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

of waste gas through a metal heat exchanger. The air preheat temperatures are limited to around 800°C and the
metal used for the recuperators must be carefully selected to resist chemical attack. The burners are located
along each side of the furnace, transverse to the flow of glass, and fire continuously from both sides, thus
allowing better control and more stable temperatures than in end-fired furnaces.
The recuperative furnace is used in the US primarily for small-capacity installations where high flexibility of
operation is required with minimal initial capital outlay, particularly where scale of operation is too small to be
economically viable. The furnace is used most often for textile fiberglass production.
Although a recuperative furnace is less energy efficient than a regenerative furnace, it does recover a substantial
amount of heat via the recuperator system in the form of combustion air operating at a lower temperature than
for regenerative furnaces. The specific melting capacity of recuperative furnaces is limited. The lower
combustion air temperatures result in lower NOx emissions. Manufacturers have improved energy efficiency in
recuperative furnaces, particularly in Europe, by bubbling, electric boosting, waste heat boilers, gas preheating
and batch/cullet preheating.
Figure III.2. Side Port Melter.
• Pot/day tank furnace
Pot furnaces are used for melting smaller quantities of glasses below 2552°F (1400°C). Pots, whether single or
multiple port, are inefficient fuel consumers and have poor temperature control. But they can be heated from
the sides as well as the top and are useful for melting heat-absorbing specialty glasses such as tableware and art
glass. Day tanks are usually preferred for experimental melts because they have better refractories and higher
attainable temperatures. Day tanks burn gas or oil and use a single opening for both charging and gathering
glass.
Energy consumption of a pot or day tank furnace is very high due to the minimal insulation, very low pull rates,
and minimal waste heat recovery. Refractory life is poor due to thermal shock from rapid batch charging and
wide variations in temperatures required for melting, refining and working from the same furnace. Output
rarely exceeds 2 tpd. Operation is intermittent where batch is charged for a melting cycle, typically overnight,
and production is worked from its holding capacity during the day.
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