U.S. patent application number 10/902300 was filed with the patent office on 2005-03-24 for glass bottles made from recycled mixed color cullet.
This patent application is currently assigned to Culchrome, LLC. Invention is credited to Lehman, Richard L..
Application Number | 20050064117 10/902300 |
Document ID | / |
Family ID | 22012618 |
Filed Date | 2005-03-24 |
United States Patent
Application |
20050064117 |
Kind Code |
A1 |
Lehman, Richard L. |
March 24, 2005 |
Glass bottles made from recycled mixed color cullet
Abstract
An automated method for recycling mixed colored cullet glass
(i.e., broken pieces of glass of mixed colors and types) into new
glass products. A computer controlled process identifies the virgin
glass raw materials, the desired target glass properties, the
composition of a batch of mixed colored cullet, and the quantity of
cullet to be used in the glass melt, and the computer controlled
process automatically determines the proper amounts of raw
materials to add to the batch of mixed colored cullet so that
recycled glass is produced having the desired coloring oxides,
redox agents, and glass structural oxides in the proper proportion.
The recycled glass is then used to make glass products such as beer
bottles.
Inventors: |
Lehman, Richard L.;
(Princeton, NJ) |
Correspondence
Address: |
WOODCOCK WASHBURN LLP
ONE LIBERTY PLACE, 46TH FLOOR
1650 MARKET STREET
PHILADELPHIA
PA
19103
US
|
Assignee: |
Culchrome, LLC
|
Family ID: |
22012618 |
Appl. No.: |
10/902300 |
Filed: |
July 29, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10902300 |
Jul 29, 2004 |
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10682450 |
Oct 9, 2003 |
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6810301 |
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10682450 |
Oct 9, 2003 |
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09455644 |
Dec 7, 1999 |
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6763280 |
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09455644 |
Dec 7, 1999 |
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09057763 |
Apr 9, 1998 |
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6230521 |
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Current U.S.
Class: |
428/34.4 |
Current CPC
Class: |
Y10T 428/131 20150115;
C03C 4/02 20130101; C03C 1/002 20130101; Y10T 428/13 20150115 |
Class at
Publication: |
428/034.4 |
International
Class: |
B32B 001/08 |
Claims
1. (Canceled)
2. (Canceled)
3. (Canceled)
4. (Canceled)
5. (Canceled)
6. (Canceled)
7. (Canceled)
8. (Canceled)
9. (Canceled)
10. (Canceled)
11. (Canceled)
12. (Canceled)
13. (Canceled)
14. (Canceled)
15. (Canceled)
16. (Canceled)
17. (Canceled)
18. A glass bottle including recycled mixed color cullet wherein
said bottle is amber in color and has a 550 nm transmission of
8-20% and a redness ratio of 1.2-3.0.
19. A glass bottle as in claim 18, wherein said amber glass bottle
has a 550 nm transmission of 12-15% and a redness ratio of
1.8-2.0.
20. A glass bottle as in claim 18, wherein said amber glass bottle
has a chromium level above trace chromium contamination levels.
21. A glass bottle as in claim 20, wherein said amber glass bottle
has a weight percent of chromium greater than 0.01%.
22. A glass bottle as in claim 21, wherein said amber glass bottle
has a weight percent of chromium of 0.01% to 0.3%.
23. A glass bottle as in claim 22, wherein said amber glass bottle
has a weight percent of chromium of 0.015% to 0.15%.
24. A glass bottle as in claim 23, wherein said amber glass bottle
has a weight percent of chromium of 0.015% to 0.10%.
25. A glass bottle as in claim 24, wherein said amber glass bottle
has a weight percent of chromium of 0.02% to 0.04%.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. Ser. No. 10/682,450
filed Oct. 9, 2003, which is a continuation of U.S. Ser. No.
09/455,644 filed Dec. 7, 1999, now U.S. Pat. No. 6,763,280, which
is a divisional of U.S. Ser. No. 09/057,763 filed Apr. 9, 1998, now
U.S. Pat. No. 6,230,521 all of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to the field of glass recycling. The
invention more particularly relates to an automated method for
recycling mixed colored cullet glass (i.e., broken pieces of glass
of mixed colors and types) into new glass products. According to a
preferred aspect of the invention, a computer controlled process is
provided whereby a recycler identifies the virgin glass raw
materials, the desired target glass properties, the composition of
a batch of mixed colored cullet, and the quantity of cullet to be
used in the glass melt, and the computer program determines the
proper amounts of raw materials to add to the batch of mixed
colored cullet so that recycled glass is produced having the
desired coloring oxides, redox agents, and glass structural oxides
in the proper proportion. The recycled glass is then used to make
glass products such as beer bottles.
[0004] 2. Description of the Prior Art
[0005] Glass recycling involves collecting used, post-consumer
glass and reusing it as a raw material for the manufacture of new
glass products. A main repository of recoverable glass is glass
containers such as beverage bottles and containers for other
products. Bulk recycled post-consumer glass suitable for melting
into recycled glass articles is known as cullet. The glass cullet
for recycling is generally provided in the form of small pieces of
glass.
[0006] Recycled containers comprise different colors, especially
amber and green, and also colorless or flint glass. There also may
be different types of glass in the respective containers, although
soda-lime-silica glass, which primarily contains oxides of sodium,
calcium and silicon, is the most prevalent. Other waste glass,
e.g., off-quality material and scrap from the manufacture of glass
products, may also be re-used in the form of comminuted or ground
glass cullet.
[0007] Approximately ten percent (10%) of municipal refuse is
glass, most of which is in the form of discarded containers from
beverages, food products and the like. To encourage recycling and
minimize waste, there are certain government legislated guidelines
to the effect that new glass products should contain a proportion
of recycled glass. There is thus a market for cullet that can be
re-used readily. Unfortunately, this normally requires that the
glass be sorted by color.
[0008] Municipal refuse glass is typically collected at the street,
processed at a central location and ground into small particles to
provide cullet for use in the manufacture of glass products.
Processing can involve, for example, color sorting by hand or by
optical techniques and removal of non-glass contaminants by hand,
optical techniques, magnetic, eddy current and metal detecting
separation techniques. These techniques are not wholly effective
for the separation and color sorting of all of the glass. In
sorting, for example, it is possible manually, or mechanically by
using a color sensing diverter mechanism, to sort glass by color.
However, much of the glass is broken in handling and cannot readily
be sorted as whole containers, and sorting of smaller pieces is
more difficult. A by-product of glass recycling, even when an
attempt is made to sort the glass by color, is a quantity of mixed
colored pieces.
[0009] The color distribution of the glass in post-consumer solid
municipal waste, and accordingly, in typical mixed color cullet,
varies regionally. A typical color distribution is approximately
65% flint (colorless), 20% amber, and 15% green. To date, mixed
colored cullet has had only limited commercial use, and may be used
as an aggregate in paving material, landfill cover, or some similar
use, but often is discarded in landfills. The mixed colored
material is substantially less valuable than color sorted
cullet.
[0010] Decolorizing techniques are known in the production of flint
glass, especially to remove the tint due to iron impurities, which
impurities tend to impart a bluish or greenish hue to "colorless"
glass. In the manufacture of colorless glass, particularly
soda-lime-silica flint glasses, the presence of iron as an impurity
in the raw materials has been a serious problem. The presence of
ferrous iron (Fe.sup.+2) tends to cause a bluish or blue-green
discoloration in the finished glass in addition to decreasing its
overall brightness. The economics of glass manufacture are such
that it is difficult to provide low cost raw materials free from
these iron impurities, and most significant deposits of sand and
limestone contain at least trace amounts of various iron salts and
oxides.
[0011] When the raw materials are melted in the glass batch at
temperatures of about 2,600 to 2,900 F (about 1,400 to 1,600 C),
significant amounts of iron present are converted to the ferrous
(Fe.sup.+2) state under the influence of the prevailing equilibrium
conditions. Decolorizers and oxidizers can be added to the glass
batch in an attempt to oxidize the ferrous (Fe.sup.+2) iron,
thereby forming ferric (Fe.sup.+3) iron, to minimize this glass
coloration. Ferric iron (Fe.sup.+3) is a relatively much weaker
colorant than ferrous iron.
[0012] In U.S. Pat. No. 2,929,675 (Wranau, et al.), a method is
disclosed for spinning glass fibers using a fluid molten glass,
which glass is optically enhanced by decolorizing the glass to make
it more transparent or translucent, so that infra-red rays of the
radiant heat supply more readily pass through the glass for heating
the spinnerette. In the Wranau method, glass which is naturally
greenish is decolorized by the addition of effective decolorizing
amounts of such materials as selenium oxide, manganese peroxide,
copper oxide or dispersed gold to the molten glass.
[0013] In U.S. Pat. No. 2,955,948 (Silverman), a glass decolorizing
method is disclosed which continuously produces molten
color-controlled homogeneous glass. In the Silverman method, flint
(colorless) and other container glass is decolorized by addition to
the molten glass of a selenium-enriched frit as a decolorizing
agent, as opposed to selenium in its free state mixed with virgin
batch raw materials. This is considered to better retain the
selenium in the finished goods without vapor loss thereof.
Silverman discloses that various commonly used materials for
decolorizing flint glass have been tried to eliminate selenium
vapor losses without success, such as various selenium compounds,
e.g., sodium and barium selenates and selenides, as well as
arsenic, by reducing the iron oxide inherently present therein.
Silverman discloses that the decolorizing agent preferably
comprises frit compositions containing the essential decolorizing
agent selenium in its Se.sup.+4 valence state, and also may contain
niter and arsenic. In Silverman's method, the decolorizing agent of
selenium-enriched frit is added to the molten flint glass and
dispersed therein in order to decolorize the glass.
[0014] In U.S. Pat. No. 3,482,955 (Monks), a method is disclosed
for decolorizing the ferrous (Fe.sup.+2) oxide content of soda-lime
glass which naturally contains up to about 0.1% by weight of
ferrous oxide. The method of Monks continuously produces
decolorized homogeneous glass using a manganese-enriched frit glass
as the decolorizing agent. Monks, in particular, provides a method
of decolorizing soda-lime glass containing iron as the impurity by
utilizing a decolorizing frit glass containing manganese that
produces no undesirable coloration of its own and adding the
decolorizing frit glass to the molten base glass. Monks teaches
that decolorizing frit glass preferably comprises oxidized
manganese in the Mn.sup.+3 state (Mn.sub.20.sub.3) and in the
Mn.sup.+2 state (MnO), which acts as an oxidizing agent to oxidize
ferrous iron to ferric iron in soda-lime glass.
[0015] Decolorizing to minimize the tint caused by trace impurities
such as a small proportion of ferrous iron is a less severe problem
than decolorizing or offsetting recycled glass that has been
heavily tinted by the addition of tint producing compounds, such as
chromium green found in high concentrations in green glass. A
sufficient treatment with decolorizing compositions may be
difficult to achieve without also affecting the clarity of the
glass or causing other quality and manufacturing problems.
[0016] In co-assigned related U.S. Pat. No. 5,718,737, a process
was described for re-using mixed colored glass cullet to make new
and useful glass products. As described more fully below, in the
described process one or more of the colors in the mixed colored
cullet is selectively colorized and/or decolorized to render it
useful in the manufacture of glass products in one of the other
colors. In particular, a batch of mixed color cullet such as
recycled municipal waste glass containing a mixture of green, amber
and flint (colorless) glass, was selectively decolorized and/or
colorized to a desired color with desired properties. For example,
the mixed colored cullet was converted to recycled amber colored
glass for the manufacture of amber glass containers, such as beer
and other beverage bottles, by selectively decolorizing for green
and colorizing to achieve an amber tint, thereby minimizing any
adverse effect on the appearance of the container due to the
relatively dark amber color.
[0017] It is desired to develop a technique for automating this
process for commercial glass production whereby different batches
of broken glass in mixed colors may be readily rehabilitated to
provide a material that is substantially as useful for the
production of recycled glass containers as sorted amber, green, or
flint glass. In particular, it is desired to expand upon the
technique described in U.S. Pat. No. 5,718,737 by automating the
recycling process and adapting it to conventional commercial glass
production processes by specifying the amount of raw materials
needed to create glass products with desired properties using
different batches of mixed colored cullet. The present invention
has been designed to meet this need in the art.
SUMMARY OF THE INVENTION
[0018] An automated method for recycling mixed colored cullet glass
(i.e., broken pieces of glass of mixed colors and types) into new
glass products in accordance with the invention meets the
above-mentioned needs in the art by providing a computer controlled
process which identifies the virgin glass raw materials, the
desired target glass properties, the composition of a batch of
mixed colored cullet, and the quantity of cullet to be used in the
glass melt, and the computer controlled process then automatically
determines the proper amounts of raw materials to add to the batch
of mixed colored cullet so that recycled glass is produced having
the desired coloring oxides, redox agents, and glass structural
oxides in the proper proportion. The recycled glass is then used to
make glass products such as beer bottles.
[0019] In particular, the present invention relates to a method of
calculating the amount of raw materials for different mixed cullet
compositions, different percentages of mixed cullet in the glass
batch, and different target glass compositions. Key indicator
parameters for the different glass colors are calculated and used
to calculate the batch composition to be formed from a particular
cullet starting material. The results are then printed out using,
e.g., Microsoft Excel, and used in conventional commercial glass
production processes.
[0020] A preferred embodiment of the method of creating recycled
glass products of a particular color from mixed color glass cullet
having glass of at least two different colors in accordance with
the invention preferably comprises the steps of:
[0021] selecting virgin glass raw materials and determining weight
percentages of respective components of the virgin glass raw
materials;
[0022] determining weight percentages of at least the respective
components of the mixed color glass cullet;
[0023] selecting the particular color of the recycled glass
products;
[0024] specifying transmission properties of the recycled glass
products of the particular color;
[0025] determining how much of the mixed color glass cullet, by
weight percent, is to be melted as a fraction of a recycled
finished glass from which the recycled glass products are to be
created;
[0026] specifying percentage composition of at least two of amber,
green, and flint glass in the mixed color glass cullet;
[0027] calculating glass coloring oxide agent levels and key glass
indicator parameters of glass of the particular color with the
specified transmission properties;
[0028] calculating a composition of the recycled finished glass,
the composition including weight percentages of the raw materials,
the mixed color glass cullet, the key glass indicator parameters,
and the glass coloring oxide agent levels; and
[0029] creating recycled glass products from the calculated
composition.
[0030] In accordance with the invention, if the particular color is
amber, the step of specifying transmission properties of the
recycled glass products comprises the steps of specifying a
thickness of a finished glass product made from the calculated
composition and specifying at least two of: an optical transmission
of the finished glass product at 550 mn (T.sub.550), an optical
transmission of the finished glass product at 650 nm (T.sub.650),
and a redness ratio (T.sub.650/T.sub.550) of the finished glass
product. For amber glass, the key glass indicator parameters
comprise at least one of iron concentration, sulfur concentration,
chrome concentration, copper concentration, and oxidation state. On
the other hand, if the particular color is green, the step of
specifying transmission properties of the recycled glass products
comprises the steps of specifying a thickness of a finished glass
product made from the calculated composition and specifying levels
of chromium and iron of the finished glass product. For green
glass, the key glass indicator parameters comprise at least one of
chromium concentration and iron concentration. However, if the
particular color is clear, the step of specifying transmission
properties of the recycled glass products comprises either the step
of determining the best possible neutral density transmission for a
finished glass product for the specified amount of mixed color
glass cullet in the finished glass product, or the step of
maximizing the amount of mixed color glass cullet used in the
finished glass product for the transmission properties specified in
the transmission properties specifying step. For clear glass, the
key glass indicator parameters comprise at least one of chromium
concentration, iron concentration, selenium concentration, cobalt
concentration, and oxidation state.
[0031] In accordance with the preferred embodiment of the
invention, the step of calculating the composition of the recycled
finished glass is performed by a computer program loaded on a host
processor, and comprises the step of calculating the proper amounts
of the respective components so that the proper coloring oxides,
redox agents, and glass structural oxides are present in the proper
proportion in the finished glass products in accordance with the
following linear equation:
M.sub.mxn X.sub.n=B.sub.m
[0032] where:
[0033] M is a matrix of dimension m by n, where n is a number of
the components from which the recycled finished glass is to be made
and m is a number of composition constraints including the key
glass indicator parameters plus essential oxide concentrations for
the finished glass products;
[0034] X is a row vector of dimension n that defines the weight
percent of each component in the recycled finished glass; and
[0035] B is a column vector of dimension m that contains target
values of the composition constraints.
[0036] Since this linear equation may have multiple solutions, the
step of calculating the composition of the recycled finished glass
preferably comprises the additional step of selecting solutions of
the linear equation which minimize costs of the components in the
recycled finished glass if the particular color is amber or green.
For example, if the particular color is amber, the components may
include compositions of clear, amber, and green cullets plus a
predetermined number of conventional glass raw materials, and the
composition constraints may include concentrations of SiO.sub.2,
Al.sub.2O.sub.3, CaO, and Na.sub.2O from the virgin glass, the
concentrations of the coloring oxides of chrome, iron, sulfur, and
copper, and a chemical oxygen demand value. On the other hand, if
the particular color is clear, then the linear equation is
preferably solved by selecting the solutions of the linear equation
which minimize iron levels in the recycled finished glass.
[0037] Preferably, the calculated composition (by weight
percentages of the recycled finished glass for a predetermined
amount of the finished glass products) and a chemical composition
of the recycled finished glass, as well as the transmission
properties of the finished glass products are printed.
[0038] The scope of the invention also includes the finished glass
products made from the combined three mix and virgin glass
composition calculated using the techniques of the invention.
Preferably, the finished glass product is a glass bottle, such as
an amber or green beer bottle.
[0039] The scope of the invention also includes a program storage
device readable by a processor and storing thereon a program of
instructions executable by the processor during the process of
creating recycled glass products of a particular color from mixed
color glass cullet having glass of at least two different colors.
In accordance with the invention, the program of instructions
causes the processor to accept as inputs a designation of virgin
glass raw materials, a designation of the particular color of the
recycled glass products, a designation of desired transmission
properties of the recycled glass products of the particular color,
a designation of how much of the mixed color glass cullet, by
weight percent, is to be melted as a fraction of a recycled
finished glass from which the recycled glass products are to be
created, and a designation of a percentage composition of at least
two of amber, green, and flint glass in the mixed color glass
cullet, and causes the processor to determine from the inputs the
weight percentages of respective components of the virgin glass raw
materials, weight percentages of at least the respective components
of the mixed color glass cullet, glass coloring oxide agent levels
and key glass indicator parameters of glass of the particular color
with the specified transmission properties, and a composition of
the recycled finished glass, the program of instructions further
causing the processor to output an indication of the composition
for use in the process of creating recycled glass products of a
particular color from mixed color glass cullet, the composition
including weight percentages of the raw materials, the mixed color
glass cullet, the key glass indicator parameters, and the glass
coloring oxide agent levels. The composition is then printed for
use as a "recipe" in creating finished glass products, such as
glass beer bottles, from a glass batch including mixed color
cullet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The objects and advantages of the invention will become more
apparent and more readily appreciated from the following detailed
description of presently preferred exemplary embodiments of the
invention taken in conjunction with the accompanying drawings of
which:
[0041] FIG. 1 illustrates the inventive technique for determining
the composition of glass batches including post-consumer mixed
color glass cullet.
[0042] FIGS. 2(a) and 2(b) together illustrate a spreadsheet of a
glass oxide calculation model from the batch formula for the
creation of recycled amber glass containers from an amber melt
including 35% recycled mixed color cullet using the techniques of
the invention.
[0043] FIG. 2(c) illustrates the glass batch formulations for the
creation of recycled green glass containers from three mix cullet
typical of that found on the East and West Coast where substantial
imported beer and wine consumption occurs, where the three mix
cullet is 35% of the total glass.
[0044] FIG. 3 illustrates the redness ratio and measured visible
transmission levels for amber, green and clear glasses from
different glass producers.
[0045] FIG. 4 illustrates the ratio of clear (flint), amber, and
green glass for different customer glass use patterns and the
products available in regional markets.
[0046] FIG. 5 illustrates the extinction coefficients for the
container glass specimens of FIG. 3 as well as the average
extinction coefficients and average transmission normalized through
3.18 mm thick glass for the major amber and green glass
manufacturers in the U.S.
[0047] FIGS. 6(a) and 6(b) respectively illustrate the glass batch
formulations for the creation of recycled amber glass containers
from a three-mix where the cullet is 50% and 75% of the total
glass, respectively.
[0048] FIGS. 7(a)-7(c) respectively illustrate the glass batch
formulations for the creation of recycled amber glass containers
from three-mix where the cullet is 25%, 50%, and 75% of the total
glass, respectively, which is typical of domestic glass
production.
[0049] FIGS. 8(a)-8(c) respectively illustrate the glass batch
formulations for the creation of recycled amber glass containers
from the standard U.S. glass production (1/3 clear glass removed)
three-mix where the cullet is 25%, 50%, and 75% of the total glass,
respectively.
[0050] FIGS. 9(a)-9(c) respectively illustrate the glass batch
formulations for the creation of recycled amber glass containers
from the standard U.S. glass production (2/3 clear glass removed)
three-mix where the cullet is 25%, 50%, and 75% of the total glass,
respectively.
[0051] FIGS. 10(a)-10(c) respectively illustrate the glass batch
formulations for the creation of recycled amber glass containers
from the trend to amber three-mix where the cullet is 25%, 50%, and
75% of the total glass, respectively.
[0052] FIGS. 11(a)-11(c) respectively illustrate the glass batch
formulations for the creation of recycled amber glass containers
from the Middle America Beer Belt three-mix where the cullet is
25%, 50%, and 75% of the total glass, respectively.
[0053] FIGS. 12(a) and 12(b) together illustrate a spreadsheet of a
glass oxide calculation model from the batch formula for the
creation of recycled green glass containers from a green melt
including 35% recycled mixed color cullet using the techniques of
the invention.
[0054] FIGS. 12(c) and 12(d) respectively illustrate the glass
batch formulations for the creation of recycled green glass
containers from three mix cullet typical of that found on the East
and West Coast where the cullet is 35% and 70% of the total glass,
respectively.
[0055] FIGS. 13(a)-13(c) respectively illustrate the glass batch
formulations for the creation of recycled green glass containers
from the standard U.S. glass production three-mix where the cullet
is 25%, 50%, and 75% of the total glass, respectively.
[0056] FIGS. 14(a)-14(c) respectively illustrate the glass batch
formulations for the creation of recycled green glass containers
from the beer belt blend three-mix where the cullet is 25%, 50%,
and 75% of the total glass, respectively.
[0057] FIGS. 15(a) and 15(b) together illustrate a spreadsheet of a
glass oxide calculation model from the batch formula for the
creation of recycled clear (flint) glass containers from the beer
belt blend three-mix, where the cullet is 25% of the total glass,
using the techniques of the invention.
[0058] FIGS. 15(c) and 15(d) illustrate the glass batch
formulations for the creation of recycled clear (flint) glass
containers from the beer belt blend three-mix where the cullet is
25% and 50% of the total glass, respectively.
[0059] FIGS. 16(a) and 16(b) respectively illustrate the glass
batch formulations for the creation of recycled clear (flint) glass
containers from the USA production three-mix where the cullet is
25% and 50% of the total glass, respectively.
DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS
[0060] A method of recycling mixed color cullet with the
above-mentioned beneficial features in accordance with a presently
preferred exemplary embodiment of the invention will be described
below with reference to FIGS. 1-16. It will be appreciated by those
of ordinary skill in the art that the description given herein with
respect to those figures is for exemplary purposes only and is not
intended in any way to limit the scope of the invention. All
questions regarding the scope of the invention may be resolved by
referring to the appended claims.
[0061] I. Mixed Cullet Recycling Method of U.S. Pat. No.
[0062] U.S. Pat. No. 5,718,737
[0063] A quantity of mixed colored glass cullet may be manually
recycled into new glass products using the technique described in
U.S. Pat. No. 5,718,737. As described therein, the mixed colored
glass cullet is generally reclaimed, post-consumer glass, although
the glass producer's waste cullet can also be mixed therewith, and
typically comprises a mixture of green glass, amber glass and flint
(colorless) glass. The mixed colored cullet is primarily made of
soda-lime-silica glass (otherwise referred to as "soda-lime glass")
and is typically provided in bulk in the form of a plurality of
broken pieces or particles produced by crushing or grinding glass
containers, the particles typically sized less than 6 mm in
diameter, such that the cullet can be readily poured or otherwise
handled and melted. Generally, at least one color may be
selectively removed, neutralized, or converted in a specified batch
of mixed color glass cullet by selective physical and/or chemical
decolorizing, at which time, the mixed color glass cullet absent
such at least one color is recovered for use in the production of
new glass products.
[0064] Amber colored glass may be produced from the mixed color
glass cullet by selectively decolorizing the green colorant in the
mixed cullet. In particular, the green glass particles which
inherently contain chromium oxide as the green colorant, and which
also may contain iron impurities, can be selectively decolorized in
the mixed colored batch to remove excessive green which lowers the
desired redness ratio or reddish hue in amber glass used to
manufacture new containers, such as amber beer bottles. The
reddish-brown hue of amber colored glass from mixed color cullet is
controlled by regulating the amounts of iron, carbon and sulfur in
the mix to impart the desired reddish-brown amber color. A similar
technique may be used to produce recycled green or flint colored
glass bottles and the like.
[0065] The mixed color glass cullet is optionally decolorized as to
at least one color, by addition to mixed color glass an effective
amount of decolorizing agent(s) as provided hereinafter, for the at
least one color to be decolorized. The method includes the step of
further colorizing the mixed colored cullet as to at least one
remaining color, by addition to the mixed colored glass, an
effective amount of colorizing agent(s) as provided hereinafter, to
enhance the remaining color. Preferably, a predetermined amount of
mixed colored cullet glass is admixed with a virgin batch of glass
containing conventional glass raw materials in the remaining color
as well as decolorizing agent(s) and colorizing agent(s) to
compensate for the mixed colored cullet to produce new glass
products containing a certain percentage of recycled mixed colored
cullet. This is particularly effective for making amber glass
containers and the like from mixed color cullet.
[0066] Conventional glass raw materials, such as those for amber,
green, or flint soda-lime-silicate glasses, and glass making
equipment, such as glass melting furnaces, lehrs, forming equipment
and the like, can be used with the method of the invention. For a
description of glass raw materials, glass manufacture and
processing techniques, reference can be made, inter alia, to S. R.
Scholes, Ph.D., Modem Glass Practice, CBI Publishing Co., Inc.
(1975) and Kirk-Othmer, Concise Encyclopedia of Chemical
Technology, John Wiley & Sons, Inc. (1985), pp. 560-565, the
disclosures of which are hereby incorporated in their
entireties.
[0067] Amber colored glass used for beverage bottles can be
produced from the post consumer (recycled) cullet. In such a
method, a quantity of post consumer (recycled) cullet is intimately
mixed together with a virgin batch of conventional glass raw
materials used for making amber colored glass, preferably
carbon-sulfur amber glass. The minimum amount of mixed colored
cullet in the batch may be affected by government regulations. It
is required by some state governments to include at least about
-10% or greater, while some state governments require at least
about 35% or greater, and, by the year 2000, will require between
about 35% and 50% by weight post consumer (recycled) cullet in the
glass. It is preferred that the mixed colored cullet is introduced
on top of a mixed virgin glass in the glass melting furnace,
typically operated at a temperature of 2,600 to 2,900 F (about
1,400 to 1,600 C), to reduce the tendency of the cullet to cause
foaming and frothing of the molten glass and resultant processing
problems.
[0068] The virgin glass raw materials for amber colored glass,
known to be capable of yielding glass-forming oxides, can include
effective amounts of major constituents, e.g., sand, limestone,
soda ash, feldspar, or the like, and minor constituents, e.g., salt
cake, gypsum, carbocite, graphite, iron pyrite, calumite, or the
like.
[0069] While the precise mechanism is not well understood, the
reddish-brown coloration of carbon-sulfur amber colored glass is
believed to be attributed to its sulfate (e.g., soda cake and
gypsum), carbon (e.g., carbocite, graphite and carbon black) and
iron (e.g., iron oxide and iron pyrite) contents. It is believed
that amber glass formation involves the colorizing reactions of the
alkali sulfates with reducing agents, such as carbon, to form
alkali sulfites, elemental sulfur and sulfides, as well as alkali
polysulfides and sulfoferrites, which compounds are all believed to
play a part in the amber coloring.
[0070] Amber container glasses absorb light in the biologically
active region of 450 NM and thereby protect the container contents
from chemically active ultraviolet radiation. Amber glass is
produced under strong reducing conditions and typically has a redox
number of about -40 to -70 and a redness ratio of in the range of
1.5-2.0.
[0071] The level of reduction present in a glass melting furnace is
represented by the redox number, RN. The redox number is given, per
ton of glass, as the pounds of salt cake (Na.sub.2SO.sub.4)
oxidizer equivalent in excess of that required to balance the
following stoichiometric equations.
C+2Na.sub.2SO.sub.4 2Na.sub.2O(glass)+CO.sub.2+2SO.sub.2
[0072] (Note that the Mass Ratio of salt cake (Na.sub.2SO.sub.4) to
carbon (C) in the balanced equation=284/12=23.7)
5C+4NaNO.sub.3 2Na.sub.2O(glass)+5CO.sub.2+2N.sub.2
[0073] (Note that the Mass Ratio of niter (NaNO.sub.3) to carbon
(C) is=340/60=5,667, thus, the salt cake/niter ratio can be
calculated by 23.7/5,667=4,182)
[0074] Hence, a positive redox number indicates oxidizing
conditions while a negative redox number reflects reducing
conditions.
[0075] The redox number can be calculated from the following
formula for batches and glasses where all oxidizing and reducing
agents are expressed in terms of salt cake, niter, and carbon
equivalents:
RN=Ss+Nn-Cc
[0076] where:
[0077] S=salt cake, lbs per ton of glass
[0078] C=carbon, lbs per ton of glass
[0079] N=niter, lbs per ton of glass
[0080] and
[0081] s=salt cake mass ratio to salt cake=1
[0082] c=salt cake to carbon mass ratio=23.7
[0083] n=salt cake to niter mass ratio=4,182
[0084] The composition of a non-limiting, purely representative
example of an amber container glass (shown in weight percentages)
is provided in Table 1.
1TABLE I Composition of Amber Colored Glass Oxide % (Wt.) SiO.sub.2
71-73 Al.sub.2O.sub.3 0.1-0.5 Fe.sub.2O.sub.3 0.2-0.5 CaO 7-9 MgO
0.1-2 Na.sub.2O 13-15 K.sub.20 0-1 MnO 0-1 SO.sub.3 0-.5
[0085] The mixed colored cullet may be selectively melted into the
virgin glass, forming a homogenous mixture. The green glass
contained in the mixed colored cullet, which has relatively high
chromium oxide content and which also may contain iron impurities,
is decolorized by the addition of an effective amount of a
decolorizing agent to the molten mixed colored cullet. The
decolorizing agent can be a chemical or physical decolorizing
agent, or both.
[0086] In physical decolorizing, complementary colors are added to
the green cullet to offset or neutralize the color green. Preferred
physical decolorizing agents include elemental or compounds of
selenium (red), manganese (red), cobalt (blue), nickel, and/or
selenides. A limitation of color blending, however, is that the
glass may be imparted with a gray (smoky) hue in offsetting the
greenness in this manner, which may render the glass less
water-white. For a typical mixed colored cullet comprising about
56% by weight flint (colorless), 22.5% by weight amber, and 21.5%
by weight green glass, it is preferred to add from about 0.001 to
0.01% by weight of selenium or comparable decolorizing agent per
100% by weight mixed color cullet, most preferably between about
0.005 to 0.01% by weight.
[0087] Instead of or in addition to physical decolorizing, chemical
decolorizing can be effected. Preferred chemical decolorizing
agents or oxidizing agents which can be added in effective amounts
to the mixed color cullet to oxidize trace amounts of ferrous
(green) to ferric iron include oxides of zinc, cerium, and arsenic,
and also can include oxidized virgin glass materials. For a typical
mixed colored cullet comprising about 56% by weight flint
(colorless), 22.5% by weight amber, and 21.5% by weight green
glass, it is preferred to add from about 0.001 to 0.01% by weight
of chemical decolorizing agent per 100% by weight mixed colored
cullet, most preferably between about 0.005 to 0.05% by weight.
[0088] The decolorized or color neutralized green colored cullet
and the flint cullet that remain can be color enhanced to amber by
adding effective amounts of typical colorizing agents for amber
glass production. Preferred colorizing agents include iron pyrite,
salt cake (sodium sulfate), sodium sulfite, sodium sulphide, carbon
(typically in the form of carbocite or graphite), and slag
(typically in the form of calumite), which are used to impart a
reddish-brown color. For a typical mixed colored cullet comprising
about 56% by weight flint (colorless), 22.5% by weight amber, and
21.5% by weight green glass, it is preferred to add from about 0.25
to 0.50% by weight of colorizing agent per 100% by weight mixed
colored cullet, most preferably between about 0.30 to 0.40% by
weight.
[0089] The molten mixture of mixed colored cullet converted to
amber color and virgin amber glass can be fined as is well known by
the addition of, e.g., salt cake, to minimize gas bubbles therein.
After fining, the glass can be directed to a glass blowing machine
or other glass forming machine in the same manner as conventionally
produced glass, e.g., in a bottle glass blowing machine for forming
amber colored beer bottles. After forming, the glass can be
annealed in a known manner, e.g., in a lehr, to remove internal
glass stresses.
[0090] This technique is not limited to the production of amber
colored glass from mixed colored cullet. It is also directed to the
production of flint or green glass from mixed colored cullet as
well. For flint glass, a virgin batch is mixed with chemical
decolorizing agents, such as, oxides of cerium and zinc to
chemically oxidize iron impurities and may also be mixed with
physical decolorizing agents having complementary colors, such as
elemental or compounds of selenium and cobalt.
[0091] This method can be better understood from the following
purely exemplary and non-limiting example.
EXAMPLE
Conversion of Mixed Broken Colored Cullet to Amber Colored
Glass
[0092] A batch of mixed colored cullet was suitably converted to
amber colored glass by the following method: First, about 2 lbs. of
mixed colored cullet comprising about 56% by weight flint
(colorless), 22.5% by weight amber, and 21.5% by weight green glass
had about 0.3 to 0.45% of Fe.sub.2O.sub.3 equivalent by weight
(based on the weight of the molten cullet) of iron pyrite added
thereto and intimately mixed together therewith. From about 0.015
to 0.07% by weight carbon (in the form of carbocite) was also added
to the mixed colored cullet to achieve a redox number of
approximately -55. These ingredients were melted to a molten state
in a glass furnace at a temperature of about 2,600.degree. F. to
2,700.degree. F. The addition of carbon (reducing agent) controls
the final amber color, i.e., as carbon content increases, the
reddish-brown hue increases. The molten mixed color cullet with
colorizing agents was then cooled and formed into patty samples by
pouring the molten cullet from crucibles. The resultant glass was
amber colored with UV transmittance of about 15%.
[0093] In this example, the amounts of each raw material was
calculated manually, which is impractical since the proper control
of glass color and composition for commercial production requires
the simultaneous control of many variables. An automated method
that provides enhanced color control and is suitable for commercial
glass production is explained in the next section.
[0094] II. Automated Mixed Cullet Recycling Method
[0095] In accordance with the present invention, a software
algorithm has been developed which facilitates the automatic
calculation of the raw materials for different mixed cullet
compositions, different percentages of mixed cullet in the glass
batch, and different target glass compositions. In particular, key
indicator parameters for the different glass colors have been
identified and are calculated using a computer program loaded on a
host processor, and these parameters are, in turn, used by the host
processor to calculate the batch composition to be formed from a
particular cullet starting material. The results are then printed
out using convenient software, e.g. Microsoft Excel, and used in
conventional commercial glass production processes.
[0096] FIG. 1 illustrates the software algorithm developed in
accordance with the invention which is loaded on a host processor
for calculating the composition of glass batches including
post-consumer glass cullet to be recycled. The first part of the
software algorithm of the invention includes the step of defining
the user-selected glass parameters. In particular, at step 10, the
user first selects from a list of options the raw materials to be
used for the virgin component of the glass. In other words, the
user specifies the type and composition of sand, limestone, aplite
(feldspar), source of slag (e.g., calumite), salt cake, melite,
soda ash, source of carbon (e.g., CARBOCITE.TM.#20) and the like to
be used for the virgin glass.
[0097] At step 15, the user defines the cullet chemical
composition, i.e., the oxide composition percentage of the clear,
amber, and green glass in the mixed cullet to be used in the
recycling process.
[0098] As shown in the sample melt of FIGS. 2(a) and 2(b) for an
amber melt including 35% recycled mixed cullet, the algorithm of
the invention inputs the oxide composition and cost of the raw
materials (step 10) and the cullet (step 15) used in preparing the
batch. The oxide percentages may be readily determined from a
chemical analysis of the materials. Typical virgin glass materials
may include: Glass sand from U.S. Silica; Limestone; Aplite from
U.S. Silica; Calumite from Calumite Corporation; Salt Cake; Melite;
Soda Ash from FMC; and Carbocite #20. Typical cullet compositions
are similar to virgin glass except that they contain coloring
oxides specific for clear, green, and amber. Various adjustments
are also made for volatile loss during melting.
[0099] Next, at step 20, the user defines the color of the target
glass desired: clear (flint), amber, or green. In the glass oxide
calculation example of FIGS. 2(a) and 2(b), the specified target
glass color is amber. If it is determined at step 30 that the
designated color is amber, then the user should define the
thickness of the transmission specimen (3.18 mm is the default) and
specify the optical transmission at 550 nm (T.sub.550) and the
optical transmission at 650 nm (T.sub.650) and/or the redness
ratio, i.e., T.sub.650/T.sub.550, in the finished glass product at
step 32. Typical values for 550 and 650 transmission through a 3.18
mm specimen are 11.5% and 23%, respectively. Accordingly, the
default value for the redness ratio is 2.0.
[0100] However, those skilled in the art of glass making will
appreciate that all amber glasses are not the same. For example, as
illustrated in FIG. 3, the redness ratio and measured visible
transmission levels for amber, green and clear glasses vary from
producer to producer, and the program of the invention preferably
accommodates this need. In FIG. 3, the transmission data is
adjusted to a glass thickness of 0.125 inch, or 3.18 mm, which is
the default thickness of the specimens, which include amber
specimens 1-6, clear specimen 8, and green specimens 7, 9, and 10.
In FIG. 3, all wavelengths are in nm.
[0101] On the other hand, if it is determined at step 30 that the
specified target glass color is green, then the user should define
the thickness of the transmission specimen (3.18 mm is the default)
and the amount of chromium (as Cr.sub.20.sub.3) and iron (as
Fe.sub.20.sub.3) desired in the finished glass product at step 34.
Typical Cr.sub.20.sub.3 and Fe.sub.20.sub.3 levels for green glass
are 0.23% and 0.25%, respectively. Greater levels produce a darker
green and lesser levels a lighter color as desired for various beer
and wine bottles. Other coloring oxides such as Mn and Ni can be
added to alter the hue of the green glass.
[0102] If it is determined at step 30 that the specified target
glass color is clear (flint), no additional input is required. The
program identifies the amount of Fe and Cr present from the raw
materials and the mandatory three-mix cullet level and, at step 36,
calculates the greatest possible colorless (i.e. neutral density)
transmission for a given cullet input or maximizes the amount of
cullet used for a specified transmission characteristic. Blue
(cobalt) and red (selenium) coloring agents may be added to give a
neutral color density, i.e., nearly uniform absorption at all
wavelengths. Depending on the amount of amber and green cullet
used, the transmission can vary from the normal 70-80% typical of
clear glass down to 30-40% for heavy three-mix loadings with lots
of amber and green glass. Thus, some reformulated glasses will be
quite gray whereas others will be quite good flint glasses when
made from three mix cullet using the techniques of the invention. A
further feature of the invention is the ability to maximize
three-mix cullet use in a glass batch. As an alternative to the
above method of batching flint glass, it is possible to specify the
minimum transmission of the flint glass and to have the algorithm
calculate the maximum amount of a certain three-mix cullet that
will permit the specified transmission. Naturally, the calculated
three-mix amount will be greater for three-mix cullets with little
green and amber glass and lesser for cullets with lots of green and
amber.
[0103] At step 40, the user defines the quantity (%) of cullet to
be used in the melting process as a percentage of the total glass,
e.g., 35, 50, 75%, where the remaining material is the typical
virgin glass. Typically, the total quantity of three-mix cullet is
between 35% and 75% but may vary based on legislative and other
requirements. In the example of FIGS. 2(a) and 2(b), the percentage
of cullet used in the melting process is designated as 35%.
[0104] At step 50, the cullet three mix ratios are specified. These
values indicate the relative amount of clear, amber, and green
glass in the cullet. These ratios may be measured by taking a core
sample of the mixed cullet to be recycled or may be determined
empirically by glass recyclers in different geographical areas.
Typically, the ratio of clear (flint), amber, and green glass for
recycling will vary according to customer use patterns and the
products available in regional markets. Typically, as shown in FIG.
4, U.S. glass container production yields approximately 60% clear
(flint) glass, 30% amber, and 10% green. However, three-mix cullet
compositions vary enormously depending upon collection and
recycling practices and also on consumer demographics and
preferences. Three-mix cullet flint levels are in the range of
30-60%, amber in the range of 25-55%, and green in the range of
5-25%. More green tends to be present in those areas that import
more foreign beers and consume more wine, as on the east and west
coasts of the United States. For the example of FIGS. 2(a) and
2(b), the percentage fractions are specified as 48.3% clear
(flint), 26.7% amber, and 25.0% green, a mix of cullet
representative of that encountered on the east and west coasts of
the United States.
[0105] Now that all the inputs are provided, the second part of the
software algorithm of the invention is executed, namely,
calculating the batch composition from the user-selected glass
parameters. At step 60, the coloring oxide ratios and glass redox
levels in the glass for the requested color properties of the
target glass product are computed via known relationships. Since
soda lime glass accounts for nearly 90% of all container glass
produced, the target glass is assumed to be a standard soda lime
silicate, modified with coloring oxides. For example, standard
container soda lime silicate glass has the following coloring oxide
percentages:
2 Oxide Weight Percent SiO.sub.2 71.5% Al.sub.2O.sub.3 1.7% CaO
10.9% MgO 1.5% Na.sub.2O 13.5% K.sub.2O 0.1%
[0106] Then, at step 70, the values of key indicator parameters in
the target glass are calculated based on the user defined inputs in
steps 10-50. Key indicator parameters are glass batch composition
and redox parameters that affect the color or the glass in a
sensitive way. For example, small amounts of Cr and/or Fe will make
a glass with color ranging from green to blue. The engineering and
control of the color of the melted glass requires close control of
these parameters and a detailed knowledge of the way in which these
oxides influence the color of the melted glass. The key indicator
parameters are different for the three glass colors considered
herein (amber, green, and clear) and will thus be discussed
separately.
[0107] Amber Glass
[0108] For amber glass, the key indicator parameters are: iron
[Fe], Sulfur [S], chrome [Cr], and copper [Cu], or other red
coloring agent concentrations, and the oxidation state of the amber
glass as expressed by the batch redox number or chemical oxygen
demand (COD) of the glass. As known by those skilled in the art and
as described previously, the redox number (RN) is a value used in
commercial glass melting to express the redox balance between
sodium sulfate (salt cake, the oxidizer) and carbon or carbon
equivalents (reducing agents). Normal redox numbers are in the
range of +10 to -30 for flint and green glass and -50 to -80 for
amber glass.
[0109] Chemical oxygen demand (COD), is a measure of the chemical
reducing power of batch constituents. COD is a way of measuring the
redox level of raw materials and glass using conventional methods
available from analytical laboratories. COD is expressed as percent
of carbon and represents, in effect, the chemical reducing power of
the raw material in terms of equivalent levels of carbon. For
example, a certain carbon additive to a glass batch may contain 78%
carbon and 22% ash. Such a material would have a COD of 78% since
it has the equivalent of 78% carbon. As a second example, a slag
raw material may contain a mixture of reduced chemical species such
as sulfide and various carbides such that its reducing power is
equivalent to 1% free carbon, even though the slag may contain no
free carbon. This raw material will have a COD of 1%. Hence, the
COD factor, when summed over all glass batch raw materials,
quantitatively identifies the reducing power of the batch in terms
of equivalent carbon levels. So, if a glass batch has a collective
COD of 0.2%, or 2000 ppm, then the amount of oxygen it will take up
can be calculated as follows for each 100 grams of glass:
100 grams.times.2000.times.10.sup.6=0.2 carbon equivalent.
C+O.sub.2 CO.sub.2 MW C=12, O.sub.2=32
[0110] Thus, 0.2 g C "demands" 32/12*0.2=0.533 g O.sub.2.
[0111] Those skilled in the art will appreciate that more reduced
batch chemistries and higher Fe, Cr, and S levels produce darker
amber glasses and that the redness ratio is increased with higher
levels of S and Cu. The necessary levels of the key indicators are
calculated from optical extinction coefficients for each
constituent, where the extinction coefficient is defined as
follows:
I=I.sub.0R.sub.fe.sup.-ext L
[0112] where I is the transmitted intensity, I.sub.o is the
incident intensity, R.sub.r is Fresnel reflection from the
interfaces, ext is the extinction coefficient, and L is the
thickness of the test specimen in mm. For example, Cr.sub.2O.sub.3
has an extinction coefficient at 550 nm of 0.484 for each weight
percent in the glass. Thus, a glass containing 0.2% Cr.sub.2O.sub.3
will have an extinction coefficient attributable to Cr.sub.2O.sub.3
of 0.484*0.2=0.097. At 650 nm, the Cr.sub.2O.sub.3 extinction
coefficient per percent oxide is 2.174. The other parameters are
treated similarly, using values obtained from the literature and/or
from spectrophotometric measurement.
[0113] FIG. 5 illustrates the extinction coefficients (ext) for the
10 container glass specimens of FIG. 3 as calculated using the
above equation for the different wavelengths (in nm). FIG. 5 also
illustrates the average extinction coefficients and average
transmission normalized through 3.18 mm thick glass for the major
amber and green glass manufacturers in the United States, where BMC
is Budweiser, Miller, and Coors (for amber), and BH is Becks and
Heineken (for green). Thus, the values used will depend on the
container glass desired.
[0114] Green Glass
[0115] For green glass, the key indicators are Cr.sub.2O.sub.3 and
Fe.sub.2O.sub.3 concentrations. Green glass is treated similarly to
amber glass except that color matching is done directly on an oxide
basis. That is, no input regarding transmission data is accepted,
but rather the user simply defines the Cr.sub.2O.sub.3 and
Fe.sub.2O.sub.3 levels desired in the finished glass. Typical
Cr.sub.2O.sub.3 and Fe.sub.2O.sub.3 levels for green glass are
0.23% and 0.25%, respectively. More Cr.sub.2O.sub.3 increases the
green intensity and more Fe.sub.2O.sub.3 increases the green and
blue intensity, depending on oxidation level. More oxidizing
Fe.sub.2O.sub.3 glasses are greenish yellow as compared to the
bluish color of reduced Fe.sub.2O.sub.3 glass.
[0116] Clear Glass
[0117] As will be appreciated by those skilled in the art, the
clear glass model seeks to minimize the effect of the color oxides
introduced from the green and amber cullet. It is not possible to
"bleach" the glass or remove the coloring oxides; it is only
possible to minimize their impact. This is done by minimizing
(using linear programming) the amount of coloring oxides entering
the glass from the virgin batch component, oxidizing the existing
iron to the ferric state, and complementing the coloring effects of
Fe and Cr (greenish) with Co (blue) and Se (red) to give a neutral
density absorption, i.e., a "colorless" glass. Thus, the key
indicators for clear (flint) glass are Cr.sub.2O.sub.3,
Fe.sub.2O.sub.3, selenium and cobalt concentrations, and the redox
number (oxidation state of the glass).
[0118] The clear glass model operates independently of user input,
aside from the cullet and batch parameters, and computes all values
internally to give the colorless glass with the highest
transmission possible. Two modes of operation are provided:
transmission optimization for a given three-mix cullet composition
and level, and cullet optimization for a given transmission
specification. Given a certain cullet mix ratio and quantity to be
used in the glass, and given the raw materials from which virgin
glass can be prepared, the minimum coloring oxide concentration is
defined. The program of the invention seeks to calculate the
composition which supplements the defined cullet levels so that the
melted glass has minimum levels of the coloring oxides for iron
[Fe.sub.2O.sub.3] and chrome [Cr.sub.2O.sub.3]. Given these levels,
the program then adds sufficient decolorizing oxides such as cobalt
(e.g., 2 ppm Co per 100 ppm (Fe.sub.2O.sub.3+Cr.sub.2O.sub.3)) and
selenium (e.g., 30 ppm Se per 100 ppm
(Fe.sub.2O.sub.3+Cr.sub.2O.sub.3)) to produce a neutral color,
uniform spectral absorption (i.e., wavelength independent
transmission) across the visible wavelength range, whereby the
glass is oxidized to a redox number in the range of +5 to +10 so
that the ferrous [Fe.sup.+2] ions are converted to ferric
[Fe.sup.+3] to minimize the coloring effect of the iron. Depending
on the amount of amber and green cullet used, the transmission can
vary from the normal 70-80% typical of clear glass down to 30-40%
for heavy three-mix loadings with lots of amber and green glass.
Thus, some reformulated glasses will be somewhat gray whereas
others will be quite good flint glasses. In a similar fashion, the
model can be used to define the maximum amount of a certain
three-mix cullet that can be used in manufacturing a flint glass
with fixed transmission specifications.
[0119] Computational Algorithm--Linear Programming
[0120] Once the key indicator parameters are defined at step 70,
the batch formula (composition) can be calculated using linear
programming methods at step 80. In particular, the proper amounts
of raw materials, including the specified cullet fraction and mix,
are computed so that the proper coloring oxides, redox agents, and
remaining glass structural oxides are present in the proper
proportion. The linear problem is as follows:
M.sub.mxn X.sub.n=B.sub.m
[0121] where:
[0122] M is a matrix of dimension m by n, where n is the number of
raw materials, including cullet, from which the batch can be
calculated and m is the number of composition constraints which
include all the key indicators plus essential oxide concentrations
for the base glass. In a typical amber composition, for example,
there might be 12 raw materials [n=12] consisting of three
different cullets [clear, amber, and green] plus nine conventional
glass raw materials such as sand, limestone, soda ash, etc. The
constraints may consist of SiO.sub.2, Al.sub.2O.sub.3, CaO,
Na.sub.2O concentrations from the base glass composition, plus the
coloring oxides of iron, sulfur, and copper concentrations, plus
the redox number (RN) value, and finally a constraint that requires
everything to add up to 100%. This totals nine constraints. Thus,
matrix M is a 9.times.12 matrix in this case. Although most of
these calculations are performed internally in the program, the
values of most of these constraints as well as other variables are
given on the bottom two rows of FIG. 2B.
[0123] X is a row vector of dimension n that defines the weight
percent of each raw material in the glass batch. This variable,
when solved, yields the batch composition.
[0124] B is a column vector of dimension m that contains the target
values of the constraints. These constraints are the target
properties of the glass in terms of oxide and key indicator values
as discussed above.
[0125] The solution to the problem is conducted in a
straight-forward manner using matrix algebra:
X.sub.n=B.sub.m/M.sub.mxn
[0126] As just noted, the batch calculation procedure of the
invention utilizes linear programming to calculate batch
compositions from the available raw materials and the defined
requirements of the melted glass. Those skilled in the art of
linear programming will appreciate that linear programming
techniques solve simultaneous linear equations. As a result, in
practically all real batch calculation cases, there is not a unique
solution but rather many solutions, arising from the fact that many
raw materials contain common oxides. For example, sand, feldspar,
slag, and cullet all contain SiO.sub.2. This multiplicity of
solutions provide a "slackness" in the model. Accordingly, the
technique of the invention includes an algorithm at step 90 for
selecting from among these numerous solutions. The presently
preferred means for performing the selection is called the
objective function, which is an additional function which is solved
to give a minimum, maximum, or target value. Most typical is for
the objective function to be a simple linear cost model in which
the total batch cost is the sum of the cost of each raw material
multiplied by the fraction of the raw material in the glass batch.
Thus, the slackness in the solution is used in amber and green
glasses to calculate at step 90 a batch formula selecting raw
materials that minimize the total batch cost. In flint (clear)
glass compositions, on the other hand, the slackness is used to
minimize the iron content in the batch. That is, the computer
program of the invention selects from the multiple solutions the
one that uses the least expensive raw materials (for amber and
green glasses) or containing a minimum of iron (for flint
glass).
[0127] At step 100, once the linear problem is solved, results are
printed which give the batch composition from raw material
quantities both in terms of 2000 lbs. glass and as weight
percentages, the chemical composition of the glass, and, for amber
glass, the estimated transmission properties. These values can then
be used quite usefully in the production of the glass by those
skilled in the glass-making art and the final step, step 110, is to
transfer these data to the glass manufacturing operation, either
manually or by computerized control to the batch weigh-out
computer. For example, the raw material amounts for a 2000 pound
glass batch of amber glass with the properties specified in FIG.
2(a) are illustrated in FIG. 2(b) and in the more comprehensive
output shown in FIG. 2(c). Suitable spreadsheet programs and
printing programs such as Microsoft Excel may be used for this
purpose.
[0128] The glass articles are then produced from the raw materials
so designated in a conventional fashion whereby the raw materials
are converted at high temperatures to a homogeneous melt that is
then formed into the articles. In particular, the molten glass is
either molded, drawn, rolled, or quenched, depending on the desired
shape and use. For example, bottles, dishes, optical lenses,
television picture tubes, and the like are formed by blowing,
pressing, casting, and/or spinning the molten glass against a mold
to cool and to set in its final shape. On the other hand, window
glass, tubing, rods, and fibers are formed by freely drawing the
glass in air (or across a bath of molten tin as in the float
process) until the molten glass sets up and can be cut to length.
Of course, other glass products such as art glass, frit, and glass
laminates may also be created using conventional techniques from
recycled glass using the techniques described herein.
[0129] In summary, the computerized method of the invention
includes a computer program loaded into the associated memory of a
host processor for providing program instructions to the host
processor to perform the steps of:
[0130] 1. inputting a raw material array (M) for n materials (sand,
soda ash, limestone, etc.) with m properties (SiO.sub.2,
Al.sub.2O.sub.3, etc.), including three mix cullet oxide
composition;
[0131] 2. defining the glass type for melting: clear, amber, or
green;
[0132] 3. determining how much cullet (by weight percent) is to be
melted as a fraction of the finished glass;
[0133] 4. determining the three-mix cullet composition (input
percentage of clear, amber, and green in cullet);
[0134] 5. specifying transmission properties of amber glass (550 nm
and 650 nm transmission percentages are required to determine level
of coloring oxides used in glass) or green glass (levels of Cr and
Fe must be specified) or determine the best glass possible for a
given cullet level for clear (flint) glass;
[0135] 6. calculating glass coloring agent levels from specified
transmission properties using known relationships between oxide
percentages and extinction coefficients;
[0136] 7. once the coloring agents are computed, storing the
composition of the glass in a row vector of length m, where each
element corresponds to the necessary level of SiO.sub.2,
Al.sub.2O.sub.3, etc., in the target glass;
[0137] 8. solving the linear problem MX=B by inverting matrix M
(using any of the accepted methods in numerical analysis, such as
Gauss-Jordan elimination, or Newton-Raphson iteration methods) and
multiplying by target vector B;
[0138] 9. using slackness generated by multiple solutions to
minimize cost in amber and green glasses calculation and to
minimize iron levels in clear glass; and
[0139] 10. printing batch composition, oxide composition, and
selected transmission parameters for each glass.
[0140] Results of Laboratory Melts for Recycled Amber, Green, and
Flint Glasses
[0141] 1. Amber
[0142] To demonstrate the ability of the amber model to produce
amber glass of good redness ratio from a three-mix cullet, a sample
of three-mix cullet typical of the East and West coasts of the U.S.
containing 48.3% flint glass, 26.7% amber glass, and 25% green
glass was used as 35% of the total amber batch, as in the example
of FIGS. 2(a) and 2(b). The target amber transmission was 11.5% at
550 nanometers and 23% at 650 nanometers for a redness ratio of
2.0. The reformulation algorithm described above calculated the
following glass batch. Note the addition of CuO to promote redness
of the amber to meet the desired redness ratio even with the
presence of 8.75% green cullet.
3 Raw Material grams Cullet, Clear 169.05 Cullet, Amber 93.45
Cullet, Green 87.50 Sand, US Silica 427.59 Limestone 73.07 Aplite,
US Silica 0.00 Calumite 89.67 Salt Cake 9.09 Melite - 40 3.81 Soda
Ash, FMC 141.27 Coal, Carbocite #20 0.272 Copper Oxide, CuO 0.127
TOTALS Cullet 350.00 Virgin Batch 744.89 Total Batch 1094.89 Glass
1000.00 Loss on Ignition (LOI) 94.89
[0143] Note that this batch is for 1000 grams of glass rather than
2000 pounds of glass as in FIGS. 2(a) and 2(b). The calculated
composition of this glass, on a batch basis (i.e. not including
volatile losses during melting), is:
4 SiO.sub.2 71.25% Al.sub.20.sub.3 1.67% CaO 11.32% MgO 1.37% Na2O
13.52% K.sub.2O 0.10% Fe.sub.20.sub.3 0.20% TiO.sub.2 0.16%
S(total) 0.39% Cr.sub.20.sub.3 0.02% CuO 0.01% Total 100.00% Redox
Number -51
[0144] The glass was melted by Corning Laboratory Services of
Corning, N.Y. according to their standard procedure. 1000 g of
glass was melted for 8 hours at a maximum temperature of
1450.degree. C. in a 1.8 liter silica crucible in an electric
furnace with an ambient (oxidizing) atmosphere without any stirring
or mixing. The oxidizing atmosphere of the melting environment and
the eight hour residence time produces an oxidized non-amber
surface of the melt, which when mixed with the amber glass during
the pour, lightens the color of the glass. The resultant glass was
poured to a patty, annealed and a section was cut for transmission
measurements. The glass has the expected glass color: a good amber
and a bit lighter than the target. Transmission results are
summarized below:
5 Parameter Target Value Measured Value 550 nm transmission 11.5
16.4 650 nm transmission 23.0 39.9 Redness Ratio 2.0 2.4
[0145] As a second example of the ability of the invention to
produce glass of good redness ratio, even when large amounts of
green cullet are added, a sample of "two-mix" cullet containing 50%
amber glass and 50% green glass was used as 40% of the total amber
glass. The target amber transmission was 11.5% at 550 nanometers
and 23% at 650 nanometers for a redness ratio of 2.0. The
reformulation algorithm described above calculated the following
glass batch.
6 Raw Material grams Cullet, Clear 0.0 Cullet, Amber 200.0 Cullet,
Green 200.0 Sand, US Silica 394.94 Limestone 55.63 Aplite, US
Silica 0.00 Calumite 89.47 Salt Cake 9.07 Melite - 40 2.63 Soda
Ash, FMC 129.48 Coal, Carbocite #20 0.0298 Copper Oxide, CuO 0.3373
TOTALS Cullet 400.00 Virgin Batch 681.58 Total Batch 1081.58 Glass
1000.00 Loss on Ignition (LOI) 94.89
[0146] Note that this batch is for 1000 grams of glass rather than
2000 pounds of glass as in FIGS. 2(a) and 2(b). The calculated
composition of this glass, on a batch basis (i.e. not including
volatile losses during melting), is:
7 SiO.sub.2 71.5% Al.sub.20.sub.3 1.7% CaO 10.9% MgO 1.37%
Na.sub.2O 13.52% K.sub.2O 0.10% Fe.sub.20.sub.3 0.20% TiO.sub.2
0.17% S(total) 0.407% Cr.sub.20.sub.3 0.04% CuO 0.07% Total 100.0%
Redox Number -51
[0147] The glass was melted by Corning Laboratory Services of
Corning, N.Y. according to their standard procedure. 1000 g of
glass was melted for 8 hours at a maximum temperature of
1450.degree. C. in a 1.8 liter silica crucible in an electric
furnace with an ambient (oxidizing) atmosphere without any stirring
or mixing. The resultant glass was poured to a patty, annealed and
a section was cut for transmission measurements. The glass has
beautiful amber color with excellent redness ratio. The intensity
was a bit darker than expected, a factor easily adjusted in
subsequent melts. Transmission results are summarized below:
8 Parameter Target Value Measured Value 550 nm transmission 11.5
6.0 650 nm transmission 23.0 18.1 Redness Ratio 2.0 3.02
[0148] Of course, changing the percentages of amber, clear, and
green cullet in the three-mix as well as the percentage of cullet
in the total glass will lead to different glass oxide compositions
to be included in the final glass batch. For example, FIGS. 6-11
illustrate the glass batch formulations for the respective
three-mix batch calculation scenarios set forth in FIG. 4 for use
in creating recycled amber glass containers using the techniques of
the invention.
[0149] FIGS. 2(c), 6(a), and 6(b) respectively illustrate the glass
batch formulations for the East/West coast three-mix where the
cullet is 35%, 50%, and 75% of the total glass, respectively.
[0150] FIGS. 7(a)-7(c) respectively illustrate the glass batch
formulations for three-mix approximately matching USA glass
production where the cullet is 25%, 50%, and 75% of the total
glass, respectively.
[0151] FIGS. 8(a)-8(c) respectively illustrate the glass batch
formulations for three-mix approximately matching USA glass
production but with 1/3 clear glass removed where the cullet is
25%, 50%, and 75% of the total glass, respectively.
[0152] FIGS. 9(a)-9(c) respectively illustrate the glass batch
formulations for three-mix approximately matching the U.S. glass
production but with 2/3 clear glass removed where the cullet is
25%, 50%, and 75% of the total glass, respectively.
[0153] FIGS. 10(a)-10(c) respectively illustrate the glass batch
formulations for the trend to amber three-mix where the cullet is
25%, 50%, and 75% of the total glass, respectively.
[0154] FIGS. 11(a)-11(c) respectively illustrate the glass batch
formulations for the Beer Belt Blend where the cullet is 25%, 50%,
and 75% of the total glass, respectively.
[0155] 2. Green
[0156] To demonstrate the ability of the green model to produce
suitable green glass from a three-mix cullet, a sample of three-mix
cullet typical of the East and West coasts of the United States
containing 47.2% flint glass, 27.2% amber glass, and 25.5% green
glass was used as 35% of the total green batch. The target
composition was Fe.sub.2O.sub.3=0.25% and Cr.sub.2O.sub.3=0.23%.
The reformulation algorithm described above calculated the
following glass batch:
9 Raw Material grams Cullet, Clear 165.36 Cullet, Amber 95.36
Cullet, Green 89.29 Sand, US Silica 437.92 Limestone 129.97 Aplite,
US Silica 48.77 Calumite 0.00 Salt Cake 12.05 Melite --40 0.37 Soda
Ash, FMC. 134.89 Coal, Carbocite #20 0.969 Copper Oxide, CuO 0.000
Iron Chromite, FeCr.sub.2O.sub.4 4.520 Chrome Oxide,
Cr.sub.2O.sub.3 0.047 TOTALS Cullet 350.00 Virgin Batch 769.52
Total Batch 1119.52 Glass 1000.00 Loss of Ignition (LOI) 119.52
[0157] The calculated composition of this glass is:
10 SiO.sub.2 72.0% Al.sub.20.sub.3 1.67% CaO 11.3% MgO 0.25%
Na.sub.2O 13.52% K.sub.2O 0.19% Fe.sub.20.sub.3 0.25% TiO.sub.2
0.07% S(total) 0.35% Cr.sub.20.sub.3 0.23% Total 100.00% Redox
Number -30
[0158] The glass was melted by Corning Laboratory Services of
Corning, N.Y. according to their standard procedure. 1000 g of
glass was melted for 8 hours at a maximum temperature of
1450.degree. C. in a 1.8 liter silica crucible in an electric
furnace with an ambient (oxidizing) atmosphere without any stirring
or mixing. The resultant glass was poured to a patty, annealed and
a section was cut for transmission measurements. The glass was a
beautiful green color, as expected. Transmission results are
summarized below:
11 Parameter Measured Value 450 nm transmission 14.9 550 nm
transmission 66.6 650 nm transmission 32.6
[0159] As in the amber example, changing the percentages of amber,
clear, and green cullet in the three-mix as well as the percentage
of cullet in the total glass will lead to different glass oxide
compositions to be included in the final glass batch. For example,
FIGS. 12-14 illustrate the glass batch formulations for three of
the respective three-mix batch calculation scenarios set forth in
FIG. 4 for use in creating recycled green glass containers using
the techniques of the invention.
[0160] FIGS. 12(a) and 12(b) together illustrate a spreadsheet of a
glass oxide calculation model from the batch formula for the
creation of recycled green glass containers including East[West
Coast three-mix cullet using the techniques of the invention.
[0161] FIGS. 12(c) and 12(d) respectively illustrate the glass
batch formulations for the East/West Coast three-mix where the
cullet is 35% and 70% of the total glass, respectively.
[0162] FIGS. 13(a)-13(c) respectively illustrate the glass batch
formulations for three-mix approximately matching the U.S. glass
production where the cullet is 25%, 50%, and 75% of the total
glass, respectively.
[0163] FIGS. 14(a)-14(c) respectively illustrate the glass batch
formulations for the Beer Belt Blend three-mix where the cullet is
25%, 50%, and 75% of the total glass, respectively.
[0164] 3. Flint (Clear)
[0165] To demonstrate the ability of the flint model to produce
clear glass with colorless absorption of a minimum level from a
batch containing three-mix cullet, a sample of Beer Belt Blend
three-mix cullet containing 55% flint glass, 40% amber glass, and
5% green glass was used as 25% of the total flint batch. The goal
of the batch computation was to minimize Fe.sub.2O.sub.3, oxidize
the glass to produce the lightest color possible, and to complement
the color of the Fe and Cr with Se and Co to produce colorless
absorption with maximum transmission.
[0166] The reformulation algorithm described above calculated the
following glass batch:
12 Raw Material grams Cullet, Clear 137.5 Cullet, Amber 100.0
Cullet, Green 12.5 Sand, US Silica 505.0 Limestone 143.7 Aplite, US
Silica 54.24 Salt Cake 6.28 Soda Ash, FMC. 154.48 Ferro Cobalt
Frit, 2% Co 0.4869 Ferro Selenium Frit, 5% Se 15.2087 Niter, NaNO3
1.5625 TOTALS Cullet 250.00 Virgin Batch 863.72 Total Batch 1113.72
Glass 1000.00 Loss of Ignition (LOI) 113.72
[0167] The calculated composition of this glass is:
13 SiO.sub.2 72.6% Al.sub.20.sub.3 1.72% CaO 11.0% MgO 0.32%
Na.sub.2O 13.9% K.sub.2O 0.20% Fe.sub.20.sub.3 0.084% TiO.sub.2
0.06% S(total) 0.20% Cr203 0.002% Se 0.0304% Co 0.0024% Total
100.00% COD 10
[0168] The glass was melted by Corning Laboratory Services of
Corning, N.Y. according to their standard procedure. 1000 g of
glass was melted for 8 hours at a maximum temperature of
1450.degree. C. in a 1.8 liter silica crucible in an electric
furnace with an ambient (oxidizing) atmosphere without any stirring
or mixing. The resultant glass was poured to a patty, annealed and
a section was cut for transmission measurements. Transmission
measurements were made by Corning Laboratory Services of Corning,
N.Y. according to their standard procedure. The glass was clear
flint color with a neutral absorption, as expected, with
transmission behavior, a bit lighter than expected, as summarized
below:
14 Parameter Measured Value 450 nm transmission 80.87 550 nm
transmission 81.38 650 nm transmission 79.33
[0169] As in the amber and green examples, changing the percentages
of amber, clear, and green cullet in the three-mix as well as the
percentage of cullet in the total glass will lead to different
glass oxide compositions to be included in the final glass batch.
For example, FIGS. 15 and 16 illustrate the glass batch
formulations for two of the respective three-mix batch calculation
scenarios set forth in FIG. 4 for use in creating recycled clear
(flint) glass containers using the techniques of the invention.
[0170] FIGS. 15(a) and 15(b) together illustrate a spreadsheet of a
glass oxide calculation model from the batch formula for the
creation of recycled clear (flint) glass containers from the Beer
Belt Blend three-mix, where the cullet is 25% of the total glass,
using the techniques of the invention.
[0171] FIGS. 15(c) and 15(d) illustrate the glass batch
formulations for the creation of recycled clear (flint) glass
containers from the Beer Belt Blend three-mix where the cullet is
25% and 50% of the total glass.
[0172] FIGS. 16(a) and 16(b) respectively illustrate the glass
batch formulations for the creation of recycled clear (flint) glass
containers from the USA production three-mix where the cullet is
25% and 50% of the total glass, respectively.
[0173] The invention having been disclosed in connection with the
foregoing variations and examples, additional variations will now
be apparent to persons skilled in the art. The invention is not
intended to be limited to the variations and examples specifically
mentioned, and accordingly reference should be made to the appended
claims to assess the spirit and scope of the invention in which
exclusive rights are claimed.
[0174] For example, those skilled in the art will appreciate that
the techniques of the invention may be used for a variety of
different virgin glass raw materials, a variety of three-mix ratios
from very small percentages (<10%) to 100% mixed color cullet
with respect to the total glass in the glass batch, a variety of
color combinations in the three-mix itself, and a variety of input
oxides. Also, the recycled glass container end products may have
any of numerous desired transmission characteristics. In a
preferred implementation, the technique of the invention is used to
create recycled beer bottles from three-mix cullet. Conventional
amber beer bottles typically have a 550 nm transmission of 8-20%
and a redness ratio of 1.2-3.0. One of the most prevalent types of
beer bottles in circulation in the United States is the amber beer
bottle used by Anheuser-Busch which has the following
characteristics: 550 nm transmission of 12-15% through a 3.18 mm
specimen, with a redness ratio of approximately 1.8 to 2.0,
depending on the level of 550 transmission. The technique of the
invention may be advantageously used to create amber beer bottles
with these characteristics from glass batches with varying
percentages of mixed color cullet.
[0175] Those skilled in the art will appreciate that although amber
beer bottles made from mixed color cullet using the techniques of
the invention will have the desired transmission characteristics,
they can be distinguished from conventional amber beer bottles
based on the chromium (Cr.sub.2O.sub.3) content. In particular,
those skilled in the art will appreciate that amber and clear
bottles made from mixed color cullet including measurable amounts
of green cullet will have chromium levels well above the trace
chromium contamination levels which would ordinarily be expected
from the use of chrome-containing refractories in glass furnaces or
from other sources of chromium contamination. Since chromium is
relatively expensive, it is not likely to be introduced into the
glass in measurable quantities from other sources. In accordance
with the invention, amber bottles made from mixed color cullet
including green glass may have a chromium weight percent in a wide
range of 0.01% to 0.3%, although narrower ranges such as 0.015% to
0.15% or 0.015% to 0.10% may also be measured. In the samples given
above, the chromium range was 0.02% to 0.04%. Of course, the weight
percentages for chromium will vary as the amount of green cullet in
the mixed color cullet varies.
[0176] All such variations are intended to be included in the
following claims.
* * * * *