The square root relationship of gas release in the early stage of desorption is widely used to provide a simple and fast estimation of the lost gas in coal mines. However, questions arise as to how the relationship wa...The square root relationship of gas release in the early stage of desorption is widely used to provide a simple and fast estimation of the lost gas in coal mines. However, questions arise as to how the relationship was theoretically derived, what are the assumptions and applicable conditions and how large the error will be. In this paper, the analytical solutions of gas concentration and fractional gas loss for the diffusion of gas in a spherical coal sample were given with detailed mathematical derivations based on the diffusion equation. The analytical solutions were approximated in case of small values of time and the error analyses associated with the approximation were also undertaken. The results indicate that the square root relationship of gas release is the first term of the approximation, and care must be taken in using the square root relationship as a significant error might be introduced with increase in the lost time and decrease in effective diameter of a spherical coal sample.展开更多
A test system of the permeability of broken coal samples mainly consists of a CMT5305 electronic universal test machine, crushed rock compaction containing cylinder and a self-designed seepage circuit, which is compos...A test system of the permeability of broken coal samples mainly consists of a CMT5305 electronic universal test machine, crushed rock compaction containing cylinder and a self-designed seepage circuit, which is composed of a gear pump, a reversing valve, a relief valve and other components. By using the steady penetration method, the permeability and non-Darcy flow β factor of broken coal samples under five different porosity levels were measured, the grain diameters of the coal samples were selected as 2.5-5 mm, 5-10 mm, 10-15 mm, 15-20 mm, 20-25 mm and 2.5-25 ram, respectively. After measuring the permeability under each porosity, the overfall pressure of the relief valve continuously increased until the coal sample was broken down. In this way, the flow type of liquid inside the broken coal samples changed from seepage to pipe flow. The correlation between breakdown pressure gradient （BPG） and porosity was analyzed, and the BPG was compared with the pressure gradient when seepage instability occurred. The results show that, ①the non-Darcy flow β factor was negative before broken coal samples with six kinds of diameters were broken down; ②the BPG of coal samples with a grain size of 2.5-25 mm was lower than that of the others; ③ the BPG of coal samples with a single diameter under the same porosity increased as the grain size increased; ④ the BPG could be fitted by an exponential function with porosity, and the exponent decreased as the grain size increased for coal samples with a single diameter; ⑤ the BPG was slightly less than the seepage instability pressure gradient. The change in liquid flow type from seepage to pipe flow could be regarded as the performance of the seepage instability.展开更多
The analytical mathematical solutions of gas concentration and fractional gas loss for the diffusion of gas in a cylindrical coal sample were given with detailed mathematical derivations by assuming that the diffusion...The analytical mathematical solutions of gas concentration and fractional gas loss for the diffusion of gas in a cylindrical coal sample were given with detailed mathematical derivations by assuming that the diffusion of gas through the coal matrix is concentration gradient-driven and obeys the Fick’s Second Law of Diffusion.The analytical solutions were approximated in case of small values of time and the error analyses associated with the approximation were also undertaken.The results indicate that the square root relationship of gas release in the early stage of desorption,which is widely used to provide a simple and fast estimation of the lost gas,is the first term of the approximation,and care must be taken in using the square root relationship as a significant error might be introduced with increase in the lost time and decrease in effective diameter of a cylindrical coal sample.展开更多
Workers of the Lakhra coal mining Sindh Pakistan were affected by a multi-factorial exposure of heavy metals. The prevalence of lead (Pb) exposures in work-related symptoms among workers of indoor and outdoor mining o...Workers of the Lakhra coal mining Sindh Pakistan were affected by a multi-factorial exposure of heavy metals. The prevalence of lead (Pb) exposures in work-related symptoms among workers of indoor and outdoor mining of Lakhra coal mining was evaluated in detail. The biological samples (scalp hair and blood) of 270 workers of Lakhra coal mining {official and control subjects} (indoor and outdoor) 18 to 55 years age group and 70 referent subjects of same age-groups were examined. The biological samples (blood and scalp hair) of workers of Lakhra coal mining and referent subjects were analyzed for calcium (Ca) and lead (Pb). Flame atomic absorption spectrometry was applied for the determination of the Ca in digested samples of studied subjects by the microwave oven whereas, the Pb contents were measured by electrothermal atomic absorption spectrometry. The validity of the methodology was checked by using the certified human hair material (BCR 397) and lyophilized human blood (Clincheck). The results indicated the higher contents of Pb in biological samples of indoor and outdoor mining workers than referents. However, the levels of Ca were found to be lower in indoor and outdoor mining workers than those of referents. It can be concluded that immediate action should be taken by recommended authorities to improve the ventilation and hygiene practices inside the industries, mines, and other workplaces.展开更多
Exhaustion of profitable coal resources makes for need of innovation including underground coal gasification(UCG).One of the most important problems of UCG is evaluation of the combustion area in underground coal seam...Exhaustion of profitable coal resources makes for need of innovation including underground coal gasification(UCG).One of the most important problems of UCG is evaluation of the combustion area in underground coal seams.Physicochemical parameters of coal,in a whole,and coal mineral substance are changed under heating and combusting.Thermo-chemical conversion of coal mineral components has an effect on magnetic characteristics of coal seam and can be used for real-time control of combusting area.To this guessing check laboratory experiments have been made as an activity of the Far Eastern Federal University.Our investigation based on a theoretical analysis and laboratory simulation tests.Typical results of the laboratory experiments are presented below.Under heating coal thermo-chemical magnetization is forming.Coal's magnetic parameters varieties from anti-ferromagnetiсto ferromagnetic.Anti-ferromagnetic pyrite and siderite presented into coal mass is transformed into magnetic hematite and magnetite under heating.Therefore,geomagnetic is expected to be a useful geophysical tool to for evaluation of combustion volume and its migration for underground coal gasification.展开更多
文摘The square root relationship of gas release in the early stage of desorption is widely used to provide a simple and fast estimation of the lost gas in coal mines. However, questions arise as to how the relationship was theoretically derived, what are the assumptions and applicable conditions and how large the error will be. In this paper, the analytical solutions of gas concentration and fractional gas loss for the diffusion of gas in a spherical coal sample were given with detailed mathematical derivations based on the diffusion equation. The analytical solutions were approximated in case of small values of time and the error analyses associated with the approximation were also undertaken. The results indicate that the square root relationship of gas release is the first term of the approximation, and care must be taken in using the square root relationship as a significant error might be introduced with increase in the lost time and decrease in effective diameter of a spherical coal sample.
基金Supported by the National Natural Science Foundation of China （50974107） the University Graduate Research and Innovation Project in Jiangsu Province （CXZZI2_0924）+1 种基金 the Applied Basic Research Project of Yancheng Institute of Technology （XKR2010010） the State Key Laboratory Open Foundation of Deep Geomechanics and Underground Engineering of China University of Mining and Technology （SKLGDUEK1014）
文摘A test system of the permeability of broken coal samples mainly consists of a CMT5305 electronic universal test machine, crushed rock compaction containing cylinder and a self-designed seepage circuit, which is composed of a gear pump, a reversing valve, a relief valve and other components. By using the steady penetration method, the permeability and non-Darcy flow β factor of broken coal samples under five different porosity levels were measured, the grain diameters of the coal samples were selected as 2.5-5 mm, 5-10 mm, 10-15 mm, 15-20 mm, 20-25 mm and 2.5-25 ram, respectively. After measuring the permeability under each porosity, the overfall pressure of the relief valve continuously increased until the coal sample was broken down. In this way, the flow type of liquid inside the broken coal samples changed from seepage to pipe flow. The correlation between breakdown pressure gradient （BPG） and porosity was analyzed, and the BPG was compared with the pressure gradient when seepage instability occurred. The results show that, ①the non-Darcy flow β factor was negative before broken coal samples with six kinds of diameters were broken down; ②the BPG of coal samples with a grain size of 2.5-25 mm was lower than that of the others; ③ the BPG of coal samples with a single diameter under the same porosity increased as the grain size increased; ④ the BPG could be fitted by an exponential function with porosity, and the exponent decreased as the grain size increased for coal samples with a single diameter; ⑤ the BPG was slightly less than the seepage instability pressure gradient. The change in liquid flow type from seepage to pipe flow could be regarded as the performance of the seepage instability.
基金provided by the Science and Technology Grant of Huainan City of China (No.2013A4001)the Key Research Grant of Shanxi Province of China (No.201303027-1)
文摘The analytical mathematical solutions of gas concentration and fractional gas loss for the diffusion of gas in a cylindrical coal sample were given with detailed mathematical derivations by assuming that the diffusion of gas through the coal matrix is concentration gradient-driven and obeys the Fick’s Second Law of Diffusion.The analytical solutions were approximated in case of small values of time and the error analyses associated with the approximation were also undertaken.The results indicate that the square root relationship of gas release in the early stage of desorption,which is widely used to provide a simple and fast estimation of the lost gas,is the first term of the approximation,and care must be taken in using the square root relationship as a significant error might be introduced with increase in the lost time and decrease in effective diameter of a cylindrical coal sample.
文摘Workers of the Lakhra coal mining Sindh Pakistan were affected by a multi-factorial exposure of heavy metals. The prevalence of lead (Pb) exposures in work-related symptoms among workers of indoor and outdoor mining of Lakhra coal mining was evaluated in detail. The biological samples (scalp hair and blood) of 270 workers of Lakhra coal mining {official and control subjects} (indoor and outdoor) 18 to 55 years age group and 70 referent subjects of same age-groups were examined. The biological samples (blood and scalp hair) of workers of Lakhra coal mining and referent subjects were analyzed for calcium (Ca) and lead (Pb). Flame atomic absorption spectrometry was applied for the determination of the Ca in digested samples of studied subjects by the microwave oven whereas, the Pb contents were measured by electrothermal atomic absorption spectrometry. The validity of the methodology was checked by using the certified human hair material (BCR 397) and lyophilized human blood (Clincheck). The results indicated the higher contents of Pb in biological samples of indoor and outdoor mining workers than referents. However, the levels of Ca were found to be lower in indoor and outdoor mining workers than those of referents. It can be concluded that immediate action should be taken by recommended authorities to improve the ventilation and hygiene practices inside the industries, mines, and other workplaces.
文摘Exhaustion of profitable coal resources makes for need of innovation including underground coal gasification(UCG).One of the most important problems of UCG is evaluation of the combustion area in underground coal seams.Physicochemical parameters of coal,in a whole,and coal mineral substance are changed under heating and combusting.Thermo-chemical conversion of coal mineral components has an effect on magnetic characteristics of coal seam and can be used for real-time control of combusting area.To this guessing check laboratory experiments have been made as an activity of the Far Eastern Federal University.Our investigation based on a theoretical analysis and laboratory simulation tests.Typical results of the laboratory experiments are presented below.Under heating coal thermo-chemical magnetization is forming.Coal's magnetic parameters varieties from anti-ferromagnetiсto ferromagnetic.Anti-ferromagnetic pyrite and siderite presented into coal mass is transformed into magnetic hematite and magnetite under heating.Therefore,geomagnetic is expected to be a useful geophysical tool to for evaluation of combustion volume and its migration for underground coal gasification.
