Experimental Research On Integrated Removal Of Multiple Pollutants From Flue Gas Under Medium Temperature Conditions

At present,environmental issues have caused widespread concern.The major environmental problems and the increasing environmental demands have constituted one of the main contradictions in the current society.In addition,coal burning is the leading cause of environmental pollution.The removal of pollutants(SO2,NOx,PM)in coal fired plants mainly adopts a graded removal method.Although this graded treatment method has a high removal efficiency for a single pollutant,it still has problems such as a complex control system,easy to induce secondary pollution,increased investment and operating costs,etc.As the emission standards of pollutants in flue gas become stricter,the number of pollutants included in environmental protection management and control increases.The single-pollutant removal like "candied haws type" at the tail of the boiler has become challenging to meet the needs of future environmental protection development.Therefore,the integrated removal of multiple pollutants from flue gas based on medium temperature conditions(200-400℃)is a significant development direction in the future.Based on it,innovative research was carried out in this thesis aiming at several core issues of the technology.In the study of NH3-SCR in the medium temperature zone,the catalyst was prepared by the citric acid method.The prepared catalyst has a high specific surface area,which can achieve the desired catalytic effect.(Fe&Mn)AlOx-based catalysts were used for high NO catalytic efficiency and N2 selectivity through an operable method with controllable structures and uniformly distributed active centers.The analysis of surface characteristics(XPS,in-situ DRIFTS)and NO conversion/selectivity was used to prove the special structure-activity relationship of the catalyst.This work directly demonstrates the importance of coordination between the adsorption of species and the electron transport that occurs at the active sites.At the same time,the reaction process has been clearly described in the in-situ DRIFTS,indicating that there is a synergistic mechanism(Eley-Rideal mechanism and Langmuir-Hinshelwood mechanism)in the reaction process.These provide a basis for an in-depth understanding of the controllable conversion rate and high selectivity of the synergistic interaction in the mediumtemperature SCR process.In terms of dry SO2 removal,a laboratory-scale dry desulfurization experiment platform using in the medium-temperature conditions was built for experimental requirements.Desulfurizers were screened on the testing platform,and the best one suitable for the experimental needs was obtained.NaHCO3 is ideal for mediumtemperature dry desulfurization;experiments on the effects of flue gas composition and different parameters on the SO2 removal effect have been carried out.The investigation found that the SO2 removal efficiency can be promoted by NOx,and water vapor,and is inhibited by CO2.The SO2 removal performance will be affected by particle size and residence time.The increase in temperature makes the desulfurization efficiency first increase and then decrease;in addition,the oxidation of sulfite is promoted by NO and water vapor.The smaller the sodium particle size,the larger the specific surface area,and the smaller the average pore size,the more conducive to adsorption.Based on the results of multi-factor experiments and related characterization tests,the influence mechanism of NO on desulfurization using NaHCO3 is proposed.According to the influence of SO2 concentration and residence time,it is concluded that the diffusion of SO2 to NaHCO3 channels is the rate control step of the mass transfer process;The insitu infrared results further confirmed the promoting effect of NO on the oxidation of sulfite.In the research of dust removal at medium temperature zone,the inertial dust removal process was simulated by combining theory and simulation using MATLAB and COMSOL softwares.As for the inertial dust removal,the Kuwabara flow field was used as the theory’s core.The growth was systematically standardized and supplemented by MATLAB numerical calculation tools to analyze the movement of particles in the fiber flow field.For ceramic fiber filter units,particle tracking and moving grid technology were introduced with porous media theory.Combining the unitization and discretization of the geometric model,the growth of the dust layer at the dust collection interface was analyzed,and the flow field and pressure drops of the ceramic fiber filter were analyzed using the COMSOL numerical simulation tool.The curve of the thickness of the filter dust layer and the pressure drops over time provide a vital guide for the engineering application of ceramic filters.Then,the feasibility of the model is verified by comparing it with the experimental results.In terms of a pilot test,a multi-pollutant removal test using a ceramic membrane filter was carried out in two sodium silicate furnaces.The dust concentration(8%O2),NOx concentration(8%O2)and SO2 concentration(8%O2)of the outlet meet the requirements of the glass furnace emission standard.The results show that removing of multipollutants from flue gas by ceramic membrane filters meets the pollutant control requirements and is technically feasible.This thesis has achievement in the research on the influencing factors and mechanisms of medium-temperature desulfurization,sulfite oxidation pathway,the selection of medium-temperature SCR catalysts,catalytic mechanism,and the simulation of ceramic membrane filters.Morever,a technical route of multi-pollutant removal in medium temperature zone has been proposed.The application of the ceramic fiber filter using for removal of multi-pollutant in medium temperature zone can be supported by the obtained data.In addition,it provides a value for the further development of integrated removal of dust,nitrogen oxides,and sulfur oxides.