OCR Text |
Show 2 incandescence at 1500°F to 2200°F depending on the specific application, with NOx emissions typically under 20-25 ppm. Under normal operating conditions, the burner surface transfers 15 to 25 percent of the heat of combustion as radiant energy. Materials used in this type of burner are highly porous matrices of ceramic or metal fibers. With proper design, the premixed fuel and air flow uniformly through all parts of the matrix. The combustion reactions, and hence, radiant output are uniform over the entire burner surface. The high porosity of the burner pad results in a low burner thermal mass with the capability to respond quickly to changing process conditions. The burner surface can be made in a variety of shapes, so that the heat transfer can be matched precisely to a load. Combustion occurs only on the very outer surface of the burner with no visible flame. The interior of the porous material remains at the temperature of the incoming reactants, allowing operational stability over a wide range of conditions. A specific type of porous surface burner, the Pyrocore ceramic fiber burner, has been sold commercially by Alzeta for over 10 years. Use of this radiant burner product has continued to grow, primarily in applications requiring uniform heat transfer or low emissions of NOx and CO. Popular applications of this technology include hydronic heaters, residential and commercial space heaters, pool heaters, and firetube boilers. Two recent developments at Alzeta have demonstrated the benefits provided by Pyrocore burners in industrial applications. • As part of the ARCS project, Alzeta has developed an improved ceramic fiber pad material (Pyrocore HT) for use in higher temperature applications than are recommended for the standard Pyrocore. The Pyrocore HT product has been demonstrated in laboratory testing and in several preliminary field tests. Demonstration in a steam-methane reformer owned and operated by Air Products and Chemical, Incorporated (APCI) is planned for 1995. Development of the high temperature pad material, heater thermal modeling results, and host site combustion system design are discussed in the remainder of this report. |