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

Innovative refining concepts include using centrifugal forces, bubbling with alternate gases, and exposing
the unrefined glass to sub-atmospheric pressures. The last concept has promise for shortening refining
time, lowering energy consumption, and using smaller devices.
A.13. Chemical and thermal conditioning
A product-forming operation produces a saleable glass product downstream of all glass melting devices.
Each forming method requires that the glass meet requirements for thermal and chemical homogeneity.
Existing devices usually involve large chambers with methods for combining controlled heating and
cooling, optimized for a relatively narrow range of pull rates or entrance temperatures.
Smaller, more flexible processes, including mechanical stirring and most recently microwave heating,
have been tried. Any new melting system must satisfy present as well as future requirements of forming
technologies and higher standards for glass quality.
A.14. Process controls (sensors, analytical/predictive, process analysis and control)
A limited number of sensors are available to provide meaningful measurements to control the melting
process. Currently, sensors are available for melting systems to control temperatures (glass, refractory and
atmospheric); pressures (furnace atmosphere pressure at the crown and at the glass level, fuel-oil and gas
pressure, fan air and oxygen pressure; flow rates [of combustion reactants or combustion components in
preferably mass units and glass flow]); flow rates (glass, combustion components); inventories (storage
bins and molten glass in process chambers); selective chemical concentrations (glass redox, combustion
atmosphere); and air emissions (NOx, SOx, CO and particulate).
Input data from sensors are essential to controlling the overall process. Advances in information
presentation and control logic have improved energy efficiency, glass quality, furnace life, and
productivity. New melting systems that incorporate faster, more dynamic processes will require more
advanced sensors and more intelligent process controls.
Technology is emerging for new sensors that measure viscosity real time (S.K. Sundaram); vision systems
that monitor and alarm if batch coverage changes or indicates a short circuiting situation; correct
combustion; or act as smart thermocouples
A.15. Environmental compliance
Traditional glass melting furnaces must comply with environmental regulations. Air emission pollutants
from fossil fuel furnaces include NOx, SOx, particulate, CO, halides and heavy metals. Some add-on
technologies can curtail emission rates but increase cost and add no product value. Process revisions show
compliance but are preferred even though they add cost because the capital investment is typically lower
and may improve product quality. For example, combustion modifications to reduce NOx are preferred
over a chemical scrubber. All-electric melting eliminates most environmental pollutants. During furnace
rebuilds, some refuse refractory materials must meet solid waste disposal requirements. Changes in
refractory practices, such as elimination of chrome magnesite, have reduced disposal costs for
regenerative furnaces.
New innovative melting systems should incorporate a means to reduce emissions. For example, the
application of sub-atmospheric refining can reduce or eliminate the use of sulphates, which contribute to
SOx and particulate emissions.
A.16. Lower capital cost
Systems that can meet expectations for glass quality, energy efficiency of operations, environmental
emission rates, and production yields will be evaluated in light of capital investment cost. Current melting
technology requires a significant capital investment per unit of glass production, limiting industry growth
186