Mathematical modeling of the reduction process of iron ore particles in two stages of twin-fluidized beds connected in series

A mathematical model is presented to describe the reduction process of iron ore particles in two stages of twin-fluidized beds (TFBs) connected in series: prereduction and final reduction stages. Main features of the model are the inclusion of particle degradation phenomenon to account for its effect on reduction of iron oxides and reduction kinetics for multiparticles having a wide size distribution. It was found that about 90 pct of overall particle degradation occurs in the prereduction stage mainly due to thermal stress and volume expansion. The reduction degree of particles larger than 1 mm decreased fast with increasing particle size in both the prereduction and final reduction stages. However, the particles sized between 0.2 and 1 mm showed mild increase in reduction degree, and steep increase for the fines smaller than 0.2 mm. The reduction degree was also gradually decreased with increasing the gas oxidation degree of feed gas in both the prereduction and final reduction stages. It was found that to obtain a desired reduction degree, it is of great importance to control the bed temperature in stage I rather than in stage II. The optimum range of residence time was 15 to 20 minutes in the prereduction stage and 30 to 35 minutes in the final reduction stage.     

Experimental investigation and thermodynamic modeling of the Cr-Ni-Si system

The constitution of the Cr-Ni-Si ternary system is established via experiment and thermodynamic modeling. In the experimental section, 35 decisive alloys, the compositions of which are based on a preliminary calculation using available literature data, are prepared by arc melting of cold-pressed pellets and annealing at 900 °C for 25 days. Water-quenched samples are analyzed by using X-ray diffraction (XRD) and differential thermal analysis (DTA) techniques. In the modeling section, a consistent thermodynamic data set for the Cr-Ni-Si system is obtained by considering the present experimental results and reliable literature data. Comparisons between the calculated and measured phase diagrams show that the experimental information is satisfactorily accounted for by the thermodynamic modeling. The liquidus projection and reaction scheme for the entire ternary system are presented.     

Computer simulation of consumable melted slabs

A mathematical model has been developed to simulate two-dimensional heat flow for a slab ingot produced as a remelted product. Various heat flow parameters have been studied to determine the influence of changes in them on local solidification time. The parameters which show the greatest influence are the heat transfer coefficient and the thickness of the slab. The rate of addition of material changes the depth of the molten pool, but does not affect local solidification time.     

感应加热熔炼Cu-Cr合金的凝固行为

采用电弧熔炼和感应加热熔炼研究了不同组成Cu-Cr合金的凝固行为.结果表明:由于高温下Cu-Cr合金与坩埚材料发生反应,氧化铝坩埚中感应加热熔炼Cu-Cr合金受到污染,澄清了Müller与Li的争议;当合金中Cr的摩尔分数大于40%时,感应加热熔炼Cu-Cr合金出现了液相分离,合金与坩埚材料的反应生成物促进了Cu-Cr合金的液相分离.     

Experimental study and modeling of the thermodynamic properties of Cu-Fe-Ni melts

The partial mixing enthalpy of nickel in ternary liquid Cu-Fe-Ni alloys is studied at 1873 K along sections characterized by ratios x _Cu: x _Fe = 3, 1, and 1/3 at x _Ni = 0–0.55. The investigations are undertaken using a high-temperature isoperibolic calorimeter. The temperature and composition dependence of the excess mixing Gibbs energy of liquid Cu-Fe-Ni alloys are described in terms of the Muggianu-Redlich-Kister model using the data obtained, the literature data on the activities of liquid alloy components, and the thermodynamic properties of melts of the boundary binary systems. This model is used to calculate isotherms of the thermodynamic properties of the liquid alloys over the entire composition range. The contribution of a ternary interaction to the integral mixing enthalpy of liquid Cu-Fe-Ni alloys is found to be mainly positive.     

Kinetics of melted copper oxidation with oxygen of the gas phase

The oxidation of melted copper with air oxygen is considered from a viewpoint of the electrochemical theory of interactions at the melt-oxygen-containing gas interface. The calculations using the experimental data show that the process proceeds in a kinetic regime. The rate-determining step is the detachment of the first electron from an adsorbed oxygen atom. The oxidation of liquid copper in a circulation gas lift is calculated.     

Mathematical modeling of work hardening of heterophase materials with nanosized strengthening particles

Work hardening and evolution of the deformational defect subsystem have been investigated in dispersion-hardened materials with metal FCC matrix and nanosized particles at various temperatures. The investigation was conducted using a mathematical model including equations of balance of deformational defects.     

Supercooling and structure of levitation melted Fe-Ni alloys

The effect of processing variables, such as supercooling, quenching rate, and/or growth inhibitors on the structure of levitation melted Fe-25 pct Ni alloys was investigated. The subgrain microstructure of samples solidified in water, molten lead, or ceramic mold was found to fall into three categories of dendritic, spherical, or mixed dendritic plus spherical morphologies. All three morphologies were observed when the samples had solidified with a superheat or a supercooling less than 175 K. At larger supercoolings, however, only the spherical morphology was observed. The structure fineness was shown to depend on the supercooling as well as on the solidification medium. The grain size and shape, on the other hand, was found to depend on the morphology of the microstructure, but not on the supercooling. The cooling rates during solidification and the heat transfer coefficient at the metal-quenching medium boundary were calculated. The coefficient for the samples solidified in water, molten lead, and ceramic mold was calculated to be 0.41, 0.52, and 0.15 w/cm2 K, respectively.     

Experimental and mathematical modeling of metal spray forming process

The metal spray forming process was examined using mathematical simulation and verified through the prototyping evaluation at Baosteel’s test and development facilities.The mathematical model comprised of four sections,including jet gas flow in the deposition chamber;single droplet behavior along its trajectory path;probability and statistical analysis of droplet mass behavior,and forecast of the shape and temperature distribution of the billet during the spray forming process.