Using green electricity instead of gas: more environmentally friendly production for brown glass tested

The production of amber glass in Germany emits around 0.58 million tonnes of CO₂ per year. A new method will soon make the process more environmentally friendly: In a research project, researchers at TU Bergakademie Freiberg have further developed an all-electric melting process for the production of amber glass and tested it on a laboratory scale. The so-called glass melting tank is heated entirely with electricity instead of natural gas: around 86 per cent of CO₂ emissions could be saved in this way. This corresponds to the annual CO₂ emissions of around 77,000 households. In addition, the amount of colour or sulphur carrier can be halved.

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Brown jars are mainly used for packaging medicines and light-sensitive foods. A brown colour carrier (in this case sodium sulphate as a sulphur carrier, iron oxide and reducing agent) is added to the raw material mixture, the so-called glass batch, for production. This mixture is melted in a gas-heated glass melting tank at temperatures of up to 1,500 °C. Heating the furnace purely electrically is not yet industrially feasible according to the current state of the art - the stability of the colour and the batch, which is crucial for stable process conditions, poses a particular challenge.

Utilise renewable energy directly

In an all-electric melting plant on a pilot plant scale, a team from the Institute of Glass Science and Technology at TU Bergakademie Freiberg has succeeded in identifying the factors that previously prevented the colour carrier in the electric glass melting tank from reliably producing the brown colour.

The plant uses the so-called cold-top process: an insulating layer of cool mixture lies on the glowing melt like a lid. "Although this saves a huge amount of energy, it makes it much more complicated to precisely control the chemical reactions and the escape of gases inside," explains project manager Dr Khaled Al Hamdan.

A special composition of colour carrier, reducing agent and refining agent has proven to be particularly suitable for the reliable formation of the brown colour body. "The ratio of the mixture additions differs significantly from traditional melting processes. By modifying the proportions of colour and reducing agent as well as the temperature profile and the top of the batch, we were able to overcome these obstacles," says Dr Khaled Al Hamdan.

In the laboratory, the team was able to prove that the production of amber glass in the all-electric melting system is reliable and of high quality. "We were able to guarantee an absolutely constant colour and at the same time stabilise the so-called cold batch blanket," explains Dr Al Hamdan. The new melting process is now being tested in cooperation with industrial partners and could make the production of amber glass much more environmentally friendly in the future

The 01IF22664N project was funded by the Federal Ministry for Economic Affairs and Energy from January 2023 to January 2026 based on a resolution of the German Bundestag.

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