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Show 1. Introduction Increasingly strict NOx regulations are being enacted worldwide. In the Tokyo area for example, local governments have implemented a guideline of a NOx limit of 60 ppm (0% 02) for gas-fired boilers, with a tougher limit of 40 ppm planned for boilers used for district heating and cooling systems. Much stricter regulations are currently being considered, posing a wide range of technical challenges for low NOx combustion. Various low NOx combustion methods have been proposed, including multi-staged combustion, exhaust gas recirculation (EG R) and lean premixed combustion. The EG R method includes the forced EG R and the self-induced EG R method. The latter has the advantage that the effect of EGR is obtained without using an auxiliary blower fan to recirculate the exhaust gas, and has a requires relatively simple burner design compared to the multi-staged-combustion method. Also, it does not necessarily need a high excess air ratio as in the lean premix combustion, thereby avoiding the reduction of combustion efficiency and heat transfer. While the self-induced EGR method has already been applied successfully to meet the present regulations (1), there appears to be a limit to the possible NOx reduction if the present method is merely improved. A novel combustion technology is thus needed, based on a new concept utilizing the self-induced EGR method. The objective of this study is to establish an ultra-low NOx combustion technology for low temperature processes, targeting a NOx emission under 20 ppm (0% 02)' This study describes a novel combustion method which maximizes use of the self-induced EG R by creating lifted flames. The generic test burner was designed and tested in a water-cooled test furnace. Compared to conventional flames, the lifted flames demonstrated substantially low NOx emission without the penalty of increased CO emission. Detailed measurements were made to gain an understanding of the lifted flame and its low NOx emission. A novel low NOx combustion technology was thus established. 2. Experimental Furnace Figure 1 shows the experimental boiler furnace used in the study. The experimental furnace |
