Guimin Lu

Molecular dynamics simulations of the local structures and transport coefficients of molten alkali chlorides.

Systematic results from molecular dynamics simulations of molten alkali chlorides (ACl) serials are presented in detail in this paper. The effects of temperature and cationic size on the structures and transport properties of molten salts have been investigated and analyzed. The local structures of molten ACl have been studied via the analysis of radial distribution functions and angular distribution functions. The coordination number of ACl decreases when ACl melts from solid and increases as cationic radius increases. Molten LiCl takes a distorted tetrahedral complex as the microconfiguration, while other melts have the tendency to keep the original local structure of the corresponding crystal. Temperature has no significant effect on the local structures of molten ACls. The results also show that the Tosi-Fumi potential predicts positive temperature dependences for self-diffusion coefficients and ionic conductivity, and negative temperature dependences for both viscosity and thermal conductivity of molten ACls. Ionic diffusivity decreases as cationic radius increases from LiCl to CsCl. The simulation results are in agreement with the experimental data available in the literature.

Catalytic Graphitization of Coal-Based Carbon Materials with Light Rare Earth Elements

The catalytic graphitization mechanism of coal-based carbon materials with light rare earth elements was investigated using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, selected-area electron diffraction, and high-resolution transmission electron microscopy. The interface between light rare earth elements and carbon materials was carefully observed, and two routes of rare earth elements catalyzing the carbon materials were found: dissolution-precipitation and carbide formation-decomposition. These two simultaneous processes certainly accelerate the catalytic graphitization of carbon materials, and light rare earth elements exert significant influence on the microstructure and thermal conductivity of graphite. Moreover, by virtue of praseodymium (Pr), it was found that a highly crystallographic orientation of graphite was induced and formed, which was reasonably attributed to the similar arrangements of the planes perpendicular to (001) in both graphite and Pr crystals. The interface between Pr and carbon was found to be an important factor for the orientation of graphite structure.

Density functional theory study on the thermodynamics and mechanism of carbon dioxide capture by CaO and CaO regeneration

Reducing CO2 emission is one of the most important events to solve the global climate problem. The carbonation reaction of CaO and the reverse reaction are potential methods for CO2 capture and concentration from dilute flue gases at high temperature. In this paper, the thermodynamics and mechanisms of CO2 capture by CaO and CaO regeneration from CaCO3 were studied and identified in the framework of density functional theory (DFT). In the calculation, the exchange-correlation term was approximated by Perdew–Wang (PW91), a function within the generalized gradient approximation (GGA) family. The reaction energies of carbonation reaction and calcination reaction were calculated to be −147.64 kJ mol−1 and 180.60 kJ mol−1, respectively. To study the reaction between CO2 and CaO, the transition states of carbonation and calcination were also analyzed. The results showed that the carbonation of CaO was rather fast, and the activation energy of carbonation reaction was 0 kJ mol−1, which indicated that the reaction process was not the rate-determining step during the process of CO2 capture. The regeneration of CaO by CaCO3 calcination occurred at higher temperature, with the activation energy of 166.85 kJ mol−1, and the rate of calcination was controlled by the chemical reaction.

Designing and optimizing a stirring system for a cold model of a lithium electrolysis cell based on CFD simulations and optical experiments

In the electrolysis lithium industry, liquid lithium metal and chloride gas need to be separated quickly because of the recombination of lithium and chloride. A new stirring system can help to separate liquid metal and chloride in lithium electrolysis cells. The stirring system was tried in a cold model to get the right parameters. Computational Fluid Dynamics (CFD) and Particle Image Velocimetry (PIV) were both employed to design and optimize the device parameters which included impeller type, diameter, position and rotational speed. PIV tests and CFD model validation were conducted in a cylindrical stirred tank. Different turbulence models were applied and the standard k–e model was considered as the most suitable one. The results show that: the propeller agitator properties of a low blade number and low installation position were advantageous to the lithium collection. The impeller diameter and rotational speed have positive effects on the expected flow field. The simulation results were applied in cold model experiments, which showed that the simulations are correct and can be used in real separator design.

Modeling of strontium chloride hexahydrate growth during unseeded batch cooling crystallization by two-dimensional population balance equation

In this study, the growth of strontium chloride hexahydrate during unseeded batch cooling crystallization was investigated and modeled by the two-dimensional population balance equation. The results suggested that in a well-mixed crystallizer, no obvious agglomeration and breakage were observed. The initial supersaturation and cooling rate were the key factors of crystal growth and the crystals grew following a size dependent mechanism. Thus, the growth of SrCl2·6H2O was modeled as a function of supersaturation, temperature, and crystal size. The calculated crystal size and size distribution showed good agreement with the experimental values, proving that the model could well predict the growth behavior of SrCl2·6H2O in the system. This study not only fills the research vacancy of SrCl2·6H2O crystallization, but also contributes to the optimal design of the crystallization process, aiming at preparing SrCl2·6H2O crystals with a larger size and a narrower size distribution.

Hydrodynamic characteristics of the two-phase flow field at gas-evolving electrodes: numerical and experimental studies

Gas-evolving vertical electrode system is a typical electrochemical industrial reactor. Gas bubbles are released from the surfaces of the anode and affect the electrolyte flow pattern and even the cell performance. In the current work, the hydrodynamics induced by the air bubbles in a cold model was experimentally and numerically investigated. Particle image velocimetry and volumetric three-component velocimetry techniques were applied to experimentally visualize the hydrodynamics characteristics and flow fields in a two-dimensional (2D) plane and a three-dimensional (3D) space, respectively. Measurements were performed at different gas rates. Furthermore, the corresponding mathematical model was developed under identical conditions for the qualitative and quantitative analyses. The experimental measurements were compared with the numerical results based on the mathematical model. The study of the time-averaged flow field, three velocity components, instantaneous velocity and turbulent intensity indicate that the numerical model qualitatively reproduces liquid motion. The 3D model predictions capture the flow behaviour more accurately than the 2D model in this study.

Coupled electro-thermal field in a high current electrolysis cell or liquid metal batteries

Coupled electro-thermal field exists widely in chemical batteries and electrolysis industry. In this study, a three-dimensional numerical model, which is based on the finite-element software ANSYS, has been built to simulate the electro-thermal field in a magnesium electrolysis cell. The adjustment of the relative position of the anode and cathode can change the energy consumption of the magnesium electrolysis process significantly. Besides, the current intensity has a nonlinear effect on heat balance, and the effects of heat transfer coefficients, electrolysis and air temperature on the heat balance have been released to maintain the thermal stability in a magnesium electrolysis cell. The relationship between structure as well as process parameters and electro-thermal field has been obtained and the simulation results can provide experience for the scale-up design in liquid metal batteries.

Effects of operational and structural parameters on cell voltage of industrial magnesium electrolysis cells

Electric field is the energy foundation of the electrolysis process and the source of the multiphysical fields in a magnesium electrolysis cell. In this study, a three-dimensional numerical model was developed and used to calculate electric field at the steady state through the finite element analysis. Based on the simulation of the electric field, the operational and structural parameters, such as the current intensity, anode thickness, cathode thickness, and anode-cathode distance (ACD), were investigated to obtain the minimum cell voltage. The optimization is to obtain the minimum resistance voltage which has a significant effect on the energy consumption in the magnesium electrolysis process. The results indicate that the effect of the current intensity on the voltage could be ignored and the effect of the ACD is obvious. Moreover, there is a linear decrease between the voltage and the thicknesses of the anode and cathode; and the anodecathode working height also has a significant effect on the voltage.

Study on Multi-Phase Flow Field in Electrolysis Magnesium Industry

Magnesium, the 8th most abundant element in the earth’s crust, was discovered and isolated by Sir Humphrey in 1808. Magnesium is classified as an alkaline earth metal. It is found in Group 3 of the periodic table. It thus has a similar electronic structure to Be, Ca, Sr, Ba and Rd. The density of magnesium at 20°C is 1.738 g/cm3. At the melting point of 650°C this is reduced to 1.65 g/cm3. On melting there is an expansion in volume of 4.2%. Magnesium is the lightest metal in large-scale commercial use. After World War II, the magnesium industry attempted to develop magnesium for a number of applications. Most of its peacetime uses take advantage of the light weight or other chemical properties. The uses of magnesium as a structural material were, however, very few. The bulk was used as an alloying element in aluminium alloys. Other uses, such as deoxidation of steel, chemical and pyrotechnics, outweighed structural uses, especially in energy-saving and environmental protection applications was wide because of its contribution to reduce energy consumption and greenhouse gas emissions. The most successful peacetime application for magnesium was in the original German Volkswagen car that was designed by Ferdinand Porsche. The VW Beetle used large magnesium alloy die castings for the crankcase and the transmission housing (both cast in halves) plus a number of smaller castings. Each Beetle contained more than 20 kg of magnesium alloy. Many of the other applications developed during the World War II, could not be quickly converted to civilian uses. Some of the uses such as aircraft wheels and aircraft engine castings and troop carrying buses were modified and then used for the basis of civilian industries. With more attention to energy and environment, magnesium will hold greater promise as a new weight-saving replacement for denser steel and aluminum alloys, and demands for magnesium will increase sharply in the future. In recent decades, demands for magnesium and its productivity increased sharply shown in Figure 1, the world productivity of magnesium reached 860,000 tons at 2007.[1-3] There are six sources of raw materials for the production of magnesium: magnesite, dolomite, bischofite, carnallite, serpentine and sea water. These sources differ in the magnesium content, in production methods, and in their origins. Some are mined from mines, some in open

Magnesium electrolyzer structural optimization based on energy balance

The diaphragmless magnesium electrolyzer was the main equipment for molten salt electrolysis to produce magnesium. The major energy-consuming in production process was electric energy. With the continuous development of science and technology, reducing energy loss had attracted peoples attention. In this paper, in order to obtain the electrolyzer with the structure of high capacity and low energy consumption, the structural parameters of electrolyzer were changed on the basis of energy balance equation, and the factors affecting electrolyze were analyzed and summarized.