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Boosting the environmental return on glass recycling

15/04/2010

  • Recycling,
  • Waste
  • Italy
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The MEIGLASS Life project developed an innovative process for recovering greater amounts of quality glass from broken or waste glass returned for recycling with less energy use.

When using recycled glass, the glass-container industry requires ‘oven-ready’ cullet – broken or waste glass – free from all contaminating substances such as ceramics, chinaware, stones, plastics or organic matter. If such contaminants are not removed, they can produce heavy foam on the melt surface. This in turn reduces the heat transfer from the flame, creates glass fining problems and increases energy consumption.

In preparing suitably clean cullet, treatment plants inadvertently discharge large amounts of glass with the non-glass contaminants during the washing process. The inexact nature of this process means 23 to 25% of the glass in the collected cullet ends up in landfill.

To address this problem, Italian mineral-treatment company Sasil and Joanneum Research in Austria developed a solution to improve the processing of cullet collected from domestic recycling points, or from rejected or recovered car windscreens. Sasil used its experience in mining different types of material used in the production of glass and ceramics to adapt a treatment process for natural minerals to cullet cleaning.

The new process can recover 98% of the glass content, greatly reducing the amount destined for landfill. It uses floatation to separate out the plastics – particularly post-consumer plastics (PCPs) – when the cullet is suspended in water. Windscreens are crushed to facilitate removal of polyvinyl butyral (PVB) and then ground up.

In addition, the separated-out plastics are converted into energy to power the cleaning process. PCPs and PVB are fed into a pyrolysis plant, which produces a mix of methane and butane without emissions. This gas is fed into a turbine to produce electrical and thermal energy for the production processes, increasing self-sufficiency.

MEIGLASS significantly improved the quality of the processed cullet. By reusing cleaner washing water, the system has in turn produced a material known as glassy sand, containing lower organic compounds. This product behaves better during the melting process used by the glass-container industry.

To evaluate the quality of this glassy sand, industrial trails have been carried out with leading Italian glass-container companies. The improved quality of the cullet has been recognised by these companies and has translated into increased sales for Sasil.

The three-year MEIGLASS projects had a total budget of €6 million of which €1.3 million came from the EU Life programme. By developing this innovative process, Sasil has provided the glass-container industry with a greater amount of high-quality recycled glass, enabling the further reduction of primary material and energy use.

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