Study On The Formation Characteristics Of Flue Gas Removal Of Nitrogen Oxides And Carbon Monoxide Based On Coal Char

Nitrogen oxides(NOx)produced by coal combustion can cause disasters such as atmospheric pollution and acid rain.The currently used ammonia method to remove NOx has shortcomings such as ammonia leakage and clogging of the flue.It has become a research hotspot.In previous research,the rotary reactor proposed by this group used CO to remove NOx,and the device was divided into an adsorption zone and a reduction zone to solve the problem of excessive oxygen in the flue gas,but the overall NOx removal efficiency was not high.The reason is that most of the adsorbed NOx is desorbed again in the reduction zone,so this paper proposes a secondary reactor to further remove the desorbed NOx.The use of activated coal char to remove nitrogen oxides is on the one hand due to the low cost of raw materials and good activity,on the other hand,coal char can also react with oxygen in the flue gas to form CO,provide raw materials for the rotary type,and form a CO cycle system.Based on the above objectives,this study mainly studied the feasibility of using active coal char to remove NOx,the interaction between components in flue gas and coal char,the reaction mechanism of active coal char to remove NOx,,while using the first principles to theoretically explain and confirm the reaction path of NOx removal by active coal char,and the design of the CO cycle system Calculation.Using active coal char as both a reducing material and a catalyst it was found that its NOx removal efficiency is not high at moderate temperatures.Adding iron powder and fully mixing it with coal char can improve the NO conversion rate.In short,after the active coal char is mixed with iron powder,a higher NO conversion rate can be obtained at 600℃.At the same time,the reaction will be affected by many factors.Studying the interaction between the components in the flue gas,such as O2,CO,CO2,H2O and SO2,and active coal char is very useful for the practical application of active coal char Help.This study found that the introduction of oxygen will significantly enhance the conversion rate of NO and the amount of CO produced.At the oxygen concentration of 2%and 600℃,NO is completely converted.When the oxygen concentration is 5%,the CO output is significantly increased to 8000ppm.When CO is introduced,the NO conversion rate is also enhanced,and the efficiency increases significantly with the increase of CO concentration.CO2 and H2O will inhibit the conversion of NO,SO2 is the opposite;adding H2O and SO2 will slightly reduce the CO yield,CO2 is the opposite;when oxygen is present,it can reduce the adverse effects of CO2,H2O and SO2 on NO conversion.In addition,experiments of coal char/coal char iron powder in the presence/absence of oxygen and promotion of CO generation were carried out,and the reaction mechanism was proposed.NO is first adsorbed on the carbon of the coal char to form monodentate nitrate and nitro compounds,which are oxidized to N2O or N2 at the oxygen vacancy,and N2 is finally released from the coal char surface.C and surface oxygen vacancies form a carbon-oxygen complex,which is unstable and quickly decomposes into CO or is oxidized into CO2.After adding oxygen,O2 is adsorbed on the coal char surface to form a large amount of oxygen vacancies;after adding iron,Fe forms iron oxide(FexOy)during the reduction of NO and is reduced by CO to metallic iron.In order to further explain the mechanism of NO removal and CO generation by activated coal char,DFT analysis method was used to systematically study the adsorption methods of NO and Fe,and to compare and analyze the changes of molecular structure and adsorption energy before and after the reaction.By optimizing the possible intermediate structure,finding a feasible reaction path to explain the experimental results and speculations.During the calculation,it was found that NO was first adsorbed to the coal char carbon site to form NCO;the intermediate NCO further formed N2O,and the resulting N2O structure was unstable and easily turned into N2.After adding Fe,the adsorption of NO changes:NO is first adsorbed to the coal char carbon site and forms Fe-N-O molecules with Fe atoms.After adding oxygen,oxygen molecules will promote the adsorption of NO,and at the same time,C reacts with oxygen to form CO,and CO reacts with NO to remove it;then,CO molecules approach O ad and obtain CO2.The results of simulation calculations in this chapter can be mutually verified by the results of coal char activity test and characterization in Chapter 2.In order to promote the practical application of the CO cycle system,its important parameters were designed and calculated,including:the heat generated by the active coal char to remove NOx,the amount of coal char iron powder that needs to be introduced per hour,the amount of CO consumed per hour,and the rotation The amount of air leakage of the type device and the amount of circulation circuit.At the same time,in order to further study the CO cycle system,the design and calculation of the entire system are divided according to whether the air leakage of the rotary reactor is considered and whether active coal char is added to the secondary reactor.The system calculation is divided into three cases:The first is to not consider the problem of air leakage,and the active coal char is not added to the secondary device,and it is replaced with other catalysts of the same efficiency(no CO),and the CO required by the system is all provided by the outside world;the second is to consider the rotation The problem of air leakage is different and different air leakage ratios are set.Similarly,no active coal char is added to the secondary reactor,only a catalyst that does not generate CO is added,and the required CO is introduced from the outside.In addition,this situation will consume more There is a lot of CO,because the oxygen in the air leakage will compete with NO and consume CO;the third most suitable experimental situation is to consider the problem of rotary air leakage and add coal char in the secondary reactor to generate CO In this case,it is necessary to calculate whether the heat generated by coal char oxidation is enough to maintain the optimal reaction temperature(600℃)of the secondary reactor.And design the basic parameters of the rotary reactor and the secondary reactor,such as volume,cross-sectional size,operating temperature;design and calculate the operating parameters,bed layer drop and flue gas pipeline of the experimental catalyst.In summary,this paper proposes the use of active coal char to remove NO and the secondary CO removal process to generate CO,to study its feasibility,the influence of flue gas composition,etc.,and the DFT method was used to simulate the entire experimental process,which confirmed the reaction mechanism.Finally,design and calculate the important parameters of the CO cycle system.