Study On The Emission Of NO Under The Condition Simulating Precalciner Of High CO₂ Concentration

The cement production of our country has ranked the first place in the world consistently for many years.The cement plant is not only the main emitting source of greenhouse gas CO₂,and a great amount of NOx which is seriously harmful to environment and human beings is emitted from the cement plant during the production process of cement plant.As a possible means of cutting the emission of CO₂ which can be applied in cement pre-calciner,the O₂/CO₂ combustion technology can also be used to decrease the emission of NOx greatly from coal.Thus it is very meaningful for O₂/CO₂ combustion technology being applied in cement pre-calciner to study the NO emitting characteristic of a blend of coal and cement raw meal in the O₂/CO₂ atmosphere.The NO emitting characteristics of coals and blends of coal and cement raw meal in high CO₂ concentration atmosphere were firstly studied in this paper.The influence laws of CO₂ concentration,temperature and O₂ concentration on the NO emitting characteristic of coals,and a blend of coal and cement raw meal were researched.The results showed that cement raw meal or the decomposing product of cement raw meal both had great aggravating effects on the NO emission in O₂/N₂ and O₂/CO₂ atmosphere,and such effects were even more significant to anthracite in high CO₂ concentration atmosphere.Besides the effects of cement raw meal were greater than those of the decomposing product.The emitting quantities of coals and blends of coal and cement raw meal had a monotonic decreasing trend with the increase of CO₂ concentration.The emitting quantities of different coals and different blends of coal and cement raw meal showed different varying trend as temperature or O₂ concentration increased.Moreover,different chars obtained from coal after combusting in pure CO₂ atmosphere and N₂ atmosphere were taken as examples?referred as CO₂ char and N₂ char below?.The NO emitting characteristics of different chars and blends of char and cement raw meal,and the combusting characteristics of different chars in high CO₂ concentration atmosphere were studied in this paper.The results showed that the NO emitting quantity of CO₂ char was smaller than that of N₂ char in O₂/N₂ and O₂/CO₂ atmosphere,and the aggravating effect of cement raw meal on the N₂ char was larger than that on the CO₂ char.Compared with the N₂ char,the combusting rate of CO₂ char was more sensitive to the change of temperature in high CO₂ concentration atmosphere.The difference between two different chars was small during the condition of relative low O₂ concentration,and it became greater as O₂ concentration increased.Cement raw meal showed inhibiting effects on the combustion of both chars.The combusting mechanism models of two chars were the same,and the model was twodimensional random nucleation and nucleus growth mechanism.Chemical pure substances were taken as additives.The effects of possible different micro-components in cement raw meal,and the possible different micro-components blended with the main component CaCO₃ on the NO generation of coals were studied in O₂/N₂ and O₂/CO₂ atmosphere.The results showed that without CaCO₃,Fe₂O₃ had the most aggravating effects on the NO emission of coal,and MgSO₄ had the most inhibiting effects,and other micro-components had slightly inhibiting effects in both atmospheres.Besides,when there was a great amount of CaCO₃,all micro-components referred in this paper showed aggravating effects on the NO emission of coal,and the effect of Fe₂O₃ was the greatest,and effect of Al₂O₃ was the weakest,and the effects of other micro-components were almost the same.The whole content of the paper was summarized and the next deeper work was talked about at the end of the paper.