U.S. patent application number 14/599472 was filed with the patent office on 2015-05-21 for glass microspheres made from a redox active glass, and methods of producing glass microspheres.
The applicant listed for this patent is Hamid Hojaji, Laura Gabriela Kocs. Invention is credited to Hamid Hojaji, Laura Gabriela Kocs.
Application Number | 20150135774 14/599472 |
Document ID | / |
Family ID | 52019721 |
Filed Date | 2015-05-21 |
United States Patent
Application |
20150135774 |
Kind Code |
A1 |
Hojaji; Hamid ; et
al. |
May 21, 2015 |
Glass Microspheres Made From a Redox Active Glass, and Methods of
Producing Glass Microspheres
Abstract
A glass melter system for manufacturing glass used for the
manufacture of hollow glass microspheres, comprising a melting zone
capable of melting a batch into a first glass melt, a processing
zone capable of processing the first glass melt, and a discharge
zone capable of discharging the first glass melt from the melter
system and forming a second glass, wherein the hollow glass
microspheres comprising the second glass.
Inventors: |
Hojaji; Hamid; (Kensington,
MD) ; Kocs; Laura Gabriela; (Feldafing, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hojaji; Hamid
Kocs; Laura Gabriela |
Kensington
Feldafing |
MD |
US
DE |
|
|
Family ID: |
52019721 |
Appl. No.: |
14/599472 |
Filed: |
January 17, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13916155 |
Jun 12, 2013 |
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14599472 |
|
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Current U.S.
Class: |
65/142 |
Current CPC
Class: |
C03B 5/031 20130101;
C03C 1/002 20130101; C03C 11/002 20130101; Y10T 428/2982 20150115;
C03B 19/109 20130101; C03B 5/193 20130101; C22C 32/001 20130101;
C03B 19/107 20130101; C03B 5/2356 20130101; C04B 14/24 20130101;
C08K 7/28 20130101; C03B 5/005 20130101 |
Class at
Publication: |
65/142 |
International
Class: |
C03B 19/10 20060101
C03B019/10 |
Claims
1. A glass melter system for manufacturing glass used for the
manufacture of hollow glass microspheres, comprising: a melting
zone capable of melting a batch into a first glass melt, a
processing zone capable of processing the first glass melt, and a
discharge zone capable of discharging the first glass melt from the
melter system and forming a second glass, wherein said hollow glass
microspheres comprising said second glass.
2. The glass melter system of claim 1, wherein at least one of the
melting zone, the processing zone, and the discharge zone of the
glass melter system is configured to receive a plurality of redox
active group components into the first glass melt.
3. The glass melter system of claim 1, wherein a total residence
time of the first glass melt in the glass melter system is less
than 18 hours.
4. The glass melter system of claim 1, wherein said glass melter
system comprising a fuel fired glass melter, an electric glass
melter, a plasma glass melter, an inductively coupled glass melter,
a radiant tube glass melter, a submerged combustion glass melter, a
hybrid glass melter and a combination thereof.
5. The glass melter system of claim 2, wherein said plurality of
redox active group components comprising at least one of a reducing
redox active group component and oxidizing redox active group
component, and wherein said plurality of redox active group
components comprising at least one member selected from the group
comprising a carbon containing material, a sulfur containing
material, a multivalent oxide containing material, a selenium
containing material, an oxygen containing material, a hydrogen
containing material, a nitrogen containing material, a phosphorous
containing material, a multivalent metal containing material, a
sulfide-sulfate pair containing material, a carbon-sulfate pair
containing material, and a combination thereof.
6. The glass melter system of claim 1, wherein the first glass melt
is stirable by at least one of electric current convection means,
forced thermal convection means, and bubbling means.
7. The glass melter system of claim 2, wherein said zones are
configured to receive said plurality of redox active group
components into the first glass melt by blending, stirring,
injecting, purging, bubbling, mixing, spraying, dipping or a
combination thereof.
8. The glass melter system of claim 2, wherein the glass melter
system is configured such that said plurality of redox active group
components are receivable into the first glass melt during one or a
combination of melting said batch, processing the first glass melt,
conditioning the first glass melt, refining the first glass melt,
and discharging the first glass melt.
9. The glass melter system of claim 1, wherein said processing zone
is capable of at least one of: receiving the plurality of redox
active group components into the first glass melt, holding and
storing the first glass melt, homogenizing the first glass melt,
refining the first glass melt, reheating the first glass melt,
controlling a residence time of the first glass melt in the melter
system, and nucleating the first glass melt.
10. The glass melter system of claim 1, wherein said processing
zone of the first glass melt comprising one or a combination of a
hold and storing section of the first glass melt, a homogenizing
section of the first glass melt, a refining section of the first
glass melt, and a reheating section of the first glass melt.
11. The glass melter system of claim 1, wherein said discharge zone
comprising at least one or a combination of a trough, an outlet
throat section, and an airlift system for discharging said first
glass melt.
12. The glass melter system of claim 1, further comprising a
plurality of movable elements installed between the zones.
13. The glass melter system of claim 4, wherein the electric glass
melter and the hybrid glass melter are configured such that a
plurality of electrodes enter the first glass melt through at least
one of a melt open surface, enter the first glass melt through a
side wall, and enter the first glass melt through the bottom.
14. The glass melter system of claim 13, wherein a material from
which the electrodes are fabricated comprising at least one of
graphite, molybdenum di-silicide, molybdenum, molybdenum alloyed
with zirconium oxide, molybdenum coated with molybdenum
di-silicide, copper, nickel-chromium super alloys, and iron.
15. The glass melter system of claim 1, further comprising at least
one of a plurality of nozzles installed in the melter system
entering the glass melter system from at least one of a bottom,
from a side wall, and from a top of the first glass melt, wherein
the plurality of nozzles are capable to deliver at least one of
air, gas, aerosol, liquids, and solids into the first glass melt
inside the glass melter system.
16. The glass melter system of claim 2, wherein said plurality of
redox active group components comprising at least one member
selected from the group consisting of a gas, a liquid, a solid, an
aerosol and a combination thereof.
17. The glass melter system of claim 1, wherein said batch
comprising at least one member selected from the group comprising
raw materials, a plurality of redox active group components, at
least one recovered material, a plurality of additives, and a
combination thereof.
18. The glass melter system of claim 11, wherein said airlift
system configured to discharge the first glass melt from the glass
melter system by a gas comprising a redox active group
component.
19. The glass melter system of claim 1, wherein at least one redox
reaction takes place in the first glass melt while said first glass
melt residing in the glass melter system, and wherein said at least
one redox reaction being a non equilibrium redox reaction.
20. The glass melter system of claim 19, wherein a termination of
said at least one redox reaction is configured to coincide with a
discharge of the first glass melt from the glass melter system.
Description
FIELD OF INVENTION
[0001] The present invention is directed to glass microspheres and
a method of manufacturing glass microspheres. More specifically,
the present invention is directed to glass microspheres made from
redox active glass, and the method of their manufacture.
BACKGROUND OF THE INVENTION
[0002] Various methods are already known in the art for the
manufacture of glass microspheres.
[0003] In accordance with the methods available in the art,
pre-formed glass particles may be converted into glass bubbles or
micro-balloons. To create the glass bubbles the glass particles
have to be post-modified to contain the ingredients necessary for
their expansion.
[0004] As known from the art, a silicate glass with over 14 wt %
sodium oxide and 0.1 Fe.sub.2O.sub.3 is initially treated with high
temperature steam and is used to form glass bubbles at about
1150-1200.degree. C. In another known example, a silicate glass
having a sodium oxide concentration of 13.5 wt % and a potassium
oxide concentration of 3.2 wt %, with 0.2 wt % of sulfur in the
form of SO.sub.4 is melted and pulverized. The so formed cullet is
dropped through a flame at about 1150-1200.degree. C. to create a
glass microsphere.
[0005] In accordance with other methods known in the art of glass
microsphere production, a pre-melted glass frit is used to produce
glass micro-bubbles with a chemical composition, expressed in
weight percent, of at least 67% SiO.sub.2, 8-15% RO, 3-8% R.sub.2O,
2-6% B.sub.2O.sub.3, and 0.125-1.50% SO.sub.3. The RO:R.sub.2O
weight ratio is in the range of 1.0-3.5.
[0006] From further art references, similar techniques to
manufacture glass spheres are also known. These techniques employ a
powdered glass with a glass composition comprising ranges of
SiO.sub.2 of 50-57%, R.sub.2O of 2-15%, B.sub.2O.sub.3 of 0-20%, S
of 0.05-1.5%, RO of 2-25%, R.sub.2O.sub.3 of 0-5%, and
R.sub.2O.sub.5 of 0-5%. From further yet art references, the use of
an essentially borosilicate glass composition is known to
manufacture glass spheres having an oxide range of SiO.sub.2 of
60-90 wt %, an alkali metal oxide range of 2-20 wt %, a
B.sub.2O.sub.3 range of 1-30 wt %, a sulfur range of 0.005 to 0.5
wt %, and other conventional glass-forming ingredients.
[0007] A particulate solid feed material having an average particle
size of up to 25 microns is introduced at the top of a heating
chamber into a "wall free" heated zone, according to a method known
in the art for the manufacture of glass microspheres. The particles
are transported to at least one flame front by a carrier gas
comprising a fuel gas and air. The carrier gases maintain the
particles in a dispersive state while the particles are heated to a
temperature where at least partial fusion occurs, while the
agglomeration of particles during fusion is inhibited. The
resulting spherical particles are cooled and separated from the gas
stream by a hot cyclone.
[0008] Yet another process for producing hollow microspheres know
in the art comprises treating glass feed particles at a temperature
above the working temperature of the glass. The particles are
suspended in a gaseous current and passed through a burner for
treatment. The particles are rapidly heated to about 1500 to
1700.degree. C. for a residence time of less than about 0.1
seconds, and are cooled suddenly to below 750.degree. C. The burner
is operated such that the air factor, that is, the ratio of the
amount of air introduced into the burner to the amount of air
necessary to produce a stoichiometric combustion, is between about
0.75 and 1.1, or preferably 0.8-0.95. The particles are passed
first through a reducing atmosphere and then through a non-reducing
atmosphere.
[0009] Other known techniques for the manufacture of glass
microspheres provide for a method in which feed material, in the
form of solid glass particles, is introduced near the bottom of a
furnace into an ascending column of hot gases. The feed material is
entrained in an upward moving hot gaseous stream. The residence
time of the particles within the furnace becomes a function of the
mass of the particle, as the larger particles ascend through the
hot zone of the furnace more slowly than the small particles due to
the force of gravity acting on the particles. As a result, the
residence time of the particles in the furnace is in direct
relationship to the heat requirements necessary to expand the solid
glass particles into hollow spheres.
[0010] Further technologies available in the art for manufacturing
hollow microspheres employ a downward furnace suitable for heating
discrete clay particles into hollow spherical particles. The
particles are fed with a vibrating feeder into a hopper of a burner
from where they are entrained in a stream of gas and passed through
a flame front inside the furnace. The particles, in expanded state,
are carried along with the flow of combustion gases and by gravity
into a container. The container is at a sufficient distance from
the combustion zone to provide a cooler zone, and solidification of
the particles occurs before the particles hit any hard surfaces or
before encountering each other to avoid agglomeration. A ratio of
air to natural gas of about 2:1.1 was found to be suitable for
raising the temperature of the particles to a range of 1350.degree.
C. to 1500.degree. C., and to create the hollow microspheres.
[0011] A low cost method of converting solid glass or ceramic
micro-particles into hollow microspheres, is also known in the art,
and consists of feeding the solid glass or ceramic micro-particles,
along with pulverized coal, into a coal-burning boiler. According
to the known method coal-burning boilers generally produce
micro-sized fused particles of ash, e.g. fly ash. A very small
percentage of fly ash particles (about 1% and less) may be hollow,
and these particles are commonly referred to as cenospheres.
According to the known method the yield of hollow micro-particles
is slightly increased by co-feeding fly or coal ash along with the
pulverized coal.
[0012] Based at least on the above enumerated known methods and
techniques, it is evident that there is still a need in the art for
methods to manufacture hollow glass microspheres that have the
following attributes:
[0013] high chemical durability in aqueous alkaline and acidic
environments;
[0014] high crushing strength;
[0015] high hydrostatic pressure rating;
[0016] high specific strength;
[0017] are an eco friendly product, able to utilize in their
make-up industrial waste byproducts, converting waste materials
into highly value added products; and
[0018] are produced by sustainable (energy efficient) methods via
fast manufacturing.
SUMMARY OF THE INVENTION
[0019] The present invention has been conceived and developed
aiming to provide solutions to the above stated objective technical
needs, as it will be evidenced in the following description.
[0020] In accordance with an embodiment of the present invention is
proposed a glass microsphere comprising a plurality of glass walls,
and a plurality of hollow spaces, wherein said plurality of glass
walls enclose at least one of said plurality of hollow spaces,
wherein said plurality of glass walls comprise a second glass,
wherein said second glass is formed by further processing a first
glass melt, wherein said first glass melt is formed by melting a
batch comprising a plurality of raw materials, and wherein the
plurality of RAG components present in the first glass melt and a
melt of the second glass is capable of providing at least one of a
plurality of redox reactions and a plurality of events in the first
glass melt and the melt of the second glass, thereby creating the
glass microsphere.
[0021] In accordance with further aspects of the present invention,
the at least one of the plurality of redox reactions is a
non-equilibrium redox reaction. The redox active group (RAG)
components are incorporated at least directly into the first glass
melt, directly into said batch, and into said batch and the first
glass melt. The plurality of redox active group (RAG) components
comprises redox active group components in at least one of a
gaseous form, a liquid form, a solid form, an aerosol form, and a
combination thereof. The first glass melt comprises at least one of
a plurality of sulfide ions and a plurality of sulfate ions, a
concentration of the plurality of sulfide ions and a concentration
of the plurality of sulfate ions comprised in the first glass melt
is greater than zero. The first glass melt and the second glass
comprise at least one alkali metal oxide, and when sodium oxide is
at least one of the alkali metal oxides, a concentration of sodium
oxide being less than 4 wt % based on a mass of either the first
glass melt and the second glass.
[0022] In accordance with another embodiment of the present
invention is proposed a method of manufacturing a plurality of
glass microspheres, comprising melting a batch into a first glass
melt in a melter system, processing the first glass melt into a
second glass, pulverizing the second glass into a plurality of
glass fragments, thermally processing the plurality of glass
fragments into a plurality of glass microspheres, providing at
least one of a plurality of redox reactions and a plurality of
events in at least one of the first glass melt and a melt of said
second glass, wherein at least one of the redox reactions and the
plurality of events are induced by a plurality of redox active
group (RAG) components.
[0023] In accordance with a further yet embodiments of the present
invention, the plurality of redox active group (RAG) components
comprises redox active group components in at least one of a
gaseous form, a liquid form, a solid form, an aerosol form, and a
combination thereof. The method further comprises incorporating the
redox active group (RAG) components into at least one of the batch,
and the first glass melt while the first glass melt is inside a
melter system, and into said batch and the first glass melt, the
incorporating step being performed by at least one of blending,
bubbling, injection, spraying, dipping, and stirring. The batch
comprises at least one recovered material. The melter system
comprises at least one of a glass-melting zone, a glass melt
processing zone, and a glass melt discharge zone. The method
further comprises incorporating the plurality of redox active group
(RAG) components inside either one of the first glass melting zone,
the processing zone, the discharge zone of the melter system. A
total residence time of the first glass melt in the melter system
during the melting step is less than 12 hours. The batch comprises
either one of a plurality of raw materials, the plurality of redox
active group components and a combination thereof. Thermally
processing said plurality of glass fragments comprises expanding
said plurality of glass fragments by a plurality of gases generated
via at least one of said plurality of redox reactions induced by
said plurality of redox active group components. At least one of
the plurality of redox reactions is a non-equilibrium redox
reaction. The first glass melt comprises at least one of a
plurality of sulfide ions and a plurality of sulfate ions, a
concentration of the plurality of sulfide ions and a concentration
of the plurality of sulfate ions comprised in the first glass melt
being greater than zero. The first glass melt and the second glass
comprising at least one alkali metal oxide, and when sodium oxide
is at least one of the alkali metal oxides, a concentration of the
sodium oxide is less than 4 wt % based on a mass of either the
first glass melt and said second glass. The plurality of redox
active group (RAG) components comprises at least one of a plurality
of redox active group reactants, and a plurality of redox group
reaction products.
[0024] In accordance with another embodiment of the present
invention is proposed a composite product comprising a combination
of the plurality of glass microspheres manufactured according to
the various embodiments of the present invention, and at least one
of a plurality of polymer matrices, a plurality of cementiteous
matrices, a plurality of fluid matrices, a plurality of solid
matrices, a plurality of fiber containing matrices, and a plurality
of metal matrices.
[0025] The methods of the present invention are found to produce
superior hollow glass microspheres of superior strength, able to
withstand high hydrostatic pressures, versus the hollow glass
bubbles manufactured by the process of simultaneous fusion of raw
materials into glass at the time of expansion.
[0026] Since residence times are relatively short at the high
temperatures required by the processing steps of melting and
thermal processing of the present invention, the embodiments of the
present invention also provide high energy efficiency in addition
to the high throughput attributes. Considering the low cost of the
recovered materials that are being utilized as the raw materials in
the batch, the present invention provides viable economics together
with environmentally friendly practices to manufacture high quality
glass microspheres.
[0027] More detailed explanations regarding these and other aspects
and advantages of the invention are provided herewith in connection
with the exemplary embodiments of the present invention.
BRIEF DESCRIPTION OF DRAWINGS
[0028] The above and other aspects, features and advantages of the
present invention will become more apparent from the subsequent
description thereof, presented in conjunction with the following
drawings, wherein:
[0029] FIG. 1 is a block diagram of an embodiment of a method for
manufacturing a plurality of glass microspheres in accordance with
the present invention;
[0030] FIG. 2 comprises representation of a glass microsphere;
and
[0031] FIG. 3 is a schematic representation of a glass melter
system in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0032] The following description of the presently contemplated best
mode of practicing the invention is not to be taken in a limiting
sense, but is made merely for the purpose of describing the general
principles of the invention. The scope of the invention should be
determined with reference to the claims.
[0033] Reference will now be made to the drawings wherein like
numerals refer to like parts throughout. As described herein below,
the embodiments of the present invention provide a plurality of
chemically durable, synthetic glass microspheres having properties
and characteristics similar or superior to the cenospheres derived
from coal combustion, and synthetic microspheres manufactured in
accordance with other methods known in the art. The preferred
embodiments also provide a method for manufacturing the plurality
of glass microspheres, including composition and processing, and
uses for the microspheres in various applications, including as
functional fillers in various composite materials, in applications
related to oil and gas industry, such as proppants for hydraulic
fracturing or hydrofracturing fluids, well casing cement, drilling
fluids, and in constructions materials.
[0034] The glass microsphere manufactured according to an
embodiment of the present invention comprises a single or a
plurality of glass walls, and a single or a plurality of voids or
hollow spaces defined and enclosed by said wall or walls. The terms
of "glass microspheres", "synthetic glass microspheres", and
"hollow glass microspheres" are interchangeably used throughout
this document to refer to a structure that comprises a plurality of
enclosure glass walls, surrounding at least one or a plurality of
hollow spaces.
[0035] The synthetic glass microsphere as described herein
generally comprises a substantially spherical outer wall and a
substantially enclosed cavity or void defined by the wall,
resembling the general configuration of harvested cenospheres from
coal burning fly ash. All these structural aspects of the glass
microsphere will be described in more detail in this document with
reference to FIG. 2. In certain preferred embodiments, the
synthetic glass microsphere has one or more of the following
characteristics:
an aspect ratio of between about 0.8 and 1; a void volume of
between about 10 and 95%, based on the total volume of the
microsphere; an outer wall thickness of approximately 2 and 55% of
the microsphere radius; a composition comprising in weight percent:
about 30 to 85% SiO.sub.2, about 2 to 30% Al.sub.2O.sub.3, 2 to 30%
divalent metal oxides selected from the group of MgO, CaO, SrO,
BaO, about 4 to 12% monovalent metal oxides selected from the group
of Li.sub.2O, Na.sub.2O, K.sub.2O, Cs.sub.2O, and 2 to 30% of other
metal oxides and chemical species, including multivalent metal
oxides which exist in multiple oxidation states such as
Fe.sub.2O.sub.3, and chemical species such as borates, phosphates,
sulfates, etc; a silica to alumina ratio of greater than about 1
(mole ratio); an average diameter of between about 5 and 1000
microns; and a particle density (e.g. apparent density) of between
about 0.1 and 2.2 g/cm.sup.3. Further structural and functional
details will be provided in this document in connection with the
glass microsphere while referring to the illustration made in the
drawings.
[0036] As will be described in greater detail below, the synthetic
glass microsphere of certain preferred embodiments of the present
invention can be formed by performing a method of manufacturing a
plurality of glass microspheres, comprising melting a batch into a
first glass melt in a melter system, processing the first glass
melt into a second glass, pulverizing the second glass into a
plurality of glass fragments, thermally processing the plurality of
silicate glass fragments to convert the plurality of glass
fragments into a plurality of glass microspheres, providing a
plurality of redox reactions and a plurality of events in at least
one of the first glass melt and a melt of the second glass, the
plurality of redox reactions and the plurality of events being
induced by a plurality of redox active group components and their
reaction products. It is of note that for simplicity of description
in the rest of this document said redox active group components and
their reaction products will be referred to simply as "RAG
components".
[0037] According to one aspect of the present invention,
non-equilibrium redox reactions are generated in the first glass
melt, and the second glass melt by the RAG components.
[0038] The RAG components are components comprising at least one of
reducing, neutral, and oxidizing species. The RAG components in
combination with glass forming raw materials form a batch that is
melted to provide a glass precursor from which a plurality of
silicate glass fragments (SGF) are made. Throughout this document,
the terms of redox active silicate glass fragments, silicate glass
fragments, SGF and plurality of glass fragments are interchangeably
used, whilst they all indicate the same glass fragments. According
to an embodiment of the invention, the glass forming raw materials
may be silicate glass forming raw materials that are melted to
provide a first glass melt, a silicate glass precursor (SGP).
[0039] According to the present invention, the RAG components are
one of intrinsic, extrinsic or a combination thereof, to the
constituents that make up the raw materials batch. The composition
of the RAG components is selected such to provide and/or influence
a plurality of redox reactions and/or physical events to take place
within the first glass melt of said raw materials. The RAG
components and/or their reaction products formed and/or
incorporated in the first glass melt are carried over to a second
glass, and further provide and/or influence a plurality of redox
reactions and/or physical events that take place within the second
glass during the reheating, melting, and the expansion of the
second glass, leading to the formation of hollow glass
microspheres.
[0040] In accordance with an embodiment of the present invention
the plurality of redox reactions and/or physical events may not be
allowed to reach their final equilibrium state and may be
intentionally terminated under a predetermined non or
quasi-equilibrium state. Such a redox reaction is termed a
"non-equilibrium redox reaction" throughout the present
document.
[0041] In the present document the terms "non-equilibrium
phenomena", "non-equilibrium chemical reactions" and
"non-equilibrium redox reactions" are used interchangeably and are
intended to be associated at least the meaning provided above, as a
plurality of redox reactions that are not allowed to reach their
final equilibrium states and may be intentionally terminated under
a predetermined non or quasi-equilibrium state or may be terminated
due to changes in the conditions to which the reactants are exposed
to during the reaction. For example, by rapidly cooling the first
glass melt below its softening temperature, as it happens by
discharging the first glass melt from a melter, or by quenching the
first glass melt in air, the plurality of redox reactions and/or
physical events taking place in the glass are intentionally
terminated (forced to terminate).
[0042] In addition, the non-equilibrium phenomena is understood in
accordance with an embodiment of the present invention as including
chemical and physical events such as chemical reactions, redox
changes, and changes in the physical properties of the first and
second glass melts, such as changes in solubilities of certain
gases or vapors in the glass melts as a function of
temperature.
[0043] In accordance with a particular embodiment of the present
invention, non-equilibrium redox reactions are achieved by
selecting the composition of the redox active group RAG components
such that it is adapted specifically for a specific first glass
composition. For any given first glass composition, an optimum
composition of the RAG components is selected from a range, to
encompass the processing temperatures and atmosphere that shall be
selected in order to optimize the non-equilibrium redox reactions
under a prescribed set of reactions and/or events, specifically
with respect to time and/or temperature. These aspects of the
invention, especially insofar as the modes of realization of the
non-equilibrium redox reactions and the reaction dynamics that are
envisioned in accordance with the various embodiments of the
present invention, are disclosed in detail in the reminder of this
document.
[0044] From the perspective of redox reaction dynamics, redox
reactions are separated at least operationally, into redox
reactions, and non-equilibrium redox reactions.
[0045] By "redox reaction" is understood a reaction that is allowed
to proceed from reactants to final reaction products without any
external interruption, until the reactants are substantially
depleted or become non-reacting. In contrast, the "non-equilibrium
redox reactions" are reactions that are induced to proceed, but are
intentionally ceased at a predetermined stage during the reaction.
The predetermined stage is determined by the reaction time and/or
reaction temperature and/or reaction dynamics, and as a result,
both reactants and reaction products co-exist in the resulting
glass melt. By triggering a ceased/dormant non-equilibrium redox
reaction, the reaction may take a different path and/or rate to
proceed, thus leading to a set of different products than otherwise
would not have been possible if the reaction would have continued
on its initial reaction path and/or with its originally intended
rate. In order to redirect a non-equilibrium reaction to take a
different path or assume different dynamics to completion, certain
reaction parameters may be altered/changed from the
initial/original reaction parameters. The parameters comprise one
or a combination of ambient conditions, pre-treatments,
incorporation of redox active group components, reaction
temperature, heating rate, the redox state of the glass melt, the
physical size of glass fragments, etc.
[0046] In accordance with an embodiment of the present invention,
the constituents of the redox active group RAG components comprise
a plurality of redox capable materials that either themselves
and/or their reaction products can change the oxidation states in
the first glass melt, and in the second glass melt based on a
predetermined set of parameters. The changes in the oxidation
states and/or the solubilities of the RAG components (including
reaction products) result in the formation and evolution of gas in
the second glass, leading to the formation of the hollow glass
microspheres. In addition, a reduction of the melting temperature
and/or viscosity of the second glass as compared to the first glass
is realized as well.
[0047] Exemplarily, the plurality of redox active group components
in accordance with the present invention include the chemical
species of carbon containing, sulfur containing, selenium
containing, oxygen containing, hydrogen containing, nitrogen
containing, phosphorous containing, and multivalent metals
containing materials. In accordance with a preferred embodiment of
the present invention, the RAG components are redox capable
materials comprising such materials as bonded and/or non-bonded
carbon, hydrogen, nitrogen, and chemical species such as sulfates,
sulfides, nitrides, nitrates, selenites, selenides, and compounds
from the group of multivalent metals, and transition metals such
as: tin, antimony, iron, copper, zinc, manganese, niobium, and
vanadium. Advantageously, the majority of these materials have
relatively low cost, and some of them already exist as impurities
in many industrial wastes and byproducts. The plurality of RAG
components comprises at least one electron donor and at least one
electron acceptor.
[0048] In accordance with one embodiment of the invention, either
pre- and post industrial, and consumer byproducts (also referred to
generally as "recovered materials" throughout this document) are
utilized as raw materials as part of the batch, in combination with
the RAG components to be melted in a first glass. In accordance
with an embodiment of the invention, the entirety or the majority
of the quantity of the plurality of the RAG components may exist
intrinsically in the recovered materials from which a batch is
prepared and which is subsequently melted to form the first glass.
As a result, only a portion of, and no additional RAG components
are needed to supply the total amount of RAG components required to
provide at least one of the plurality of the non-equilibrium redox
reactions and the plurality of events to take place in the
resulting first glass melt, and the second glass melt that lead to
the creation of the glass microsphere.
[0049] However, in the absence of all or of a part of the necessary
quantity of RAG components in the starting raw materials in the
batch, further RAG components are added either to the batch prior
to melting the batch into a first glass melt, or during the melting
of the first glass, or upon processing the first glass melt while
in a melter system, or upon discharging the first glass melt from
the melter system. Said plurality of redox active group components
are added into the first glass melt either inside or outside the
melting zone of the melting system. As it will become apparent
later in this document, the function of the RAG components is at
least to produce gas in melt of the second glass and to lower the
melting temperature of the second glass as compared to the first
glass.
[0050] The non-equilibrium redox reactions of the present invention
are time and temperature dependent, in addition to exhibiting
potential dependencies on other parameters, such as the
characteristics of their surrounding environment and
atmosphere.
[0051] As described above, preferred embodiments of the present
invention also provide methods of manufacturing a plurality of
glass microspheres. Referring now to FIG. 1, FIG. 1 is a block
diagram of an embodiment of a method of manufacturing a plurality
of microspheres, in accordance with the present invention. The
method is denoted with 100 in FIG. 1.
[0052] It is to be understood that a plurality of other variations
from the embodiments of the present invention presented herein will
be apparent to a person skilled in the art. Said plurality of other
variations is as well considered to be comprised within the scope
of the present invention.
[0053] In accordance with an embodiment of the present invention,
the method 100 of manufacturing a plurality of glass microspheres
comprises the steps described in the following.
[0054] In accordance with a first step of method 100, in accordance
with one embodiment of the present invention, a plurality of
silicate glass precursor (SGP) raw materials 202 are combined with
a plurality of redox active group (RAG) components 204.
Exemplarily, the materials 202 and the components 204 may be
combined by blending in step 102, to form a combination or a batch
200. In the following the terms "combination of the plurality of
silicate glass precursor (SGP) raw materials and plurality of redox
active group (RAG) components" and the terms "batch" or
"combination" with be used interchangeably and employed as having
the same meaning.
[0055] Exemplarily the plurality of silicate glass precursor (SGP)
raw materials 202 comprise at least one or a combination of glass
raw materials. Such glass raw materials are known to a person
skilled in the art of glass making. Alternatively, materials 202
are made entirely or in part from a plurality of materials selected
from a group comprising a silicate containing material, an
aluminosilicate containing material, a borosilicate containing
material, a lime silicate containing material, an incineration ash,
a slag, coal ash, bottom ash, an asbestos containing waste
material, an incineration ash/residue, a municipal waste material,
a hazardous waste material, a radioactive waste material, and a
medical waste material. All of the above enumerated materials 202
may be recovered materials. It is to be understood that the above
mentioned materials 202 are only exemplary and their enumeration is
not exhaustive. Any other materials apparent for the person skilled
in the art are considered to be included within the scope of the
present invention.
[0056] In accordance with another exemplary embodiment of the
present invention, the plurality of silicate precursor (SGP) raw
materials 202 may also include glass forming oxides, intermediate
glass forming oxides, and glass modifier oxides. Exemplarily, the
glass forming oxides are silica, phosphorous oxide, and boron
oxide. Exemplarily, intermediate glass forming oxides are alumina,
zirconia, titania, ferric iron. Exemplarily, the glass modifier
oxides are oxides of calcium, magnesium, zinc, ferrous iron, and
alkali metals. Again, any other glass forming oxides, intermediate
glass forming oxides and glass modifier oxides apparent to a person
skilled in the art are considered to be within the scope of the
present invention.
[0057] In accordance with a further exemplary embodiment of the
present invention the plurality of silicate glass precursor (SGP)
raw materials 202 comprises non-waste raw materials, such as
silica, siliceous material, alumina, alumina silicate materials,
boron oxide, borosilicates, calcium silicates, aluminates, alumina
bearing materials, lime and magnesium bearing materials such as
limestone and dolomite, and alkaline oxide bearing compounds and
minerals such as phosphates, carbonates and hydroxides of alkali
metals. The above enumeration is not exhaustive and any other
materials apparent for the person skilled in the art are considered
to be included within the scope of the present invention.
[0058] According to yet another embodiment of the present
invention, the plurality of silicate glass precursor (SGP) raw
materials 202 may consist entirely or partially of waste materials
or byproducts. These materials are used in combination with the
plurality of redox active (RAG) components 204 to prepare the batch
200, and subsequently the first glass melt 206. In a particular
embodiment of the present invention, a recycled waste material or
byproduct may already be in a vitrified form. In addition, the
vitrified waste material may intrinsically comprise the required
concentration and types of the RAG components 204. In such case,
the vitrified waste material is treated as the first glass 206. On
the other hand, if there was not a sufficient concentration and
types of the RAG components intrinsically present in a vitrified
waste material, then the necessary amount of RAG components 204 is
combined with that particular vitrified waste material in the batch
200 before proceeding to prepare the first glass melt 206. The
reference to "sufficient" amounts in this document will be expanded
upon in more detail while discussing specific examples. It is
intended that the amounts and the types of the RAG components be
present in amounts that lead to: producing enough gas for making
hollow-microspheres, and to lowering the melting temperature of the
second glass. The second glass and the hollow microspheres will be
described later in this document at least in connection with the
illustration of FIGS. 1 and 2.
[0059] Exemplarily, the recycled waste materials and byproducts are
at least one of fly ash, bottom ash, incineration ash, waste
glasses, blast furnace slag, alumina silicate containing materials,
vitrified asbestos waste material, vitrified hazardous waste
materials, vitrified radioactive waste materials, spent inorganic
catalysts, red mud, kiln dust, spent oil shale, and residual
biomass.
[0060] The recovered waste byproducts 202 may be selected from at
least one or more of a silicate material, an aluminosilicate
material, a borosilicate material, coal ash, bottom ash, slag,
waste glass, an alumina containing material, a titania containing
material, a zirconia containing material, a vitrified asbestos
containing material, a vitrified hazardous waste material, a
vitrified gamma emitting nuclear waste material, a biomass
containing material, etc.
[0061] The compositional range of the silicate glass precursor SGP
raw materials 202 is dependent on the target glass composition for
the first glass 206, and consequently the second glass 208. In
addition, the amount of each candidate raw material entering into
the SGP raw materials mix depends on the constituents of the RAG
components. For example, gypsum (CaSO.sub.4.2H.sub.2O) supplies
sulfate ions as a part of the RAG components, and calcium ions that
become a part of the first glass. In one way, the chemical
composition of the batch 200 is more representative of the first
glass 206, excluding the volatiles (e.g. water vapor), and the RAG
components 204.
[0062] The SGP raw materials 202, in accordance with another
embodiment of the present invention, are substantially free of any
redox active components 204. In accordance with yet another
embodiment of the present invention, the SGP raw materials 202
include all or a portion of the redox active components 204
intrinsically in their make up.
[0063] In accordance with the present invention, several distinct
embodiments are envisioned: A first embodiment when the SGP raw
materials 202 already intrinsically comprise a sufficient amount of
RAG components 204. In this case, no further RAG components are
added to the batch 200. A second embodiment wherein the SGP raw
materials 202 already comprise intrinsically RAG components 204,
but not in sufficient amounts. In this case the balance of the RAG
components 204 are added to batch 200. In a third embodiment the
SGP raw materials 202 are practically devoid of the RAG components
204. In this case, like the previous case, the RAG components 204
are added to the batch 200. In all the three embodiments listed
above, additional RAG components may be added to the first glass
melt 206 to adjust parameters such as rate, termination, reaction
products, etc. of the redox reactions. Other modalities of
providing RAG components 204 to the raw materials 202 may be
apparent to the skilled person aiming to practice the present
invention. All said modalities are comprised within the scope of
the present invention. Further in this document will be shown an
embodiment of the invention wherein the addition of the RAG
components 204 to the first glass melt 206 takes place either
exclusively or in combination with addition of the RAG components
to the SGP raw materials 202 via batch 200 and melting of the batch
200 to the first glass melt 206.
[0064] The RAG components 204 according to one embodiment of the
invention are in the form of oxides, hydroxides, anions, metals,
cations, chemical species, chemical compounds, elements, or a
combination thereof.
[0065] In accordance with one exemplary embodiment of the present
invention, the RAG components 204 may comprise one or a combination
of compounds or species containing sulfur, carbon, oxygen,
nitrogen, hydrogen, phosphorous, a multivalent metal such as a
multivalent transition metal. The sulfur containing material(s) is
selected from at least one of sulfates, sulfites, sulfides, and
elemental sulfur. Alternatively, in accordance with another
embodiment of the present invention, the RAG components 204
comprises at least one or more of sulfur containing material(s),
carbonaceous material(s), and iron containing material(s), in
addition to other appropriate redoxable materials, chemical
species, and chemical compounds.
[0066] In accordance with another embodiment of the invention, at
least a portion of the requested RAG components 204 are an integral
part of the recovered waste byproduct(s). Alternatively, the RAG
components 204 are comprised in additives added to batch 200 in
addition to the raw materials 202 and the RAG components 204, or
the RAG components 204 may be separately added to the batch 200
prior to vitrification of the batch into a first glass 206. The RAG
components 204 may also be added during the melting of the first
glass, and/or after the melting of the first glass 206, in the
various zones of the melter system.
[0067] The step 102 of method 100, the combination step or the
blending step of raw materials 202 with RAG components 204 is
carried out in a blender such as a V-blender, a mill, a
homogenizer, and in any other conventional and non-conventional
mixers and blenders.
[0068] The RAG components 204 are in one of a solid, a liquid, a
gaseous form, an aerosol form or a combination thereof. In
accordance to one embodiment of the invention, the gaseous RAG
components 204 comprise at least one of air, oxygen, nitrogen,
hydrogen, steam, hydrocarbons, gaseous organics, CO.sub.2, CO,
H.sub.2O (liquid and/or vapor and/or steam), SO.sub.2, SO.sub.3,
H.sub.2S, NH.sub.3, and a combination thereof. In another
embodiment of the invention, the RAG components 204 are solids in
the form of fine powders and solid aerosol. For example, carbon in
form of coke, coal, or fine graphite powder in a gas carrier stream
or liquid carrier stream is injected into the first glass melt 206
formed by melting the batch 200 to trigger a rapid redox reaction,
such as reduction of sulfates, and multivalent metal oxides.
[0069] In accordance with the embodiment of the invention wherein
the presentation of the RAG components 204 is in liquid form, the
injectable liquid RAG components 204 are for example one of liquid
water, peroxide, a soluble sulfate or sulfuric acid, liquid fuels,
liquid oils, and liquid hydrocarbons. Said liquid RAG components
204 may be injected into the plurality of silicate glass precursor
(SGP) raw materials 202, the batch 200, and the first glass melt
206 at various locations in the melter, such as a secondary melt
chamber, a glass-refining chamber and the discharge chamber of the
melter system. Solid form RAG components 204 may include iron
bearing minerals and oxides, and sulfur bearing compounds and
minerals such as gypsum, salt cake, sulfides, and carbonaceous
materials, such as carbon, or a carbon containing material(s).
[0070] The RAG components 204 are elected such to trigger
non-equilibrium redox reactions, such as oxidizing and reducing
reactions.
[0071] In accordance with a preferred embodiment of the invention,
the RAG components 204 included in the batch 200 are solids and
comprise sulfates, transition metal oxides and compounds, and
carbonaceous materials. Sulfates also include sulfites. In
accordance with another preferred embodiment of the invention, the
gaseous and/or aerosol form of RAG components 204 may be optionally
purged/bubbled inside the first glass melt 206. Alternatively, the
RAG components 204 are included in the first glass melt 206 by at
least one injection, spraying, dipping, and stirring, or a
combination thereof.
[0072] The gaseous RAG components 204 are added to the first glass
melt alone or in combination with one or more of solids, liquids,
and other gases that include SO.sub.3, SO.sub.2, H.sub.2S, H.sub.2,
N, CO.sub.2/CO, H.sub.2O, O.sub.2, hydrocarbons, NH.sub.3, air, and
various organic gases. All the gaseous RAG components 204 may be
purged or bubbled inside the first glass melt 206.
[0073] According to the present invention, the concentrations of
several RAG components 204 in the batch 200 based on the weight
percentage of the component over the dry mass of the batch 200 are
as follows: sulfates/sulfites calculated as SO.sub.4.sup.-2 is from
0.1 to 5%, sulfides and sulfur calculated as S.sup.-2 from 0 to 2%,
carbonaceous materials calculated as elemental carbon, from 0 to
3%, multivalent and/or transition metals calculated as metal
oxides, from 0.1 to 25%, and nitrates/nitrites/nitrides calculated
as N from 0 to 2%.
[0074] In accordance with one embodiment of the present invention,
the compositional range of the first glass 206 in weight percentage
falls within: 30-85% SiO.sub.2, 4-12% of R.sub.2O (R.sub.2O is one
or combination of Li.sub.2O, Na.sub.2O, K.sub.2O), 2-30%
Al.sub.2O.sub.3, 2-30% RO(RO is one or a combination of MgO, CaO,
SrO, BaO), and 0-30% of other oxides and chemical species such as
B.sub.2O.sub.3, TiO.sub.2, etc.
[0075] The type and the amount of RAG components 204 elected to be
combined, exemplarily via blending in a given batch 200, is based
on the chemical composition of the SGP raw materials 202, and the
redox reactions desired to be induced, which collectively will
determine the specific physical and chemical properties of the
glass microspheres created by practicing the method of the present
invention. As previously mentioned, the RAG components 204 may be
intrinsic to the SGP raw materials 202, or may be blended as
partial or as completely separate entities with the SGP raw
materials 202, prior or during the step 104 of method 100 of
melting the batch 200 into the first glass melt 206.
[0076] According to the present invention, the RAG components 204
are capable to provide non-equilibrium redox reactions in the first
glass melt 206, as it will be described in more detail further in
this document.
[0077] According to the present invention, the plurality of RAG
components 204 are capable to go through redox reactions and/or
events in the first and second glass melts 206 and 208. By redox
reactions are understood reduction-oxidation reactions. The redox
reactions generally comprise chemical reactions, and the events
comprise reversible and irreversible chemical reactions, and
physical changes/events such as thermal reboil, and sublimation.
During the occurrence of the redox reactions in the first and
second glass melts 206 and 208, the RAG components 204 change their
corresponding oxidation states of their ions/chemical species.
[0078] The redox reactions envisioned to occur in accordance with
the present invention are at least one of an oxidation reaction, a
reduction reaction, and a combination thereof. As such, a series of
electron transfers take place between the constituents of the RAG
components 204, that are elements, molecules, ions, and chemical
species. The oxidation is associated with the loss of electrons
resulting in an increase in oxidation state, and the reduction is
associated with the gain of electrons resulting in a decrease in
oxidation state by either one or a plurality of atoms, molecules,
ions, and chemical species of the corresponding RAG component
204.
[0079] In addition to the SGP raw materials 202, and the RAG
components 204, other additives may be added to constitute a
combined batch 200. The additives may comprise a variety of
recovered materials, and various chemical compounds, and chemical
species that become a part of the batch 200 and therefore a part of
the first glass 206. The additives are added to achieve the
targeted composition of the first glass melt 206.
[0080] According to one embodiment of the present invention, the
batch 200 may include various recovered waste byproduct(s), and a
plurality of additives and/or glass additives. The plurality of
additives and/or glass additives in addition to other chemical
compounds, and chemical species may comprise one or more of the
following compounds: silica, siliceous materials, aluminosilicate
materials, alkaline earth metal containing materials, alkali metal
containing materials, phosphate-containing materials,
boron-containing materials, and a combination thereof.
[0081] In accordance with various embodiments of the invention the
RAG components 204 are an integral part of either one or both the
recovered waste byproduct(s), and the additives, or are externally
added to the batch 200 prior to or during the vitrification of the
batch 200 into the first glass melt 206, or are added directly to
the first glass melt 206, or to a combination thereof.
[0082] Exemplarily, when a recovered waste byproduct, such as type
C fly ash is used as the primary source for the SGP raw materials
202 a siliceous additive with high silica content is blended in
batch 200 to increase the silica content of the first glass 206.
Examples of such siliceous sources are ground silica sand, silica
flour, diatomaceous earth, and ground quartz. In general, the
majority of additives comprise one or more of glass formers, glass
intermediate oxides, and glass modifiers. For examples, some common
additives are materials that contain one or more of boron oxide,
phosphorous oxide, titania, alumina, alkali metal oxides, and
alkaline earth metal oxides.
[0083] As it will be disclosed in detail in the following portions
of this document, with the means and methods of the present
invention it is possible to manufacture glass microspheres 212 from
SGP raw materials 202 having low alkali metal oxide content, of
equal to less than 12 wt % of total alkali metal oxides on mass
basis of the resulting first glass 206. In one preferred embodiment
of the present invention, in order to provide a limit for the
alkali content of the SGP raw materials 202, when sodium oxide is
at least one of the alkali metal oxides, the concentration of
sodium oxide in the first glass 206, and consequently as well in
the second glass 208, should be below 8 wt %, and preferably less
than 4 wt % based on a mass of either the first glass melt and the
second glass. As a result the glass microspheres 212 manufactured
from said SGP raw materials 202 will have exceptionally high
chemical durability, as indicated by their very low leach rates in
aqueous alkaline environments.
[0084] One way to determine the chemical durability of the glass
microspheres 212 provided via the means and methods of the present
invention, is by employing the test prescribed by standard ASTM
C1285-02, referred to as the "product consistency test (PCT) test".
An acceptable PCT test result in accordance with the present
invention is a composite leach rate that is less than 500
g/m.sup.2day (e.g. g/m.sup.2 per day) at a pH of about 11, and a
temperature of about 90.degree. C. A preferred composite leach rate
is less than 100 g/m.sup.2day under the same test conditions
mentioned above, averaged over test duration of 3 days.
[0085] An alternative criteria to determine the suitability of the
glass microspheres 212 with respect to the chemical durability is
based on a comparative leach test, that benchmarks the glass
microspheres of the present invention against cenospheres that are
harvested from fly ash, a coal combustion byproduct. Under a
suitable comparative test protocol, the microspheres created by
employing the means and methods of the present invention are tested
under identical conditions side by side with the cenospheres. For
example, in one aspect of the present invention, an acceptable
comparative chemical durability test result for the microspheres
212, reported in terms of leach rate, is not more than 20% above
the leach rate obtained under the identical conditions for the
cenospheres.
[0086] In accordance with a second step of method 100, in
accordance with one embodiment of the present invention, the batch
200 resulting from the combination step 102 is melted in a step 104
in a melter system. The result of said melting step 104 is the
first glass melt 206.
[0087] The step 104, of melting of the batch 200 into the first
glass melt 206 is carried out in a glass melter system under a
variety of conditions elected depending on the redox state desired
to be obtained in the first glass melt 206. The variety of
conditions are controlled via controlling parameters, that for the
melting of batch 200 are one of melting temperature, melting time,
melting dynamics, such as stirring/agitation, and the melt redox
state. The melt redox state is controlled intrinsically by
non-equilibrium redox reactions, and extrinsically by melting
either under one of reducing, neutral or oxidizing conditions. The
extrinsic conditions apply to both the ambient and the melt pool
environments where the glass melting is taking place.
[0088] Details regarding what constitutes a glass melter
appropriately configured to fulfill the requirements mentioned
above will be disclosed in the subsequent sections of this
document. Further, known, and unknown details regarding melter
configuration, envisioned by a person skilled in the art of melter
design and not mentioned expressly but suggested and or hinted to
in this document are as well considered to constitute a part of the
present invention.
[0089] The redox reactions that the RAG components 204 are going
through within the first glass melt 206 and the second glass 208
have the combined effects of lowering the melting temperature of
the second glass melt 208 to a temperature that is lower than the
melting temperature of the first glass melt 206, while at the same
time producing a volume of gas that is employed to manufacture the
plurality of hollow glass microspheres 212 from the second glass
208. It shall be understood that the RAG components 204 in
accordance with the present invention include both the reactants
and the reaction products of the RAG components. In one embodiment
of the present invention, the "glass-flow point temperature" of the
second glass melt 208 is lowered as the result of the occurrence of
the redox reactions provided by the RAG components 204. This
lowering is measured as compared to the glass flow-point
temperature of the first glass melt 206. By definition, the glass
viscosity at the glass-flow point temperature is about 10.sup.5
poise. In another embodiment, the melting temperature of the second
glass melt 208 is lowered as the result of the occurrence of the
redox reactions provided by the RAG components 204 as compared to
the melting temperature of the first glass melt 206. In yet another
embodiment, according to the present invention the "glass
working-point temperature" of the second glass melt 208 is lowered
as the result of occurrence of the redox reactions provided by the
RAG components 204 as compared to the glass working-point
temperature of the first glass melt 206. By definition, the glass
viscosity at the glass working-point temperature is about 10.sup.4
poise.
[0090] In accordance with the present invention, the melting
temperature of the second glass 208, is dependent on the
concentration of ferrous iron in the second glass 208. For a given
concentration of total iron in the forms of ferric and ferrous iron
in the second glass 208, more ferrous iron corresponds to a lower
melting temperature of the second glass 208. In a general scheme,
more ferrous iron corresponds to a more reduced second glass 208.
In contrast, more ferric iron corresponds to a more oxidized second
glass 208. Depending on the redox state of the second glass 208 as
being either oxidized, or reduced, there is a temperature
difference of at least 10.degree. C., preferably 40.degree. C., and
most preferably 80.degree. C., between the melting temperatures of
oxidized and reduced forms of the second glass 208.
[0091] Exemplarily, according to one embodiment of the present
invention, the first glass 206 is melted under oxidizing conditions
as dictated by the melting parameters and/or the melter
requirements and/or limitations. For example, the electrodes in the
melting zone of the melter system will last longer in contact with
an oxidized glass as opposed to a situation when they are in
contact with a reduced glass. The redox state of the first glass
melt 206 can be changed in the melter system via direct
incorporation of the RAG components 204 into the first glass melt
206, as will be disclosed further in more detail. In the melter
system, reducing RAG components in gaseous or aerosols forms are
brought in contact with the first glass melt 206 in a processing
zone of the melter system, or in a discharge zone outside the
melting chamber. The contact is made by injecting, purging, or
bubbling the RAG components 204 in the form of gas and/or aerosol
into the first glass melt 206.
[0092] As previously mentioned in this document the RAG components
204, according to the invention, are in the form of solids,
liquids, gases, aerosols, and comprise oxides, hydroxides, anions,
cations, chemical compounds, chemical species, elements, or a
combination thereof. The RAG components 204 are capable of
providing at least one non-equilibrium redox reaction in either one
or both the first glass melt 206, and the second glass melt
208.
[0093] As it is described in detail in this document, according to
one embodiment of the present invention, a plurality of glass
microspheres 212 are manufactured from the batch 200 that comprises
at least one of a plurality of silicate glass precursor raw
materials 202 and at least a plurality of RAG components 204. The
RAG components 204 included in the batch 200 undergo redox
reactions while in the melter system while forming the first glass
melt 206, and as such, the RAG components reaction products are
created in the first glass melt 206.
[0094] A composition of the SGP raw material 202 according to one
embodiment of the present invention, is preferably an alumina
silicate based composition. A glass created from an alumina
silicate based SGP raw material 202 exhibits high chemical
durability in alkaline environments, and is suitable for forming
thin partition walls or envelopes, surrounding the gas bubbles
within glass microspheres 212. As such, the glass microspheres 212
are capable of withstanding high isostatic pressures of well over
1000 psi. Various additives, such as glass formers and glass
modifiers may be added to the alumina silicate based SGP raw
material 202 to impart specific properties. For example, in one
possible embodiment, boron oxide is added as a glass former to
extend the glass forming temperature range and to reduce the
divitrification potential of the first and second glass melts 206
and 208. The composition of the second glass 208, for applications
wherein the hollow glass microspheres 212 are to be exposed to high
alkaline environment, needs to be highly chemically durable. For
this reason in accordance with one embodiment of the present
invention, the first glass 206, and consequently the second glass
208 comprise low concentrations of alkali metal oxides, and
moderate to high concentrations of alumina, and alkaline earth
metal oxides.
[0095] As it was previously mentioned, according to one aspect of
the present invention, the SGP raw materials 202 comprise raw
materials that are non-waste materials, and are considered ordinary
glass raw materials. These SGP raw materials 202 are combined with
the corresponding RAG components 204 to form the batch 200. As an
alternative, the SGP raw materials 202 comprise and may be melted
in step 104 from a combination of recovered materials, and
non-waste raw materials. Exemplarily of the recovered materials are
blast furnace slag, fly ash, bottom ash, red mud from aluminum
smelting processes, kiln dust, spent oil shale, mine tailings, and
spent catalysts.
[0096] The SGP raw materials 202 may be combined with the RAG
components 204 in a melted or a non-melted state. In the embodiment
of the invention where the SGP raw materials 202 are in a
non-melted state, the RAG components 204 may all be added to the
batch 200 prior to melting the SGP raw materials, or optionally
they may be added during or after the melting of the SGP raw
materials 202. As discussed above, the RAG components 204 may
include one or a combination of solids, liquids, gases, vapors,
aerosols that are introduced and incorporated into the first glass
melt 206 during one or a combination of melting, processing the
melt, conditioning the melt, refining the melt, and discharging
processes, collectively referred to "while in the melter system".
The introduction and/or incorporation of the RAG components 204
into the first glass 206 while in the melter system is carried out
by blending, stirring, injecting, bubbling, mixing, spraying,
dipping or a combination thereof. Other technique of incorporating
the RAG components 204 into the first glass melt 206 while in the
melter system used by a person skilled in the art are within the
scope of the present invention.
[0097] Feeding and melting the batch 200 into a glass melter system
are carried out in one or a combination of a batch method, a
semi-continuous method, and a continuous method. The glass melter
envisioned in accordance with the present invention is selected
from one or a combination of a fuel fired glass melter, an electric
glass melter, a plasma-torch glass melter, an inductively coupled
glass melter, a radiant tube glass melter, and a submerged
combustion melter.
[0098] Glass melter designs, including the melter geometry and the
specifications of the energy input and control systems, must be
adaptable to the composition of the first glass 206 and to aim at
the successful execution of the redox reactions while in the melter
system, leading to the formation of the second glass 208. Examples
of fuel fired glass melter types envisioned to be used in
accordance with the present invention are one or a combination of a
regenerative end or cross fuel fired melter, a recuperative end or
side-fuel fired melter, and a hybrid melter (combination of fuel
firing and electric boosting). Fuel firing is preferably carried
out by oxy fuel burner systems.
[0099] Within an electric type melter the molten glass acts as a
conductor of electricity and in the process it heats up. Under
ideal conditions, as much as 95% of the electricity is converted
directly into heat by joule heating. The electrodes of the electric
type resistance melter are placed either inside or outside the
glass pool formed by the first glass melt 206. When the electrodes
are placed inside the glass pool or glass tank, the electric type
resistance melter operates in a direct heating mode. In an indirect
mode of operation, the electrodes are placed outside the glass pool
or the glass tank. In an all electric melter, the melter primary
chamber geometry is determined based on the position of the
electrodes in the melter, electrode current density, production
rate, load voltage, load power, and glass discharge types, such as
a bottom discharge, or a side charge. Alternatively, as disclosed
earlier heat may be provided to the glass melter via other heating
methods, singularly or in combination.
[0100] In hybrid melters, the energy input is provided by the dual
action of burning fuels and electrical boosting. The fuel burners
are preferably oxy-fuel burners and electrical boosting is provided
by appropriate AC power supplies.
[0101] Exemplary, the melting step 104 is carried out in a hybrid
melter with a submerged combustion burner that is inserted directly
in the glass pool. Alternatively, the submerged combustion burner
is placed in an auxiliary compartment of the melter outside the
primary melting area. A submerged combustion burner is capable of
firing gaseous and liquid fuels, alone or in combination, such as
firing with natural gas, hydrogen, and other combustible gases and
fuel oils. Air, oxygen, oxygen-enriched air is used as the fuel
oxidant. The submerged combustion burner operates to provide either
an oxidizing or a reducing atmosphere. Submerged combustion burners
achieve localized temperatures in excess of 1600.degree. C.
[0102] Referring now briefly to the illustration of FIG. 3, in FIG.
3 is illustrated schematically a glass melter system 300 envisioned
to be used in accordance with one embodiment of the present
invention. Glass melter 300 according of the present invention
comprises three zones, namely a melting zone 310, a processing zone
320, and a discharge zone 330. In the melting zone 310, apart from
phenomena that are related to the melting of the materials
introduced into the melter, the RAG components 204 may be as well
introduced, as mentioned above, either directly into the glass
melt, or as additional RAG components 204 mixed with the materials
to be melted. The processing zone 320 is intended to allow at least
the following processes to take place in the melter system 300: the
introduction and incorporation of the RAG components 204 into the
first glass melt 206, holding and storing the first glass melt 206,
homogenizing the first glass melt 206, refining the first glass
melt 206, and reheating the first glass melt 206. The discharge
zone 330 comprises at least one or a combination of a trough, an
outlet throat, an airlift system, glass re-heaters, plenum air
heaters, and other related auxiliary components.
[0103] In an all electric melter or a hybrid melter, additional
electrodes are optionally installed between the melting zone 310
and the processing zone 320, and between the processing zone 320
and the discharge zone 330 to act as a barrier between the zones
while maintaining the temperature of the glass melt flowing from
the melt zone 310 into the processing zone 320, and into the
discharge zone 330. This prevents an undesirable glass melt
return-flow between the zones of the melter system 300.
[0104] In accordance with a possible embodiment of the present
invention, the main source of energy of the melting zone 310 is an
oxy-fuel heating system with the appropriate burners installed
along the sides of the melting zone 310 structure. The energy input
for melting is further increased by an electric boosting system in
the melting area. A boosting system in the melting area supplies
additional energy directly to the glass bath and leads to a higher
melting capacity.
[0105] In accordance with one embodiment of the present invention,
the processing zone 320 is compartmentalized, for example with the
help of refining banks placed at equal or varying glass depths to
allow incorporating RAG components 204 into, and/or refine the
first glass melt 206. Movable gates/barriers are also installed
between the compartments to provide the ability to divert or bypass
the molten glass to move upwards, downwards, or side ways towards
the glass discharge zone 330 while maintaining a high
temperature.
[0106] In accordance with an embodiment of the present invention in
an all electric melter system 300, the electrodes are installed
into the melting zone 310 from the top. The electrodes are inserted
through the melter plenum structure and enter the glass pool
through the melt open surface. This way they can be pulled out of
the melter for inspection and possible replacement. In such an
arrangement, the formation of an electrically conductive layer on
the top of the melter, such as molten salts must be either avoided,
or disrupted. This is because the electrodes' leads at the entry
region into the melt pool will be contacted with the conductive
layer and thus will experience a very high current density, almost
equivalent to being short out. If left exposed for long enough time
to the conductive layer, the electrode lead will be severely
damaged.
[0107] Should the formation of a conductive salt layer be likely,
the electrodes may enter the melter through side wall blocks of the
refractories or from the bottom. If metals collect at the bottom of
the melter, care needs to be taken to keep out the precipitated
metals away from the electrical path of the electrodes. In a
situation when metal precipitation results in formation of a molten
metal layer at the bottom of either the melting zone 310, or the
processing zone 320, a sloped bottom is provided to collect and
discharge the molten metal layer in a controlled manner out of the
melter via a corresponding bottom discharge provided in each
zone.
[0108] The electric melter system 300 uses various electrode
materials, such as non-metallic electrodes such as graphite,
ceramic electrodes such as molybdenum di-silicide, and metallic
electrodes. Exemplary for the metal and metal alloy electrodes are
electrodes made of molybdenum, molybdenum alloyed with zirconium
oxide, molybdenum coated with molybdenum di-silicide, copper,
nickel-chromium super alloys such as Inconel.RTM. alloy 690, and
iron, among others. The metal electrodes may additionally be water
or air cooled to prolong the service life of the electrodes. Air or
water cooling of the electrodes in the electric type resistance
melter alleviate the limitations in operating temperature and shift
the operating temperature to higher temperatures than otherwise
would be possible. In one embodiment of the present invention,
indirect electric heating substitutes or complements the direct
electrical heating, by using for example molybdenum disilicide
electrodes.
[0109] The batch 200 is charged preferably over the entire area of
the melt pool in the melting zone 310 through one or a combination
of doghouses on a side wall, and from the melter top. The batch
200, from a feed hopper, is spread over the molten glass pool for
example by a vibratory chute. The batch floats on the top of the
glass pool, and is optionally pushed or swept by a pusher to form a
cold cap. The cold cap greatly reduces radiation heat losses to the
melter plenum space, and provides an efficient barrier against
particulate emission to the melter off gas system.
[0110] In accordance with the present invention, the melter system
300 is preferably continuously fed, and continuously drained
through one of an airlift system, and/or gravity, and/or a
forehearth. The extent and depth of the cold cap is adjusted by
controlling the rate of feeding the batch 200 to the melter, and
the rate of discharging glass out of the melter. Exemplarily, a
cold cap layer provides above 80% surface coverage over the melt
pool having an average layer thickness, ranging from several
centimeters to tens of centimeters. As a result, the overall
thermal efficiency of the melter is improved as indicated by an
average power consumption of equal or preferably less than one Kwh
per kg of the first glass 206 produced. The power consumption
number varies depending on the yield of the batch 200 to the first
glass 206. As an exemplary case, a yield almost equal to one
indicates that low volume of volatiles are lost from melting the
batch 200 to the first glass melt 206.
[0111] It is advantageous to provide a bottom drain situated at the
bottom of the melter, in either one of zones 310, 320, and 330 to
drain the glass or the potentially molten metals from the bottom of
the melter. The drain nozzle is heated by electric heating means.
The electric heating heats the glass or metal in the drain-hole and
maintains the temperature necessary for the required draining rate.
Glass is drained from the bottom by the action of the gravity. The
drain can be started or stopped at any time by switching the
electrical heating means on or off.
[0112] Air or other gases are blown into the melter through special
bubbler nozzles installed in either one of the melter bottom, side,
and/or entering the glass melt from the top. This produces bubbles
in the glass and as the bubbles rise to the surface of the glass
melt, keeps the glass melt pool in the melter agitated. The
bubbling gas is exhausted into the furnace off-gas system. The
upward movement of the bubbles produces strong localized convection
currents around their path, and these currents move the glass
upwards and cause an increase in the glass melt temperature at the
bottom of the glass pool, which otherwise would be cooler than the
top. The bursting bubbles on the glass surface also create an
effective barrier that prevents the unmelted batch from moving
downward prematurely. In most cases, bubbler tubes are made from
durable refractory materials such as molybdenum disilicide, and are
installed in strategically elected points in the melter for maximum
effectiveness.
[0113] The melting time is defined as the residence time of a
portion of the batch 200 from a time that the batch 200 is fed to
the melter till the time that the first glass 206 is discharged in
step 204. The residence time of the first glass in the melter
system in step 204 is estimated as the capacity of the melter in
kilograms, divided by the batch feed rate to the melter, in
kilograms per hour. The residence time is measured in hours. The
residence time of the batch 200 in the melter system 300 until the
discharge of the first glass melt 206 under continuous and
non-interrupted operation is less than 18 hours, and preferably
under 12 hours, and most preferably is equal to or under 5
hours.
[0114] In accordance of the present invention, irrespective of the
type of melter used, the melting temperature of the batch materials
200 is between 1200 to 1600.degree. C. The actual value of the
temperature in this range is strongly correlated with the chemical
composition of the batch 200.
[0115] A plurality of non-equilibrium redox reactions take place
while and/or after the batch 200 is melted into the first glass 206
in step 204.
[0116] When RAG components are an integral part of the batch 200,
or when the RAG components are added in the melter 300 or when both
cases are present, then the batch 200 has to reside in the melter a
time that is long enough to melt into a first glass melt 206.
However, the residence time in the melter should not exceed the
time that is required to complete the redox reactions that will be
initiated by the RAG components 204. Hence, in order to achieve the
desired non-equilibrium redox reactions, the reactions need to be
terminated for example by moving or discharging the first glass
melt 206 from the melter. As such, the temperature of the glass
melt is dropped and the glass solidifies, and the corresponding
redox reactions are not able to proceed in the solid glass to reach
their equilibrium points.
[0117] Since the melting residence time is kept relatively short, a
faster dissolution of the batch materials 200 has to be ensured. To
ensure efficient heat transfer and thus faster dissolution of the
batch materials 200 into the glass pool in the melter, the melt is
preferably agitated, in accordance with one embodiment of the
present invention. Melt stirring or agitation is achieved by at
least one of an electrical means, such as electric current
convection, a thermal means, such as forced thermal convection,
mechanical means, such as stirring, and bubbling means. Bubbling
gases via lances (bubblers, nozzles) into the glass pool is an
efficient way to provide agitation in the melt pool. According to
the present invention, oxidizing, reducing, and neutral gases
and/or vapors and/or aerosols are as well used for bubbling the
glass pool. Oxidizing, reducing, and neutral gases and/or vapors
and/or aerosols are elected to be introduced into the glass pool
depending on the redox reactions to be initiated or enhanced or
terminated in the glass melt. For example, to provide an oxidizing
melt environment, oxygen or a mixture of air and oxygen is used. To
provide for a reducing environment, for example forming gas
(mixtures of hydrogen and nitrogen), hydrogen sulfide, a variety of
gaseous hydrocarbons, and ammonia is used. To provide for a neutral
environment, air, and/or nitrogen, or inert gases are used.
[0118] The flow rate of the bubbling gas or of the other media
provided is adjusted as appropriate, adjustment that can vary from
several liters per hour to tens of liters per minute. The numbers
of lances/bubblers, their locations, together with the airflow
patterns from the lances into the melt pool are adjustable in order
to provide for the desired residence time and the desired redox
state of the first glass melt 206 before being discharged from the
melter. In accordance with one embodiment of the present invention,
the bubblers are located at or near the bottom portion of the
melting chamber beneath the glass pool, for providing the gas
bubbles directly into the glass melt. Bubbling or purging gas
and/or aerosols may be provided as well in other parts of the
melter, outside the main melting chamber, as will be disclosed
later.
[0119] Glass mixing efficiency should be balanced against the melt
pool contact refractory erosion rate. Accordingly, to achieve
non-equilibrium redox state in the first glass melt 206, it is
within the scope of present invention to maximize the melting rate
while keeping the eroding rate of the contact refractories
reasonably low.
[0120] In one aspect of the invention, the gases and/or aerosols
used for providing agitation in the glass melt, for example by
bubbling, can also take part in providing the non-equilibrium redox
reactions in the first glass melt 206, and thus as such are
considered to be "part of the RAG components" 204. The gaseous
and/or aerosols RAG components thus have the dual function of
providing agitation in the glass melt/pool and at the same
initiating and/or assisting, and/or terminating the non-equilibrium
redox reactions of the first glass melt 206. In one embodiment of
the present invention, the gaseous and/or aerosolic RAG components
204 are introduced in the processing and discharge zone 330 of the
melter system 300. Exemplarily, they may also be introduced in the
processing zone 320, that exemplarily comprises one or a
combination of a holding and storing section, a homogenizing
section, a refining section, a reheating section, sections that all
pertain to the first glass processing zone 320. Exemplarily, the
gaseous and/or aerosolic RAG components 204 are introduced in the
discharge zone 330 that comprises one or combination of trough
and/or outlet throat section, and the airlift section, sections
that pertain to the first glass discharge zone 330.
[0121] The introduction of the RAG components 204 in the melter
system 300 results in the initiation, continuation and enhancement,
or the termination of the non-equilibrium redox reaction taking
place in the melter system 300. In accordance with the present
invention, concurrent redox reactions may take place in the melter
system 300, and multiple RAG components 204 may be introduced
simultaneously or in stages to provide for either one or a
combination of initiation, enhancement/continuation, and
termination of the corresponding redox reactions.
[0122] In accordance with one aspect of the present invention, the
melting step 104 comprises the further introduction in the first
glass melt of specific RAG components 204, that are introduced by
at least one of bubbling, injection, or by any other introduction
method into the first glass melt 206 in order to incorporate
certain desirable chemical and/or redox properties into the first
glass melt 206. Exemplarily, the further RAG components are
introduced by bubbling oxygen into the first glass melt 206 in
order to shift the glass redox to be more oxidizing. Exemplarily,
hydrogen is also introduced as RAG component 204 to reduce the
oxidation state of the first glass melt 206. Because of the direct
incorporation of the further RAG components 204 into the first
glass melt 206 fast redox changes are induced in the first glass
melt 206. These redox changes, that take place fast in the first
glass melt 206, also affect the oxidation state of the multivalent
metal ions present in the first glass melt 206 as a part of the RAG
components 204. Single and multivalent metals can be added as a
part of the RAG components 204 directly to the first glass melt 206
for scavenging oxygen from the glass and in the process forming the
corresponding metal oxides.
[0123] An advantage of introducing gaseous and/or aerosolic RAG
components 204 in the discharge zone 330 of the melter system 300
is that the introduced RAG has the dual function of lifting the
molten glass and at the same time providing for non-equilibrium
redox reactions in the melter system 300. In an exemplary case, the
introduced RAG components 204 terminate the redox reaction(s)
taking place in the first glass melt 206 present in the discharge
zone 330 of the melter system 300, or in another case, initiate a
redox reaction that will be continued in the second glass 208 when
said second glass 208 is melted in a firing furnace. Another
advantage is that the non-equilibrium redox reactions are isolated
to the glass present in the discharge zone 330, and thus only
affect the glass being discharged and not the entire glass pool
residing inside the processing and melting zones 310, and 320.
[0124] Therefore, advantageously the first glass melt 206 present
in the main glass pool residing in the melting zone 310 is enabled
to selectively have a redox state that is the least damaging or
corrosive to the melter electrodes and contact refractories, but is
different from the targeted redox. The redox of the first glass
melt 206 is subsequently adjusted and tuned to the desired state
downstream from the main glass pool, for example in the processing
zone 320, and/or in the discharge zone 330, or in any other
auxiliary chambers present in the melter 300 before the first glass
melt 206 is finally discharged from the melter system 300.
[0125] As mentioned before, instead of or in combination with the
glass melting by Joule heating, other forms of glass melting are
also within the scope of the present invention including melting
using a plasma torch, an inductively coupled source, a fossil fuel
source, a submerged burner, and a combination thereof.
[0126] For example, in the case of employing iron as the
multivalent metal in the RAG components 204, by creating a reducing
condition in the melter system 300, a portion of the ferric ions is
converted to ferrous ions. Also, in another example, incorporating
hydrogen sulfide as a part of the gaseous RAG components in the
first glass melt 206 has the dual effect of reducing the glass and
forming a metal sulfide. As mentioned above, the presence of
sulphur in the form of sulfate and sulfide in the second glass
melts 208 leads to the formation of sulfur dioxide in the glass,
with the desirable effect of creating the glass microspheres.
[0127] In accordance with another embodiment of the present
invention, the RAG components 204 are introduced in the first glass
melt 206 in the melter system 300 as liquids in the form of liquid
aerosols.
[0128] The liquids, in the form of either one of liquid droplets
(mist), stream, aerosol or a combination thereof, are injected into
the first glass melt 206 while in the melter system 300. For
example, a liquid-gas mixture is injected into the first glass melt
206 while in the melter system 300 or while the first glass melt
206 is discharged from the melter 300. The liquid may be water
based, or liquid organic based. Exemplarily, water dissolves in the
first glass melt 206 in relatively low quantities (e.g. about 0.1
to 0.2 wt %), but it is a very powerful fluxing agent in the glass,
and lowers the viscosity and the melting temperature of the
resulting glass. In addition, water is an effective blowing agent,
useful in expanding the second glass melt 208 contained in the
silicate glass fragments 210, into hollow glass microspheres
212.
[0129] In accordance with yet other aspects of the present
invention, the RAG components 204 added to the first glass melt 206
are presented as solids and liquids in the form of a fine powders,
spray or fine droplets, solid aerosol, liquid aerosol, or a
combination thereof, and added as such to either the batch 200
and/or the first glass melt 206.
[0130] Solids, exemplarily in the form of either fine powders or
solid aerosol, are injected into the first glass melt 206 at
various locations in the melter system 300. For example, carbon in
form of coke or fine graphite powder in a gas carrier stream or
liquid carrier stream is injected into the first glass melt 206 to
induce reduction of the chemical species of the first glass 206 via
corresponding redox reactions. In the process, the carbon oxidizes
to carbon dioxide and/or carbon monoxide, leaving the melter system
300 through the off-gas system. Metal powders such as magnesium,
copper, iron, etc. also when added directly to the first glass melt
206 as a part of the RAG components tend to oxidize in the molten
glass without producing any appreciable gaseous reaction
products.
[0131] Liquids, exemplarily in the form of liquid aerosol,
slurries, and spray, are also injected into the first glass melt
206 at various locations in the melter system 300. For example,
solutions, slurries, organics liquids, hydrocarbons, fuels and
alike are injected with or without a gas carrier into the first
glass melt 206 to provide corresponding redox reactions.
[0132] The first glass melt 206 formed from a batch comprising the
SGP raw materials 202 and the RAG components 204 has a melting
temperature above 1000.degree. C., and preferably between
1200.degree. C. and 1500.degree. C.
[0133] Exemplarily, gaseous RAG components 204 are air, oxygen,
nitrogen, hydrogen, steam, hydrocarbons, gaseous organics,
CO.sub.2, CO, H.sub.2O (vapor), SO.sub.2, SO.sub.3, H.sub.2S,
NH.sub.3, and a combination thereof. Exemplarily, the injectable
liquid RAG components 204 are one or a combination of liquid water,
peroxide, sulfuric acid, liquid fuels, organic liquids, slurries,
and solutions of various chemical species. Exemplarily, the
injectable solid RAG components 204 are solid carbonaceous
materials such as anthracite powders, graphite powders, metallic
materials such as iron dust, and various chemical species such as
sulfur, nitrides, borides, carbides, etc.
[0134] As noted previously, if the SGP raw materials 202 already
include redox active components intrinsically, then the redox
active components comprised by the SGP raw materials 202 are
counted as a part of the RAG component 204. Solid RAG components
204 that may be intrinsically present in the SGP raw materials 202
include iron bearing minerals and oxides, multivalent metal oxides,
and sulfur bearing compounds and minerals such as gypsum, salt
cake, carbonaceous materials, such as carbon, or a carbon
containing material(s).
[0135] The first glass 206 preferably has a total alkaline metal
oxides content of less than 12 wt %, more preferably, less than 10
wt %, and most preferably less than 6 wt %. The preferred
concentration of sodium oxide in the first glass 206 is less than
10 wt %, and more preferably less than 8 wt %, and most preferably
less than 4 wt %. All the wt % (weight percentage) numbers are
calculated based on the mass of the first glass 206.
[0136] Discharging the first glass melt 206 from the melter may be
carried out by using a gaseous RAG component 204, or a gaseous
stream/carrier that includes a RAG component 204 to lift the glass
melt and discharge it out of the melter. According to this
embodiment of the invention, the gas stream has the dual function
of lifting the glass out of the melter 300 and providing the RAG
components 204 needed for triggering the non-equilibrium
reactions.
[0137] By discharging the melted batch 200 or the first glass melt
206, and as the glass cools to room temperature, the redox
reactions taking place in the glass melt are conveniently
terminated or stopped from progressing. There are different ways to
discharge the first glass melt 206 from the melter 300.
Exemplarily, the first glass melt 206 is discharged by an airlift
system, out of the melter system 300 from the side or from the top
of the melter 300. Another option is to gravity discharge the glass
from the bottom. It is also envisioned to discharge the glass by
overflowing into a trough as the glass inventory inside the primary
melt pool (e.g. melting zone 310) reaches a threshold. In another
melter configuration, the melter may be tilted in order to
discharge the glass.
[0138] Any or a combination of discharge methods may be employed to
adopt and couple the discharge operation to the steps of processing
the glass in step 106, such as simultaneous forming operation and
cooling the first glass melt 206. Exemplarily the discharge methods
are discharging the glass between air-cooled or water-cooled
counter rotating a pair of metal rollers to simultaneously forming
glass ribbons, and cooling the first glass melt 206.
[0139] In accordance with the present invention, the method 100
also comprises a step of processing 106 of the first glass melt
206, that was created at least by the step of melting the batch 200
at step 104. At step 106, the first glass melt 206 is processed
into a second glass 208.
[0140] In accordance with various embodiments of the present
invention, the processing step 106 comprises at least one or a
combination of the following steps: shaping/forming the discharged
first glass melt 206 and cooling the first glass melt 206.
[0141] According to the present invention, the glass that is
discharged from the melter 300 and cooled to room temperature is
identified as the second glass 208.
[0142] Within step 106, the first glass melt 206 is cooled forming
solid glass of various forms and shapes. The solid forms comprise a
plurality of flakes, fragments, ribbons, fibers, sheets, rods,
pellets, gems, spheres, or a combination thereof. It should be
noted that any other shapes of the second glass 208 are within the
scope and spirit of the present invention. In one embodiment of the
invention, a heat and steam recovery system is also employed to
recover either the heat and/or the steam liberated by the first
glass melt 206 during the cooling step 106. The recovered heat is
utilized for various purposes, including preheating the batch 200,
or for heating the primarily and the secondary air utilized in a
firing furnace in step 110.
[0143] In one embodiment of the present invention, air cooled or
water cooled steel rollers are used to cool and flatten the
discharging molten first glass 206 into a thin ribbon that can be
easily broken up into small fragments.
[0144] In accordance with another embodiment of the invention, the
discharging molten first glass 206 is water quenched by directing
and dropping the discharging molten first glass 206 directly into a
water bath. Due to thermal shock, in contact with water, the
suddenly cooled molten glass shatters into small fragments. This is
an effective way of cooling and fragmenting the molten first glass
206, followed by a drying step before further size reducing the
resulting fragments of second glass 208.
[0145] In accordance with one embodiment of the present invention,
upon cooling in step 106, the solid second glass 208 is pulverized
in step 108 to provide a plurality of glass fragments (SGF) 210
having a predetermined average particle size, and particle size
distribution. In accordance with one embodiment of the present
invention, step 108 includes one or more size reduction processes,
such as a coarse pulverization step followed by a finer size
reduction step, and a screening step.
[0146] According to the present invention one or a combination of
hammer mills, jaw crushers, and rotary crushers are used for coarse
grinding of the second glass 208. One of centrifugal mills, disc
mills, ball mills, jet mills, impact mills, high-speed rotary
mills, and similar equipment may also be used for finer size
reduction of the fragments obtained from the coarse grinding of the
second glass 208. Without being bound to a specific size reduction
method, fluid bed jet milling is a preferred method of fine
grinding and size reduction and classification of the glass
particles suitable for use as the plurality of glass fragments SGF
210. The fluid bed jet mill incorporates dense phase micronization
using opposing jets in combination with centrifugal air
classification, all within a common housing. This combination
allows for comminution/size reduction by particle on particle
impact for breakage and a high degree of particle dispersion for
improved separation resulting in a narrower particle size
distribution, zero to very low contamination, and a lower overall
energy consumption compared to other commercially available
techniques. This size reduction method ideally provides a top
particle size of about 150 microns, with a tunable narrow size
distribution at a desired range (for example between 50-120
microns), and having a tail end of the particle size distribution
at less than 5 wt % below 5 microns. Should larger top size SGF
fragments be desired, e.g. above 150 microns, a disc mill equipped
with an air classification unit is used.
[0147] The silicate glass fragments 210 are as well screened in
step 108. The undersized fraction of the silicate glass fragments
210 is optionally recycled back to the batch 200 in step 102 to be
blended in, or to be directly fed to the melter 300. On the other
hand, the oversized portion of the silicate glass fragments 210 is
optionally recycled back to the fine grinding step to be size
reduced. The preferred average particle size of the silicate glass
fragments 210 is determined by end use of the plurality of the
glass microspheres 212 manufactured in accordance with the present
invention. For example, if the glass spheres 212 are to be used in
the oil and gas well drilling cement (i.e. drilling mud), oil and
gas well casing, and oil and gas hydraulic fracturing applications,
the average particle size of the silicate glass fragments 210 is in
a range of 1-1000 microns, preferably in a range of 5-600 microns.
A typical ratio of the particle size of the hollow glass
microspheres 212 (spherical diameter) to the average particle size
of the silicate glass fragments 210 (e.g. equivalent spherical
diameter) is from 1.01 to 3.0 and preferably from 1.035 to 2.7. A
ratio of greater than one means the glass microspheres 212 are
expanded compared to the silicate glass fragments 210. Exemplary,
at a ratio of 1.5, a silicate glass fragment 210 at an average
particle size of about 100 microns forms a hollow glass microsphere
212 of an approximate average particle size of 150 microns. The
particle density (apparent density) of such glass microsphere is
estimated from the expression:
.rho..sub.h=.rho..sub.f(d.sub.f/d.sub.h).sup.3
where .rho..sub.h, and .rho..sub.f are the apparent particle
density of the glass sphere 212, and of the silicate glass fragment
respectively, and d.sub.f, and d.sub.h are the mean diameter of the
silicate glass fragment 210, and of the glass sphere 212,
respectively. The apparent and true densities of the glass fragment
210 are essentially equal, with the assumption that there are no
substantial internal porosities in the glass fragment 210. Assuming
an apparent particle density of 2.4 g/cc for the silicate glass
fragments, the estimated particle density of the glass microsphere
212, having a particle size of about 150 microns is about 0.7-0.75
g/cc at a ratio of 1.5. Exemplarily, at a ratio of 2.4, the
resulting hollow glass microsphere 212 would have a particle size
of about 240 microns, and an approximate particle density of about
0.17-0.18 g/cc.
[0148] The above examples assume that the apparent particle density
of the plurality of glass fragments 210 is about 2.4 g/cc (e.g.
equal to the particle true density). It must be understood that the
glass fragments 210 may include micro-bubbles throughout their
volume, and as a result have a lower apparent particle density than
2.4 g/cc. Nevertheless, according to the present invention the
glass fragments 210 are considered substantially solid.
[0149] The method 100 of manufacturing a plurality of glass
microspheres further comprises the step 110 of thermally processing
the plurality of silicate glass fragments 210 to convert said
plurality of silicate glass fragments 210 into a plurality of glass
microspheres 212. Said conversion occurs due to the provision of at
least one of a plurality of redox reactions and plurality of events
in at least one of the first glass melt 206, and a melt of the
second glass 208, the plurality of redox reactions and the
plurality of events being induced by a plurality of redox active
group (RAG) components 204.
[0150] In step 110, the plurality of glass fragments 210 is heated
in a furnace, preferably in a suspended state, to a temperature
where the viscosity of the glass is less than 10.sup.5 poise,
preferably less than 10.sup.4 poise, and most preferably less than
10.sup.3 poise, temperature at which the silicate glass fragments
210 assume a round shape while residing in the suspended state
inside the furnace. A temperature at which the above enumerated
conditions are fulfilled is denominated the "firing temperature"
and the time necessary for the above enumerated conditions to occur
is denominated "residence time". The redox reaction(s) induced or
associated with the RAG components 204, this time present in the
second glass melt 208, (including the reaction products of the RAG
components formed previously by the non-equilibrium redox reactions
in the first glass melt 206) generate at least one gaseous product
expanding the softened plurality of glass fragments 210 into a
plurality of hollow glass microspheres 212 while in the
furnace.
[0151] The plurality of glass fragments 210 comprise the second
glass 208.
[0152] The redox reactions occurring in the second glass melt 208
are affected by either one of the oxygen concentration and the
fugacity in the furnace hot zone within the atmosphere surrounding
the softened plurality of silicate glass fragments 210. The redox
reactions that are triggered by the RAG components 204 within the
softened glass fragments 210 are somewhat sensitive to the oxygen
fugacity within the heated zone of the furnace.
[0153] According to the present invention, the process of gas
generation within the heated glass fragments 210 coincides with the
formation of fluxes that tend to lower the melting temperature of
the second glass 208. The redox reactions associated with the RAG
components 204 provide gaseous products that expand the molten
plurality of silicate glass fragments 210 into the hollow glass
microspheres 212. Also, the redox reactions associated with the RAG
components 204 provide fluxing oxides that lower the melting
temperature of the second glass 208 as compared to the melting
temperature of the first glass 206. In order to facilitate the
occurrence of the redox reactions in the second glass melt 208 in
accordance with one embodiment of the present invention, an
appropriate atmosphere for the operation of the firing furnace is
established, while the glass fragments 210 are being heated,
melted, and expanded into the glass microspheres 212. It has been
found that firing a gas burner near its stoichiometric
oxygen-to-gas ratio provides said appropriate atmosphere and is an
appropriate condition in the furnace that provides a relatively
neutral atmosphere surrounding the silicate glass fragments 210
while in the hot zone of the furnace.
[0154] In accordance with an embodiment of the method of the
present invention, heating and converting the silicate glass
fragments 210 to a plurality of glass microspheres 212 occurs by
heating them in a combustion zone inside a fossil fuel-fired
furnace, in particular a gas-fired furnace. In such a
configuration, the combusting process provides the necessary heat
for converting the silicate glass fragments 210 to the hollow glass
microspheres 212. In addition, the air-gas mixture entering the
furnace, and the combustion flu gases exiting the furnace, provide
gas phase transfer for the silicate glass fragments 210, and for
the glass microspheres 212 in and out of the combustion zone of the
furnace, respectively.
[0155] In accordance with the present invention, other heating
sources may be employed instead of or in combination with a fossil
fuel fired furnace. These heating sources include but are not
limited to electric heating, plasma heating, RF heating
(microwave), and IR (infrared) heating. The fossil fuels according
to the present invention may comprise a variety of gaseous fuels,
such as natural gas, propane, liquid fuels, such as heavy liquid
fuel oils, distillate fuels, such as kerosene, solid fuels, such as
coal and other organic solids, and a combination thereof. The
preferred fuel is natural gas, which is readily accessible in the
most geographical areas, burns clean, suits the widely available
range of burner configurations, and is suitable for co-feeding of
solid particles.
[0156] In accordance with one aspect of the invention, the
gas-fired furnace employed is preferably of the vertical type, in
which the combustion of air and gas creates a turbulent combustion
zone. As the temperature of the silicate glass fragment 210 reaches
the working temperature of the second glass 208 (e.g. working
temperature corresponds to a glass viscosity of about 10,000 poise)
the fragments assume a viscoelastic state, at which they are
capable of entrapping gaseous products being created via the redox
reactions or by other means, and are capable to expand. The
expansion action forces the silica glass fragments 210 to blow from
inside out to form the plurality of hollow glass microspheres 212.
Thereinafter, the plurality of hollow microspheres 212 is conveyed
out of the furnace by the combustion flu gases. Preferably, a
predetermined volume of cooling air is introduced downstream from
the combustion zone to cool the glass microspheres 212, while the
glass microspheres 212 are being conveyed out of the furnace.
[0157] It is important that the softened glass fragments 210 and
the newly formed glass microspheres 212 do not impinge on the
interior hard surfaces of the furnace. Otherwise, they will adhere
to the interior hard surfaces forming a tacky layer that leads to a
sticky substrate that encourages further glass build-up during the
operation of the furnace. In addition, there should be enough
separation distance between the glass particles in the furnace in
order to avoid particle-to-particle interaction/impingement to the
extent possible; otherwise, the agglomeration of particles becomes
a problem. The glass layer buildup on walls or the interior
surfaces of the furnace in accordance with one embodiment of the
present invention is stopped by providing an air curtain near the
wall to keep the particles away from the wall, or by other known
techniques. Particle to particle impingement frequency is minimized
by reducing the amount of particle loading of the silicate glass
fragments 210 in the gas phase, entering and exiting the combustion
zone of the furnace.
[0158] The plurality of the glass microspheres 212 is immediately
cooled after exiting the combustion zone of the furnace in step
112. Cooling air and/or dilution air is introduced inside the
furnace downstream from the combustion zone, which cools the glass
microspheres rapidly to below the softening temperature of the
glass. Additionally, cooling air and/or dilution air may also be
introduced in the ductwork after the furnace that is leading to the
off-gas treatment system. In the off-gas treatment system, the
plurality of hollow glass microspheres 210 is separated from the
carrier gases (e.g. flu gas plus dilution air) in cyclones and/or
various filtering systems. The plurality of hollow glass
microspheres 210 is then cooled to room temperature by appropriate
means, collectively in step 112. Mechanical and/or pneumatic means
are used for further transport of the glass microspheres 212 to
storage areas or to loading stations within or outside the
manufacturing facilities. Sampling ports are provided at various
locations downstream from the furnace to collect samples of the
glass microspheres 212. Samples are analyzed at least for the bulk
and particle densities, and percentage of sinkers and floaters.
Based on the results revealed by the sample analysis, appropriate
corrective actions may be carried out to adjust the desired
properties of the spheres, including but not limited to adjusting
the firing temperature, the residence time, and the ambient
atmosphere in the furnace.
[0159] The need and the availability of the RAG components 204 that
are added to the first glass melt 206 is ascertained as well by
measuring the density of the produced glass microspheres 212.
Should the density of the glass microspheres 212 produced be lower,
then more gas is necessary to produce glass microspheres 212 with a
lower density. Therefore, as much more RAG components are added to
the first glass melt as needed. This is after the firing
temperature and the residence time in the furnace are optimized and
fixed. As such, RAG components 204 with larger capability of gas
generation should be included in the second glass melt 208. The
necessary RAG components may be added to the first glass melt 206
in the melter system 300 as one option, and to the batch 200, as
another option. One advantage of adjusting the RAG components in
the glass melter 300, and specifically, in the processing and/or
discharge zones of the melter system 300, as opposed to making a
corrective action in the batch 200 is that it takes a significantly
shorter turn around time to accomplish the corrective action on the
density of the produced glass microspheres 212. Another advantage
is that a relatively low volume of potential glass reject, which is
off the desired specification, needs to be dealt with. The
capability of adjusting the RAG components 204 in the melter system
300 also makes it possible to manufacture glass microspheres 212
with varying densities on a non-interruptive basis. Hence, the
present invention provides a method of adjusting or varying
densities of the glass microspheres in a very quick and efficient
way via adjustments of the RAG components 204 in the melter system
300. Exemplarily, the particle density of the glass microspheres
212 is a sensed parameter (for example measured by a pycnometer)
that is fed back to a control mechanism that adjusts the RAG
components (e.g. types and amounts) in a closed or open loop
control fashion. The control tactic or methodology is built in an
existing empirical database that includes the variation of the
sensed parameter (e.g. density) as a function of types and amounts
of the RAG components 204. It would be apparent to a person skilled
in the art as how such a control mechanism may be implemented, for
example manually and/or automatically.
[0160] The residence time in the furnace is determined as the
average time that the glass fragments spend in the heated zone of
the furnace. Therefore, the residence time is calculated as the
length of the heated zone of the furnace divided by the linear
velocity of the silicate glass fragments 210 travelling through the
heated zone. The residence time of the glass fragments in the
furnace is within a fraction of a second to less than 10 seconds,
and preferably from 0.2 seconds to 4 seconds. However, a residence
time outside the range specified above is as well within the scope
of the present invention. In general, the residence time is a
function of the peak firing temperature and reflective radiative
heating inside the furnace, which is controlled by the geometry and
operating mode of a firing furnace.
[0161] Exemplarily, the furnace may be a vertical furnace that is
fed with the silicate glass fragments 208 in an upward, or a
downward fashion. It is also within the scope of the present
invention to utilize a firing furnace that is not vertically
oriented, such as a horizontally oriented furnace, and an inclined
oriented furnace. The orientation is defined as the direction
parallel to the longest axis of the furnace. An inclined oriented
furnace has a non-zero angle between the furnace orientation and
the horizontal direction.
[0162] In accordance with one aspect of the present invention, the
silicate glass fragments 210 resulting from grinding the second
glass 208 are substantially free of large gas bubbles, but may
contain advantageously micro-sized gas bubbles and/or nucleated
micro-bubbles.
[0163] Nucleated micron and sub-micron size bubbles (collectively
called micro-bubbles) formed within the first glass melt 206 due to
the occurrence of non-equilibrium redox reactions comprising any
one or a mixture of gaseous SO.sub.2, SO.sub.3, O.sub.2, CO.sub.2,
H.sub.2, CO, N.sub.2, NO.sub.N, H.sub.2O, etc., and carried over to
the second glass 208 are tolerable in accordance with the present
invention. The nucleated micro-bubbles in the second glass 208 are
carried through the remainder of the glass pulverizing operations,
and eventually are retained within the resulting silicate glass
fragments 210. The total volume of the micro-bubbles within a
silicate glass fragment 210, compared to the total volume of the
silicate glass fragment 210 is relatively small, i.e. several
percentage points or less. As the silicate glass fragments 210 are
reheated in the furnace to the firing temperature, the nucleated
micro-bubbles expand and grow in size, an event that is referred to
according to the present invention as "thermal reboil". The growth
rate of the nucleated bubbles in the second glass melt 208 becomes
significant above 1100.degree. C., and especially between
1200-1500.degree. C. The thermal reboil alone and/or in combination
with the other gas generation means, such as physical reboil, redox
reactions, and sublimation, leads to the formation of the hollow
glass spheres 212. These aspects of the present invention will be
explained in detail in the remainder of the present document.
[0164] In accordance with another aspect of the present invention,
physical reboil, which is also the result of incorporating the RAG
components 204 either in the batch 200, and/or to the first glass
melt 206 in the melter system 300, contributes as well to the
expansion of the silicate glass fragments 210 to hollow glass
microspheres 212. The physical reboil process occurs due to changes
in the solubility of the chemical species in the glass melt as a
function of temperature under atmospheric conditions. The onset and
the rate of the physical reboil gas evolution is affected by the
composition of the second glass melt 208, as well as by changes in
the furnace ambient conditions, that affect the solubilities of
dissolved gases in the second glass melt 208. For example, in one
embodiment of the present invention, the presence of sulfur as
sulfate in the second glass 208 leads to "sulfur reboil" upon
heating the silicate glass fragments 210 in the furnace. For
example, the solubility of dissolved SO.sub.3 in the second glass
melt 208 decreases by about 3 orders of magnitude upon heating from
1100.degree. C. to 1400.degree. C. Hence, in the event that the
concentration of SO.sub.3 in the second glass is such that it
exceeds the solubility limit above 1100.degree. C., a physical
reboil occurs which is associated with the release of SO.sub.3 from
the interior of the silica glass fragments 208, resulting in
expansion of the silica glass fragments 210, and thus in the
formation of the hollow glass microspheres 212. The onset of the
physical reboil is also dependent on the equilibrium partial
pressure of oxygen in the heating zone of the furnace. The
phenomena of the thermal reboil, sublimation, and the physical
reboil are referred to further generally as a plurality of events
that take place in the melt of the second glass 208.
[0165] Aside from the thermal and physical reboils, the present
invention relies primarily on the RAG components 204 to provide
redox reactions capable of generating gaseous reaction products to
expand the silicate glass fragments 210 into the plurality of
hollow glass microspheres 212, as it will be disclosed later in
more detail.
[0166] The chemical reactions occurring in the second glass melt
208 in accordance with the present invention comprise one or more
of reactions involving decomposition, oxidation, dissociation,
reduction, and recombination of chemical species associated with
the RAG components 204. Other forms of gas generation in a melt of
the second glass 208 due to physical events or processes such as
nucleation, saturation, evaporation, and sublimation are also
within the scope of the present invention, and are considered under
the category of the plurality of events. Irrespective of how the
gas is generated, the gaseous products as they are being generated
are either trapped, or entrapped, or entrained, or a combination
thereof in the second glass melt 208 from which the silicate glass
fragments 210 are formed, and aid in forming the plurality of
hollow glass microspheres 212.
[0167] Preferred RAG components 204 in the batch 200 comprise
sulfur (in the form of one or more of sulfates, sulfites, and
sulfides), multivalent metals, and transition metals in the form of
compounds and chemical species, and various carbonaceous materials
including carbon itself. As mentioned earlier, RAG components 204,
in the form of gaseous, liquids, aerosols (solids and/or liquids)
may be mixed, or injected, or purged, or bubbled, or a combination
thereof, into the first glass melt 206. Common gaseous reaction
products generated during RAG components redox reactions (also
referred to as RAG reactions) include SO.sub.3, SO.sub.2, H.sub.2S,
CO.sub.2/CO, H.sub.2O, O.sub.2, NH.sub.3, and NO.sub.R. Other
gaseous species that might be present, such as entrapped air, and
nitrogen are not considered a direct gaseous reaction product. All
the gaseous reaction products can be also used as gaseous RAG
components to be purged or bubbled inside the first glass melt 206
in addition to those listed before.
[0168] CO.sub.2 and/or CO gas is released during the decomposition
of carbonates, and/or due to oxidation of carbonaceous materials of
the RAG components 204. The carbonaceous materials of the RAG
components 204 include bonded carbon (in organic substances),
unburned carbon (UBC) that is found in thermally processed
industrial byproducts, graphite, carbide, coke, anthracite,
carbocite, loose carbon powders, etc.
[0169] Sulfur containing gaseous reaction products are present when
sulfates/sulfites/sulfides are included as a part of SGP raw
materials 202 and/or the RAG components 204. According to the
present invention, all the sulfate/sulfite/sulfide ions,
multivalent and transition metal ions, and carbonaceous materials
either in elemental or compound forms, other than carbonates in the
resulting first glass melt, are considered to be the constituents
of the RAG components 204, regardless of having been introduced
intrinsically with the SGP raw materials 202, and/or with the RAG
components 204.
[0170] With respect to the sulfur portion of the RAG components
204, it is of note that sulfur solubility is sensitive to the
oxidation state of the first glass melt 206. Under reducing
conditions, sulfur dissolves as sulfide ions, and as sulfate, while
under oxidizing conditions. The reduction of the oxygen partial
pressure inside or outside the first glass melt 206 shifts the
equilibrium between sulfide and sulfate towards sulfide, with a
reduction in overall sulfur solubility, resulting in degassing the
first glass melt 204 by releasing SO.sub.2. Hence, the sulfide
solubility is generally lower than the sulfate solubility in the
first glass melt 206. Changes in the chemistry of the first glass
melt 206 also alter the overall sulfur solubility (sulfates and
sulfides are referred to in general way as sulfur). In addition,
the overall sulfur solubility depends on the first glass melt 206
temperature, since the sulfate solubility decreases with increasing
the temperature, while the solubility of sulfide increases with
increasing the temperature. Therefore, changes of temperature of
the first glass melt 206 affect the concentration of sulfur, in the
forms of sulfate and sulfide, in opposite directions.
[0171] For example, to yield sulfides from sulfate in the first
glass melt 206, (since the source of sulfur in the RAG component
204 is primarily sulfate), a reducing RAG component, such as
carbon, is included in the batch 200, and/or directly introduced
into the first glass melt 206 while inside the melter system 300.
Since redox reactions are time and temperature dependent, according
to the embodiments of the present invention, a desired balance
between the concentrations of sulfide and sulfate in the first
glass melt 206 is achieved by adjusting the residence time of the
first glass melt 206 in the melter system 300. Said adjustment may
be performed to adjusting the redox state of the first glass melt
206, that is controlled by the introduction of additional RAG
components 204 directly to the first glass melt 206, and the
ambient conditions of the melter system 300.
[0172] In accordance with one aspect of the present invention, the
plurality of redox reactions comprise the reaction of sulfates with
sulfides in the second glass melt 208.
[0173] The solubility of sulfur decreases with decreasing the
alkali content of the first glass melt 206. The amount of sulfate
ions (as SO.sub.4) in the first glass melt 206, according to the
present invention, is typically less than 5 wt % based on a
combined mass of batch 200 that includes both the SGP raw materials
202 and the RAG components 204. The solubility of sulfate as
SO.sub.4 in a typical first glass melt 206 according to the present
invention is from about 0.2 to about 2.0 wt % based on the mass of
the first glass 206. Alkali sulfates, when present in the batch
200, melt at a temperature of around 900.degree. C., and remain in
the first glass melt 206 as sulfate under an oxidizing condition
until appreciable decomposition starts to occur, at or above
1100.degree. C. In a continuous melting operation, the temperature
rise occurs in the cold cap region, whereby the temperature of the
fresh batch 200 on the top is considerably cooler than the batch
temperature that is near the molten glass underneath.
[0174] In the presence of reducing components in the RAG components
204, such as the presence of unburned carbon, the decomposition of
sulfates occurs at a lower temperature, e.g. around 800.degree.
C.
[0175] Should an oxygen sink, internal or external to the first
glass melt 206, or an oxygen getter, enter the first glass melt 206
as a part of the gaseous RAG components 204, the oxygen from the
sulfate ion is consumed and/or scavenged in the first glass melt
206, and SO.sub.2 gas is released. The results may be interpreted
in terms of sulfate solubility and non-equilibrium effects. For
example, when a multivalent metal ion, such as iron, is present as
a part of the RAG components 204, both reduced and oxidized forms
of sulfur (e.g. sulfate and sulfide), and iron (e.g. ferrous and
ferric) may coexist in the first glass melt 206, and subsequently
in the second glass melt 208 that forms the silicate glass
fragments 210, as a result of the non-equilibrium redox reactions
taking place in the first glass melt 206.
[0176] According to an embodiment of the present invention, a
composite redox value, calculated based on a concentration of the
at least one electron donor component and on a concentration of the
at least one electron acceptor component in said first glass 206,
is used to determine the amounts and types of the RAG components
that are to be incorporated into the first glass 206. In addition,
when the entire quantity of RAG components 204 is not incorporated
from the beginning into batch 200, the composite redox value takes
into account any RAG components 204 in any forms that are to be
incorporated into the first glass melt 206 within the melter system
300, in addition to taking into account the amounts added in the
batch 200.
[0177] Exemplarily, when the RAG components 204 are incorporated
directly into the first glass melt 206, normally the rate of their
addition is reported as a mass flow rate. One way to convert the
mass flow rate to concentration is as follows: Since the mass of
glass produced per unit time is generally known, then the wt % of a
particular RAG component on a mass basis of the first glass melt
206 is calculated as:
(M.sub.RAG*100)/(M.sub.Glass+M.sub.RAG)
where, M.sub.RAG is the mass flow rate of the particular RAG
component in kg/hr, and M.sub.Glass is the mass of glass produced
in kg/hr, prior to incorporation of the particular RAG component.
Different units for mass flow rate may be used, however, the unit
used has to be the same unit as the one used for reporting the mass
of the glass produced per unit time.
[0178] The composite redox value is calculated based on
concentrations of the RAG components 204 in the first glass melt
206. As mentioned earlier, the RAG components 204 overall are
either electron donors or acceptors. To calculate the composite
redox number, factors are assigned to the corresponding
concentrations of the RAG components 204 in the first glass 206, in
wt %. The factors are: for carbon as elemental carbon (-7.0), for
sulfate as SO.sub.4 (+0.5), nitrates as NO.sub.3 (+0.2), and
sulfides as S (-0.6). Should other components be present in the RAG
204 a skilled person would know how to assign the applicable
coefficients to said components based on tables available in the
art. In the above example, a positive factor indicates an oxidizing
chemical species, and a negative factor indicates a reducing
chemical species. For example, in a situation whereby the first
glass melt 206 comprises approximately 2 wt % sulfate as SO.sub.4,
and 0.4 wt % carbon, as C, the composite redox number is calculated
as:
Composite redox number=2*(+0.5)+0.4*(-7.0)=-1.8.
[0179] According to the present invention, the composite redox
number of the first glass melt 206 is negative, preferably between
-0.05 to -20, and more preferably between -0.1 to -10. As such, the
composite redox value of the redox active group components is less
than zero. In other embodiments of the invention the composite
redox value is equal to zero.
[0180] According to various embodiments of the present invention,
sulfates, may be in the form of alkaline earth metal sulfates, such
as calcium and magnesium sulfates, alkali metal sulfates such as
sodium and potassium sulfates, multivalent, and transition metal
sulfates, such as zinc, copper and iron sulfates, and a combination
thereof. The term "sulfates" encompasses sulfites, bi-sulfite, and
bi-sulfates. The solid sulfides, in general may be in the form of
any metal sulfides, preferably in the form of multivalent, and
transition metal sulfides, such as zinc and iron sulfides. Bounded
sulfides from slag, and iron pyrite FeS.sub.2, other stable metal
sulfides, may be used as well. Gaseous hydrogen sulfide is a source
of sulfide directly incorporable into the first glass melt 206
while in the melter system 300. The slag resulting from some
incineration processes (e.g. municipal waste incineration) is an
economical source of sulfides, with the majority of sulfide being
in the form of iron sulfide. Iron pyrite in most cases loses one
sulfur atom at relatively low temperatures, which combines with
oxygen and is being released as SO.sub.2 from the batch at a
relatively low temperature, e.g. below 800.degree. C.
[0181] According to the embodiment of the present invention,
wherein essentially all the RAG components 204 are incorporated
into the batch 200, as a general guideline, the concentrations of
several common RAG components 204 in the batch 200 in weight
percentage based on the mass of the first glass 206 are as follows:
sulfates, calculated as SO.sub.4, from 0.1 to 5 wt %, sulfides,
calculated as S, from 0 to 2 wt %, carbonaceous materials,
calculated as C, from 0 to 3 wt %, multivalent metal oxides from
0.1 to 20 wt %, and for nitrates/nitrites/nitrides, calculated as
N, from 0 to 2 wt %. All or a portion of the RAG components
comprising sulfates and multivalent oxides are preferably
incorporated into the first glass melt via the batch 200, while
other RAG components 204 are incorporated either via the batch 200,
and/or via direct addition to the melter system 300, depending on a
target composition of the RAG components 204 in the second glass
208.
[0182] A transition metal present in the RAG components 204,
according to an embodiment of the present invention, is iron.
Ferric ion based on its ionic potential is a weak acid in the glass
network, meaning that it can participate in the glass network in a
similar manner with aluminum and boron ions. On the other hand,
ferrous ion is a base and has the tendency to donate electrons to
the glass network (in particular to the oxygen ions), similarly to
calcium and magnesium ions. In terms of glass structure, ferrous
ion acts as a glass network modifier lowering the viscosity of the
glass, whereas ferric oxide in most cases becomes a part of the
glass network formers, leaving the viscosity practically unchanged
or slightly higher. In terms of glass making, lowering the
viscosity of a glass is normally associated with lowering the
melting temperature of the glass.
[0183] According to one embodiment of the present invention, in
order to lower the melting temperature of the second glass 208
compared to the first glass 206, an increase in the concentration
of ferrous oxide relative to the total concentration of iron, as
iron oxide in the second glass 208 takes place. This is
accomplished by in-situ formation of ferrous oxide from the iron
compounds present in the second glass melt 208 in the process of
producing hollow glass microspheres. Since the first glass melt 206
is the precursor to the second glass 208, the relative
concentration of the iron compounds in the first glass melt is
adjusted in the melter system 300 by incorporating the appropriate
RAG components 204 into the first glass melt 206. The RAG
components 204 are incorporated into the first glass melt 206 in
the form of gases, vapors, liquids, solids, aerosols and a
combination thereof. The incorporation of the RAG components 204
into the first glass melt 206 while in the melter system 300, is
carried out by one or a combination of blending, injection,
bubbling, spraying, dipping, and stirring in an appropriate
section/compartment of the melter system 300, including the melting
zone 310, the processing zone 320, discharge zone 330, or in a
combination thereof. In one exemplary embodiment, the first glass
melt 206 is melted under neutral melting conditions, and as such,
the majority of iron in the first glass melt 206 remains in the
ferric form in the glass pool within the melting zone 310. At least
one reducing RAG component 204 is introduced into the first glass
melt 206 while in the processing zone chamber 320. The reducing RAG
component 204 may be selected from a variety of fluids and/or
solids, for example an aerosol of carbon particles in air, a
hydrocarbon gas such as acetylene, hydrogen sulfide,
hydrogen/nitrogen mixtures, and alike. The reducing RAG component
204 is bubbled, injected, or sprayed into the first glass melt 206
in the processing zone 320 of the melter 300 or the discharge zone
330 depending on the desired residence time associated with the
non-equilibrium redox reactions involved. By proceeding this way,
the relative concentration of the iron compounds in the first glass
melt 206 is adjusted, and/or residual carbonaceous materials are
introduced into the glass melt 206, as another source of gas
formation while producing the hollow glass microspheres 212.
[0184] Accordingly, during thermally processing the glass fragments
210 in step 110 to produce the plurality of glass microspheres 212
the concentration of cationic ferrous iron in the second glass melt
208 is increased. Consequently, the viscosity of the second glass
melt 208 is lowered, and so is the melting temperature of the
second glass melt 208, by comparison with the melting temperature
of the first glass melt 206.
[0185] According to another embodiment of the present invention, to
shift the balance of iron to ferrous oxide, a portion of the
sulfate comprised in the RAG components 204 is converted to sulfide
in the first glass melt 206. One method to accomplish this shift is
by including carbonaceous materials, such as carbon, in the RAG
components 204, by either incorporating them in the batch 200,
and/or directly into the first glass melt 206 in the melter system
300. Carbon, as a part of the carbonaceous materials, scavenges
oxygen primarily from sulfate/sulfites during the non-equilibrium
redox reactions and in the process forms iron sulfide, CO.sub.N,
and possibly SO.sub.2. In one embodiment elemental sulfur as a part
of the RAG components 204 is incorporated in the same manner as
described in connection with the carbon example above into the
first glass melt, which results in the formation of iron sulfide in
the first glass melt 206. In another embodiment, iron sulfide
and/or iron pyrite as a part of the RAG components 204 is
incorporated, in the same manner as described in connection with
the carbon example disclosed above into the first glass melt, which
also results in the formation of iron sulfide in the first glass
melt.
[0186] In accordance with other embodiments of the present
invention, similar chemical species to the sulfate-sulfide pair may
also be used in the same manner as described above in connection
with the sulfate-sulfide pair. An example is the selenite-selenide
pair, SeO.sub.3.sup.2---Se.sup.2-.
[0187] Exemplarily, the redox reaction involving ferric iron and
carbon from a carbonaceous source in the first glass melt 206 is
carried out in a non-equilibrium manner to convert less than 80% of
the total iron to ferrous iron (e.g. ratio of ferrous iron to total
iron less than 0.8). To accomplishing the above, the parameters
that need to be controlled include: the type and concentration of
the RAG components to be incorporated into the first glass melt
206, the melting time/residence time of the first glass melt 206 in
the melter system 300, the agitation/bubbling rate and methods
applied to the first glass melt 206, and the redox environment of
the melter system 300. As a result of the non-equilibrium redox
reactions in the first glass melt 206, the preferred RAG components
204 reaction products, and chemical species that remain in the
second glass 208 preferably comprise at least one of sulfide,
sulfate, carbon compound, and iron. Other oxidizing and reducing
chemical species analogous to sulfur compounds, multivalent metals,
and other transition metals can be used in addition or instead of
sulfur compounds and iron for the same purpose.
[0188] According to the present invention, the conversion of the
first glass melt 206 into the second glass 208 occurs outside the
melter system 300. The conversion occurs when the first glass melt
206 is cooled to form the second glass 208. Hence, in a broad
scope, the glass being discharged from the melter system 300 is
essentially the first glass melt 206 being converted to the second
glass 208. It is also possible to characterize the composition of
the second glass melt 208 as being essentially the same glass
composition as being discharged from the melter system 300.
Further, the composition of the silicate glass fragments 210 is
essentially the same as the composition of the second glass 208,
and wherein the second glass 208 has been fragmented.
[0189] In accordance with one embodiment of the present invention,
sulfides are introduced into the batch 200 as part of the RAG
components 204. For example, iron sulfide is provided as part of
the RAG components 204 either by introducing into the batch 200 or
by forming it in-situ in the melter system 300 by bubbling hydrogen
sulfide in the first glass melt 206. This is similarly the case as
well for ferrous iron, ferric iron, and sulfate/sulfites that may
be incorporated in the first glass melt 206 as a part of the RAG
components 204, to provide the desired concentration of iron
sulfide, ferrous-ferric ions, and sulfate ions to be carried over
into the second glass 208.
[0190] The sulfur in the RAG components 204 that is introduced to
the batch 200 is provided from one or more of salt cake, gypsum,
metal sulfates and bi-sulfates, iron pyrite, slag, flyash, bottom
ash, and other waste byproducts and recycled materials. In addition
or alternatively, a sulfur source may be introduced into the melter
system 300 and be incorporated into the first glass melt 206, to
compensate or replace the source of sulfur in the batch 200. The
sources of RAG components to the first glass melt 206 according to
a broader scope of the present invention, may be supplied either to
the batch 200, or by direct incorporation into the first glass melt
206 while in the melter system 300, or both.
[0191] According to the present invention, the sulfide to sulfate
ratio (e.g. S.sup.2-/SO.sub.4.sup.2-) in the second glass 208
affects the viscosity of a second glass melt 208 as related to the
ratio of Fe.sup.+2/Fe (Fe represent total iron in the glass). The
reaction between sulfide and sulfate in the second glass 208
provides the gaseous reaction product(s) required to form the
hollow glass microspheres 212 in step 110. In the presence of
multivalent metal cations, such as iron in the second glass 208, as
the molar ratio of sulfide to sulfate is increased, the ratio of
Fe.sup.+2/Fe (total) is also increased.
[0192] According to the present invention, due to the
non-equilibrium redox reactions taking place in the first glass
melt 206, it is possible to create iron sulfide in situ co-existing
with the sulfate in the first glass melt 206. The combination of
sulfide-sulfate is carried over to the second glass 208, and it has
simultaneously the double advantage of providing gaseous reaction
products that serve to manufacture hollow glass microspheres 210
from the molten silicate glass fragments 208, and of lowering the
melting temperature of the second glass melt 208. The redox
reaction between iron sulfide and sulfate in the second glass melt
208 of the silicate glass fragments 210 provides the network
modifier/flux of ferrous oxide that lowers the melting temperature
of the second glass 208, as compared to the melting temperature of
the first glass 206, without sacrificing the chemical durability of
the resulting plurality of the glass microspheres 210.
[0193] The decomposition of sulfates while melting the first glass
206, without and with the presence of carbon is presented in
reactions (1) and (2), respectively:
SO.sub.4.sup.2-SO.sub.3+O.sup.2- (1)
SO.sub.4.sup.2-+C-->SO.sub.2+CO+O.sup.2- (2)
[0194] As it may be observed above in accordance with the reaction
(1), the sulfate ion SO.sub.4 decomposes into sulfur trioxide
SO.sub.3 and one oxygen ion (e.g. O.sup.2-). This reaction occurs
in the absence of reducing components. However, when a reducing
component, such as carbon, is present in the RAG components 204,
the sulfate ion in combination with carbon follows reaction (2),
whereby it decomposes into sulfate dioxide SO.sub.2, an oxygen ion,
and CO. The reaction (2) is generally the rate-controlling step for
reaction (1), requiring a reducing component such as carbon. In a
situation when an oxidized multivalent metal oxide is also present
as a part of the RAG components 204, the oxygen required to oxidize
a reducing component is primarily supplied by sulfates in the first
glass melt 206 as a primary source, and by the multivalent metal
oxide, such as ferric oxide, as a secondary source. As the melting
of the batch 200 into the first glass melt 206 progresses, the
carbon first reduces the sulfates to gaseous SO.sub.2, and
secondly, ferric iron to ferrous iron, and in the process the
negative redox ratio of iron (Fe.sup.+2/Fe total) increases. In the
process, depending on the amount of carbon available in the first
glass melt 206, sulfides may also form in the first glass melt 206
according to following reaction:
SO.sub.4.sup.2-+2C--->S.sup.2-+2CO.sub.2 (3)
[0195] If in the process of the oxidation of carbon, according to
the reaction (3), CO is also created, the following reaction takes
place, when sulfate ion or other oxygen sources are available in
the first glass melt 206:
SO.sub.4.sup.2-+4CO--->S.sup.2-+4CO.sub.2 (4)
[0196] Reaction (3) is analogous to reaction (2), with the
exception that the molar ratio of carbon to sulfate ion is two
times larger. Reactions (3) to (4) are redox reactions presenting
the in-situ creation of sulfides in the first glass melt 206. As
previously disclosed, the carbon is provided by the RAG components
204, included either in the batch 200, and/or incorporated into the
first glass melt 206 while processing in the melter system 300.
[0197] The reactions (3) and (4) may be fashioned with iron as the
multivalent metal cation in combination with the sulfide ion. In
accordance with the present invention, it is possible that other
multivalent metal ions present in the first glass melt 206 also
participate in conjunction with the ferrous/ferric ions in the
above reactions.
[0198] It is also possible to incorporate elemental sulfur into the
first glass melt 206, which reacts with the metal ions present in
the first glass melt 206 to produce sulfides. The reactions (3) and
(4) above demonstrate that carbon is capable to shift the overall
valence state of the sulfur from sulfate (also sulfite) to sulfide.
These reactions occur at a temperature above 900.degree. C. One
advantage of incorporating carbon into the first glass melt 206
while in the melter system 300 is that the first glass 206 is
melted in the melting zone 310 under neutral or in fact oxidizing
conditions in order to prolong the life of the electrodes, and
contact refractories. The incorporation of carbon is subsequent to
the melting process and is carried out in the processing zone 320
of the melter system 300, which in accordance with one embodiment
of the invention is substantially isolated from the melting zone
310. In the melter system 300, the zones are designed such that the
first glass melt 206 flows substantially in a one-way direction
from the melting zone 310 to the processing zone 320, and from the
processing zone 320 to the discharge zone 330. In a situation where
a molten salt layer comprising sulfates is formed over the first
glass melt 206, the sulfate layer is reduced to primary SO.sub.2
gas with the incorporation of a carbonaceous RAG component directly
into the first glass melt 206 while in the melter system 300.
[0199] According to the present invention, the redox reactions (3)
and (4) occurring in the first glass melt 206 are terminated before
reaching equilibrium and/or completion. As it was disclosed
previously, it is advantageous to have a combination of sulfate and
sulfide (e.g. sulfate-sulfide pair) in the second glass 208 for the
purpose of providing gaseous reaction products that serve to
manufacture hollow glass microspheres 210 from the molten silicate
glass fragments 208, and for the purpose of lowering the melting
temperature of the second glass melt 208. The termination of the
redox reactions is achieved by discharging the first glass melt 206
from the melter and allowing the glass to cool down rapidly. The
viscosity of the glass increases exponentially with decreasing
temperature, and as such the redox reactions come to a stop quickly
as the discharged glass is cooled and solidifies. The extent by
which the non-equilibrium redox reactions advance towards
completion is controlled by the residence time of the first glass
melt 206 in the melter system 300. Since the redox reactions are
stopped before reaching equilibrium in the first glass melt 206,
the non-equilibrium redox reactions reactants, and the reaction
products in the solidified first glass melt 206 are carried over
into the second glass 208 from which the silicate glass fragments
210 are made. In accordance with the present invention, the cooled
and solidified first glass melt 206 is defined or characterized as
the second glass 208.
[0200] In the thermal processing step 110, the silicate glass
fragments 210 are rapidly heated inside the firing furnace to the
melting temperature of the second glass 208. The following chemical
reaction occurs in the second glass melt 208:
3SO.sub.4.sup.2-+S.sup.2--->4SO.sub.2+4O.sup.2- (5)
[0201] Reaction (5) requires that both sulfide and sulfate ions are
present in the second glass 208. The cations of the two anionic
species may be the same or different. As disclosed before, iron is
an example of a cation for the sulfide anion, but other multivalent
metal cations are as well within the scope of the present
invention, such as zinc, copper, and tin. For example, when iron
sulfide is present, the reaction (5) is:
3SO.sub.4.sup.2-+FeS-->4SO.sub.2+FeO+3O.sup.2- (6)
[0202] Reaction (6) can be rewritten as well for ferric sulfide;
however, it is believed that the majority of the iron sulfide is
present as ferrous sulfide in the glass second melt 208 in the
furnace. As disclosed previously, the resulting ferrous oxide
behaves like a glass network modifier, resulting in the
depolymerization of the melt and in lowering the viscosity of the
second glass 208 compared to the first glass 206. The reaction (6)
in most cases has an onset temperature of about 1050.degree. C.,
and a near completion temperature of about 1600.degree. C., with a
peak rate at about 1350.degree. C.-1550.degree. C., depending on
the furnace atmosphere, and the chemical composition of the second
glass 208.
[0203] The present invention, as illustrated in the chemical
reaction (6), is capable of providing the double advantage of
lowering the melting temperature of the second glass 208 (e.g.
lowering the viscosity), by in-situ generating fluxing ferrous
iron, while simultaneously forming the ample volume of sulfur
dioxide gas that is necessary for the creation of the plurality of
hollow glass microspheres 212 from the silicate glass fragments
210.
[0204] In case that there are more sulfide ions in the second glass
melt than the stoichiometric ratio of the reaction (5) with respect
to the sulfate ions present, a portion or all the excess sulfide
goes through an oxidization reaction according to reaction (7), as
follows:
2FeS+3O.sub.2-->2FeO+2SO.sub.2 (7)
[0205] According to the reaction (7), additional expansion gas,
e.g. SO.sub.2, and additional fluxing oxide (e.g. FeO) is produced
by an oxidation reaction of sulfide in the second glass melt
208.
[0206] An additional source of expansion gas in the second glass
melt 208 while in the furnace is from un-reacted carbon carried
over from the first glass 206 to the second glass 208. The
un-reacted carbon reacts with the sulfate, and/or other oxidizers
in and out of the molten silicate glass fragments 210 (e.g. second
glass melt 208). The reaction is similar to the reaction (2), and
results in forming SO.sub.2, and CO.sub.x (1.ltoreq.x.ltoreq.2).
The oxygen from the combustion air inside the furnace is an
external source of oxidizer.
[0207] The physical reboil of SO.sub.2/SO.sub.3 which may occur in
the furnace at the same time with reaction (7) also adds to the
total volume of gas created and available for further expanding the
silicate glass fragments 210 to hollow glass microspheres 212. The
physical reboil is triggered in the second glass melt 208, by
exceeding the solubility limitations of the sulfur oxide gases in
the second glass melt 208.
[0208] In accordance with another embodiment of the present
invention, a predetermined amount of carbon, e.g. residual carbon,
is allowed to remain in the first glass melt 206. This is carried
out preferably by directly incorporating a carbonaceous RAG
component 204 in the first glass melt 206, while in the melter
system. Optionally, this can be accomplished via residual carbon
carried over from the RAG components 204 that were included in the
batch 200. The advantage of having residual carbon is that this
residual carbon consumes any remaining sulfate, according to
reaction (3), thus creating CO.sub.2 gas that is utilized further
for the expansion of the silicate glass fragments 210. In addition,
any sulfide formed, after the exhaustion of the residual carbon, is
oxidized by oxygen in the furnace to provide additional SO.sub.2
also being utilized for the further expansion of the silicate glass
fragments 210 to hollow glass microspheres 212. Finally, when both
ferric and ferrous iron are present in the melt of the second glass
208 of the silicate glass fragments 210, residual carbon promotes
the reduction of ferric iron to ferrous iron and the creation of
CO.sub.2 gas in the process. Again, the created CO.sub.2 gas is a
source of gas available to expand the silicate glass fragments 210
to hollow glass microspheres 212. Since the majority of iron would
be in the form of ferrous iron, a significant reduction in the
melting temperature of the second glass 208 is attained compared to
the melting temperature of the first glass 206. Carbon carry over
into the second glass 208 is possible, because of the ability to
incorporate carbon at the stage of the melt processing in the
melter system 300. As such, the carbon impregnated first glass melt
206, resides only a short time in the melter system 300 before
being discharged and cooled. As a result, the carbon is not fully
consumed in the first glass melt 206 and is carried over into the
second glass 208. This is another example of a non-equilibrium
redox reaction occurring in the first glass melt.
[0209] Providing a first glass melt 206 with any other short lived
chemical species while in a molten state is accomplished by
impregnating the first glass melt 206 in the processing zone,
and/or discharge zone of the melter system 300 with the desired
short lived chemical species. This allows the chemical species to
be carried over to the second glass 208. The impregnation is
achieved by incorporating a desired chemical species, such as for
example carbonaceous materials, into the first glass melt 206 while
in the melter system 300. As previously disclosed the incorporation
is realized by various methods including bubbling or injecting the
chemical species in the melter system 300 in such zones like the
processing zone 320, and the discharge zone 330 of the melter. The
chemical species will undergo a targeted reaction when the second
glass is reheated and is melted.
[0210] The sulfate redox reactions involving carbon (e.g. added as
a part of the RAG components to the batch 200 and/or in the form of
gaseous, liquid, solid carbonaceous materials and aerosols bubbled
and/or injected into the first glass melt 206) are influenced by
the relative concentration of carbon to sulfates, the reaction
time, and the melt temperature.
[0211] In accordance with the present invention, direct conversion
of sulfates to sulfides is achieved in the first glass melt 206
while in the melter system 300 by incorporation of a carbonaceous
chemical species such as carbon into the first glass melt 206.
[0212] In the case that carbon is not totally consumed in the first
glass melt 206 due to the non-equilibrium redox reactions, as
disclosed previously, a portion of the unreacted carbon will be
carried over to the second glass 208 as the residual carbon.
[0213] In accordance with the present invention, and the above
disclosure, there is more than one source of gas formation within
the second glass melt 208 during the expansion of the silicate
glass fragments 210 to the hollow glass microspheres 212. Thus, it
is possible to increase or decrease the volume of gas created
during the expansion of the silicate glass fragments 210 in such a
way to obtain the desired average particle density of the
corresponding hollow glass microspheres 212. As disclosed above, as
the concentration of sulfides and residual carbon are increased in
the second glass 208 via non-equilibrium redox reactions induced in
the first glass melt 206, a larger volume of expansion gas is
generated in the second glass melt 208 resulting in lowering the
particle density of the hollow glass microspheres 212 to very low
values, e.g. below 0.4 g/cm.sup.3. According to one aspect of the
present invention, the combined volume of gas generated in the
second glass melt 208 causes the silicate glass fragments 210 to
expand, and is due to more than one gas forming chemical species
simultaneously and more than one gas generation mechanisms
generating gas in the molten silicate glass fragments 210 en-route
to the hollow glass microspheres 212.
[0214] As the ratio of carbon to sulfate increases in the RAG
components 204, under equilibrium conditions, more sulfate is
consumed to form sulfides and/or SO.sub.2. However, depleting the
sulfate completely from the first glass melt 206, and consequently
from the second glass 208 is not recommended, otherwise reaction
(5) might not take place in the second glass melt 208. Henceforth,
the non-equilibrium redox reactions are important to take place in
the first glass melt 206.
[0215] As disclosed previously, and in accordance with the present
invention, the volume rate of gases generated in the second glass
melt 208 within the silicate glass fragments 210 is in a direct
relationship with the particle density of the resulting plurality
of hollow glass microspheres 212, e.g. the higher gas generation
volume rate, the lower particle density.
[0216] The advantages provided by the method of the present
invention are evident, as the amount of gas created during the
expansion of the silicate glass fragments 210, employed for the
creation of the glass microspheres 212, is precisely controlled by
controlling the concentrations of sulfides, sulfates, and residual
carbon in the second glass 208. In addition, the amount of ferrous
iron oxide created in the second glass 208 due to redox reactions
as disclosed previously affects the melting temperature of the
second glass 208 and as such the melting temperature of the
silicate glass fragments 210 in step 110.
[0217] In the event that either or both thermal and physical
reboils phenomena are also present, the firing temperature and the
residence time in the furnace are also adjusted to control the
total volume of gas generated in glass melt of the second glass 208
by measuring the average particle density of the hollow glass
microspheres 212.
[0218] One method of evaluating the necessary process parameters,
such as the types and amounts of RAG components 204, the residence
times in the melter system 300 and the firing furnace, melting and
firing temperatures, requires measuring at least one of the
particle density, the mechanical strength, the chemical durability,
and other physical and chemical characteristics of the glass
microspheres 212.
[0219] For example, one measurement data set is appropriately
arranged (i.e. graphically or tabulated) to show the results of
measuring the particle density of the glass microspheres 212 as a
function of the firing temperature for a given residence time
inside the firing furnace. A second set of data is arranged to show
the results of measuring the particle density of the glass
microspheres 212 as a function of the residence time for a given
firing temperature. Another example is related to the hydrostatic
pressure and/or crushing strength of the hollow microspheres 212 as
a function of particle density. Other such representations may be
as well performed apart from the ones exemplarily specified above,
to aid with the evaluation of the necessary process parameters and
to learn regarding any necessary changes in said parameters.
[0220] Exemplary for a desired hydrostatic pressure rating and/or
crushing strength of the glass microsphere 212, a corresponding
targeted particle density is determined from the data
representation. To affect the particle density of the glass
microspheres 212, the important processing parameters are the
residence time in the heated zone of the furnace, the temperature
of the heated zone of the furnace, and the volume of gas being
generated in the second glass melt contained in the molten silicate
glass fragments 210 while in the furnace. In practice, the
residence time is not significantly variable, since the length of
the furnace is fixed. The linear velocity of the silicate glass
fragments 210 inside the furnace can be varied some, as the volumes
of the combustion air and gas entering the furnace for a given
solid loading, may vary but not significantly. Optionally the
firing temperature may be varied, which affects the volumes of the
combustion air and gas. However, the preferred option in accordance
with the invention is to affect the volume of gas being generated
within the second glass melt 208, by adjusting the types and
concentration of the RAG components 204 in the melter system 300 as
discussed in detail previously in connection with the capability to
manufacture glass microsphere 212 with varying densities.
[0221] As previously discussed, the plurality of sulfide compounds
are either included as part of the RAG components 204 entering the
batch 200 from which the first glass melt 206 is created, or
alternatively are formed in-situ in the first glass melt 206 while
residing inside the melter system 300. In accordance with the
present invention, the concentration of total sulfides, calculated
as S.sup.2- in the second glass 208 is from 0.001 to 2 wt % based
on the mass of the second glass 208.
[0222] In accordance to the present invention, the molar fraction
of sulfide (as S.sup.2-) over total sulfur
(S.sup.2-+SO.sub.4.sup.2-) in the second glass 208 is greater than
zero.
[0223] The atmosphere within the furnace employed for heating and
expanding the silicate glass fragments 210, in accordance with the
present invention, is controlled to be either neutral, oxidizing,
or reducing. When the furnace is operated under neural to mildly
reducing conditions the relative concentration of thermal NOx in
the flu gases is decreased, which is environmentally advantageous.
Another advantage of the present invention is due to having the
ability to lower the melting temperature of the second glass 208
compared to the first glass 206. Yet another advantage of the
present invention is the ability to generate gas in the second
glass 208 from multiple sources. All the advantages above lead to
the ability of lowering the firing temperature requirements for the
second glass that in turn results in improving the fuel efficiency
of the manufacturing process, and hence the ability of economically
manufacturing high quality hollow glass microspheres 212.
[0224] The sulfide compounds of the RAG components 204 include both
synthetic and mineral compounds of sulfides. According to the
present invention, in addition to or instead of sulfides,
selenides, antimonides, bismuthinides, and sulfosalts may also be
used, but they are normally more costly than the synthetic and
mineral compounds of sulfides containing S.sup.2-. Examples of the
sulfide compounds that are used according to the present invention
are one or a combination of acanthite Ag.sub.2S, chalcocite
Cu.sub.2S, bornite Cu.sub.8FeS.sub.4, galena PbS, sphalerite ZnS,
chalcopyrite CuFeS.sub.2, pyrrhotite FeS, millerite NiS,
pentlandite (Fe,Ni).sub.9S.sub.8, covellite CuS, stibnite
Sb.sub.2S.sub.3, pyrite FeS.sub.2, molybdenite MoS.sub.2, and other
metal and transition metal sulfides. Iron sulfide, with the general
formula Fe.sub.1-xS, is one sulfide compound to be used according
to one embodiment of the present invention, wherein x varies from
zero to 0.5. Iron sulfide, for example, in the form of pyrite, is
readily commercially available at relatively low cost. Another
source of iron sulfide is from vitreous, semi-vitreous, or
crystalline industrial byproducts such as incineration slag,
incineration ash, bottom ash, and flyash. Ferric sulfide is also
acceptable.
[0225] In accordance with one embodiment of the present invention,
all or a portion of the materials that constitute the batch 200 are
derived from recovered materials. As disclosed earlier in this
document, the "recovered materials" are waste materials, either of
hazardous or non-hazardous nature. Converting non-hazardous
recovered materials to hollow glass spheres provides a highly value
added product, while preserving natural resources, by decreasing
the demand for mined raw materials. Exemplarily, asbestos
containing waste materials, in accordance with the present
invention are melted as a part of the batch 200 into the first
glass 206 in the melting zone 310. Any adjustments to the RAG
components are carried out either via batch 200 and/or inside the
melter system 300 such as in the melting zone 310, the processing
zone 320, and the discharge zone 330. In this way, not only a
hazardous waste material is safely vitrified, but also the
resulting vitrified material forms a second glass 208, which is
suitable to be converted to high quality glass microspheres 212.
The embodiment of the invention disclosed above for the asbestos
containing waste materials is equally applicable for other waste
materials, such as incineration ash, radioactive waste materials,
and any other vitrifiable waste materials.
[0226] In accordance with one embodiment of the present invention,
a vitrified waste material that has a combination of RAG components
and/or RAG components reaction products, such as at least one
sulfur compound, and a multivalent metal, is used directly as the
second glass 208 from which silicate glass fragments 210 are made.
Accordingly, the vitrified waste material is pulverized and sized
in step 108, forming the plurality of silicate glass fragments 210.
The resulting silicate glass fragments 210 are heated in step 110
to form glass microspheres 212, which in this case are directly
produced from pulverization of a vitrified waste material.
Exemplary vitrified waste materials to be used as the second glass
208 are: vitrified asbestos waste materials, vitrified hazardous
waste materials, vitrified radioactive waste materials, vitrified
incinerated municipal waste materials, vitrified incineration ash,
and vitrified medical waste materials.
[0227] Converting hazardous materials into non-hazardous recovered
materials, and then into glass microspheres provides better
handling, more efficient storing, and the possibility of reuse of
the recovered materials. Examples of a non-hazardous (landfillable)
industrial byproducts are fly ash, bottom ash, and in some cases
incineration ash. Examples of hazardous materials converted into
non-hazardous recovered materials and consequently into glass
microspheres, are asbestos containing waste materials, and
medical/municipal waste materials that are vitrified into
essentially non-hazardous glassy materials. Another example of a
hazardous industrial byproduct is vitrified nuclear waste that
despite being considered radioactive, the radioactive isotopes
contained in it, are securely fixed into the molecular structure of
the glass, resulting in glasses that are chemically very durable
and physically highly stable. The vitrified nuclear waste glass is
used as the second glass 208 in accordance with the present
invention to manufacture radioactive glass microspheres. Most of
the vitrified low level nuclear glasses contain RAG components 204,
in the form of iron oxide, and sulfur compounds. The glass
microspheres 212 are essentially solid when there is not sufficient
gas forming RAG components 204 present. On the other hand, the
microspheres are hollow when there are sufficient gas forming RAG
components 204 present. The resulting glass microspheres find uses
in many applications, including radiation source miniaturization,
medical applications, etc.
[0228] According with an embodiment of the present invention, the
vitrified hazardous waste materials are used instead of batch 200
to create the first glass 206. In certain cases when sufficient RAG
components 204 (or RAG reaction products) are already present in
the vitrified hazardous waste materials, they are treated as the
second glass 208, and further processed in accordance with the
steps 108, 110, and 112 to manufacture corresponding glass
microspheres. The resulting glass microspheres created in
accordance with this embodiment of the invention, find use in many
applications that require an inexpensive, and high performance
filler particles for composites. Another example of a post consumer
non-hazardous consumer byproducts that may be used instead of or in
addition to the batch 200 is incineration ash resulting from
incinerating waste materials.
[0229] The method 100 of manufacturing a plurality of glass
microspheres proposed by the present invention is discussed in more
detail in connection with various example embodiments described
herewith. The following examples demonstrate exemplary embodiments
of the present invention at least insofar the method of
manufacturing a plurality of glass microspheres.
Example 1
[0230] This example describes an embodiment of the present
invention in which fly ash is used as a part of the batch 200.
Additionally, the present example illustrates the embodiment of the
present invention wherein the RAG components 204 are intrinsic
and/or integral to the SGP raw materials 202.
[0231] Fly ash is an industrial byproduct that falls into the
category of materials defined herein as "recovered materials". ASTM
C618 provides two types of fly ash classifications; Class F:
SiO.sub.2+Al2O3+Fe2O3.gtoreq.70%, and Class C:
SiO.sub.2+Al2O3+Fe2O3.gtoreq.50%. All in wt %.
[0232] The RAG components in fly ash comprise unburned carbon,
which can vary from 0.2 to as high as 3.5 wt %, in addition to iron
oxides, and sulfur compounds. Iron oxides are almost always present
in fly ash, mostly in the form of magnetite (FeO+Fe.sub.2O.sub.3)
and sulfur in the forms of sulfates, sulfites, or sulfides.
[0233] A typical class F fly ash, has less sulfur than a class C
fly ash. The initial content of sulfur as sulfate in the flyash is
usually less than 1 wt % depending on how much sulfur has been
scrubbed off from the flu gas via a flu gas desulfurization unit.
Without a significant scrubbing action, the amount of sulfate may
be around 0.5%, and the molar ratio of unburned carbon to SO.sub.3
varies from less than one to as much as 10.
[0234] The wt % of the major oxides in the class F fly ash are:
SiO.sub.2 35-65 wt %, Al.sub.2O.sub.3 20-45 wt %,
FeO--Fe.sub.2O.sub.3 3-12 wt %, and CaO 1-10 wt %. In this example,
iron oxide(s), sulfur compounds, and unburned carbon are considered
part of the RAG components 204, despite of being constituents of
the fly ash that is part of the SGP raw materials 202. Therefore,
the RAG components 204 are intrinsic (integral) to the SGP raw
materials 202.
[0235] According to one embodiment of the present invention,
deficiencies in the RAG components are compensated by dosing the
appropriate amount of a deficient component to either the batch
200, and/or the first glass melt 206 while in the melter system. In
contrast, if the RAG components are already part of the fly ash,
any RAG component deficiencies are compensated by adding extra SGP
raw materials 202 to the batch until the concentration of a
particular RAG component is brought within the desired range in the
batch 200. The resulting batch 200 may also require the addition of
those RAG components 204 that may have become deficient due to the
addition of additives. A batch 200 is prepared with Fly ash (type
F) 40-80 parts, silica sand 20-30 parts, gypsum 1-3 part, and 0-25
parts of one or a combination of lime stone, dolomite, salt cake,
soda-ash, Pyrex glass cullet, a soda lime glass cullet, and potash.
The resulting batch 200 has a composition that falls within the
prescribed range of composition for the first glass melt 206
disclosed earlier. The composite redox number of the batch 200 is
within the range of -0.1 to -10.
[0236] Next, the batch 200 is blended prior to being melted in an
electric melter system 300. The residence time in the melter system
300 is about 5 hours. The melter system 300 comprises a primary
melting zone 310, where a glass melt pool is created at an average
temperature ranging from about 1300.degree. C.-1450.degree. C. as
measured in the molten glass between the electrodes. The melter is
operated with a cold cap over the molten glass in the primary
melting zone 310. The melter system 300 has a processing zone 320,
and a discharge zone 330 comprising a side airlift assisted
discharge port. Bottom gravity assisted discharge ports are
provided in melting zone 310, and the processing zone 320 to empty
the molten glass inventory of the melting zone, and the processing
zone when needed in such occasions like repair, and scheduled shut
down periods. In case a molten metal layer formed at the bottom of
the either zone, the molten metal layer may be discharged through
the bottom discharge ports. The melter electrodes housed in the
primary melting chamber 310, comprise molybdenum alloyed with
zirconium oxide, and are powered with a three phase AC power
supply.
[0237] As the batch 200 melts into the first glass 206, a portion
of the unburned carbon in the ash oxidizes by oxygen in air forming
CO.sub.2 within the cold cap, and near the molten glass interface.
As the melting progresses from the cold cap to the glass pool,
another portion of the unburned carbon reacts with sulfate
according to the redox reaction (2), forming SO.sub.2 gas. The
remaining unburned carbon as it comes into intimate contact with
the first glass melt 206, reacts with sulfate according to the
redox reactions (3) and (4), forming a plurality of reaction
products that include iron sulfide. The non-equilibrium redox
reactions (3) and (4) are terminated before reaching the
equilibrium state by effectively discharging the first glass melt
206 from the melter system 300. Injection ports accessible through
the plenum of the processing zone of the melter system 300 allow
the delivery of the additional RAG components 204 to be directly
incorporated into the first glass melt 206 while in the melter
system 300. Pressurized air assisted graphite spray nozzles are
provided to deliver graphite powder or any other gaseous or liquid
RAG components 204 into the melter system 300. The capability of
being able to incorporate directly the RAG components 204 into the
first glass melt 206, while in the melter system 300 allows for
controlling an accurate balance/amount of gas forming species that
are carried over to the second glass 208. The discharged glass is
cooled rapidly over a large steel plate forming the second glass
208. Because of terminating the redox reactions before reaching
equilibrium in the melter system 300, a predetermined mixture of
sulfate and sulfide coexists in the second glass 208. The resulting
second glass 208 is then pulverized in step 108 to an average
particle size of about 60-80 microns forming the silicate glass
fragments 210.
[0238] Next, the silicate glass fragments 210 are suspended in a
combustion air stream entering a burner system provided inside a
firing furnace at an average rate of approximately 1 kg of
particles per 1 m.sup.3 of air. The firing furnace is an upward
vertical gas fired cylindrical furnace. A co-concentric burner
fueled with natural gas is used and the injection velocity at an
axial upward direction is set to be about 2-10 m/s. The amount of
combustion air supplied to the furnace is adjusted to be close to
the stoichiometric air-gas ratio in such a way to have a relatively
neutral ambient atmosphere surrounding the silicate glass fragments
210. In the combustion zone of the furnace and at an average firing
temperature of about 1300-1550.degree. C. (as measured in the
combustion zone), the silicate glass fragments 210 melt and expand
to form the hollow glass microspheres 212. Outside ambient air is
allowed to enter the furnace near the top after the combustion
zone, resulting in a sharp temperature drop and immediate cooling
of the microspheres. The furnace is under a mild vacuum, and glass
microspheres 212 are collected in a hot cyclone. The overall
residence time in the furnace averages to less than 4 seconds.
[0239] It is of note the glass microspheres 212 are manufactured in
accordance with an embodiment of the method of the present
invention that comprises a glass melting step in which
non-equilibrium redox reactions are provided by a redox active
group, followed by a glass remelting step, capable of
self-generating gas by at least one redox reaction to form a
plurality of hollow glass microspheres.
[0240] It is also of note that in accordance with an embodiment of
the method of the present invention, RAG components are
incorporated directly into a glass melt. The method takes advantage
of the non-equilibrium redox reactions occurring in the glass melt
upon incorporation of the RAG components. Accordingly, a glass melt
with a desired composition is formed inside the multizone melter
system. The melter system comprises at least a melting zone, a
processing zone, and a discharge zone having discharge means to
discharge the molten glass at will. The glass melt is transferable
from the melting zone to the processing zone essentially in a
one-way forward movement, and not vice versa. As such, the glass
melt can move from the melting zone to the processing zone, but not
in the opposite direction. In the processing zone of the melter
system, the RAG components are incorporated into the glass melt,
and are uniformly dispersed into the glass melt. The glass melt
from the processing zone, upon incorporation of, or impregnation
with the RAG components, is discharged from the melter system. The
discharged glass upon cooling is fragmented. The RAG components in
the glass fragments upon heating and remelting in the furnace go
through predetermined redox reactions and form a plurality of
gases. The plurality of gases is entrapped in the molten glass
fragments and as a result the molten glass fragments expand, and
hollow glass microspheres are formed. Therefore, to summarize, the
glass microspheres have been formed, in accordance with the above
example by a method comprising the following steps: forming a
batch, melting the batch into a first glass melt in a melting zone
of multizone melter system, transferring the first glass melt from
a melting zone to a processing zone, impregnating the first glass
melt with RAG components while in the melter system, discharging
and cooling the first glass melt from the melter system to form a
second glass, pulverizing the second glass into glass fragments,
heating and melting the glass fragments, expanding the molten glass
fragments into hollow glass microspheres by generating and trapping
gas via the RAG components in the second glass melt, and cooling
the hollow glass microspheres.
[0241] It is of note that no art reference discloses utilizing
industrial waste or recycled byproducts as raw materials to melt a
glass precursor from which silicate glass fragments suitable for
making hollow glass microspheres are manufactured by the process
outlined above.
Example 2
[0242] In accordance with a further example of the present
invention, a municipal waste incineration-ash, and/or a medical
waste incineration-ash, is used as a part of the SGP raw materials.
Silica flour is added in order to increase the silica content of
the composite batch 200. As a part of the RAG components 204,
gypsum is added to the batch 200 to adjust the sulfate content to
achieve a prescribed chemical composition for the first glass melt
206. The resulting batch 200 is melted in the same type melter
system that is employed in the Example 1. Hydrogen sulfide, with
and without a carbonaceous RAG component 204, such as graphite is
incorporated into the first glass melt 206 while in the melter
system 300, in order to control the gas volume generated in the
second glass melt 208 via the redox reactions while in the furnace.
The first glass melt 206 is discharged from the melter system 300,
cooled, and pulverized to form the silicate glass fragments 210.
The newly formed silicate glass fragments 210 are reheated in the
firing furnace to about 1300-1550.degree. C. to form the glass
microspheres 212. The average residence time in the furnace is less
than 4 seconds. In accordance with this example, a value added
product is made from otherwise waste materials that in most cases
are regulated and may not be land filled in unregulated landfill
areas.
Example 3
[0243] In yet another example of the present invention, a vitrified
low level radioactive waste material is treated as the second glass
208. The second glass 208 is a borosilicate-based glass. The solid
pieces of the second glass 208 are pulverized and screened to
obtain the desired silicate glass fragments 210. The silicate glass
fragments are fired in a firing furnace that has suitable off gas
treatment capabilities for radioactive gaseous and particulate
emissions. The firing temperature is set around 1200-1400.degree.
C. The resulting radioactive glass microspheres 212 are chemically
durable and stable. The radioactive glass microspheres may be used
as a radiation source, for example in medical applications. In
addition, the radioactive glass microspheres can be reused, and
repackaged easily as a flowable solid material.
Example 4
[0244] In accordance with another example of the present invention,
value added glass microspheres are produced from the asbestos
containing waste materials. The asbestos containing waste materials
normally contain gypsum and iron wires (i.e. metal mesh screen) in
their makeup (e.g. examples of intrinsic RAG components). The
asbestos containing waste material of the present example is a part
of the SGP raw materials, and included in the batch 200. Silica
flour is added to the batch 200 to bring the silica level of the
first glass melt 206 within the prescribed range in accordance with
the present invention. No additional RAG component is added to the
batch 200. Next, the batch 200 is melted in a similar melter system
300 employed in the Example 1. A mixture of hydrogen and nitrogen
gas is incorporated into the first glass melt via bubbling into the
processing zone 320 of the melter system 300 to adjust the balance
of sulfide-sulfate in the first glass melt 206, and consequently in
the second glass 208 in accordance with the present invention. The
first glass melt 206, which represents the vitrified asbestos waste
containing materials upon cooling, forms the second glass 208, and
is ground-up to form the silicate glass fragments 210. The silicate
glass fragments 210 are reheated in the firing furnace to about
1300-1500.degree. C. to form glass microspheres 212. The average
residence time in the furnace is less than 4 seconds. Further redox
adjustments are carried out by injecting graphite powders into the
first glass melt to produce hollow glass microspheres with an
average particle density of less than 1 g/cc. This example also
illustrates the embodiment of the invention wherein an elemental
multivalent metal (e.g. iron) is used as one of the RAG components
204.
Example 5
[0245] This example illustrates an embodiment of the present
invention wherein glass raw materials are used as SGP raw materials
202, in addition to the RAG components 204 in making up the batch
200.
[0246] The SGP raw materials 202 comprise in accordance with the
present example silica flour (or equally ground quartz), kaolin,
dolomite (of particulate dimensions of under 200 mesh), potash
feldspar (orthoclase), and soda ash. The RAG components 204 in
accordance with the present example comprise iron oxide (rust),
gypsum (of particulate dimensions under 200 mesh), and carbon
(powdered graphite). The batch 200 is formed with varying
concentrations of ingredients of the SGP raw materials 202 as
follows: silica sand, 10-40 parts, kaolin, 30-60 parts, dolomite,
20-40 parts, potash feldspar, 10-15 parts, soda ash 2-3 parts, and
the RAG components 204.
[0247] The RAG components 204 exemplarily comprise iron oxide
(rust), 1-5 parts, and gypsum, 2-5 parts. Carbon at a total level
of 0.1-2 parts is added both to the batch 200, and is incorporated
directly into the first glass melt 206 while in the melter system
300. The composite redox number of the first glass 206 is less than
zero.
[0248] After forming the batch 200 by combining the above
enumerated SGP raw materials 202, and the RAG components 204, the
batch 200 is melted in a melter system 300. The melting of the
batch 200 in the melting zone of the melter 310 to form the first
glass 206 takes between 5-10 hours at an average temperature
between 1300-1450.degree. C. as measures in the melt pool.
[0249] As with the previous examples, a melter 300 is preferably
operated with a cold cap over the molten glass in the primary
melting zone 310. Carbon is delivered to the first glass melt 206
in the form of graphite powder entrained in pressurized air, with
and without hydrogen sulfide. The mixture is bubbled into the first
glass melt 206, while in the processing zone 320, to induce
non-equilibrium redox reactions leading to a desired balance
between sulfide and sulfate ions in the first glass melt 206, and
consequently the second glass 208. In the above process, residual
carbonaceous materials are provided in the first glass melt 206
when desired. Hydrogen sulfide and carbon are effective means to
adjust the particle density of the hollow glass microspheres 212.
As the first glass melt 206 enters the discharge zone 330, the
non-equilibrium redox reactions have reached the desired non
equilibrium state and the first glass melt 206 is discharged from
the melter 300 via a melt discharge trough. The discharged glass is
cooled rapidly over a large steel plate forming the second glass
208. Because of terminating the redox reactions before reaching
equilibrium in the melter system 300, by discharging and rapidly
cooling the molten glass, a mixture of sulfate and sulfide coexist
in the second glass 208. The resulting second glass 208 is then
pulverized in step 108 to an average particle size of about 60-80
microns forming the silicate glass fragments 210.
[0250] Next, the silicate glass fragments 210 are converted into
hollow glass spheres 212 by following a procedure similar to the
procedure outlined in the Examples above. The resulting hollow
glass microspheres 212 have a structure similar to the one
schematically represented in FIG. 2, that will be described in
detail bellow. The average particle density of the obtained hollow
glass microspheres 212 is below 1 g/cm.sup.3.
Example 6
[0251] Example 6 illustrates an embodiment of the present invention
wherein carbon is added to the first glass 206 while in the melter
system 300. In accordance with this embodiment of the present
invention the SGP raw materials 202, are the ones used as discussed
above in connection with Example 5, are combined with the RAG
components 204 exemplarily discussed above in connection of the
Example 5, except carbon, to form the batch 200. The batch 200 is
subsequently melted in the melting zone 310 of the melter system
300. A graphite powder spray, in combination with pressurized air
is used to inject fine graphite powder into the first glass melt
206 while in the melter. As an alternative, fine powder graphite or
coke, or carbon black (with an average particle size of less than
10 microns), is entrained in a gaseous, vapor, or liquid carrier at
a loading such that it is dispersed uniformly into the first glass
melt while in the melter system 300, for example by injection or
spraying into the molten glass. The first glass melt 206 is
discharged and further processed in accordance with the method of
the present invention, and as disclosed above as well in connection
with Examples 1 to 5, to manufacture the glass microspheres
212.
Example 7
[0252] This example illustrates an embodiment of the present
invention wherein iron is added as part of the recycled waste
byproduct to the glass forming constituents of the SGP raw
materials 202 of the Example 5. Calcined red mud (from the aluminum
smelting process), at a level of 15-25 parts, is included in the
SGP raw materials 202. As a result, there is no longer a need to
add soda ash, since the calcined red mud contains about 5-8 wt %
sodium oxide. Additionally, iron oxide (rust) is no longer added,
since red mud contains about 45-55 wt % iron oxide. Subsequently,
the first glass 206 is melted, and converted to the second glass
208 as outlined in connection with either one of the examples 5,
and 6 above. The resulting second glass 208 is pulverized to form
the silicate glass fragments 210, which are then converted to
hollow glass microspheres 212 in accordance with the embodiments of
the method of the present invention. The resulting hollow glass
microspheres 212 are precursor for production of ferrimagnetic
hollow glass ceramic microspheres. This is achieved by
heat-treating the glass microspheres 212 at a temperature below the
deformation temperature of the microspheres. Upon heat treatment,
and due to formation of nano-size magnetite crystals that are
homogenously dispersed in the glass wall of the microsphere 212,
glass-ceramic microspheres with strong ferromagnetic properties are
produced. By increasing the concentration of iron in the first
glass 206, for example via the addition of more red mud in the raw
materials 202, glass microspheres with iron oxide content of 10-20
wt % are obtainable.
[0253] The present invention enables the production of highly
durable and strong hollow glass microspheres at a high throughput
using inexpensive raw materials. The throughput is high because the
combined residence time in the melter system 300 and the firing
furnace is less than 12 hours, and preferably 5 hours or less. This
makes the production process to be highly sustainable (energy
efficient) since it is possible to take advantage of fast
manufacturing methods. Another advantage of the method of the
present invention is that the RAG components 204 inherently exist
in the many forms of the recovered materials, thus a relatively low
cost for the raw materials can be realized. This makes possible the
production of an eco friendly product, by utilizing industrial
waste byproducts and converting them into high value added
products.
[0254] According to the embodiments of the present invention, the
glass microspheres 212 manufactured according to the methods of the
invention are used in at least one of the following applications:
in the oil and gas industry, as light weight fillers for various
composites, in building materials, in the automotive and aeronautic
industries, in the medical industry, integrated in paints and road
signs, and as functional fillers for various composite materials.
Additionally, the glass microspheres manufactured according to the
method of the present invention are suitable to be subjected to
various surface treatments and modifications to impart desired
surface functionalities to the resulting microspheres. Examples are
coloring the surface, coating the surface with various functional
coatings such as magnetic, electrically conductive, light
reflective, self-cleaning, and attaching surface functional groups
to the microsphere surface such as ionic chemical species,
organo-functional groups such as silanol functional group, and
hydroxyl functional groups. Hydraulic fracturing involves pumping
fracturing fluids into an oil or gas well at high pressure to
create fractures in the rock formation that allow oil or gas to
flow from the fractures to the wellbore. The fracturing fluid is
normally water based, and comprises propping particles (proppants)
and other additives. The microspheres 212 of the present invention
that have very high crushing strength above 5000 psi, and
preferably above 10,000 psi are excellent candidates as propping
particles to keep fractures open once they are produced under high
pressure.
[0255] Therefore, an embodiment of the present invention, also
comprises a composite product, comprising a combination of the
plurality of glass microspheres manufactured in accordance with the
present invention, and at least one of a plurality of polymer
matrices, a plurality of cementiteous matrices, a plurality of
fluid matrices, a plurality of solid matrices, a plurality of fiber
containing matrices, and a plurality of metal matrices.
[0256] Due to the superior acid and alkaline resistance of the
glass microspheres 212 manufactured according to the present
invention, the glass microspheres can be safely used in high
alkalinity environments, such as in cements and concretes, and in
hydraulic fracturing liquids that are acidic. The cements may
comprise one or a combination of Portland cement, aluminous
cements, lime cements, magnesium based cements, calcium
sulfo-aluminate cements, phosphate cements, gypsum, geopolymers,
and others. The glass microspheres 212 manufactured according to
the present invention are also used in acidic environments, such as
in acidic hydrofracking fluids. The glass microspheres 212 of the
present invention can be coated and/or surface treated with a
variety of coating materials and surface treatment agents and
equipment. The coating materials comprise inorganic coating
materials, organic coating materials, and a combination thereof.
The coating is applied to the external surface of the microspheres
212 to impart specific surface properties to the microspheres 212.
Examples of such coatings are colorants, electrically active,
magnetically active coating, reflective, chemically active,
mechanical property enhancing, and biologically active. The surface
treatments include: silanization, passivation, activation, ion
exchange, etc.
[0257] Cements or other mediums containing the glass microspheres
of the present invention are used in applications related to the
oil and gas industries, such as in oil and gas well drilling
cement, oil and gas well cementing casing, and oil and gas fracking
including but not limited to shale oil fracking, and hydraulic
fracking. Since in these types of applications the utilized
microspheres are required to have relatively high hydrostatic
pressure rating, normally above 1,000 psi and as high as 20,000
psi, the glass microspheres of the present invention are
particularly suitable for these applications.
[0258] Referring now to FIG. 2, FIG. 2 comprises a schematic
illustration of a glass microsphere produced in accordance with the
methods of the present invention.
[0259] The glass microsphere manufactured according to the various
embodiments of the present invention comprises in its most general
embodiment a plurality of glass walls, and a plurality of hollow
spaces, the plurality of glass walls enclosing the at least one of
the plurality of hollow spaces. The plurality of glass walls
comprises a second glass. The second glass is formed by further
processing a first glass melt. The first glass melt is formed by
melting a batch comprising at least one of a plurality of raw
materials. The plurality of RAG components present in the first
glass melt and a melt of the second is capable of providing at
least one of a plurality of redox reactions and a plurality of
events in the first glass melt and the melt of the second glass,
thereby creating the glass microsphere.
[0260] In accordance with one embodiment of the present invention,
the glass microsphere manufactured according to the embodiments of
the present invention comprises a single or a plurality of glass
walls, and a single or a plurality of void spaces defined by said
wall or walls. The terms of "glass microsphere(s)" and "hollow
glass microsphere(s)" are interchangeably used throughout this
document to refer to a structure that comprises one or a plurality
of enclosure glass walls, forming a plurality of interior and/or
exterior (outer) partition walls, surrounding at least one or a
plurality of hollow spaces.
[0261] FIG. 2 comprises representation of a glass microsphere
produced in accordance with the methods of the present invention.
In accordance with FIG. 2, the exemplary hollow glass microsphere
20 comprises a spherical outer glass wall 22 and a substantially
enclosed cavity or void 24 defined by the outer glass wall 22. The
configuration of the sphere 20 in FIG. 2 resembles the general
configuration of harvested cenospheres from coal burning fly ash.
The outer glass wall 22 comprises a homogenous second glass
208.
[0262] A hollow glass microsphere as shown in FIG. 2 has a specific
strength, which is defined by the crushing strength of the
microsphere divided by the particle density of the microsphere in
the range of about 40-340 MPa/(g/cm.sup.3), where MPa is mega
Pascal. The specific strength over a value of 100, normally
represents glass microspheres having a particle density over
0.4-0.5 g/cm.sup.3. Also, the smaller the average particle size is,
the higher the specific strength would be.
[0263] In certain preferred embodiments, the hollow glass
microsphere has one or more of the following characteristics, which
are also generally characteristics of harvested cenospheres:
an aspect ratio of between about 0.8 and 1; a void volume of
between about 10 and 95%, based on the total volume of the
microsphere; an outer wall thickness of about 2 and 54% of the
microsphere radius.
[0264] Referring now to FIG. 3, FIG. 3 is a schematic
representation of a glass melter system 300 in accordance with the
present invention.
[0265] As mentioned previously in this document, a glass melter
system 300 is employed at least for melting the components of the
batch 200. The melter, one possible configuration of which is shown
in FIG. 3, comprises three zones, namely a glass melting zone 310,
a glass processing zone 320, and a glass discharge zone 330. In the
melting zone 310, apart from phenomenons that are related to the
melting of the batch 200 into the first glass melt 206, the RAG
components 204 may as well be introduced. The RAG component 204 is
in accordance with one embodiment of the present invention in a
gaseous form. Alternatively, additional RAG components 204 are
mixed with the materials of the batch 200 to be melted. The
processing zone 320 is configured such that to allow certain
processes to take place that are related the first glass melt 206
while in the melter system 300 including but not limited to: the
introduction and incorporation of the RAG components 204 into the
first glass melt 206, controlling the overall residence time, by
storing or releasing the first glass melt 206 from the melter
system 300, homogenizing the first glass melt 206, nucleating the
first glass melt 206, refining the first glass melt 206, and
reheating the first glass melt 206. The discharge zone 330
comprises one or a combination of a trough, an outlet throat, an
airlift system, re-heaters, etc. The RAG components 204 can be
incorporated into the first glass melt 206 as well inside the
discharge zone 330, right before, and while being discharged from
the melter system 300.
[0266] Although the foregoing descriptions of certain preferred
embodiments of the present invention have shown, described and
pointed out some fundamental novel features of the invention, it
will be understood that various omissions, substitutions, and
changes in the form of the detail of the apparatus as illustrated
as well as the uses thereof, may be made by those skilled in the
art, without departing from the spirit of the invention.
Consequently, the scope of the present invention should not be
limited to the foregoing discussions.
* * * * *