Different Degrees Of Metamorphism Research Articles

Migration characteristics of constant elements in the process of coal dissolution by liquid CO2

The effect of liquid CO2 on coal dissolution plays a key role in improving coal bed methane (CBM) recovery and CO2 geological storage. In order to study the effect of liquid CO2–H2O reaction on the migration of mineral constant elements in coal, three kinds of coal samples (lignite, bituminous coal, and anthracite) with different degrees of metamorphism were selected as the research objects. The one-factor experiments of dissolution of liquid CO2 and water-bearing coal samples were carried out by simulating the temperature and pressure of the stratum. X-ray fluorescence spectroscopy (XRF) was used to test the changes in the relative content of constant elements in coal samples after liquid CO2 injection under different pressure conditions. Scanning electron microscopy (SEM) was utilized to observe the evolution pattern of the surface features of the coal before and after the dissolution of liquid CO2. A quantitative analysis of coal pore development characteristics was conducted based on low-temperature N2 adsorption/desorption experiments, and isothermal adsorption experiments were carried out before and after etching the coal samples to understand the adsorption characteristics of CH4 and CO2 by coal under different pressure conditions. The research results indicated that the migration ability of constant elements in coal showed a trend of first decreasing and then increasing with the increasing degree of coal metamorphism. Among the three selected coal samples, the migration ability of constant elements was found to be strongest in anthracite, followed by lignite and bituminous coal. Most of the element migration in coal was carried out through chemical reactions (hydrolysis, carbonation, redox), while some elements were primarily transported through physical means (such as the low-temperature impact of liquid CO2). The dissolution process expands the original pore space of coal and generates new pores, greatly increasing the coal's capacity for CO2 adsorption. These findings deepen our understanding of mineral dissolution in coal by liquid CO2 and provide important insights for achieving efficient and long-term coalbed CO2 geological storage and enhanced methane recovery techniques.

Kosygina I.M., Makarov A.S., Potapchuk I.M. RHEOLOGICAL CHARACTERISTICS OF OIL-WATER-COAL DISPERSION SYSTEMS BASED ON DG COAL AND COMMA XTECH 5W-30 WASTE OIL

Nowadays, the problem of the shortage of energy carriers, their economy, environmental friendliness, and the possibility of combining various clean or spent products of fuel materials for their fuller use and obtaining maximum energy is becoming more and more common. One of the effective solutions to this problem is the development of composite fuel, which consists of coal of different degrees of metamorphism, as well as liquid dispersion media of different chemical nature. The most famous liquid fuel is hydrocarbon fuel, which has several advantages over the burning of pure coal. But one of its disadvantages is its low caloric content due to its content of up to 40% of water by mass of coal. For rational burning of coal-based fuel, it is advisable to limit the water content to 10-15%. Therefore, it was proposed to replace part of the water environment with organic liquids - used oils, oil sludge, and safflower oils. For oil-hydrocarbon fuels, it is important to have certain characteristics - viscosity and stability for transportation, storage, and spraying of these systems. At the same time, oil-hydrocarbon emulsions are affected by various external factors, such as temperature, changing their characteristics. Therefore, in this work, the influence of temperature on the rheological properties of oil-hydrocarbon fuels was studied. During the analysis of the results of the conducted studies, it was established that there is a sharp decrease in the viscosity of the medium when the temperature increases from 10 °C to 20 °C. A further increase in temperature leads to a smaller decrease in the change in effective viscosity and at a temperature in the range from 60 °C to 70 °C, a slight decrease in the rate of change in rheological characteristics is observed. The obtained data indicate that transportation of OHCS by tanks or pipelines will not significantly affect the fluidity and stability of the systems.
 Keywords: composite fuel; oil-hydrocarbon emulsion; long-flame gas coal; temperature dependence.

Study on the catalysis of copper-based compounds on coal spontaneous combustion and its mechanism

ABSTRACTTo study the effect of the copper element in coal on the spontaneous combustion process of coal, corresponding copper-containing compounds were added to the coal-based on their occurrence state, and thermodynamic experiments and in-situ diffuse reflectance infrared spectroscopy experiments were conducted. Thermodynamic oxidation experiments have shown that the catalytic effects of Cu (NO3)2, CuCl2, CuCl, and Cu2O on three types of coal with different degrees of metamorphism are mainly reflected in the accelerated oxidation stage. After adding copper-containing compounds, the ignition temperature of coal decreased by 22.1°C to 134.4°C, the heat release increased by 1.33 to 3.19 times, and the CO emission and oxygen consumption rate also increased. CuCl has the greatest impact on the ignition point temperature of coal and increases the oxygen consumption rates of DNH and TS by 2.32 and 1.51 times that of raw coal. CuCl2 has the strongest catalytic effect on coal oxidation heat release. Through in-situ diffuse reflectance infrared spectroscopy experiments, it was found that the reaction rate of fatty hydrocarbons in the oxidation process of three types of coal with the addition of copper-containing compounds increased to 1.3–3 times that of raw coal, and the oxidation rate of oxygen-containing functional groups also significantly increased, while the cracking temperature of aromatic structures significantly decreased. This is because copper ions, as strong free radicals, induce free radical chain reactions in coal and exhibit a strong promoting effect on the coal oxygen reaction process.

Rapid preparation of porous carbon by Flash Joule heating from bituminous coal and its adsorption mechanism of methylene blue

Porous carbon is an extensively used adsorbent for the removal of dye. However, the conventional high-temperature carbonization and activation method with prolonged heating and annealing process was complicated, energy-consuming and polluting, which greatly limit the large-scale production. In this study, rapid and efficient preparation of porous carbon by the Flash Joule heating (FJH) method was realized for the first time using three bituminous coal samples with different degrees of metamorphism. The preparation process was completed in less than 1 s without chemical treatment, the process was more environmentally friendly. The physical and chemical properties of porous carbon were analyzed and the adsorption mechanism of porous carbon on methylene blue (MB) was investigated. The results showed that the specific surface area of porous carbon prepared by Shuozhou (PC-SZ), Gujiao (PC-GJ) and Changzhi (PC-CZ) could reach 601.95, 361.91 and 256.33 m2·g−1, respectively. The diversity in chemical properties of coal with different metamorphic degrees leads to the different properties of porous carbon. PC-SZ had a higher content of oxygen-containing functional groups and defects. The adsorption experiments indicate that PC-SZ had the best adsorption capacity on MB. The adsorption process was fitted by pseudo-second-order model commendably. It was found that more lattice defects and larger interlayer spacing made PC-SZ to become an excellent adsorbent of methylene blue (MB). Therefore, FJH can be an innovative approach for preparing porous carbon with excellent adsorption properties and is expected to achieve large-scale production.

Effects of CaO addition on the reactivity and reaction kinetics of coke

ABSTRACTIn recent years, researches have shown that highly reactive coke for blast furnace ironmaking not only reduces fuel ratio but also reduces carbon emissions. Therefore, the research on developing high reactivity coke has received unprecedented attention. In this work, CaO was added into coals with different degrees of metamorphism to caking coke to study the effect of CaO amount on the non-isothermal gasification reaction behavior of coke. Results showed that the reactivity is significantly improved as the mass of added calcium oxide accounting for less than 0.4% of the dry coal mass. However, CaO exerted little effect on the micro-strength and structural strength of coke. The analysis of Mercury intrusion porosimetry of coke samples demonstrates that the addition of CaO increased the porosity of coke, resulting in the contact area with CO2, leading further to an increase in coke reactivity. At different heating rates, as the amount of CaO added increased, both the initial reaction temperature and the corresponding temperature of the maximum reaction rate of the gasification from CO2 decreased little by little. The addition of CaO was increased from 0% to 0.6%, the activation energy of the reaction was decreased by 16.41 kJ/mol. The kinetic model of the gasification of coke by CO2 conforms to the unreacted shrinking core model. The reaction mechanism function is converted from f(α) = 3(1-α)2/3 to f(α) = 2(1-α)1/2 (α means carbon conversion ratio), indicating that the addition of CaO accelerates the dissolution rate of coke by CO2.

Study on the Adsorption/Desorption Characteristics of Protogenetic CO in Coal Seams

ABSTRACT In recent years, abnormal CO gas overruns have often occurred in coal mining workings. CO overruns were thought to be caused by the underground blasting work or spontaneous combustion of coal seams; however, minimal attention has been given to the causes of the desorption and release of adsorbed CO in the coal seams. Additionally, insufficient research has been conducted on the generation, distribution and adsorption and desorption characteristics of protogenetic CO in coal seams. Therefore, a self-built comprehensive testing system for coal seam adsorption and desorption was used to study the characteristics of the depressurization desorption and thermal desorption of coal with different degrees of metamorphism during coal seam mining. The results showed that under isothermal conditions, the amount of CO adsorption and desorption of coal samples increased with increasing pressure; under temperature rise conditions, the gas adsorption-desorption was in a dynamic equilibrium process under certain conditions. When the temperature increased, the equilibrium was beneficial to the desorption direction. The initial temperature range of CO production at different equilibrium pressures was 45–55°C. With increasing pressure, the initial temperature point of CO gas production moves forward and was significantly lower than the initial temperature of coal spontaneous combustion. Our research results further supplement the source of underground protogenetic CO gas and provide theoretical support for the accurate prediction of CO coal spontaneous combustion.

Study on molecular structure characteristic and optimization of molecular model construction of coal with different metamorphic grade

To investigate the structural properties of coal molecules with different degrees of metamorphism, in this study, we used Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and solid-state nuclear magnetic resonance carbon spectroscopy (13C NMR) to investigate the structural properties of three coal molecules with different degrees of metamorphism and finally constructed and optimized the coal molecular model. The experimental results showed that with the deepening of the deterioration degree, the proportion of oxygen-containing functional groups in the coal molecules was gradually reduced, the long fatty chains were shortened and reduced, and the aromaticity was enhanced. With increasing coalification, pyridine nitrogen and thiophene sulfur are becoming important components of the nitrogen- and sulfur-containing organic matter in coal. Coal metamorphism promotes the aromatization and condensation degree increase of coal molecular structure, which makes the coal molecular structure evolve into a microcrystalline structure with higher order degree. With this increase of coal rank, the carbon ratio around the bridge (XBP) increased from 0.12 to 0.47. The low-rank coal was dominated by benzene rings with low polymerization degree, and the high rank coal was dominated by aromatic structures, such as tetracene with a high degree of polymerization. The molecular formula of lignite finally constructed was C219H159O21N3, that of coking coal was C235H164O7N4S, and that of anthracite was C286H108O5N4S. The coal molecules constructed in this study provide a theoretical basis for the study of the molecular structure properties of coal with different degrees of metamorphism.

Energy Variation Features during the Isothermal Adsorption of Coal under High-Temperature and High-Pressure Conditions

This paper aims to describe methane adsorption in coal under the conditions of high temperature and high pressure, as well as quantitatively decipher the change rule of energy in the isothermal adsorption process. The isothermal adsorption test was carried out with four groups of middle-rank coals from the Linxing area with different degrees of metamorphism. The impacts of the degree of deterioration of coal, temperature, and pressure on adsorption were analyzed with regard to the adsorption amount, adsorption potential, and adsorption space. Additionally, the energy change during the adsorption of methane by the coal was considered. The results show that the coal adsorption capacity hinges on the degree of deterioration of the coal, as well as the pressure and temperature. Additionally, the impact of temperature upon coal methane adsorption under depth conditions is highlighted. Like the adsorption space, the adsorption potential is an important parameter used to quantitatively characterize the adsorption ease and adsorption capacity; furthermore, the adsorption potential of millipores exceeds that of mesopores, as they are capable of offering a larger specific surface area for adsorption. The total decrease in the surface free energy during adsorption increases as the pressure increases; simultaneously, the increase rate is fast and then slow. The total decrease in the above-described free energy diminishes as the temperature escalates. Under the same pressure, the total decrease in the aforementioned free energy increases as the reflectance of the specular body of the coal increases. The decrease in the aforementioned free energy at each point of pressure lessens as the pressure grows; notably, when the pressure is comparatively low, the reduction is very fast. As the pressure escalates continuously, the decrease speed is slow. Regarding the effect of pressure and temperature upon adsorption, the adsorption gas volume of coal exists in a conversion depth from 1200 m to 1500 m; at the same time, the impact of pressure upon adsorption is dominant up to this depth. Additionally, beyond this depth, temperature gradually comes to have the greatest impact on adsorption.

Pore and gas desorption characteristics of primary coal with different degrees of metamorphism

AbstractPore difference characteristics and adsorption/desorption experiments of primary coal with different degrees were explored to study the characteristics of pore structure and gas desorption. The results show that the pore volume increases with the increase in the degree of metamorphism. In primary coal with different degrees of metamorphism, the distribution of micropores, small pores, and medium‐sized pores (by volume) is WY < PM < CY. The distribution of large pore volume and visible pore volume was WY > PM > CY. According to the pore volume distribution law of different metamorphic primary coals, the average pore diameters of WY, PM, and CY were 68.40, 45.60, and 30.50 nm, respectively. The porosity and specific surface area of primary coal with different degrees of metamorphism show a distribution pattern such that WY > PM > CY. For large pore and visible pore, the pore volumes of WY, PM, and CY coal were 0.0785, 0.0587, and 0.0300 mL/g, respectively, and the proportions were 81.86%, 74.49%, and 55.25%, respectively. The porosity of WY, PM, and CY were 11.57%, 9.03%, and 6.57%, respectively, and the specific surface areas were 6.917, 5.826, and 5.611 cm3/g. According to the desorption characteristics of coal bodies with different metamorphic degrees at different time nodes found that the gas desorption at different time nodes shows similar changes under the same adsorption equilibrium pressure. The higher the degree of coal metamorphism, the greater the amount of gas desorption, and the faster the desorption amplitude. The desorption intensity of WY coal is significantly higher than that of PM and CY coal with the increase of desorption time which also verifies the measurement results of pore structure and adsorption constant.

Ti-Bearing Minerals: from the Ocean Floor to Subduction and Back

Abstract Rutile, titanite, and ilmenite are the most common Ti-bearing minerals in metamorphic rocks. Experimental constraints have shown that titanite is stable at low-grade metamorphic conditions, rutile at high pressure (HP), and ilmenite at high temperature, low pressure (HT-LP) conditions. Yet, petrological evidence suggests that titanite can also be stable at low temperature, HP (LT-HP). This implies that both titanite and rutile can be used to develop proxies to track HP metamorphism, which can have interesting applications. In this study, we have investigated the natural occurrence and chemistry of Ti-bearing minerals in gabbroic rocks and basalts that record different degrees of metamorphism, including LP amphibole-bearing gabbros from the ocean floor (Mid-Atlantic and Indian ridge IODP LEGs) and from an obducted ophiolite (Chenaillet) and HP Alpine metagabbros and metabasalts, including blueschist and eclogite facies rocks from the Western Alps and Corsica. We have performed detailed petrography, Raman spectroscopy and analyzed major and trace elements mineral chemistry using EPMA and LA-ICPMS. We found that rutile is stable at low pressure (< 2 kbar) in ocean-floor amphibole-bearing gabbros, lower than experimental constraints had previously suggested. Rutile is also found in eclogitic metagabbros from the Western Alps and can be chemically distinguished from LP rutile. Blueschist metagabbros from the Western Alps and eclogitic metabasalts from Corsica have titanite stable instead of rutile. While the titanite to rutile transition is pressure- and temperature-dependent, we demonstrate how small variations in bulk-rock Ti/Ca and Ca/Al values within the NCKFMASHTO chemical system may shift their stabilities. High-pressure titanite from these metamafic rocks exhibits La depletion and low La/SmN values in comparison to titanite from amphibolite-facies mafic rocks. La/SmN or Nb together with Yb and V can be used to distinguish HP titanite from titanite formed under other P–T settings. These new systematics can be useful in studies using detrital Ti-bearing minerals to probe the HP metamorphic record through time.

Experimental study on microstructural modification of coal by liquid CO2 extraction

Liquid CO2 injection into coal seam for CH4 displacement is one of the important means to strengthen gas extraction and carbon sequestration in recent years. After liquid CO2 is injected into coal seam, physical and chemical interactions occur with coal through the process of “liquid phase seepage-phase transformation supercharging-gas–liquid mass transfer”, and microscopic characteristics of coal such as pore distribution, surface chemical properties and adsorption characteristics change. Three kinds of coal samples with different degrees of metamorphism were selected as research objects, theoretical analysis, numerical simulation and experimental testing were combined to carry out research on the modification of coal body by liquid CO2 extraction. The results show that with the increase of extraction pressure, the diffusion rate of small organic molecules in coal increases, which is conducive to the dissolution of small organic molecules; In larger pores, the contact area between liquid CO2 and pore surface increases, and small molecular organic matter is easy to precipitate; The infrared spectra of raw coal and residual coal after extraction are basically the same, and the absorption peak intensity is significantly different, liquid CO2 extraction does not significantly damage the macromolecular structure of coal. The research results have important reference value for liquid CO2 anti-reflection coal seam and geological storage.

Thermodynamic characteristics of methane adsorption on coals from China with selected metamorphism degrees: Considering the influence of temperature, moisture content, and in situ modification

A better understanding of the thermodynamic characteristics of methane (CH4) adsorption on coal surfaces is needed for the high-efficiency coalbed methane (CBM) preextraction or prevention of coal and gas outbursts. In this study, atomistic representations of selected coal samples with different degrees of metamorphism, such as long flame coal, coking coal, and anthracite coal obtained from China were created; CH4 adsorption isotherms considering the temperature, moisture content, and microwave in situ modification for CBM preextraction were simulated and analysed. The coal molecular structural results showed that as the degree of coal metamorphism increased from long flame coal to coking coal and anthracite coal, the functional groups in the molecular structure of the coal reduced, while the degree of graphite increased. In situ modification of coal facilitated this process. The saturation adsorption capacity of CH4 decreased and then increased with increasing coal metamorphism degree and decreased linearly with increasing temperature. When water molecules were present, the adsorbed CH4 showed different degrees of decreasing trends with increasing moisture content. The isosteric heat of CH4 adsorption followed the order of coking coal > anthracite coal > long flame coal. The isosteric heat gradually decreased with increasing methane adsorption, and the presence of water molecules had a limited effect on the isosteric heat. In situ modification disrupted the self-conjugated hydrogen bonds, reduced the oxygen-containing functional groups, and decomposed some associated minerals in the coal samples. After in situ modification, the amount of methane adsorption decreased due to a greater contribution from the functional group change than that from the pore volume change, and the modification effect was more evident for the low-rank coal samples than for the middle and high metamorphism degree coal samples. In situ modification applied in the coal seams could contributed to designs for CBM exploration, and the results of this experiment and simulation could provide a novel theoretical basis for in situ modification technology.

Study on evolution characteristics of thermal contribution functional groups in low temperature oxidation process of bituminous coal

In order to study the key functional groups that play a major role in heat during the low-temperature oxidation of bituminous coal, this paper takes three kinds of bituminous coals with different degrees of metamorphism as the research objects, analyzes the variation law of thermal effect parameters during low-temperature oxidation of coal by C80 microcalorimetry experiment, and calculates and analyzes the activation energy of different oxidation stages by oxidation kinetics method. The change rule of functional groups during low temperature oxidation was analyzed by Fourier transform infrared experiment. The correlation between heat and functional groups was comparatively analyzed by using the grey correlation degree and frequency ratio model method, and the key functional groups of bituminous coal that play a major role in heat at different oxidation stages were identified. The results showed that with the deepening of metamorphism degree, the heat flow curve and exotherm gradually decrease, while the characteristic temperature and activation energy gradually increase. Among them, from Caojiatan's long-flame coal to Dongtan's gas coal, the exotherm decreased by 35.5 %, and the maximum endothermic rate temperature and heat balance temperature increased by 3.43 °C and 13.32 °C respectively. With the deepening of metamorphism degree, the content of hydroxyl groups keeps increasing, the content of aliphatic hydrocarbons, aromatic functional groups and fatty ethers first decreases and then increases, and the content of carboxyl groups first increases and then decreases. The correlation analysis between the gray correlation method and the frequency ratio model method shows that as the degree of metamorphic deepened, the key functional groups that play a major role in heat change from COOH to OH in the rapid endothermic stage, from-CH2- to COC in the slow endothermic stage, and from OH to COOH in the rapid exothermic stage. The key functional groups of bituminous coal, which play a major role in heat, follow the evolution of OH → CH2, COC → COOH as the oxidation stage advances.

Gas Diffusion Characteristics and Size Effect in Coal Particles with Different Degrees of Metamorphism

Coalbed methane (CBM) is a green unconventional energy source where the gas diffusion efficiency in coal directly limits the production capacity. Therefore, different gas adsorption experiments were used to determine the diffusion characteristics of coal samples with varying degrees of metamorphism. The influence law based on the gas type, pore structure, and coal sample size on the gas diffusion coefficient was analyzed, and the synergistic control effect of various factors on diffusion was discussed. The results show that when the particle size is the same, the diffusion coefficient of different gases shows the change rule of CO2 > N2 > CH4, and the diffusion coefficient of different samples is positively correlated with the degree of pore development. When the particle size is different, the diffusion coefficient is negatively correlated with the pore development degree and positively correlated with the sample particle size. The effective diffusion coefficient is consistent with the diffusion coefficient when the particle size of the sample is the same, and the effective diffusion coefficient is opposite to the diffusion coefficient when the particle size decreases. The analysis reveals that the diffusion coefficients of different gas are limited by the diameter of gas molecular dynamics, and the diffusion coefficient is reduced with the decrease in the diameter of the gas molecular dynamics. The change of diffusion coefficient caused by particle size change is positively correlated with the change of diffusion cross section caused by size effect. The difference between the effective diffusion coefficient and the diffusion coefficient mainly comes from whether the effective diffusion path is calculated. Therefore, when the particle size is constant, the effective diffusion coefficient can replace the diffusion coefficient to characterize the diffusion behavior. When the particle size is different, it is more appropriate to use the diffusion coefficient to characterize the gas diffusion behavior. The significance of the research findings in revealing gas transport in the coal matrix and coalbed methane formation is substantial.

CO2 adsorption-deformation-percolation characteristics of coals with different degrees of metamorphism and improvement of dynamic prediction model

The deformation and permeability changes occurring during CO2 adsorption in the coal body are important factors affecting CO2 injectability. In order to reveal the characteristic laws of adsorption, deformation and permeability of coal in the process of CO2 adsorption by different coal rank coals, the test experiments of adsorption, deformation and permeability of different coal rank coals under the condition of constant external force were carried out. The adsorption capacity of different coal samples for CO2 was obtained as anthracite > coking coal > long flame coal; The radial deformation ɛ2 and axial deformation ɛ1 of coal after CO2 gas adsorption by anthracite are the closest (ɛ2/ɛ1 is about 1.37), coking coal is the second (ɛ2/ɛ1 is about 1.73), long-flame coal is the largest (ɛ2/ɛ1 is about 2.72), In other words, the higher the coal rank, the more significant the degree of internal homogeneity and isotropy of the coal body, and the mean value of the volume deformation of CO2 adsorbed by long-flame coal is 1.07 and 1.17 times higher than that of coking coal and anthracite. The permeability curves of CO2 adsorption in all three coal samples decreased first and then increased, and the permeability of CO2 in coking coal was the largest, and the sensitivity coefficient of CO2 permeability in coal to adsorption pressure showed a trend of rapid decrease and then small increase. Based on the CO2 adsorption-deformation-percolation variation law of coal, an improved dynamic prediction model of adsorption (fitting accuracy 0.9850 ∼ 0.9963), an improved dynamic prediction model of coal body deformation (fitting accuracy 0.9889 ∼ 0.9921) and an improved dynamic prediction model of permeability (fitting accuracy 0.9848 ∼ 0.9914).

INVESTIGATION OF IGNITION AND THERMAL DECOMPOSITION OF COAL FUEL, WASTE AND SAWDUST OF DIFFERENT DEGREES OF METAMORPHISM BASED ON MACHINE LEARNING METHODS

An experimental study of the thermal decomposition of coal fuel, waste, and sawdust of different degrees ofmetamorphism using a simultaneous thermal analyzer (STA) has been carried out. The heating rates in STA experiments were set at 5°C/min, 10°C/min, 20°C/min, and 30°C/min. A comparative analysis of machine learning algorithms for predicting the thermal decomposition of coal fuel is shows that a mathematical model based on an artificial neural network model can accurately simulate thermogravimetric (TG) mass loss curves for various fuels and refined products with an average coefficient of determination of 99%.

Effect of the quality indices of coal on its grindability

Purpose is to determine the effect of quality indices of coal characterized by different degrees of metamorphism as well as petrographic and ultimate composition on the values of its grindability defined by the Protodyakonov and Hardgrove methods. Methods. 14 coal samples being a part of the raw material base of coking and chemical enterprises of Ukraine were studied. In terms of the samples, the parameters of technical, petrographic, and ultimate analysis were identified. GOST 21153.1-75 Rocks. Method of determining the Protodyakonov strength coefficient and ISO 5074:2015 Bituminous coal. Determination of Hardgrove grindability index were used to identify coal grindability. Graphical and mathematical dependencies between the indices of coal quality (R0, Vdaf, Cdaf, Oddaf) and values of its grindability (f and HGI) were developed. Findings. The obtained mathematical and graphic dependencies of the effect of different indices of coal quality (R0, Vdaf, Cdaf, Oddaf) on the values of its grindability (f and HGI) were obtained. It is shown that dependence of coal quality indices with its strength coefficient (f) is much lower (R2 = 0.550-0.716) than with the Hardgrove grindability index (HGI): R2 = 0.807-0.937. Originality. For the first time, comparative measurements of coal grindability according to the Protodyakonov and Hardgrove methods have been performed. It has been identified that the value of these indices are inversely proportional and described by a second-order polynom. Practical implications. The obtained graphical and mathematic dependencies can be used to predict the operation of crushing equipment for both individual coal and the one of different grade and ultimate composition at coking-chemical and heat-producing enterprises.

REGIONAL METAMORPHISM AND STRATIGRAPHY OF THE BASEMENT OF UKRAINIAN SHIELD

Stratigraphic complexes of the Lower Precambrian are everywhere metamorphosed. That is why the stratigraphic dismemberment of the Lower Precambrian has always been inextricably linked with the study of metamorphism. For some time, metamorphism was even used as a sign of the relative age of stratigenic metamorphic complexes according to the principle – “the higher the degree of metamorphism, the older the complex”. The high-temperature complexes of granulite and amphibolite facies belonged to the Archean, while the less metamorphosed complexes belonged to the Proterozoic. But already at the beginning of the widespread use of methods of isotope dating of metamorphic shield complexes, the most ancient age determinations were obtained from weakly metamorphosed complexes. After that, the degree of metamorphism was no longer taken into account in the stratigraphic dismemberment of the shield basement. The degree of metamorphism of the complexes has not been taken into account for a long ago when compiling official stratigraphic schemes of the Precambrian of the Ukrainian Shield, in which isotope dating plays a leading role. This led, according to many geologists, to distortions in the schemes of the real stratigraphy of the basement of the region. The authors of the article believe that the degree of metamorphism can still be used in the development of the stratigraphy of the Ukrainian Shield and, above all, in the stratigraphic study of individual megablocks. The possibility of such use of metamorphism is considered in the cycle of publications in which this is the first article. The article presents the characteristics of stratigraphy and metamorphism of all megablocks of the Ukrainian Shield. In the structure of the megablocks of the Ukrainian Shield, as well as all the shields of ancient platforms, the following stratigenic metamorphic complexes of the Lower Precambrian have been established, differing in the type and degree of metamorphism: a) granulite-gneiss, b) amphibolite-gneiss, c) greenstone (metavolcanogenic), d) ferruginoussiliceous- shale (metavolcanogenic-chemogenic-terrigenous), e) gneiss-shale (metacarbonate-terrigenous). It has been established that in all megablocks granulite-gneiss complexes are represented and are the most ancient, and all younger complexes are always less metamorphosed than the previous ones. Thus, the relationship between the degree of metamorphism and relative age in individual megablocks is preserved, but this feature cannot be extended to the entire shield. Coeval complexes of neighboring megablocks may have different degrees of metamorphism, and younger complexes of one of the megablocks are sometimes more intensely metamorphosed than older ones in the neighboring megablock.

Research of combustion of solid fuel mixture based on coals of different degrees of metamorphism in the regions of Yenisei Siberia

THE PURPOSE. Consider the combustion process of two coals of different degrees of metamorphism and their mixtures using thermogravimetric analysis based on the change in mass and the rate of change in mass during the heating of fuels. Determine the main characteristics of fuels and the combustion process (temperature of ignition and burnout of the coke residue). Determine the tendency to slagging of coal mixtures. METHODS. When solving the tasks, the thermogravimetric method (TGA). RESULTS. The article provides a brief overview of the combustion of non-design fuels at thermal power plants. The results of technical and elemental analysis of Chernogorsk bituminous coal and Balakhta brown coal are presented. A technique for determining the ignition temperature and burnout of the coke residue is described. The thermograms of the combustion process of two coals of different degrees of metamorphism and their mixtures are presented. The main characteristics of their combustion have been determined. A qualitative analysis of the surface of fuel particles for the presence of pores and cracks is shown. The calculation of the tendency to slagging of coal mixtures has been carried out. CONCLUSION. Thermogravimetric analysis showed an earlier ignition of the Balakhta brown coal in comparison with the Montenegrin bituminous coal. With an increase in the proportion of Balakhta coal in the coal mixture, the profile of the combustion curves shifts to the region of lower temperatures. The addition of 25% Balakhta coal reduces the ignition temperature of Chernogorsk coal by 16%, with an increase in the proportion of Balakhta coal in the mixture, the ignition temperature does not change. Balakhta coal has a high tendency to slagging furnace walls, in contrast to Chernogorsk coal, therefore, an increase in its mass fraction in the coal mixture increases the tendency to slagging furnace screens.

Phenomena and mechanism of slagging and corrosion in energy use of coal with a high content of salts

Purpose. Determination of the main mechanisms of slagging and corrosion of heating surfaces when using coal or other raw materials with a high content of alkali and alkaline earth metals. Experimental determination of mineral phases of ash residues of burning composite raw materials with the participation of salty coal and the influence of component composition on the formation of refractory compounds. Methodology. Critical analysis and generalization of achievements in the developed theories of slagging and corrosion of surfaces during the combustion of problematic carbon raw materials (salty coal, biomass, some wastes, etc.). Determination of the main approaches to the problem of using coal with a high pollution factor. Selection of objects of experimental study on composite raw materials, including coal of different degrees of metamorphism and salinity. Identification of minerals of ash residues of individual fuels and their blends using X-ray phase analysis (X-ray diffraction). Semi-quantitative phase analysis of diffractograms was performed using MATCH! software. Findings. Modern views on the causes of slagging and corrosion processes during the combustion of fuel with a high salt content are highlighted. It has been determined that the process of intensive slagging is associated with a certain ratio of sodium, calcium and iron compounds. The composition and features of the mineral phases of ash residues of composite fuel with the participation of salty coal are experimentally established. The influence of the content of components on the formation of certain mineral phases of mixed ash was determined. Originality. For the first time, the prospects of using two-component blended fuel with the participation of Ukrainian salty coal have been studied. The analysis of minerals in ash residues of salty coal and its blends was carried out. It has been determined that the main part of Na in ash of salty coal of the Bohdanivske deposit in the Northern Donbas is in the form of sulfates and silicates. For the first time, the composition and ways of formation of new refractory mineral compounds in the ash formed during the combustion of composite fuel from coal of different metamorphism and salinity have been established. Practical value. Based on the analysis of literary sources and conducted studies, the dependence of the ash composition on the minerals of the initial fuel and on the ratio of various components in the blends was determined. The proposed approach has a predictive power, as it allows predicting the formation of the main refractory ash minerals. The expediency and prospects of involving salty coal in the fuel base of Ukraine as a component of blended fuels are shown.