Glass is produced by melting raw materials (mainly silica sand, soda ash and limestone), and often cullet (recycled container glass or waste glass from manufacturing) in glass furnaces of different sizes employing different technologies. Glass products and their characteristics, as well as the production and processing routes involved in their production show large variations. However, batch preperation, melting and refining, conditioning and forming, and finishing (annealing, tempering, polishing or coating) steps are found in virtually all glass plants and are the most important from an energy point of view.
Melting furnaces – employing combustion-heating (with air-fuel or oxy-fuel burners), direct electrical heating, or a combination of the two (electric boosting) – are the major energy users. In general, the energy necessary for melting glass may account for over 75 % of the total energy (in terms of final energy) requirements of glass manufacture, with an average of about 65 % of the total energy input when considering all the sectors of the glass industry4. Typically, melting furnaces operate with an overall efficiency of 50 – 60%, and 20 – 25% of the energy input to glass production is lost from structures and 25 – 35% is lost with the flue gases2. Melting furnaces are also the most important area for efficiency improvement, followed by followed by refining and conditioning5.
Improved process control, increased cullet use, increased furnace size, use of waste heat in batch and cullet preheating or in steam generation, use of oxy-fuel technologies, and reduction of rejects are the major energy saving efficiency opportunities for the sector2.
Although theoretical minimum energy use is 2.8 GJ/t for soda-lime glass and 2.35 GJ/t for borosilicate and crystal, in practice average energy use varies between 5.75 – 9/0 GJ/t.
Energy intensity in glass furnaces can show high variations, depending on the size and technology of the furnace and the amount of cullet used. Based on analysis for 123 container glass and 23 float glass furnaces the energy intensity of continuous glass furnaces in Europe and the United States were reported as 4 – 10 GJ/t of container glass and 5–8.5 GJ/t of flat glass. The most energy efficient furnace identified in this study shows an energy consumption of 3.82 – 3.85 GJ/t, based on 50% cullet and taking into account the primary energy consumption for electricity generation2.
As different glass products have different characteristics and different production routes, significant variations are also observed in the energy requirements of different glass products. In the table below, typical specific energy consumption values attained with the use of energy efficiency measures are provided.
Furnace Energy Consumption
(GJ/tonne melted glass)
Overall Energy Consumption
(GJ/tonne finished product)
|Bottles & Jars||<100 t/d||5.5 – 7||<7.7|
|>100 t/d||3.3 – 4.6|
|Electric furnaces||2.9 – 3.6|
|<100 t/d||7 – 9||<16|
|>100 t/d||4.8 – 6|
|All capacities||5 – 7||<8|
|Continous filament glass fibre|
|All capacities||7 –14||<20|
< 24 for capacities < 100 t/da
< 18 for capacities > 100 t/d
|<100 t/da||6.7 – 9.5|
|>100 t/d||5 – 6|
|Electric furnacesb||3.4 – 4.3|
|All products||Electric furnacesb||3.9 – 4.5||20 <|
|Soda-lime glas||Conventional furnaces||5 – 10|
|Borosilicate glass||10 – 15|
|Glas wool||All capacities||2.7 – 5.5||< 14|
|Stone wool||All capacities||4.2 – 10||< 12|
|High temperature insulation wool|
|All capacities||6.5 – 16.5||< 20|
|Oxy-fired furnaces||≤ 9|
|Air/fuel & enriched air/fuel furnaces||≤ 13|
a : Values do not include installations equipped with pot furnaces or day tanks which energy consumption for the melting process may be in the range of 10 – 30 GJ/tonne melted glass.
b: Data reported refer to energy at the point of use and are not corrected to primary energy.
The glass industry is divided into four major segments. These segments and their approximate market shares, as of 2008, are as following:
- Container glass (45 %)
- Speciality glass (33 %)
- Flat glass (16 %) and,
- Fibre Glass (6 %)6 .
Even though flat glass accounts only about 16% percent of the global glass industry, most information on market structure focus on this segment. The global market for flat glass in 2010 was approximately 56 million tonnes. This is dominated by Europe, China and North America, which together account for around three-quarters of global demand for flat glass. Of total global market demand in 2010, it is estimated that 33 million tonnes was for high quality float glass, 1 million tonnes for sheet glass and 2 million tonnes for rolled glass. The remaining 20 million tonnes reflects demand for lower quality float, produced mainly in China. The significance of China as a market for glass has been increasing rapidly since the early 1990s as the country has become more open to foreign investment and the economy has expanded. In the early 1990s China accounted for about one fifth of world glass demand, but now accounts for 51%7.
The glass industry is dominated by set of large manufacturers active primarily in the flat-glass and glass-container sectors.
Since the 1960s, the glass industry as a whole has reduced specific energy consumption by approximately 1.5 % per year. Today this figure is lower, as the thermodynamic limits are approached8.
This section provides information on the various international and national organizations that focus on energy efficiency in the glass industry.
This section contains information on the various international and national programs that focus on energy efficiency in the glass industry.
- organizational practices and policies;
- team development;
- planning and evaluation;
- tracking and measurement;
- communication and employee engagement and;
- evaluation and corrective measures (US EPA, 2010).
While an EnMS can help organizations achieve greater savings through a focus on continuous improvement in energy efficiency, it does not guarantee energy savings or carbon dioxide reductions. To achieve cost savings, an EnMS must be combined with effective plant energy benchmarking and appropriate plant improvements.
This page will be updated with examples of EnMs implementation in the glass industry.