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_

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