Evaporation in industrial glass melt furnaces

Process conditions in glass furnaces, especially the settings of the combustion system, determine the rate of the evaporation processes at the glass melt surface. Reduction of volatilization to lower dust and heavy metal emissions, to minimize the refractory attack by the aggressive volatile components, and to limit depletion of volatile glass components at the glass melt surface is of great technological importance. This can be achieved by changes in burner design and burner positioning, optimizing combustion control and avoiding extreme glass surface temperatures. Such high local temperatures at the glass surface may lead to very high concentrations of PbO, NaOH or KOH vapors attacking the crown materials of the furnace. Evaporation model studies show the potential of process measures for the reduction of evaporation and minimizing depletion of alkali, lead or boron compounds at the glass melt surface. Sodium depletion down to 80% of the original content can take place at the glass melt surface, in lead silicate melting processes depletion may reduce the lead concentrations by more than 50%. Industrial tests support the results of modeling studies and show the effects of the settings of the combustion processes on glass-melt evaporation kinetics