An industrial ecology of the US glass industry

Resources Policy. Vol. 23, No. 3, pp. 109-124. 1997

Pergamon

PII: S0301-4207(97)00020-2

© 1997 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0301-4207/97 $17.00 + 0.00

An industrial ecology of the US glass industry Matthias Ruth and Paolo Dell'Anno Center for Energy and Evnironmental Studies, Boston University, 675 Commonwealth Avenue, Boston, MA 02215 USA

The US glass industry produces a wide variety of products for industrial and end use purposes. Towards that end, large amounts of raw materials are extracted and used, energy is degraded and pollutants are generated and released into the environment. The industry has long recognized its influence on material cycles and energy flows through the e c o n o m y - e n v i r o n m e n t system. It is now in the process of adopting a systems perspective to tackle the problems associated with its material and energy use. To operationalize that systems perspective a dynamic computer model of the container, flat and fiberglass sectors of the industry is developed on the basis of time series data, engineering information and insights from industry experts. The model includes the extraction stage of the main raw materials, transportation of raw materials and discarded products - - both back to producers and to landfills - - and the various manufacturing processes of the desired products. On the basis of the model, material and energy use and CO2 emissions profiles for the years 1988-2028 are quantified under a variety of scenarios on production rates, technology change and recycling. © 1997 Elsevier Science Ltd. All rights reserved Keywords: glass industry, energy use, technical change, COz emissions, glass recycling

1. I n t r o d u c t i o n

The recognition that industrial systems are embedded within a larger socio-economic and ecological system is far from novel, yet poses notable challenges when we wish to use it as the basis for an assessment of the consequences of industrial change for the totality of affected systems. One key component in such an assessment must be the material cycles and energy flows that link the various systems with each other (Ruth, 1993; Ayres and Simonis, 1994). Industrial systems extract materials and fuels from their environment, change their thermodynamic states to produce desired products and in the process generate wastes. Some of these waste products can be used within the economy, others are released back into the environment where they can trigger undesired physical, chemical and biological processes that have repercussions for the socioeconomic system. Industrial ecology chooses a systems perspective as the basis for analysis in an attempt to identify the implications that alternative technologies and products have for material cycles and energy flows in the

ecosystem (Socolow et al, 1994; Allenby and Richards, 1994). The objective is not just to organize and summarize engineering information that describes industrial material and energy use and how they affect the larger systems within which industry operates, but to elucidate likely future resource use and emission profiles and to optimize industrial processes and product designs such that depletion of resource endowments and environmental waste absorption capacities are minimized (Jelinski et al, 1992; Frosch, 1994; Wamick and Ausubel, 1995). Typically, optimization is done in a static or comparative static setting using materials flow or life cycle analysis as if firms or industries were able to instantaneously choose a variety of different inputs and technologies to generate desired products (Graedel and Allenby, 1995). The strength of these approaches lies in their ability to handle a large set of data that describe, for example, technological aspects of the production processes, toxicity of inputs and emissions, product characteristics, and economic variables. However, static and comparative static approaches are of limited use in attempts to identify

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Ecology of the US glass industry: M Ruth and P Dell'Anno resource use and emissions profiles of an industry over time and to inform management and policy decision making in an effort to change the institutional setting such that an industrial ecology can be realized over the long-run. In this paper we apply methods of dynamic modeling (Hannon and Ruth, 1994; Ruth and Hannon, 1997) to extend industrial ecology into the time domain in which industrial change takes place. The goal of the dynamic model developed below is to assess material and energy use and emissions profiles in the US glass industry. On the basis of engineering information, aggregate industry data, and insight from industry experts we attempt to address some of the main challenges that have been recently identified by industry leaders (Glass: A Clear Vision for a Bright Future, 1996). Among these challenges are a growing competition from alternative materials and the need to drastically reduce process energy use and air and water emissions, and to increase recycling of available post consumer products (Glass: A Clear Vision for a Bright Future, 1996). In this paper we will concentrate on a set of material and energy use issues that significantly affect cost of production and environmental performance in the container, flat and fiberglass sectors of the US glass industry. We present a dynamic computer model that captures material and energy use in the extraction of the major raw materials, changes in technology at various production stages, changes in the rates of production and recycling, and transportation of raw materials and discarded products for recycling and landfilling. On the basis of this model we assess likely future profiles of industrial material and energy use and CO2 emissions. The paper is organized as follows. In Section 2 we provide a brief overview over some of the major characteristics of the US glass industry. This overview provides the backdrop against which we discuss in Sections 3 and 4, respectively, raw material use by the industry and the various production stages from raw materials to finished products. In Section 5 we attend to the issue of cullet use - - the major avenue by which the industry can reduce its demand for raw materials and close an important material cycle. We describe the dynamic model of the US glass industry and the model results in Sections 6 and 7, respectively. We close the paper with a set of conclusions for the management and policy implications of the industrial ecology of the US glass industry.

glass fibers and specialty pressed and blown glasses. Due to their diversity in production technology and product characteristics, the specialty pressed and blown glasses are not part of the analysis of this paper. Measured in terms of the volume of its output, the largest of the four sectors of the glass industry is the container industry which accounts for about 61% of the total national glass output (Papke, 1993). As of 1995, 66 container plants were engaged in the US in the production of packaging for a wide variety of products, including food, beverages and pharmaceuticals. In 1995, about 10.5 million tons of glass containers (38.4 billion containers) were produced. Although the glass container industry accounts for the largest share of the total glass market, it has declined greatly since 1978 when about 14million tons (46 billion containers) were produced (Figure 1). The main reasons for this decline were the increased competition from plastic (PET) bottles in the soft drink market and aluminum cans in the beer market, the rising price of oil, and stricter emissions standards. The combination of these factors led to the closure of 48 plants between 1979 and 1992, and resulted in a highly consolidated industry. Flat glass, used for automotive windshields, mirrors and tabletops, as well as for commercial and residential architecture, is the second largest category of products produced by the US glass industry. In 1995, production of flat glass reached 4.44 million tons with a value of $1.9 billion (Bureau of the Census, 1996). Overall, this sector of the industry has enjoyed steady growth in recent years with an average annual increase of about 2.3% since 1991 (Figure 1). Its continued success will depend upon growth in construction and automotive manufacturing and the expansion of foreign markets. Between 1988 and 1993, export revenues have increased from 13.6% to 21% of total revenues. But to offset strong competition from

100 Container Glass

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2. Industry overview The glass industry is an important part of the US economy, providing over 150 thousand skilled jobs and producing a wide variety of consumer products worth an estimated $22 billion dollars each year (Glass: A Clear Vision for a Bright Future, 1996). The industry is composed of four major manufacturing categories. These are container glass, flat glass,

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.1 1960 1965 1970 1975 1980 1985 1990 1995 2000 Year

Figure 1 US glass production by type. Source: Bureau of the Census, various years.

Ecology of the US glass industry: M Ruth and P Dell'Anno foreign flat glass in the US market, further growth in exports is pivotal. The third largest category of products is glass fiber - - a group of products subsuming glass which is formed into fibers with diameters of one-tenth to a few thousandths of a millimeter (Papke, 1993). There are two main types of fiberglass: insulating wool and textile (matte) fiberglass. Insulating wools are used in a variety of domestic and industrial applications to reduce heating and cooling costs. Textile fiberglass is used for reinforcing rubber tires, plastics, and roof shingles, as well as for electrical insulation tapes, and filter clothes. These types of glass fibers are different from optical fibers which are used in high-tech applications and considered part of the specialty glass sector. Between 1963 and 1990 production of glass fiber grew substantially (Figure 1). During this period, fiberglass insulation production increased from 0.5 to 1.6 million tons while production of textile fiberglass rose from 0.1 to 0.98 million tons. Estimated 1995 production of fiberglass insulation and textile fiberglass is 1.73 and 1.19 million tons respectively.

3. Raw materials Container and flat glass, the two largest glass categories, utilize soda-lime glass as their main material input. The four main components in this type of glass are sand (SiO2), limestone (CaCO3 or [CaMg(CO3)2]), soda ash (Na2CO3), and (for container glass) feldspar which contains aluminum silicates, potassium, calcium and sodium. The production of finished container glass from virgin material inputs, requires approximately 0.65 tons of industrial sand, 0.22 tons of soda ash, 0.19 tons of limestone, and 0.11 tons of feldspar/ton of glass. For fiat or 'float' glass, about 0.73 tons of industrial sand, 0.24 tons of limestone, and 0.23 tons of soda ash are needed. These input quantities sum to 1.17 and 1.2 tons of raw materials/ton of finished container and flat glass, respectively (Davis, 1992). The excess 0.17 and 0.2 tons are released primarily as CO2 during the melting stage of production as the raw materials react with one another. Fiberglass insulation, or glass wool, is produced with boro-silicate glass. Although the composition of this type of glass varies depending on the manufacturer, the typical composition is 0.54 tons of sand, 0.22 tons of soda ash, 0.10 tons of borate, 0.11 tons of feldspar, and 0.19 tons of limestone. Textile fiberglass is made predominantly with E-lime aluminosilicate glass. This glass is typically composed of 0.54 tons of sand, 0.34tons of clay, 0.15 tons of borate, and 0.12 tons of limestone/ton of product. Domestic reserves of the raw materials used in glass production are very large. Therefore, these materials are relatively inexpensive and there is little concern in the industry about the effects of depletion of these minerals. Yet, their extraction, processing

and transportation requires energy which needs to be taken into account in an effort to capture the main material cycles and energy flows through the industry.

4. Glass production The four major processes involved in glass manufacturing are batch preparation/formulation, melting/ refining, forming and post-forming. The first stage, in which raw materials are mixed, is very similar for each type of glass. Although varying considerable in scale, the melting/refining stage is also similar in the production of container glass, flat glass, and textile fiberglass. The last two processes, in which the glass is formed and treated, are quite different in each case. Batch preparation~formulation Batch formulation is the process by which specific proportions of raw materials are mixed to yield a particular type of glass. In recent years, the glass industry has moved towards a completely automated batching system (Bauer and Bailey, 1992). This process involves moving raw materials, including cullet, from storage silos to adjacent weigh hoppers, and ensures a high quality of the mix and reduces energy consumption for batch preparation and formulation. Once the proper proportions of each material are achieved for the desired composition, the materials are transported by conveyor belts to rotary or pan type mixers. After the batch has been thoroughly mixed, it is fed into the furnace to be melted. Melting~refining There are three basic steps in glass melting. The first is the actual melting in which the raw materials are converted into a homogeneous liquid. In the subsequent refining stage, bubbles are removed from the melted batch. In the final stage of homogenization, thermal and chemical variations are eliminated from the molten glass (Wooley, 1992). In the case of container glass melting, the mixed batch is continuously fed into an opening at the back end of the melting tank. Due to its lower density, the batch floats atop the molten glass where it gradually melts. As the melt moves through the tank, the bubbles which are created by chemical reactions, gradually break or dissolve. Because of the formation of many small bubbles, the fining process is usually very slow, limiting the pull rate of the melter (Wooley, 1992). The limitations on the speed of the process affect the extent of energy efficiency improvements. Once the melt has been refined, it moves into a conditioning chamber in which the molten glass undergoes homogenization to eliminate compositional variation and to reduce temperature variations. Compositional variation in the melt is reduced with a series of skimmers, overflows, and stirring mechanisms. The reduction of temperature variations mainly occurs

lll

Ecology of the US glass industry: M Ruth and P Dell'Anno

in the forehearth, a channel at the end of the conditioning chamber. As the melt enters this channel, it is cooled while heat is applied to keep it at a uniform temperature which is required in the forming stage. Typical container tanks have melting areas of 60180 m 2, deliver 100-500 tons/day (Wooley, 1992), and exhibit economies of scale with regard to their energy consumption/ton of product. Because of the higher quality requirements, float (flat) glass melters differ from container glass melters in a few important respects. In order to keep the compositional variation of the melt parallel to the sheet surface, float glass tanks have a narrow section, called a waist, which separates the melting from the conditioning stage. Also, the lack of a forehearth requires a much longer tank to allow the cooling required before the forming stage (Wooley, 1992). Float tanks have areas of 200-500 m 2 with output of 300800 tons/day. Similar to container tanks, float tanks show returns to scale in their energy consumption/ton of product. For wool-type fiberglass production, melting is predominantly done with all electric, cold-top furnaces. Because of the electrical resistance of glass wool, electric melting is ideal (Wooley, 1992). These furnaces are similar in design, yet smaller, than the regenerative furnaces described above. Also, in these furnaces, the entire melt surface is covered by a batch layer which is 2-6 in thick. Therefore, melting occurs in a thin layer at the bottom of the batch allowing volatile compounds to condense in the layers of batch above. About 90% of the glass produced in the US is melted in regenerative furnaces. They are characterized by chambers made of ceramic refractory material located on each side of the melting tank in which heat exchange occurs. Air flows through these chambers and is heated before combining with fuel at the combustion ports. The combustion ports are electricity boosted, natural gas or oil fired furnaces in which flames heat a thin layer of molten glass from above (Wooley, 1992). The electricity boost supplies between 10 and 30% of the total energy required for melting through electrodes which are immersed in the melt (Wooley, 1992). The benefits of electric boosting include increased output, and reduced gas or oil use leading to fewer emissions at the manufacturing site (Gaines and Mintz, 1994). The melting and refining stage accounts for 5068% of the energy used in glass production and has become the focus of industry conservation efforts (OTA, 1993). State-of-the-art technologies such as electric boosting, better refractories, oxygen enriched combustion air, and chemical boosting could reduce the energy use in this stage by 8-37% from current average practices. Advanced technologies such as submerged burner combustion and ultrasonic agitation could further reduce energy consumption by an additional 38-63% (Energetics, 1990). The thermodynamic minimum energy requirement for melting

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glass is 2.2 million Btu/ton (Glass: A Clear Vision f o r a Bright Future). Forming~post-forming Following melting and refining stages, the various glass products are shaped into desired forms using technologies that are significantly different for each type of glass. Narrow-necked glass containers are formed using the 'blow and blow' method of manufacturing. Forming starts as gobs of glass are cut and shaped by gob feeders attached to the end of the forehearth. The gobs are dropped through a chute and into a mold where air forces the gob to the bottom, forming the top of the container. Another blow is applied to the center of the gob to form the inside of the container. These partially formed gobs are then placed into a finish mold where they are reheated and given another burst of air to form the final shape (Stevens, 1992). Then, a coat of titanium oxide or tin is applied for scratch resistance and the bottles are moved by conveyer to the annealing furnace (Gaines and Mintz, 1994). For large-mouth, and some light-weight beverage containers, the 'press and blow' method of production is used. In this process, the initial mold is formed by a plunger rather than air. The energy used for either method is typically supplied by electricity. Since the early 1970s, the float process has been the dominant method of forming soda-lime flat glass. This process begins as molten glass at 2100°F is poured through a spout and onto a large bath of electrically heated, molten tin. Tin baths can be up to 150 ft long and 13 ft wide. Here, gravity causes the molten glass to settle to a thickness of 7.1 ram, but thicknesses can be varied from 1.5 to 25 mm by stretching or compressing the glass (Stevens, 1992). The top of the molten glass is exposed to a controlled atmosphere above the bath which helps cool the glass to a temperature of 650°F before exiting (Stevens, 1992). Once formed, the glass must be slowly cooled to room temperature to relieve internal stresses. This process, called annealing, is performed in large, predominantly gas-heated chambers (Energetics, 1988). Flat glass used in automotive and architectural applications is then strengthened by heating the glass to a temperature of about 1150°F and then rapidly cooling it with forced air at ambient temperatures (Energetics, 1988). Much of this glass is then laminated for use as automobile windshields and for some architectural applications. The most common method for the formation of glass wool is the rotary process in which molten glass is poured into a round, spinning container with small holes in its sides. The centrifugal force causes the molten glass to flow through the holes in tiny horizontal streams (Tooley, 1992). As these streams exit, they are blown downward with a strong, continuous flow of air causing them to harden. Finally, they are sprayed with a binding agent and fed through a curing oven where they are compressed to the desired thickness (Tooley, 1992). For the production of textile

Ecology of the US glass industry: M Ruth and P Dell'Anno

fibers, molten glass is poured into an electrically heated forming bushing with 200-3000 tiny holes at the bottom depending on the product (Tooley, 1992). As the molten glass passes through the holes, it is cooled to form continuous fibers. The fibers are then chemically coated and made into strands or yarns. Forming accounts for 12-33% of energy used in glass production while post-forming accounts for 1118% of that energy (OTA, 1993). State-of-the-art technology such as computerized inspection could reduce energy use by up to 20% in the forming stage and by up to 28% in the post-forming stage. Use of advanced technologies such as better mold design and improved glass strengthening techniques could save an additional 10 and 14% of the energy used in forming and post-forming, respectively (Energetics, 1990). The production stages of the different glass types are each similar with regard to the general sequencing of the processes, yet different with regard to their material and energy use and emissions profiles, and the rate at which these profiles are likely to change in the future. The similarity of the process sequencing makes it possible to develop industry models that are similar in structure for each of the sectors of the industry. However, the significant differences in the technological parameters that describe the industry, make it necessary to treat these sectors separately and not aggregate them with each other. Their interaction via a shared resource base and exchange of technological knowledge, in turn, make it necessary that the three models of all sectors are run and assessed in interaction with each other. One specific form of interaction among the sectors is present in their use of recycled products, which is discussed in detail in the following section.

5. Cullet use in glass manufacturing Recycled glass, known in the industry as cullet, can be used as a direct substitute for virgin materials in the glass manufacturing process. Using cullet has several important benefits that include lowering the consumption of raw materials, reducing the release of CO2 formed in the chemical reaction of raw materials, increasing the life of the furnace up to 30% due to lower melting temperatures, and reducing energy use during the melting stage of production. A decline in energy use reduces total fuel costs as well as pollution abatement costs due to lower emissions of NOx, SO2 and particulates (Papke, 1993; Glass Packaging Institute, 1996b). The glass industry has always utilized in-house (domestic) cullet in the production process. But since 1970, the use of post consumer cullet has risen steadily. By 1991, cullet accounted on average for about 30%, or 3.0 × 106 tons, of the total inputs for glass container production. About 2.1 × 106 tons was post consumer cullet and the remaining 0.9 x 106 tons consisted of in-house cullet (Gaines and Mintz, 1994).

The actual amount of cullet used in the manufacture of glass varies widely from plant to plant depending on the access to a steady supply which meets each company's quality specifications. Although cullet utilization rates have risen significantly in recent years, a large portion is going unused. As of 1995, only 37.4% of glass containers in the municipal solid waste stream were recycled (Glass Packaging Institute, 1996a). This is relatively low compared to the recycling of other materials in the municipal waste stream. For instance, in the case of plastic bottles, steel cans, and aluminum cans, 41, 48 and 63% are recycled, respectively (Dorgan, 1995). One of the main obstacles to increase the use of cullet lies in the non-homogeneity of waste glass colors and the rising amount of contaminants and impurities which are mixed with recycled glass (Papke, 1993). The three main colors of glass used to produce containers are flint or clear, amber or brown, and green, which account for 64, 23 and 13% of the total production, respectively (Gaines and Mintz, 1994). Flint glass is the most color-sensitive of the three with a tolerance of 1% green or 5% amber cullet in the batch mix. Amber glass can tolerate 10% green cullet, while up to a 50% mixture of amber and flint cullet can be used in the production of green glass (Papke, 1993). In addition to the problem of color mixing, ceramic and metal contamination (especially aluminum bottle caps) has also contributed to the limited use of cullet in glass manufacturing. Although beneficiation and intermediate processing facilities have been built by the industry to deal with these problems, the technologies are costly and operation of these facilities requires a steady supply of culler at stable prices. Problems associated with the supply of post-consumer cullet may be alleviated with the proliferation of municipal recycling programs and container deposit legislation. The industry is currently pursuing solutions to the problems associated with post-consumer cullet. These solutions include mechanical color sorting, glass coatings, and 'ecology glass' which is made with all three colors. The current method of manual color sorting is highly ineffective when dealing with small pieces of glass. This has led to industry supported attempts to design systems which use light beams to determine the color of glass and air jets and paddles to separate those colors (Papke, 1993). An even simpler method to eliminate problems with color contamination is the use of thin plastic coatings. These coatings can be made with a variety of colors and they vaporize during re-melting without affecting the quality of the new glass (Bisio and Boots, 1995). This solution would allow container production with clear glass alone, and would reduce the thickness and weight of glass containers because of the added strength from plastic coatings. Finally, the use of mixed-color cullet to produce a greenish-yellow 'ecology glass' could expand the use of cullet. While this type of glass has had

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Ecology of the US glass indust~: M Ruth and P Dell'Anno some success in other countries, acceptance in the US is expected to be low. In order to realize production cost savings and to respond to legislative pressures, the use of post-consumer cullet has become common in glass fiber production. Most glass wool producers now use varying amounts of post-consumer cullet with an average of about 30% (NAIMA, 1996). Owens-Coming reports that compared to 100% raw materials, the use of 30% cullet reduces silica use by 60%, soda ash use by 40%, and saves 10% in energy costs (Papke, 1993). With results like this, the use of cullet is likely to grow substantially if reliable supplies of container cullet can be established in the future. However, the vast majority of cullet use in fiberglass manufacturing is currently from recycled flat glass, not from container glass because insulation manufacturers have geographically limited access to large container cullet markets (Guter, 1996). The lack of access to a major source of material inputs has become a concern for the industry as the supply of flat glass cullet has become extremely tight (Guter, 1996). High quality requirements of flat glass and textile fiberglass currently preclude the use of post-consumer cullet. Therefore, cullet use in the production of these types of glass is limited to in-house scrap or rejects. While in-house cullet use among flat glass manufacturers is on average approximately 20%, it may range between 10 and 50% depending on the age and efficiency of their furnaces and the level of demand (Benny, 1996). High rates of in-house cullet use are an indication of inefficient production that generates significant quantities of scrap glass or are a result of excess capacity. At times of low demand, plants will opt for the continuation of the production process and subsequently crush and remelt the output rather than shut down furnaces. Consequently, the overall benefits associated with high rates of cullet use in flat and textile fiber glass manufacturing are much smaller than in the container and insulation fiber glass sectors. The significant differences in access to post-consumer cullet, in cullet quality requirements and use of cullet in manufacturing make it necessary to analyze the three glass production sectors separately. A disaggregate treatment becomes all the more important for the purpose of an assessment of future material and energy use and emissions profiles as each of the sectors is characterized by a different rate of change in cullet use and a different technically feasible maximum rate of cullet use.

6. Glass industry model Model structure Each of the three sectors of the glass industry are characterized by distinct technological parameters, rates of change in cullet use and rates of technology adoption. These differences are reflected in the model below to assess over time changes in the energy and material use and CO2 emissions profiles in the con-

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tainer, flat, and fiber glass sectors. The main part of the dynamic computer model consists of modules for each of the three glass sectors of the industry. These modules are outlined in Figures 2-5. Additional modules are set up to trace materials and energy through the industrial ecosystem. Particularly, the model captures the extraction of raw material, transportation, and electricity generation in the rest of the economy. The latter is included in the model to account for CO2 emissions associated with electricity use and assumes a fuel mix that is equal to the US average, and changes in fuel mix as projected by the Department of Energy (Table 1). In the model, the fuel mix after the year 2010 is held constant at the 2010 levels. In order to assess the time profiles of material and energy use and emissions, a number of assumptions are made about changes in production, cullet use rates, and production technologies. The basis for these assumptions are aggregate time series data for each of the three sectors along with engineering studies and information obtained from industry experts, some of which has been presented above. Additional assumptions on the dynamics of the productive systems are the subject of this section. Their implications for the model results are discussed in detail below. Production Future rates of production in the three sectors of the glass industry depend to a significant extent on the industry's ability to successfully compete with other materials. Competition is most notable for containers, where plastic bottles and aluminum cans have made significant inroads into markets traditionally dominated by the glass industry. Competition for fiberglass comes in part from various ceramics, plastic foams, and other composites, while part of flat glass production may be substituted for by corrugated plastic products. In many of these cases, the fragility and weight of glass products are two of the main drivers for product substitution. In order to successfully compete for these markets, the industry has significantly reduced the weight of its products. The trends in replacement of glass from its traditional applications combined with reductions in weight per unit of product is likely to affect the growth rates of the industry's sectors. These effects will be different among the sectors, with containers noticing most of the replacement, and flat glass products the least. Some analysts estimate a 1-2% decline in glass container production for the next 5 yr, but industry sources contend that the demand for glass containers will remain constant during that period (Papke, 1993). Forecasts indicate that demand for glass fibers will increase 2.8%/yr to 6.5 billion pounds by the year 2000 (The Freedonia Group, 1995). The increased demand for wool insulation production will be largely the result of mandatory and consumer incentives for greater thermal efficiency. However, long-term production rates will be highly dependent upon future energy costs as well as competition from foamed plas-

Ecology of the US glass industry': M Ruth and P Dell'Anno

Landfill Process

Q

Flow

Figure 2 Structure of the container glass module tics. Future growth in textile fiberglass is primarily the result of increasing demand for lightweight, strong replacements for metal and wood in a variety of applications. To capture the effects of alternative growth rates for the material and energy use and CO2 emissions profiles of the different sectors of the industry, three scenarios are investigated. The first uses an autoregressive integrated moving average (ARIMA) regression of past production rates and projects those rates into the future. All regression parameters are significant at a 99% confidence interval and have an R2>0.90. Alternatively, an annual rate of increase in production of 1 and 3% is assumed for each of the three industry sectors. The corresponding production quantities and model results are discussed in more detail below. Technological change Two sets of assumptions are used to model technological change in the industry and its effects on energy use and CO2 emissions over time. Two alternative sets of assumptions are made to reflect different rates of adoption of energy saving technologies for each of the four stages of production (batch preparation, melting and refining, forming, and post-forming). Both

scenarios follow estimates provided by Energetics (1990) and are based on surveys of engineering information on production technologies. The first scenario assumes that technologies that are currently considered state-of-the-art will be fully implemented by the year 2010. Most notable among these technologies are a more widespread use of computerized control and inspection at the batch preparation, forming and post-forming stages, and electric and chemical boosting at the melting and refining stages. Alternatively, advanced technologies that may be currently only used in laboratories or pilot plants will have found full adoption by the year 2010. Examples include batch and cullet preheating, thermomechanical recuperation for melting and refining, and excess heat extraction from generators. In order to translate the projections about future technology use into the model, trends in efficiency improvements are interpolated from the engineering specifications under the assumption that efficiency improvements show exponential decline (Table 2). The corresponding rates of energy efficiency changes are run for a 40-yr time frame, starting in 1988. Actual data from 1988 to the present is used to calibrate the model. The fuel mix of the four production stages is shown

115

Ecology of the US glass industry: M Ruth and P DelI'Anno

( ~ I] / ]

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Electricity, ) NaturalGas J

( S o d a ash ~ C o a l , ~ ExtractionJ "

~Batch.~ (-M n drefin~e Form"~Post-" ~ e l t a ~[ [orm

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Figure 3 Structure of the flat glass module in Table 3. All energy is assumed to either be from gas or electricity (Ross, 1993). No changes are expected in the fuel mix, in part because significant changes in fuel use have already taken place in response to the two oil price shock and recent restructuring in the industry, and new technologies will also predominantly rely on the use of electricity and natural gas. Cullet use Currently, only the container and fiber glass insulation sectors utilize post-consumer cullet in their production process. As the benefits associated with increasing cullet use have been studied and quantified, the demand for high quality cullet has grown tremendously in recent years and is expected to continue its rise until upper bounds of technically feasible rates of cullet use are reached. The rates are currently 85 and 50% for the container and fiber glass sectors, respectively. These limits are the result of a wide range of cullet compositions which require specific batch adjustments by each manufacturer. Approach towards these limits are assumed to be at constant rates. The model has been set up to allow the rates

116

of growth in post-consumer cullet use in production of container glass and fiber glass insulation to follow historic average rates, or alternatively, to lie below or above those rates. Energy use for raw material supply and transportation The model captures not only the energy requirements of producing semifinished and finished glass products but also the energy that is needed for the extraction of raw materials. However, both the energy used per ton of extraction and the fuel mix of the extractive sectors are held constant (Table 4). These assumptions were made in lieu of consistent, quality data which is needed to estimate future changes in energy efficiencies of the extractive sectors. For each type of glass, material composition varies widely depending upon the manufacturer and specific application in which the glass is used. In light of these variations, the model uses the typical composition of each type of glass and assumes that they remain constant over time. In addition to quantifying the energy consumed in raw material extraction, cullet processing, and glass

Ecology of the US glass industo,: M Ruth and P Dell'Anno

~ ~

atglasscullet) ~~j°llecti°n and |

Process

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Figure 4 Structure of the fiberglass insulation module manufacturing, the model also accounts for energy used in the transportation of raw materials and cullet. With the exception of sand, it is assumed that all raw materials are transported by diesel-powered freight trains consuming 388Btu/ton-mile (Davis, 1994). Trucks using 1 200 Btu/ton-mile are assume to transport the sand used in glass manufacturing (Gaines and Mintz, 1994). Furthermore, raw material transportation distances were estimated using average distances between the various manufacturing facilities and the major areas of raw material extraction. In the case of cullet use in container manufacturing, the model simulates transportation energy use for the entire recycling loop. This includes the energy used to transport post-consumer glass to either a landfill or a material recovery facility for recycling. Furthermore, energy use is estimated for the transport of scrap glass produced at material recovery facilities to a landfill, to transport cullet to beneficiation facilities for further processing, and finally to transport processed cullet to glass manufacturing plants. For each

stage of the loop, it is assumed that trucks of varying energy efficiencies are used to transport glass different distances between each point. These numbers are based on those reported by Gaines and Mintz who use Chicago and Omaha as examples of typical recycling practices (Gaines and Mintz, 1994). For flat glass cullet used in fiberglass insulation manufacturing, the energy used to transport the cullet from its source to beneficiation facilities and then to fiberglass insulation manufacturing facilities is also quantified.

7. Model results Production

To compare the model results under various assumptions, a base case is defined using the A R I M A forecast of production rates and assuming adoption of state-of-the-art technologies. The base case also assumes annual rates of increase in the proportion of post-consumer cullet use of 8.6 and 1%, respectively,

117

Ecology of the US glass indust~: M Ruth and P Dell 'Anno

_~

Sand Extraction

__(Clay Extraction ___~ Borate Extraction I

(Batch . ~ ( M e l t a n d ~ ( ~ ~ ~ ( - r e f i n e - ~

)

imestone~ Extraction

Form ~ _ ~ ) form ~ ,

~

r

~

_

~

Process

O

Flow

Figure 5 Structure of the textile fibreglass module Table 1

Fuel

mix in US electricity generation Source:Departmentof Energy (1992)

1990 Forecast for 2010

Coal share

Oil share

Natural gas share

Renewablesshare

Nuclearshare

0.52 0.52

0.04 0.04

0.13 0.18

0.12 0.12

0.19 0.14

in the container glass and fiberglass insulation sectors of the industry. The first set of model runs (Figures 6-9) capture the impacts of a 1 and 3% annual increase in each of the four types of glass compared to the ARIMA forecast. For container glass production (Figure 6), the results show that in the base case, improvements in energy and material use efficiency and increasing post-consumer cullet use offset the effects that increasing production has on total energy consumption. Total energy use continually declines from 1995 to 2028. If production increases at an annual rate of 1%, efficiency improvements and increasing postconsumer cullet purchases lead to a slow rate of decline in total energy use until the year 2012. By the year 2012, the proportion of post-consumer cullet use 118

reaches its maximum of 85%, and the total energy use begins to steadily rise thereafter. If production increases at an annual rate of 3%, the energy savings from increasing production efficiency and rising proportions of cullet use cannot keep pace with the demand in energy. As a result, total energy use increases at an increasing rate (Figure 6). In the base case, declines in total energy consumption of flat glass production parallel the efficiency improvements in energy and material use that occur at a decreasing rate (Figure 7). If production increases at a rate of 1% annually, energy use declines until the year 2024 and then levels out as room for further significant efficiency improvements is exhausted and production levels stabilized. In the case of a 3% annual production increase total energy consumption

Ecology of the US glass industr3,: M Ruth and P Dell'Anno Table 2

Energy use by glass production technologies Ton of product/ton finished glass (1985)

Process

Source: Energetics (1990)

Process mix ave annual % change a

Million Btu/ton of Energy use, ave annual percentage change" product (1985)

State-of-the art (2010)

Advanced (2010)

0.27 8.10

0.47 1.85

NA 3.97

0.20 NA

1.45 2.20

0.44 1.30

0.86 1.92

NA NA

0.25 0.23

0.53 6.34

0.40 1.10

NA 2.99

1.20 1.13

NA NA

0.24 NA

4.01 1.84

0.90 1.09

1.32 1.30

1.30 1.24

NA NA

NA NA

1.15 9.89

0.40 0.35

NA 4.31

1.11 1.00

NA NA

NA NA

7.24 2.74

0.75 0.63

1.17 0.84

State-of-the art (2010)

Advanced (2010)

1.32 1.26

NA NA

0.19 0.20

1.26 1.20

NA NA

1.32 1.26

Flat glass Batch preparation Melting and refining Forming Post-forming Container glass Batch preparation Melting and refining Forming Post-forming Fibrous glass Batch preparation Melting and refining Forming Post-forming

~Assumes exponential decline in efficiency improvements. NA indicates no change from current to state-of-the-art or advanced technologies.

Table 3

Electricity

Batch preparation Container glass Flat glass Fiberglass ins. Text. fiberglass Melt and refine Container glass Flat glass Fiberglass ins. Text. fiberglass Forming Container glass Flat glass Fiberglass ins. Text. fiberglass Postforming Container glass Flat glass Fiberglass ins. Text. fiberglass

Table 4

c o n t i n u e s to i n c r e a s e at a n i n c r e a s i n g rate. T h e r e l a t i v e l y f a s t a n n u a l r i s e in p r o d u c t i o n o f 3 % o f f s e t s a n y efficiency improvements. T o t a l e n e r g y u s e in f i b e r g l a s s i n s u l a t i o n m a n u f a c t u r i n g (Figure 8) i n c r e a s e s s l i g h t l y f o r t h e first 18 y e a r s a n d s u b s e q u e n t l y d r o p s s l i g h t l y b e l o w its starti n g v a l u e in t h e b a s e s c e n a r i o . T h i s p a t h is d u e to an ARIMA production forecast which increases slowly in t h e first h a l f o f t h e run a n d l e v e l s o f f in t h e s e c o n d half c o m b i n e d with a slowly increasing rate o f cullet use. A 1 a n d 3 % i n c r e a s e in p r o d u c t i o n , r e s p e c t i v e l y , o f f s e t a n d o v e r w h e l m i n c r e a s e s in c u l l e t use, l e a d i n g to s t e a d i l y r i s i n g a n n u a l total e n e r g y use. F i n a l l y , in t h e c a s e o f t e x t i l e f i b e r g l a s s p r o d u c t i o n , all t h r e e s c e n a r i o s r e s u l t in i n c r e a s i n g a n n u a l total e n e r g y u s e (Figure 9). In t h e b a s e c a s e , total e n e r g y u s e r i s e s at a m o d e r a t e , s t e a d y r a t e t h r o u g h o u t t h e run. U n t i l t h e late 1990s, e n e r g y c o n s u m p t i o n is h i g h e s t in this s c e n a r i o b u t u l t i m a t e l y l e v e l s o u t to lie b e t w e e n t h o s e e n e r g y u s e t r e n d s f o r a 1 a n d 3 % a n n u a l rate of production increase.

Fuel mix in glass manufacturing (%) Natural gas

100 100 100 100

-----

--100 --

100 100

100 100 100 100

-----

-10 ---

100 90 100 100

100

Fuel mix in raw material extraction (%)

Material extraction

Electricity

Natural gas

Oil

Coal

Gasoline

Sand Soda ash Limestone Feldspar Borate Clay

33 -29 7 8 7

46 40 7 28 40 28

14 -51 14 3 14

7 60 6 51 49 51

--7 ----

119

Ecology of the US glass industry." M Ruth and P Dell'Anno 4.0(0+8

7.00e+7 6.00e+7

3.00e+8

3% a

5.00e+7

n

n

u

a

~

4.00e+7 -

2.00e+8

annual i n c . , ~ . _ . . . . . _ ~ 3.00e+7' 1.00e+8 1985

.

.

.

.

I

.

.

.

.

I

1995

.

.

.

.

I

2005 year

.

.

.

.

2015

I

•

2.00e+7 .... 1985

•

2025

Figure 6 Total energy use in glass container manufacturing for alternative production rate tbrecasts

J .... 1995

~ .... 2005 year

~ .... 2015

~ • • 2025

Figure 9 Total energy use in textile fiberglass manufacturing for alternative production rate forecasts 1.80e+8

1.40e+8 1.20e+8 ~

1.00e+8 8.00e+7

3% a ~

1

n

n

%

u

a

~

2

1.60e+8

~

1.40e+8

~

t he-art

annual inc. 1.20e+8 '

advanced -

-

-

-

-

~

~

6.00e+7 base case ~ 4.00e+7

.... 1985

J .... 1995

~ .... 2005 year

i .... 2015

~ • • 2025

Figure 7 Total energy use in flat glass manufacturing for alternative production rate forecasts

1.00e+8 .... 1985

~ .... 1995

~ .... 2005 year

~ .... 2015

~ , • 2025

Figure 10 Total energy use in container glass manufacturing - - state-of-the-art vs advanced technology scenarios 8.00e+7'

1.60e+8 7.00e+7' 1.40e+8 6.00e+7 1.20e+8 5.00e+7

1.00e+8 !

advanced

4,00e+7 ~

J

1% annual inc.,

base case

3,00e+7 2.00e+7 1985

.

4.00e+7 .... 1985

~ .... 1995

~ .... 2005 year

~ .... 2015

0 , • 2025

Figure 8 Total energy use in fiberglass insulation manufacturing for alternative production rate forecasts

Technology change The w i d e range in the type and size o f the e q u i p m e n t used in the p r o d u c t i o n o f various glasses results in differences in the potential for efficiency i m p r o v e ments. The s e c o n d set o f m o d e l scenarios (Figures 10-13) assess the i m p a c t o f the use o f a d v a n c e d techn o l o g i e s b y 2010 as c o m p a r e d to the base case which is b a s e d on a d o p t i o n o f state-of-the-art technologies. F o r each type o f glass, various rates o f decline in

120

~

8.00e+7

.

.

.

i

1995

.

.

.

.

I

.

.

.

2005 year

.

I

.

2015

.

.

.

i

,

•

2025

Figure 11

Total energy use in flat glass manufacturing - state-of-the-art vs advanced technology

energy and material use are a s s u m e d in each o f the four m a j o r stages o f production (Table 2). The techn o l o g y scenarios are run using the A R I M A forecasts o f p r o d u c t i o n rates. In the container glass sector, the use o f a d v a n c e d t e c h n o l o g y causes the total energy use to drop from 120.3 to 107.1 trillion Btu in the final y e a r (Figure 10). This represents a savings o f about I 1%. In the case o f flat glass, a savings o f about 31% results as e n e r g y use drops 42.7 trillion Btu to 29.6 trillion Btu

Ecology of the US glass industry: M Ruth and P Dell'Anno 5.5e+7

1.0"

~e_o

0.8

f_the_art ~'~""...-,.,~.~

10% annual i n c . ~ / ~ e

///

4.5e+7 0.6

m~

c ~ ~e

0.4

~

'

~

'

-

"

5% annual inc

3.5e+7 ca,

2.5e+7 .... 1985

, .... 1995

, .... 2005 year

i .... 2015

J , • 2025

Figure 12 Total energy use in fiberglass insulation manufacturing - - state-of-the-art vs advanced technology

0.2 0.0 .... 1985

, .... 1995

, .... 2005 year

, .... 2015

, • • 2025

Figure 14

Proportion cullet used in glass container manufacturing under various growth rates

5.00e+7 0.55 0.50

=

4.00e+7

s

t

a

t

e

~

5% annual inc.

0.45 "

//

0.40 3.00e+7

j

i

advanced ~

.//

/ / 4 [ - -

3% annual inc.

0.30 1 2.00e+7 .... 1985

, .... 1995

, .... 2005 year

, .... 2015

, • • 2025

Figure 13 Total energy use in textile fiberglass manufacturing - - state-of-the-art vs advanced technology

if advanced technology is employed (Figure 11). For fiberglass insulation, the advanced technology scenario causes total energy use to drop substantially from 46 to 26.3 trillion Btu, a savings of 42.8% (Figure 12). Similar savings of 45.6% are observed in textile fiberglass production where total energy use declines from 48.2 to 26.2 trillion Btu (Figure 13). Although the composition of textile fiberglass is different than that of fiberglass insulation and no post-consumer cullet is used, technological change is assumed to occur at the same rate.

Expansion in cullet use The last set of model scenarios (Figures 14-17) depict the effects that different rates of growth in cullet use in the container glass and fiberglass insulation sectors have for the industry's material and energy use profiles. The first scenario for container glass manufacturing assumes an increase in cullet use of 8.6%, which is equal to the average actual increase observed between 1988 and 1995. Alternatively, rates of 5 and 10% are assumed. For fiberglass production, three scenarios are run for increases in cullet use of 1, 3 and 5%, respectively. For all of these scenarios that investigate the impacts of various levels of cullet use it becomes clear that since already major achieve-

0.25/ .... 1985

, .... 1995

, .... 2005 year

, .... 2015

, • • 2025

Figure 15 Proportion cullet used in fiberglass insulation manufacturing under various growth rates

1.80e+8 1.70e+8 1.60e+8 ~

~

¢

5% annual inc.

1.50e+8 1.40e+8 1.30e+8 1.20e+8 1985

1995

2005

2015

2025

year

Figure 16 Total energy used for container glass manufacturing using various rates of growth in the proportion of cullet used

ments have been made in parts of the industry, increases in cullet use are likely to ' b u y ' the industry roughly a decade in its efforts to improve energy consumption. Once the maximum rate of cullet use is reached, further energy efficiency improvements become primarily dependent on the rate at which new technologies are adopted.

121

Ecology of the US glass indust~: M Ruth and P Dell'Anno 5.5e+7

2e+8 1% annual inc.

2

a~

4.5e+7

\ 5% annual" "

\ ~

. ~

electricity

le+8

3% annual inc.

"~ jcoal

3.5e+7 .... 1985

~ .... 1995

~ .... 2005 year

~ .... 2015

9.00e+6

7.0(0+6

~

6.00e+6 '

0e+0 1985

1995

2005 year

2015

2025

Figure 20 Total energy use glass production (base case)

Transportation energy use in the flat and fiberglass insulation sectors levels out in the long run. This is due to stabilizing production rates in the case of flat glass. In the case of insulation, it is due to low and declining importance of shipments of post-consumer cullet combined with a constant rate of production. Only the textile fiberglass sector shows a continued rise in transportation energy use as production continues to increase throughout the model run.

8.00e+6

~,

V

~ • • 2025

Figure 17 Total energy used for fiberglass insulation manufacturing using various rates of growth in the proportion cullet used

¢oil

5.00e+6 '

4.00e+6 .... 1985

i .... 1995

i .... 2005 year

i .... 2015

~ • • 2025

Figure 18 Total transportation energy for container glass production (base case)

Transportation Figures 18 and 19 show the energy use for transporting raw materials and cullet to the production facilities and for disposing discarded glass products to landfills. Each of these results are for the base case scenario. The model indicates a sharp increase in transportation energy use for container glass production as cullet use increases. Once the maximum rate of cullet use is reached in the container glass sector, transportation energy use levels out.

Energy use and CO: emissions profiles The dynamics of each of the sectors of the glass industry lead to the industry aggregate energy and emissions profiles shown in Figures 20 and 21. Each of these profiles are shown for the base case and include energy use emissions in extraction, manufacturing and transportation. Figure 20 depicts energy use for extraction of raw materials and generation of finished products by fuel type. Natural gas is the dominant fuel type until 2009 from when on electricity supplies most of the energy. Oil (including distillates) and coal are only of minor importance and are not likely to significantly change their share in the aggregate fuel mix of the industry aggregate.

1000000

1.6' fiberglass insulation

800000 ~"-~n~, '~

1.4

a~

t,.9

1.2"

O ~9

1.0"

fiberglass/"

600000 '

400000 '

fiberglass insulation ~

textile ~

0.8" 200000 . 1985

~ 1995

. . . . . . . . . . 2015 2025

2005

0.6 .... 1985

year

Figure 19

122

Total transportation energy (base case)

Figure 21

CO

2

~ .... 1995

~ .... 2005 year

~ .... 2015

emissions/ton of glass product

~'' 2025

Ecology of the US glass industry: M Ruth and P Dell'Anno C O 2 emissions are shown in Figures 21 and 22 per ton of glass product and for the glass industry as whole. These figures include emissions from electricity generation, in addition to the emissions from resource extraction, manufacturing and transportation. Emissions decline on a per ton of product basis for all of the glass types of the model (Figure 21). While the share of CO2 from coal temporarily increases, CO2 emissions from natural gas combustion and raw material melting significantly decline (Figure 22). The declines in CO2 emissions from raw material melting are to a large degree due to increased cullet use, and thus come to a slow-down as the container and insulation fiberglass sectors reach their maximum cullet use rates. CO2 emissions from burning oil and distillates play only a minor role in the overall profile.

8. C o n c l u s i o n s The model of the US glass industry is based on a dynamic systems perspective within which changes in container, fiat and fiberglass can be investigated with regard to material and energy use, and CO2 emissions. Towards that end, the model includes the extraction stage of the main raw materials, transportation of raw materials and discarded products - - both back to producers and to landfills - - and the various manufacturing processes of the desired products. Wherever supported by reliable data, the model incorporates rates of change in the material and energy use efficiencies of the various stages of the production process and portrays the likely consequences of these changes with respect to material, energy and CO2 emissions profiles. In short, the model provides a dynamic representation of the industrial ecology of US glass manufacturing. Only a small set of scenario results are presented above. Perhaps the most striking result is the limited extent to which cullet use reduces long-run energy consumption profiles, even under moderate production growth rates. Consequently, in order for the industry to become increasingly sustainable, promotion of recycling is only part of a strategy that must 18 16"

Total, ~ [ ~

14 " 12

g

10' 8

~--~__~_~Nat.

Gas

6' Coal '/~

4'

Raw material j ~ melting

2' 0

.

1985

.

.

.

!

1995

.

.

.

.

I

.

.

.

.

2005

|

.

2015

.

.

.

I

•

•

2025

year

Figure 22 CO2 emissions in glass production by source (base case)

in the long run involve aggressive development and implementation of highly energy efficient technologies. Given the speed at which technologies have found adoption in the industry over the last twenty years and given model results that indicate that aggressive recycling can lead to noticeable declines in energy consumption over only approximately one decade, it seems imperative that significant investments are considered well before maximum rates of cullet use are reached. The limited ability to decrease the industry's energy use and CO2 emissions per ton of product through increased cullet use has important implications for management and industrial policy that attempts to promote sustainable material and energy use. First, an increase in electricity use in the industry will bring with it increased emissions from the combustion of coal, not just of CO2 but also of SOx and NOx. Thus, to reduce total emissions associated with glass production requires that increasing attention is given to those pollutants. Second, light-weighting of container glass products by using plastic films will improve their recyclability because the need to differentiate glass products by color can in principle be eliminated. However, lightweighting will improve in essence the reuse of abundant materials such as sand at the expense of petrochemical products that are used to make the films and are burned in the process of recycling. Whether the net effect of light-weighting is an increase or decrease in petroleum depletion depends on the energy savings in transportation of raw materials and cullet to the manufacturing site. Third, high mandated recycling rates and post-consumer content of finished products will increase the contribution of the transportation sector to the emissions associated with making glass products available to society. Since much of the transportation takes place by truck mobile source emissions are likely to increase. Fourth, the use of cullet is in part limited by the access to post-consumer scrap. These limitations are particularly apparent in the fiberglass sector of the industry. Improving access to cullet may be achieved by facilitating the establishment of firms close to the cullet source. This would both further close material cycles and reduce the need for long-distance transport. Fifth, mandated recycling rates and post-consumer content of glass products has been a major driver for change in the industry. These mandates have, so far, had significant environmental and cost saving effects on the industry. As maximum feasible cullet use rates are approached, the marginal cost of cullet use is likely to increase and marginal environmental benefits may disappear. It is therefore imperative to begin to consider additional instruments that guide industry towards sustainable practices as maximum cullet use rates are approached. These policy instruments should

123

Ecology o f the US glass industo,: M Ruth and P Dell'Anno

be chosen with an eye towards the energy efficiencies of US glass manufacturing. Acknowledgements This paper has been made possible in part by the support from Roy F Weston, Inc. (WESTON), West Chester, PA, USA. Valuable input was provided by Linda Gaines and Marianne Mintz (Argonne National Lab), Ernie Guter (Owens-Coming), and Robert Drake (Glass Technical Institute). References Allenby, B R and Richards, D J (eds) (1994) The Greening ~f Industrial Systems. National Academy Press, Washington, DC. Ayres, R U and Simonis, U E (eds) (1994) Industrial Metabolism: Restructuring for Sustainable Development. United Nations University Press, Tokyo. Bauer, W C and Bailey, J E (1992) Engineered Materials Handbook: Vol. 4 Ceramics and Glasses. Raw Materials/Batching. ASM International. Materials Park, OH. Benny, J (1996) personnal communication. Glass Association of North America, August. Bisio, A and Boots, S (1995) Encyclopedia of Energy Technology and the Environment, Vol 4. Wiley Interscience, New York. Bureau of the Census, various years. Current Industrial Reports. Government Printing Office, Washington, DC. Davis, J R (1992) Engineered Materials Handbook: Vol 4 Ceramics and Glasses. Testing, Characterization, and NDE. ASM International. Department of Energy (1992) Annual Energy Outlook. Government Printing Office, Washington, DC. Dorgan, S (1995)Statistical Record of the Environment, 3rd edn. Gale Research Inc., New York. Energetics (1988) The US Glass Industrv: An Energy Per~speetive, prepared for the US Department of Energy, Office of Industrial Programs. Report No DOE/RL/0(1830)-T60. Energetics (1990)lndustr'; Profiles: Glass, prepared for the US Department of Energy. Office of Industrial Technologies, Report No DOE/RL/0(1830)-T60. Frosch, R A (1994) Industrial ecology: minimizing the impact of industrial waste. Physics Today, Nov, pp 63-68. Gaines L L and Mintz, M M (1994) Energy Implications of Glass

124

Container Recycling. Report ANL/ESD-18. Argonne National Laboratory, Argonne IL. Glass Packaging Institute (1996b) Glass Container Recycling Stays at Record High in 1995. Glass Packaging Institute, Washington, DC. Glass Packaging Institute (1996a) Solid Waste and Recycling Policy. Glass Packaging Institute, Washington, DC. Glass: A Clear Vision for a Bright Future (1996) Prepared by representatives of the glass industry. Idaho National Energy Laboratory, Idaho. Graedel, T E and Allenby, B R (1995) Industrial Ecology. Prentice Hall, Englewood Cliffs, NJ. Guter, E (1996) Personnal communication. Owens Coming Inc., September. Harmon, B and Ruth, M (1994) Dynamic Modeling. Springer-Verlag, New York. Jelinski, L W, Graedel, T E, Laudise, R A, McCall, D W and Patel, C K N (1992) Industrial ecology: concepts and approaches. Proceedings of the National Academy of Sciences 89, 793-797. NAIMA (1996) Fiberglass Insulation - - Using Recycled Materials Helps Maintain Environmental Balance. North American Insulation Manufacturers Association, Alexandria, VA. OTA (1993) Industrial Energy Efficieny. Office of Technology Assessment. Government Printing Office, Washington, DC. Papke, C (1993) Glass Recycling and Reuse From Municipal Wastes. Recycling Sourcebook, Gale Research Inc., New York. Ross, P (1993) An Overview of the Glass Industry' and its Natural Gas Use. Presented at the Annual Meeting of the Industrial Gas Technology Commercialization Center. Ruth, M (1993) Integrating Economics, Ecology attd Thermodynamics. Kluwer Academic, Dortrecht, The Netherlands. Ruth, M and Hannon, B (1997) Modeling Dynamic Economic Systems. Springer-Verlag, New York. Socolow, R, Andrews, C, Berkhout, F and Thomas, V (eds) Industrial Ecology and Global Change. Cambridge University Press. Stevens, H J (1992) Engineered Materials Handbook: Vol. 4 Ceramics and Glasses. Forming. ASM International. Materials Park, OH. The Freedonia Group, Inc (1995) Glass Fibers in North America. Cleveland, OH. Tooley, F V (1992) Engineered Materials Handbook: Vol 4 Ceramics and Glasses. Fiberglass. ASM International, Materials Park, OH. Warnick, I K and Ausubel, J H (1995) National material metrics for industrial ecology. Resources Policy 21, 189-198. Wooley, E (1992) Engineered Materials Handbook: Vol. 4 Ceramics and Glasses. Melting~Fining. ASM International, Materials Park, OH.