Coupled reaction kinetics of duplex steelmaking process for high phosphorus hot metal

Abstract

The duplex steelmaking process has been proven to be an effective solution for the utilisation of high phosphorus iron ore, yet systematic analyses of the dephosphorisation rate and mechanism of duplex process for high phosphorus hot metal are seldom reported. Comprehensive exploration and discussion on the kinetics of duplex steelmaking process for high phosphorus hot metal are thus required. First, based on the kinetic model proposed by Robertson et al., a modified coupled reaction kinetic model was formulated and employed to analyse the dephosphorisation process of duplex melting for high phosphorus hot metal. Furthermore, a series of experiments were carried out to validate the accuracy of the established model, and the calculated results showed good agreement with the experimental data. Finally, a parametric study was conducted to perform a further discussion of the mechanism of duplex steelmaking process for high phosphorus hot metal.     

Kinetics of Nitrate Reduction by Iron at Near Neutral pH

Although considerable research has been conducted on nitrate reduction by zerovalent iron (ZVI), the process kinetics at near neutral pH has not been studied thoroughly. In this study, a kinetic model with a double-Langmuir-adsorption formulation was developed to represent site saturation effects of aqueous Fe2+ and NO3? on nitrate reduction in a ZVI system at near neutral pH. Both an analytical solution and a numerical solution of the proposed model were developed. The kinetic parameters were evaluated based on batch experiments with two types of ZVI. Sensitivity analysis indicates that it is rather difficult and unreliable to estimate the parameters of the proposed multivariable nonlinear kinetic model from a single test curve. A better strategy is to obtain reliable parameters by designing specific experiments to target one parameter each time. The results indicate that, although the values of the kinetic parameters might change with different types of iron powder, the kinetic model can fit the experimental data very well, and therefore is consistent with the proposed mechanism.     

垃圾填埋场厌氧产气动力学模型的研究

在实验室垃圾厌氧降解实验研究的基础上,进行了降解过程的厌氧菌产气动力学分析和厌氧反应器动力学分析,通过数理分析得出了生活垃圾厌氧产气动力学模型。     

垃圾填埋场厌氧产气动力学模型的研究

在实验室垃圾厌氧降解实验研究的基础上，进行了降解过程的厌氧菌产气动力学分析和厌氧反应器动力学分析，通过数理分析得出了生活垃圾厌氧产气动力学模型。     

Finite element investigation of backbone binder removal from MIM copper compact

Abstract

Finite element (FE) model based on kinetic analysis was developed to describe the thermal debinding process of previously solvent debinded metal injection moulded (MIM) copper compacts. Thermophysical properties (specific heat, density, thermal diffusivity and thermal conductivity as a function of temperature) of MIM copper compact were measured using differential scanning calorimeter, laser flash analyser, thermogravimetry analyser and pushrod dilatometer. The proposed model is solved numerically to study binder removal and binder distribution during thermal debinding. The investigations included the analysis of residual (backbone) binder content for cylindrical MIM copper compacts at different temperatures and positions. The FE calculations are strongly based on measured thermophysical data and kinetic analysis of copper system. The FE simulated and experimental results were compared to validate the underlying FE model based on FE temperature field calculations. Drawing the real furnace temperature conditions in finite calculation can result in obtaining more accurate data.     

Magnetite oxidation in a traveling grate pellet plant: A computer model

A mathematical model of the packed bed of a traveling grate pelletizing machine has been written. This model allows simulation of the temperature profiles in the packed bed of the machine while magnetite oxidation occurs. Knowledge of kinetic data for magnetite oxidation of ore balls of the concentrate concerned is required for simulation. Temperatures measured during industrial pot tests compare well with those predicted by the model. Results for ore balls of two concentrates were compared. KARL D. LIBSCH, formerly Graduate Student, Lehigh University, Bethlehem, Pa. 18015     

Identification and characterization of kinetically competent carbinolamine and alpha-iminoglutarate complexes in the glutamate dehydrogenase-catalyzed oxidation of L-glutamate using a multiwavelength transient state approach

A highly constrained and heavily overdetermined multiwavelength transient state kinetic approach has been used to study the oxidative deamination of L-glutamate catalyzed by beef liver glutamate dehydrogenase. Spectra generated using the known enzyme-reduced coenzyme-substrate spectrum served as models for deconvolution of kinetic scan data. Deconvolution of the multiwavelength time course array shows formation of three distinguishable intermediates in the reaction sequence, an ultrablue-shifted complex, an ultrared-shifted complex, and a blue-shifted complex. The ultrablue-shifted entity is identified as the enzyme-NADPH-alpha-iminoglutarate complex (ERI) and the ultrared as the enzyme-NADPH-alpha-carbinolamine complex (ERC). The blue-shifted complex is characterized as the E-NADPH-ketoglutarate species (ERK). The location of these species along the reaction coordinate has been determined and their kinetic competency in the reaction sequence has been established by fitting the concentration time courses of the components for both the alpha-deuterio- and the alpha-protio-L-glutamate reactions to the now highly constrained differential equations derived from a kinetic scheme involving the sequential formation of alpha-iminoglutarate, alpha-carbinolamine, and alpha-ketoglutarate-reduced coenzyme complexes, following the formation of two prehydride transfer complexes.     

On a Testing Methodology for the Mechanical Property Assessment of a New Low-Cost Titanium Alloy Derived from Synthetic Rutile

Mechanical property data of a low-cost titanium alloy derived directly from synthetic rutile is reported. A small-scale testing approach comprising consolidation via field-assisted sintering technology, followed by axisymmetric compression testing, has been designed to yield mechanical property data from small quantities of titanium alloy powder. To validate this approach and provide a benchmark, Ti-6Al-4V powder has been processed using the same methodology and compared with material property data generated from thermo-physical simulation software. Compressive yield strength and strain to failure of the synthetic rutile-derived titanium alloy were revealed to be similar to that of Ti-6Al-4V.     

3D Unsteady RANS Modeling of Complex Hydraulic Engineering Flows. II: Model Validation and Flow Physics

A chimera overset grid flow solver is developed for solving the unsteady Reynolds-averaged Navier-Stokes (RANS) equations in arbitrarily complex, multiconnected domains. The details of the numerical method were presented in Part I of this paper. In this work, the method is validated and applied to investigate the physics of flow past a real-life bridge foundation mounted on a fixed flat bed. It is shown that the numerical model can reproduce large-scale unsteady vortices that contain a significant portion of the total turbulence kinetic energy. These coherent motions cannot be captured in previous steady three-dimensional (3D) models. To validate the importance of the unsteady motions, experiments are conducted in the Georgia Institute of Technology scour flume facility. The measured mean velocity and turbulence kinetic energy profiles are compared with the numerical simulation results and are shown to be in good agreement with the numerical simulations. A series of numerical tests is carried out to examine the sensitivity of the solutions to grid refinement and investigate the effect of inflow and far-field boundary conditions. As further validation of the numerical results, the sensitivity of the turbulence kinetic energy profiles on either side of the complex pier bent to a slight asymmetry of the approach flow observed in the experiments is reproduced by the numerical model. In addition, the computed flat-bed flow characteristics are analyzed in comparison with the scour patterns observed in the laboratory to identify key flow features responsible for the initiation of scour. Regions of maximum shear velocity are shown to correspond to maximum scour depths in the shear zone to either side of the upstream pier, but numerical values of vertical velocity are found to be very important in explaining scour and deposition patterns immediately upstream and downstream of the pier bent.     

A Differential Scanning Calorimetry Method for Construction of Continuous Cooling Transformation Diagram of Blast Furnace Slag

The continuous cooling crystallization of a blast furnace slag was studied by the application of the differential scanning calorimetry (DSC) method. A kinetic model describing the correlation between the evolution of the degree of crystallization with time was obtained. Bulk cooling experiments of the molten slag coupled with numerical simulation of heat transfer were conducted to validate the results of the DSC methods. The degrees of crystallization of the samples from the bulk cooling experiments were estimated by means of the X-ray diffraction (XRD) and the DSC method. It was found that the results from the DSC cooling and bulk cooling experiments are in good agreement. The continuous cooling transformation (CCT) diagram of the blast furnace slag was constructed according to crystallization kinetic model and experimental data. The obtained CCT diagram characterizes with two crystallization noses at different temperature ranges.     

小方坯连铸机结晶器凝固传热的分析

根据安钢德马克小方坯的现场数据，建立了小方坯连铸机结晶器的二维凝固传热模型，采用有限差分法对数学模型求解，得到铸坯在结晶器内的表面温度分布和坯壳的生长规律，同时讨论了拉速、过热度、结晶器冷却水强度对铸坯的表面温度和坯壳生长的影响．     

Anisotropic shrinkage during sintering of glass-powder compacts under uniaxial stresses: Qualitative assessment of experimental evidence

The shrinkage anisotropy that occurs during sintering of glass-powder compacts under uniaxial compressive stresses is considered. Available experimental data from the literature are used to calculate a shrinkage anisotropy factor (k) and to study its dependence on the applied stress and progress of densification. The factor k is defined by the ratio between axial and radial strains. The experimental data are interpreted in terms of qualitative trends proposed for the variation of k with the progress of sintering for a constant applied load. It is shown that when sintering densification predominates over viscous deformation induced by an external load at the onset of the process, k increases with the sintering time. The existence of a stage at which the shrinkage anisotropy factor becomes negative is confirmed by the analysis of available experimental data. The trends for the variation of k are also given for the case of the externally induced deformation predominating over sintering densification. However, no sufficient experimental data were found to validate the proposed trends in this case. The prediction of the theoretical model of Scherer for viscous sintering under uniaxial stresses is shown to agree qualitatively with the experimental trends. In connection with the use of dilatometry in sintering kinetic studies, the effect of small stresses on shrinkage anisotropy is highlighted.     

Melatonin, its receptors, and relationships with biological rhythm disorders

Melatonin is a neurohormone produced during the night by the pineal gland. Its secretion is regulated by circadian and seasonal variations in daylength, transmitted via visual projections to the suprachiasmatic nucleus which functions as a circadian clock in mammals. Melatonin has been proposed to act as an internal synchronizer of circadian rhythms generated at different levels of the organism. The chronobiotic effects of melatonin in humans have been mainly studied in circadian rhythm sleep disorders related to jet lag, shift work, blindness or aging. Alterations of the melatonin profiles have also been reported in other biological rhythm disorders.     

Three-Dimensional Mean Velocity Analysis of a 30 Degree Bend Flow

The 3D velocity profiles of the 30° bend flow of Flack and Johnston have been analyzed in terms of the existing 3D turbulent boundary layer theories. Various cross-flow and near-wall similarity models were tested. Coles's cross-flow model described the velocity profiles satisfactorily. The wall function matched the data well, and the experimentally determined wake functions collapsed into a narrow band, which was however different from the originally suggested wake function. A new form of wake function has been proposed. Among the near-wall models, Hornung and Joubert's and Prahlad's models matched the data very well and excellent near-wall similarity from the wall to the boundary layer edge was achieved. This is rather unexpected in a 3D turbulent boundary layer flow with large skewing. The excellent performance of these two near-wall models could not be attributed to any particular reason.     

Distribution-Free Monte Carlo Simulation: Premise and Refinement

From cost estimation to reliability analysis, Monte Carlo simulation has found its niche in a wide variety of applications in civil engineering. With recognition of correlations among variables, recent efforts have been devoted to model the correlations more accurately and with no restriction on the form of marginal distributions, i.e., being distribution free. Yet, the conventional method introduced by Iman and Conover, although widely accepted, is bound to have errors: The generated correlation matrix may bear no resemblance to the desired correlation matrix. The purposes of this study are to shed light on the underlying premises of the conventional method and to refine the method by reducing the errors to an acceptable level automatically. A particle swarm optimization algorithm is proposed to repair invalid (nonpositive definite) correlation matrices and to bring the generated correlation matrix into conformity with the desired target. The effectiveness of the proposed algorithm has been verified in estimating cost of electrical services based on historical data.     

Importance of Kinetic Models in the Analysis of Steelmaking Reactions

In this paper, examples of the use of a kinetic model in the analysis of a steelmaking process will be discussed. In decarburization by BOF, the relation between C and O contents is different from that obtained by equilibrium calculations. By the use of kinetic models, it was clarified that the O content in the metal is controlled not only by the C content but also by the FeO activity in the slag. In the vacuum degassing process, the partial pressure calculated on the basis of the relation between C and O contents is much higher than the operation pressure. The kinetic model which considers the circulation between the molten steel in the vacuum vessel and that in the ladle is well known; furthermore, various decarburization mechanisms were proposed. Hot metal dephosphorization occurs under non‐equilibrium conditions because the oxygen potential of the slag and that of the hot metal are different. Process analysis is performed by considering the reaction kinetics based on the coupled reaction model. Recently, a new reaction model has been proposed; this model considers the solid slag, liquid slag, and liquid metal phases and the reaction between the solid and liquid slag, in addition to the reaction between the liquid slag and liquid metal.     

A mathematical model for heap leaching of one or more solid reactants from porous ore pellets

A mathematical model is derived in dimensionless form for heap leaching of one or more solid reactants from nonreactive, porous, spherical ore particles. The model is for the interpretation of column and heap leaching data and for use in the design and scaleup of heap leaching pro-cesses. Data from experimental column leaching tests are presented which validate the model. The scope of the present study is limited to the case where the rate-controlling reagent is a component of the lixiviant solution only and not of the gas phase. The effects of particle-scale kinetic factors, heap scale and operating variables, competition between multiple solid reactants, and particle size distribution are examined using the concept of the heap effectiveness factor. It is shown that heaps operate either «homogeneously,» with distribution of reagent throughout the heap at all times, or in a «zone-wise» manner, depending mostly on a single parameter. The observed value of this parameter deviates from the predicted value in inverse proportion to the degree of contact effectiveness between the lixiviant solution and the ore particles. A rough correlation between the contact effectiveness and Reynolds number is generated from the simulation of column test results.     

Some Studies to Establish the Reaction Mechanism for the Reduction of Iron Ore‐Graphite Composite Pellets in a Packed Bed Reactor

In this article an attempt has been made to propose a reaction mechanism for the reduction of iron ore‐graphite composite pellets in a packed bed reactor through experiments and mathematical models developed by the authors previously, along with some new supportive experimental data. A tailor made thermo‐gravimetric setup with a provision of packed bed has been developed to carry out isothermal experiments at elevated temperature and in controlled atmosphere. A kinetic model that calculates the evolution of various phases of iron oxides and a thermal model that calculates the temperature at the surface and centre of the cylindrical packed bed have been used along with experimental data under different operating conditions to formulate the reaction mechanism. It is proposed that reduction of iron ore‐graphite composite pellets in packed bed is initially heat transfer controlled and become mass transfer controlled at the later stage of reduction. The role of heat and mass transfer has been ascertained by observing the effect of C/Fe₂O₃ molar ratios, size of pellets, and CO gas in reactive atmosphere on the extent of reduction and the predicted temperature gradient, carbon consumption rate within the packed bed during the course of reduction.     

Mathematical modeling of mixing phenomena in a gas stirred liquid bath

A macroscopic, steady state energy balance model has been formulated to describe mixing phenom-ena in a liquid bath stirred by injecting gas through a straight nozzle fitted axially at the bottom of the vessel. This, along with experimental data on a water model previously reported, was employed to make predictions. Input energy terms considered in the model consist of buoyancy energy and empirically determined fraction of gas kinetic energy. Dissipation of energy was attributed to liquid circulation and bubble slip. The two-phase plume was assumed to be a truncated cone whose dimen-sions depended upon operating conditions. Numerical solution of model equations gave liquid velocity and gas hold-up inside the plume as well as liquid circulation rate and liquid velocity in the region outside the plume. Influence of process variables, e.g., gas flow rate, bath height, and nozzle diameter, have been predicted. Validity of the model has been established by comparing some pre-dicted entrainment ratios with those experimentally measured by other investigators. Empirical cor-relations to predict circulation time and circulation number have been proposed. Circulation number was found to vary between 2 and 12 in contrast to the existing assumption in the literature of a con-stant value of 3. Usefulness of these correlations in predicting mixing time for industrial vessels has been demonstrated. Formerly a Graduate Student in the De-partment of Metallurgical Engineering at the Indian Institute of Technol-ogy, Kanpur