| Mine fire is one of the major disasters underground. In recent years, spontaneous combustion causes several cases of the production safety accident in mines, bringing huge casualties and property losses, also has a bad impact on society. Thus the State Administration of Work Safety put forward the principle of “In advance to prevent” to control the fire underground in the "Mine production safety plan during twelfth five-year period”, regarded “fire causes mechanism analysis, fire prevention, monitoring and warning" as key research areas to capture, specifically mentioned the control of internal fire hazard caused by coal spontaneous combustion and the prevention of internal fire. Therefore, perfection spontaneous combustion mechanism and further research of prediction and warning technology have a great significance on scientific decision of prevention of spontaneous fire.Spontaneous combustion of coal is affected by many factors, such as the physicochemical properties of coal and many external factors. This paper studied the impact of the water environment on spontaneous combustion. The coal samples were carried out by the self-developed oil bath type coal low temperature oxidation experimental system. The influence of the water’s p H and soaking time on the ability of coal low temperature oxidation was studied, which is characterized by standard oxygen consumption rate of coal. The experiments of constant temperature and heating up show that, alkaline water environment can partly reduce the coal oxidation ability when the temperature exceeds 55℃,but neutral and acidic water environment can promote the coal oxidation ability.The CO production rate of spontaneous combustion is the main parameters of research throughout the production of CO and the source of CO transport equation in goaf. Paper completed the low-temperature oxidation experiment of 14 coal samples from Luning and Malan Coal Mine. Formulas for calculating the standard CO formation rate during the experiment of low-temperature oxidation of coal was derived. The standard CO formation rate in the same mine at the same temperature and different oxygen concentrations are equal by substituting the experimental data. It shows that CO production rate and ambient oxygen concentration is directly proportional of spontaneous combustion of coal, and can calculate the amount of CO generated at different locations in goaf.Space and geological condition of goaf is complex, it is unable to realize the real-time monitoring of the internal gas concentration, while the similar simulation experiment of spontaneous combustion still exist many problem, especially the simulation for working face advancing. So most theory and technology of index gas are summed in laboratory conditions of spontaneous combustion of coal. Spontaneous combustion conditions of actual goaf is complex, and it will be a large deviation to use the relevance of Experimentally derived concentration of each gas to coal temperature to predict the degree of spontaneous combustion. As a result, the numerical simulation has become an important method and means for study the spontaneous combustion. More reasonable mathematical model, advanced numerical methods and supports of observational data is necessary.According to the law of conservation of mass and Fick’s law, CO transport equation was set up, and boundary conditions were determined, thereby CO concentration field mathematical model was set up. Based on the research of spontaneous combustion multi-field coupling mechanism of our group, the coupling relationship among carbon monoxide concentration field, flow field, oxygen concentration field and the temperature field was studied and the multi-field coupling mode of spontaneous combustion which includes CO concentration field was set up. According to the actual characteristics of goaf, this paper determined the solver scope of each field, completed meshing and node ID in solver area. Based on the two-dimensional finite volume method, the CO concentration field equation and other field equations were dispersed. This paper also introduced a discrete process of CO concentration field and given the discrete formula of flow field, oxygen concentration field, the gas temperature field and solid temperature field in goaf.By making use of the two-dimensional finite volume method proposed by our research group, we make the CO concentration field of goaf spontaneous combustion field coupling model discretized and get the field of linear equations of each node. We develop our own "CO migration of goaf spontaneous combustion simulation system" by using the iterative method, and then we make coupling iteration to the goaf spontaneous combustion. Combining with the actual situation, we get the distribution of goaf flow field, oxygen concentration field, gas temperature field, solid temperature field and CO concentration fields. Through a large number of computer numerical calculation of different working face pressure difference, working face advancing speed and thickness of the remaining coal, we get the highest temperature in goaf between 0~200℃ and CO concentration in upper corner of logarithm linear function relation, which is of great significance for the actual prediction of goaf coal spontaneous combustion.The reason why CO concentration in 6122 working face upper corner of Fen Xi mining group is overrun is analyzed, and we solve the problem successfully by setting voltage-sharing ventilation scheme. Firstly, through the field observation on the CO concentrations in working face upper corner, the characteristics of abnormal gush is qualitative, and the source of the high CO concentration is analyzed. Secondly, we observe the temperature distribution in 6122 working face by using the “coal mining working face goaf temperature observation system” developed by our research group. Eight probe is layout along the working face inclined direction, and "mining goaf temperature observation wiring plan" is put forward according to the site condition, the temperature change in goaf is successfully observed. Results show that the highest temperature in goaf 18℃, the goaf spontaneous combustion will not occur, then the numerical simulation results also show that the goaf spontaneous combustion fire will not occur. On the basis of position of the coal seam condition, we synthetically judge that 6122 working face upper corner CO overrun is caused by adjacent layer on the working face or old kiln of high CO concentration leak on the carrier of air leakage caused by intermittent flow. For the air leakage in goaf, we lay down the voltage-sharing ventilation management measures, design the working face fan-throttle combined pressurizing scheme, calculate the fan for air volume, complete the fan selection, determine to choose two 55 kw local fan, reasonably arrange the position the distribution for fan and throttle. In order to ensure the stability of the pressure equalization system,the corresponding safety measures was developed based on the "2-4" model. After implementation of voltage-sharing ventilation, seeing from the condition of air leakage in working face and the observation result of the CO concentration in upper corner after voltage-sharing ventilation, the voltage-sharing ventilation system have achieved good effect, it successfully solved the problem of working face upper corner CO overrun.After the end of 6120 working face mining, we determine to set permanent double wall airtight in the stop line combining with practical situation on site, and reserve beam tube system to detect the CO concentration changes in goaf, which is used to determine the goaf spontaneous combustion situation. Soon, we find that the CO concentration in airtight goaf area is higher, it will leak to the surrounding normal mining working face, which affect the safety production of working face. Therefore, we decide to adopt a nitrogen injection control measure in airtight area, and provide the nitrogen injection design on site. Firstly, we research the mechanism of nitrogen injection against fire, combined with inerting index of oxygen concentration of the various circumstances against fire; secondly, we determine the field nitrogen injection volume, complete the nitrogen injection equipment type selection, set the field nitrogen injection piping layout plan, choose the reasonable nitrogen gas transportation pipeline and nitrogen injection pipe diameter, and draw the corresponding nitrogen injection piping layout. After the beginning of airtight nitrogen injection on site, we observe the goaf gas composition and concentration among nearly 20 months, and draw the concentration change rule figures of CO, N2, O2 based on the observation data before and after the nitrogen injection. Researches show that nitrogen injection in goaf has a significant effect to goaf remaining coal spontaneous combustion fire, so it solved the governance issues of high CO concentration in airtight areas. Behavior-based accident causation "2-4" model was used to the safety management of airtight goaf, and corresponding management measures were formulated accordingly.The main innovation of this paper contains three points as follows:(1) Demonstrated the direct relationship between the generation rate of CO in the spontaneous combustion of coal and the concentration of oxygen in the environment. Established the formula of the generation rate of CO in the low-temperature oxidation of coal during the experiment according to the hypothesis of CO in the spontaneous combustion of coal and the concentration of oxygen in the environment are direct relationship. Conducted the low-temperature oxidation experiment using the coal from Lu Ning and Ma Lan under different oxygen concentration and different temperature. Substituted the result into the formula of the generation rate of CO and obtained the law of the generation rates of CO are identical in the same colliery under the same temperature and different oxygen concentration. This suggests that the total production capacity of CO and the total consumption capacity of oxygen are proportional in the coal spontaneous combustion. And thus confirmed the hypothesis which is mentioned before is correct.(2) Established the quantitative relationship between the highest temperature in the goaf and the CO concentration on the corner. Sutted up the CO transporting equation in the goaf by using the law of conservation of mass and the low of Fick. Established the spontaneous combustion multi-field coupling model containing the concentration field according to the research of the spontaneous combustion multi-field couplingWhich our group had before. Based on the finite volume to have the model discreted and prepared coupled solver software. Finally we get the CO migrating situation in the goaf and the distribution of other field. Established the quantitative functional relationship between the highest temperature and the CO concentration in the corner through extensive numerical experiments. The study suggest that the maximum temperature in the mine-out area and the logarithm of CO concentration in the upper corner are of a good linear relationship.(3) Behavior-based accident causation "2-4" model, pressure ventilation of working face and closed nitrogen injection and other means have been used. Developed the controlling measures of the CO concentration overrunning in the upper corner and the high concentration CO controlling measures after the fire area closed, and all these measures got good results. Determined the reason why the CO overrun in the upper corner is that high concentration CO release from the mine-out area in the adjacent layers or small coal mines according to on-site air leakage observation, mine-out area temperature observation and numerical simulation study combining the in-site situation in the mine in the Fen Xi. And we decided to adopt the measure of pressure ventilation to control the matter. Designed pressure ventilation scheme and safety measures of pressure ventilation had been formulated based on “2-4” model. The result suggests that the pressure ventilation has a good effect on the reducing the CO concentration in the upper corner. For the high concentration of CO after the working place was closed, we designed closed nitrogen injection extinguishing measures and Closed nitrogen injection program. By using the Beam tube system to observe the diversification of the CO concentration in the mined-out area, we got the result that continuous nitrogen injection could inhibit the spontaneous combustion in the closed area, and could get good effect. |
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