Na/Ca/Fe金属间相互作用对高碱煤热解氮变迁的影响

Effects of Na/Ca/Fe intermetallic interactions on nitrogen transformations in high-alkali coal pyrolysis

  • 摘要: 我国新疆高碱低阶煤具有低灰、高钠和高反应活性的特点,开发高碱煤清洁高效转化为高值化学品技术,将对解决高碱煤资源利用、助力“双碳”目标的实现具有重要战略意义。高碱煤中活性矿物组分Na、Ca、Fe对煤热解具有催化活性,对氮的演化有显著影响。目前尚缺乏矿物组分之间相互作用对燃料氮热转化的影响机制研究。阐明金属间相互作用对高碱煤热解过程中氮变迁的影响,对制定高碱煤梯级利用过程中氮在气、液、固三相中分配的调控策略具有重要的指导意义。通过等体积浸渍法与顺序浸渍法分别将Na、Ca、Fe单金属和双/三金属负载到脱灰煤上,开展高碱煤固定床热解氮转化研究。利用GC-MS、XPS、溶液吸收法,定量分析单金属与双/三金属对煤热解含氮产物分布影响,对比分析热解试验结果与理论计算值,研究双/三金属间相互作用关系。通过分析煤样热解含氮产物的产率/残留率变化,研究双/三金属对高碱煤热解氮转移路径的影响。结果表明:双/三金属通常对氮向气相的迁移具有金属间拮抗作用,对HCN、NH3的抑制强于单金属。Na/Ca、Fe/Ca组合对半焦中N−6、N−5组分向焦油中杂环氮、胺−N等物质的转化具有金属间的协同作用,其对焦油中含氮物质生成的促进作用往往强于单金属。Na/Fe、Na/Fe/Ca组合对半焦内部N−6向N−Q的转化起到金属间的协同作用,促进了氮的固定。

     

    Abstract: China Xinjiang high-alkali low-rank coal has the characteristics of low ash, high sodium content and high reactivity. Developing clean and efficient conversion technology for high alkali coal into high-value chemicals will have important strategic significance for solving its resources utilization and helping to achieve the “dual carbon” goal. The mineral components Na, Ca and Fe in high-alkali coal have catalytic activity in coal pyrolysis, which has a significant influence on nitrogen transformation. There is still a lack of research on the effects of interactions between mineral components on the thermal conversion mechanisms of fuel-N. This study aims to elucidate the effects of intermetallic interactions on nitrogen transformation during pyrolysis of high-alkali coal. The results have significant implications for formulating control strategies of nitrogen distribution in gas, liquid and solid phases during the cascade utilization of high-alkali coal. Na, Ca, Fe mono-metal and poly-metals were added to deashed coal by equal volume impregnation and sequential impregnation methods, and nitrogen transformation was studied in fixed-bed pyrolysis of high-alkali coal. GC-MS, XPS and solution absorption method were used to quantitatively analyze the effects of mono-metals and polymetals on the distribution of nitrogen-containing products in coal pyrolysis, and interactions between them were analyzed by comparing the results of experiments results with theoretical calculations results. The effect of poly-metals on the pathway of N transformation in pyrolysis of high-alkali coal was studied by analyzing yield/residual rate of nitrogen-containing products. The results indicate that poly-metals usually exhibit an intermetallic antagonism on the migration of nitrogen into the gas phase, with stronger inhibition of HCN, NH3 than monometallic. The synergistic effects of Na/Ca and Fe/Ca significantly enhance the conversion of N−6 and N−5 in char to heterocyclic nitrogen and amine-N in tar, which demonstrates stronger promotion of nitrogen-containing compound formation in tar compared to mono-metallic systems. Furthermore, Na/Fe and Na/Fe/Ca play a synergistic role for conversion of N-6 to N-Q in char though intermetallic interaction, thus promoting the fixation of nitrogen in char.

     

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