As part of the ZeroCO2-Glas project, a revolutionary glass melting process in connection with a new type of glass melting tank is to be developed in an all-encompassing approach, with which glass for container production can be melted in a CO2-neutral manner. The actual glass production takes place in a glass melting tank, namely the melting of the glass from the raw material mixture and from the melting of recycling cullet. Melting is the most energy-intensive step in the glass production process. To achieve CO2 neutrality, R&D work must be carried out on the following points:

Container glass is currently made of a mixture of

  • Sand (SiO2),
  • Soda (Na2CO3),
  • Lime (CaCO3) or dolomite (CaMg (CO3)2)),
  • Recycling cullets as well as
  • Other ingredients (e.g. for coloring) melt it.

With soda and lime or dolomite, CO2 is introduced into the process and released. As part of the project, an alternative raw material quantity is to be developed to avoid the entry of CO2 into the process. To this end, various approaches will be examined: Soda should be completely avoided on the basis of a new, innovative composition of container glass almost without sodium. A patent based on preliminary work is in filing. Nevertheless, sodium necessary in small quantities should be replaced by sodium hydroxide

At the moment, glass melting furnaces are almost exclusively fired with air or oxygen by burning natural gas. This releases CO2 in the exhaust gas. The project aims to develop the conditions for the combustion of hydrogen with oxygen. The combustion of hydrogen/oxygen only produces H2O, i.e. water, which can be split into hydrogen and oxygen by means of hydrolysis. In addition to “clean” combustion, another advantage of the use of hydrogen and oxygen is that both can be produced using regenerative electricity. However, the natural gas used so far cannot easily be replaced by hydrogen. For example, because hydrogen burns with a flame that has other properties (energy content, heat conduction, heat radiation, speed, etc.) as a natural gas flame. Therefore, for example, the shape and length of the flame have to be changed. In addition, the burner and the entire furnace must be adapted to the increased seizure of water vapor. The fuel change also influences the glass quality and the flue gas. To this end, appropriate technical measures and/or the operational management concept shall be adapted.

The innovative glass melting furnace is designed as a hybrid heater with hydrogen and electricity in the range 80-20 %/20-80 % of the two energy sources. It can be fueled with hydrogen or natural gas on the burner side. However, it is not bivalent in the strict sense between these two fuels, because the burners have to be exchanged for the change of fuel.

Whether container glass can actually be produced CO2-neutrally depends on the technical design of the glass melting furnace. Therefore, an innovative design will be developed within the framework of the project, characterized by the following main features:

  • Division of the glass melting furnace into a deep melting furnace and a deep working tray through an intermediate flat purifier area (Semi-segmentation, Space Utilization) In conventional glass melting furnaces, convection flows support the melting process. The convection currents should, if possible, form a double roller. However, this also results in a relatively long residence time of the glass in the furnace, because most of the glass does not leave the furnace directly but enters the convection stream. Furthermore, as a quality problem, fresh, strongly bubble-containing melt and already melted glass repeatedly mix through the convection currents. In the novel glass melting furnace, these effects are to be avoided in order to significantly shorten the melting process without loss of quality and to significantly reduce its energy requirements. This is to be achieved, among other things, by the greater separation of the melting process from the purification and by the creation of a vortex within the glass melt (see also electrodes).
  • Loading of the particularly conditioned raw material batch from below the glass level into the glass melt (Submerged Feeding, Layered batch) As described above, burnt lime and dolomite dust strongly and NaOH is strongly corrosive. Therefore, they cannot be used in conventional glass melting furnaces in which the loading takes place from above the glass melt. The loading of below the glass mirror into the glass melt is the prerequisite in order to be able to use burnt lime or dolomite and NaOH at all. By conditioning the batch before loading (layered batch), the raw materials are protected from dust during loading and corrosive-acting NaOH is encapsulated. In addition, the layered batch can positively influence melt kinetics. In addition, the flow of the batch introduced into the furnace by the melt strengthens the preheating of the batch. In contrast to the mixture on the melt, the hot flow introduced by the burners can reach the melt more freely.
  • Electrodes on the bottom or in the side walls of the melting furnace (Vortex Melting) The electric boosting of the melt enables very precise and flexible control of the melting process. Furthermore, the electrodes are intended to produce a defined vortex within the glass melt, which would lead to a faster melting of the mixture and dissolving of the sand particles. This effect results from the interaction of the melting furnace (see above) with the electrodes. In summary, the above three technical features of the innovative glass melting furnace are intended to completely avoid CO2 emissions and optimise the melting process, thereby significantly reducing energy.

It would be optimal if the development objectives were to be achieved at a), b) and c) equally. However, it should also be possible to load the innovative glass melting furnace with a conventional batch of raw materials and/or to fire it with natural gas.

The aim of the project is to create a prototype (Mini Melter) of a glass melting tank with a processing capacity of approx. 2.4 t/day. This is to be scaled up to industrial scale after successful completion of the project applied for funding by combining physical and computer-based modelling results. The outstanding feature of the ZeroCO2-Glass project is that CO2 is completely avoided both on the energy input side and on the raw material side. In comparison, other projects aim exclusively at CO2 avoidance on the energy input side.