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GLASS FORMING & PROCESSING: A New Option for Oxy-Fuel

May 1, 2004
A next-generation flat flame oxy-fuel burner is giving glass manufacturers a new way to improve energy efficiency while minimizing equipment and maintenance costs

In 1994, the first flat flame oxy-fuel burner for the glass industry was patented,1 and the first field results were reported at the 1994 and 1995 Glass Problems Conferences.2,3 The burner's broad, luminous flame provided enhanced heat transfer with a typical energy reduction of 5% compared to traditional tube-in-tube conical oxy-gas burners. However, the flat flame burners were sensitive to turndown, which caused recirculation and led to refractory damage. The burners also had a high capital cost and associated maintenance issues, and required an oil backup. To overcome these challenges, a next-generation flat flame burner was needed.

A demonstration of the new burner in an oxy-fuel container furnace.

Partnering for Improvement

BOC Gases partnered with Maxon Corp., Muncie, Ind., to develop this next-generation technology. The partnership combined BOC's experience in glass furnace combustion (including its patented Convective Glass Melting [CGM] combustion system4 and the flat flame oxy-fuel burner) with Maxon's experience developing oxy-fuel burners. (Maxon developed one of the first commercialized oxy-fuel burners with Corning in the late 1980s and a dual fuel low emission burner* in the 1990s.)

Built in 2000, the Maxon test furnace was used initially to validate the improved heat transfer of the CGM, and also to develop CGM propane and CGM oil. It has also been used in the development of the next-generation flat flame burner. Using existing BOC patents1 and Maxon's LE patents,5 the goal of the development was to produce a product with high heat transfer, low emissions and high durability so that it provides the lowest total cost among flat flame burners in terms of purchase and maintenance over the life of the furnace.

*The Maxon Oxy-Therm LE

The performance of the new burner was validated in this Maxon test furnace.

Benefits of the New Technology

The result of these efforts was a low emission flat flame (LEFF) burner.** Released for field trials in 2001, the burner was first installed in an oxy-fuel container furnace in 2002. The burner design comprises a single size block that accepts different capacity fuel nozzles. The nozzles are interchangeable without the use of tools and can be drilled to a manufacturer's specific capacity, which ensures at least a 5:1 turndown at all capacities.

Using Maxon's patented staging system, more than half of the oxygen is secondary and introduced to the flame in a staged configuration. With less than half of the oxygen as primary, the heat release and related flame turbulence within the block is low, providing a cool block discharge with low momentum expansion that eliminates recirculation. Avoiding both recirculation and block overheating is key to burner survivability and minimal maintenance. The initial field trial burner operated continuously for eight months and did not requiring cleaning.

While significantly improving durability, the deep staging also has an additional two-fold effect of minimizing the formation of NOx and improving heat transfer. The staging delays the rate of mixing and thus lowers the peak flame temperature exiting the burner block by the entrainment of furnace gases. The delayed mixing and higher residence cause the gas to dissociate or "crack" and form carbon, which improves the luminosity and increases the radiative heat transfer from the flame.

Minimizing the combustion that takes place within the burner block maximizes the flame length and provides increased heat release along its length. Reducing the heat release local to the burner minimizes the risk of damage to either the breast walls or tuckstones.

By lengthening the flame, the width also increases, thereby increasing the flame's total surface area. The higher surface area provides a higher radiative heat transfer to both the glass and superstructure.

**The Maxon Oxy-Therm LEFF

Avoiding recirculation and block overheating is key to burner survivability and minimal maintenance.

Proven Performance

Extensive testing by BOC and Maxon in three separate dedicated test furnaces confirmed that the new burner has both lower NOx and higher heat transfer than the original flat flame oxy-fuel burner developed for the glass industry. In an additional ongoing commercial demonstration in a borosilicate glass furnace, two original flat flame oxy-fuel burners were replaced with the new burner technology. The result has been a reduction in energy by several percent and an improvement in quality.

The new burner was designed primarily for 100% oxy-fuel furnaces in a variety of glass market segments. While the burner might not be ideal for all glass applications (for instance, it cannot be used for the oxygen boosting of air-fuel furnaces), it gives glass manufacturers one more option in their quest to maximize throughput and yield while minimizing capital investment, maintenance requirements and energy consumption.

For more information about the new burner technology, contact: