Direct Reduction Of Refractory Iron Ore Powder And Exper-imental Study On Non-blastfurnace One-step Iron-making

China’s steel production capacity is very huge, and iron ore is heavily dependenton imports, which has been a threat to the healthy development of the nationaleconomy. Making full use of the abundant low grade ore resources has become thecurrent problem to be solved. The ore dressing of low-grade iron ore, such as hematiteand siderite, is very difficult, as a result, it is difficult to use for blast furnaceironmaking. The blast furnace ironmaking has some disadvantages, including the longprocess, high energy consumption, serious pollution, so exploring a new ironmakingprocess with reliable technology and reasonable economical cost, which could alleviatethe domestic iron ore resources pressure and decrease energy consumption andenvironmental pollution, has important scientific value and practical significance.In this thesis, hematite was reduced using CO and H₂, respectively, in thesimulated fluidized bed reacting furnace. The influence of hematite grain size,reduction temperature, reduction time and gas flow rate on metallization degree ofdirect reduction iron were investigated systemically. The reduction capacity of CO andH₂and the reduction mechanism of hematite were thoroughly analysed. Hematite andsiderite were reduced using coal, respectively. The influence of the loading method ofiron ore powers and pulverized coal, reaction temperature and time on metallizationdegree of direct reduction iron were deeply investigated, and the coal-based reductionreaction mechanism was discussed. On the basis of gas-based and coal-based directreduction experiments, one-step ironmaking experimental study for hematite andsiderite was carried out in the laboratory, which could provide a reference for the nextsemi-industrial test. The experimental results show that when reducing hematite powders using CO inthe simulated fluidized bed reactor, the better reaction conditions were found asfollows: the hematite grain size is40¹60μm, the reaction temperature is950℃, thereaction time is60min, and the flow of the reducing gas is0.36m3/h, and under thesereaction conditions, the metallization degree of direct reduction iron is about69.10%.When using H₂as the reducing gas and the reaction time is30min, under the samereaction conditions, the metallization degree of direct reduction iron is about94.6%,which indicates that the reducing power of H₂is far stronger than CO in hightemperature. The reduction of Fe₂O₃is carried out step by step in accordance withFe₃O₄, FeO and Fe, and the reduction of FeO is the rate-determining step. Thereduction reaction using CO and H₂is exothermic reaction and endothermic reaction,respectively.The loading method of iron ore powers and pulverized coal has a great effect onthe coal-based direct reduction. When reducing hematite powers at1000℃for3.5h,the metallization degree of direct reduction iron with the loading of concentric circlesand stratification are more than90%, while the metallization degree of direct reductioniron with the loading of mixing is about only79.81%. The results could be caused bythe CO concentration differences on the reaction interface. When reducing sideritepowders at1000℃for3.5h, the metallization degree of direct reduction iron with theloading of concentric circles is about96.22%. The laboratory one-step ironmakingexperimental result show that the iron ore powders were first reduced at1000℃, andthen heated to1550℃and continue to be reduced in molten state. The results showthat the separation of slag and iron is better, and after cooling, the iron bulk can beobtained. The early direct reduction of the iron ore powders is very important for theone-step ironmaking result.