A glass melting furnace is designed to melt raw materials into glass. Depending on the intended use, there are various designs of glass melting furnaces available. They use different power sources. These sources are mainly fossil fueled or by fully electric power. A combination of both energy sources is also realized. A glass melting furnace is made from a refractory material.
Basics The glass raw materials are fed to the glass melting tank in batches or continuously. The components (the batch) are melted to form a liquid glass melt. In addition to the basic components, the batch also contains cullet from recycled glass to save energy. The cullet content can be up to approx. 85% - 90% (green glass), depending on the requirements of the desired glass color. When changing the glass color (recoloring), the entire process often takes several days in large glass melting furnaces. For economical operation, the glass melting furnaces are operated around the clock throughout the year for so-called mass glass (hollow glass, flat glass). Apart from one to max. two smaller planned intermediate repairs, during which the furnace is taken out of operation, a so-called furnace journey (campaign) up to the general repair (rebuild) can last up to 16 years and more (depending on the product group). The capacity can range from about one ton to over 2000 tons and the daily throughput can range from a few kilograms to over 1000 tons. The operating temperature inside the furnace, above the so-called glass bath is about 1550 °C. This temperature is determined by the composition of the batch and by the required amount of molten glass - the daily production - as well as the design-related energy losses. Glass furnaces are operated with a flue gas heat recovery system to increase the energy efficiency. The reduction in CO2 emissions required, due to the climate change mitigation, has led to various concepts to reduce or replace the use of fossil fuels, as well as to avoid the CO2 released during the melting of the batch through an increased recycling content.
Day tanks
This historical type of glass melting tank produces in batches (discontinuously); it is used to melt glasses that are only required in small quantities. The maximum melting area of day tanks is 10 m2, and the melting capacity is between 0.4 and 0.8 t/m2 of melting area. The pot furnace is one type of this. The furnace consists of a refractory masonry basin with a depth of 40 to 60 cm (bottom furnace), which is covered with a vault with a diameter of 70 to 80 cm (top furnace). At the beginning of the 21st century, day tanks still existed in some mouth glass works and artisan workshops, as well as in some special glass manufacturers, where small quantities of high quality glass are melted, e.g. optical glass. Day tanks are not taken out of service at the end of the day; the temperature is simply lowered overnight. Since the refractory material typically cannot tolerate large temperature changes and this leads to increased corrosion (consumption) of the same, such rapid cooling cannot occur anyway. If the day tank is taken out of operation, e.g. for maintenance, cooling/heating times (two to several days) must be observed which are adapted to the refractory material. Smaller furnaces (studio furnaces) in artisan studios are excepted. There, the refractory lining is designed accordingly.
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