New silica refractory for oxy/fuel glass melting

Silica brick crowns have a long history of good performance in glass furnaces. Container, float, tableware and TV operations have continued to use silica brick successfully as the need for higher quality has demanded higher operating temperatures. The attributes of silica brick are long life, excellent insulation at low cost, and minimal defects as silica is the dominant glass oxide. Oxygen/fuel combustion has been rapidly replacing conventional direct-fired air/fuel furnaces as well as many recuperative, regenerative and electric furnaces. In this new environment, silica refractories are severely stressed as a consequence of the increased alkali concentrations in the atmosphere over the melt associated with the loss of nitrogen in oxy/fuel combustion. This higher alkali atmosphere can contribute to more rapid slagging and rat-holing in corners, in areas adjacent to thermocouple blocks and at the skew line. This paper shows that, based on laboratory measurements, improvements in the silica refractory can provide a three to four-fold improvement in resistance to alkali attack over commercial silica refractories. Tests included the insertion of samples into a soda-lime container furnace and an alkali vapor test.