Increased Cullet Use

The use of cullet in a glass furnace can significantly reduce the energy consumption because cullet has a lower melting energy requirement than the constituent raw materials – as the endothermic chemical reactions associated with glass formation have been completed – and its mass is approximately 20 % lower than the equivalent batch materials (IPTS/EC, 2013. p.214). However, some of the energy savings can be offset by the energy requirements in crushing, cleaning, sorting, and transportation of the cullet. In addition to energy savings, cullet use reduces the amount of raw materials used, decreases energy use in producing the raw materials, and increases the life of the furnace by up to 30% due to decreased melting temperatures and a less corrosive batch (Worrell et al., 2008. p. 67). Cullet is also easier to preheat than raw materials, and its use can increase the output of the furnace. Cullet use is generally applicable to all types of furnaces, i.e. fossil fuel-fired, oxy-fuel-fired and electrically heated furnaces. Most sectors of the glass industry routinely recycle all internal cullet, with the exception of continuous filament glass fibre production (IPTS/EC, 2013. p.314).

Cullet can be internal (rejected glass from the production line) and external (post-consumer glass from consumer or external industrial sources). The composition of external cullet is difficult to define accurately and due to quality concerns caused by the impurities, its usability in certain product groups – notably luxury container glass, tableware, special glass and flat glass – remains limited. Container glass segment, on the other hand, can use significant quantities of external cullet. In the EU, external cullet use in container glass production varies from <20% to >90, with the average being around 50%. Internal cullet usage is limited by the availability of cullet at the correct quality and composition. In general, the average amounts of internal cullet used are around 25 % for soda-lime products, although amounts as high as 50 % are possible depending on the type of article produced; for lead crystal, average amounts of 35 % are normally applied (IPTS/EC, 2013. p. 314).

Cullet use, however, is not free from disadvantages such as the following:

  • Metallic impurities, such as bottle caps or foil from wine bottles, can cause significant refractory damage and shorten furnace life;
  • Presence of ceramic will lead to quality problems and will result in rejects;
  • At high cullet levels, composition and therefore the physical characteristics will be hard to control, potentially causing quality problems;
  • Organic content in cullet may lead to color and refining difficulties;
  • Presence of aluminum in cullet may significantly reduce mechanical strength of end products;
  • Impurities may give rise to undesired air emissions. (IPTS/EC, 2013. p. 315)
Development Status Products

Increased Cullet UseCosts & Benefits

Parent Process: Melting and Refining
Energy Savings Potential

As a general rule, every 10 % of extra cullet results in a 2.5 – 3.0 % reduction in furnace energy consumption (IPTS/EC, 2013. p. 314)

Based on a study in german-speaking European countries, energy savings are estimated at around 8 MJ for every percent increase (by weight) in cullet use (Worrell et al., 2008. p.67)

CO2 Emission Reduction Potential

The use of cullet generally results in significant cost savings as a result of the reduction in both energy and raw material requirements. Economics will depend on availability and cost of cullet.

Increased Cullet Use Publications

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Increased Cullet Use Reference Documents

Best Available Techniques (BAT) Reference Document for the Manufacture of Glass

As a reference of the EU Industrial Emissions Directive (2010/75 EU) this new version provides extensive information on Best Available Techniques (BATs) applicable to European Glass Manufacturing Industry for reducing environmental impact. The document is prepared by the  Institute for the Prospective Technological Studies of European Commission's Joint Research Center. 

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