Research on complex air leakage method to prevent coal spontaneous combustion in longwall goaf.
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ABSTRACT:
SUBMITTER: Wang K
PROVIDER: S-EPMC6396930 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Accurate predictions of the coal temperature in coal spontaneous combustion (CSC) are important for ensuring coal mine safety. Gas coal (the Zhaolou coal mine in Shandong Province, China) was used in this paper. A large CSC experimental device was adopted to obtain its characteristic temperatures from the macroscopic characteristics of gas production. A simulated annealing-support vector machine (SA-SVM) prediction model was proposed to reflect the complex nonlinear mapping between characteristic gases and the coal temperature. The risk degree of CSC was estimated in the time domain, and the model was verified by using in situ data from an actual working face. Furthermore, back-propagation neural network (BPNN) and single SVM methods were adopted for comparison. The results showed that the BPNN could not adapt to the small-sample problem due to overfitting and the output of a single SVM was unstable due to its strong dependence on the setting of hyperparameters. Through the SA global optimization process, the optimal combination of hyperparameters was obtained. Therefore, SA-SVM had higher prediction accuracy, robustness, and error tolerance rate and better environmental adaptability. These findings have certain practical significances for eliminating the hidden danger of CSC in the gob and providing timely warnings about potential danger.
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Project description:The "three stages" division of coal spontaneous combustion is fuzzy and lacks adequate risk and warning levels corresponding to its divisions; additionally, the targeted prevention measures for each stage have not been described. To address the shortcomings of the "three stages" division, the "five stages" division was proposed to more clearly analyze the stage changes of the spontaneous combustion of coal. The "five stages" method divides the process of the spontaneous combustion of coal into five stages, including: the latent stage, heat accumulating stage, evaporation stage, active stage, and hypoxic stage. The critical point of each stage was determined using adiabatic oxidation experiments and programmed heat experiments. As the critical point of the latent stage, the temperature of zero activation energy is approximately 55-70°C. In the heat accumulating stage, the critical point is the temperature (approximately 90°C) where the external moisture of coal evaporates violently while the internal moisture of coal has not yet fully evaporated. During the evaporation stage, the temperature (approximately 105°C) where the internal moisture has evaporated completely represents the end of this stage and the start of the active stage (105-170°C). When the oxygen concentration drops to 5%, the spontaneous combustion of coal enters the hypoxic stage. Thus, an oxygen concentration of 5% represents the critical point of the start of the hypoxic stage (above 170°C). After the analysis of each stage, risk and warning levels were determined. Considering the major prevention measures of the spontaneous combustion of coal, a staged warning and disposal table was created.
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Project description:The study aim was to investigate whether household bituminous ("smoky") coal use and personal exposure to combustion emissions were associated with immunologic/inflammatory marker levels. A cross-sectional study of healthy never-smoking women from rural Xuanwei and Fuyuan, China was conducted, which included 80 smoky coal and 14 anthracite ("smokeless") coal users. Personal exposure to fine particulate matter (PM2.5) and benzo[a]pyrene (BaP) was assessed using portable devices, while 67 circulating plasma immunologic/inflammatory markers were measured using multiplex bead-based assays. Multivariable linear regression models were employed to estimate associations between smoky coal versus smokeless coal use, indoor air pollutants, and immunologic/inflammatory markers. Six markers were altered among smoky coal users compared to smokeless coal, including significantly decreased interferon-inducible T-cell alpha chemoattractant (CXCL11/I-TAC), and increased serum amyloid P component (SAP). CXCL11/I-TAC was previously found to be reduced in workers exposed to high levels of diesel engine exhaust, which exhibits similar constituents as coal combustion emissions. Further, there was evidence that elevated PM2.5 and BaP exposure was associated with significantly diminished levels of the serum amyloid A (SAA); however, the false discovery rates (FDRs) were >0.2 after accounting for multiple comparisons. Inflammatory processes may thus mediate the carcinogenic effects attributed to smoky coal emissions.
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Project description:The relationship between the properties of coal and its tendency to spontaneous combustion is critical for the environment, safety concerns, and economy. In this study, to eliminate the complex influence of moisture; the samples having similar moisture content were selected from Shanxi and Henan provinces. The chemical properties, physical properties, and tendency of coal samples to spontaneous combustion were characterized based on the conventional analysis, mercury intrusion porosimetry, fractal dimensions, and crossing point temperature (CPT). The results confirmed that the coal rank, volatile matter, oxygen contents, and fixed carbon content had a good linear relationship with the CPT. The relationship between the ash content and CPT presented a "U-shaped" non-linear correlation. For the pore size distribution, the total pore volume also possessed a linear positive correlation with the CPT. The fractal curves could be distinctly divided into two stages: low-pressure (<20?MPa) and high-pressure (>20?MPa), from which the fractal dimensions were obtained using the Sponge and Sierpinski models. The relationship between the fractal dimensions (Ds1, Ds2, and Dg1) and CPT could be divided into two distinct stages: a decrease in the CPT with increasing fractal dimensions (2.6-2.85), and then an in increase in the CPT. CPT decreased with increasing parameters of D1, D2, H, and D10, and it gradually increased with increasing D-10-D10, D-10-D0, and D0-D10. The above characteristics are important to comprehensively and systematically reveal the mechanism of spontaneous combustion.
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Project description:In neurosurgical cases, problems related to wound healing can vary from simple wound dehiscence to multilayer defects. This study demonstrates an effective method to prevent persistent cerebrospinal fluid (CSF) leakage using reinforcing acellular dermal matrix in neurosurgical patients with wound dehiscence. A 52-year-old woman was admitted for management of recurrent glioblastoma. After tumor removal surgery, the patient experienced sustained CSF leakage from the wound despite reparative attempts. The plastic surgery team performed wound repair procedure after remnant tumor removal by the neurosurgery team. Acellular dermal matrix was applied over the mesh plate to prevent CSF leakage and the postoperative status of the patient was evaluated. No sign of CSF leakage was found in the immediate postoperative period. After 3 years, there were no complications including CSF leakage, wound dehiscence, and infection. We hereby propose this method as a feasible therapeutic alternative for preventing CSF leakage in patients experiencing wound problem after neurosurgical procedures.
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Project description:Sustainable building material design relies mostly on energy saving processes, decrease of raw materials consumption, and increase of waste and by-products recycling. Natural and lightweight artificial aggregates production implies relevant environmental impact. This paper addresses both the issues of residues recycling and energy optimization. Particularly, three coal combustion wastes (Weathered Fly Ash, WFA; Wastewater Treatment Sludge, WTS; Desulfurization Device Sludge, DDS) supplied by the Italian electric utility company (ENEL) have been employed in the manufacture of cold bonded artificial aggregates. Previously, the residues have been characterized in terms of chemical and mineralogical compositions, water content, particle size distribution, and heavy metal release behavior. These wastes have been used in the mix design of binding systems with the only addition of lime. Finally, the artificial aggregates have been submitted to physical, mechanical, and leaching testing, revealing that they are potentially suitable for many civil engineering applications.
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Project description:In order to effectively prevent and control spontaneous combustion of residual coal in the goaf and reduce the waste of nitrogen caused by setting the position of nitrogen injection, 1303 fully mechanized coal caving faces of the Jinniu Mine are studied. By deploying a bundle tube monitoring system in the inlet air side and return air side of the goaf, changes in gas concentration in the goaf are continuously monitored. In addition, the distribution area for spontaneous combustion three-zone in the goaf is divided into heat dissipation zone, oxidized spontaneous combustion zone, and suffocation zone. Simulations from the COMSOL Multiphysics 5.3 software provide insight based on the three zones division standard of spontaneous combustion in the goaf. The gradual deepening of the nitrogen injection position into the goaf affects the lower limit of the oxidized spontaneous combustion zone significantly, but the impact on the upper limit of the oxidized spontaneous combustion zone is not obvious and is negligible. With regard to the width of the oxidized spontaneous combustion zone, it initially decreases followed by a gradual increase. Numerical calculations suggest the optimal nitrogen injection position is 40 m from the roof cutting line, with an oxidized spontaneous combustion zone width of 28 m. Based on the simulation analysis results, nitrogen injection controlling measures have been adopted for spontaneous combustion of residual coal in the goaf of the 1303 fully mechanized coal caving faces, and coal self-ignition in the goaf has been successfully extinguished.
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Project description:Coal gangue has the shortcomings of low calorific value and refractory burnout, while polyvinyl chloride has the advantages of a long combustion process and high calorific value. In order to make up for these shortcomings of coal gangue, the possibility of a treatment method based on co-combustion of coal gangue with polyvinyl chloride, which can be centrally recovered from municipal solid waste, is proposed. In order to analyze the combustion effect of a mixture of these two substances, experimental samples were prepared by mixing these two substances in three different ratios, and they were tested by thermogravimetric analysis. The experimental results were compared, analyzed and evaluated. The effects of the proportion of polyvinyl chloride in the mixture on the temperature parameters, activation energy, and interaction during co-combustion were analyzed. In order to analyze the interaction during co-combustion of the two, a coupling analysis method for mixed combustion is presented, and the effectiveness of this method is verified by comparing with the correlation analysis results of co-combustion. The results show that co-combustion can mitigate the ignition difficulty and burnout of coal gangue. When the proportion of polyvinyl chloride in the mixture was increased from 20% to 80%, the maximum weightlessness rate of the first stage rapidly increased from 4.5%/min to 15.6%/min; however, that of the second stage slowly increased from 3.7%/min to 4.2%/min. A 20% proportion of polyvinyl chloride showed the most significant promotion of co-combustion, with a maximum coupling coefficient of 0.00318, which was 1.11 and 1.35 times greater than that of 50% and 80% proportions, respectively. Co-combustion can reduce the activation energy of coal gangue during the initial and end stages. Therefore, co-combustion is helpful to improve the problems of low calorific value and refractory burnout of coal gangue.
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Project description:The thermochemical and kinetic behavior of co-combustion of coal, municipal sludge (MS) and their blends at different ratios were investigated by thermogravimetric analysis. Simulation experiments were performed in a vacuum tube furnace to determine the conversion behavior of toxic elements. The results show that the combustion processes of the blends of coal and municipal sludge are divided into three stages and the combustion curves of the blends are located between those of individual coal and municipal sludge samples. The DTGmax of the sample with 10% sludge addition reaches a maximum at the heating rate of 20 °C/min, indicating that the combustion characteristics of coal can be improved during co-combustion. Strong interactions were observed between coal and municipal sludge during the co-combustion. The volatilization rates of toxic elements decrease with an increasing proportion of sludge in the blends during co-combustion, which indicates that the co-combustion of coal and sludge can effectively reduce the volatilization rate of toxic elements. The study reflects the potential of municipal sludge as a blended fuel and the environmental effects of co-combustion of coal and municipal sludge.
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Project description:Electron paramagnetic resonance (EPR) spectroscopy was used to measure the free radicals in the particulate matter (PM) emissions from wood and coal combustion. The intensity of radicals in PM dropped linearly within two months of sample storage and stabilized after that. This factor of storage time was adjusted when comparing radical intensities among different PM samples. An inverse relationship between coal rank and free radical intensities in PM emissions was observed, which was in contrast with the pattern of radical intensities in the source coals. The strong correlation between intensities of free radical and elemental carbon in PM emissions suggests that the radical species may be carbon-centered. The increased g-factors, 2.0029-2.0039, over that of purely carbon-centered radicals may indicate the presence of vicinal oxygen heteroatom. The redox and biology activities of these carbon-centered radicals are worthy of evaluation.
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