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A new hybrid furnace combines air-fuel and oxy-fuel technologies to provide improved quality, productivity and fuel efficiency compared to conventional glass melting processes.
The benefits of using oxygen for combustion in glass making are well understood. Most notably, by replacing air (which contains almost 80% inert nitrogen) with pure oxygen, combustion efficiency is substantially increased. The effect of reducing the amount of nitrogen entering the furnace can be seen in Figure 1 (p. 24), which shows the energy carried out of the furnace for three distinct cases: air-fuel with no heat recovery, air-fuel using regenerators and full oxy-fuel.
An air-fuel system with no heat recovery loses 81% of the heat input to the furnace in the form of hot gases exiting the furnace. This leaves only 19% of the heat "available" for melting the glass and overcoming other heat losses associated with the furnace (i.e., through refractories, water-cooled jackets, aircooled equipment and furnace openings). The addition of a heat-recovery device, such as a regenerator or recuperator, reduces the amount of heat loss by pre-heating the air used in the combustion process. While this is a great improvement, 45% of the heat input to the furnace is still lost to the atmosphere in furnaces using the most efficient of these air-fuel designs. For both of the air-fuel cases described, very high temperatures and high nitrogen concentrations exist in the furnace, leading to high NO^sub x^ emissions.
In oxy-fuel furnaces, the temperatures are also high, but the scarcity of nitrogen means that very little NO^sub x^ is formed. The volume of the flue gases is approximately 20% of that found in air-fuel furnaces, so that the amount of heat carried out with these gases represents only 35% of the heat input. Compared to a regenerative furnace, the amount of heat available for melting the glass is increased by almost 20%. Figure 2 (p. 24) shows the effect of oxygen enrichment on total available heat for a fixed flue gas temperature.
A full oxy-fuel furnace represents the most thermally efficient fossil fuel-based glass melter commonly used in the industry. This technology uses specially designed oxy-fuel burners and flow control systems, incorporates different furnace designs with respect to burner and flue locations, and eliminates heat recovery devices such...