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source: LIFE02 ENV/IT/000764
No. 03 | 2008
W o r l d w i d e I n f o r m a t i o n
Position PaperWEEE: EERA ask for a better legislation
Scharf-BergmannAluminium has to stay in Germany
Winfrid RauchWalking f loors are a cheap alternative
FacesNews Analysis
FeatureFeature
A report about the LIFE programme of the European Commission
Brussels manage the waste of the worldBrussels manage the waste of the worldA report about the LIFE programme of the European Commission
SpecialRepRoductioN
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Analysis | Moving Floors
In waste treatment plants (WTP), moving floors (or “walk-
ing floors”) are used to transfer, to store and to feed waste
in a just-in-time process. Different WTP applications and
various waste specifications ask for special machine char-
acteristics. System advantages make moving floors a less
expensive and more performing solution than other sys-
tems such as belt conveyors or push floors. RECYCLING
m@gazine-Expert Winfrid Rauch analyses this technique.
2.Theprofilesarelinkedtothecylinders.Normally,thereare
threecylinders.Eachcylinderislinkedtoonegroupof
profiles.Now,thefirstgroupofprofilesgoesbacksimulta-
neously.Astheheapissupportedbyallprofiles,theback-
wardsmovementofthethirdpartofprofilesisacceptable
withoutanymovementoftheheapitself.Inotherwords:
theheaprestsintheforwardpositionbecausethepartial
returnoftheprofileshasnoimpact.
3.Thesecondgroupofprofilesgoesback.Theheaprests.
4.Thethirdgroupgoesback.Theheaprests.
Moving floor applicationsMovingfloortechnologycomesfromtrailertechnology.Itis
commonknowledgethataluminiummovingfloorsintrucks
helptochargeanddischargeitems.Theirlightweightand
easyhandlingare intheir favour for theseapplications.
Trucksneedtheirmovingfloorsystemonlyforchargingor
dischargingmoments,forexample:oneperday.Mostinstal-
A less expensive and more performing solution than other systems
Function principleThemovingfloor(or‘walkingfloor’)isaconveyingprinciplethat
worksonadiscontinuing,pushingmovement.Aheapofprod-
uctsormaterialsliesonseveral(aluminiumorsteel)profiles.
Onemovingcycleiscomposedbythefollowingfoursteps:
1.Allprofilesadvancetogether.Theirmotorisationisdoneby
hydrauliccylinderswhicharepositionedbehindorunder
theprofiles.Theheapadvancesasfarasthecylinders
coursepermitsit.
Moving floors for WTPsMoving floors for WTPs
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Editorial
lationsinWTPworkintheoneortwoshifts.Thusthemoving
floorsareinconstantuse.WTPprocessconditionsarediffer-
entfromthoseintrucks.
InWTPs,movingfloorsareusedinstationaryapplications
suchas:
- MSWtransferstation:Anintermediatestoragepermitsto
distributeondemandwastecomingfromcollecttrucks
goingto40tonnestrailers.
- incomingstorageinWTP:adynamicstorageisneededto
createafluidWTPthroughput.Thesemovingfloorbun-
kerspossessoftenakindofmeteringdrum.Thismetering
devicehelpstocreateaconstantflowrate.
- Intermediatestorage:aftermainsortingsteps,moving
floorbunkerscanbefoundunderthesortingcabin.
- Outgoingstorage: intheendofWTPprocess,outgoing
materialsareputintobalesorstackedfordirecttruck
charging.Thisisoftendoneforpapersandcardboards.
PerformancesThespeedofmovingfloorsislinkedtothehydraulicunit.A
standardhydraulicunitneedsabout1.5secondstomove
threecylindersforwardandnearlythesametimetopush
backeachofthem.Foronecycle,wecancalculatewith1.5
secondsx4=6secondsforonecompletemovement.In
oneminute,wewillhavetenfullcycles.
Ifwecanmovetheheapforwardabout100mm(stand-
ardhydrauliccylindercourse)inonecycle,wecanforwardit
about10x10mm=1m/min.
Speedreductionisdonebybreaksbetweenhydraulicmove-
ments.Inthisway,wecanlowerspeedfrom1m/minto0.5
m/minuntil0.1m/minoreven1cyclein2minutes=0.05
m/min.
Thethroughputofmovingfloorsischaracterisedbythemov-
ingfloorspeedandthechargingheight.Aconventionalmov-
ingfloorcanbechargedwithabouttwometersofmaterial
heap.
So,wecancalculate:
- speed:1m/min
- heapheight:2m
- widthofthebunker(example):2m
- throughput:1x2x2m3/min=4m3/min=240m3/h
Foragivendensity,wecandefinehourlythroughputof
materials.Forexample:paperandcardboards=about
200kg/m3=0.2t/m3
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Analysis | Moving Floors
Productthroughput=volumethroughputxdensity=240
m3/hx0.2t/m3=48t/h.
Thisisatheoreticalvaluebecauseoffollowingelements:
- heapheight:normallythechargingheightisneverstable.
- friction:sidewallsholdbacktheheapbyfriction.
- movementbackwards: in theabovedescriptionof the
principle,itwasassumedthattheheapdoesnotgoback
whenonecylindergoesback.Inreality,alittlepartofthe
heap(thebottompart)hasatendencytomovebackmini-
mally.
Thestoragevolumeofamovingfloorbunkerisgivenbythe
followingelements,forexample:
- heapheight:2m
- widthofthebunker:2m
- length:6m
- bunkervolume:24m3
InWTPconception,thefeedingcapacityispriorityforthe
incomingfeedinghopper.Suchafeedinghoppershouldgive
atime-autonomytotheuserthankstoitssufficientstorage
volume.Whiletippingfromanincomingtruck,themoving
floorshouldnotoverflow.
Intermediatestorageareasmustbeconceivedaccordingto
downstreamneeds.Forexample,abalingpressshouldbale
allPETmaterialsofoneshiftinoneturn.
Fortheoutgoingstoragebunkers,othercriteriawillapply.For
example,atrailermustbeloadedinoneturn.Thatmeans,a
storagevolumeshouldcontaineasilythe90m3ofthetrail-
ercapacity.
Theinstalledpowerisquitelittleincomparisontoothercon-
veyingsystems.Asdescribedherebefore,themovingfloor
transportstheheaponlyalittledistance.Therefore,the
effortissmall.
Themovingfloorbunkerwith24m3withspeed=about0.8
m/minneedsahydraulicunitof4kW.
Construction characteristics of moving floorsDuetothedifferentapplications,severaltypesofmoving
floormodelsareusedtoday.Wetrytogiveanoverviewof
theircharacteristics:
- bunkervolume:thechargingconditionsgivenecessary
widthsandlengths.Fortransportreasons,movingfloor
manufacturersliketosellunitsthatdonotexceedawidth
ofthreemetresandalengthof13metres.
- profilematerial:aluminiumiscommonintruckapplica-
tions.ForstationaryWTPapplications,steelprofilesare
usedforheavymaterialssuchasMSW,paper,cardboards,
D3E,industrialwasteandrefusals.Steelprofilescansup-
porthighchargesarelesssubmittedtofrictionanddefor-
mation.Aluminiumprofilesareoftenusedforlightmateri-
alssuchasPETbottles,PE,PPandPSproducts.
- leaktightness:Intrucks,thefloorhastobeleaktight.
Naturally,forthiskindofuse,amovingfloorwillhaveside
seals.Thesesealsmightbeo-ringsorothersealingcom-
ponentwhichwillbeincontactwithneighbouringprofiles.
InstationaryWTPapplications,experienceshowsthatlab-
yrinthsealings–or‘noncontactseals’–maybemoreuse-
fulbecauseoffinematerials.Frictionbecomesimportant
whenwasteisloadedwithahighportionofdust,organics
andlittlematerials.Sidesealswilldisappearandthefloor
willnotbewaterproofasitwasinthebeginning.Steel
platesformingalabyrinth(nevercompletelyleaktight)
maintaintheoriginalmachinebehaviour.
- hydraulicunitandcylinders:somemanufacturerspropose
morethanthreehydrauliccylinderspermachine.Insome
specialapplications,suchashighdutyperformances,this
configurationmaybeuseful.InthestandardWTPapplica-
tions,threecylindersaresufficienttomakethefourstep
movement.Thehydraulicunitandthecylinderscanbe
putbehindthemovingfloor.Thisisrecommendedwhen
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Editorial
theuserdoesnothaveaccessunderthefloor.Inallother
cases,thestandardconfigurationisdonewithcylinders
underthemovingfloor.
System alternatives: belt conveyors and push floorsDuringthefirstRecyclingTechnologySeminaryinSalzburg
(August2005),thecompaniesTEAMGruber(beltconvey-
ors),FMW(pushfloors)andMatthiessen(movingfloors)
comparedtheirtechnologiesandmachinecharacteristics.
Pushfloors(or‘slidingframes’)canbefoundinflatsilosof
bulkmaterials.Theyareequippedwithhugehydrauliccylin-
dersthatpushseveralsteelframestoandfro.Theframes
slideonaconcretefloorandhavetheshapeofaladder
withwedges.
Duringtheforwardmovement,thematerialismovedintothe
directionofthecylinderbythebluntsideofthewedges.So
thebottompartoftheheapwillbepushedtotheexit.This
exitisnormallyatransversalscrewconveyor.
Duringthebackwardmovement,thewedgesslideunder-
neaththematerial,sinceinthatcase,thesharpsideismov-
ingforward.Sotheheapwillnotbepushedbackwards.
BeltconveyorscanbefoundinanyapplicationinWTPs.Their
machineconceptcanbesummarisedbythefollowingele-
ments.Theconveyorpossessesagearmotorgivingthetrac-
tionontheconveyorbelt.Thebeltreceivesitstensionby
thetensionscrewontheoppositeendoftheconveyor.The
beltglidesonasmoothsteelplateorrollingunits.Thesteel
structureintegratessidewallsinordertoimprovethroughput
ratesmostofthetimes.
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System advantagesIncomparisontostandardbeltconveyor,themovingfloor
hasthefollowingadvantages:
- width:standardbeltconveyorsrarelygobeyondtwometers
inwidth.Amovingfloorcaneasilymakesix,nine,twelve
ormoremeterscombingdifferentmovingfloorunits.
- chargingheight:standardbeltconveyorshavedifficulties
acceptingheightsbeyondtwometers.Thebeltandits
backingstructuremustbeconceivedespeciallyforthis.
Themovingfloorscanaccept–bytheirconstructionprin-
ciple–materialheightsgreaterthanthreemeters.
- price:movingfloorsarelessexpensiveforheavymaterials
(papers,MSW,incomingmixtures)ifthestoragevolumeis
higherthan20m3.
Incomparisontopushfloors,themovingfloorhasthefol-
lowingadvantages:
- principle:thewedgesofthepushfloorareintheheap;
theymovetheheapinside.Theprofilesofthemovingfloor
areundertheheap;theysupporttheheapwithoutany
movementinsideoftheheap.Mechanicallyspeaking,this
meansinthefirstcasehighduty(stronghydrauliccylin-
ders)andinthesecondcaselowefforts(littlehydraulic
cylinders).Installedpowerwillbedifferent.
- largeitems:asthepushfloorworksinsideoftheheap,it
mayencounterproblemswithlarge,heavyitems.Themov-
ingfloormovesforwardanykindofmaterial.
- price:inflatsilos,pushfloorsareinstalled.Often,their
priceisnothighwhenthepurchasercountsonlytheslid-
ingframesandnottheconcreteworkstomakethebun-
kerorsilofloor.Movingfloorsarepartofthebunkerfloor.
Theyreplacetheconcreteflooritself.Experienceshows
that inmediumrangestoragevolumesupto150m3,
movingfloorsrepresentamoreeconomicalsolution.For
biggerbulkstoragesilos,pushfloorsarecertainlymore
interesting.InWTPapplicationsforhugestoragevolumes,
onewoulduseloadinganddischargingmachinessuchas
grapnels,loadingengines,conveyorsorshovels.
Movingfloorsareagoodsolutionandanessentialparame-
terforthedesignofWTPsstorageandconveyingdevicesand
oftheirexploitationcosts.Detailedanalysisisnecessaryto
evaluatethecomparisonwithalternativesolutions. v
Analysis | Moving Floors
Sources:- BRT/Germany:http://www.brt.info/DOM-BRT-BIZ/MovingFloor.htm
- CargoFloor/Netherlands:http://www.cargofloor.nl/site/en_cargofloorstation
- KeithWalkingFloor/USA:http://www.keithwalkingfloor.com/stationary_eng.html
- Legras/France:http://www.legras.fr/index.php?id=220
- MatthiessenEngineering/France,WinfridRauch,www.matthiessen-engineering.com:photosfromMatthiessenmachinesin
Germany,AustriaandFrance
- MatthiessenEngineering,TEAMGruber,FMWFördertechnik:FirstRecyclingTechnologySeminaryinSalzburg“Storage,meter-
ingandconveyingofwaste”,August2005
- MatthiessenLagertechnik/Germany:http://www.bagsplitter.com/sites/recycling_de.php?sitelang=de&content_order_
show=6
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