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

IV.7.2. Refining zones for electric melters (Saint-Gobain, 1983; Pilkington, 1989;
Trevelyan, 1989; Glaverbel, 1988)
The objective of four patents filed in the 1980s for electric melters was to use a special zone or
compartment to refine electrically melted glass for the required quality of float glass. Patents by
Saint-Gobain (1983), Pilkington (1989), Trevelyan (1989), and Glaverbel (1988) have in
common the idea that refining requires an increase in temperature and convective currents to
raise the molten glass to the surface and avoid return currents. The differences in each method
are the ways in which the currents are organized.
IV.8. Preheating batch and cullet
In the energy-intensive process of glassmaking, much heat is lost through exhaust gases that can
otherwise be used to preheat batch and cullet. The basic function of preheating technology is to
transfer heat from the glass furnace exhaust gases into the batch and cullet and increase
production of the furnace. When batch and cullet and exhaust gas handling are integrated in a
preheating system, energy costs can be saved and some emissions can be reduced.
During preheating, the batch can be agglomerated to simplify heat exchange techniques. Fluid
beds are adapted and special silos are used. During air preheating, 57 percent of the non-electric
glass melting systems surveyed in our study used metallic recuperators.
During the early 1980s, heat recovery technology was of interest to conserve energy due to the
high cost of fuel and lack of availability during the energy crisis of the 1970s. Also, boosting
existing furnaces to increase production was preferable to the high capital investment of
enlarging furnaces. Because research and development of preheating technology was hampered
by limited funds and long periods of payback on investment, commercial success of preheating
technology was limited. Yet the technology to conserve energy is worthy of study as costs of
energy escalate in the United States.
Since the European glass industry has historically been challenged with higher energy costs than
that in the United States, more innovative technology has been developed to conserve energy in
the glass melting process. In at least seven preheating systems known to be operating on furnaces
in Europe greater capital investment and operating costs are justified by the higher value placed
on saving energy at the time of this writing.
A number of innovative approaches have been taken to develop preheating systems. In addition
to preheating the batch, the temperature of the flame is lowered and NOx generation is reduced.
In a LoNox furnace, batch is preheated as it floats on the surface of molten glass with the hot
combustion gases, and the cullet is heated when these gases are cooler. In the PPG system,
preheating and partial pre-reaction occur in a rotary kiln. (Barton, ICG, 1992)
During batch preheating, useful heat is recovered from furnace as exhaust gases to increase
production and conserve energy. By recovering energy with a preheating system, glass producers
could reduce furnace utility operating costs (fuel and oxygen) or boost furnace production, thus
reducing the unit capital cost of producing additional glass. With batch/cullet preheating to
approximately 1000 ˚ F (538 ˚ C), approximately 0.5 mmBtu/ton of glass produced can be
recovered in the glass melting process. During preheating, the batch can be agglomerated to
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