Study On Experiment And Mechanism Of Denitrification By CO In Cement Precalciner

At present,there are more than 3,000 cement enterprises in China and more than1,800 new dry production lines.The NO_x emission concentrations generally exceed 850mg/Nm³.NO_x produced by cement kilns has become the third largest NO_x emission source in China except for electricity and motor vehicles,causing serious environmental pollution.NO_x in cement kilns is mainly produced by fuel combustion,of which about60%of the fuel is burned in the cement precalciner.Therefore,it is of great significance to study the denitrification technology for cement precalciner.Cement precalciner contains high concentration of calcium-based substance?mainly CaO?and high concentration of CO₂,and there is a reduction atmosphere?mainly CO?due to the application of hierarchical combustion technology.For this reason,it is of great scientific significance and engineering application value to study the influence factors and mechanism of CO denitrification efficiency in high-concentration CaO/CO₂ environment in cement precalciner.In this paper,the effect of CaO,CO₂ concentration and CO concentration on denitrification efficiency was studied by means of an experiment in high CaO/CO₂environment operated by fluidized bed reactor.The result shows that CaO can catalyze NO reduction by CO and CO₂ can inhibit NO reduction by CO.The reduction rate of NO could be improved by increasing the concentration of CO.In addition,the catalytic activity of CaO was found to decrease as CO₂ concentrations increased or the reaction time increased.Based on the experimental results,the adsorption and reaction processes of CO₂,CO and NO on CaO surface were studied by molecular dynamics simulation.According to the order of the chemical adsorption energy of the three gases on the surface of CaO:CO₂?-1.869 eV?<NO?-0.781 eV?<CO?-0.669 eV?,it can explains why CO₂ decreases the reduction rate of NO and the catalytic activity of CaO.According to the calculation results of the reaction energy barrier:CaO surface CO denitrification?2.06 eV?<CO denitrification?10.84 eV?in the absence of CaO,it verifies that CaO can catalyze NO reduction by CO.Finally,the microscopic reaction mechanism of NO reduction by CO catalyzed by CaO was studied by means of characterization and in-situ DRIFT.The results show that the catalytic reduction reaction mechanism of CO and NO on the surface of CaO is essentially a process of oxygen atom transfer which depends on oxygen vacancies,that is,CO captures oxygen on the surface of CaO to form oxygen vacancies,forcing O atoms of NO to add to oxygen vacancies.Thus,NO is converted to nitrogen,nitrate,and other forms.The research results not only clarify the influence mechanism of various factors on the efficiency of CO denitrification in cement precalciner,but also give the support of theoretical data.It has important engineering application value for improving the denitrification technology of cement precalciner and reducing the emission of nitrogen oxides in cement precalciner.Moreover,it is of great scientific significance to promote the recognition of microscopic mechanism of NO reduction by CO catalyzed by CaO.