Moisture-holding capacity of coals

As a result of a comprehensive study of 63 samples of coal concentrates (from Ukraine, Russia and countries outside the former Soviet Union), it was established that the prediction of the moisture-holding capacity of coals can be appropriately performed according to their values of W ^a, R ₀, O _d ^daf , and O _s ^daf . It was found that the oxidation of coal increased its moisture-holding capacity; however, in this case, the absolute change in this parameter was smaller than the error of its determination (0.5%). Therefore, upon the oxidation of almost 30% of the organic matter of coal, the moisture-holding capacity increased by only 0.4%. There is a close correlation between the maximum moisture capacity of coals and the water pore volume, and this correlation was described by a linear equation in the studies.     

Ignition temperature of coal. 1. Influence of the coal’s composition,structure, and properties

The reactions of coal with the materials used in determining the ignition temperature of unoxidized coal according to Ukrainian State Standard DSTU 7611:2014 are analyzed. First, the ignition temperature of various types of coal from Ukraine, Russia, Canada, Australia, the Czech Republic, Poland, and Indonesia is determined. The influence of the composition, structure, and properties of the coal on its ignition temperature is assessed. The ignition temperature of the unoxidized coal is found to be closely related to the content of organic carbon C^daf and aromatic carbon C_ar, the structural parameter δ characterizing the degree of saturation of the coal’s organic mass, and also the vitrinite reflection coefficient R_o and the yield of volatiles V^daf.     

IR Spectroscopy in Rank and Group Assignment of Coal

The possibility of express determination of the characteristics V _IR ^daf , R_{o, IR}, y_IR, ΣLC_IR, and A _IR ^d used in the ranking of coal on the basis of IR spectroscopy is assessed for a specific example: Kuznetsk coals of different maceral composition and metamorphic development. The IR characteristics are compared with values obtained by standard methods (V^daf, R_{o, r, y}, ΣLC, and A^d).     

Predicting the classification characteristics of coal. Part 3. Gross calorific value of dry,ash-free coal

For 63 samples of Ukrainian, Russian, and imported coal, equations for predicting the gross calorific value Q_s^daf on the basis of the following coal characteristics are developed: W^a, O_d^daf, Q_s^af, and C_ar. The error is within the standard tolerances (σ ≤ 0.3 MJ/kg). With sufficient accuracy, Q_s^daf may be predicted from equations based on petrographic characteristics such as the vitrinite reflectance, the content of liptinitegroup minerals, and the sum of lean macerals (I + 2Sv/3). In these equations, the coefficients correspond to the heat of combustion of the vitrinite components at different metamorphic stages, the liptinite, and the lean macerals.     

Composition and Properties of Brown Coal from the Bodonskoe Deposit in Buryatia

The composition and properties of coal from the Bodonskoe deposit were studied. It was shown that this is low-sulfur (S ^d = 0.3–1.0%) and medium-ash grade 1B brown coal with a high yield of volatile substances (V ^daf = 56.1–60.9%). The humic acid content varies from 32.3 to 50.8%. The heat of combustion of coal is Q _s ^daf = 26.0–27.4 MJ/kg. The concentrations of toxic elements in the coal samples are at a background level.     

Basic functional relations in coal petrology

Functional relations between the parameters of the organic system and external factors are established. The following parameters of the organic system are considered: the petrographic composition of the coal’s organic mass, expressed as the ratio of newly formed components F/Vt; the ash content A ^d ; and the concentration of microelements in the coal. The external factors considered are the partial pressure \({p_{{O_2}}}\) of pfree oxygen (in aerobic conditions), the oxygen activity [O₂] (in anaerobic conditions), and the activity of HCl^–, HS^–, and Cl^– in the infiltrating aqueous solution. The microelement content in the coal’s organic mass is determined from the concentrations in the infiltrating solution that reaches the organic system. The influence of the petrographic composition and the ash content of the coal on its microelement concentration is assessed. The characteristics of the mic roelements and their removal from associations in paragenesis are discussed.     

Relations between the reflection coefficients of the basic groups of macerals: A review

Quantitative relations are found between the structural and chemical characteristics of macerals of the basic coal groups (vitrinite Vt, inertinite I, liptinite L), on the one hand, and their reflection coefficients R _r and the corresponding dispersions σ _R , on the other. For coal of a particular metamorphic stage, the reflection coefficient declines in the series I > Vt > L, on account of the reduction in aromatic chemical structure and in the degree of condensation of the aromatic blocks. In the metamorphic series, the reflection coefficients of the macerals rise; the values for Vt and L at intermediate stages converge. The dispersion of the reflection coefficients (and hence the reflectograms) is due to the spread in characteristics of the chemical structure of the coal’s organic content, as confirmed by calculations for the vitrinite of D, G, Zh, and K coal.     

Predicting the classification characteristics of coal. Part 2. Maximum moisture content

Analysis of 63 samples of coal concentrates (from Ukraine, Russia, the United States, Canada, Australia, and Poland) currently employed at Ukrainian coke plants indicates that the prediction of the maximum moisture content of coal may expediently be based on R _o and Q _s ^daf , determined, respectively, in plant laboratories and in power-station laboratories. The maximum moisture content of metamorphically distinct coals does not depend on their ash content (in the range 3.7–35.3%) nor on the chemical composition of the ash, expressed by the basicity index B _b (in the range 1.24–27.18) and the base/acid ratio I _b (in the range 0.198–1.832). Although the oxidation of coal also increases the maximum moisture content, this change is less than the error in its determination (0.5%). The oxidation of practically 30% of the coal’s organic mass increases the maximum moisture content by no more than 0.4%     

Rapid Quality Assessment of Coal

No satisfactory methods are available for rapid and reliable prediction of one or more coal characteristics. The ignition temperature t_ig of coal, determined in assessing the oxidation of coal in accordance with Ukrainian State Standard DSTU 7611:2014, may be regarded as a useful predictor of coal quality. Research shows that t_ig depends on the composition and ordering of the coal’s organic mass. Mathematical and graphical means of predicting the V ^daf and R_o values of coal are developed.     

Composition and properties of coals from the Yurty coal occurrence

Coals from the Yurty coal occurrence were studied. It was found that the samples were brown non-coking coals with low sulfur contents (to 1%) and high yields of volatile substances (V ^daf to 53.4%). The high heat value of coals Q _s ^daf was 20.6–27.7 MJ/kg. The humic acid content varied from 5.45 to 77.62%. The mineral matter mainly consisted of kaolinite, α-quartz, and microcline. The concentration of toxic elements did not reach hazardous values.     

Production and Use of Lignite-Based Coke Briquets with High Hot Strength

A production technology has been developed for strong briquets (with high CSR and M₂₅) based on coke derived from Kansko-Achinsk lignite. A mixture consisting of lignite coke and binder (Zh and KZh coal) is crushed (to particle size less than 0.2 mm) and mixed with strengthening additive. This blend (57.7% lignite coke + 19.2% binder + 23.1% additive) is shaped into briquets, which are roasted at 1000°C and cooled in the absence of air. For the briquets, CSR = 58.8% and M₂₅ = 97.4%. The strength in drop tests is 99.1%, and the wear resistance is 99.2%. Technical analysis of the briquets shows that W = 1–2%, A^d = 8–10%, V^daf = 3–7%, S^d = 0.2–0.4%, P^d = 0.014%, and C_fix = 85–88%. The briquets are characterized by distinctive physicochemical properties, such as high activity with respect to CO₂ (\(K_{CO_2}\) = 4.6 cm³/g s; CRI = 66.1%). Its electrical resistivity ρ = 8 Ω cm for the 3–6 mm size class; and its developed porosity is 50–56%. Applications of the briquets are outlined.     

Properties of the solid thermolysis products of brown coal impregnated with an alkali

The mechanism of formation of a porous active carbon framework is considered, and the properties of the solid thermolysis products of brown coal (Aleksandriisk deposit, Ukraine) with potassium hydroxide are studied. The yields of the solid thermolysis products (Y _STP, %) and potassium humates, the rate of the interaction of the solid thermolysis products with KOH at 700–900°C, the specific surface areas (S _BET, m²/g), the adsorption capacities for methylene blue (A _MB, mg/g) and iodine (A _I, mg/g), and the specific activities of surface areas A _MB ^′ = A _MB/S _BET and A _I ^′ = A _I/S _BET (mg/m²) are determined under variation of the KOH/coal ratio (R _KOH < 18 mol/kg) and temperature (110–900°C).     

Coal enrichment with separation into fractions by density

The proposed model of the coal composition consists of formulas for the mineral component Ml and organic mass (the vitrinite Vt, inertinite I, and liptinite L maceral groups) as a function of the density ρ. The model includes differential and integral density distribution functions of the total coal mass and formulas for the coal properties as a function of the density. That permits modeling of the profound transformation of coal with enrichment and separation into fractions by density.     

Oxidation of coke with petroleum-based coking additives

The properties of coking batch may be stabilized by means of DK coking additive based on the products of petroleum pyrolysis, characterized by low ash content (A^d = 0.4%), high sulfur content (S_t^d= 4.1%), and high yield of volatiles (V^daf = 17.2%) relative to coal concentrates. Individual coking of DK coking additive yields a product (particle size >40 mm) with postreactive strength CSR = 77–79%, reactivity CRI = 18–22%, and density 1200–1400 kg/m³. Differential scanning calorimetry of experimental coke samples reveals six stages in their heat treatment in air: preliminary heating, intense oxidation, gasification of carbon, surface combustion of the gaseous products, their flare combustion, and oxidation of the residue. The use of DK coking additive in the coking batch shifts the oxidation process to higher temperatures and ensures the largest interval of heat liberation at elevated heating rate, with up to 50% DK additive. With increase in the content of DK additive from 30 to 50%, the activation energy is increased by 4.56 kJ/mol for each additional 10%. In that case, the supply of atmospheric oxygen to the combustion zone must be improved     

Properties of adsorbents prepared by the alkali activation of Aleksandriisk brown coal

Highly microporous adsorbents (micropore fraction of ～70%) were prepared by the alkali activation-thermolysis (800°C, 1 h) of brown coal (C ^daf = 70.4%) in the presence of potassium hydroxide at the KOH/coal weight ratio R _KOH ≤ 2.0 g/g. The dependences of the specific surface areas and adsorption capacities of the adsorbents for methylene blue (A_MB, mg/g), iodine (A_I, mg/g), and hydrogen (\(A_{H_2 } \), wt %) on R _KOH were determined. The adsorbents obtained at R _KOH ≥ 1.0 g/g exhibited developed specific surface areas and good adsorption characteristics (A_I = 1000–1200 mg/g, A_MB = 200–250 mg/g, and \(A_{H_2 } \) ≤ 3.16 wt % at 0.33 MPa). The high capacity for hydrogen allowed us to consider brown coal adsorbents as promising materials for use as hydrogen accumulators.     

Solid-phase synthesis and characterization of rare-earth chromates

Simple chromates(V) MCrO₄ (M = Sc, Y, Gd, Er, or Yb) and chromate(V) vanadates Gd(CrO₄) _x (VO₄)_{1 ? x} have been synthesized by a solid-phase method. All compounds crystallize in the xenotime-type structure, space group I4₁/amd, Z = 4. The unit cell parameters have been calculated as follows: for GdCrO₄, a = 7.209(5) Å, c = 6.318(4) Å; for ErCrO₄, a = 7.088(2) Å, c = 6.231(1) Å; for YbCrO₄, a = 7.034(1) Å, c = 6.205(2) Å; for YCrO₄, a = 7.108(3) Å, c = 6.254(3) Å; and for ScCrO₄, a = 7.012(2) Å, c = 6.188(2) Å. Symmetry D _2d , established for the CrO₄ tetrahedron during the Rietveld structure refinement, is verified by IR spectroscopy. The MCrO₄ simple chromates are paramagnets; their magnetic moments range from 1.7 to 8.1 μ _B .     

Metamorphic development, degree of reduction, and other characteristics of Donets Basin coal

Analysis of the elementary composition and parameters V ^daf , y, and Q _s ^daf of coal from more than 100 beds in the Donets Basin indicates that the considerable difference in the properties of coal characterized by reduction (in terms of S _t ^d ) and uniform metamorphic development (according to C ^daf ) is due to variation in the ratio of the number of hydrogen and oxygen atoms (H/O_at) in the molecular component of the coal’s organic mass.     

Relation between the petrographic content of mineral components in coal and its ash content

Empirical and analytical relations are established between the content of mineral inclusions Ml determined by petrographic analysis of the coal according to State Standard GOST 94.14–93 and the ash content A ^d of dry coal according to State Standard GOST 11022-95. In the empirical approach, statistical methods yield relations between Ml and A ^d in the form of regression equations for coals of a particular region and a system of beds with a complex set of minerals. In the more general analytical approach, Ml is divided into microcomponents (sulfides, carbonates, clay materials, quartz, etc.). Taking account of the densities of the components and their transformation on combustion, a quantitative relation between Ml and A ^d may be established for specific coals or their fractions in enrichment.     

Local turbulent energy dissipation rate in an agitated vessel: New approach to dimensionless definition

Using theory of turbulence, particularly using turbulence spectrum analysis, the relations ε^* = ε/(u ⁴/ν) = const., v_K/u = const. and Λ/η_K = const. were derived. Assuming that u ∝ (Nd) from this it follows that the widely used dimensionless local turbulent energy dissipation rate defined as ε/((N ³ d ²) is directly proportional to impeller Reynolds number, i.e. ε/((N ³ d ²) ∝ Re, and length scale ratio Λ/d is indirectly proportional to impeller Reynolds number, i.e. Λ/d ∝ Re^–1, in an agitated vessel at high Reynolds number. The relations obtained by turbulence spectrum analysis were used for estimation of local turbulent energy dissipation rates experimentally measured by Ståhl Wernersson and Trägårdh (1998, 1999) covering the range of Re = 87600–910200 and own experimental data covering the range of Re = 50000–189000. The experiments have been performed in tanks of 300 mm and 400 mm in the inner diameter for three different viscosities and for various impeller rotational speeds.