Oxy-steam燃烧初期H_(2)O及其衍生基团对煤−N迁移转化的影响机理  

Effect of H_(2)O and its-resulting groups on coal-nitrogen evolution and transition in the initial stage of oxy-steam combustion

作　　者：岳爽 丁浩浩 赵硕[1] 张月[2] 洪迪昆 邓海顺[1] YUE Shuang;DING Haohao;ZHAO Shuo;ZHANG Yue;HONG Dikun;DENG Haishun(School of Mechanical Engineering,Anhui University of Science&Technology,Huainan 232001,China;Department of Energy Power&Mechanical Engineering,North China Electric Power University,Baoding 071000,China)

机构地区：[1]安徽理工大学机电工程学院,安徽淮南232001 [2]华北电力大学能源动力与机械工程学院,河北保定071000

出　　处：《煤炭学报》2024年第11期4617-4626,共10页Journal of China Coal Society

基　　金：安徽省高校自然科学研究资助项目(2023AH051188);国家重点研发计划资助项目(2022YFB4100204);安徽省自然科学基金资助项目(2408085QE176)。

摘　　要：近年来,以O_(2)、H_(2)O为工质的第3代富氧燃烧——氧-水蒸气(Oxy-steam)燃烧技术,因其巨大的CO_(2)捕集潜力及优良的系统可靠性而备受关注。然而,H_(2)O对煤粉着火燃烧的影响十分复杂且非线性,尤其对于高浓度H_(2)O(体积分数30%~80%)作用下的煤氮热变迁机理尚且不明,传统的低氮燃烧技术或将不再适用于O_(2)/H_(2)O燃烧,进而加剧氮氧化物(NOx)排放超标风险。为此,借助基于ReaxFF的分子动力学(Molecular Dynamics,MD)模拟,结合原子示踪方法,研究O_(2)/H_(2)O燃烧前期脱挥发分阶段煤中有机氮的迁移转化特性,重点关注了含氮官能团赋存形态的演化过程及含氮前驱物生成反应路径,为开发适用于Oxy-steam燃烧的低氮燃烧调整工艺提供理论基础。结果表明:脱挥发分阶段初期,H_(2)O的存在促进了氢氧基团尤其是·OH自由基与羟基官能团(C—OH)的生成,有利于含氮官能团所在芳香环的裂解以及含氮前驱物的释放,但这种影响在脱挥发分前期并不明显;大量氢氧基团的生成促使位于芳香环内部的季氮(N-Q)向处于碳链边界的吡啶氮(N-6)发生转化,同时加剧了煤中原有的N-6、吡咯氮(N-5)向氧化型/不定型氮(N-X)发生迁移,导致煤脱挥发分阶段前期,湿环境下得到的固相燃烧产物中N元素多以N-6、N-X的形式存在,煤中含氮官能团稳定性更低、活性更高;此外,随着煤氮热变迁过程的进行,H_(2)O及其衍生基团的存在改变了含氮前驱物的生成来源,提高了N-6向HCN、N-5向NH_(3)的转化率,但相同工况下HCN、NH_(3)产率受H_(2)O的影响不大。The 3^(th) generation oxy-rich combustion technology,that is oxy-steam combustion with O_(2) and H_(2)O as working medium,has recently attracted much attention due to its great potential and stability in the field of CO_(2) capture.Given that the effect of H_(2)O on coal ignition and combustion is complex and non-linear,it is still unclear about the effect of H_(2)O on coal-nitrogen evolution,particularly in high H_(2)O concentration.In this case,the traditional low-nitrogen combustion technology would not be suitable for O_(2)/H_(2)O combustion,increasing the risk of excessive nitrogen oxide(NOx)emissions.In this paper,the migration and transition of organic nitrogen during coal devolatilization in O_(2)/H_(2)O combustion has been studied by using the ReaxFF molecular dynamic(MD)simulation and combining atomic labeling method,emphasizing on the migration route of nitrogen-containing functional groups and the formation of nitrogen-containing precursor.This will help to develop the technology of low-nitrogen combustion for the oxy-steam combustion.Results show that in the initial stage of coal devolatilization,the presence of high H_(2)O concentration greatly promotes the formation of hydroxyl group(e.g.OH radical and C—OH group).It is beneficial to break aromatic ring and to release nitrogen-containing precursors,but it is not obvious in the initial stage of coal devolatilization.The formation of a large number of hydroxyl groups promotes the conversion of quaternary nitrogen(N-Q)in the aromatic ring to pyridine nitrogen(N-6)at the carbon boundary.In the meanwhile,the migration of N-6 and pyrrole nitrogen(N-5)to oxidized/amorphous nitrogen(N-X)is intensified.In the initial stage of coal devolatilization,the solid products obtained at high humidity have higher contents of N-6 and N-X,a lower stability of nitrogen-containing functional groups in coal,as well as a higher activity of reactivity sites.As time goes on,the presence of H_(2)O and its resulting groups change the source of nitrogen-containing precursors.

关 键 词：氧-水蒸气燃烧 脱挥发分阶段 H_(2)O 含氮前驱物 分子动力学 

分 类 号：TQ534[化学工程—煤化学工程]