| The direct alloying technology of manganese ore used in converter has been studied since the1980’s. The manganese yield can hold in the level of70%by the technology of hot metal pretreatment and less slag steelmaking, which are mature in many Japanese steel companies. But there is essential difference between our country and Japanese in steelmaking process, and industrial tests show that the yield of manganese fluctuates in the range of5～25%generally. Therefore, the economic benefits are not obvious. This paper proposes a new method of direct alloying using manganese ore briquette containing carbon, which is put into the furnace after the end of the oxygen blowing. So MnO contained in briquette will be reduced rapidly to Mn by solid carbon and diffused into the steel to improve the Mn yield. Compared with the traditional process, the effect of large amount of slag, low content of end point carbon and high oxidizing of slag on the Mn yield would be reduced in the new process.The self-reduction rules of natural manganese ore briquette containing carbon and manganese-rich slag briquette containing carbon were studied in this paper, and the volatility of manganese and suppression measures in the self-reduction process were discussed. Then the direct alloying of Manganese in BOF was simulated in a medium-frequency induction furnace, and the coupling kinetic modeling was established. The effect of direct alloying process on temperature of the furnace was analyzed, and the solutions and suggestions about industrial production of manganese direct alloying were proposed.(1) The experimental results of the natural manganese ore briquette containing carbon show that the best carbon ratio is1.2in briquette, reduction temperature has little effect on the reduction of briquette, and CaF2can effectively improve the reduction rate in the early stage of reduction. The reduction process can be divided into two stages according to the reduction results. In the early stage, the reduction rate is controlled by chemical reaction and the kinetic equation is In the later stage, the reduction rate is controlled by (2) Manganese mainly exists in the form of2MnO·SiO2in the manganese-rich slag, and appropriate CaO should be added to increase its reducibility by replacement MnO. The results of the self-reduction experiments of manganese-rich slag briquette containing carbon show that the reduction rate can be more than90%when the carbon ratio is1.2and the basicity is1.0, and CaF2can effectively improve the reduction rate. The kinetic of self-reduction was analyzed. The apparent activation energy of chemical reaction is24.07kJ/mol, and the apparent activation energy of internal diffusion is107.55kJ/mol. Therefore, the reduction rate of briquette is controlled by mass transfer of CO in the product layer, and the kinetic equation(3) The manganese-rich slag can be reduced more fully than the natural manganese by making a comparative analysis about self-reduction test. When the self-reduction continues for about10min, the reduction degree of manganese oxide and iron oxide is about70%in the natural manganese briquette without adding flux, and the volatilization rate of Mn is about8.3%. However, under the same conditions, the reduction degree of manganese oxide is about90%in the manganese-rich slag briquette without adding flux, and the volatilization rate of Mn is about7.2%.(4) The volatility of Mn was studied in the self-reduction process of manganese-rich slag briquette containing carbon. The results show that the volatilization rate is the largest in the first3min of reduction process, and gradually reduces with the increase of the liquid slag. The addition of CaF2makes the slag melting point reduce and the reduction rate accelerate. So liquid slag generated in a shorter time inhibites the volatilization of Mn. When the self-reduction lasts for about10min, the volatilization rate of Mn reduces about40%by5%CaF2added in briquette. The kinetic model of Mn volatility was established according to the unreacted core contraction model for manganese-rich slag briquette, in which the carbon ratio is1.2, the basicity is1.0, and CaF2is5%. The calculating results show that in the first5min of reduction process, the reduction rate is simultaneously controlled by chemical reaction and internal diffusion. The apparent activation energy of chemical reaction is24.99kJ/mol, and the apparent activation energy of internal diffusion is29.23kJ/mol through calculation. In the5～10min stage of reduction process, the reduction rate is controlled by internal diffusion, and the apparent activation energy of internal diffusion is219.79kJ/mol. Therefore, the diffusion resistance for the later stage is larger than the early stage.(5) The direct alloying in BOF was simulated in25kg medium-frequency induction furnace. The results show that the yield of Mn fluctuates in the range of30%～70%in the process of direct alloying by manganese-rich slag briquette containing carbon. Based on the mass transfer of [Mn] and (MnO), the coupling kinetic modeling was established, and calculated by Matlab. The calculating results show that reduce of the amount and oxidizability of the slag has obvious effect on improving the yield of Mn. Therefore, tapping at low carbon should be avoided in the practical production.(6) The melting reaction process of direct alloying with self-reduction briquette in the converter furnace can be divided into three stages. Based on the calculation of maximum absorption thermal in each stage, a formula of maximum temperature drop is established. When the amount of slag is60kg/t, tapping quantity is100t and the addition of briquette is100kg, the maximum temperature drop formula is as follows. Maximum temperature drop of slag:Tslag max=12.6℃/(100kg). Maximum temperature drop of molten steel:Tsteel max=(1.74+1.38ζ’-0.13a)℃/(100kg)(7) It is suggested that self-reduction briquette of manganese ore could be added once after operation of TSO in direct alloying process, and the mount of briquettes rises from5kg/t to20kg/t gradually. In addition, Ar flow rate in converter should be turned on full force in order to enhance the mixing effect. Feeding rate should be as homogeneous as possible to prevent local supercooling. Finally, an operation of high catch carbon in converter is implemented to gain high yield of Mn. |
PDF Full Text Request