| The flue gas from non-thermal power industries exhibits low flue gas temperature(<300?)and complex composition,which limits the utilization of the traditional SCR denitration catalyst(300-450?)for NOx removal from the flue gas of non-thermal power industries.Industrial solid waste can be used for the purification of flue gas pollutants,which can achieve the co-processing of multiple pollutants.The wet desulphurization using steel slag has been operated stably in industrial-scale devices,in which a certain amount of denitration efficiency is observed together with desulphurization.However,the denitration efficiency is relatively low.In this dissertation,aiming at the two problems that NOx from low-temperature flue gas cannot be removed efficiently and the value-added utilization of steel slag is insufficient,an integrated technology of catalytic NO oxidation via gas-solid catalytic reactions combined with NO2 absorption enhanced by reductive additives for simultaneous desulphurization and denitration using steel slag was proposed.In this technology,steel slag was a catalyst for NO oxidation and absorbent for desulphurization and denitration.The mechanism analysis of NOx removal by steel slag,the preparation of steel slag-based catalysts for NO oxidation,the development of additives to enhance NO2 absorption,and the resource reuse of tailings and wastewater from desulphurization and denitration using steel slag were investigated.As a result,a new technology of simultaneous desulphurization and denitration from low-temperature flue gas using steel slag combined with the resource reuse was proposed.The main contents and conclusions are as follows:(1)The mechanism of NOx removal by steel slag in the wet denitration process using steel slag was investigated.The leaching behavior of steel slag under weak acid conditions was investigated.Results showed that the leaching concentrations of Ca2+,Mg2+,and Mn2+ increased constantly with the decrease of slurry pH.The effects of reaction conditions on NOx removal in a bubbling reactor were investigated.Results showed that the increases of OR(ratio of NO2 to NOx)and SO2 concentration promoted NOx removal,and 100%SO2 removal efficiency and 83.4%NOx removal efficiency under the optimal condition were obtained.The mechanism of NOx removal by steel slag was investigated.Results showed that the existence of Mn2+ promoted NOx removal,and Mn2+ in liquid phase could react with NO2 and produced Mn3O4 and MnO(OH),thereby enhancing NOx removal.Based on the above results,the route of NO2 removal in a steel slag system could be summarized as follows:1)The hydrolysis reaction of NO2;2)The redox reactions of NO2 with the reducing Mn2+and S(?)in liquid phase.(2)Aiming at the problems of low oxidation efficiency and large consumption of hydrogen peroxide,acidized steel slag catalysts for catalyzing H2O2 to oxidize NO into NO2 or other high-valence NOx were developed.The acidized steel slag catalysts were prepared by acid treatment,and the preparation conditions of catalysts were investigated.As a result,the optimal preparation condition(acid type:HCl solution,acidification degree:70%)was obtained.The catalyst was characterized via XPS,FTIR and PL spectrum,and results showed that the active sites including Fe species(FeOSi et.al.),porous C-S-H and SiO2 gels with 2-4 nm pore,and SiOAl were enriched on acidized steel slag.The catalytic oxidation conditions were optimized in the homemade catalytic reactor,and within 36-h test,NO conversion of>90.0%and average SO2 conversion of<1.8%under the optimal condition were obtained.Catalytic reaction mechanism was further investigated via XPS,EPR and FTIR,and results showed that Fe(?)effectively dispersed into porous C-S-H and SiO2 gels was the highly active site,and the produced ·OH and HO2·/O2·-could oxidize NO into NO2,HNO3,and N2O5.(3)Aiming at the problem that NO2 cannot be removed simultaneously in a wet desulphurization process,low-cost compound additives(consisting of the equal molar of sodium thiosulfate and ammonium sulfate)to enhance NO2 absorption were screened,which could be used for wet Ca-based desulphurization systems.Reaction conditions were optimized in a homemade spraying column,and within 24-h test,100%SO2 removal efficiency and 78.0%NOx removal efficiency under the optimal condition were obtained.When NO2-concentration was 3.0 mol/L,NOx removal efficiency was kept at>70.0%,indicating that the compound additive could tolerate high NO2-concentrations.Mechanisms of the compound additive to enhance denitration were further investigated via ion chromatography and gas mass spectrometry.Results indicated that S2O32-and NH4+ in the compound additive and Mg2+ leached from steel slag had a synergistic effect for NOx removal,in which S2O32-acted as a reducing agent and an oxidation inhibitor of MgSO30 enhanced NO2 removal.NH4+ inhibited the denitration product(NO2-)from decomposing into NO and NO2,thereby accelerating NOx removal.(4)Aiming at the tailings and wastewater from the desulphurization and denitration using steel slag,the resource reuse of the tailings and wastewater was investigated.The tailings was analyzed via XRF and XRD,and results indicated that the tailings contained gypsum and silicate and other cementitious materials.As a result,the performance of the cement and baking-free brick products prepared with the tailings as raw materials could meet the national standards(GB 175-2007 and GB 28635-2012).According to the characteristics of the wastewater composition,a technology of ammonia distillation-pH adjustment-precipitation-crystallization was proposed to achieve impurities removal,nitrite recovery and recycling of denitration additives,and the purity of the recovered sodium nitrite product reached the national standard(GB/T 2367-2016).Based on the above results,the technological design and economic calculation of the integrated technology were further carried out,and this technology combined with the current mature low-nitrogen combustion technology of coke oven flue gas could achieve the ultra-low emission of coke oven flue gas.In the industrial plant,the denitration performance of the compound additive was verified.Results showed that SO2 and NOx removal efficiencies were stable at about 99%and 50%,respectively,and the reliability of the compound additive was further verified. |
PDF Full Text Request