11.15 Glass Manufacturing

11.15.1 General1-5

Commercially produced glass can be classified as soda-lime, lead, fused silica, borosilicate, or

96 percent silica. Soda-lime glass, since it constitutes 77 percent of total glass production, is discussed

here. Soda-lime glass consists of sand, limestone, soda ash, and cullet (broken glass). The

manufacture of such glass is in four phases: (1) preparation of raw material, (2) melting in a furnace,

(3) forming and (4) finishing. Figure 11.15-1 is a diagram for typical glass manufacturing.

The products of this industry are flat glass, container glass, and pressed and blown glass. The

procedures for manufacturing glass are the same for all products except forming and finishing.

Container glass and pressed and blown glass, 51 and 25 percent respectively of total soda-lime glass

production, use pressing, blowing or pressing and blowing to form the desired product. Flat glass,

which is the remainder, is formed by float, drawing, or rolling processes.

As the sand, limestone, and soda ash raw materials are received, they are crushed and stored in

separate elevated bins. These materials are then transferred through a gravity feed system to a weigher

and mixer, where the material is mixed with cullet to ensure homogeneous melting. The mixture is

conveyed to a batch storage bin where it is held until dropped into the feeder to the melting furnace.

All equipment used in handling and preparing the raw material is housed separately from the furnace

and is usually referred to as the batch plant. Figure 11.15-2 is a flow diagram of a typical batch plant.

The furnace most commonly used is a continuous regenerative furnace capable of producing

between 45 and 272 megagrams (Mg) (50 and 300 tons) of glass per day. A furnace may have either

side or end ports that connect brick checkers to the inside of the melter. The purpose of brick

checkers (Figure 11.15-3 and Figure 11.15-4) is to conserve fuel by collecting furnace exhaust gas heat

that, when the air flow is reversed, is used to preheat the furnace combustion air. As material enters

the melting furnace through the feeder, it floats on the top of the molten glass already in the furnace.

As it melts, it passes to the front of the melter and eventually flows through a throat leading to the

refiner. In the refiner, the molten glass is heat conditioned for delivery to the forming process.

Figures 11.15-3 and 11.15-4 show side port and end port regenerative furnaces.

After refining, the molten glass leaves the furnace through forehearths (except in the float

process, with molten glass moving directly to the tin bath) and goes to be shaped by pressing,

blowing, pressing and blowing, drawing, rolling, or floating to produce the desired product. Pressing

and blowing are performed mechanically, using blank molds and glass cut into sections (gobs) by a set

of shears. In the drawing process, molten glass is drawn upward in a sheet through rollers, with

thickness of the sheet determined by the speed of the draw and the configuration of the draw bar. The

rolling process is similar to the drawing process except that the glass is drawn horizontally on plain or

patterned rollers and, for plate glass, requires grinding and polishing. The float process is different,

having a molten tin bath over which the glass is drawn and formed into a finely finished surface

requiring no grinding or polishing. The end product undergoes finishing (decorating or coating) and

annealing (removing unwanted stress areas in the glass) as required, and is then inspected and prepared

for shipment to market. Any damaged or undesirable glass is transferred back to the batch plant to be

used as cullet.

10/86 (Reformatted 1/95) Mineral Products Industry 11.15-1
Figure 11.15-1. Typical glass manufacturing process.

Figure 11.15-2. General diagram of a batch plant.

11.15-2 EMISSION FACTORS (Reformatted 1/95) 10/86
Figure 11.15-3. Side port continuous regenerative furnace.

Figure 11.15-4. End port continuous regenerative furnace.

10/86 (Reformatted 1/95) Mineral Products Industry 11.15-3
11.15.2 Emissions And Controls1-5

The main pollutant emitted by the batch plant is particulates in the form of dust. This can be

controlled with 99 to 100 percent efficiency by enclosing all possible dust sources and using

baghouses or cloth filters. Another way to control dust emissions, also with an efficiency approaching

100 percent, is to treat the batch to reduce the amount of fine particles present, by presintering,

briquetting, pelletizing, or liquid alkali treatment.

The melting furnace contributes over 99 percent of the total emissions from a glass plant, both

particulates and gaseous pollutants. Particulates result from volatilization of materials in the melt that

combine with gases and form condensates. These either are collected in the checker work and gas

passages or are emitted to the atmosphere. Serious problems arise when the checkers are not properly

cleaned in that slag can form, clog the passages, and eventually deteriorate the condition and efficiency

of the furnace. Nitrogen oxides form when nitrogen and oxygen react in the high temperatures of the

furnace. Sulfur oxides result from the decomposition of the sulfates in the batch and sulfur in the fuel.

Proper maintenance and firing of the furnace can control emissions and also add to the efficiency of

the furnace and reduce operational costs. Low-pressure wet centrifugal scrubbers have been used to

control particulate and sulfur oxides, but their inefficiency (approximately 50 percent) indicates their

inability to collect particulates of submicrometer size. High-energy venturi scrubbers are

approximately 95 percent effective in reducing particulate and sulfur oxide emissions. Their effect on

nitrogen oxide emissions is unknown. Baghouses, with up to 99 percent particulate collection

efficiency, have been used on small regenerative furnaces, but fabric corrosion requires careful

temperature control. Electrostatic precipitators have an efficiency of up to 99 percent in the collection

of particulates. Tables 11.15-1 and 11.15-2 list controlled and uncontrolled emission factors for glass

manufacturing. Table 11.15-3 presents particle size distributions and corresponding emission factors

for uncontrolled and controlled glass melting furnaces, and these are depicted in Figure 11.15-5.

Emissions from the forming and finishing phases depend upon the type of glass being

manufactured. For container, press, and blow machines, the majority of emissions results from the

gob coming into contact with the machine lubricant. Emissions, in the form of a dense white cloud

that can exceed 40 percent opacity, are generated by flash vaporization of hydrocarbon greases and

oils. Grease and oil lubricants are being replaced by silicone emulsions and water soluble oils, which

may virtually eliminate this smoke. For flat glass, the only contributor to air pollutant emissions is

gas combustion in the annealing lehr (oven), which is totally enclosed except for product entry and

exit openings. Since emissions are small and operational procedures are efficient, no controls are used

on flat glass processes.

11.15-4 EMISSION FACTORS (Reformatted 1/95) 10/86
Table 11.15-1 (Metric And English Units). PARTICULATE, SULFUR OXIDES, AND NITROGEN OXIDES EMIS

FOR GLASS MANUFACTURINGa

EMISSION FACTOR RATING: B

Process

Particulate Sulfur Oxides Ni

kg/Mg lb/ton kg/Mg lb/ton kg/M

Raw materials handlingb (all types of glass) Neg Neg

0

0

0

Melting furnacec

Container

Uncontrolled 0.7 1.4 1.7 3.4 3.1 

(0.4 - 0.9) (0.9 - 1.9) (1.0 - 2.4) (2.0 - 4.8) (1.6 - 4

w/low-energy scrubberd 0.4 0.7 0.9 1.7 3.1 w/venturi scrubbere <0.1 0.1 0.1 0.2 3.1 w/baghousef Neg Neg 1.7 3.4 3.1 w/electrostatic precipitatorg Neg Neg 1.7 3.4 3.1 

Flat

Uncontrolled 1.0 2.0 1.5 3.0 4.0 

(0.4 - 1.0) (0.8 - 3.2) (1.1 - 1.9) (2.2 - 3.8) (2.8 - 5

w/low-energy scrubberd 0.5 1.0 0.8 1.5 4.0 w/venturi scrubbere Neg Neg 0.1 0.2 4.0 w/baghousef Neg Neg 1.5 3.0 4.0 w/electrostatic precipitatorg Neg Neg 1.5 3.0 4.0 

Pressed and blown

Uncontrolled 8.4 17.4 2.8 5.6 4.3 

(0.5 - 12.6) (1.0 - 25.1) (0.5 - 5.4) (1.1 - 10.9) (0.4 - 1

10/86 (Reformatted 1/95) Mineral Products Industry 11.15-5
Table 11.15-1 (cont.).

Process

Particulate Sulfur Oxides N

kg/Mg lb/ton kg/Mg lb/ton kg/M

w/low-energy scrubberd 4.2 8.4 1.3 2.7 4.3 w/venturi scrubbere 0.5 0.9 0.1 0.3 4.3 w/baghousef 0.1 0.2 2.8 5.6 4.3 w/electrostatic precipitatorg 0.1 0.2 2.8 5.6 4.3 

Forming and finishing

Containerh,j Neg Neg Neg Neg Neg Flat Neg Neg Neg Neg Neg Pressed and blownh,j Neg Neg Neg Neg Neg 

Lead glass manufacturing, all processesk ND ND ND ND ND 

a Reference 2-3,5. ND = no data. Neg = negligible. Ranges in parentheses, where available. Expressed as kg/Mg (lb/t

produced. b Not separated into types of glass produced, since batch preparation is the same for all types. Particulate emissions are almost all plants utilize some form of control (i. e., baghouses, scrubbers, centrifugal collectors). c Control efficiencies for the various devices are applied only to the average emission factor. d Approximately 52% efficiency in reducing particulate and sulfur oxides emissions. Effect on nitrogen oxides is unkno

e Approximately 95% efficiency in reducing particulate and sulfur oxide emissions. Effect on nitrogen oxides is unknowf Approximately 99% efficiency in reducing particulate emissions. g Calculated using data for furnaces melting soda lime and lead glasses. No data available for borosilicate or opal glasseh Organic emissions are from decorating process. Can be controlled by incineration, absorption, or condensation, but eff

known. j For container and pressed and blown glass, tin chloride, hydrated tin chloride and hydrogen chloride are also emitted dtreatment process at a rate of <0.1 kg/Mg (0.2 lb/ton) each. k References 6-7. Particulate containing 23% lead.

11.15-6 EMISSION FACTORS (Reformatted 1/95) 10/86
Table 11.15-2 (Metric And English Units). VOC, CARBON MONOXIDE, AND LEAD EMISSION FAC

FOR GLASS MANUFACTURINGa

EMISSION FACTOR RATING: B

Process

VOC Carbon Monoxide 

kg/Mg lb/ton kg/Mg lb/ton kg/M

Raw materials handlingb (all types of glass)

0

0

0

0 ND 

Melting furnacec

Container

Uncontrolled 0.1 0.2 0.1 0.2 ND 

(0 - 0.2) (0 - 0.4) (0 - 0.2) (0 - 0.5)

w/low-energy scrubberd 0.1 0.2 0.1 0.2 ND w/venturi scrubbere 0.1 0.2 0.1 0.2 ND w/baghousef 0.1 0.2 0.1 0.2 ND w/electrostatic precipitatorg 0.1 0.2 0.1 0.2 ND 

Flat

Uncontrolled <0.1 <0.1 <0.1 <0.1 ND w/low-energy scrubberd <0.1 <0.1 <0.1 <0.1 ND w/venturi scrubbere <0.1 <0.1 <0.1 <0.1 ND w/baghousef <0.1 <0.1 <0.1 <0.1 ND w/electrostatic precipitatorg <0.1 <0.1 <0.1 <0.1 ND 

Pressed and blown

Uncontrolled 0.2 0.3 0.1 0.2 ND 

(0.1 - 0.3) (0.1 - 1.0) (0.1 - 0.2) (0.1 - 0.3)

10/86 (Reformatted 1/95) Mineral Products Industry 11.15-7
Table 11.15-2 (cont.).

Process

VOC Carbon Monoxide 

kg/Mg lb/ton kg/Mg lb/ton kg/M

w/low-energy scrubberd 0.2 0.3 0.1 0.2 ND w/venturi scrubbere 0.2 0.3 0.1 0.2 ND w/baghousef 0.2 0.3 0.1 0.2 ND w/electrostatic precipitatorg 0.2 0.3 0.1 0.2 ND 

Forming and finishing

Containerh,j 4.4 8.7 Neg Neg ND Flat Neg Neg Neg Neg ND Pressed and blownh,j 4.5 9.0 Neg Neg ND 

Lead glass manufacturing, all processesk ND ND ND ND 2.5 

a Reference 2-3,5. ND = no data. Neg = negligible. Ranges in parentheses, where available. Expressed as kg/Mg (lb/t

produced. b Not separated into types of glass produced, since batch preparation is the same for all types. Particulate emissions are almost all plants utilize some form of control (i. e., baghouses, scrubbers, centrifugal collectors). c Control efficiencies for the various devices are applied only to the average emission factor. d Approximately 52% efficiency in reducing particulate and sulfur oxides emissions. Effect on nitrogen oxides is unkno

e Approximately 95% efficiency in reducing particulate and sulfur oxide emissions. Effect on nitrogen oxides is unknowf Approximately 99% efficiency in reducing particulate emissions. g Calculated using data for furnaces melting soda lime and lead glasses. No data are available for borosilicate or opal glh Organic emissions are from decorating process. Can be controlled by incineration, absorption or condensation, but effi

known. j For container and pressed and blown glass, tin chloride, hydrated tin chloride and hydrogen chloride are also emitted dtreatment process at a rate of <0.1 kg/Mg (0.2 lb/ton) each. k References 6-7. Particulate containing 23% lead.

11.15-8 EMISSION FACTORS (Reformatted 1/95) 10/86
10/86 (Reformatted 1/95) Mineral Products Industry 11.15-9

Figure 11.15-5. Particle size distributions and emission factors for glass melting furnace exhaust.

Table 11.15-3 (Metric Units). PARTICLE SIZE DISTRIBUTIONS AND EMISSION FACTORS

FOR UNCONTROLLED AND CONTROLLED MELTING FURNACES

IN GLASS MANUFACTURINGa

EMISSION FACTOR RATING: E

Aerodynamic Particle

Diameter, :m

Particle Size Distributionb

Size-Specific

Emission Factor,

kg/Mgc

Uncontrolled ESP Controlledd Uncontrolled

2.5 91 53 0.64

6.0 93 66 0.65

10 95 75 0.66

a References 8-11.

b Cumulative weight % of particles < corresponding particle size. c Based on mass particulate emission factor of 0.7 kg/Mg glass produced, from Table 11.15-1. Sizespecific emission factor = mass particulate emission factor x particle size distribution, %/100. After

ESP control, size-specific emission factors are negligible. d References 8-9. Based on a single test.

References For Section 11.15
References For Section 11.15

1. J. A. Danielson, ed., Air Pollution Engineering Manual, 2nd Ed., AP-40, U. S. Environmental

Protection Agency, Research Triangle Park, NC, May 1973. Out of Print.

2. Richard B. Reznik, Source Assessment: Flat Glass Manufacturing Plants,

EPA-600/20-76-032b, U. S. Environmental Protection Agency, Cincinnati, OH, March 1976.

3. J. R. Schoor, et al., Source Assessment: Glass Container Manufacturing Plants,

EPA-600/2-76-269, U. S. Environmental Protection Agency, Cincinnati, OH, October 1976.

4. A. B. Tripler, Jr. and G. R. Smithson, Jr., A Review Of Air Pollution Problems And Control In

The Ceramic Industries, Battelle Memorial Institute, Columbus, OH, presented at the 72nd

Annual Meeting of the American Ceramic Society, May 1970.

5. J. R. Schorr, et al., Source Assessment: Pressed And Blown Glass Manufacturing Plants,

EPA-600/77-005, U. S. Environmental Protection Agency, Cincinnati, OH, January 1977.

6. Control Techniques For Lead Air Emissions, EPA-450/2-77-012, U. S. Environmental

Protection Agency, Research Triangle Park, NC, December 1977.

7. Confidential test data, Pedco-Environmental Specialists, Inc., Cincinnati, OH.

8. H. J. Taback, Fine Particle Emissions From Stationary And Miscellaneous Sources In The

South Coast Air Basin, PS-293-923, National Technical Information Service, Springfield, VA,

February 1979.

9. Emission test data from Environmental Assessment Data Systems, Fine Particle Emission

Information System (FPEIS), Series Report No. 219, U. S. Environmental Protection Agency,

Research Triangle Park, NC, June 1983.

10. Environmental Assessment Data Systems, op. cit., Series No. 223.

11. Environmental Assessment Data Systems, op. cit., Series No. 225.

11.15-10 EMISSION FACTORS (Reformatted 1/95) 10/86