| Low temperature simultaneous desulfurization and denitrification tech NOlogy is based on semi dry desulfurization to achieve the collaborative removal of NOx and SO2.Therefore,it is necessary to study in detail the removal reaction path of NOx and SO2 on the surface of Ca(OH)2 and spent absorbent and improve the collaborative removal effi-ciency.Based on this background,this paper studies the gas-solid reaction mechanism of the collaborative removal of NOxand SO2.Firstly,the spectrum of Ca(OH)2 reaction with NOx and SO2 was measured by in-situ diffuse reflectance device,and the composition and structure of the product were analyzed.Secondly,the synergistic removal efficiency,the ratio of reactant and product generation and consumption,the influence of temperature and O2 were studied by using fixed bed experimental platform.The reaction process and mechanism of NOx/SO2 and calcium hydroxide were studied by gaseous reactant transient techniques.The detailed reaction path of gas-phase transformation was given,and the reaction mechanism was explained from the point of gas-solid reaction rather than solution ion reaction.Then the reaction model of fixed bed desulfurization and denitrification was established,the experimental data were fitted,the parameters such as diffusion coefficient,reaction rate constant,at-tenuation factor were obtained,the reaction mechanism was verified,and the synergistic removal of NOx and SO2 was explained from the micro point of view by DFT calculation.Finally,the new process was validated by industrial test and application.In this paper,we found that as regard to the NO2 removal the disproportionation of two NO2 occurs first,and then react with Ca(OH)2 by acid-base reaction to produce the product.In the early stage of the reaction,Ca(NO2)(NO3)is formed,and then it will be oxidized by NO2 to Ca(NO3)2.With the reaction going on,the product structure experi-enced the changes of surface bridge nitrate,chelating and bindentate nitrate,Monodentate nitrate and bulk free-like nitrates.The reaction order of NO2 is about equal to 2.The removal of NO2 is divided into two parts,N2O4 reaction and two NO2 reactions.NO2 can oxidize Ca(NO2)2,while it is difficult to oxidize Ca SO3.NO reacts weakly with Ca(OH)2,and the products are nitro-nitrito and nitrito species.When NOx and SO2 are removed on the surface of Ca(OH)2,the main products are Ca(NO3)2 and Ca SO4.The the formation of multi-molecular active intermediates contain-ing sulfur and nitrogen,which decompose into the final product are the key step form the from reactant to product.The infrared spectrum between 1000?850cm-1rises rapidly and then decreases,that is,Ca SO3 will be partially oxidized.NO and NO2 has synergistic removal effect.When NO2 and SO2 are removed together without O2,NO2 is converted into NO.O2 has NO effect on the reaction of Ca(OH)2 and SO2 to form Ca SO3,however more Ca SO4 is produced when there is O2.The reaction product of Ca(NO2)2 and SO2 is Ca S2O6.NO can be removed at the same time during the process of SO2 removal.When SO2 or NO2"reversely buckled"on Ca2+site,the O2 potential adjacent to Ca2+can syner-gistically adsorb NO2 or NO.Referring to the model research,the nucleation expansion model is proposed to modify the reaction area,which can fit the experimental data better when there is diffusion effect.In this paper,a new technology of simultaneous desulfurization and denitrification based on semi dry method is proposed,which moves up the absorbent spout to form a high concentration area of SO2,realizes the efficient collaborative removal of SO2 and NOx. |
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