Search

The differences in intensity, acoustic emission (AE), and seepage characteristics between raw coal and briquette coal were studied under a triaxial compression experiment. The two stress-strain curves of raw coal and briquette coal had similar trends and could be divided into five development stages in the triaxial compression experiment. The transverse and axial deformations of briquette coal were larger than those of raw coal, and the compressive strength and elastic modulus of briquette coal were smaller than those of raw coal. The cumulative AE count and energy of the whole compression process of raw coal were higher than that of briquette coal. The seepage velocities of gases increased with the deformation and failure of coal samples, and its variation trend corresponded to the failure stage of coal samples. Their permeability velocity was small at the initial stage of raw coal and briquette coal. However, the maximum permeability velocity of briquette coal was much higher than that of raw coal after the failure of coal samples. Both raw coal and briquette coal had strong stress sensitivity. The permeability of the two types of samples decreased exponentially with the increased effective stress. The seepage velocity of briquette coal was most sensitive to axial force and deformation, while that of raw coal was more sensitive to radial deformation. The research results provide references for the experimental study of using briquette coal instead of raw coal as well as for exploring coal and gas outburst mechanisms in coal seam. [ABSTRACT FROM AUTHOR]

Significant load fluctuations are encountered when cutting the coal rock using the shearer spiral drum, causing excessive drum wear. Thus, a coupling discrete element model of coal‐rock was developed, and the discrete element method and multi‐body dynamics were used to build a two‐way coupling simulation model of coal rock drum cutting. The drum wear was analyzed, along with the pick and spiral blade wear positions. The results have shown that the pick wear is primarily concentrated at the pick tip and the shaft shoulder, while the outer spiral blade edge blade is generally worn near the pick root. The maximum wear depth obtained in the simulation was 0.00316 mm. The tangential cumulative energy of the drum and the normal cumulative energy were 1.794e5 and 7.819e4 J, respectively. The friction wear of the drum was more prominent compared to the impact wear. By using a single factor method, the relationship between the drum rotational speed, traction speed, rock firmness coefficient, cutting depth, and spiral blade angle, and drum wear was obtained. Finally, it was concluded that the study at hand provides a quick and straightforward way to study drum wear law. [ABSTRACT FROM AUTHOR]

When delivering the lignite to the beneficiaries, manual sampling is practiced from the means of transport which, although it is tributary to human error generating subjective controversies between the parties, excludes the investment and responsibility for the realization of an adequate installation. The installation for automatic sampling of lignite samples, which was proposed to be made at the Jilţ Sud loading point, is fully made and is working. [ABSTRACT FROM AUTHOR]

Developments in femtosecond laser induced breakdown spectroscopy (fs-LIBS) applications during the last two decades have further centered on innovative métier tie-in to the advantageous properties of femtosecond laser ablation (fs-LA) introduced into LIBS. Yet, for industrially-oriented application like coal analysis, no research has exposed to view the analytical capabilities of fs-LA in enhancing the physical processes of coal ablation and the impact into quantitative correlation of spectra and data modeling. In a huge coal market, fast and accurate analysis of coal property is eminently important for coal pricing, combustion optimization, and pollution reduction. Moreover, there is a thirst need of precision standardization for coal analyzers in use. In this letter, the analytical performance of a one-box femtosecond laser system is evaluated relative to an industrially applied coal analyzer based on five objectives/measures: spectral correlation, relative sensitivity factors, craters topology, plasma parameters, and repeatability. Despite high-threshold operation parameters of the fs system, competitive results are achieved compared to the optimized analytical conditions of the ns-coal analyzer. Studies targeting the in-field optimization of fs-LIBS systems for coal analysis can potentially provide insights into fs-plasma hydrodynamics under harsh conditions, instrumental customization, and pave the way for a competitive next-generation of coal analyzers. [ABSTRACT FROM AUTHOR]

Highlights • A surface activation function (SAF) can be expressed as F X = X a 1 - X c. • The intrinsic reaction rate can be expressed as R (X) = k P O 2 m F (X). • The effects of temperature and O 2 concentration on SAF can be ignored in Regime I. • It is suitable to use isothermal SAF to obtain accurate kinetic parameters. Abstract The kinetics of coal/char oxyfuel combustion by isothermal and non-isothermal thermogravimetric analysis is still controversial. The two methods were compared according to the kinetics of two coal chars (NCP anthracite, DT bituminous) combustion in kinetics-controlled regime I under different O 2 /CO 2 and O 2 /N 2 atmospheres. We have developed a surface activation function (SAF, F (X)) to describe the reactive specific surface area of char conversion, and then the intrinsic reaction rate can be expressed by R (X) = k P O 2 m F (X) , the autocatalysis model (ACM) of F X = X a 1 - X c was found to be suitable under both isothermal and non-isothermal conditions, however, the exponents a and c in ACM as well as the activation energies (E) differ under these two conditions. These controversial results may be caused by the exponential function exp(− E / RT), which changes with the conversion ratio under non-isothermal conditions, which in turn affects the nonlinear modeling results of SAF. According to the isothermal study, temperature has no effect on the form of SAF in Regime I. Thus it is reasonable to use the intrinsic SAF obtained from isothermal experiments (F (X) iso) to fit the non-isothermal data. The modeled results show that E NCP = 207–220 kJ/mol under different O 2 /CO 2 and O 2 /N 2 atmospheres, greater than those under isothermal conditions (178–179 kJ/mol). While E DT = 159–165 kJ/mol, this agrees well with the isothermal result (163–167 kJ/mol). Furthermore, it indicates that the O 2 partial pressure (P O 2 ) has no influence on E , even though increasing P O 2 or replacing CO 2 in the O 2 /CO 2 mixture with N 2 increases the intrinsic reaction rate. [ABSTRACT FROM AUTHOR]

Highlights • Molecular structure of the middle-high rank coals were systematically characterized. • The A(CH 2)/A(CH 3) of coal samples decrease with the increasing R o from 0.4 to 2.6%. • The new coalification jump at R o = 4.2–4.8% is unreported in previous studies. • Using chemical structure parameters to evaluate the coal rank has limitation. Abstract In recent years, the major coal producing areas in China have entered the period of deep mining, with coal rank changing from low-rank coal (LRC) to middle-high rank coal (MHRC). Even though material properties of MHRC, such as pore size and shape, have attracted increasing attentions, its molecular structures still remains unclear. This study probes molecular structural properties of five MHRC samples using X-ray diffraction (XRD), Raman and Fourier transform infrared (FTIR) spectroscopy. Test results show that with the deepening of coalification, the aromatic rings of MHRC increase gradually. The aliphatic side chains between the aromatic rings continuously fall off. The ordered structure of coal continues to enhance, resulting in an increase in the degree of graphitization of coal. The average lateral sizes (L a), stacking heights (L c) and interlayer spacing (d 002) of the crystallite structures of MHRC samples derived from the XRD range from 20.65 to 31.68, 10.62 to 19.21 and 3.42 to 3.66 Å, respectively. The L a values derived from the Raman spectra using the classical linear relationship between 1/L a and the I D1 /I G band ratio are higher (36.36–59.91 Å) than the values obtained from XRD. The FTIR spectra reveals that MHRC samples contain aliphatic functional groups such as CH 2 and CH 3 , aromatic functional groups such as C C and aromatic ring CH, and oxygen-containing functional groups such as OH, C O and C O. The aromaticity (f a) of the coal samples determined by FTIR ranges from 0.66 to 0.98, and compared with the f a valued from XRD (0.63 to 0.93), which shows that the MHRC contains abundant of aliphatic components. On the basis of these results, the structural parameters obtained by different spectral techniques are also used to comparatively study the effects of coalification on the molecular structure of coals. The structural parameters of coal derived by these methods reflect the coalification jumps at R o = 0.5, 0.7–0.9, 1.2, 2.6, 3.3, 3.5–4.0 and 4.2–4.8%. Among them, the jump at R o = 4.2–4.8% is unreported in previous studies and should be further studied in subsequent research. The application range of structure parameters used to evaluate the coal rank such as d 002 , L a (XRD), f a and G-D 1 should be considered because of coalification jumps. The parameters such as 'C', I D1 /I G and L a (Raman) are better choices for evaluating coal rank for their better correlation with R o. It is worth pointing out that these parameters have implications for coalification and should be concerned in further study. [ABSTRACT FROM AUTHOR]

Abstract In practical engineering, borehole drainage is the most effective and widely used method of extracting coalbed methane (CBM). The drainage radius of a borehole is a key parameter in determining the design and layout of drainage boreholes, and the interaction among boreholes in multiple-borehole system significantly influences the drainage radius of each individual borehole. Therefore, the physical simulation experiments of gas drainage with single, double, and multiple boreholes were carried out using a self-developed device. This paper discusses the drainage radius considering borehole interaction based on 3D monitoring of gas pressure in coal, which can provide reference data for numerical simulation and offer practical guidance for engineering. The results show that multiple boreholes lead to a faster drop in gas pressure along the monitoring line and require less time to reach the safety line, with two distinct propagation patterns observed in the effective drainage zones. Besides, a calculation model was proposed for obtaining the drainage radius of a borehole. The drainage radius can be fitted using a power function with respect to drainage time, with larger values giving an increase in the drainage radius. Meanwhile, a benchmark borehole was selected from which the gas pressure decrease coefficients at different monitoring points are calculated; these coefficients reflect the degree of borehole interaction. The relationship between the pressure decrease coefficient and drainage time is approximated by a negative exponential function, with multiple boreholes exhibiting more intense interaction. Finally, it is found that the influence of other boreholes on monitoring points near the reference borehole is relatively small and subject to a time lag. [ABSTRACT FROM AUTHOR]

Abstract Desorption is routinely employed for assessing the recoverability of coalbed gas resources. However, desorption behavior is strongly affected by coal structure. Canister desorption experiments on undeformed and mylonitic coals collected from drill holes in the Zhina Coalfield (Southwest China) were conducted to study temporal desorption rates and gas compositional shifts. Low-pressure N 2 and CO 2 adsorption tests revealed that the micropores, mesopores, and macropores in mylonitic coal have larger pore volumes and greater specific surface areas compared to those of undeformed coal. The "ink-bottle-shaped" pore is the main type of pore structure in mylonitic coal, whereas undeformed coal shows well-developed slit-shaped pores with good interconnectivity. The detailed desorption experiments in this study lasted 61 d and 110 h for undeformed and mylonitic coal, respectively. For undeformed coal, CH 4 and C 2 H 6 concentrations steadily increased with desorption time, whereas N 2 and CO 2 concentrations progressively decreased. The gas compositional shift of mylonitic coal during the entire desorption process could be divided into two stages: an initial stage, when CH 4 and C 2 H 6 concentrations in the desorbed gas increased (within the first 12 h), and a later stage, when they decreased rapidly; N 2 and CO 2 concentrations exhibited the opposite trend. The two-stage gas compositional shifts in mylonitic coal are likely linked to its pore structure. Gases in the "parallel-plate-shaped" pores of undeformed coal are mobile, whereas those in ink-bottle-shaped pores of mylonitic coal have restricted mobility. This is because CO 2 and N 2 can enter the narrow throats (with diameters of 3.3–3.8 Å) of ink-bottle-shaped pores, which are inaccessible to CH 4 and C 2 H 6 because of their larger diameter, causing the late-desorbed gas of mylonitic coal to be relatively enriched in CO 2 and N 2. The initial desorption rate of mylonitic coal is much greater than that of undeformed coal, which is closely related to developed microfractures in mylonitic coal. The desorption rate of undeformed coal is a power function of time, whereas that of mylonitic coal can be divided into two stages in which the relationship between desorption rate and time is a power function. The results suggest that the two-stage desorption rate is attributable to the molecular sieve effect due to the presence of massive ink-bottle-shaped pores in mylonitic coal. [ABSTRACT FROM AUTHOR]

Highlights • High coal conversion and CH 4 yield could be simultaneously achieved in CCHG. • Co-Ca catalyst triggered catalytic coal depolymerization and char hydrogasification. • Individual Co and Ca had inferior catalytic activity towards coal hydrogasification. • Ca retarded Co sintering, and more importantly initiated graphite carbon conversion. • CH 4 and tar yield could be moderated through varying catalyst loading. Abstract Coal catalytic hydrogasification (CCHG) was carried out in a lab-scale pressurized fluidized bed to study the cobalt-calcium (Co-Ca) catalyst on the gross distribution of products by changing the addition amount of the catalyst. The CH 4 formation behaviors and the structure properties of gasified coal char were analyzed to elucidate the role of Co and Ca in the dual catalyst system. Results show that 90.0 wt% of carbon conversion and 77.3 wt% of CH 4 yield could be simultaneously achieved in 30 min with the help of 5%Co-1%Ca catalyst through hydrogasification at 850 °C and 3 MPa. Co-Ca dual catalyst triggered coal catalytic hydropyrolysis and coal char catalytic hydrogasification in succession. However, neither individual Co nor Ca had profound catalytic activity towards the condensed aromatic rings in coal structure. Co alone was prone to agglomerate during CCHG, resulting in the inactivation and blockage of the micropore structures. The addition of Ca retarded Co sintering and more importantly mediated Co-C interaction, making Co penetrating into the interior of coal matrix to accelerate the carbon conversion. The catalytic process of CCHG was summarized and the probable interaction between Co-Ca-C was discussed. The findings in this work will provide the theory foundation for the design of the catalyst in the pressurized fluidized bed gasifier. [ABSTRACT FROM AUTHOR]

Highlights • Devolatilization and oxidation in high H 2 O concentrations were studied in TGA. • Devolatilization behaviour was not affected by steam but by the coal rank. • Oxy-steam combustion promoted a decrease in ignition and burnout temperature. • Direct coal oxidation allowed devolatilization and oxidation kinetics calculation. • Kinetic parameters were alike for conventional, oxy-fuel and oxy-steam combustion. Abstract Oxy-steam combustion and devolatilization performance of three different coals (anthracite, blend of bituminous coals and low-rank coal) was studied in a thermobalance with a water vapour furnace under variable steam concentrations (0, 20, 40 and 70 vol% H 2 O) in N 2 and CO 2. Two oxygen concentrations were used during the combustion tests (20 and 30 vol%). Devolatilization behaviour was similar under N 2 and CO 2 atmosphere and increasing steam concentration did not affect significantly the observed reactivity and the reaction temperature range. Replacing CO 2 with 20 vol% H 2 O during combustion tests produced a decrease in ignition and burnout temperatures. When H 2 O content increased to 40 and 70 vol%, this effect was only found with high-rank anthracite. Maximum mass loss rates for the low-rank coal with high volatile content were up to four times higher than with the other two coals. During direct oxidation experiments, DTG curves of anthracite and the coal blend showed a double peak, corresponding to devolatilization and oxidation reactions. This allowed determining independent kinetic parameters (E a and A) for both stages. An only DTG peak was detected with the low-rank coal since devolatilization and oxidation reactions took place simultaneously owing to its high reactivity. Devolatilization and oxidation kinetics followed a first-order reaction using the Coats-Redfern integral method. Significant differences were not observed between the activation energies of the three coals when comparing conventional (N 2), oxy-fuel (CO 2) and oxy-steam conditions (70 vol% H 2 O in CO 2), although E a values were higher for the devolatilization stage than for the oxidation process. [ABSTRACT FROM AUTHOR]

Highlights • Effect of high-pressure CH 4 adsorption/desorption on coal samples was studied. • Microcrystalline structures were studied by XRD, HRTEM, and Raman spectra. • CH 4 irreversibly damaged the crystallites and reduced their size. • The crystallite stacking was affected, especially the stacking height. • The trends for different coal ranks were also examined. Abstract Methane adsorption/desorption not only causes coal matrix shrinkage and swelling, but also has an important influence on the microcrystalline structure of coal. In this study, high-pressure isothermal adsorption/desorption experiments were carried out for 8 coal samples with different degrees of metamorphosis. The microcrystalline structure of the samples before and after methane adsorption/desorption were quantitatively examined using X-ray diffraction, high-resolution transmission electron microscopy, and laser Raman spectroscopy. The results showed that after methane adsorption/desorption, the interplanar spacing (d 002) of the coal samples increased, and the unit stacking height (L c) and unit lateral size (L a) of coal crystallites decreased as compared with the raw samples. The changes in L c were greater than those in L a for the same sample. In other words, deformation from high-pressure adsorption/desorption has an especially significant impact on L c. Furthermore, the fringe spacing of the samples increased, and the proportion sized 0.36–0.40 nm increased in the frequency histogram. While the fringe length showed a decreasing trend, the proportion in the range of 0.30–1.00 nm was significantly increased in the frequency histogram. In addition, the D peak positions of the samples increased while those of the G peak decreased, and their difference decreased. Moreover, the full widths at half maximum of G and D peaks, and the area ratio between D and G all increased. These results are of great significance for further understanding the source of excess coalbed methane (CBM) and its state. [ABSTRACT FROM AUTHOR]

Abstract Better understanding the microcosmic mechanism of CO 2 , O 2 , and N 2 competitive adsorption can benefit the effective CO 2 storage and fire prevention by injecting coal-fired flue gas into the goaf. Toward this aim, macromolecular coal model was established. Grand Canonical Monte Carlo and Molecular Dynamics simulation were carried out at single, binary, and ternary component systems under the conditions of 298.15–318.15 K and up to 10000 kPa. Simulation results demonstrate that the absolute adsorption amount decreases with the increase of temperature and water content in coal, and increases with the pressure increasing and corresponding bulk mole fraction. The competitiveness is CO 2 > O 2 > N 2 basing on the ternary adsorption selectivity of CO 2 /O 2 (5.6–24.2), CO 2 /N 2 (8.4–29.3), and O 2 /N 2 (1.2–1.5). The isosteric adsorption heat of CO 2 (about 29.1–30.9 kJ/mol) is nearly double of O 2 or N 2 (about 16.6–17.3 kJ/mol), and CO 2 occupies stronger adsorption sites without being affected by O 2 or N 2. The interaction energy between CO 2 and coal is greater than O 2 or N 2 due to the electrostatic energy and much larger van der Waals energy. The adsorbed molecules swell the coal and the trend of self-diffusion coefficients with pressure is consistent with loading and volumes. So the flue gas injecting into the goaf is better than pure N 2 , and can store large amounts of CO 2 (0.406 mmol/g), meanwhile inhibit the coal spontaneous combustion, visually displayed by density distributions. The findings provide essential evidence for injection parameters such as temperature, pressure, gas concentration, injectivity, moisture, and so on. [ABSTRACT FROM AUTHOR]

Highlights • The performance of soybean phospholipid in reducing capillary pressure was tested. • The wettabilities of different surfactants on high-rank coal were comparatively measured. • The flow back time of fracturing fluid in the microfractures of coal was derived. • A new compound surfactant was developed to decrease water blocking damage. • The permeability of coals at different effective stresses and soak times was used to test surfactant performance. Abstract Changing wettability of coal rock surface for enhanced gas recovery, surfactant is widely used in coalbed methane exploitation. Recently, soybean phospholipid as non-toxic and degradable natural surfactant has gained increasing importance. However, effect of soybean phospholipid on wettability of high-rank coal is still unclear. In this work, typical high-rank coals were selected from the Qinshui Basin to analyze this effect mechanism. Experiments including surface tension, surface contact angle, coal fines imbibition, dispersion effect as well as gas-based permeability were carried out. Moreover, water locking mechanism of fracturing fluid in microfractures of coal reservoir was analyzed in detail. Results show that surface of high-rank coal is negatively charged in solution and have weak hydrophilicity. Soybean phospholipid can significantly reduce the surface tension of gas-liquid, and increase wettability of coal surface. Thus, soybean phospholipid contributes coal fines to disperse observed from filter cake using scanning electron microscope. Additionally, many conventional surfactants e.g. SDBS, CTMAB, OP-10 as well as soybean phospholipid were experimentally compared in performance in reducing capillary pressure. Results indicate that single soybean phospholipid do not show perfect performance. Specially, the imbibition rate of single soybean phospholipid solution along the pipe filled with coal fines was lower than that of conventional anionic and cationic surfactants, but still higher than that of stilled water and non-ionic surfactant. To further improve the capability of soybean phospholipid solution, composite surfactant was prepared with soybean phospholipid and OP-10. We found that composite surfactant at the mass ratio of 1:3 has a lowest capillary pressure with low surface tension and large contact angle. Finally, effect of three typical surfactants on permeability of coal was investigated. Results show that this suggested compound surfactant may be conducive to discharge of fracturing fluid from coal reservoir microfractures as well as improve gas-phase relative permeability in coal engineering practice. [ABSTRACT FROM AUTHOR]

Highlights • Effects of phosphorus on different ash composition coal fusion behaviors were investigated. • AFT variation trend was varied for different coal ashes at the same mass ratio of P 2 O 5. • Low melting-point (MP) berlinite formation resulted in AFT decrease for high-aluminun coal. • Silicon in silicates was substituted by phosphorus and transferred into different MP phosphates. Abstract A large quantity of livestock manure and sewage sludges produced annually in China, and the co-gasification with coal provides a promising way for these clean and large-scale utilization. The livestock manure and sewage sludges generally contain high phosphorus content. To explore the influences of phosphorus on the fusion temperatures (AFTs) of different coals and their mechanisms, the ash fusion variation behaviours of high aluminum Shajuzi coal (SJZ) and high calcium Zhundong coal (ZD) or Yimi coal (YM)) with different mass ratio phosphorus pentoxides (P 2 O 5) were investigated by an AFT tester, x-ray diffraction, and FactSage software. The P 2 O 5 addition could change the AFTs of three coals effectively, however the changing trend was different due to the difference in their ash-composition. With increasing P 2 O 5 mass ratio, low melting point (MP) berlinite formation and high MP mullite content decrease resulted in decreases in the AFTs of SJZ mixture; while high MP calcium phosphates formation led to the AFTs of ZD or YM mixture increase. At high temperature the silicon in silicate or silicaluminate in ash compositions was gradually substituted by phosphorus with increasing P 2 O 5 mass ratio and transformed into different MP phosphates because the ionic potential of P5+ (147 nm−1) was higher than that of Si4+ (95 nm−1), which resulted in different variation behaviours in the AFTs of mixture. [ABSTRACT FROM AUTHOR]

Highlights • The CBM production are impacted significantly by macrolithotype. • The hydraulic fracture initiation and propagation was evaluated using the PFC2D software. • The impact of macrolithotype on hydraulic fracture under the stress was investigated. Abstract Macrolithotypes control the pore-fracture distribution heterogeneity in coal, which impacts stimulation via hydrofracturing and coalbed methane production in the reservoir. Here, the aspects of coalbed methane production that are impacted by macrolithotype were determined from production data from 56 wells in the Hancheng Block, China. The macrolithotype contribution had a significant influence on the well productivity, with dull lithotype-rich (dull and semi-dull coal) coal having significantly lower productivity than wells with bright lithotype-rich (bright and semi-bright coal) coal. The main reason for this difference is that macrolithotypes impart a fracture distribution, which further impacts the hydrofracture stimulation and subsequent coalbed methane production. Here, the hydraulic fracture was evaluated using the appropriate mechanical behavior for each macrolithotype with PFC2D software, and the impact of the macrolithotype on hydraulic fracture initiation and propagation, which are controlled by stress and mechanical properties, was investigated systematically. The result showed that the hydraulic fracture propagation types are controlled by the pre-existing natural fractures. Furthermore, due to the well-developed natural fracture network, the hydraulic fractures in bright coal were mainly composed of the opening, steering propagation, and compound types, forming a lattice-like fracture network. Dull coal is denser, and its hydraulic fractures are characterized as an isolated fracture distribution. The conclusions were verified through monitoring of hydraulic fracture by the microseism wells which show that the fracture in the bright coal is more likely to match the "complex fracture network" description, and the "simple" case when the dull coal is fractured. Meanwhile, the hydraulic fractures mainly open at a shallow depth, but with the increase in depth, the hydraulic fractures are dominated by the crossing type. If the hydraulic fractures are the opening type, only at a higher liquid pressure can the natural fractures in dull coal be initiated. Thus, the difference between hydraulic fractures in bright and dull coal lead to different flow paths and ultimately result in a variation of coalbed methane production. Therefore, during coalbed methane output, a bright coal reservoir will have more potential than a dull coal reservoir, which provides a scientific base for coalbed methane exploration and development. [ABSTRACT FROM AUTHOR]

Abstract The poor flotation efficiency of low-rank coal in the flotation process is due to the large and rich pore structure on its surface. In this study, the changes in the pore structure before and after pore compression pretreatment were analyzed by a scanning electron microscope and Brunauer–Emmett–Teller analysis. The effects on the flotation were then evaluated by analyzing the results of collector adsorption experiments and flotation kinetics tests. After pore compression, the pore state on low-rank coal surface was from open to half-closed and then closed. Further, the pore volume, specific surface area, and average pore diameter of the particles decreased from 0.02497 to 0.01214 cm3/g, 17.383 to 5.006 m2/g, and 9.6992 to 5.7466 nm, respectively. In addition, the adsorption rate of the collectors improved and the equilibrium adsorption time of n-dodecane decreased from 436 s to 250 s, whereas the adsorption rate of water decreased with the porosity of the coal after pore compression. Meanwhile, according to the flotation results, the maximum clean coal yield (74.44%) was obtained within 400 MPa of pressure pretreatment using n-dodecane as a collector; this value is 20.46% points higher than that of raw coal flotation using n-hexane as the collector. Furthermore, it was also found that a collector with too high a viscosity or too short a carbon chain causes the total cumulative yield of the low-rank coal to decrease. It is anticipated that the results of this work can provide guidance in low-rank coal flotation applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Surface hydrophobicity of low-rank coal was enhanced by the adsorption of DTAB. • The head group of DTAB adsorbed on the low-rank coal surface and alkyl chains was exposed. • The adsorption of DTAB decreased the interaction energy and number of hydrogen bonds. • The mobility of water molecules was improved due to the surface repulsive effect. Abstract This study investigated the mechanism of improving the surface hydrophobicity of low-rank coal by adsorbing dodecyltrimethylammonium bromide (DTAB). Experimental tests were conducted to analyze the adsorption characteristic of DTAB on the coal surface including the adsorption amount, Zeta potential, wetting heat, and X-ray photoelectron spectroscopy measurement. Furthermore, the adsorption configuration, spatial location of the simulation systems, and the coal–water interaction were investigated by molecular dynamics (MD) simulation at the atomic scale. Experimental results indicate that the hydrophobicity of the low-rank coal first increased, then decreased as the DTAB concentration increased. The electrostatic force plays a dominant role in the adsorption of DTAB on low-rank coal surface. The adsorption of DTAB reduced the wetting heat between water and low-rank coal because the oxygen-containing groups were covered. The decrease in hydrophobicity at high DTAB concentration was due to the formation of a bilayer or micelle adsorption. MD simulation results show that the adsorption of DTAB reduced the thickness of the water adsorption layer. The nitrogen atoms of DTAB were oriented toward the coal surface, such that the alkyl chains were oriented to the water phase, thereby producing an additional repulsive effect and subsequently inhibiting the adsorption of water molecules. As a result, the number of hydrogen bonds and the interaction energy between water molecules and low-rank coal decreased, indicating that the hydrophobicity of low-rank coal was enhanced. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A catalyst was prepared from fly ash disposed as waste from iron and steel industry. • Acid activated fly ash had enhanced Brønsted acidity and surface area of 113 m2/g. • Developed catalyst yielded 62% furfural at 170 °C in 210 min. • In 35 ppt saline water, furfural yield improved to 68%. Abstract For the first time, application of acid-treated coal fly ash as a catalyst for selective dehydration of d -xylose to furfural was investigated in this work. Coal fly ash had been treated with sulphuric acid to promote de-alumination and consequently enhance the silanol concentration in the modified catalyst. This Brønsted acidic catalyst had been effective to convert 85% d -xylose to yield 62% furfural at 170 °C. On addition of 35 ppt of NaCl to the system furfural yield was improved to 68%. This promising result in equivalent salinity of sea water might open up possibilities to investigate inexpensive sea water as a replacement of distilled water to improve the product yield. The catalyst was stable enough to sustain minimum of 6 cycles of run. Apart from the abundant availability and cheap price of fly ash, utilizing it for heterogeneous catalysis drives to mitigate disposal problems of fly ash to partial extent. The dual advantages make the system eco-friendly. [ABSTRACT FROM AUTHOR]

Abstract To better understand the fractal characteristics of coal fracture network and find the relation between 2D and 3D fractal dimensions, the improved box counting method was utilized to calculate 2D and 3D fractal dimensions based on high resolution CT images of 4 coal samples (R o from 2.915% to 4.69%). Based on the calculated 2D and 3D fractal dimension, the size of representative element volume (REV), the relationship between D f2 and D f3 and the relationship between porosity and fractal dimension were investigated extensively. As the complement of previous theoretical studies, the exponential relationship between porosity and fractal dimension was proved. By deducing formulas based on fractal theory, the ratio of the minimum pore size to the maximum pore size could be obtained. Evidently, the relation between 2D and 3D fractal dimension of coal could be expressed as D f 3 = C D f 2 + 1 , and the slope of the line, C, depends on the average 2D fractal dimension of the sample. [ABSTRACT FROM AUTHOR]

Abstract In present study, the volatilization of arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb) by the burning of coal samples in the electric furnace was evaluated. The coal samples were obtained from different blocks of newly developed Thar coal field, Pakistan. The replicate coal samples were heated/burned in an electric furnace at laboratory scale for three temperature intervals (200, 400 and 900 °C). The ash obtained after each temperature intervals were analyzed for selected toxic elements. The resulted data indicated that the total contents of As, Cd, and Pb in coal samples of block X and XI were found in the range of 16.8–18.5, 4.21–4.72, and 14.2–18.8 mg/kg, respectively. Whereas, 67.8–79.7%, 34.3–36.8% and 9.89–10.8% of As, Cd, and Pb, respectively, were volatized out after combustion of coal samples at 900 °C. The total contents of Hg in selected coal samples of block X and XI were observed in the range of 0.985–1.46 and 0.992–1.41 mg/kg, respectively. The contents of Hg volatilized out via burning in a furnace at 200 °C and 400 °C, were observed in the range of 32.0–36.5% and >91.0% of its total contents, respectively, whereas at 900 °C, it was not detected in ash. The partitioning and mobility of studied toxic elements in residue termed as (laboratory made ash) obtained after burning at 900 °C, was carried out by three-step sequential extraction scheme. The resulted data of present study will give a better knowledge about the quality of coal and its burning product, which may help to take measure to reduce the adverse effects on the environment in future. Graphical abstract Image Highlights • Volatilization of toxic elements in laboratory made ash of coal samples at different temperature. • Burning of coal samples in an electric furnace at 900 °C, 67.0–79% of total arsenic was volatized out. • The coal samples heating in electric furnace at 400 °C, Hg volatilize out > 91.0% of its total contents. • Partitioning of toxic elements in residual ash of coal was carried out by sequential extraction scheme. • The 2.9, 6.4, 1.34% of total contents of As, Cd and Pb in ash of coal were water soluble/bioavailble [ABSTRACT FROM AUTHOR]

The quality of coals from, Erzurum varies widely. Two coal samples from this area were compared. The first has a composition of 19% ash, 5700 kcal, and 3% sulfur while the other has 49.20% ash, 3000 kcal, and 1.6% sulfur composition. It is understood that the first coal sample is a high-quality coal. Although the ash content of the second coal sample is determined to be high and the calorie value is low, the low sulfur content is advantageous for the environment. This study aimed at increasing the quality of coal samples by carrying out experiments for reducing the ratio of ash and sulfur with Knelson's enrichment processes. Chemical analysis, sieve analysis experiments, %ash, %moisture, and %calorie values of each fraction are determined from two different C1 and C2 coal samples taken from the Balkaya village belonging to Şenkaya, Erzurum. Then, %ash, %yield, and %sulfur analyzes were carried out on the coal samples using the Knelson gravity separator enrichment method, and the results were evaluated for coal samples. [ABSTRACT FROM AUTHOR]

Pore connectivity is an important property of coal. To explore the connectivity of pore-fractures in terms of macropores and mesopores in high-rank coal, two coal samples collected from the coal seam #3 in the southern Qinshui basin were selected. A pore-fracture network model of high-rank coal on the nanometer (10-100 nm) to micrometer (0.1-10 μm) scale is constructed, and key parameters are extracted using the 3D (three-dimensional) digital spatial characterization based on 3D scanning with FIB-SEM (Focused Ion Beam Scanning Electron Microscopy). Then, the connectivity of the pore-fractures and the contribution of pores with different genetic types to the connectivity of the high-rank coal are confirmed. The results show that the pores and throats of high-rank coal in coal seam #3 in the southern Qinshui basin are very narrow, with predominant mesopores < 50 nm in width. The tortuosity of the coal samples is low, and the cross-section is predominantly square and triangular in shape, which means that the capillary resistance is small. The connectivity of the pores is poor, and mesopores play an important role in the pore connectivity. Linear differential shrinkage pores are the main connected pores on the nanometer scale and communicate with irregularly rounded and elliptic differential shrinkage pores, secondary pores, and mineral pores. The types and contents of the minerals in coals determine the morphological characteristics and degree of development of the differential shrinkage pores, and have an important influence on the pore connectivity in high-rank coal. The content of quartz determines the degree of development of the linear differential shrinkage pores, and is the primary reasons for the differences in the connectivity of the two samples. [ABSTRACT FROM AUTHOR]

Coal properties are associated with both elements and molecular structure. In this study, to improve the analysis performance of coal properties (e.g. the volatile content and calorific value), a data fusion scheme for combining laser-induced breakdown spectroscopy (LIBS) and Fourier-transform infrared spectroscopy (FTIR) was proposed in order to simultaneously extract elemental and molecular information. Ward's minimum variance method was applied to classify coal samples and determine the calibration set and the validation set prior to establishing the calibration model. A partial least-squares (PLS) model was employed to analyze the volatile content and calorific value using the second derivative FTIR spectrum (2ndDev-FTIR), LIBS, and a combination of LIBS and the second derivative FTIR spectrum (LIBS&2ndDev-FTIR), respectively. The analysis results of these three schemes were compared. The root mean square error of prediction (RMSEP) of the volatile content was decreased from 2.937% (2ndDev-FTIR) and 1.622% (LIBS) to 0.884% (LIBS&2ndDev-FTIR), and the RMSEP of the calorific value was also decreased from 1.095 MJ kg−1 (2ndDev-FTIR) and 0.613 MJ kg−1 (LIBS) to 0.559 MJ kg−1 (LIBS&2ndDev-FTIR). Similarly, the same trend was indicated in the average absolute error (AAE) and the average relative error (ARE). The improvement in the predictive performance can be attributed to the synergy between the elemental information obtained from LIBS and the molecular information gained from FTIR spectroscopy. The results demonstrated the feasibility of combining LIBS and FTIR spectroscopy to provide an improved analytical result for the volatile content and calorific value of coal. [ABSTRACT FROM AUTHOR]

In this investigation, the possibility of carboxylic acid used as collector to float low-rank coal was explored and alkane was also used to be compared. The effect of different lengths of carbon chain of carboxylic acid and alkane on flotation performance was studied. XPS and contact angle measurements were adopted to determine the properties of low-rank coal and make explanations for flotation results. The XPS results showed that there were many hydrophilic functional groups, such as C-O, C=O, and O=C-O, on the surface of low-rank coal. Accordingly, the contact angle of raw coal is low, which indicates that the low-rank coal is difficult to float. The flotation results showed that the flotation of low-rank coal in the presence of carboxylic acid contributed to better flotation performance than that obtained by alkane, which indicated that carboxylic acid can be more effective collector than alkane to float low-rank coal. The combustible matter recovery increases first and then decreases with the increase of carbon atoms in molecular structure of carboxylic acid. And this indicates that a proper length of carbon chain has great importance for improving flotation performance of carboxylic acid used as collector. [ABSTRACT FROM AUTHOR]

Copyright of Investigaciones Historicas is the property of Universidad de Valladolid, Facultad de Filosofia y Letras and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A thin basement coal seam mining model under different overlying strata conditions was developed using the discrete element software UDEC. This approach is used to discuss the safety mining of the thin basement coal seams. Fracture development in overlying and rock strata movement law in the stope was discussed. The relationship between support and surrounding rocks under different overlying strata conditions was analyzed. Lastly, a field industrial test was conducted based on the research results. A few major conclusions could be drawn. Under load transmission in loose water-bearing strata, causing a large-scaled rock strata movement to advance into the working face is easy when only one bearing stratum exists in the overlying strata. Meanwhile, the support bears strong loads, which can easily be collapsed. When two bearing strata exist in the overlying one, the upper bearing stratum can form a voussoir beam structure. Loads on the support decreased substantially compared with those under single bearing stratum, whilst the probability of pressing frame was reduced accordingly. A weathered zone above the stope was reinforced by ground J-type drilling pregrouting, thereby improving the physical and mechanical properties and increasing the bearing capacity of the rock strata in the grouting range and safety mining of the working face in the lower coal seams. Research results provide important references for the safety mining of thin basement coal seams under similar conditions. [ABSTRACT FROM AUTHOR]

Abstract The present work investigated an effective reductive desulfurization method for thiophene sulfur in high organic sulfur coal utilizing the potassium tert-butoxide/hydrosilane. Maximum decreases of 65.8% and 64.2% in organic sulfur for Xinyu coal and Guxian raw coals were, respectively obtained under the optimized conditions of the molar ratio of reductive assistant to sulfur of coal (15), treatment time (80 min), temperature (215 °C). According to the results of XPS, more than 80% mercaptan, sulfoether and thiophene on the raw coals surface were removed without destroying the macromolecular structure of coal. Sulfur on treated coal surface samples mainly existed in the form of sulfonate and sulfone due to the hydrolysis and oxidation of intermediate products generated in the reduction desulfurization reaction. These findings confirmed the possibility of effective removal for thiophene sulfur in coal utilizing the reductive system, which could give a reference for thiophene sulfur removal of high organic sulfur coal. [ABSTRACT FROM AUTHOR]

Abstract Coal organic microspheres (COM), a novel material originated from the organic components of coal, were obtained from brown coal directly using a one-step treatment in a flow of water. Here, we studied in detail the effect of hydrothermal conditions on morphology, yield, elemental composition, functional groups, and molecular composition of COM, at temperatures of 250, 300, 350, and 380 °C, pressures of 4, 10, 20, and 24 MPa, and holding times of 0, 30, 60, and 90 min. The holding time influences COM production: longer holding time leads to higher yields and larger particle size. The hydrothermal temperature and pressure, which control the properties of water, have a significant influence on the yield, shape, and particle size of COM. The properties of water affect the COM yields as follows: 1) when the phase of water is liquid, the lower density, viscosity, and static dielectric constant gives higher yields; 2) the yield obtained in supercritical water is higher than that in subcritical water; 3) phase transformation of water from liquid to gas decreases the yield. Additionally, the particle size of COM can be controlled by the temperature, and the pressure affects the shape of COM greatly; even nano-sized particles are produced at 350 °C and 10 MPa. From the molecular composition results, low-molecular weight compounds with small double bond equivalents decompose under supercritical water condition. Large amounts of organic compounds in brown coal are thermally decomposed and extracted under hydrothermal conditions, and then spherical COM particles form and grow from small to big during the cooling process. These results are helpful for clarifying the formation mechanism of COM, and enable control of COM yield and properties. [ABSTRACT FROM AUTHOR]

ABSTRACT In order to study the variation of electrical parameters in the process of spontaneous combustion of coal, first, 9 characteristic temperature points of 5 kinds of coal samples at low temperature oxidation stage and high temperature spontaneous combustion stage were obtained based on temperature programmed experiment and thermogravimetric experiment. According to these experiments samples at characteristic temperature points were prepared. Then, the complex impedance parameters of each coal sample are measured at the alternating current of 20 Hz to n × 106 Hz, and the volume resistivity and the complex permittivity of the coal sample are obtained by calculation. Finally, the volume resistivity temperature model and the complex dielectric constant temperature model of coal samples are obtained by fitting the electrical parameters at 100 kHz test frequency. The results showed that the volume resistivity of coal samples decreased rapidly in the mid-low frequency and slowly in the mid-high frequency. Under the fixed test frequency, the volume resistivity of coal samples rises first and then decreases with the increase of temperature. Both the real and imaginary parts of the complex relative permittivity of coal samples decrease with the increase of temperature, and the slope of the curve decreases gradually. Highlights • Resistivity of coal decreases rapidly in mid-low frequency and slowly in mid-high. • At fixed frequency coal's resistivity rises first and then decreases with temperature. • The real and imaginary parts of coal relative permittivity show a same change rule. • Permittivity decreases with increasing temperature; the slope gradually decreases. [ABSTRACT FROM AUTHOR]

Rapid and online analysis of coal properties is extremely important for reasonable and clean utilization of coal. In this study, laser-induced breakdown spectroscopy (LIBS) was applied for analysis of coal properties. The kernel extreme learning machine (K-ELM) method was used to establish a nonlinear model, and particle swarm optimization (PSO) was used as the variable selection method to eliminate useless information and improve prediction ability of the model. The influence of different pretreatment methods was also investigated by 10-fold cross validation (CV); moreover, based on the optimal pretreatment method, three K-ELM models with full spectra, characteristic lines and PSO were developed and compared for predicting ash content, volatile matter content and calorific value of coal. The root mean squared error of cross-validation (RMSECV), correlation coefficient of cross-validation (RCV), root mean square error of prediction (RMSEP) and correlation coefficient of prediction (RP) were used to evaluate model performance; the corresponding RMSEP and RP values were 1.8957% and 0.9936 for ash content based on the K-ELM model with characteristic lines, 1.0874% and 0.9945 for volatile matter, and 0.6999 MJ kg−1 and 0.9872 for calorific value based on the K-ELM model with PSO. The results demonstrate that LIBS coupled with K-ELM and variable selection is a promising technique for rapid analysis of coal properties, and it will also be helpful for effective, clean utilization of traditional energy sources. [ABSTRACT FROM AUTHOR]

The Jurassic Yanan Formation is one of the most important coal‐producing formations and hydrocarbon source rocks in the Ordos Basin, North China. To evaluate the shale gas potential of the Yanan shale, a total of 48 samples from north Ordos Basin were sampled, and their geochemical, petrological, mineralogical and pore characteristics were investigated. It was found that the shale samples are a suite of early mature source rock. The total organic carbon (TOC) content ranges from 0.33% to 24.12% and the hydrogen index (HI) ranges from 43.31mg/g to 330.58 mg/g. The relationship between Tmax and HI indicates the organic matter is type II‐III. This conclusion is also supported by the organic petrological examination results, which shows that the kerogen is mainly liptinite and vitrinite. Minerals in the samples are composed mainly of quartz, clay and feldspar, and the clay minerals are composed of prevailing kaolinite, illite/smectite, chlorite and a small amount of illite. Under scanning electron microscope, OM pores in the Yanan shale are scarce except pores come from the kerogen intrinsic texture or clay aggregates within the organic particles. As the weak compaction caused by shallow burial depth, interparticle pores and intraparticle pores are common, the hydrocarbon storage capacity of the Yanan shale was improved. According to evaluation, the Yanan shale is considered as a good shale gas reservoir, but its hydrocarbon potential is more dependent on biogenic and coal‐derived gas as the thermogenic gas is limited by the lower thermal maturity. [ABSTRACT FROM AUTHOR]

Copyright of Archives of Mining Sciences is the property of Polish Academy of Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A comprehensive analysis of coal quality factors affecting coal agglomeration characteristics was carried out. The influence weight of seven main coal quality indices on agglomeration was calculated by the entropy method. Furthermore, a reliable and comprehensive coal quality index was obtained to evaluate the characteristics of coal agglomeration by the agglomeration experiment results. The proximate analysis, ultimate analysis, and petrographic analysis results were applied for the analysis of organic constituents. The XRF and ash fusion temperatures were applied for the analysis of inorganic constituents. Results show that there is an absolute positive correlation between the C/H, FC/V and the characteristics of coal agglomeration. Both of the vitrinite content and the average reflectivity of the vitrinite have a positive effect on the coking ability of coal. Alkali oxides not only have a low melting point but also can react with Si and Al to form low melting point eutectics. Both of these characteristics result in coal ash slagging. The entropy method was adopted to analyze the effect weight of C/H, FC/V, vitrinite content Vi, vitrinite average reflectivity R ave , ash deformation temperature (DT), Base/Acid ratio (B/A) and Silicon ratio (G) on the agglomeration characteristics of coal. The weights are 11%, 10%, 26%, 12%, 9%, 14% and 18%, respectively. Among them, vitrinite content had the largest effect, and DT had the least effect. In addition, an empirical index of coal agglomeration characteristics is proposed, and the discriminant limits are provided. The results are helpful to the evaluation of coal agglomeration, and useful to the safe and efficient operation of boilers. [ABSTRACT FROM AUTHOR]

This study aims to produce activated carbon from low-rank coal from East Kalimantan, Indonesia by a mechano-chemical method and to determine its adsorption parameters: hydrogen uptake/capacity, activation energy, the structural heterogeneity parameter, and the isosteric heat of adsorption. The hydrogen uptake/capacity of the coal was determined by a volumetric adsorption test using constant-volume-variable-pressure (CVVP). The characteristic adsorption parameters, such as hydrogen uptake, characteristic energy and heterogeneity structure factor, were determined using the coupled Langmuir and Dubinin-Astakhov (D-A) isotherm models, with the assumption that the hydrogen uptake value would be similar, irrespective of the model used. We found that the mechano-chemical method significantly reduced the particle size of the activated carbon relative to the untreated control, by approximately 60%. In addition, the activation process yielded a higher surface area for the activated carbon (390 m2/g) compared to the untreated control (90 m2/g). We also found that greater surface area led to a greater uptake of hydrogen by the activated carbon (40.17±1.56)×10-3 kg/kg than by the untreated control (7.94±1.56)×10-3 kg/kg. We also found that the heterogeneity factor of the activated carbon was 3.73±0.23, lower than the untreated control 4.65±0.56, which reflects the more heterogeneous pore diameter sizes for the activated carbon compared to the untreated control. Lastly, using the obtained adsorption parameters, we observed that the hydrogen uptake-dependent isosteric heat of adsorption on the activated carbon changed rapidly in the initial and final stages compared to the untreated control due to the adsorption of hydrogen by smaller pores which reside inside larger ones. [ABSTRACT FROM AUTHOR]

The aim of this paper was to develop a model that can characterize the actual micropore structures in coal and gain an in-depth insight into water’s seepage rules in coal pores under different pressure gradients from a microscopic perspective. To achieve this goal, long-flame coals were first scanned by an X-ray 3D microscope; then, through a representative elementary volume (REV) analysis, the optimal side length was determined to be 60 μm; subsequently, by using Avizo software, the coal’s micropore structures were acquired. Considering that the porosity varies in the same coal sample, this study selected four regions in the sample for an in-depth analysis. Moreover, numerical simulations on water’s seepage behaviors in coal under 30 different pressure gradients were performed. The results show that (1) the variation of the simulated seepage velocity and pressure gradient accorded with Forchheimer’s high-velocity nonlinear seepage rules; (2) the permeability did not necessarily increase with the increase of the effective porosity; (3) in the same model, under different pressure gradients, the average seepage pressure decreased gradually, while the average seepage velocity and average mass flow varied greatly with the increase of the seepage length; and (4) under the same pressure gradient, the increase of the average mass flow from the inlet to the outlet became more significant under a higher inlet pressure. [ABSTRACT FROM AUTHOR]

The formation of resultant volatiles is closely related with chemical structure of char during the pyrolysis process. In this study, all-components, that are semi-char, tar and gas product obtained by Shenfu coal pyrolyzed under various residence time at 435 °C were comprehensively analyzed at molecular level, aiming to reveal the reaction pathways responsible for the evolution of chemical structure of coal/char. The results showed that CO 2 and CO were the predominant pyrolysis gas product which inferred high content of organic oxygen species in low-rank Shenfu coal. At the initial stage of pyrolysis, cracking of bridged bonds, especially heteroatom bridged bonds, such as O, N and S, would produce relatively stable radicals in semi-char. Phase change of light components and decomposition of asphaltene in mobile phase can be strongly related with light tar aliphatic compounds formation. At the middle and later stage of pyrolysis, thermal cracking of polar radicals and decomposition of solvent extracted metaplast materials made predominant contribution to tar formation. In addition, the cracking of peripheral aromatic structures of coal/char skeleton structure, through which secondary reaction (such as methylation and dehydrogenation reaction) took place, would result in tar (light tar and heavy tar) and H 2 formation. [ABSTRACT FROM AUTHOR]

A study was undertaken to investigate the structure, electrical conductivity and dielectric properties of low-rank coals during microwave pyrolysis. The mechanism of dielectric response during microwave pyrolysis was also discussed. The pyrolysis conditions were a microwave power of 800 W and different radiation times; dielectric properties were measured using a vector network analyzer at a frequency of 2450 MHz, and the electrical conductivity was measured using a four-probe resistivity tester. Results show that with increasing microwave radiation time, the functional groups gradually cracked and fell off, and the structural order was gradually enhanced. In addition, the order of the structure increased the number of sp 2 -hybridized carbon atoms on a single plane and increased the delocalized electrons between the graphite crystal planes. The complex relative permittivity and resistivity of the semi-cokes exhibited a significant dependence on microwave radiation time and pyrolysis temperature, especially after 15 min of microwave radiation. By comparing the calculated and measured values of imaginary parts, it could be deduced that the electric conductive loss is also an important part of the microwave attenuation mechanism in the process of microwave pyrolysis, as important as the relaxation loss and the interface polarization loss. [ABSTRACT FROM AUTHOR]

This paper presents pyrolysis simulations of a multi-component structure model of Fugu sub-bituminous coal containing 23,898 atoms with ReaxFF MD. The slow heat-up and long-time isothermal simulations were performed using the GPU-enabled ReaxFF MD code of GMD-Reax and reaction analysis code of VARxMD. The simulated pyrolyzate evolution trends and pyrolysis stages proposed based on lumped pyrolyzates agree fairly with literature. Major reaction pathways for early generation of CO 2 , H 2 O, CH 4 and H 2 in the activation and primary pyrolysis stages are found closely associated with carboxyl and methoxyl groups, indicating the significant role of oxygen-containing groups in the initialization of Fugu coal pyrolysis. Compared with reported experiments, the coal tar yield is over-predicted, while the gas yield is slightly under-estimated. To shorten the simulation time from 2 ns to 250 ps, an increase of 400 K in average on the basis of temperature range of 1200–2200 K is needed that will result in the over-prediction for the yields of gas and tar, as well as under-prediction for the non-volatile yield. This work suggests that ReaxFF MD simulation is useful for revealing the overall scenario and detailed reactions in coal pyrolysis but cautions should be taken for proper elevated temperatures. [ABSTRACT FROM AUTHOR]

It is difficult to yield a high combustible matter recovery in the flotation of low rank coal with common oily collectors. This study focuses on the enhancement in flotation performance of low rank coal by combining diesel oil with didodecyldimethylammonium bromide (DDAB), as well as its corresponding intensifying mechanism. The adsorption of DDAB and/or diesel oil on the pure coal and quartz surfaces was investigated based on the zeta potential and FTIR analyses, while the floatability of the coal and quartz samples before and after pretreatment was evaluated by the attachment time and flotation results. The results indicated that DDAB had great effects on the zeta potentials of coal and quartz, and the isoelectric points of these two samples were observed at the DDAB concentrations of about 0.007 and 0.006 g/L, respectively. Additionally, according to the FTIR analyses, the physical and chemical adsorptions were proposed to interpret the adsorption of DDAB, and diesel oil and mixed diesel oil/DDAB on the coal surface, respectively. Meanwhile, the diesel oil’s adsorption of on the coal surface was enhanced by the conditioning process with the mixed DDAB/diesel oil. In contrast, diesel oil adsorption on the quartz was very little in quantity. As a result, a great difference in surface hydrophobicity between the coal and the quartz was attained, and an excellent flotation performance was obtained by using the mixed DDAB/diesel oil. However, a too low surface tension of flotation pulp caused by the excessive DDAB seems to be unfavorable to the flotation of coal samples. In this case, water with less surface tension was readier to spread on the coal surface than diesel oil, thereby making the coal hydrophilic and meanwhile hindering the diesel oil’s spreading on its surface. [ABSTRACT FROM AUTHOR]

The purpose of this investigation was to explore the effect of low-temperature pyrolysis on the wettability and floatability of the long-flame low-rank coal particles. Changes in surface functional groups of long-flame coal were measured before and after pyrolysis and the surface free energy of the coal particles was calculated by the van Oss–Chaudhury–Good theory. As the pyrolysis temperature was increased to 500 °C, the total surface free energy γ S and the base part γ S - of the long-flame coal decreased from 42.63 to 41.26 mN·m −1 and from 28.19 to 2.18 mN·m −1 , respectively. The reductions in γ S and γ S - indicated a significant increase in hydrophobicity of the long-flame coal after pyrolysis. In addition, the wetting heat of the coal became less negative, indicating significant restriction of the hydrophilicity of the coal surface. The zeta potential of the coal was measured before and after pyrolysis; pyrolysis significantly affected the coal’s zeta potential, which became less negative as the pyrolysis temperature was increased. Thus, the electrostatic repulsion between bubbles and coal particles decreased after pyrolysis, and therefore the attachment time of bubbles to coal particles decreased by up to 72.73%. The flotation recovery of the coal particles increased by up to 38.20% as the pyrolysis temperature was increased to 500 °C. [ABSTRACT FROM AUTHOR]

Highlights • A coal proximate analysis method based on a combination of visible-infrared spectroscopy and deep neural networks. • This method can fate examines the moisture, ash, volatile matter, fixed carbon, sulphur and low heating value in coal. • Compared with traditional coal analysis, this method has unparalleled advantages and important value for practical applications in terms of efficiency, speed and accuracy. • We proposed a new CNN-AELM deep neural network algorithm. Abstract The proximate analysis of coal is the umbrella term for the six indexes that include the moisture, ash, volatile matter, fixed carbon, and sulphur contents and the heating value. Burning of coal creates carbon dioxide, sulphur dioxide and nitrogen dioxide which are main reasons causing air pollution. Therefore, before utilizing coal, it is indispensable to analyse coal. The traditional proximate analysis of coal mainly relies on chemical analysis, which is time-consuming and costly. Hence, a method to construct a coal analysis is introduced in this paper. By using the method to analyse moisture (%), ash (%), volatile matter (%), fixed carbon (%), and sulphur (%) contents and the low heating value (J/g). We first obtained different coal sample from different coal areas in China. Then, measured the spectral data through the spectral analysis instrument and extracted spectral features through a convolutional neural network. Finally, we applied the extreme learning machine algorithm to construct the prediction and analysis model of the spectral feature data. The experimental result shows that the model in the study can predict the components of coal. Compared with the chemical analysis method, this method has unparalleled advantages in terms of financial efficiency, speed and accuracy. [ABSTRACT FROM AUTHOR]

The main purpose of this study was to investigate the effects of low molecular compounds in coal on the formation of benzene, toluene, xylene and naphthalene (BTXN) in the catalytic upgrading of tar from coal pyrolysis by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Low molecular compounds were extracted from mineral-free lignite (Coal DA) and bituminous coal (Coal DB), and then the gaseous tars from the pyrolysis of residual coal (Coal DAR and Coal DBR), extraction solution (AE and BE) and mineral-free coal were subjected to catalytic cracking using USY zeolite as catalyst. The results show that the total amount of BTXN in the extraction solution and residual coal is 27% and 4.8% lower than that in Coal DA and Coal DB during catalytic upgrading of gaseous tars, respectively. The presence of low molecular compounds can result in a significant increase in the BTXN amount after catalytic reforming. The extraction solution in Coal DA are predominantly aliphatic compounds (72.7%) and Oxygen-containing aromatics (21.9%), whereas that in Coal DB is naphthalene series (33.1%), condensed aromatics (29.4%), and aliphatic compounds (23.5%). Phenols and condensed aromatics in low molecular compounds can be cracked into BTXN under the catalysis of USY zeolite. More heavy aromatics are cracked to light arene instead of polycondensation in the presence of aliphatic compounds. [ABSTRACT FROM AUTHOR]

The present study focuses on the investigation of the optical anisotropy, optical sign, textural heterogeneity and deformational features of the maceral grains along with the Raman spectral characteristics of the seven coal samples collected from the Himalayan fold-thrust belts of Sikkim State, India. The coal samples were extremely fragile and pulverized due to the intense tectonic deformation. The maceral composition revealed the dominance of semifusinite over collotelinite grains. The calculated maximum vitrinite reflectance (5.94–8.66%) and mean random reflectance (4.11–5.36%) suggest anthracite A rank of the coal samples following ISO 11760:2005. The proximity of the intermediate reflectance axis value (R INT ) to maximum reflectance axis value (R MAX ) as well as the range of Reflectance Indicating Surface (RIS) style (R st ) values (−9.98 to −19.37) indicates the biaxial negative optical texture of the vitrinite grains. The augmented bireflectance values due to enhancement of the R MAX associated with strong decline in R MIN may suggest the commencement of pregraphitization. In addition, the strong linear correlation ( r  = 0.94) of the RIS-anisotropy (R am ) parameter with the bireflectance values may imply the role of tectonic stress on the optical transformations of the samples. The range of the peak temperature (334.94–369.01 °C) calculated from mean random vitrinite reflectance may suggest the effect of thermo-stress coupling on the metamorphism of these coal samples. Microlithotype study combined with deformational aspects of macerals shows the presence of “deformed”, “sheared” and “smashed” grains within each sample, which may, additionally, document the tectonic stress influence on the coal particles. Moreover, relatively, larger area of ‘defect band 1 (D 1 )’ than that of ‘graphitic band (G)’ along with the broad G band in the first order Raman spectra may indicate the considerable presence of structural dislocations and aromatic compounds with disordered bond angle within the microstructure induced by the tectonic deformation. The lowest intensity of the ‘defect band 4 (D 4 )’ may suggest the preferential removal of aliphatic compounds from the samples in response to the tectonic stress degradation. In addition, the relative area ratio calculated from the D 1 and the G bands (AD 1 /(AD 1  + AG)) may indicate that the studied anthracite samples would have attained the metamorphic temperature ranging from 325.12–387.89 °C. [ABSTRACT FROM AUTHOR]

This paper describes the occurrence of significant authigenic analcime (NaAlSi 2 O 6 · H 2 O) in the middle Jurassic coal from the northeastern Ordos Basin and discusses its origin. Twelve coal samples from borehole ZK31-19 in the Dongsheng Coalfield were collected and analyzed. The coals are characterized by a low-medium ash yield, high volatile matter and low sulfur contents. The major-element oxides in the studied coals are mostly at similar or much lower concentrations compared to the averages for Chinese coals. Similarly, most trace elements are depleted or in concentrations close to the respective averages for world low-rank coals. Based on Seredin-Dai's classification, the REY (rare earth elements and Y) in the coal mainly display N- and H-type distribution patterns, with no Ce and Eu anomalies. Coal sample ZK31-19-12 from the lower Zhiluo Formation contains analcime up to 23 wt%, with a high Na 2 O concentration of 1.23% (both on a whole-coal basis). The analcime occurs as lath, as subhedral granular crystals in fissures or pores and as anhedral crystals in the organic matrix. Furthermore, significant analcime has also been observed by SEM in coal from the upper Yan'an Formation (sample ZK31–19-10), which mainly occurrs as anhedral crystals. No evidence of analcime forming from precursors of volcaniclastic material, alkali zeolites or other silicates was detected, therefore, it is deduced that the analcime in the studied coals formed by authigenic precipitation. The Na 2 O content in the studied coal seams displays a vertical variation different from that of the ash yield ( A d ) and those of the detrital-dominated elements, such as SiO 2 , Al 2 O 3 , TiO 2 , Zr, Nb and Th, indicating a different origin of Na compared with other detrital materials of terrigenous origin. Combined with the evidence of the obvious Na peak in authigenic amorphous material and gypsum mineral by SEM, it can be inferred that the source of Na may derive from the fluids. The paleoclimatic change (from subtropical warm and humid to semi-arid and arid hot, during the deposition period of the Yan'an to the Zhiluo Formation) may provide favorable conditions for analcime authigenesis, leading to its abundant precipitation in the lower Zhiluo Formation and its limited occurrence in the upper Yan'an Formation. Such paleoclimatic change is also significant for the U mineralization in the lower Zhiluo Formation. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) has been widely used to evaluate the pore size distribution (PSD) properties of coals. However, the NMR signal itself only provides a relative distribution of pore size. To calculate an absolute pore size distribution from the NMR data, the T 2 cutoff value needs to be known. Meanwhile, the T 2 cutoff value is an indicator to divide the irreducible fluid and movable fluid in porous rock and a key factor for permeability prediction. Conventionally, the T 2 cutoff value is obtained by centrifugal experiments, the process of which is complicated and time consuming, and some T 2 cutoff value prediction models are not suitable for coals with complex pore structures. Hence, a new method is needed for T 2 cutoff value prediction. In this study, we performed scanning electron microscopy (SEM), low-temperature nitrogen adsorption/desorption (LTNA) and NMR experiments on 12 coal samples. The results of SEM and LTNA reveal the complex pore structures of the coals. According to the results from centrifugal experiments, the T 2 cutoff value is in the range from 0.5–2.8 ms for subbituminous coals, whereas it is 15–32 ms for anthracite coals. We present a fractal theory based method for T 2 cutoff value prediction. Using the estimated T 2 cutoff values, we calculated the movable porosities, PSD and permeability for the selected coals. The results show that the proposed permeability model provides significantly better permeability estimation than classic (Coates and SDR) models. These methods are applicable not only for coals, but also for other unconventional gas reservoir rocks such as gas shales. [ABSTRACT FROM AUTHOR]

Copyright of Energy Policy Journal / Polityka Energetyczna is the property of Mineral & Energy Economy Research Institute of the Polish Academy of Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

High-temperature rheometry and 1 H nuclear magnetic resonance (NMR) are two complementary techniques that have been used to investigate fluidity development quantitatively in the <53  μ m and 53–212  μ m size fractions of high ash Indian non-coking coals and imported non-coking, medium coking and good coking coals. It was found for the 53–212  μ m size fraction of the Indian bituminous coal with higher ash content (30 wt%) that, despite its high complex viscosity (>10 5  Pa·s), the maximum concentration of fluid H was quite similar to that of the good coking coal (40%). This Indian non-coking coal developed fluid H with the highest mobility (T 2L  > 150  μ s) in the coal series, regardless of the particle size fraction studied. The probable explanation for this abnormal behavior is that the mineral matter prevents bulk movement in the sample but the local mobility of the fluid phase is still high on the nanometer scale. Blending the two Indian non-coking coals with the highly fluid medium coking coal gave higher viscosities (i.e. lower fluidity) than predicted by the polymer blend rule, probably again due to the high mineral matter restricting bulk flow. This negative effect was less pronounced with the higher ash coal suggesting that the high mobility of the fluid entities in this coal might prevent the destruction of fluid entities evolving from the medium coking coal. Partial demineralization of the high ash Indian non-coking coal to 17 wt% through a sink-float method did not decrease the complex viscosity of this coal but reduced the maximum mobility of the fluid H to levels observed with the lower ash content (20 wt%) Indian coal. Therefore, this reduction in mobility could be directly related to the mineral matter in the Indian non-coking coal. [ABSTRACT FROM AUTHOR]

Blast furnace coal injection is a vital part of modern ironmaking, reducing the amount of coke reductant required in the process and increasing its efficiency. However the injection of different coals or their blends, into the raceway formed by the hot blast, has technical issues due to the very short particle residence times and the limited availability of oxygen in this region. This makes complete burnout difficult and limits the range of coals suitable for this application, leading to partially burnt chars being carried out of the raceway into the blast furnace shaft and potentially into the off-gas system. This paper explores the fate of these chars, from a range of different coals, looking at how this influences the selection for injection and the implication of these on the blast furnace. In particular, we have looked beyond the limitations of selecting coals based on proximate analysis alone by examining in more detail other physical and chemical properties and their potential effect on the process. A drop tube furnace (DTF) has been used to synthesise chars in a high heating rate environment, and although burnout and volatile loss values suggest suitability of some coals for blast furnace injection, additional problematic effects have been identified and measured such as char swelling and agglomeration which may impact the gas permeability of the furnace. A TGA/DSC has been used to measure the gasification of chars by the Boudouard reaction and compare the thermal impact of more reactive samples. While other studies have concentrated on the combustion of injection coals to determine their suitability, this one focuses on the implications of the partially burnt chars formed by incomplete reaction in the raceway. [ABSTRACT FROM AUTHOR]

The article describes comprehensively, on the basis of inventoried sites, issues related to the suitability of coal slurry deposits for the energetic and economical application. The effect of inventory was the localisation of 62 coal-slurry deposits in which almost 16,5 mln Mg of coal slurry was stored. Due to the fact that part of the sites, on which coal slurry was stored, were subject to anthropogenic transformation a mathematical formula was developed that allows determining with the assumed accuracy the amounts of coal slurry produced and environmentally stored. The conducted estimated analysis, using this formula, showed that since 1945, there have been nearly 120 mln Mg of coal slurry stored in the environment that is eight times more than it was inventoried and what is currently recognised in official statistics. In order to develop the most cost-effective beneficiation technology of inventoried coal slurry deposits, detailed qualitative studies were conducted afterwards. They were carried out on the basis of an authorial research methodology which defines the scope of necessary physical and chemical parameters that must be determined for the particular samples of coal slurry. The obtained results show significant diversification in the quality of coal slurries stored in the particular settling ponds. The reason for this is the diversification of types of technological coal that come from the particular coal mines that used these settling ponds, as well as the efficiency of the technological solutions in terms of preparation processes applied by the particular coal mines. For this reason, there was an individual approach necessary to develop technologies of their preparation in order to obtain a full value fuel that meets the requirements set by the power sector. In the paper, the results of the analysis of the energetic potential of identified coal slurry deposits before and after the preparation process are also presented. Estimation of energetic potential was made using the authorial double-option algorithm. The presented results of coal slurry preparation studies and the analysis of their energetic potential have shown that as a result of preparation a significant amount of this potential is lost. This is the effect of movement of the finest grain of coal grains to refuse. The most favourable results, meaning the smallest losses of energetic potential according to the preparation results, were obtained using flotation technology. The conducted tests enable one to conclude that there is a possibility of preparation of coal slurry stored in the deposits. However, considerable losses of the energetic potential of these materials should be expected. [ABSTRACT FROM AUTHOR]