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

A variety of products with different quality levels can be produced from a single furnace. Flat glass for
picture frame production has a lower standard than mirror glass. Cosmetic, tabletop condiment jars and
candleholders can all be produced on the same furnace to different standards. Bushing-drawn fiberglass
has different glass quality requirements for chopped strand compared to woven product.
• Changes in product lines or forming technology
Within the refractory lifetime of a glass-melting furnace, forming technology is often implemented on
downstream production lines, often requiring different pull rates or delivery temperatures.
• Melting fuel curtailment or substitution
Seasonal supply of fuel can vary, resulting in curtailment of natural gas and the use of standby fuels
(propane, distillate or residual oils, etc.) and the need to accommodate the melter configuration.
Flexibility of a furnace can be affected by size, but larger melters are usually more energy efficient.
Furnaces that can be easily idled during business cycles may experience shorter refractory life due to
damage from continuous heating and cooling. The Pouchet type, all-electric furnace has significant
flexibility, but is an example of a smaller melter that requires lower capital investment with higher
operating costs. Devices that separate the melting of cullet from raw material batch, such as the Seg-Melt
concept, allow other compromises not possible in conventional furnaces.
A.3. Raw material oxide source selection
To meet service and fabrication specifications, glass products require a number of physical properties.
The oxide chemistry of the glass being produced determines all of these properties. In turn, the raw
material source of the glass oxide determines the glass chemistry. Raw material sources can be
manipulated to produce the same, or similar, glass chemistry. For example, Al2O3 can be obtained from
felspathic minerals, recycled blast furnace slag (calumite), aluminum hydroxide or clay. Alternatively,
melting configuration can accommodate the physical nature and interaction in the glass fusion process of
different raw materials.
The same glass product can be produced by altering the glass chemistry, requiring the use of new raw
materials or eliminating existing ones. The substitution of lithium (LiO2) for other alkalis (Na2O, K2O)
can be justified on the basis of furnace melting performance. One fiber E-Glass producer removed B2O3
from the glass formulation, which impacted the furnace’s melting and refractory requirements.
A.4. Raw material beneficiation
The oxides required to produce a desired glass chemistry most typically come from natural industrial
minerals. The material can be mined and sized in a few steps. Producers must take a number of steps to
improve the quality of the minerals and simultaneously influence melting performance. Refractory
mineral contaminants are removed with froth flotation methods rather than dissolved by excessive melter
temperatures. Grinding sand into a fine particle size has been used successfully to melt difficult glass
(low-alkali) compositions.
Prereaction (or calcination) of limestone has been used for many years to drive off CO2 prior to use in
glass furnaces. This allows the glass furnace to obtain higher pull rates and better glass seed quality.
Recently, synthetic alkaline earth silicates (diopsite, wollastonite) have been produced by prereactions
with silica and lime. Used in existing furnaces, they can increase throughput by approximately 15 percent
with no additional energy consumption. However, this material is often unavailable or costly.
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