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

furnaces generally have better specific energy efficiencies than fossil fuel furnaces, but
the operating energy cost per ton of glass will typically be higher.
Some of the more general factors affecting the energy consumption of fossil fuel–fired
furnaces are outlined below. For any particular installation it is important to take account
of the site-specific issues that will affect the applicability of the general comments given
below. These factors also affect the emissions per ton of glass of those substances that
relate directly to the amount of fossil fuel burned, particularly NOx and SO2.
The capacity of the furnace significantly affects the energy consumption per ton of glass
melted, because larger furnaces are inherently more energy-efficient due to the lower
surface area-to-volume ratio.
The furnace throughput is also important, with all furnaces achieving their most energyefficient
production at the highest production rate. Variations in furnace load are largely
market-dependent and can be quite wide, particularly for some container glass and
domestic glass products.
As the age of a furnace increases, its thermal efficiency usually declines. Toward the end
of a furnace campaign, the energy consumption per ton of glass melted may be up 15–
20% higher than when the furnace was first commissioned.
The use of electric boosting improves the energy efficiency of the furnace. However,
when the cost of electricity and the efficiency of electrical generation and distribution are
taken into account, the overall improvement may be lower. Electric boost is generally
used to increase the melting capability and life of the furnace, as well as to reduce
emissions (per ton of glass melted), rather than to improve energy efficiency.
The use of cullet can significantly reduce energy consumption, partly because the
chemical energy required to melt the raw materials has already been provided. As a
general rule, each 10% increase in cullet usage results in an energy saving of 2–3% in the
melting process.
Oxy-fuel firing can also reduce energy consumption, particularly in smaller furnaces. The
elimination of the majority of the nitrogen from the combustion atmosphere reduces the
volume of waste gases leaving the furnace by 60–80%. Therefore, energy savings are
possible because it is not necessary to heat the atmospheric nitrogen to the temperature of
the flames, and a significantly lower volume of hot combustion products exit the furnace.
Environmental considerations
Pollution from soda-lime glass production is minimal and mostly caused by sodium
sulfate particulate. Similarly, borosilicate glasses have borate compound particulate.
Other soda-lime contaminants include SOx, NOx, CO2, and possibly hydrocarbons.
Secondary controls include scrubbers, bag houses, electrostatic precipitators, and
sometimes optimizing operating conditions. Volatilization of lead, fluorine, and other
species for specialty glass manufacture must be carefully controlled. All-electric melting
and new batching procedures have been helpful in reducing volatilization. Electrostatic
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