Research On The Iron Ore Packing Bed Properties Based On Orthogonal Test And The Co-processing Of Waste SCR Catalysts By Sintering

The iron ore sintering is an essential step closely related to productivity,quality and energy consumption during steel production.Driven by green development of steel industry,the iron ore sintering undertakes three major functions of steel manufacturing,energy conversion and waste disposal,so as to achieve perfectly combinated return in economy,environment and society.Sintering can be viewed as a two-stage process of granulation and packing under cold state followed by ignition sintering under hot state.Granulation and packing process under cold state signigicantly influence the structure of green bed and subsequently determines the productivity and quality of the sinters.Sintering process produces sinters while providing a high-temperature environment for the co-processing of solid waste,which is considered to be an important way to realize the green development of steel industry.Under this prospect,the present work focuses on investigating the porous structure characteristics of cold packed bed,and conducts preliminary exploration on the co-processing of waste denitration catalysts during iron ore sintering.Firstly,high resolution X-ray computed tomography was applied to derive the three-dimensional structural information of packed bed,and Taguchi orthogonal experiment was conducted to investigate the importance of moisture,hydrated lime and concentrate levels on granule properties and porosity distribution,and determine the optimum granulation factors combination for improving packed bed homogeneity.Moisture was found to be the dominant factor affecting granule size;Bulk bed porosity was significantly affected by all three selected factors of moisture,hydrated lime and concentrate levels,and the percent contribution order was shown as hydrated lime?55.10%?>moisture?29.12%?>concentrate?14.36%?.The whole packed bed was found to exhibit significant inhomogeneity.Axial porosity increases from the bottom upwards along the packed bed height,and radial porosity appears a symmetric parabolic distribution where porosity achieves the minimum of 0.3 at bed center and increases sharply near the wall.To achieve the homogeneous packed bed of iron ore granules,the optimum granulation factors combination for decreasing axial and radial porosity segregation are determined by S/N ratio analysis.Secondly,the thermal melting technology was proposed for waste SCR catalysts treatment based on iron ore sintering.In order to explore the feasibility of co-processing for waste denitration catalysts by sintering,the melting characteristics of waste SCR catalyst blending with additives were firstly studies.It is concluded that the additives formula of 39.00 wt.%Fe₂O₃,6.50wt.%CaO,3.30 wt.%SiO₂ and 1.20 wt.%Al₂O₃ achieves the optimal fluxing behavior which significantly decreases the initial melting temperature from 1223?to 1169?.The whole heating process of waste SCR catalysts is divided into three stages including solid reaction stage,sintering stage and primary melting stage.Furthermore,the additives formula used in this study is consistent with the typical sintering raw material,which demonstrates the feasibility of iron ore sintering for co-processing of waste SCR catalysts,and provide theoretical support for a novel way to dispose of hazardous waste SCR catalysts.Finally,in order to investigate the immobilization of heavy metals As,Pb,Se and V in waste SCR catalyst during co-processing by iron ore sintering,melting treatment experiment was conducted in a high-temperature tubular furnace to investigate the effects of melting temperature and melting time on heavy metals leaching toxicity and volatilization.The results indicated that the heavy metals in waste SCR catalyst can be effectively stabilized by melting treatment technology.The melting temperature significantly affected heavy metals leaching and volatilization characteristics of waste SCR catalyst,the leaching concentrations of As,Pb,Se and V decreased significantly with increasing melting temperature;The volatilization rate followed the order of Pb>Se>As>V,in which the volatilization rates of Pb and Se increased first and then decrease with increasing temperature,and that of As and V were almost zero.With the increase of melting time,the leaching concentrations of As,Se and V were increased first and then decreased,and that of Pb was monotonously decreased with melting time;The melting time exerted little influence on heavy metals volatilization.