Sedimentation is one of the mostversatile separation processes.Pieralisi Vertical Separators (Disc-Stack Separators) are ideally suited toseparation processes where thephysical characteristics ofsedimentation can be applied thanks todensity difference.

Centrifugal sedimentation is often avery good and economical alternativeto other separation processes such as:• Filtration: based on particle size,• Micro-Filtration: based on particlesize in the sub-micron range,

But what can we do if we do not haveenough time or if we want toincrease capacity? Going back toStokes’ Law, to obtain an highersettling velocity and consequently toaccelerate the sedimentationprocess, we can replace gravitationalacceleration “g” by centrifugalacceleration “ˆ2 r”.The centrifugal acceleration “ˆ2 r”produced in a Pieralisi VerticalSeparator is up to ten thousandtimes higher than the ordinary forceof gravity “g”. As a consequence,settling velocity is up to ten thousand

times faster, and separation canbe achieved in a very short timeand/or using very small volumes.

SEDIMENTATION

The most common advantages ofcentrifugal sedimentation, moreappropriately termed CentrifugalSeparation are:• compact size of equipment,• low capital investments,• versatility,• ease of use,• low operating costs,• high performance.

The basic principle of separation bysedimentation allows for thesimultaneous separation of threedifferent, immiscible substances.PIERALISI Vertical Separators makeuse of this three-phase separationregime. None of the alternativeprinciples mentioned above canachieve this result. Sedimentation isthe physical process wherebysuspensions and emulsions (or acombination of both) areexposed to gravitational force,either the earth’s gravity or byusing a centrifuge. By applying g-force, the droplets and/orparticles acquire settling velocity (vg)and are sent to the bottom/wall ofthe container/centrifuge bowl.

Settling velocity (vg) increases with:• bigger particle diameter,• higher density difference,• lower dynamic viscosity of the fluid

environment.

Settling velocity can be estimated viaa well-known equation known asStokes’ Law:

Sedimentation is used in manyindustrial processes where it isnecessary to separate substancesthat are mixed together (dispersion).With a suitable recipient and thetime needed to complete thesedimentation process, the two ormore substances with differentdensities will be separated (stratified)

within the recipient, the lightestgoing to the surface, the heaviest tothe bottom. (See illustration below)

ADVANTAGES

INCREASING CAPACITY

Separationof

The Principles

Separator FPC18technical drawing

Separator S300technical drawing

Modified Stokes’ Law

N.B. Stokes’ Law can of course only be usedwhen the settling process takes place underconditions when the Reynolds-No. is below0,25. For higher Reynolds-No., the Grassmannsystem has to be used, which takes advantageof two dimension-less parameters: theArchimedes number and the Omega number.

• Flotation: based on physical-chemical behaviour, i.e. surfacetension. In many cases centrifugalsedimentation and anothercomplementary technology arecombined to achieve the requiredprocess results.

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Pieralisi Vertical Separators combine very high rotational speed, a unique design and special materials. They generate a very highcentrifugal force which, when used for sedimentation purposes, ensures extremely efficient equipment. The mixture to beseparated is forced through a conical disc stack, where multi-layer sedimentation takes place. The separation happens veryquickly as the mixture passes through the parallel thin channels of the disc stack. A medium-sized Disc-Stack Separator, whenusing high centrifugal force, can be compared to the efficiency of a sedimentation tank with a surface area of 60,000 m2, thesame size as 10 football fields. In technical terms, this separator hosts an “equivalent settling area” of 60,000 m2 .

Construction materialsThe structural parts of the bowl aremade of special stainless steel, theinside parts in contact with theproduct are made of suitablematerials for the processingenvironment: stainless steel, brassor bronze. The housing of theVertical Separator is in stainlesssteel, aluminium, or cast iron. The gear box is made of cast ironor cast iron coated with stainlesssteel. The gasket material is alwaysselected according to the process.

TransmissionThe movement is always generatedby an electric motor and istransmitted by means of:• clutch and worm gear,

• flexible coupling worm gear,• set of pulleys and flat belt,• rigid coupling and frequency drive.A special transmission version makesuse of a high-speed motor coupleddirectly to the vertical shaft.

Feeding and discharge of process liquidsThe mixture generally is fed in througha stationary feed pipe in the centre ofthe bowl. The separated liquid may bedischarged from the Vertical Separatorby an overflow or by a built-incentripetal pump.

DESIGN FEATURES

SPECIAL VERSIONS

HOW DOES IT WORK?

Thousands of “g”s are produced in thebowl of the Disc Stack Separator, thecentrifugal force being the product ofthe high rotational speed and the largesize of the bowl. The rotation isgenerated by an electric motorconnected to the horizontal shaft bymeans of an elastic coupling or clutch.Thanks to the gear ratio produced byspecially-designed gears, the movementis transferred to the vertical shaft. The bowl is assembled on the conicaltop-end of the vertical shaft. The processing liquid is fed into thecentre of the bowl through thestationary feed pipe. Subsequently theinflow is accelerated by means ofspecially-designed accelerators, forced

PieralisiVertical

Separators

in the first instance to the perimeter ofthe bowl, and then through the discswhere multi-layer separation takesplace. The separated liquid(s) flow tothe top of the bowl where they are

discharged by overflow or by centripetalpumps. The solids captured via thedescribed settling process are collectedat the perimeter of the bowl, and thendischarged intermittently. This discharge

is activated by ahydraulic systemlocated underneaththe separation area.In essence, thesolids aredischarged viaopenings at theperimeter of thebowl which areopened and closedby the down- andupwards movementof either a slidingpiston or bowlbottom (see picture).

Feed

Paring disc “light“ phase

Paring disc “heavy“ phase

DistributorDisc stack

Sludge space

Ring valve

Operating liquidDistributor disc

Sludge ports

Outlet “light“ phase

Outlet “heavy“ phaseSECTIONOF A BOWL

Sanitary versionSpecially-designed all-stainless-steelSeparators, designed to be usedwith a CIP cycle for cleaning

purposes. This version incorporatesa so-called “gap-optimised” design toallow for easy flushig of all criticalsections.

ATEX versionSpecially-designed and certifiedVertical Separators, designed to beinstalled in hazardous areas and forthe treatment of potentiallyinflammable products, i.e.Separators complying with II2G EExcp IIB TB4. These separators can bepurged with nitrogen to minimise therisk of ignition and to fulfil ATEXrequirements.

Hermetic versionHydro-hermetic device installedinside the bowl, designed to ensurethat contact with the surroundingenvironment is avoided, and toprevent oxidation and gas leaks.

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Vertical Disc-Stack Separators are normally designed for one type of separation only, but in some cases, more versatileversions are available that can carry out two different types of separation. Below is a list of the range of disc stacks and bowldesigns used for different types of separation.

PIERALISI Disc-Stack Separators are able to simultaneously process dispersions of two liquids and one solid.The Pieralisi product range offers two main equipment solutions: one with solids retention (requiring manual cleaning) known asthe S-Type, and the other with automatic, intermittent solids discharge, known as the FPC-Type. Four different sizes areavailable for both types of equipment. The tables below show types and sizes, with some general indications of dimensions.

Applicationsand Technical

Features

Environmental Processes� treatment and disposal processes of sludge from municipal and industrial waste water � drying of animal slurry � drying of biomass � thermal sludge dryingChemical Processes� production processes involving intermediate or end products and integrated recycling and recovery processes � processes within HDPE, PVC and PP polymer production � production processes for thepharmaceutical and biotech sector � minerals and ores production processes� production processes for non-fossil fuels,such as biodiesel and ethanol

Recycling� treatment processes for drilling mud � treatment and recovery processes forindustrial fluids � recycling of polymers and their respective recyclables � recycling of service water in industrialprocessesOleo-chemistry� production processes for oleo-chemistryderivates � refining processes for ediblevegetable oils, excluding olive oilMineral- Fuel and Lube Oils Processes� purification and conditioning of fuels� purification of lube oils � treatment and recovery of mineral andfuel oils � treatment of slop-oils from

AREAS OF APPLICATION FOR PIERALISI SEPARATION SOLUTIONS

refineries and lagoons, of slops from lubeoils, of bilge waterAnimal-Based Products� treatment of by-products from the fish-processing and meat-processingindustriesFood Production� processing and recovery of non-liquid food products � processing of citrus fruit � wine and sugar processing � recycling of food-related productsDairy Products and Juices� production processes of dairy and cheese products � recycling of relatedwaste materials � processing of fruit andvegetable juices.

CLARIFICATION PURIFICATION (SEPARATION) CONCENTRATION (SKIMMING)

Separation of suspended particles from aliquid (e.g. fruit juices, cell biomass).

Concentration of a light liquid dispersedthroughout a heavy liquid (e.g. skimming ofcream from milk).Simultaneous separation of solids is also possible.

Separation of a heavy liquid from a main lightliquid (e.g. separation of water fromlubricating oil).Simultaneous separation of solids is also possible.

SEPARATORS WITH SOLIDS RETAINING BOWL SEPARATORS WITH AUTOMATIC DISCHARGE

5

S200

11

S250

25

S300

40

S400

9

FPC 6

14

FPC 12

24

FPC 18

38

2 6 8 12 4 7 12 16

7600 6400 6400 5800 7100 6500 6400 5800

5000 8000 30000 50000 8000 16000 30000 50000

1,0 x 0,7 x 1,2 1,2 x 0,8 x 1,4 1,5 x 0,8 x 1,7 1,7 x 1,0 x 2,0 1,3 x 0,9 x 1,4 1,6 x 1,2 x 1,4 1,7 x 1,3 x 1,7 1,8 x 1,4 x 1,9

300 500 950 1600 1100 1400 2000 2600

FPC 24Type

Bowl Volume [L]

Sludge Space Volume [L]

Bowl Speed [rpm] max.

Hydraulic Capacity [L/h]

Dimension L x W x H [m]

Mass [kg]

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Separators for

STEAM

CONDENSATE

H 3 O P 4

H O a N

PROCESS-W.

STEAM

GUMS

CHILLED W.

DEGUMMED OIL

GUMS

HO

LD

ING

T

AN

K

BUFFER TANK

WASH-W. RECYCLING

WASH- WATER

% 0 5

% 0 5 FLASH DRYING

VACUUM

CONDENSATE

CRUDE OIL

FILTER M M

M

GU

M C

ON

DIT

ION

ING

WASTE WASH-W

GUM SEPARATION

WASHING

DYN. MIXER

DYN. MIXER

STAT. MIXER

STEAM GENERATOR

POTABLEWATER

WATER OUTLET

SHELL AND TUBE HEAT EXCHANGER

M CLEAN SLOP OIL

M70

HOTWATER

inv

inv

SOLIDSOUTLET

DE-EMULSIFIERDOSING UNIT

PUMPING SKID

UNTREATEDSLOP OIL

SLOP OIL TO BE TREATED

SERVICEWATER

HEAT EXCHANGER

WATER TREATMENT

OILTANK WATER TANK

SLOP OILS

VEGETABLE OILS:DegummingNeutralizationWashing

BIODIESEL

Biodiesel - Slop oils - Vegetable oils

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