| OCR Text |
Show the furnace in Fig. 3 show that the NOx concentration increased in a similar way with any burner type, even at an excess air ratio of 1.3. The low rate of NOx concentration increase at high furnace temperatures with the MK burner suggests that the EGR effect was enhanced by increasing the temperature, in this cylindrical furnace. 4) Effect of combustion air temperature In many practical cylindrical furnace applications, the combustion air is warmed by heat exchange with the flue gas to save energy. Usually, however, energy saving by this process opposes NOx concentration reduction. Fig. 12 shows that this was also true for the test. With both LC burners, increasing the combustion air temperature affected the firing space in a similar way to raising the excess air ratio. Therefore, the amount of unused air increased, and this cooled the combustion flame. For this reason, NOx concentration is believed to be less dependent on air temperature with LC type than MK burners. 5) Effect of burner load When the loads on two burners, A and B, were decreased, the NOx concentration increased (Fig. 13). This seems to have been a result of weakened EGR effect, brought about by combustion gas flow speed reduction. With three burners, A, B, and C, there was only a slight rise in NOx concentration when the thermal input was raised to 300 Mcal/h. But when each burner's load was cut to two-thirds, there was a large increase in NOx concentration (Fig. 14). 6) Effect of off-stoichiometric combustion Combustion was performed with different excess air ratios for burner A (in the lower part of the furnace) and burner B (located in the upper part). The mean excess air ratio of the two burners was kept at 1.1. Under air-rich burner A and gasrich burner B conditions, the NOx concentration of the two LC burner types was lower than that under basic conditions. Peculiarly, the LC-h burner NOx concentration decreased with increased furnace temperature. A similar phenomenon occurred with the MK burner at furnace temperatures exceeding 800°C. The LC-m burner's low NOx concentration was almost constant. It is thought that reburning of the flue gas generated by burner A may have occurred when it ascended and mixed with the gas-rich flame of burner B. 7) Cyclic combustion Three MK burners were operated cyclically in pairs (AB 9 BC ~ CA ~ AB, etc.), at 30-second intervals (Fig. 17, MK-ROT). Each burner's pilot was burning continuously. We expected this combustion system to reduce the NOx concentration by moderating - 4 - |
