Pressure relief to increase permeability significantly improves gas extraction efficiency from coal seams. In this paper we report results from simulations using FLAC3D code to analyze changes in coal displace- ment a...Pressure relief to increase permeability significantly improves gas extraction efficiency from coal seams. In this paper we report results from simulations using FLAC3D code to analyze changes in coal displace- ment and stress after special drill slots were formed. We investigated the mechanism of pressure relief and permeability increase in a high-gas and low-permeability coal seam through the modeling of gas flow. This allows the development of the technology. Slotting across rock layers in the coal seam with a rotary type cutter was then applied in the field. The results show that pressure relief and permeability increases from slotting the coal seam can increase the transport and the fracture of the coal. This expands the range of pressure relief from the drilling and increases the exposed area of the seam. The total quan- tity of gas extracted from slotted bore holes was three times that seen with ordinary drilling. The concen- tration of gas extracted from the slotted drills was from two to three times that seen using ordinary drills. The gas flow was stable at 80%. Improved permeability and more efficient gas extraction are the result of the slotting. The roadway development rate is increased by 30-50% after gas drainage. This technology diminishes the lag between longwall production and roadway development and effectively prevents coal and gas outburst, which offers the Drosnect of broad anDlication.展开更多
土壤气相抽提(SVE)技术在污染土壤修复中得到越来越广泛的应用。结合不同区域的地层条件,通过不同梯度的抽提真空度试验,分析了各因素的影响关系,并确定了相关参数来进行SVE系统设计。试验结果表明:抽气流量随抽提真空度提升而增大,但超...土壤气相抽提(SVE)技术在污染土壤修复中得到越来越广泛的应用。结合不同区域的地层条件,通过不同梯度的抽提真空度试验,分析了各因素的影响关系,并确定了相关参数来进行SVE系统设计。试验结果表明:抽气流量随抽提真空度提升而增大,但超过40 k Pa后,增大趋势缓慢;在地层均质情况下,试验井真空度与径向距离呈正相关,但非均质时,有可能出现距离远真空度反而高的情况;当抽提真空度为35 k Pa时,试验井真空度整体效果达到最优;利用公式法和直线图解法分别确定试验区土壤空气渗透率及影响半径,计算结果在经验值范围内,且符合试验区地质条件。对土壤气相抽提技术在实际应用层面进行了说明,为以后类似地层条件下污染场地的原位修复工程提供了技术及工艺参数参考。展开更多
The bleed hole diameter,depth,and boundary layer thickness are key design parameters of a supersonic bleed system.The evolution trend of single-hole bleed flow coefficient with the ratio of boundary layer thickness to...The bleed hole diameter,depth,and boundary layer thickness are key design parameters of a supersonic bleed system.The evolution trend of single-hole bleed flow coefficient with the ratio of boundary layer thickness to bleed hole diameter and the ratio of bleed hole depth to diameter is investigated by numerical simulations under choking and non-choking conditions.The results show that the subsonic leading edge of the circular hole and the subsonic part of the boundary layer are the main factors causing lateral flow of the bleed hole.The effect of diameter on bleed mass flow rate is due to the viscous effect which reduces the effective diameter.The larger the ratio of displacement thickness to bleed hole diameter,the more obvious the viscous effect is.The depth affects bleed flow rate by changing the opening and closing states of the separation zone.When a certain depth is reached,the development of the boundary layer reduces the effective captured stream tube and thus reduces the bleed mass flow rate.The main objective of the study is to obtain the physical mechanism of the bleed hole size parameters affecting the bleed mass flow rate,and to provide theoretical guidance for the selection of the size of bleed holes in the design of a porous arrays bleed system in hypersonic inlets.展开更多
基金supports provided by the National Key Basic Research and Development Program (No.2011CB201205)the National Natural Science Foundation of China (No.50534090)+3 种基金the Independent Research of State Key Laboratory of Coal Resources and Mine Safety(No.SKLCRSM08X03)the State Key Laboratory of Coal Resources and Mine Safety of Research Foundation of China University of Mining & Technology (No.09KF09)the National Natural Science Foundation of Youth Science Foundation (No.50804048)the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (CXZZ12_0958)
文摘Pressure relief to increase permeability significantly improves gas extraction efficiency from coal seams. In this paper we report results from simulations using FLAC3D code to analyze changes in coal displace- ment and stress after special drill slots were formed. We investigated the mechanism of pressure relief and permeability increase in a high-gas and low-permeability coal seam through the modeling of gas flow. This allows the development of the technology. Slotting across rock layers in the coal seam with a rotary type cutter was then applied in the field. The results show that pressure relief and permeability increases from slotting the coal seam can increase the transport and the fracture of the coal. This expands the range of pressure relief from the drilling and increases the exposed area of the seam. The total quan- tity of gas extracted from slotted bore holes was three times that seen with ordinary drilling. The concen- tration of gas extracted from the slotted drills was from two to three times that seen using ordinary drills. The gas flow was stable at 80%. Improved permeability and more efficient gas extraction are the result of the slotting. The roadway development rate is increased by 30-50% after gas drainage. This technology diminishes the lag between longwall production and roadway development and effectively prevents coal and gas outburst, which offers the Drosnect of broad anDlication.
文摘土壤气相抽提(SVE)技术在污染土壤修复中得到越来越广泛的应用。结合不同区域的地层条件,通过不同梯度的抽提真空度试验,分析了各因素的影响关系,并确定了相关参数来进行SVE系统设计。试验结果表明:抽气流量随抽提真空度提升而增大,但超过40 k Pa后,增大趋势缓慢;在地层均质情况下,试验井真空度与径向距离呈正相关,但非均质时,有可能出现距离远真空度反而高的情况;当抽提真空度为35 k Pa时,试验井真空度整体效果达到最优;利用公式法和直线图解法分别确定试验区土壤空气渗透率及影响半径,计算结果在经验值范围内,且符合试验区地质条件。对土壤气相抽提技术在实际应用层面进行了说明,为以后类似地层条件下污染场地的原位修复工程提供了技术及工艺参数参考。
基金supported by the National Natural Science Foundation of China(No.11472304)the Graduate Innovation Grant of Hunan Province(No.CX2017B006),China。
文摘The bleed hole diameter,depth,and boundary layer thickness are key design parameters of a supersonic bleed system.The evolution trend of single-hole bleed flow coefficient with the ratio of boundary layer thickness to bleed hole diameter and the ratio of bleed hole depth to diameter is investigated by numerical simulations under choking and non-choking conditions.The results show that the subsonic leading edge of the circular hole and the subsonic part of the boundary layer are the main factors causing lateral flow of the bleed hole.The effect of diameter on bleed mass flow rate is due to the viscous effect which reduces the effective diameter.The larger the ratio of displacement thickness to bleed hole diameter,the more obvious the viscous effect is.The depth affects bleed flow rate by changing the opening and closing states of the separation zone.When a certain depth is reached,the development of the boundary layer reduces the effective captured stream tube and thus reduces the bleed mass flow rate.The main objective of the study is to obtain the physical mechanism of the bleed hole size parameters affecting the bleed mass flow rate,and to provide theoretical guidance for the selection of the size of bleed holes in the design of a porous arrays bleed system in hypersonic inlets.
