煤燃烧过程中燃料型NO_(x)生成及还原机理研究进展

Research progress on formation and reduction mechanism of fuel-NO_(x) during coal combustion

燃料型NO_(x)是煤燃烧烟气中氮氧化物的主要组成部分,抑制燃料型NO_(x)的生成是低氮燃烧技术中降低NO_(x)排放初值的关键手段。燃料型NO_(x)的生成实属非常复杂的物理化学过程,涉及许多相互竞争的机制,受多个因素的综合影响。煤燃烧过程中燃料型NO_(x)的生成主要包括煤热解过程中挥发分N的释放过程、挥发分燃烧过程中NO_(x)的生成及还原过程、焦炭燃烧过程中NO_(x)的生成及还原过程。综述煤燃烧过程中燃料氮的迁移转化规律的研究结果,对煤燃烧中均相和非均相氮化学反应的详细机制进行整理并分析燃料型NO_(x)形成的内在机理,发现煤热解过程中煤中氮迁移形成挥发分N和焦炭N,迁移过程由煤种和热解条件共同决定。热解条件不仅影响挥发分N的释放,还影响焦炭的反应活性,从而影响焦炭燃烧及焦炭N的转化过程。挥发分N主要以HCN和NH;的形式存在,通过详细的均相氮化学机理建立挥发分NO_(x)的生成预测模型,以期较为准确地预测煤燃烧过程中挥发分NO_(x)的形成过程。焦炭N的转化过程主要涉及焦炭N-O;和焦炭-NO 2个反应,焦炭NO_(x)的形成是受煤种、温度、氧气浓度、矿物组分、焦炭粒径、焦炭反应活性等因素交互影响的综合结果,研究焦炭N的转化需综合考虑各因素的影响。

Fuel NO_(x) is the main component of nitrogen oxides in coal combustion flue gas,and inhibiting the formation of fuel NO_(x) can effectively reduce the initial value of NO_(x) emissions.The formation of fuel NO_(x) is a very complex physical and chemical process involving many competing mechanisms and it is affected by multiple factors.The formation of fuel NO_(x) during coal combustion mainly includes:the release process of volatile N during coal pyrolysis;the formation and reduction process of NO_(x) during the combustion process of volatile matter;the formation and reduction process of NO_(x) during the combustion process of coke.This paper summarized the research results of the transfer and transformation of fuel nitrogen during coal combustion,sorted out the detailed mechanisms of homogeneous and heterogeneous nitrogen chemical reactions in coal combustion,and analyzed the internal mechanism of fuel NO_(x) formation.During coal pyrolysis,nitrogen in coal migrates to form volatile N and coke N,and the migration process is determined by coal type and pyrolysis conditions.Pyrolysis conditions not only affect the release of volatile N,but also affect the reactivity of coke,thereby affecting the combustion of coke and the conversion of coke N.Volatile N mainly exists in the form of HCN and NH;.The volatile NO_(x) generation prediction model established by the detailed homogeneous nitrogen chemical mechanism can more accurately predict the formation process of volatile NO_(x) during coal combustion.The conversion process of coke N mainly involves two reactions(coke N-O;and coke-NO).The formation of coke NO_(x) is comprehensively influenced by the interaction of coal type,temperature,oxygen concentration,mineral composition,coke particle size,coke reactivity and other factors.As a result,the study of coke N conversion needs to comprehensively consider the influence of various factors.