Home – Home – Jornals – Numerical Analysis and Applications 2022 number 4

The present paper is addressed to the estimation of the local (point-wise) approximation error on the ensemble of the numerical solutions obtained using independent algorithms. The variational inverse problem is posed for th approximation error estimation. The considered problem is ill-posed due to invariance of the governing equations to the shift transformations. By this reason, the zero order Tikhonov regularization is applied. The numerical tests for the two-dimensional equations describing the inviscid compressible flow are performed in order to verify the efficiency of considered algorithm. The estimates of approximation errors, obtained by the considered inverse problem, demonstrate the satisfactory accornce with the Richardson extrapolation results at significantly less computational costs.

The estimation of the functional of the diffusion process in a domain with a reflecting bounry, which is obtained on the basis of numerical modeling of its trajectories, is considered. The value of this functional coincides with the solution at a given point of a bounry value problem of the third kind for a parabolic equation. A formula is obtained for the limiting value of the variance of this estimate under decreasing step in the Euler method. To reduce the variance of the estimate, a transformation of the bounry value problem is used, similar to the one that was previously proposed in the case of an absorbing bounry.

This article discusses the mixed finite element method combined with backward-Euler method to study the hyperbolic p-bi-Laplace equation, where the existence and uniqueness of solution for discretized problem is shown in Lebesgue Sobolev spaces. The mixed formulation and the inf-sup condition are then given to prove the well posed of the scheme and the optimal a priori error estimates for fully discrete schemes is extracted. Finally, a numerical example is given to confirm the theoretical results obtained.

This paper proposes a new method for the numerical solution of a pure Neumann problem for the diffusion equation in a mixed formulation. The method is based on the inclusion of a condition of unique solvability of the problem in one of the equations of the system with a subsequent decrease in its order by using a Lagrange multiplier. The unique solvability of the problem obtained and its equivalence to the original mixed formulation in a subspace are proved. The problem is approximated on the basis of a mixed finite element method. The unique solvability of the resulting saddle system of linear algebraic equations is investigated. Theoretical results are illustrated by computational experiments.

A unitoid matrix is a square complex matrix that can be brought to diagonal form by a Hermitian congruence transformation. The canonical angles of a nonsingular unitoid matrix A are (up to the factor 1/2) the arguments of the eigenvalues of the cosquare of A, which is the matrix A^-*A. We derive an estimate for the derivative of an eigenvalue of the cosquare in the direction of the perturbation in A^-*A caused by a perturbation in A.

In this paper, we introduce a new convergence mode to deal with the generalized spectrum approximation of two bounded operators. This new technique is obtained by extending the well-known ν-convergence used in the case of classical spectrum approximation. This new vision allows us to see the ν-convergence assumption as a special case of our new method compared to the hypotheses needed in old methods, those required in this paper are weaker. In addition, we prove that the property U holds, which solves the spectral pollution problem arising in spectrum approximation of unbounded operator.

The aim of the work is to analyze the existing and used methods of direct molecular modeling of physical processes and phenomena. In particular, methods of molecular dynamics, Brownian dynamics, direct statistical Monte Carlo modeling, and stochastic molecular modeling are discussed. In all cases, the main features of these methods, the accuracy of modeling and development prospects are analyzed. Examples of solving original problems, in particular, modeling of gas transfer coefficients in the volume and nanochannels are considered.

The effect of the Reynolds number on the mechanism of formation of an instantaneous local flow separation that occurs in the near-wall region of a turbulent boundary layer is experimentally studied. The features of application of the high-speed planar PIV method with a high spatiotemporal resolution are discussed. Comparison of the measurement results obtained within a viscous sublayer of a turbulent boundary layer with the results of other studies showed the generality of the mechanism for the formation of an instantaneous local flow separation in the range of dynamic Reynolds number 207 ≤ Re _τ ≤ 672.

The article presents the results of numerical simulation of the boundary layer of air on a heated surface in the presence of weak acceleration. The numerical model consists of a system of Prandtl equations describing dynamic and thermal processes in the boundary layer, and a κ-ω-γ turbulence model that allows reasonably simulating the laminar-turbulent transition and turbulence suppression. Finite-difference methods were used to solve differential equations. For some calculated cases, the turbulence model was switched off in order to obtain parameters of a known laminar flow. Modeling has shown that in the considered flow conditions, the occurrence and development of a local laminarized region near the wall is possible. In this case, the boundary layer includes the near-wall laminar and external turbulent sections. This nature of the flow leads to a level of friction and heat exchange that correspond to the intermediate flow relative to laminar and turbulent flows under the same conditions.

Known approaches to the determination of flow parameters in the test section of impulse wind tunnels are analyzed, and ways towards their improvement are outlined. An algorithm for calculating flow parameters in short-duration supersonic high-enthalpy wind tunnels using the experimental values of pressure in the prechamber, the total pressure behind the normal shock, and the flow velocity and stagnation temperature as a function of time, is developed. It is shown that the results of measurements and calculations using the developed algorithm for determining flow parameters fairly well comply with the calculations of flow parameters based on the gas-dynamic relations taking into account the losses of heat in the working path of the wind tunnel.

The paper discloses the study of flow crisis in the Ranque-Hilsch vortex tube with a squared cross-section channel. Previous studies have found the conditions for developing the hydraulic crisis for air flow in this type of tube. The crisis phenomenon is related to the event when the longitudinal velocity at the nearwall vortex-circulation zone interface approaches the value of velocity for spreading centrifugal waves along this boundary. The paper presents and discusses the new detail results in measuring the kinematic parameters of the crisis flow, including the parameter of velocity pulsation. The evidences of a hydraulic jump neat the exit of the swirl flow to the tube working channel.

The formation of circulation vortex cells in a liquid medium of a gas-vortex bioreactor has been experimentally studied. The study was carried out in an industrial glass bioreactor with a volume of 10 liters and a reactor vessel diameter D = 190 mm. The vortex motion of air was generated by a paddle wheel (activator) when 50 and 80% of the reactor vessel was filled with the model medium. A 65% water solution of glycerol with density ρ = 1150 кг/м³ and kinematic viscosity ν = 15 мм²/с was used as a model medium. To observe the pattern of vortex motion, the method of particle image velocimetry (PIV) was used. It is shown that when the activator rotates, the meridional and circulation motions of the liquid occur simultaneously. Regularities of the vortex motion of the model medium are determined depending on the reactor filling and the intensity of activator rotation. It is found that the cells of centrifugal circulation appear under the interface; with an increase in the activator rotational speed they develop into the depth of the reactor. It is established that centrifugal circulation of liquid develops similarly as it takes place in a closed vortex flow of one liquid and in a system of limited vortex motion of two immiscible liquids.

An intake has to provide air for the engine uniformly with minimum total pressure loss. Nowadays, regarding the usage of S-shaped intakes, optimization of these ducts has been considered. Uniform distribution of flow at the compressor inlet directly influences the engine performance, and non-uniformity of flow increases surge occurrence possibility. Flow separation along the duct causes a reduction of pressure recovery and engine thrust force. This research has optimized an S-shaped intake to reduce the total pressure loss and flow distortion. The genetic algorithm and artificial neural networks have been combined to decrease the computational cost. Two optimizations, using different conditions, have been studied. In the first case, by modifying centerline coordinates and area ratio of sections, new geometries have been produced, which have caused an improvement of 32.5 % in pressure recovery coefficient and a decrease of 35.8 % in flow distortion. In the second optimization, the shape of each section has also been changed. Super ellipse, egg-shaped and circular profiles are considered as cross sections of the duct. The second optimization has improved the pressure recovery coefficient by 35.5 % and decreased flow distortion by 39.2 %.

Results of numerical simulation of a supersonic (М_∞ = 7) flow past a cylinder with a frontal gas-permeable porous insert (porosity 95%, pore diameter 2 mm) installed at angles of attack α = 0÷10° are reported. The numerical modeling was performed based on the solution of three-dimensional Reynolds-averaged Navier-Stokes equations using three skeletal models: a model of intersecting hollow spheres, a model of non-intersecting hard spheres with a random arrangement of pores, and a model consisting of a set of toroidal elements. The calculated data on the drag coefficients and on the lift force of a cylinder with a frontal gas-permeable high-porosity insert are compared with the results of experiments carried out in the T-327 wind tunnel of ITAM SB RAS. A comparative analysis of the results of using three-dimensional skeletal models of highly porous cellular materials for modeling supersonic flows around bodies with gas-permeable porous inserts installed at various angles of attack is performed.

The density and thermal expansion coefficients of polycrystalline, liquid and amorphous phases of Fe₆₀Co₂₀Si₈B₁₂ alloy in the temperature range of 293÷1650 K have been measured by the monochromatic gamma-ray attenuation technique. The features of crystallization of the melt and amorphous film have been investigated. Reference tables of properties have been developed, their errors have been estimated, and approximation equations have been obtained.

The presented research investigated the thermal diffusivity (α) and the thermal conductivity (λ) of one of the most promising heat-resistant nickel alloys, Inconel 617. The measurements were carried out in the temperature range from 300 to 1475 K using the laser flash method on the LFA-427 setup. The estimated errors of the received data depending on temperature were 2-4% and 3-5% for α and λ, respectively. A comparison with the known literature data was made. The fitting equations for the temperature dependences of the studied properties have been received and a table of reference values has been compiled, which can be used in various engineering and scientific tasks.

A three-dimensional turbulent round jet impinging on a heated flat plate is investigated numerically. The effects of the nozzle geometry and nozzle-to-plate distance on the dynamical and thermal behavior are explored. A round nozzle and nozzles fitted with either 4 or 6 chevrons are considered. Three nozzle-to-plate distances are studied: H/D = = 2, 4, and 6. The Reynolds number equals 5000. The results show that the chevrons improve the heat transfer near the area of stagnation. This improvement can reach up to 110 % in specific regions. It is also found that the wall heat flux is appreciably non-uniform for the small distance H/D = 2. Degraded heat transfer is recorded between the plate and the fluid in narrow radial passages of fluid downstream of the stagnation point for the small value of H/D. They turn out to be quasi-potential flow streams, along the target wall and facing the chevron apices, characterized by high convective velocities and nearly no turbulence. Increasing the distance to H/D = 6 yields a somewhat axisymmetric thermal behavior. Effects on Nusselt number values averaged over circular surfaces centered on the stagnation point and of variable radius on the target wall are highlighted.

The experimental study was performed for a submerged turbulent jet that enters a slot channel with the height of h = 4 mm. The oscillating turbulent jet is generated by a fluidic oscillator with two feedback channels and the exit nozzle with the throat width of d = h . The working fluid is distilled water. The two-component velocity field was acquired using the PIV method with a high resolution up 50 5 kHz. The information was gained about the sweeping turbulent jet (both structure and dynamics) entering a slot channel for the Reynolds number in the range from 1500 to 8000. The jet flow to the slot channel generates large-scale 2D vortex structures. The travel frequency of those structures depends on the jet sweeping frequency produced by a fluidic oscillator. Comparison of the research result with available experimental data demonstrated that for a flow in a slot channel (with geometry h/d = 1) has a smaller angle of jet sweeping. For a higher Re number we observe a variation in distributions of average and pulsation characteristics of the sweeping jet as well as a decrease in the dimensionless jet sweeping frequency.

Experimental data on reconstruction of the spatial structure of a swirl jet in a burner model are presented. An isothermal case of free jet mixing with ambient air at various levels of flow swirl is considered. The high-swirl flows under study are accompanied by the collapse of the vortex core and intense coherent flow pulsations associated with large-scale vortex structures. Experimental data on distributions of axial and tangential velocities were obtained by Particle Image Velocimetry (PIV). The contribution of coherent flow fluctuations to turbulent transport is estimated based on the Proper Orthogonal Decomposition (POD). The frequency of periodic pressure pulsations was measured using acoustic sensors. The frequency of the precessing vortex core (PVC) and the corresponding velocity distributions were measured at a fixed Reynolds number (16500). A nonmonotonic dependence of the Strouhal number on the flow swirl was obtained. The spatial vortex structure was visualized under isothermal conditions. Using POD analysis, it was shown that with an increase in swirl, the precession radius and the pitch of the helical structure of the PVC increase.

Results of an experimental study of the kinematic structure of flow and the transfer of heat in gradient flows are reported. A field measurement method (SIV) was used to obtain profiles of velocities and turbulence characteristics in characteristic sections of diffuser and confuser channels. Based on the results of thermal measurements, the distributions of the heat-transfer coefficient on the wall of a flat diffuser/confuser were obtained in a wide range of regime parameters. The mechanisms of the formation of the transfer of heat in gradient flows are analyzed. It is shown that, in a diffuser channel, the transfer of heat on the wall as a whole depends on the flow parameters at the diffuser inlet. For a confuser channel, this relation can be determined using the local values of longitudinal flow velocity.

The wetting dynamics of modified capillary-porous surfaces made of aluminum and titanium was experimentally studied at free-convective heat exchange with the environment. The influence of the concentration of ethyl alcohol and its initial temperature on the wetting front velocity has been established. The volume concentration of alcohol in the mixture varied from 0 to 95.5%. The characteristic modes of changes in the height of the liquid rise over capillary-porous surfaces over time have been expressed in the form of power dependences.

The two-phase flow was experimentally studied in three horizontal channels of rectangular cross-section: 0.23×1 mm, 0.51×1 mm, and 1×1 mm. Distilled water was used as a liquid, and nitrogen was used as a gas. The paper considers in detail the features of two-phase flow formation. The effect of the rectangular channel height on the boundaries of two-phase flow regimes was investigated. It was found that the region of the bubble flow is hardly affected by the channel height; however, with a decrease in the latter, the region of the slug flow decreases significantly, while the region of the slug-annular flow expands. The characteristics of the slug flow have been studied in detail. The dependences of the length of gas slugs and liquid bridges on the reduced liquid velocity, the reduced gas velocity, and also the channel height have been studied. A comparison with known correlations is made and it is shown that they describe the experimental data in a narrow range of parameters, and as the height of the rectangular channel decreases, the data scatter increases.

The large-eddy simulation method was applied to study of isothermal swirled gas flow in a model combustion chamber at Reynolds number Re = 15000. The study identified a coherent vortex structure: this is a precessing vortex core which contributes to pressure pulsations reaching a maximum inside a model front device. It is possible to suppress this coherent structure by gas injection in a site of highest pressure pulsations. The study covers three regimes with additional gas injection with the amplitude about 1 - 5 % of the superficial flow velocity. Analysis of instant, average and spectral characteristics revealed that the developed method of flow control is a tool for suppression of low-frequency oscillation by factor of two.

Mathematical simulation was applied to flame spreading and the flame front speed through the air suspension of boron particles as a function of pressure, excess oxidant ration and the particle size. Simulation accounts for a change in heat and mass transfer with a reduction of the particle size from micro-size to nano-scale. The model of flame front propagation through boron particle suspension in air (with account for molecular-kinetic mechanism of heat and mass transfer) allows analysis of the normal speed of flame propagation as a function of initial size of boron particles, oxidant excess ratio and pressure. The conditions were estimated and existence of extremes and flat zones was justified due to a change in heat and mass transfer regime change in a continuous medium while transition to the free-molecular flow regime.

The experimental results obtained by the dilatometric method for thermal expansion of the Hastelloy C276 alloy in the temperature range of 100 - 370 K are presented. Temperature dependences of thermal properties have been obtained. The obtained results have been compared with the data for thermal expansion of superconducting tapes of the “Amperium” and “SuperOx” brands Keywords:

The reaction of hydrogen transfer from coal tar pitch and petroleum pitches to α-methylstyrene with the formation of cumene was investigated in glass ampoules within the temperature range of 200-360 °C and reaction time of 15-60 min and when passing α-methylstyrene through a layer of coal tar pitch. It is shown that the formation of non-chromatographable products of α-methylstyrene condensation with polycyclic aromatic compounds of pitches occurs simultaneously. The dependences of α-methylstyrene conversion, the selectivity for cumene and condensation products on the temperature and reaction time, the ratio of pitch/α-methylstyrene are determined. The amount of hydrogen transferred from pitches to α-methylstyrene was determined, and the results obtained were compared with the literature data on the transfer of hydrogen from pitches obtained using anthracene as a hydrogen acceptor.

A systematic study of the relationship between the composition and structure of skeletal-dendritic ferrospheres isolated from fly ash formed in the combustion of Ekibastuz coal, carried out by means of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), allowed us to establish the general routes of their formation and the peculiarities of the influence of mineral precursors on their structure. The groups of globules were distinguished exhibiting a linear correlation between the content of silicon, iron and aluminium oxides in the gross composition of the polished sections. It is shown that the investigated ferrospheres are formed from the melt droplets of the general FeO-SiO₂-Al₂O₃-CaO system during their cooling and crystallization of individual phases. The formation of melt droplets occurs due to the sequential transformation of dispersed products from thermal conversion of mineral precursor associates, such as siderite, quartz, calcite and aluminosilicate components in the carbon matrix. The aluminosilicate precursor determining the structure of globules is hydromica of illite group. The crystallization of the ferrospinel of skeletal-dendritic globules occurs due to the “seed” of Al,Mg-ferrospinel, which is formed as a result of the thermochemical transformation of the illite of the initial coals. The observed general trend to changes in the structure of ferrospheres from coarse-grained crystalline skeletal type to fine-crystalline skeletal-dendritic globules is explained by a decrease in the content of the main spinel-forming oxides FeO, Al₂O₃ and MgO in the melt microdroplets.

Results of the classical method for determining the tendency of coals to spontaneous ignition from the rate constant of oxygen sorption are compared with those obtained using the improved method of thermogravimetric analysis (TGA). To study the sorption capacity of the studied coal samples by thermogravimetric analysis, it is proposed to heat the samples at a constant heating rate of 5 °C/min to 300 °C instead of high temperatures (1000 °C), implying coal combustion. The chemical activity of coal samples with respect to oxygen is to be calculated from the maximum mass gain within the temperature range corresponding to oxidation. As a result of the experiment, on the basis of thermogravimetric dependences, differences were revealed in the behaviour of coal samples, prone and not prone to spontaneous ignition. In comparison with the classical V. S. Veselovsky’s method of determining the tendency of coals to spontaneous ignition, the TGA method allows one to get a more complete picture of the chemical activity of coals, which affects the reliability of assigning the analyzed sample to the category of spontaneous ignition hazard.

Because of the high level of cardiovascular diseases in the Kemerovo Region, it is extremely important to reveal a relation between exposition to dust from the coal industry and human health. One of the first steps for this disclosure is investigation into the physical and chemical properties of dust in the hospitals of Kemerovo (Kemerovo Region - Kuzbass), which is reported in this paper. It is found that the object analysed is a mixed type, not uniform, and contains organic and inorganic parts. The major mineral part is silica, which agrees with its content in fly ashes characteristic of the region. Constant concentration ratios of aluminium, silicon and manganese allow an assumption that the dust is built up by similar types of aluminosilicates containing manganese within the structure. Low amounts of sulphur and high amounts of calcium simultaneously indicate the presence of calcite and/or feldspar in the dust. High contents of sodium and calcium can be caused by the application of detergents. The dust is classified as PM_0.1-PM₁ according to particle sizes. The relationship of the properties of dust with the characteristics of the industrial orientation of the region is outlined.

Nanostructured composites obtained by forming a filler (Co₃O₄ nanoparticles) during thermal decomposition of two kinds of precursors (Co(N₃)₂ and Co(OH)₂) in the air on the surface of carbon matrices with significantly different morphology (single-walled carbon nanotubes and highly porous material from raw coal) are characterized, and the influence of matrix type on composite properties is considered. It is established that the characteristics holding the greatest significance for electrode materials, that is, the distribution of filler particles over composites, their sizes, matrix stability against oxidation, and, most importantly, the electrical capacitance characteristics of composites, are determined first of all by matrix morphology. This relationship manifests itself in the regularities of matrix oxidation during the formation of Co₃O₄ nanoparticles within its volume, acting as a catalyst for this process. Highly porous matrix is most prone to oxidation, and for this reason an increase in filler content and oxygen concentration is observed in the subsurface layers, which leads to a substantial decrease in electrical capacitance. In composites based on almost non-oxidized multiwall C-tubes, a noticeable increase in capacitance occurs due to the contribution of Red-Ox electrode processes involving Co₃O₄ particles. Composites based on single-walled C-tubes coalesced into dense “ropes” occupy an intermediate position.

The TUBALL material consisting of single-walled carbon nanotubes (SWCNTs) is characterized. The features of the formation of nanostructured composites through the reduction of HAuCl₄ solutions by the matrix (carbon) on the outer surface of coalesced nanotubes are considered, their morphology and the features of occurrence of thermally stimulated processes are studied, as well as their electrochemical properties in supercapacitor (SC) model cells. According to transmission electron microscopic data, the incorporated gold nanoparticles are probably shaped as flattened ellipsoids with particle size of 6-30 nm (30-40 nm according to X-ray diffraction data) and are located on the surface of “ropes”, which are close-packed ensembles of parallel SWCNTs. According to the results of sorbometry, the internal channels of SWCNT (1-2 nm) and extended pores between them are accessible to sorbed nitrogen, but inaccessible to the precursor solution. The sizes of coherent scattering regions, estimated from the broadening of X-ray diffraction reflections, turned out to be larger than particle sizes determined by means of TEM, which is due to their anisometric nature. The study of thermally stimulated processes in composites shows that gold deposition on the SWCNT surface leads to an increase in the stability of C-matrix against oxidation. Investigation of Au/SWCNT nanocomposites as electrode materials for supercapacitors shows that decorating the surface of SWCNT “ropes” with gold causes a significant decrease in the active component of the impedance and an increase in the electric capacitance of the SC cells in the region of high potential scanning rates, as a consequence of an increase in charge density at TUBALL/Au/electrolyte interfaces during polarization, and a decrease in electric resistance. The greatest effect (an increase in capacity by a factor of 3.0-3.5) was observed for the nanocomposite electrode 2 wt. % Au/SWCNT.

In this work we studied the effect of pulsed nanosecond laser radiation (532 nm, 14 ns, 6 Hz, 0.2-0.6 J/cm²) on brown coal samples in an argon atmosphere. H₂, CH₄, C₂H₂, CO and CO₂ were found in the composition of gaseous products formed in the pyrolysis of coal samples. It is shown that with an increase in the laser radiation energy density, the volume fraction of acetylene in the composition of gaseous products of coal pyrolysis increases, while the volume fractions of methane and carbon dioxide, on the contrary, decrease. The volume fractions of hydrogen and carbon monoxide in the studied range of laser radiation energy density are close to constant. The volume of combustible gases formed per unit mass of the reacted coal sample increases with increasing laser radiation energy density in the range of 0.2-0.5 J/cm². With a further increase in the energy density of laser radiation, the volume of combustible gases formed per unit mass of the reacted coal sample remains practically unchanged.

Results of investigation into the composition of humic acids (HA) and fulvic acids (FA) isolated from brown coals by means of proximate and ultimate analysis, IR, and EPR spectroscopy are presented. It is shown that the yield of HA exceeds the yield of FA. The maximum yield (60-68 %) was detected for HA from naturally oxidized brown coal. It has been established that lignite FA and HA have significant differences in the structural and group composition: FA are characterized by the higher content of the fragments of aliphatic structures, alcohols, carboxylic acids, and esters. Humic acids are characterized by the higher content of aromatic fragments.

Carbon sorbents were obtained at different ratios of coal/alkali from coals of the Kaa-Khem, the Mezhegey and the Elegest deposits. It is established that the necessary mass ratio of coal/alkali for these coal samples at the activation stage is 1 : 3 or 1 : 4. The excess alkali concentration worsens textural characteristics. It is shown by means of IR spectroscopy and thermogravimetry that alkaline treatment causes chemical changes in the molecular structure: the content of oxygen-containing fragments increases, the amount of carbon in aromatic structures decreases, which causes a decrease in caking capacity. The revealed features include a significant decrease in the final temperature and narrowing of the interval of the main decomposition of the coal organic mass, changes in the mass loss curves within the temperature range of 500-750 °C, corresponding to the zone of decomposition of the aromatic structures in coal. Physicochemical regularities of material formation and optimal conditions providing the production of sorbents with high texture characteristics from sintering coals were determined. On the basis of the studies of adsorption characteristics of the samples (for iodine and methylene blue), it is concluded that it is reasonable to use the obtained carbon sorbents for the purification of industrial wastewater from organic pollutants (phenol, pyridine, etc.).

Based on the results of adsorption studies, a procedure for modifying the porous carbon sorbent with tributyrin has been developed. The synthesis of tributyrin and the procedure of its quantitative determination in ethanol solutions by means of spectrophotometry are described. Carbon sorbent samples modified with tributyrin were obtained. Their properties have been studied using a complex of physicochemical methods. The possibility of using the modified sorbent as a drug of prolonged action is studied: tributyrin desorption from the carbon sorbent under model conditions in contact with 0.9 % NaCl (physiological solution) and in ethanol is investigated. It is established that in contact with the test solutions, the modifier deposited on the carbon carrier is desorbed within 6 h.

Methods of scanning electron microscopy, NMR spectroscopy, XRD, thermal analysis and gas chromatography-mass spectrometry have been used to study the composition, structure and morphology of particles of α₂-fraction powders isolated by the method of selectively soluble groups from medium-temperature coal-tar pitch. It is shown that the α₂-fraction is mainly a mixture of condensed aromatic compounds containing N, O and S heteroatoms, while sulphur is mainly contained in the form of heat-resistant thiophene compounds. The study of coke particles formed during the thermolysis of the α₂-fraction showed that in the temperature range from 300 to 600 ^oC, a dense structure with carbon content 90-93 % is formed from the substances of the α₂-fraction. Further heating up to 1200 ^oC leads to an increase in the carbon content up to 97 %, while the coke particles form a layered structure with pronounced anisotropy, approaching the structural characteristics of L_a and L_c to “premium class” needle cokes.

The dispersed fractions of industrial high-calcium fly ash (HCFA), selectively collected in the form of fractions 1-4 (Fr1-Fr4) on fields 1-4 of the electrostatic precipitators of the ash collecting unit at the Krasnoyarsk TPP-2, are systematically characterized. The fluidity parameters of ash mortars prepared from 100 % of each of the fractions at a ratio of water/binder = 0.5 were determined. It has been established that the value of fluidity decreases with an increase in the specific surface area of the fractions from Fr1 to Fr4. The parameters of cement-ash mortars with the replacement of cement by 50 and 20 % of each of the four fractions were determined. It has been established that at a 20 % HCFA content, the fluidity of cement-ash mortars of all fractions meets the requirements of GOST 1581-2019 for oil well cements. The samples based on finely dispersed fractions Fr3 and Fr4 meet the requirements for compressive strength on the second day of hardening. The specimens of ash-cement composites with high strength, more than 50 MPa for the 28th day of hardening, were prepared on the basis of the Fr4 fraction. In particular, high compressive strength (62-90 MPa) has been achieved for composite cements containing 80 and 90 % of the Fr4 fraction of HCFA in the presence of the superplasticizer Melflux 5581 F, which promotes efficient dispersion of finely dispersed HCFA in the liquid phase, faster and more complete interaction of active components with the formation of hardening hydrated phases. The addition of 5 % microsilica, which promotes the formation of an additional amount of calcium hydrosilicates, made it possible to achieve an increase in strength up to 108 MPa. The results obtained show that finely dispersed HCFA can be used as the components of oil well cements to improve the flowability of cement-ash slurries and improve the strength properties of highly filled ash-cement composite materials.

It is shown that the yield of humic acids increases by 20-30 % during the mechanical treatment of coals with a complex of oxidative-alkaline reagents. Upon the mechanochemical oxidation of the organic matter of brown coals, the molecular weight of humic acids and the percentage of aliphatic fragments in their structure decrease, while the content of phenolic and carboxyl groups increases. Ion exchange processes during the mechanical treatment of coals with mineral salts are accompanied by a decrease in the content of Na⁺ cations and an increase in Ca²⁺, Mg²⁺ cations in the composition of water-soluble humic substances. The concentration of SO₄^2- ions increases in samples of humic substances obtained from coals after mechanical treatment with ammonium sulphate.

The urgent problems of decarbonization in the power-generating sector are analyzed, along with the potential routes to solve ecological problems connected with CO₂ evolution from the combustion of coal - one of the major kinds of fuel for power generating facilities in the world, and especially in Russia and in Kazakhstan. The technology and equipment of the technological line for low-temperature (not higher than 75 °C) hydroconversion of power-generating coal into high calorific (heat of combustion 45 MJ/kg), ecologically safe (purified from ash) liquid hydrogenated coal fuel (HCF) with low carbon content (less than 45 %) are described. The methods for processing coal fuel in the form of water-coal suspension are considered. The routes to conserve the coal industry are discussed, relying on the production of hydrogenized coal fuel with low prime cost from power-generating coal, which will ensure technologically efficient and ecologically safe transition to low-carbon power engineering with zero greenhouse gas emission.

The history of processes for obtaining synthetic fuels by liquefying coals is described. Coal processing technologies are analyzed since the time of F. Bergius up to the present day. Modern hydrogenation processes are described. The basics of single-stage coal liquefaction technologies are described: Kohleoel (Ruhrkohle, Germany), NEDOL (NEDO, Japan), H-Coal (HRI, USA), Exxon Donor Solvent (ExxonMobil, USA), and Solvent Refined Coal (SRC-I and SRC-II, Gulf Oil, USA), as well as two-stage technologies for producing synthetic liquid hydrocarbons from coal: Brown Coal Liquefaction (NEDO, Japan), Catalytic Two-stage Liquefaction (DOE, HTI, USA), Integrated Two-stage liquefaction (Lummus, USA) , Liquid Solvent Extraction (British Coal Corporation, UK), Supercritical Gas Extraction (British Coal Corporation, UK). The scientific foundations of the processes for obtaining biochars from different kinds of biomass by means of hydrothermal carbonization are described. The existing technologies based on this process are indicated. The possibility to upgrade modern coal chemistry in line with “green chemistry” by integrating biomass and the products based on it into coal chemical processes is shown.