Medium Volatile Bituminous Coal Research Articles

Adsorption of CO2/CH4 on the aromatic rings and oxygen groups of coal based on in-situ diffuse reflectance FTIR

The adsorption mechanisms of CH4 and CO2 on the coal surface is the theoretical basis for CO2 sequestration with enhanced coalbed methane recovery (CO2-ECBM). Molecular simulation is the main method to study the adsorption mechanism at present, but the model used in the process of molecular simulation could not accurately characterize the coal macromolecular structure. Therefore, we used in-situ diffuse reflectance Fourier-transform infrared spectroscopy (FTIR) to study the adsorption of CO2/CH4 on the aromatic rings and oxygen groups of coal. The results showed that CO2 and CH4 were physisorbed on the aromatic rings, and the aromatic rings represented the primary competitive adsorption sites for CO2 and CH4, CO2 was preferentially adsorbed at the top of the aromatic ring compared to CH4. Both carboxyl and carbonyl groups were beneficial for CO2 adsorption but not for CH4 adsorption. Compared to aromatic rings, the adsorption affinity of carboxyl groups for CO2 were stronger. The results of this study revealed the adsorption mechanisms of CO2 and CH4 on the aromatic rings and oxygen groups, as well as the impact of oxygen groups on the gas adsorption capacity, providing a theoretical basis for applying CO2-ECBM in the medium-volatile bituminous coal reservoirs.

The occurrence of coalbed methane in the depocentre of the Upper Silesian Coal Basin in the light of the research from the Orzesze-1 deep exploratory well

The Orzesze-1 exploratory well with a depth of 3708 m (TVD) was drilled in 2019–2020 in the depocentre of the Upper Silesian Coal Basin (USCB). The methane content in the coal seams has been tested to a depth of 2840 m and the sorption capacity of the coal to a depth of 2576 m. These are the deepest measurements in the USCB so far. The vertical distribution of methane content in the borehole shows two depth zones of interest, the first at a depth 883 m to about 1300 m (maximum methane content about 12 m3/t coaldaf) and another in the range of 1500–2840 m, that is, to the maximum measurement depth, so the actual lower boundary depth of this zone is unknown. The maximum methane content here exceeds 18 m3/t coaldaf at a depth of >2800 m. Both zones are separated by an interval of reduced methane content of about 5 m3/t coaldaf at a depth of approximately 1400 m. The gas composition is dominated by methane (∼90%), and the content of carbon dioxide increases to approximately 15% at a depth of >2300 m. The methane-bearing zone at ∼900–1300 m corresponds to the zone of high- and medium-volatile bituminous coal (second coalification jump), while the highest methane content at a depth of >2800 m was determined in anthracite. The methane sorption capacity of the coal seams oscillates between 16 and 40 m3/t coaldaf with a maximum in anthracite at a depth of >2800 m, where the temperature of the rock approaches 100 °C and the deposit pressure exceeds 28 MPa. The highest sorption capacity in anthracite results from its inner structure characterised by the predominance of ordered aromatic lamellas and the dominance of vitrinite macerals (>70%), which contain coal micropores accumulating adsorbed methane. The comparison of the sorption capacity of the tested coal and the measured methane content displays undersaturation of 11–59%, however, due to significant gas content in the deep zone (depth > 1500 m), the drilling area can be considered as a prospect for further exploration and development of coalbed methane (CBM).

High temperature viscoelastic behaviour of sugarcane bagasse char and coal blends: Role of oxygen and porosity of char on fluidity reduction

This paper focuses on the introduction of sugarcane bagasse, an agricultural byproduct, as a renewable carbon-based additive to metallurgical coal to produce biocoke for the steel industry. Through subjecting pelletized sugarcane bagasse samples to various pyrolysis conditions, chars with varying properties were generated. With increasing final pyrolysis temperature (200, 400, 600, and 800 °C), a rise in carbon content and decline in oxygen, nitrogen and hydrogen levels in the chars were observed. The presence of an inert purge gas during pyrolysis prompted abundant micropore formation between 400 and 600 °C, yielding high specific surface area (SSA > 300 m2/g) chars at 600 °C and 800 °C. Conversely, chars produced in a fixed (unpurged) nitrogen environment exhibited minimal porosity and consequently low SSAs (<5m2/g). These various chars were then blended (at 10 % addition) with a medium-volatile bituminous coal to evaluate their impact on the viscoelastic properties of the coal. Chars pyrolyzed to lower final temperatures had the greatest detrimental effect on blend fluidity due to (1) their continued devolatilization which introduced void spaces in the blend creating pathways for the exhaust of coal volatiles, and (2) their elevated oxygen content, which scavenged essential mobile hydrogen needed to facilitate viscoelastic behaviour. Furthermore, chars with similar oxygen content but substantially different (by over two orders of magnitude) SSAs generated comparable coal-char blend viscosity profiles, indicating that the presence or absence of micropores in an additive does not significantly influence the viscoelastic behaviour of the coal. The reduction in blend fluidity for the addition of chars pyrolyzed to 800 °C was comparable to the modelled addition of inertinite macerals, implying that these high-temperature chars predominantly serve as inert solid additives. Comparison to a blend with 10 % mesoporous activated charcoal as the additive confirmed that it is mesopores that destroy fluidity, while micropores do not play a significant role. Mesopores were identified to adsorb/trap the relatively large tar-like compounds that are responsible for coal plasticity. Collectively, this research identifies three key factors contributing to fluidity reduction in coal-additive blends: void creation, oxygen content, and mesoporosity. These findings offer insights into optimizing biocoke production processes.

Recognition and (semi-)quantitative analysis of REE-bearing minerals in coal using automated scanning electron microscopy

The recognition and quantification of rare earth and yttrium (REY) minerals in coal is extremely important for understanding their geological origin and developing high-efficiency extraction techniques. This study developed an automated image analysis by scanning electron microscopy (AIA-SEM) method for characterizing REY minerals in coal. Carbon and copper were used as grey-scale calibration standard to assure the consistency per experiment and differentiate organic matter and minerals with different brightness. Two critical issues in determining REY including rapid recognition of fine REY-bearing particles and accurate classification and quantification of REY minerals in coal are resolved by (1) establishing grey threshold standard to locate REY-bearing grains and a two-step image scan; (2) developing classification criteria supplemented with spot- and EDS-mapping analysis for questionable particles. By using the established method, a total of 166 REY-bearing mineral grains were identified from 12,930 particles in a medium-volatile bituminous coal (REY concentration: 149.21 ppm; ash yield: 21.25%). It is found that Ca-REE flurocarbonates, monazite, and (Sc, Y)-bearing zircon are the dominant REY species in the studied coal sample. REE-aluminophosphates are also important hosts for REE in coal, with total amounts being >10%. REY minerals are fine in particle size. Over 50% of monazite, xenotime, Ca-REE flurocarbonate, and REE-aluminophosphate have particle size below 5 μm and monazite occurs mostly as submicron particle. Most REY minerals (> 60%) are embedded into coal macerals as included minerals. About 80% of REY-bearing phosphates and zircon are partly or completely encapsulated in clay minerals, whereas more than half of Ca-REY-fluorocarbonates mineral grains is free of other minerals.

Revisiting the petrology of lower Pennsylvanian (Namurian and Langsettian) coals in southern West Virginia and southwestern Virginia, USA

Namurian and Langsettian coals representing a vertical span of about 650 m were sampled from cores in southern West Virginia and western Virginia. The coal rank ranges from medium through low volatile bituminous. Historically, a significant portion of the production from the region has been for smokeless steam coals and for metallurgical coal. Despite the presence of thrust faults and the potential for fault-induced movement of mineralizing fluids, a depth-of-burial/geothermal-gradient model, as proposed earlier, appears to be sufficient to describe the increase of rank with depth. The coals generally have >70% total vitrinite (mineral-free basis) and a telovitrinite/(telovitrinite + detrovitrinite) ratio exceeding 0.75. Fusinite dominates the inertinite group macerals. An unnamed Langsettian coal had a high liptinite content but, otherwise, in part owing to the difficulty of detecting liptinites in medium and low volatile bituminous coals, liptinite appears to be sparse. Among the coals in the study, not all of them have been extensively mined. The Pocahontas coals represent the most significant economic resource.

Coal petrology, sedimentology and depositional environment of the Parvadeh coals in the Upper Triassic, Tabas Block of Central-East Iran

Peat forming environment strongly influences the economic value of any coal seam and coal-bearing strata. Hence, palaeoenvironmental studies provide important information for coal resource exploration. In this context, detailed studies on selected coals from the Parvadeh Area, Iran, were conducted using sedimentology, coal petrology, X-ray diffraction (XRD), scanning electron microscopy- energy dispersive X-ray analyzer (SEM-EDX), and proximate analysis. The sedimentary facies above and below the coal seams are mainly marine or marine-influenced facies, supporting that the coal-forming mires in the Parvadeh Area developed in a paralic environment, where the base level must be closely related to sea level. Sulfur contents are moderate to high and mark the influence of brackish/marine water, especially during transgression after peat growth in a lower delta plain environment. The peat-forming mires extended on coastal/delta plain lobes. The lower delta plain/coastal plain coals are characterized by lateral continuity and substantial thickness, whereas few coals possibly representing the upper delta plain are thin and more discontinuous. The detrital nature and composition of the numerous partings and the overall high ash yield in the coal seams indicate an active tectonic area with high rates of creation of accommodation space over peat growth. Coal petrology and coal facies analysis exhibits a permanently high water table within a forest swamp and mostly rheotrophic conditions, sometimes with connection to the seawater. According to paleoenvironmental reconstructions, it seems that coal layers may be thicker, with less sulfur (pyrite), but more clastic minerals and partings toward the western part of the area. Although these coal seams presently have low economic potential for the mining operation, partly due to great depth, this humic, high-volatile to medium-volatile bituminous coal may be suitable for exploration of coal bed methane resources.

Gas desorption and diffusion characteristics in different rank coals under different pressure-drop conditions

To compare gas desorption and diffusion characteristics under different pressure-drop conditions, different rank coals were collected to conduct desorption and diffusion experiments under the direct pressure-drop condition (DPDC) and the progressive pressure-drop condition (PPDC). Moreover, mercury injection capillary pressure (MICP) analysis was performed to determine pore structure characteristics. When the pressure-drop condition is changed from DPDC to PPDC, the initial desorption rate decreases, while the desorption volume and diffusion coefficient increase, suggesting the damage on desorption capacity and diffusion capacity resulted from DPDC. The maximum changes of these three parameters occur in the medium-volatile bituminous coal, which decrease from 0.255 to 0.063 cm3/(g·min), increase from 2.96 to 18.82 cm3/g and increase from 0.4732 × 10−10 to 3.8239 × 10−10 cm2/s, respectively. Micropores and transition pores predominate in all samples. With increasing coal rank, the pore volume generally shows a decreasing trend, whereas the fractal dimension shows an increasing trend. The difference in diffusion coefficient between DPDC and PPDC of different rank coals is predominated by micropores, which arises from the various diffusion regimes at different pressure ranges in micropores. Specifically, the rapid pressure-drop rate in DPDC causes the atmospheric pressure condition, and Knudsen diffusion and Transitional diffusion play dominant roles in micropores, resulting in the lower diffusion coefficient. The difference in desorption volume between DPDC and PPDC of different rank coals is predominated by transition pores, which results from the water block effect in transition pores. In DPDC, large bubbles easily form in transition pore throats and show large deformation when they pass through transition pore throats, which increases capillary resistance and intensifies the water block effect. However, in PPDC, the size of gas bubbles in the same transition pore throats is smaller than that in DPDC, which weakens the water block effect and enhances desorption capacity. This research can provide strategies for optimizing the pressure-drop rate during CBM production. PPDC is more suitable for CBM exploration. The drainage intensity should be reduced, or secondary reformation measures should be taken to reduce the proportions of micropores and transition pores in DPDC to reduce the damage of desorption capacity and diffusion capacity.

Potential effect of carbon dioxide injection on the functional groups of medium volatile bituminous coals analysed using in-situ diffuse reflectance Fourier-transform infrared spectroscopy

CO2 sequestration with enhanced coalbed methane recovery (CO2–ECBM) is a promising technology for mitigating CO2 emissions. To implement CO2–ECBM, complex interactions must be elucidated between CO2 and coal during CO2 sequestration, but the mechanism through which coal and CO2 interact remains controversial mainly because coal contains a complex macromolecular structure. Therefore, we used in-situ high-pressure diffuse reflectance Fourier-transform infrared spectroscopy to investigate the potential impact of the CO2 injection on the functional groups of medium volatile bituminous (MVB) coals. The results of this study showed that CO2 physisorption could be found near the MVB coal macromolecular CH bonds, and the interactions between the MVB coal macromolecular CH bonds and CO2 kept strengthening with increasing CO2 injection pressure. Injecting CO2 into the MVB coal disrupted the weak interactions between aromatic layers, and supercritical CO2 (ScCO2) could disrupt the physical association between small molecular compounds and the coal macromolecular structure, which extracted hydrocarbon and oxygen-containing compounds, and thus reduced the content of oxygen-containing functional groups and -CH2- in the MVB coal. The coal macromolecular CO bonds were not conducive to methane adsorption on the coal surfaces, injecting high-pressure CO2 (P = 7 MPa, 8 MPa) into the MVB coal matrix irreversibly damaged the coal macromolecular CO bonds, which enhanced the CH4 adsorption capacity and was not conducive to CH4 desorption. The results of this study showed that injecting ScCO2 into the MVB coal could change the coal macromolecular structure and reduce the content of oxygen-containing functional groups and -CH2-, thus affecting the properties of MVB coal reservoir, such as porosity, permeability, and mechanical characteristics, which could advance knowledge of the theoretical usefulness for CO2-ECBM recovery and sequestration in the MVB coal reservoirs.

Enrichment of critical elements (Li-Ga-Nb-Ta-REE-Y) in the coals and host rocks from the Daping Mine, Yudongnan Coalfield, SW China

Critical elements in coals and host rocks have attracted much attention due to their growing demand and rising economic significance. This research reports new data of elevated critical elements and mineralogical characteristics of the coals and host rocks from the Daping Mine, Yudongnan Coalfield, neighboring to the previously reported coal-hosted Li and rare earth elements plus yittrium (REY) ore deposit of the Donggou Mine in the same coalfield. The coal in the Daping Mine is mainly a medium-volatile bituminous coal and characterized by a low-ash yield (Ad = 13.08–30.32 %, 19.65 % on average) and a high-sulfur content (1.75–9.25 %, 3.43 % on average). Critical elements including Li, Ga, Nb, Ta, REY are enriched in the coal. Minerals in the Daping coal are mainly clay minerals (including illite, mixed layer of illite/smectite (I/S), kaolinite, and chamosite) and pyrite, and to a lesser extent, calcite, anatase, and marcasite, with traces of zircon, celestite, and baddeleyite. Lithium is mainly associated with illite, and Ga, Nb, Ta, and REY also have an inorganic affinity. The terrigenous materials of the Daping coal were from the intermediate-felsic rocks at the top of the Kangdian Upland rather than the basalts. Hydrothermal solutions also make a great contribution to the enrichment of critical elements and minerals. High-temperature solutions (>200 °C) may be responsible for the weakly negative Eu anomalies. The coal ashes in the Daping Mine have significant concentrations of Li2O (2583 ppm on average), Ga (83.5 ppm on average), (Nb, Ta)2O5 (143 ppm on average), and REO (oxides of REY, 1125 ppm on average), all of which are higher than their respective cut-off grades. Moreover, the floor strata are enriched in these critical elements. Thus, the coal ashes and floor strata are potential resources for extraction of these critical elements.

High-Strength Formed Coke from Torrefied Biomass and Its Blend with Noncaking Coal

In continuation of our previous study on production of high-strength metallurgical coke from torrefied softwood (cedar), we studied coke production from a mixture of torrefied cedar (TC) and noncaking coal by pulverization to sizes <100 μm, mixing, binderless hot briquetting, and carbonization. These sequential processes produced coke with a tensile strength of 5–17 MPa, which was equivalent to or greater than that of conventional coke (5–6 MPa), from TC-coal mixtures over the entire ranges of TC mass fraction in briquette of 0–100%, torrefaction temperature of 250–300 °C, and choice of coal (sub-bituminous or medium-volatile bituminous coal). The mixing of TC and coal hindered densification of coke due to hindrance of shrinkage of more-shrinkable TC-derived particles during the carbonization under many of the conditions. Nevertheless, positive synergy occurred in the coke strength at TC mass fractions of over 50%, where coal-derived particles were dispersed in the matrix of TC-derived particles, bonded to them during the carbonization, and behaved as a reinforcement of the matrix. The bonding between TC-derived and coal-derived primary particles was revealed by scanning electron microscopy. Copulverization of mixed TC and coal to sizes <40 μm before the briquetting gave cokes having strengths as high as 23–28 MPa. The fine pulverization increased the frequencies of mutual bonding of TC-derived particles and coal-derived particles and bonding between TC-derived and coal-derived particles per coke volume. The strength of coke from the TC-coal mixture generally followed volume-based additivity of strengths of cokes from TC and coal. This was realized by mixing primary particles of TC and coal within ≈10 μm scale or even smaller.

Permeability variations of lignite and bituminous coals under elevated pyrolysis temperatures (35–600 °C): An experimental study

Studies on permeability under pyrolysis temperatures (PTs) can provide instructions for syngas production of underground coal gasification (UCG). Permeability variations of lignite, high volatile bituminous coal (HVBC) and medium volatile bituminous coal (MVBC) under elevated PTs (35°C–600 °C) were studied. Structure and weightlessness as well as maturity of coal detected by methods of micro structure observation, nuclear magnetic resonance, thermogravimetric analysis, and liquid yield measurement, were investigated and clarified to probe the factors influencing permeability variation. The results showed: (1) permeability of lignite and HVBC as well as MVBC increased during 35–200 °C. Lignite permeability decreased during 200–600 °C while HVBC and MVBC permeability decreased during 200–400 °C and then increased during 400–600 °C; (2) for coals with different maturities, pyrolysis reactive strength controlled the permeability. Lignite permeability were always the greatest followed by HVBC, and MVBC permeability were always the lowest, at PTs of 125–500 °C; (3) for an individual coal, permeability variation was controlled by the relative strength between positive factors (water and volatiles’ discharge, stable char framework, increased inertoid content, and high porosity of char) and negative factors (blocking of penetration channels by tars or char fines or a mix of these two, closure of macro-pores and fractures, and unstable char framework).

Permeability Loss of Bituminous Coal Induced by Water and Salinity Sensitivities: Implications of Minerals' Occurrence and Pore Structure Complexity.

Water sensitivity (WS) and salinity sensitivity (SS) are key issues to be investigated for instructing coalbed methane (CBM) production. This work studied the influences of minerals and pores on WS and SS of medium-volatile bituminous coal (MVBC) and highly volatile bituminous coal (HVBC) deposited in northwestern China by detecting and observing minerals using the TESCAN Integrated Mineral Analyzer, simulating WS and SS, and characterizing pore structural complexities using rate-controlled mercury penetration. The results show that (1) kaolinite is mainly distributed as irregular particles or fragile aggregates attaching on the bedding surface or filling in meso-pores or transition pores, showing a high potential for detachment; (2) MVBC and HVBC in this study are characterized as medium to weak WS and weak SS, respectively; (3) for HVBC during the WS or SS process, kaolinite distributed in meso-pores or transition pores first detaches and then migrates to the narrow throat of macro-pores and super macro-pores, leading to volume decreases of macro-pores and super macro-pores and loss of permeability; and (4) kaolinite filling in macro-pores of MVBC detaches, then migrates, and finally deposits in super macro-pores after WS and SS, leading to losses of super macro-pore volume and permeability. Results of this study can enhance the scientific knowledge on WS and SS of coal during CBM development.

Mechanism of solvent extraction-induced changes to nanoscale pores of coal before and after acidification

As the most widely used reservoir stimulation method, hydraulic fracturing requires the injection of large volumes of fluid with certain viscosity, mainly formed by water and various additives in a certain proportion, into coal seam for the purpose of improving the permeability of coal reservoir, and thus the selection of appropriate fracturing fluid is very important to improve the fracturing effect. In the study, using a medium-volatile bituminous coal as the research object, solvent extraction experiments of coal samples before and after acidification under different solvent concentrations were carried out. After the soluble low molecular weight compounds in coal were extracted and dissolved, and the differences in pore structure parameters and their mechanisms in coal were investigated by using low-temperature liquid nitrogen adsorption apparatus and capillary coalescence theory. The research results show that, after tetrahydrofuran (THF) extraction with different concentrations, the pore volume (PV) of each pore size section for raw coal decreases, and with the increase of the pore size, the decreasing PV tends to be stable. The PV of acidified coal increases significantly in all pore size ranges, especially in the range of 5 ∼ 10 nm. Compared with unacidified coals, the low-temperature nitrogen adsorption isotherm of acidified coals after extracted with different concentrations of THF were more prominent in the relative pressure of 0.8 ∼ 1.0. As THF concentration increases, the fractal dimension D of raw coal and nitrogen adsorption capacity decrease, while the fractal dimension D of acidified coal and nitrogen adsorption capacity increase and are significantly bigger than those of raw coal. The nitrogen adsorption capacity of raw coal and acidified coal shows an inverted “N” and “N” trend, respectively, and the nitrogen adsorption capacity of the residue with 50%THF extraction after acidification reaches the maximum value of 1.47 cm3/g. This study suggests that adding a certain proportion of organic solvent (THF) and acid into fracturing fluids can be beneficial to improve reservoir porosity and thus increasing gas production.

Elemental composition of dispersed vitrinite in marine Jurassic source rocks of the Vulcan Sub-basin, Australia: Implications for vitrinite reflectance suppression

The vast majority of petroleum exploration wells in the offshore basins of Western Australia bottom in Jurassic sedimentary rocks for which vitrinite reflectance results commonly appear to be anomalously low. Light element electron probe microanalysis (EPMA) of dispersed vitrinites in five samples of marine, Jurassic, potential source rocks from three petroleum exploration wells drilled in the Vulcan Sub-basin, Timor Sea, enables better understandings of this problem. The elemental abundance of carbon, oxygen, nitrogen, sulphur, aluminium and silicon were measured, and hydrogen content was calculated by difference. The EPMA method was validated by comparison of microprobe results for vitrinite in an Australian, Permian, medium volatile bituminous coal, with those determined by conventional elemental analysis according to the Australian ‘standard method’. Results on the Vulcan Sub-basin samples show that hydrogen contents of the Jurassic vitrinites are anomalously high, plotting as ‘type II’ ‘oil prone’ organic matter, on a van Krevelen-type diagram (atomic H/C vs O/C), a region normally associated with liptinite macerals. Implications of the EPMA results were investigated using fluorescence alteration of multiple macerals (FAMM) analyses, a laser-based technique that enables determination of the degree of vitrinite reflectance suppression. The elemental analyses, together with associated optical microscopy, confirm the occurrence of vitrinite having suppressed reflectance in marine Jurassic rocks of the Vulcan Sub-basin, which has important consequences for petroleum exploration if using vitrinite reflectance data in modelling thermal maturation and petroleum generation. In addition, the perhydrous vitrinites themselves may have considerably more petroleum generation potential than previously thought.

Dynamic Evolution of Nanoscale Pores of Different Rank Coals Under Solvent Extraction

During the coalification process, coalbed methane (CBM) is formed and mainly adsorbed in the pores of coal. Pore structure evolution is critical to CBM adsorption/desorption and extraction. This paper puts forward two parameters, namely the variety degree x and variety gene σ, for characterizing pore structure through mercury injection tests. Then, under extraction with different solvents, the dynamic evolution characteristics of nanoscale pores are addressed and quantified by taking four different rank coals (lignite, medium-volatile bituminous coal, low-rank anthracite and mediumrank anthracite) from different coal mines of China as the study object. The results indicate that the content of meso- and macropores after solvent extraction is much larger, but that there is no obvious law with the content of transition pores and micropores in the size range of 50-7.2 nm, according to the basic data sets of specific surface area (SSA) and pore volume (PV) of all coal samples. This phenomenon can be explained by the pore increase and expansion effects in nanoscale pores during solvent extraction. Generally, with the increasing of the solvent extraction degree, the difference in variety degree x with respect to the total PV and total SSA of different coals shows a significant decreasing trend, which expresses a homogeneous development in the change in pore structure. In regard to different solvents, benzene mainly causes pore expansion in meso- and macropores, and CS₂ has a great effect on micropores. Whereas acetone plays an important role in mesopores and transition pores with pore expansion, THF has various effects on different size pores. Further study with higher variety gene σ values shows that the total PV mainly depends on the change in the absolute content of meso- and macropores. While the change in the absolute content of transition pores and micropores (less than 50 nm) has a great influence on the total SSA. As the extraction degree increases, the influence of the transition pores and micropores on the total PV is increased, and then, the content of meso- and macropores also plays an important role on the total SSA. However, this effect is highly different for raw coals of different ranks.

Enrichment of V in Late Permian coals in Gemudi Mine, Western Guizhou, SW China

This paper reports on the petrological and geochemical compositions of K9 and K4 coals in the Late Permian Longtan Formation in the Gemudi Mine, which is located in the western Guizhou, southwest (SW) China. Critical metal concentrations have not been reported and there is a significant difference in the V concentration between the lower part and the upper part in the K9 coal of Gemudi Mine. Thus, it is a good research object of the enrichment mechanism of V. The studied coals are medium volatile bituminous coals that are characterized by a medium–high ash yield (21.7% and 37.7% on average, respectively) and a low sulfur content (0.81% and 0.18% on average, respectively). Vitrinite is the major maceral group in both coals, and collotelinite and collodetrinite contribute the most to it. Clay minerals (mainly kaolinite, illite, and illite/smectite mixed) are the majority of the minerals, quartz, carbonite minerals and pyrite are also found in the coal samples. Correspondingly, SiO2 and Al2O3 are the major components in ash, and both of them are highly correlated with the ash yield. Vanadium (213 μg/g on average) is the single enriched element in K9 coal, and it is also enriched in K4 coal. Vanadium is significantly enriched in the lower part of K9 coal, but it is depleted in the upper portion. A correlation analysis indicated that V in K9 coal mainly has an organic association, and it is positively related to telinite. Whereas, the cell and crack filling chlorite is likely to be the predominant occurrence mineral of V. Terrigenous detritus from the Emeishan basalt in the Kangdian Upland represents main origin of V in Gemudi coals, and hydrothermal fluids reformed some part of V in the K9 coal. The reducing depositional environment provides the preservation conditions as well.

A Predictive Model for the Anisotropy Index of Semi-Coke Derived from the Properties of Colombia's Eastern Cordillera Coals

This study developed a theoretical model for the determination of the Coke Anisotropy Quotient (CAQ) of semi-coke from the properties of its precursor coal. This is an useful parameter to define the resistance and reactivity of semi-coke in the blast furnace. For 36 semi-coke samples, a textural analysis was performed alongside a fluidity test to determine the real CAQ. The main textures observed were: isotropic and circular for high volatile bituminous coals (HVB); lenticular and fine ribbons for the medium volatile bituminous coals (MVB); and medium and thick ribbons for the low volatile bituminous coals (LVB). The CAQ varied in a range from 1 to 11. A principal component analysis (PCA) and multiple regression allowed to discriminated the importance of certain coal properties, in determining the CAQ to be recognized and to estimate parameters of the mathematical model. The statistical analysis suggested that CAQ can be best predicted from the fluidity, volatile matter, and Ro of the parent coals. The veracity of this model result was then tested using a second dataset from Poland. This work optimizes the usefulness of standard datasets in the prediction of CAQ's offering a means of quality control that could be implemented in Colombian coke production.

Quantification of pore modification in coals due to pulverization using synchrotron small angle X-ray scattering

Small angle X-ray scattering (SAXS) has been widely employed to characterize the pore structure of coal and other geomaterials. However, in the many previous experimental investigations by SAXS, the probed samples were not standardized in terms of shape and particle size, even for the same geomaterial. The influence of pulverization on the pore structure of coal is generally ignored by the researchers using SAXS for structure characterization. In this study, SAXS is used to investigate the effect of pulverizing on pore modification of virgin coal. Two kinds of coal with different ranks were selected and pulverized for SAXS measurements. Both powder samples (five particle size fractions) obtained by grinding and slice samples were investigated. The results show that the nano-pore structure of coal has been significantly modified due to pulverization. The sample pore volume per unit mass increases with the decrease of sample particle size. Pulverizing the slice sample into the minimum particle sample particle size of 0.075–0.125 mm leads to an increase in the pore volume per unit mass of coal by 39.53% and 18.29% for tested medium volatile bituminous coal and anthracite, respectively. Pulverization can reduce the volume of smaller pores (<20 nm) and increase the volume of larger pores (>20 nm). After grinding the original sample into the minimum particle size of 0.075–0.125 mm, the fractal dimension of the tested medium volatile bituminous coal and anthracite decreased by 0.266 and 0.179, respectively. Surface fractal dimension of pore decreases with the reduction in coal particle size. In the case of the powder coal sample, the increase in pore volume (especially for pore greater than 20 nm) and the reduction of fractal dimension are beneficial to the diffusion of gas in coal and promoting the desorption of residual gas. This study may provide a quantitative insight into the effect of pulverization on pore structure of coal sample. Moreover, it is of great significance for understanding the mechanism of coalbed methane storage and migration and is helpful for the selection of the sample size in SAXS experiments.

Investigating the effects of broad ion beam milling to sedimentary organic matter: Surface flattening or heat-induced aromatization and condensation?

Previous work has proposed transfer of kinetic heat energy from low-energy broad ion beam (BIB) milling causes thermal alteration of sedimentary organic matter, resulting in increases of organic matter reflectance. Whereas, other studies have suggested the organic matter reflectance increase from BIB milling is due to decreased surface roughness. To test if reflectance increases to sedimentary organic matter (vitrinite) caused by BIB milling were related to molecular aromatization and condensation, Raman and Fourier transform infrared (FTIR) spectroscopies were used to evaluate potential compositional changes in the same vitrinite locations pre- and post-BIB milling. The same locations also were examined by atomic force microscopy (AFM) to determine topographic changes caused by BIB milling (as quantified by the areal root-mean-square roughness parameter Sq). Samples consisted of four medium volatile bituminous coals. A non-aggressive BIB milling approach was used with conditions of 5 min, 4 keV, 15°incline, 360° rotation at 25 rpm and 100% focus (1.5 kV discharge; ∼100 μA). This gentle BIB milling caused vitrinite reflectance (VRo) increases of 12 to 36% of the original values determined optically before milling (average 26% increase). When molecular proxies from FTIR (A- and C-factor, branching ratio) were plotted against each other for the same vitrinite locations pre- and post-milling, mean data points for each sample generally lie within error of a 1:1 line. Likewise, mean Raman thermal proxy [full-width half maximum of G-band (G-FWHM), Raman band separation (RBS) and D1/G band intensity ratio] values were similar for pre- and post-milled locations, also plotting within error of a 1:1 line. AFM confirms the majority (24 of 36) of pre- and post-ion milled surface pairs were smoother (lower Sq values) after BIB milling. These results are interpreted to indicate VRo increase induced by the gentle BIB milling conditions used in this study is an effect of decreased diffuse reflectance due to flatter surfaces, causing more photons to reflect directly back to the detector. Little evidence was observed for molecular aromatization and condensation of vitrinite molecules following BIB milling (with the conditions used). The presence of milling-induced artifacts, including differential milling effects dependent on location and the development of self-organized patterned structures, indicate much work remains in standardization of BIB milling before its promulgation as a routine sample preparation technique for organic petrography. These results provide better understanding of anthropogenic-induced changes to geological samples caused by the now widespread adoption of BIB milling as a disruptive innovation in sample preparation.

CH4, CO2, N2 diffusion in Bowen Basin (Australia) coal: relationship between sorption kinetics of coal core and crushed coal particles

To improve the general understanding of diffusive processes in coal and investigate if representative reservoir properties can be estimated from measurements on crushed coal particles, adsorption and desorption experiments on crushed samples and large, intact core samples are carried out. Diffusion properties are analysed for methane, carbon dioxide and nitrogen up to a pressure of 10 MPa at a temperature of 35 °C. The samples are a low volatile bituminous coal and a medium volatile bituminous coal from Australia's Bowen Basin.A bidisperse model (a simplified version of the Ruckenstein model for micro-pore dominated flow), characterised by a ‘fast’ and a ‘slow’ fraction, is required to describe the observed diffusion behaviour. Results from the modelling show that effective diffusivities of the core samples are typically an order of magnitude lower than for the crushed coals, and the ‘slow’ effective diffusivities are typically at least one order of magnitude lower than the corresponding ‘fast’ effective diffusivities. A pressure dependency of the effective diffusivities is noted but an explicit relationship with gas content could not be established. This may be due to the experimental set-up, which does not eliminate the effect of differential pressure.Calculation of the diffusion path length for the coal core reveals that the diffusion path length in coal may not be constant but decreases with increasing matrix gas content as a result of coal swelling. Furthermore, there is a distinct difference between the diffusion paths derived from the ‘fast’ and the ‘slow’ fractions; the ‘slow’ diffusion path of the coal core is 100s of microns shorter than the ‘fast’ diffusion path. The faster diffusion associated with the longer diffusion path is interpreted to relate to micro-porosity, while slower diffusion via the shorter diffusion path is interpreted to relate to macro-porosity.