Research On Embedded SCR Denitrification Technology For Pelletized Flue Ga

In the long-process of iron-making,the pelletizing process is a key step to turn iron ore into pellet.Compared with sinter,pellet exhibits the advantage of lower pollutant and carbon emission.The emission intensities of SO2,NOx and CO2 for pellet are 1/3～1/2 of those for sinter.With the rapid development of the pelletizing industry,it is of increasing importance to explore the efficient purification technology for pelletizing flue gas.At present,the low-medium temperature SCR device is arranged after the desulfurization device,whereas the temperature at this site for the pelletizing flue gas decreases to under 100℃,which is much lower than that required for low-medium temperature SCR denitration(200-280℃).It is necessary to increase the temperature of the flue gas by consuming large amount of fuel,such as the blast furnace gas,leading to an obvious increase of the CO2 emission.Hence,it is meaningful to explore an efficient ultra-low NOx emission technology with low energy consumption.In this work,the widely used pellet production process(grate-kiln)in China was taken as the research object.Based on the unique technique characteristics of the grate-kiln pellet production process and its demand of ultra-low emission of NOx,a low energy-consumed embedded SCR denitration technology was proposed and investigated.The V-W/Ti catalysts with good resistance to H2O,SO2,metal dust poisoning and high temperature were optimized for embedded SCR denitration technology.The main results are as fllow:(1)The NOx-containing flue gas was generated in the kiln and mainly migrated from the klin-PH(preheating)-DDD(downwind drying)unit,where the concentration of NOx was between 900-1100 mg/m~3.The temperature of the NOx-containing tributary flue gas was 350-500℃,which basically accorded with the temperature range of SCR by V2O5-based catalyst.Compared with the low-medium temperature SCR technology,it was no longer necessary to reheat the flue gas,showing remarkable CO2 emission reduction effect.(2)The composition of catalysts was optimized to V2O5(0.5%)and WO3(5%)with good resistance to H2O,SO2,metal dust and high temperature under the complex pelletizing flue gas.The conversion of NO of 0.5V-5W/Ti-5%Dust catalyst remained at 93%during the 72-hour test at 475℃ with no decreasing tendency,while maintaining a low production concentration of N2O as a by-product.It was believed that 0.5V-5W/Ti could still maintain outstanding catalyst performance in the embedded SCR reactor for pelletizing flue gas in the bellows of PH unit.(3)Considering the CO(500-1000 ppm)contained in PH unit,the Cu-V-W/Ti catalysts were prepared by impregnation method.Through the design of coupling employment of 0.5V-5W/Ti and 2Cu-0.5V-5W/Ti catalysts in a reactor,the NO conversion rate was about 95%with a CO conversion rate of 80%.