Influence of H₂O Thermal Effect on the Formation of Ultrafine PM During Char Combustion

ABSTRACT

To clarify the influence of H₂O thermal effect on the formation of ultrafine particulate matter (PM), Huangling coal char was burned in a high-temperature drop tube furnace at 1800 K under various O₂/N₂/H₂O and O₂/N₂/H₂O/Ar atmospheres. The introduction of Ar in the simulating atmosphere was designed to counteract the thermal effect of H₂O. Results indicated that after eliminating the thermal effect of H₂O, the yield of ultrafine PM continuously increased in higher H₂O content. Compared with no H₂O, the mass and number yield of ultrafine PM in O₂/N₂/H₂O/Ar atmosphere with 30% H₂O content increased by 35.5% and 58.9%, respectively. H₂O thermal effect, gasification reaction, and char oxidation reaction during coal char combustion played a significant role in the formation of ultrafine PM. Oxidation reaction was the primary factor affecting the formation of ultrafine PM, and its relative contribution was more than 62.9%, whereas the thermal effect of H₂O showed an overall negative net effect on the formation of ultrafine PM. With the H₂O content varied from 5% to 30%, the contribution of H₂O thermal effect to mass yield was in the range of −19.1% to −18.0%, while that to number yield was −33.1% to −30.6%. Once the H₂O content reached 10%, the enhancing effect of H₂O gasification reaction on the yield of ultrafine PM surpassed the negative contribution of H₂O thermal effect. For a given H₂O content, elevated O₂ concentration weakened the negative contribution of H₂O thermal effect.

KEYWORDS:

• H₂O
• thermal effect
• ultrafine particulate matter
• Ar
• char combustion

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The present work was supported by the Fundamental Research Funds for the Central Universities (Grant No. xtr042019007).