氨煤混燃过程中NH/煤焦/O_(2)异相体系N氧化的分子机理  

Molecular mechanism of N oxidation in ammonia-coal co-firing

作　　者：陈萍 王莹 汪辉春 蒋博宇 顾明言 樊建人[2] CHEN Ping;WANG Ying;WANG Huichun;JIANG Boyu;GU Mingyan;FAN Jianren(School of Energy and Environment,Anhui University of Technology,Maanshan 243002,China;State Key Laboratory of Clean Energy Utilization,Zhejiang University,Hangzhou 310000,China)

机构地区：[1]安徽工业大学能源与环境学院,安徽马鞍山243002 [2]浙江大学能源清洁利用国家重点实验室,浙江杭州310000

出　　处：《煤炭学报》2023年第2期1037-1046,共10页Journal of China Coal Society

基　　金：安徽高校自然科学研究项目重点资助项目(KJ2021A0381);能源清洁利用国家重点实验室开放基金资助项目(ZJUCEU2021011);煤燃烧国家重点实验室开放基金资助项目(FSKLCCA2206)。

摘　　要：为了实现双碳目标,降低煤电碳排放势在必行。无碳燃料氨与煤混烧被认为是降低火电碳排放的有效途径之一。而氨作为N源,增加了氨煤混燃NOx排放量升高的可能性,因此,深入研究氨煤混燃NO生成机理对实现氨煤混燃低碳低氮燃烧十分关键。采用量子化学方法探究了当NH3以NH形式存在时氨煤混燃N的氧化机理,并采用波函数分析NH和O_(2)在煤表面的吸附行为。计算结果表明,NH在C5表面吸附形成中间体IM1的过程为放热过程,放热量高达754.79 kJ/mol,且C原子为电子供体而失电子,NH为电子受体而得电子,促进C—N键键合。进一步探究O_(2)以不同方式吸附时NH/煤焦/O_(2)体系的反应机理,得出NH/煤焦/O_(2)共燃体系首先发生NH在煤焦表面的氧化,随后煤焦表面残余氧或体系中O_(2)将煤焦-N进一步氧化。NH/煤/O_(2)异相体系中NH通过不同反应路径生成氧化产物NO、NO_(2)和HNO,对应决速步能垒分别为120.67、323.37和193.50 kJ/mol,说明氨-N/煤-N生成NO的过程更易进行。动力学结果表明,各温度下生成NO的决速步速率明显高于NO_(2),且随着温度升高,生成NO的决速步速率与HNO的逐渐接近。NH氧化产物释放后,残留在煤焦表面氧进一步与C结合成CO释放,实现了共燃体系氨燃料中N和煤粉中C的氧化。随后煤焦-N与体系中O_(2)发生异相氧化,实现煤焦-N向NO的转化。在微观层面揭示了氨燃烧生成NO过程中重要过渡产物HNO形成的分子机理,明晰了另一氧化产物NO_(2)的生成路径,为发展氨煤的混合燃烧机理提供理论支撑和数据参考。In order to achieve the dual carbon goals,it is imperative to reduce the carbon emissions in coal-fired power plants.Carbon-free fuel ammonia and coal co-combustion is considered to be one of the effective ways to reduce carbon emissions from thermal power plants.Ammonia as an N source increases the possibility of increased NO x emissions from ammonia-coal co-combustion.Therefore,an in-depth study of the NO formation mechanism of ammonia-coal co-firing is very important to realize low-carbon and low-nitrogen emission of ammonia-coal co-firing.In this study,a quantum chemical method was used to explore the oxidation mechanism of N in ammonia-coal co-combustion when NH 3 exists in the form of NH,and the adsorption behavior of NH and O_(2) on the coal surface was analyzed by wave function.The calculation results showed that the adsorption process of NH on the C5 surface to form the intermediate IM1 is a highly exothermic process with 754.79 kJ/mol.Moreover,the C atom is an electron donor and lost electrons,and the NH is an electron acceptor and obtained electrons,which promotes the C—N bond.The reaction mechanism of the NH/char/O_(2) system when O_(2) is adsorbed in different ways was further explored.It was concluded that in the NH/char/O_(2) co-combustion system the oxidation of NH first occurs on the char surface,and then the residual oxygen on the char surface or O_(2) in the system oxidizes the char-N.In the NH/coal/O_(2) heterogeneous system,the NH generates oxidation products NO,NO_(2) and HNO through different reaction paths,and the corresponding rate-determining step energy barriers are 120.67,323.37 and 193.50 kJ/mol,respectively.It was concluded that the process of the NO formation from ammonia-N/coal-N is easier to carry out.The kinetic results showed that the rate-determining step rate of NO formation is significantly higher than that of NO_(2) at all temperatures,and with the temperature increase,the rate-determining step rate of NO formation is gradually close to that of HNO.After the release of NH

关 键 词：氨煤混烧 NH 煤焦-N NO HNO 

分 类 号：TK16[动力工程及工程热物理—热能工程]