Study On The Effects Of CO₂/H₂O On The Generation Characteristics Of Nitrogen Oxides During Coal Combustion Process

In recent years,oxy-Fuel combustion technology has received widespread attention,and there is a large amount of CO₂ and steam in the atmosphere,which causes changes in the combustion characteristics of pulverized coal and the generation characteristics of pollutants.In order to explore the formation characteristics of nitrogen oxides in the combustion process in the presence of a large amount of steam and CO₂,the precipitation and transformation paths of coal nitrogen and the reduction reaction between coal char and NO were studied for three atmospheres.The characteristics of NO formation during the combustion of pyridine and pyrrole under different CO₂/H₂O atmosphere were investigate.The results show that the addition of steam and CO₂ can inhibit the formation of NO during homogeneous combustion,and the inhibition of NO formation by steam is more obvious.When steam and CO₂ coexist,the production of NO is lower,but it is not a linear superposition of the results when the two gases are present respectively.The simulation study of chemical reaction kinetics further revealed that the influence of CO₂/H₂O on the homogeneous formation of NO was mainly because the addition of H₂O could inhibit the conversion from HCN to CN,and promote the hydrolysis reaction of HCN to form NH₃.The further dehydrogenation of NH₃ is converted into NH₂ which has strong reducibility to NO,thereby inhibiting the formation of NO.The research on the form and transformation of nitrogen in coal char under different temperature and CO2/H2O atmosphere shows that the mass fraction of N-X and N-Q in coal char decreased with the increase of steam concentration.The conversion between different nitrogen forms is mainly affected by H radicals and OH radicals brought by steam.There are several paths of conversion between nitrogen forms:the decomposition of N-Q exposes internal N atoms to form N-6;N-6 reacte with H radicals to form protopyridine N-Q;the break of N-O bond in N-X to form N-6;N-6 reactes with OH radicals to form N-X;the oxidization of N-6 to form pyridone N-5.Studies on the formation and reduction of char-NO under different atmosphere of O₂/CO₂/H₂O showed that both steam and CO₂ can promote the reduction of NO,and the promotion of steam is more obvious.Under reducing atmosphere,steam can promote char nitrogen into gas phase.N-6,N-5,and N-X enter the gas phase in the form of HCN after pyrolysis,and N-Q enters the gas phase in the form of NH₃ after pyrolysis.In the presence of O₂,the reduction of NO is inhibited.Because O₂ can promote the oxidation of the nitrogen-containing intermediate phase,and react with the char surface active site to reduce the char surface active site,while competing with reducing gases such as NO,H₂,CO.