Powerchina Hubei Electric Engineering Co.,Ltd.
School of Energy and Power Engineering,Huazhong University of Scienceand Technology
State Key Laboratory of Coal Combustion and Low Carbon Utilization,Huazhong University of Science and Technology

燃煤锅炉掺烧低碳氨燃料可以实现大幅碳减排,煤掺氨燃烧中的NO生成与排放问题十分关键。煤中含有Ca、Fe、K、Na等多种典型矿物元素,其对煤燃烧以及掺氨燃烧过程中NO生成与排放影响不尽相同。前人对Ca、Fe、K等矿物元素在煤掺氨燃烧中对NO的生成与还原进行了研究,但是矿物元素Na在煤与富氮燃料氨混合燃烧中NO生成与还原的作用仍不明晰。为了研究煤掺氨燃烧过程中高温贫氧区的NO还原机制以及矿物元素Na的作用机制,采用密度泛函理论进行了模拟计算。首先,利用典型Zigzag模型构建了不同位置吸附Na的焦炭模型,计算结果表明Na原子更易吸附于焦炭边缘未饱和碳上,而不是平行于焦炭吸附。其次,针对NO和NH的不同吸附顺序进行了吸附能计算,结果表明NO和NH分别吸附于Na原子两侧的结构更为稳定,比无Na参与的吸附能最大增加−49.31kJ/mol。然后,探究了6种反应物构型的反应详细步骤,其中H原子迁移至焦炭表面后形成N2分子的限速步能垒明显更低。同时,结果表明Na的参与明显降低了反应限速步的能垒,减少了77.12kJ/mol(路径5相比于路径2)。最后,对6条路径的限速步进行了动力学计算,结果表明Na的存在促进了反应的进行,且在低温下更为明显(路径5相比于路径2加快了4259倍),同时也降低了反应对温度的依赖性。

Coal-fired boilers can realize significant carbon emission reduction by using co-combustion with ammonia which is one of thelow-carbon fuels. NO generation and emission in ammonia-coal co-firing is very critical. Ca,Fe,K,Na,and other typical mineral elementsin coal have different effects on NO generation and emission during coal combustion and ammonia-coal co-firing. The effects of Ca,Feand K on NO generation and reduction in coal-ammonia co-firing have been investigated, but the role of Na is still not clear. Toinvestigate the mechanism of NO reduction in the high-temperature oxygen-poor region during ammonia-coal co-firing and the role ofthe mineral element Na,quantum chemical calculations were carried out. Firstly,the char model for adsorption of Na atom at variouspositions was constructed using a typical Zigzag model. The calculation results showed that Na atom were more likely to be adsorbed onunsaturated carbon at the edge of the char rather than adsorbed parallel to the char. Next,adsorption energy calculations were carried outfor different adsorption orders of NO and NH. The results showed that NO and NH were more stable to adsorbed on both sides of Naatom. Compared to configuration without the participation of Na,the maximum increase in adsorption energy of the configuration withNa participation is −49.31 kJ/mol. Then,the detailed steps of the reaction were explored for six reactant configurations. The migration of H atom to the char surface to form the N2 molecules showed a significantly lower rate-limiting step energy barrier. Meanwhile,the results showed that the involvement of Na significantly reduced the energy barrier of the rate-limiting step of the reaction by 77.12 kJ/mol (Path 5 compared to Path 2). Finally,kinetic calculations of the rate-limiting steps of the six paths were performed. The results showed that the presence of Na promoted the reaction and was more pronounced at low temperatures (4 259-fold for Path 5 compared to Path 2),as well as reduced the temperature dependence of the reaction.

国家重点研发计划资助项目(2023YFB4005704);企业高校合作研发资助项目(03-Q-Q-2022-020)

张保华,曲名新,何文俊,等.煤掺氨燃烧中Na对氨/焦还原NO的机理[J].洁净煤技术,2024,30(11):33−43.

ZHANG Baohua, QU Mingxin, HE Wenjun, et al. Mechanism of Na on NO reduction by ammonia and char during ammonia-coal co-firing process[J].Clean Coal Technology,2024,30(11):33−43.