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

system. Applications for the technology might be flat glass, fiberglass, container glass, sodium
silicate and specialty glasses. The approach would be particularly attractive where rapid
changeover in glass composition is needed and where additives and colorants are being used that
are sensitive to the traditional elevated temperatures used in refining.
Development barrier: The PPG P-10 melting system was patented but development was
forestalled reportedly because of higher net cost of operation.
IV.4.1. Glass Plasma Melter (Great Britain, 1994)
Plasma melting of glass was explored by the British glass industry in 1994 to compare the
efficiencies of electrical plasma-arc and submerged electrode melting of soda-lime-silica glass.
The project aimed to demonstrate the energy savings that would be possible from the inherently
high melting efficiency combined with the flexibility to operate the furnace at high or low power.
The furnace for the pre-competitive R&D project was built at British Glass by a team of furnace
designers and operators from Pilkington, who operated a research furnace of similar size to the
demonstration furnace, and Glass Furnace Technology Ltd. (GFT), who had considerable
experience in the design and construction of commercial glass furnaces. The Research Group of
British Glass and the British Department of Trade and Industry initially funded the project.
Subsequent government funding, obtained through the Future Practice Program of the United
Kingdom Department of the Environment, was administered by the Energy Technology Support
Unit (ETSU).
The furnace built at British Glass incorporated a melting zone 0.6m 2 in area and 400 mm deep.
With conventional electrode heating and 100-150kg/h, using plasma in place of conventional
electrical firing, the furnace had a throughput of 60 kg/h. Following the melting zone, a riser
incorporated electrodes to boost and control the temperature of the glass in the sonic refining
stage, which included sonic horns. The depth of glass at this point was 125 mm to allow for
sonic treatment of the full depth of glass.
The project successfully demonstrated high melting efficiency. Using the submerged electrodes,
an average efficiency of 5 GJ/tonne (4.26 mmBtu/ton) was achieved (GJ/tonne x
0.852=mmBtu/ton). The GJ/tonne from a fossil fuel-fired furnace of a similar size would be
approximately 14.5-15.3 mm Btu/ton). Energy losses in the plasma melting due to the greater
requirement for water cooling and the greater radiation losses indicated that efficiencies could
not equal those of submerged electrodes.
The principal limitations at this time are torch materials and design. The commercial plasma
torches used in this project were a less expensive version of the torches used in steelmaking. A
cost-projection comparison between commercial plasma torches and conventional electric
boosting confirmed that plasma would be significantly more expensive.
Higher energy densities can be introduced with plasma arc melting (250 kVA) compared with
submerged electrodes (100 kVA). Plasma melting is, therefore, more rapid than conventional
electrical melting. In small tonnage, specialized applications that require intermittent production
or rapid product changes, such as frit manufacture and in short-term runs of specialized glasses
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