Experimental Study On Selective Catalytic Reduction Of NO_x With CO In Sintering Flue Gas

Nitrogen oxides(NOx)is a major source for air pollution.There are two major sources of NOx industrial gas after the combustion of fossil fuel and automobile exhaust of the mobile combustion engines,which are diffcult to be controlled due to their wide existence.The amount of NOx produced in the iron and steel industry accounts for about 8.7wt%of the total nationwide NOx emissions,which is less than the power plants,the NOx produced in sintering representing about 45%~65%NOx emissions in the iron and steel industry.Growing environmental awareness in recent years has resulted in the introduction of more rigorous environmental laws and regulations,the permit emission concentration of air pollutants for sintering of steel industry will be more stringent.As a consequence,it is necessary to research a suitable method to reducing the amount of NOx emitted from sinter plants.To date,there are four methods for reducing the amount of NOx emitted from sinter plants:the technologies take NH3 as the reducing agent,physical adsorption method,forced oxidation method,catalytic oxidation method.But these methods either need huge capital investment and high operational cost or have high water consumption,secondary pollution,oxidant leakage.In this paper,after comprehensive analyzed the current situation of controlling the NOx emission in sintering of steel industry and the main characteristics of sintering flue gas,this study proposed a new method of using the CO existing in sintering flue gas as the reducing agent and relies on a catalyst to promote the reduction of NOx by CO.and then investigate this method by thermal experimental studies.Based on the principle of the Gibbs energy minimization,using the HSC Chemistry 5.1 to respectively analyze the complex chemical reactions when CuO/Cu2O,Co3O4/CoO?MnO2/Mn3O4,CeO2/Ce2O3 under the atmosphere which contains CO,NO,O2,SO2,H2O at the same time.Through the thermodynamic analysis,choosing the CuOx as the main active site of the catalyst,CoOx,MnOx as the promoters to enhance the activity of the catalyst at low temperatures,CeOx as the promoter to enhance the resistance to SO2 of the catalyst.At the first part of the experiment,CuOx-MnOx/Al2O3 and CuOx-CoOx/Al2O3 were prepared,then the activities of the catalysts were determined under steady state,involving a feed steam which a fixed composition,NO 550 ppm,CO 9000ppm,O2 16%and N2 84%by volume as diluents,the reactions were carried out at different temperatures with a space velocity of 10000h-1,at the second part of the experiment,the activity of Cu-Mn/Al2O3(Cu/Mn=1.5)and Cu-Mn-Ce/Al2O3(Cu/Mn/Ce=1.5:1:1.5)were determined and compared under steady state,involving a feed steam which a fixed composition,NO 550 ppm,SO2 200ppm CO 9000ppm,O2 16%and N2 84%by volume as diluents,the reactions were carried out at different temperatures with a space velocity of 10000h-1.The research results as follows.(1)Temperature is the most important factor which influence the activity of the catalysts.The NO average conversion on sample Cu-Co/Al2O3 increases with increasing temperature,Cu-CO/Al2O3 exhibited the highest activity at 180?.The NO average conversion on sample Cu-Mn/Al2O3 increases with the temperature first and then decreases,Cu-Mn/Al2O3 exhibited the highest activity at 160?.Among the Cu-based catalysts,in the temperatue range the activity of Cu-Mn/Al2O3 are better than Cu-Co/Al2O3,the most activity catalyst is Cu-Mn/Al2O3(Cu/Mn=1.5).(2)Our results indicated that,when 200ppm SO2 were added to the reaction gas,the NO conversion on Cu-Mn/Al2O3(Cu/Mn=1.5)was decreased,the resistance to SO2 of Cu-Mn/Al2O3(Cu/Mn=1.5)was enhanced by doping CeOx,but it can not completely neutralize the influence of SO2,the duration of Cu-Mn-Ce/Al2O3(Cu/Mn/Ce=1.5:1:1.5)was test at 160?,In the beginning stages the conversion of NO was higher than 90%,after I h test,the conversion of NO was still higher than 50%.