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

Abstract

ABSTRACT The experiments with λ p (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 λ p on operating characteristics of the self-preheating burner was investigated in detail. Besides, the combustion characteristics of the high temperature preheated fuel and NOX emission were discussed. The results showed that with increasing λ p, the temperatures in the self-preheating burner climbed and the main compositions of the coal gas (excluding N2) were CO, H2, CO2, and CH4. When λ p 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 λ p and the combustion efficiencies were all higher than 98%. No significant HCN was detected during the experiments, indicating that NH3 was the major precursor of NOX. On one hand, with the increase of λ p, more fuel-N was released during the preheating process, resulting in more fuel-N conversion to N2 and NH3. On the other hand, increasing λ p could elevate the combustion temperatures in the self-preheating burner, which would affect the heterogeneous reduction of NOX on the char surface in the DFC. Therefore, the exit NOX emission was the lowest for λ p was 0.35.