Coal Type Research Articles

Effect of turbulent fluctuation on the ignition of millimeter particle: Experimental studies and numerical modelling with a new correlation of nusselt number

Understanding the influencing mechanism of turbulent fluctuation on the ignition characteristics of millimeter coal particles is essential. In this work, to study the effect of turbulent fluctuation on ignition time, millimeter coal particles are subjected to a specific flow field, generated in a furnace with symmetric fans. A one-dimensional model with the new proposed correlation and the Ranz-Marshall (R-M) correlation for Nu (Nusselt number) is established to simulate the coal ignition process. In addition, the effects of fan speed, temperature, particle diameter, particle distance and coal type on the ignition time are investigated. It is found that an increase in fan speed from 0 to 3000 rpm leads to a particle Reynolds number Rep increase from 0 to 22.5, and a turbulent particle Reynolds number Ret∗ increase from 0 to 71.5. With a consideration of the fluctuation effect, the new correlation of Nu gives a better prediction of ignition time compared to the R-M correlation. Moreover, the ignition time is revealed to decrease with an increasing fan speed and an elevating temperature. While the ignition time shows merely an initial boost with enlarging particle distance, it exhibits a linearity with the term of particle diameter dp1.3–1.7 and Reynolds numbers (Nu∗/Nu)–0.6 (Nu∗ is turbulent Nusselt number). Based on this relationship, the difference of predicted ignition time is calculated at different Rep and Ret∗. It is shown that at low Rep or high Ret∗ values, the new correlation should substitute for the R-M correlation.

High-Temperature Ash Melting and Fluidity Behavior upon the Cocombustion of Sewage Sludge and Coal.

Wastewater treatment produces a large amount of sludge, where the minimizing of the disposed sludge is essential for environmental protection. The co-combustion of sludge with coal is a preferable method for sewage sludge disposal from the economic and environmental perspective. The co-combustion of sludge has been widely used in the industry with the advantages of large processing capacity. The melting characteristics of ash are an important criterion for the selection of the co-combustion methods and furnace types. In this study, two types of sludge and four types of coal with different ash melting points were selected, where the ash melting behavior upon co-combustion is investigated by experimental and thermodynamical approaches. Especially, the slag fluidity upon co-combustion is explored via a modified inclined plane method. It has been found that the presence of SiO2 and CaO in sludge substantially enhances its fusion temperature owing to the high content of CaO, while SiO2 acts as a solvent, facilitating the co-melting of other oxides and raising the sludge fusion temperature. Fe2O3 exhibits a specific mass fraction within the range of 10-20%. Furthermore, the presence of CaO and SiO2 prohibits the flow ability of the slag at high temperatures, and Fe2O3 promotes the flow ability for sludge at high temperatures. With increasing base/acid ratio, the sludge flow velocity increases remarkably and peaks at 1.6. The interaction between Fe-Ca and Si-AI significantly affects the fluidity significantly. The findings are expected to optimize the condition of co-combustion and desirable furnace design for the incineration of sludge.

Coal conversion to SNG: Thermochemical insights through kinetic-free modeling in entrained flow gasifier

In this study, a kinetic-free thermodynamic equilibrium model consisting of five units was developed to predict SNG production via coal gasification, using two distinct feeding technologies (SFT and DFT) and two coal ranks (BT and BL) in an entrained flow gasifier using Aspen Plus (V10), and comparing results with empirical data. The alignment between simulation outcomes and experimental observations is verified, and analysis of various parameters' impacts on product gas composition and yield is conducted. Sensitivity analysis reveals consistent trends across different coal ranks. The O2/coal ratio emerged as a key factor, demonstrating notable effects on syngas composition and yield. Specifically, increasing the O2/coal ratio from 0.3 to 1.0 enhanced H2 and CO2 proportions in the syngas which are beneficial for SNG production, as hydrogen is a key component for SNG. Elevating the O2/Coal ratio from 0.2 to 0.6 (optimal) favors CGE, facilitating high-quality syngas production. Additionally, increasing the CO2 flow rate up to 3 ton/hr improves the HHV of syngas, beyond which HHV declines. Raising the W/C ratio from 0.3 to 1.0 leads to decreased HHV for BL and BT coal. Additionally, increasing the W/C ratio from 0.3 to 1.0 decreases HHV. Therefore, it is crucial to undergo the production of SNG within the optimal ranges, and these findings provide crucial insights into optimizing gasification parameters for enhanced syngas production across various feed technologies and coal types to produce desired syngas results.

Necessary CO2 emissions improvement based on rural residential coal/stove-specific coal combustion and prefectural-differentiation synergistic effect of pollutants and carbon emission reduction

Rural residential coal combustion (RRCC) is an important CO2 emission source in rural areas and these emissions vary greatly by coal and stove types. The lack of CO2 emission estimations for different coal-stove combinations restricts refinement and region-differentiated synergistic reduction of pollution and CO2 emissions from RRCC. This study established the coal and stove specific CO2 emissions inventory of RRCC based on investigated coal combustion of various coal and stove types, taking the region of Hebei in China as an example. The synergistic reduction effect of CO2 and pollutants was evaluated using 4 emission reduction scenarios. CO2 emission was 67.4% higher than estimates of RRCC based on the Statistical Yearbook and IPCC emission factors. The combination of bituminous coal and an advanced coal stove was the greatest contributor (62.1%) to CO2 emissions. Bituminous coal burnt in home Arcola has the highest per capita hourly and per unit calorific value CO2 emission, 2.3 and 2.4 times higher than the combination of anthracite briquette coal and pit coal stove and the combination of bituminous coal and an advanced coal stove, respectively. Except for NOx and CO, the coal-stove combination with the lowest per capita hourly and per unit calorific value emissions is anthracite briquette coal and an advanced coal stove. Scenario analysis shows that updated coal stoves feature the highest pollutant emission reduction, but greater CO2 and NOX emissions. For individual cities, synergistic pollution and carbon reduction is seen in Tangshan and Qinhuangdao, and organic carbon, CO, and SO2 have better synergistic positive reduction with CO2, while NOX has shown a negative effect with CO2 in other cities with the best coal and stove update scenario. Compared with the coal and stove update scenario, emission reduction effects with clean fuel substitution varies across cities. This study is helpful to understand the possible non-synergy of pollutant and CO2 reduction in the process of RRCC management. Attention should be given to issues related to the synergistic control plan of pollution and CO2 reduction for RRCC with local adaptation.

Can the Gondwana, Oligocene, and Palaeocene-Eocene coals of India be used as a strontium isotope chronometer?

Strontium isotope data of the Gondwana, Oligocene, and Palaeocene-Eocene coals of India has been compiled for the first time in this report. The Gondwana coals of peninsular India from the Talcher, Ib, Rajmahal, Wardha, and Korba coalfields have the highest mean 87Sr/86Sr value of 0.731762 ± 0.000034 (2σ). Compared with the high radiogenic 87Sr content of the non-marine Gondwana coals, the Oligocene coals from the Makum coalfields in Assam and the Palaeocene-Eocene coals of Meghalaya in North East India had mean 87Sr/86Sr values of 0.708998 ± 0.000029 (2σ) and 0.716335 ± 0.000032 (2σ) respectively. The Sr concentration (mg/kg) of the three types of coal decreased in the order of Oligocene (170.6 mg/kg) > Palaeocene-Eocene (45 mg/kg) > Gondwana (35.6 mg/kg). The one-way ANOVA test done on the strontium data of the three types of coal showed significant differences (at p < 0.05) in the mean 87Sr/86Sr values of the Gondwana and Palaeocene-Eocene coals but homogeneity in the Oligocene coals. The high 87Sr/86Sr and low Sr content in the Gondwana coals can be attributed to silicate weathering products in these coals. In the coals of Meghalaya, the 87Sr/86Sr ratios are influenced by both silicates and carbonates. The Rb/Sr versus 87Sr/86Sr plots for both the Gondwana and Palaeocene-Eocene coals showed a weak positive correlation in contrast to the Oligocene coals. The mean 87Sr/86Sr value of the Oligocene coals was similar to the range of 87Sr/86Sr values obtained in marine-derived gypsum in the Miles coal of China and therefore, provides an opportunity for the construction of a strontium isotope chronometer.

Study on the evolution characteristics of molecular surface active sites of low-rank coal in low-temperature oxidation stage

Compared with other coal types of coal, low - metamorphic coal contains numerous active sites, making it susceptible to spontaneous combustion and posing significant risks during production, transportation, and storage. To further reveal the evolution characteristics and laws of low-rank coal's active sites during the process of low-temperature oxidation of coal (LTOC), X-ray photoelectron spectroscopy (XPS), 13C nuclear magnetic resonance (13C NMR), and Fourier transform infrared (FTIR) experiments were used to determine the basic structural parameters such as the valence state of non-carbon features, types of carbon elements in coal macromolecules, and structure and quantity of functional groups. Combined with molecular modelling software (GaussView 6.0) and macromolecular calculation software (Grimme-XTB), macromolecular models of coal at different temperature points were constructed, and the surface energy field distribution was calculated. The number and energy change information of chemical and physical adsorption sites of low-rank coal during heating were obtained. The results show that during the LTOC, the chemical adsorption sites such as aliphatic hydrocarbons (-CH3/-CH2) have higher reactivity and can be converted into oxygen-containing functional groups (-CHO, –OH, –COOH); the number of physical adsorption sites increased first and then decreased, and reached the maximum at 50 °C. Coal exhibited a higher affinity for O2 at this temperature. The peroxide (-C-O-O-H) undergoes thermal decomposition, leading to H2O and weight loss of coal. The –CO and –COO structures undergo decarboxylation to generate CO, CO2, and other gases. This study comprehensively revealed the evolution of active sites through two key coal oxygen processes, physical and chemical adsorption, based on the gradual temperature elevation of low-rank coal. This holds immense significance for improving and enriching the understanding of the mechanism of coal spontaneous combustion(CSC), preparing more targeted CSC inhibition, and formulating efficient fire prevention and extinguishing measures.

Ignition characteristics of single coal particles under ammonia co-firing conditions

To meet the goal of an international carbon-neutral framework, the promotion of clean coal utilization occupies a vital position in reducing greenhouse gas emissions. Ammonia co-firing is considered as a potential strategy for future power generation to reduce fossil energy consumptions, soot, CO2 emissions, and hydrocarbon pollutants. In the present work, the ignition characteristics of single coal particles under ammonia (NH3) co-firing conditions were investigated. Particles were injected with NH3 or N2 into a hot flue gas environment at 1550 K generated by a CH4-fired Hencken burner. Temporally resolved images of CH* chemiluminescence and char thermal radiation were captured. Combining the signal profiles, ignition modes and characteristic times of single burning particles were studied with different coal types, carrying atmospheres, and O2 contents. When the carrier gas was replaced by NH3 atmosphere, the ignition delay time of all coal particles was greatly shortened, and the time interval from ignition to peak, as well as the combustible component burnout time, were both lengthened due to the promoted devolatilization and combustion reaction rates of coal particles caused by the NH3 flame. Concerning the ignition mode in the NH3-blended cases, the homogeneous ignition behaviors of the lignite particles were further enhanced, while the bituminous particles transitioned to the homogeneous-heterogeneous united ignition mode. As the O2 content in the flue gas increased, the ignition of all coal particles was advanced monotonously, and the chemiluminescence became more intense in both N2 and NH3 atmospheres.

The effect of surfactant on biosolubilization of weathered coal

AbstractWeathered coal is a type of coal with barren utility value, which is exposed on the surface for a prolonged time or shallowly buried in coal seams, and the physicochemical properties of weathered coal have changed compared with high‐quality coal. China is also a country with large reserves of weathered coal, therefore, the value utilization of weathered coal has received tremendous scientific attention. Herein, the main purpose is to explore the combined effect of surfactants and microorganisms on bioconversion of weathered coal to produce humic substances. Tween‐80, Phanaerochaete chrysosporium (J1) and Trametes versicolor (J2) were selected as surfactants and engineering strains to convert weathered coal. 3D fluorescence spectra were used to analyze the species and contents of humic acids during the biosolubilization process of weathered coal. Results revealed that both J1 and J2 exhibited good performance on weathered coal biosolubilization (increasing 10% and 14% compared to the control, respectively). The intensity of weathered coal biosolubilization was significantly increased by 15% and 12% when J1 and J2 were applied in combination with Tween‐80. And the addition of Tween‐80 also distinctly reduced the molecular weight of humic substances. In summary, surfactant plays an important role in bioconversion of weathered coal, while molecular weight of humic substances was different that weathered coal biosolubilization under the co‐action of J1 and Tween‐80 increased and J2 with Tween‐80 was opposite. In short, this project might provide a new strategy for exploring the biodegradation of weathered coal.

Synthesis of multilayer graphene and its graphene derivatives from coal

In our study, we selected three prevalent coal types from Xinjiang: Dahuangshan coal (referred to as Y-coal), Black Mountain coal (B-coal), and Kuche coal (K-coal). Initially, we assessed their morphological differences using electron microscopy. Subsequently, we evaluated the superiority of Y-coal through Thermogravimetric Analysis (TGA). Furthermore, we compared their performances using various electrochemical tests, including the J-V curve, dark current curve, open-circuit voltage curve, and Electrochemical Impedance Spectroscopy (EIS) curve. Ultimately, we investigated the potential of synthesizing graphene from Y-coal and its derivatives. The first step was the preparation of multilayer graphene (MG) by treating Y-coal with acid to obtain demineralized coal, followed by treatment in a tube furnace to obtain ultrafine powdered MG. The second step was then followed by successive oxidation and ultrasonication of the already obtained MG to obtain graphene oxide (GO). Finally, ascorbic acid (VC) was selected to treat GO to prepare an aqueous suspension of reduced graphene oxide (rGO). MG (2θ = 26.2°), GO (2θ = 12.4°) and rGO (2θ = 25.5°) were obtained by XRD analysis. C 1s and O 1S were analyzed by XPS spectra. The functional groups −OH, C=O, and −C=C–, which are unique to graphene and its derivatives, were comparatively analyzed using infrared spectroscopy. The change of π→π* was analyzed by the UV–vis method. The absorbance was further found in combination with PL spectra. Immediately after, the morphology of graphite and its derivatives was analyzed by SEM, HRTEM, the physical properties by contact angle and BET, and finally the content of elements C and O by EDS. The successful demonstration of the superiority of the synthesized MG and its derivatives was achieved.

Hookahs and smoldering hookah coals as an object of forensic fire and technical expertise

The subject of the study is to establish the involvement of smoldering hookah coals in the occurrence of a fire during the production of a forensic fire-technical examination. Currently, there is no universal concretized algorithm for determining the involvement of tobacco smoking devices and hookah coals in the occurrence of a fire for all possible cases of fire. The authors have attempted to combine well-known information about the detection of signs of exposure to combustible materials from a relatively low-power ignition source with the results of experiments and studies of smoldering hookah coals. Two types of hookah coals were selected as objects of research: cubic natural charcoal for hookah, fast-burning cylindrical coal. Cotton fabric, cotton wool, paper, wood (pine), synthetic carpet with fine pile, synthetic carpet with large pile, soft decorative elements with synthetic filling and a pillowcase made of furniture fabric, PVC floor materials (linoleum, PVC tiles), floor panels, lined with polymer films (laminate). In conducting this study, a systematic approach was applied to the analysis of the situation of a fire-related incident, as well as general scientific empirical and theoretical research methods (observation, comparison, description, measurement, analysis and synthesis, etc.) The results of empirical studies confirm the hypothesis of the formation of deep charring zones in places of contact of hookah charcoal with combustible materials (wood, laminated floor coverings). Based on the results of experimental studies, a step-by-step algorithm for constructing versions about the occurrence of a fire from smoldering hookah charcoal is formulated, including focusing the attention of an expert (a person conducting an inspection of the scene of an incident related to a fire) on the need to take into account factors such as the time of the fire and the induction period of ignition, the presence of conditions for heat accumulation, the presence of air exchange, the presence of an air inflow into the smoldering zone, the presence of signs of the dynamics of fire propagation, characteristic of low-power ignition sources. It is noted that the probability of burning from smoldering hookah coal increases in cases where conditions are created for the smoldering process to proceed with minimal heat loss, the possibility of heat accumulation and the presence of an oxidizer (oxygen in the air) in sufficient quantities.

Coal crisis in China: development, mechanism, causes and possible consequences

This article analyzes the dynamics of coal prices and systemic changes in the coal market in the PRC, revealing the internal Chinese mechanism of the coal crisis that broke out in the PRC in 2020. The data studied and the conclusions obtained in the article refute the widely held view in expert circles, according to which the cause of the coal crisis in China was the rejection of Australian coal. The study was carried out by analyzing a data array on the dynamics of changes in the price of coal for different types of coal and for different regions and provinces of China. In particular, the article is based on data on the dynamics of coal prices in Shaanxi and Hubei.&#x0D; The results of this research provide useful insight into both the nature of the coal crisis and the patterns of the system of formation of coal prices in the PRC, partially touching on the issue of the integrity of the Chinese coal market. The statistical data referring to the coal prices is viewed through the prism of the concept of a “multi-track” pricing system put forward by M. V. Karpov and, in general, confirms fruitfulness and significance of his theory. Also, the article, based on data from the Hong Kong Stock Exchange, shows the commercial practical significance of the findings and the importance of having up-to-date information data on dynamics of coal prices in China.

Characterization and property evaluation of low-cost electrically conductive bamboo charcoal from Dendrocalamus sericeus Munro.

Bamboo (Dendrocalamus sericeus Munro) is fast-growth plant with abundant biomass for conversion to fuel and various uses, including insulation and electronic applications. Bamboo charcoal produced in a low-cost furnace was separated into bamboo coal with electrical conductivity (bamboo coal 1) and without electrical con-ductivity (bamboo coal 2), subjected to proximate analysis and evaluation of adsorption and fuel properties. In addition, structural properties were studied based on surface area analysis using the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods, Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Of the two bamboo coal types, bamboo coal 1 with electrical conductivity had better adsorptive properties, such as a greater iodine number value (240 mg g-1), while the BET and the BJH methods showed that the surface area was 36.653 m² g-1 with a pore volume of 0.052 cm3 g-1 and a pore size of 15.292 Å. In addition, it was better for use as a deodorant and as a solid fuel for cooking with a longer total burning time (81 min). Bamboo coal 2 had lower moisture (5.75%), and ash (6.56%) contents, with a higher heating value (6913 kcal kg-1), indicating that bamboo coal 2 was good for deodorant usage and could have potential for development as an insulator with a hydrophobic and fire-retardant coating material. Bamboo coal 1 had a graphite crystalline structure and could have potential with additional further graphene development for electronic uses.

Structures and contributions of active substances in the latent oxidation of coal based on the oxygen isotope tracer method

The oxygen isotope tracer method was used to determine the structures and contributions of the active substances that trigger coal spontaneous combustion (CSC). After artificially changing the oxygen isotope ratio, the coal samples were subjected to isothermal oxidation under different conditions (different temperatures, different oxidation times and different coal types) in an 18O2 atmosphere. First, the oxidation gases were obtained with cyclic oxidation experiments. The basic parameters were provided for tests of the gas isotopes. The oxidation products labeled with 18O were then analyzed with an isotope ratio mass spectrometer. The original active substances in the coal were determined. Evolution of the functional groups in the coal was determined by XPS. The transformation paths of the active substance were analyzed. The results showed that during the oxidation process, more than 70 % of the CO was generated from the original hydroxyl and aldehyde groups in the coal, and more than 99 % of the CO2 was generated from the original carboxyl groups in the coal. Inhibition of oxidative decomposition of hydroxyl, aldehyde and carboxyl groups can effectively control CSC and solve the problem of CO overflow caused by low-rank coal oxidation.

Development of a Dynamic Prediction Model for Underground Coal-Mining-Induced Ground Subsidence Based on the Hook Function

Underground coal-mining-induced ground subsidence deformation is a common geological disaster impacting buildings, transportation and water supplies. Models predicting ground subsidence dynamically with high precision are important for the prevention of damage derived from ground subsidence. In this paper, the Hook function is utilized to develop a model describing the velocity of ground subsidence due to underground coal mining. Based on the subsidence velocity model, a dynamic subsidence model is established by taking an integral of the velocity model. Coefficients of the model, which depend on maximum subsidence, maximum subsidence velocity and the time corresponding to the maximum subsidence velocity, are related to the geological and mining conditions of the coal seam being investigated. A Levenberg–Marquardt-algorithm-based method is also proposed to calculate the optimal model coefficients based on subsidence velocity observations. Four continuously operating Global Navigation Satellite System (GNSS) stations were constructed above a typical longwall coal mining working face in the Jining mining area, China. These GNSS stations collected subsidence observations over two years, which were used to validate the developed prediction model. The results show that the root-mean-square (RMS) of the model-predicted ground subsidence error is 56.1 mm, and the maximum relative error is 2.5% for all four GNSS stations, when the ground subsidence is less than 6000 mm.

Study on radiation characteristics of coal fired boiler changing with burnout rate

The burnout rate is an important parameter in the combustion of pulverized coal. During the process of pulverized coal burnout, its radiation characteristics and the entire coal-fired boiler vary with the burnout rate, which is a very complex process and current research is not clear enough. This study proposes a new single particle pulverized coal burnout model, which incorporates pore volume correction to fit the density ratio and diameter ratio of multiple coal types with varying burnout rates as the theoretical basis. Using Mie theory, Jiaozuo coal particles are calculated average absorption and scattering efficiency in the band of 0.39 ∼ 16 μm, which is used as the basis for correcting particle emissivity and scattering factor. Then, through user defined function (UDF) in the simulation software, the particle radiation characteristics are modified from the original constants of 0.9 and 0.6 to linear and polynomial models that vary with the burnout rate. Not only do the spatial distribution rules of the coal-fired boilers radiation characteristics with the burnout rate of the furnace be obtained, but also the temperature distribution of the furnace under different particle radiation characteristics models is compared. The results show that the pulverized coal burnout model is consistent with the experimental results in literatures. High burnout rate corresponds to low mass concentration of furnace particles, and low absorption and scattering coefficients. Using the above model to calculate the particle emissivity and scattering factor that vary with the burnout rate, after UDF embedding, the error between the simulation results and the on-site cross-sectional temperature and thermal imaging detection decreases from 4.81 % to 2.59 %, reflecting the high accuracy and rationality of the burnout model and particle radiation characteristic correction method.

Effect of calcium-based additives on NO release of coals under different combustion modes

The nitrogen oxides and sulfur oxides released from coal combustion pose serious environmental hazards, but there exists a contradiction between low-nitrogen combustion and efficient desulfurization, necessitating a deeper understanding of the impact of calcium-based desulfurization agents on NOx release. Based on one-stage and two-stage horizontal furnaces, the effects of temperature, coal types and CaO on the release of NO were explored under the coupled combustion and the separated combustion. The experimental results indicate that: under both conditions, the NO emissions of coals decrease with the increase of temperature. The reaction time of separated combustion is shorter than that of coupled combustion. Under the coupled combustion, the order of NO emissions is: anthracite (AC) > bituminous coal (BC) > lignite (LC) > high chlorine coal (HC), and the order are mainly affected by the content of N in coal. At 800 °C, the fuel-N conversion rates of BC, AC, LC, and HC are all the highest, and the rates are 20.52 %, 25.93 %, 14.90 %, and 15.34 %, respectively. As the temperature rises, both volatile-N and char-N emissions show a downward trend. The NO emissions in the separated combustion are greater and the fuel-N conversion rates of BC, AC, LC, and HC are 44.11 %, 47.31 %, 40.44 % and 32.21 %, respectively. The reduction reaction between char and NO plays a crucial role. After the addition of CaO, there is a significant increase in NO release, indicating that CaO has a catalytic effect on the release of volatile-N and char-N. Under the separated combustion, the impact of CaO on NO emissions is relatively minor, and sometimes it leads to a reduction in NO emission. The role of CaO on the NO release is multifaceted.

Quality management in a 3D geological model – reliability of predicted hard coal quality parameters

This paper presents some of the results of the project undertaken in JSW SA, which aim was to create a three-dimensional model of the deposits that make up the company and schedule company’s production. The assessment of the quantity of coals without analysis of qualitative data, i.e. physicochemical parameters, coking parameters, and optical petrographic analysis is not suitable for obtaining commercial contractors. To obtain information on the quality of the coal seam, the geological service of the mine takes coal samples. In the stratigraphic model and quality model, dedicated interpolators are used for interpolation and extrapolation. In the seam quality model, the most optimized interpolators are Inverse and Height. Modelled parameters such as volatile parts content and random vitrinite reflectivity were analysed in detail. The Height interpolator looks for both a random and a linear dependency. It extracts random changes locally while searching for linear dependencies and extrapolates them to a deposit area that does not have qualitative data. There is a risk of extrapolating a given value to infinity. Nevertheless, the amount of data and the area modelled allows you to close its scope at an acceptable level. A separate POLYGON interpolator based on mxl express surfaces was created to map coal type range. It uses interpolated quality parameters at a given location, generating a range of a particular type of coal. Setting the trend of variability makes it possible to predict higher coal types in deeper, unrecognized batches of deposits according to documented variability in parameters.

Key Bearing Structure Instability Mechanism: A Case Study in Mining Under Close‐Distance Coal Pillar

This study is aimed at solving the issue of mining under the boundary coal pillar of the close‐distance coal seam that causes roof falling. This study established a new key bearing structure model for analyzing the structural instability mechanism when mining under the coal pillar at the working face by taking Shaping Coal Mine as an example. The purpose of this study is to analyze the formation process, load transfer mechanism, and two failure types of the key bearing structure using theoretical analysis and numerical simulation. Additionally, this study discussed the timing and method of roof control for different key bearing structure failure types. Research shows that the instability of the key bearing structure composed of the coal pillar, interlayer rock, and lower coal body is the important reason behind the roof falling. The instability types of key bearing structures include the coal pillar instability type and the cantilever beam instability type. The stability width of the interlayer rock cantilever beam and the coal pillar jointly ascertain the failure type of the key bearing structure. In the 9204 working face, the key bearing structure was destroyed when the coal pillar was 14 m wide, resulting in the roof stress being as high as 31.81 MPa. The stress drop phenomenon can be used as a boundary to divide the failure process of the key bearing structure into three stages. The pressure relief of the coal pillar and interlayer rock cantilever beam is an effective way to deal with this problem, and the coal pillar instability type needs to be pressure relieved earlier than the cantilever beam instability type. The research findings offer new insights into the roof stability control of mining under the coal pillar.

Dual-energy X-ray transmission identification method for coal and gangue with different thicknesses and densities

To reduce the thickness effect influence of dual-energy X-ray transmission (DE-XRT) and solve the problem of identifying coal and gangue with different thicknesses and densities, this paper proposes a method based on the Bayesian optimisation KNN model to classify the pixels of images. The gray feature I and R-values are used to train the classifier to recognize unknown classification pixels. The proportion of classified pixels in the images of a single target is used as the classification parameter. This method reduces the effect of thickness in R-I two-dimensional space. Considering the change in the density of different coal types and taking the density at the boundary between the coal and gangue as 1.8 g/cm3, the recognition rate reached 97.74 %. For raw coal with a 5–150 mm thickness range, the accuracy of identifying predischarged gangue reached 99.16 %. Our study provides a new method and practical guidance for DE-XRT coal preparation.

Optimization of extrinsic parameters for beneficiation of coal with the help of Cronobacter sp

ABSTRACT Beneficiation increases the calorific value of low-grade coal and extracts environmentally sensitive elements. Bacteria may be used as eco-friendly coal cleaning tool, but the treatment is influenced by several extrinsic and intrinsic factors. This study examined five extrinsic factors, namely particle size of coal, pulp density, bacterial biomass concentration, number of bacterial beads (immobilized bacterial cells) and the duration of treatment. For optimization, the test runs were designed using Taguchi L16 orthogonal array, determining optimal values through S/N ratio analysis and individual parameter contribution using ANOVA. The optimal conditions obtained for sub-bituminous coal beneficiation using Cronobacter sp. are 80–120 mesh particle size, 30% pulp density, 750 mg bacterial biomass/g coal, 25 bacterial beads, and six days of treatment resulting in 13.36% ash yield reduction. Particle size had the highest impact (69.4%), followed by treatment duration (13.1%), pulp density (6.3%), bacterial biomass (6.3%), and bacterial bead number (4.8%). A regression model attributed only 42% influence of these extrinsic factors on inorganic removal from coal. Therefore, further research on other factors, particularly intrinsic ones, in inorganic matter liberation is imperative. These findings can be used for designing experiments that optimize the extraction of cleaner fuel from various types of low-grade coal.