The enhanced SO3 formation by alkali-metal sulfates from ash in the post-flame region during the combustion of high-alkali coal

Xiao, Haiping; Cheng, Qiyong; Shi, Hao; Li, Jian; Ru, Yu

The enhanced SO3 formation by alkali-metal sulfates from ash in the post-flame region during the combustion of high-alkali coal

2020

Xiao, Haiping | Cheng, Qiyong | Shi, Hao | Li, Jian | Ru, Yu

High alkali-metal sulfate contents in ash from high-alkali coal are a result of the alkali metals’ strong sulfur-capturing capacity. In this work, the effects of sulfates in ash on SO₃ formation were investigated by adding alkali-metal sulfates (Na₂SO₄ and K₂SO₄) to ash and performing experiments to simulate SO₃ formation. The results show that Na₂SO₄ and K₂SO₄ addition significantly increased SO₃ formation and the formation rate increased with increasing temperature. The formed SO₃ concentration increased by 6.8 ppm (adding Na₂SO₄) and 6.3 ppm (adding K₂SO₄) at 1000 °C. These increases are the result of SO₃ release from sulfate during the formation of aluminosilicates such as NaAlSi₃O₈ (albite), NaAlSiO₄ (nepheline), KAlSiO₄ (kalsilite), and KAlSi₃O₈ (feldspar) with the SiO₂ and Al₂O₃ in the ash. This was confirmed by X-ray diffraction (XRD) and thermodynamic calculation. In addition, increasing the SO₂ concentration increased the SO₃ concentration and decreased the SO₃ conversion ratio. Graphical abstract Note: This data is mandatory.

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