Energy and Environmental Implications

Ravi Jain Ph.D., P.E. , ... M. Diana Webb M.L.A. , in Handbook of Environmental Engineering Assessment, 2012

Glass

Glass can be recycled back into glass furnaces, but difficulties in the glassmaking operation present problems that make recycling unattractive in many cases. First, glass "formulas" include not only silica but limestone, soda ash, and, in many cases, coloring agents that are blended, melted, and refined in precise operations. Reclaimed glass necessarily results in the blending of formulas and the inclusion of many foreign substances, the end products of which are highly unpredictable. As a consequence, recycled glass is considered usable for only a limited range of products, which offsets much of any cost saving.

Some glass products are manufactured with about 25 percent cullet (waste glass) as a component. The use of cullet reduces energy consumption in two ways: 1) The heat required to melt cullet may be 33 to 50 percent less than that required to produce glass from the virgin raw materials, and 2) the use of cullet requires the addition of fewer additives, thus saving the energy required to mine the inorganic chemicals usually added. These energy savings from the use of cullet are partially offset, however, by the energy required to collect, beneficiate, and transport waste glass (Renard, 1982).

The separation of glass from other wastes poses a second problem to glass recycling. This process may vary from simple hand classification, accomplished during time of collection, to complex automated separation operations employing air classification, dense media separation, or froth flotation. Color separation must also be accomplished and may be done at the time of collection or via automated optical systems. So-called source separation, where glass of different colors is separated at each household, is a feature of many U.S. community's recycling programs. The separation may take place in each home, for curbside pickup, or may be accomplished at the time of drop-off at neighborhood centers. In Europe, especially Germany, this is accomplished through placement of large metal bins in densely populated neighborhoods. Three bins are provided, one for each glass color—green, brown, and white (clear)—and each station serves several thousand residents. The cullet obtained through this separation is much more likely to be useful than mixed materials containing different colors. Data collected in 2009 by the European Glass Container Federation show recycling rates of 90 percent or higher for Belgium, the Netherlands, Sweden, and Switzerland, and an overall return rate of about 67 percent for all of Europe. In contrast, the Environmental Protection Agency (EPA) reports that the recycling rate for the United States is about 26 percent. Utilization of returnable bottles and containers assures that the effective use of a given container will be greatly increased, thereby decreasing the necessity for more containers and the waste produced as each container is emptied. Discouragement of "throwaway" containers promotes not only less waste production, but less energy expenditure for manufacturing as well. When the total energy consumption involved in collecting, returning, washing, and refilling glass bottles is compared to that required in delivering the same volume of beverage to the consumer in a throwaway container, a significant energy savings is apparent. One study has indicated that "a complete conversion to returnable bottles would reduce the demand for energy in the beverage (beer and soft drink) industry by 55 percent, without raising the price of soft drinks to the consumer" (Hannon, 1972). Unfortunately, many bottling companies see mandated recycling, especially through use of deposit containers, as an unmitigated horror. They lobbied successfully against deposits and returnable containers in many states in the 1980s. Reclaimed glass may be used for secondary products other than glass containers, such as for aggregate in road construction, manufacture of insulating materials, or brick production.

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STUDIES ON HIGH TEMPERATURE LOW NOX COMBUSTION FOR GLASS FURNACES

J. Korstanje , ... Martin , in The Institute of Energy's Second International Conference on Combustion & Emissions Control, 1995

2.3 Burners

The performance of a total of 9 different burners was investigated on the furnace: 6 natural gas burners, one LPG burner, one HFO burner and a gas atomizing oil burner. For each test a total of four burners were mounted in the underport firing mode, two on each side of the furnace. The burners were designed for a net thermal input of 540 kW. A summary of the burners used is given below.

Single-hole

This type of burner is commonly used in glass furnaces. The single-hole burners were designed to give three gas injection velocities for natural gas: 125, 175 and 225 m/s. The nozzle design is shown in Figure 3.

Figure 3. Single-hole burner nozzle.

Double impulse burner

The double impulse burner shown in Figure 4 was designed to provide a flame that would suit the test furnace. The burner has a high velocity central gas jet surrounded by a low velocity annular gas flow. The flame length is determined by the impulse of the central flow, while the annular flow completes the thermal input. The two gas flows can be adjusted to optimize the flamelength. The greater the proportion of gas through the annulus the longer the flame will be.

Figure 4. Double impulse burner.

Multihole

Figure 5 shows the Mk 1 version of the multihole burner nozzle(7). The design is aimed at spreading the gas through the whole of the combustion space above the load. It also incorporates a mechanism to provide a very low velocity flow at the centre which it is hoped will be cracked by the surrounding flame. A second version of the burner (Mk 2) was also tested on the furnace. This burner has twice as much gas going through the central hole, while the velocity is kept the same as the Mk 1 burner.

Figure 5. Multihole burner nozzle Mk 1.

LPG

The LPG burners were designed for an injection velocity of 125 m/s. They were of the same design as the single-hole natural gas burners (Figure 3).

Heavy Fuel Oil

The oil burners are proprietary burners. Each of the two burners used 5 m3 (n)/h of compressed air for atomisation of the oil at 2.75 bar.

Mixed oil and gas

The mixed oil and gas burner is a gas atomizing oil burner shown in Figure 6. A different nozzle was fitted for each oil/gas ratio.

Figure 6. Mixed oil and gas burner.

The properties of the various fuels used at the trials are listed in Table 1.

Table 1. Fuel Properties

Natural Gas HFO LPG
Mean molecular weight 18.11 kg/kmol 43.37 kg/kmol
Stoichiometric air requirement 9.75 vol/vol 11.00 m3(n)/kg 23.45 vol/vol
Calorific value (gross) 38.68 MJ/m3(n) 42.22 MJ/kg 93.91 MJ/m3(n)
Calorific value (nett) 34.91 MJ/m3(n) 39.93 MJ/kg 86.40 MJ/m3(n)
Density (15°C, 1 atm) 0.77 kg/m3(n) 1.00 kg/l 1.83 kg/m3(n)

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Current and future oxygen (O2) supply technologies for oxy-fuel combustion

N.M. Prosser , M.M. Shah , in Oxy-Fuel Combustion for Power Generation and Carbon Dioxide (CO2) Capture, 2011

10.4.3 Impact of elevated pressure oxygen production

Oxygen production at pressures significantly above atmospheric is commonly needed. Even relatively low pressure applications, such as glass furnaces and primary metal ore smelters, often require modestly elevated pressure oxygen to accommodate system controls and burners. Steel manufacture is a large traditional user of oxygen, and final refinement of steel in the basic oxygen furnace requires oxygen at about 30  bar. Oxygen supply for gasifiers is usually needed at 40–90   bar. Prior to about 1990, elevated pressure oxygen supply was usually generated by means of an oxygen compressor. Unlike the liquid oxygen pumped processes of Fig. 10.7 and Fig. 10.8, oxygen was withdrawn from the base of the low pressure column as a vapor and warmed as it passed through the primary heat exchanger. The oxygen was available at slightly above atmospheric pressure at the warm end of the PHX, from which it was fed to the suction of the product oxygen compressor. However, very high compressor costs and significant safety concerns associated with oxygen compressors have led to the prevalence of liquid oxygen pumped air separation processes. In these processes, oxygen pressure is generated from the liquid pump. A high pressure stream such as air from the BAC is needed at sufficient pressure and flow to vaporize the oxygen. The additional power for the high pressure oxygen production is primarily from the BAC. Capital cost for the high pressure oxygen is due to the high pressure BAC, the oxygen pump, and the cost differences for the PHX.

While power plants are operated at low pressures, the efficiency benefits of operating an oxy-coal power plant at high pressure have been studied in Hong et al. (2009) and Zheng et al. (2007). Hong et al. (2009) considered boiler pressures up to 10 bara, in Zheng et al. (2007) pressures up to 80 bara were considered. Figure 10.13 illustrates the increased power and cost on a normalized basis to deliver oxygen to higher pressure boilers. The total capital of the air separation plant is relatively unaffected by oxygen pressure. The increased capital cost of the BAC and liquid pump is mitigated by savings in the PHX. The PHX cost tends to decrease as a result of more effective heat transfer and smaller cross-sectional flow areas, even though higher working pressures are required. The cost of oxygen increases by about 21% for an 80 bara boiler with a power cost of US$0.10/kW-h, and by about 26% with a power cost of US$0.15/kW-h, as illustrated by the curves in Fig. 10.13.

10.13. ASU power and oxygen cost related to delivered pressure.

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Combustion of Coal Without Grates

Wilfrid Francis , Martin C. Peters , in Fuels and Fuel Technology (Second Edition), 1980

16 Metallurgical Applications and Cement Manufacture

—Usually central or Bin and Feeder system.

—Oxidizing or reducing flames can be produced at will.

—Ash is detrimental in many metallurgical operations. Advantageous in cement manufacture because sold at cement prices.

(a) Annealing Furnaces

—Steel and malleable cast iron—reduces scale losses

—consumption, 0.5–0.6 tons —improves output

fuel/ton castings —reduces cost.

(b) Small Forge and Drop Forge Furnaces

—Billets 70 to 500 mm square—multiple burners.

—Fuel consumption up to 1 2 ton per ton of billets.

To avoid contamination of billet, ash fusion temperature should be > 100°C more than maximum temperature of metal.

(c) Heavy Forge Furnaces (5–200 ton ingots)

—Avoid ash coming into contact with product (also in glass furnaces). Sulphur spoils surface, causes brittleness and bloom.

—Fuel is burned outside stock chamber in precombustion chambers.

—Fine grinding required to ensure ash entrained in flue gases. Find grinding also permits more sulphur to pass into flue gases.

(d) Melting Furnaces (Reverberatory)

—Burners are placed at back of chamber. Fuel consumption 1 2 ton/ton alloy.

—Where molten metal is covered by a layer of slag, coal ash of low fusion point is not objectionable.

(e) Copper Smelting

< 20 ton/day in Great Britain.

< 750 ton/day in U.S.A.

Multiple swivel-type burners.

Cycle takes 24 hr. Temperature 1100–1300°C.

(f) Cement Manufacture

Rotary furnace 3–6 m in diameter, 35–180 m long. Slight angle to horizontal. Burner at lower end and feed towards burner, where clinker is discharged.

Long flame required—ash in coal is generally similar in composition to Portland Cement therefore one of the few applications where high ash coal is welcomed, e.g. 20–30%.

(g) Marine Boilers

Difficulties—slag and ash deposits.

—variability of fuels.

—Bunker C oil used almost exclusively now on new ships.

(h) Colloidal Fuel

Thirty–to thirty-five per cent pulverized fuel is ground in fuel oil—powdered coal requires wetting. Firing as with heavy fuel oil. Reasonably stable but little used now.

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From NORM by-products to building materials

J. Labrincha , ... J.L. Provis , in Naturally Occurring Radioactive Materials in Construction, 2017

7.4.5.1 Technical properties

In a wide review published in 2007 (Selby, 2007) the ceramics sector is analyzed considering its different products as glazed tiles, porcelain tiles, sanitary ware such as baths and wash basins, frits, ceramic pigments, and engineering ceramics. The main ceramics using NORM raw materials are refractories as well as tiles in which zirconia (the NORM raw material) is mixed with other constituents. In 2005, about 54   wt% of the zircon produced was consumed in ceramics production, while refractories required about 14%. In the same year, 39% of produced zirconia was used in refractories, while 33% was consumed in pigments, and 12% in advanced ceramics and catalysts (Selby, 2007).

Refractories are materials that are designed to maintain strength, dimensional stability, and chemical resistance at high temperature. They are manufactured in the form of bricks, fibers, nozzles, slide gates, valves, and grouts. One of the largest uses of zircon and zirconia in refractories is in the glass industry, where the linings of glass furnaces are made from a combination of zircon and zirconia bricks. The zircon bricks for glass furnaces typically contain 30%–40% zircon. Zirconia is commonly used for nozzles, slide gates, filters, and ceramic linings, where the zirconia content approaches 94%. Refractories are typically made from alumina, magnesia, clays, binders, and zircon or zirconia. There are two methods of fabrication: (a) mixing of the ingredients, pressing into the desired shapes, drying, and kiln firing and (b) mixing of ingredients, melting in a furnace and casting the molten mass into the desired shapes ( Selby, 2007).

The main application in the ceramics field is in glazed tiles and sanitary ware. In this application the ceramic has a two-piece body—a clay-based ceramic body is covered with a silicate/borate glaze to provide waterproofing, durability, and decoration. Zircon is added to the glaze for opacification and to provide a white color. The zircon may be added in the milled form as micronized zircon or as a frit. The concentration of milled zircon in the glaze is up to 20% (Selby, 2007).

Frits are ceramic glasses containing silica and boric acid and are manufactured by melting all constituents together and then quenching in water, followed by milling. Their use allows a water-soluble constituent to be added to the glaze and converted into an insoluble form and also to control the vitrification point of the glaze. The zircon content of frits is usually 10%–20% (Selby, 2007).

In contrast to the glazed ceramics, porcelains have a one-piece ceramic body; however, they may also be glazed for decorative purposes. Porcelain ceramic tiles are more resistant to wear than the glazed variety and they are composed of clays, quartz, feldspars, and nepheline syenite together with zircon. In this application the zircon is used in the milled form at concentrations of up to 15% (Selby, 2007).

Ceramic pigments are manufactured by mixing zirconia, quartz, sodium fluoride, and an appropriate chromophore. After firing, the product is milled (Selby, 2007).

There are many "high tech" uses for zirconia in the engineering field such as coatings, grinding media, and cutting tools. Zirconia coatings are applied by plasma spraying, while grinding media are manufactured by high-pressure forming and sintering. Zirconia contents are 60%–95%. Cutting tools are made by fusion of zirconia with alumina, with a ZrO2 content of 5%–10% (Selby, 2007).

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Glass and Energy

Christopher W. Sinton , in Encyclopedia of Energy, 2004

3.2 Glass Melting Furnaces

There are several types of melting furnaces used in the glass industry depending on the final product, raw materials, fuel choice, the size of operation, and economic factors. A melter can be either periodic or continuous. The latter is most widely used in large-scale operations. Continuous melters maintain a constant level by removing the glass melt as fast as raw material is added. Table II shows the three major types of furnaces and their advantages and disadvantages. The energy for melting comes from either the combustion of fossil fuels or electricity. The temperature necessary for melting ranges between 1300 and 1550°C. All furnaces are lined with high-temperature refractory materials to keep the corrosive melt from escaping and to insulate the melter.

Table II. Advantages and Disadvantages of Different Furnace Types

Furnace type Advantages Disadvantages
Regenerative Long furnace life Higher NO x levels
Long-term experience Higher capital cost
Direct fired (mostly oxygen/fuel) Reduction in fuel Refractory corrosion
NO x reduction Short-term experience
Lower capital cost Cost of oxygen production
Particulate reduction
Electric Efficient High electricity cost
No one-site pollution Short furnace life

Regenerative combustion furnaces recover heat from the exhaust stream to preheat the incoming combustion air by alternatively passing the exhaust and combustion air through large stacks of latticework refractory brick (regenerators or checkers). There are two sets of regenerators, so that as one is being preheated by the exhaust gases the other is transferring heat to the incoming combustion air (Fig. 3). The cycle is reversed approximately every 20 min. Most glass-container plants have either end-fired (burners at each end) or cross-fired (burners on each side) regenerative furnaces, and all flat glass furnaces are cross-fired with five or six ports on each side with two burners for each port. Combustion air preheat temperatures of up to 1400°C may be attained, leading to very high thermal efficiencies. A variant of the regenerative furnace is the recuperator, in which incoming combustion air is preheated continuously by the exhaust gas through a heat exchanger. Recuperative furnaces can achieve 800°C preheated air temperatures. This system is more commonly used in smaller furnaces (25–100  tons per day). For large-capacity installations (>500   tons per day), cross-fired regenerative furnaces are almost always used. For medium-capacity installations (100–500   tons per day), regenerative end-port furnaces are most common.

Figure 3. Diagram of a cross-fired regenerative furnace. This type is often used in large-volume production of container and flat glass. From U.S. Department of Energy (2002). "Energy and Environmental Profile of the U.S. Glass Industry."

A direct-fired furnace does not use any type of heat exchanger. Most direct-fired combustion furnaces use oxygen rather than air as the oxidizer. This is commonly called oxy-fuel melting. The main advantages of oxy-fuel melting are increased energy efficiency and reduced emission of nitrogen oxides (NO x ). By removing air, nitrogen is removed, which reduces the volume of the exhaust gases by approximately two-thirds and therefore reduces the energy needed to heat a gas not used in combustion. This also results in a dramatic decrease in the formation of thermal NO x . However, furnaces designed for oxygen combustion cannot use heat-recovery systems to preheat the oxygen. Initially, furnaces that use 100% oxy-fuel were used primarily in smaller melters (<100   tons per day), but there is a movement toward using oxy-fuel in larger, float glass plants.

An electric furnace uses electrodes inserted into the furnace to melt the glass by resistive heating as the current passes through the molten glass. These furnaces are more efficient, are relatively easy to operate, have better on-site environmental performance, and have lower rebuild costs compared to the fossil-fueled furnaces. However, fossil fuels may be needed when the furnace is started up and are used to provide heat in the working end or forehearth. These furnaces are most common in smaller applications because at a certain size, the high cost of electricity negates the improved efficiency.

Some regenerative furnaces use oxygen enrichment or electric boost to optimize the melting process. Electric boosting adds extra heat to a glass furnace by using electrodes in the bottom of the tank. Traditionally, it is used to increase the throughput of a fossil fuel-fired furnace to meet periodic fluctuations in demand without incurring the costs of operating a larger furnace. It is also used to enhance the pull rate (the output at the forming end) of a furnace as it nears the end of its operating life.

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Glass

Solomon Musikant , in Encyclopedia of Physical Science and Technology (Third Edition), 2003

VII Manufacture

The manufacture of glass has three essential operations: batching, melting, and forming. In the batching operation, the raw materials are weighed, mixed, and milled as necessary to provide a mixture that can be melted to provide the glass composition desired. Some of the more common raw ingredients are listed inTable XIV. Trace impurities can be a serious problem to the glass maker. One of the most common impurities is iron oxide, which imparts a greenish hue to the glass and prevents heat transfer by radiation through the glass during the melting phase. For high-transmitting fused quartz, extremely high-purity quartz sands are used.

TABLE XIV. Glass-Making Materials

Raw material Chemical composition Glass-making oxide Percent of oxide
Sand SiO2 SiO2 100.0
Soda ash Na2CO3 NaO2 58.5
Limestone CaCO3 CaO 56.0
Dolomite CaCo3·MgCO3 CaO 30.4
MgO 21.8
Feldspar K2(Na2)O·Al2 O 3·6SiO2 Al2 O 3 18.0
K2(Na2)O 13.0
SiO2 68.0
Borax Na2B4 O 7·10 H2O Na2O 16.3
B2 O 3 36.5
Boric acid B2 O 3·H2O B2O3 56.3
Litharge PbO PbO 100.0
Potash K2CO3·1.5H2O K2O 57.0
Fluorspar CaF2 CaF2 100.0
Zinc oxide ZnO ZnO 100.0
Barium carbonate BaCO3 BaO 77.7

a From Shand, E. B. (1958). "Glass Engineering Handbook," McGraw-Hill, New York.

The particle size of the batching materials is a signifcant variable and must be controlled within close limits to assure a satisfactory melting process. Accuracy of weighing and mixing operations that do not cause segregation in the dry batch are essential to obtaining the homogeneous glass melt desired.

VII.A Melting

Melting is performed in a gas, oil, or electrically heated furnace. Batch melting in pots or day tanks is used for small quantities of glass. Continuous furnaces ranging from less than 1 ton of glass per day to 1500 tons per day capacity are used in larger production operations. The continuous furnaces are built up from refractory ceramic components and often operate continuously for periods on the order of 1 year before being shut down for rebuild. These furnaces are divided into a large melting section followed by a shallow, narrow refining section (the forehearth) where the glass temperature is reduced preparatory to the forming operation. In fossil-fuel-fired furnaces the hot combustion gases are located above the molten glass. In electric resistance furnaces the glass is directly heated by immersed electrodes. Small induction-heated glass furnaces are used for specialty glasses.

The temperature of the glass in the melting section of the furnace is dependent on the composition. For typical commercial glasses, melting temperatures vary from 1500   °C for soda–lime glass to 1600   °C for aluminosilicate glass.

VII.B Refining

The melting and refining processes are very complex. At the cold end of the furnace where the batch is introduced, melting is initiated by the fluxes, which melt first and then dissolve the more refractory ingredients. Elimination of the water vapor and other gases dissolved in the melt takes place in the downstream section of the furnace prior to the entry of the glass into the refining section. In the forehearth the glass is cooled, thereby adjusting its viscosity to the level needed by the forming equipment.

VII.C Forming

Forming operations include drawing the glass into a sheet, bottle blowing, pressing, tube drawing, rolling into flat glass, and fiber drawing. Fibers can be drawn into continuous strands for textile application or drawn by means of steam or compressed-air jets into fine, discontinuous strands useful for thermal insulation.

After forming, the glass usually has to be annealed to minimize residual strains that could lead to fracture of the glass or, in the case of optical materials, cause unacceptable variations in the optical properties.

VII.D Finishing

Finally, the ware is subjected to secondary finishing operations such as cutting, grinding, polishing, or thermal or chemical treatments to produce the end item.

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Nanoglass and Nanostructured Chalcogenide Glasses

B. Karmakar , ... M. Garai , in Glass Nanocomposites, 2016

15.3.2.2 Synthesis and Characterization

To achieve the desired property in glass and corresponding glass-ceramics, selection of glass system and composition, both are equally important. Ma et al. [41] studied the crystallization of Ge-Sb-Se system for preparing IR-transmitting glass-ceramics and observed that the addition of 5% gallium (Ga5Ge25Sb10Se60 composition) stabilize glass phase. ChGs are generally prepared by melting technique with the starting high purity chalcogens (S, Se, and Te) and other Gr-13/Gr-14/Gr-15 elements like Ga, Ge, As, Sb, etc. in a silica ampoule. High vacuum is necessary to avoid the oxygen contamination with the chalcogenide batch mixture. To avoid the oxygen contamination, ChG batch is prepared inside a glove box (where air, oxygen, and water vapor pressures are almost zero). Rocking of the silica ampoule is also required to ensure the homogenization of the melt. After melting the ChG batch in rocking furnace, glass is obtained on sudden air cooling the sealed ampoule. To remove the mechanical strain, ChGs are then annealed at a temperature near the T g value.

In order to initiate nucleation phenomena followed by crystallization, ChGs are heat-treated in a vacuum-sealed silica tube at different temperatures above T g value. For the thermal treatment of ChGs to induce crystallization, differential scanning calorimetric (DSC) curve (Figure 15.8a) becomes helpful [40,42]. Based on the knowledge of nucleation-rate-like curve of 90GeS2⋅   10Ga2S3 glass (inset of Figure 15.8a), Lin et al. [40] has prepared glass-ceramic containing β-GeS2 nanocrystals by single-step heat-treatment at 466   °C. And the nucleation of this ChG glass occurs in the temperature range from 390 to 475   °C, where nucleation rate reaches a maximum at 445   ±   5   °C (Figure 15.8a).

Figure 15.8. (a) DSC thermograph (heating rate of 10   °C/min) of GeS2-Ga2S3 glass. The inset shows the height of the crystallization peak, (δT)p, as a function of nucleating temperature for 3   h heat-treatment. (Reproduced from Ref. [ 42 ] with permission, Copyright © Springer.) (b) XRD patterns of GeS2-Ga2S3-Tm2S3 glass (bottom) and corresponding glass-ceramics heat-treated at 458   °C for 25   h (top). The inset shows the STEM image of the glass-ceramic sample.

 (Reproduced from Ref. [40] with permission, Copyright © AIP Publishing LLC.)

In addition to the heating temperature, the second important parameter is represented by the annealing time. Lin et al. [40,42] synthesized homogeneous 90GeS2·10Ga2S3 glass by melt quenching at 980   °C (18   h) in an evacuated (about 10−   3  Pa) quartz ampoule by a mixture of high purity (99.999%) Ge, Ga, and S elements. Chalcohalide glass with the composition of 65GeS2-25Ga2S3-10CsI (mol%) doped with 0.6   wt% Tm3   + ions was prepared by Dai et. al. [43] using the conventional melt-quench technique. IR transparent chalcohalide nanocrystalline glass-ceramic was then prepared by heat-treating the host glass at 440   °C [43].

CGCs obtained by the heat-treatment technique is qualified first by checking the IR transmission spectra. And to get precise information on the size and the number of crystalline phases in the glassy matrix, optical and scanning electronic microscopes are used. For the confirmation of crystalline phases developed on heat-treatment, powder XRD technique is used (Figure 15.8b). As seen from Figure 15.8b, the 80GeS2·10Ga2S3 glass on heat-treatment at 458   °C for 25   h, is converted to glass-ceramic containing Ga2S3 nanocrystals. Its inset shows the STEM image, evidencing the nanocrystallinity in the glass-ceramic sample.

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Health and Safety

DA Dolbey Jones BEng, FIEE, MIOSH , in Electrical Engineer's Reference Book (Sixteenth Edition), 2003

24.2.3 Other injuries

24.2.3.1 Acoustic shock

Accounts of the after-effects of lightning strikes frequently refer to temporary or permanent impairment of hearing and sometimes ruptured eardrums. This is in most cases almost certainly caused by the intense acoustic shock wave sent out when a column of air (the lightning channel) rapidly expands on being suddenly heated to about 15000°C by the passage of the enormous current in a lightning discharge. The range of danger is probably limited to a few feet.

24.2.3.2 Arc eye

This is a painful condition resembling pepper in the eyes and develops some hours after exposure (even momentary) to an intense source of ultraviolet light. It occurs mainly when a person works near arc welding and looks directly into the brilliant light given out by the electric arc.

Fortunately 'arc eye' lasts only a short time, no more than a day or two, and although painful leaves no permanent injury. Treatment is by the application of a soothing lotion.

This complaint is easily prevented by the use of protective goggles with side protection, as worn by welders. The usual victims are assistants and bystanders without goggles, although ordinary glass cuts out much of the ultraviolet light.

Theoretically there is a risk of a form of cataract caused by prolonged exposure to infrared light which affects persons who work for long periods on glass furnaces, etc.

24.2.3.3 Fractures and torn muscles

Strains and fractures may arise from falls following an electric shock. e.g. from a crane or ladder. It may not be apparent at the time that the victim has suffered an electric shock and that the heart may be in fibrillation. If they are unconscious artificial resuscitation would be the advised first aid treatment.

24.2.3.4 Burns and side effects

Burns are probably the most serious after-effect of electrical accidents. They are the principal danger with direct currents or at very low voltages (below about 80 V). With low alternating voltages shock is the typical injury although there may also be severe burning. At extra-high voltages shock may not be as important it being the actual current and flash burns which tend to be severe with large areas of the body affected. Severe electrical burns have led to many deaths, usually after several days or even weeks of painful suffering. Burns may be of several types:

Contact burns

These occur when the person has touched a live conductor. They may be local and very deep reaching to the bone, or very small, being just an area of 'white' skin which may be easily overlooked at a post-mortem examination. The position of such small burns may be important in reconstructing an accident and should be recorded.

Arc burns

These may be extensive, and of any degree, particularly when there has been a high-voltage flashover. Provided that the person survives the initial wound and surgical shock, and the surface area involved is not too large, they are likely to make a good recovery because the injury should be largely sterile. They may, however, be badly scarred or even lose a limb. The large fault current levels which now exist on many low voltage distribution circuits poses a serious risk of arc burns if a flashover is caused. There have been a considerable number of fatalities to electrical staff due to this cause, usually when they have attempted to work on live low voltage (230/400 volt) busbars and switchboards without adequate training and proper insulated tools.

Radiation burns

These burns arise from short-circuit arcing and are, in effect, a severe form of sunburn. Some radio frequency (RF) equipment can also impart burns which can be deep. RF burns usually occur due to contact with the charged conductor but this will depend on the power output of the equipment and the frequency.

Vaporised metal

When an open fuse or small conductor fuses some copper (silver or tin) is vaporised and at close quarters this may burn or impregnate the face or hands. This is usually harmless unless it enters the eyes in which case the result is potentially serious.

Deep burns and necrosis

There is the potential danger of deep burns destroying tissues below the skin even though superficially there is only a small injury. Thus electrical burns, and in particular high-voltage contact burns, must be taken seriously and the person kept under medical supervision. However, such burns are rare.

Metal fume fever

This is caused by inhaling metal or metallic oxide fumes, e.g. by a welder working in an enclosed space.

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Solar Thermal Systems: Components and Applications

G. Leftheriotis , P. Yianoulis , in Comprehensive Renewable Energy (Second Edition), 2022

3.10.4.1.1 Manufacture

The raw materials used for the production of float glass typically consist of 72.6% sand (silicon dioxide), 13.0% soda (sodium carbonate), 8.4% limestone (calcium carbonate), 4.0% dolomite and 1.0% alumina. Another 1.0% of various additives is also present. These are compounds for the adjustment of the physical and chemical properties of the glass, such as colorants, refining agents, etc. The raw materials are mixed in a batch mixing process, then fed together with suitable cullet (waste glass), in a controlled ratio, into a furnace of approximately 1500 °C. Common flat glass furnaces are 9  m wide, 45   m long, and contain more than 1200 tons of glass. Once molten, the temperature of the glass is stabilized to approximately 1200   °C to ensure a homogeneous specific gravity. The molten glass is fed into a "tin bath," a bath of molten tin (about 3–4   m wide, 50   m long, 6   cm deep), through a delivery canal (de Jong, 1989). The amount of glass allowed to pour onto the molten tin is controlled by a gate. Once poured onto the tin bath, the glass spreads out in the same way that oil spreads out if poured onto a bath of water. In this situation, gravity and surface tension result in the top and bottom surfaces of the glass becoming approximately flat and parallel. The molten glass does not spread out indefinitely over the surface of the molten tin. Despite the influence of gravity, it is restrained by surface tension effects between the glass and the tin. The resulting equilibrium between the gravity and the surface tension defines the equilibrium thickness of the molten glass (T), given by the relation (Rawson, 1974):

(24) T 2 = S g + S gt + S t 2 ρ t g ρ g ρ t − ρ g

with ρ g the glass density, ρ t the tin density, S g , S gt , and S t the values of surface tension at the glass-air, glass-tin and tin-air interfaces respectively. For standard soda-lime-silica glass under a protective atmosphere and on clean tin the equilibrium thickness is approximately 7   mm.

Tin is suitable for the float glass process because it has a high specific gravity, is cohesive, and immiscible into the molten glass. Tin, however, is highly reactive with oxygen and oxidizes in a natural atmosphere to form Tin dioxide (SnO2). Known in the production process as dross, the tin dioxide adheres to the glass. To prevent oxidation, the tin bath is provided with a positive pressure protective atmosphere consisting of a mixture of nitrogen and hydrogen. The glass flows onto the tin surface forming a floating ribbon with perfectly smooth surfaces on both sides and an even thickness. As the glass flows along the tin bath, the temperature is gradually reduced from 1100   °C until the sheet can be lifted from the tin onto rollers at approximately 600   °C. The glass ribbon is pulled off the bath by rollers at a controlled speed. Variation in the flow speed and roller speed enables glass sheets of varying thickness to be formed. Top rollers positioned above the molten tin may be used to control both the thickness and the width of the glass ribbon. Once off the bath, the glass sheet passes through a lehr kiln for approximately 100   m, where it is further cooled gradually so that it anneals without strain and does not crack from the change in temperature. On exiting the "cold end" of the kiln, the glass is cut by machines. A block diagram of the float process is shown in Fig. 6.

Fig. 6

Fig. 6. Block diagram of a typical float line.

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