glass recycling project
TRANSCRIPT
FEASIBILITY STUDY OF REUSING/RECYCLING GLASS WASTE IN
PRODUCTION OF HOUSE HOLD GLASS MATERIALS AND
MATERIALS USED IN THE CONSTRUCTION INDUSTRY
BY
KYAMBADDE SOLOMON
10/U/4636/CET/PE
A PROJECT REPORT SUBMITTTED TO THE DEPARTMENT OF
PHYSICS IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR
THE AWARD OF DIPLOMA IN CERAMIC SCIENCE AND
TECHNOLOGY OF
KYAMBOGO UNIVERSITY
JULY 2012
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APPROVAL
This to certify that KYAMBADDE SOLOMON completed this project report under my
supervision and it is ready for submission
Signed: …………………………………….
Supervisor: Mr. Wabwai Masaba
Date: ……………………………………….
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DECLARATION
I Kyambadde Solomon do hereby declare that this research proposal contains a true record of the activities and work I was involved in during the research period in Kyambogo University and Bajjo glass.
Signed…………………………………..
Date……………………………………..
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DEDICATION
This research proposal is dedicated to my uncle Katende Austin in appreciation of his great work and courage he gave me during the session of my research.
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ACKNOWLEDGEMENTS
I wish to most sincerely acknowledge the valuable information I received from the technicians at the Bajjo glass Seeta- Mukono. My supervisor Mr.Wabwai Masaba who was also able to help in the preparation of this research proposal is also much appreciated for the corrections made in this research proposal.
I also give my sincere thanks to Walugembe Amos who unveiled to the idea about glass recycling as a good research project to work on.
Further thanks go to my sister Nanyonjo Irene for the responsibility she has taken and the courage she provided throughout the session of my research and I pray that the Almighty God reward her abundantly in her work.
Not forgetting the support and time my colleagues at the Guild café provided in typing, editing
and printing out my research proposals.
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TABLE OF CONTENTS
APPROVAL................................................................................................................................................. i
DECLARATION......................................................................................................................................... ii
DEDICATION............................................................................................................................................ iii
ACKNOWLEDGEMENTS........................................................................................................................ iv
LIST OF FIGURES........................................................................................................................................viii
LIST OF TABLES............................................................................................................................................ ix
CHAPTER ONE - INTRODUCTION.........................................................................................................1
1.0 Executive Summary...........................................................................................................................1
1.1 Abstract.............................................................................................................................................1
1.2 Context..............................................................................................................................................2
1.4 Project Objective...............................................................................................................................2
1.5 Operational Objectives......................................................................................................................2
1.6 Good Practice Examples Based on the Following Agreed Criteria:...................................................3
CHAPTER TWO – LITERATURE REVIEW............................................................................................4
2.0 THE CHEMISTRY OF GLASS BOTTLES......................................................................................4
2.1 Identification and General Description of Glass................................................................................4
2.2 Chemical-Physical Properties of Glass..............................................................................................5
2.2 Waste Glass Terminology:.................................................................................................................5
2.2.1 Cullet..........................................................................................................................................5
2.2.2 Internal Cullet.............................................................................................................................6
2.2.3 External Cullet............................................................................................................................6
2.2.3.1 Pre-Consumer Cullet................................................................................................................6
2.2.3.2 Post-Consumer Cullet..............................................................................................................6
2.3 Glass Cullet Contaminants.................................................................................................................7
2.4 Non-Glass Material Components.......................................................................................................7
2.5 Glass Material Components...............................................................................................................7
2.6 Packaging/Storage.............................................................................................................................8
2.7 Production Cost.................................................................................................................................9
CHAPTER THREE – METHODOLOGY................................................................................................10
3.0 SOURCES OF RECYCLED GLASS..............................................................................................10
3.1 Sourcing..........................................................................................................................................10
3.2 Cullet Preparation............................................................................................................................10
3.3 Batch Chemical Additions...............................................................................................................11
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3.4 Melting............................................................................................................................................12
3.5 Melting Procedure...........................................................................................................................13
3.6 Sample Forming..............................................................................................................................13
3.7 Color Contamination.......................................................................................................................13
3.8 Color Compatibility Tests................................................................................................................14
3.9 Annealing........................................................................................................................................14
3.10 Recommended Processing Methods..............................................................................................15
3.10.1 Feedstock Acquisition.............................................................................................................15
3.10.2 Feedstock Preparation.............................................................................................................15
3.10.3 Drying.....................................................................................................................................16
3.10.4 Pulverizing..............................................................................................................................16
3.10.5 “Powders” Processing.............................................................................................................17
3.10.6 Dust Control...........................................................................................................................17
3.10.7 Final Debris Removal.............................................................................................................17
3.10.8 Sizing......................................................................................................................................18
3.10.9 Packaging/Storage..................................................................................................................18
3.11 Machines used in glass recycling...................................................................................................19
CHAPTER FOUR – RESULTS AND DISCUSSIONS............................................................................24
4.0 LABORATORY TESTING PROGRAM........................................................................................24
4.1 Particle Morphology........................................................................................................................24
4.2 Permeability.....................................................................................................................................25
4.3 Crushing and sorting of waste glass.................................................................................................25
4.4 Transport of glass cullet to cullet users............................................................................................27
4.5 Recycling techniques.......................................................................................................................27
4.6 Waste Glass Recycling Techniques in the Flat Glass Industry........................................................28
4.7 Batch Chemicals..............................................................................................................................29
4.7.1 Fluxing Agents.........................................................................................................................29
4.7.2 Colorants...................................................................................................................................29
4.7.2 Opacifying Agents....................................................................................................................30
4.8 Waste Characteristics.......................................................................................................................30
4.9 Pollution Prevention and Control.....................................................................................................30
CHAPTER FIVE – CONCLUSION AND RECOMMEDATIONS..........................................................32
5.0 IMPLEMENTATION PLAN..........................................................................................................32
5.1 Market Opportunity.........................................................................................................................32
5.2 Reaching the Customers..................................................................................................................32
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5.3 SWOT Analysis...............................................................................................................................32
5.4 Recommended Processing Methods...............................................................................................33
5.5.1 Labor Requirements.................................................................................................................33
5.5.2 Cost Analysis.............................................................................................................................34
5.6 Experimental Procedure..................................................................................................................34
5.6.1 Source of Glass Cullet...............................................................................................................34
5.6.2 Batch Chemicals........................................................................................................................35
5.6.3 Melting Procedure....................................................................................................................35
5.6.4 Sample Forming........................................................................................................................36
5.6.5 Color Contamination.................................................................................................................36
5.6.6 Batch preheating......................................................................................................................36
5.6.7 Sand dissolution........................................................................................................................37
5.7 Fining zone...........................................................................................................................................38
5.7.1 Refining and conditioning.........................................................................................................39
5.7.2 Deep refiner..............................................................................................................................39
5.7.3 Cullet Inspection.......................................................................................................................39
5.7.4 Color Specification....................................................................................................................40
5.7.5 Contamination Limits................................................................................................................41
5.8 Conclusion.......................................................................................................................................41
APPENDIX I................................................................................................................................................42
Economic evaluation of the project.......................................................................................................42
APPENDIX II...............................................................................................................................................44
FACTS ABOUT GLASS RECYCLING...............................................................................................44
APPENDIX III..............................................................................................................................................45
GLOSSARY..........................................................................................................................................45
APPENDIX IV..............................................................................................................................................48
REFERNCES............................................................................................................................................48
LIST OF FIGURES
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Figure 1........................................................................................................................................19Figure 2........................................................................................................................................20Figure 3........................................................................................................................................21Figure 4........................................................................................................................................22Figure 5........................................................................................................................................23
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LIST OF TABLES
Table 1 Equipment list (fixed capital)........................................................................................................42Table 2 Production cost data......................................................................................................................43
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CHAPTER ONE - INTRODUCTION
1.0 Executive Summary
Natural glass, known as obsidian, was widely utilized by prehistoric man, and glass has been
made by people for approximately 9000 years. It was first known to be developed in the
Middle East around 7000BC, and glass bottles were made in Egypt in 1500BC. By the
Renaissance, colored glass, crystal and mirrors had all been developed and were being made in
Venice.
Glass has two important properties. Firstly it does not have a definite melting point but softens
gradually over a range of temperatures. The explanation of both these properties lies in the fact
that glass has no ordered structure, but is instead a super cooled liquid. A sheet of glass left to
stand for a long time, perhaps one hundred years, will actually flow and change its dimensions
slightly.
1.1 Abstract
Glass waste from broken glasses disposed in dust bins or rubbish pits are hazardous to the
environment and human.
The recycling of glass is not feasible due to the chemicals contained in it therefore it is important
to seek applicable technological ways in order to manage the significantly increasing glass
wastes.
A promising application is to reuse glass as cullet (crushed glass aggregates) in the making of
house hold glass and construction materials like use of cullet in Portland cement concrete (PCC).
The properties of glass provide attributes for many commercial products. As some of these
products reach the end of their useful life and are discarded, there is the opportunity to have the
material recycled into other useful products. This alternative is preferred over having the material
being disposed to the environment causing landfills. Glass can be re-melted and re-fabricated
over and over again without any deterioration of the material properties. Limitations for
recycling of glass involve the level of contamination from other categories or colors of glass, as
well as from a variety of non glass materials
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1.2 Context
Due to increasing technology many glass products have been produced which after use have been poorly disposed off; this has brought an effect to the environment and the people living in it that is to say glass is non bio degradable leading to low levels of soil fertility and dangerous harm to human beings. Therefore due to this implication of poor disposal of glass waste, it is of great importance if it is reused to make useful materials like house hold glass products and also reused in the construction industry especially as addition to Portland cement concrete.
1.4 Project Objective
The strategic objective established for this project is to increase awareness and
dissemination of information on good practices of glass recycling with the aim to
increase the quantity and quality of the cullet available.
To provide a proper way of disposal of glass waste that is to gazette an area where waste
glass is to be dumped there after collected and taken to recycling centers.
To reuse glass in the manufacture of household glass products.
To curb down the levels of glass pollution in the environment.
To minimize the importation of glass products from outside countries.
There will be creation of employment opportunities for people in a long run.
1.5 Operational Objectives
Identification of the different types of glass recycling collection schemes operating across
the country.
The type of factors affecting the success of an effective glass collection scheme.
Evaluation of the performance of the different glass collection schemes
Identification and description of best practices for glass selective schemes leading to
closed loop recycling
Dissemination of information on the identified best practices
The result of this study would create local job generating industry to produce slabs used
in construction and glass house hold materials. This will also reduce on the number of
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glass materials imported since I shall be able to produce our own glass materials. A
friendlier environment will be created after a new way of disposing off glass waste will
be introduced.
1.6 Good Practice Examples Based on the Following Agreed Criteria:
Quality of the glass collected for recycling.
Total costs for society.
Areas achieving high recycling rate.
Efficient collection schemes (kerbside, bottle banks, deposit)
Sectorial differences for glass collection (commercial, household).
Legal context and responsibilities.
Geographical content (urban, semi-urban, rural etc).
Financial context and incentives.
Colour-separate glass collection versus mixed glass collection.
Innovation in glass collection schemes and processes.
Communication: Education, awareness raising and other targets.
The following objectives were identified for this project:
What are the different types of glass recycling collection schemes operating across
Europe?
Which factors affect the success of an effective glass collection scheme?
Evaluate the performance of the different glass collection schemes
Identify best practices for glass collection schemes leading to closed loop recycling
(bottle to bottle)
CHAPTER TWO – LITERATURE REVIEW
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2.0 THE CHEMISTRY OF GLASS BOTTLES
For some of the methods of reusing or recycling glass containers, the chemistry of the glass is
critical. The information provided here is somewhat general, but should be of assistance for those
uses which depend on the chemical composition.
The composition of uncolored glass containers is given as the following:
Material Composition
SiO2 71.5-73.5%
Na2O 12.5-15.5
CaO 7.8-10.8
MgO 0.1-3.6
Al2O3 0.4-2.2
K2O 0.4-1.0
BaO 0.0-0.5
B2O3 0.0-0.2
Fe2O3 0.04-0.05
2.1 Identification and General Description of Glass
What all glass materials have in common is a vitreous or amorphous state, originated by the
relatively fast cooling and solidification of an initial molten state. The fast cooling prevents
atoms, molecules or ions to organize into a more thermodynamically favourable crystalline
structure. Therefore, glasses are not arranged in an orderly repeating pattern in all three
dimensions like crystals but are characterised by an amorphous structure.
As a consequence, glass does not melt at a certain temperature like other solids but softens
slowly when heated up.
The most common type of glass is formed by melting a mixture of silica (SiO2), soda ash
(Na2CO3), and lime (CaCO3) at high temperatures, followed by cooling during which
solidification occurs without crystallization.
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2.2 Chemical-Physical Properties of Glass
In its simplest chemical form, glass can consist of pure silica, in which case it is called “quartz
glass” or “fused quartz”. However, the production of amorphous glass from pure silica is highly
energy intensive, requiring temperatures of around 1900 °C. As such, quartz glass is only
produced for applications requiring high chemical resistance and hence belongs to the special
glass types.
In order to lower the energy requirements for glass production, most of the glass is composed of
silica (SiO2) plus other compounds. Silicon has the role of a so-called "network former", and it is
the main element used as network former. Alternative network formers are boron or germanium.
The network formers create a highly cross-linked network of chemical bonds.
Aside from network formers, glass contains also "network modifiers", which are alkali-oxides
added as fluxing agents for lowering the melting point of glass (sodium, potassium, lithium,
etc.), alkaline earth metal oxides (calcium, magnesium, barium, strontium, etc.), and other metal
oxides (i.e. Aluminum oxide). The network modifiers change the bonding relationships and
structural groupings, resulting in changes in the physical and chemical properties of the glass.
The modifiers are usually present as ions, compensated by nearby non-bridging oxygen atoms,
bound by one covalent bond to the glass network and holding one negative charge to compensate
for the positive ion nearby.
Glass may also contain other added substances (e.g. Lead, Titanium, Aluminum, Zirconium,
Beryllium, Magnesium, Zinc), which may act both as network formers (e.g. Pb4+ replacing Si4+)
and as network modifiers, depending on the glass composition.
2.2 Waste Glass Terminology:
2.2.1 Cullet
In general, the word cullet can be used to refer to either "broken glass" or to "waste glass". A
distinction should be made regarding internal vs. external cullet: this distinction is important
because internal cullet is not regarded as waste, while external cullet (which can be pre- or post-
consumer) is classified as waste. When using the word "cullet" in the context of end-of-waste it
will always refer to external cullet.
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2.2.2 Internal Cullet
Is composed of defective products detected and rejected by a quality control process during the
industrial process of glass manufacturing, transition phases of product changes (such as thickness
and colour changes) and production off cuts. The basis of the definition of internal cullet is the
fact that these materials are immediately absorbed by the respective industrial process as a raw
material for a new melting operation, not leaving the glass manufacturing plant. Internal cullet
cannot be considered as waste as it was never a product.
2.2.3 External Cullet
Is "waste glass that is collected and/or reprocessed with the purpose of recycling". External cullet
can be of two types:
(1) Pre-consumer, also called post-industrial glass cullet, and
(2) Post-consumer glass cullet.
2.2.3.1 Pre-Consumer Cullet
Is waste glass resulting from the manufacturing of products that contain glass as one of their
components, and which leaves the specific facility where it was generated, becoming waste but
not reaching the consumer market. An example of pre-consumer cullet is the glass cullet
constituted by off cuts and pieces from defective manufacturing of e.g. the production of car
windows from flat glass, which leave the car window manufacturing facility and are re-melted in
the flat glass manufacturing facility.
2.2.3.2 Post-Consumer Cullet
Is waste glass originated after the use of the glass products at the consumer market.
The majority of cullet is container glass and flat glass cullet. However, cullet can also come from
insulating mineral wool, or from continuous-filament glass fibres. In these cases, especially for
the case of High Temperature Insulation Wools (HTIW), the waste glass has a fibrous structure
rather than the crushed-glass appearance that is usually associated with the word cullet.
The term cullet will be used in this document to refer to reprocessed cullet, that is, external cullet
that conforms to a set of minimum quality criteria; and the objective of this project is to define
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the minimum quality criteria for reprocessed cullet to obtain the status of end-of-waste. Some
types of reprocessed cullet may have reached a quality that is considered high enough that no
additional sorting or cleaning steps are needed for its direct input into a glass furnace; in this
case, some studies refer to the reprocessed as furnace-ready cullet.
The report sometimes will also make reference to collected cullet; in this case, it is a type of
cullet that generally conforms to lower quality specifications than reprocessed cullet and may not
be suitable as direct input for re-manufacturing into new glass products.
2.3 Glass Cullet Contaminants
Contaminants are materials present in glass cullet that are unwanted for its further use.
Contaminants can be classified in two groups: non-glass material components, and glass material
components that are detrimental for new glass manufacturing.
2.4 Non-Glass Material Components
Metals (ferro-magnetic and non-ferro-magnetic)
Non-metal non-glass inorganic
Ceramics, Stones and Porcelain (abbreviated in Europe as “CSP” or “KSP”)
Glass ceramics, also called pyro-ceramics or vitro-ceramics: These are heat-resistant
non-glass ceramic materials
Organics (food remains, strapping, plastic, wood, textiles)
Hazards (hazardous materials contained in bottles and jars, medical or chemical refuse
contained within needles and syringes)
2.5 Glass Material Components
Glass product quality is severely affected by the presence in glass cullet of glass types different
from the main glass cullet type. For example:
To manufacture flat glass, only flat glass cullet can be used (flat glass manufacture does
not accept for example container glass cullet)
To manufacture container glass (of soda-lime physico-chemical composition), it is not
possible to use non-soda-lime glasses that are sometimes deposited by mistake in
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collection banks, such as: domestic lead-crystal glass or special borosilicate glasses
coming for example from light bulbs and tubes (which present an undesirable higher
melting point).
To manufacture flint container glass, there is a limit on what percentage of green
container glass cullet is used. Above that limit, the green glass cullet is adverse for new
flint glass manufacturing.
The contamination of glass by vitro-ceramics is a relatively new type of contamination. The
recycling industry is concentrating on research towards sorting equipment for vitro-ceramics.
These developments are rather new and immature. Therefore it is regarded as important to
promote better collection schemes to minimize the inclusion of vitro-ceramic contaminants in the
cullet.
The next problematic contaminants of glass cullet are metals. The effect of metal contaminants is
that as they fall to the bottom of the glass furnace, they may cause damage to the furnace walls
and bottom.
Metals originate from caps or cans thrown into the waste glass collection banks. Table 3 presents
the origin and effect of different types of metal contaminants in glass cullet.
2.6 Packaging/Storage
Provisions need to be made for both packing and weighing the final product. Bagging,
palletizing, bulk bagging and wrapping requirements will depend on product specifications and
quantities required by the customer, as well as the customary packaging expected in a particular
industry. Research should be performed to determine the packaging requirements for the
perspective markets, then finding packaging systems to fulfill those requirements. The processor
must respond to market packaging expectations, rather than expecting the market to respond to
the processor’s convenience
2.7 Production Cost
Production costs include the costs of labor, building and equipment rental, utilities, gasoline, oil,
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Maintenance and supplies cost of dust and debris disposal. Continuous labor is required to
perform maintenance tasks and replace parts, line up feedstock, change the dust collector barrel,
move bulk bags of product, and weigh the product. If the system is properly designed, however,
one full-time operator is probably adequate in a small-scale operation.
Gasoline, oil, lubrication, and rental costs should be calculated for a forklift (for moving the
product and bins) and bobcat (for loading feedstock onto the in feed conveyor). Building rental
costs should be based on the floor space required for equipment as well as the space required to
stockpile materials.
CHAPTER THREE – METHODOLOGY
3.0 SOURCES OF RECYCLED GLASS
Obtaining a quality glass for blowing or casting from post-consumer bottle glass is based on four
major processes: sourcing, cullet preparation, addition of batch chemicals, and melting. In order
to obtain a glass with good working characteristics which are discussed below in details; The
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sources are post-consumer clear, brown, and green glass from curbside collections around town,
and post industrial glass scrap from bottling companies around the country (like Coca-Cola,
Pepsi bottling companies plus Nile and Uganda breweries). The post-consumer glass is
contaminated with paper fibers from labels and food particle residue that could promote bacterial
growth in finished waterborne products.
3.1 Sourcing
Connecting with a reliable source of post-consumer recycled glass is the first critical step. First
and foremost, the cullet must be clean (that is free of dirt, rocks, metals, other glasses like Pyrex
or automobile head lamps, and ceramics). Forming partnerships with local restaurants,
company cafeterias, bottling companies, retail and whole sellers of glass products (flat glass, and
other kinds of glass) around town.
A busy local restaurant or cafeteria or bar can also provide a large stable supply of glass
containers from a single beverage brand. It is for such restaurants or bars to supply clean single
source glass.
A curbside glass collection scheme using a small wheeled bin to be considered to be put along
the streets with more sellers (whole and retail) of glass to dispose it at a particular point. This
makes it easier for collection on trucks and limits the risk of contamination when it is placed
together with some other rubbish along the streets.
3.2 Cullet Preparation
Preparing the cullet for melting consists of cleaning the cullet, removing any remaining debris,
and crushing it to an appropriate size, that is required.
Pour the glass out onto a screen or flat surface in order to wash it and search for contaminants
prior to using it in a melt. If any debris or dirt is present, it will need to be removed. Excessive
amounts of paper (i.e. other than the remaining bottle labels) should be removed, since, as the
ash generated during the melt can cause contamination problems.
Since recycled glass is obtained from a variety of sources. In this case, it is best to crush the glass
to a like size, ideally less than 1/4 inches, to insure uniform melting.
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It should be noted that, whenever possible, the glass should be crushed to between 1/16 and 3/4
inches, especially if large quantities of chemicals are to be added to the batch. The amount of
crushing necessary to prepare recycled glass depends to some extent on the product being made.
For the small scale hand blowing and casting workshops, it is usually best to crush the glass to a
size that allows it to melt with the addition of the oxidizers, fluxes, and fining agents. These
chemicals do not combine well with cullet larger than 3/4 inch, which generally take longer to
melt and can result in bubbles, chunks of chemicals, striate, or cords in the final product.
3.3 Batch Chemical Additions
Glass melts for freehand blown objects, on the other hand, need a long working range. Multiple
re-heatings during the freehand process further drive off the dissolved gases and the volatile
alkalis in the glass, raising the viscosity and shortening the working range.
To each 100 pounds of glass, the following chemicals were mixed and added:
2 lbs. soda ash
33 g. borax
175 g. niter
150 g. fluorspar
1/2 lb. lithium carbonate
50 g. antimony oxide
25 g. manganese dioxide
It is practice to add glass cullet to raw batch materials in order to promote rapid melting of the batch and thus solving the energy costs especially if the glass cullets are of similar composition.
3.4 Melting
Since the quantities of ware produced in small scale glass workshops are relatively small, glass is
most often melted in ceramic crucibles or small refractory-brick lined pots; usually at the highest
temperature that the walls, roof, and pot or crucible can endure.
At melting temperatures of 2350 to 2600 degrees Fahrenheit, the viscosity of the glass is lowered
to a point that allows the bubbles to rise readily through the melt. The raw materials interact
chemically during the melting process and thereby alter much of their individual composition.
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The gases given off in bubbles during the decomposition of some of the raw materials serve a
useful purpose by agitating the melt and making it more homogeneous.
At these temperatures, however, the rate at which the furnace is attacked and dissolved by the
corrosive elements in the glass is accelerated. At a temperature of 2,600 degrees Fahrenheit, it
has been noticed that a small scale workshop is capable of melting 7 tons of glass in a 13 hour
melt cycle. This requires that furnaces be made with AZS (Alumina-Zirconia-Silica) liners and
super-duty silica brick crowns. These dense refractories are able to resist dissolution for 15- 18
months of continuous operation.. Raw batch chemicals and the high heat required to melt the
virgin materials are the most harmful (corrosive), while straight cullet and lower temperatures
are actually the least damaging. Straight cullet requires about 10% less energy to melt.
During the trial melts, the furnace was charged at regular intervals for three hours at about 2350
degrees Fahrenheit. The glass was then allowed to melt at the same temperature for another four
hours, and finally left to idle for several hours. The final step of rapid cooling is called
squeezing.
Squeezing appears to effectively eliminate the large free oxygen and gas bubbles present at
higher temperatures. The furnace temperature is then slowly raised back to the working
temperature. This melt cycle is capable of producing a very clean glass, free of fines and small
bubbles.
The crucible in a pot furnace can either be invested in other refractory material or freestanding,
and heated with natural gas, propane, or electric elements as energy sources. The most energy
efficient furnace for a small workshop is the multi-phase electric freestanding pot furnace with
solid state rectifier power controls. The freestanding crucible is also more fragile, however, so
care must be taken to use the correct melting procedures, cullet gradations, and batch recipes.
3.5 Melting Procedure
Each melt day, four separate batches of 25 to 30 pounds each were weighed out and mixed
thoroughly. Each batch was charged into separate crucibles in an experimental test furnace that
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contained four freestanding crucibles, each with a capacity of 30 pounds. The charge cycle was
varied according to the glasses being melted. Generally, each crucible was charged regularly at
four intervals, with the last two charges being the smallest. The melt temperature was then
allowed to 6 increases slowly for one to two hours to complete the melt. Finally the furnace
setting was turned down to allow the glass to slowly cool to the working temperature required
the following day.
3.6 Sample Forming
Samples of each glass formulation were pressed in a hand-press using a patterned four-inch
square tile mold. This stage of the process is critical in that this is the stage at which all the
working characteristics of the glass determined. The glass melt was initially gathered in a gob
from which a thread was pulled. From the thread pull, an initial read on the viscosity was taken
and the temperature was adjusted as required. Once the melt temperature was satisfactory, the
tiles were pressed. Thread samples were also pulled to determine the annealing temperature of
each formula melt. Set times were short, as desired for pressing molds, between five and ten
seconds. The sample tiles pressed each day were annealed through a cooling down cycle of eight
hours.
3.7 Color Contamination
Cross-contamination was a major concern during the melt progressions. Since the project could
not afford a new crucible for every formula, the melts were organized to minimize prior melt
contamination. Formulas were sequenced in crucibles that utilized similar colorants and base
glasses. For instance, the pot used to melt copper colored opals was initially used to melt
transparent colors. Once a sequence ran its course, the crucible was exchanged for a new one. To
keep track of contamination, the melt progressions were fully documented with each melt listing
the crucible number and prior melt formula number.
3.8 Color Compatibility Tests
The linear expansion coefficient of the new glass should be tested to evaluate whether it is
compatible with German color bars. The pull test is a quick method of evaluating color
23
compatibility. Equal amounts of color and clear glass from the furnace are placed side by side,
heated together, and pulled into a long thin thread. As soon as the thread sets up it is placed on
the floor and broken into 12 - 18 inch lengths. The two glasses will bend toward the glass with
the higher Linear Expansion Coefficient (LEC). If when placed against a straight edge, the
curvature displacement in the thread is less than 1/4 inch over one foot of length then the glass is
said to ‘fit,’ and the glasses may be used together. If the curvature displacement is greater than
one inch, then the glasses will probably break apart at some point in time, even months or years
later. The more accepted method for determining LEC compatibility is to blow two thin
cylinders, one with the glass color on the outside and the other with the glass color on the inside.
Cut narrow rings out of each cylinder and score with a glass cutter and break along the score. If
the higher expansion (LEC) is on the outside the ring will pull away from the score, and if on the
inside the ring will close. It is necessary to wait until the pieces are annealed to perform this test.
3.9 Annealing
After a glass article is formed, it must be annealed to remove the internal stresses that were
created during the forming process. This is done by “soaking” the formed glass in an annealing
oven at a pre-determined temperature. This temperature depends on both the thickness and
geometry of the product. One way to determine the annealing temperature is to pull a rod out of
the tank glass, approximately 1/4-inch in diameter and 18 inches in length. One end is then
captured between two firebricks and cantilevered out into the oven. The temperature is slowly
brought up until the rod begins to bend. The time that the glass must spend at the annealing
temperature is highly dependent on the thickness of the glass, ranging from 5.5 minutes for 1/4”
glass, to a little over two hours for 11/4” glass. This initial soak is followed by a controlled
cooling cycle of a similar duration
3.10 Recommended Processing Methods
It is critical to test recycled materials from known sources processed by known processing
equipment, because the physical characteristics of the processed material may vary widely
depending on the source and processing strategy.
24
Processing post-consumer or post-industrial recycled glass into high-grade, industrial quality
glass sand generally consists of the following steps, described in detail below:
Feedstock Acquisition Feedstock Preparation Drying Pulverizing Debris Control Dust Removal Sizing Packaging/Storage
3.10.1 Feedstock Acquisition
It is important to first assess the characteristics and availability of recycled feedstock. Glass that
is free of ferrous metal and other debris is preferable, to reduce both the wear on crushing
mechanisms and the cost of debris removal. Suppliers of post-consumer and post-industrial glass
should both be considered. Any possible effects from chemical or physical differences between
types of glass should be taken into account for each possible application. Feedstock may also be
obtained directly from generators, such as local drop box sites, community recycling centers,
local restaurants, company cafeterias, or other heavy users of glass.
3.10.2 Feedstock Preparation
Before any crushing, the glass may be run over a magnetic removal device to pull out any large
pieces of ferrous metal. A picker station following the magnet is necessary for visual inspection
and removal of other large contaminants. The glass is then fed through a glass breaker and
reduced to cullet. Therefore, they tend to remain in larger pieces than the glass during crushing.
The cullet is then passed through a 3/4" screen to remove gross debris. Running the glass over a
second magnetic head pulley after the glass is broken into cullet should remove any remaining
ferrous metal that may have been attached to the glass.
3.10.3 Drying
Glass must be dried prior to pulverization if the sand is to be dry sized, especially if using mesh
sizes smaller than 1/8". The glass is much easier to dry prior to the final pulverizer because it has
25
a smaller surface area from which to evaporate the water before final crushing. Drying also helps
to prevent the wet glass dust from plugging dust collection bags.
The most commonly used type of dryer is a tumbling rotary drier, fueled by natural gas or
propane.
3.10.4 Pulverizing
Multiple row hammer mills, consisting of multiple hinged, free swinging bars or “hammers”
attached to pivots fixed to a rotating shaft, seem to work well for producing glass sand, as the
multiple impacts tend to produce grains that are relatively uniform in size and not shardy. The tip
speed of the hammers and the retention time determine the product size.
Conventional single-pass hammer mills have also been successfully used if the cullet is properly
prepared and the hammer tip speed and flow are controlled properly.
If the multiple row hammer mill is used, the angle at which the hammer mill barrel sits should be
adjusted in order to optimize the retention time in the mill and to spread wear evenly over the
hammers, increasing the time between shutdowns for hammer replacement.
The distance between the hammers and the mill walls also affects system performance. Placing
the hammers too close to the walls can cause excessive wear to both the hammers and the walls.
If the hammer tips are too far from the walls, however, the impact efficiency is reduced.
It is advantageous to operate the hammer mill at a rotor tip speed and feed rate that will pulverize
the glass but leave any remaining debris intact, so that it may be screened out later. The optimal
speed for this purpose, according to one professional, is 3,500 feet per minute.
3.10.5 “Powders” Processing
Some potential markets for very fine (smaller than 200 meshes) glass are under investigation. In
many of these potential markets, fine glass substitutes for other fine silica or dry clays. The
equipment used to process glass to that grade of fineness is not covered in this report. Ball mills
and vibratory mills have been in use for many years for that sort of processing. The physics of
reducing one hundred percent of the input of a glass processing machine to 200 mesh material
differ markedly from those employed with the generation of the 1/8-inch material described in
this report. For that reason, although some of the pulverizers described here may be adjusted to
26
produce more or less very fine glass, the process is not an efficient one and results in extensive
wear. On the other hand, all pulverizers produce some dust, as described below. That dust, if
properly captured and secondarily processed, can be marketed as a byproduct of the main
process outlined in this report.
3.10.6 Dust Control
It is necessary to control glass dust generated by the pulverizor. Ambient dust can be controlled
by pulling a negative pressure on the outlet of the pulverizor. The dust is pulled first across a
drop-out box or through a cyclone, where the velocity slows down and the heavier pieces fall
into a barrel. After the dropout box, the fan draws the dust into a bag house for collection.
If possible, the fan should be placed at the exit of the bag house out of the stream of material,
because glass flowing over the blades will wear them down very quickly. Bags should be porous
enough to prevent plugging and to maintain a negative air pressure. With additional processing,
it may be possible to recover marketable fractions from the very fine glass collected in the dust
control system.
3.10.7 Final Debris Removal
Final debris removal is accomplished through a well designed combination of dust control and
screening. A correctly sized dust control fan pulls a negative pressure adequate to remove the
finest mesh glass and light weight contaminants, including paper and plastic. After the dust
control, a small rotating trammel screen with a carefully calibrated mesh size will remove
heavier contaminants that have remained larger than the glass through the pulverizor.
3.10.8 Sizing
Screening systems for fine aggregates have been developed over the decades and are available in
every size and many configurations. Two basic types of screening systems for industrial
aggregate applications are circular and tilted bed rectangular vibratory screens. Either type of
screen can be built up to any number of layers for multiple size gradations. Material to be
screened enters from the top and passes from deck to deck. The top screen has the largest
27
opening size. At each deck, the aggregate larger than the screen size opening is removed from
the flow.
In circular screens, the aggregate flows in a circular course around the screens, with the oversize
exiting through an outlet hose at each level. In rectangular screens, the aggregate enters at the
elevated end of the screen and flows across, with the finer aggregate dropping through the screen
while the oversize flows off the end. In general, rectangular, tilted bed screens have greater
capacities, while flat circular screens do a better job of separating the material. Circular screens
may be adequate for feed rates of up to two tons per hour. Above that rate, a multiple decked
screen may be necessary.
Most manufacturers of screening systems will perform test runs in their laboratories to provide
data on flow rate and efficiency of separation for a new material.
A perspective system buyer can have a barrel of glass processed in the type of pulverizor he is
considering sent to a screen manufacturer for test.
3.10.9 Packaging/Storage
Provisions need to be made for both packing and weighing the final product. Bagging,
palletizing, bulk bagging and wrapping requirements will depend on product specifications and
quantities required by the customer, as well as the customary packaging expected in a particular
industry.
Research should be performed to determine the packaging requirements for the perspective
markets, then finding packaging systems to fulfill those requirements. The processor must
respond to market packaging expectations, rather than expecting the market to respond to the
processor’s convenience.
3.11 Machines used in glass recycling.
The Silipaktor
The machine has been designed specifically for the small scale recycling industries and enables meaningful cost savings to be made for premises generating significant volumes of waste glass. The unique 220 litre steel bins hold nearly 300 kgs of crushed glass (cullet) which equates to more than five 240 litre bins or slightly more than a single 1,100 litre wheelie-bin filled with
28
uncrushed glass. This enables precious 'back-of-house' space to be saved. Numerous bottles can be fed into the machine at a time, saving staff time. Bottles of all sizes and colours can be crushed together, saving time and the risk of accidents during the sorting process. Removal of the cullet is considerably quieter than dealing with whole bottles, eliminating concerns over the sensitive issue of noise at collection times.
Figure 1: The Silipaktor
29
Figure 2: Stainless Steel Lump buster on a Carbon Steel Elevated Stand
.
30
Figure 3 : Stainless Steel Lump buster on a Stainless Steel Stand with a pneumatic cylinder that lifts the hinged loading chute, so that the material slides into the machine for crushing.
31
Figure 4 Carbon Steel Lump Abrador.
32
Figure 5 Recycling plant
33
CHAPTER FOUR – RESULTS AND DISCUSSIONS
4.0 LABORATORY TESTING PROGRAM
4.1 Particle Morphology
·Roundness is a property related to the curvature of the sharpest corner present on a particle.
Qualitatively, particles can be described as being very angular, angular or sub-angular (VA, A or
SA) and sub-rounded, rounded or well-rounded (SR, R and WR). The size parameter most
significant for well screen design is the D10, commonly referred to as the Effective Size.
Typically well filter packs are designed to have an effective size larger than the well intake
screen and small enough to limit the migration of fines from the surrounding natural formation.
The Coefficients of Uniformity (CU) and Curvature (CC) are parameters that describe the shape
of a given particle size distribution curve. CU is equal to D60/D10. CC is equal to
(D302)/(D10*D60). The materials tested are highly uniform (i.e., CU= less than 2) which means
the samples are comprised of particle populations with very little variation in size. A high degree
of uniformity is desirable for well packing because little or no segregation of particles by size
can occur during installation and typically pressure head loss is less through more uniform well
packing.
Visual descriptions of each material tested were conducted using 10X magnification and the
criteria of Form, Sphericity and Roundness describing sediment grains. Particle shape influences
the packing arrangement the media particles can take. The packing arrangement can affect the
medium’s porosity and permeability. Particles may be classified as “C” for compact (or
equidemensional), “B” for Bladed, “E” for elongated (or rodlike) and “P” for platy (or disclike).
For purposes of this study the dimensions were visually estimated and the approximate term was
selected from a triangular comparison chart (reproduced in Appendix A). Sphericity is a
property whose definition states how nearly equal the three dimensions of an object are. A true
sphere has a sphericity of 1.0 and typical natural sand grains have sphericity values of 0.6 to 0.7.
For purposes of this study this property was estimated visually. · Roundness is a property related
to the curvature of the sharpest corner present on a particle. Qualitatively, particles can be
34
described as being very angular, angular or sub-angular (VA, A or SA) and sub-rounded,
rounded or well-rounded (SR, R and WR).
4.2 Permeability
The permeability or hydraulic conductivity of a material plays a decisive role in judging product
applicability. The intent with well pack design is to replace the zone immediately surrounding
the well screen with more permeable material which has a net effect of increasing the effective
diameter of the well
4.3 Crushing and sorting of waste glass
The first phase of treatment upon arrival of waste glass at the reprocessing plant is visual
inspection.
Visual inspection is undertaken by experienced staff with good knowledge of the processing
technology of the plant. Lorries tip their load for visual inspection, to determine the processing
needs.
In some cases, the operator may decide that the contamination is too high for an economic
treatment, and the load is disposed of without treatment.
If inspection results in acceptance, the material is crushed. Crushing reduces the glass piece size
to the size suitable for further sorting or cleaning. Afterwards the organics may be dried at
ambient air, or removed by washing, before the material passes sieves to reduce the organic
content as well as magnetic separators and Eddy current separators to reduce the metal content.
Highly contaminated materials may pass several times sieving as well as magnetic and Eddy
current steps until they are clean enough to pass an optical sorting. In the different phases of the
process, air suction removes lighter components such as paper and plastics.
Manual sorting can also be part of the sorting steps, removing by handpicking large pieces of
foreign material such as plastics, paper, textiles, or ceramics/stone/porcelain. An increasing
problem for container glass cleaning is the recent trend of using transparent thin foils attached to
glass, instead of paper labels. Some adhesives of these foils lead to increased rates of waste
because they cannot be separated from the glass. Radio frequency identification (RFID) tags
35
might also raise problems for recycling if their use will increase in the future, as suggested by
members of the TWG.
The most complex process is optical sorting. Here, glass pieces are first sorted into different
flows according to grain size. The flow passes through one or more optical sorting machines.
Each sorting machine is equipped with cameras and sensors that use white light, laser light and
infrared backlight.
The opaque non-glass materials are detected. Different colours of glass can also be detected
depending on how they transmit the different incident light beams. Detection triggers blowout
commands.
Blowout jets are used to eject target impurities at precisely the right moment. Regarding color
impurities, this technique allows improving color separation, but not to the extent of a complete
separation into single colour waste glass streams. In the last years, fast X-ray fluorescence
detection systems combined with blow out techniques have become available as well. The X-ray
system is able to sort out undesired glass fractions that cannot be detected with infrared
technique, like lead glass, refractory glass and glass ceramic. Within milliseconds, material with
defined characteristics is blown out of the cullet, independent from the size, shape, or colour of
the particle. Finally, automatic quality control is combined with manual quality control by
qualified staff overseeing the final separation result. The outcome of these steps is cullet with a
certain quality.
Pre-consumer glass waste, collected at a direct customer of the glass manufacturer, can spare
some of the mentioned reprocessing steps. For example, a car manufacturing company buys flat
glass from a glass manufacturer to be used in car windows. Some of the flat glass in the car
manufacturing company ends up as waste during the production process of making car windows.
This flat glass waste may be directly returned to the flat glass manufacturing company. It is a
prerequisite for such direct return without processing that the waste glass has no contamination
during its processing at the product manufacturing industry (in the example, the car
manufacturing industry). Usually, this practice takes place in cases where long-term customer
relations exist, e.g. within two steps of the glass supply chain that share ownership.
36
4.4 Transport of glass cullet to cullet users
Because of its relatively high density, low specific value, and frequent abundance of the raw
materials that glass cullet substitutes, glass is mostly produced and consumed locally, and waste
glass is collected and used locally.
4.5 Recycling techniques
The processed and transported cullet can be subject to a number of recycling techniques.
However, a main issue here is compatibility, a crushing and sorting of waste glass
The first phase of treatment upon arrival of waste glass at the reprocessing plant is visual
inspection.
Visual inspection is undertaken by experienced staff with good knowledge of the processing
technology of the plant. Lorries tip their load for visual inspection, to determine the processing
needs.
In some cases, the operator may decide that the contamination is too high for an economic
treatment, and the load is disposed of without treatment.
If inspection results in acceptance, the material is crushed. Crushing reduces the glass piece size
to the size suitable for further sorting or cleaning. Afterwards the organics may be dried at
ambient air, or removed by washing, before the material passes sieves to reduce the organic
content as well as magnetic separators and Eddy current separators to reduce the metal content.
Highly contaminated materials may pass several times sieving as well as magnetic and Eddy
current steps until they are clean enough to pass an optical sorting. In the different phases of the
process, air suction removes lighter components such as paper and plastics.
Manual sorting can also be part of the sorting steps, removing by handpicking large pieces of
foreign material such as plastics, paper, textiles, or ceramics/stone/porcelain. An increasing
problem for container glass cleaning is the recent trend of using transparent thin foils attached to
glass, instead of paper labels. Some adhesives of these foils lead to increased rates of waste
because they cannot be separated from the glass. Radio frequency identification (RFID) tags
might also raise problems for recycling if their use will increase in the future, as suggested by
members of the TWG.
37
The most complex process is optical sorting. Here, glass pieces are first sorted into different
flows according to grain size. The flow passes through one or more optical sorting machines.
Each sorting machine is equipped with cameras and sensors that use white light, laser light and
infrared backlight.
The opaque non-glass materials are detected. Different colours of glass can also be detected
depending on how they transmit the different incident light beams. Detection triggers blowout
commands.
Blowout jets are used to eject target impurities at precisely the right moment. Regarding color
impurities, this technique allows improving color separation, but not to the extent of a complete
separation into single colour waste glass streams. In the last years, fast X-ray fluorescence
detection systems combined with blow out techniques have become available as well. The X-ray
system is able to sort out undesired glass fractions that cannot be detected with infrared
technique, like lead glass, refractory glass and glass ceramic. Within milliseconds, material with
defined characteristics is blown out of the cullet, independent from the size, shape, or colour of
the particle. Finally, automatic quality control is combined with manual quality control by
qualified staff overseeing the final separation result. The outcome of these steps is cullet with a
certain quality.
Pre-consumer glass waste, collected at a direct customer of the glass manufacturer, can spare
some of the mentioned reprocessing steps. For example, a car manufacturing company buys flat
glass from a glass manufacturer to be used in car windows. Some of the flat glass in the car
manufacturing company ends up as waste during the production process of making car windows.
This flat glass waste may be directly returned to the flat glass manufacturing company. It is a
prerequisite for such direct return without processing that the waste glass has no contamination
during its processing at the product manufacturing industry (in the example, the car
manufacturing industry). Usually, this practice takes place in cases where long-term customer
relations exist, e.g. within two steps of the glass supply chain that share ownership.
4.6 Waste Glass Recycling Techniques in the Flat Glass Industry
The use of cullet in flat glass manufacturing requires high cullet quality because the majority of
products are colorless and do not allow impurities. Besides own production waste (internal
38
cullet), flat glass industry uses external cullet, but nearly exclusively from processors of flat glass
because this guarantees receiving specific cullet properties. It is estimated that about 95% of
waste glass from flat glass processing is recycled.
The return of specific flat glass cullet quality from processing industries is eased by the fact that
many processing companies (e.g. insulation glass producers) are owned by companies also
producing flat glass. Although direct return from processing to melting is possible, flat glass
producers prefer to contract waste glass treatment companies to be sure that contaminations are
minimized, caused in particular by metals from spacer bars of insulation glass production or
stones from waste storage and handling.
The automotive glazing sector is actively involved in discussions on the treatment of ELV glass
and provides advice and assistance to the economic operators involved. Cullet derived from ELV
can often meet the quality requirements for the insulation mineral wool, container glass and the
flat glass industries.
4.7 Batch Chemicals
The majority of the chemicals were sourced from local suppliers, such as the local pottery supply
house in Seattle. The chemicals added to the base glasses in the test melts consisted of fluxing
agents, coloring agents, and opacifiers.
4.7.1 Fluxing Agents
Several different fluxes were used to facilitate melting the base glasses, including borax, potash,
(K2CO3) and tin dioxide (SnO2), which acts to keep the colorant in solution. Silicon carbide was
added as a batch reducer.
4.7.2 Colorants
Colorants were added to the batch to either color balance and/or colorize the base glasses.
Copper was added as copper carbonate. Cobalt was added as cobalt carbonate, sodium as sodium
nitrate, and zinc as zinc oxide. Manganese was introduced as manganese dioxide. The rare-earth
ion Nd3+ was introduced as 96% purity neodymium oxide, Nd2O3. Cerium was added as cerium
oxide, and titanium as titanium dioxide, TiO2.
39
4.7.2 Opacifying Agents
Two sets of opacifying agents were used during the laboratory melts to obtain opal colors, as
described above. The first used phosphorus and fluorine, added as phosphoric acid, H3PO4, and
calcium fluoride, CaF2 (fluorspar). The second used PAF. In one instance, bone ash was
introduced for phosphorous content, replacing phosphoric acid
4.8 Waste Characteristics
Two types of air emissions are generated: those from the combustion of fuel for operating the
glass-melting furnaces, and fine particulates from the vaporization and recrystallization of
materials in the melt. The main emissions are sulfur oxides (SOx), nitrogen oxides (NOx), and
particulates, which can contain heavy metals such as Arsenic and lead. Particulates from lead
crystal manufacture can have a lead content of 20–60% and an arsenic content of 0.5–2%.
Certain specialty glasses can produce releases of hydrogen chloride (HCl), hydrogen fluoride
(HF), arsenic, boron, and lead from raw materials. Container, pressing, and blowing operations
produce a periodic mist when the hot gob comes into contact with the release agent used on the
molds. Cold-top electric furnaces, in which the melt surface is covered by raw material feed,
release very little particulate matter, as the blanket acts as a filter to prevent the release of
particulate matter. Some releases of particulates will take place in tapping, but furnace releases
should be of the order of 0.1 kilogram per ton (kg/t) when operated this way. Lead glass
manufacture may result in lead emissions of about 2–5 kg/t. In all cases, the concentration of
heavy metals and other pollutants in the raw flue gas mainly depends on the type of fuel used,
the composition of the feed material, and the portion of recycled glass. High input of sulfates or
potassium nitrate may increase emissions of sulfur dioxide and nitrogen oxides, respectively.
Where nitrate is used, more than two thirds of the introduced nitrogen may be emitted as
nitrogen oxides.
4.9 Pollution Prevention and Control
Oxygen-enriched and oxyfuel furnaces are used in specialty glass operations to reduce emissions
or to make possible higher production rates with the same size furnace. Although oxyfuel
40
furnaces may produce higher NOx emissions on a concentration basis, they are expected to yield
very low levels of nitrogen oxides on a mass basis (kg/t of product). Low-NOx furnaces, staged
firing, and flue gas recirculation are available to reduce both concentration and the mass of
nitrogen oxide emissions. These techniques are also available for air-fuel-fired furnaces.
Nitrogen oxide levels can be controlled to 500–800 milligrams per cubic meter (mg/m3). The
type of combustion fuel used affects the amount of sulfur oxides and nitrogen oxides emitted.
Use of natural gas results in negligible sulfur dioxide emissions from the fuel compared with
high sulfur fuel oils. Fuel oil with low sulfur content is preferable to fuel oil with high sulfur
content if natural gas is not available. An efficient furnace design will reduce gaseous emissions
and energy consumption. Examples of improvements include modifications to the burner design
and firing patterns, higher preheater temperatures, preheating of raw material, and electric
melting. Changing the composition of the raw materials can, for example, reduce chlorides,
fluorides, and sulfates used in certain specialty glasses. The use of outside-sourced cullet and
recycled glass will reduce energy requirements (for an estimated 2% savings for each 10% of
cullet used in the manufacture of melt) and thus air emissions (up to 10% for 50% cullet in the
mix). Typical recycling rates are 10–20% in the flat glass industry and over 50% for the blown
and pressed glass industries.
The amount of heavy metals used as refining and coloring or decoloring agents, as well as use of
potassium nitrate, should be minimized to the extent possible. In the furnace, particulates are
formed through the volatilization of materials, leading to formation of condensates and of slag
that clogs the furnace checkers. Disposal of the slag requires testing to determine the most
suitable disposal method. It is important to inspect the checkers regularly to determine whether
cleaning is required. Particulate matter is also reduced, for example, by enclosing conveyors,
pelletizing raw material, reducing melt temperatures, and blanketing the furnace melt with raw
material.
41
CHAPTER FIVE – CONCLUSION AND RECOMMEDATIONS
5.0 IMPLEMENTATION PLAN
In the initial stages, I will start with the establishment of small/medium scale firm with support
of Non-Government Organisation (NGO) in order to sustain in case of initial losses. I will try to
capture the market by different means of marketing (Electronic, Print, and media). When my
product captures target proportion of market, I will then plan for the extension of the firm, either
by expanding the plant size in the same area or installation of new plant on new piece of land.
5.1 Market Opportunity
Despite minor fluctuations in the consumption of glass over the years, it is showing an increasing
trend. I predict that in future this demand will be increasing; as a result production capacities will
be needed to be increased to meet the country’s demand.
5.2 Reaching the Customers
Customers are not waiting for my product to be launched instead I am providing them a
substitute to a more expensive product. In order to be successful, I need to introduce myself to
the market. For this purpose, I will market my product(s) through different mediums (Websites,
Emails, Print, and Media,). Different types of awareness programs will be used to make people
buy recycled glass products. I am aware that this sort of awareness programs costs a lot but this
way is the most effective way in case of our product.
5.3 SWOT Analysis
This summary tries to outline factors that will influence the production either positively or negatively.
i) Strengths
Low price. Environment Friendly. Low resource consumption. Less garbage in the society.
42
ii) Weaknesses.
Unavailability of Machinery. Lack of Human expertise in recycling in the country. People may not accept these products if I do not rightly market it. Lack of markets for collected materials. Lack of funding for recycling. Poor participation by residents in materials collection.
iii) Opportunities
Employment Opportunities. Demand Supply gap, creates a room for our business. Purchasing power of the people will be increased so they will favour our products.
iv) Threats
Glass importers and manufacturers based in Kenya may react on this establishment and may negatively affect my profitability and sustainability.
5.4 Recommended Processing Methods
When evaluating the feasibility of using a recycled material in a new application, it is important
to first document baseline requirements for target markets.
This baseline information can be compared to data obtained from tests performed on the recycled
materials. It is critical to test recycled materials from known sources processed by known
processing equipment, because the physical characteristics of the processed material may vary
widely depending on the source and processing strategy.
5.5.1 Labor Requirements
Two operators were used to run the system. At least one operator is required, and must be a good
Mechanic/welder to maintain the equipment. The dryer/pulverizer and the entire system was
difficult to keep operating for any length of time. Due to the frequent breakdowns and
modifications required, considerable mechanical work was required to maintain the system. This
situation is typical of a prototype system where much work has to be done by hand instead of
43
with machinery. Any such system would be doing well to achieve a 65% operating time with two
operators, as there are other things, besides maintenance, that they must do, such as lining up
feedstock, changing the dust collector barrel, moving bulk bags of product, and weighing the
product.
5.5.2 Cost Analysis
The cost of operation of the small prototype system, which has a capacity of about one tph, is
300,000/= per ton of product including bags and pallets. Aside from the excessive wear cost, the
volume is too low at one tph to be cost effective. A two tph system with a small, separate dryer
would be a more efficient system, and the cost could drop to about 215,000/= per ton of product
(excluding amortized capital costs and depreciation). If the product could be sold for an average
of 312500/= per ton including bag and pallet charges, a small profit could be obtained.
5.6 Experimental Procedure
The prototype melts were designed to simulate the melt conditions at the client’s facility. This
included procedures for beneficiating the base recycled glass, sourcing glass-maker chemicals,
controlling melting conditions, press-forming the final product and annealing the samples.
Further, a flexible melt sequence was required to accommodate daily results/failures. Each aspect
of the process was fully documented.
5.6.1 Source of Glass Cullet
The glass is presorted into the truck at the curb. The glass was crushed with a hand-crusher to
obtain a cullet sizing of two-inch-minus and washed to remove gross contamination. Ceramics,
metals, lead wrappers, and some plastic were also removed. All paper foils, and other colored
glasses were left in the cullet. The debris was weighed to determine the percentage of material
that was removed. This was generally less than one percent by weight for all the glass received.
This cullet worked fine for transparent glasses. To produce quality opal colors, the cullet should
be pulverized to at least a 150 mesh size.
44
5.6.2 Batch Chemicals
The majority of the chemicals were sourced from local suppliers, such as the local pottery supply
house in Seattle. The chemicals added to the base glasses in the test melts consisted of fluxing
agents, coloring agents, and opacifiers.
i. Fluxing Agents
Several different fluxes were used to facilitate melting the base glasses, including borax, potash,
(K2CO3) and tin dioxide (SnO2), which acts to keep the colorant in solution. Silicon carbide was
added as a batch reducer.
ii. Colorants
Colorants were added to the batch to either color balance and/or colorize the base glasses.
Copper was added as copper carbonate. Cobalt was added as cobalt carbonate, sodium as sodium
nitrate, and zinc as zinc oxide. Manganese was introduced as manganese dioxide. The
rare-earth ion Nd3+ was introduced as 96% purity neodymium oxide, Nd2O3. Cerium was added
as cerium oxide, and titanium as titanium dioxide, TiO2.
iii. Opacifying Agents
Two sets of opacifying agents were used during the laboratory melts to obtain opal colors, as
described above. The first used phosphorus and fluorine, added as phosphoric acid, H3PO4, and
calcium fluoride, CaF2 (fluorspar). The second used PAF. In one instance, bone ash was
introduced for phosphorous content, replacing phosphoric acid.
5.6.3 Melting Procedure
Each melt day, four separate batches of 25 to 30 pounds each were weighed out and mixed
thoroughly. Each batch was charged into separate crucibles in an experimental test furnace that
contained four freestanding crucibles, each with a capacity of 30 pounds.
The charge cycle was varied according to the glasses being melted. Generally, each crucible was
charged regularly at four intervals, with the last two charges being the smallest. The melt
temperature was then allowed to increase slowly for one to two hours to complete the melt.
45
Finally the furnace setting was turned down to allow the glass to slowly cool to the working
temperature required the following day.
5.6.4 Sample Forming
Samples of each glass formulation were pressed in a hand-press using a patterned four-inch
square tile mold. This stage of the process is critical in that this is the stage at which all the
working characteristics of the glass determined. The glass melt was initially gathered in a gob
from which a thread was pulled. From the thread pull, an initial read on the viscosity was taken
and the temperature was adjusted as required. Once the melt temperature was satisfactory, the
tiles were pressed. Thread samples were also pulled to determine the annealing temperature of
each formula melt. Set times were short, as desired for pressing molds, between five and ten
seconds. The sample tiles pressed each day were annealed through a cooling down cycle of eight
hours.
5.6.5 Color Contamination
Cross-contamination was a major concern during the melt progressions. Since the project could
not afford a new crucible for every formula, the melts were organized to minimize prior melt
contamination. Formulas were sequenced in crucibles that utilized similar colorants and base
glasses. For instance, the pot used to melt copper colored opals was initially used to melt
transparent colors. Once a sequence ran its course, the crucible was exchanged for a new one. To
keep track of contamination, the melt progressions were fully documented with each melt listing
the crucible number and prior melt formula number.
5.6.6 Batch preheating
Charging a thin batch layer or charging a thin compressed batch sheet in an internal batch
preheating zone requires a new design for this part of the furnace. A counter flow heat exchange
between the flue gases and the thin batch can heat up a blanket of a few centimeters thickness (3-
4cm) within about 10 to 15 minutes to 2282 °F (1250 °C). This requires a shallow internal
preheating area of about 20 to 25m2 for 250 tpd. Energy savings of more than 10 percent can be
achieved by this internal batch preheating system.
46
5.6.7 Sand dissolution
To speed up the heat transfer from the surface to the deeper glass melt layers, strong convection
by stirring, bubbling, or large temperature differences is important in the sand grain dissolution
section of the segmented melter. Sand grain dissolution is enhanced by this convection and the
resulting velocity gradients. The temperature should not exceed the fining onset temperature.
Extra heat input in this section is only 5 to 10 percent of the total net heat input required to melt
the glass. Efficient insulation should limit energy losses through the furnace walls.
To avoid excessive evaporation, the glass surface temperature should be controlled at a level just
below 2552 °F (1400 °C) for soda-lime glass melting. Homogenization of the melt takes place in
this section. The velocity gradients must be minimized at the refractory walls to limit the
dissolution of refractory components in the melt. The sand grain dissolution, or melting section,
is connected to the fining section by a narrow or shallow canal. According to the calculations, re-
circulation can be practically limited to a level of 20 to 30 percent of the forward flow current.
Just upstream from the primary fining zone, the melt should be heated at least to the fining onset
temperature and, depending on the volume and pressure in this compartment, a certain excess
temperature above the fining onset temperature value.
The total net amount of enthalpy required to heat the melt to these temperatures is only 5 to 10
percent of the total net heat input. Relatively cheap fossil fuel combustion can provide this heat.
However, this will lead to high glass melt surface temperatures from exposure to the flames, as
in conventional furnaces, and to poor heat transfer. Another option is to use electric energy to
heat the hottest part of the furnace (fining section). The extra electric energy added in the fining
compartments is more expensive then fossil energy, but it comprises only about 7 to 10 percent
of the total energy consumption for melting. This small amount of electric energy is more
effectively used, and most of the energy for the melting process can be supplied by fossil fuels.
Therefore, all the molten glass in a small section of the furnace is raised to a very high
temperature by using a small amount of electric energy, enhancing the fining for the total melt
without large increases in energy costs. In common electric boosting, the electric energy
provides 176 supplemental energy input in a form more effective than would be possible by
increasing the primary fuel. Traditionally, electric boosting is applied to avoid low bottom
temperatures in a tank in which colored glass is melted.
47
5.7 Fining zone
In the fining zone, the glass melt should not be exposed to strong mixing effects; a plug flow
regime is preferred. Residence time required in the fining zone depends on the depth of the melt
in this area. A deep melt requires a long residence time and a high surface temperature, if heated
from above, to obtain a sufficiently high temperature level in the bottom layers of the melt. The
temperature gradients from the surface to the bottom and both ends of the furnace to the hot spot
cause glass convective flows to well upward, resulting in the formation of a spring zone, or
spring line, for refining where a line of bubbles or foam exists near the forward fuel firing port.
This defines the end of refining and the beginning of thermal conditioning, also the highest
temperature glass in the furnace.
Low-pressure will enhance bubble growth and bubble removal, as well as gas stripping.
A plug flow shallow fining zone, using electric energy and low pressure (<0.3 bar), will require a
very low residence time for complete fining (one to two hours). Low pressure fining requires a
high, well-sealed fining shaft. The refractory must be lined on the inside with a nonporous
material such as molybdenum or a noble metal shield. A lining at the outside can also be used to
seal the low pressure-fining shaft, but the gases in the inner material layers will limit the rate of
evacuation. The sub atmospheric fining shaft has to be a rather tall design, 2 to 4m above the
level of the melting section, to compensate for the pressure difference between the melting
section, atmospheric, and the finings section. Sub atmospheric refining (SAR) is considered one
of the key technologies advance the glass melting process. SAR has the potential to obtain higher
quality glass while reducing cost and environmental emissions.
After an effective primary fining process, a melt with low concentrations of dissolved gases and
only small bubbles from the fining gas remains. Gases in the bubbles can redissolve in the melt
during controlled cooling from the primary fining temperature (2552- 2912 °F [1400-1600 °C])
down to the temperatures of 2192-2372 °F (1200-1300 °C). The volume of the refiner zone
depends on the quality of the primary fining process and the cooling rate achievable in the refiner
or working end. A deep refiner helps in the separation of a melt without seeds and a melt
containing retained seeds. The required residence time in the working end or refiner depends on
the completeness of the primary fining stage and on the required cooling rate.
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5.7.1 Refining and conditioning
The glass melt must be cooled down slowly in the refining and conditioning section to avoid
freezing in residual seeds. To obtain a melt with uniform viscosity needed for forming, the
cooling process should be uniform. For soda-lime silica melts, slow cooling between 2642 and
2282 °F (1450 and 1250 °C) is essential because gases dissolve in the melt with a relatively high
gas diffusion rate. Cooling of the melt in the working end is best performed in a series of small
mixers to ensure uniform cooling. The temperature 177 control per mixer will optimize the
cooling rate and contribute to homogeneity, especially if cords or knots have been formed by the
interaction of molten glass with the refractory lining.
5.7.2 Deep refiner
The well de-gassed melt flows on top and then downstream along the bridge wall and sidewalls
into the throat in this deep refiner segment. The melt in the center re-circulates, allowing small
bubbles to be removed in the refiner part. Homogenization occurs because of the strong re-
circulation. The difference between minimum and average residence time (volume/pull) is still a
factor of five but this concept allows a reduction of the tank volume of about 25 percent
compared to conventional furnaces.
5.7.3 Cullet Inspection.
Fine Cullet
This specification is representative of the quality needs of the fiberglass industry and covers
glass food and beverage containers (soda-lime-silica) only. Any other types of glass are
considered contaminants and may provide justification for load rejection based on agreement
between negotiating parties and discretion of buyer. Other types of glass considered to be
contaminants include: Pyrex®, crystal, ovenware, windows, light bulbs, ceramics, plate glass, art
glass, mirror glass and others.
Size Specification
Grade C fine cullet must yield 100 weight percent passing a 6.3 mm (1/4 inch) screen, with no
more than 0.5 weight percent retained on a No. 12 screen, and no more than 15 weight percent
49
passing a No. 200 screen.
5.7.4 Color Specification
In the fiberglass industry, color-sorting is optional and specific color quantities and mixes-may
be negotiated between supplier and purchaser. The established color specification will ensure a
consistent color mix from shipment to shipment.
Flint
A color distribution with flint as the predominant color. The percent by weight composition
of flint and other allowable color(s) will be established by trading parties. This color
composition will vary no more than + 3 weight percent for each color from shipment to
shipment.
Amber
A color distribution with amber as the predominant color. The percent by weight composition of
flint and other allowable color(s) will be established by trading parties. This color composition
will vary no more than + 3 weight percent for each color from shipment to shipment.
Green
A color distribution with green as the predominant color. The percent by weight composition of
green and other allowable color(s) will be established by trading parties. This color composition
will vary no more than + 3 weight percent for each color from shipment to shipment.
Mixed color cullet
A color distribution with up to 25 weight percent amber content allowed, and an established
weight percent content for each other color that varies no more than + 3 weight percent from
shipment to shipment.
5.7.5 Contamination Limits
Organic material -not to exceed 0.1 weight percent.
50
Ferrous metal - not to exceed 0.005 weight percent.
Non-ferrous metal - not to exceed 0.01 weight percent
Other inorganic material - not to exceed 0.3 weight percent of the entire sample weight, with no
inorganic particles retained on a No. 12 screen, and no more than 0.1 weight percent retained on
a No. 20 screen, and no more than 0.2 weight percent retained on a No. 20 screen.
5.8 Conclusion
Pre-sorted post-consumer bottle glass can be readily remelted and chemically modified to
produce a wide variety of colors. Test trials demonstrated that brown cullet can be decolorized to
a nearly colorless, neutral hue, and then recolorized into transparent colors. Green cullet was
color balanced using manganese, and then recolorized into other relatively dense transparent
colors. Further research is required to obtain lighter green-cullet based transparent colors.
The results of this study suggest that it is also possible to generate a wide range of opal colors
from green, brown, or clear cullet. Each color formula must be developed on site, however, to
make adjustments for workability, color concentration, color hue, melt redox equilibrium,
melting environment and raw material sourcing. Strict control over the melting, forming and
annealing processes is also required, whether using phosphate-fluorine opacifiers or the alumina-
fluorine opacifiers. Minimizing melt times will help to reduce fluorine volatilization. For the
various green-based colored opals and the clear based white opals, the fluorine was difficult to
blend, and separated in the melt, using two-inch-minus cullet. Several attempts were made to
improve the melt conditions and arrive at appropriate PAF concentrations.
The best results were obtained using a 150 to 200 mesh pulverized glass sand and a shortened
melt time. If these adjustments are made, a whole set of opal colors can be obtained from
recycled glass 10
The transparent glass formulas produced relatively consistent and satisfactory results. Successful
formulas were developed for producing grape purple, amethyst, honey amber, swim pool blue,
and yellow-green colors.
The only transparent color that was not successfully attained was bright red.
51
APPENDIX I
Economic evaluation of the project
Table 1 Equipment list (fixed capital)
ITEM COST
Impactor or Hammer mill 1,875,000/=
Bag Packer with Beam Balance 62,500/= /ton
Other Equipments 9,700,000/=
TOTAL
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Table 2 Production cost data
Item Units UG.Shs
Operator #1 hour 700/=
Operator #2 hour 700/=
Operator #3 hour 700/=
Manger/Supervisor month 240,000/=
Building Rental Square feet/month 4,167,500/=
Equipment Rental month 2,625,000/=
Electricity kwh 2000/=
Maintenance Materials month 1,575,000/=
Other Expenses month 9,375,000/=
53
APPENDIX II
FACTS ABOUT GLASS RECYCLING Glass was discovered more than 5,000 years ago.
Glass takes one million years to break down naturally.
Recycling a glass jar saves enough energy to light a bulb for four hours.
Most bottles and jars contain at least 25% recycled glass.
Glass never wears out -- it can be recycled forever. We save over a ton of resources for
every ton of glass recycled that is 1,330 pounds of sand, 433 pounds of soda ash, 433
pounds of limestone, and 151 pounds of feldspar.
A ton of glass produced from raw materials creates 384 pounds of mining waste. Using
50% recycled glass cuts it by about 75%. We get 27.8 pounds of air pollution for every
ton of new glass produced.
Recycling glass reduces that pollution by 14-20%.
Recycling glass saves 25-32% of the energy used to make glass.
The oldest examples of glass are Egyptian beads dating from 12,000 BC.
Seventy per cent of consumers believe that glass packaging suggests quality.
Glass is 100% recyclable and can be endlessly recycled with no loss in quality.
Many glass making terms have entered the language:
54
APPENDIX III
GLOSSARYCollection: The gathering of waste glass, including the preliminary sorting and preliminary
storage of waste glass for the purposes of transport to a waste treatment facility.
Cullet: The word cullet can be used to refer to either "broken glass" or to "waste glass". A
distinction should be made regarding internal vs. external cullet. This distinction is important
because internal cullet is not regarded as waste, while external cullet (which can be pre- or post-
consumer) is classified as waste. When using the word "cullet" in the context of end-of-waste it
will always refer to external cullet. The term cullet will be used in this document mainly to refer
to reprocessed cullet, that is, external cullet that conforms to a set of minimum quality criteria.
The report sometimes makes reference to collected cullet; in this case, it is a type of cullet that
generally conforms to lower quality specifications than reprocessed cullet and may not be
suitable as direct input for re-manufacturing into new glass products.
Cullet, internal: Internal cullet is composed of defective products detected and rejected by a
quality control process during the industrial process of glass manufacturing, transition phases of
product changes (such as thickness and colour changes) and production off cuts. The basis of the
definition of internal cullet is the fact that these materials are immediately absorbed by the
respective industrial process as a raw material for a new melting operation, not leaving the glass
manufacturing plant.
Internal cullet cannot be considered as waste as it was never a product.
Cullet, external: External cullet is "waste glass that is collected and/or reprocessed with the
purpose of recycling". External cullet can be of two types: (1) pre-consumer, also called post-
industrial glass cullet, and (2) post-consumer glass cullet.
(1) Pre-consumer cullet is waste glass resulting from the manufacturing of products that contain
glasses one of their components and which leaves the specific facility where it was generated,
becoming waste but not reaching the consumer market. An example of pre-consumer cullet is the
glass cullet constituted by off cuts and pieces from defective manufacturing of e.g. the
production of car windows from flat glass, which leave the car window manufacturing facility
and are re-melted in the flat glass manufacturing facility.
55
(2) Post-consumer cullet is waste glass originated after the use of the glass products at the
consumer market.
Disposal: Any operation which is not recovery even where the operation has as a secondary
consequence the reclamation of substances or energy
Flint cullet: Colourless cullet.
Glass: Generic term referring to a material of an amorphous structure, composed essentially of
silicates.
Glass consumption: Glass that is purchased and consumed in the market within a country or
group of countries, plus imports from the outside, minus exports to the outside.
Glass production: Glass that is manufactured by a country or group of countries. Some of it is
unsold, some of it is sold in the market within the list of countries, and some of it is exported.
Importer: Any natural or legal person established within the European Union who introduces
cullet which has ceased to be waste into the customs territory of the EU.
Manufacturer: Glass manufacturer.
Non-glass components: Also known as contraries or impurities, are non-glass materials that
result of imperfect sorting, such as ferrous and non-ferrous metals, organic materials (paper,
plastic, wood) or inorganic material objects or residuals (ceramics, stones and porcelain).
Producer: The holder who transfers cullet to another holder for the first time as cullet which has
ceased to be waste.
Qualified staff: Staff who are qualified by experience or training to monitor and assess the
properties of cullet.
Recycling: Any recovery operation by which waste materials are reprocessed into products,
materials or substances whether for the original or other purposes (following the definition of the
Waste Framework Directive (2008/98/EC)). It includes the reprocessing of organic material but
does not include energy recovery and the reprocessing into materials that are to be used as fuels
or for backfilling operations.
Recycling rate: Amount of collected waste glass that is re-melted for making new glass,
compared to the total waste glass generated, in percentage terms.
Reprocessing plant: Broad term used to define any of the intermediate actors in the waste glass
chain between the end-users and the glass manufacturing plants. It encompasses companies or
56
institutions undertaking activities such as collection, sorting, grading, classification, cleaning,
crushing, compacting, trading, storing, or transporting. The input material to these plants is waste
glass. The output is glass that may either be waste or non-waste.
57
APPENDIX IV
REFERNCES
Annual Book of ASTM Standards, Vol. 6.01, Paint; Tests for Formulated Products and Applied Coatings.
Federation Series on Coatings Technology; Introduction to Polymers and Resins by Joseph A. Prane.
Recycled Glass: Development of Market Potential. Final Report, Dr. Guna Selvaduray, Materials Engineering Department, San Jose State University for the City of San Jose, July 14, 1994, 45 pages.
Pulverized Waste Recycled Glass as Filter Media in Slow Sand Filtration”, Gray & Osborne, Inc., 1995, 42 pages, on the Internet at http://www.cwc.org/glass/gl954rpt.pdf, accessed July 9, 2003
Glass Technology Services, Ltd (UK), http://www.glass-ts.com/home/home.html, a subsidiary of
British Glass. They help industry develop glass products (the technical arms of British Glass),
they have capabilities to perform testing of glass products.
"Recycled Glass Market Study & Standards Review - 2004 Update", written by ENVIROS and
published by The Waste & Resource Action Program, Oxon, UK (2006)
"UK Glass Manufacture – a mass balance study", British Glass Manufacturer' Confederation
(2004) available at http://www.britglass.org.uk/Files/UKGlassManufactureAMassBalance.pdf