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The kinetics of the reduction of magnetite concentrate particles by H2+CO mixtures have been investigated in drop-tube reactors (DTRs) to obtain rate expressions for the design of novel flash ironm...

The kinetics of CO reduction of magnetite concentrate particles was investigated in drop-tube reactors (DTR) to obtain a rate equation for the design and analysis of a flash ironmaking reactor. The...

The reduction of magnetite concentrate particles by H2 has been investigated in drop-tube reactor (DTR) to obtain a rate equation that can be applied to the design and analysis of an ironmaking fla...

A computational fluid dynamics (CFD) model was developed to simulate a Large-Scale Bench Reactor (LSBR) applied to the flash ironmaking technology, in which the kinetics of magnetite concentrate reduction, separately determined in a drop-tube reactor, was incorporated. This article reports on a CFD study to test the effects of operating conditions, including O2/natural gas ratio and gas flow rates, on the product gas composition, temperature, heat loss through the walls of the LSBR, and reduction degree of the magnetite concentrate. Further, a comprehensive, general, and realistic boundary condition for heat transfer through the wall is incorporated in the CFD model, and thus, the CFD model presented in this article is completely predictive for the design of an industrial reactor.

An experimental investigation of the reduction of magnetite concentrate particles was conducted in a laboratory-scale flash reactor representing a novel flash ironmaking process. In this reactor, methane was partially oxidized by oxygen to form a reducing H2 + CO gas mixtures. The test variables in this work included the particle residence time, the extent of excess reducing gases, particle feeding mode, and flame configuration. The experimental results obtained from this reactor proved that the concentrate particles can be reduced directly in a flash reactor utilizing natural gas. More than 80 pct reduction was achieved in this reactor despite its low operating temperature (1170 °C). In addition, a three-dimensional computational fluid dynamics model was developed to describe the reduction of concentrate particles in this reactor. The model was used to simulate the fluid flow, heat transfer, and chemical reactions involved. The gas phase was simulated in the Eulerian frame of reference, while the particles were tracked in the Lagrangian framework. The partial combustion of methane by oxygen was also simulated in this study. The temperature profile obtained from the simulations satisfactorily agreed with the experimental measurements, while the calculated reduction degrees consistently over predicted the experimental values. This was attributed to the soot formation as a consequence of methane cracking due to large metal surface of the reactor. The soot formation led to a high-water vapor generation in the partial combustion, which lowered the excess of hydrogen.

The rate analysis involving a solid of nonbasic geometry in general requires a complex numerical solution. A closed-form expression of the reaction rate for such a solid would be very convenient and greatly simplify the analysis. A method for this purpose was developed in this work for solids with shapes of finite cylinders and finite rectangular parallelepipeds reacting under the rate control by chemical reaction or mass transfer, which may be extended to other irregular shapes. In this method, an appropriate shape factor is first obtained under the conditions of a topochemical reaction, which is then applied to the unified rate expressions previously obtained for solids of three basic shapes. Good agreements between the rates predicted with the appropriate shape factors and the exact or numerical solutions were obtained for both reaction-controlled and pore-diffusion-controlled reactions.

Based on density functional theory and volume-based thermodynamics methods, the crystal densities (ρ), heats of formation (HOFs), detonation performance, specific impulse (Isp), impact sensitivities (H50) and Gibbs free energies of formation of eight series novel energetic salts composed of 4-nitro-7-(4-nitro-1,2,3-triazol-1-olate)-furazano[3,4-d]pyridazine-based anions and ammonium-based cations were studied. Results show that all title salts possess high ρ and positive HOFs. Therein, ammonium and hydroxylammonium salts exhibit the highest ρ and detonation performance in each series and several even surpass those of HMX and RDX. For guanidinium-based salts in every series, when the number of NH2 group in cations increases, the HOFs, Isp and H50 of corresponding salts improve, but their ρ values decrease. Consequently, detonation performance of guanidinium-based salts are close to each other (H series are similar to RDX). Otherwise, introducing N → O oxidation bond to anions is an effective method to improve ρ, detonation performance and Isp of the corresponding salts compared A with B-H series, but it decreases H50. However, all guanidinium-based salts show lower impact sensitivities than RDX and HMX. Meanwhile, the position of N → O oxidation bond also has an effect on these properties.

The kinetic analysis of the reduction of hematite concentrate particles by individual reducing gas H2 or CO was performed using a computational fluid dynamics (CFD)-based approach in this paper. The particle residence time was calculated through the integration of the equation of particle motion. Non-uniform particle temperature profiles inside the reactor were obtained, and were taken into consideration for the kinetic analysis. The calculated reduction degrees based on this approach are in good agreement with the experimental values.

It is argued in this paper that the initial rate should not be used for the measurement or analysis the kinetics of a fluid–solid reaction, especially for a reaction in which the effect of pore diffusion starts appearing even moderately as the reaction proceeds. Even in the absence of external mass transfer effects, it is shown in this work by rigorous mathematical analysis that the range of conditions where the initial rate represents the intrinsic kinetics is very narrow. For an initially non-porous solid in the absence of external mass transfer effects, the very initial rate should mathematically be the intrinsic rate even when pore diffusion becomes important as the reaction proceeds. However, even in this case, the range of conditions for this statement is very limited. For the reaction of an initially porous solid, the rate at time zero is already affected by pore diffusion unless its effect is negligible over the entire range of conversion. Furthermore, the initial reaction rates of porous solids reacting under large values of k/De ratio (chemical reactivity is much greater than the capacity for pore diffusion) have an apparent rate constant of \( \sqrt {k \cdot D_{\text{e}} } \) and thus pore diffusion alone does not control the initial rate no matter how large the effect of pore diffusion is overall.

A three-dimensional computational fluid dynamics (CFD) model was developed to study the hydrogen reduction of magnetite concentrate particles in a laboratory flash reactor representing a novel flash ironmaking process. The model was used to simulate the fluid flow, heat transfer, and chemical reactions involved. The governing equations for the gas phase were solved in the Eulerian frame of reference while the particles were tracked in the Lagrangian framework. The change in the particle mass was related to the chemical reaction and the particle temperature was calculated by taking into consideration the heat of reaction, convection, and radiation. The stochastic trajectory model was used to describe particle dispersion due to turbulence. Partial combustion of H2 by O2 injected through a non-premixed burner was also simulated in this study. The partial combustion mechanism used in this model consisted of seven chemical reactions involving six species. The temperature profiles and reduction degrees obtained from the simulations satisfactorily agreed with the experimental measurements.

A computational fluid dynamics (CFD) approach, coupled with experimental results, was developed to accurately evaluate the kinetic parameters of iron oxide particle reduction. Hydrogen reduction of magnetite concentrate particles was used as a sample case. A detailed evaluation of the particle residence time and temperature profile inside the reactor is presented. This approach eliminates the errors associated with assumptions like constant particle temperature and velocity while the particles travel down a drop tube reactor. The gas phase was treated as a continuum in the Eulerian frame of reference, and the particles are tracked using a Lagrangian approach in which the trajectory and velocity are determined by integrating the equation of particle motion. In addition, a heat balance on the particle that relates the particle temperature to convection and radiation was also applied. An iterative algorithm that numerically solves the governing coupled ordinary differential equations was developed to determine the pre-exponential factor and activation energy that best fit the experimental data.

In this paper, the method of electroless deposition of nickel-phosphorous composite coating on the sample surface is employed. The effect of the complexing agent ratio on the surface morphology and phase composition of nickel-phosphorus coating when the main salt and reducing agent concentration unchanged has been studied. The influence of heat treatment on properties and microstructure of coatings are also investigated. Experimental results show that in the case of salt and reducing agent concentration unchanged, complexing agent concentration has strong effect on the morphology of the coatings and the crystal structure of the composite coating. During heat treatment, the morphology of the composite coating changed significantly, and the hardness was improved a certain degree for all the samples, which is related to the precipitation of Ni3P.

Based on viscoelastic fluid mechanics, this paper presents a simulation model of the flow behaviour of thin polymer film during nanoimprint lithography (NIL). The polymer is imprinted at a constant temperature of 180oC and at a constant imprint speed of 100nm/s by using a tool with a single convex feature of 100 nm in width and 500 nm in height. At the imprint beginning, only a very limited area adjacent to the tool top is affected by the imprint, but subjects to a sudden change of pressure. With the imprint process forward, the wave-like polymer front and the trumpet-shaped profile are predicted to travel out from the imprint patterns. When the tool base intimately contacts the polymer film, another sudden change of the pressure occurs in the area under the interface between the polymer surface and the tool base. These results are of significance to understand the flow behaviour of NIL.