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

3.D. Segmented Melting System
Ruud Beerkens, TNO, the Netherlands
Presented at the International Congress on Glass 2001
One of the most important technological challenges in developing a segmented tank
furnace for the glass melting process is regulating the rate of heating the batch from room
temperature to fusion temperatures. Without backflow or with only modest re-circulation
from the hot spot area to the batch blanket, the batch must be heated from above by the
flames or underneath the blanket by electrodes. To limit consumption of electric energy,
a method must be developed to effectively heat a thin batch blanket by the flames or flue
gases. Using waste gases of oxygen-fired furnaces to preheat batch may be the way to
improve energy efficiency.
In the segmented melting concept presented in 2001 at the International Congress on
Glass, the batch-preheating zone becomes an extended part of the glass furnace. The
combustion gases flow from the combustion space to the recuperator or regenerator,
passing first over the batch blanket in the extended batch-preheating zone. Heat transfer
is most effective in a counter flow direction of the waste gas relative to the batch blanket
moving into the melting end. The heat transfer is mainly from the topside, with hardly
any heat being provided underneath the batch unless boosting electrodes are used in the
premelting zone.
In the batch heating section, the total net heat demand of 80 to 90 percent has to be
transferred to the material. The flow is mainly plug flow, and the final temperature must
be 212-302˚F (100-150 ˚C) below the fining onset temperature to avoid early
decomposition of the fining agent. The batch must be charged as a very thin batch layer
to increase the heat penetration into the batch blanket. By decreasing the batch thickness
by 50 percent, the heating rate for the center of the batch will increase by a factor of four.
Batch boosting may help heat the batch blanket from underneath.
The most critical aspects of the segmented melter design are the heat transfer to the melt
in the first section and the time available for fining in the shelf sections. Although it is
expensive to do so, electrodes can be used to aid the melting process. Thin batch layers,
bubbling, and counter flow heat exchange between the flames or exhaust gases and the
batch or melt will improve the process. Fining can be supported by a very shallow shelf,
a longer shelf size, or evacuating the space above the fining zone or other techniques such
as sonic waves, preconditioning of the melt by a fast diffusing gas, or extra heating to
reduce fining time by about 50 percent.
In this furnace design, the different segments are directly connected to each other by
either narrow canals, which limit backward moving glass flows, or by overflow weirs that
prevent all back flows when the melt from a previous section is gently poured into the
next basin. The glass melt film poured into the basin can be rather thin and the heating of
the film by flames can be performed. This method increases the temperature of the melt
within a short time when the melt passes the connection between the melting zone and
the fining shelf.
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