Study On Preparation Of New Burden And Metallurgical Behavior In Hydrogen-Rich Blast Furnace

With the aggravation of global warming,low-carbon production by reducing CO2 emissions has become the focus of social attention.The iron and steel industry with coal as the energy structure is the main battlefield for reducing carbon emission intensity in China.Based on the current situation of iron and steel production,the traditional blast furnace ironmaking technology has matured,and it has reached the theoretical limit to continue to deepen energy conservation and emission reduction with the existing technology.Only by developing breakthrough hydrogen metallurgical technology can we further save energy and reduce emissions.The increase of hydrogen content in the blast furnace changes the thermodynamic and kinetic conditions of the burden reaction,which leads to the change of burden reaction behavior,and then affects the reduction process,property evolution and metallurgical behavior of the burden in blast furnace.In addition,the increase of hydrogen content changes the temperature and gas flow distribution in the furnace,and finally affects the efficiency of blast furnace operation.Therefore,it is necessary to strengthen the study on the evolution law of burden properties and metallurgical behavior under the condition of hydrogenrich low-carbon ironmaking process and to analyze the adaptability of different burden structures under the new process conditions.Given the application of hydrogen in blast furnace ironmaking process,starting from the preparation and efficient utilization of raw materials,this paper explores a new charging technology for the production of pre-reduced sinter based on sensible heat updraft of sinter and the production of composite pellets based on sinter return fine,analyzes the influence of mixed charging of nut coke and sinter on the smelting process of hydrogen-rich blast furnace,studies the influence of different charging structures on the permeability of softening-melting process,and expounds the adaptability of burden properties and structure to the new process,which provides reference for the establishment of charging index control system.Utilization of pre-reduction burden in the blast furnace ironmaking process is an important measure for realizing low-carbon operation.In this paper,a new process for the production of pre-reduced sinter based on sensible heat updraft of sinter was put forward.The effects of sinter temperature and reducing gas composition in the pre-reduction cooling section on the metallization rate and sieve size distribution of pre-reduction sinter were studied,and the metallurgical properties of pre-reduced sinter with different roasting systems under hydrogenrich smelting in blast furnace were studied.The results showed that the metallization rate and proportion of large particle size of pre-reduction sinter increase with the increase of sinter temperature.When the sintering temperature was 950℃ and the reducing gas was the mixture of H2 and CO,the metallization rate of the pre-reduced sinter was up to 35.5%.When the sintering temperature was lower than 750℃,the carbon deposition reaction between H2 and CO reduces the proportion of large particle size of the pre-reduced sinter significantly.Based on the study of the influence of the roasting system on the metallurgical properties of pre-reduced sinter,it could be seen that compared with the traditional sinter,the reduction degradation index,reducibility index,and softening-melting properties of pre-reduced sinter were improved,and the permeability of the stock column were improved,which was beneficial to the improvement of blast furnace production efficiency.Based on the comprehensive effects of sinter temperature and reducing gas composition on the metallization rate,sieve size distribution,and metallurgical properties of pre-reduced sinter,the quality of the pre-reduced sinter was better when the sintering temperature was higher than 750℃ and the reducing gas was a mixture of H2 and CO.In addition,the new process could organically combine sinter sensible heat utilization,flue gas circulation,and denitrification to form a complete technological process,which had a good development prospect.In addition,based on the experimental process,it was found that the sintering hydrogen enrichment process had the characteristics of enhancing the reduction of the material layer,prolonging the high-temperature section,and improving the permeability of the material layer,which provided favorable conditions for phosphorus reduction and removal based on sintering process.To realize a new method of pre-reduction sinter production by hydrogenrich sintering gasification and dephosphorization coupled with sintering sensible heat,it was of great significance for the utilization of rich high-phosphate iron ore in our country.This paper preliminarily explored the gasification behavior of phosphorus under the condition of hydrogen-rich sintering process.The results showed that in hydrogen-rich atmosphere,when the reduction temperature was 1100℃ and the reduction time was 60min,the maximum dephosphorization rate was 29.51%.Efficient utilization of sinter return fine is an important measure to reduce cost and increase efficiency,energy saving,and emission reduction.This paper explores a new path of green and efficient utilization of sinter return fine to produce composite pellets.Through the shunt granulation of sinter return fine,taking the sinter return fine of large particles as the core and adding iron concentrate to produce composite pellets,the recycling of part of sinter return fine could be realized in the process of pellet roasting.The effect of the roasting system on the metallurgical properties of composite pellets was studied by experiments to analyze the feasibility of blast furnace.The experimental results indicated that for the composite pellets,the coated concentrate was consolidated through normal Fe2O3 recrystallization.While near the surface of core return fine,the liquid phase formed due to its low melting point and assimilated the adjacent concentrate,then the liquid phase consolidated and consolidates with the temperature decreasing.Compared with regular pellets,due to the differences between internal and external double-layer structures and element migration,the compressive strength and reduction swelling index of composite pellets were decreased,but the reducibility index was improved.The core return fine of composite pellets was in close contact with the outer pellets,and the interaction rapidly changes the phase structure and slag phase composition at high temperatures,thus improving the softening-melting properties of the burden.In addition,the reduction degradation index of composite pellets was significantly higher than that of sinter,so the air permeability of the upper part of blast furnace can be improved by replacing part of sinter with composite pellets.Therefore,adding composite pellets was conducive to the development of indirect reduction in blast furnace,reducing fuel ratio and improving production efficiency.According to the comprehensive effect of roasting system on the consolidation and metallurgical properties,the roasting temperature and time were determined as 1250℃ and 30min respectively.The production of composite pellets can be carried out without changing the traditional pellet process.Production practice has proved that the use of nut coke is an important measure for alleviating the increasingly tense relationship between coke supply and realizing low reducing agent ironmaking.The requirement of high coke strength for hydrogen enrichment in blast furnace increases the number of nut coke in the screening process,and hydrogen enrichment in blast furnace affects the reaction behavior and column behavior of charge.Therefore,it is of great significance to analyze the effect of mixed charging of coke and ore on reduction and soft melting behavior in the furnace under hydrogen-rich conditions for further efficient utilization of coke,improving blast furnace smelting operation and realizing low-carbon smelting.In this paper,the effect of mixed charging of nut coke and sinter on reduction and softening-melting properties in the hydrogenrich smelting process of blast furnace is studied.The results showed that the close contact between nut coke and sinter promoted carbon dissolution and water-gas reaction to generate more CO and H2,thus increasing the reduction potential in the gas mixture and promoting sinter reduction.The consumption of nut coke could prevent the loss of conventional coke in the lump zone and maintain good quality when it reaches the lower part of the blast furnace.With the increase of nut coke and hydrogen-rich ratio,the softening-melting properties of the burden were improved.This change narrowed and lowered the position of cohesive zone,triggering an enlargement of indirect reduction zone,which was conducive to strengthening blast-furnace smelting and saving coke.The permeability resistance of the burden bed was reduced,which was beneficial to good airflow distribution and gas utilization rate.The interface characteristics of coke-iron-slag in the soft melting process were analyzed by quenching experiment.The results showed that there was a slag layer between nut coke and metal iron phase in the softeningmelting process,and the slag could quickly fuse with the ash distributed on the nut coke surface to dissolve it,thus increasing the carburizing reaction rate and improving the dripping behavior of the burden.In addition,through the study on the behavior of soft-melting coke,it was known that the porosity of coke was increased,the chemical bond was destroyed,the graphitization degree was increased and the reactivity was improved due to the influence of gasification and slag iron erosion.Based on the above research,the structure evolution law and action mechanism of nut coke in the hydrogen-rich blast furnace smelting process were clarified,and the behavior theory of nut coke in the blast furnace was perfected.Reasonable burden structure directly affects the smooth operation and fuel consumption of the blast furnace,relates to the improvement of the quality of iron,and is the basis for realizing good smelting index of blast furnace.The softeningmelting property of burden determines the internal shape of the high-temperature zone,gas distribution,and permeability of blast furnace,which is the key factor affecting the stability and smooth operation of blast furnace.Based on mastering the metallurgical properties of single charge,this paper studies the influence of adding pre-reduced sinter,composite pellets,and nut coke on the softeningmelting characteristics of comprehensive burden structure and the interaction behavior between typical charges.The results showed that with the change of burden structure,the interaction between different burdens results in the change of microstructure and slag phase composition,resulting in the difference of softening-melting performance.Compared with the traditional sinter,the prereduced sinter had higher FeO content,and the enhanced interaction with pellets promotes the production of low-melting-point phases such as fayalite,which reduces the air permeability of the column.The softening-melting properties of composite pellets instead of traditional sinter and pellets first increased and then decreased,and the effect was the best when 20%was added.Based on the influence of different burden structures on the softening-melting performance,and through the study of high-temperature interaction between typical burdens,the optimal collocation was studied.Based on the traditional burden structure,a proper amount of pre-reduced sinter,composite pellets,and nut coke were added to form a new burden structure of pre-reduced sinter+composite pellets+pellets+lump ore+nut coke,which significantly improves the softening-melting permeability performance.The improvement of the permeability performance of the new burden structure could be summarized into four aspects:(1)The softening-melting behavior of the burden was different from each other,forming the role of "ore window";(2)The interaction between the burden improved the slagging behavior of the burden;(3)Nut coke changed the reduction process of iron oxide and the fusion of ash and gangue affects the phase composition of slag;(4)The reduction performance of iron-bearing burden was improved,and it presents a thin shell with non-density and good air permeability at high temperatures,which was beneficial to air flow.