The influence of borehole arrangement of soundless cracking demolition agents(SCDAs) on weakening the hard rock

The hard roof difficult to collapse easily causes gas accumulation, which threatens the production safety of coal mine. Therefore, roof pre-cracking is required. Although blasting and hydraulic fracturing can also crack the roof, blasting can easily induce rock bursts, whereas hydraulic fracturing needs complex equipment. In contrast, soundless cracking demolition agents(SCDAs) with noise-free, dust-free, and safe characteristics have obvious advantages. The main component of SCDA is calcium oxide, which reacts with water to produce higher expansion pressure. In this paper, focused on the angles of the borehole, the effect of SCDA is analyzed by numerical simulation based on Pingdingshan coal mine. The research results showed that the azimuthal angle a(between borehole projection and the roadway direction) does not significantly affect the efficacy of SCDAs, whereas the influence of borehole elevation angle b is far more significant than that of the azimuthal angle. Therefore, the angle b is a dominant factor influencing the effect of SCDAs. Based on different effects of SCDAs at different angle of boreholes, the weakening unit was established, so the SCDAs could give full play to roof fracturing. Moreover, field tests validated the importance of borehole angle on weakening the hard roofs.     

Comparative filtration and dewatering behavior of vitrinite and inertinite of bituminous coal: Experiment and simulation study

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.     

Experimental research into the effect of gas pressure,particle size and nozzle area on initial gas-release energy during gas desorption

Coal and gas outburst is a violent disaster driven by released energy from gas desorption. The initial expansion energy of released gas(IEERG) is a new method to predict coal and gas outburst. In this paper,an instrument for IEERG measurement was developed. Compared with previous setups, the new one which is equipped with three convergent nozzles and quick-release mechanism gets improved in data acquisition and gas sealing and releasing performance. To comprehensively know the effect of gas pressure, particle size, and nozzle area on IEERG, a series of experiments were carried out with this new setup.The variable control test results indicated that the gas pressure-IEERG curves remain the linear trend and the particle size-IEERG curves maintain the negative exponential trend for nozzle areas at 1.13, 2.26, and3.39 mm2, respectively. The increase in nozzle area leads to deceases in value of IEERG and absolute value of slope of fitting curves in each test. In addition, the orthogonal experiment showed that the influence of gas pressure, nozzle area, and particle size on IEERG decreases in turn. Only gas pressure had a marked impact on IEERG. This work offers great importance in improving the accuracy of prediction of coal and gas outburst.     

Interpretable modeling of metallurgical responses for an industrial coal column flotation circuit by XGBoost and SHAP-A “conscious-lab” development

Surprisingly, no investigation has been explored relationships between operating variables and metallurgical responses of coal column flotation (CF) circuits based on industrial databases for under operation plants. As a novel approach, this study implemented a conscious-lab “CL” for filling this gap. In this approach, for developing the CL dedicated to an industrial CF circuit, SHapley Additive exPlanations (SHAP) and extreme gradient boosting (XGBoost) were powerful unique machine learning systems for the first time considered. These explainable artificial intelligence models could effectively convert the dataset to a basis that improves human capabilities for better understanding, reasoning, and planning the unit. SHAP could provide precise multivariable correlation assessments between the CF dataset by using the Tabas Parvadeh coal plant (Kerman, Iran), and showed the importance of solid percentage and washing water on the metallurgical responses of the coal CF circuit. XGBoost could predict metallurgical responses (R-square > 0.88) based on operating variables that showed quite higher accuracy than typical modeling methods (Random Forest and support vector regression).     

煤矸石制备聚合氯化铝铁钙与应用试验研究

以煤矸石为原料,经过高温焙烧、酸浸、聚合、熟化等过程制备了高效无机高分子絮凝剂聚合氯化铝铁钙（PAFCC）,通过单因素试验研究了PAFCC制备条件对浊度、COD和UV₂₅₄去除率的影响。试验结果表明,PAFCC最佳聚合条件为pH值2、聚合温度60℃、聚合时间5 h、在40℃下熟化28 h。混凝结果表明：制备的PAFCC对浊度有极好的去除效果,达95.70%,同时,对COD、UV₂₅₄也有一定的去除效果,去除率分别达到47.51%、45.98%。炼化废水混凝结果表明：PAFCC对浊度和总磷有较好的去除效果,同时,对COD及氨氮也有一定的去除效果,效果明显优于传统PAC。     

Transferred arc plasma processed mullite from coal ash and bauxite

Coal ash disposal is one of the main problems in thermal power plant unit. Currently, a number of waste management systems are being tried for effective disposal of coal ash. In this paper, coal ash from thermal power plant unit was successfully utilized for synthesis of mullite ceramic by using transferred arc plasma processing (TAP) technique. For this purpose, bauxite was added with coal ash by 0, 25, 50 and75 weight ratio. The compositions were thoroughly mixed by ball milling and were melted in the transferred arc plasma torch at 10 kW input power level for 3 min. Argon was used as plasma forming gas. The phase and microstructure formation of the melted samples were investigated by XRD and SEM images. The results show that the additions of bauxite greatly influenced the phase formation of mullite during the processes.     

The utility of coal molecular models

There are a large number (> 125) of molecular representations for coals that span the rank range over seven decades. However, their utility has mostly been in representing chemical structural features, rather than in probing physical structure or exploring the structure-behavior relationship. This paper examines the utility of coal models and reviews the existing and emerging opportunities for coal models to contribute to coals effective utilization via demystification of the structure-behavior relationship. Coal models have been used to explore the coalification pathway, including contraction with water removal. Physical evaluations have probed the density of models as a check on their accuracy. Pore size distribution and sorption have been explored in simple pores and more recent work with carbon dioxide, water and methane sorption within the porous structure of large-scale (< 20,000 atoms) model. Pair distribution frequency and small angle X-ray scattering simulations have also been compared with experimental observations and offer an additional check on the constitution of the model structure. Simulated HRTEM and simulated (calculated) NMR spectra also exist. Models have been disassembled in efforts to represent the pyrolysis process, char formation, and char reactivity (including the role of ion-exchangable ions). Similar to the pyrolysis models, direct liquefaction has been explored with a pyrolysis style approach. Coal-solvent swelling, and coal-solvent solubility have also been explored. While considerable progress has accompanied improvements in computational power and software advances, it is the generation of the model that is the most significant barrier to the meaningful utility of these models. The ability to generate large-scale models (incorporation of molecular weight diversity and structural diversity) with new automation approaches, coupled with new dynamic force-fields that can simulate reactive events in complicated materials like coals, offers a new hope for the utility of coal or char molecular models to probe our understanding and aid in the scientific method rather than our current informed trial and error approach.     

Numerical modelling of the carrier gas phase in a laboratory-scale coal classifier model

The pneumatic transport of fine ideally combustible coal dust to the burner furnace is an important process in coal fired power plants. The strongly swirling air phase responsible for the particle separation and transport in a coal pulverising mill was characterised experimentally and numerically. Measurements of the swirl velocity component were taken in a scaled laboratory model of the device and compared to CFD model. In particular, an evaluation of the turbulence models used to describe the flow was performed. The modified isotropic k-epsilon turbulence models (RNG k-ε and Realizable k-ε) were compared to the anisotropic Reynolds stress model (RSM) and their ability to predict the bulk flow structure present in the classifier was assessed. The experiments showed that the swirling flow structure, responsible for coarse-fine particle classification, has several flow regimes which are governed by the areas it is bounded by. The numerical model predictions generally corroborate the results. However, a distinction in performance between the three models can be made based on accuracy, solution generation time and numerical stability. The RSM model predicted both the trends and magnitude the most accurately when compared to the isotropic models. However, the Realizable k-epsilon model, with its relatively low solution generation time, shows potential when using CFD as a classifier design optimization tool. The investigation has given some insight on single phase classifier flow and suggests a design improvement based on the results.     

Suppression of floatability of pyrite in coal processing by carrier microencapsulation

Carrier microencapsulation, CME, is a technique to form a thin layer of metal oxide or hydroxide on pyrite surface using a water soluble organic carrier combined with metal ions. The present study investigated the effect of CME using a tris-catecholato complex of Si⁴⁺, Si(cat)₃²⁻ on pyrite-coal separation by dynamic bubble pick-up experiments and Hallimond tube flotation experiments using coal, pyrite, and a coal-pyrite mixture. The mineral samples were treated in 0-5 mol m^− 3 Si(cat)₃²⁻ solutions at pH 4-9 at treatment times of 1-24 h. Dynamic bubble pick-up experiments showed that CME treatment converted the pyrite surface from hydrophobic to hydrophilic but did not affect coal's hydrophobic surface. The results of the Hallimond tube flotation experiments of a coal-pyrite mixture at pH 7-9 in the presence of kerosene as a collector showed that pyrite floatability was selectively suppressed after 1 h CME treatment with 0.5 mol^− 3 Si(cat)₃²⁻ while both coal and pyrite were floated without the treatment. This indicates that CME treatment is effective in suppressing pyrite floatability in coal-pyrite flotation.     

Thermal decomposition of coal fly ash by concentrated sulfuric acid and alumina extraction process based on it

The industrial applications of acidic leaching processes for alumina extraction from coal fly ash (CFA) have been limited due to its excessive usages of acid and fluoride. This limitation can be lifted by calcining the CFA with the concentrated sulfuric acid at high temperature. When CFA was mixed with the concentrated sulfuric acid of same amount and calcined at 300 °C, most of its aluminum components were transformed into aluminum sulfate. Excessive sulfuric acid was recycled by collecting sulfur trioxide produced during heating process. Morphological and X-ray diffraction evidence indicated that mullite inside CFA was thermally decomposed. Alumina and mullite were transformed into aluminum sulfate. A practical process of alumina extraction from CFA was developed based on this observation. The adoption of calcination process significantly reduced the sulfuric acid usage, shortened the process cycle, and eliminated the use of fluoride. The alumina extraction efficiency was improved up to 85%.