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

Two shortcomings of electric furnaces are that the glass produced is insufficiently refined for some
requirements, such as color TV faceplates. Furnace refractories are corroded more rapidly than in combustionheated
furnaces. Several patents have been developed to address the problems in electric melting of residence
time in tank and refractory wear and resultant glass quality. (See Table III.1 for Advantages and Disadvantages
of Electric Melting.)
Table III.1. Advantages and Disadvantages of Electric Melting
Advantages
Very low direct emissions
Potentially increased melting rate per m 2 of furnace area
Improved direct energy efficiency
Lower raw material costs in some cases
Electric melting gives better quality,
more homogeneous glass in some cases
Reduced capital cost and
furnace space requirements
Potentially more simple operation
Disadvantages
High operating cost
Reduced campaign length
Not currently technically and economically
viable for very large-scale glass production
Less flexible and not adapted to large pull variations
for high quality glasses
Associated environmental implications
of electricity generation
• Mixed-fuel furnaces
The method of electric boosting adds extra heat to a glass furnace by passing an electric current through
electrodes in the bottom of a melting tank. It can contribute 2 to 20 percent of total energy input. Many
furnaces install electric boosting for use when needed.
Traditionally, electric boosting has been used to increase throughput of a fossil fuel-fired furnace to meet
periodic fluctuations in demand without incurring the fixed costs of operating a larger furnace. Electric
boosting devices can be installed while a furnace is in operation. Electric boost can be applied to end port, side
port, and unit melters. Practice has shown that electricity applied near the back end of the furnace, where batch
is added, can reduce fossil fuel needs because it lowers the temperature of the melt surface and reduces batch
volatilization.
Electric boosting, which assists glass melting by improving convective currents within the furnace, thus
facilitating heat transfer and aiding refining, became possible when molybdenum electrodes were developed in
the 1950s. The method is commonly used in fossil fuel-fired glass furnaces to increase productivity and furnace
capacity, improve glass quality, and minimize air emissions. More than half of all regenerative tank glass
furnaces were electrically boosted in the 1990s.
In container and float glass furnaces, electric boosting might be limited (