ESE: Mr Fleischmann, which area of industrial glass production requires the most energy?
Industrial glass production can be subdivided into raw material processing, melting, forming and annealing. Glass is melted at temperatures of up to 1500 °C. This process requires the most energy. This high temperature allows for both product quality and quantity. Fuels cover about 75 percent of energy consumed annually. In Germany, that is about 53 petajoules of fossil fuels. That equates to nearly five percent of the transportation sector’s energy requirements.
ESE: Do glass production facilities already use energy storage solutions to increase the efficiency of the glass manufacturing process and reduce carbon emissions?
The glass industry has already been using heat storage technology in glass melting furnaces for over 150 years. The Siemens brothers integrated a regenerator into a glass melting furnace for the first time in 1867, establishing it as an important component. Since then, the exhaust gases released in the combustion process have been used to preheat the combustion air for the melting process. On account of the high medium temperatures (exhaust gases up to 1500 °C), ceramic stones serve as a heat storage medium, storing the heat for about 20 to 30 minutes and then releasing it.
ESE: How much energy can be saved by employing this high-temperature storage system?
This short-term displacement storage allows for enormous energy savings. About a third of the energy required for melting the glass is covered by the preheating of the combustion air with the support of the regenerator chambers. This adds up to about 16 petajoules in Germany each year, which goes to show that the regenerator contributes significantly to reducing carbon emissions. However, the physical optimum of this principle has nearly been reached.
ESE: Where is there still potential for carbon emissions reduction in glass production?
This is precisely the topic of the HVG’s Kopernikus study “Flexibilitätsoptionen in der Grundstoffindustrie II” (Flexibility options within basic industry II), which was funded by the German Federal Ministry of Education and Research. We worked together with our partners to investigate two primary questions: Can additional heat storage units be integrated into the existing process chain? And, against the background of expanding energy production from volatile renewable sources, can parts of the process chain be electrified and the process’s energy supply secured with the help of heat storage units? The electrical energy currently consumed in glass production corresponds to about 25 percent of all the energy required in the process.
ESE: Which area of production did you concentrate on in your investigations?
We concentrated on both the melting process and the cooling process which follows the forming process. Purely electric manufacturing is hindered by two obstacles. First of all, the industrial glass production process comprises a tightly interlinked process chain with directly linked steps. Since electricity is not guaranteed to be available at all times, this poses a challenge that is yet to be resolved. Second of all, this type of manufacturing is not guaranteed to be profitable with current electricity prices. Moreover, adapting the electrical infrastructure would be extraordinarily expensive, as drawing multiple megawatts of additional electricity would become necessary. Guaranteeing flexible and reliable operation would require temporary storage solutions which are not yet available at the technical scale.
ESE: Do you see any potential for reducing carbon emissions in the cooling portion of the glass manufacturing process?
Yes, this is possible. Current technology relies on gas burners for annealing the glass – a process which allows the glass to cool evenly, eliminating stress. If this process is not completed properly, the glass is more prone to fracture. As part of the Kopernikus study, we examined whether air which is heated by electrical energy can be used for annealing. We do not currently perceive this as easily achievable since it would require introducing high heat transfer densities into a very small space. But it is not impossible.
ESE: What steps can the glass industry take towards decarbonisation?
One specific characteristic of glass manufacturing cannot be forgotten: The furnaces are in operation for up to 20 years without interruption. That means that innovations in furnace construction will not manifest themselves in glass factories overnight, but rather will be introduced gradually over time.
There will be a comprehensive grouping of potential solutions in the medium and long term, which all together will significantly reduce carbon emissions in the glass manufacturing industry. In addition to green power, synthetic fuels such as methane and hydrogen will play an important role in the decarbonisation process, as will overall increased energy efficiency. The glass industry is already well on its way to achieving carbon neutrality in the medium term.
ESE: Are you experiencing increased economic pressure to decarbonise glass manufacturing?
Yes, the glass industry is under the same pressure as other industrial sectors, and not just commercially. Our industry faces many tough challenges, including legislation and continuously rising prices for carbon emission allowances. We in the glass industry are also in competition with other packing material industries such as plastic and paper, always contending for the lowest carbon footprint, amongst other advantages. There is also continuously growing demand from our customers – for example the food industry – for carbon-neutral packaging, because that is what the end customer is looking for.
