高硫炼焦煤化学结构及硫赋存形态对硫热变迁的影响

利用红外、拉曼、热重及XANES等技术对不同煤阶高硫炼焦煤的化学结构、原煤及焦样形态硫分布进行了准确判定,对煤中化学结构及硫赋存形态与硫的热变迁行为进行了关联分析。结果表明,高硫炼焦煤中硫的热变迁行为不仅与硫赋存形态有关,而且受化学结构不同的高硫炼焦煤热解挥发分释放特性的影响。较低煤阶高硫炼焦煤中脂肪结构热分解产生大量挥发分,且挥发分释放温区较宽,形态硫分解产生的活性硫与挥发分中富氢组分相结合,形成更多的含硫气体转移到气相中,提高了热解脱硫率,焦炭体相中噻吩硫相对含量高于表面,硫化物硫则与之相反。煤化程度升高,煤中稳定噻吩类硫含量增多,挥发分释放量减少,热解脱硫率降低,且形态硫在焦炭体相与表面的分布差异不明显。无机硫脱除率与黄铁矿硫分解程度直接相关,热解过程中也将形成部分新的无机硫滞留于焦中。煤结构及有机硫的赋存形态决定了有机硫脱除率,煤阶升高时有机硫脱除率明显降低。

Effect of chemical structure and sulfur speciation of high-sulfur coking coals on sulfur transformation during pyrolysis

The chemical structure, content and distribution of sulfur forms in coal and coke of four high-sulfur coking coals were characterized by FT-IR, Raman, TG, and sulfur K-edge XANES technique, and effects on sulfur transformation during pyrolysis were also investigated. The results show that sulfur transformation behavior is related to the sulfur forms in coal as well as the release of volatile matters during pyrolysis. For lower rank coking coals, decomposition of unstable aliphatic structure releases plenty of volatiles with wider range. The interactions between sulfur radicals from cleavage of sulfur forms and hydrogen-rich radicals in volatiles promote release of sulfur into gas phase. This increases total sulfur removal and results in the higher content of thiophene in coke bulk than that on coke surface, while sulfide compounds have an opposite distribution. The degree of aromatization and relative content of thiophene increase with increasing coal rank, leading to lower desulfurization rate and unapparent difference of sulfur distribution between bulk and surface of coke. Inorganic sulfur removal is related to degree of decomposition of pyrite directly, and inter-conversions of sulfur species during pyrolysis process would generate new inorganic sulfur and retain in coke ultimately. Organic sulfur removal is determined by the coal structure and organic sulfur forms, and decreases obviously with increasing coal rank.