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

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 NO_X 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 NO_X. 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 NO_X on the char surface in the DFC. Therefore, the exit NO_X emission was the lowest for λ_p was 0.35.

KEYWORDS:

• Self-preheating
• combustion
• NO_X emission

Additional information

Funding

This work was supported by the National Key R&D Program of China [2017YFB0602005]; Strategic Priority Research Program of the Chinese Academy of Sciences [XDA21040100]; Youth Innovation Promotion Association of the Chinese Academy of Sciences [2019148].