Saturation of copper-iron mattes with solid magnetite

Conditions which lead to the saturation of simple copper-iron mattes with solid magnetite have been evaluated in this study. Diagrams have been developed which illustrate quantitatively the surface of saturation of matte with magnetite in the phase and stability diagrams for the Cu-Fe-S-0 system at 1468 K and 1 atm total pressure. Conditions fo. simultaneous saturation of matte with magnetite and gas (P _so2 + P _s2= 1 atm) have also been estimated by extrapolation of the data on magnetitesaturated mattes. Comparison of the results with compositions of mattes from oxygen-enriched smelters indicates that these smelters operate at magnetite saturation under conditions close to equilibrium. Conditions during oxygen-enriched smelting can be predicted from the diagrams given in this paper and correlation equations for the oxygen and sulfur concentrations in magnetitesaturated matte which were previously developed from the experimental data. D. L. KAISER, formerly Research Fellow at Massachusetts Institute of Technology.     

Effect of a self-rotating oxygen lance system on mass transfer between slag and molten steel

To improve the efficiency of the steelmaking process,a system of self-rotating lance was designed,and corresponding cold simulation mechanism was developed.The influence of the self-rotating lance on the mass transfer rate between slag and molten steel was investigated by comparing this novel system with the traditional oxygen lance.The results show that the self-rotating lance can stably rotate with a gas jet as the power source.The mass transfer rate increases with an increase in the top and bottom blow flow rates and with a decline in the lance position.Approximately 13.7% of the top blow flow rate is converted to stirring energy,which is approximately twice that of the traditional oxygen lance,and the mass transfer rate can increase by over 30%.Furthermore,the impact energy can be concentrated at different depths of the molten bath by adjusting the rotational speed.With the same energy density,the mass transfer rate produced by the self-rotating lance is higher;however,the influence of the energy density on the mass transfer rate is low when the rotational speed is 30-50 r/min.     

The importance of convective mass transfer in the reduction of hematite

The relative importance of transport phenomena, as opposed to chemical phenomena, in controlling the kinetics of hematite reduction has been debated for a long time. Recent measurements of gaseous diffusion coefficients in the porous iron and intermediate oxide layers produced by the reduction have shown that gaseous diffusion plays an increasingly important role, especially towards the end of the reaction. Convective mass transfer, however, is still assumed to play a negligible role, principally because of the way in which the reduction rate of hematite particles varies with the gas flow rate, and with the parti-cle diameter. The established theories of convective mass transfer are used in this paper to show that the observed variations would occur whatever contribution convective mass transfer was making to controlling the reduction rate. The observed variations, therefore, give no indication as to the relative importance of convective mass transfer. This paper then, makes a quantitative comparison between the mass transfer rates necessary to sus-tain the reaction rates observed in recent hematite reduction experiments and the rates predicted by the established theories of mass transfer. This comparison shows that con-vective mass transfer can play a major role in controlling the reduction rate, although the relative magnitude of its contribution varies with particle size, and with reduction temperature.     

The importance of convective mass transfer in the reduction of hematite

The relative importance of transport phenomena, as opposed to chemical phenomena, in controlling the kinetics of hematite reduction has been debated for a long time. Recent measurements of gaseous diffusion coefficients in the porous iron and intermediate oxide layers produced by the reduction have shown that gaseous diffusion plays an increasingly important role, especially towards the end of the reaction. Convective mass transfer, however, is still assumed to play a negligible role, principally because of the way in which the reduction rate of hematite particles varies with the gas flow rate, and with the particle diameter. The established theories of convective mass transfer are used in this paper to show that the observed variations would occur whatever contribution convective mass transfer was making to controlling the reduction rate. The observed variations, therefore, give no indication as to the relative importance of convective mass transfer. This paper then, makes a quantitative comparison between the mass transfer rates necessary to sustain the reaction rates observed in recent hematite reduction experiments and the rates predicted by the established theories of mass transfer. This comparison shows that convective mass transfer can play a major role in controlling the reduction rate, although the relative magnitude of its contribution varies with particle size, and with reduction temperature.     

固态和液态钢的激光诱导等离子体比较

比较了产生于室温固态钢以及高温液态钢上激光诱导等离子体的特征、原子铁的激发温度以及电子密度。通过在386～400nm波长范围的中性铁原子发射谱线, 由波尔兹曼作图法确定了铁原子的激发温度。通过测量AlI394.4nm的谱线宽度, 估算了电子密度。对固体钢来说, 铁元素的激发温度从延迟时间为10μs时的10800K下降到延迟时间为80μs时的7300K。当延迟时间分别为10μs和70μs时, 产生于固态钢和液态钢上等离子体间的激发温度并没有显著差别。在铁元素和铝元素大部分的中性原子线中, 可以观察到液态钢的谱线宽度比固态钢的谱线宽度更窄。当激光脉冲的观察延迟时间均为10μs时, 产生于液态钢上等离子体的电子密度大约为(0.99±0.15)×10¹⁷/cm³, 这相当于产生在固态钢上等离子体电子密度的46%。     

A simulating investigation into the characteristics of the mass transfer between molten steel and particles in the 150 t RH-IJ refining

The characteristics of the mass transfer between powder particles and liquid steel in the Ruhrstahl Heraeus process injection(RH-IJ)refining were simulatively investigated by the use of a 1/4 scale water model of a 150 t Ruhrstahl Heraeus(RH)degasser.The influences of the lifting gas flow rate,the up-snorkel and down-snorkel inner diameters and the size of powder particles on the characteristics of the mass transfer were examined.The results show that under the condition that the inner diameters of both the up-snorkel and the down-snorkel are the same,the mass transfer coefficient in the liquid,k increases with the increase of the inner diameter of the up-snorkel,the particle size and the lifting gas flow rate(Qg).However,the increase of Qg should not result in a saturated circulation rate.Under the current working condition,k ranges from 3.392×10-5 m/s to 2.661×10-4 m/s.On the other hand,with a given lifting gas flow rate and up-snorkel inner diameters,the mass transfer weakens with the increase of the down-snorkel inner diameter.An inherently nonlinear relationship between the circulation rate(Ql)of molten steel in the RH degasser and k,which increases with the increase of Ql,was found.Under the condition of other parameters being the same,k increases with the increase of the powder particle size.In order to enhance the mass transfer,it is better not to use extremely fine powder.     

Mass transfer between solid and liquid in a gas-stirred vessel

Mass transfer between solid and bulk liquid in an axisymmetric gas-stirred water model of a metallurgical reactor has been investigated both experimentally and theoretically. To this end, mass transfer rates from benzoic acid compacts submerged in an aqueous gas bubble driven system were measured via a weight loss technique. In conjunction with the weight loss measurements, liquid velocity and turbulence kinetic energy distributions in the bath were also mapped via laser doppler velocimetry (LDV). From the detailed LDV measurements, relevant dimensionless groups such as $\operatorname{Re} _{loc,r} \left( { = \frac{{d\rho \sqrt {u^2 + v^2 } }}{\mu }} \right)$ and $\operatorname{Re} _t \left( { = \frac{{d\rho \hat u}}{\mu }} \right)$ were estimated. Experimental measurements indicated that flow parameters varied from one location to another within the system. The corresponding variation in dissolution rates was, however, less pronounced. Such a trend was observed for all three gas flow rates studied. It was found that experimentally measured dissolution rates can be correlated with the measured flow and turbulence parameters (viz., √u ²+v ² and û) in terms of a previously reported dimensionless correlation, viz., Sh=0.73 (Re_loc,r )^0.25 (Re _t )^0.32 (Sc)^0.33. Parallel to flow measurements, a two-phase turbulent flow model was also applied to numerically compute the distributions of mean and fluctuating velocity components in the vessel. Embodying the predicted velocity components in the aforementioned correlation, mass transfer rates were recalculated. A comparison between the two sets of Sherwood numbers (estimated on the basis of the experimentally measured and theoretically predicted flow fields) suggests that solid-liquid mass transfer rates in a gas-stirred vessel can be predicted reasonably well via an axisymmetric, steady-state, two-dimensional turbulent flow model.     

Model study of mixing and mass transfer rates of slag-metal in top and bottom blown converters

Water model experiments have been conducted to clarify mixing rates of molten steel and mass transfer rates between slag and metal in LD and Q-BOP furnaces using six different circular tuyere arrangements. Splashing and ‘spitting’ were also examined with a view to finding a quiet bath with minimum mixing time and maximum mass transfer rate. Froude’s similarity criterion was fulfilled to determine gas flow rate and bath depth. Complete mixing time of water determined by tracer technique had been 0.9 second to 1.8 seconds for Q-BOP as compared to 6 seconds to 13 seconds for LD. This shows that the stirring intensity in Q-BOP is remarkably larger than that of LD. A simple relationship τ = 5.9(Q/N) ^−0.49 was obtained with gas flow rateQ and number of tuyereN. This indicates that flow rate of gas per tuyere should be intensified to realize better mixing. Mass transfer coefficient K_Ba for bottom blowing was found to be almost double that for top blowing. Of all the tuyere configurations studied for Q-BOP’s, a half circular tuyere arrangement was found to be the best considering all aspects of mixing, mass transfer, and bath agitation.     

Mass transfer between solid and liquid in vessels agitated by bubble plume

Mass transfer from solid benzoic acid cylinders to a gas-stirred aqueous bath has been investigated both theoretically and experimentally. Two typical gas injection configurations, the conventional central injection and the C.A.S. (C omposition A djustment by S ealed Argon Bubbling) were employed and the rates of dissolution of the acid compacts at various locations in the bath were measured at different gas-flow rates. These demonstrated that the mass-transfer rates are the highest in the two-phase region, while elsewhere in the bath, these were found to be practically identical. Furthermore, mass-transfer rates at the corresponding locations were found to be relatively greater for the conventional central injection than those for the C.A.S. configuration. Distribution of velocity and turbulence intensity in the vessel were computed theoretically using a previously reported calculation procedure. Based on these, values of various relevant dimensionless numbers were estimated so as to assess the adequacy and effectiveness of heat and mass-transfer correlations reported in the literature. These, however, did not fit with the present experimental observations. For this reason, a new correlation has, therefore, been proposed and it is shown that the experimental data can be described reasonably well by the equation Sh = 0.73 (Re_loc,r)^0.57 (T_i)^0.32 (Sc)^0.3. This correlation also embodies more plausible definitions of Reynolds number (Re_loc,r) and the turbulence intensity (Ti) in contrast to those reported in literature, since it has been derived using the local resultant mean velocity and the local fluctuating velocity in the fluid.     

Distribution of lead between copper and matte and the activity of PbS in copper-saturated mattes

The distribution coefficients of lead between copper and matte phases have been measured at 1405 and 1505 K and correlated with lead and iron concentrations in metallic copper and matte. Experiments covered the ranges of 0.009 to 1.8 and 0 to 11 wt pct lead and iron in matte, respectively. Distribution coefficients of lead between copper and iron-free matte, at infinite dilution of lead, have been determined to be 3.60 and 4.06 at 1505 and 1405 K, respectively. From the measured values of distribution coefficients, the Raoultian activity coefficients of PbS in copper-saturated matte have been calculated. At the temperatures and matte compositions investigated, activities of PbS deviate negatively from Temkin's ideality. At infinite dilution, the following equation correlating the Raoultian activity coefficients of PbS, , with matte composition and temperature has been obtained: In , whereN _FeS , is the mole fraction of FeS in the Cu₂S-FeS-PbS matte. The present values of γ _PbS ^o must be used exclusively in conjunction with the following Gibbs free energy of formation: Pb(l) + 1/2S₂(g) = PbS(l); ΔGℴ = −26730 + 12.20T (cal/mol). M. NAGAMORI, Formerly Associate Professor of Metallurgy at The University of Utah,     

Fluid flow and mass transfer in an inductively stirred four-ton melt of molten steel: A comparison of measurements and predictions

Experimental measurements are reported on melt velocities and on the rate at which immersed carbon rods dissolve in a 4-ton induction furnace, holding a low carbon steel melt. These measurements are compared with theoretical predictions, based on the numerical solution of Maxwell’s equations and the turbulent Navier-Stokes equations. In general, good agreement has been obtained, both regarding the absolute values of the velocities and the mass transfer coefficients and the trends predicted by the theoretical analysis. In addition to providing further proof regarding the applicability of the mathematical modeling technique, the principal contribution of the work is that it provides an improved insight into the behavior of inductively stirred melts. In particular it was found that for an inductively stirred melt both the velocities and the rate of turbulence energy dissipation are relatively uniform spatially, in contrast to bubble stirred systems, where most of the agitation is confined to the jet plume and to the near surface region. It was found, furthermore, that the mass transfer coefficient characterizing the rate of dissolution of immersed carbon rods depends both on the absolute values of the melt velocity and on the local values of the turbulence intensity; thus significant mass transfer will occur in the region of the eye of the circulation, where the absolute value of the mean velocity is small. On leave at Massachusetts Institute of Technology     

A correlation for estimation of mass transfer rates of solids in gas stirred ladle systems

Mass transfer between solid and liquid in gas stirred cylindrical vessels has been analysed both theoretically and experimentally. To this end, starting from an appropriate “single particle-fluid correlation”, a relationship applicable to a system of suspended solids has been deduced and represented according to: . On the basis of this, dissolution of solids in two different aqueous models of gas stirred ladles has been investigated and it has been demonstrated that the correlation produces estimates which are in reasonable agreement with the experimental observations. Furthermore, it is shown that the present correlation has a form analogous to the one, derived much earlier by Kolmogoroff from the theory of isotropic turbulence.     

UV/VIS-spectroscopy of molten and solid CaO-MgO-SiO2 - slags

The previously developed high temperature set-up has been used to monitor the redox state of molten slags at 1500°C directly by UV/VIS spectroscopy. Slags of the CaO-MgO-SiO₂-system were doped with Fe₂O₃ mass contents of 0.80 and 5%. Spectroscopical results at different oxygen partial pressures of the investigated Fe³⁺ charge-transfer (CT) transitions in the wavelength range between 200 and 800 nm were found to be representative for the redox state of the slag. The peak positions and shifts give further information about the optical basicity and the structure of molten slags. The time dependence of the oxidation/reduction equilibrium process was measured and evaluated concerning diffusion mechanisms. In Cr₂O₃-doped silicate-slags in the liquid state CrO₃ - and Cr³⁺- species occur. The different CrO₃-species (CrO₄^2- and Cr₂O₇^2-) in silicate slags have been indicated spectroscopically and registed quantitatively. Further investigations on Cr₂O₃-doped slags uncovered the well known evaporation of chromium out of molten slags as a decrease in the CrO₃ concentration in time. In the molten slag the CrO₃ slowly evaporates, which can be seen spectroscopically as a decrease in the CT-band intensity. The results obtained on numerous optical parameters of molten slags will establish the application of reflection spectroscopy at high temperatures.     

Raman spectra of solid,molten, and gaseous gallium trichloride

The structure of crystalline, molten (from the melting to the critical temperature), and gaseous (at high vapor pressures) gallium trichloride is studied by Raman spectroscopy for the first time.     

Kinetics of mass transfer of manganese and silicon between liquid iron and slags

The kinetics of mass transfer of Mn and Si between liquid iron and slags were investigated in laboratory experiments at 1600°C in MgO crucibles with 1500 g iron and 250 g slag. Three different slags consisting of CaO-MgO-MnO-SiO₂, MgO-MnO-SiO₂ and MgO-MnO-Al₂O₃-SiO₂ were used. The concentration-vs.-time curves, experimentally measured under defined flow conditions generated by gas stirring, were evaluated by application of a multi-component transport model in order to obtain the mass transfer coefficients. The numerical values of the thus determined measured mass transfer coefficients were compared with values calculated by a theory of mass transfer at liquid-liquid interfaces. The measured and theoretical values were in good agreement with each other in the case of reduction of MnO from the slag by Si in the metal, provided that the measurements had been carried out below a critical stirring intensity, above which metal droplets were emulsified in the slag. Experiments, where sulphur was dissolved in the metal melt and where the sulphur contents were systematically varied, showed no changes of the mass transfer coefficient in comparison to sulphur-free melts. The experimental mass transfer coefficients for the reduction of silica from the slag by manganese in the metal were smaller than those calculated by the mentioned mass transfer theory. This could be explained by inhibition of surface renewal under the influence of solid reaction products precipitated at the interface.     

炉缸冷却壁对流换热系数计算及烘炉传热特性

 炉缸冷却壁冷却性能主要体现在冷却水与水管间的对流传热。因为工程上常用计算对流换热系数的经验公式不能满足不同的水流状态从而导致炉缸热应力分析误差较大，所以以某高炉炉缸结构为例，首先利用传热学准数方程推导出冷却水处于不同流动状态时对应的综合对流换热系数表达式，同时探讨了对流换热系数经验公式的适用范围；然后通过迭代计算推导出了冷却水处于层流状态下考虑衰减热阻时的综合对流换热系数表达式；最后对烘炉状态下炉缸侧壁传热模型进行瞬态传热与冷却分析，得到了微水烘炉甚至闭水烘炉的热工依据，可为初步制定高炉烘炉制度进行评估和完善。     

Kinetics of reactions between magnetite and carbon monoxide between 723 and 823 K

The kinetics of some reactions between carbon monoxide and magnetite were investigated between 723 and 823 K. Gas-phase mass-transfer effects within and near the porous samples and surface-reaction kinetics were considered. The experiments were done on sintered magnetite disks whose void fraction was 15 to 20 pct. A continuously weighed rotating disk reactor provided uniform mass transfer to the sample faces. The reacted disks were analyzed by Mössbauer spectroscopy and other methods. The only product species found were cementite and carbon, which suggested the existence of two reactions: the formation of cementite and carbon dioxide directly from magnetite and carbon monoxide, and the disproportionation of carbon monoxide to carbon dioxide and free carbon. These reactions were modeled mathematically. The surface kinetic data for both reactions were found to be compatible with rate expressions which were directly proportional to the square of the partial pressure of carbon monoxide and approximately inversely proportional to the partial pressure of product carbon dioxide.