| Because the requirement on the quality of steel is becoming higher and higher, and sulfur is the main impurity element of steel, the control of its content has become very important. Due to low cost, hot metal external desulfurization, as the main means of controlling sulphur content in steel, is paid more and more attention.Since the 1930s, technology of external desulfurization and desulfurizer appear endlessly. Because of many advantages of magnesium, magnesium and magnesium-based desulphurizer, as the main desulphurizer, are applied widely. But magnesium, as a desulphurizer, has some defects, such as expensive, higher steam pressure, so many people want to find a new desulphurizer to replace magnesium-based desulphurizer.A new method was attempted to develop by our group that magnesium vapor pruduced by desulfurizer(composition of reducing agent and oxidant mainly by magnesium oxide) in the high temperature condition of hot metal was reacted with sulfur in the hot metal. In this paper, the new MgO-based desulfurizer of this method was researched. The study included the calculation of thermodynamics, kinetics analysis, hot metal desulfurization experiment, kinetics analysis of desulfurization, and comparison between this method and industrial method. The conclusion was showed as following.(1) Thermodynamic calculationThrough thermodynamic calculation,4 different reducers are compared, the results of Al and Ca are best; the result of Si is just OK, used Si and added CaO, when the pressure of magnesium vaper is about 0.18atm, reaction will happen at 1350℃; the result of C is the worst, added CaO can not change the result, when the pressure of magnesium vaper is about 0.003atm, reaction will happen at 1350℃;(2) Kinetics studyThrough DSC, the activation energy, E, of Al+light-burned dolomite reaction is the smallest, which is 314.903kJ7mol, and the reaction order is 2.29; the activation energy between Si-Fe+dolomite and Al+MgO is equal, and E are 2948.54 kJ/mol and 2638.17kJ/mol; the activation energy of C+MgO is the biggest, which is 24474.7kJ/mol, the reaction can hardly occur.Through the experiment produced Mg vapor, the Mg production rate increases with increased temperature and gas flow rate; the reaction velocity of light-burned dolomite+Al is the fastest, the reduction rate is above 90% after 30 min, the reaction velocity of light-burned dolomite+Si-Fe+3% CaF2 is equal to that of MgO+Al, the reaction velocity of MgO+C is the slowest. The reaction velocity of MgO+Al with in 15min is fast, when the MgO disappears (the reduction rate is 74%), the velocity becomes slow; in the system of light-burned dolomite+Si-Fe, adding more Si-Fe or 3% CaF2 can promote reaction, the result of Ar and Si is better than that of N2 and Si-Fe, there is no effect of pressure on experiments.Used Arrhenius equation, E of different systems are calculated, the E of MgO+C is the biggest, the reaction can hardly occur; the E of dolomite+Al is the smallest, the reaction can easily occur, E of dolomite+Si-Fe is equal to that of MgO+Al.Through the discussion of Mg vapor production, the reaction is mainly controlled by diffusion of Mg vapor left the ball. The Mg vapor pressure is different, there is an interface in the ball, the reaction velocity at the interface is very fast, while the reaction velocity outside or inside the interface is slow.Light-burned dolomite+Si-Fe are chosen as the desulfurizer, the equation can be gotten as followed. Y=(8.32-0.011×T+3.01×10-6×T2)×e[-1/(1301.96-1.49×T+4.32×10-4×T2)]+(-13.49+0.017×T-4.82×10-6×T2)(3) 5kg desulfurization experimentThe result of injection method is better than that of power injection method and throwing ball method.Through the desulfurization experiments of light-burned dolomite+Si-Fe, desulfurization rate increases with increased T, Q, additive mass, Si-Fe mass, initial sulfur content and Si content in Si-Fe. Resulfurization can be inhibited by added CaO on the surface of molten iron. The desulfurization rate is below 50% when the desulfurizer mass is below 2.5 times of theory. The best experiment conditions are that T=1340℃, used 75 Si-Fe, ratio is 1.2, added 3% CaF2 desulfurizer mass is 18.13g, PAr is 0.1MPa, gas flow is 0.2m3/h, added 25g CaO on the surface of molten iron. The desulfurization rate is 97%, the end sulfur content is 0.0012%.Through the desulfurization experiments of other system, the results of MgO+C are worst, the desulfurization rate is 23%; the desulfurization rate of MgO+Ca-Si is 43%; the results of used Al are best, especially dolomite+Al, the velocity of it is biggest, the S content is below 0.0050% in 6min; the S content is below 0.0050% in 10min by used dolomite+Si-Fe and desulfurization rate is above 85%.(4) Kinetics analysis of desulfurization experimentThe control step is the mass transfer between Mg and S at bubble-molten iron interface. The results of calculation and experiment are fitted will, and the equation of bubbles desulfurization can be gotten.(5) It pilot tests of hot metal external desulfurizationThe results show that the sulfur content can decrease with used this desulfurizer. In the pretreatment condition, the desulfurization rate is 94.5%, and the end sulfur content is 0.0023%.(6) Comparison with industryCompared between this method and industrial method, the Mg bubble velocity and the cost of this method are smaller than that of industrial method. The cost of the method saved 37.07% and 32.51% compared with KR method and Mg injection method, respectively.Through above analysis, the desulfurizer is feasible in principle, the desulfurization rate is high, and the cost is small. |
PDF Full Text Request