3.24 0.28 9.42
Fe2O3 1.30 5.79 1.90 96.17 0.63
CaO 47.60 3.30 0.51 0.51 40.01
MgO 0.46 1.25 0.07 0.70 8.55
SO3 0.90 3.37 0.13 0.11 2.70
P2O5 0.00 0.00 0.00 0.00 0.00
TiO2 0.00 0.00 0.00 0.00 0.00
Na2O 0.10 0.73 0.03 0.03 0.32
K2O 0.50 3.10 0.31 0.04 0.57
______________________________________
CLINKER ANALYSIS
SLURRY CLINKER
______________________________________
SiO2 11.78 21.21
Al2O3 2.64 4.96
Fe2O3 2.71 3.74
CaO 44.45 65.81
MgO 0.47 1.91
SO3 0.91 0.70
P2O5 0.00 0.22
TiO2 0.00 0.22
Na2O 0.11 0.24
K2O 0.54 0.50
TOTAL 99.51
S/R 2.32
A/F 1.44
C3S 63.09
C2S 13.21
C3A 7.98
C4AF 11.38
______________________________________
Table VII illustrates a test mix calculation having 30% blast-furnace slag,
1.81% mill scale, 0.33% sand, and 67.86% limestone.
TABLE VII
______________________________________
TYPE I WITH 30% BLAST FURNACE SLAG ADDED
______________________________________
ELEMENTS MIDL. LS ORE SAND B-F SLAG
______________________________________
SiO2 8.25 0.81 90.00 35.76
Al2O3 2.31 0.28 3.24 9.42
Fe2O3 1.30 96.17 1.90 0.63
CaO 47.60 0.51 0.51 40.01
MgO 0.46 0.70 0.07 8.55
SO3 0.90 0.11 0.13 2.70
P2O5 0.00 0.00 0.00 0.00
TiO2 0.00 0.00 0.00 0.00
Na2O 0.10 0.03 0.03 0.32
K2O 0.50 0.04 0.31 0.57
______________________________________
CLINKER ANALYSIS
SLURRY CLINKER
______________________________________
SiO2 8.44 20.31
Al2O3 2.26 5.39
Fe2O3 3.76 4.46
CaO 46.16 64.43
MgO 0.46 3.09
SO3 0.88 0.70
P2O5 0.00 0.22
TiO2 0.00 0.22
Na2O 0.10 0.24
K2O 0.49 0.50
TOTAL 62.55 99.57
S/R 2.06
A/F 1.21
C3S 60.37
C2S 12.75
C3A 7.92
C4AF 13.57
______________________________________
Clearly, Tables III, IV, V, VI, and VII confirm that the addition of
blast-furnace (air-cooled) slag is suitable as the raw material for the
manufacture of cement clinker.
FIG. 3 illustrates the process of the present invention wherein the
feedstock material and blast-furnace slag are combined as illustrated in
FIG. 1 before entering the kiln at the feed-end thereof. At step 76, the
feedstock material is provided and combined at step 78 with the
blast-furnace slag that has been crushed and screened to obtain particles
of which the predominant particle sizes have a maximum diameter of
substantially 2 inches or less at step 80. The combined material is then
fed into the feed-end of the rotary kiln at step 82.
In FIG. 4, the process feeds the blast-furnace slag and the feedstock into
the feed-end of the rotary kiln separately as illustrated in FIG. 2. In
such case, at step 66 the feedstock material is provided and conveyed by a
conveying means at step 68 to the inlet or feed-end of the rotary kiln.
The blast-furnace slag is crushed and screened to obtain the particle
sizes having a predominant particle size with a maximum diameter of
substantially two inches or less at step 72 and the resultant end product
is conveyed at step 74 to the inlet or feed-end of the rotary kiln. At
step 70, the feedstock and blast-furnace slag is heated in the rotary kiln
until cement clinker is formed.
Thus there has been disclosed a method and apparatus for forming cement
clinker with the addition of coarse blast-furnace slag which is fed, with
the feedstock material into the feed-end of the rotary kiln. Coarse
blast-furnace slag is defined herein as blast-furnace slag that has been
crushed and screened to particles having a predominant particle size up to
a maximum diameter of substantially 2" in diameter. Many advantages are
obtained by the present invention. No fine grinding, pulverizing or
comminution of the slag is required. Large quantities of coarse slag up to
the predominant 2" particle size can be incorporated into the cement
clinker composition with only minor chemical changes required in the
regular material fed to the rotary kiln.
No drying of the slag is required. Inherent moisture normally runs one to
six percent. In the wet process rotary kiln system, substantial moisture
reduction and savings are realized. In the dry process rotary kiln system,
the blast-furnace slag may be dried but it is not necessary.
With the present invention, coarse blast-furnace slag can be utilized in
the production of cement clinker by the way of the rotary kiln as part of
the initial feedstock. The blast-furnace slag and wet (or dry) feedstock
are injected into the feed-end of the rotary kiln as separate materials.
They also may be injected together at the feed entrance of the kiln with
prior blending. No plugging of the kiln has been experienced due to mud
ring or clinker buildups. In both the wet and the dry process rotary
kilns, the blast-furnace slag has a cleaning effect on material buildup as
it moves through the kiln.
Only slight chemical changes are required for the normal feedstock to
accommodate the blast-furnace slag. This usually means that the feedstock
must be richer in lime content. The chemical compound structure of the
coarse blast-furnace slag transforms to the desired cement clinker
structure during the heat treatment within the rotary kiln by diffusion.
Because grinding, pulverizing or comminution of the blast-furnace slag is
not required, substantial energy savings are realized using this invention
to produce cement clinker. Production increases are almost proportional to
the amount of slag utilized. Further, the environ_mental condition of the
rotary kiln process improves because of the low volatile content of the
blast-furnace slag. Further, recycling of the blast-furnace slag improves
the environment and provides a useful outlet for blast-furnace slag rather
than the blast-furnace slag occupying vast areas of land space for
storage. Thus recycling of the blast-furnace slag improves the environment
and reduces the cost of cement production substantially.
While the invention has been described in connection with a preferred
embodiment, it is not intended to limit the scope of the invention to the
particular form set forth, but, on the contrary, it is intended to cover
such alternatives, modifications, and equivalents as may be included
within the spirit and scope of the invention as defined by the appended
claims.
* * * * *
|
|
 |
|
 |
Description |
|
