No formation and its reduction through co-flow methane reburn in a pulverised coal combustion process under various overall equivalence ratio

Abstract

Computational simulation has been carried out to investigate the NO formation/depletion in pulverized coal combustion process. Newlands Bituminous coal is injected along with career air through a central hole of an axi-symmetric burner. A certain amount of co-flow methane is injected coaxially as reburn fuel. The effect of overall equivalence ratio on NO formation and NO reburn are mainly focused in this study. Species concentration for various species are also investigated, because both NO formation and depletion are related closely to various species concentration. From the study it is observed that, at overall equivalence ratio φ=0.8 and 1.0, although the rate of Thermal-NO, Prompt-NO and Fuel-NO formation is high but due to narrow reaction zone and higher air velocity, a weak NO concentration field is observed. On the other hand, a higher NO concentration has been observed with higher equivalence ratio (ratio φ=3.0, 6.0 and 9.0). It also has been observed, the maximum NO reduction efficiency at φ=0.8, 1.0 and 3.0 is in between 1% to 7%, whereas for φ=6.0 and 9.0, the maximum NO reduction efficiency is 27% and 34% respectively. Therefore, co-flow methane injection NO reduction method is more suitable for highly rich mixture conditions. Moreover, the percentage of coal burnout is also relatively higher for higher equivalence ratio condition.

Keywords

• Pulverized Coal
• Combustion
• Equivalence Ratio
• Co-flow Methane
• Reburn

References

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