Experimental Study On Carbon Black Particle Oxidation Process Based On Fixed Bed Reactor

Diesel particulate filter（DPF）is one of the most effective systems to reduce particulate emissions outside the engine,and gradually becomes the mainstream technology of diesel engine emission reduction.However,after a certain period of driving,DPF must be oxidized for regeneration,otherwise it will lead to poor exhaust of the engine,which will lead to the deterioration of engine conditions,increase of fuel consumption and other side effects.Regeneration is a key problem for the reliable use of DPF.The particulate emission of DPF during regeneration is increasing sharply,which is a research hotspot at present.Because the carbon black in DPF is a cross flow stacking mode,in order to better understand the DPF particle emission characteristics during regeneration,it is necessary to start with the oxidation characteristics of the uniformly stacked carbon black particle layer,and first understand the gas and particle emission characteristics during its own oxidation.Based on the fixed long bed reactor,the effects of the inflow parameters,NO₂ and catalyst on the oxidation and emission of the uniform packed particle layer,and the oxidation characteristics of carbon black particles in different oxidation stages are analyzed in detail.Firstly,this paper studies the influence of the inflow parameters on the oxidation and emission characteristics of the uniformly deposited particles.By changing the oxidation temperature,the incoming flow rate and analyzing the gas components and particle emissions at the exhaust outlet,the results show that:in the oxidation process of the uniformly stacked particle layer,the carbon black particles will produce the wave peak of the number and concentration of particles when they start to oxidize;in the oxidation process,CO₂ is generated first,then CO is generated,and the reaction to generate CO is more intense;in the whole reaction process,the amount of CO is generated At the flow rate of 5L/min,with the increase of oxidation temperature,the amount of CO production and oxidation efficiency gradually increase,and the fluctuation of the number concentration and average particle size of particles in tail gas is more obvious.In addition,when the oxidation temperature remains constant,the concentration of CO and CO₂ decreases with the increase of the flow rate,the oxidation of carbon black is not fully uniform,and the average particle size of particles fluctuates greatly.Secondly,the effects of nitrogen dioxide（NO₂）and cerium oxide（CeO₂）on the oxidation and emission characteristics of the uniformly deposited particles are studied.By changing the concentration of NO₂,the mixing ratio of carbon black and CeO₂,and analyzing the gas components and particle emissions at the exhaust outlet,the results show that when NO₂participates in the reaction,the concentration of CO in the exhaust gas is still higher than that of CO₂.However,with the increase of NO₂ concentration,the peak value of CO concentration decrease.When NO₂ is involved in the reaction,it will inhibit the formation of CO,enhance the oxidation of the packed particle layer,and make the particles more easily split into small particles to be discharged together with the incoming flow.The second concentration peak appears,and the nuclear membrane particles with an average particle size of about 10 nm are mainly discharged.With the increase of NO₂ concentration,the total amount and concentration of particulate matter gradually increase.In addition,when the catalyst is mixed with carbon black,the concentration of CO₂ in the exhaust gas begins to be higher than that of CO,and with the increase of the proportion of mixed catalyst,the amount of CO production becomes less and less.When m（PU）:m（CeO₂）=1:5,almost no CO gas is produced.When a large proportion of CeO₂ particles are mixed,the oxidation of carbon black particles is relatively sufficient and uniform,and there is no peak of particle concentration.The average particle size of particles discharged from the exhaust gas fluctuates slightly and mainly in the nuclear membrane state below 50 nm.Finally,the oxidation characteristics of different oxidation stages are studied.By analyzing the samples of carbon black with the same oxidation temperature,different oxidation time and different oxidation temperature at the same oxidation time,the results show that the activation energy of carbon black particles in different stages is different with the oxidation reaction on the time scale,and the carbon black particles generally decrease at first and then increase at the macro level The process of particle oxidation is easy to oxidize first and then relatively difficult to oxidize.Under the condition of the same oxidation time and different oxidation temperature,it is found that the basic structure of the carbon black particles tends to be round through the microscopic analysis of the electron microscope.The outer layer of the carbon black particles is composed of the ordered carbon layer similar to the"onion"crystal structure.In addition to the ordered elastic layer structure,there are some disordered carbon layers inside to form its"core".With the increase of oxidation temperature,the core of basic carbon particles tends to be regular and form a more stable shell.Therefore,compared with the first stage,obvious"onion"structure can be observed in other stages,with higher degree of graphitization and more orderly,leading to the decrease of oxidation activity and increase of activation energy of particles.Through the appeal study,it is found that the exhaust emission characteristics of the uniform stacked particle layer are affected by oxidation temperature,inflow flow rate,NO₂ and CeO₂.When the uniformly stacked particle layer begins to oxidize,the quantity and concentration of particles at the outlet increase sharply,mainly in the form of nuclear membrane particles;when the particle layer oxidizes violently,it is easy to have a temperature wave peak;when NO₂ participates in the reaction,it will increase the emission of particles;when CeO₂ and carbon black are mixed,the oxidation reaction will increase the emission of nuclear membrane particles;the oxidation characteristics of carbon black particles are different in different oxidation stages,generally in the time dimension The activation energy first decreases and then increases.