328 Radiant Burners

Continuous fiber-reinforced ceramic composites are easily formed into flat sheets and cut into shapes. Radiant burner screens are an example. Radiant burners are among the most efficient with very low NOx formation. One design has a manifold through which gaseous fuel is fed and ignited. Efficiency is increased by adding a mesh screen directly in front of the manifold (Fig. 3.12). The screen protects the burner from damage and sustains emissivity. It also acts as a rever-beratory screen because it reflects the burners heat back onto it, completing

FIGURE 3.12 Radiant burners and their screens may be flat as shown here or cylindrical. These screens protect the burner from rough handling and falling refractory and increase burner efficiency. CFCC screens operate at higher temperatures enabling maximum efficiency.

combustion and spreading the flame uniformly across its surface. The screen nearly doubles the radiated heat. Radiant burners use natural-gas to provide uniform high heat transfer efficiently with low emissions. They are used in residential warm air furnaces, commercial deep-fat fryers, dryers for the plastics industry, commercial greenhouses, and residential and commercial water heaters. Other industrial applications include fire-tube and fluid-tube boilers, process heaters, paper dryers, and high-efficiency volatile organic compound incineration. Other processes that could benefit from this method include metal treating, organic chemical oxidizing, plastic curing, and drying paint and paper and other materials.

Honeywell, Alzeta, Visteon, and an automotive manufacturer teamed to evaluate CFCC reverberatory screen radiant burners in a glass treating facility. The CFCC has survived the thermal fatigue of 1000 h of operation at 1100° -1200°C (2000° -2200°F) plus 15,000 thermal cycles, and 32,000 on-off cycles with no sign of deterioration. They experienced higher throughput, faster processing, lower fuel consumption, greater furnace temperature control, reduced emissions, and lower energy costs. Fuel consumption was reduced by 33%. Heat flux from the burner doubled. Overall performance increased by 35%. Retrofit of the previous process with the CFCC reverberated radiant burner would result in less downtime, lower maintenance, increased efficiency, reduced energy consumption, longer life, and lower life-cycle costs.

Alzeta Corporation manufactures several types of radiant burners. One type is used to incinerate perfluorocarbons from the semiconductor industry. A second is used in a high-efficiency boiler system. CFCCs enable an operating efficiency of 88% versus a previous 84%. This saves 40 billion Btu/year. Each unit emits 10 ppm less NOx than previous ones. A third CFCC unit is used in residential water heaters. It operates at 87% versus 80-85% for burners with metal screens and produces less than 20 ppm NOX. The CFCC burner saves 30 billion Btu/year.

A fourth type of CFCC screened burner is the Pyrocore radiant burner product line. CFCCs enable Alzeta to offer a longer warranty on this burner. Pyrocore burners are generally used in boilers in virtually every industry. It reduces the emission of global warming gases by 90-98% from each burner.

Continuous fiber-reinforced ceramic composites enable higher temperature operation, increased efficiency, true of many industrial processes. Higher temperature operation results in more complete combustion, reduced fuel consumption, and lower emissions. CFCCs screens are tough, durable, thermally stable, dimen-sionally stable, corrosion-resistant, and thermally shock resistant. They can be retrofitted onto existing burners or used in their original manufacture. If 10% of radiant burners used CFCC screens, 50 billion cubic feet of natural-gas would be saved per year and NOX emissions reduced by 35,000 tons. Additional savings would be realized through elimination of downstream NOX control equipment and higher product yield as a result of more uniform heat transfer.

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