Investigation Of Combustion And Porous Structure Evolution Characteristics Of Sinter Bed In Iron Ore Sintering

The iron ore sintering is a pre-process of blast furnace ironmaking,providing raw materials for the blast furnace.The airflow resistance of the sinter bed determines the yield of the sinter product.The sinter bed can be simplified into three zones,namely raw material zone,high temperature zone,and sintered zone.The high temperature zone dominates the airflow resistance of the whole sinter bed.However,the measurement of the structure in the high temperature zone is very difficult,resulting in extremely lack of relevant data.In addition,the iron ore sintering process is the main source of NOx emissions in all links of the ironmaking and steelmaking.It is imperative to push forward the reform of ultra-low emission in the iron and steel industry,therefore the pressure for NOx reduction in the iron ore sintering process has increased sharply.Selective catalytic reduction denitrification technology is the mainstream flue gas denitrification technology.However,the life of the catalyst is short under harsh operating conditions,and a large number of waste denitrification catalysts need to be treated in a harmless manner.Based on the above background,this work carried out the research on the quasi-particle combustion and the evolution characteristics of the porous structure of the bed during the iron ore sintering process.Moreover,the influence of adding waste denitration catalyst into sinter raw materials on the iron ore sintering process was studied.Firstly,the combustion characteristics of the quasi-particles were studied by using a tube furnace test rig.Al₂O₃ powder was used to mix with coke to prepare the simulated quasi-particles instead of iron ore and flux to avoid the effect of various chemical reactions on the coke combustion.By calculating the correlation coefficient between the combustion model and time at different temperatures,it was determined that the D₁ model was the most suitable model to describe the combustion mechanism for simulated quasi-particles.Through studying the influence of recirculating flue gas composition on fuel-N conversion characteristics of simulated quasi-particles.It was found that the fuel-N conversion rate of simulated quasi-particles increases with increasing O₂ concentration.The rise of CO and CO₂ concentration both decrease the fuel-N conversion rate of simulated quasi-particles.Different types of quasi-particles under real sintering conditions were constructed on the basis of the previous research,and the effects of coke particle size and ratio,core particle size and adhesion layer thickness on the mass conversion rate of the quasi-particles were studied.In addition,the most suitable models to describe the combustion mechanism of different types of quasi-particles were determined by studying the effects of temperature on the mass conversion rate of the quasi-particles.The D₁ model was most suitable for describing the combustion process of S,S’,P type quasi-particles,while the D₃ model is suitable for describing the combustion characteristics of C-type quasi-particles.Secondly,the three-dimensional reconstruction of samples in different zones of the sinter bed was characterised by using X-ray computed tomography（XCT）.The pore characteristics and structure differences of the raw material zone,high temperature zone and sintered zone were compared and analyzed.And the absolute permeability and corresponding streamline and pressure distribution of the raw material zone and sintered zone were calculated.Although the pores of 0-0.4 mm account for more than 60%in number,the volume fraction of these microscopic pores is very small,and has little effect on the airflow channel and the thermal physical properties of the sinter.The area porosity of the raw material zone in all directions is more uniform while that of the high temperature zone and the sintered zone is randomly distributed.Compared with the raw material zone,the high temperature zone and the sintered zone have larger pore diameters,thicker gas flow channels,and fewer pores.By calculating the absolute permeability of the raw material zone and the sintered zone,it is found that the absolute permeability of the sintered zone is much better than that of the raw material zone.The influences of raw material characteristics,including granulation moisture,coke rate,quicklime addition level on the pore structure of the high temperature zone were further studied by using X-ray computed tomography technology on the basis of the previous research.The results show that with the increase of granulation moisture,the adhesion layer of quasi-particles becomes thicker,the liquid phase formed at high temperature has lower viscosity and better fluidity,and the increase of flame front propagation speed promotes the formation of airflow channels.The porosity of the sinter in the high temperature zone is greater,and the number of closed pores is less.The anisotropy of sinter leads to extremely uneven distribution of pores in all directions.Due to the more sufficient fusion,the number of pores in low moisture conditions is relatively more evenly distributed in all directions,and the number of pore segments and nodes are less.With the increase of the coke rate,the melting and solidification of sinter material are more sufficient,the solid matrix changes from granular to cohesive,and the integration becomes more obvious.The total volume,the total length,segments and the number of nodes of the pores all drop with higher coke rate.The quicklime enhances the fluidity of the melts,and the coalescence of bubbles in the liquid phase is easier to achieve.The total pore volume and total length,the number of pore segments and nodes of the pore skeleton all decrease with the increase of quicklime addition level.Finally,a new method of using iron ore sintering process to dispose of waste denitration catalyst was innovatively proposed.The effects of adding different proportions of waste denitration catalyst on the permeability of green bed,flame front propagation,mineral phase microstructure and sinter index were studied.Through the calculation of the comprehensive index,it is determined that 2%waste denitration catalyst is an acceptable proportion in iron ore sintering process.In addition,the influences of granulation moisture and coke rate on the treatment of waste denitration catalyst in iron ore sintering process were studied.More granulating moisture increases the flame front speed,and the excessive cooling of the sinter bed reduces the sinter strength.The optimized granulating moisture is determined to be 6.5%by the calculation of the comprehensive index.The increase of coke rate can reduce the porosity of the sinter,increase the sinter strength,productivity,and yield.