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

precipitator (EP) dust collected from a stack can be recycled and may, in some cases,
partially offset the operating cost of the pollution control device. Powdered coal as a
reducing agent controls the decomposition of sodium sulfate more efficiently than
increased temperature. Therefore, less sulfate can be used, which results in lower
emissions with equivalent glass fining. Higher cullet ratios are also known to reduce
emissions. New operating procedures or furnace modifications, such as combustion
techniques with higher radiant heat transfer and lower velocities, reduce volatilization.
Summary
The most important melting techniques used within the glass industry are summarized
here. The choice of melting technique will depend on many factors, but particularly
required capacity, glass formulation, fuel prices, existing infrastructure, and
environmental performance. The choice is one of the most important economic and
technical decisions made for a new plant or for a furnace rebuild. As a general guide (to
which there are inevitably exceptions): for large capacity installations (> 500 tpd), crossfired
regenerative furnaces are almost always employed. For medium capacity
installations (100–500 tpd), regenerative end-port furnaces are favored, though crossfired
regenerative, recuperative unit melters and in some cases oxy-fuel or electric
melters may also be used according to circumstances. For small capacity installations
(25–100 tpd), recuperative unit melters, regenerative end-port furnaces, electric melters,
and oxy-fuel melters are generally employed.
The overriding factors are required capacity and glass type. The choice between a
regenerative or a recuperative furnace is an economical and technical decision, but
current environmental regulations have become significant factors in choosing melting
technology. As an example, the choice between conventional air-fuel firing and electrical
or oxy-fuel melting is an important decision. Similarly, other specific melting techniques
are discussed separately in the substance-specific sectors.
Each of these techniques has inherent advantages, disadvantages, and limitations. For
example, at this time, the best technical and most economical way of producing highvolume
float glass is with a large cross-fired regenerative furnace. The alternatives are
either still not fully accepted in the sector (i.e., oxy-fuel melting) or compromise the
economics or technical aspects of the business (i.e., electric melting or recuperative
furnaces).
The environmental performance of the furnace is a result of a combination of the choice
of melting technique, the method of operation, and the provision of secondary (add-on)
abatement measures. From an environmental perspective, melting techniques that are
inherently less polluting or that can be controlled by primary means within the process
are generally preferred to those that rely on secondary abatement. However, economic
and technical practicalities have to be considered, and the final choice should be an
optimized balance. The environmental performance of the various melting techniques
will differ greatly depending on the glass type being produced, the method of operation,
and the design. Electric melting differs from the other techniques described because it is a
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