•Three maceral-rich fractions were obtained by maceral float-and-sink method.•Pyrolysis behavior of the separated maceral-rich fractions were evaluated.•The tar yield from pyrolysis of ...vitrinite-enriched fraction increased to 15.68 %.•The mechanism of free radical fragments in tar formation was further explored.
An ideal way of clean and efficient utilization of low-rank coal by separating it into different maceral-rich fractions and then choose the appropriate utilizing method based on its composition and structure was proposed. In this paper, the coal sample was successfully separated into vitrinite-enriched coal (VC), inertinite-enriched coal (IC) and mineral-enriched coal (MC) by macro maceral separation method, and the structure and pyrolysis characteristics of different maceral-rich fractions were studied. The XRD analysis revealed that VC exhibited a higher degree of structural disorder, whereas the IC displayed greater aromaticity and graphitization. Raman analysis showed a higher proportion of amorphous carbon structure in VC, indicative of abundant side-chain active components. Conversely, IC contained more ordered aromatic rings and a higher degree of aromatic condensation. FTIR analysis confirmed that VC contained the highest aliphatic hydrocarbon content and aliphatic long-chain structures, while IC showed a lower aliphatic/aromatic ratio. The pyrolysis of different maceral-rich fractions indicated that VC pyrolysis produced the largest amount of tar (15.68 %), which was 4.37 % higher than that of the raw coal’s 11.31 %, and contained a large number of aliphatic hydrocarbons and phenols. In contrast, the tar yield of IC pyrolysis was 1.08 % lower than that of raw coal, and the tar was composed of more polycyclic aromatic hydrocarbons such as biphenyl, naphthalene and benzene series. The maceral macro separation of low-rank coal effectively realizes the separation and enrichment of different type of components in coal, which was beneficial to its subsequent cascade utilization.
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•Chemical structures of three two-dimensional coal planes were investigated.•The results of Raman mapping and petrography analysis were in-situ coupled.•Good self-correlations between ...Raman spectral parameters were found.•Coal macerals show different chemical structure characteristics in micro-scale.•High resolution chemical imaging of coal in micro-scale was realized.
Raman mapping and petrography analysis of three two-dimensional planes including typical coal macerals in a lignite were done and coupled. The self-correlations between Raman spectral parameters and the relationship between Raman spectral parameters and random reflectivity (Rf) of coal maceral particles were set up. The results indicate that the area ratio of D band to G band (AD/AG) and intensity ratio of D band to G band (ID/IG) should not be equal, and they were not well related to Rf of coal maceral particles. Good self-correlations between full width at half maximum intensity of G band (G FWHM), the total area of first-order Raman spectrum (SAll) and fluorescence interference degree defined as drift coefficient α were found. G FWHM, SAll and α are also well related to Rf and can act as good indicators for chemical structure characteristics of coal maceral particles. With the increase of Rf, the relative amount of polyolefin, small aromatic rings, C–H, C-O, O–H etc. substitutional groups in vitrinite and liptinite decreases drastically, while the increase of aromatic ring size mainly takes place in inertinite. Chemical imaging of two-dimensional coal planes at a very high resolution was realized by drift coefficient α, and reproduction of the distribution of coal macerals in micro-scale is reasonable. The Raman mapping technology developed can be further used to deeply study the chemical structures of detailed coal macerals. This study can be further extended for rapid identification and detection of coal macerals by micro-Raman spectroscopy.
Industrial applications of coal rely on understanding its macromolecular structure, which is primarily controlled by coal type and rank. The present study assessed five (5) samples from different ...collieries extracting coal from the No. 4 Seam of the Highveld Coalfield and their float products, produced at relative densities (RD) of 1.7 and 1.9 g/cm3. The aim was to assess changes in maceral composition and coal quality following the density fractionation, and to use Raman Spectroscopy to compare differences in macromolecular structures between the parent samples and the float products. Raman parameters were also determined for specific macerals, i.e., semifusinite and collotelinite. Mean random vitrinite reflectance (%RoV) values for the studied coals range between 0.57 and 0.60% (medium rank D/C bituminous) and the parent coals are inertinite-rich (70.3 to 88.7 vol% mmf), enriched in semifusinite and inertodetrinite. Following density fractionation, reactive macerals (a combination of liptinite, vitrinite, and reactive semifusinite) are enriched in the float products (designated by “F”), specifically in the products obtained at the 1.7 RD. In comparison, the proportion of inert macerals is higher in the F1.9 samples. These differences in maceral composition are reflected in the Raman spectra and parameters. Although the G and D1 bands for the parent coals and F1.9 samples are similar, these bands are narrower than for the F1.7 samples, indicative of greater aromaticity. The G FWHM values for the F1.9 samples are comparable to those for the parent coal samples, and lower than for the F1.7 samples. This reflects larger differences in maceral composition between the parent coals and the F1.7 samples. In contrast, the D1 FWHM values for the float products, particularly the F1.7 samples, are slightly higher than the parent coals, reflecting a disordered aromatic character mainly related to the presence of aliphatic chains. The Raman spectra for the F1.7 samples are more like that for collotelinite. In contrast, the Raman spectra and parameters (G and D1 FWHM) for the F1.9 samples are more comparable to semifusinite. Thus, the increased aliphaticity for the F1.7 samples is attributed to the relative enrichment of reactive macerals, whereas higher aromaticity for the F1.9 samples reflects a larger proportion of inert macerals. Raman spectroscopy expanded on the petrographic data by interrogating the macromolecular structure of the isorank Highveld coals and their float products. This may assist in predicting the behaviour of the coals during industrial applications (i.e., liquefaction, gasification, combustion, and carbon fibre production).
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•An effective metric is proposed to quantify the maceral composition of coal.•The task of maceral group identification is defined as a semantic segmentation task.•The proposed ...end-to-end way bypasses the steps limiting the traditional strategies.
Correct identification macerals is important for analyzing petrographic characteristics of coal. Traditional methods based on manual measurement are time-consuming and physically demanding. Thus, automation of this process is highly desirable. However, currently available machine learning-based methods mostly depend on handcrafted features, and do not work in analyzing complex samples. There is still much room to enhance the robustness and generalization ability for these automatic methods. To address these issues, we interpret the task of maceral group identification as a semantic segmentation task. In this study, we design an improved U-net model with enhanced attention gates, and evaluate the performance with various encoder backbones. Experimental results on 89 photomicrographs indicate that the proposed method achieves the state-of-the-art segmentation accuracy of 91.56%. The model achieves mean absolute errors of 5.95%, 4.43% and 2.19% for the predicted proportion of vitrinite, inertinite and liptinite, respectively. It shows that the improved U-net model has significant potential for automating accurate identification of maceral groups.
•The density of maceral concentrate reflects the volatile release of 20–40 µm particles at 1550 °C.•The Q-factor of the lowest density vitrinite concentrates approached the theoretical maximum, with ...samples derived from low volatile coals producing Q-factors over 5.•Development of graphitic nature in pyrolysis char is a function of the maceral concentrates density.•With the addition of a small nozzle, a TIG welder can be converted into a gas preheater.
The impact of macerals and their pyrolysis behaviour on pulverized coal injection (PCI) combustion in blast furnaces is unclear. At present, a coal’s combustibility is considered to be related to its volatile content, as measured by the proximate analysis, alone, even though it is known that some coals’ performances do not follow this trend Elliott et al. (2013) . The impact of coal macerals, particularly vitrinite, on volatile release, was therefore assessed by pyrolysing maceral concentrates in a drop tube furnace with a preheated gas. Maceral concentrates produced from 5 coals with a range of rank were used. The density of the maceral concentrates was found to influence volatile release under elevated heating rates, at 1550 °C. The graphitic nature of the resulting char was also found to depend on the density of the maceral concentrate from which the char was produced.
•Structural features of residue char from maceral concentrate gasification were revealed.•The shrinkage ability of inertinite char residual is stronger than that of vitrinite.•The fresh vitrinite ...char has lower order degree and more active sites.•The amount of vitrinite residual char active sites decreases rapidly during gasification.
Gasification fine slag contains a high content of carbon, which causes waste of resources and environmental hazards. In essence, fine slag is a comprehensive reflection of the separate gasification of various macerals in coal. In this study, different macerals concentrates were firstly prepared from Yangchangwan (YCW) and Meihuajing coal (MHJ). The structure and pyrolysis characteristics of different macerals as well as the morphology and molecular structure of gasification residue carbon at different conversion levels were then investigated by a series of characterization techniques. The results show that the aromatic degree of inertinite concentrates of both coals is greater than that of vitrinite. During the active pyrolysis stage of 200–600 °C, the weight loss rate of vitrinite is higher than that of inertinite, and the weight loss rate reaches maximum at about 445 °C. Maximum thermal weight loss rate of YCW and MHJ vitrinite is 1.39 and 1.43 times higher than that of inertinite. The shrinkage ability of inertinite char is stronger than that of vitrinite and the surface of inertinite residue carbon is rougher and rich in porous structures during gasification, resulting in a higher final gasification carbon conversion level. The fresh vitrinite char obtained from pyrolysis has lower order degree and more active sites. As the gasification proceeds, the content of active sites in vitrinite gasification residue carbon decreases rapidly, while inertinite remains relatively stable. This research innovatively links the properties of macerals with the structure of residue carbon, which is helpful to deepen the understanding of the correlation between coal microstructure and reactivity.
Raman spectrometry is a rapid, non-destructive alternative to conventional tools employed to assess the thermal alteration of organic matter (OM). Raman may be used to determine vitrinite reflectance ...equivalent OM maturity values for petroleum exploration, to provide temperature data for metamorphic studies, and to determine the maximum temperatures reached in fault zones. To achieve the wider utilisation of Raman, the spectrum processing method, and the positions and nomenclature of Raman bands and parameters, all need to be standardized. We assess the most widely used Raman parameters as well as the best analytical practices that have been proposed. Raman band separation and G-band full-width at half-maximum are the best parameters to estimate the maturity for rocks following diagenesis–metagenesis. For metamorphic studies, the ratios of band areas after performing deconvolution are generally used. Further work is needed on the second-order region, as well as assessing the potential of using integrated areas on the whole spectrum, to increase the calibrated temperature range of Raman parameters. Applying Raman spectroscopy on faults has potential to be able to infer both temperature and deformation processes. We propose a unified terminology for OM Raman bands and parameters that should be adopted in the future. The popular method of fitting several functions to a spectrum is generally unnecessary, as Raman parameters determined from an un-deconvoluted spectrum can track the maturity of OM. To progress the Raman application as a geothermometer a standardized approach must be developed and tested by means of an interlaboratory calibration exercise using reference materials.
Primary paleoproductivity provides basic organic matter for the formation of high-quality hydrocarbon source rock. A progressive method to quantitatively calculate paleoproductivity on the basis of ...total organic carbon (TOC) has been proposed to evaluate the contribution of primary paleoproductivity to a hydrocarbon source rock with high organic matter abundance. In this study, pyrite contents, organic maceral compositions and high-resolution sedimentation rates (SRs) were used to recover the amount of organic matter oxidation and to exclude the effect of terrestrial clastic input during the deposition of the Chang 7 sediment. Multiple calculation methods were used to quantitatively reconstruct paleoproductivity, and the results suggest that the Ordos Basin was a eutrophic lacustrine basin (approximately 2 × 104 mg C cm−2 kyr−1 to 10 × 104 mg C cm−2 kyr−1) during the Chang 7 stage compared with modern lake productivity. The paleoclimatic analysis indicates that a warm humid paleoclimate was beneficial for increasing the weathering intensity, which could have provided more nutrient inputs to the depositional environment with incoming terrestrial debris. In addition, the plate collision between the North China Block and Yangtze Block generated moderate volcanic ash that spread to the study area and provided large amounts of essential nutrients for algae blooms. Moreover, a brackish water condition promoted upward mixing of deep water, which inhibited water mass stratification and then facilitated primary paleoproductivity. In general, the Chang 7 high-quality hydrocarbon source rock is a result of increased paleoproductivity resulting from suitable paleoclimate conditions, brackish water masses and abundant essential nutrient inputs.
•The productivity is recovered after assessing oxidation and dilution of organic matter.•The productivity of Ordos Basin amount to 105 mg C cm−2 kry−1 indicating a eutrophic basin.•Paleoclimate and volcanism were the two main factors affecting high productivity.
•Three-dimensional molecular models of vitrinite and inertinite were constructed.•13C NMR show that the aromatic carbon formed the basic skeleton of two macerals.•Macerals have similar contents of ...alcohol hydroxyl, phenol hydroxyl and ether.•Combination of aliphatic carbon and oxygen in inertinite is higher than that in vitrinite.
In order to study the structural properties of coal macerals in-depth, the proximate analysis, ultimate analysis, 13C solid nuclear magnetic resonance (13C NMR), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were employed to analyze the vitrinite and inertinite properties of Shanghaimiao bituminous coal. The results show that the vitrinite contains more hydrocarbon, nitrogen and sulfur elements than the inertinite while the inertinite contains more oxygen elements than the vitrinite. The 13C NMR results show that the vitrinite has more side chains of aliphatic hydrocarbons than the inertinite while the inertinite has more aromatic rings and more oxygen-aliphatic structures than the vitrinite. The FTIR results show that the contents of alcohol hydroxyl, phenol hydroxyl and ether in the vitrinite is similar to that in the inertinite. However, the inertinite contains more carboxyl groups than the vitrinite. The XPS results show that the nitrogen element is mostly in the form of pyridine, and the sulfur element is mostly in the form of mercaptan and sulfoether in the coal. Based on the above-mentioned analysis, we constructed the molecular structure models of the vitrinite and inertinite. The molecular formula of vitrinite is C126H99O12N3S2 while the molecular formula of inertinite is C131H98O17.
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•Coal macerals were characterized by AFM both in area and aqueous.•Interaction between the montmorillonite 001 surface and silica were measured.•Chaotrope or kosmotrope properties of ...the 001 surface were proposed.•Liptinite is attractive with the artificial “kosmotropic surface”, vice versa.
In coal beneficiation, the clean coal would be easily contaminated with the super fine montmorillonite particles coating on it. This interaction between coal (hydrophobic) and montmorillonite (hydrophilic) surfaces is the interactions between the asymmetric systems. Previous studies detected the force between the montmorillonite and graphite or between the montmorillonite mounted tip and coal substrate to represent the interactions between 001 surface and coal. However, there is still lack of experimental direct measurement on the interaction between montmorillonite 001 surface and coal macerals. In this study, proposes methods for determinine the interactions between coal macerals and 001 surface of Na-, K- and Ca- montmorillonite directly by using an atomic force microscope (AFM). The results indicate that the 001 surface of Na- and Ca- montmorillonite served as the chaotropic and kosmotropic surface when it is adjacent to coal surfaces, with an attractive force and repulsive force occurring between them, respectively. The 001 surface of K-montmorillonite served as the chaotropic surface and kosmotropic surface while it is close to liptinite and inertinite, respectively. This chaotropic or kosmotropic property of the surface is determined by the coordination number of the cations and wettability of the hydrophobic surface simultaneously.
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