Partitioning characteristics of gas channel of coal-rock mass in mining space and gas orientation me

International Journal of Mining Science and Technology 23(2013)873-877Contents lists available at Science DirectInternational Journal of Mining Science and TechnologyELSEVIERurnalhomepagewww.elsevier.com/locate/ijmstPartitioning characteristics of gas channel of coal-rock mass in miningspace and gas orientation methodZhao Zhiqiang Ma Nianjie Jia Housheng Cheng Yuanpingl of resource and Safety Engineering, China University of Mining 8 Technional Engineering Research Center for Coal Gotrol, China University of8 Technolohou 221008. ChinaARTICLE INFOA BSTRACTArticle historIn order to research the influence of coal-rock mass morphology of mining space on the flow law of gas,Received 22 March 2013the laboratory physical model and numerical computation methods were adopted to simulate coal min-Received in revised form 20 April 2013Accepted 10 May 2013ing activities. The simulation results indicate that, after coal seam mining the loose rock accumulationber 2013body of free caving, ordered rock arrangement body of plate damage rich in longitudinal and transversefractures and horizontal fissure body formed by rock mass deformation imbalance are formed frombottom to top in the mining space. For these three types of accumulation bodies, there are essentialGas channeldifferences in the accumulation state, rock size and gas breakover characteristics. According to thisPartitioning characteristicsthe coal-rock mass in the mining space is classified into gas turbulence channel area, gas transitional flowchannel area and gas seepage channel area. In the turbulence channel area, the gas is distributed transGas orientation methodersely and longitudinally and gas diffuses in the form of convection with Reynolds number re more than0: in the transitional flow channel area, one-way or two-way gas channels are crisscross and gas is oftransitional flow regime with Re between 10 and 100. In the seepage channel area, there are a few verticalas channels with Re less than 10. In this paper, the researches on the gas orientation method in differentpartitions were further carried out, gas orientation methods of low-level pipe burying, middle-levelinterception and high-level extraction were determined and an on-site industrial test was conductedachieving the effective diversion of gas and verifying the reasonableness of gas channel partitiono 2013 Published by Elsevier B V. on behalf of China University of Mining Technology1 Introductioncoal mines is mainly guided by the theory of"upper three zonesbut the theory of"upper three layers"was proposed from theCoal mine gas drainage is both the need for safety guarantee of aspect of overburden destruction and roof control in coal miningoal energy production and the demand for fully mining energy without considering the gas flow regime characteristics whichesources, which has become a basic national policy of China have an important influence on the gas drainage. The engineering[1, 2]. Gas drainage is classified into ground extraction and practice shows that the change area of gas flow regime characterunderground extraction, forming a gas channel is essential to istics does not completely coincide with the division boundary ofUnderground gas drainage, while mining fissure is the main reason the traditional"upper three zones". Therefore, on the basis of existfor gas channel. Researching the development and evolution law of ing mine pressure research achievements including theory ofmining fissure is the basis to judge the formation and expansion of"upper three zones", the gas channel of coal-rock mass in thegas channel and conduct gas drainage design [ 3-5. In coal mining mining space is partitioned by considering the gas flow regimeof China, in the research of overburden failure and mining fissure characteristics and gas orientation method is studied based ondevelopment law, many mining scholars with academician Qiathe gas channel partition, providing a theoretical basis for aceMinggao as the representative have done a lot of work and system- rately guiding the gas drainage designatical research to form the theory of"upper three zones"in overburden movement and destruction on the stope, i. e caving zone,fissure zone and bending sinking zone, playing a major guiding role 2 Gas channel development law of coal-gas mass in miningin roof control and disaster prevention and treatment on coal stope space[6-8 At present, the underground gas drainage design in ChineseAfter the overburden strata are influenced by mining, asynchro-nous bending and中国煤化工 enerated betweenCorponding author. Tel. +86 18618405706the rock strataeparation layersE-mailaddresscaikuangren@126.com(z.Zhaowhere gas canCN MH Channels generatedh t: /d. do, oree o m imes.2013. 10014 hned Dy Elsevier Bv, on ehalt of China University ot Mining technolOgy74Science and Technology 23(2013)873-877by rock mass deformation, instability and destruction caused by insufficient channel communication, which is very difficult to formmining are called mining gas channels, which can greatly change gas channel network. There is a little increasing in air permeabilityof coal-rock mass, providing a space for the of coal seam, larger than the original air permeability of coal massfollowing and convergence of pressure relief gas [9In order to research the development and distribution law of6 To sum up, after coal seam mining, loose rock accumulationdy of free caving, ordered rock arrangement body of platehe overburden gas channels, the laboratory similar simulation test damage rich in longitudinal and transverse fractures and horizon(Fig. 1)and numerical simulation test(Fig. 2)were carried out in tal fissure body formed by rock mass deformation imbalance arethe coal seam group mining in Yangquan mining areaformed from bottom to top in the mining space, with essentialBy comprehensively analyzing the test results, it is found that difference in accumulation state, rock size and breakover characwithin the range of 8-12 times mining height from the bottom teristics of the three types of accumulation bodiesof stope, the overburden strata are crushed, most of the areas areaccumulated by blocks, the gas channels are dominated by large 3 Gas flowing characteristics and gas channel partitioningcracks and gaps with very large randomness and the separationlayers have large characteristic size and permeability3. 1. Gas flowing characteristics of different coal-rock massesWhile within the 12-18 times of mining height, the overburdenstrata are relatively complete, with rock layers arranged in order,the gas channels are dominated by tensile gaps or fissures, one- nel is consistent with the ordinary flow field, according to Reynoldsway or two-way gas channels are crisscross, some channels are number, the flow regime of gas in the mining gas channel can bemutually connected, forming masses of gas channel networks divided into three areas: laminar flow seepage area, transitionaland the air permeability of coal seam increased obviously, creating area and turbulence area, according to Kozeny-Carman rule, thefavorable conditions for coal seam gas to flow along or penetrate Reynolds number Re can be expressed as(10)the seam. Fig 3 shows that the vertical displacement field in thisarea has a relatively large gradient indicating that the verticalchannels relatively develop wellR,-evelveWithin the range above 18 times mining height, the overburdenstrata move overall, and only a few vertical tensile fissures have where p is the fluid density, kg/m: Vthe local seepage speed, m su the flowing dynamic viscosity coefficient, kg/(m-s): v the dynamicviscosity coefficient of fluid, m /s; and e the local seepage coeffi-cient of the seepage fieldWhen Re <10, the seepage viscosity resistance is dominatedcompared with the seepage inertia, gas flow regime belongs tolaminar flow seepage, which can be described with Darcy law[1,12]:Vk dpu dxwhere k is the permeability of coal seam, m u the absolute viscosFig. 1. Diagram of similar simulation test in Yangquan mining area.ity of gas, Pas: p the gas pressure of the coal seam, MPaWhen 10< Re< 100, the seepage inertia force is gradually dom-inated the gas flowing is in the transitional flowing area betweenthe linear seepage and turbulence, belonging to nonlinear seepageand Darcy law does not apply any longer, the flowing controlequation can be described with exponential model or Darcymodel [13, 14V1=-A1(ij=1,2,3)(v+pV2)(1j=123Fig. 2. Diagram of numerical simulation test in Yangquan mining areawhere Ai is the component in each direction of the permeability,m p the coal seam gas pressure, MPa; mi the gas state index inu the gas dynamic vicosity, m/s: k the permeability, m", p the mass density, kg/m; andβ the non-Darcy flowRegas flow enters the turbulence area, submitting to Navier-Stokeequation [15.32Mgo中国煤化工According to theCNMH Breakover characteristics and gaui three types offracture coal-rock masses in the mining space, the coal-rock masig. 3. vertical displacement field of overburden strata in the work planein the mining space is divided into gas turbulence channel area, gasZ. Zhao et al. International Journal of Mining Science and Technology 23(2013)873-877transitional flow channel area and gas seepage channel area freholes at the 3 m position of upper vertical pipe; the correspondingosition of floor is also of vertical construction to drill a hole with a(1)Height and gas flowing characteristics of gas turbulence length of 2 m and a diameter of 133 mm, the floor is of pouring tochannel areafix the long vertical pipe and the long vertical pipe in the goaf isWithin the range of 8-12 times of mining height from the bot- connected to the extraction dry pipe with the rubber pipe 30 mtom of stope, the coal seam is crushed, a majority of the areas are long as shown in Fig 4. Bedding pressure pipe the pressure pipeccumulated by blocks, the gas channels are crisscross with rela- is adopted for gas drainage of goaf in the roadway section and anandomnessovered by ventilation negative pressure anti-compression, anti-static electricity polyethylene gas pipe withand air leakage on the stope for the flowing of gas in this area, it a diameter of 219 mm is inserted every 12 m to drain the gas in theis mainly to consider the convection diffusion caused by mechan- goaf as shown in Fig. 5ical action, with a relatively high flow speed and Reynolds numberIt can be seen from Fig. 6 that during pressure pipe, the gasgenerally greater than 100drainage concentration is 2-5% with an average of 2.8% and the(2) Height and gas flowing characteristics of gas transitional gas drainage scalar is 1.2-6.5 m/min with an average of 2.54 m3/flow channel areamin, realizing the effective diversion of gas in the gas turbulenceWithin the range of 12-18 times of mining height from the bothannel areatom of stope, the overburden strata are relatively complete, whichare still of layered distribution, the one-way or two-way gas chan- 4.2. Middle level interception orientation method in the gasnels are crisscross, some gas channels are mutually connected and transitional flow channel areathe permeability increases significantly compared with the originalcoal seam Under the influence of gas pressure gradient and ventiThe gas transitional flow channel area and gas turbulence chanlation power of the stope, the gas flow speed increases, presenting nel area are connected. Under the ventilation power of workinga transitional flow regime, with Reynolds number ranging from 10 face the upper pressure relief gas will enter the stope space alongto 100, submitting to the nonlinear seepage law.(3)Height and gas flowing characteristics of gas seepage chan- will be intercepted under negative pressure by the special roadwayWithin the range above 18 times mining height, the overburdenfor high-position gas drainage or large diameter directional borestrata move overall, only a few vertical gas channels with insufficient communication between channels, there is a little increaseLong vertical pipein air permeability of coal seam, with Reynolds number less thanInduction port10, submitting to darcy lawAir roadway roof4. Gas orientation method based on mining gas channelAir roadwayAt present, many effective extraction methods and technologiesorking Air roadway Dry pipare applied in underground gas drainage [16-18. In the coal mineproduction, the problems concerning mine gas cannot be solved bya single gas orientation method and many gas orientation methodsFig 4. Gas drainage method in goaf with long vertical pipe.uired to be comlof gas channel to realize the comprehensive extraction of mine gasThe above gas channel partition during mining provides a theoretExtracOrifice plateical basis for the reasonable selection of gas orientation methodvalveand the gas orientation methods including low-level pipe burying,iddle-level interception and high-level extraction are adoptedrespectively based on the characteristics of different gas channelpartition and gas flow regime for the on-site industrial testt Goaf4. 1. Low-level pipe burying orientation method of gas turbulenceFig. 5. Arrangement diagram of pressure pipe extraction in the goaf of retainingThe gas turbulence channel area is bottommost the goaf, where foadway along godgas concentration is of layered increasing distribution in the vertill direction and increases with the layer, reaching the maximumat the upper edge of gas turbulence channel area. In the dip direc-Gas drainage concentrationGas drainage scalartion, influenced by the mine ventilation, the gas concentration onthe return air side is higher. The roadway on the return air sideis of upward drilling to the upper edge of gas turbulence channelarea and then the vertical gas drainage screen pipe is installed toealize the gas orientation in the gas turbulence channel areaThe shaqu mine 24207 working face is of gas drainage with vertical swing pipe and bedding pressure pipe. vertical swing pil中国煤化工10the roof of roadway is of vertical construction to drill a hole withCNMHGa length of 12 m and diameter of 133 mm, the long vertical pipehich is the metal iron pipe with a diameter of 108 mm and lengthof 12 m is placed into the bore, it is the screen pipe with smallFig. 6. Gas drainage effect in gas turbulence channel areaZ Zhao et al/International Journal of Mining Science and Technology 23(2013)873-877Gas drainage concentrationt Gas drainage concentration76-177-208-229-1510-1311-26Fig. 7. Gas drainage effect of methane-extraction roadwayDateFig 9. Gas drainage effect of grids bores through rock and coal seamGas drainage concentrationGas drainage scalarset along the working face in the center of intaking air roadway086and returning air roadway of working face. A 5 m long extractiondrill site, vertical to the extraction roadway, is set in the gas drainage roadway of floor every 30 m with a drill site section area of5 m. a set of gas drainage bores comprising 6 bores is set fanwisein each drill site with a diameter of 100 mm and spacing of 29 mFor 80201 working face, the air permeability of protected layerincreases 1237 times and the gas drainage rate is more than 60%(see Fig. 9), realizing the effective artificial diversion of gas seepage三8hannel area. The safety production of working face can be ensuredwhen the gas emission rate of the protected working face reachesDate200 m/minFig. 8. Gas drainage effect of large diameter directional borehole.arranged in the gas transitional flow channel area to realize the gas 5 Conclusionsin the gas trransitional flow channel area. The gas drain间0(m2nhe return air way, but not more than center line of working facein longitudinal and transverse fractures and horizontal fisThe trend of high extraction roadway of 14203 working face issure body formed by rock mass deformation imbalance wereparallel to that of belt roadway, 20 m away from the belt roadwaformed from bottom to top in the mining space, the accumuand above the recovery coal mass, 8-10 times of the mining heightlation state, rock size and gas breakover characteristics ofThe high extraction roadway is laid with 320 mm pipelines con-he three types of accumulation bodies have essentialnecting with the extraction pipeline at the end roadway and thedifferencesentrance of roadway will be closed and then the extraction can(2) According to the gas flow characteristics of the three differbe conducted after pressure relief.ent types of accumulation bodies, the coal-rock mass in theFor the gas drainage of special high-level gas drainage roadway,mining space is classified into gas turbulence channel areathe average extraction concentration is 58. 2% and the gas drainagegas transitional flow channel area and gas seepage channelquantity is 8 m min, accounting for more than 50% of the gasarea. In the turbulent channel area, the gas is distributedemission rate of working face(see Fig. 7). For the gas drainage oftransversely and longitudinally and gas diffuses in the formlarge diameter directional borehole, the gas drainage concentrationof convection with Reynolds number more than 100; in theis greater than 40% and the gas drainage rate is 15 m /min and thetransitional flow channel area, one-way or two-way gasgas concentration in the return air is below 0.6%(see Fig. 8), real-channels are crisscross and gas is of transitional flow regimeizing the effective gas diversion of gas transitional flow channelwith Reynolds number between 10 and 100: in the seepageareamolds number less than 104.3. High-level orientation method of gas seepage channel area(3)Based on the characteristics of different gas drainage channel partition and gas flow regime the gas orientation methAs the gas channel of seepage region is of low development, theods of low-level pipe burying, middle-level interception andcoal seam gas cannot flow along the gas channel after pressure re-high-level extraction are adopted for on-site industrial test.lief and activation and only a small amount of coal seam gas canensuring the safety of working facng the gas drainflow into the stope through the gas channel and be drained, thereage efficiency, realizing the effective diversion of gas andfore, the high-level extraction method such as grid bores throughverifying the reasonableness of gas channel partitionrock and coal seam can be used as the artificial channel to realizehe gas orientation of gas seepage channel areaThe gas diversion test is conducted at the Xinjing Mine lubei中国煤化工15# coal seam to 3# coal seam is 125 m and the gas seepage chan. AcknowledgmentsDistrict 80201 working face, in which the average distance fromCNMHGfrom the floor of 3#f coal seam, a gas drainage roadway of floor is Research Program of China(No 2011CB20120 e State Key Basiel area is between 3# and 15# coal seams. at the place 15 m faFinancial supports for this work, provided byZ Zhao et al. International Journal of Mining Science and Technology 23(2013)873-877References[9) Zhang Y, Xu LF, Liu KM, Li Y], Zhang B, Li WB. Study on formation mechanismand evolution of gas flow channel in mining coal and rock, J China Coal Soc[1 Yuan L Scientific thinking and countermeasur2012:37(9):1444-50tilization in China. Sci Technol Rev 2011; 29(22[10 Hu GZ, Xu JL, Wang HT.[2] Cheng YP, Fu JH, Yu QX. Development of gastechnology in coallel applied to low permeability coal. J China Univ Min Techmines of China. J Min Safety Eng 2009: 26(2 ): 127-39.[3] Cheng YP, Zhou DY, Yu QX, Zhou HX, Wang HF. Research on extract ion and[11 Bei E, Li JS, Chen CX. 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