48. Glass

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Contents

1. Scope

2. Environmental impacts and protective measures

2.1 Air

2.1.1 Waste gases/Flue gases
2.1.2 Dust

2.2 Noise
2.3 Water
2.4 Soils
2.5 Workplace
2.6 Ecosystems

3. Notes on the analysis and evaluation of environmental impacts

3.1 Inspection and maintenance of environmental protection installations

4. Interaction with other sectors

5. Summary assessment of environmental relevance

6. References

1. Scope

The main raw materials used by the glass industry are sand, lime, dolomite, feldspar, as well as soda, borosilicates and numerous additives which embrace practically the entire periodic system of elements. Its products are a large number of glasses with different properties, many of them further processed after manufacture (Table 1).

Table 1 - Glass products

In the modern glass industry the raw materials are no longer generally extracted by the companies themselves but are purchased in the desired chemical and physical composition, e.g. in terms of granulation, moisture content, impurity (for the environmental relevance of the extraction of raw materials refer to the environmental brief Surface Mining). The substantial differences between the materials to be dosed and mixed necessitate the use of mixing and processing plants where the mixtures are melted in tank furnaces, more rarely in pot furnaces, or special furnaces. Cupola furnaces are still sometimes used for mineral fibres, and electric melting systems are used for manufacturing ceramic fibres. The flue gases formed during melting are nowadays cooled by regenerative or recuperative plants, thereby reducing the specific fuel consumption.

After melting, the glasses are moulded. Most glasses must then be cooled according to the subsequent application, to avoid glass stresses. Glasses are frequently further processed by thermal, chemical and physical post-treatments, such as clamping, pouring, bending, gluing, welding and grinding. Hollow glassware is frequently decorated. Fibres are drawn, centrifuged, blown or extruded after melting, using a variety of technologies.

The capacities of the individual glass-producing companies vary considerably, and it is often the case that several melting systems with different production programmes are combined in one works. Pot furnaces have a capacity of 3-8 t/day, whilst the tank capacities for special glasses range from 8 to 15 t/day in most cases. In specialist fields, however, the outputs are much higher, e.g. tanks for container glass melt between 180 and 400 t/day, float glass tanks attain melting capacities of between 600 and 1000 t/day.

The melting temperatures of the glass generally range between 1200 and 1500°C, the temperature depending for the most part on the mixture and the product to be manufactured. The amount of energy required to melt 1 kg of glass is between 3700 and 6000 kJ. The capacities and energy consumptions indicated above are average values which depend on the design and operating time of the tank, the production programme and the actual tank load. The specific energy consumption should be reduced by the use of waste fragments wherever possible.

2. Environmental impacts and protective measures

2.1 Air

2.2.1 Waste gases/flue gases

In a glass works waste gases are formed during melting of the glass as a result of combustion of the fuels used. In addition to the combustion residues, such as sulphur dioxide (SO₂) and nitrous oxides (NO_x), flue gases also contain compound components such as alkalis (Na, K), chlorides (-Cl), fluorides (-F) and sulphates (-SO₄).

Sulphur dioxide (SO₂)

Sulphur dioxide or SO_x emissions, made up of SO₂ + SO₃, lie within the range of 1100 to 3500 mg/Nm³ of waste gas in the case of regeneratively heated glass tanks within one firing period. Where the chambers are insufficiently scrubbed much higher peak values, as high as 5800 mg/Nm³ of waste gas, are found at the start of the firing change.

Electrically heated or electrically booster-heated tanks can be operated continuously at a lower SO_x load (< 500 mg/Nm³). On the other hand, the use of heavy oil with a very high sulphur content (up to 3.7%) gives rise to extremely high emission values. Natural gas, which does not normally contain any sulphur, does not affect the formation of SO_x. Some of the sulphur emission is also caused by the addition of sulphate to the mixture.

The currently applicable Technical Instructions on Air Quality Control (TA-Luft 1986) indicates a maximum value for sulphur dioxide of 1800 mg/Nm³ of waste gas, thus in normal glass tanks absorption of the excess sulphur dioxide is required. The sulphur dioxide content can be reduced by feeding magnesium, calcium carbonate and soda into the flue gas. The dusts forming during this process must also be filtered out again.

  Nitrous oxides (NO_x)

A further environmental problem in glass manufacture is posed by the NO_x loads occurring, which can range from 400 to 4000 mg/Nm³ of waste gas. During nitrate refining, i.e. the reduction of the proportion of bubbles or nodules in the glass mass by nitrates, these values are considerably increased. The Nox content depends on the air preheating temperature, the air coefficient (excess air) and the process and type of tank used. NO_x content can be reduced using catalysts with ammonia (NH₄). This process, which is currently undergoing large-scale trials, promises to reduce NO_x content to below 500 mg/Nm³ NO_x load.

The NO_x limits applicable in Germany (1991) for the different tanks are summarised in Table 2.

Table 2 - Nitrous oxide emissions under applicable version of TA-Luft
[Technical Instructions on Air Quality Control]

The emission values of nitrate-refined tanks must not exceed twice the above-mentioned values.

  Fluorine/chlorine

The fluorine contents of the waste gas (calculated as HF) must not exceed certain values since plants and animals can be harmed by fluorine. Fluorides are contained in almost all raw materials used in glass manufacture. Through the addition of waste fragments originally melted with fluorspar to the melting process, the fluorine concentration in the waste gas may exceed 30 mg/Nm³.

The low fluorine limit value prescribed in Germany under TA-Luft 1986 of < 5 mg/Nm³ can only be achieved through systematic selection of raw materials or through additive reactions with calcium and alkali compounds.

Chlorine compounds, which are introduced into the mixture primarily through soda or salt-contaminated raw materials, also cause problems. Measurements have indicated gaseous chloride concentrations of between 40 and 120 mg/Nm³ of waste gas. Problems with gaseous chlorine emissions (HCl) arise mainly in heavy-oil-fired plants. Like sulphur dioxide, chlorides must also be absorbed by calcium or sodium compounds in the mixture.

2.1.2 Dust

One problem area in the glass industry is the dust emission of the glass melting furnaces caused by the high temperatures, and the evaporation of mixture components which sublimate as fine dusts. The dust concentration of different melting tanks without filters is indicated in Table 3.

Table 3 - Dust concentration in the waste gas of glass tanks - Measured values -

1) Waste gas in the normal condition, 8% oxygen in the waste gas

The values indicated in the table show that glass furnaces without filter systems have high dust concentrations in the waste gas. The prescribed limits of 50 mg/Nm³ of dust in Germany (TA-Luft 1986) are difficult to achieve without dedusting plants. Electrostatic dust precipitation, fabric dust filters with sorption or wet scrubbing may be used, depending on the type and capacity of the furnace. However, the dedusting systems must also help to reduce fluoride, sulphate and chloride emissions, as well as toxic heavy metals.

Emissions of lead, cadmium, selenium, arsenic, antimony, vanadium and nickel are particularly critical. These environmentally harmful dusts, which are formed primarily during the manufacture of special glasses in the waste gas, can only be separated by dust filters.

2.2 Noise

The noise generated is particularly significant in the glass industry during melting, moulding and cooling and in the chambers of the compressors, whilst hardly any problematic noise loads are generated in the areas of extraction, processing, packing and finishing.

In the furnaces noise levels of up to 110 dB(A) may be reached during melting and in the feeder. The large fans which produce the quantities of air required and the compressors also generate relatively high levels of noise. However, few workplaces are situated in the vicinity of these noise sources. In modern works these workplaces are provided with static noise protection devices. The control systems of the plants can be soundproofed or can be installed outside the noise zone. Hearing protection must be worn for short-term working in these zones.

An extremely critical area in terms of noise emission, which is also affected by high temperatures and oil vapours, is the container glass moulding area with compressed-air-controlled machines; here the noise load generally exceeds 90 dB(A). In recent years improvements have been made with modified air guides. So far, attempts to enclose the machines for soundproofing purposes have been unsuccessful because of the need for regular oil lubrication of the units and cleaning of the moulds. When the glasses are cooled, noise is generated by fans but can be reduced by suitable designs and enclosures.

To avoid noise nuisance, glass works must be erected at least 500 m away from areas of habitation. The distance from residential areas should be such that no more than 50 to 60 dB(A) is immitted during the day, and no more than 35 - 45 dB(A) during the night.

2.3 Water

The total water consumption per tonne of glass produced varies considerably. Circulating systems should be installed so that only small quantities of additional fresh water are required. The main water-consuming areas of a glass works are:

- cooling of the compressors required for generating compressed air
- cooling of the diesel units sometimes used for power generation
- quenching basins for excess glass
- finishing and refining of glass by grinding, drilling etc.

The wastewater produced in these sectors is cooled and reused, but part is also tapped for other functions, such as:

- moistening the mixture for dust prevention
- cooling of flue gases, particularly in EGR dedusting plants
- moistening of lime products for dry sorption filter plants.

The average water consumption in a glass works should be less than 1 m³/t of glass produced. The cooling water of the cutting devices and moulding machines, the compressors, any emergency power diesel generators used and also the water from the quenching basins underneath the production machines may be contaminated by oil. This effluent must be cleaned by oil separators. In Germany, if water is discharged it must meet the minimum requirements regarding discharge of effluent into watercourses (direct dischargers). By virtue of these regulations no more than 0.5 mg/Nm³ of depositable substances may reach the effluent in glass production.

Special disposal arrangements are required for the sewage produced (see the environmental brief Wastewater Disposal).

2.4 Soils

In the area surrounding modern glass works which meet the existing environmental regulations regarding waste gas and dust, are equipped with the necessary cleaning systems and have a suitable internal wastewater circuit and water separator, there is unlikely to be any contamination of the soil or consequent damage to plants or animals.

2.5 Workplace

Employees of glass works may be endangered or oppressed particularly by noise and in certain workplaces by heat. Hardly any dust problems arise in well-maintained glass works, but in special cases, e.g. in the manufacture of special glasses, toxic dusts may pose a health hazard.

In principle no workplace within a plant should be exposed to a continuous noise level in excess of 85 dB(A); at this level hearing protection should be provided, and from 90 dB(A) protection must be worn in all cases. Hearing protection is compulsory in noise-intensive process areas, even when employees remain there only for a short time.

So far it has not been possible, for technical reasons, to enclose glass moulding machines, particularly the noisy container glass machines, or to automate them completely, so that employees must wear hearing protection in these areas. Noise from burner systems, fans and compressors can easily be avoided; firstly there are hardly any workplaces in the vicinity of these machines, and secondly the control units of the machines can be screened against dust, heat and noise. When carrying out maintenance and repair work, employees must wear the prescribed hearing protection and, if necessary, protective clothing.

In the event of stoppage or unexpected breakdown of tanks or faults in the preheating system very high temperatures may occur, since some tanks are operated at temperatures in excess of 1500°C. Work in such emergency situations must be carried out under supervision, and protective devices to facilitate the work, such as thermal protective suits, must be available in all works in case of emergency. Contingency plans must be drawn up and regular drills carried out to ensure rapid, targeted intervention in emergency situations.

According to recent studies, glass and mineral fibres are suspected of having carcinogenic effects. Regular medical examinations should therefore be carried out in glass works to identify any problems arising at an early stage and forestall adverse consequences.

2.6 Ecosystems

Glass works process 70 - 80% natural raw materials (sand, feldspar, dolomite, lime), but these are not generally extracted in the vicinity of the works. About 75% of the natural raw material is quartz sand which nowadays is rarely extracted by the glass works themselves. The soda required is manufactured in Germany synthetically from salt (NaCl) and carbon dioxide, the latter being extracted from limestone. Soda may also be extracted from natural deposits occurring mainly in the USA. Certain of the other raw materials are synthetic or cleaned raw materials such as sodium and boron compounds.

Approximately 1.2 - 1.3 tonnes of raw materials are required to melt one tonne of glass, but the area required for extracting the glass raw materials cannot be determined accurately because the deposits in question are not used exclusively for the glass industry and the extraction levels vary considerably.

If a works carries out its own extraction, the environmental protection aspects must be considered as early as the extraction planning phase, particularly as regards water management and the constant need for recultivation. The extraction and recultivation costs must be added to the raw material costs (see the environmental brief Surface Mining).

When selecting the site of a glass production centre, the environmental factors must also be taken into account. In the case of sites in areas which have so far been used for agricultural purposes alternative sources of income must be examined, particularly for affected women. Besides complying with the applicable regulations regarding waste gas, dust, noise and water, the subsoil conditions, landscaping and infrastructure must also be examined. The infrastructure includes, among other things, recruitment and housing of employees, traffic and transport systems and the existing and planned industrialisation of the area.

Since the environmental impacts are not limited to the works area, the population groups concerned, particularly women and children, should be provided with access to medical care.

The addition of a recycling system for waste glass may on the one hand reduce the energy requirement for glass manufacture and on the other hand substantially relieve pressure on refuse tips. In a similar vein, disposable packaging systems should be replaced by reusable packaging systems.

3. Notes on the analysis and evaluation of environmental impacts

The limits - based on TA-Luft (Technical Instructions on Air Quality Control) and TA-Lärm (Technical Instructions on Noise Abatement) and other regulations - summarised in Table 4 for waste gas, dust and noise are now applicable in Germany and are being adopted in similar form by most European countries. The minimum requirements in Germany regarding treated wastewater discharged into receiving bodies of water are also indicated.

Table 4 - Limitation of hazardous substances under TA-Luft (Technical Instructions on Air Quality Control) and the 17th Administrative Regulation (VwV) according to § 7a of the Federal Water Act (WHG)

Glass works, which are generally large-scale plants, produce considerable emissions. In principle a maximum of 1800 mg SO₂Nm³ should be established as the mean guideline value for avoiding serious environmental pollution. The NOx emissions must not exceed the currently applicable values, and nitrate refining should be dispensed with because of the high NO_x levels generated.

No separate wet or dry sorption plants are required to comply with these relatively high mean values. Accurate control of the tank heating is vital in order to attain the required values.

Fluorine and chlorine emissions which may give rise to direct damage must be kept as low as possible. The values indicated above can be achieved by suitable selection of raw materials and fuels and systematic monitoring of burner operation. A further benefit is that energy consumption can be further reduced by conforming to these guideline values, resulting in greater economy.

The dust emission from glass furnaces should not exceed 50 mg/Nm³. A dedusting plant should always be installed in order to comply with this limit.

It is vital to adhere to the emission limits for toxic dusts (heavy metals) such as cadmium, lead, fluorine, selenium and arsenic; the maximum values specified in TA-Luft must not be exceeded.

For individual substances, the Compendium of Environmental Standards contains notes on evaluating environmental relevance.

It is absolutely essential to comply with the regulations on permissible noise levels, since failure to prevent or protect against noise can result in permanent injury of employees.

To avoid environmental pollution, the limits laid down for direct water dischargers must be observed, particularly regarding heavy metal concentrations in the effluent.

If no national regulations exist, values in line with German or European standards should be established for the erection of new glass works, particularly in areas already suffering from serious environmental pollution. Special regulations must be introduced for plants already in operation. The parameters defined for the principal hazardous substances must in future be regularly monitored and disclosed by the glass works, so that appropriate steps can be taken immediately in the event of nonconformance (see 3.1).

For all practical purposes it may be assumed that in order to comply with the limits indicated all alkali borosilicate, borate, lead and most special glass furnaces must be equipped with dedusting systems. Allowance must be made for these dedusting and sorption systems as early as the planning phase.

In countries with low-cost electricity it is possible to construct glass furnaces of special design which produce far lower emissions and do not require expensive environmental protection equipment. The energy requirement per kg of glass can also be reduced by introducing such melting methods.

3.1 Inspection and maintenance of environmental protection installations

A control centre independent of the production process must be established to comply with existing environmental protection regulations. The responsible personnel must be enabled to perform and monitor all inspection functions including measurements relating to environmental protection in the works. They should be available for consultation on investments and take charge of negotiations with environmental protection authorities. Moreover, this department is responsible for ensuring that all environmental protection installations are regularly maintained and upgraded. This internal environmental department is also responsible for staff training.

4. Interaction with other sectors

Glass works which rely on numerous secondary operations, such as workshops, compressed air generation, fuel stores, galvanisation shops, refining shops, transport and packing departments etc. are also affected by regulations applicable in other sectors.

Because of the relatively high transport costs, container glass factories must be located near their main customers. Modern sheet glass works, on the other hand, can only operate economically with capacities upwards of 600 t/day, thus they supply their products to more distant sales areas and are reliant on good transport facilities.

Table 5 - Environmental impacts of adjacent sectors - Glass -

5. Summary assessment of environmental relevance

The effects of glass works on the environment and workplace are caused by noise, dust, effluent and flue gases.

Table 6 - Environmental impact of process stages (glass)

Key: 1 very slight; 2 slight; 3 moderate; 4 considerable

In some cases technological and processing developments and improvements have already been implemented, e.g.:

- Arsenic and tellurium are now only used as refining agents in exceptional cases.
- Fluorspar is no longer used as a flux.
- The specific outputs of the tanks have been increased with a simultaneous reduction in energy consumption.
- Wastewater circuits have been introduced.
- Numerous noise protection devices have been installed.
- Wet, electric and dry sorption plants have been installed for dust extraction.
- Tank designs and fire management systems have been improved.

Many of the processes so far tested in individual cases are capable of further technical improvement and more economic design, paying particular attention to environmental regulations. The expected costs of environmental protection devices and measures may be as much as 20% of the total investment costs of a glass works.

Proper maintenance is essential to environmentally acceptable operation of the plants. Suitable training must be given and personnel generally made aware of environmental concerns.

Early involvement of neighbouring population groups in the planning and decision-making processes will enable measures to be devised to deal with any problems arising.

In countries which have no legal guidelines it should be ascertained as early as the planning stage, based on the raw materials to be used and the process technology applied, what environmental protection measures are necessary and appropriate. Environmental protection equipment provided should be of robust design so that the life of this equipment is appropriate to the overall project and so that simple, low-cost maintenance can be guaranteed.

6. References

Allgemeine Vewaltungsvorschriften über genehmigungsbedürftige Anlagen nach § 16 der Gewerbeordnung 1985.

Allgemeine Verwaltungsvorschrift über Mindestanforderungen an das Einleiten von Abwasser in Gewässer - 41. AB-Wasser VwV, 1984.

Betriebswacht, Datenjahresbuch 1991, Berufsgenossenschaft der keramischen und Glas-Industrie, Würzburg.

1. Bundesimmissionsgesetz (BImSchG), 1985.

Entwurf zur Abwasserverordnung: Deutscher Industrie- und Handelstag, Anhang 17, Sept. 21, 1990.

Glass Manufacturing, Effluent Guidelines, World Bank, August 1983.

Guidelines of the Bundesministerium des Inneren [German Federal Ministry of the Interior] regarding the BImSchG, directives of the Council of the European Community.

TA-Luft: Erste Allgemeine Verwaltungsvorschrift zum Bundes-Immissionsgesetz, GMBR 1986 (A).

Siebzehnte Verordnung zur Durchführung des Bundes-Immissionsschutzgesetzes 1990 (Verordnung über Verbrennungsanlagen für Abfälle und ähnliche brennbare Stoffe, 17. BImSchV).

Barklage-Hilgefort H.J.: Minderung der NOx-Emission durch feuerungstechnische Maßnahmen, Glastechnische Berichte 58, Nr. 12, 1985.

Bauer H.D., Mayer Dr. P.: Zusammenführung staubmeßtechnischer Daten und arbeitsmedizinischer Befunde am Beispiel von Asbesteinwirkungen, Sonderdruck aus "Der Kompaß" 91, Nr. 7 1981.

Bundesverband des Deutschen Flachglashandels e.V., Glasfibel, Vertrieb Kelasa GmbH Cologne, 1983.

Doyle T.J.: Glassmaking Today, An Introduction to Current Practice in Glass Manufacture, Portcullis Press, Redhill, 1979.

Förster H., Feck G.: In Vitro - Studien an künstlichen Mineralfasern, Sonderdruck, Zbl. Arbeitsmed. Bd. 35, Nr. 5, 1985.

Gebhardt F., Carduck E. und Arnolds J.: Chloremissionen von Glasschmelzwannen, Glastechnische Berichte 51, Aachen 1978.

Gilbert G.: Zur Ausbreitung von Schadstoffen, insbesondere von Stickoxiden in der Atmosphäre, Glastechnische Berichte 51, Aachen 1978.

Kircher U.: Emissionen von Glasschmelzöfen - Heutiger Stand, Glastechnische Berichte 58, Frankfurt 1985.

Markgraf A.: Abgasentstaubung hinter Glasschmelzöfen mit filternden Abscheidern und vorgeschalteter Sorptionsstufe zur Beseitigung von HF und HCI, Glastechnische Berichte 58, Nr. 12, Stadthaben, 1985.

Mayer P., Bergass: Grenzwerte für Asbest am Arbeitsplatz und in der Umwelt unter besonderer Berücksichtigung der keramischen und Glas-Industrie, Sprechsaal 2/80, 1980.

Mayer P., Bergass: Glasfaserstäube und ihr gesundheitlicher Einfluß auf den Menschen, Sonderdruck der Zeitschrift, Die Berufsgenossenschaften e.V., Bonn.

Schaller K.H., Weltle D., Schile R., Weissflog S., Mayer P. und Valentin H.: Pilotstudie zur Quantifizierung der Bleieinwirkung in der keramischen und Glas-Industrie, Sonderdruck Zbl. Arbeitmed. Bd 31, Nr. 11, 1981.

Tiessler H.: Zum Einsatz eines Elektro-Entstaubers an einer Spezialglaswanne für Alkali-Borosilikatglas, Glastechnische Berichte 51, Nr. 7, 1978.

Winterhoff G.: Abgasentstaubung periodisch arbeitender Glasschmelzöfen, Glastechnische Berichte 58, Nr. 12, 1985.

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