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

silica sand with a variety of industrial minerals to produce a particular glass. The industry
segments share common concerns: purchase of batch materials, purchase of energy, and
melting of batch and cullet.
Moreover, they are concerned about such issues as environmental compliance and
delivery of high-quality glass to downstream operations. Other areas of common interest
include oxygen combustion; electric boosting; bubbling; and batch preheating. Each
segment faces different challenges to comply with governmental regulations.
Environmental concerns of segments
Some technologies are better than others in their degree of environmental pollution. The
melting process within combustion-based melters inherently pollutes the environment
with NOx, SOx, and particulate emissions. Cold-top electric melters do not emit these
pollutants. However, the higher temperatures of electric melters lead to shorter furnace
life, and cost of electric power is higher than that of fossil fuels. Conventional furnaces
have faced ever-increasing requirements for reduced air emissions. Particulate matter
from batch volatile components, i.e., SOx, alkali or borates, all require some level of
control under regional, state and federal regulations. All add-on devices require high
capital and operating costs but do not improve productivity. Many factories have space
restrictions that prevent add-on options. Regenerative furnace designs with chromebearing
refractories may need to be adapted due to more restrictive waste disposal
regulations.
Alternative technologies must be compared with conventional furnaces based on all
configurations that meet emission control requirements. Particulate control involves a
variety of process modifications, batch adjustments, or add-on devices such as bag houses
or electrostatic precipitators. Adjustments to sulfur-containing batch components or addon
wet or dry scrubbers are needed to control SOx from low-sulfur fuels. Modifications
to the combustion process, changing temperatures and reaction possibilities, and postcombustion
gas treatment revert NOx back to N2.
Emissions from a glass furnace fired with fossil fuels take the form of combustion
products, namely oxides of sulfur, thermal NOx, and carbon dioxide. Other emissions
arise from particulate carryover and decomposition of batch materials, particularly CO2
from carbonates, NOx from nitrates, and SOx from sulfates. Sulfate is required in
modest levels as a refining agent as well as to promote oxidizing reaction. Emissions
from low level halides or metals and fluoride formulations may also occur where these
raw materials are present in a batch.
Emissions of all volatile batch components are considerably lower in electric furnaces
than in conventional furnaces due to the reduced gas flow and absorption, condensation,
and reaction of gaseous emissions and the heat from the melt. However, electric melting
is not currently in use in the US for large volume glass production (>300 tpd). Production
of continuous filament E-glass using 100 percent electric melting is not considered
economically or technically viable. Higher alkali insulating wool fiberglass can be
produced in cold-top all-electric furnaces, up to 200 tpd. A number of these furnaces
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