Zhe Shi

Study on Apparent Kinetic Prediction Model of the Smelting Reduction Based on the Time-Series

A series of direct smelting reduction experiment has been carried out with high phosphorous iron ore of the different bases by thermogravimetric analyzer. The derivative thermogravimetric (DTG) data have been obtained from the experiments. One-step forward local weighted linear (LWL) method , one of the most suitable ways of predicting chaotic time-series methods which focus on the errors, is used to predict DTG. In the meanwhile, empirical mode decomposition-autoregressive (EMD-AR), a data mining technique in signal processing, is also used to predict DTG. The results show that (1) EMD-AR(4) is the most appropriate and its error is smaller than the former; (2) root mean square error (RMSE) has decreased about two-thirds; (3) standardized root mean square error (NMSE) has decreased in an order of magnitude. Finally in this paper, EMD-AR method has been improved by golden section weighting; its error would be smaller than before. Therefore, the improved EMD-AR model is a promising alternative for apparent reaction rate (DTG). The analytical results have been an important reference in the field of industrial control.

Dimensionless Analysis and Mathematical Modeling of Electromagnetic Levitation (EML) of Metals

Electromagnetic levitation (EML), a contactless metal melting method, can be used to produce ultra-pure metals and alloys. In the EML process, the levitation force exerted on the droplet is of paramount importance and is affected by many parameters. In this paper, the relationship between levitation force and parameters affecting the levitation process were investigated by dimensionless analysis. The general formula developed by dimensionless analysis was tested and evaluated by numerical modeling. This technique can be employed to design levitation systems for a variety of materials.

Applications of Electromagnetic Levitation and Development of Mathematical Models: A Review of the Last 15 Years (2000 to 2015)

Electromagnetic levitation (EML) is a contact-less, high-temperature technique which has had extensive application with respect to the investigation of both thermophysical and thermochemical properties of liquid alloy systems. The varying magnetic field generates an induced current inside the metal droplet, and interactions are created which produce both the Lorentz force that provides support against gravity and the Joule heating effect that melts the levitated specimen. Since metal droplets are opaque, transport phenomena inside the droplet cannot be visualized. To address this aspect, several numerical modeling techniques have been developed. The present work reviews the applications of EML techniques as well as the contributions that have been made by the use of mathematical modeling to improve understanding of the inherent processes which are characteristic features of the levitation system.

Dimensionless Analysis and Numerical Modeling of Rebalancing Phenomena During Levitation

Electromagnetic levitation (EML) has proved to be a powerful tool for research activities in areas pertaining to materials physics and engineering. The customized EML setups in various fields, ranging from solidification to nanomaterial manufacturing, require the designing of stable levitation systems. Since the elevated droplet is opaque, the most effective way to research on EML is mathematical modeling. In the present study, a 3D model was built to investigate the rebalancing phenomenon causing instabilities during droplet melting. A mathematical model modified based on Hooke’s law (spring) was proposed to describe the levitation system. This was combined with dimensionless analysis to investigate the generation of levitation forces as it will significantly affect the behavior of the spring model.

Study on the Second Phases of (Y,Nb)-Codoped TiO2 Ceramic

Microstructures and crystal structures of the second phases YNbO4 and YTiNbO6 in (Y,Nb)-codoped TiO2 ceramics were investigated at different sintering temperature and calcination temperature. The (Y,Nb)-codoped TiO2 ceramics and the second phase ceramic samples were prepared by the traditional electronic ceramic process. The microstructure, chemical composition and crystal structures of samples were characterized by SEM, EDS and XRD. The results show that there exist second phases of YNbO4 and YTiNbO6 in (Y,Nb)-codoped TiO2 ceramic. With the sintering temperature and calcination temperature rising, the second phase YNbO4 will transmit to YTiNbO6.

Photocatalytic Properties of (Fe, N)-Codoped TiO2

Fe, N)-codoped TiO2 were prepared by calcining the Fe-doped TiO2 samples accomplished by precipitation method in the nitrogen atmosphere, and the photocatalytic properties of (Fe, N)-codoped TiO2 at different temperatures were investigated. The samples were characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and ultraviolet-visible (UV-vis). The results show that the (Fe, N)-codoped TiO2 powder samples calcined at 600°C are dispersed well with more hydroxyl groups on its surface. The absorption edge of the (Fe, N)-codoped TiO2 is 429nm due to the effects of mixed crystal, which means the improvement of photocatalytic capability.

Study on Separation of Iron from Waste Slag of Pyrite Processing

The work presented here investigates the optimum conditions for maximum recovery of iron from the waste slag. The most advantageous option for industrial trial is roasting of the waste slag under reducing condition followed by magnetic separation selected from various options for recovery of iron from the waste slag. The experimental results show that under the treatment condition in this work, about 70% of the iron was recovered from the waste slag, where the iron content in the concentrate is 57%. After further treatment with chlorinated segregation-magnetic separation, the iron content in the recovered slag can reach 83%. After the treatment, sulphur content in the concentrate was reduced significantly and gangue materials, such as SiO2, Al2O3, and TiO2, were reduced effectively. This paper is mainly focused on the results of reduction roasting- magnetic separation. Recovery of iron from the waste slag is of great interest for maximum use of mineral resource, reduction of environment impact, and improvement of economical benefits to the related companies.

Effect on Position of Electromagnetic Stirring on Inclusion Behaviors in Billet

A considerable number of research works have been carried out to study the effects of electric current and frequency of Electromagnetic Stirring (EMS) on the quality of cast steels, but there are only a few studies available addressing the effects of EMS location on inclusion removal and steel cleanliness An ideal position of EMS will improve inclusion floatation and separation from liquid steel. However, inappropriate installation will lead to the entrapment of the slag into liquid steel, and impact the quality of cast billet. The current applied for these plant trials was 300A at a frequency of 3Hz,positions form axial centers of EMS to the top of the mold were 450mm, 510mm and 690mm respectively . 130 billets of medium carbon steel were produced and samples were taken for spectral analysis to study the effects of installation location of EMS on steel cleanliness. The experimental results show that the optimum position of EMS should be placed 510mm from the top end of the copper mold when the electrical current is 300A at frequency of 3 Hz. The three parameters of placement of EMS in paper were obtained from the simulation results, and this paper focused mainly on the effect EMS position on inclusion behaviors in billet.

Mathematical Modeling of Decarburization in Levitated Fe-Cr-C Droplets

Using carbon dioxide to replace oxygen as an alternative oxidant gas has proven to be a viable solution in the decarburization process, with potential for industrial applications. In a recent study, the transport phenomena governing the carbon dioxide decarburization process through the use of electromagnetic levitation (EML) was examined. CO2/CO mass transfer was found to be the principal reaction rate control step, as a result gas diffusion has gained significant attention. In the present study, gas diffusion during decarburization process was investigated using computational fluid dynamics (CFD) modeling coupled with chemical reactions. The resulting model was verified through experimental data in a published paper, and employed to provide insights on phenomena typically unobservable through experiments. Based on the results, a new correction of the Frössling equation was presented which better represents the mass transfer phenomena at the metal-gas interface within the range of this research.

Steel ladle exchange models during steelmaking and continuous casting process

The models and influencing factors of steel ladles exchange during the steelmaking and continuous casting process of H steel plant were investigated. Based on analysis of the operation process and turnover time of steel ladles, relationship models for the turnover number, turnover rate, continuous casting number, number of ladles with additional turnover, and number of ladles without additional turnover were built. The turnover rules of steel ladles for one basic oxygen furnace (BOF) matching one continuous caster (CC) and two BOFs matching two CCs modes were simulated by using a Gantt chart. The models of steel ladle exchange were proposed for casting of a single CC and overlapping casting of two CCs. By analyzing the influencing factors, the following conclusions were drawn. The exchange ladle should not have the task of transporting liquid steel in the CC that stops casting earlier. The end time of the empty ladle in the CC that stops casting earlier should be earlier than the start time of the full ladle in the CC that stops casting later. After evaluating the factors influencing the start casting time, turnover cycle, casting time, continuous casting number, and overlapping time, a prioritization scheme of steel ladle exchange was proposed based on the steel grade. First, the turnover cycle and single heat casting time were determined; based on these, a reasonable ladle turnover number was calculated. Second, the turnover number and continuous casting number were optimized for maximizing the number of ladles without additional turnover. Lastly, to reduce the casting number during the overlapping time to be lower than the turnover number, the overlapping time was shortened.