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Show The alloy em ployed in the fabrication of Pyromat burners has been designed to withstand the high temperature oxidizing environment existing on the burner surface. Current experience demonstrates significantly improved service life can be expected from Pyromat burners compared to Pyrocore burners. Performance Characteristics of Radiant Burners The low NOx emissions generated by porous radiant burners result from their ability to minimize combustion temperatures over a wide range of operating conditions. Pyrocore and Pyromat burners contain the combustion reactions in intimate contact with the outer surface of the burner element. As a result, a substantial fraction of the heat of combustion is rapidly dissipated from the products of combustion and gas temperatures are maintained significantly below those occurring in conventional flame-type burners. NOx emissions are thereby controlled below 25 ppm under normal operation. In addition, these low NOx flame emissions are achieved without quenching the combustion reactions to the point of causing elevated CO or unburned hydrocarbon emissions as can sometimes occur with low NOx flame burners. Therefore, like the NOx, the CO and unburned hydrocarbon emissions are also less than 25 ppm under most conditions. Figure 2 provides NOx emissions data at various excess air levels while operating at a reduced surface heat release rate of 70,000 Btu/hr-ft2. Whereas conventional and low NOx flame burners show increased NOx emissions when operating at elevated excess air, radiant burners generate lower NOx emissions when excess air is increased. Porous radiant burner NO emissions are most strongly affected by reactant stoichiometry, while N02 emissions are unaffected by such changes and are typically less than 4 ppm. As described above, the NOx emiSSIons characteristics of Pyrocore and Pyromat radiant burners are controlled by the thermal conditions existing on the burner's surface. Since surface heat release rates and burner stoichiometry have a direct effect on burner surface temperatures, radiant burner 3 AFRC90-PAPER #253 combustion systems can be easily designed to meet specific NOx emissions limitations for a wide variety of applications. At full load conditions, energy exchange with process loads normally results in burner surface temperatures in the range of 18000F to 2OOOoF. As heat release rates are reduced, energy balance effects correspondingly reduce surface temperatures and therefore NOx emISSIOns. Figure 3 shows this effect for a variety of applications. The spread in the data between different applications reflects variations in the nominal load heat release rates of the equipment presented. While some equipment may be designed to operate at 70,000 Btu/hr-ft2 at full load, other types may operate as high as 180,000 Btu/hr-ft2• Burner stoichiometry adjustments can also be used to reduce NOx emissions even further. Figure 4 shows how NOx emissions are reduced at high excess air for a range of applications. One of the more interesting differences in the NOx emissions characteristics between radiant burners and 10w-NOx flame burners is the ability of these burners to operate with combustion air preheat without increasing NOx emissions. Figure 5 shows the independence of these emissions with preheat temperatures ranging from ambient to 400°F. Typical staged combustion 10w-NOx burners show a doubling of NOx emissions with SOOoF preheat. In applications where recuperative preheat can be used to improve system thermal efficiency, radiant burners can be successfully employed without any NOx emissions penalty. Figure 6 shows how rapidly porous radiant burner surface temperatures stabilize during ignition and shutdown. Their superior responsiveness translates into significant benefits related to matching process load requirements. Industrial applications of Alzeta's Pyrocore Model PC radiant burners include immersion tube fluid heaters, ftretube boilers, and air heaters. The Model PC burner, a circular cylindrical segmented burner, is typically installed inside a concentric frring tube to exchange heat to the process load. The Model PO burner is a segmented burner with a |
