scholarly journals Multifield Coupled Dynamic Simulation of Coal Oxidation and Self-Heating in Longwall Coal Mine Gob

2020 ◽  
Vol 2020 ◽  
pp. 1-16 ◽  
Author(s):  
Shuanglin Song ◽  
Shugang Wang ◽  
Shuang Jiang ◽  
Yuntao Liang ◽  
Peiyu Hu
Keyword(s):  
Heat Transfer ◽  
Particle Size ◽  
High Temperature ◽  
Maximum Temperature ◽  
Coal Oxidation ◽  
Self Heating ◽  
Working Face ◽  
High Temperature Area ◽  
Residual Coal ◽  
Temperature Area

The spontaneous combustion of residual coal in coal mine gob has long been a problem and poses a threat to the safe production of coal. Therefore, it is of great significance to conduct an in-depth study of the oxidation and self-heating progress of residual coal in the gob. Considering that the geometric dimensions and physical characteristics of the gob will change during the advance of the working face, the purpose of the present paper is to determine how the coal self-heating develops during and after coal mining. A fully coupled transient model including gas flow, gas species transport, and heat transfer in the gob and the butt entries, as well as heat transfer in the surrounding strata, is developed to quantify the evolution of coal self-heating in gob during and after mining. The model was solved by COMSOL Multiphysics package and then verified by comparing the field data with the simulated data. On this basis, parametric studies including the influences of the surrounding strata temperature, airflow temperature, coal-rock particle size, and advance rate of the working face on coal oxidation and self-heating in the gob were conducted. The results show that a tailing phenomenon of the high-temperature area is formed on the air inlet side of the gob during mining, and the temperature in the high-temperature zone decreases gradually due to the accumulation and compaction of the gob and heat dissipation to the surrounding strata. Also, although the temperature in gob increases gradually after the stopping of mining, the high-temperature area migrates towards the working face. Moreover, when the temperature of the surrounding strata is consistent, different ventilation temperatures have no obvious effect on the maximum temperature of the gob at the initial mining stage, whereas the higher ventilation temperature results in the higher self-heating temperature after several days of mining. Finally, the smaller average particle size or faster advance rate results in a lower maximum temperature of gob.

scholarly journals Investigation of the kinetics of spontaneous combustion of the major coal seam in Dahuangshan mining area of the Southern Junggar coalfield, Xinjiang, China

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Li Shen ◽  
Qiang Zeng
Keyword(s):  
Particle Size ◽  
High Temperature ◽  
Coal Seam ◽  
Spontaneous Combustion ◽  
Heating Temperature ◽  
Characteristic Temperature ◽  
Mining Area ◽  
Particle Sizes ◽  
Coal Oxidation ◽  
Increasing Temperature

AbstractIn the present paper, with using diverse methods (including the SEM, the XRD, the TPO, the FTIR, and the TGA) , the authors analysed samples of the major coal seam in Dahuangshan Mining area with different particle sizes and with different heated temperatures (from 50 to 800 °C at regular intervals of 50 °C). The results from SEM and XRD showed that high temperature and high number of pores, fissures, and hierarchical structures in the coal samples could facilitate oxidation reactions and spontaneous combustion. A higher degree of graphitization and much greater number of aromatic microcrystalline structures facilitated spontaneous combustion. The results from TPO showed that the oxygen consumption rate of the coal samples increased exponentially with increasing temperature. The generation rates of different gases indicated that temperatures of 90 °C or 130 °C could accelerate coal oxidation. With increasing temperature, the coal oxidation rate increased, and the release of gaseous products was accelerated. The FTIR results showed that the amount of hydroxide radicals and oxygen-containing functional groups increased with the decline in particle size, indicating that a smaller particle size may facilitate the oxidation reaction and spontaneous combustion of coal. The absorbance and the functional group areas at different particle sizes were consistent with those of the heated coal samples, which decreased as the temperature rose. The results from TGA showed that the characteristic temperature T3 declined with decreasing particle size. After the sample with 0.15–0.18 mm particle size was heated, its carbon content decreased, and its mineral content increased, inhibiting coal oxidation. This result also shows that the activation energy of the heated samples tended to increase at the stage of high-temperature combustion with increasing heating temperature.

Numerical Simulation of Interior Flow in Evaporation Droplet

2014 ◽  
Author(s):  
Qingming Dong ◽  
Zhentao Wang ◽  
Yonghui Zhang ◽  
Junfeng Wang
Keyword(s):  
Numerical Simulation ◽  
High Temperature ◽  
Internal Flow ◽  
Surface Force ◽  
Droplet Surface ◽  
Force Model ◽  
Marangoni Flow ◽  
High Temperature Area ◽  
Interior Flow ◽  
Temperature Area

In this present study, the VOF (Volume of Fluid) approach is adopted to capture the interface, and CSF (Continuum Surface Force) model to calculate the surface tension, and the governing equations are founded in numerical simulation of evaporating droplets. In this work, a water droplet is assumed to be suspending in high temperature air, and the gravity of a droplet is ignored. During evaporating process of the droplet, the internal circulation flow will be induced due to the gradient of temperature at the droplet surface. The interface flows from high temperature area to low temperature area, which pulls the liquid to produce convective flow inside the droplet called as Marangoni flow. Marangoni flow makes the temperature distribution tend to uniformity, which enhances heat transfer but weakens Marangoni flow in turn. So, during droplet evaporation, the internal flow is not steady.

Spontaneous Combustion Characteristics and Air Leakage Control Technology of Half Isolated Island Fully Mechanized Caving Face

2013 ◽  
Vol 718-720 ◽  
pp. 1639-1644 ◽  
Author(s):  
Yu Bing Mu
Keyword(s):  
High Temperature ◽  
Spontaneous Combustion ◽  
Coal Pillar ◽  
Combustion Characteristics ◽  
Air Leakage ◽  
Tracer Gas ◽  
Danger Zone ◽  
Working Face ◽  
High Temperature Area ◽  
Safe Mining

The 3-105 half isolated island fully mechanized caving face in Tengdong coal mine which in complex geological and high temperature condition, has a spontaneous combustion feature that is different from normal advancing mechanized caving face, such as slowly advance speed, stress concentration and air leakage of inside-impending gob. To overcome the dangerous possibility of spontaneous combustion between the roof coal seam inside-impending gobs, small coal pillar and adjacent gob of half isolated island fully mechanized caving face, analysis spatial structure of overlying strata roof and spontaneous combustion characteristics. Based on the result of pressure can be measured and tracer gas test of air leakage channels, determine the potential air leakage areas. The MEA plugging wind material is pumped into roadway and SPA-4 plugging wind material is spray around known air leakage or high temperature area to eliminate the hazards of spontaneous combustion of the potential danger zone, and protects the safe mining of the working face.

Study of phase transformation temperatures of alloys based on Fe–C–Cr in high-temperature area

2018 ◽  
Vol 133 (1) ◽  
pp. 41-48 ◽  
Author(s):  
Ľubomíra Drozdová ◽  
Bedřich Smetana ◽  
Simona Zlá ◽  
Vlastimil Novák ◽  
Monika Kawuloková ◽  
...  
Keyword(s):  
Phase Transformation ◽  
High Temperature ◽  
Transformation Temperatures ◽  
High Temperature Area ◽  
Temperature Area

scholarly journals Effective thermal conductivity of loose residual coal in goaf: Comparative analysis of experiment and model

2022 ◽  
pp. 014459872110695
Author(s):  
Chunhua Zhang ◽  
Jiahui Shen ◽  
Mei Wan
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Particle Size ◽  
Ambient Temperature ◽  
Effective Thermal Conductivity ◽  
Void Fraction ◽  
Coal Particle ◽  
Spontaneous Combustion ◽  
Relative Errors ◽  
Residual Coal

The effective thermal conductivity (ETC) model of loose residual coal in goaf is a method to study the heat transfer law of spontaneous combustion in goaf. In order to study the effect of coal particle size and ambient temperature on heat transfer, coal samples of different sizes were taken from the FuSheng (FS) mine, and the void fraction, the thermal conductivity (TC) of the residual coal under different ambient temperature were tested. Additionally, four types of ETC models of loose residual coal in goaf were obtained and the average relative errors of the TC were analyzed. The results showed that the void fraction, the coal particle size and ambient temperature have different effects on the spontaneous combustion of the residual coal. The effect of coal sample size on the heat transfer is 100 times that of the ambient temperature. The changes in the ETC and average relative error of the different models were consistent. The heat transfer in the spontaneous combustion of residual coal has a direct relationship with the spatial distribution and heat transfer modes of the loose residual coal in the goaf.

Inverse Arithmetic of the Equivalent Heat Transfer Coefficient of Mine Goaf

2011 ◽  
Vol 328-330 ◽  
pp. 1013-1016
Author(s):  
Shuai Heng ◽  
Feng Gao ◽  
Xing Guang Liu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
High Temperature ◽  
Transfer Coefficient ◽  
Measured Data ◽  
Heat Sources ◽  
Calculating Method ◽  
Temperature Forecast ◽  
Working Face ◽  
Conservation Of Momentum

In order to calculate the dissipating capacity of heat sources and improve the veracity of airflow temperature forecast of mine, the equivalent heat transfer coefficient of mine goaf was calculated by means of inverse arithmetic based on the law of conservation of momentum and measured data from a high temperature working face. The results of calculation show that the equivalent heat transfer coefficient of mine goaf can reflect the heat dissipating characteristics generally and reduce the calculating method of the heat dissipating capacity of mine goaf, then it can be used better in the airflow temperature forecast.

Contour Extraction for Images of High Temperature Long Shaft Heavy Forgings

2012 ◽  
Vol 562-564 ◽  
pp. 1655-1659
Author(s):  
Qin Xiang Xia ◽  
Zhe Lin Li ◽  
Wei Qi Zong ◽  
He Qing Xie
Keyword(s):  
High Temperature ◽  
Hot Forging ◽  
Ccd Camera ◽  
Measuring Method ◽  
Contour Extraction ◽  
B Spline ◽  
High Temperature Area ◽  
The Mean ◽  
Temperature Area

Non-contact measuring method based on CCD camera is desirable for product quality of high temperature long-shaft heavy forgings. In the light of the characteristics of RGB primary color and halation in forging image, the mean red gray value in the high temperature area is proposed as the dynamic threshold to acquire external contours. Internal edges in the image of the hot forging are blurry and discontinuous. For these characteristics, a method based on quadratic B-spline curve is employed to extract and fit the internal contours. Experiments show that this method can effectively remove pseudo features and extract accurate internal and external contours for images of high temperature squaring and chamfering forgings of 900 0C to 1050 0C.

Compared Analysis of Embankment Thermal Stabilities in High Temperature Permafrost Regions with and without Climatic Warming

2012 ◽  
Vol 204-208 ◽  
pp. 1822-1829
Author(s):  
Dong Qing Li ◽  
Xing Huang ◽  
Jian Hong Fang
Keyword(s):  
Climate Change ◽  
High Temperature ◽  
Climate Warming ◽  
Eastern Tibetan Plateau ◽  
Cement Concrete ◽  
Thermal Stabilities ◽  
Stable Conditions ◽  
High Temperature Area ◽  
Permafrost Regions ◽  
Temperature Area

The heat stabilities of embankment on the high temperature permafrost regions in the eastern Tibetan Plateau without climate warming and with air temperature rising speed of 0.04°C/a were modeled, and the heights of embankment were discussed and figured out, comparatively and respectively for asphalt-paved, concrete and gravel road surface, according to the natural geographic and geologic conditions in the high temperature permafrost regions in the district. The different confined conditions about embankment critical heights with climate warming and without climate warming were discussed in the paper. Finally, the result had been obtained by numerical calculation: in the high temperature area, for the two types of laying of cement concrete and gravel surface road, the two critical heights of the thermal stable conditions were (road operation for 30 years), respectively, do not consider climate change as 2.5 m and 2.0 m, consideration of climate change were 3.5 m and 3.0 m.

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