Alfa Laval – Decanter Centrifuge Technology

Alfa Laval in briefAlfa Laval is a leading global providerof specialized products and engineered solutions.Our equipment, systems and services are dedicated to helping customers to optimize the performanceof their processes. Time and timeagain.We help our customers to heat,cool, separate and transport productssuch as oil, water, chemicals, beverages, foodstuffs, starch and pharmaceuticals.Our worldwide organization worksclosely with customers in almost 100countries to help them stay ahead.How to contact Alfa LavalUp-to-date Alfa Laval contact detailsfor all countries are always availableon our website at www.alfalaval.comPCD00002EN 0702Alfa Laval – decanter centrifuge technologySeparating solids from liquids

Separating solids from liquids plays a key role incountless industrial processes.Decanter centrifuges from Alfa Laval perform thiscrucial function exceptionally well.

Working principlesVFD-controlled motorfor screw conveyorPond of clarified liquidOutlet for clarified liquidContinuous separationVirtually all branches of industry needto separate solids from liquids at somepoint in their manufacturing processes.Alfa Laval has more than fifty years ofexperience in meeting this requirementusing decanter centrifuge technology.The decanter centrifuge is based onthe simple idea of a clarifier or settlingtank, in which particles, sediment andsolids gradually fall to the bottom dueto the force of gravity.Accelerating the processHowever, such clarification is anextremely slow process and was notable to meet industry’s needs for morerapid, controllable results.The idea behind the development ofthe decanter centrifuge was thereforeto provide the continuous mechanicalseparation of liquids from solids, tokeep pace with modern industrialdemands.In essence, a centrifuge is a clarifierwhose base is wrapped around a4 Alfa Laval Separationcentre line. Rotating this unit rapidlymeans that the effect of gravity isreplaced by a centrifugal force – theeffect of which can be up to 4000times greater.This force is then used to separatesolids from liquids efficiently in amanner that is easy to control.Depending on the particularconfiguration and surroundingequipment, a decanter centrifuge canbe used to separate a wide range ofdifferent solids from one or two liquidphases, on a continuous basis.Screw conveyor

Surface areaWeirsFeed systemSide walldepthCake removalCakecompactionClarifier becomes a decanter centrifugeInlet tubeSolids deposited onbowl wallErosion-protectedsolids discharge portsMain motorConical beach sectionHow a decanter centrifuge worksA decanter centrifuge separates solidsfrom one or two liquid phases in onesingle continuous process. This is doneusing centrifugal forces that can bewell beyond 3000 times greater thangravity.The sediment formed by the solidparticles is continuously removed bythe screw conveyor, which rotates at adifferent speed than the bowl. As aresult, the solids are gradually“ploughed” out of the pond and up theconical “beach”.When subject to such forces, thedenser solid particles are pressedoutwards against the rotating bowlwall, while the less dense liquid phaseforms a concentric inner layer. Differentdam plates are used to vary the depthof the liquid – the so-called pond – asrequired.The centrifugal force compacts thesolids and expels the surplus liquid.The dried solids then discharge fromthe bowl. The clarified liquid phase orphases overflow the dam platessituated at the opposite end of thebowl. Baffles within the centrifugecasing direct the separated phases intothe correct flow path and prevent anyrisk of cross-contamination.The speed of the screw conveyor maybe automatically adjusted by use of thevariable frequency drive (VFD) in orderto adjust to variation in the solids load.Alfa Laval Separation 5

The keyto exceptional performanceWide-ranging performanceAlfa Laval decanter centrifuges provideexceptional performance whenseparating solids from liquids, andmake it possible to do so continuously,efficiently and controllably.Decanters are invariably the first choiceto meet such separation needs byvirtue of their high reliability, continuousoperation, low capital cost/capacityratio and low maintenance costs.Alfa Laval decanter centrifuges aredesigned to handle a wide range ofsolid particles with diameters from 5mm to a few microns.Decanter units can also handle slurrieswith a solid content from as low as0.1% w/w to more than 65% w/w.Decanter centrifuges can acceptvariations in the feed more effectivelythan other types of centrifuge orseparation equipment.Performance criteriaFive crucial factors determine theperformance of decanter centrifuges: the centrifugal force required forsedimentation of the solids the clarification area necessary to“capture” the solids the differential speed required totransport the solids out of thedecanter the hydrodynamic design, whichdetermines the exact parameters forthe turbulence the design of the conveyor andbeach sections, which are importantfor efficient solids transportation.6 Alfa Laval SeparationIn specifying a decanter centrifuge for aparticular application, a series of otherspecific design considerations has tobe taken into account: the pitch of the conveyor feed zone design beach angle bowl surface abrasion resistance materials used in construction.The four main sectionsAlfa Laval decanter centrifuges featurefour main sections, each optimized formaximum performance.Inlet zoneThe inlet zone accelerates the feedslurry up to the speed of the bowl. Aproperly designed inlet zone keeps anydegradation of the feed solids to aminimum as well as avoiding disturbance of the sediment in the bowl.

A number of feed zone specificationsare available for Alfa Laval decantercentrifuges, each designed to ensuremaximum performance in conjunctionwith a specific process.Screw conveyorThe key to good decanter performancelies in the efficient, effective scrolling ofthe sedimented solids. The design ofthe screw conveyor is therefore crucial.Alfa Laval has the expertise needed tomatch the demands involved in specificindustrial processes with specificconfigurations of flight pitch, lead angleand differential speed, in order tosecure the best possible results.Solids discharge sectionDepending on the application, theconsistency of the separated solidscan vary from a dry powder to a paste.The configuration of the dischargezone is therefore chosen to enablesuch “cakes” to exit as effectively aspossible.Innovative Alfa Laval design enableserosion-prone components used in thesolids discharge zone to be replacedon site at low cost and with a minimumof disturbance to production.Liquid discharge sectionIn a two-phase decanter, the liquidlevel is regulated by dam plates.When operating in a three-phasemode, each phase discharges over aset of dam plates into separate baffledcompartments in the casing.In certain applications, a centripetalpump discharge that utilizes thepressure head developed by therotating liquid phase is used to pumpthe liquid from the decanter.Liquid phase outletThree-phase designLight liquid phase outletHeavy liquid phase outletParing disc designLiquid outletAlfa Laval Separation 7

Benefits and featuresThe Alfa Laval differenceThe ability to separate the liquid andsolid components of often highlycomplex, high-value processingstreams – and to do so with meticulouscontrol, low cost and high reliability –requires decanter centrifuge technologythat is second to none.When the profitability of an entireprocess is at stake, it is important thatthe customer has a partner that can berelied on to meet the highly complexdemands associated with modernindustrial separation.And with facilities all over the world,Alfa Laval is in a position to providecustomers with superior products,superior service and superior results atany location.Experience countsAlfa Laval has more than fifty years ofpractical experience with the designand manufacture of high performancedecanter centrifuges.Research and developmentAlfa Laval conducts extensive ongoingR&D into all the technologies involvedin the design and operation of decantercentrifuges.This puts us in a unique position totranslate customer requirements intoefficient, reliable machine design andsolutions.Our know-how and specialist processexperience put us in a unique positionto match the exact needs of eachcustomer and each particularapplication and installation.Materials technologyAlfa Laval uses high-grade stainlesssteel for all parts that come intocontact with the process, in order toavoid any risk of the corrosionassociated with the use of carbonsteel. Corrosion leads to productcontamination, lack of balance, highmaintenance and lengthy down time.8 Alfa Laval Separation

Ease of maintenance and minimumdown time are important for users ofdecanter centrifuges. Rotatingcomponents of Alfa Laval decantercentrifuges exposed to high stress aretherefore machined from high-strengthcentrifugally cast stainless steel. Thisensures castings with a uniform grainstructure free from flaws and defectsas well as a completely weld-freefinished component. The results aremaximum strength, unparalleledreliability and a long service life.In decanter centrifuges, the optimalchoice of materials for eachcomponent is crucial for success.Abrasion resistanceWear caused by the abrasive action ofsolids affects both the performanceand service life of all centrifuges. AlfaLaval metallurgists identified this wearas the result of low stress scratchingabrasion and were therefore able todevelop ways of eliminating its effects.Seal technologySpecial casing seals capable of dealingwith pressure differentials are requiredwherever the processing involvessolvents or toxic materials. The typesof seals used, and the details of theirdesign, depend on the requirementsassociated with each particularprocess. Continual refinement of theseal technology used in Alfa Lavaldecanter centrifuges is ensured by ourtechnological resources. This is an areawhere Alfa Laval expertise andexperience make a key difference.All wear-prone areas of Alfa Lavalcentrifuges – the feed zone, solidsdischarge output zone, bowl and scroll– are therefore protected by abrasionresistant material, selected to matchthe pattern of wear in each particularindustrial process.Alfa Laval Separation 9

Benefits pay offApplicationsAfter fifty years of experience with decanter centrifuges, Alfa Laval has referenceinstallations that are second to none, across a wide range of industries.Process industry applicationsMineral processing industryKaolin clay and calcium carbonate processing, bentonite and titanium dioxide manufacturersOil/gas exploration and petrochemical industryOil and gas exploration, oil refineries and related industries, lubricating oil additives and waste oil stream recyclingOrganic chemical industryOrganic intermediate and end productsPolymer industryThermoplastics including PVC, polypropylene, polystyrene, synthetic rubber and fibresInorganic chemical industryBleaching agents, acids, silica products and fertilizersEthanol productionProcessing of grain alcohol spent wash and molasses fermenter residuesStarch processingBased on wheat, maize, tapioca, cassava and potatoesWaste recyclingRecovery and recycling of waste streams from the sectors listed aboveCorporate Brochure 1210 Alfa Laval Separation

Food applicationsAnimal proteinFish and meat by-product processingSurimi processingEdible protein recoveryBreweryRecovery of extract, wort and yeastCoffee and teaExtraction of instant coffee and teaDairyRecovery of casein, lactose, whey fines and cheese finesEdible oilClarification of palm oil, olive oil and pressed seed oilJuiceExtraction from fruit, berries and vegetablesPectinRecovery of extracted pectinVegetable proteinExtraction from soybeans, oil seeds and leguminous cropsWineMust and wine clarificationAlfa Laval Separation 11