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• Explored the feasibility of processing image-encoded coal reflectance spectroscopy using deep-ensemble learning method. • Proposed a novel diffusion model for generating a large quantity of spectral images, overcoming the challenge of data acquisition in mining environments. • For the task of identifying anthracite coal, bituminous coal and lignite, a deep-ensemble learning model IRDE-Net is proposed with the advantages of high accuracy and speed. • Based on the comparison of the identification results of the different methods, the costs and pollution caused by the different methods in the coal application process were quantified. Accurate coal type identification is essential for efficient coal utilization. This study proposes a coal type identification method based on image-encoded reflectance spectra and deep-ensemble learning. Firstly, we encode the reflectance spectra into images using methods based on Gramian Angular Summation Field (GASF), Gramian Angular Difference Field (GADF), Markov Transition Field (MTF), and Recurrence Plot (RP). These encoding methods facilitate the establishment of relationships between spectral bands, reflectance properties, and coal types. Subsequently, a novel diffusion model is introduced for learning from the spectral images and generating a substantial number of spectral images to augment the dataset. Finally, this study proposes a deep-ensemble learning model, IRDE-Net, designed to effectively learn both global features and local key features of spectral images. The experimental results demonstrate that IRDE-Net achieves optimal identification performance on spectral images encoded using the MTF method. The model attained an Accuracy of 94.29%, Precision of 94.36%, Recall of 94.29%, and F1 score of 94.31%. This study conducts a comparison with various advanced methods, quantifying the costs and pollution resulting from misidentification in the coal application process by different methods. It clearly demonstrates the significant contribution of the approach proposed in this study to the practical application of energy resources. [ABSTRACT FROM AUTHOR]

[Display omitted] • Low-rank coals with different moisture contents were prepared by salt solution method. • Influencing mechanisms of moisture, adsorption equilibrium pressure, and stress constraint were explored. • Diffusion models for particle coal and coal bodies were compared and analyzed. Gas extraction is one of the primary methods for guaranteeing secure coal mining and the effective use of high-quality energy. It is crucial to study the CH 4 desorption and diffusion pattern of low-rank bituminous coals under moisture and stress conditions. Because in low-rank bituminous coals, moisture in the coal will occupy the adsorption position and diffusion channel of methane (CH 4), affecting the efficiency of coalbed methane extraction. Herein, low-rank bituminous coals with varying moisture contents were prepared using the salt solution method, and their physical characteristics were described. CH 4 desorption characteristics were investigated across particle and lump coal to analyze the impact of moisture, adsorption equilibrium pressure, and confining pressure. The applicability of the unipore and time-varying diffusion models in elucidating CH 4 diffusion characteristics was evaluated. The small-molecule models of low-rank bituminous coals with different moisture contents were established using the molecular simulation method, which was also used to conduct diffusion kinetic simulations to characterize the diffusion behaviors. Finally, the mechanism of moisture, confining pressure, and adsorption equilibrium pressure on CH 4 desorption and diffusion properties were investigated. The findings can serve as a theoretical foundation for estimating the risk of coal and gas outbursts and guiding methane extraction management in low-rank bituminous coal mines. [ABSTRACT FROM AUTHOR]

• Different rank coals were successfully converted into LIGs by a self-designed CO 2 infrared laser device. • The effect of coal rank on the synthesis of C-LIG was explored by XRD, XPS, Raman, SEM and HRTEM. • LIG-ZJ has the optimal structural orientation, the largest aromatic layer size and the lowest average graphene layer number. • LIG prepared from low volatile bituminous coal has an excellent electrochemical performance. The laser-induced technique is a cost-effective and environmentally-friendly method for upgrading coal into high value-added graphene materials. Here, laser-induced graphenes (LIGs) were prepared from different rank coals in one-step under vacuum conditions using a designed CO 2 infrared laser device. The characteristics of laser-induced products were studied by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The electrochemical characteristics of coal-based laser-induced graphenes (C-LIGs) were examined in a three-electrode test system. Results show that subbituminous coal, bituminous coal, and low-metamorphic anthracite can form LIG with fewer layers after laser irradiation. The morphology of C-LIG is a layered porous structure. Corrugated folds can be observed at the edges of the C-LIG layer. There are only a few layers of graphene, with the majority of them concentrated in 2–10 layers. The most interesting result is that LIG prepared from low volatile bituminous coal has the highest crystallinity, the largest aromatic layer size, and the lowest average graphene layer number. Furthermore, LIG made from low volatile bituminous coal (LIG-ZJ) exhibits excellent electrical double-layer capacitive behavior, low equivalent series resistance (3.73 Ω), good rate capability, excellent cycling stability, greater Coulombic efficiency, and high mass specific capacitance. The LIG-ZJ electrode exhibits a high specific capacitance of 1879.92 F/g at 1 A/g, which is nearly ten times greater than that of most activated carbon electrodes reported. In addition, its power density and energy density can reach up to 924.07 kW/kg and 217.11 Wh/kg. These results indicate that coal-based laser-induced graphene has significant potential for application in the field of electrochemical energy storage. [ABSTRACT FROM AUTHOR]

• Pyrolysis of bituminous coal under high-temperature thermal shock is studied. • Relationship between pyrolytic gas product and particle morphology was analyzed. • Carbon matrix purification is a successive process linear with temperature rise. • Graphitization of coal carbon structure was found to exist an abrupt temperature. The current investigation aims to reveal the pyrolysis characteristics and particle microstructure evolution of bituminous coal under the high-temperature thermal shock. In the experimental temperatures, the purification of carbon matrix in the coal char is a successive process linear on temperature. In contrast, the graphitization process of carbon structure existed a transition temperature (1600 ℃). Specifically, the range of 1000–1500 ℃ is critical for the transformation of amorphous carbon to disordered graphite, but the growth of graphite microcrystals was minimally affected. While the range of 1600–1900 ℃ is critical for the formation of the graphite-like carbon structure. It is characterized by the release of defective structures such as oxygen-containing functional groups, and a significant increase in crystal size. Although beneficial for the subsequent study of carbon materials, the ordered graphite transformation led to the deactivation of char. The pyrolysis behavior study under thermal shock insight into the thermal behavior of coal char in high-temperature furnaces, as well as a new idea for the clean utilization of coal resources. [ABSTRACT FROM AUTHOR]

Homogeneous ignition and the evolution of near-spherical volatile flames from coal and biomass particles are investigated under laminar flow conditions experimentally with a collaborative endeavor of numerical simulations. Specifically, high-volatile bituminous (hvb) coal and walnut shell biomass particles are combusted in N 2 / O 2 and CO 2 / O 2 atmospheres with an ambient temperature of approximately 1800 K. Simultaneous laser-induced fluorescence of OH radicals (OH-LIF), diffuse back-illumination, and Mie scattering measurements are employed to study early-stage volatile combustion of two fuels. Particle size, morphology, dynamics, homogeneous ignition delay times, and volatile flame structures are evaluated by implementing advanced data processing approaches. Detailed numerical simulations are performed to encompass hard-to-measure information such as the bulk rates of particle heating and volatile release rate. Experimental results indicate that hvb coal and walnut shell particles of the same size exhibit slight difference in ignition. This is explained by the fact of early release of a relative large amount of moisture from biomass observed in detailed simulations. Moreover, ignition is delayed as particle size increases, however, only marginal difference was observed when replacing N 2 with CO 2. Increasing particle diameter also weakens the flame, which is visualized by the OH-LIF for the first time. Although the flame structure remains similar for two fuels (up to 8 ms after ignition), its intensity is further suppressed by the higher heat capacity (ρ c p ) of CO 2. The dimensionless flame stand-off distance increases with particle diameter. After the ignition, a continuously rising flame distance is observed for small particles, however, it shows a decrease-and-increase behavior of large particles. This implies a dynamic process: volatile out-gassing accelerates at increasing temperature after ignition, pushing the gas flame away from the particle. The volatile release rate plays a critical role in shaping flame structure and its evolution, in contrast to the relatively minor influence of inert gas composition and the chemical composition of fuels released. • Ignition and volatile flame structures of single walnut shell and bituminous coal particles are focused on. • Advanced multi-parameter diagnostics are supported by detailed numerical simulations. • Air and oxy-fuel conditions are compared with the same ambient gas temperature of about 1800 K. • Effects of oxygen enrichment and particle diameter on ignition delay time and volatile flame development. • Temporal evaluation of volatile flame structures and flame stand-off distances are evaluated. [ABSTRACT FROM AUTHOR]

• The feasibility of a new method for assisted combustion by HHO gas from water electrolysis was verified. • HHO gas co-firing produces no additional carbon emissions and improves flue gas emissions. • Lignite has the best combustion stability among the three power coals at ultra-low loads. • HHO gas co-firing enhances the combustion stability of multiple coals at ultra-low loads. • Flame separation occurs during the co-firing of HHO gas with some coal types. Flexible peak shaving of thermal power has higher requirements for stable combustion and pollutant emissions at low loads in boilers. This study proposes assisting ultra-low-load combustion with clean fuel (HHO gas) generated from water electrolysis, while reducing additional carbon emissions. Based on a 200 kW down-fired one-dimensional furnace, the actual peaking process of a power station boiler was simulated to perform a combustion characterization study during the load reduction of three typical coals used for electricity. The effects of HHO gas-assisted combustion on the flue gas emissions under excess airflow conditions and combustion stability at ultra-low loads were investigated. The results show that as the load decreased to 20 %, the actual concentration of CO 2 in the flue gas of bituminous coal combustion decreased by 64.69 %, the concentration of the pollutants CO and SO 2 decreased, and the converted concentration of NO X first increased and then decreased, reaching the maximum under 30 % load. As the HHO gas was introduced and the flow rate increased, the oxygen content in the furnace slightly increased by 0.52 %, CO 2 , NO X , and H 2 O concentrations increase, and the emissions of CO and SO 2 decreased. The furnace temperature of lignite was the lowest during conventional load combustion of the three pulverized coals; however, the degree of change in the furnace temperature of lignite was the lowest during load reduction. Under ultra-low load (30 %), the combustion instability coefficients (β T) of bituminous coal, lean coal, and lignite were 0.012, 0.0065, and 0.00070, respectively, and the combustion stability was gradually enhanced. The HHO gas noticeably assisted the ultra-low-load stable combustion of the three pulverized coals. Under the co-firing of HHO gas, the temperature reduction rate and β T of bituminous and lean coal decreased to their lowest levels, while the temperature inside the lignite furnace increased. In the co-firing of lean coal and lignite, the HHO gas burned before the pulverized coal, and the flame formed was closer to the burner outlet, appearing as a phenomenon of the separate combustion of the HHO gas and pulverized coal flame. [ABSTRACT FROM AUTHOR]

• Characterized the variations in desorption volume, desorption strain, and gas component concentrations throughout the desorption process under different CO 2 /CH 4 compositional ratios. • Investigated the factors affecting concentration changes during the desorption process under varying CO 2 /CH 4 compositional ratios. • Analyzed the enhancement of CH4 desorption during co-directional desorption under different compositional ratios. CO 2 -ECBM (Enhanced Coalbed Methane recovery) offers the dual benefits of increasing methane production and reducing carbon emissions through sequestration. Previous studies have primarily focused on the competitive adsorption effects of different gas compositions during the CO 2 -ECBM. However, the dynamic changes in desorption volume, desorption strain, and gas composition for different compositional ratios of CO 2 /CH 4 after injecting CO 2 remain unclear. Therefore, high-volatile bituminous coals from the southern margin of the Junggar Basin are chosen for desorption experiments with five different compositional ratios of CO 2 /CH 4. Desorption volume, desorption strain, and gas composition of the coal samples are monitored during the desorption process. Finally, the mechanism influencing the dynamic changes in gas composition during desorption is analyzed. The results indicate that as CO 2 concentration increases, both desorption volume and desorption strain correspondingly increase. At the same desorption volume, a higher CO 2 concentration results in greater desorption strain. For different compositional ratios of CO 2 /CH 4 , CH 4 concentration gradually decreases while CO 2 concentration gradually increases over desorption time. The concentration of the desorption gas is influenced by the initial CO 2 concentration and the pore structure. Specifically, higher initial CO 2 concentrations, better pore opening, and more developed mesopores and macropores lead to greater changes in composition concentrations during desorption. Different concentrations of CO 2 all promote CH 4 production, with higher CO 2 concentrations enhancing CH 4 production efficiency more significantly, especially for samples that are more difficult to produce. The research findings can provide guidance for the efficient production of CBM after CO 2 injection. [ABSTRACT FROM AUTHOR]

• Study establishes a strong correlation between coal properties, density-based separation, and beneficiation outcomes. • Significant variations in physical, chemical, and organic petrographic properties across different size fractions and density ranges. • The beneficiation process effectively reduces impurities and enhances the quality of non-coking coal, making it suitable for blending with imported coking coal. • The study reveals specific density ranges within indigenous Singrauli non-coking coals that are suitable for blending, offering resource optimization in the steel industry. India possesses extensive coal reserves, primarily consisting of non-coking coal, and is one of the vital resources for the energy sector. However, the steel industry necessitates coking coal for steel production. Recognizing the abundance of non-coking coal, this study is aimed at coal beneficiation across diverse size fractions and density ranges with an aim to identify the density closely aligning with coking coal parameters, thereby facilitating the blending of beneficiated non-coking coal with imported coal. We investigate the physical, chemical, and organic petrographic properties of non-coking coals (bituminous coal), spanning various size fractions and density ranges. Proximate and ultimate analyses reveal significant variations in ash yield, moisture content, volatile matter, fixed carbon content, carbon, hydrogen, nitrogen, sulphur, and oxygen content across different size fractions and density intervals. Our results show that all the size fractions with density < 1.4 (kg/m3) has less than 15 % of ash yield. Sink-and-float gravity separation effectively segregates coal components based on density, demonstrating a clear trend of increasing ash yield with higher density fractions, accompanied by decreased moisture, volatile matter, and fixed carbon. Ultimate analysis indicates a declining trend in carbon content (Ad basis) as density increases, highlighting the impact of density-based separation on coal composition. Organic petrographic analysis reveals variations in maceral composition, with density-based distribution influencing the abundance of vitrinite, liptinite, and inertinite group macerals. The fraction with a density of less than 1.3 (kg/m3) shows an average of 62.40 % reactive macerals, while that with density ranging from 1.3 kg/m3 to 1.4 kg/m3 exhibits an average of 49.96 % reactive macerals (Vitrinite + Liptinite), making it suitable for blending with coking coal for coke production. The Vitrinite Reflectance of raw coal and processed coal sample shows an average Ro% 0.68, which can be suitable for blending in coking coal. Additionally, gross calorific value (GCV) analysis indicates a decline in energy content with increasing density, emphasizing the importance of balancing impurity reduction with energy preservation in coal beneficiation processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pyrolysis pretreatment of PVC/tire was proposed before co-combustion with coal. • Pyrolysis pretreatment improved the fuel properties of PVC/tire. • Pyrolysis pretreatment enhanced the co-combustion performance of coal and PVC/tire. • Synergistic effects between coal and PVC/tire char occurred during co-combustion. Co-combustion of coal and municipal solid waste (MSW) is an effective method to utilize MSW and reduce CO 2 emission from coal-fired power plant. However, several undesired properties of MSW (such as poor homogeneity, poor grindability, high moisture content, high chlorine content) limits the extensive application of co-combustion technology. In this study, the low-temperature pyrolysis pretreatment of typical MSW (PVC/tire) was innovatively proposed before co-combustion with coal. The H/C atomic ratio of PVC char and tire char was similar to common sub-bituminous coal and bituminous coal. After pyrolysis, large amounts of chlorine and sulfur were eliminated from PVC and tire. The graphitized structure of PVC was formed whereas the graphitized structure of tire was weakened. The ignitability, burnout characteristics and combustion reactivity of coal were improved after the addition of PVC, tire, PVC char and tire char. The comprehensive combustion characteristic index of various mixtures was also increased after pyrolysis. The highest comprehensive combustion characteristic indexes of PVC char and tire char were obtained at 325 °C and 350 °C, respectively. Obvious synergistic effects among the individual components were observed during co-combustion. The activation energy of coal was greatly decreased after the addition of PVC, tire, PVC char and tire char. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydrogeochemistry was studied by hydrous thermal simulation experiment. • Analysis of main ion sources and the relationship between ions in water products. • The δ18O and δD values vary from −5.0 ‰ to −2.8 ‰, and from −34.3 ‰ to −6.7 ‰. • The water-coal reaction in the thermogenesis can lead to 18O and D drift. • 450 °C is a demarcation point between the release and migration of trace elements. The hydrochemical composition and stable isotope characteristics of coal seam water play a crucial role in the exploration and development of coalbed methane (CBM). However, most current studies are based on the produced water samples from CBM wells, lacking an in-depth understanding of the evolution mechanism of hydrochemical composition and stable isotope in coal seam water during the coal-to-hydrocarbon process through hydrous thermal simulation experiments. In this study, a large-scale closed-system hydrous thermal experiment was conducted at temperatures ranging from 250 °C to 550 °C, in intervals of 50 °C, using low-rank bituminous coal from the Hedong coalfield on the eastern margin of Ordos Basin. The evolution of conventional ions, trace elements, and stable isotopes in water products during coal-to-hydrocarbon was investigated. The results show that CO 2 yields are higher than CH 4 yields at temperatures ranging from 250 °C to 500 °C, and CH 4 content increased significantly at 550 °C. Water ions are affected by leaching at temperatures of 250 °C–450 °C, with Ca2+ being the dominant cation. Due to sulfate dissolution and desulphurization, SO 4 2− is the prevalent anion at temperatures of 250 °C–350 °C, while HCO 3 − becomes dominant at 400 °C and 450 °C. The stable hydrogen and oxygen isotopes (δD and δ18O) of water products have good correlation with R o respectively. At 250 °C–350 °C, deionized water dissolves oxygen-containing minerals, and oxygen atoms in water and coal exchange, resulting in δ18O drift. The increase in δD value is due to the exchange of δD between hydrocarbon in coal and deionized water. At 400 °C and 450 °C, the growth rate of δ18O value slows, and a large amount of gaseous products (H 2 S and CH 4) react with water, resulting in D drift. The contents of Li, Sr, Rb, Ba, V, and Ga do not decrease significantly from 250 °C to 400 °C. However, the contents of Sr, Rb, Ba, V, and Ga in coal products decreased except for the increase of Li content at 450 °C, indicating that these trace elements begin to release and migrate into the water. This study explains the evolution mechanism of coal seam water chemistry and isotopes driven by thermal metamorphism, and enables the applicability of coal seam water chemistry in supporting the exploration and development of thermogenic CBM. [ABSTRACT FROM AUTHOR]

• Study the reduction performance of low metamorphic degree YJL bituminous coal with abundant reserves in reducing high-phosphorus oolitic hematite. • The iron particles in the roasted product obtained from YJL bituminous coal as reductant were smaller and more dispersed, but the DRI indexes were similar to that of the DRI obtained from JS anthracite. • YJL Bituminous coal with high volatile content and H element content produced abundant reducing gas in the reduction process to reduce high-phosphorus oolitic hematite. • Reduced iron products with TFe grade, TFe recovery and phosphorus content of 94.51 %, 87.47 %, 0.062 %, respectively can be obtained by using 30 % limestone and 35 % YJL bituminous coal. Coal-based direct reduction of high-phosphorus oolitic hematite is an effective method to realize the utilization of this kind of refractory iron ore resources with huge reserves. The performance of YJL bituminous coal with low metamorphic degree was compared with JS anthracite as reductants in the process of iron extraction and phosphorus removal of high-phosphorus oolitic hematite using the technique of direct reduction-magnetic separation. The mechanisms of reduction roasting and beneficiation of high-phosphorus oolitic hematite were studied employing X-ray diffraction (XRD) and scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) and thermogrvimetric-differential scanning calorimetry analysis (TG-DSC). Results showed that the reduction results using these two reductants were comparable. For treating the raw ore with total iron (TFe) grade of 50.49 % and phosphorus content of 1.35 %, the direct reduced iron (DRI) with TFe grade of 93.97 %, TFe recovery of 86.14 % and phosphorus content of 1.20 % were obtained using 30 % YJL bituminous coal. The corresponding indexes using 30 % JS anthracite were 94.58 %, 86.15 % and 1.25 %, respectively. When 30 % limestone and 30 % YJL bituminous coal were added, the DRI with phosphorus content of 0.062 %, TFe grade of 94.51 % and TFe recovery of 87.47 % were obtained. The iron minerals were proved to be reduced following the sequence of Fe 2 O 3 → Fe 3 O 4 → FeO (Fe 2 SiO 4 , FeAl 2 O 4) → Fe. The iron particles generated using YJL bituminous coal as reductant were smaller and more dispersed, they can still be recovered by grinding and magnetic separation. From TG-DSC, the total weight loss of YJL bituminous coal and JS anthracite were 33.97 % and 12.63 %, respectively. YJL bituminous coal and JS anthracite occurred depolymerization and decomposition reactions at 350 °C and 400 °C, respectively, producing and releasing a large amount of volatiles substances. YJL bituminous coal releases more reducing gases, mainly including H 2 , gaseous hydrocarbons and CO. And below 820 °C, the mixture of YJL bituminous coal and high-phosphorus oolitic hematite has a higher weight loss at 16.9 % than that of JS anthracite (7.86 %), indicating that YJL bituminous coal was more reactive to high-phosphorus oolitic hematite than JS anthracite at this stage. This work provided an effective utilization method for low metamorphic degree bituminous coal. [ABSTRACT FROM AUTHOR]

• The release of gas-phase nitrogen during coal gasification was studied. • The effect of pressure and blending ratio of gasifying agent was clarified. • ReaxFF-MD combined experiments to provide a reference for coal-N migration pathways. Coal gasification is the leading technology of clean coal technology such as Integrated Gasification Combined Cycle (IGCC). The release pattern of gaseous nitrogen during coal gasification is crucial for clean coal technology. This paper investigated the gaseous nitrogen emission characteristics of pressurized gasification through experiments and molecular dynamics studies. The experimental results show that the elevated temperatures promoted the release of NO and accelerated the conversion of nitrogen-containing precursors (HCN, NH 3). However, high pressure weakened the effect of temperature and resulted in the decreased emissions of HCN, NH 3 , and NO. Because high pressure facilitated the conversion of fuel nitrogen to nitrogen. The emissions of HCN and NH 3 decreased as the CO 2 blending ratio increased, while NO emissions increased. The observed difference was primarily attributed to the amounts of free radicals and was also related to gas-phase reactions involving H 2 O and CO 2. Furthermore, as the primary nitrogen-containing structure in bituminous coal, the pyrrole was used in Reactive force field molecular dynamics (ReaxFF MD) to study the release of gas-phase nitrogen during gasification process. The simulation results show that both temperature and pressure promote the migration of pyrrole nitrogen and also provided the main nitrogen migration paths during gasification which can be used to (indirectly) confirm the experimental analysis. The O 2 /N 2 /CO 2 gasification system supplied additional O and OH radicals to enhance NO emissions, while H 2 O directly participated in reaction paths such as CN, NCO → NH i or provided H radicals to increase NH 3 emissions. [ABSTRACT FROM AUTHOR]

• After the CADW, gas outburst risk was reduced, water injection effect was rose. • Residual CH 4 and total mixed gas in JZ coal reduced by −79.50% and –33.39%. • Water injection volume and coal moisture content increased by 10.30 % and 3.5% ∼ 15.8%. • The permeability of JZ coal was reduced by 88%. The CO 2 -alkaline-water two-phase displacing gas and wetting coal (CADW) measure can effectively prevent coal and gas outburst and reduce mine dust concentration, while relevant research on its effects and action mechanism is insufficient. In this work, effects of the CADW in low-metamorphic bituminous coal and its action mechanism were investigated deeply. The experimental results revealed that, after using the CADW, the risk of gas outburst was reduced evidently compared with conventional water injection. The residual methane and mixed gas in JZ coal reduced by -79.50% and -33.39% severally. The water-injection effect was also enhanced obviously. During injecting water, the maximum pore pressure at 20, 40, 60 mm away from the drilling increased by 10.80%, 5.96%, 1.80%, respectively. The water-injection rate, total volume and radial moisture content of JZ coal all increased distinctly, with the increment of 4.45%∼28.14%, 10.30% and 3.45%∼15.82% respectively. The increment of moisture content rose with distancing the drilling. In addition, the CADW could notably improve the water-lock effect, the permeability of JZ coal was reduced by 88%. As a result, the methane migration, from deeper coal seam to the exposed working face, was inhibited effectively. The results can provide significative guidance for the application of the CADW technique, gas outburst prevention and dust concentration reduction. [ABSTRACT FROM AUTHOR]

• Distinguished from the traditional static method of measuring the adsorption of water vapor on coal samples, this paper adopts the dynamic method to carry out water vapor adsorption experiments on coal samples of three different coal rank, and the results are compared with the measured volume of mercuric pressure method and liquid nitrogen method for comparative study. • The pore model of bituminous coal was skillfully constructed by means of built-in cylinder, and the flow and adsorption behaviors of water vapor-containing gas flow in the pores of coal samples were simulated based on molecular dynamics method, which visually demonstrated the influence of pore shape on water vapor adsorption. • According to the results of the study, four control mechanisms of the pore structure characteristics of coal samples on water vapor adsorption were summarized and generalized to provide theoretical basis for the dynamic adsorption process of water vapor in the pores of coal samples. In order to study the dynamic adsorption process of water vapor in the pore structure of different coal samples (YJL for lignite, SEK for bituminous coal and BJ for anthracite). The pore structure characteristics of the three coal samples were analyzed by mercuric pressure method, liquid nitrogen adsorption method and infrared spectroscopy. Further, the water vapor adsorption capacity of the three coal samples under different humidity conditions was determined by dynamic water vapor sorption (DVS) experiments. In addition, the monolayer adsorption and multilayer adsorption at different humidity were calculated using the Dent model. The results showed that YJL had the largest surface pore volume and oxygen functional group parameter (IO = 12.41), and its water vapor adsorption capacity was also the highest. However, under high humidity conditions, the presence of a large number of pore throats in the YJL coal samples hindered multilayer adsorption, resulting in a water vapor adsorption percentage of only 18.07 %. On the other hand, SEK has a small oxygen functional group parameter (IO = 5.81), poor pore connectivity, and a certain pore throat structure, resulting in a low water vapor adsorption capacity of SEK coal samples, with a water vapor adsorption proportion of only 23.76 %. BJ coal has a large pore volume and a large number of oxygen functional groups on the surface (IO = 8.84), which has a good pore connectivity and the least number of pore throats structure, resulting in a water vapor adsorption ratio is higher at 87.38 %. On this basis, cylindrical and wedge-shaped pore models of coal samples were constructed, and molecular dynamics simulations were carried out to investigate the adsorption characteristics of water vapor in these pore models. The results show that the adsorption process of water molecules in coal develops continuously with "initial-water chain-water bridge-water lock". By summarizing and analyzing the above experimental results, four control mechanisms of coal pore characteristics affecting water vapor adsorption were clarified. These findings are of great significance for studying the movement of water vapor in coal seams and understanding the degree of water confinement caused by hydraulic control measures. [ABSTRACT FROM AUTHOR]

• High temperature and high pressure simulation experiments of coal graphitization are carried out. • The graphitization difference between vitrinite and inertinite in coal is comparatively analyzed. • Efficient graphitization process require a synergistic combination of temperature and pressure, where an excessive or insufficient pressure can inhibit graphitization. It has been recognized that vitrinite and inertinite exhibit different evolutionary characteristics during coalification processs, but the study of their evolutionary differences after entering the graphitization process is limited. To investigate the graphitization differences, this study conducted high-temperature high-pressure (HT-HP) experiments under different temperature and pressure conditions. The precursor used in the HT-HP experiments was concentrated inertinite-rich samples and vitrinite-rich samples obtained through manual selection, and the parent coal is low volatile bituminous coal (R max (%) = 1.7). X-ray diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM) were employed to compare and analyze the graphite lattice evolution of the maceral. The experimental results indicated the following: (1) During the construction of the three-dimensional graphite lattice, vitrinite and inertinite exhibited differences in response to temperature and pressure conditions. Inertinite had a higher graphitization threshold compared to vitrinite, and once reached or exceeded, inertinite underwent rapid graphitization seen by the significant decrease of the interlayer spacing d 002 ; (2) In terms of defect healing, under the same stress conditions, vitrinite was more sensitive to temperature compared to inertinite as observed by the Raman parameters R2 and R3; (3) By comparing the development of graphite structure under different temperature and pressure conditions, we found that both efficient graphitization process and development of the graphite structure require a synergistic combination of temperature and pressure, where an excessive or insufficient pressure can inhibit graphitization and even dismantle and damage the formed graphite structure. [ABSTRACT FROM AUTHOR]

• Sugarcane bagasse pyrolyzed in an unpurged inert environment yielded chars with minimal porosity. • Chars with lower oxygen content were less detrimental on the fluidity of coal-char blends. • Micropores in chars did not influence the viscoelastic behaviour of coal-char blends. • Sugarcane bagasse pyrolyzed to 800 °C behaved similarly to inertinite macerals in a coke blend. • Mesoporous additives adsorb volatile compounds that are responsible for coal plasticity. 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. [ABSTRACT FROM AUTHOR]

The manuscript under discussion is problematical owing to conflicting and contradictory coal rank indicators listed in the Methods section and in the title and text. The subbituminous rank as per the title does not match the high volatile A bituminous volatile matter or the Rock-Eval T max or the medium to low volatile bituminous vitrinite maximum reflectance. Further, the volatile matter and the Rock-Eval T max do not match the vitrinite maximum reflectance. Since the coal is said to have thermoplastic properties, the proper delineation of a subbituminous versus bituminous, i.e., non-caking versus caking coals, coal rank is critical for the proper interpretation of the results. [ABSTRACT FROM AUTHOR]

• A kind of calcium-rich construction waste was used as catalyst after calcination. • Catalytic gasification performance of bituminous coal was significantly improved. • The catalyst loading amount added into bituminous coal had a saturated value. • More defects and amorphous structures on surface of chars were identified. A disposable Ca-containing catalyst was generated from a sort of calcium-rich construction demolition waste and utilized in the steam gasification of a bituminous coal in a fixed bed reactor. The effects of catalyst loading amount, gasifying temperature and catalyst loading method on steam gasification with respect to the production of syngas with high H 2 /CO mole ratio and CH 4 content were investigated. The H 2 and CO molar yields as well as carbon conversion increased noticeably with the increase of catalyst loading amount despite there was a saturation quantity. After loading 6.0 wt% catalyst into coal by kneading method, the carbon conversion and total gas molar yield increased from 52.56% and 136.06 mmol/g-C to 62.77% and 160.23 mmol/g-C, respectively. At low temperature, kneading method displayed superiority over mechanical mixing method in steam gasification performance of bituminous coal while they had approximately the same catalytic effect on coal steam gasification at high temperature. Characterization of SEM images and Raman spectroscopy of coal chars derived from catalytic pyrolysis confirmed that addition of catalyst changed the micro-crystal structure and formed more defects and amorphous structures. Overall, the catalyst showed satisfactory catalytic effect in steam gasification of bituminous coal and could be used as a suitable alternative of CaO for syngas production. [ABSTRACT FROM AUTHOR]

[Display omitted] • The surface tension and contact angle reduced with the addition of NaCl. • The adsorption between water and coal surface was enhanced by NaCl. • Some water molecules penetrate into the coal body. • Sodium ions can hydrate with water molecules and limit their movement. To further enhance the wetting ability of surfactants to coal, the mechanism of improving the wetting performance of SDS to bituminous coal by the addition of inorganic salt NaCl was studied through a combination of molecular dynamics (MD) simulation with experimental measurements. In the experiment part, the surface tensions of the mixed NaCl-SDS solutions and the contact angles on the bituminous coal surface were measured. Furthermore, MD simulations were conducted to investigate the adsorption characteristics and wetting mechanism of a mixed NaCl-SDS solution on the coal surface at the atomic scale. In this process, the static potentials of the H 2 O molecule, coal molecule and SDS molecule were calculated, and the number of hydrogen bonds (H-bonds) formed throughout the whole simulation process, the average H-bond length, the relative concentration distribution (RCD) curve and the mean square displacement (MSD) curve were obtained. The experimental results showed that the surface tension and contact angle were both decreased by the addition of sodium chloride in mixed solutions. When 0.6 mol/L NaCl was added, the surface tension and contact angle reached the minima of 30.45 mN/m and 13.01°, respectively. The MD simulation results showed that, after the addition of NaCl, diffusion and migration of H 2 O molecules were limited, the number of H-bonds increases, the average bond length decreased, the sorption between H 2 O molecules and coal molecules was enhanced, and the hydrophilicity of coal surface was improved, which meant that the wetting ability of SDS solution to bituminous coal was enhanced by adding NaCl. The effect of the added NaCl in improving the wettability of SDS on coal was explored from two perspectives with macroscopic experiments and microcosmic simulations, and the added NaCl improved the effects of dust suppressants, and played a key role in preventing dust hazards in coal mines. [ABSTRACT FROM AUTHOR]

• Acidification technology enhances coalbed methane mining and dust suppression efficiency. • X-ray CT reveals the impact of acetic acid on coal sample microcomponents and structure. • Acetic acid increases bituminous coal porosity with longer dissolution time. • Mineral volume fraction in coal decreases, stabilizing after 36 h of acetic acid treatment. • Acetic acid modifies pore and fracture spaces, improving coal reservoirs' potential. Undeveloped pores and fractures in coal seams constrain coalbed methane mining and dust disaster prevention significantly. The existing hydraulic fracturing technology has achieved some effects in coal seam modification. Still, there are hidden dangers in inducing microseismicity and other aspects. Applying acidification technology for pore and fracture modification improves the efficiency of coalbed methane mining and dust suppression. In this paper, 75% concentration of acetic acid was utilized to treat columnar coal samples, and the experimental method of X-ray computed tomography was applied to study the role of dissolution time on the microcomponents and structure of samples. The experimental results showed that the porosity increased with the dissolution time; the effect of acetic acid on the pore expansion and mineral dissolution showed three periods, i.e., the beginning of the reaction period (0 ∼ 12 h), the full reaction period (12 ∼ 48 h), and the reaction slowing down period (>48 h). The mineral volume fraction showed an overall decreasing trend; before 36 h, the dissolution of acetic acid on the mineral structure within the coal was faster, making it loose, which in turn accelerated the dissolution of coal, and after 36 h, the dissolution effect of acetic acid weakened, and the mineral was gradually stabilized. Acetic acid first reacts with minerals in large quantities. With the increase of products, the solution's ionic complexity increases, so acetic acid accelerates the ionization of more H+ ions, and the solution's acidity increases. After a while of dissolution, the content of acetic acid decreases, the ionized H+ ions are not enough to continue to react with the minerals, and the rate of the mineral's crystal particle size reduction slows down gradually. In conclusion, acetic acid has the potential for pore and fracture modification of coal reservoirs. It can affect the mineral through dissolution, at the same time, improve the porosity. The research results provide an essential reference for using acidification technology to modify the pores and fractures in coal seams. [ABSTRACT FROM AUTHOR]

• The pronounced retardation in the low-temperature oxidation process of methane-bearing coal samples was elucidated. • The inhibitory mechanism of coal oxidation by adsorbed gas molecules was elucidated. • The impact of microstructure on the gas desorption and oxidation at various stages for methane-bearing coals was elucidated. The coupling of coal spontaneous combustion and high methane is ubiquitously observed in coal mining and poses a significant jeopardy to production safety. The extant studies are largely focused on altering external methane conditions and fail to investigate the spontaneous combustion properties of methane-laden coal samples. This study conducted an evaluation of the microstructure of typical coal samples, followed by a fractal analysis. It discovered that the surface structure of the specimen is relatively homogeneous, and the mesopores (2–4 nm) exhibit a significant influence on the specific surface distribution. The overall pore structure is characterized by a multiplicity of peaks, which renders the coal sample markedly segmented during methane desorption, oxygen consumption, and gas products generation. The low-temperature oxidation tests under various working conditions reveal that methane desorption is a crucial factor in determining the spontaneous combustion pattern of the coal sample. The degree of methane desorption bears a close association with the oxygen concentration, and at an oxygen concentration of approximately 2 %, there is a turning point for gas generation and oxygen consumption. The present investigation provides a qualitative and quantitative exposition of the relevant laws, offering guidance for fire prevention and suppression in pertinent mines. [ABSTRACT FROM AUTHOR]

• Combined Raman, FTIR, XPS, and HRTEM to reveal the chemical evolution of TACs. • Lattice fringes at semi-graphite stage show complete orientation in micrographs. • Chemical evolution of TACs explored in three-dimensional space. • Three stages are derived for describing the evolution of TACs. Thermally altered coals (TACs) have different chemical properties compared to normally buried coals owing to the influence of igneous intrusion. This discrepancy in chemical components of TACs has not been fully revealed, which leads to their underutilization and potential risks in exploitation. Igneous intrusion causes the rearrangement of aromatic rings and the formation of graphite-like features in TACs. Several studies have examined the changes in coal rank and aromaticity during this process but have not explored the overall evolution. In particular, the lateral extension and vertical stacking of aromatic layers in TACs during graphitization are still unknown. To this aim, a range of TACs was collected, from bituminous to semi-graphite. Four experimental analyses were conducted to characterize the chemical structure evolution of TACs, including Raman spectroscopy, Fourier-transform infrared spectrometer (FTIR), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM). The analysis of the measured parameters indicates that the chemical structure of TACs undergoes evolution as it approaches igneous intrusion. These changes involve an increase in the size of the aromatic structural units, a reduction in structural defects, and an increase in the degree of order. In addition, there is a gradual transition of sp2-sp3 hybridized aromatic rings to sp2 hybridized aromatic rings, resembling the process of graphite formation. The HRTEM micrographs also reveal an enlargement in the size and angular orientation of aromatic fringes. In summary, the evolution of TACs can be categorized into three stages: a) rapid growth of basic structural units (BSU) from bituminous coal to anthracite; b) lateral connections of BSUs from anthracite to meta -anthracite; and c) lateral straightening of BSUs from meta -anthracite to semi-graphite. Understanding this evolutionary mechanism is highly significant in analyzing the formation of pores and in enhancing the utilization and safety of TACs. [ABSTRACT FROM AUTHOR]

• A series of four ex-situ UCG tests using large coal samples of two different ranks were carried out. • The formation of tar compounds was studied depending on the process conditions. • A significant effect of gasification pressure and coal rank on the yield and composition of UCG tars is demonstrated. The yield and composition of tar depending on coal rank and pressure during underground coal gasification (UCG) were studied. Two coals were used in a series of ex-situ UCG experiments: a Welsh semi-anthracite (Six Feet) and a Polish bituminous coal (Wesoła). Four high-pressure gasification trials under two distinct pressure regimes (20 and 40 bar) were conducted. The tar samples were collected directly from the reactor outlet. The following groups of compounds were analysed by use of gas chromatography (GC-MS): light monoaromatic hydrocarbons (BTEX – benzene, toluene, ethylbenzene and xylenes), polycyclic aromatic hydrocarbons (PAHs) and phenols. A series of gasification experiments revealed significant differences in tar yields and composition depending on the coal rank and gasification pressure. Significant decreases in tar contents were observed with the increase in gasification pressure from 20 to 40 bar for both coals. The total yields of the analysed tar components per kg of gasified coal were 2.58 g and 0.41 g for the experiments conducted on the Six Feet samples at 20 bar and 40 bar, respectively. The corresponding values for the Wesoła coal amounted to 5.48 g and 0.95 g. In all experiments, BTEX was a dominant group of tar components, constituting 69–86 % of the total tar yield within the tested range of compounds. The present study further proves that gasification pressure has a significant effect on the chemical composition of the produced UCG tars for both coal samples under study. [ABSTRACT FROM AUTHOR]

[Display omitted] • The formation of K aluminosilicates mainly contributes to the retention of K in ash. • For K 2 CO 3 and K 2 SO 4 in biomass, coal retains much higher content of K than for KCl in biomass. • For KCl in biomass, organic compounds in coal facilitates K to form aluminosilicates. A steam atmosphere increases the retention of K. • The agglomerates formed after co-gasification are more easily to be broken than that formed from the gasification of biomass alone. Co-gasification of biomass and coal has many advantages, which also mitigates some of the ash-related problems induced by potassium (K) in biomass. However, this effect varies with the occurrence mode of inorganic K in biomass, which varies with the species of biomass. Therefore, the present work investigated the effect of a bituminous coal on the transformation of K and the ash chemistry of bed agglomeration (without considering the effect of fluidization) during co-gasification (steam and CO 2 atmospheres) for different types of inorganic K (K 2 CO 3 , K 2 SO 4 and KCl) in biomass. The results show that for both K 2 CO 3 and K 2 SO 4 in biomass, K is mainly retained as KAlSiO 4 and K 2 SO 4 in the gasification ash with KAlSiO 4 being the dominant phase. In addition, for K 2 CO 3 in biomass, more KAlSiO 4 and less K 2 SO 4 are formed under the steam atmosphere than under the CO 2 atmosphere. However, the K retention of the ash or the agglomerate for both K 2 CO 3 and K 2 SO 4 in biomass is similar and is much higher than that for KCl in biomass, which tends to release and to induce other ash-related problems. In addition, both the organic compounds of coal and the gasification atmosphere significantly alter the reaction between coal with KCl in biomass: The majority of KCl reacts with coal to form KAlSiO 4 , the formation of which is quite limited for the coal ash; More K is retained in the ash and more KAlSiO 4 is formed under the steam atmosphere than under the CO 2 atmosphere. Lastly, although co-gasification with coal (silica sand as the bed material) cannot stop the formation of agglomerates for K 2 CO 3 , K 2 SO 4 and KCl in biomass, these agglomerates are more easily to be broken than those produced from the gasification of biomass alone, thus mitigating bed agglomeration in fluidized-bed reactors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coal derivatives were viable substitutes for raw coals to produce HyperCoal. • Thermal extraction transformed coal into HyperCoal based on hydrogen-carbon ratios, while coal derivatives showed distinct behavior. • Coal derivatives extracts exhibited higher compressive strength, suitable as HPCBs binders. • A clean and efficient coal utilization route to prepare HPCB from DCLR thermal extract was established. • This study expands bituminous coals utilization and explores more raw materials for HPCB. In this study, the thermal extraction of various coal and derivatives by N-methylpyrrolidone was systematically compared and the extract was used as binder to prepare hot-pressed coal briquettes (HPCBs). The results demonstrate the effectiveness of thermal extraction in converting coal to HyperCoal, and the conversion yields varied from 12 to 71%. While the extraction tends to have a linear relationship with hydrogen-carbon ratio of raw coals, this relationship was not directly observed for derivatives due to inherent changes occurring during production. Proximate analysis of the extract reveals a reduction in ash content to below 1% while an increase in volatile matter by more than 8%. XPS and FTIR spectra demonstrate the high efficiency of thermal extraction in extracting hydrocarbons, but poor for compounds such as alcohols, phenols, ethers, and carboxylic acids. The extracts, rich in hydrocarbons, exhibited excellent thermoplasticity, making them suitable binders for HPCBs preparation. Among the extracts, coal derivatives exhibited higher compressive strength compared to coals. Consequently, the extract derived from direct coal liquefaction residue with the highest compressive strength was selected for preparing HPCB. Furthermore, we investigated the application characteristics of the HPCB and identified its great potential for use in COREX melting-reduction ironmaking. The preparation of HPCB is vital for expanding the utilization of bituminous coals while reducing dependence on lump coal and coking coal resources. [ABSTRACT FROM AUTHOR]

• Accurate characterization of porous structure and fluid mobility of coal utilizing 1H NMR. • Study of pore throat evolution processes and response to pore conversion trends. • Analyze T1-T2 spectrum to obtain development characteristics of coal pores. • Freeze-thaw cycles promote the connectivity and expansibility of coal pores. Microwave-LN 2 cyclic processing (MLCP) is a clean and high-efficiency anhydrous fracturing technology. The change in the porous structure of coal after freeze-thaw cycles significantly affects development efficiency of coalbed methane (CBM) in low porosity and permeability reservoirs, while there is a lack of in-depth macro-meso-micro studies. The damage mechanism of coal under microwave-LN 2 cold and thermal shock and the evolution of pore fluid reservoir space is based on cross-scale pore characterisation. This paper evaluates the multi-scale porous structure variations of coal before and after MLCP was assessed by hydrogen nuclear magnetic resonance (1H NNR) and field emission scanning electron microscopy (FE-SEM). The evolutionary trends in coal pore fluid fugacity space under freeze-thaw cycles was indirectly characterised by T 1 - T 2 spectra. Additionally, utilizing T 2 distribution, peak area and pore throat changes reflect the evolution trend of coal pore space. The results indicate that as the cycles increased, the coal free water and total fluid reservoir space gradually expanded beyond the cycle threshold (n > 10), the free-fluid index rose to 25.68 %, and the free fluid saturation increased by 20.39 %. Additionally, the NMR permeability of the coal increased by 98.37–1471.65 %, and the pore throat distribution increased by 28.05 %. Comprehensive analysis showed that as the cycles progressed, the free water space in the pore space increased significantly, the proportion of bound water gradually decreased, and the internal pores and fluid space of the coal were improved. This study provides fundamental support for multidimensional evaluation of the porous structure of microwave-LN 2 freeze-thaw cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] • A stabilizer in a small proportion (1%) has little effect on ignition and combustion. • Ignition and burnout can be improved by increasing the reactive additive share. • Sodium lignosulfonate is the most promising non-oil stabilizer. • Soy lecithin is less promising according to a set of indicators. • Re-equipment of a thermal power plant for burning waste-derived slurry can pay off in 1 year. The paper presents the results on the influence of stabilizing additives on the viscosity, sedimentation, ignition, combustion and emission profile of fuel slurries derived from coal slime. Soy lecithin, sodium lignosulfonate, rapeseed oil, and diesel fuel of 1 wt% were stabilizers. A slurry without stabilizers and with waste turbine oil were tested for a comparison. All the mixtures met the standard viscosity required for pumping and spraying (less than 1,000 mPa·s at a shear rate of 100 s−1). The use of additives reduced the proportion of the separated liquid during fuel storage (up to 6 times). Diesel fuel with a share of 1% reduced the ignition temperature of a fuel slurry by 30 °C and accelerated gas-phase ignition by 10–12%. The slurries with additives of waste turbine oil and sodium lignosulfonate were the most effective. Their integral efficiency indicator was 0.906 and 0.865, respectively. In feasibility study, the transition from bituminous coal to stabilized fuel slurries were analyzed, considering the new technological chain and equipment, the generated power and fuel cost. The cost for the full cycle of preparation of the slurry coal slime–water–soy lecithin will be 7.5% higher than when using bituminous coal. For the rest of the studied fuels, the estimated payback period for capital investments is about 1 year. [ABSTRACT FROM AUTHOR]

• Water imbibition significantly controls the water injection effect on coal seams. • The imbibition rate decreases with the increased time following a linear function. • The contact angle of all coal samples is negatively proportional to the SI rate. • LF-NMR shows that water is primarily stored in adsorption and seepage pores. • Fractal analysis reveals the effect of the roughness and connectivity on the SI. The spontaneous imbibition (SI) of water plays a crucial role in determining the wetting effect of water injection in coal seams. It is significant to investigate the flow behavior of water in coal during the SI. Contact angle measurement, SI experiment, and low-field nuclear magnetic resonance (LF-NMR) tests have been conducted to measure the properties of coal from different regions of China. The mass change of the coal by SI is related to the square root of time divided into three-stage linear functions in which the slope represents the imbibition rate of coal. The imbibition rate decreases with the increased SI time. The contact angle of bituminous coal is smaller than that of anthracite and is negatively proportional to the SI rate and capacity index C. Water is primarily stored in the adsorption and seepage pores, and little in microfractures. It shows that the fractal dimensions of the partial free pore (D b) and total pores (D) decline in a form of power law, while the fractal dimension of the free pore (D z) declines irregularly. D -10 and D 10 are strongly linear with the T 2 spectrum area of adsorption pores, seepage pores, and microfractures, respectively. It indicates that the low-probability measurement area can represent the adsorption pores, and high-the probability measurement area represents seepage pores and microfractures. Adsorption pores play an important role during SI (DSI). The difference between the amplitude increments of adsorption pore and that of seepage pores/microfractures is the key factor affecting multifractal parameters of T 2 spectra. The linear relationship between H and D b reveals that water preferentially enters a pore with lower roughness and better connectivity DSI. The process of SI has been divided into three stages in terms of SI rate. The transport process of water within the coal at different stages has been discussed as well. The results of this work are of great significance for optimizing the coal seam water injection and reducing the risk of underground coal mine disasters. [ABSTRACT FROM AUTHOR]

• This study has positive significance for CO 2 geological storage, and the later the breakthrough time, the longer the CO 2 adsorption time. • The experimental study of CO 2 injection for CH 4 displacement in different coal ranks was studied. • Combined with the volume fraction of produced gas, permeability and flow rate, the effect of gas injection displacement is analyzed and discussed. • The gas production of CH 4 increases with the increase of coal rank. The dominant mechanism of CH 4 gas production was different before and after CO 2 breakthrough. Coal seam gas extraction is an important part of green mining. At the same time gas injection for enhanced coalbed methane recovery (ECBM) has been proposed as an environmentally friendly, low-carbon and effective technology to increase methane production. To study the influence of coal rank on carbon dioxide (CO 2)-ECBM efficiency, lignite, bituminous coal, and anthracite were tested using the Gas Flow and Displacement Testing Apparatus (GFDTA). Data indicated that: (1) in lignite and anthracite, outflow CO 2 and CH 4 fractions changed at higher rates as compared with bituminous coal. At the end of the experiments, lignite and anthracite displayed CH 4 outflow fractions of 0.19% and 7.73%, respectively; (2) at the initial stage of the experiments, permeability rapidly decreased. Later, a fast increase was followed by a stable phase. In lignite and anthracite, the increment in permeability during the rapid increase stage was significantly larger than that of bituminous coal. (3) The CH 4 flow rate of the three coal ranks showed a decreasing trend. Before the breakthrough, CH 4 flow rate decreased rapidly and slowed down. After the breakthrough, CO 2 flow displayed a linear increasing trend and later reached stability. (4) In general, CH 4 production increased with the increase in coal rank. The variation of CH 4 production is manifested in two phases with different dominant factors. In the first stage, CH 4 production was mainly affected by permeability, and followed the order lignite > anthracite > bituminous. In the second stage, CH 4 production was mainly controlled by the displacement effect, following the order anthracite > bituminous coal > lignite. [ABSTRACT FROM AUTHOR]

• A LF-NMR water drop experiment on powder coal is outlined to assess wettability. • CO 2 –H 2 O-coal interaction decrease coal wettability and alter the coal pore architecture. • Dynamic wetting process and evolution of coal pores were evaluated. • The relationship of water wetting and pore evolution was explained. As CO 2 has a strong affinity to coal surface, coal seams are considered as an attractive geological formation for CO 2 sequestration. Naturally occurring coal seams are often saturated with free water in the cleats as well as moisture. Hence, the wetting behavior of coal by water is an important aspect in the study of coal properties. However, carbon dioxide, which replaces methane on the surface of coal, interacts with water and coal for a long time. Geochemical reactions of CO 2 -H 2 O-coal system can change the surface properties and pore structure of coal. Studies on wettability of coal altered by CO 2 -H 2 O-coal interaction are rare. This paper explored the wettability alteration and wetting dynamic behavior of two bituminous coals in Huainan and Huaibei coalfield using low-field nuclear magnetic resonance (LF-NMR) combined with CO 2 -H 2 O-coal interaction experiments. The results show that dynamic wetting of water in the coal mainly depends on the pores structure. The geochemical reaction changed the pore structure of coal reservoir, further promoted the hydrophobicity of coal surface, and thereby affected the dynamic wetting process of water. Moreover, the wetting of large pores in coal is not significantly affected by the weakening of hydrophilicity, whereas wetting in small pores is obviously affected by the enhanced hydrophobicity, which may be beneficial to the adsorption and storage of CO 2 in the coal. [ABSTRACT FROM AUTHOR]

• CO 2 atmosphere can reduce NO x emissions during pressurized devolatilization. • The CO-NO homogeneous reaction has a weak influence on NO emissions. • The elevated pressure can increase CO emissions but reduce NO x emissions. Pressurized O 2 /CO 2 combustion technology is a new power generation technology that can achieve CO 2 capture efficiently. In this study, we investigated the pressurized devolatilization of Shenhua bituminous coal in a pressurized drop tube furnace experimental system at 1273 K. The evolution mechanism of carbon/nitrogen gas–solid products during the pressurized devolatilization process was analyzed using online measurements and offline analysis. We found that increasing the pressure from 0.3 to 1.2 MPa promoted the emission of CO and inhibited emission of NO. N 2 O emissions were insensitive to the change of pressure, and NO 2 emissions were almost zero under the experimental conditions. The introduction of CO 2 decreased the production of NO x and primary sources of nitrogen-containing gas-phase products were N-5 and N-6 active groups. Therefore, pressurized O 2 /CO 2 combustion technology can effectively reduce NO x emissions in the devolatilization of pulverized coal and impact the subsequent char-combustion process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coal type affects particulate emission composition and cytotoxicity. • Water-soluble ions dominate PM 10 from honeycomb, anthracite, and industrial coals. • PM 10 from bituminous coal is dominated by carbonaceous components. • Heavy metals and water-soluble ions in PM 10 strongly correlated with cytotoxicity. • Limiting anthracite coal combustion is crucial in air quality for public health. Inhalable particles (PM 10 , particulate matters with an aerodynamic diameter < 10 μm) emitted from coal combustions is one of the most significant contributors to air pollution, endangering human health. The compositions of emissions and corresponding health risks of different types of coal sources are currently unclear. To address this, ten distinct types of coal were burnt, and original PM 10 samples were collected using dilution channel samplers. Subsequently, we performed a componential analysis on the collected samples and conducted in vitro cytotoxicity tests. Results showed that PM 10 from honeycomb, anthracite and industrial coals were dominated by water-soluble ions, while bituminous coal was dominated by carbonaceous components. Although heavy metal contents were lower than other investigated components in these PM 10 , they were still enriched in Fe, Pb and Zn. The NH 4 +, Cl- and SO 4 2- account for a large proportion of water-soluble ions. PM 10 induced obvious cytotoxicity to human lung cell A549, and the ability of anthracite coal to induce cellular TNF-α production was greater than that of honeycomb and bituminous coal. For IL-6, industrial coal elicited a stronger response than bituminous coal, followed by honeycomb and anthracite coal. Correlation analysis revealed that although heavy metals (Fe, Mn, Co, Ni, Cu) and water-soluble ions (K+, Ca2+, F-) accounted for less particle mass, they were strongly and significantly correlated with oxidative stress and inflammatory damage (r > 0.6, p < 0.05). Considering the actual coal consumption amount, our study identified restricting anthracite coal combustion should be a crucial focus for aerosol pollution control and public health protection policies. The results of the study not only increase the understanding of the chemical composition and cytotoxicity of PM 10 from the perspective of source emissions, but also provide targeted advice on the control of coal combustion, which is of great significance in environmental research, public health policy and air pollution control efforts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synchrotron radiation-induced SAXS is introduced into the research of coal extraction process. • Fractal dimension, radius of gyration and pore size distribution are combined to study all extraction products. • Influence of particle size on the evolution of coal microstructure during the extraction is focused on. • The work promotes thoroughly depicting the pore structure of coal and residue at a molecular level. Because of the unique physicochemical textures induced by reduced particle size, superfine pulverized coal presents attractive characteristics in different utilization processes, including solvent extraction. In this work, the synchrotron radiation-based small angle X-ray scattering (SAXS) with high precision was used to quantitatively characterize all the products during the coal extraction process, including raw coal, extract, and residue. In addition, the evolutions of pore structures (solid state) and aggregate configurations (liquid state) were focused on. The results show that the fractal dimensions of pore surfaces are mainly related to the pore sizes and corresponding quantity distributions. When the particle size is less than 14 μm, the comminution induced mechanical effect on the pore surface gradually changes from impact to polish during the superfine grinding. Additionally, the fractal dimension decreases with the decline of particle size and ash content, whilst increases for the lower ranked coals. As for the extraction process, the extraction effect of tetrahydrofuran on anthracite coal is relatively better, while pyridine is more effective for bituminous coal. The diverse driving force caused by particle size effect leads to different radii of the gyration of the extracted aggregates, indicating the selected bituminous coal has active sites that are susceptible to reacting with aromatic compounds, while anthracite has a large number of active sites that accept electrons. Finally, the surface fractal dimension of the extraction residue declines about 2% and 4% for HN and NMG coal respectively, and the decreasing trend declines for larger coal particles. Interestingly, this decreasing trend of bituminous coal is more evident, which indicates the pore surface of bituminous coal is easier to react with solvent. The research sheds light on thoroughly depicting the pore structure of coal and residue at a molecular level, which promotes a better understanding of the solvent extraction mechanisms. The results also provide a new perspective for constructing more comprehensive coal molecular models in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • The pectin-modified dust suppressants with different methoxy levels were prepared. • Comprehensive studies of wetting performance, structural properties and dust suppression performance experiments were carried out. • For the first time, the dust suppression properties of LAT and HAT were compared at the molecular level. • LAT effectively enhances the hydrophilicity of coal and has a significant effect on wetting and agglomeration of coal. Low methoxy level pectin (LM-PC) and high methoxy level pectin (HM-PC) were utilized as materials to produce environmentally friendly dust suppressants, and the impact of pectin modification with different methoxy levels on wetting and agglomeration of coal was investigated. The results of contact angle and settling experiments reveal that the low methoxy level pectin-modified dust suppressant (LAT) can effectively wet coal, and the optimum modification conditions are determined. FTIR spectra of coal samples treated with LAT and high methoxy level pectin-modified dust suppressant (HAT) demonstrate that the absorption peak area ratios of hydrophilic functional groups increase by 4.00 % and 2.61 % compared to the original coal. XPS spectra indicate that the increases in carboxyl and hydroxyl functional groups are the reason for the improvement of wettability in bituminous coal. Compared to the coal samples treated with HAT, the increase of hydrophilic functional groups is higher in LAT treated coal samples. Through the dust suppression performance characterization experiments, it is concluded that LAT is more effective than HAT in reducing coal dust. The mechanism of dust suppressants on the wetting properties of coal was revealed at the molecular level. Experimental and mechanistic analyses show that LAT can effectively wet and agglomerate coal dust while remaining environmentally friendly and economical. [ABSTRACT FROM AUTHOR]

• High nitrogen amendment changed the microbial community structure. • High nitrogen amendment increased 40.78 % of metabolites. • High nitrogen increased the genes relating to methane metabolism and β-oxidation. • High nitrogen increased the abundance of methanogenic Methanosarcina and Methanoculleus. Improving the bioavailability of coals is an effective way to increase the production of secondary biogenic coalbed methane (CBM); however, information on the influence of different elements on the biological methane yield is lacking. In this study, the effect of high nitrogen amendment on biological methane yield was analyzed by indoor anaerobic culture experiments with two samples from different coal seams in a mining area. The results showed that the methanogenic rate increased by 1.89–3.43 times after 40 days under the high nitrogen amendment. The high nitrogen amendment changed the microbial community structure and increased 40.78% of the metabolites in the coal samples, 62 of which were related to methane metabolism, degradation of aromatic compounds, fatty acid degradation, polycyclic aromatic hydrocarbon degradation, and degradation of other benzene series. Metagenomic analysis showed that high nitrogen amendment also caused significant changes in functional gene composition and increased the abundance of functional genes related to methane metabolism, β-oxidation and the degradation of toluene and phenol. In addition, the high nitrogen amendment increased the relative abundance of methanogenic Methanosarcina and Methanoculleus and some bacterial taxa belonging to orders Clostridiales and Thermoanaerobacterales. Among them, a total of 17 metagenome assembled genomes (MAGs) were reconstructed, most of which can produce hydrogen and have the ability to degrade aromatic compounds into acetate. In summary, this study indicated the importance of nitrogen as a single element in biological methanogenesis that helps to stimulate biological methane yield for the exploration and development of CBM. [ABSTRACT FROM AUTHOR]

• Co-combustion of coal and pyrolytic biochar under oxy-fuel atmosphere were studied. • Formation mechanism of fouling from combustion of coal and biochar was clarified. • Combined effects of impaction and capture dominated the formation of ash deposits. • The agglomerated and sintered CaO particles suppressed the growth of inside deposits. • Mass concentration of PM 1 determined the inside deposition under oxy-fuel condition. Co-combustion of coal and pyrolytic biochar under oxy-fuel atmosphere is a promising option for addressing CO 2 problems in power plants, where the issue of ash fouling during combustion was considered in this study. A high-Ca pyrolytic biochar from pilot-scale trail and a high-Si Utah bituminous coal were selected for single- and co-combustion on a drop tube furnace (DTF) coupled with fouling sampling system under the atmosphere of air and oxy50 (CO 2 :O 2 = 50:50 vol%) at 1300 ℃. The fouling deposits were collected and characterized by various techniques to investigate the formation mechanism of ash deposits. The results indicated that the combined effects of impaction and capture resulted in the different deposition propensity from coal and biochar combustion under both air and oxy50 conditions. Besides, co-firing can inhibit the formation of ash deposits during coal combustion under air atmosphere when the blended biochar was greater than 50%, while the deposition propensity of the blend with 80% biochar rapidly aggravated under oxy50 atmosphere. The fine particles act as "glue" to fix coarse particles from impaction were the main source of the inside deposits from coal combustion, whereas the inside deposits from biochar combustion were dominated by agglomerated and sintered fine particles. Co-firing can weaken the "glue effect" from coal combustion, and finally presented as mitigated deposition propensity of inside deposits. Switching to oxy50 condition, the enhanced sulfidation of deposits and scavenging of alkali metal suppressed the growth of inside deposits from coal combustion, while that had minor impact on biochar. The inhibitory effect of co-firing on inside deposits diminished with the increased biochar under oxy50, where the deposition propensity of the blend containing 80% biochar was higher than that in air-firing. [ABSTRACT FROM AUTHOR]

The laboratory method used for coal calorific value measurement has a significant hysteresis. In this paper, an on-site measurement method of coal calorific value based on high power laser rapid ignition is proposed. The effects of oxygen transverse passage velocity, thermal insulation crucible bracket and coal samples on the measurement time, unburned rate and calorific value measurement error are gradually investigated. The experimental results shows that the measurement error of calorific value is within 2% and unburned rate is within 2% at the oxygen transverse passage velocity of 120 mm/s of Huainan bituminous coal. Then the utilization of porous thermal insulation crucible bracket has shown a good performance in heat dissipation to shorten the measurement time without increasing the unburned rate. Then, the effects of coal sample thicknesses, species and particle sizes on calorific value measurement are investigated. Results show that under the coal thickness from 4.2 to 5.4 mm, the calorific value measurement error is within 3%, and the unburned rate is within 2% of Huainan antiminous coal. Finally, the results shows that the method has a good performance on different coal species and particle sizes which the calorific value measurement error is within 5%. This research quantifies the effects of the experimental condition parameters on the measurement of coal calorific value based on laser ignition, which lays the foundation for the subsequent development of online coal calorific value meter. • An on-site coal calorific value measurement based on laser ignition. • New structural design of coal combustion chamber and thermal insulation crucible bracket. • Analysis of influencing factors and performance of this method. • The hysteresis is significantly reduced and the measurement error meets the needs of the power plant. • Prerequisites for corresponding instrument development. [ABSTRACT FROM AUTHOR]

Pyrolysis experiments on a high volatile bituminous Columbian coal were performed in a laminar drop tube reactor at T = 1300 K and 1475 K. Measurements in CO 2 were carried out at different residence times up to 150 ms, and the data were complemented by end-point measurements in N 2 at approximately 165 ms. These low residence times are typical for the duration of pyrolysis in pulverized coal flames. Mass loss has been determined by solid sampling based on the ash tracer method, and the evolution of porosity was evaluated. Pyrolysis mass loss kinetics were determined based on a single first order reaction and a competing two-step reaction model with distributed activation energies. The particle temperature and residence time needed for the determination of the kinetics were derived by CFD simulations. Results indicate that, despite the low residence time selected, the influence of the Boudouard reaction on mass loss and, hence, evolution of porosity cannot be neglected. In general, porosity increases with increasing residence time and progressing mass loss and porosity is influenced by the both, the release of volatiles and the contribution of gasification. [ABSTRACT FROM AUTHOR]

• Mercury occurrence and thermal stability in high ash bituminous coal were determined. • The relations of Hg content with organic sulfur, sulfate and sulfide were obtained. • Mercury species in various density fractions were quite distinct. • The matrix-bound Hg, HCl soluble Hg, HgS and Hg(NO 3) 2 ·xH 2 O were thermally unstable and released before 400 °C. • The pyrite-bound Hg mainly enriched in density >2.0 g/cm3 fraction and released at 400–600 °C. The high-ash coals have gradually become essential energy resources due to their availability, and the occurrence of Hg in coals and its thermal stability could be significantly influenced by ash-forming minerals. In this work, a high-ash bituminous coal was divided into 4 density fractions using sink-float procedure. The sequential chemical extraction procedures, temperature-programmed pyrolysis and TG/DTG experiments were carried to investigate the Hg occurrence and thermal stability in different samples. The results showed that the Hg contents in samples has a positive relation with the ash, sulfate and sulfide contents, and the correlation coefficients were 0.868, 0.535 and 0.924, respectively. However, the negative value with correlation coefficient of 0.751 between the Hg and organic sulfur content was obtained. The Hg species in different samples were quite distinct, the organic matrix-bound Hg was the dominate form in SG1 with the content of 76.14%, the SG2 and SG3 were mainly composed of HCl soluble Hg and Hg(NO 3) 2 ·xH 2 O, and the Hg species occurred in SG4 were mainly HCl soluble Hg and pyrite-bound Hg. In the process of pyrolysis, the matrix-bound Hg, HCl soluble Hg, HgS and Hg(NO 3) 2 ·xH 2 O were thermally unstable and could be released into gas in the drying and desorption stage of 30–400 °C, while the pyrite-bound Hg mainly released with the decomposition of pyrite in the temperature range of 400–600 °C. There was only little Hg released in the temperature range of 600–850 °C, indicating the negligible relationship of Hg with carbonate and silicate minerals. [ABSTRACT FROM AUTHOR]

• Normal alkanes and arenes are the most abundant in SP I and SP 1 , respectively. • Both SP 2 and SP II are rich in arenes. • Alkyl-substituted benzenes in SP I and SP II are higher than those in SP 1 and SP 2. • Abundant heteroatom-containing species are concentrated into SP 3 and SP III. • N 1 and N 1 O 1 species are predominant in SP III and SP 3 , respectively. Liuhuanggou bituminous coal (LBC) and its extraction residue (ER) were thermally dissolved sequentially in cyclohexane, toluene, and ethanol at 300 °C to obtain soluble portions (SPs) 1–3 (SP 1 -SP 3) from the thermal dissolution (TD) In the total yield (TY) of 10.4% and SPs I-III (SP I -SP III) from the TD in the TY of 4.9%, respectively. The SPs were analyzed by multiple analytical tools, including gas chromatograph/mass spectrometer (GC/MS), quadrupole exactive orbitrap mass spectrometer (QEOTMS), and Fourier transform infrared spectrometer. The analysis with GC/MS shows that normal alkanes are the most abundant in SP I , while arenes are predominant in SP 1 , SP 2 , and SP II. According to the analysis with QEOTMS, abundant heteroatom-containing organic species were concentrated into SP 3 and SP III with molecular masses of 150–750 u. The relative contents of N 1 and N 1 O 1 species are predominantly high in SP III and SP 3 , respectively. [ABSTRACT FROM AUTHOR]

• Group combustion characteristics of coal char and petroleum coke were studied. • Effect of particle concentration on delayed burnout time ratio was characterized. • Particles inside group combustion performed different combustion characteristics. • Oxygen diffusion and particle concentration were main causes for burning delay. The combustion characteristics of particle group are different from the combustion of a single particle, owing to the physicochemical effect and interaction among particles. The current work investigated the effect of the increasing particle concentration on the group combustion with the consideration of temperature and solid fuel type, including bituminous coal char and petroleum coke. A visual imaging technology was used to record and analyze the combustion process and group evolution of burning particles in the two-dimensional scale. Results showed that a delayed combustion phenomenon was found for both coal char and petroleum coke with the increasing particle concentration in a group. The burnout time increased in multiples from the combustion of a single particle, dispersed particles to a particle group. The total carbon conversion and combustion rate of the particle group significantly decreased with the increasing particle concentration in the group, especially for the bituminous char of a high reactivity. With increasing the combustion temperature, the burnout time was additionally prolonged from 20% to 80% between the internal and external particles in the particle group. The theoretical analysis with the consideration of Stefan flow, gas diffusion, and gas-solid reaction was used to propose the delayed combustion mechanism, and the results matched well with the experimental data. The increasing particle concentration in the group, which consumed the oxygen, generated the advance effect of Stefan flow, and hindered the oxygen diffusion, was the key factor to delay the group combustion. For the group combustion of petroleum coke with low reactivity, although the surface reaction was the controlling step, the reactant gas diffusion inside the group could not be ignored. For the group combustion of coal char particle with high reactivity, the diffusion of the reactant gas in the group was the dominant controlling step for the delayed combustion behavior. [ABSTRACT FROM AUTHOR]

• The characteristics of a plastic layer were identified by penetrometer resistance (PR). • The plastic layer consists of PR increasing, descending, constant and re-rising zone. • PR constant and re-rising zone are critical to the development of coke crystalline structure. The characteristics and carbonization behavior of a coking coal during the formation of a plastic layer was analyzed by using a thermogravimetry–plastometer–swelling pressure apparatus. The characteristics of the plastic layer were identified by using a penetrometer. The structural transitions across the plastic layer were investigated by scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray diffractometry. Various carbonization behaviors are believed to be interrelated and depend significantly on the evolution of the plastic layer. The plastic layer can be divided into four structural zones with different penetrometer-resistance (PR) characteristics, namely, the increasing, decreasing, constant, and re-rising PR zones. The four structural zones of the plastic layer present a physical morphology of softening-fusion, melt-bubbling, foamlike, and a compression pore structure, respectively. At the PR constant zone, it appears that larger amounts of condensed aromatic rings developed because of an accumulation of tar and volatile precursors. In the PR re-rising zone, it appears that a rearrangement of aromatics occurred because of the enhanced conversion of ring systems and condensation. These findings may have an important role in revealing the coking mechanism of coal through the plastic layer and can provide guidance to evaluate the coking performance of coal. [ABSTRACT FROM AUTHOR]

This work investigated the effects of different ash co-products on the combustion of solid fuels, in particular the fuel-nitrogen behaviour: The fuel-ash additive combinations investigated were: Firstly, biomass ashes added to bituminous coals, representative of those used in power stations; Secondly, a low reactivity coal; Thirdly, a high-N biomass (olive cake) was chosen as a high reactivity fuel and studied with a power-station pulverised coal fly ash as an additive. These five solid fuels have a wide fuel ratio, FR (i.e. the ratio of fixed carbon to volatile matter content). The ash additives were a pulverised fly ash (PFA) and a furnace bottom ash (FBA) from wood pellet combustion in a UK power station. Fuels (with and without additives) were studied for nitrogen partitioning during (i) devolatilisation and for (ii) NO x formation during combustion, using two different electrically heated drop tube furnaces (DTF) operating at 1373 K. Devolatilisation was also studied via ballistic-heated thermogravimetric analysis (TGA). The extent of impact of additives on volatile yield under devolatilisation conditions was dependent on fuel ratio, high FR has the greatest increase in volatile release when co-feeding the additive. Under devolatilisation conditions, there is a correlation between volatile nitrogen and carbon conversion for all the fuels tested. Thus, additives liberate more volatile-nitrogen from the coals and also deliver enhanced carbon conversion. A mechanism is proposed whereby ultra-fine particles and vapours of reactive compounds from the additives interact with the reacting fuel/char particle and influence N-release during both devolatilisation and char burn-out. The enhanced conversion of fuel-nitrogen to volatile-nitrogen and the reduction of char-nitrogen can lead to reductions of NO x emissions in emissions-controlled furnaces. This approach could assist fuel-flexible power stations in achieving their NO x emission targets. [ABSTRACT FROM AUTHOR]

• Stationary HTW gasification of high volatile bituminous coal. • Carbon conversion rate of 88% was reached. • Impacts on gas composition by temperature staging within the gasifier. • Optimization of gasifier performance. Processing of difficult feedstock's like high-ash coal or biogenic residues poses a challenge for most common gasification technologies. The High-Temperature-Winkler (HTW™) gasifier, as part of the fluidized bed gasification technologies might very well provide a solution for these feedstock's. Gasification takes place in the two characteristic zones of the gasifier (bubbling fluidized bed zone and post gasification zone) enabling dry ash removal, while the majority of heavy hydrocarbons like tars are converted. A semi industrial HTW™ pilot plant was erected at the Institute for Energy Systems and Technology by retrofitting a circulating fluidized bed reactor in cooperation with thyssenkrupp Industrial Solutions AG (former ThyssenKrupp Uhde GmbH). Commissioning was successfully carried out in June 2015 using pre-dried lignite. This study shows the usability of the HTW™ technology for an increased variety of feedstocks, by means of high volatile bituminous coal (HVBC). Furthermore, significant workload was put into identification of optimizations for the pilot plant in order to increase performance, handling and quality of the gasification process. During the 5 days of continuous operation, 7.4 tons of HVBC were gasified to examine the gasifier behavior depending on the feedrate, temperature and distribution of gasification agents. During these tests syngas containing more than 50 vol% CO and H 2 was produced. The syngas quality significantly increases with the temperature, while the gasifier load and the particle size showed mixed results. Increasing the load (feedrate) of the gasifier resulted in decreasing temperatures. More particles were entrained into and through the post gasification zone, reducing efficiency and carbon conversion rate as well as syngas quality. Optimizations of the gasifier include removal of the loop seal from the return leg, reducing the overall CO 2 injection by at least 20%. Furthermore, an optimized cyclone was developed to significantly increase separation efficiency and carbon conversion rate. Increased temperature of the gasification agents will benefit the overall energy balance of the gasifier increasing performance and syngas quality and decreasing freeboard velocity. The temperature dependence of the gasification of HVBC indicate significant improvement in syngas quality for this feed by an increase of gasifier temperatures. The evaluation and verification of these optimizations will be done during the next longterm tests of the gasifier using pre-dried lignite. [ABSTRACT FROM AUTHOR]

• A CLC unit modified by implementing ring-type internals in the fuel reactor. • Internals modified the solids distribution in the reactor. • Combustion efficiency enhancement due to the internals is experimentally confirmed. • The oxygen demand was decreased by 20%. • Internals improved the oxidation of volatile matter. Chemical Looping Combustion (CLC) with solid fuels has been widely developed by using two interconnected fluidized beds, the fuel reactor and the air reactor, with an oxygen carrier continuously circulating between them. Experience gained in this process shows that high CO 2 capture values can be reached. However, complete combustion of the fuel is not achieved, with some H 2 , CO and CH 4 as the main unconverted compounds in the combustion products from the fuel reactor. It is believed that the combustion efficiency can be increased by improving the gas-solid contact in the fuel reactor. In this work, the solids distribution in the fuel reactor was modified by using ring-type internals with the objective of enhancing the gas-solid contact. Two experimental campaigns were carried out in a 50 kW th CLC unit burning a bituminous coal with ilmenite particles in the temperature interval of 900–1000 °C. The first campaign was conducted with the original riser of the fuel reactor, which was characterized by a smooth section from bottom to top. For the second campaign, three ring-type internals were implemented in the riser in order to modify the solids distribution in the fuel reactor. The presence of the internals had a beneficial effect on the coal combustion. The major benefit was an improved oxidation of volatile matter in the form of CH 4 and the full conversion of H 2. As a result, the total oxygen demand decreased by 20%, from 12.2% to 9.8%, with the implementation of the internals. [ABSTRACT FROM AUTHOR]

• Coal waste streams were studied to minimize potential environmental impacts. • Conductivity screening and acid-base accounting tests were performed. • Less 10% of materials cause elevated conductivity of supernatant. • Segregation and isolation of such fractions minimizes release of elements. • Modifications to preparation plants and waste disposal practices were formulated. An environmental concern at coal preparation operations is the release of elements resulting from the oxidation or dissolution of certain minerals contained in the process waste streams. Using a standard conductivity test, the electrical conductivity (EC) of water samples obtained from mixing with various particle size and density fractions of a given plant waste material were measured as an indicator of total dissolved solids. The net neutralization potential (NNP) of the fractions were also measured to predict the pH of the supernatant upon disposal. As a result, the particle size and density fractions contributing to high EC levels were identified with the objective of potentially extracting and isolating these fractions which can significantly reduce the negative environmental impacts. The results showed that the EC generated from coarse refuse streams were significantly higher than the values obtained from fine refuse streams. Based on the NNP values, the coarse refuse stream generates highly acidic pH, while the fine refuse in contact with water produces circumneutral pH. Furthermore, the high specific gravity (>2.68) fractions which comprised less than 10% of the coal waste streams were found to be the primary source of elevated EC levels. The remaining fractions were found to be of minimal environmental concern. Based on the obtained results, modifications to the coal preparation plants were proposed to minimize the environmental concerns of coal waste disposal. Modifications include pyrite removal from the spiral refuse and desulfurization of flotation feed and sieve bend underflow streams using low-cost mineral spiral circuitry. After the segregation, the pyrite (high density) fraction, which encompasses around 1% of the coarse and fine refuse streams, will be isolated/encapsulated and the fine refuse stream dewatered and co-disposed with the coarse refuse stream. The proposed modifications to the processing and disposal practices not only minimize the generation of acid mine drainage thereby reducing the release of trace elements and EC of the discharged water, but also enhances the recovery and quality of the final clean coal product. [ABSTRACT FROM AUTHOR]

• Calcination of coal sources decomposes structure of associated mineral matter. • Calcination as a pre-treatment step prior leaching increases REE recovery. • Recovery of light REEs preferentially increase by 50–65 percentage points. • Exceeding 600 °C causes a reduction in poor volume and REE recovery. • Evidence suggests strong correlation between REEs and phosphorus. The pretreatment of middlings and coarse refuse material collected from a Pocahontas No.3 coal source using calcination was investigated for the potential of improving the leaching recovery of rare earth elements. Calcination at 600 °C significantly and preferentially improved light REE (LREE) recovery to values in the range of 80–90% using 1.2 M HCl. The positive effect was due to the increased pore diameter and volume as well as thermal decomposition of the minerals associated with the LREEs. Heavy REE recovery was not increased after calcination at 600 °C due to the need for higher temperatures to achieve thermal decomposition of HREE minerals. Furthermore, some HREEs were also associated with sulfide minerals (e.g., pyrite) which were transformed into low-solubility oxides (e.g., hematite) after roasting at 600 °C. Based on the leaching characteristics of the major elements (Fe, Al, Ca and Mg) and REEs along with SEM-EDX data, it was concluded that REEs in the two samples mainly occurred as phosphate minerals. In the middlings, some of the minerals were completely encapsulated by kaolinite, which was less apparent in the coarse refuse. In addition, it was found that a portion of the REEs (10–25%) in the samples were associated with the organic matter and micro-dispersed minerals in the organic matrix, was released after calcination and easily recovered using 0.1 M (NH 4) 2 SO 4 solution at pH 5. Scandium primarily occurred in mineral forms with minimum amounts associated with ion-adsorbed clays and organic association. [ABSTRACT FROM AUTHOR]

Highlights • Chars were obtained from fast pyrolysis to 1600 °C in a high temperature wire mesh reactor. • Volatile yield for different coal and biomass fuels was calculated. • Nitrogen partitioning for different coal and biomass fuels was obtained. Abstract Nitrogen oxides (NO x) are atmospheric pollutants specifically targeted by legislation which imposes limits on emissions from large scale plant. During combustion, part of the Nitrogen fuel will be released as a component of the volatile matter compounds and as volatile nitrogen, while part will remain in the char. Thus, the fate of volatile-N and char-N becomes crucial for the formation of NO x and, consequently, for determining the concentrations of NO in solid fuels combustion systems. In pulverized fuel combustion, major routes for conversion of the volatile-N are either NO or N 2 , while char-N reacts through a set of heterogeneous reactions as the char is oxidized. Measuring high temperature char nitrogen content of the fuels directly reduces the likely uncertainty in NO x emissions from solid fuels on modern power stations using deep furnace air staging High temperature volatile-N and char-N partitioning is investigated by pyrolyzing fuels in a high temperature (1600 °C) wire mesh apparatus (HTWM) and analyzing the resulting char. White wood biomass, olive waste, torrefied wood, two bituminous coals and one anthracite coal were used on this study. The volatile yield at high temperatures has been obtained for each sample. The fate of nitrogen released during the pyrolysis as volatile matter and the nitrogen retained in the char has been evaluated for different biomass samples. The nitrogen in the char was measured using a total nitrogen analyzer. Results show a large change in on the volatile yield compared with proximate analysis values for both coals. Only moderate change was observed on the volatile yield for both of the woody biomass that already have high values on proximate analysis, and just a slight increase was obtained on the volatile yield for the olive waste. Differences were found on the fate of nitrogen retained in the char that would lead to NO x formation. The biomass samples release most of their fuel-nitrogen as volatile (between 80 and 95%) while on the coals the volatile nitrogen is wide more variable depending on the coal sample. [ABSTRACT FROM AUTHOR]

Highlights • The oxidation reactivity of the functional groups was qualitatively analyzed. • The oxidation characteristics of the treated coal were measured. • Macroscopic performance was characterized by microscopic characteristics. • The inhibiting effects of the four ionic liquids were compared. Abstract The effects of ionic liquids (ILs) on the macrostructures and characteristic parameters of coal samples during low-temperature oxidation (30.0–200.0 °C) were investigated. The Fourier transform infrared (FTIR) spectroscopy results clearly illustrated that the destruction of functional groups in the coal molecular structure was prominent, and that the benzene rings in the coal molecular structure were barely affected. Therefore, it can be inferred that ILs played a primary role in the destruction of functional groups in the side chain of the coal molecular structure; thus, the aromatic ring was barely affected. Moreover, the inhibition of the functional group at high temperatures by the ILs was also barely effective. The analysis results of the temperature-programmed testing system indicated that the CO concentration and the production rate of CO by coal samples treated with the ILs presented decreasing trends. This result was in sound agreement with the FTIR results for the quantity of carbonyl groups in oxidation stage. The oxygen consumption rate of the sample treated with the ILs gradually decreased beyond the cracking temperature. Moreover, the difference between the thermal release intensity of coal samples treated with the ILs and that of raw coal gradually increased beyond the critical temperature. The inhibiting effect of [Bmim][BF 4 ] appeared to be greater than that of other ILs, and [Bmim][I] and [Emim][BF 4 ] exerted a slight influence on the low-temperature oxidation process of coal samples. Therefore, we conducted a comprehensive comparison of the inhibiting effect of four ILs on bituminous coal during low-temperature oxidation and found that the ILs can be listed in the following order on the basis of their inhibiting effect: [Bmim][BF 4 ] > [Bmim][NO 3 ] > [Emim][BF 4 ] > [Bmim][I]. [ABSTRACT FROM AUTHOR]

Abstract Biogenic coalbed methane has been attracted much attention due to massive reserves and green performance, but the current research is relatively weak. To further investigate its formation mechanism, the experimental simulation of biogas generation was performed by using lignite, high-volatile bituminous coals and their treated coals as substrates for 90 days. The results show that the lignite has a greater biogas potential than high-volatile bituminous coal in this study. Total gas production in lignite groups (L-BZ-1 and L-LJ-1) is 12.6% more than the bituminous coal groups in the experimental simulation. This is because the lignite has a low degree of thermal evolution and rich in soluble organic matter: chloroform asphalt "A" (CAA), which plays an important role in microbial metabolism to produce biogas. The CAA in coal has a conversion rate of 3.08 mL/g into biogas in this experimental simulation. The saturated hydrocarbons and nonhydrocarbons are more biodegradable components in the CAA. In saturated hydrocarbons, the n -alkanes with shorter chains or an odd carbon number are preferentially degraded. In the experimental simulation, biogas generation results in the consumption of a large number of organic matters with heteroatomic groups such as hydroxyl, carboxyl, pyridine and nitrogen oxides. Aliphatics show a stronger bioactivity than aromatics. The aromatic structure in coal is a few biodegraded in the later stage. [ABSTRACT FROM AUTHOR]