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

Melter controls are extremely sophisticated and must function precisely for melter temperature,
glass composition, product durability, waste loading limits, glass redox control, and glass cooling
requirements. Melting rates have been increased by the addition of reducing agents such as
formic acid, sucrose and nitrates. The exothermic reactions that occur at critical stages in the
vitrification process are responsible for the rate increases. Nitrates are balanced by reducing
agents to avoid persistent foaming that would destabilize the melting process. Melter residence
times are minimized to homogenize glass and assure the acceptable quality of the glass. Research
at the Westinghouse Savannah River facility has determined that melters and waste-processing
facilities can be reduced in size if mechanical agitation is used to minimize heat transfer
requirements for effective melting. A new class of melters has been designed and tested. Melt
rates have exceeded 155 kg . m -2. h -1 with dry feed (1.77 sq.ft. per ton per day). The melt rate is
eight times greater than in conventional waste glass melters of the same size. [Bickford, D.F., et
al., “Control of radioactive waste glass melters. I, preliminary general limits at Savannah River,”
J. of the Am. Cer. Society, 73[10], 2896-2902 (Oct. 1990); Bickford, D.F., et al., “Control of
radioactive waste glass melters. II, Residence time and melt rate limitations,” J. of Am. Cer. Soc.,
73(10), 2903-2915 (Oct. 1990).]
Development barriers for broader, commercial application of this technology are materials of
construction and insufficient funding.
IV.7. Innovative electric melting technology
Electric furnaces have two shortcomings. The quality of the glass produced in all-electric
furnaces is not sufficient for some requirements, such as color TV face plates. Furnace
refractories are corroded more rapidly than in combustion-heated furnaces. These two
drawbacks to electric melting have been addressed and a number of technologies have been
patented. The following examples of innovations in non-conventional melting suggest the variety
and extent of research and development in this area. (Barton, ICG, 1992)
IV.7.1. Suspended electrodes (Saint-Gobain, 1986)
One of the main objectives of suspended electrode technology, patented by Saint-Gobain in
1986, was to reduce the temperature of and wear on the refractories at the sides and bottom of a
cold-top electric furnace. This was done by choosing a suitable position at which to locate the
vertical electrodes that were supported at their upper ends. As the energy is dissipated closer to
the batch blanket, higher production is possible for a given throat temperature. By varying the
depth of immersion of the electrodes, it is also possible, within limits, to independently vary the
output of glass and temperatures. Another possible advantage is the ability to melt glasses whose
resistivities are comparable to, or higher than, those of the furnace refractories.
Suspending electrodes from the top of the furnace has several advantages. Temperature can be
lower in the bottom and throat. Positions and lengths of electrodes can be changed after startup
to adjust the furnace impedance.(Saint-Gobain, Levy, P.E., et al. FP2599734(1986); Barton,
1993)
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