Shenzhou 2-Phase Centrifuge

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

Working principles:

Continuous separation

Virtually 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 a 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.

How a decanter centrifuge works

A 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.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.

The key to exceptional performance:

Wide-ranging performanceA shenzhoul 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.shenzhou 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 for• the turbulence• the design of the conveyor andbeach sections, which are importantfor efficient solids transportation.

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 sections SHENZHOU 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 SHENZHOU 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.SHENZHOU has the expertise needed tomatch the demands involved in specificindustrial processes with specifiction configurations 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.

Benefits and features:

The A 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 counts  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,SHENZHOU is in a position to providecustomers with superior products,superior service and superior results atany location.Research and development SHENZHOU 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 technology SHENZHOU 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.

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. SHENZHOU 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  SHENZHOU Centrifuges – 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.

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 SHENZHOU decanter centrifuges is ensured by ourtechnological resources. This is an areawhere SHENZHOU expertise andexperience make a key difference.

Benefits pay off:

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 above

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