The Basic Research Of Carbothermic Reduction With High Pellets Bed

Recently more and more attention has been paid on alternative ironmaking process due to the sustainable development.Aimed for the development of the new technology of low coal rate,high metallization degree and high productivity(PSH furnace),the reaction characteristics of carbothermic reduction with high pellets bed are studied in present project.The effects of C/O(C is calculated based on the total carbon of coal),reducing time and some optimized methods on the metallization degree and productivity of direct reduced iron(DRI)are investigated by electric furnace experiments.In addition,Reflected light microscope,scanning electron microscope with EDS,and high performance X-ray diffraction were used for fundamental analysis.Based on the experimental investigation and fundamental analysis,the main findings could be summarized as follows.(1)The MD of pellets with C/0=1.2 is higher.When the reducing time in furnace is 50min,the MD of whole DRI bed is about 57.31%.When the reducing time in furnace is 60min,the MD of whole DRI bed is about 80.23%.Hot charging crucible can increase the MD of DRI,especially for the bottom layer of DRI due to the hot bottom of crucible.In case of hot charge,when the reducing time in furnace is 50min,the MD of whole DRI bed increases from 57.31%to 85.24%.When the reducing time in furnace is 60min,the MD of whole DRI bed increases from 80.23%to 87.07%.Therefore,the optimum parameters are C/O=1.2,hot charging crucible,and 50min of reducing time in furnace.(2)In case of 16-18mm and total one layer of pellets operation,the MD of DRI is about 83.95%(20min),and the productivity is about 26.51 kg-MFe/m2.h or 41.49kg-DRI/m2.h(this case is defined as common operation).But In case of 16?18mm and total five layers of pellets operation,the MD of DRI is about 86.84%(50min),and the productivity is about 58.60 kg-MFe/m.h or 84.88kg-DRI/m.h,and the productivity of metallic iron is about 2.21 times of common operation.(3)Smaller pellets(12?14mm)are not benefit for the heat transfer in pellets bed,which can result the lower MD and more residual carbon.Aimed for highest productivity,the opmized operation parameters are 20-22mm of pellets size,total four layers(the height of pellets bed is about 80mm).For this case,the MD of DRI can reach 92.28%(45min),the productivity can reach 67.20kg-MFe/m2.h or 91.80kg-DRI/m2.h,and the productivity of metallic iron is about 2.53 times of common operation.(4)Alkali and volatilization are not the reasons for the serious crack of pellets made by Ore B.Probably the lattie transfer is one of reasons for it,and should to be further investigated in future.Compared with 100%of Ore B mixed with Coal D,if 50%of Ore B is substituted by Ore A(50%Ore B + 50%Ore A),the MD of total DRI bed is increased from 80.89%to 88.52%,the tumble strength index(TI)is increased from 73.46%to 98.30%.And the size of metallic phase in DRI is bigger,which is benefit for storage and transportation.The reduction effect can also be improved if the process of magnetic roasting and pelletizing reduction was applied,with no burst occurring on pellets and significantly improving of DRI metallization rate.Based on the above investigation,the optimum parameters are:making pellets by Ore A and Coal D,C/0=1.2,20-22mm of pellets size,total four layers(the height of pellets bed is about 80mm),hot charging crucible,and 50min of reducing time in furnace.MD of the whole DRI bed under this condition is about 92.28%,the productivity can reach 67.20kg-MFe/m2.h or 91.80kg-DRI/m2.h.