The Basic Experimental 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) in China Steel of Taiwan, the reaction characteristisc of carbothermic reduction with high pellets bed are studied in present project.The effects of C/O, reducing temperature, reducing time and some optimized methods on the weight loss, metallization degree, shrinkage and density of direct reduced iron (DRI) are investigated by electric furnace experiments. Experiments by natural gas furnace are carried out based on the electric furnace experiments. In addition, Reflected light microscope, scanning electron microscope with EDS, and high performance X-ray diffraction were used for fundamental analysis.(1) The calculation equation of central temperature of pellet is built: T0＝A(Tt-T∞)exp(Bt)+T∞. The values of A and B can be determined by experiments.(2) Metallization degree (MD) of pellets with C/O=1.0is lower due to the insufficient reductant, the MD of pellets with C/O=1.2and C/O1.4is similar. But when the C/O is1.4, there is more residual carbon in DRI. Therefore,1.2is the reasonable C/O based on MD and residual carbon.(3) When the reducing time in furnace is50min, the MD of whole DRI bed is about57.31%. When the reducing time in furnace is60min, the MD of whole DRI bed is about80.23%. The diameter of DRI shrinks to70%of green pellets, and the cross section becomes50%of green pellets. And the density of DRI can reach3.0g/cm2. The increase of MD of bottom layer is the key to increase the MD of the whole DRI bed.(4) Keeping insulating material can increase the MD of DRI, When the reducing time in furnace is50min followed by10min of keeping insulating material, the MD of whole DRI bed increases from57.31%to76.70%. When the reducing time in furnace is60min followed by10min of keeping insulating material, the MD of whole DRI bed increases from80.23%to 85.22%.(5) 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 is50min, the MD of whole DRI bed increases from57.31%to85.24%. When the reducing time in furnace is60min, the MD of whole DRI bed increases from80.23%to87.07%. Therefore, the optimum parameters are C/O=1.2, hot charging crucible, and50min of reducing time in furnace.(6) Experimental results in natural gas furnace show that, a) when the maximum furnace temperature is1450℃, and reducing time is60min, the MD of whole DRI bed is79.75%. b) When the maximum furnace temperature is1500℃, and reducing time is50min, the MD of whole DRI bed is83.02%.So, the reducing temperature is more important than reducing time in PSH process. The MD of DRI may be higher if the natural gas furnace is properly rebuilt.The investigation results of this project can give some references for industrial application of PSH process in future.