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Crushing mechanism plays a vital role in liberation of coal macerals (organic constituents), which aid in coke making. Due to the use of impact mills, vitrinite maceral grains shatter and participa...

Since coal washeries generate huge quantities of high-ash rejects as waste, effective utilization of coal rejects help in sustainable coal preparation. Out of different coal rejects, tailings from froth-flotation process can be a potential material for the extraction of clean coal due to its fine size, availability in the slurry form, presence of good carbon values, and better liberation properties. In the present study, three different methodologies i.e., chemical method, chemico-physical method, and physical method are explored to separate clean coal with >49.8% yield for their utilization in coke making process. The chemical method of demineralization by alkali-acid leaching shows a high clean coal yield of 65.4%; however, the alteration of vitrinite-group macerals makes it unsuitable for coke making process. Chemico-physical method of clean coal separation by hydrothermal extraction followed by density separation results in clean coal at 49.8% yield with an increase in vitrinite group macerals, which shows a positive impact on rheological and coking properties. The physical separation method by ultrafine grinding followed by density-gradient-centrifugation resulted in 58.2% of clean coal yield with coking properties similar to the clean coal obtained in conventional coal beneficiation plants. By adopting chemico-physical method and physical method of coal cleaning, the overall clean coal yield of the washery can be improved by >5.1%. Also, there is no deterioration in coke properties such as coke strength after reaction and coke reactivity index by using the prepared clean coal in coal blend.

In this study, the rotary triboelectrification separation technology is applied to the separation of macerals for low rank coal, which has not been studied by previous researchers. The effects of a...

In this paper, the enhanced gravity separation of maceral components was studied based on the characteristics of maceral components for low-rank coal from Shendong. Vitrinite and ash content were o...

The liberation characteristics of long flame coal from the Chinese Shenhua were studied by comparison of ball grinding and rod grinding. First, the effects of grinding time on maceral liberation un...

Organic matter in black shales is composed of oil-prone macerals, such as alginite and amorphous organic matter (AOM), and non-oil-prone macerals, including vitrinite and inertinite. Organic matter...

As part of a study to determine the origin of oil and gas in the Berea Sandstone in northeastern Kentucky and southeastern Ohio, 158 samples of organic-rich shale from the Upper Devonian Olentangy and Ohio Shales and the Lower Mississippian Sunbury Shale, collectively referred to as the “black shale,” were collected and analyzed from 12 cores. The samples were analyzed for total organic carbon (TOC) content, organic petrography, and programmed pyrolysis. Previously acquired analytical data for 11 samples from 2 additional wells in eastern Kentucky were also used. Most of the samples were organic rich (>5 wt. % TOC), high in sulfur (>2.0 wt. %), and dominated by liptinite macerals. The vitrinite reflectance (VRo) and equivalent vitrinite reflectance (VReq) values, calculated from bitumen reflectance (BRo) measurements, were found to be in close agreement. The calculated reflectance values from programmed pyrolysis temperature at which the maximum release of hydrocarbons occurs (Tmax) showed better agreement with measured VRo after Tmax was corrected for excessive hydrogen index values for several samples. Thermal maturation parameters were found to increase in a northwest–southeast direction, paralleling an increase in black shale thickness and depth of burial. The thermal maturity proxies indicate the northwestern part of the study area to be more thermally mature than previously indicated. Geochemical and biomarker data from Berea oils indicate migration of oil from more thermally mature to less thermally mature areas. As such, the occurrence of petroleum liquids in the Berea Sandstone cannot be predicted directly from conventional thermal maturity proxies (Tmax, VRo, and BRo) because these methods do not account for migrated petroleum.

The concentrations and distributions of industrially valuable trace elements associated with germanium in the coals of the Spetsugli section of the Pavlovsk brown coal deposit in Primorskii krai was studied using mass spectrometry and laser microanalysis. The concentrations of a number of metals in traditional types of ores at a minimum industrial level were established. Geochemical associations of industrially valuable metals and other impurity elements were identified. Maximum concentrations of many trace elements in low-ash coals were noted. The distribution of a number of trace impurity elements in the coal matter and the macerals of coals was studied, and conclusions on the genesis of trace elements were drawn.

Pores associated with organic matter are well known to play a significant role in shale gas capacities. However, an extremely high heterogeneity of organic pores often impacts our evaluation of reservoir quality. In this work, we analyze the formation mechanisms of the heterogeneity based on positioning observation method using a combination of field emission scanning electron microscopy and optical microscopy. These analyses were conducted on six lacustrine shale samples at the gas window in the Lower Cretaceous Shahezi shale, which is located in the Changling Fault Depression of Songliao Basin. The results reveal that organic pore heterogeneity is mainly attributed to four controlling factors. (a) One is different hydrocarbon generation potentials among different macerals. The degree of pore development from high to low is solid bitumen, vitrinite, and inertinite. The content of carbon by the weight percentage of solid bitumen, vitrinite, and inertinite is in the opposite order, which reflects that the different hydrocarbon generation potential of each maceral is the dominant factor. (b) Another one is the remnants of primary pores in organic matter with plant cell structures. Well preserved telinite, fusinite, and semi-fusinite show cell structures, and the cells that are not completely compressed or not fully filled retain the original residual pores. (c) The third one is evolutional differences of individual solid bitumen. Not all solid bitumen developed organic pores, which is mainly attributed to the difference of solid bitumen reflectance in different solid bitumen particles. The solid bitumen reflectance of porous solid bitumen is mostly distributed between 1.6% and 2.0%, in which oil cracking to gas is dominant and porous residual solid bitumen subsequently forms. The solid bitumen reflectance of non-porous solid bitumen peaks in 1.2–1.6%, which is in the stage of kerogen transformation and oil generation with rare pore development. (d) The last one is the catalysis of clay minerals. All organoclay complexes develop abundant sponge-like pores due to catalysis during the transformation from smectite to illite. A high content of illite in the mixed layers I/S increases the specific catalytic activities, promoting the organic matter and solid bitumen to further generate hydrocarbon and form pores. Most organic–inorganic mixtures develop pores also because of catalysis from inorganic minerals.

New organic–geochemical investigations of the Eocene Cambay Shale (Cambay Basin, India) from five wells and an open-cast lignite mine reveal that the total organic carbon ranges from 0.37 to 10.68 wt. %, with an average of 2.43 wt. %. The pseudo–Van Krevelen diagram, hydrogen index versus the maximum pyrolysis yield temperature (Tmax) crossplot, and the visual kerogen assessment of the Cambay Shale indicate the dominance of type III kerogen, with some well samples showing mixed type III and II kerogen. The vitrinite reflectance values range between 0.46% and 0.7%, with Tmax values ranging from 387°C to 441°C and are consistent with an immature to early oil generation stage. The dominance of vitrinite macerals and high pristane–phytane (Pr/Ph) ratios (>6) of the well samples indicate an oxic to dysoxic depositional environment, whereas the presence of Botryococcus braunii and low Pr/Ph ratios (

The coking behavior of coal is an important facet in utilization of coal in metallurgy and in other industries. The carbonization behavior of coal mainly depends on coal rank, petrographic composition, ultimate composition and rheology of coal. Coal petrography has become very useful technique for establishment between formulation of coal blend composition and coke quality prediction. It is generally established that blend containing optimal reactives produces the coke of maximum strength. The coking properties of coal not depend only on the macerals composition, but also on the way in which the macerals are distributed among one another, forming preferential associations called microlithotypes. The measurements of relative proportion of microlithotypes are called microlithotype analysis. In present work, distribution of macerals (microlithotype) in coal samples were studied and correlated with the coke quality. Beneficiation by wet method were carried out (only indigenous coal) by washing media of specific gravity 1.30 to 1.40 to achieve

The concentration and distribution of germanium in coals from the Spetsugli section of the Pavlovsk brown coal deposit in Primorskii krai was studied using mass spectrometry and laser microanalysis. The maximum concentrations of germanium in low-ash coals were established. The distribution of germanium in the vitrinite group macerals of coals and in mineral impurities was studied. A conclusion on the accumulation of germanium in coals at the stage of ancient peat accumulation was made.

The Woodford Shale and the overlying Mississippian limestone constitute one of the prolific unconventional hydrocarbon targets in central and northern Oklahoma. With the advantage of horizontal drilling technology, Devonian and Mississippian mudrocks have become important topics for research to understand the petroleum system fundamentals, including sources of hydrocarbons for these unconventional reservoirs. In this study, organic geochemistry and petrography of Mississippian mudrocks and the Woodford Shale were examined. The key study core is from Lincoln County, Oklahoma, representing the Mississippian mudstone and Woodford Shale. Three additional cores in Payne County and one core from Logan County were studied. Core samples were assessed for hydrocarbon generation potential using Rock-Eval pyrolysis together with biomarker analysis using gas chromatography–mass spectrometry. Organic and thin-section petrography was performed to identify maceral composition and develop a sedimentary facies classification. Mudrocks within the Mississippian section exhibited adequate organic richness for petroleum generation, thereby augmenting the established generation potential of the Woodford Shale. Several unique Mississippian biomarkers were identified, including diterpenoids and extended tricyclic terpanes. Macerals of the Mississippian rocks exhibit dominance of lamalginite and bituminite, whereas Woodford macerals are high in telalginite. Based on the organic matter composition and sedimentology, six facies were identified within the Mississippian mudrocks. Furthermore, based on organic richness and key biomarker ratios, the Mississippian succession is divided into three units. Organic and sedimentological signatures suggest a shoaling-upward succession from the Woodford Shale to the Mississippian carbonate.

—Coal beds and coal sheets in oil fields consist of coalified material, with similarities and differences due to the conditions in which it was formed. Coal petrography is widely used to assess the properties of coal, and IR spectroscopy is being actively introduced. In tests, the vitrinite reflection coefficient and maceral composition are measured by microscopy and IR spectroscopy for core samples of coal and kerogens. Comparison of the results shows that IR spectroscopy may be used to study the genetic properties of kerogens.

Organic liquids are used to prepare the density medium to produce clean coal composites for coal quality and coking test evaluations during the coal exploration stage. Perchloroethylene (PCE) is co...

The amount of coking coal in all over the world is scarce while it is an essential commodity for steel making; in an economical way, no alternative of coking coal is found out till now. Though, so ...

The potential of occurrence of coal self-heating is controlled by various properties, both intrinsic and extrinsic. In the intrinsic properties, the maceral content has an important role in influen...

This study investigates the role of zooclasts in the bulk organic matter composition, kerogen type, and hydrocarbon generation potential of the lower Paleozoic marine Alum shale in Baltoscandia, northwestern Europe. The results show that graptolite periderm is composed of non-granular cuticles and granular filling. The graptolite cuticle is non-fluorescing and has a well-polishing measurable surface, while the graptolite granular fraction is semi-translucent and has brownish fluorescence, suggesting remaining hydrocarbon generation potential. The graptolite granular fraction shows similar optical characteristics to fluorescing diagenetic solid bitumen. Both the graptolite granular fraction and diagenetic solid bitumen have low intensity yellow to brown fluorescence and contribute to generative potential (Rock-Eval S2). The sum of semi-quantitative zooclastic cuticle (non-granular graptolite cuticle, chitinozoan cuticle, and vitrinite-like) and diagenetic solid bitumen content, obtained from maceral point-counting, correlates with the non-generative organic carbon content. Enrichment of zooclastic cuticle in the samples is displayed as enrichment of inert organic carbon, and hence bulk geochemical kerogen of type III. This refractory carbon-rich maceral enrichment results represents autochthonous ‘refractory organic carbon dilution’ and will lead to Hydrocarbon Index (HI) underestimation. Confined hydrous pyrolysis was used to compare the hydrocarbon generation process of a zooclastic cuticle-lean sample (0.2 vol%) and a zooclastic cuticle-rich (1.6 vol%) sample. Results indicate that there are four stages of hydrocarbon generation in the artificial maturation of unconventional source rock of the Alum Shale. The zooclastic cuticle-lean sample has higher hydrocarbon generation potential and more oil-prone than the zooclastic cuticle-rich sample, which is gas-prone and generates more CO2. This difference in hydrocarbon generation is attributed to differences in the organic constituent composition.

The overmature Precambrian to Lower Paleozoic marine shales from China contain relatively simple organic matter (OM) composition, which is dominated by in-source solid bitumen (i.e., solid bitumen in the hydrocarbon source rocks). The thermal evolution behavior of the original OM and the determination of thermal maturity in the Precambrian to Cambrian marine shales have been challenging for decades. The vitrinite-like maceral (VLM) is widely present in these marine shales, and its origin is still unknown. To address these issues, the immature Proterozoic Xiamaling shales from China and the immature Cambrian Alum shales from Sweden, and a Chinese immature Carboniferous coal were heat-treated at temperature range of 300 ◦C to 550 ◦C. The carbonized residue of the artificially matured samples was examined for their morphological and reflectance variation, and the results were compared with data on the other overmature natural shales from China and Sweden. OM components are similar in the Xiamaling and Alum immature oil shales, consisting of filamentous algae, matrix bituminite, bituminite, VLM and liptodetrinite, and rare thucholites are present in the Xiamaling shales. The algal-derived OM decomposed gradually due to hydrocarbon generation at 300–350 ◦C. OM is mainly composed of the in-source solid bitumen in the artificially heated shales after 350 ◦C, similar to the overmature Precambrian to Cambrian natural shales, and the in-source solid bitumen gradually loses its mass with increasing thermal maturity. The in-source solid bitumen is derived from the thermal cracking of the retained oil or the direct conversion of algal-derived liptinite macerals (e.g., the bituminite) or their mixture. VLM in the Xiamaling oil shales can not be observed after 350 ◦C, but VLM is still present in the Alum oil shales. It can be inferred that there is a different source of VLM in these shales, and VLM in the Xiamaling oil shales contains more volatile material. The VLM in the Xiamaling shales may be biodegradation products of liptinites under anoxic environments. The origin of VLM in the Cambrian Alum shales requires further study to be verified, although it is certain that graptolites are not its sources. The reflectance of in-source solid bitumen (SBRo) increases with heat-treated temperature in both the Xiamaling shales and the Alum shales, but at different rates, which may be due to the difference of the original kerogen composition in these shales. VLM reflectance (VLMRo) and SBRo in sections perpendicular to bedding can be used to determine the maturation level of the Precambrian-Cambrian sediments. Their relation to equivalent vitrinite reflectance (EqVRo) can be expressed by the following equations: EqVRo = 1.07 × VLMRo – 0.18, EqVRo = 0.87 × SBRo + 0.25 (in the Precambrian sediments) and EqVRo = 1.15 × SBRo + 0.01 (in the Cambrian sediments). This work was supported by the National Natural Science Foundation of China (No. 41773031), the National Key Research and Development Program of China (No. 2017YFC0603102) and the Science Foundation of China University of Petroleum, Beijing (No. 2462020YXZZ021 and 2462021QNXZ001). One of the co-authors (V.S.) wishes to acknowledge the support of OP RDE, MEYS Czech Republic (Reg. No. CZ.02.1.01/0.0/0.0/16_019/0000728), which enabled him to contribute to this study

The rare earth elements (REE) possess a beneficial combination of chemical and physical properties, making them valuable for most advanced branches of engineering and technology. Alternative sources of REE are desirable due to limited reserves of conventional REE containing minerals over the world combined with disproportionate supply over demand in the commodity markets. This study investigated the occurrence of REE and carbon nanotubes (CNTs) in Cretaceous Nigerian coals for prospective industrial applications. Results show that the coals’ crystalline mineral matter comprises quartz, kaolinite, and illite with minor quantities of feldspar, hematite, magnetite, calcite, dolomite, which indicate detrital mineral origins. Elemental relationships (such as Al2O3/TiO2, Cr/Th vs. Sc/Th, and Co/Th vs. La/Sc) suggest sediment-source regions with mafic, intermediate or felsic compositions. REE are either strongly fractionated or characterized by light-enrichment along with outlook coefficient (Coutl) values that suggest the coals are prospective substitute sources for REE and yttrium (REY) recovery. Several minerals including jarosite, goethite, epsomite, ferrohexahydrite, natrojarosite, rozenite, and gypsum were detected in trace amounts. REE mineral phases were not identified but only amorphous phases containing Ce, La, Nd, Th, Pr, Sm, Gd, Tb, Dy, Ho, and Hf. Maceral composition (high vitrinite), presence of iron-containing minerals (hematite and magnetite), high carbon contents, reduced volatile matter and low ash content favoured the formation of naturally occurring multi-walled carbon nanotube (MWCNTs) structures in Maiganga (MGA) coal. Hence, the present study is the first scientific report on the naturally occurring REEs and MWC nanophases in Cretaceous coals from the Benue Trough.

Measuring the degree of organic matter (OM) alteration caused by uranium (U) irradiation is important in the effective evaluation of the hydrocarbon potential and thermal maturity of U-rich source rocks. This study investigates OM alteration in the Baltoscandian U-rich, lower Paleozoic Alum shale obtained from three research wells in the thermally immature parts of eastern Sweden and western Estonia. The results show a marked increase in the proportion of refractory, non-generative organic carbon (NGOC) in the U-rich shale. Fluorescence spectrometry of unicellular alginites and lamalginites show a reduction of up to 95.6% in fluorescence relative intensity (RI) with increase in U content from 29 to 401 ppm. Fluorescence spectra of the liptinites exhibit a marked “red shift” as expressed by increase in red(R)/green(G) quotients. This change in fluorescence properties of the liptinites is associated with up to 77.6% decrease in hydrogen index (HI) and hence loss of hydrocarbon generation potential. Furthermore, organic molecules show significant loss of aromatic moieties as well as aliphatic constituents resulting in a more condensed macromolecular structure. The measured random reflectance of solid bitumen (BRo) appears to be significantly elevated in micro scale proximity to the U-containing minerals. The heterogeneous distribution of U-containing minerals and the contact with solid bitumen attributes to the wider range of BRo values and lead to the overall increase in mean BRo in samples with high U contents. In contrast, Ro values of zooclast macerals (GRo, e.g., graptolite, chitinozoans and vitrinite-like fragments) appear to be less influenced by U irradiation and hence are a more reliable maturity indicator in U- rich lower Paleozoic shales.

Shales are of significant interest as reservoirs, seals and overburden in petroleum exploration and production, geological storage of CO2 and in the nuclear waste industry. Their properties and microstructure are difficult to measure and image and as such, there are still considerable gaps in our understanding of shale behaviour. The advent of more advanced and quantitative imaging methods along with novel sample preparation techniques including synchrotron imaging and K-edge subtraction with a contrast fluid, scanning (SEM) and transmission electron microscopy (TEM), have combined to allow the resolution of pores in the matrix and the organic matter in gas shales down to the nanometre scale. Textural quantification methods include neutron diffraction to quantify clay fabric alignment in siliciclastic shales as well as stress-dependent calcite c-axis orientation in carbonate-rich gas shales. The contents of the pores are also critical to the assessment of the preservation state of shales as well as the degree of water/gas saturation in resource shales. Combinations of dielectric analysis and 2 and 23 MHz nuclear magnetic resonance (NMR) measurements in siliciclastic and carbonate-rich gas shales can resolve not only the location of water, but also the interaction between water and mineral/organic surfaces in addition to the water and oil content. The organic content of shales is of particular interest in unconventional resources and this has driven application of Fourier transform infra-red (FTIR), to distinguish both mineral and organic maceral components in gas shales and Raman spectroscopy, which is increasingly used for organic matter characterisation in high maturity shales. Ultimately, shales are extremely complex nano-composite materials which require the application of multiple techniques to help determine their bulk physical and flow properties as well as factors controlling fabric and pore orientations and structure.

Maceral compositions take a great role in coalbed methane adsorption. Two controversial viewpoints coexist on the effect of maceral compositions to coalbed methane adsorption. One is vitrinite has better adsorption capacity than inertinite and the other is inertinite has enhanced adsorption capacity than vitrinite. In order to clarify this issue, a series of coal samples were collected and highly purified vitrinite and inertinite concentrates were gained by heavy-fluid flotation and centrifugal separation. Isothermal adsorption experiments of methane were performed to these concentrates with equilibrium moisture and their ultimate adsorption volume were obtained finally. The results show that the adsorption capacity of vitrinite is weaker and the capacity of inertinite is stronger for low-rank coal. For high-rank coal, the adsorption capacity of vitrinite is stronger and the capacity of inertinite is weaker. Along with the increase of coal rank, the adsorption capacity of vitrinite rises gradually and the adsorption capacity of inertinite declines little by little. This result shows that the adsorption capacity of coal to methane not only relates to contents of vitrinite and inertinite, but also relates to metamorphic grade of the coal, because with the increase of metamorphism of coal, molecular structure, functional group and pore characteristic of vitrinite and inertinite change gradually, which results in tremendous changes in the adsorption capacity of coal.

Three types of lithofacies, which are organic-rich massive tuffaceous shale lithofacies (RMTSL), organic-rich laminated and cloddy diamictite lithofacies (RLCDL) and organic-lean massive dolomite lithofacies (LMDL), developed in Lucaogou Formation in this research area. Qualitative descriptions and quantitative analyses were implemented to figure out the reasons why only RMTSL can be considered as potential reservoir from the perspective of unconventional oil and gas resources. RMTSL shows the least development degree of the cracks, and displays the largest content of organic matter, which is mainly in the range of 5%∼9%. Organic matter in RMSTL is mainly composed of solid organic matter rather than residual bitumen. The kerogen in RMSTL is chiefly Type I and Type II1 organic matter. Lamalginite is the major component for macerals in RMSTL, which means a better oil generation potential than the other two lithofacies. LMDL interbedded with RMTSL displays a better oil generation potential than thick LMDL. Tuffaceous materials is the key for oil accumulation in Lucaogou Formation fine-grained sediments. The porosity of RMTSL is the highest because of tuffaceous materials alteration. Phytoplankton flourished at the intermittent periods of volcanic eruption because material from volcanic eruptions caused natural iron fertilization. These flourishing phytoplankton would deposit with tuffaceous matter and become sedimentary organic matter. The LMDL contained terrestrial organic matter, which cannot generate as much acid and hydrocarbon as phytoplankton during thermal maturity. Moreover, LMDL contains much less tuffaceous material. All these reasons led to low porosity and oil generating potential for LMDL. For RLCDL, the micro cracks caused by organic matter evolution and tuffaceous material alteration make it difficult to be cemented together tightly, which stop RLCDL from preserving much hydrocarbon.

The Panji Deep Area in Huainan Coalfield, Southern North China is a newly discovered deep coal-bearing block with abundant coalbed methane (CBM) resources. To date, systematic geological studies regarding CBM reservoir in this region are still deficient, thereby seriously hindering the further exploitation and utilization of CBM in Huainan Coalfield. Results indicate that No.13–1 coal seam in the Panji Deep Area has good material conditions for CBM accumulation and preservation. All the coal samples from the No.13–1 coal seam are medium ash and medium−high volatile bituminous coals (Ro,max, 0.72–0.82%), which have different proportions of macerals and minerals. Pore structure and morphology analyses indicate that No.13–1 coal samples have various pore types and complex pore structures. Among them, the ink-bottle shaped pores are mainly observed with a pore size diameter of 4 nm. The gas content of No.13–1 coal samples is 16.11–21.83 m3/t (avg. 18.16 m3/t), which is strongly affected by the effective thickness of coal reservoir, reservoir pressure and temperature. Gas content is significantly positively correlated with burial depth, reservoir pressure, and temperature below 700 m, 6 MPa, and 34 °C, respectively. However, the upward trend tends to be constant after these demarcation points. Numberous micropores hold the retention capacity of coal matrix to methane molecules, thus the residual gas content increases along with the volume and surface area of micropores. By contrast, the correlations between gas content and coal thickness and roof thickness are not obvious. The total CBM resource of No.13–1 coal seam is approximately reserve of 205.36 × 108 m3. Moreover, the total CBM resources in the northern and southern parts of the Panji Deep Area are 73.83 × 108 m3 and 131.53 × 108 m3, respectively. On the basis of multi-level fuzzy model and the evaluated factors, the most favorable areas for CBM development of the No.13–1 coal seam were predicted to be around Zhutuan and south Gugou town in the Panji Deep Area.

Knowledge about the full range of pore sizes in a coal seam is important to investigate the gas storage capacity and pore connectivity for the exploration and development of coalbed methane. To bet...

The results of the petrographic and chemical analysis of brown coal from the Mugunsk deposit in the Irkutsk Coal Basin are presented. The most common groups of macerals and a number of toxic and potentially toxic elements were identified.

Three maceral samples with vitrinite content of 88, 77 and 66 vol% (mmf) obtained from an Australian coking coal were investigated to understand the difference in their thermoplastic development. Each sample was packed in a quartz tube and heated from the bottom by a heating plate of which temperature was set to slowly ramp from room temperature to 900 °C. A thermocouple was inserted at 55 mm from the base to monitor the temperature change at this position as heat transferred through via thermal conduction. At the end of the experiment, the thermocouple measured temperatures at 469, 485 and 495 °C for the three respective maceral samples, suggesting a greater thermal gradient existed in samples with higher vitrinite concentration. The heated samples were then analysed by laser desorption/ionization time of flight imaging mass spectrometry (LDI-TOF-IMS) to track the change in molecular weight distribution across the sample length. Significant intensity of ionisable species was recorded in regions close to the thermocouple position for all maceral samples. Samples with higher vitrinite content displayed a greater molecular weight discrepancy (∆m/z) in the plastic region compared to that in samples with lower vitrinite content, indicating a larger molecular variation occurred in these samples.

During the past decades, exploration activities carried out in the Western Desert of Egypt by several oil companies revealed the oversimplified approach to the study of sedimentary basins in this region. The current study evaluates and discusses the palynology and palynofacies of the clastic succession of the Kharita Formation (Albian) in one of the most petroliferous, deep seated, fault controlled basins in the Western Desert of Egypt, the Abu Gharadig Basin. Although the focus is on the palynofacies association, the hydrocarbon potential of the Kharita Formation will also be addressed by means of organic petrology and Rock-Eval pyrolysis. Marine Cretaceous source rocks have generated substantial quantities of oil and gas in the Abu Gharadig rift Basin. Moreover, Abu Gharadig Basin is characterized by containing not only oil/gas generating source rocks but also reservoir rocks with appreciable porosities and permeabilities. Palynological, TOC/Rock-Eval pyrolysis, and vitrinite reflectance (VRo%) data from 26 cuttings samples recovered from the Kharita Formation in the BED 2-1× well, are presented. The palynological age dating (AL-2 Palynozone) confirmed early to middle Albian age based on the first downhole appearance of the marker Concavisimisporites punctatus. The optical and visual characterization of the palynofacies associations showed two distinct palynofacies associations that alternated with each other. Kerogen type III to III/II was recorded based on the dominance of phytoclasts and opaque organics. Some intervals showed a slight dominance of amorphous organic matter (AOM). Thermal Alteration Index (TAI) values of 2+/3-measured on the psilate trilete spores, in combination with vitrinite reflectance (VRo) values in the range from 0.51 to 0.62%, and the yellow to dull-yellow colors of the liptinite macerals exhibited under UV light excitation indicate immature to the early stage of the oil window. Tmax values from Rock-Eval pyrolysis range from 426 to 438 °C also confirm the low maturity of the organic matter. Thin coal stringers were recorded within the Kharita Formation having slightly higher VRo,ran values (0.64 to 0.76%), which is possibly the result of differences in mineral matrix variations within the Kharita Formation. Based on the low TOC (avg. 0.71 wt%), S2 (avg. 0.97 mg HC/g rock), and HI (avg. 149 mg HC/g TOC) values from pyrolysis, the hydrocarbon potential of the Kharita Formation in the studied well is considered to be low.

In this paper we report the petrological characteristics of the high volatile A bituminous coal from the Yueliangtian coalfield, Guizhou, southwestern China. The random reflectance and maceral quantities were measured by a Leitz Orthoplan microscope. The maceral assemblages are dominated by collodetrinite, fusinite, and semifusinite. Occurring to a lesser extent are telinite, collotelinite, micrinite, and sporinite; along with traces of vitrodetrinite, corpogelinite, macrinite, secretinite, inertodetrinite, cutinite, resinite, and liptodetrinite; and, in some cases, exudatinite, barkinite, as well as funginite. Degraded vitrinite, fusinite, and semifusinite coupled with fecal pellet-derived macrinite revealed that fungi or bacteria participated in the formation of the peat. Funginite, hyphae, and fungus rootlets observed in the coal further confirmed microbial participation. The studied coal seam, especially the lower portion, displays typical attributes of brecciation: vitrinites exhibited crumbled, deformed, and uneven occurrences based on the degree and extent of tectonic movements they suffered; fusinite and/or semifusinite fragments were dispersed or cemented by gelinite or exudatinite; and carbonate and carbonate-pyrite mineralization occurred in the cell lumens of fusinite/semifusinite and carbonate veins, respectively. The Panxian fault westwards of the Yueliangtian coalfield plus other tectonic movements are responsible for brecciation in the studied coals. Faded resinite and telinite verified oxidation in the peat deposit.

Oil and gas production from shale formations has proven to be economical because of advances in hydraulic fracturing but remains very challenging in part because of the presence of the ductile, polymer nature of the hydrocarbon source material, kerogen. This organic matter is intertwined among silicates, aluminosilicates, and other minerals as fine laminae that weave among the shale rock fabric, adding soft mechanical cohesion to the material. A potential solution has been developed, a new type of reactive fracturing fluid composed of strong oxidizers such as bromate (BrO3–), which could mitigate the adverse effects of the polymeric nature of kerogen on the hydraulic conductivity of the fractured shale formation. High-resolution scanning electron microscopy of kerogen-rich shale samples before and after fluid treatment demonstrates notable porosity enhancement evident by cracks forming in the macerals and augmenting the volumetric porosity. The stability of the reactive components at elevated reservoir te...

This paper aims to explore the disseminated characteristics of minerals in this kind of middling coking coal as the washed middling coal of some coking coal preparation plants is still diff...

The macerals effective dissociation is the precondition for the macerals enrichment. The macerals dissociation generally adopts the crushing and grinding process. Selective grinding is achi...

During the End-Permian mass extinction event (EPME) there is extensive evidence for depletion of oxygen in the marine realm. Atmospheric models based upon biogeochemical cycling predict a comparable decline leading up to this event and have been postulated as a possible driver for marine depletion. However, these models contrast with broadly contemporaneous empirical evidence from charcoal in coals. New charcoal data from the temporally well-constrained late Permian Xuanwei Formation coals of eastern Yunnan Province, China, deposited just prior to the onset of the Permian-Triassic Transitional Beds, supports the coarser analysis and further challenges these biogeochemical models. Inertinite group macerals, comprising fusinite, semifusinite, macrinite, inertodetrinite, secretinite, all funginite with elevated reflectance, and some micrinite, are proxies for wildfire activity, and indicate abundant evidence for this phenomenon in the latest Permian and preclude low levels of atmospheric oxygen concentration coevally. Henceforward, we will employ the term ‘inertinite group macerals sensu amplo’ to refer to just these precise macerals, though these encompass what are the overwhelming preponderance of inertinites in most coals. Both inertinite abundance and reflectance indicate an increase in fire activity and intensity towards the End-Permian faunal crisis. Quantitatively, these inertinite data indicate atmospheric oxygen concentration was high and at the close of the Paleozoic was probably elevated to levels well above those of the present-day. The elevated fire activity at this time may have functioned as a causal link to explain some localized oxygen depletion in the marine realm as a result of post-fire increased run-off and erosion. However, globally depressed atmospheric oxygen concentration at the End-Permian was not a driver of extensive marine anoxia at that time.

Four selectively mined lithotypes and a run-of-mine coal (ROM) have been obtained from the Yallourn coal seam in the La Trobe Valley, Victoria, Australia and a partial maceral separation of each of them has been carried out using the sink-float method with centrifugal force on a laboratory scale. The yields of liptinite-rich float fractions were between 22.5 and 2.8 wt% in the order of Pale > Light > Med-light ≈ ROM > Dark. Elemental analysis and FTIR showed that the liptinite-rich float fractions had higher H/C ratios and aliphaticities than the corresponding vitrinite-rich sink fractions and this was confirmed by solid state 13C NMR. Pyrolysis-GC-MS using a pyrolysis temperature of 650 °C showed little difference in the distribution of aliphatic peaks but dramatic changes in the relative abundance of triterpenoids between lithotypes and in some cases between float and sink fractions of a lithotype. Variations in yields with pyrolysis temperature suggested that the triterpenoids are loosely bound to the main coal structure.

The deconvolution and resolution of overlapping bands in the Raman spectra of a suite of coals studied by curve-fitting methods has improved our understanding of the main structural changes in naturally matured coals. Even though much work on deconvolution of Raman spectra has been done, the systematic evolution of chemical structures is not well established. In this study we used a suite of 28 coal samples from Australia with vitrinite reflectance ranging from 0.38 to 3.52%. The micro-Raman spectra of vitrinite macerals from selected coals were acquired using a custom-made Raman spectrometer and supplemented by other Raman spectra previously acquired under the same experimental conditions. In the spectral deconvolution procedure, the second derivative curve-fitting method was used to determine the number of peaks and peak positions of the Raman spectra. Each band was tentatively assigned to a corresponding chemical structure by references to the interpreted major structural changes likely to have taken place during coalification. These parameters included PD (the position of D band), RBS (the distance between G band and D band), FWHMG (full width at half maximum of G band), IG/IGL (the intensity ratio of G band and GL band), and AR/b (the ratio of Raman integrated area and the slope of the spectral background). All of these Raman parameters are found to have a very good correlation with Ro% with R2 higher than 0.90. While five simple equations have been proposed and may be used to estimate thermal maturity of coals, two equations (Eq. (4) for Ro% from 0.38 to 1.5 and Eq. (5) for Ro% from 1.5 to 3.52) are best suitable to predict thermal maturity of coals with the most accuracy.

The occurrence of amber in the Central Carpathian Paleogene Basin is reported here for the first time. The amber has been analyzed by means of optical microscopic methods, infrared spectroscopy, gas chromatography/mass spectrometry, and pyrolysis-gas chromatography/mass spectrometry to understand the amber composition, origin, taphonomy, alteration, and diagenesis. Organic petrographic and reflectance analyses of organic matter from amber-bearing sediment was carried out to get information about paleoenvironment and maturity of sedimentary rock. Analyses confirmed polylabdane structure associated with Class Ib -type of amber and its possible origin from the conifer family Araucariaceae. It is characterized by a high degree of maturity, where both temperature and exogenic processes have participated in its conversion. Heterogeneity of reflectance values in the resinite suggests that amber was not redeposited from an older and more mature sedimentary unit. The discrepancy between the maturity of the amber and amber-bearing sedimentary rock, along with abundant char and inertinite macerals indicates a probability of thermal alteration of the amber under the influence of heat from a wildfire and increased maturity occurring before its ultimate burial in a deep-sea environment. The assemblage of terrigenous macerals and numerous char and inertinite particles which were found in amber-bearing sediment, as well as in the amber crust, suggest forest-swamp type vegetation affected by wildfires. The presence of amber and predominantly terrigenous organic matter, besides mud rip-up clasts derived from freshwater sediments in deep-marine deposits, indicates a direct connection of terrestrial environments to the deep-water depositional system.

Solid organic matter (OM) in sedimentary rocks produces petroleum and solid bitumen when it undergoes thermal maturation. The solid OM is a ‘geomacromolecule’, usually representing a mixture of various organisms with distinct biogenic origins, and can have high heterogeneity in composition. Programmed pyrolysis is a common method to reveal bulk geochemical characteristics of the dominant OM, while detailed organic petrography is required to reveal information about the biogenic origin of contributing macerals. Despite the advantages of programmed pyrolysis, it cannot provide information about the heterogeneity of chemical compositions present in the individual OM types. Therefore, other analytical techniques such as Raman spectroscopy are necessary. In this study, we compared geochemical characteristics and Raman spectra of two sets of naturally and artificially matured Bakken source rock samples. A continuous Raman spectral map on solid bitumen particles was created from the artificially matured hydrous pyrolysis residues, in particular, to show the systematic chemical modifications in microscale. Spectroscopic data was plotted for both sets against thermal maturity to compare maturation rate/path for these two separate groups. The outcome showed that artificial maturation through hydrous pyrolysis does not follow the same trend as naturally-matured samples although having similar solid bitumen reflectance values (%SBRo). Furthermore, Raman spectroscopy of solid bitumen from artificially matured samples indicated the heterogeneity of OM decreases as maturity increases. This may represent an alteration in chemical structure towards more uniform compounds at higher maturity. This study may emphasize the necessity of using analytical methods such as Raman spectroscopy along with conventional geochemical methods to better reveal the underlying chemical structure of OM. Finally, observation by Raman spectroscopy of chemical alteration of OM during artificial maturation may assist in the proposal of improved pyrolysis protocols to better resemble natural geologic processes.

The Bakken Formation is a major unconventional shale play in North America, which lacks an independent calibration for accurately correlate thermal maturity from programmed pyrolysis (via temperature of maximum pyrolysis yield, Tmax) with optical methods (e.g., bitumen reflectance). In the present study, several samples from the upper and lower members of the Bakken Formation in North Dakota were analyzed by detailed organic petrography, bitumen reflectance, and Rock-Eval 6 pyrolysis. Organic petrography showed that the organic matter consists of various types of bitumen, amorphous matrix bituminite, liptodetrinite, acanthomorphic acritarch, marine alginite, granular micrinite, and inertinite macerals. Fluorescence color under UV light of macerals from the liptinite group was used to confirm the thermal maturity level. Due to the scarcity/absence of primary vitrinite, RO measurements on solid bitumen particles were converted to equivalent vitrinite reflectance (VRO-Eq) using a published correlation equation from the coeval New Albany Shale. Overall, geochemical analysis from Rock-Eval pyrolysis reveals almost similar trends for the upper and lower members, which allowed proposing a single correlation for VRO-Eq to Tmax for the Bakken Shale. Comparing the observed relationship for the Bakken Shale with the previously established models for the Devonian Duvernay Shale (Canada) and the Mississippian Barnett Shale (United States) shows discrepancies. Results confirmed the necessity of developing a specific equation for the Bakken Shale members to relate vitrinite and solid bitumen reflectance data to Tmax from Rock-Eval pyrolysis. Furthermore, the outcome of this study indicated that linear trends cannot accurately represent the relationship between these two parameters, considering the kerogen kinetics and non-linear relationship between transformation ratio (TR) and Tmax. Therefore, a polynomial correlation, a better fit to the data, was proposed to more accurately represent the nature of this relationship.

In order to assess the applicability of mechanical method for testing the surface energy of coal, the surface energy of ten coal specimens of two macroscopic lithotypes (semidull and semibright) with metamorphic degree in anthracite stage and a carbonaceous mudstone specimen from a certain mine were tested and analyzed at different temperatures. The results showed that the measurements of surface energy are affected by the test methods, test temperature, coal macerals and minerals, and coal surface roughness. For coal and rock solid materials with strong heterogeneity, the mechanical method is simpler than the optical method and the error is smaller. The surface energy of coal specimens varies from 22.08 to 28.08 mJ·m−2 at room temperature of 293 K by mechanical method. With the increase of temperature, the surface energy of the specimens decreases linearly, and the coefficient of variation of the measured surface energy of various specimens exponentially increased. The surface energy of carbonaceous mudstone specimen is the largest, followed by semidull coal specimens and semibright coal specimens. In contrast, the order of decrease rate of surface energy with temperature increases is semibright coal, semidull coal and carbonaceous mudstone. The surface energy of the specimens exhibited a negative exponentially decreasing trend as the surface roughness increased. The study results provide a basis for further improving the test methods of the surface energy of heterogeneous solid materials, and the application of engineering methods to improve the extraction efficiency of coalbed methane by changing temperature.

The petrology and palynology of coals from the Permian-aged Waterberg Coalfield, situated in the Limpopo Province of South Africa, are considered. The Waterberg Coalfield contains a significant portion of the country's coal reserves, but is still comparatively underexplored. Detailed maceral analyses, combined maceral-microlithotype analyses, mean random and maximum vitrinite reflectance analyses, etching, and palynology studies were undertaken on coals from four productive horizons. There is a general upward trend in vitrinite content through the sequence (15–59 vol% mineral matter free), dominated by collotelinite, along with a slight decrease in coal rank. The lower Vryheid Formation coal has a comparatively low mineral matter and high inertinite content, dominated by inertodetrinite. The upper Grootegeluk Formation samples contain above 35 vol% mineral matter, and liptinite contents ranging from 14 to 21 vol%. The use of blue-light fluorescence in conjunction with incident light (single-scan method) revealed that liptinite is intimately associated with inertodetrinite and mineral matter, specifically clays and occasionally pyrite. It is evident that the liptinite maceral content has previously been under-reported in the Waterberg coals. The palynofloras correlate with the well-studied Witbank Coalfield. The petrography, along with the palynology, essentially confirm the palaeoenvironment of the Karoo Basin as progressing from a cooler, more oxidising environment, to a wetter, seasonal environment.

Coal-Supercritical CO2 (S-CO2) interaction causes severe mechanical alterations in coal that can possibly affect the mechanical competency and the coal seam integrity. Conventional static mechanical testings often fail to conduct repetitive and temporal measurements on coal specimens in the process of coal-S-CO2 interaction, thus unable to attain at decisive and reliable conclusions. Moreover, the said techniques fail to capture the mechanical anisotropies of heterogeneous coal mass that arise due to complex spatial distribution of mineral/maceral phases and fracture network. We combine three non-destructive techniques, viz. gamma-ray attenuation, ultrasonic technique and micro computed tomography to evaluate the S-CO2 interaction induced localized and anisotropic micro-structural alterations and the consequent mechanical response of a heterogeneous coal core specimen. Dynamic moduli were computed at radial and axial directions at natural condition, after 14 days and 45 days of S-CO2 interaction, and the resultant mechanical alterations were elucidated with the 3D-reconstructed micro-CT data collected at the same stages. Visualization and quantification of coal micro-structure emphasize that S-CO2-interacted coal mass is subjected to severe micro-cracking due to differential and free swelling, drying induced shrinkage and surface energy reduction, which can possibly lead to mechanical degradation. Spatial distribution of minerals and fractures at specific orientations significantly affects the gamma and ultrasonic wave propagation, thus can be successfully utilized to reflect the mechanical anisotropies. For same interaction condition and period, coal mass exhibits mechanical anisotropies and strength alterations at different levels, in which more heterogeneous mineral/maceral distribution causes significant localized mechanical alterations in mineral-rich areas, compared to that of comparatively homogeneous coal-rich regions. Temporal evaluation of strength parameters suggests that regardless of the considered orientations, significant strength alterations occur at initial stage of the coal-S-CO2 interaction process and the longer interaction causes only a slight strength reduction. Overall results conclude that S-CO2 induced mechanical property alterations in heterogeneous coal are highly localized and anisotropic, thus should be carefully evaluated in CO2 sequestration and ECBM extraction processes.

Among the fossil fuels, coal is the most widely used one all over the world for different purposes and is a stable source of energy. Coal mining has serious hazards such as spontaneous combustion. ...

The Mamfe basin is thought to be a rift splay segment of the southern Benue Trough and is genetically link to the Abakaliki and Anambra sub-basins in Nigeria. In the Mamfe basin very little studies have been done on maceral characterization and hydrocarbon generative potential of the Cretaceous black shale. Organic petrography and Rock–Eval pyrolysis studies were done on the black shale outcropping in the basin. The objectives were to determine the types of macerals present, and their relative abundance as well as their hydrocarbon generation potential; to assess the black shale's source rocks richness and quality; and to evaluate the source rock thermal maturity and the relationship between maturity and hydrocarbon generation. The results of this investigation indicated that the maceral content include relatively low percentages of vitrinite (4.9%), inertinite (3.4%) and scare liptinite (0.5%). The total organic carbon of the samples vary from 0.17 to 4.53 wt%, (mean = 1.11 wt%) indicating poor to good source rocks generative potential while the S1 values ranges from 0.04–1.25 mg HC/g rock, (mean = 0.23 mg HC/g rock), indicating poor–fair source rocks generation potential. Most of the samples are mature-peak mature for gaseous hydrocarbon generation. Based on the organic petrography and geochemical analyses performed on the black shale samples of the Mamfe Formation, they are described as mainly humic type III-reworked/oxidized type IV kerogen. The genetic potential of these source rocks is low and free hydrocarbon are absent. Given the prevalence of type III/IV kerogen, thermal maturity levels and hydrocarbon yield, it can be concluded that the source rocks of the Mamfe Formation have some moderate to fair potential for gaseous hydrocarbon which have not yet been generated at the present outcrop levels.

Eight cokes made from coals/blend with different properties (vitrinite mean maximum reflectance = 0.90–1.66, logarithm Gieseler maximum fluidity = 4.16–1.30) were subjected to gasification and annealing simulating the conditions within an ironmaking blast furnace (BF). The specific methodology utilised included gasification of coke with BF gas-temperature profile from 900 to 1400 °C (corresponding from the thermal reserve zone to the cohesive zone) and annealing of coke up to 2000 °C (corresponding to the raceway region). The coke microstrength and macrostrength were determined using ultra-micro indentation and tensile test to understand the effect of coal precursor properties on the strength of the resulting coke and the changes when processed under the simulated BF conditions. Under the high temperatures in the simulated BF processes, the cokes from different coals showed significant differences in their properties, even though most of them had similar Coke Reactivity Index (CRI) and Coke Strength after Reaction (CSR) values. Coke microtextures experienced significant reflectance loss and structure change upon simulated BF gasification and annealing conditions. The decreases in mean maximum reflectance and bireflectance were more severe for the coke produced from the high rank coal. The cokes made from coals with higher rank and lower Gieseler maximum fluidity exhibited greater change in their microstructure upon high temperatures. As a result, microstrength of cokes produced from these coals decreased more than that of coke made from the parent coals with a lower rank and higher Gieseler maximum fluidity; this tendency was more significant in the Reactive Maceral Derived Components (RMDC) than Inert Maceral Derived Components (IMDC) microtextural type. Degradation of macrostrength of cokes produced from coals with higher rank and lower maximum fluidity was also more severe due to the greater decrease in their microstrength.

In order to achieve high-quality coal resources in western China, this study focused on a coal sample from the Shangwan Coal Mine, owned by the China Shendong Group, and employed scanning electron microscopy (SEM), mineral liberation analysis (MLA), and maceral component quantitative analysis for investigating the coal sample’s liberation characteristics and crack distribution patterns after pre-grading and microwave processing. The results show that the physical properties of coal maceral components significantly affected the related enrichment performances, and many intra-group and inter-group cracks were produced under the induction of microwave radiation. The cracks then developed and stopped growing among the different maceral components and mineral components, thereby inducing selective and random pulverization along the crack growth direction in further pulverization process and effectively enhancing the liberation properties of different components. Using the Sandbox method, the fractal dimension of the cracks on the particle surface was calculated to be 1.01, which confirmed the self-similarity of the cracks on the coal surface. Multi-intensification maceral liberation also yielded favorable grading performances. The inertinite content was the highest (75.23%) in grade-3 product, while the vitrinite content was the highest (66.3%) in grade-1 product; the corresponding enrichment ratios were 2.15 and 1.59, respectively. Moreover, the ash content in grade-2 product was the lowest, which dropped by 3.61% compared with that in raw coal sample.

This paper studied the macerals enrichment of the low-rank coal which produced by Shigetai Coal Mine, Shenhua Group. The coal sample fed to the Falcon were the product of the rod mill after...

This paper examines the hydrocarbon generation and storage potential of lithotypes, macerals, kerogen type relative to thermal maturity. To investigate authors had collected lithotype (vitrain, durain and fusain) samples from the high volatile sub-bituminous coal of Barjora area, SE of Raniganj coal basin, India. Relevant analyses viz. Rock Eval pyrolysis (REP), total organic carbon (TOC), micropetrography, vitrinite reflectance (Romv) and Fourier Transform Infrared Spectrometry (FTIR) were carried. The geochemical analysis indicates that the studied lithotypes have excellent potentiality of generating hydrocarbon in respect of TOC and S2 (under Rock-Eval pyrolysis) and it increases from vitrain to durain to fusain. Also, the free hydrocarbons which was recorded under S1 curve of Rock Eval pyrolysis, was observed to be highest within the fusain lithotype (21.73 mg HC/g rock). Further, the thermal maturity (Tmax: 418–423 °C) and mean vitrinite reflectance (Romv: 0.42–0.56%) indicate the samples are immature in nature. However, ↑Vt60 (vitrinite grains having a reflectance greater than 0.60%), indicates that thermogenic gas generation was occurring to some degree in almost all the samples. Moreover, comparison between geochemical and petrographical analysis it has been inferred that storing capability of hydrocarbons also increases from vitrain to durain to fusain. The higher capability of hydrocarbons within the fusain (in comparison to durain and vitrain) may be due to presence of large amount of fusinite and semifusinite macerals. The production index (PI) also shows similar trend with increasing S1 value. The FTIR study demonstrates that the fusain has higher intensity of aliphaticity than that of vitrain and durain. The higher intensity of aliphaticity in the fusain may be due to presence of considerable amount of bituminite and other liptinites within the cavities/cell lumens. All the observation suggests that fusain has the highest hydrocarbon generation and storage potentiality, whereas durain has less and vitrain has least generation potentiality in comparison to fusain.

Coal samples and by-products resulting from the combustion process collected from seven combined heat and power (CHP) plants and heating plants located in Upper Silesia, southern Poland, were subjected to petrographic analysis. The coal used as a fuel in these plants was collected from mines of the Upper Silesian Coal Basin; it occurs in a wide range of coalification and has variable quality parameters. The coal is dominated by macerals from the vitrinite group; however, a high content of macerals from the inertinite group has also been observed. Based on petrographic analysis of ash and slags, a highly variable mineral matter content, confirming variable combustion efficiency, has been found. In the case of samples collected from large CHP plants with pulverized and fluidized bed boilers, the mineral matter content is high. The share of mineral matter in combustion products clearly decreases in the case of smaller power plants and heating plants, especially those using grate boilers. The increased content of unburned coal can be explained by the fact that coals of higher rank are often used as fuels in the mentioned plants. The greatest diversity of char forms can be observed in the case of samples collected from small CHP plants. In the case of three samples of slag, collected from small heating plants using grate boilers, additional presence of coke, thermally altered, and unaltered coal has also been found.