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

Capital-intensive manufacturing businesses such as glass have struggled especially in the
past 10 years to earn rates of return that exceed corporate capital costs. This concern for
capital productivity has been a major stimulus for research and development of glass
melting technology. Because the cost of building large furnaces can exceed $20 million,
less capital-intensive, smaller furnaces have found a place in the glass industry. Even
though they are less energy efficient and more expensive to build per unit of glass
produced, they are more flexible for meeting marketing demands and rebuild time is
short.
Furnace life
As a trade-off for improved capital productivity, manufacturers accept some deterioration
in energy efficiency and production capacity by delaying “cold rebuilds.” While
operating an aging furnace, manufacturers also risk catastrophic failures and unplanned
production outages that affect their ability to meet their commitments to customers. By
extending furnace life, capital investment can be deferred as long as possible, usually
until quality, safety, or production demands are jeopardized. Furnace life varies with
glass composition, type of refractory used, and operating factors such as quantity of glass
produced each year in the furnace. Typically, furnace life is five to 14 years for
traditional, large-volume glass products.
The industry is more willing to consider a revolutionary concept to develop a melting
system with lower construction costs as they relate to capital investment and meeting
environmental regulations. At present no manufacturing segment has a standardized
melting furnace, in part because the industry has continually optimized furnaces to
balance demands for specific production rates, glass quality, acceptable energy
consumption and useful life.
Refractories
Longer refractory life is an important goal in advancing glass-melting technology.
Industrial glass melting furnaces are constructed with a number of different
classifications of refractories. Refractory materials are selected for properties that serve a
specific purpose. Many factors influence the choice of a suitable refractory for a given
application. In some cases, maximum service temperature may be the deciding factor. In
others, high refractoriness must be coupled with resistance to thermal shock. Chemical
resistance to batch, raw material components, metals, refractory erosion slags, or
disintegration by reducing gases may be most important factors. High insulation value
might be desirable in some cases, or high thermal conductivity in others.
High-temperature properties of refractories depend mainly on their microstructures,
particularly bonding structures and the presence of low-melting components. The
properties of refractories that can be determined most readily are chemical composition,
bulk density, apparent porosity, apparent specific gravity, and strength at atmospheric
temperatures. These properties may be used as controls in the manufacturing and quality
control process. At elevated temperatures the key determining properties of refractories
are hot modulus of rupture, hot crushing strength, creep behavior, refractoriness under
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