Study On The Characteristics Of Sodium Precipitation In Coal And Its Effect On NO Formation In H₂O/CO₂ Atmosphere

In recent years,with the development of new combustion technologies such as oxygen-enriched/steam combustion,as well as the emphasis on the application of high alkali metal content coal,the migration and transformation law of alkali metals and their impact on coal under complex atmospheric conditions rich in steam and CO₂ The research on the influence of NOx and other pollutant generation characteristics in the combustion process has also been paid more and more attention.In order to reveal the influence of the H₂O/CO₂ atmosphere on the precipitation characteristics of sodium in coal and the influence of sodium in the H₂O/CO₂ atmosphere on the reaction process of coal char and NO,this paper aims at the precipitation conversion path of sodium in different concentrations of H₂O/CO₂ atmosphere and the reaction of sodium on coal char-NO has been systematically studied.Taking 5%Na Cl impregnated coal as the research object,coal char samples with the same char conversion rate under steam and CO₂ atmospheres were prepared,and the effects of steam and CO₂ atmospheres on sodium precipitation characteristics during coal thermal conversion were investigated.Studies have shown that the addition of steam and CO₂ can promote the release of sodium in the coal during thermal conversion,but with the increase of steam and CO₂ concentration during the reaction,the sodium precipitation rate gradually decreases.This is mainly because the gasification of steam and CO₂ is beneficial to the volatilization of sodium in coal to the gas phase,but it also promotes the conversion of water-soluble Na Cl to other soluble forms such as ammonium acetate,hydrochloric acid and insoluble.This reduces the release of sodium from coal to a certain extent.For the char produced under different atmospheres,the char structure was analyzed and characterized.At the same time,the temperature-programmed thermogravimetric experiment was carried out to study the change rule of coal char combustion reactivity.Studies have shown that the addition of a certain concentration of steam and CO₂ during the coking process will change the structure of coal char,which is beneficial to the improvement of coal char combustion reactivity.The combustion reactivity of 2%Na Cl impregnated coal char prepared under the atmosphere of steam and CO₂ is higher than that of 5%Na Cl impregnated coal.Analysis shows that although 2%Na Cl impregnation coal char has fewer oxygen functional groups and a smaller specific surface area than 5%Na Cl impregnated coal,but it has a lower degree of aromatization.Therefore,the structure of 2%Na Cl impregnated coal is more conducive to combustion reactivity improvement.The experiment further prepared coal char impregnated with different sodium loadings,and studied the reaction process of Na Cl impregnated coal char and NO under steam and CO₂atmospheres.The results show that increasing the concentration of steam and CO₂ in the atmosphere can promote the improvement of NO reduction rate.The main reason is that the gasification of steam and CO₂ changes the structure of coal char and produces a large amount of CO,which promotes the reduction of NO.As the sodium content in coal char increases,the NO reduction rate increases first and then decreases.This is because more sodium evaporates to the gas phase and reduces NO homogeneously,and the sodium remaining in the coal char can catalyze coal char-NO reaction process;When sodium is excessive,part of the pore diameter of the coal char is blocked,and the reduction of NO on the surface of the coal char is hindered.