Alfa Laval – disc stack separator technology

Alfa Laval – disc stack separator technology

Controlling the separation of liquids and solids

Separating different liquid phases and solids fromeach other plays a key role in countless industrialprocesses.

Alfa Laval has been at the forefront in this field for wellover 110 years – which is why disc stack separatorsfrom Alfa Laval perform this crucial separation functionexceptionally well.

Alfa Laval – disc stack separatortechnology

Kinds of equipment normally used for solids separation

separation. Decanter centrifuges aregenerally used for greater solidsconcentrations with larger particlesizes. Disc stack separators, on theother hand, are ideal for a wide rangeof separation tasks that involve lowersolids concentrations and smallerparticle and droplet sizes. This appliesto both liquid–liquid and liquid–solidseparation.

The most difficult separation tasks canoften involve three phases, with hardlyany difference in the density of theseparate liquid phases and with theparticles to be separated very small insize. In such applications, no othertechnology can compete with discstack separator technology.

4 Alfa Laval – disc stack separator technology

Continuous separationVirtually all branches of industry needto separate different liquid and solids atsome point in their manufacturingprocesses. Alfa Laval has well over acentury of experience in meeting theserequirements using different kinds ofcentrifuge technology.

The basic centrifuge idea is based onwhat happens in a settling tank, inwhich particles, sediment and solidsgradually fall to the bottom, and theliquid phases of different densityseparate due to the force of gravity.

However, such clarification is anextremely slow process and is unableto meet industry’s needs for rapid,controllable results. The general ideabehind centrifuges is therefore toensure that the mechanical separationof different liquid phases and solids canbe carried out on a rapid, continuousbasis in order to meet the demandsassociated with modern industrialprocesses.

Accelerating the processIn essence, a centrifuge is a settlingtank whose base is wrapped around acentre line. Rotating this entire unitrapidly means that the effect of gravityis replaced by a controllable centrifugalforce that can have an effect up to10,000 times greater.

This force is then used to separateliquids from other liquids and solidsefficiently and with great accuracy, andin a manner that is easy to control.

Types of centrifugeThere are several different basic typesof centrifuge normally used in industrial

Amount of solids

Filters

Disc stackseparators

Decantercentrifuges

30%

20%

10%

0.1 μm 1 μm 10 μm 100 μm 1 mm Particle size

40%

Working principles

A brief general explanation of how disc stack separators work

Alfa Laval – disc stack separator technology 5

Inserting special plates (the “discstack”) provides additional surfacesettling area, which contributes tospeeding up the separation processdramatically. It is the particularconfiguration, shape and design ofthese plates that make it possible for adisc stack separator to undertake thecontinuous separation of a wide rangeof different solids from either one ortwo liquids.

The concentrated solids phase formedby the particles can be removedcontinuously, intermittently or manually,depending on separator type and theamount of solids involved in thespecific application.

The clarified liquid phase (or phases)overflow close to the rotating axis, inthe outlet area on top of the bowl. Theliquids then flow into separatechambers. Each separated liquidphase then leaves the bowl due to theforce of gravity or by means of a paringdisc, which is a special pumpingdevice. The chambers can be sealedoff from each other to prevent any riskof cross-contamination.

How a disc stack separator worksA disc stack separator separates solidsand one or two liquid phases fromeach other in one single continuousprocess, using extremely highcentrifugal forces.

When the denser solids are subjectedto such forces, they are forcedoutwards against the rotating bowlwall, while the less dense liquid phasesform concentric inner layers.

The area where these two differentliquid phases meet is called theinterface position. This can be easilyvaried in order to ensure that theseparation takes place with maximumefficiency.

Settling tank Settling tank with discs Disc stack separator

The whole is the sum of parts

Advanced technology involves many forms of specialist know-how

Alfa Laval has the expertise needed tomatch the demands associated withspecific industrial processes byproviding particular disc stack configur-ations that ensure a flow evenly spreadamong the discs, along with anoptimized flow pattern in thedisc stack itself.

The layout and design of thedistribution holes also have a crucialinfluence on good performance. Theseensure that the process flow is evenlyspread among all the discs, for themost efficient results.

Liquid discharge sectionOnce separated, the liquid must oftenbe conveyed out of the separator asdelicately as possible. In someapplications, it is important that oxygenpick-up is kept to a minimum, and thattemperature increases in the liquidmust be avoided in order to preventproblems later in the process. AlfaLaval has designed solutions to theseand many other detailed requirements,in order to provide our customers withthe best possible process conditionsfor their operations.

Disc stack separators normally featurefour main sections.

Inlet zoneThe inlet zone accelerates the processliquid up to the speed of the rotatingbowl. A properly designed inlet zonemakes sure that the feed solids andliquids are not degraded or affected inany other way. Good inlet design alsoprevents foaming, reduces the sheerforces in the product, minimizestemperature increases and avoidsdisturbance of the separationprocesses taking place in the bowl.

A number of different inlet configur-ations are available for Alfa Laval discstack separators, each designed toensure maximum performance inconjunction with a specific process.

Disc stack areaThe key to good separation perform-ance lies in the efficiency of the discstack, which is the heart of theseparator. The design of the disc istherefore crucial.

Outlet zone

Inlet zone

Disc stack

Bowl wall

Solids discharge ports


The most straightforward way ofdischarging the liquid phases is the useof open outlets.

In most applications, however, a headof pressure is needed. This is createdby a stationary paring disc withspecially designed channels. This discdecelerates the rotating liquid andtransforms the kinetic energy from thisinto pressure, thus pushing the liquidout of the separator via the channels inthe disc. The pressure needed for theparticular process is normally regulatedby a valve on the outlet.

Solids discharge sectionThere are three basic ways of removingthe solids from disc stack separators� continuous solids discharge, in whichsolids and liquid exit via nozzles inthe periphery

� intermittent solids discharge, in whicha carefully designed system opensports in the bowl periphery atcontrolled intervals in order toremove the collected solids

� manual removal, in which themachine is stopped and the bowl isopened so that the collected solidscan be removed manually.

The solution most appropriate for aparticular application depends on acombination of factors. The mostimportant of these are the amount ofsolids in the liquid, the nature of theparticular application and theconsistency of the solids once theyhave been separated.

Separator systemNaturally, the overall efficiency of a discstack separator as part of a productionset-up is heavily dependent on manyother ancillary systems and equipment.

Unparalleled experience means thatAlfa Laval has a unique capability forproviding all the necessary equipmentto achieve maximum efficiency in thecontinuous separation of different liquidphases and solids in countlessindustrial processes.

This can be done on the basis of highlyefficient, standardised equipmentpackages and fully tested modularunits, or specially customized discstack separator installations to meetindividual liquid–liquid and liquid–solidseparation requirements.


Solids retention Intermittent solids discharge Continuous solids discharge

The keys to exceptional performance

The Alfa Laval differenceThe ability to separate the liquid andsolid components of often highlycomplex, high-value processingstreams – and to do so withmeticulous control, low cost and highreliability – requires disc stack separatortechnology that 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.

History, experience and expertiseAlfa Laval has more than one hundredand ten years of practical experiencewith the design and manufacture ofhigh-performance disc stackseparators. Alfa Laval therefore has ahighly comprehensive body ofknowledge relating to the use of discstack separators in countlessapplications.

We are able to combine this know-ledge with the results of our R&D work,making it possible to undertakecontinuous improvements in theperformance of Alfa Laval disc stackseparators in order to optimize theresults that our customers can getfrom their industrial processes.

Technology leadershipAlfa Laval conducts extensive R&D inall the technologies associated with thedesign and operation of disc stackseparators. Our know-how andspecialist process experience put us ina unique position to match the exactneeds of each customer and eachparticular application and installation.

� Fluid dynamicsA disc stack separator only workssatisfactorily if the liquids are handledcorrectly. Some applications dependon smooth handling for goodseparation results and to maintain thequality of the end product. In others,oxygen pick-up or temperatureincreases are completely unacceptable.The flow through the inlet is also crucialwhen handling soft solids, and inensuring low sheer forces in delicateliquids and solids.

Considerable specialist knowledge andadvanced machining capacity arerequired to design and manufacture theextensive range of angled and curveddisc stack spacers and specially

shaped paring discs required to meetthe needs of modern process industry.

More than 25 years of in-depth studiesin fluid dynamics have given Alfa Lavalexceptional knowledge and insight intothe complex details of what takesplace inside the disc stack separatorduring operation. This is reflected in thedesign of our equip-ment and is amajor advantage when dealing withspecific customer demands.


� Materials technologyOne of the major challenges for discstack separators is that they often haveto deal with the combination of a highlycorrosive environment and the extremestresses that stem from operating withforces of more than 10,000 G. Onlyrelatively few materials can cope withthis. We therefore use advanced high-strength stainless steels, such asduplex and superduplex stainless steel,in the design of Alfa Laval disc stackseparators. To ensure maximum

reliability, all bowl parts are die forged.This provides a bowl that is completelyweld-free as well as ensuring that theparts feature a uniform grain structurefree from flaws and defects.

However, these are not the onlychallenges a disc stack separator mustmeet. The liquids being processed cancontain abrasive particles or require theuse of advanced sealing technologies.Alfa Laval has extensive applicationexperience that has enabled us to buildup a vast list of special materials thatwe can make available to customers inorder to meet virtually any processchallenge. These include manyadvanced stainless steels, tungstencarbide, nickel-based alloys for use inspecial environments, and specialpolymeric and ceramic sealingcompounds.

The results are maximum strength,unparalleled reliability and prolongedservice life. In disc stack separators,the correct choice of materials for eachcomponent is crucial for operationalreliability and commercial success.

� Ancillary technologiesBecause of the strength and reach ofAlfa Laval’s industrial capacity, thecompany is able to optimize the waysin which disc stack separatortechnology can be implemented inconjunction with other equipmentand processes.

Our exceptional know-how about

ancillary technologies, control systemsand technical interfaces make itpossible to extract crucial marginaladvantages from disk stack separatortechnology.


Technology leadership� Fluid dynamics� Materials technology� Ancillary technologies

Energy and the environmentMuch of the world’s energy from diesel, turbine and nuclearpower stations is generated with the help of disc stackseparators from Alfa Laval. We also help industry in general andthe oil and gas sector in particular to purify wastewater andindustrial fluids, and to handle slop oil. The Processes producingbio-diesel fuel use disc stack separators from our company.Notable challenges in the field of energy and environmentalengineering include:

� Removing heavy phase liquids/fine solids from a lightphase liquidIn gas turbine fuel treatment, Alfa Laval disc stack separatorsperform a key role in conditioning gas turbine fuels byremoving water, salt and solids to prevent these damagingthe turbine. This often involves removing small amounts ofheavy phase liquids and fine solids from a light phase liquid,in order to achieve the required high degree of purity.

� Bio-diesel productionThe chemical process to convert vegetable oils from rawmaterial such as rape seed into diesel fuel use disc stackseparators in several steps, separating the fuel frommethanol or water.

� Removing light phase liquid/fine solids from a heavyphase liquidTo achieve maximum cleanliness in conjunction with thecleaning of deckdrain and other water on offshore platforms,Alfa Laval disc stack separators remove oily contaminantswith a high degree of effectiveness. This means that thewater can be safely returned to the sea with no damage tothe environment.

� Breaking up tight oil/water emulsions stabilized withparticlesAlfa Laval disc stack separator equipment is able to separatewidely ranging emulsified mixtures of oil, water and solidsfrom oil platforms, refineries and other sources. For slop oil,this makes it possible to reclaim the oil at the same time aseliminating a potential environmental hazard.

Corporate Brochure 12

Application examples


Meeting the challengeVirtually every form of processing industry all over the world relies onbeing able to separate a wide variety of liquids into their componentparts, in addition to separating solids and particles from liquids.

Process industryAlfa Laval helps process industry customers to optimize theirperformance and deal with their separation processchallenges across a wide range of industries. Alfa Lavalknow-how, combined with our extensive range ofequipment, serves industries that include chemicals,petrochemicals, steel, paper, sugar and starch.Notable challenges in the process industry field include:

� Ensuring clean oil additivesIn the production of oil additives, Alfa Laval disc stackseparators remove any excess fine solids such as metalsalts, lime, etc. that might be present.

With disc stack separator units capable of running attemperatures in excess of 200°C, Alfa Laval providescustomers with a continuous, sealed process that replacestraditional filters. This makes it possible to avoid filter lossesand the operating costs and consumables associated withfilter equipment – and there are no hazardous wastesfor deposit.

� Sorting abrasive particles by sizeAlfa Laval equipment helps manufacturers of kaolin-basedpaper coating material clean and classify the kaolin in onesingle process, by sorting it on the basis of particle size.

Alfa Laval disc stack separators are available with a specialdesign that provides a high degree of resistance to theabrasion caused by kaolin. This results in equipment that ishighly reliable, providing customers with low servicerequirements that can be a major advantage in the often-remote locations of kaolin mines.

� Improving equipment service lifeDisc stack separators from Alfa Laval often play a key role incustomers’ processes in a rather indirect way.

Separating out water and other impurities and removingmetal particles from a wide variety of oils and lubricantsmeans that process motors, compressors, hydraulics,production lines, etc. are more reliable and have anextended service life. This kind of treatment can either bydone continuously or by using mobile hook-up solutions.



Life scienceAlfa Laval disc stack separators are widely used in thebiotechnology and pharmaceutical industries. For decades,Alfa Laval technology has been widely used in the harvestingof microorganisms. However, recent developments in thefield of genetic engineering and cell culture processing havenow made it possible for the biopharmaceutical industry todevelop and produce a whole range of new therapeuticproducts and treatments. Because they provide customerswith exceptional reliability, hygiene standards andperformance, Alfa Laval disc stack separators play a crucialrole in these technically advanced processes.Among the major challenges in this field are:

� Producing sensitive vaccines and antibodies understerile conditionsThere have been radical developments in new vaccines formany different diseases and ailments, from hepatitis andinfluenza to snake bites.

Alfa Laval provides disc stack separators that make itpossible to turn these research developments intocommercially viable production by meeting the challenge ofmaking the equipment fully contained, easy to sterilize andcompletely safe for the staff supervising the process.

Antibodies are also very difficult to separate and recover. AlfaLaval’s unparalleled understanding of fluid dynamics pavesthe way to unprecedented results in this delicate field, wherehygiene and sterility are paramount.

� Separating delicate mammalian cell culturesA completely new generation of drugs and medicines –derived from mammalian cell cultures – is currently emerging.These organisms are extremely delicate.

This means that any separation processes must involve themost gentle and low shear acceleration possible. The abilityto adhere to exceptional standards of hygiene is also akey issue.

Alfa Laval’s unique fully hermetic solids disc stack separatorswith intermittent discharge are specifically well suited for thistask.

� Undertaking a huge range of different cell separationtasksMany different microbial cells are used in the production ofantibiotics and other medicines. The particular type ofproduct (intracellular, extracellular or inclusion body), thecharacteristics of each particular organism (bacteria, yeast,mycelium, etc.), the required flow rates, the need forabsolute sterility and the need for full containment are allimportant considerations when a customer needs to decideon a specific separator solution.

Alfa Laval has the both the experience and the technicalknow-how to meet all customer needs for a huge range ofdifferent cell separation tasks, providing both intermittent andcontinuous solids discharge using either disc stack separatoror decanter centrifuges.

Food processingAlfa Laval is prominent in a considerable number of foodproduction activities and processes throughout the world.Disc stack separators are used in food industries of all typesand are designed to suit the specific requirementsassociated with each application and separation duty.Special features are available to minimize oxidation andproduct temperature increase. These can be combined withspecial designs to allow for the stringent standards ofcleanliness and hygiene demanded by the food industry.

Disc stack separators meet a whole spectrum of customerneeds, from small, seasonal olive oil and wine operations tolarge systems integrated into customers’ manufacturingprocesses that work around the clock, such as in breweriesand vegetable oil plants.Among the major challenges in the field of food productionare:

� Reducing kieselguhr consumption and increasingfilterabilityBeer is passed through kieselguhr filters to reach therequired standards of clarity and brightness. Alfa Laval discstack separators make it possible for breweries tosignificantly reduce the amount of kieselguhr used and toexploit the capacity of such filters in full, saving both timeand money. The disc stack separators include special designfeatures to eliminate oxidation of the beer and to minimizeproduct losses.

Reducing energy and chemicals consumption in thevegetable oil industryImproving product quality and reducing losses in vegetableoil refining, along with efficiently removing gums and soapstock during production, all contribute to profitability.Inventions such as the Centrizoom adjustable paring deviceenable fine tuning during production so that highly viscousgums can be removed from the oil. Hermetic inlets andspecial disc configurations provide excellent separationcapability and reduce the consumption of both energy andchemicals.

� Creating the best quality olive oilsAll top-quality extra-virgin olive oils have one thing incommon. They are processed in high-speed separators toremove both the remaining fines and any small amounts ofwater left after upstream processing.Features that ensure efficient separation along with aminimum of heating and oxidation of the oil are integral partsin Alfa Laval disc stack separators for olive oil processing.

� Recovery of cold-pressed lemon oilEteric oils extracted from lemons are used to create flavoursand aromas in a large number of different products, includingconfectionery, beverages and cosmetics.The delicate nature and the high value of these oils requirespecially designed separators. Completely hermeticallysealed units with carefully designed inlets and outlets make itpossible to avoid product deterioration and losses, thusensuring maximum yield.


Service countsIn 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 throughoutthe world.

Alfa Laval has full control over theentire supply chain, which means thatwe can provide customers withresponse times, availability and leadtimes that are second to none.

Service when it fits inThe service requirements for Alfa Lavaldisc stack separators 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 disc stack separators ensure thatany service work required involves theabsolute minimum of disturbanceto operations.

Nonstop performance



Alfa Laval in briefAlfa Laval is a leading global providerof specialized products and engineeredsolutions.Our equipment, systems andservices are dedicated to helpingcustomers to optimize the performanceof their processes. Time andtime again.We help our customers to heat,cool, separate and transport productssuch as oil, water, chemicals,beverages, foodstuffs, starch andpharmaceuticals.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.com

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Alfa Laval – disc stack separator technology