The role of gases in glass melting processes

Abstract

The formation of gases and vapors during glass melting and the interaction between furnace atmospheres and industrial glass melts have an important impact on the emissions of glass furnaces, the glass properties and the quality of the glass products. Degassing or fining of glass melts is necessary to obtain a glass without gaseous inclusions. A simulation model has been developed which describes the behavior of gas bubbles in glass melts, depending on the process conditions. This model can be used to optimize the fining process in industrial furnaces. Foam formation on top of glass melts blocks the radiation from the combustion chamber of glass furnaces into the melt. Laboratory tests are used to find practical ways to reduce foaming during melting of sulfate-containing glasses. These tests show the importance of the furnace atmosphere on foam behavior in glass meldng tanks. Volatilization is the major source of particulate emissions in most glass furnaces. Volatilization rates from glass melts can be reduced by lowering the hot-spot temperatures and local gas velocities directly above the melt. One of the most important issues for glass makers today is the NOₓ formation of fossil fuel-fired furnaces. Results from West European glass producers show the possibility to decrease the formation levels of NOₓ by delayed mixing of the fuel and the oxidant and by intelHgent combustion control. Increased levels of water vapor in the glass furnace atmosphere will give higher water concentrations in the glass melt. In water rich glass melts, the sulfate retention will be often much less than in glasses molten in dry atmospheres. The water vapor effects the viscosity, radiative properties and the redox state of the melt. Because of these effects, the color of glasses molten in oxy-fuelfired furnaces, with high water vapor concentrations, may be different from glass molten in air-fired furnaces, using the same batch composition.