U.S. patent application number 09/789687 was filed with the patent office on 2001-08-23 for synthetic silicate pellet composition and methods of making and using thereof.
This patent application is currently assigned to Minerals Technologies Inc.. Invention is credited to Hockman, John Albert, Tomaino, Gary Peter.
Application Number | 20010016550 09/789687 |
Document ID | / |
Family ID | 23648112 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010016550 |
Kind Code |
A1 |
Tomaino, Gary Peter ; et
al. |
August 23, 2001 |
Synthetic silicate pellet composition and methods of making and
using thereof
Abstract
A synthetic silicate pellet is provided having a component(s) of
calcium and magnesium, either together or in the alternative. Such
pellet is further provided with either an aluminate silicate binder
and/or an ion flow catalyst. The synthetic silicate pellet has use
as a glass batch component.
Inventors: |
Tomaino, Gary Peter;
(Easton, PA) ; Hockman, John Albert; (Bath,
PA) |
Correspondence
Address: |
Terry B. Morris
Minerals Technologies Inc.,
One Highland Avenue
Bethlehem
PA
18017
US
|
Assignee: |
Minerals Technologies Inc.
|
Family ID: |
23648112 |
Appl. No.: |
09/789687 |
Filed: |
February 21, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09789687 |
Feb 21, 2001 |
|
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09416000 |
Oct 12, 1999 |
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6211103 |
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Current U.S.
Class: |
501/27 ; 501/122;
501/128 |
Current CPC
Class: |
C03C 1/026 20130101 |
Class at
Publication: |
501/27 ; 501/122;
501/128 |
International
Class: |
C03C 006/02; C04B
035/04; C04B 035/16 |
Claims
What is claimed is:
1. A composition comprising a silicate material having an empirical
formula of Ca.sub.xMg.sub.ySi.sub.zO.sub.(x+y+2z), wherein the
values of x, y, and z are such that at least one of x and y are not
zero and said values are such that said composition is suitable as
a glass precursor material; and an alumina silicate binder in an
amount effective to impart a compression strength sufficient to
enable a pellet formed from said composition to be handled at
ambient temperature and sintered without substantial structured
damage to said pellet.
2. A composition comprising a silicate material having an empirical
formula of Ca.sub.xMg.sub.ySi.sub.zO.sub.(x+y+2z), wherein the
values of x, y, and z are such that at least one of x and y are not
zero and said values are such that said composition is suitable as
a glass precursor material; and a catalyst comprising a compound
selected from the group consisting of lithium, potassium and
sodium, said catalyst being in an amount sufficient to effectively
control the ion flow in a pellet formed from said composition so
that said ion flow effectively forms wollastonite, diopside, or
enstatite formation during sintering of said pellet.
3. The composition of claim 2 comprising a silicate material having
an empirical formula of Ca.sub.xMg.sub.ySi.sub.zO.sub.(x+y+2z),
wherein the values of x, y, and z are such that at least one of x
and y are not zero and said values are such that said composition
is suitable as a glass precursor material; an alumina silicate
binder in an amount effective to impart a compression strength
sufficient to enable a pellet formed from said composition to be
handled at ambient temperature and sintered without substantial
structured damage to said pellet; and a catalyst comprising a
compound selected from the group consisting of lithium, potassium
and sodium, said catalyst being in an amount sufficient to
effectively control the ion flow in a pellet formed from said
composition so that said ion flow effectively forms
wollastonite-type, diopside-type, or enstatite-type formation
during sintering of said pellet; and silica fines in an amount such
that said composition is suitable as a glass precursor
material.
4. The composition of claim 1 having the ratio of x to y of about
one-half to about ten.
5. The composition of claim 4 wherein said ratio is about one to
about two.
6. The composition of claim 1 wherein the binder is about 0.1 to
about ten weight percent.
7. The composition of claim 2 wherein the catalyst comprises one or
more compounds selected from the group consisting of lithium
carbonate, lithium hydroxide, sodium carbonate and sodium
hydroxide.
8. The composition of claim 2 wherein the catalyst is about 0.01 to
about twenty weight percent.
9. The composition of claim 8 wherein the catalyst is sodium
hydroxide and is about 0.05 to about 5 weight percent.
10. The composition of claim 3 wherein said silica fines are sands
having a measurement of up to about 30 mesh size.
11. The composition of claim 2 wherein the catalyst is in an amount
to effectively form diopside-type formation.
12. The composition of claim 3 wherein the catalyst is in an amount
to effectively form diopside-type formation.
13. A process of for producing a sinterable mass comprising a
silicate material having an empirical formula of
Ca.sub.xMg.sub.ySi.sub.zO.sub.(x+- y+2z), wherein the values of x,
y, and z are such that at least one of x and y are not zero and
said values are such that said composition is suitable as a glass
precursor material, an alumina silicate binder and an ion flow
catalyst and silica, said process comprising setting the relative
values of x, y, and z so that said material is suitable as a glass
precursor material, and setting the binder proportion in said
sinterable mass to enable formation from said mass of a form
sinterable without substantial structural damage to said form.
14. A process of for producing a sinterable mass comprising a
silicate material having an empirical formula of
Ca.sub.xMg.sub.ySi.sub.zO.sub.(x+- y+2z), wherein the values of x,
y, and z are such that at least one of x and y are not zero and
said silicate material is suitable as a glass precursor material,
an alumina silicate binder and an ion flow catalyst and silica,
said process comprising setting the relative values of s, y, and z
so that material is suitable as a glass precursor material, and
setting the proportion of said catalyst in said mass to effectively
produce a desired wollastonite-type, diopside-type, or
enstatite-type composition during sintering of said form and
forming said sinterable mass into a form suitable for
sintering.
15. A process of claim 13 for producing a sinterable mass
comprising a silicate material having an empirical formula of
Ca.sub.xMg.sub.ySi.sub.z- O.sub.(x+y+2z), wherein the values of x,
y, and z are such that at least one of x and y are not zero and
said silicate material is suitable as a glass precursor material,
an alumina silicate binder and an ion flow catalyst and silica,
said process comprising setting the relative values of x, y, and z
so that said material is suitable as a glass precursor material,
setting the binder proportion in said sinterable mass to enable
formation from said mass of a form sinterable without substantial
structural damage to said form, and setting the proportion of said
catalyst in said mass to effectively produce a desired
wollastontie-type, diopside-type, or enstatite-type composition
during sinterable of said form, and forming said sinterable mass
into a form suitable for sintering.
16. A process for producing a molten glass comprising heating
silica with a batch component comprising a source of sodium and a
sized synthetic silicate comprising a silicate material having an
empirical formula of Ca.sub.xMg.sub.ySi.sub.zO.sub.(x+y+2z),
wherein the values of x, y, and z are such that at least one of x
and y are not zero and said values are such that said composition
is suitable as a glass precursor material; and an alumina silicate
binder in an amount effective to impart a compression strength
sufficient to enable a pellet formed from said composition to be
handled at ambient temperature and sintered without substantial
structured damage to said pellet; and silica fines in an amount
such that said composition is suitable as a glass precursor
material.
17. A process for producing a molten glass comprising heating
silica with a batch component comprising a source of sodium and a
sized synthetic silicate comprising a silicate material having an
empirical formula of Ca.sub.xMg.sub.ySi.sub.zO.sub.(x+y+2z),
wherein the values of x, y, and z are such that at least one of x
and y are not zero and said values are such that said composition
is suitable as a glass precursor material; and a catalyst
comprising a compound selected from the group consisting of
lithium, potassium and sodium, said catalyst being in an amount
sufficient to effectively control the ion flow in a pellet formed
from said composition so that said ion flow effectively forms
wollastonite-type, diopside-type, or enstatite-type formation
during sintering of said pellet; and silica fines in an amount such
that said composition is suitable as a glass precursor
material.
18. A process of claim 16 for producing a molten glass comprising
heating silica with a batch component comprising a source of sodium
and a synthetic silicate pellet comprising a silicate material
having an empirical formula of
Ca.sub.xMg.sub.ySi.sub.zO.sub.(x+y+2z), wherein the values of x, y,
and z are such that at least one of x and y are not zero and said
values are such that said composition is suitable as a glass
precursor material; an alumina silicate binder in an amount
effective to impart a compression strength sufficient to enable a
pellet formed from said composition to be handled at ambient
temperature and sintered without substantial structured damage to
said pellet; a catalyst comprising a compound selected from the
group consisting of lithium, potassium and sodium, said catalyst
being in an amount sufficient to effectively control the ion flow
in a pellet formed from said composition so that said ion flow
effectively forms wollastonite-type, diopside-type, or
enstatite-type formation during sintering of said pellet; and
silica fines in an amount such that said composition is suitable as
a glass precursor material.
19. The process of claim 14 wherein a diopside-type composition is
formed during sintering.
20. The process of claim 15 wherein a diopside-type composition is
formed during sintering.
21. The process of claim 17 wherein a diopside-type composition is
formed during sintering.
22. The process of claim 18 wherein a diopside-type composition is
formed during sintering.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to glass-making,
and, more particularly, to a method of making a synthetic
calcium/magnesium silicate pellet having varied properties, such
synthetic silicate pellets themselves, and to the using of such
synthetic silicate pellets in glass-making systems.
BACKGROUND
[0002] In general, glass-making involves the combination of
precursive materials for melting and reacting together to form a
desired glass composition. The volume and use of glass is such that
natural resources are traditionally favored with a cost-optimal
amount of beneficiation of such materials for glass-production
purposes.
[0003] Some of the historical glass-making schemes involved the
combining of sand (as a silica source), lime (as a calcium source)
and soda ash (as a sodium source) along with other materials and
processing to form the ubiquitous glass products. Such processes
traditionally suffered from, and continue to suffer from,
production limitations. Among the more critical limitations are
batch-free time (the time required to completely dissolve the
combined materials) and the fining time (the time to remove gases
from the melt which form undesired bubbles in the melt and
resulting glass). Other limitations involve the handling problems
associated with the precursive materials, such as crumbling,
dusting, clumping, sintering deficiencies and the like.
[0004] Progress has been made in the glass-making processes by the
use of specially processed or beneficiated materials intended for
use as glass precursive materials. In particular, a class of
synthetic silicates have been developed encompassing various forms
of synthetic calcium silicates, magnesium silicates and/or calcium
magnesium silicates. Exemplary of such materials are SYNSIL.TM.
synthetic silicates. While such synthetic silicates can provide
beneficial results, there continues to be a need for enhanced
precursive materials for the glass-making technologies.
SUMMARY
[0005] An object of the present invention is to provide a synthetic
silicate as a precursive glass-making material in a composition and
form which reduces handling problems in the glass-making
process.
[0006] Another object of the present invention is to provide a
synthetic silicate as a precursive glass-making material in a
composition and form which enhances the melting process in the
glass-making process
[0007] These and other objectives are achieved by providing a
synthetic silicate composition comprised of a calcium/magnesium
silicate material of controlled formulation, an alumina silicate
binder, a catalyst and silica fines. The binder and catalyst are
alternatively present or both may be present, providing
respectively preferred advantages of enhanced compression strengths
and enhanced melting characteristics.
DETAILED DESCRIPTION OF INVENTION
[0008] An embodiment of the present invention is a novel
composition comprising (i) a silicate material having an empirical
formula of Ca.sub.x Mg.sub.y Si.sub.z O.sub.(x+y+2z), wherein the
values of x, y, and z are such that at least one of x and y are not
zero and the values are such that the novel composition is suitable
as a glass precursor material; (ii) an alumina silicate binder in
an amount effective to impart a compression strength sufficient to
enable a pellet formed from the novel composition to be handled at
ambient temperature and sintered without substantial structured
damage to said pellet; and (iii) silica fines in an amount such
that the composition is suitable as a glass precursor material.
This composition has use as precursive material in the glass-making
process. Other additives or elements of composition may be added
with regard to the particular specific glass being produced. The
manufacturer of such glass will make the adjustments to the
variables of the elements of the composition so as to be suitable
for his intended end glass product.
[0009] One embodiment of the present composition invention is a
silicate material having an empirical formula of
Ca.sub.xMg.sub.ySi.sub.zO.sub.(x+- y+2z) The values chosen for such
empirical formula are such that the composition is suitable as
glass precursor material as discussed above. Either x or y may be
zero, but both x and y are not zero. Accordingly, the silicate
material may be of a nature as to be a wollastonite-type
(Ca.sub.XSi.sub.1O.sub.3) material or a diopside-type
(Ca.sub.XMg.sub.YSi.sub.2O.sub.6) material or an enstatite-type
(Mg.sub.YSi.sub.1O.sub.3) material and the like. What is meant by
"type" material is exemplified as follows: a wollastonite-type
material may in fact be natural or synthetic wollastonite
(Ca.sub.1Si.sub.1O.sub.3) or a compound whose elemental proportions
approximates such formula. Similarly, a diopside-type material may
be a natural or synthetic diopside
(Ca.sub.1Mg.sub.1Si.sub.2O.sub.6) or a compound with similar
elemental proportions. For instance, the proportions of calcium to
magnesium need not necessarily be one to one. In a preferred
embodiment of the present invention a preferred ratio of calcium to
magnesium is about one-half to about ten, more preferably about one
to about two. A particularly more preferred range is a proportion
of calcium to magnesium between the values of about 1.4 to about
1.7. Similarly, an enstatite-type material may be a synthetic or
natural enstatite (Mg.sub.1Si.sub.1O.sub.3) or a compound with
similar elemental proportions. For instance, an enstatite-type
material may not strictly have a one to one proportion between the
magnesium and silica in the compound. Accordingly the present
invention involves compounds with a general empirical formula of
Ca.sub.xMg.sub.ySi.sub.zO.sub.(x+y+2z), whose relative proportions
may duplicate the natural wollastonite, diopside, or enstatite
material or be approximations. In all instances for the present
invention, however, at least a significant amount of calcium or
magnesium should be present in the silicate material. Other
non-listed elements may be present in non-effective amounts in the
compounds as trace or contaminant materials as long as such does
not significantly alter the benefits of the present inventive
compositions in the intended glass formation products. Throughout
the specification it will also be appreciated by those in the art
that the empirical values for the oxygen content may not strictly
be x+y+2z, but will be sufficiently approximate to such so that the
composition is able to perform as though mathematically balanced
and chemically equivalent.
[0010] The alumina silicate binder can be any alumina silicate
binder whose use permits the forming of a pellet with sufficient
compression strength so as to be handled at ambient temperatures in
the manufacturing process and then sintered in a kiln, furnace or
other heating apparatus. Throughout this specification the "pellet"
form can be of any structure or shape such as an amorphous glob, a
sphere, a bead, a brickette, a cube, a wafer, a flake or a cylinder
shape and the like. For instance, when sintered in a rotary kiln,
the preferred formation is a cylindrical or spherical pellet whose
size and aspect ratio is suitable for the intended glass
manufacturing process using such pellet. A sufficient amount of the
alumina silicate binder is used to substantially reduce the
breakage of the pellet and the formation of powder or fines in the
heating apparatus, such as those which might appear in a rotary
kiln causing wall build up and kiln rings. Such formations affect
the thermal profile in a heating apparatus, such as a kiln, and
results subsequently in insufficient burning or sintering of the
material. Accordingly, there should be a sufficient amount of
binder so as to substantially reduce or prevent insufficient
sintering of the pellet for the ultimate intended use.
[0011] The alumina silicate binder comprises a form of aluminum
oxide useable as a binder component. The alumina component is
preferably purified or pure aluminum oxide but can comprise natural
forms, such as corundum derivatives, and the like. Accordingly, the
alumina silicate binder can be of or derived from any of the
numerous types of clay containing various proportions of aluminum
oxides and silicates and like material, such as (but not limited
to) sodium aluminosilicates, sodium aluminate, zeolites and the
like. The alumina silicate binder is preferably in an amount of
about 0.1 to about 10 weight percent or higher. One advantage of
the use of such binder is the flexibility of using a wider range of
silica material (eg. sand sizes) so as to maximize pellet packing
density with resulting enhancement of the compression strength.
Such enhancement of the compressive strength is not reliant on such
selection of sands in the present invention but is further enhanced
thereby.
[0012] The silica fines in the present invention are those which
are suitable for the intended glass use for product, such as
natural sands or recycled fines from a glass-making process or
other recovery. The amount of such silica fines may range up to
about 60 weight percent of the composition or even higher in
specific applications. In a preferred embodiment the silica fines
are sands having a measurement of up to about 30 mesh size.
[0013] Another embodiment of the present invention is a composition
comprising (i) a silicate material having an empirical formula of
Ca.sub.x Mg.sub.y Si.sub.z O.sub.(x+y+2z), wherein the values of x,
y, and z are such that at least one of x and y are not zero and the
values are such that the composition is suitable as a glass
precursor material; (ii) a catalyst comprising a compound selected
from the group consisting of lithium, potassium and sodium, the
catalyst being in an amount sufficient to effectively control the
ion flow in a pellet formed from the composition so that the ion
flow effectively forms the desired wollastonite-type, diopside-type
or enstatite-type product during sintering of the pellet; and (iii)
silica fines in an amount such that the composition is suitable as
a glass precursor material.
[0014] The catalyst useable in the present invention is a catalyst
which comprises any Group I compound, preferably lithium, potassium
or sodium or a combination thereof. A preferred catalyst is
selected from a group consisting of lithium carbonate, lithium
hydroxide, sodium carbonate and sodium hydroxide or combination
thereof. The catalyst should be in an effective amount so as to
react in a manner to cause a controlled melt, preferably one that
allows an exchange of ions within the pellet from an area of high
density to an area of low density. The preferred amount of catalyst
is in a range of about 0.01 to about 20 weight percent, more
preferably from about 0.05 to about 5 weight percent catalyst in
the composition. A preferred catalyst is sodium hydroxide in a
liquid form.
[0015] Another preferred embodiment of the present invention is a
composition comprising (i) a silicate material having an empirical
formula of Ca.sub.x Mg.sub.y Si.sub.z O.sub.(x+y+2z), wherein the
values of x, y, and z are such that at least one of x and y are not
zero and the values are such that the composition is suitable as a
glass precursor material; (ii) an alumina silicate binder in an
amount effective to impart a compression strength sufficient to
enable a pellet formed from the composition to be handled at
ambient temperature and sintered without substantial structured
damage to the pellet; (iii) a catalyst comprising a compound
selected from the group consisting of lithium, potassium and
sodium, said catalyst being in an amount sufficient to effectively
control the ion flow in a pellet formed from the composition so
that the ion flow effectively forms wollastonite-type,
diopside-type, or enstatite-type formation during sintering of the
pellet; (iv) and silica fines in an amount such that the
composition is suitable as a glass precursor material. As can be
appreciated from the disclosures hereinabove, this preferred
embodiment provides the advantages of both the use of an alumina
silicate binder and a catalyst material in the composition.
[0016] In another aspect, an embodiment of the present invention is
a process for producing a sinterable mass comprising a silicate
material having an empirical formula of
Ca.sub.xMg.sub.ySi.sub.zO.sub.(x+y+2z), wherein the values of x, y,
and z are such that at least one of x and y are not zero and the
values are such that the composition is suitable as a glass
precursor material, an alumina silicate binder, an ion flow
catalyst and silica, the process comprises setting the relative
values of x, y, and z so that the material is suitable as a glass
precursor material, and setting the binder proportion in the
sinterable mass to enable formation from the mass of a form
sinterable without substantial structural damage to the form.
[0017] In yet another embodiment, the present invention is a
process for producing a sinterable mass comprising a silicate
material having an empirical formula of
Ca.sub.xMg.sub.ySi.sub.zO.sub.(x+y+2z), wherein the values of x, y,
and z are such that at least one of x and y are not zero and the
values are such that the composition is suitable as a glass
precursor material; an alumina silicate binder; an ion flow
catalyst and silica. The process comprises setting the relative
values of x, y, and z so that the material is suitable as a glass
precursor material, and setting the proportion of the catalyst in
the mass to effectively produce a desired diopside-type composition
during sintering of the form, and form the sinterable mass into a
form suitable for sintering.
[0018] A preferred embodiment is a process for producing a
sinterable mass comprising a silicate material having an empirical
formula of Ca.sub.xMg.sub.ySi.sub.zO.sub.(x+y+2z), wherein the
values of x, y, and z are such that at least one of x and y are not
zero and the silicate material is suitable as a glass precursor
material, an alumina silicate binder, an ion flow catalyst and
silica. The process comprises setting the relative values of x, y,
and z so that the material is suitable as a glass precursor
material, setting the binder proportion in the sinterable mass to
enable formation from the mass of a form sinterable without
substantial structural damage to the form, setting the proportion
of the catalyst in the mass to effectively produce a desired
diopside-type composition during sinterable of the form, and form
the sinterable mass into a form suitable for sintering.
[0019] In yet another embodiment, the present invention is a method
of producing a molten glass using a synthetic silicate precursor
which reduces handling problems and enhances the melting process to
produce the molten glass. This method involves heating silica with
a batch component which provides the major portion of sodium in the
resultant molten glass and which provides the synthetic silicate,
as described hereinabove, having the desired amounts of magnesium
and calcium components. Accordingly, a preferred method is forming
a synthetic silicate pellet in accordance with one of the inventive
embodiments described hereinabove and combining such with the
necessary amounts of silica and sodium to form a desired molten
glass and heating such material to form such molten glass. The
sources of silica and sodium can be those typical in the glass
industry and the glass melting procedure of a type typically used
in glass batching processes.
[0020] Accordingly, one embodiment of the present invention is a
process for producing a molten glass comprising heating silica with
a batch component comprising a source of sodium and a synthetic
silicate comprising a silicate material having an empirical formula
of Ca.sub.xMg.sub.ySi.sub.zO.sub.(x+y+2z), wherein the values of x,
y, and z are such that at least one of x and y are not zero and the
values are such that the composition is suitable as a glass
precursor material; an alumina silicate binder in an amount
effective to impart a compression strength sufficient to enable a
pellet formed from the composition to be handled at ambient
temperature and sintered without substantial structured damage to
the pellet; and silica fines in an amount such that the composition
is suitable as a glass precursor material.
[0021] Another embodiment is a process for producing a molten glass
comprising heating silica with a batch component comprising a
source of sodium and a synthetic silicate pellet comprising a
silicate material having an empirical formula of
Ca.sub.xMg.sub.ySi.sub.zO.sub.(x+y+2z), wherein the values of x, y,
and z are such that at least one of x and y are not zero and the
values are such that the composition is suitable as a glass
precursor material; a catalyst comprising a compound selected from
the group consisting of lithium, potassium and sodium, the catalyst
being in an amount sufficient to effectively control the ion flow
in a pellet formed from the composition so that the ion flow
effectively forms wollastonite-type, diopside-type, or
enstatite-type formation during sintering of the pellet; and silica
fines in an amount such that the composition is suitable as a glass
precursor material
[0022] In yet a more preferred embodiment, the present invention is
a process for producing a molten glass comprising heating silica
with a batch component comprising a source of sodium and a
synthetic silicate pellet comprising a silicate material having an
empirical formula of Ca.sub.xMg.sub.ySi.sub.zO.sub.(x+y+2z),
wherein the values of x, y, and z are such that at least one of x
and y are not zero and the values are such that the composition is
suitable as a glass precursor material; an alumina silicate binder
in an amount effective to impart a compression strength sufficient
to enable a pellet formed from the composition to be handled at
ambient temperature and sintered without substantial structured
damage to the pellet; a catalyst comprising a compound selected
from the group consisting of lithium, potassium and sodium, said
catalyst being in an amount sufficient to effectively control the
ion flow in a pellet formed from the composition so that the ion
flow effectively forms the desired wollastonite-type,
diopside-type, or enstatite-type formation during sintering of the
pellet; and silica fines in an amount such that the composition is
suitable after sizing as a glass precursor material. The preferred
values for x and y are as stated hereinabove as well as the
preferred aluminum silicate binders and catalysts.
[0023] The following examples are illustrative of the present
invention but do not limit the scope thereof.
[0024] The following terms are described to assist in the
understanding of the experiments, but are not to limit the scope of
the invention herein.
[0025] Muffle Furnace--Laboratory scale furnace in which
temperature can be adjusted in order to simulate the heat of a
rotary kiln. Used for measuring pellet strength at various
temperatures.
[0026] Rotary Kiln--A refractory lined cylinder, usually inclined,
which rotates and can be heated. In this application it provides
for commercial scale calcination of the pellets.
[0027] Compression Tester--The tester consists of a platform that
has a piston positioned above it. The piston is slowly lowered at a
fixed velocity until it comes into contact with the pellet and the
pellet breaks apart. The instrument provides the pounds of force
required to break the pellet.
[0028] Attrition Tester--A 3 foot by 6-inch cylinder that rotates
end to end. The amount of breakage of pellets at hot temperatures
can be determined and the tester simulates a rotary kiln.
[0029] "Unimin" Sand--Brand name of sand used for providing the
source of silicon dioxide (silica, .alpha.-quartz).
[0030] Blender/Mixer Hydration Test--This test is to determine the
degree of hydration of CaO in a blender or mixer. This test
utilizes a moisture balance, platinum crucible, analytical balance
and lab furnace. Before performing this test the amount of CaO and
MgO in the original lime sample must be determined (EDTA titration
is the easiest way to determine this). Also, the lime/sand ratio
used in the blender or mixer must be known. A sample from the
blender or mixer is placed the moisture balance to drive off all
free moisture and dry weight recorded. The material is placed into
the crucible and heated to 600 C. for thirty (30) minutes. The
material is reweighed and placed back into the furnace at 950 C.
for thirty (30) minutes. The calcined material is reweighed. Using
these weights and the information about the lime/sand samples,
degree of hydration can be determined.
[0031] Pellets--Mixing and hydrating the dolomitic lime and calcium
oxide with silica to generate a mixture that is rolled into
"pellets" and dried. Pellets are roughly one half inch in
diameter.
[0032] Soak--Dwell times at a certain temperature that a pellet is
subjected to in the furnace or kiln.
[0033] Cold Compression Strength Test--Used to determine the
strength of dried pellets at ambient temperature.
[0034] Hot Compression Strength Test--Used the evaluate the
compression strength of pellets over a set thermal profile. The
same tester is used to measure hot compression strength as cold
compression strength.
[0035] Pellet Attrition Test--This simulates the dynamics of a
rotary kiln to test for breakage and production of fines of
standard pellets. Representative pellets are selected and placed in
a lab furnace at a desired temperature for thirty (30) minutes.
Remove the pellets and allow to cool enough for handling. Two
hundred fifty (250) grams of pellets (larger than 6 mesh) are
weighed out and carefully poured into the attrition tube (described
above). Rotation speed is set at one revolution per minute for
thirty (30) minutes. At the end of the rotation cycle, the contents
are emptied from the attrition tube onto a 6-mesh sieve and lightly
shaken to pass the fines through the sieve. The material that did
not filter through the sieve is then weighed to determine the
amount of fines that were lost through the sieve.
[0036] Sintering--Pellets are passed through a muffle furnace or
rotary kiln in which a temperature profile is followed to produce a
desired product.
[0037] Kiln Ring--A powder or fines build-up on the wall of the
kiln. This causes changes in the thermal profile of the kiln thus
reducing efficiency.
[0038] "Secar 71"--Brand of calcium aluminate cement produced by La
Farge Cement. This is a fast setting cement that is advertised as
30% calcium and 70% aluminate.
Binder Additive for Pelletization
[0039] Example 1 and Example 2 illustrates the increase in pellet
strength when cement is added to aid in binding the components of
the invention. After the components of the formulation are mixed
together, the material is then "rolled" into one half inch diameter
pellets. Compression and attrition testing is done as described
below.
EXAMPLE 1
Control Batch
[0040] Seventy-two (72) pounds of pebble lime and seventy-seven
(77) pounds of sand are placed in a ribbon blender. Three (3)
pounds of sodium hydroxide is dissolved in thirty-six (36) pounds
of water. This solution is added to the blender at a rate of 1.1
pounds per minute until hydration is complete. After the completion
of water addition continue to mix for two (2) minutes. This
material is then formed into one half inch in diameter pellets and
air-dried for twenty-four (24) hours.
Six Percent Calcium Aluminate and Fume Silica Binder
[0041] Forty-seven (47) pounds of pebble lime, forty-seven pounds
of sand, and six (6) pounds of fume silica are placed in a ribbon
blender. Two (2) pounds of sodium hydroxide is dissolved in
twenty-three (23) pounds of water. This solution is added to the
lime, sand, and silica mixture at 1.1 pounds per minute until
hydration is complete. After completion of water addition, six (6)
pounds of Secar 71 cement is added to the blender and blending is
continued for two (2) minutes. This material is the formed into one
half inch in diameter pellets and air-dried for twenty-four (24)
hours.
[0042] Twenty-one representative pellets are selected from each of
the formulations above. Individual pellets are placed on the tester
and evaluated as outlined above. An average of the results is given
in TABLE 1.
1TABLE 1 Compression Strength Test (pounds) Ambient Temperature
Temp. 500.degree. C. 600.degree. C. 700.degree. C. 800.degree. C.
900.degree. C. 1000.degree. C. 1100.degree. C. Control 34.3 56.4 34
17.1 12 3 1 N/A 6% Secar 71 61.7 71.6 31.8 18.0 20.0 17.6 25.4
18.8
EXAMPLE 2
[0043] An attrition test, as described above, is done on the
pellets produced through the processes described in Example 1. An
attrition test is done as described above, to determine the amount
of fines produced by the dynamic motion of a rotary kiln. In this
test the mixture with no binder is compared with the mixture in
which six (6) percent of Secar 71 cement is added.
[0044] After thirty (30) minutes in the attrition tester the
control pellets had sixty seven and one half (67.5) percent fines
while the pellets with six (6) percent binder had only fifteen and
one tenth (15.1) percent fines. This correlates to over a
seventy-seven (77) percent increase in usable product when using a
binder.
Effect of a Catalyst on Producing Desired Product
EXAMPLE 3
[0045] In this example, six hundred (600) grams of pulverized
dolomitic lime is mixed with seven hundred thirty one (731) grams
of silica in a blender. Seven hundred thirty (730) grams of water
are added and mixed three (3) minutes. This gives a material that
is formed into one half-inch cubes and dried overnight at
110.degree. C. A second mixture is made according to this procedure
except that one (1) percent, by dry wt., NaOH is dissolved in the
water and this solution is added to the lime/silica mix. The
results are shown in TABLE 2.
2TABLE 2 Catalyst Effect of NaOH "Control Experiment" 1350.degree.
C. - 45 minutes 1350.degree. C. - 45 minutes No NaOH With NaOH
Substance % Crystalline Phase % Crystalline Phase Diopside 2-4
51-68 .varies.-Quartz 45-60 7-10 Cristobalite 2-4 2-4 Akermanite
2-4 10-15 Merwinite 2-4 2-4 Lime 2-4 None detected <0.5
Periclase 10-15 2-4 .UPSILON.-Ca.sub.2SiO.sub.4 7-10 None detected
<1.0 Larnite, Ca.sub.2SiO.sub.4 2-4 None detected <1.0
Cyclowollastonite, 2-4 None detected CaSiO.sub.3 <1.0
onticellite, CaMgSiO.sub.4 None detected 4-7 <0.5 Amorphous
Phase <5 <5 (glass-SiO.sub.2,Ca/Mg silicate)
* * * * *