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The experiments with  λp  (ratio of the primary air flow to the theoretical combustion air) were launched on a bench-scale coal preheating combustion test rig. The effect of  λp  on operating characteristics of the self-preheating burner was investigated in detail. Besides, the combustion characteristics of the high temperature preheated fuel and NO X  emission were discussed. The results showed that with increasing  λp , the temperatures in the self-preheating burner climbed and the main compositions of the coal gas (excluding N 2 ) were CO, H 2 , CO 2 , and CH 4 . When  λp  is 0.35 and 0.43, the conversion ratios of carbon, fixed carbon and volatile matter were both above 50%. The high combustion temperatures at the preheating fuel nozzle exit were caused by the rapid ignition of the coal gas and the recirculation of the high temperature flue gas. The unburned carbon content of the fly ash was slightly increased with the increase of  λp  and the combustion efficiencies were all higher than 98%. No significant HCN was detected during the experiments, indicating that NH 3  was the major precursor of NO X . On one hand, with the increase of  λp , more fuel-N was released during the preheating process, resulting in more fuel-N conversion to N 2  and NH 3 . On the other hand, increasing  λp  could elevate the combustion temperatures in the self-preheating burner, which would affect the heterogeneous reduction of NO X  on the char surface in the DFC. Therefore, the exit NO X  emission was the lowest for  λp  was 0.35.

Effect of the Primary Air Ratio on Combustion of the Fuel Preheated in a Self-preheating Burner