18流化床输送系统

18FluidizedMotionConveyingSystems流化床运动输送系统1INTRODUCTION前言Althoughtheseconveyingsystemshavebeeninuseforwelloveronehundredyears,theyhavebeenratherneglected.Thisisdespitethefactthattheyarewidelyusedformaterialssuchascement,flyashandalumina,andareveryeconomicaltooperate.Themainproblemisthattheyhave,untilrecently,onlybeenabletooperateonadownwardinclineandasaconsequencehavebeenreferredtoasairassistedgravityconveyorsorairslides.Theyhavenowbeendevelopedtooperatehorizontallyandhaveconsiderablepotentialforfurtherdevelopment.虽然这些输送系统已被使用超过100多年，它们一直没受到重视。事实上它们被广泛用于如水泥，粉煤灰和氧化铝等物料，并且运行的经济性很好。直到最近，它们的主要问题是只能倾斜向下运行，并因此被称为空气辅助重力输送机或“气动溜槽”。现在它们已发展到水平运作，并有进一步发展的巨大潜力。Fluidizedmotionconveyingcanberegardedasanextremeformofdensephasepneumaticconveying.Itisessentiallyanextensionofthismethod,withthebulkparticulatematerialmadetoflowalongachannel.Intheair-assistedgravityconveyorthechannelisinclinedatashallowdownwardangleandthepredominantfactorcausingflowisthegravitationalforceonthematerial.Itthisforthisreasonthatair-assistedgravityconveyingsystemsarepotentiallyveryeconomicaltooperate.流化床运动输送可被视为超密相气力输送。实质上它是这种方式的延伸，散装颗粒料沿一个通道流动。在空气辅助重力输送机种这个通道是小角度倾斜向下，流动的主导因素是作用在物料上的重力。因为这个原因，空气辅助重力输送系统可以很经济地运行。1.1ConveyingTechnique输送技术Thetechniquetoachieveconveyingisessentiallytomaintainanaeratedstateinthebulkparticulatematerial,fromthemomentthatitisfedintotheupperendofthechannel,tothepointatwhichitisdischarged.该技术得以实现输送的实质是维持散装颗粒物料的充气状态，从它进入通道高端处到它的排放点处。Figure18.1Theprincipleofair-assistedgravityconveying.空气辅助重力输送机的原理。Thisisachievedbymeansofthecontinuousintroductionofair,orothergas,atarelativelylowflowrateandpressure,intoaplenumchamber,inordertofluidizethematerial.TheprincipleofoperationisillustratedwiththesketchinFigure17.1.通过将相对低流量和压力的空气不断通入一个充满物料的槽中，以使物料流态化，从而实现这一点。图17.1中的示意图描述了运行的原理。Theairpassesthroughafalsebottom,ormembrane,madeofasuitableporousmaterial,whichrunstheentirelengthofthechannel.Withpowderedmaterials,andthosecontainingfineparticles,thechannelisgenerallyenclosed,asshowninFigure18.2[1],Bythismeanstheentireconveyingsystemcanbetotallyenclosed.Thefluidizingair,afterpassingthroughthebedofmaterialslidingonthemembrane,flowsoverthetopofthebedofmaterialandisventedthroughasuitablefilterunit.空气穿过一个由适当的多孔材料制成的、与通道全长相等的假底或膜。输送粉料和那些含有细小粒子的物料，通道一般是封闭的，如图18.2所示[1]，这样整个输送系统可以完全封闭。流化空气穿过在膜上滑动的料床后，从料床顶部流过，并通过适当的通风过滤装置排出。Sincethebulksolidmaterialiskeptlivebymeansofthesteadyflowofair,thematerialflowsfreelydowntheslope,evenwhentheangleofinclinationisrelativelysmall.Thequantityofairusediskepttotheabsoluteminimumnecessaryinordertoreduceboththeinter-particulateforces,andthefrictionalforcesbetweentheparticlesandtheinternalchannelsurfaces,sufficienttoallowthematerialtoflow[1].Theairrequirementsforfluidizedmotionconveyingsystems,therefore,arerelativelylowandsotheydoneedtobemaintainedbetweenreasonablycloselimitsinordertooptimizeconveyingconditions.由于空气源源不断地通入，散装固体物料保持活力，甚至当倾角相对较小时，物料也能顺着斜坡自由地流动。所用的空气量保持在所必须绝对最低的限度上，目的是减少颗粒内部的作用力和颗粒与内部通道表面之间的摩擦力，并足以使物料流动[1]。因此流化床运动输送系统所需的空气相对较低，所以他们的确需要保持在合理接近的限制之间以优化输送条件。Figure18.2Typicalair-assistedgravityconveyor.典型的空气辅助重力输送机。1.2SystemAdvantages系统优点Fluidizedmotionconveyinghasalltheadvantagesofpneumaticconveying,butwithfewofthedisadvantages.Itprovidesatotallyenclosedenvironmentforthematerial,isveryflexibleinlayout,andhasnomovingparts.Withair-assistedgravityconveyorstheonlydrawbackisthefactthatmaterialcanonlybeconveyedonadownwardgradient,butasmentionedabove,thesystemdoeshavedevelopmentpotentialthatismakinghorizontalconveying,atleast,adistinctpossibility.流化床运动输送具有气力输送的所有优点，而只有很少的缺点。它提供了一个对物料完全封闭的环境，布局灵活，而且没有运动部件。空气重力输送机唯一欠缺的地方是只能沿向下坡度输送物料，但如上所述，该系统确实有水平输送的潜力，至少是有明显的可能性Aparticularadvantageoverpneumaticconveyingisthattheconveyingvelocityisverylow.Indilutephasepneumaticconveying,solidsloadingratiosthatcanbeachievedareverylowandconveyingvelocitiesareconsequentlyrelativelyhigh.Asaresult,powerrequirementsaremuchhigherthanalmostanyalternativemechanicalconveyingsystem.Operatingproblemsassociatedwithabrasiveparticles,suchastheerosivewearofsystemcomponents,anddegradationoffriableparticles,canbesoseverethatpneumaticconveying,asameansoftransport,isoftennotconsideredforsuchmaterials.相对于气力输送所独具的一个优点是输送速度非常低。稀相气力输送中能实现的固气比非常低，故输送速度是比较高的。因此功率需求几乎比任何其他机械输送系统都要高。与磨料有关运行问题，如系统组件的冲蚀磨损和易碎颗粒的降级，是如此的严重以致通常不考虑用气力输送来运输这类物料。If,inapneumaticconveyingsystem,thematerialcanbeconveyedindensephase,powerrequirementswillbelowerandoperatingproblemswillgenerallybereduced.Influidizedmotionconveyors,however,solidsloadingratiosareevenhigherandconveyingvelocitiesaremuchlowerthanthoseindensephaseconveying.Asaresult,powerrequirementsareonaparwithbeltconveyors,andoperatingproblemsassociatedwithabrasiveandfriablematerialsarealmostnonexistent.如果在气力输送系统中，物料能以密相输送，那么功率需求会降低，而且运行问题一般也会减少。而流化床运动输送机中，固气比甚至更高且输送速度大大低于密相输送。因此功率需求和皮带输送机在一个级别上，而且几乎不存在和磨料及易碎物料相关的运行问题。1.3DesignTolerance设计容忍度Thegeneralprincipleoffluidizedmotionconveyingisverysimpleandthismethodofconveyinghasaparticularadvantageofbeingessentially'workable'.Withpneumaticconveyingsystemsitiscriticalthattheconveyinglineinl