Recycling of cullet and filter dust in the German glass industry

Increasing ecological constraints linked with economic advantages have induced the recycling of cullet predominantly in the container glass industry as well as the recycling of filter dust in various branches of glass production. The recycling of cullet, originating from non-refillable glass packaging was introduced more than 20 years ago, whereas the recycling of filter dust originating from waste gas treatment, was started only a few years ago. The transition from employing basically constant raw materials to utilizing increasing amounts of recycled glass as the major batch material and the introduction of filter dust as an additive (refining agent) have imposed new challenges on glass melting. Difficulties result from the incorporation and possible enrichment of impurity components such as metals and halogens and furthermore from the unknown and changing amounts of organic contaminations. Special efforts will be discussed which help to improve the reproducibility of glass melting with high portions of cullet by employing an in-situ control of the redox state in the glass melt.