RESUMO
To study thermal behaviour during spontaneous combustion of an open-pit coal mine, mixed slag (coal, oil shale, and coal gangue) was taken as the research object. Laser thermal conductivity analyser and differential scanning calorimetry were used to test thermophysical parameters and heat release characteristics of the minerals. The parameters can be employed to calculate the apparent activation energy using the Arrhenius equation and evaluate the thermal behaviour of open-pit mixed slag. The results indicate that thermophysical parameters have stage characteristics. Thermal diffusivity and thermal conductivity of minerals, especially mixed slag, have a strong correlation with temperature. Heat flow of minerals exhibits five characteristic stages, and heat flow of the samples is consistent with the change in heating rate. During the heating process, thermal diffusivity and heat flow of the mixed slag are between those of a single mineral. Except for the mixed slag at 15 and 20 °C/min, the initial exothermic temperature of the other samples is mainly concentrated at 50-80 °C. Thermal energy release of the sample is mainly concentrated in the accelerated exothermic stage and rapid exothermic stage. Thermal energy release of mixed slag in rapid exothermic stage is always greater than that in accelerated exothermic stage, and the proportion of thermal energy release in these two stages exceeds 98 %. The apparent activation energy during the accelerated exothermic stage is lower, making it easier to release heat, and rapid exothermic stage is relatively high, which can readily lead to heat accumulation. Thermal analysis reveals that the thermal behaviour of mixed slag is significantly different from that of a single mineral. Its unique exothermic characteristics can provide a more accurate theoretical basis for the prevention and control of environmental pollution caused by slag spontaneous combustion.
RESUMO
To study the dynamic evolution law of the oxidation heating process of coal spontaneous combustion in the goaf during the advancing process of the working face, a dynamic model of oxidation heating of coal spontaneous combustion in the goaf was established on the basis of deformed geometry. Through numerical simulation research, the evolution and migration laws of seepage field, oxygen concentration field, temperature field, and high-temperature area of coal spontaneous combustion in the goaf during the advancement of the working face was obtained. The results indicate that the distribution of the bulking coefficient, porosity, and permeability of the falling coal and rock mass in the goaf is nonuniform. They are relatively large in the area near the working face and the inlet and return airway and remain relatively unchanged with the advancement of the working face, but they are constantly decreasing in the location of the gob in the middle and deep. The oxygen concentration in the goaf presents an asymmetrical distribution. The oxygen concentration distribution area on the inlet side is wider than that on the return air side. At the same depth of the goaf, the oxygen concentration gradually decreases from the inlet side to the return air side; after the advancement distance exceeds 200 m, the air leakage in the goaf basically disappears, and the oxygen concentration decreases to zero. The high-temperature area of coal spontaneous combustion oxidation in the goaf was mainly concentrated on the air inlet side and extended toward the return air side. The advancing speed has a significant effect on the oxidation heating process of coal spontaneous combustion in the dynamic goaf. Under the same propulsion distance, when the advancing speed is 6 m/day, the highest temperature in the goaf is about 40 °C, and when the advancing speed is 2 m/day, the highest temperature in the goaf is as high as 120 °C. The smaller the advancing speed, the higher the heating rate of the goaf and the closer the high-temperature area to the working surface. The higher the advancing speed, the lower the temperature of the high-temperature point of the goaf and the greater the depth of the high-temperature point of the high temperature area; when the advancing speed is 2 m/day, the highest temperature point in the goaf is 70 m away from the working face, whereas when the advancing speed is 6 m/day, it reaches 174.6 m.
RESUMO
With the development of higher education, there are a large number of college graduates turn into the labor market, and college students' employability has become a popular topic. In order to explore the factors that affect employability's improvement and what factors employability includes, this article summarizes the previous research on employability, uses university graduates of Shaanxi Province as research examples, and investigates the employability factors of college graduates. With the help of SPSS software, data analysis is conducted on the 220 valid questionnaires. The study uses reliability and validity analysis to verify the quality of the questionnaire, takes the exploratory factor analysis to test the employability factors of college students, and employs multiple linear regression analysis to test the factors that influence employability's improvement. The results of the research show that individual traits, social experience, and workplace training have a significant impact on college students' employability; knowledge understanding and learning ability, self-management ability, emotional intelligence, generic skills, professional ability, and career planning capability are the important factors of the employability which college students should master. Our research results update the influencing factors of employability, so that contemporary college students have a new understanding of employability, and help them to improve their employability more pertinently.
