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Density functional theory study of the heterogenous interaction between char-bound nitrogen and CO2 during oxy-fuel coal combustion
Combustion and Flame ( IF 5.8 ) Pub Date : 2020-06-01 , DOI: 10.1016/j.combustflame.2020.02.026
Shanhui Zhao , Rongyue Sun , Xiaolong Bi , Xiaojun Pan , Yi Su

Abstract In order to have a deep insight into the NO formation mechanism during oxy-fuel combustion, density functional theory (DFT) was used to investigate the interaction between char(N) and CO2 at molecular level. The geometric structures, orbital electron distribution properties and reaction paths were calculated and optimized. The outer orbital electron properties of char(N) and CO2 indicate that CO2 acts as the oxidizer, which tends to attract electrons from char(N) during char(N)-CO2 interaction. The geometries and Mulliken properties of three initial chemisorption intermediates indicate that char(N) may mainly undergo two oxidation/gasification paths: one is carbon atom oxidation by CO2 to form CO via initial chemisorption structure of IM1. The other is nitrogen atom combination with oxygen atom and further to be oxidized to form NO via initial chemisorption structure of IM2. The initial chemisorption reactions of CO2 on char(N) surface are exothermic reactions and take place spontaneously at the operation temperature during oxy-fuel combustion. According to the reaction energy barriers and kinetic analysis, path 1 and path 2 have the comparative probability during char(N)-CO2 interaction to produce CO and NO. Nevertheless, NO produced in path 2 will further be in-situ reduced by CO over char surface, which will lead to low NO concentration in flue gas during oxy-fuel combustion.

中文翻译:

富氧煤燃烧过程中炭结合氮与CO2异质相互作用的密度泛函理论研究

摘要 为了深入了解富氧燃烧过程中NO的形成机理,采用密度泛函理论(DFT)在分子水平上研究了char(N)与CO2之间的相互作用。计算并优化了几何结构、轨道电子分布特性和反应路径。char(N) 和 CO2 的外轨道电子特性表明 CO2 作为氧化剂,在 char(N)-CO2 相互作用过程中倾向于从 char(N) 吸引电子。三种初始化学吸附中间体的几何形状和马利肯性质表明,char(N)可能主要经历两种氧化/气化途径:一种是通过 IM1 的初始化学吸附结构被 CO2 氧化碳原子形成 CO。另一种是氮原子与氧原子结合并通过IM2的初始化学吸附结构进一步氧化形成NO。CO2 在炭(N) 表面的初始化学吸附反应是放热反应,在氧燃料燃烧期间在操作温度下自发发生。根据反应能垒和动力学分析,路径1和路径2在char(N)-CO2相互作用过程中产生CO和NO的概率比较大。然而,在路径 2 中产生的 NO 将进一步被炭表面上的 CO 原位还原,这将导致氧燃料燃烧过程中烟气中的低 NO 浓度。CO2 在炭(N) 表面的初始化学吸附反应是放热反应,在氧燃料燃烧期间在操作温度下自发发生。根据反应能垒和动力学分析,路径1和路径2在char(N)-CO2相互作用过程中产生CO和NO的概率比较大。然而,在路径 2 中产生的 NO 将进一步被炭表面上的 CO 原位还原,这将导致氧燃料燃烧过程中烟气中的低 NO 浓度。CO2 在炭(N) 表面的初始化学吸附反应是放热反应,在氧燃料燃烧期间在操作温度下自发发生。根据反应能垒和动力学分析,路径1和路径2在char(N)-CO2相互作用过程中产生CO和NO的概率比较大。然而,在路径 2 中产生的 NO 将进一步被炭表面上的 CO 原位还原,这将导致氧燃料燃烧过程中烟气中的低 NO 浓度。
更新日期:2020-06-01
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