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PCD00002EN 0909
Alfa Laval – decanter centrifuge technology
Separating solids from liquids
Alfa Laval in brief
Alfa Laval is a leading global provider of specialized products and engineeredsolutions.
Our equipment, systems and servicesare dedicated to helping customers to optimize the performance of theirprocesses. Time and time again.
We help our customers to heat, cool,separate and transport products suchas oil, water, chemicals, beverages,foodstuff, starch and pharmaceuticals.
Our worldwide organization works closelywith customers in almost 100 countriesto help them stay ahead.
How to contact Alfa Laval
Up-to-date Alfa Laval contact details for all countries are always available on our website at www.alfalaval.com
Separating solids from liquids plays a key role in countless industrial processes.
Decanter centrifuges from Alfa Laval perform this crucial function exceptionally well.
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 a
4 Alfa Laval – decanter centrifuge technology
Working principles
Continuous 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.
centre 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.
Pond of clarified liquid
Outlet for clarified liquid Screw conveyor
VFD-controlled motor for screw conveyor
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”.
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.
Alfa Laval – decanter centrifuge technology 5
Solids deposited on bowl wall
Conical beach section
Erosion-protected solids discharge ports
Inlet tube
How 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.
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.
Weirs Side walldepth
Cakecompaction
Surface area Feed system Cake removal
Clarifier becomes a decanter centrifuge
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.
Main motor
The key to exceptional performance
In 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 disturb-ance of the sediment in the bowl.
6 Alfa Laval – decanter centrifuge technology
Wide-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 for
sedimentation of the solids• the clarification area necessary to
“capture” the solids• the differential speed required to
transport the solids out of the decanter
• the hydrodynamic design, which determines the exact parameters for
• the turbulence• the design of the conveyor and
beach sections, which are important for efficient solids transportation.
Alfa Laval – decanter centrifuge technology 7
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 outlet
Three-phase design Paring disc design
Light liquid phase outletHeavy liquid phase outlet
Liquid outlet
8 Alfa Laval – decanter centrifuge technology
Benefits and features
The 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.
Experience countsAlfa Laval has more than fifty years ofpractical experience with the designand manufacture of high performancedecanter centrifuges.
This puts us in a unique position totranslate customer requirements intoefficient, reliable machine design andsolutions.
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.
Research and developmentAlfa Laval conducts extensive ongoingR&D into all the technologies involvedin the design and operation of decantercentrifuges.
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.
Alfa Laval – decanter centrifuge technology 9
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.
All wear-prone areas of Alfa Lavalcentrifuges – the feed zone, solidsdischarge output zone, bowl and scroll– are therefore protected by abrasion-resistant material, selected to matchthe pattern of wear in each particularindustrial process.
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.
After fifty years of experience with decanter centrifuges, Alfa Laval has referenceinstallations that are second to none, across a wide range of industries.
10 Alfa Laval – decanter centrifuge technology
Process industry applications
Mineral processing industryKaolin clay and calcium carbonate processing, bentonite and titanium dioxide manufacturers
Oil/gas exploration and petrochemical industryOil and gas exploration, oil refineries and related industries, lubricating oil additives and waste oil stream recycling
Organic chemical industryOrganic intermediate and end products
Polymer industryThermoplastics including PVC, polypropylene, polystyrene, synthetic rubber and fibres
Inorganic chemical industryBleaching agents, acids, silica products and fertilizers
Ethanol productionProcessing of grain alcohol spent wash and molasses fermenter residues
Starch processingBased on wheat, maize, tapioca, cassava and potatoes
Waste recyclingRecovery and recycling of waste streams from the sectors listed above
Benefits pay off
Applications
Alfa Laval – decanter centrifuge technology 11
Food applications
Animal proteinFish and meat by-product processingSurimi processingEdible protein recovery
BreweryRecovery of extract, wort and yeast
Coffee and teaExtraction of instant coffee and tea
DairyRecovery of casein, lactose, whey fines and cheese fines
Edible oilClarification of palm oil, olive oil and pressed seed oil
JuiceExtraction from fruit, berries and vegetables
PectinRecovery of extracted pectin
Vegetable proteinExtraction from soybeans, oil seeds and leguminous crops
WineMust and wine clarification
12 Alfa Laval – decanter centrifuge technology
In modern industrial processes,efficient, well-planned service plays animportant part in maintaining profitableoperations.
Full controlAlfa Laval operates with a highlysophisticated Nonstop Performanceconcept made possible by ourworldwide network of service andspare parts distribution centres in morethan fifty countries throughout the world.
Nonstop Performance
Service counts
Alfa Laval – decanter centrifuge technology 13
Alfa Laval has full control over the entiresupply chain, which means that we canprovide customers with response times,availability and lead times that aresecond to none.
Service when it fits inThe service requirements for Alfa Lavaldecanter centrifuges are minimal, andplanned preventive maintenance is thekey to making sure this always remainsthe case.
Alfa Laval’s worldwide servicecapabilities and vast experience withthe contract maintenance and serviceof decanter centrifuges ensure that anyservice work required involves theabsolute minimum of disturbance tooperations.
14 Alfa Laval – decanter centrifuge technology
Separating solids from liquids plays a key role in countless industrial processes.
Decanter centrifuges from Alfa Laval perform this crucial function exceptionally well.
PCD00002EN 0909
Alfa Laval – decanter centrifuge technology
Separating solids from liquids
Alfa Laval in brief
Alfa Laval is a leading global provider of specialized products and engineeredsolutions.
Our equipment, systems and servicesare dedicated to helping customers to optimize the performance of theirprocesses. Time and time again.
We help our customers to heat, cool,separate and transport products suchas oil, water, chemicals, beverages,foodstuff, starch and pharmaceuticals.
Our worldwide organization works closelywith customers in almost 100 countriesto help them stay ahead.
How to contact Alfa Laval
Up-to-date Alfa Laval contact details for all countries are always available on our website at www.alfalaval.com
