Glass Melting Technology: A Technical and Economic ... - OSTI

preparations are beneficial. These factors enhance the initial melting rate, which leaves
smaller silica grains for later stages and thus reduces their buoyancy force.
When a part of sodium oxide is introduced by sulfate, the degree of segregation decreases
as the fraction of sulfate increases. This behavior is attributed to better wetting of silica
grains at early stages of melting if sulfate is added, which leads in turn to a more uniform
spatial distribution of silica grains in the melt. The stirring action of bubbles produced by
sulfate decomposition at high temperatures helps to overcome other mechanisms causing
melt segregation. This helps remix the demixed melt and sweep other gas bubbles from
the molten material, and decreases the time to dissolve refractory components.
Initial melting within a batch pile can be influenced by the furnace atmosphere. Levels of
combustibles (CH4, CO or C) above the melt on a continuing basis can be compensated
for by adjusting batch redox components. Some ingredients, such as carbon or niter, are
intentionally added for this purpose. Short-term variations can have some differing
influences on the glass, as judged by the ferrous to ferric iron ratio or varying redox
sensitive components such as SO3. Cullet reuse can contribute significant redox
influences from organic contaminants or non-standard glass compositions being present.
The physical geometry of the batch piles can make these additions more or less effective.
Well-wetted batch produces a batch pile with a high volume-to-surface ratio, and it also
has a high saturation of water from initial vaporization.
The rate of volatile species from other materials can also be influenced by the furnace
atmosphere. This is especially true for alkali and borates attempting to reach equilibrium
with the atmosphere. Higher natural concentrations in the furnace atmosphere (due to
longer dwell time in the melter) will result in lower volatile loss rates from the melt and
greater retention in the glass. The higher concentration of water in the atmosphere of oxyfuel-fired
furnaces can significantly increase the rate of volatilization.
Raw material particle size ranges and properties can result in dusting properties being
exhibited in the furnace environment. Some limestones have a “popcorn” decomposition
effect called decrepitation, which requires extra batch-wetting efforts. Air and gas
velocities will have an influence on the extent to which some of these reactions can
influence glass chemistry and resultant quality. Regenerator plugging and superstructure
refractory concerns must be addressed with the furnace’s influence on volatile condensate
properties.
Similarly, charging practices can result in refractory concerns triggered by volatile
dusting and condensate changes. These problems relate to the reactivity of certain
chemical reactions that, over a period of time, can affect structural life issues and also
jeopardize quality through reaction product contamination entering the glass.
Glass-forming constituents must be understood and controlled to minimize their influence
on the dissolution of container walls, interactions with electrodes, evaporation, absorption
of gases from the atmosphere, demixing and reboil. Refractory walls may be a source of
stones, bubbles and inhomogeneities. Reboil reintroduces bubbles on reheating. In
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