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

Technology for direct heating within the molten glass can be achieved when an electrical current is driven
through the resistant molten glass to release Joulian heat. Alternatively, microwave, inductive or plasma
heating systems might be used to heat molten glass directly. However, these techniques require research
and testing to become viable systems.
A.9. Waste heat recovery
Hot products of combustion gases leave the melters of fossil fuel furnaces. Efficiency of combustionbased
furnaces can be measured by how cold the exhaust gases are in the exhaust stack. Some enthalpy
energy from those gases can be recovered by recuperator or regenerator systems, and this energy returned
to the melter by preheating the combustion air. This method allows higher operating temperatures with
increased melting rates and improved glass quality.
With no heat recovery, exhaust temperatures of a furnace exceed 2400˚F (1315˚vC). With recuperators,
exhaust temperatures exceed 1800°F (982°C). With regenerators, exhaust temperatures exceed 600–
1000°F (316–538°C). Exhaust gases have always been considered for waste heat recovery. Steam boilers
to generate electricity are an alternative method used in Germany by Heye Glas. Use of gas reformers, or
thermochemical recuperation, by other industries is a concept that might be adaptable to glass furnaces.
The most advantageous use of furnace exhaust heat seems to be for preheating the batch and/or cullet
charged into the furnace. Configurations to capture the exhaust heat for reuse that are cost effective and
operator use friendly need to be developed.
A.10. Fusion (sand solution) process
Final dissolution of more refractory raw material components (sand, feldspathic, chromite colorants, etc.,
is one of the rate-limiting components of the glass fusion process. Historically, this process has been
accomplished by either extended time in the furnace or higher operating temperatures. As modern
refractories reach practical limits for their operating temperatures and demands for throughput increase,
alternate processes are needed.
Researchers have identified the need to develop a driven system to accelerate the rate of solution of batch
components as well as remove evolving gases from the melt. Shear forces may be increased mechanically
by physical stirrers or by changing the heating process via such electrically based means as microwave or
plasma. High-speed stirrers, bubblers, or submerged combustion all have technical merit to mechanically
agitate a glass melt.
A.11. Zonal separation
Glass manufacturers recognize the need to optimize the steps to convert raw materials to final molten
glass ready for forming. Within a single chamber, traditional melters must heat solids, create fusion,
refine the melt, and condition the molten glass. By separating each step into distinct chambers or zones
within multiple-duty devices, each process can be intensified and optimized. Residence time for each step
can be reduced, and less interference will occur between adjacent steps.
A.12. Refining (seed removal)
Removal of gaseous inclusions (seeds) from the glass is another rate-limiting step. Current technology
uses chemical, thermal and physical means to refine a glass melt. Each has drawbacks. Chemical refining
increases particulate emissions or causes other environmental problems. Thermal refining uses more
energy and exposes other components of the melter exposed to temperatures that reduce useful life.
Reducing glass depth, as by using a shelf refiner, shortens refractory life and causes refractory defects to
enter the melt.
185