Lignite oxidative desulphurization: notice 3—process technological aspects and application of products

International Journal of Coal Science & Technology - The study reviews the process of oxidative desulphurization of high-sulphur Ukrainian lignite, which was performed by coal treatment using...     

Determining deformation and strength of a filling mass during stoping by the inverse problem solving

The authors have developed a method for quantitative estimation of filling mass deformation and strength characteristics in the course of stoping at sheet ore deposits by the in situ measurements of relative displacements of points at the mined-out stope boundary. The article also analyzes the structure of objective functions of the formulated inverse coefficient problems for the elastic-plastic rock deformation model, and examines their solvability.     

Oxidation of coal in industrial conditions. 1. Kinetics of natural oxidation

In the light of research on the artificial oxidation of coal in the laboratory, earlier results on the natural oxidation of coal in open storage at different coke Ukrainian plants are analyzed. On the basis of the kinetics of coal oxidation in natural conditions, the need to correct existing standards for open storage is evaluated. Since the dependence of the degree of oxidation d _o on the storage time is sigmoid, the results are analyzed on the basis of the Avrami-Erofeev equation for the kinetics of heterogeneous reactions. The constants of that equation and the rate constants of oxidation are calculated for enriched coal of different ranks (G, Zh, K, and OS) in summer and winter. The influence of the degree of metamorphism on the rate constant of natural oxidation in summer and winter is mathematically described. On the basis of the Avrami-Erofeev equation, limiting open-storage times for the coal are established. The earlier limiting storage times must be corrected.     

Effect of the conditions of sintering of sodium-reduced tantalum powders on their characteristics

The effect of the granulation and heat treatment of sodium-reduced tantalum powders with a specific surface area of 2.5–3.6 m²/g on the bulk density, the powder flow time, and the specific surface area of the powders and the specific capacitance of the anodes made of them is studied. It is shown that heat treatment of a granulated powder in vacuum at 1100°C or in a mixture with magnesium at 800°C makes it possible to achieve the required powder flow time.     

Relation between the maximum moisture content of coal and its porous structure

Seven coal samples and two anthracite samples are subjected to technical, petrographic, and elementary analysis. The maximum moisture content and total pore volume (for water) in the samples are determined. There is a linear relation between the maximum moisture content and total pore volume. The corresponding correlation coefficient is 0.99, and the coefficient of determination is 98.1%. The relation of the coal porosity with the yield of volatiles and the carbon content in the coal’s organic mass (characterizing its metamorphic stage) is assessed. The corresponding correlation coefficient is 0.86–0.98, while the coefficient of determination is 73.8–95.6%.     

Ignition temperature of coal 3. Multicomponent coal mixtures

The ignition temperature of three-component mixtures is determined. The mixtures contain coal of different metamorphic development, in various proportions. It is found that the actual ignition temperature differs from the values calculated on the basis of the sum rule; the actual ignition temperature is lower. A formula is derived for predicting the ignition temperature of three-component and multicomponent mixtures.     

Effect of the oxygen content in a salt solution on the characteristics of sodium-reduced tantalum powders

The characteristics of the tantalum powders produced by sodium thermal reduction from salt melts based on K₂TaF₇ and NaCl with various amounts of added oxycompounds K₃TaOF₆ and K₂Ta₂O₃F₆ are studied. At a molar ratio of oxygen to tantalum of 1.25 in the initial melt, capacitor tantalum powders with a specific surface area more than 3 m²/g are produced. The specific capacitance of the anodes made from these powders reaches 58 mC/g.     

Sodium thermal reduction of tantalum powders from melts with tantalum pentaoxide additions

The effect of the oxygen concentration in a melt on the characteristics of sodium-reduced tantalum powders, which were produced from potassium heptafluotantalate-based melts with tantalum pentaoxide additions, is studied. An increase in the oxygen content in the initial melt from 0.35 to 2.0 wt % leads to an increase in the specific surface of the formed powder from 1.2 to 3.5 m²/g. The specific charge of anodes made from these powders is 37800–70700 CV/g.     

Influence of the beam current density distribution on the spatial resolution of a nuclear microprobe

The paper discusses the effect of nonuniform distribution of the ion beam phase density on the nuclear microprobe resolution. The deconvolution of the beam brightness distribution parameters was performed on the base of the beam current distribution measurements in the object collimator plane. This information gives a possibility to define the ion distribution in the phase set for a beam to be transformed by the probe-forming system into the target plane. A criterion for selecting the optimum collimator dimensions was the highest beam current for the fixed beam spot size (FWHM). This approach, with allowance for the initial distribution, makes it possible to obtain a higher beam current intensity at the center of the spot.     

Pressure distribution in a hydrocarbon-bearing formation based on the daylight surface movement measurements

The article describes the procedure of estimating spatial distribution of pressure in a producing formation under mining by the land surface geodesy survey data. The numerical experiments show that the single-valued resolvability of the inverse problem requires the land surface movement to be measured both in vertical and horizontal directions.