Experimental Research Of Carbon-containing Pellet Under Gas-solid Coupling Reduction

With the awareness of environmental protection enhence,adding Chinese government makes several policies for energy saving and pollutant reduction in iron-making industry.Non-blast furnace ironmaking technology for it’s advantages such as environmentally friendly,energy saving and pollutant reduction,becomes the most potential technology to meet the need of iron-making industry.The project "Development and Demonstration of Efficient and Clean Production Technology Under Full Oxygen Metallurgy" was put forward to meet the requirement of environmental protection.The project creatively proposes the technology of deeply self-reduction technology of fine ore to treat iron ore powder with closed-loop utilization of gas.The project is aim to solve problems such as:incapably deep reduction of iron ore powder and inefficient utilization of gas,by analyzing the iron-carbon migration and the change rules of valence in the process of iron ore powder self-reduction.In this paper,the research object is titanomagnetite taken from Panzhihua.Bituminous coal was used as reductant.Carbon-containing pellets are prepared and directly reduced.The gas-solid synergistic reduction reaction of carbon-containing pellets was studied from thermodynamics and dynamics by means of metallographic microscope,X-ray diffractometer and scanning electron microscopy.The direct reduction of carboncontaining pellets and the gas-solid synergistic reduction of rotary kiln were explored.The conclusions are as follows:(1)The thermodynamic calculation of gas-solid synergistic reduction of titanomagnetite shows that in the temperature range of 1000-1100℃,Fe can easily be reduced from the combined state to the elemental state,while Ti can not.During the reduction of Fe,high temperature can inhibit iron oxide from being reduced.So the reaction temperature should not be too high.(2)The study about the influence of the type and amount of carbon-containing pellet binders on the pellet strength shows that the most suitable binder in this experiment is molasses,and under the condition of 8%water addition,30 min balling time and 3h dry time of 100℃,and the mathematical relationship between the falling strength of carboncontaining pellet and the amount of binder and the ratio of carbon to oxygen is obtained as follows:z=0.8127x-0.5048y+1.2.(3)By investigating the mechanism and process of gas-solid synergistic reduction of carbon-bearing pellets in muffle furnace reveals that the prolongation of reduction time,the increase of reduction temperature and the increase of carbon content are beneficial to the metallization rate.When C/O is below 1.0,the existing form of Ti changes from titanomagnetite to ilmenite with the reduction reaction proceeding,while to ferric titanium oxide when C/O is above 1.0.In additions,kinetic studies show that the gas diffusion in solid phase product layer is the limting step of carbon-containing pellets to reduction.Under the experimental conditions,the correlation between activation energy of reaction and carbon content in pellets is not obvious,and all the activation energy with different carbon contents are around about 60 kJ/mol.(4)The reduction of carbon-containing pellets with carbon-oxygen ratio of 0.6 in a small rotary kiln is investigated under reducing atmosphere(CO(50%),H2(40%)and N2(10%)).And come to the following conclusions:the metallization rate increased linearly with the increase of heating time,and the reduction reaction rate increased significantly above 900℃.However,900℃ is too low so that the diffusion and aggregation of iron metals are too slow,and lots of iron oxides are still not reduced.And when the temperature is above 1000℃,it is advantageous to the reduction of pellets and the aggregation of iron metals.Besides when the temperature is above 1100℃,the metals are joined together and a preliminary separation of slag and iron occurs,with the reduction degree of iron oxides very high.What’s more,when the temperature is 1100℃,the liquid phase appears in the pellets,and this temperature should be avoided to reach in the production process of rotary kiln.