Search

The volatile combustion and NO release characteristics of pulverized fuel (PF) flames in an optical flat-flame entrained-flow reactor were investigated by CH*/NO* chemiluminescence imaging. Pyrolyzed bituminous (PB) char with an ultralow volatile content (Vdaf≈10%) and a comparative coal sample of Shenhua (SH) bituminous coal with a high volatile content (Vdaf = 34.2%) were studied under different ambient O2 mole fractions (10%∼30%). The initiation of the combustion region of PB char occurs later than SH bituminous coal, owing to its low volatile contents, a slow devolatilization rate, and homogeneous-heterogeneous ignition/combustion mode. By measuring probed solid and gas samples, the conversion ratios of fuel-N to NO and the releasing ratios of volatile-N/char-N were determined in ignition process. Semi-quantitative NO release integral intensity and volatile combustion intensity results were obtained by integrating the NO* or CH* chemiluminescence intensity in the corresponding reaction region. The volatile combustion and NO release show good synchronous for Shenhua bituminous coal, which means that the NO releasing originated predominantly and owned higher conversion ratio from the volatile-N in the ignition region. The NO release integral intensity and NO emission of SH bituminous coal decreased with O2 concentration increased from 20% to 30%, which indicates that the enriched-O2 environment is beneficial for high volatiles bituminous to decrease NOx emission in ignition stage. For PB char, NO releasing originated predominantly from the char heterogeneous reactions of char-N in its ignition and combustion late stage.

To investigate the effect of surfactants in compound solution on the wetting-agglomeration properties of the bituminous coal dust, this paper selected anionic surfactants SDS, SDBS and non-ionic surfactants APG0810 and PPG400 for compounding with agglomerated solutions 0.05 wt% XTG (xanthan gum). The sink test, surface tension test, viscosity test, fourier transform infrared spectroscopy(FTIR) and scanning electron microscope(SEM) were used to investigate the wettability and agglomeration of the four compound solutions and analyze the agglomeration wetting mechanism. The results show that SDBS has the most obvious improvement in the wettability of compound solution. The surface tension of SDBS + 0.05 wt% XTG is 28.98 mN/m after CMC value and sinking rate will reach 14.29 mg/s with 0.6 wt% SDBS in compound solution; Furthermore, FTIR results showed that surface hydroxyl content of bituminous coal dust treated by 0.2 wt% SDBS + 0.05 wt% XTG solutions has increased 26.3% than that treated by 0.05 wt% XTG, which promoted the adsorption of xanthan gum molecules on the coal surface. The presence of surfactants decreases the viscosity and surface tension of compound solution, and xanthan gum–surfactants interaction will promote bituminous coal dust agglomeration effect. This agglomeration mechanism is mainly reflected in the distribution mechanism and bituminous coal dust can form to large agglomerates under this action.

Understanding the relationship between the coal structure and its reactive behaviour is of great significance to achieve clean coal conversion and its efficient utilisation. One of the key tasks is to elucidate the molecular structure and chemical bonding information of coal. Owing to the complexity of the chemical structure of coal, studies on the molecular structure of coal, especially coal models with complex particle structures of different sizes for bituminous coal from northwest China, are highly warranted. In this work, the molecular structure characteristics and chemical index of a Qinghua bituminous coal sample collected from the Ningdong area, China, were assessed. Using a combination of material characterization, computation, and molecular modelling methods, a standard method for modelling complex coal structures from single molecules of macerals to particles of various sizes was developed. The single molecular structure of vitrinite and inertinite present in Qinghua coal can be expressed as C269H196N4O13S and C255H179N3O14S, respectively. Then, a series of complex particle models of various sizes were established based on the single molecular structure models of vitrinite and inertinite. Among these models, the size of the complex particles was as large as 11 nm, with the total atomic number approaching 60,000. Furthermore, the energetic and structural features of the complex coal particle structures were also explored based on their energy decomposition and radial distribution function analysis. In addition, the chemical structure index analysis was performed for different coal macerals to further understand the internal relationship between its structure and application.

Oxy-fuel combustion with low NOx emission has been received more attention in recent years. In this work, a series of oxygen-staged experimental investigations of Shenmu bituminous coal with the preheated combustion technology was carried out under O2/CO2 atmosphere to obtain the effect of oxygen-staged on combustion and NOx emission. The results showed that the increase of excess oxygen coefficient of the primary air(λPr) decreased the temperature difference at each measuring point in the circulating fluidized bed, promoted the production of coal gas, facilitated the release of elements, and improved the mass conversion ratio of volatile matter up to 92.3%. Besides, the increase of λPr inhibited the conversion process of N-5 to N-6. At the same time, the release of nitrogen-containing volatile matter during the partial gasification process was also reduced. As the λPr increases, reducing the excess oxygen coefficient of the secondary air(λSe) or increasing the oxygen partial pressure of primary air were beneficial to reduce the emissions of NOx to a certain extent.

Semi-coke is a low-volatile solid carbonaceous fuel, which is quite difficult to combustion individually. Co-processing semi-coke with bituminous coal has the potential for efficient and clean utilization of powdery semi-coke, while the co-pyrolysis is an important step and the physical-chemical properties of residual solid products yield great influences on subsequent combustion characteristics and NOx formation. However, less work, if any, has aimed at the co-pyrolysis of bituminous coal and semi-coke, and the synergistic mechanisms on physical and chemical properties of solid products have yet to be fully understood. Even limited oxygen may generate remarkable influences on co-pyrolysis behaviors. In addition, limited oxygen is possibly present during pyrolysis process, which has been rarely paid attention to. In this work, the physicochemical properties of solid co-pyrolysis products of bituminous coal and semi-coke were investigated experiment, while the effects of multiple atmosphere composition were also emphasized, including CO2/N2 atmosphere, N2 atmosphere with limited O2, and CO2/N2 atmosphere with a little O2. The results indicate that the dehydrogenation and polycondensation of bituminous aromatics are observed over 700 °C. The semi-coke and bituminous coal have the synergistic effect in the co-pyrolysis process. In N2 atmosphere with little oxygen, the pore development mainly occurs as the O2 concentration is below 3%. The residual char is over-ablated with the further increasing oxygen content. When the atmosphere contains O2, a small number of nitrogen oxides are formed. The present work can provide a scientific guidance for the utilization of semi-coke in large-scale and the design of power plant co-fired with semi-coke. This work is also beneficial to improve combustion reactivity of blended fuel, determine the optimal blending ratio and control NOx emissions.

In this work, a comprehensive and systematic study on synergistic effect and kinetics of three coal ranks (anthracite coal, bituminous coal, and waste coal), and three biomass materials (wheat straw, sawdust, groundnut) were performed under different blending ratios. The kinetic parameters of coal and biomass devolatilization were estimated by means of thermogravimetric analysis (TGA) at 10, 20, 30 and 40 Kmin−1. These kinetic parameters were subsequently validated using Artificial Neural Network (ANN) Model. Further, for fitting the experimental data, a numerical approach to distributed activation energy model (DAEM) has been evaluated and the experimental findings were compared with simulated data. Subsequently, the kinetic and thermodynamic parameters were estimated and compared with three model-free methods viz., KAS, OFW, and Friedman. The results from TG study indicate that the interactions between the waste coal with higher rank coal and biomass samples present an inhibitive effect during the devolatilization process. Furthermore, the values of activation energy were found in the range of 270, 250, 149 kJmol−1 by using OFW, KAS and Friedman model, respectively. Additionally, the thermodynamic parameters viz., enthalpy (ΔH), Gibbs free energy (ΔG) and entropy (ΔS) were estimated as 275.2 kJ mol−1, 184.5 kJmol−1, and 59.7 Jmol−1, respectively.

At present, there are few studies on the development, evolution, and quantitative analysis of internal pores and cracks after heat treatment of coal. On the basis of this, low-temperature nitrogen ...

Through high-voltage electrical experimental equipment fracturing coal, experiments were conducted on anthracite and bituminous coal soaked in distilled water and different concentrations of AlCl3 ...

Coal is one of the most important energy sources in China, and bituminous coal accounts for 80% of China's total coal. However, there are still some deficiencies in the previous understanding of the failure and mechanical characteristics of bituminous materials under external loads of different strain rates (especially high strain rates). To investigate the tensile and fracture mechanical properties of bituminous coal at different strain rates, the GCTS multifunctional rock mechanical loading device and Hopkinson bar dynamic loading system were employed. The crack extension process and crack distribution after damage of bituminous coal specimens were also analyzed by high-speed camera and CT scanning instrument. The results show that the peak stress distribution of the Brazilian disc (BD) bituminous coal samples ranged from 3.5 MPa to 5 MPa. The main crack expansion path of the internal splitting is not straight due to the non-homogeneity of the coal sample itself. And the secondary cracks of the specimen are more developed and mostly located in the middle region with transverse spreading. The average peak load of the notched semicircular bending (NSCB) coal samples tends to decrease with increasing depth of the notch. In addition, dynamic crack initiation toughness of NSCB bituminous coal specimen decreases continuously as the initiation time increases. The relationship between fracture toughness and crack initiation time is an approximate exponential function. The normalized dynamic fracture toughness test value of bituminous coal is higher than that of steel material, but lower than that of granite.

This study investigates changes in the concentration and types of free radicals in the process of coal heating, first rising and then falling. Hailar lignite, Panjiang bituminous coal, and Yangquan anthracite were selected as coal test samples. The results show that the lignite’s concentration of free radical changes during heating is greater than that of bituminous coal or anthracite. It clearly shows that lignite is more prone to spontaneous combustion. In the heating and cooling portion of the experiment, the concentration of free radicals during the cooling process was much more than that of free radicals at the same temperature during the heating process. These results obtained from this research study can provide a reference for the prevention and control of the spontaneous combustion of coal with changes in temperature. This study provides a theoretical basis for the prevention and control of spontaneous combustion of coal and the selection of retarding agents and methods in the process of flame retarding by testing the free radical changes of coal at different temperatures. Also, it provides a reference for preventing and controlling coal oxidation with the change in temperature, first rising and then falling.

In Zabrze, Dąbrowa Górnicza and Tarnowskie Góry towns, seven underground tourist trails are located in historical mines. Four of them were developed in the central part of the Upper Silesian Coal Basin, two of which, at the “Królowa Luiza” (“Queen Louise”) Adit (comprising the former coal mine “Królowa Luiza” and the drainage Main Key Hereditary Adit remnant), and two others at the “Guido” Mine in Zabrze town. The next one was developed in the eastern part of the Upper Silesian Coal Basin, in a part of the “Sztygarka” Training Coal Mine in Dąbrowa Górnicza. Two other trails are located in Tarnowskie Góry town, in the border zone between the Upper Silesian Coal Basin and the Silesian-Kraków Monocline. These are the relics of the historical lead, zinc and silver ore mine, and the “Czarny Pstrąg” (“Black Trout”) drainage adit. The bituminous coal deposits are hosted in the Upper Carboniferous clastic formations, which fills the Upper Silesian Coal Basin. The metal ores are hosted in Middle Triassic dolomites, which belong to the southern margin of the Silesian-Kraków Monocline. The geotourism attractiveness of all these historical mines was demonstrated by selected annual statistical data of tourist attendance. In general, the interest in these facilities has been growing since decades, same as the popularity of industrial heritage in the Upper Silesia. These three towns have become very widely known in Poland and in the world.

Coal-based graphite has become the main material of emerging industries. The microstructure of coal-based graphite plays an important role in its applications in many fields. In this paper, the effect of carbon disulfide/N-methyl-2-pyrrolidone solvent mixture extraction on the microstructure of bituminous coal-based graphite was systematically studied through preliminary extraction coupled with high-temperature graphitization. The graphitization degree g (75.65%) of the coal residue-based graphite was significantly higher than that of the raw coal-based graphite. The crystallite size La of the coal residue-based graphite was reduced by 47.06% compared with the raw coal-based graphite. The ID/ IG value of the coal residue-based graphite is smaller than that of the raw coal-based graphite. The specific surface area (16.72 m2/g) and total pore volume (0.0567 m3/g) of the coal residue-based graphite are increased in varying degrees compared with the raw coal-based graphite. This study found a carbon source that can be used to prepare coal-based graphite with high graphitization degree. The results are expected to provide a theoretical basis for further clean and efficient utilization of the coal residue resources.

Coal pores not only serve as the storage space for coalbed methane but also provide channels for gas migration. The accurate characterization of coal pore structures is of significance to study the methane adsorption behaviors. In this work, the quantitative relationship between gas adsorption and pore characteristics was investigated in depth for bituminous coals. Results of scanning electron microscopy showed that the surface morphological characteristics of these samples differ greatly. Some typical pore types including cylindrical pores and conical pores were found in these samples. The remarkable hysteresis loop was observed, which is attributed to the bottle-shaped pores with poor connectivity. Fractal theory was introduced to quantitatively evaluate the surface roughness of coal. Pore fractal dimensions, D1 and D2, were calculated using low-pressure N2 gas adsorption data, and their values were in the range of 2.125–2.721 and 2.084–2.461, respectively. D1 was larger than the corresponding D2 for the same sample, suggesting that micropore structures in coal were more complex when compared with mesopores and transition pores. Both D1 and D2 were enhanced with increase in micropore specific surface area, but they were reduced with increase in mesopore specific surface area. Gas adsorption in coal was estimated from the perspective of fractal dimension. Judging from the fitting degree, the influence of D1 on adsorption capacity of coal was remarkably greater than that of D2. D1 is expected to be used as one of the major adsorption indicators in the future study.

In this contribution we present results from a case-study, which was performed in collaboration between geophysicists and explosive ordnance disposal technicians at the Rohožník military training range in SW Slovakia. The aim of this study was to locate a deep-penetrated unexploded Mk-82 aerial bomb using high-definition digital magnetometry. The location where this bomb had entered the ground was known but its final position needed to be determined so that a safe excavation and disposal could be conducted. However, the detection of this unexploded ordnance object was complicated by the presence of intense magnetic interference from a number of near surface ferrous items including non-explosive test bombs, fragmentation and other iron junk. These items contributed a localised, high amplitude of magnetic clutter masking any deeper source. Our strategy was to approach the problem in three stages. First, we used magnetic data to locate the near surface items. After the detection and before the excavation of the searched objects, two quantitative interpretation methods were used. These involved an optimised modelling of source bodies and the application of a 3D Euler deconvolution. Both methods yielded acceptable results, but the former was found to be more accurate. After the interpretation phase, many of the items were then safely excavated and removed individually. A second magnetic mapping was then performed and from this data which was now significantly less cluttered, we were able to identify but not quantify, two deep source items and to confirm that all remaining near surface items were significantly smaller in size than a Mk-82 bomb. As the remaining near surface sources were interpreted as being contained within the surface one metre of soil and being small they could be assured to be non-explosive, it was considered most practical to mechanically excavate and remove this soil and the remaining objects contained.

Low-ash-melting-point bituminous coal and high-ash-melting-point anthracite coal are mixed and burned in different proportions. The ash melting characteristics of blended coal were determined experimentally. At the same time, the ash samples of bituminous coal, anthracite, and blended coal were analyzed by X-ray diffraction (XRD), and the ash melting characteristic improvement mechanism of blended coal was analyzed by quantum chemical calculations. The results show that when high-ash-melting-point anthracite is added, the ash melting characteristics of blended coal are improved, and the deformation temperature, softening temperature, hemispheric temperature, and flow temperature of the blended coal are significantly increased. The melting point of blended coal ash with a bituminous coal ratio of less than 50% can meet the requirements of blast furnace injection. The reason for the improved melting characteristics of the blended coal ash is that mullite in anthracite ash reacts with gehlenite in bituminous coal ash during the combustion process to produce anorthite.

This paper deals with the characterisation of inorganic constitutions generated at various operating conditions in the context of underground coal gasification (UCG). The ex situ small-scale experiments were conducted with coal specimens of different rank, from the South Wales Coalfield, Wales, UK, and Upper Silesian Coal Basin, Poland. The experiments were conducted at various gaseous oxidant ratios (water: oxygen = 1:1 and 2:1), pressures (20 bar and 36 bar) and temperatures (650°C, 750°C and 850°C). Increasing the amount of water in the oxidants proportionately decreased the cationic elements but increased the concentrations of anionic species. The temperature played minor impact, while the high-pressure experiments at temperature optimum to produce methane-rich syngas (750°C) showed significant reduction in cationic element generation. However, both coal specimens produced high amount of anionic species (F, Cl, SO4 and NO3). The “Hard” bituminous coal from Poland produced less gasification residues and condensates than the South Wales anthracitic coal due to its higher reactivity. The inorganic composition found in the solid residue was used in the theoretical calculation to predict the dissolved product concentrations when the solid residue interacts with deep coal seam water in the event of UCG cavity flooding. It was evident from the solubility products of the Cr, Ni and Zn that changes in the groundwater geochemistry occur; hence, their transportation in the subsurface must be studied further. Supplementary Information The online version contains supplementary material available at 10.1007/s11356-021-15780-8.

Co‐pyrolysis synergy between cornstalk and bituminous coal was investigated based on the physicochemical properties of the char. The char was prepared by directly putting the individual or blended materials into a heated resistance furnace at 600°C or 800°C. The performance of surface morphology and mineral matters was not notably changed by co‐pyrolysis, indicated by scanning electron microscope and X‐ray diffraction. However, N2 and CO2 adsorption‐desorption isotherms confirmed that surface area and pore structure were strongly influenced, particularly in large micropores and mesopores. Ultimate analysis and inductively coupled plasma optical emission spectrometer measurement revealed excessive depositions of carbon, alkali, and alkaline‐earth metal species in co‐pyrolysis char. Energy‐dispersive X‐ray spectrometer analysis examined the elemental surface distribution, suggesting that co‐pyrolysis under moderate temperature strongly favored inhibiting potassium release. The non‐isothermal thermogravimetry‐differential scanning calorimeter experiments under air atmosphere were conducted for char combustion reactivity, which was expected to be instructive for deeper understanding about co‐pyrolysis synergy and reutilization of the char. The thermal behaviors during combustion of co‐pyrolysis char clearly resembled a single fuel, which completely varied from those of the char blends. Besides, co‐pyrolysis chars and char blends were superior in total heat release compared with the simple addition of calculated values from individual char. Based on these observations, key factors of the synergy were supposed to have consisted of free radical reaction, secondary char formation, and the migration of alkali and alkaline‐earth metal species.

To explore the feasibility of converting oxy-fuel combustion flue gas into valuable syngas through char gasification process, the reactivity of three types of char (bituminous coal char, biochar, and waste char) were experimentally studied under atmospheric pressure in a fixed-bed reactor. The effects of flue gas flow rate and temperature, CO2/H2O/O2 ratio, char types on the char gasification characteristics were mainly investigated. It was found that when the flue gas temperature is 1200 °C or even higher, no matter which char is used, >90% CO2 conversion rate can be reached in line with the Boudouard equilibrium. The reactivity of biochar-H2O is relatively higher than that of waste char-H2O. Besides, 5% oxygen ratio in CO2/H2O mixture is preferred to promote the gasification reaction to some degree. It is important to balance the fixed carbon conversion rate and CO/H2 yield in syngas to decide the optimum residence time of char. Overall, it is a novel way of CO2 reduction and waste resources utilization.

In this study, co-gasification behaviors and synergistic interaction of bituminous coal and walnut shell under CO2 atmosphere were investigated by using a thermogravimetric analyzer. The evolution of physicochemical properties of samples was characterized with an inductively coupled plasma emission spectrometer, an X-ray fluorescence spectrometer, and an X-ray diffractometer. The results indicated that the addition of walnut shell significantly enhanced the gasification reactivity of coal, and coal/biomass blend ratio of 7:3 showed an intense gasification. Moreover, a significant co-gasification interaction was observed in the char gasification stage and demonstrated that a high coal/biomass blend ratio induced the formation of amorphous carbons and further accelerated the co-gasification reaction. Meanwhile, the active inorganics were severely released as 30 wt% bituminous coal added to walnut shell, causing a deteriorative gasification reactivity. Furthermore, three kinetic models illustrated that the coal/biomass blend ratio of 7:3 required a minimum activation energy to initialize gasification. The findings in this work would be beneficial for revealing the co-gasification mechanism of biomass and coal, and provide a useful basis on their multi-scale applications.

Coalbed methane is a lucrative energy source, but its development relies heavily on the fracturing of coal seam and underground extraction during mining. This study of mining stress paths, pore pressure, and permeability of a coal body was aimed to overcome the constraints of low coal permeability under the stress applied to a coal seam group. Variation in the applied stress changes the effective stress in coal and its permeability (which also depends on pore pressure). The effects of different mining intensities, repetitive cyclic loading and unloading, and pore pressure on gas permeability in a coal mine are revealed and discussed. The permeability evolution curve can be described by quadratic polynomial equations and split into three (decreasing, stable, and increasing) stages. When the stress environment with low axial deviatoric stress changes to that with high axial deviatoric stress and when the stability stage becomes longer, the goodness of quadratic polynomial data fitting is reduced. Cyclic loading and unloading with different axial stress paths have different effects on coal permeability. Increased axial and confining pressures decrease the permeability and pore pressure sensitivity of permeability. Because the obtained permeability-pore pressure curves contain a stable stage, this sensitivity is more pronounce in the low and high pore pressure stages.

The Qinshui basin is an important coal-accumulating basin in China, and its Late Paleozoic coal is an important source rock of coalbed methane in the basin. Its thermal evolution and gas generation characteristics determined the grade of coalbed methane resources, especially the coal measure free gas resources in the basin. Late Paleozoic coal samples were collected for organic geochemical analysis, a high-volatile bituminous coal was used for hydrous pyrolysis, to propose the thermal evolution characteristics, gas generation characteristics, thermal evolution, and free gas accumulation model, and the Ordos Basin is compared. The results show that the variation trends of various geochemical parameters are different with the increase in R o. Hydrous pyrolysis shows that the gas production potential of coal is excellent. The gases produced consist mainly of CH4, C2-, CO2, and H2. C2- is produced only before the simulated temperature of 550 °C, and oil is produced only before the temperature of 500 °C. The thermal evolution stages can be divided into the immature stage, symbiosis stage, wet gas stage, and dry gas stage, and the symbiosis stage can be divided into the preliminary stage and mainly gas stage. R o, T max, (2+3)MP/(1+9)MP, saturated+arene, V daf, and H/C can be used as indicators of the thermal evolution stages. On the plane, the distribution of thermal evolution stages of the Shanxi Formation and the Taiyuan Formation is very alike. The gas generating strength of the Taiyuan Formation is higher than that of the Shanxi Formation. The gas generating strength in the north of the Taiyuan Formation is higher, while that in the south of the Shanxi Formation is higher. The second gas generation stage has a good spatio-temporal configuration relationship with accumulation factors, and the gas production is large, which is beneficial to the enrichment of the coal measure free gas resources. Relatively, the Ordos Basin has better prospects for exploration and development.

Different types of coal have different characteristics and performances. In thermal coal plant, deposition of coal ash inside the furnace causes slag formation inside the boiler rear path and consequently reduces the heat transfer process and boiler efficiency. Besides, accumulation of ash on the boiler tube surfaces form layers of slags and blocks the flue gas flow out of the boiler. Therefore, the purpose of this study is to investigate the relationship between sub-bituminous coal base acid ratio towards the heat transfer process inside large-scale boilers. The base acid ratio for sub-bituminous coal is measured before firing inside large-scale boiler of studied the thermal plant which has a generation capacity of 700 MW. This study found correlation between high furnace rear path temperature (FRPT) that is observed to be above 800℃, with the build up of ash accumulation inside the boiler, for the studied coal. Thus, a high base acid ratio causes the accumulation of coal ash, thus reducing the heat transfer process which results in high FRPT of the boiler. Therefore, it proves that a base acid ratio is an indicator for coal performance during firing inside the boiler.

The purpose of this study is to develop the kinetic model and to find the optimum leaching conditions for maximum alumina dissolution from sintered nepheline syenite resource in the alkaline solution. About 80% of alumina (smaller than 5% of silica) was effectively recovered at 80 °C, 3 M NaOH, particle size less than 88 μm, agitation speed of 800 rpm, and leaching time of 60 min with a minimum amount of silica dissolution. Based on the kinetic model and the obtained reaction degree of each effective parameter, the experimental data were simulated. The simulation results proved that the leaching process for alumina was controlled by diffusion through the solid product layer and reaction at the interface of unreacted core that was confirmed by the value of activation energy (15.53 kJ/mol). The provided optimum conditions could be effective to decrease the silica dissolution, and to improve the alumina recovery.

The polythermal crystallization method has been used to extract sodium and potassium carbonate salts as valuable by-products. The salt production was carried out using an alkaline carbonate solutio...

To deeply explore the spontaneous combustion disaster of coal caused by air leakage and oxygen supply, low-temperature coal oxidation experiments under different oxygen concentrations (DOC) were carried out. Within the coal spontaneous combustion characteristic measurement system, a synchronous thermal analyzer (STA) and a Fourier transform infrared spectrometer (FTIR), the macro laws of gas and heat generation under DOC are analyzed, and the mechanism of the development of coal spontaneous combustion restricted by the lean-oxygen environment is also revealed. The results show that the change of oxygen concentration (OC) does not affect the critical temperature value and gas index change trend, but the lean-oxygen environment reduces the gas concentration and heat production rate very obviously. According to the temperature of the intersection, OC needs to be lowered to less than 5% when preventing spontaneous combustion of coal. The chain thermal reaction lags in the lean-oxygen environment, and the pyrolysis activity is significantly reduced. Meanwhile, the temperature points at T6 and T7 show significant differences. Furthermore, with increasing OC and temperature, the content of the aliphatic hydrocarbon presents an overall trend of first increasing, then decreasing, and continuously increasing after stage IV. It is concluded that •OH, aliphatic hydrocarbons, aromatic hydrocarbons, and carboxyl groups are the key groups for the coal spontaneous combustion evolution under DOC. To combine the spontaneous combustion reaction of coal in the DOC environment, the reaction path of the index gas in the macroscopic phenomenon and the reason for the concentration differences are revealed, the mechanism for exotherm varies caused by OC is clarified, and the microscopic inhibition affection on the chain reaction within the lean-oxygen environment is also explored. The results put forward the key groups evolution mechanism under the DOC for coal oxidation, which could provide the technical guidance for the fire prevention and control on coal mines.

To investigate the influence of basic characteristics of oil shale dust on wet dust removal, oil shales (Longkou oil shales Y1, Y2S2, and Y2S1 and Fushun oil shale) with different oil contents, brown coal (M1), and bituminous coal (M) were selected from a typical mining area in China to test their physiochemical parameters. Their proximate component, chemical structures, surface morphology, and mineral contents were determined. The sedimentation experiments of oil shale dust and coal dust were implemented using three anionic surfactants (AOS, SDS, and SDBS) and a nonionic surfactant (AEO-9), and the wettability of oil shale dust was analyzed and compared with that of coal dust. The experimental results indicate that the moisture content, volatile content, fixed carbon content, and content of oxygen-containing functional groups of oil shale are higher than those of the coal sample; otherwise, contents of ash, SiO2, aliphatic hydrocarbon, and aromatic hydrocarbon are lower. It can be found that oil shale has semiclosed pores, poor connectivity, a small pore size, a large specific surface area, and a rougher surface, which will lead to poorer wettability of oil shale. The wettability of oil shale can be improved by adding surfactants but is still weaker than that of the coal samples. Anionic surfactants are better than nonionic surfactants in improving the wetting performance. Among them, AOS shows strong wetting ability to oil shale dust. The research results of this paper have an important practical significance for analyzing the wettability of oil shale and controlling oil shale dust.

Burnout related problem occurs in the utility boiler burning low volatile coals. The in-furnace co-firing of low volatile coal (LV) experiments and simulation were carried out in a tangentially fired PC furnace to investigate the effect of co-firing ratio, injection position and particle size on NOx emission and carbon in fly ash (Cfh). The results of full-scale experiment show that Cfh increases from 2.16% to 4.21% as the LV co-firing ratio rises from 33% to 50%, while the NOx emission increases from 356.0 mg/Nm3 to 385.2 mg/Nm3 (@6% O2). The model is validated against the experimental data. The numerical simulation results show that NOx increases from 308 mg/Nm3 to 567 mg/Nm3 when the co-firing ratio of LV increases from 0% to 100%, while Cfh increases from 1.20% to 7.15%. It is found that the contribution of top two layers (E and F) to the total Cfh is significantly higher than that of the other layers. Under the working conditions of burning bituminous coal in the bottom layer and lean coal (particle size 70 μm) in the upper five layers, Cfh is 5.4%. When the particle size of lean coal in the five layers is reduced to 40 μm, Cfh rapidly decreases to 2.0%. And the Cfh can be reduced to 2.5% when only the top two layers feeding lean coal with smaller particle size (40 μm). Only 40% marginal cost of coal grinding is needed to reach the marginal benefit corresponding to 83% Cfh improvement while all layers of LV coal are ground into the small size.

The microscopic mechanism of the competitive adsorption of CH4, CO2 and N2 in coal is the theoretical basis for enhancing coal seam gas recovery by injecting CO2 (CO2-ECBM). Based on this principle, this work used Grand Canonical Monte Carlo and Molecular Dynamics to investigate the microscopic adsorption mechanism of single, binary, and ternary component gases in Wiser bituminous coal molecules. The adsorption mechanism was explored by changing gas composition and concentration. The comparison of adsorption separation coefficients suggested that CO2 had the highest adsorption capacity, whereas N2 had the lowest capacity. When the CO2 concentration in the gas mixture was high, the adsorption amount was large and the adsorption separation coefficient was small. This finding indicated that high concentrations of CO2 had negative effects on competitive adsorption. Energy changes were also evaluated. The potential energy between CO2 and the framework was the strongest among the two other gases. The inhibition of CH4 adsorption intensified with decreasing molar fraction of CO2. This phenomenon was explained from the perspective of heat of adsorption. As the molar fraction of CO2 in the adsorption system decreased, the heat of the isotherm adsorption increased. Meanwhile, the adsorption system became unstable and the capacity of CH4 adsorption on the framework weakened. Results provide a theoretical basis for the use of CO2-ECBM.

The possibility of using the waste from the production of mineral wool (MW) and nepheline-syenite (NS) in the production of ceramics in order to improve the physical and mechanical properties as well as the frost resistance of the samples was investigated. The use of NS in amounts 5 – 15% increases the compression strength of the samples to 17% and reduces the density, water absorption, and ultrasound speed in the samples to 5.2, 12.5 and 7% after firing at 1060°C. An increase in the NS amount due to an increase in the number of pores with diameters 0.02 – 0.1 μm in the samples promotes diminishes the damage to samples during freezing– thawing processes.

Number of down-fired boilers burning bituminous coal or anthracite blended with bituminous coal has exceeded 10% of the total down-fired boilers in China. However, lacking of the industrial-scale r...

In this paper, conventional thermogravimetric analysis and a new congruent–mass thermogravimetric analysis were used to study the reaction mechanism of the co-pyrolysis process of coal and biomass in the thermogravimetric analyzer, the effects of heating rate and carrier gas flow rate on co-pyrolysis were investigated, and kinetic analysis was conducted for the major pyrolysis stages to explore whether there was a synergistic effect in the co-pyrolysis process. The surface morphology of pyrolytic coke was evaluated by the fractal dimension method. The results show that congruent–mass thermogravimetric analysis can compare the interactions in the co-pyrolysis process more intuitively and reduce the influence of initial mass on the determination of interaction relationship. Synergistic effect appears in co-pyrolysis of coal and biomass. With the increase of heating rate, the thermogravimetric hysteresis appeared and the thermogravimetric curve gradually moved to the high temperature region. With the increase of carrier gas flow rate, the synergistic effect weakens. The kinetics of different reaction stages was analyzed by Coats–Redfern method; the results show that the activation energy required in the main co-pyrolysis stage of the mixture is lower than that in the pyrolysis stage alone. The micromorphology shows that biomass coke has a more developed pore structure than coal, and the box dimension indicates that co-pyrolysis increases the surface irregularity of coke. It is of great significance to judge the interaction mechanism of two or even multiple mixed samples in the process of co-pyrolysis.

This study investigates the potential of solid fuel blending as an effective approach to manipulate ash melting behaviour to alleviate ash-related problems during gasification, thus improving design, operability and safety. The ash fusion characteristics of Qinghai bituminous coal together with Fushun, Xinghua and Laoheishan oil shales (and their respective blends) were quantified using a novel picture analysis and graphing method, which incorporates conventional ash fusion study, dilatometry and sintering strength test, in a CO/CO2 atmosphere. This image-based characterisation method was used to monitor and quantify the complete melting behaviour of ash samples from room temperature to 1520 °C. The impacts of blending on compositional changes during heating were determined experimentally via X-ray diffraction and validated computationally using FactSage. Results showed that the melting point of Qinghai coal ash to be the lowest at 1116 °C, but would increase up to 1208 °C, 1161 °C and 1160 °C with the addition of 30%–50% of Laoheishan, Fushun, and Xinghua oil shales, respectively. The formation of high-melting anorthite and mullite structures inhibits the formation of low-melting hercynite. However, the sintering point of Qinghai coal ash was seen to decrease from 1005 °C to 855 °C, 834 °C, and 819 °C in the same blends due to the formation of low-melting aluminosilicate. Results also showed that blending directly influences the sintering strength during the various stages of melting. The key finding from this study is that it is possible to mitigate against the severe ash slagging and fouling issue arising from high calcium and iron coals by co-gasification with a high silica-alumina oil shale. Moreover, blending coals with oil shales can also modify the ash melting behaviour of fuels to create the optimal ash chemistry that meets the design specification of the gasifier, without adversely affecting thermal performance.

Co-gasification of renewable biomass and coal is a promising technique to reduce greenhouse gas emission beside increasing gasification performance instead of individual coal gasification. In this study, the co-gasification performance of pine bark (PB) biomass and Barapukurian bituminous coal (BBC) have been assessed using a high-temperature entrained flow gasifier using CO2 reactant. Results show that increasing biomass concentration increases the carbon conversion, syngas quality and cold gas efficiency (CGE), while reduces emission. For example, an addition of 20% biomass with coal increased the carbon conversion by 21.5, 10.6 and 4.5%-point at temperatures of 1000, 1200 and 1400 °C compared to pure coal gasification. Similarly, increasing biomass ratio in the blend increased the yield of CO by 11–36 vol% under different temperatures. Also, the CGE, fragmentation index ( F I = ∑ i n F D o ) and alkali and alkaline earth minerals in ash were increased with increasing biomass ratio in the blend. Overall, at least 50% of coal can be replaced with renewable biomass considering performance and emission characteristics, making the technology more sustainable.

The utilization of powdery semi-coke as a power fuel in pulverized coal-fired power plants has become a new and potential technique to consume the excess powdery semi-coke. The characteristic of low volatile results in poor combustion performance and high NOx emission, and to co-fire with bituminous coal is a practical strategy to address this problem. However, the co-combustion characteristics and the inherent interaction between semi-coke and coal remain insufficiently understood. In addition, the influences of secondary air arrangement, the boiler operation load, and the fuel type on co-combustion process are still unclear, which is urgent to be further explored. In the present study, experiments and numerical simulations were jointly utilized to inquire into the co-combustion behaviors and NOx emission features of semi-coke and coal. The results demonstrated that the “out-furnace method” was a suitable choice for small-capacity boiler when the proportion of semi-coke was 33%, due to the limited combinations of the semi-coke injection position. It was recommended that semi-coke was preferred to be injected from the middle layers of the furnace under the “in-furnace method” to improve the overall co-combustion performance. The critical value of the separated over fire air ratio in this study was 27.5%, over which a slight drop of carbon content in fly ash could come about. Moreover, the elevation in the proportion of separated over fire air gave rise to the significant decline of NOx concentration. The constricted secondary air arrangement was preferred to be employed due to the high boiler efficiency. The separated over fire air and the surrounding air needed to maintain a wide-open degree to prevent the increase of NOx emissions and the coking of nozzles. For the load reduction regulation method adopted in this study, the NOx concentration first rose and then dropped, while the burnout ratio decreased obviously as the operation load was reduced. Different combinations of coal and semi-coke generated significant influences on co-combustion behaviors within the furnace. The NOx generated by high-volatile fuel (bituminous coal) combustion was mainly affected by volatile-N, while the NOx generated by low-volatile fuel (semi-coke) was mainly impacted by char-N. This study is of guiding significance for the efficient and clean utilization and beneficial to the large-scale application of powder semi-coke in power plants.

We have developed the first experimental acoustic properties measurement during gas-hydrate formation and dissociation in crushed bituminous coal samples. We also compare the results with acoustic properties measurements during freezing and thawing water in the same samples. The results show a more complicated behavior that differs from similar experiments with sand. For the samples with adsorbed water, it does not freeze at anticipated temperatures, but acoustic velocities gradually increase with the decreasing negative temperatures. It is caused by complicated pore surface structures causing partial formation of ice/hydrate from bound water at different temperatures. We also observe that, for the same samples, the acoustic properties change significantly, becoming stronger during gas-hydrate formation than during freezing. We explain it by competitive sorption of methane and water in the coal pore space; methane under pressure replaces part of the adsorbed water from micropores so that this water can easily form hydrate. The difference in the acoustic properties of frozen and hydrate-bearing coal samples is important for developing seismic methods for geophysical characterization of coal seams.

To improve the ignition behavior and to reduce the high NOx emissions of blended pulverized fuels (PF) of semicoke (SC), large-scale experiments were conducted in a 300 kW fired furnace at various nozzle settings, i.e., ratios (denoted by hf/b) of the height of the rectangular burner nozzle to its width of 1.65, 2.32, and 3.22. The combustion tests indicate that the flame stability, ignition performance, and fuel burnout ratio were significantly improved at a nozzle setting of hf/b = 2.32. The smaller hf/b delayed ignition and caused the flame to concentrate excessively on the axis of the furnace, while the larger hf/b easily caused the deflection of the pulverized coal flame, and a high-temperature flame zone emerged close to the furnace wall. NOx emissions at the outlet of the primary zone decreased from 447 to 354 mg/m3 (O2 = 6%), and the ignition distance decreased from 420 to 246 mm when the hf/b varied from 1.65 to 3.22. Furthermore, the ratio (denoted by SR/SC) of the strong reduction zone area to the combustion reaction zone area was defined experimentally by the CO concentration to evaluate the reduction zone. The SR/SC rose monotonously, but its restraining effects on NOx formation decreased as hf/b increased. The results suggested that in a test furnace, regulating the nozzle hf/b conditions sharply reduces NOx emissions and improves the combustion efficiency of SC blends possessing an appropriate jet rigidity.

The filtration and dewatering of fine clean coal not only ensure industrial water recycle in coal washing plant, but also reduce the moisture of coal product in order to meet the requirements of combustion or coking industry. Fine clean coal is mainly composed by organic matter, and the property difference of different organic matter determines the filtration and dewatering behavior. In this investigation, vitrinite and inertinite were separated from a clean bituminous coal, and the comparative filtration and dewatering behavior of vitrinite and inertinite were conducted. The results showed that inertinite has lower dewatering rate and higher filter cake moisture than vitrinite. The analysis of filter cake structure showed that inertinite particle is easier to be broken into small particles due to the difference of mechanical properties, thus forming more compact filter cake than vitrinite. The analysis of particle surface properties showed that vitrinite is more hydrophobic than inertinite, which makes water easier drained from filter cake. The simulation study showed that the structure of inertinite is more porous than that of vitrinite, and the interaction between inertinite and water is stronger than that between vitrinite and water. This study provides a theoretical basis for improving coal dewatering by selectively improving coal maceral hydrophobicity.

By thermogravimetry (TG) experiments, evolution behaviors and properties of thermal oxidation processes at low temperature (< 230.0 °C) of a bituminous coal with five moisture contents were investi...

The waste tire is a fuel with the potential to partially replace coal due to the high heat value. In the present study, the combustion characteristics of the tire powders, bituminous coal, and their blends were examined using the thermogravimetric analyzer. The influence of heating rate on tire powders combustion and the burnout characteristics of their blends were studied. The increase of the heating rate caused the combustion temperature of the tire powders to become high but reduced the maximum weight loss rate. The combustion characteristics of the blends of coal and tire powders approached the combination of those of the individual sample, suggesting that the interaction effects between coal and tire powders were slight. Furthermore, the influence of different ratios on ignition characteristics, burnout temperature, and combustion effect of the blends was studied at the optimal combustion rate. The addition of tire powders improved the ignition characteristics, reduced the burnout temperature and increased the burnout rate of coal to a certain extent. An increase in the proportion of tire powders led to a decrease in the activation energy in the temperature range of 349-465 °C, whereas it caused an increase from 465 °C to burnout, which could be attributed to the fact that the volatile matter was more combustible than fixed carbon within 349-465 °C, and the combustion effect of fixed carbon in the tire powders gradually manifested in the combustion from 465 °C to burnout when the tire powders content increased.

This study used an entrained flow gasifier to assess the pyrolysis and gasification performance of Bangladeshi Barapukurian bituminous coal. The pyrolysis and CO2 gasification were conducted at temperatures of 1000°C–1400 °C under atmospheric pressure. The carbon conversion, syngas yield and pollutant emissions of coal using two different particle size of 90–106 and 250–300 μm have been analysed under CO2 concentration of 10–80 vol%. Solid residue (char/ash) was analysed by using scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX) and X-ray diffraction (XRD) methods. Results show that the release of volatile matter increases up to the temperature of 1200 °C. However, the temperature needs to increase at 1400 °C for the complete carbon conversion. Based on the CO/H2 ratio, syngas conditioning is required while using a temperature of 1200 °C or above, especially over the stoichiometric CO2 concentrations. Considering the heating value of syngas for power generation, the use of CO2 should be limited to less than 20% at a temperature of 1200–1400 °C. Particle size is important for carbon conversion but there is no significant impact on the heating value of syngas. Installation of the syngas cleaning system is required to drop the pollutants emission from the ppmv range to the ppbv range.

To study the effect of different inorganic iron compounds on the biological methanation of CO2 sequestered in coal seams, a biogas production experiment was carried out through use of bituminous coal D (China) and indigenous microorganisms, by adding bicarbonate and inorganic iron compounds. It is found that the addition of FeCl2 or FeS2 promoted methane production. FeS2 resulted in the highest methane concentration (30.54%) and methane production (0.191 mmol/g), which increased by 30.46% and 38.11%, respectively. The pH of the experimental group was lower than that of the control group during the whole process. The chemical oxygen demand (COD) first increased and then decreased, and the COD peak value greatest increased by 3.07% after FeCl2 was added. The ammonia nitrogen content in the liquid phase with FeCl2 or FeS2 was improved obviously (11.01% and 6.76%), and the microorganisms were increased accordingly. Scanning electron microscopy and energy dispersive spectrometry (SEM-EDS) showed that the microorganisms reacted with coal and iron after addition of Fe to generate several amorphous substances on the surface of coal, and further enhanced biomethane production. This study provides a new method for the utilization of CO2 sequestered in coal seams and the rational development of high sulfur coal.

To carry out an in-depth study of the macromolecular differences of vitrinite and inertinite with metamorphism degree, ultimate analysis, Fourier transform infrared (FTIR) spectroscopy, micro-Raman...

The thermal behavior of ash components in two bituminous coal samples [Upper Freeport (the “UF”) and Illinois #6 (the “IL”)] was investigated under air and argon atmospheres in the temperature range of 800–1200 °C using thermal gravimetric–differential thermal analysis, X-ray diffraction transmission electron microscopy (TEM), and TEM–energy dispersive X-ray spectrometry measurements. The UF treated under air formed the needle-like crystals which were assumed to be mullite-related substances formed by transformation of andalusite, because the crystals are mainly composed of SiO2 and Al2O3. In contrast to the UF, the IL did not generate such crystals; however, when the IL was treated under air after carbonization under Ar, crystals appeared. The composition of the UF with an Al/Si ratio higher than that of the IL favored the formation of mullite-related substances, while the presence of lime in the IL inhibited the formation of mullite-related substances. Oldhamite was formed by the reaction of lime with sulfur at the carbonization of the IL under Ar and remained even at the successive air treatment. As lime was consumed, the formation of mullite-related substances was ceased to be inhibited under air after Ar treatment.

This study systematically investigated the co-slagging characteristics of high-rank coal and biomass ashes considering entrained flow slagging gasifier. Despite favourable performance parameters, coal might not be feasible for entrained flow gasification because of not forming slag within the gasifier operating temperature (1200–1500 °C). To overcome this issue, co-gasification can be a potential solution, which simultaneously helps to reduce the carbon footprint and environmental impact. Hence, this study studied the feasibility of co-gasification of coal and biomass by testing co-slagging behaviour of bituminous coal and pine park biomass ashes. The slag viscosity is measured using a Brookfield DV-III Ultra rheometer coupled with a high-temperature furnace. Results show that pure coal ash does not form slag using the maximum furnace temperature of 1670 °C. However, co-slagging by 50/50 (wt./wt.) ratio of coal and biomass ash (PB50) significantly drops the slagging temperature due to the higher fluxing agents (i.e. CaO) in biomass ash. The temperature of critical viscosity was determined to be 1390 °C using PB50 ash, which maintained the maximum industrial viscosity limit of 25 Pa s up to the temperature of 1360 °C.

Investigations on the molecular composition of coal pyrolysis products can help us to improve nonfuel utilization of coal. Meanwhile, the molecular composition of coal pyrolysis products is also influenced by the characteristics and depositional environment of coal. However, due to the extremely complex nature of coal, direct investigation of the molecular composition of coal pyrolysis products is still a challenge. In the present work, the data of the molecular composition of bituminous coal pyrolysis products are obtained by online pyrolysis coupled to comprehensive two-dimensional gas chromatography and mass spectrometry (online py-GC×GC-MS) and are divided into nine molecular groups depending on the aromaticity of the pyrolysis products and separating power of the GC×GC-MS. Chemometric tools, hierarchical cluster analysis, and principal component analysis are employed to reveal the correlations among the molecular composition of coal pyrolysis products and coal characteristics. The results show that the nine molecular groups of bituminous coal pyrolysis products can be divided into two clusters, the "aromatic group" and the "aliphatic group", and that the eight coals are divided into three clusters, all of which can be interpreted by the depositional environments and δ13CVPDB values of coals. Moreover, a simple and empirical equation for estimation of coal tar from hydropyrolysis can be obtained depending on the chemometric results of the molecular composition of the coal pyrolysis products. By application of chemometrics, the molecular composition of coal pyrolysis products can provide preference to industrial utilization of coal.

Owing to the enormous demand for and growing large-scale use of coal in the China, India, and USA, speculation has arisen about possible hazards to environmental quality and human health. The contents of fly ash and volatile matter in low-quality coal are extremely harmful to the environment. As a result, there is still much to be explored regarding known hazards and harms to the natural environment of the Earth. For the detection of high-quality coal, we propose a new method of distinguishing coal quality in terms of different “coal types” (i.e., anthracite, bituminous coal, subbituminous coal and lignite) and efficiently separating gangue and rock from the production lines of coal preparation plants (CPPs) by exploiting infrared machine vision and convolutional neural networks (CNNs) for deep learning, which can make coal use less harmful to humans and nature and/or more useful for general welfare. In this article, we conducted two experiments. First experiment is to study the reactions of coal types, gangue and rock with infrared radiation at temperatures of 50°C, 70°C, 90°C, 110°C, and 150°C. Second experiment, several common CNN models (i.e., AlexNet, DarkNet-53, GoogLeNet, NasNet_Mobileb, ResNet-18, MobileNet-v2, Inception-v3 and DenseNet-201) are trained and tested to classify coal types and distinguish gangue and rock. We achieve a remarkable classification accuracy of 100% in these training and testing processes when employing the ResNet-18 and DenseNet-201 models.