Glass: Blueprint for the industry of the future

If we succeed in drastically reducing carbon dioxide (CO₂) emissions in the glass industry, then it will work everywhere else too. That sounds like a bold claim. But it’s not entirely far-fetched. “The lessons we are learning in our project can be applied to many other industries. And hydrogen plays an important role in this,” says Hendrik Schricker from the Chair of Technical Thermodynamics (LTT) at RWTH Aachen University.

The LTT is one of three RWTH institutions collaborating with glass manufacturer Saint-Gobain in the COSIMa funding project to drastically reduce CO₂ emissions in glass production. COSIMa stands for: CO₂-neutral Saint-Gobain industrial site in Herzogenrath – feasibility study. It is a funded project of progres.nrw. The other RWTH institutes involved are the Institute for Industrial Furnace Technology and Heat Engineering (IOB) and the Institute for Power Generation and Storage Systems (PGS). The Gas and Heat Institute Essen e. V. (GWI) is also involved in the project, which will end in 2025.

“We can deliver results that can be used as a template for various glass manufacturing sites,” explains Daniel Jost, one of the scientists involved. They can provide Saint-Gobain with a feasibility study that gives the glass manufacturer a way to solve a problem with many variables. Namely, how best to convert a glass production site to be climate-friendly for the future.

Learning for other industries

The glass sector faces virtually all of the challenges that large parts of industry are facing on the road to climate neutrality. The glass industry requires extremely high temperatures – around 1,600 degrees Celsius – for the most important process step, glass melting.

This is what happens when natural gas is burned. The process releases CO₂, which is harmful to the climate. Thanks to technological advances, emissions have already fallen significantly. In the past, more than one tonne of CO₂ was emitted per tonne of glass produced, but this has now been reduced to half a tonne of climate-damaging CO₂.

According to the Federal Association of the Glass Industry, this currently means emissions of 3.9 million tonnes for 7.4 million tonnes of glass produced in Germany per year. That is around 0.65 percent of the CO₂ emissions reported by the Federal Statistical Office for Germany for 2023. ‘There are larger emitters, such as the steel industry. But if we want to decarbonise holistically, we have to look at every industry,’ adds Hendrik Schricker.

Another special feature of glass is the experience that can be applied to other areas. ‘The melting process is very energy-intensive and accounts for around 80 percent of emissions,’ explains Daniel Jost. The emissions released from the material during melting must also be taken into account. In addition to sand, glass consists of various carbonates such as sodium carbonate (Na₂CO₃) or calcium carbonate (CaCO₃). These release CO₂ during the melting process. Solutions are needed here to capture the emissions.

Twice green: hydrogen and electricity

Most of the CO₂ can be saved by replacing natural gas. Daniel Jost and Hendrik Schricker believe that two approaches can be used simultaneously. “We can replace natural gas with hydrogen. Hydrogen burns at a similar or higher temperature. Production would have to be converted for this. That is feasible,” says Daniel Jost. In theory. In practice, green hydrogen is more expensive than natural gas due to the process costs. It is therefore conceivable that in future a large proportion of the energy required for the melting process will be sourced from electricity. However, a completely electric melting process is technically difficult to implement.

The large melting tanks of the future should therefore be able to do both: run on electricity and hydrogen. The aim is to operate the melting tank electrically as far as possible. Because it has a continuously high energy requirement, batteries and contracts for the guaranteed purchase of renewable energies are becoming increasingly important as a buffer. It will then be necessary to investigate whether sufficient locally generated green electricity is available for the energy-intensive melting process. In addition, the supply of hydrogen via a pipeline is being investigated as an alternative to local hydrogen production. This will enable glass producers to increase their security of supply with a mix of electricity and hydrogen.

The COSIMa team is not only focused on the technical possibilities of the future. ‘We think in techno-economic terms,’ says Hendrik Schricker, explaining that price developments on the energy market are also factored into the calculations. Here, too, the glass industry has a characteristic that is typical of other energy-intensive sectors: it has expensive equipment that needs to remain in service for as long as possible. In the steel industry, this equipment is blast furnaces, and in the glass industry, it is melting tanks.

“These melting tanks are usually in operation for 20 years. Replacing them is expensive and takes a long time,” says Daniel Jost. It is therefore an investment that requires careful consideration at the time of replacement as to how the new system should be designed with a view to the energy system of the future. ‘We try to factor in how energy prices might develop over the service life of the melting pot,’ says Hendrik Schricker. A simple example: today, natural gas is still significantly cheaper than green hydrogen as a fuel gas. Whether this will remain the case over the entire service life, taking CO₂ costs into account, is questionable.

The COSIMa energy optimisation model will be completed in 2025, helping to make the glass industry part of a green future.

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