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

In the regenerative furnace, two regenerator chambers contain checker bricks to absorb waste heat from the
exhausting combustion gas products. One chamber is heated by waste gas from the combustion process while
the other preheats incoming combustion air. The furnace is fired on only one of two sets of burners at any
given time. The flow alternates from one side to the other about every 20 minutes, and combustion air passes
through the checkers and is preheated before entering the combustion chamber.
With this waste heat recovery method, preheat combustion air temperatures up to 2600°F (1426°C) may be
attained. Thermal efficiencies are greater in the regenerative furnace than in direct-fired unit melters. Greater
capital costs are required for building and maintaining the additional refractory structures and reversal
equipment. Space requirements are also greater. The high capital cost of regenerative furnaces makes them
economically viable only for large-scale glass production (>100 tpd). They are commonly used for container
and flat glass making.
A regenerative furnace may have side ports or end ports. With either configuration, the melters are usually
larger than 750 ft 2 and produce more than 300 tpd in side port furnaces. They are used mostly by flat glass
furnaces and have three to seven ports on each side. Their large flame coverage of the melting surface helps to
yield higher melting rates and more stable melting conditions because of good heating control along the full
length of the furnace. End-port furnaces have single entry and exhaust ports in the back wall. Regenerator
chambers share a common wall. With this configuration, structural heat losses are lower and thermal efficiency
is higher. The two regenerative chambers are situated at one end of the furnace with a single port. The flame
path forms a U-shape, returning to the adjacent regenerator chamber through the second port. This arrangement
is more cost effective than the cross-fired design but is less flexible for adjusting the furnace temperature
profile, and therefore is less favored for larger furnaces.
A modern regenerative container furnace has an overall thermal efficiency of 40 percent when the best
construction and insulation practices are followed. Waste gas losses are around 30 percent, and structural
losses make up most of the remaining 30 percent. End-fired furnaces are more thermally efficient, up to 10
percent higher than side-fired. But combustion control is more limited and furnace size is currently limited to
around 1300 ft 2 . Float glass furnaces are less efficient than container glass furnaces because the specific pull of
a float furnace is much lower due to greater refining quality requirements.
Figure III.1. End Port Melter
• Recuperative furnace
Since the 1940s, glass manufacturers have used recuperative furnaces that employ heat exchangers, or
recuperators, for heat recovery. In these furnaces, incoming cold air is preheated indirectly by a continuous flow
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