Refractory Degradation in Glass tank Melters. A Survey of Testing Methods

The major objective in glass tank melters is to optimize the entire process by reducing the maximum temperature of melting, improving refractory performance and/or improving melter fuel efficiency. The required characteristics of refractories used in melters are: thermal shock resistance, corrosion resistance, controlled expansion behavior, low thermal conductivity, and adequate creep resistance. The corrosion of the refractories in the melter may be due to batch carryover (lime, soda, fluorides, lead oxide, borax, silica, other glass constituents), volatile fluxes (i.e., volatile alkali oxides penetrating pores, where solid, liquid, and gas coexist), and melt attack, mainly at the metal line. Erosion often follows the initial corrosion, washing away refractory grains after the original bond has dissolved. Corrosion test designs are usually based on operation and reaction temperatures, reaction rates, and the formation of coatings on the refractory surface. Refractories for glass furnaces normally are limited to compositions based on A12O3, ZrO2, and SiO2, with or without Cr2O3. Alumina-zirconia-silicate (AZS) refractories in contact with molten glass form a viscous silicate layer adjacent to the refractory thus restricting contact, and therefore, increasing corrosion resistance. When AZS blocks are used in superstructures, they are exposed to high temperature combustion products. At temperatures above 1475 0C, the bond strength between the embedded ZrO2 crystals and the alumina is reduced, attributed to the variation in the thermal expansion characteristics of A12O3 and ZrO2. Superstructure and crown refractories are subjected to corrosive reactions with the vapor species of the batch components and batch carryover. In the melting of soda-lime glasses, the vapor species are primarily soda and sodium sulfates; for borosilicat