| Slag is one of by-product in iron and steel industry smelting process. With the rapid growth of steel production, slag production is also increasing quickly. Currently the use of steel slag is still low value-added products, and physical sensible heat carried by slag and useful elements in converter slag are not taken full use, resulting in the waste of slag waste-heat in iron and steel industry. The research of direct utilization of molten slag can not only promote the recycle technology of slag’s effective component, but also take use of physical sensible heat in steel slag to get high value-added products, which is of great significance for energy conservation and sustainable development of the steel industry.On the basis of concluding the domestic and foreign research of the comprehensive utilization of steel slag, this article mainly studies using melting modification of steel slag to smelt ferroalloy, combined with current status and trends of development of metallurgical industry. Using practical converter slag from a steel company as raw materials, through the modified processing of molten steel slag by adding SiO2as modifier, this experiment acquire reasonable modified ingredients and control the reasonable temperature and appropriate carbon content, in order to make the possibility of using melting modification of steel slag to smelt ferroalloy. By the using commercial thermodynamic software, this experiment consider the influence of modified slag composition, temperatures and amounts of reducing agent on target alloy products, to acquire the appropriate smelting conditions. Considering the effect of original slag, modification of steel slag and carbon content on reduction of modified steel slag, the metallurgical behavior of elements in the slag during the restore process is mastered in the reaction of different components, and the material balance and heat balance is calculated. The results of the research showed following:(1) Using reaction product of the original slag smelting ferroalloy at1800℃, with appropriate amount of carbon, main composition of the obtained alloy is w(Ca)=17.36%、 w(Si)=16.94%、w(Fe)=38.45%, where the rest is carbon and other metal, and the utilization rate of CaO、SiO2、FeO in original residue are18.41%、73.4%、100%; in addition to CaO(52.6%) in products slag phase, there is CaC2(35.35%) generated. The gas product mainly contains CO gas. The heat balance analysis shows that theoretical energy consumption of1ton of original slag smelting ferroalloy is6.40×109kJ, and theoretical energy consumption of pure oxides with the smelting of the alloy is5.31×109kJ, which shows it does not meet the energy saving effect.(2) Apply modified slag to smelting ferroalloy at1800℃, in the shortage of carbon content, the alloy main composition of w(Ca)=8.79%, w(Si)=51.63%, and w(Fe)=19.80%could be obtained, where the rest is carbon and other metal. The utilization rate of CaO, SiO2, and FeO in original residue was18.12%,62.33%, and100%respectively. In products slag phase, CaO(57.61%) and SiO2(37.66%) were measured. And the gas product this time consisted of not only CO, but also SiO. The heat balance analysis indicated that theoretical energy consumption of the modified slag smelting ferroalloy was8.81×109kJ, and theoretical energy consumption of pure oxides with the smelting of the alloy was8.15×109kJ, which showed that it failed to meet the energy saving effect.(3) Apply modified steel slag to smelting ferroalloy, in the shortage of carbon content, the alloy composition of w(Ca)=17.67%,w(Si)=51.60%, and w(Fe)=13.65%could be obtained, where the rest is carbon and other metal. The utilization rate of CaO, SiO2, and FeO in original residue was52.87%,90.05%, and100%respectively. In products slag phase, CaO(52.18%) and SiO2(27.46%) could be measured. And the gas product this time mainly consisted of CO gas, more than95%. The heat balance analysis indicated that theoretical energy consumption of the modified slag smelting ferroalloy was1.10×1010kJ, and theoretical energy consumption of pure oxides with the smelting of the alloy was1225503.1J, where it could save1.23×1010kJ with modified steel slag per ton. Measured by its alloy products can save energy2614. U/g. Producing one ton of the alloy can save2.614×109J, converted into electricity, about saving726.2kW·h/t.(4) In the process of melting modification, it is helpful to the deoxidization of Ca through adding into SiO2, and reduction rate is rising from18.41%to52.87%. With the increasing of CaO utilization, making the slag fully restored, physical sensible heat of steel slag is effectively used. Energy-saving effect of using modified converter slag melting ferroalloy has greatly been raised. (5) The appropriate composition of slag is about60%w(SiO2). And the appropriate temperature is range at1750～1850℃. At the same time, the appropriate amount of reductant is about35%. |
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