Suspension mechanism and application of sand-suspended slurry for coalmine fire prevention Suspension mechanism and application of sand-suspended slurry for coalmine fire prevention

Suspension mechanism and application of sand-suspended slurry for coalmine fire prevention

  • 期刊名字:矿业科学技术学报(英文版)
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  • 论文作者:Xu Yongliang,Wang Lanyun,Chu T
  • 作者单位:State Key Laboratory Cultivation Base for Gas Geology and Gas Control
  • 更新时间:2020-11-03
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论文简介

Intermational Journal of Mining Science and Technology 24 (2014) 649 -656Contents lists available at ScienceDirectInternational Journal of Mining Science and TechnologyEL SEVIERjournal homepage: www. elsevier. com/locate/ijmstSuspension mechanism and application of sand-suspended slury forCosMakcoalmine fire preventionXu Yongliang a,b, Wang Lanyun a,b,*, Chu Tingxiang a, Liang DonglinaaState Key Laboratory Cultivation Base for Gas Geology and Gas Control, Henan Polytechnic University, jaozuo 454003, Chinab State Key Laboratory of Coal Resources and Safe Mining, China University of Mining 8 Technology, Xuzhou 221116, ChinaARTICLEINFOA BSTRACTArticle history:North and west China has abundant coal resources, however, such resources make these regions prone toReceived 7 October 2013serious mine fire disasters. Although the copious sand and fly ash resources found in these areas can beReceived in revised form 12 January 2014used as fire-fighting materials, conventional grouting is expensive because of water shortage and loessAvailable online 19 August 2014particles. A new compound material (i.e, a sand-suspended colloid), which comprises a mineral inorganicgel and an organic polymer, is developed in the current study to improve the quality of sand injection andreduce water wastage when grouting. The new material can steadily suspend the sand, through the addi-Keywords:tion of a small amount of colloid yielding steady sand-suspended slurry. The process of producing theSand-suspended colloidslurry is convenient and quick, overcoming the shortage of sand-suspending thickeners which need heatSand-suspended slurrySuspension mechanismDual-electrical layerSpace work modelThe dispersion effect of the sand-suspended colloid is demonstrated by the incorporation of the electro-Fire preventionstatic effect by the double- electric layer and the steric hindrance effect on the sand particles, ensuring thestability of the colloid system and the steady suspension of sand particles in the sand-suspended colloid.Mechanical analysis indicates that the sand is suspended steadily under the condition that the rock sandparticles stress on the lower part of the fluid is less than the yield stress of the colloid. Finally, the fire-prevention technology of sand suspension was applied and tested in the Daliuta Coal Mine, achieving suc-cesful results.◎2014 Published by EIsevier B.V. on behalf of China University of Mining & Technology.1. Introductionpreventing based on its simple operation and low cost. However,thethe cost of conventional grouting for fire prevention is high dAt present, coal is still the most important energy in China. Andto shortage of water and loess particles in north and west China.there are plenty of coal in north and west China. However, theNevertheless, abundantexploitation of coal in north and west China has led to the frequentarea can be used as materials for coalmine fire fighting.occurrence of serious mine fire disasters. In order to prevent theUntil now, some studies have reported the grouting for fire pre-coalmine fire, many measures are widely used, such as ventilationvention in coalmines, and the conventional sand injection areby even air pressure, grouting the mud or three-phase foam,mainly applied [6- -8]. The ratio of water to sand must reach 7:1spraying inhibitor, injecting N2 or CO2, etc. [1-5]. Therefore, theto 15:1 if the fly ash or sand with water is simply injected to ensurefire-fghting measures in the coalmines have some shortages asthat the sand would not subside [9-11]. The technology, however,follows: (1) grouting the mud could consume plenty loess whichtends to waste large amounts of Water, leading to the severe abra-competes with the arable land; (2) grouting the fly ash couldn'tsion of the pipeline [12]. Otherwise, according to the reports, theplug leakage effectively; (3) spraying inhibitor and injecting theemulsion fracturing fluid in oilfield, the drilling fluid and the com-nitrogen could diffuse with the leakage and couldn't cool the highpletion fluid could settle the sand for less than 1 h, in which thetemperature areas effectively; and (4) the grouted foam has theratio of water to sand could reach 3:5 [13-15]. But these couldn'tshorter steady time and couldn't become solid. Currently, the con-match the demand for coalmine fire prevention. Moreover, thereventional grouting is one of the most widely used measures for fireare no reports about the materials for settling the sand abroad.Therefore, a new kind of appending material, called sand-sus-* Corresponding author. Tel: +86 391 3986252.pended.ollod.us中国煤化工dy to improve theE-mail adrer: lanyun.wang@gmail.com (L Wang).utilization raticYHCNMH Ghttp://dx.doi.org/10.101 6/j.jmst.2014.03.02950Y Xu et a./ntermational Journal of Mining Science and Technology 24 (2014) 649-656 .2. Developing the sand-suspended colloid and testingsuspended character2.1. Developing the sand-suspended colloid .The compound appending material of sand-suspended colloid is(a) Suspension state at the itial time(b) Suspension statc ater 5 hcomposed of an inorganic mineral gel, an organic polymer and thedispersant; here, the inorganic gel is used as the base. Fig. 1 showsFig. 2. Suspension results at 0.2% concentration.images of the three different concentrations of the sand-suspendedolloid.2.2. Testing suspended characterThe materials of the sand-suspended colloid were taken to pre-pare colloids with different concentrations. The suspension effectsof the colloids were also investigated. Different concentrations ofcolloid materials and sand were selected and used for the suspen-(6) Supension state after 5 dayssion experiments. The grain size was set at under 0.5 mm. ColloidFig. 3. Suspension results at 0.3% concentration.concentrations of 0.2%, 0.3%, 0.4%, and 0.5% were chosen to preparethe sand-suspended slurries with different mass ratios of 4:1, 2:1and 1:1, respectively. Figs. 2-5 present the suspension states ofsand in the sand-suspending slurries at different periods.The results of the suspension experiment show that the colloidwith a concentration of 0.3% and higher can steadily suspend thesand. The colloid with a concentration of 0.2% could not suspendthe sand, which completely deposited after 5h (Fig. 2). The sam-(a) Suspension state at the initial time(b) Suspension state after 5 daysples that suspend the sand well, especially those with concentra-ions of 0.4% and 0.5%, are unable to deposit any sand afterFig. 4. Suspension results at 0.4% concentration.5 days, which is in accordance with the demand for stabilization.The stabilization of the sand-suspended colloid is derived fromthe elastic cohesive action, wherein the power source is the inter-i grainsar。hudroraction forceng the: colloid.ninathree -dimensional net construction of the colloid. The sand-sus-pended experiments and the stabilization tests show that the com-pound colloid demonstrates sand- suspending stability.(b) Suspension statc ater 5 days2.3. Flowing test of the sand-suspending slurry in the pipelineFig. 5. Suspension results at 0.5% concentration.The system for preparing the sand-suspending slurry and simu-lating the flow in pipeline was developed in the laboratory to meetthe needs of the coalmines. The system consists of the preparationPoints for testing pressureequipment for the slurry, the blender, the pump for transporting,and the straightness pipeline. The volume of the_ preparation中125pipelineequipment is 2 m', and is capable of preparing 30 m3/h of slurry.The power plant is a type G85-1 pump with a single screw, whichhas a maximum flow of 43.5 m3/h. The pump, with the import andexport diameters of 150 mm, has apoweyer of 15 kW and has the. Slury aterability to transport the slurry with particles as large as 10 mmφ 100 pipelineand viscosity as high as 200 Pas. The length of the straight pipelineis 80 m with a straight layout. The straight pipeline with the inputdiameter of 100 mm and the output diameter of 125 mm was usedPileline for waterto test the resistance of the pipeline. Fig. 6 displays the entiresystem.Flow meterType G8S-I pump PreparationegusrmuenforslurFig. 6. Mortar pr中国煤化工”-on system.The 0.5% solution:THCNM HGThen, the sand-suspension experimeuVILIL a wwaler-to-sand ratio(a) 0.2% concentration(b) 0.4% concentration(0) 0.5% concentrationof 2:1. The sand-suspending slurry was prepared using the prepa-Fig. 1. Photographs of sand-suspended colloids in different concentrations.ration equipment in the upper proportion at normal temperatureY. Xu et al/nteratioa. Journal of Mining Science and Technology 24 (2014) 649- 656651and pressure. The slurry was transported through the single screwopump in the pipeline and into the preparation equipment for circu-lar use. The test result shows that the sand from the sand-suspend-ing slurry can maintain the stability of the suspension state; theslurry can also take more sand with less water, thus leading to amore stable suspension. Results also demonstrate that the com-pound colloid is an ideal material for suspending sand, becausethe preparation process does not require high temperatures, andFig. 8. Interaction between MG and Ca2+.the whole operation process is both simple and convenient.3. Stabilization of the sand-suspended colloidsynchronously stop the coagulation of the colloid particles and3.1. Mechanism of the sand -suspended colloid in waterequably separate the particles in the colloid system. The compoundappending material of the sand- -suspended colloid changes theThe sand-suspended colloid prepared in the laboratory does notflow character, which leads to the formation of a high-viscositydehydrate and subside, indicating that the colloid is stable and hascolloid with an interaction and features the electrostatic repulsionn efectofthespaceconsiderably apparent viscosity. The appearance of colloid stabil-of the inorganicarticlesand the reictionization is also related to the interaction between the colloidal par-reticulation structure.ticles and the water molecule.The colloid can effectively remain stable for some time, even forThe inorganic mineral in the sand-suspended colloid cannot becompletely dissolved by water, but the mineral can swell withsystem. After verifying that the sand-suspended colloid haswater, dispersing the particulates that, in turn, surface chargesremained stable for five days when placed in a laboratory at northe anions in the colloid [10]. The particulates in the colloidmal temperature and pressure levels, we find that the colloidencumber the flow of the colloid because of the refection with sta-belongs to a relatively stable system. The present paper explainstic electricity; in turn, this increases the viscosity of the sand-sus-the essential reasons for the relative stability of the colloid.pended colloid.The most important physical property of the colloid is the ten-The organic polymer of the sand-suspended colloid distilleddency for the mass point in a colloid system to spontaneouslyfrom the natural plant alga is a kind of polysaccharide biopolymer;aggregate [18]. The colloid particles continuously collide in a liquidit has a molecular structure comprising mannuronic acid and gulu-medium, especially in an aqueous solution. Colloid stability is con-ronic acid arranged with an anomalistic block in the linear mole-tingent upon the interaction between the particles in a colloid sys-tem during collision. Therefore, the research on colloid stabilitycule chain (FigThe strong hydrophilicity of the sand: -suspended colloid turnsmust examine the interaction between the particles and the aque-the clloid into a viscous liquid after being dissolved in water con-taining salt (Na*, K*, NH4*), magnesium, mercury salts, and otherThe colloid particles can stably suspend in a colloid systemderivatives. The solubility of the sand-suspending thickenerswhen the repulsive force among the colloid particles is sufficiently(SSTs) increases with an increase of the pH value, and the aqueousgreat, such that the collision caused by the van der Waals force andsolution of the SST is homogeneously transparent, with pH valuethe Brownian movement can be counteracted, and the sedimenta-ranging from 5.8 to 7.5 [16,17]. Furthermore, the viscosity changestion action pulled by the gravity can also be offset [19]. The repul-into an inverted campaniform-shape curve with the pH value,sive force mainly comes from two aspects: the repelling interactionwhich peaks at a pH value of 7.among the particles with the same kind of charge (positive or neg-The organic polymer solution has the ability to link with theative), and the nonionic materials adsorbed on the surface of thedivalent metals (Ca2+, Cu2+, and Pb2+) of the inorganic mineralparticles.gel, thereby forming an extensive reticulation structure, such asThe particles with the same charge in the colloid produce repul-the structure of the segmented block copolymer. Fig. 8 shows thesion to maintain the stability of the colloid system and to keep theinteraction between MG and Ca2+system from dispersing. The charges on the surface of the particlesThe average number of functional groups with chemical andproduce electrostatic attraction with the opposite charge as well asphysical crosslinking achieves a definite degree, wherein macro-repulsion with the same charge. This movement leads to the for-molecules build into boundless reticulation structures. Therefore,mation of a double-electric layer through the surface gathering ofconfeecting the inorganic mineral gel and the organic polymer ofthe opposite charge and the surface leaving of the same charge.the colloid causes the reticulation structure of the colloid to tangle,Fig. 9 shows that the opposite charges disperse in the liquidenhancing the water assembling ability and increasing thehase, acting as a diffusion layer for the electrostatic interactionviscosity of the colloid system. The dispersant in the material canand the molecular heat movement.stabilitytheory! of chargedDarjaguin and Verwey proposed acolloid particles called the Derjaguin and Landau, Verwey and( OH/Coo OHenergy and gravitational potential energy can be found betweenthe micelle; second, the relative stability or coagulation of the cMloid system depends on the relative amount of repulsion potentialenergy and suction potential; third, the repulsion potential energy,HCgravitational pote.tial energy of the十otHO~ood Hparticles change \中国煤化工e, the gavtationpredominates at aC N M H Gthe repulsion pre-fodominates in anotMHalIg.The DLVO theory considers the colloid to be stable under certainFig. 7. Connection diagram of the MG salt structure.conditions, depending on the interaction between the colloidal52Y. Xu et al/ntereational Journal of Mining Science and Techmologyv 24 (2014) 649-656an energy barrier, Vnax. The particles must overcome the energyExtemalbarriers at this time to move closer to each other. The total poten-Solid surfacetial is reduced violently when the particles overcome the energybarrier. Therefore, the movement of the particles closer to each. Caon ofyrion sellother occurs more easily when the energy barrier is small.-一 Negaive ionThe thermodynamic energy level of the dispersion clloid parti-chagtd ngarve器cle is represented by kT (k is the Boltzmann constant, and T is thelctrolyte solutionabsolute temperature). Under the ambient condition,黎kT-25.59x 10-3eV. Most of the particles remain stable in adecentralized state when the energy barrier is higher than thethermodynamic energy. An energy barrier of 15kT is enough to- Elementary hydntion shellestablish a highly dispersed system based on the DLVO theory.However, a 15 kT energy barrier is not enough to establish a stableFig. 9. Distribution of the doubl-elecric layer structure [20|.system as it requires an energy barrier from 40 to 50 kT [23].According to the DLVO theory, the mechanism behind the sand-.. acualotideustem Can theexnlainedas follows:colloid Dar-paricles of a potential energy.. The total potential energy equalssuspendedColloldsystemcanpe Cexprete Charetictureoftheticle surface in a cllildl system forms the Charge stuctureort.tnethe sum of the van der Waals atraction potential energy and thedouble etric layer owing to the infuence of Cllidal partiteelectrotatic repulsion potential energy caused by the double elec-interaction force and the fact that the colloidal particles are burdentric layer. The two kinds of potential energy include the attractionelectric. Moreover, under the combined action of attract potentialpotential energy (i.e.. the function of the distance between the col-and repulsive potential, colloidal particles are constantly nearloidal particles and the distance into certain proportional rela-one another; when the interparticle forces come to a certain dis-tions), and the electrostatic repulsive potential (i.e, it decreasestance, the curve of the interparticle electrical potential energywith the distance according to the index function).appears as a peak, and an energy barrier is established. When theThe potential energy of the colloid particles is the sum of theenergy barrier is higher than the thermodynamic energy, most ofgravitational potential energy and the repulsive potential energy.the particles remain stable in a decentralized state. The sand-sus-The potential energy could be denoted as Eq. (1) given bypended colloid reaches a certain viscosity and retains a certainVπ=VA+Vk1)fluid form at this time. The existence of the organic polymersystem further strengthens the stability of the sand-suspended col-is drawn to particle space H (Fig.10). Theloid system in the distribution of a wider space grid structure,The peol prarererewver tPeaetsts WitpRre short distanethereby limiting the thermodynamic movement of the colloidgravitational potential energy Vn creacts within aishort distaneparticles and weakening the thermodynamic sports ability of thewhile the repulsive potential energy VR reacts in further distances.colloid particles.Gravitation quickly increases with the cdosest particles when. H→0, Vi→∞. Vk also rises with the closing of the distance,increasing more and more towards a constant. Meanwhile, the4. Suspension mechanism of sand suspended colloid to solidattraction potential energy VA and the repulsive potential energyparticlesVk are zero when the distance between the particles is farther.Repulsive potential energy itally works when the colloidal parti-The dispersal system involves the dispersal of substance parti-cles gradually move closer to each other, that is, a certain repulsivecles (i.e.. dispersed phase) into another material called dispersionforce is present at this time. Va is unable to play a role until itmedium. A liquid dispersal system uses a liquid dispersion med-reaches a certain distance if the particles can move closer to eachium, while a coarse dispersal system has dispersed phase particlesother by overcoming Vx The infuence of Va is more remarkablesizes that are big enough to be seen by the naked eye or a micro-when the space between the clloial particles is smaller. On thescope (particle size larger than 100 nm). The yellow mud, fly ashone hand, V(1) is the potential curve where the repulsive force isslurry. or ordinary mortar in all these suspended systems havegreater than the suction, resulting in stable colloidal particles. Onsomecrystals that are insoluble in water; thus, the system belongsthe other hand, V(2) is the curve where the repulsive force is unablesomersasieare aispersesystem. Wherein the coalescenceto overcome the gravity between the particles at any distance. Attoa lyophobic coarse dispersed systerm,. Wwhereninleatonseveralthis point, the colloidal particles mutually gather, eventually pro-system is unstable and easily causes extreme peipitionin Severalmethods were adopted in the current work to stabilie the systemVk increases dramatically when the colloidal particles are nearduce precipitation.[23]. First, the suspended particles were charged, forming a dou-h other. Meanwhile, VA decreases at a slightly lower speed,ble-electric layer that produced an electrostatic repulsion actionWherein thecurve of the total potential appears peaks and buildsbetween particles. Next, inorganic or organic polymer compoundsundswere added into the system, forming an adsorption layer from theparticles surface, which had a certain mechanical strength to hin-der particles from mutually approaching through a stronger stericeffect; this transformed the suspended particles in a stable dis-persed state. Then, a solvation membrane with a special structureand a particularity qualitative on the particles surface was formed,destroying the solvation layer ordered structure and producingrepulsive force from the solvation contact when two particlesmutually approached each otherDitnce between7 Ya中国煤化工4.1. Characteristics oHCN M H Gidle surfaceThe solid particle surface is usually charged in order to maintainFig. 10. Potential enery cuve between clial partidles (21.electrical neutrality; the adjacent surface is expected to have equalY. Xu et al/nteratioa. Journal of Mining Science and Technology 24 (2014) 649- 656653and opposite charges, thus forming the double -electric layerThe soluble calcium salts in the mountain sand particles ionize[24- -26]. Given that colloid particle surface burdens electricity,solventtification. These free calcium ions are adsorbed in priority on thewater. Likewise, the crystal or small particle surface in the colloidsurface of the mountain sand particles based on the law of adsorp-forms a double-electric layer when the colloid mixes solid particlestion. The positive electricity drives the surface of the mountainsuch as fly ash, mountain sand, or loess particles. The mountainsand particles to attract an anion ion in the liquid and a repulsionsand-suspended colloid system can be classified as a lyophobicpositive ion. The anion is concentrated on the surface of the moun-and coarse dispersed system, which is an unstable system.tain sand particles, while the positive ions move away from theHowever, the laboratory experiments on suspended sand havesurface, forming a double-electric layer. The larger size of theshown that the mountain sand-suspended colloid systemmountain sand particles forms the double-electric layer by adsorb-remained stable for a long time. Han et al. stated that a system ising the calcium ion, and the surface shows a positive electricalstable when it is electrically neutral [27]. Due to the negativelyproperty (Fig. 11).charged surface of colloid particles, to ensure that the entireThe spatial interaction model of the double-electric layer hassystem is electrically neutral, the surface characteristics of sandseveral characteristics. The surface of the mountain sand particlesparticle must be investigated further.with a positive charge attracts the colloidal particles with a smallerSamples tests and analyses were conducted. We selected moun-particle size and those that show a negative electrical propertytain sandparticles,which werinfltrated in distilled waterunder static actionThe whole mountain sand-suspended colloid(according to the laboratory tests, tap water from Xuzhou citysystem is electrically neutral when the double -electric layer struc-had 0.01 76% soluble calcium ion mass). The particles were mea-ture of sufficient anion colloidal particles is adsorbed into the sur-face of the mountain sand particles. The colloidal particles thatplexometric titration test. The soluble calcium salt content was0.3 g (Ca2+)/kg (sand). The mountain sand particles provided theexclude the free particles in the colloid under the action of thecalcium ion from the components of feldspar (Na, Ca) AISizOg/electrostatic repulsion force, thus moving the particles away from(Na, K)AISi3Os) and calcite (CaCO3).each other. The DLVO theory states that the interparticle repulsionWhen the mountain sand particles infiltrate into the water, thepotential energy, the gravitational potential energy, and the totalsoluble calcium salt leads to mild ionization and produces a certainpotential energy change, depending on the distance. Attractionamount of Cat*. The general law of ion adsorption states that ionpredominates at a certain distance range, and repulsion predomi-(with the same chemical elements as the original compounds) isnates in another distance range. Therefore, repulsive force plays aadsorbed prior to ionization. Therefore, for mountain sand particlesleading role in the double-electric layer of the colloidal particlesthat contain ingredients of feldspar (Na, Ca)AISi3Os/(Na,K)AISi3Og)and the sand particles at a certain distance. Moreover, the particlesand calcite (CaCO3), Ca2+ is adsorbed prior to the surface, and calleddo not aggregate and settle under the action of the repulsion forcepotential de-termining ion. The mountain sand-suspended sandbetween particles, which is similar to the mountain sand particlescolloid system must be electrically neutral to make the system sta-surface under the action of electrostatic attraction between parti-ble; thusan anion wpower that is both eccles, resulting in viscous and stable sand-suspended colloid. Theitha power thatioth equal to and syIically opposite from Ca2+ is needed for balance. The surface chargematerials of thend-suspennded colloid contain some organicand reverse ion of the ambient medium comprise the double- elec-macromolecule polymer with a more branched chain. The maintric layer (Fig. 11). In conclusion, the charge of the mountain sandparticles surface becomes positive.the surface of the mountain sand particles. The branched chain4.2. Interaction between the suspended solid particles and the colloidstretches out, forming a 3D distribution on the surface of themountain sand particles as well as a space hindrance functionThe sand-suspended colloid has stable suspension ability com-between the particles. Space agglomeration between the particlespared with the mountain sand particle in the system based on theis hindered, stabilizing the mountain sand particle suspension intheory of the double- electric layer. Here, the suspension mecha-he colloid system. The larger-sized particles do not clot ornism of the mountain sand particles is explained by presenting acoalesce.spatial interaction model of the double ecrtic layer of the parti-Therefore, the dispersing effect of the sand-suspended colloidcles (Fig. 12). .system on the mountain sand particles is the synergy effectbrought about by the space steric effect and the space electrostaticinteraction influence of the double -electric layer, in accordancewith the spatial interaction model of the double -electric layer ofthe particles. The stability of the colloid and the steady suspensionoftbemotnta)f the mountaintem are thus guaranteed.5. Mechanical condition for suspending solid particles in sand-suspended colloidThe double electronic model explains the suspension mecha-nism of the sand particles in a colloid system from particle to par-ticle interaction. .fthe suspension isHeldwateranalyzed in this s中国煤化工of the mountain。Sandessand in a suspendeC N M H Gtudy the mechan-| Double-electicYHFreewater Bound water.Neutta waterical condition of thUiIu pallilics 111 a sand -suspendedcolloid. This is because the mountain sand particles size is largerFig. 11. Mountain sand particles double -electric layer model.and the action of gravity for mountain sand particles is significant.54Y. Xu et a./nterationmal Journal of Mining Science and Technology 24 (2014) 649- -656/ DoubleterirDouble- etree0-layer of sandpaticlesarticleslYelectosatie rpuson日Double lerice layer sruction of cloillFig. 12. Spatial interaction model of the double ecric layer of the particles.The sand particle is regarded as a sphere, and in this case, theThe colloid can bear the stress produced by the gravity action of thesubsiding sand particles in the sand-suspended colloid are ana-mountain sand particles because the stress value is less than thelyzed. The subsiding particles lead to the higher viscosity of theyield stress, that is, the stress change of the gravity action ofsand-suspended colloid. The smaller sand particles subside morethe mountain sand particles to lower sand-suspended colloid fluidslowly. Based on the tested fluid data, the viscosity of the suspend-is not enough to change the mobile geodetic deformation ofing colloid with 0.5% concentration is η=0.9 Pa.s under a lowthe sand-suspended colloid. Therefore, the mountain sand doesshearing rate and the density is ρ≈1.00 x 103 kg/m'. The sand)t subside. The main criterion for the suspension of the sand-particle diameter is tested as d = 0.5 mm with a particle densitysuspended colloid is whether the yield stress of sand-suspendedof ρs= 2.48 x 103 kg/m3. The hydraulic resistance Fis F= 3rnd-o,colloid is greater than the particles stress of the action of gravity,where the sedimentation velocity is o, and the Reynolds number iswhich lowers fluid flow.Theoryi2Re<1 based on the Stokesy [25].F= 3π.n.d.o2)6. Application of the sand-suspended slurry for fire preventingin coal mine_ρggd2∞o=18η3)The purpose of developing a sand-suspended colloid is to pre-pare sand-suspended slurry for application in coalmine fire pre-In the colloid system, the particles can achieve the maximum sedi-vention [28]. The Daliuta Coal Mine was chosen as the venue formentation velocity of 00 only when the gravity and the resistancethe tests to ensure the work faces withdrawing successfully andof particles are equal. The gravity of the particles is G= 1/6pgrd'.safely.The greatest, sedimentation velocity 00 is obtained when G= F,and 00 = egf are obtained.6.1. General situation of Daliuta Coal MineThe data are substituted, yielding 0o = 248.103 x98<(05x10-3 x3600= 1.35 m/hThe Daliuta Coal Mine is located in Shaanxi province. The lengthWe found that 1.35 m/h is too fast for suspension. Otherof the coalfield is 89 km, and the width is 74 km. The minablemechanics conditions are needed to maintain sand suspensionfor a long period. The slurry from the sand-suspended colloid withmineable coal seams located in seams 1-2, 2- -2, and 5-1. The coala concentration of 0.5% takes too long to subside. Thus, the domi-types are non-caking coal and jet coal. The seam of the coalfieldnant factors of the colloid that can suspend sand include both thehides the shallow with a simple geological structure. Otherwise,viscosity of the fluid and other mechanical conditions. Further-the coal seam easily and spontaneously combusts with the poormore, mountain sand particles are unable to subside when thegas-bearing capacity.mortar is under static conditions. The mountain sand particlesare assumed to be spherical, and the fluid stress under the particles6.2. Using the sand- suspended slurry in coal mineis given byThe fully mechanized work face of 21,302, 21,301, and 21,303 in_G _ 1/6p.grd*seam 1-2 had been mined one after another. More coal was found1/2rd2in the goaf during the actual mining, and the air leakage w.5 alsofound to be serious. The three work faces had an average coal seamdensity of particles, kg/m3; and d the diameter of the spherical par-ticles, m. Here, d = 0.5 mm, and using the solution of Eq. (4), we findTherefore, fire prevention is necessary because of the largethatamounts of coal in the goaf, the serious air leak, and the high ten-dency of spontaneous combustion.is=*x2.48x 103 x9.8x0.5x 10-3 = 4.05PaIn arranging the workshop on the ground, the colloid materialwas prepared with a ratio of 5%o within the water for dissolving.The yield stress to= 4.57 Pa is found by analyzing the rheologicalThe prepared sand-suspended colloid and the sand with a volumebehavior of the sand-suspended colloid. The yield stress for theratio of 3:1 were thelspended slurry.yield pseudoplastic fluid is obtained when the shear stress of theThe work progress of中国煤化Tesemd a5 Torfluid is greater than the yield value, which allows the fluid to flow;lows: (1) the 20 tonT出C N M H G transported tootherwise, the fluid suffers an elastic deformation and does notthe mine entrance;wa SWLLiICu io 5 ton with aflow. Meanwhile, To≥Ts can be found by comparing to and Tssmaller vehicle; and (3) the slurry was carried to the fire seal ofTherefore, the sand-suspended colloid remains in a soft solid form.the 21,303 work face, after which the slurry was injected intoY. Xu et al./ International Jourmnal of Mining Science and Technology 24 (2014) 649 -656655the sand not only through the influence of the colloid poly-mer in the main chain, but also through the carboxyl andsand-suspended colloid system benefits from the burdenelectric formation of the electric-double layer structure ofthe colloidal particles.(3) In this study, we analyzed the mechanical conditions of thesteady suspension of sand particles in the colloid system(a) Equipment dstributionot(b) Preparing the surrybased on the principle, which states that under the conditionwherein the stress of rock sand particles on the lower part ofFig 13. Preparing the sand-suspended sury.the fluid (Is = 4.05 Pa) is less than the yield stress of the col-loid itself (To= 4.57 Pa), then the sand particles with size of0.5 mm below can suspend steadily in the colloid.(4) The sand-suspended slurry intended for coal mine fire pre-vention has a remarkable effect and can be utilized in otherfield applications anonstted by the results in DaliutaCoal Mine.AcknowledgmentsThe authors gratefully acknowledge the support of the research(a) Injecting the surryto(b) Ijecting the surry tofunds provided by the National Natural Science Foundation ofthe tank wagonthe goafChina (Nos. 51304071, 51304073) and the Open Projects of StateFig 14. Injecting the sand-suspended slury.Key Laboratory of Coal Resources and Safe Mining, China Univer-sity of Mining & Technology of China (No. 12KF02). We also wishthe goaf through the slurry pipe with a supercharged pressureto thank the reviewers and editors for their professional and con-structive comments, which greatly improved this paper.pump.The pressure of the pump station was above 5 MPa. The volumeReferencesof the sand-suspended slurry, where 85 injecting points can eachinject 200 m3 of slurry, was 17 ,000 m*. And the whole procedure[1] Qin BT, Lu Y. Experimental research on inorganic solidifed foam for sealing airlasted for 3 months.Figs. 13 and 14 show the scene of the coalmine for preparing[21 Cao K, Zhong Xx, Wang DM, Shi GQ, Wang YM, Shao zL Prevention and controland injecting the slurry.of coalfield fire technology: a case study in the Antaibao Open Pit Mine goafThe results show that the coal in the goaf of the 21,303 workburning area, China. Int J Min Sci Technol 2013;22(5):657-63.[3] Hu XM, Wang DM, Wang SL. Synergistic efets of expandable graphite andface is no longer spontaneously combustible after injecting thesand-suspended slurry, ensuring that the nearby work faces canthermal stability of a polyisocyanurate-polyurethane foam. Int] Min Scibe mined scessfully and safely. Otherwise, the sand-suspended[4] Yu SI, Yu MG, Xie FC, Pan RK, Lu LX, Chang XH. An inorganic foaming gel forTechnol 2013;23(2):13-20.slurry also could be transported by the supercharged pumppreventing spontaneous combustion in a top-coal flling region. J China Univthrough the pipeline in the coalmine smoothly.5] Yao BH, Wu Y, Liu JS. The efect of the fracture distribution on CO2 injectioninto a coal seam. Int J Min Sci Technol 2012;22(1):115-20.7. Conclusions[6] Liu BY, Liu ZB, Fan JF. Study on sand- fling fire prevention and extinctiontechnology in goaf of spontaneous combustion coal seam of Hongmiao mine. JThe study is made systematically and thoroughly in order to[7] Wang DM, Li zH, Qin BT, Liang XY, Chen jH. 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