Different Kinds Of Coal Research Articles

Research on the Application of THz-TDS in Coal–Rock Interface Recognition

The recognition of coal–rock interface is very crucial for research in the intelligent production of coal mines. To this end, the study investigated the application of terahertz time-domain spectroscopy in the recognition of coal–rock interface, including the identification of coal–rock and coal–rock mixtures, as well as the accurate characterization of coal seam thickness. Terahertz detection was used to obtain the optical parameter information of pressed pellets prepared by mixing two different kinds of coal and two kinds of rock. Based on the experiment’s results, a database was established for the identification of coal–rock interfaces for coal mining machines. The terahertz detection was performed on 10 different kinds of sheet anthracite with different thicknesses, and the terahertz spectra of coal seams with different thicknesses were simulated and calculated using simulation software. By comparing the two effective mining thicknesses, parameters can be provided for coal seam mining. The experiment and simulation show that the terahertz time-domain spectroscopy technology has a promising application prospect in the identification of coal–rock interface.

Electronic, Structural, and Magnetic Upgrading of Coal-Based Products through Laser Annealing.

Most coal-to-product routes require complex thermal treatment to carbonize the raw materials. However, the lack of unified comparison of products made from different kinds of coals downplays the role of initial coal chemistry in high-temperature reactions. Here, we used a CO2 laser to investigate the roles that aromatic content and maturity play in the structural evolution and doping of coals during annealing. Results show that a bituminous coal (DECS 19) with aromatic content and maturity in between higher rank, more mature anthracite (DECS 21) and lower rank, lower maturity lignite (DECS 25) leads to more graphite-like structure observed from the highest 2D peak on the Raman spectrum and conductivity (sheet resistance ∼30 ohm sq-1) after lasing. When nitrogen dopants are incorporated with saturated urea dopants into coals through laser ablation, nitrogen preferentially incorporates at the edge sites of graphitic grains. Furthermore, oxide nanoparticles can be incorporated into the graphitic backbone of coal to modify their electronic and magnetic properties through laser annealing. Leveraging tunable magnetic behavior, we demonstrate a soft actuator using both conductive and magnetic coal-Fe/Co oxide. Through laser annealing, we propose a paradigm to understand and control coal chemistry toward flexible and tunable doping and magnetism.

Research on Coal and Rock Type Recognition Based on Mechanical Vision

In order to identify different kinds of coal, rock, and gangue, the FPV integrated image transmission camera is used to collect images of 6 types of coal, 8 types of rocks, and 2 types of coal gangue, and the images are processed based on the two-dimensional discrete wavelet transform (2D-DWT) based on the steerable pyramid decomposition (SPD). The maximum likelihood estimation method is used to estimate the parameters, and, the coal and rock types are judged by comparing the similarity of each image. The results show the following: (1) in the eight kinds of rocks, the recognition accuracy of shale and limestone is 90%, that of anorthosite is 95%, and those of other rocks are 100%; (2) the accuracy of comprehensive identification of coal, rock, and gangue is 93%, the comprehensive of coal and gangue is 78%, and the rock classification is 97%; (3) the identification time of 6 types of coal samples, 8 types of rock samples, and 2 types of coal gangue samples are in the range of 2 s∼3 s, which is far less than 10 s, which can meet the requirements of coal and rock identification in terms of recognition speed; and (4) according to 20 groups of data, the range, variance, and standard deviation of the same coal gangue sample meet the accuracy requirements of coal and rock identification. The identification method provides an effective method to improve the efficiency of coal separation, effectively determine the distribution of coal and rock, and timely adjust the cutting height of shearer drum and the operation parameters of various fully mechanized mining equipment, so as to improve the recovery rate of coal resources.

Micromechanism Analysis of Surfactant Wetting of Coal Based on 13C NMR Experiments.

With the gradual improvement in coal mine mechanization and automation, the dust concentration at production sites is increasing significantly as the production efficiency improves, which not only poses a substantial threat to the occupational safety and health of workers but also affects the safe production and social stability of mines. At present, wet dust removal is the most economical and effective technical dust removal measure. However, most coal seams in China have poor wettability, unclear microscopic wetting mechanisms, and poor dust removal effects. Therefore, based on experiments and numerical analysis, this paper qualitatively studies the influencing factors of surfactants on coal wettability and quantitatively constructs an innovative evaluation model of the influence of the microstructure of coal and surfactants on wettability. First, based on 13C NMR experiments, the structural parameters of coal and several surfactants were obtained. Second, the wettability relationship between the coal and the surfactants was determined by optical titration, and the key factors affecting the wettability of coal dust and the wettability of the surfactants were selected. Then, using numerical analysis and function fitting analysis and combining the structural parameters with the coal wetting results, the relationship between the microstructure of the surfactants on different kinds of coal and the wettability of the coal samples was established. The results show that the ether group, the phenol or aromatic ether carbon, the fatty methyl group, and the aromatic methyl group in the surfactants have a substantial influence on the wettability. The research results can provide scientific guidance for the development of efficient and environmentally friendly compound dust suppressants to realize clean production in mines.

Carbon-bearing Wastes as the Binders for Coal Briquette Production

The search of optimal compositions for different kinds of coal (lignite and hard coals) with the slam of lean coal for briquettes production was done. Some cheap and non-toxic binders for increasing mechanic stability and water resistance of coal-slam briquettes were experienced. Tree best kinds of binders from coke-chemical industry wastes for improving the properties of coal briquettes were chosen. The main technological parameters of coal briquetting without a binder additive - humidity, size of the pressed coal (dried), pressing pressure, drying temperature and pressing duration are in a certain relationship. To obtain a given briquette strength when changing one of the parameters, it is necessary to change another or several parameters. The dependence of the mechanical strength of briquettes on each individual parameter is often extreme. The value of the parameter at which the maximum strength of the briquettes is obtained is taken as optimal. For coals with good briquetting properties, this extreme dependence of the mechanical strength on individual briquetting parameters is more pronounced, especially for the bending and compressive strength of briquettes. Therefore, in the production of briquettes, an important element in the composition of the coal composition is the binder. The article discusses the search for a binder for the production of fuel briquettes using various grades of coals based on local raw materials.

Estimation of radiological impact on residents due to household storage of coal used for heating in Serbia

This paper aims to estimate a potential radiological risk from different kinds of coals used for domestic heating in Serbia, by measuring the activity concentration of radionuclides and radon exhalation rate. The obtained radon mass exhalation rate ranges from (5.3 ? 3.1) mBqkg?1s?1 to (70.3 ? 9.4) mBqkg ?1s?1 and was highest for lignite type of coal. It is estimated that coal stored in the basement could contribute up to 50 Bqm?3 of indoor radon concentration at the ground level. Activity concentrations of 226Ra, 232Th, 40K, 238U, 235U, and 210Pb in analysed coal samples agree with previously reported concentrations of coal used in Serbia. The values of radium equivalent concentration and external hazard index indicate that the used coal does not represent a significant radiation hazard.

Comparative study on the characteristics of condensable particulate matter emitted from three kinds of coal.

Condensable particulate matter (CPM) is quickly formed by several gaseous substances in flue gas after emission and belongs to primary particulate matter emitted into the atmosphere by stationary sources. Many studies have shown that current CPM emissions from coal-fired stationary sources far exceed filterable particulate matter, and the issue of CPM emissions has attracted widespread attention. The current research on CPM mainly focuses on its emission characteristics in stationary sources and its migration characteristics in pollutant-controlled equipment, lacking the characteristics of CPM directly generated by fuel combustion. In this study, a one-dimensional flame furnace is used as a stable source of flue gas in the laboratory. The concentration (including inorganic and organic components) and chemical composition (including water-soluble ions, metal elements, and organic matters) of CPM are obtained by the combustion of three kinds of coal (Inner Mongolia lignite, Jinjie bitumite, and Ningxia anthracite) that China consumes in large amounts. The characteristics of CPM including emission factors obtained from different kinds of coal under various experimental conditions are comparatively analyzed. Moreover, a scanning electron microscope-energy-dispersive spectrometer is used to observe the morphology and elemental composition of CPM collected on the filter membrane after the combustion of different kinds of coal. Results show that CPM is mainly in the form of droplets or spheres, and heavy metal elements such as Hg, As, Se, and Sb are detected. These valuable data will enrich people's understanding of the characteristics of CPM generated by coal combustion and can provide data references for evaluating the influence of CPM on the environment.

Preparation and characterization of activated carbons from different kinds of coal

Initial coal was purified in heavy liquid with a density 1.3 cm3 of ZnCl2 solution and purified coal was carbonized and the initial coal samples of each deposits were purified by pyrolysis. Thus, the yield of pyrolysis hard residue in the enriched sample was slightly higher than in the hard residue of initial coal. Therefore, pyrolysis hard residue of purified coal (carbonized sample) was activated at 800°C for 2 hours by preheated water steam. Activated carbons (ACs) and non-activated and non-carbonized coal from Baganuur, Ereen and Nariin Sukhait deposits were technically analyzed and their iodine number, BET surface area, pore volume and adsorption of methylene blue (MB) were determined. When these results were compared, these indicators increased 5-17 times in the Baganuur activated carbon (BN-AC), Ereen activated carbon (E-AC) and Nariin Sukhait activated carbon (NS-AC) as compared to inactivated coal.

Raman Spectroscopic Study of Coal Samples during Heating

Raman spectroscopy can be used to record the characteristic spectra of carbonaceous materials. The D and G bands are the most popular and most important spectral characteristics when discussing carbonaceous materials. In this paper, a Raman spectroscopic study of different coals was first carried out using a 355 nm wavelength laser beam as an excitation source. The spectral parameters of the resultant spectra were evaluated and analyzed. Raman spectral characteristics of different kinds of coals were explored. The high temperature-dependent Raman spectra of the coals were further collected in a temperature range from 298 to 1473 K in order to investigate the transformations of the internal structure of the coals during the pyrolysis process. An abnormal blue shift of the G band occurred at moderate temperature (600–900 K), and the intensity of the G band became weaker at high temperatures, indicating pyrolysis and graphitization of the sample at moderate and high temperature, respectively.

Law of gas production during coal heating oxidation

Coal spontaneous combustion is a great threat to mine safety, and gas is the key index to describe coal spontaneous combustion. Taking the coal samples of different kinds of coal as research object, the temperature programmed oxidation experiment was carried out, and the gases produced by coal samples at different temperatures were collected and analyzed by gas chromatography. This research studied the variation characteristics of gas species and gas concentrations in different coal samples during heating oxidation. The experimental results show that different coal samples produce different kinds of gases in the process of heating and oxidation. The order of gas production is CO, C2H6, C2H4, C3H8, and the relationship between gas production and temperature is approximately exponential. With the increase of coal metamorphic degree, the turning point temperature of sharp rise in coal sample gas production rate become higher, the oxidation ability of coal sample decreases, and the quantity of gas production decreases during the same time period.

Fundamental study on fuel-staged oxy-fuel fluidized bed combustion

The concept of a fuel-staged oxy-CFB (oxy-fuel circulating fluidized bed) combustion technology is proposed by this article to extend the operation range of an existing air-fired CFB boiler retrofitted for oxy-fuel operation. Experiments were designed to study the combustion behavior of a single coal particle at different locations of the furnace (dense bed and freeboard), which should differ largely from those in the conventional feeding to dense bed. Three different kinds of coal under various atmospheres were studied in a visualized fluidized bed combustor, by on-line monitoring the temperature of fuel particle and volatile flame simultaneously. As expected, shorter ignition delay time (td) was observed in the dense bed due to the stronger heat transfer than that in the freeboard. However, surprisingly, shorter devolatilization time (tv), higher peak temperature (Tpeak) and shorter burnout time (tb) were observed in the freeboard of the furnace, which were probably due to higher mass transfer rate of oxygen from gas phase to the reacting particle. When N2 was replaced by CO2, both the td and tb increased while the flame and particle temperature decreased significantly.

Mechanism on the contribution of coal/char fragmentation to fly ash formation during pulverized coal combustion

In this paper, the correlations between coal/char fragmentation and fly ash formation during pulverized coal combustion are investigated. We observed an explosion-like fragmentation of Zhundong coal in the early devolatilization stage by means of high-speed photography in the Hencken flat-flame burner. While high ash-fusion (HAF) bituminous and coal-derived char samples only undergo gentle perimeter fragmentation in the char burning stage. Simultaneously, combustion experiments of two kinds of coals were conducted in a 25 kW down-fired combustor. The particle size distributions (PSDs) of both fine particulates (PM1-10) and bulk fly ash (PM10+) were measured by Electrical Low Pressure Impactor (ELPI) and Malvern Mastersizer 2000, respectively. The results show that the mass PSD of residual fly ash (PM1+) from Zhundong coal exhibits a bi-modal shape with two peaks located at 14 µm and 102 µm, whereas that from HAF coal only possesses a single peak at 74 µm. A hybrid model accounting for multiple-route ash formation processes is developed to predict the PSD of fly ash during coal combustion. By incorporating coal/char fragmentation sub-models, the simulation can quantitatively reproduce the measured PM1+ PSDs for different kinds of coals. The sensitivity analysis further reveals that the bi-modal mass distribution of PM1+ intrinsically results from the coal fragmentation during devolatilization.

Air- and oxygen-blown characterization of coal and biomass by thermogravimetric analysis

This paper reports on the results of air-blown combustion and oxy-combustion kinetic characterization (comparing two different isoconversional methods: Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose) of different kinds of coal (from Italy, South Africa and Hungary) and biomass (pine and eucalyptus chips) by thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC) together with the assessment of different characteristic combustion parameters. It can be observed that the burning rate of fuels can be improved by the oxy-combustion process, shortening the burning time (a mean reduction of the burnout time of 14% and 22% can be observed for coal and biomass samples, respectively). Moreover, biomass shows better ignition performance than coal and enhances combustibility indexes (S and Hf), especially in oxy-combustion conditions. For example, the S index, which reflects combustion properties, increases by an order of magnitude for biomass combustion and oxy-combustion with respect to coal values, thus indicating a higher combustion activity for biomass; an opposite trend can be observed for the Hf index, which describes the rate and intensity of the process and is lower for biomass than for coal, thus indicating better performance for wood chips combustion. Kinetic analysis shows that the activation energy Ea varies with conversion values, reflecting the kinetic complexity in both the processes. Moreover, with the same range of heating rates (10 ≤ β ≤ 50 °C/min) and for the overall range of conversion (0.1 ≤ α ≤ 0.9), both of the models used fit the experimental data in combustion regime, whereas the increase of the oxygen concentration makes the results reliable for coal samples and more sensitive to weight loss for biomass samples.

Coal use for world economy: Provision and transfer network by multi-region input-output analysis

Concerns surrounding climate change and environmental challenge make the coal utilization network essential not only for understanding the pattern of energy provision and transfer, but also for illustrating the interaction between anthropogenic activities and ecological systems at global level. This paper fills the research gap by dint of multi-regional input output model to outline coal embodied routes from natural boundaries to economic activities, and to identify the central hubs in the global coal supply chain, based on the most recent available statistics for 2011. As the economic value and environmental influences of different kinds of coals could be remarkably diverse, the separation of coal categories in systematic analysis could provide fundamental information regarding the displacement and teleconnection of coal utilization in the world. The estimation shows that in weight 64.99% of coal direct supply is ultimately embodied in international trade, indicating the crucial roles of trade interlinks in global coal utilization. Apart from this, the findings pertinent to sectoral structure, regional supply chain and per capita characteristics of coal embodied utilization, could be valuable to identify the global energy routes driven by international trade as well as to facilitate energy and environmental policy.

Effects of different coals on mercury distribution in a 6 kWth circulating fluidized bed under air and O2/CO2 atmosphere via experiment and thermodynamic equilibrium calculation

Mercury distribution is important to know clearly under O2/CO2 atmosphere. Although some reports in published about mercury transform under oxy-coal combustion, different kinds of coal on the mercury distribution in a 6 kWth circulating fluidized bed under air and O2/CO2 atmosphere via experiment and thermodynamic equilibrium calculation has been little studied. Hg2+ concentration was lower under oxy atmosphere compared to that under air atmosphere. The percentage of mercury oxidized was affected by the unburned carbon contents of fly ashes.According to thermodynamic calculation, five major products associated with mercury would be generated: Hg0, HgO, HgS, HgCl, and HgCl2. Moreover, from 350 °C to 1200 °C, the mole percent of Hg0 arrives its peak. The mole percent of HgO in the flue gas is decreased according to the following order: 40%O2/60%CO2 > 30%O2/70%CO2 > 21%O2/79%CO2 > air.

A Method for Combustion Calculation Based on Proximate Analysis and Net Calorific Value of Coal

For the combustion calculation of coal fired boiler, a new concept of oxygen consumption for combustible material was proposed which was different from the traditional oxygen consumption for elements. A mathematical model was developed for the combustion calculation. The calculation formulas of theoretical air and flue gas volume were established through reasonable hypothesis and simplification, which were based on proximate analysis and net calorific value of coal. In contrast to the results of the elemental analysis for the 15 different kinds of coals which are typical in China, the average relative error of formulas is lower than 2%, the biggest relative error is 7.11%, which can be used for the control over boiler operation, testing and debugging, and calculation of heat transfer.

Study on the Pyrolysis Kinetics of Blended Coal in the Fluidized-bed Reactor

The micro fluidized bed reaction analyzer (MFBRA) was employed to investigate the emission characteristics and the formation kinetics of methane which was released from different kinds of coal and the blended coal during the coal pyrolysis. The results show that under the same pyrolysis condition, the initial release temperature of methane and the pyrolysis activation energy (E) decreases with increasing volatile content of the coal, while the maximum releasing rate and the total volatilization amount of methane increased, indicating that the higher the volatile content of coal, the easier the pyrolysis reaction. Coal blending can change the quality parameters of the single coal. The water content, volatile content and ash content of the blended coal were equal to the weighted average of corresponding single coal, while the activation energy (E) of blended coal was not equal to the weighted average of corresponding single coal.

Reduction Mechanism of Composite Consisted of Coal and Hematite Ore by Volatile Matter at 700–1100 K

In the drive to mitigate global warming, the iron and steel industry has made efforts to reduce carbon dioxide gas emissions. Utilization of a composite material consisting of carbonaceous material and iron ore is expected to be an effective way to solve the issue. Volatile matters in carbonaceous materials have a potential to reduce emissions by lowering the reduction temperature.In this study, the reduction by volatile matter in a coal/hematite ore composite was fundamentally examined. Different kinds of coal were chosen as carbonaceous material samples. The reduction experiment using the prepared composites was conducted by varying the heating rate as 0.08, 0.17, and 0.33 K/s, up to a temperature of 1473 K under Ar–5%N2 gas flow. The outlet gas composition was analyzed and the results were used to calculate the reduction degree.Reduction degree of hematite ore initially increases with increasing content of volatile matter in coal. However, beyond a certain point, further increase in the volatile matter content of the coal did not give a significant change in the reduction degree. For the evaluated coals, the amounts and types of gases generated are not different each other. H2 gas seems to form together with solid carbon via decomposition of hydrocarbon gases. Such gases and solid carbon may contribute to the reduction. Moreover, reduction by H2 was promoted in the early stage of the reactions by decreasing heating rate. The data indicate that control of the heating rate is a possible way to promote reduction at low temperature.

Effects of different kinds of coal on the speciation and distribution of mercury in flue gases

Laboratory-scale experiments on dropper tube coal combustion furnace with six kinds of coal were carried out, and the speciation and distribution of mercury in the flue gas were studied. The analyzed raw coals included Tangshan bituminous coal, Gaoping anthracite coal, Liupanshui lean coal, Xiaolongtan lignite coal, Indonesia lignite coal, and Yichang lignite coal. The combustion experiments were conducted at temperature of 900 °C, 1000 °C, 1100 °C, 1200 °C, respectively. The results show that, the content of gaseous element Hg in flue gas increased with the rising temperature of combustion and flue gas, for anthracite coal and lean coal with higher coal rank, the content of particle Hg in flue gas reached 10–15% while the content was lower than 5% for lignite coal with lower coal rank, and the percentage of gaseous mercury increases with the increase of the content of sulphur in coal.

Forecast Research of Combustion Stability of Pulverized Coal

The combustion stability of pulverized coal is very essential for utility boilers. That is the key issue to keep the operation of the whole power-generation unit in a safe state. The amount of volatile matter is used to anticipate the combustion state of pulverized coal. As a widely accepted concept, higher volatile matter content would result in more stable combustion state. But in some cases, the coal with high volatile matter content led to poor combustion states, even resulted in the flameout of the burner. More method is needed to judge the coal and to predict the combustion stability. With research on the approximate analysis of the coal composition, the heat value of volatile matter was calculated. Such heat value varies obviously for different kinds of coal. The ratio of the heat value of volatile matter to the heat value of fixed carbon is supposed to describe the combustion stability of pulverized coal. The application of the method judges the coal better than using the amount of volatile matter alone.