| Recently,abundant coal resources have been found in Xinjiang Province,but there are rich in sodium,which has significant effects on the formation and reduction of NOx.Therefore,a comprehensive study on the transformation of sodium during coal combustion is necessary for developing the low NOx emission combustion technology.Meanwhile,the combination of NN is an important step for N2 formation during the NO reduction by char.Consequently,it has great meaning to explore the reaction mechanism of NO heterogeneous reduction by nitrogencontaining char and the effect mechanism of sodium on it for the control emission during high alkali coal combustion.Based on the background,using collection of related data and combination of fixed bed experiments and density functional theory calculation study the above contents.Firstly,by summarizing the relevant data of published papers,it found that sodium in almost high alkali coal is mainly water-soluble sodium.Meanwhile,when the combustion temperature is over 1000℃ and reduction atmosphere,sodium volatilizes from coal to gas phase and it exists in gas as Na.Therefore,in the follow-up study,the deashed coal was loaded with NaCl to represent the typical alkali metal sodium in high alkali coal,and Na is introduced into the Char（N）in the theoretical calculation.In the fixed bed experiment,the reduction rate of NO and the evolution curve of flue gas composition and content at the outlet were compared at 1300℃ and 1400℃.It was found that in the initial stage of heterogeneous reduction of NO,the chemical adsorption stage of NO,low addition of NaCl promoted the NO reduction,and the promotion gradually increased with the increase of addition amount;Moreover,NaCl promoted NO chemisorption and made more NO chemisorption on the surface of char.At the same time,the content of N-6 in char is positively correlated with the amount of no adsorption,and the increase of temperature is beneficial to the heterogeneous reduction of NO promoted by sodium.However,in the second stage of char gasification,the addition of NaCl inhibited the heterogeneous reaction between CO2 and carbon atoms at the edge of char,and the nitrogen-containing heterocycles on the surface of char were less involved in the heterogeneous reduction of NO.On the other hand,NaCl accelerated the NO growth rate in the second stage,which indicated that NaCl inhibited the regeneration of active sites.Based on density functional theory,Gaussian 16 and Multi wfn were used to further explore the NO heterogeneous reduction mechanism by nitrogenous char and the effect of sodium on it.It is found that in the first stage of the reaction,sodium can promote the NO heterogeneous reduction by increasing the heat release of NO chemisorption and reducing the highest energy barrier of N2 release.In the second stage.sodium inhibited CO formation by increasing the highest energy barrier of CO analytical attachment,which was consistent with the experimental results.C3 atom reduces the contribution to the frontier orbit of the char edge,reduced the chemical activity of the reactant,was not conducive to the subsequent reaction,and is consistent with the experimental results. |
