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

glass. Electric boost is often used to support the pull rate of a furnace as it nears the end of its operating life or
to increase the capacity of an exiting furnace.
Two approaches to use mixed melting are fossil fuel firing with electric boost or electrical heating with fossil
fuel support, a less common technique. A hot top or mixed melter is usually a conventional all-electric furnace
with supplemental fossil fuel firing added for additional output or to promote gas evolution through the batch
blanket. Although this configuration is much less efficient, it is necessary to produce chemically reduced glass
compositions or to use high cullet ratios.
Electric boosting will reduce the direct emissions from the furnace through partial substitution of combustion
by electrical heating for a given glass pull rate. However, high levels of electric boost are not used on a longterm
basis for base-level production because of high operating costs.
By overcoming technical and economic limitations of electric boosting, more of the environmental benefits of
electric melting could be realized.
III.3. Conclusion
To develop practical glass melting technologies that will meet the requirements of glassmaking in the 21st
century, the basic mechanisms of traditional glass melting must be fully understood. Currently, large-scale
continuous furnaces are used for melting, refining and homogenizing most commercial glasses, whether they be
soda-lime, lead crystal and crystal, or borosilicate glasses.
The conventional method of providing heat to melt glass is to burn fossil fuels above a batch of continuously
fed batch material and to withdraw the molten glass continuously from the furnace. The melting process for
silica-based batches can be classified into three groups: particle melting, blanket melting, and pile melting. The
melting technique used depends on the capacity needed, the glass formulation, fuel prices, existing
infrastructure, and environmental performance.
For the energy-intensive process of glass melting, fuels are either fossil fuels (for recuperative, regenerative,
pot/day or unit melter furnaces); oxy-fuel; electric furnaces; or mixed-fuel (fossil fuel electrically boosted).
More than 50 percent of industrial glass furnaces in the US are regenerative furnaces. Because oxygen-fired
furnaces do not involve radical redesign of fossil fuel furnaces, they require relatively low risk in converting to
oxy-fuel, and some 25 percent of the glass furnaces in the US have converted to this technology in the past
decade. Electric furnaces produce a homogeneous, high-quality glass while reducing polluting emission.
Electric boosting can increase the production of a fossil fuel furnace and is less costly than expanding furnace
capacity for higher production.
Current glass melting technologies are adaptations of the continuous, large melter furnace Siemens design and
each provides alternative methods of melting for requirements of specific types of glasses. A furnace is chosen
for its ability to address the main concerns of glassmakers: dissolution of all solid particles, homogenization,
and removal of gaseous products. See Section Two, Chapter 1, for a Primer of Glass Melting.
58