Konfektionierung von Rohstoffgemengen der Glasindustrie mit dem Ziel einer Steigerung der Umsatzgeschwindigkeit

The failoring of raw materials is driven by the intention to increase the conversion rate of those to a glass melt. In the current work the development rests on an earlier finding by Niggli 1913, and on the observation that the entire amount of limestone and dolomite in a batch can be liquefied by a reaction with soda ash to a salt-like low-viscosity melt below 950 °C. The optimized carbonate can be realized in different ways, e.g., by introducing double carbonate as a novel raw material from the start, or by segmented batching strategies. The new raw material is manufactured by melting sodium carbonate and limestone. This generated double carbonate is characterized thermodynamically newly and kinetically. First, with the help of data out of literature, the exothermal formation of the double carbonate could be verified. As another result of the thermodynamical analysis, it can be shown that for the production of 1 t of glass for a reference batch as well as for a batch including the double carbonate the specific heat Hex is about 610 ± 3 kWh/t. The ± is based on the uncertainties of the calculation of the enthalpy of formation for the different raw materials. Particularly the H° of a natural Dolomite, which is used in the reference batch not in the batch with double carbonate, can deviate ± 1-2 %. Another interesting question is the rate determining mechanism of this accelerated batch melting, which can be identified with measurement to get the reaction order of the CO2-release of the double carbonate as about ~1. The formation of the double carbonate is an exothermic reaction. In comparison the conversion of a conventional limestone is faster than a double carbonate, but the limestone decomposes to calcium oxide, which constrains the following reactions. However, the double carbonate reacts to a salt-like carbonate melt. The conversion to a salt-like melt needs a few seconds more of time, but in general the reaction with the other raw materials to a glass melt is accelerated. The double carbonate is characterized by using X-ray diffraction and is then tested in a batch by using an up-scaling method from mg to kg range. A significant acceleration is seen at scales stretching from the grain-to-grain to the 10 kg range. As a result it can be reported that a significant increase of the conversion rate can be realized. Therefore a batch with double carbonate melts about 60 K lower than a batch of conventional raw materials, and within 10 % less time