OCR Text |
Show enhances the thermal performance by increasing the emittance of the surface. This material has a maximum use temperature of 1750 deg F (954 deg C) in burner applications. Operating temperatures can be enhanced by applying a dense silicon carbide coating through a chemical vapor deposition (CVD) process. As shown in Table 3, the dense coating also increases strength. Tiles of this material combination have exceeded 11,000 hours of near continuous operation in life test hoods with temperatures above 1900 deg F. Although the dense CVD SiC coating enhances performance, costs are also increased. Currently, the increase is 2 - 4 times the baseline cost depending on geometry. The increase is expected to drop in half as volume grows. However, materials development activities are underway at Hi-Tech with funding from the Gas Research Institute to develop low cost, high performance reticulated ceramics for a variety of gas burning applications including infrared burners. The current focus of this activity is on the silicon carbide system, specifically an oxide bonded material. Results of this work will be presented at a later date, however preliminary investigations have shown that the thermal shock resistance of the LAS/CVD SiC system can be achieved. Reticulated ceramics offer a wide range of size and shapes for gas burning applications. Flat shapes can easily be fabricated to 12" x 12" and greater if necessary. Thickness can range from 0.375" up to 1.5". Coatings can be applied to block off specific areas. Fig. 4 illustrates some of these features. Tubular configurations can also be fabricated as shown in Fig. 5. Diameters up to 8" have been made and it is expected that 12" diameters are possible. Wall thickness down to 0.25" have been obtained although this 4imension is somewhat dependent on diameter. In summary, gas fired burners based on reticulated ceramics offer high efficiency, and low NOx combustion. These burners are currently being used in paper and coating drying but offer the flexibility to be used in a wide range of other applications from paint curing to hot water boilers. OTHER POLLUTION ABATEMENT APPLICATIONS In addition to the "active" approach where reticulated ceramics participate in the combustion process they can also be used in the "passive" mode to treat post combustion flue gas streams. Included in this type of application are incinerator baffles, catalyst supports, and diesel particulate trap s • t. |