Anthracite Samples Research Articles

Nanodiamond Formation at the Lithogenesis and Low-Stages of Regional Metamorphism

Samples of gilsonite from Adzharia, anthraxolite and graphite of coal from Taimyr, shungite from Karelia, and anthracite from Donbass are studied using Raman spectroscopy. Peaks at 1600 cm−1, indicating the presence of nanographite, are recorded in all samples. The anthracite sample from Donbass, 1330 cm−1, corresponds to the sp3-line of carbon hybridization conforming to a nanodiamond. It is concluded that in nature diamonds can be formed at late stages of lithogenesis (catagensis, metagenesis), and for coals, it can occur at the zeolite stage of regional metamorphism of rocks, before the green schist stage.

Multi-scale quantitative characterization of 3-D pore-fracture networks in bituminous and anthracite coals using FIB-SEM tomography and X-ray μ-CT

To study the three-dimensional (3-D) pore-fracture networks of bituminous (BC) and anthracite (AC) coals, a combination of focused-ion beam-scanning electron microscopy (FIB-SEM) tomography and X-ray computed micro-tomography (X-ray μ-CT) was used to characterize 3-D pore-fracture characteristics at different scales. First, as observed in the SEM images, organic-matter (OM) pores, shrinkage-induced pores and dissolution pores are developed in BC samples with pore sizes ranging from ∼25nm to 600nm, and are independently distributed within OM and partial pores filled with minerals. In contrast, a large number of gas pores are widely developed in the AC sample with a cluster distribution in OM, and the pore widths range from ∼10nm to 2μm. Second, we reconstructed the 3-D pore-fracture networks of the BC and AC samples, and quantitatively characterized the porosity, 3-D pore-throat characteristics and its connectivity using the Pore Network Model (PNM) in Avizo. The results indicate that the pores in the BC sample are poorly connected and isolated from each other, whereas the pores in the AC sample are well connected by the throats. There is a logarithmic correlation between the cumulative throat volume and throat size, indicating that the smaller throats make the main contribution to the throat volume. Moreover, the normalized pore size distribution obtained from FIB-SEM and X-ray μ-CT analysis shows that both BC and AC samples exhibit a three-peak structure, but the nano-scale pores are more developed in the AC sample and its 3-D pore morphologies are more complex than those of the BC sample. Furthermore, the macro-pores and micro-fractures in the two coal samples show complex spatial distribution, interconnectivity and tortuosity. The total resolved porosity is 1.108% for BC samples consisting of 0.279% of FIB-SEM and 0.829% of X-ray μ-CT, and 6.082% for AC sample composed of 4.194% of FIB-SEM and 1.888% of X-ray μ-CT, including the connected and non-connected porosity. These results show that the pore-fracture networks of the AC sample are more conducive to CBM storage and flow ability than those of the BC sample. Therefore, this finding provides an accurate method of evaluating the physical properties of coal reservoirs and assists in understanding the mechanisms of CBM storage and transport.

Influence of high-energy impact on the physical and technical characteristics of coal fuels

Currently, in the world’s large-scale coal-fired power industry, the combustion of pulverized coal is the most widely spread technology of combusting the coals. In recent years, the micropulverization technology for preparation and combustion of the coal has been developed in this field. As applied to the small-scale power industry, the method of combusting the coal in the form of a coal–water slurry has been explored for years. Fine coal powders are produced and used in the pulverized-coal gasification. Therefore, the coal preparation methods that involve high-dispersion disintegration of coals attract the greatest interest. The article deals with the problems of high-energy impact on the coal during the preparation of pulverized-coal fuels and coal–water slurries, in particular, during the milling of the coal in ball drum mills and the subsequent regrinding in disintegrators or the cavitation treatment of the coal–water slurries. The investigations were conducted using samples of anthracite and lignite from Belovskii open-pit mine (Kuznetsk Basin). It is shown that both the disintegration and the cavitation treatment are efficient methods for controlling the fuel characteristics. Both methods allow increasing the degree of dispersion of the coal. The content of the small-sized particles reground by cavitation considerably exceeds the similar figure obtained using the disintegrator. The specific surface area of the coal is increased by both cavitation and disintegration with the cavitation treatment producing a considerably greater effect. Being subjected to the cavitation treatment, most coal particles assume the form of a split characterized by the thermodynamically nonequilibrium state. Under external action, in particular, of temperature, the morphological structure of such pulverized materials changes faster and, consequently, the combustion of the treated coal should occur more efficiently. The obtained results are explained from the physical point of view.

Hydromechanical responses of coal powders by CO2 adsorption

Enhanced coal bed methane recovery is a promising method to produce methane gas while storing carbon dioxide (CO2) in coal bed seams. Although the adsorption of the injected carbon dioxide on coals is known to cause swelling and softening of coals, its roles in the worsening of transport and mechanical characteristics have not been fully quantified. Thus, this study examined the effect of carbon dioxide adsorption on the mechanical characteristics (stiffness and strength), permeability and P-wave velocity of coals by using a modified triaxial strength apparatus. Anthracite coal powder samples from Kyung-Dong, Korea, were used in this study. It was confirmed that carbon dioxide adsorption reduced the permeability due to the carbon dioxide-induced swelling and increased the P-wave velocity, possibly owing to additional consolidation of softened coals. Upon completion of carbon dioxide adsorption, a series of multistage triaxial shear strength tests were performed under a consolidated-drained condition. Clear reductions in the mechanical strength and stiffness of the coal samples were observed, confirming the carbon dioxide-induced softening effect on coals. The results suggest that carbon dioxide adsorption heavily affects the mechanical and hydraulic properties of coals, in particular, confirming the carbon dioxide-induced swelling and softening effects on coals.

Temperature and deformation changes in anthracite coal after methane adsorption

Micropores are the primary sites of methane adsorption in coal, and the heterogeneous mesostructures of coal create the non-uniform distribution of the micropores in coal. Using a thermal infrared imager, the temperature distribution on the surface of an anthracite sample during methane adsorption/desorption was tested in this paper, and a new method is advanced to calculate methane adsorption capacity in coal based on its temperature increment. The results confirm the strongly non-uniform distribution of methane adsorption in coal. A X-ray CT scan test demonstrates that the volumetric zones of coal sample with a strong methane adsorption capacity have a lower average density. In these regions, the clay minerals with developed micropores also have a strong methane adsorption capacity. During the coal skeleton deformation of methane adsorption, the high density is hard to be squeezed, while low density areas are likely to be squeezed. Therefore, the complexity density distribution in coal leads to the incompatibility of deformation, which make the direct determination of regional uptake a challenge; From the SEM micrographs of the same coal sample with different densities determined by the X-ray CT scan, the mesostructures of cell cavity pores with non-compact packing of the clay minerals appear to be the primary sites of methane adsorption in coal, and the telocollinite with fewer pores has a lower methane adsorption capacity.

Effect of Rabi splitting on the low-temperature electron paramagnetic resonance signal of anthracite

Specific distortions of the EPR signal of bulk anthracite are observed at low temperatures. They are accompanied by variations in the microwave oscillator frequency and are explained by the manifestation of the Rabi splitting due to the strong coupling between electron spins and the cavity, combined with the use of an automatic frequency-control (AFC) system. EPR signals are recorded at negligible saturation in the temperature range of 4–300K with use of the AFC system to keep the oscillator frequency locked to the resonant frequency of the TM110 cylinder cavity loaded with the sample. For the sample with a mass of 3.6mg the line distortions are observed below 50K and increase with temperature lowering. The oscillator frequency variations are used to estimate the coupling strength as well as the number of spins in the sample. It is shown that the spin-cavity coupling strength is inversely proportional to temperature and can be used for the absolute determination of the number of spins in a sample. Our results indicate that at low temperatures even 1016 spins of the anthracite sample, with a mass of about 0.5mg, can distort the EPR line.

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

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

Petrology and chemistry of sized Pennsylvania anthracite, with emphasis on the distribution of rare earth elements

Sized samples of anthracite were obtained from three preparation plants (breakers), several beneficiating multiple coals, in the Pennsylvania Anthracite Fields. Vitrinite reflectance spans 5.07% Rmax (anthracite, approaching meta-anthracite) in the east to 2.36% Rmax (semi-anthracite) in the west. Maceral distributions do not show the size partitioning observed in many bituminous coals. All sites showed distinct Gd anomalies, possibly a function of hydrothermal metamorphism of the coals. The rare earth distribution pattern (L-, M-, and H-type) within the products from each breaker are similar. Principal components analysis confirmed an observation from the latter assessment that coals from the same breaker tend to cluster together, but distinct from the clusters of the other breakers.

Study on rapid pyrolysis and in-situ char gasification characteristics of coal and petroleum coke

Rapid pyrolysis characteristics of three different rank coals and two petroleum cokes were investigated using a drop tube furnace. Moreover, gasification characteristics of char samples were studied in an in-situ heating stage. The results showed that H2 and CO were the main gaseous pyrolysis products of coal samples. The relative content of H2 and CO increased with increasing pyrolysis temperature. The volume fraction of H2 in syngas increased with increasing coal rank, whereas that of CO showed the contrary trend. Anthracite and petroleum cokes (Petcoke 1 and Petcoke 2) exhibited a great similarity in gas release characteristics. There was a maximum value for the specific surface area and graphitization degree of char samples with increasing pyrolysis temperature. The results of in-situ heating stage experiments indicated that the most of char particles reacted with CO2 in the shrinking particle mode at the initial stage. Char samples of petcokes and anthracite were similar in slow consumption of particle skeleton during gasification. Interestingly, petcokes demonstrated particle migration, residual agglomeration, and rapid consumption at the later reaction stage. The variation trend of the area shrinkage ratio of char samples was well verified by the TGA results.

Structure and gasification of coal from the Gukovo-Gryaznovskoe deposit

The structural elements of the organic matter and the composition of an anthracite sample from the Gukovo-Gryaznovskoe deposit in Rostov oblast were considered. The process of layer coal gasification was studied at atmospheric and elevated pressures.

THERMOGRAVIMETRIC ANALYSIS OF CHANGES IN PARAMETERS OF CUPOLA COKE AND ANTHRACITE

Thermogravimetric analysis of cupola coke and anthracite samples was carried out using a Setaram derivatograph by means of test charge diluting in powder thermo-inert solvent. Method applicability in comparative evaluation of various carbon materials properties is shown. At heating up to 1500 °C the behavior of coke and anthracite differs slightly; that allows suggesting the possibility of replacing coke by anthracite. Ash residues melt formation and their crystallization during subsequent cooling depends on the amount and composition of ash and can infl uence signifi cantly the course of technologic process.

Size effects in the conduction electron spin resonance of anthracite and higher anthraxolite.

Electron paramagnetic resonance spectroscopy of conduction electrons, i.e. Conduction Electron Spin Resonance (CESR), is a powerful tool for studies of carbon samples. Conductive samples cause additional effects in CESR spectra that influence the shape and intensity of the signals. In cases where conduction electrons play a dominant role, whilst the influence of localized paramagnetic centres is small or negligible, the effects because of the spins on conduction electrons will dominate the spectra. It has been shown that for some ratios of the bulk sample sizes (d) to the skin depth (δ), which depend on the electrical conductivity, additional size effects become visible in the line asymmetry parameter A/|B|, which is the ratio of the maximum to the absolute, minimum value of the resonance signal. To study these effects the electrical direct current-conductivity and CESR measurements are carried out for two amorphous bulk coal samples of anthracite and a higher anthraxolite. The observed effects are described and discussed in terms of the Dyson theory. Copyright © 2015 John Wiley & Sons, Ltd.

Thermogravimetric analysis of the parameters of foundry coke and anthracite

Thermogravimetrical analysis of foundry-coke and anthracite samples is undertaken on a Setaram derivatograph by dilution of a weighed powder sample in thermally inert solvent. This method may be used for comparison of the properties of different carbon-based materials. On heating to 1500°C, there is little difference in the behavior of the coke and anthracite, indicating that coke may be replaced by anthracite. The quantity and composition of the ash affects the formation of the melt of ash residues and their solidification on subsequent cooling. This behavior has significant influence on the process.

NON-MINERAL INORGANIC CONSTITUENTS OF BUKIT ASAM COAL NATURE AND MODE OF OCCURRENCE

The nature and mode of occurrence of the non-mineral inorganic fractions in coal from the Bukit Asam coalfield South Sumatra Basin Indonesia were analysed using a combination of selective leaching, low temperature ashing, XRD, XRF and electron micropobe techniques. Geologically the rank of coal at Bukit Asam was influenced by igneous intrusion. Fourteen coal samples were used in this study. Samples are chosen to represent different rank levels as well as seam horizons. The inorganic elements, in the form of dissolved salts, exchangeable ions and organometallic complexes, although present in small proportions, contribute significantly to the mineral matter components of Bukit Asam low rank coal. Electron microprobe analysis showed small but significant concentrations of inorganic elements (Al, Ca and Fe) occurring in the individual macerals in two sub bituminous and twosemi anthracite samples. There is a tendency for some of the elements, particularly Ca and Al to be lost from the organic matter with rank advance. The concentrations of elements indicated by the microprobe are relatively in good agreement with the levels of element mobility indicated by selective leaching of the same whole-coal samples. The results of this study also suggest that non-mineral inorganic was likely act as a precursor for the reactions resulting in the formation of new minerals in the high rank coals at Bukit Asam.

Laboratory investigations of gas flow behaviors in tight anthracite and evaluation of different pulse-decay methods on permeability estimation

Permeability evolution in coal is critical for the prediction of coalbed methane (CBM) production and CO2-enhanced-CBM. The anthracite, as the highest rank coal, has ultra-tight structure and the gas flow dynamics is complicated and influenced by multi-mechanistic flow components. Gas transport in anthracite will be a nonlinear multi-mechanistic process also including non-Darcy components like gas as-/desorption, gas slippage and diffusion flow. In this study, a series of laboratory permeability measurements were conducted on an anthracite sample for helium and CO2 depletions under both constant stress and uniaxial strain boundary conditions. The different transient pulse-decay methods were utilized to estimate the permeability and Klinkenberg correction accounting for slip effect was also used to calculate the intrinsic permeability. The helium permeability results indicate that the overall permeability under uniaxial strain condition is higher than that under constant stress condition because of larger effective stress reduction during gas depletion. At low pressure under constant stress condition, CO2 permeability enhancement due to sorption-induced matrix shrinkage effect is significant, which can be either clearly observed from the pulse-decay pressure response curves or the data reduced by Cui et al.'s method. But within the same pressure range, there is almost no difference between Brace's method and Dicker & Smits's method. Gas slippage effect is also significant at low pressure for low permeability coal based on the obtained experimental data.

Polar polycyclic aromatic compounds from different coal types show varying mutagenic potential, EROD induction and bioavailability depending on coal rank

Investigations of the bioavailability and toxicity of polycyclic aromatic compounds (PAC) have rarely considered the heterogeneity of coals and the impact of more polar PAC besides polycyclic aromatic hydrocarbons (PAH).Earlier, we investigated the toxicity of eight heterogeneous coals and their extracts. In the present study, the hazard potential with respect to mechanism-specific toxicity of polar fractions of dichloromethane extracts from coals was studied. Polar extract fractions of all coal types except for anthracite induced EROD activity (determined in RTL-W1 cells), independent of coal type (Bio-TEQs between 23±16 and 52±22ng/g). The polar fractions of all bituminous coal extracts revealed mutagenic activity (determined using the Ames Fluctuation test). No significant mutation induction was detected for the polar extract fractions from the lignite, sub-bituminous coal and anthracite samples, which indicates a higher dependency on coal type for polar PAC here.Additionally, information on bioavailability was derived from a bioaccumulation test using the deposit-feeding oligochaete Lumbriculus variegatus which was exposed for 28days to ground coal samples. Despite the high toxic potential of most coal extracts and a reduced biomass of Lumbriculus in bituminous coal samples, bioaccumulation of PAH and mortality after 28days were found to be low. Limited bioaccumulation of PAH (up to 3.6±3.8mg/kg EPA-PAH) and polar PAC were observed for all coal samples. A significant reduction of Lumbriculus biomass was observed in the treatments containing bituminous coals (from 0.019±0.004g to 0.046±0.011g compared to 0.080±0.025g per replicate in control treatments).We conclude that bioavailability of native PAC from coals including polar PAC is low for all investigated coal types. In comparison to lignite, sub-bituminous coals and anthracite, the bioavailability of PAC from bituminous coals is slightly increased.

Experimental Study on Coal Sample's Methane Desorption Law in Different Adsorption Balance Pressures

Taking 7 group anthracite coal samples which size is 1¡«3mm from different coal mines of the same mine field as research objects, there carried coal samples' methane adsorption and desorption experiment under the condition of about 1Mpa¡¢2Mpa¡¢3Mpa¡¢4Mpa adsorption equilibrium pressures and adsorption equilibrium temperature 20¡æ. The coal samples' cumulative methane desorption volume of each minute were measured in the initial 30 minutes time, and there obtained the desorption data. Based on experimental data analysis found that the methane desorption law between cumulative methane desorption volume and desorption time is fit to SUN Chong-xu Formulate (Q=ati). Then aimed to the same coal sample, the desorption eigenvalues of different adsorption equilibrium pressures were studied using SUN Chong-xu Formulate based on the experiment data. The study results show that the coal sample's desorption eigenvalues of different adsorption equilibrium pressures keeps a constant, and the average eigenvalues is 0.237 for these experiment samples. Then 1~3mm size coal samples can be used to determent methane content when the loss time less than 8 minutes.

The use of thermomechanical analysis to characterise Söderberg electrode paste raw materials

Continuous self-baking electrodes, i.e. Söderberg electrodes, are commonly employed in the industrial operation of submerged arc furnaces to conduct electrical energy from a transformer(s) to the smelting zone inside the furnace. Söderberg electrodes are formed from Söderberg electrode paste consisting of two components, i.e. a binder that is mostly a coal tar pitch and a solid filler that can be either coke or calcined anthracite. In this paper it is demonstrated how thermomechanical analysis can be used to characterise the thermal dimensional behaviours of Söderberg electrode paste raw materials. Two case study coal tar pitches, three anthracites and a pre-baked graphite electrode sample were characterised. Results indicated that the method applied can be used to determine the baking isotherm temperature more accurately than previously. Enhanced knowledge of the baking isotherm temperature is critical to ensure safe, profitable and continues furnace operation. The results also indicated that the coal tar pitches shrunk approximately 12% if exposed to temperatures above the baking isotherm temperature up to 1300°C, while the anthracites calcined at 1400°C expanded 0.6–1.0% in the same temperature range. The magnitude differences in thermal dimensional behaviour and difference in motion (shrinkage vs. expansion) indicates the vulnerability of a Söderberg electrode baked for the first time at temperatures exceeding the baking isotherm temperature. In contrast to the calcined anthracites, the uncalcined anthracite samples shrunk 6–8% if exposed to temperatures up to 1300°C. This stresses the importance of the efficiency of the calcination process of the anthracite prior to Söderberg electrode paste production to enhance dimensional stability of the Söderberg electrode paste. The results also indicated that the method detailed in this paper can be used by Söderberg electrode paste producers to optimise the selection of raw materials and to do quality control on calcined anthracite.

Numerical description of coalbed methane desorption stages based on isothermal adsorption experiment

Quantitative description of desorption stages of coalbed methane is an important basis to objectively understand the production of coalbed methane well, to diagnose the production state, and to optimize the management of draining and collection of coalbed methane. A series of isothermal adsorption experiments were carried out with 12 anthracite samples from 6 coalbed methane wells located in the south of the Qinshui Basin, based on the results of isothermal adsorption experiments, and an analytical model was developed based on the Langmuir sorption theory. With the model, a numerical method that adopts equivalent desorption rate and its curve was established, which can be used to characterize the staged desorption of coalbed methane. According to the experimental and numerical characterizations, three key pressure points determined by the equivalent desorption rate curvature that defines pressure-declining desorption stage, have been proposed and confirmed, namely, start-up pressure, transition pressure and sensitive pressure. By using these three key pressure points, the process of coalbed methane desorption associated with isothermal adsorption experiments can be divided into four stages, i.e., zero desorption stage, slow desorption stage, transition desorption stage, and sensitive desorption stage. According to analogy analysis, there are differences and similarities between the processes of coalbed methane desorption identified by isothermal adsorption experiments and observed in gas production. Moreover, it has been found that larger Langmuir volume and ratio of Langmuir constants are beneficial to earlier advent of steady production stage, whereas it is also possible that the declining production stage may occur ahead of schedule.

Effect of coal quality on its desulphurization 1. influence of the organic matter

The desulphurization process of different coal types has been studied. The coal was treated by air-steam mixture in the fluidized-bed reactor under the conditions similar to isothermal ones. The influence of temperature and oxidant composition affecting the pyrite (which is the coal component) chemical conversion on the desulphurization efficiency has been investigated for coal with different metamorphism degree. The dry and wet samples of anthracite and brown coal were compared in order to propose the direction of brown coal pyrite conversion followed by the hydrogen sulphide production.