PIERALISI Decanter Technology1

PIERALISI Centrifuge Training

Centrifuges for Solid-Liquid, Liquid-Liquid and 3 Phase Separation3-Phase Separation

Decanter:A continuous settling centrifugeA continuous settling centrifuge

Presented by:Prof. Dipl.-Ing. M. H. Kopf

July 2010 1PIERALISI Decanter Technology

Decanter: a continuous settling centrifugeWhat we are talking about:What we are talking about:

2PIERALISI Decanter TechnologyJuly 2010

Decanter: a continuous settling centrifugeOverview and basic principle:

A DECANTER is also named solid-bowl conveyor centrifuge. The latter name already describes very well the main parts of the machine and their functions.

Overview and basic principle:

y p

BowlCentrate Discharge Ch b

ConveyorScraper Scraper

DriveChamber

y

Gear Box

Solids Discharge Feed PipeSetting

Differential speed

3

chamberDifferential speed

July 2010 PIERALISI Decanter Technology

Decanter: a continuous settling centrifugeProcess technologies with a decanter:

Clarifying of liquids with simultaneous +

Process technologies with a decanter:

settling of feed-solids

Sludge thickening +

Dewatering of crystalline solids,sludges and pasty solids

+

Wet classifying for particulate solids

S ti f lid

+

Sorting of solids(using a special, density-adapted fluid)

3 Ph ti

+

+3-Phase-separation, (liquid / liquid / solid dispersions)

+

++

4

Extraction +

July 2010 PIERALISI Decanter Technology


You could think of a decanter as the result of a geometry-change with which the settling area of a flat settling tank has be transformed to a concentrical cylinder wrapped around


g y ppa center-line.

Feed Solids discharge

Liquid discharge

5July 2010 PIERALISI Decanter Technology

Decanter: a continuous settling centrifugeOverview and basic principle

You could think of a decanter as the result of a geometry-change with which the settling area of a flat settling tank has be transformed to a concentrical cylinder wrapped around

Overview and basic principle

g y ppa center-line.

Doing that, the solids-scraper shown below is transformed to a conveyor.

Conveyor FeedFeed

Solids discharge

Liquid discharge

6July 2010 PIERALISI Decanter Technology


You could think of a decanter as the result of a geometry-change with which the settling area of a flat settling tank has be transformed to a concentrical cylinder with wrapped


g y pparound a center-line.

The “tank-bottom” forms the bowl.

Bowl


Decanter: a continuous settling centrifugeMain parts schematic cross section:Main parts, schematic cross section:


Decanter: a continuous settling centrifugeThe main parts 3 D cut:The main parts, 3- D cut:

BowlBowlEffluent weirs

Solids outlet

Gear-box

Feed inlet

Main drivemotor

Feed tube

motor

Secondary motor(differential speed)


Decanter: a continuous settling centrifugeApplying G force:

As the bowl is rotating a centrifugal acceleration is developed, the effect of which is similar to the gravitational acceleration in the earth field – only the magnitude is very

Applying G-force:

g y g ymuch different.

G-force: > 2.500 x g


Decanter: a continuous settling centrifugeBasic calculations:Basic calculations:

( )ieNiv rrh −=Pond dept

( )Mean radius ( ) 2/rrr iem +=

G-force: C-Valueg

rC2

m rω⋅

=

11

g

PIERALSI Decanter TechnologyJuly 2010

Decanter: a continuous settling centrifugeSizing and scale up: Theory of equivalent settling area ΣSizing and scale-up: Theory of equivalent settling area Σ

The eq i alent settling area Σ is the prod ct of m ltipl ing the settling areaThe equivalent settling area Σ is the product of multiplying the settling areawith the C-value.

Remember: the settling area is the area onto wich particles are settling and on g p gwhich the vector of the driving force stands rectangular.

)r(cylm clr2 ⋅⋅⋅π=Σ

12

)r(cylm m

PIERALISI Decanter TechnologyJuly 2010

Decanter: a continuous settling centrifugeSizing and scale up: The pond volumeSizing and scale-up: The pond volume

Th d l (bl l d) i l l t d i f ti l i ith thThe pond volume (blue colured) is calculated as a circumferrential ring with the:- the inner bowl diameter as outer diameter and- the inner liquid diamter as inner diameter- the length is the cylindr. length as minimum. g y g

( ) cyl2

i2

epond lrrV ⋅−⋅π=


Decanter: a continuous settling centrifugeSizing and scale up: Important remarkSizing and scale-up: Important remark

Si th di t d th l th t b t k i t t f l l ti bSince the diameters and the length to be taken into account for calculation can be varied, i.e. depend on the piont of view and the basic assumptions made, there aredifferent equations calculating for the same parameter.In example we have 7 different calculations to get Σ and at least 3 for the pond-volume.p g p


Decanter: a continuous settling centrifugeDewatering on the conical extension: Crystalline productsDewatering on the conical extension: Crystalline products

C Product:- crystalline particles- rel. low fitration resistance

Conveyor flight

Dewatering:by drainage

Decanter bowl:shallow pond

- by drainage - liquid flows back into the pondthrough the cake porosity

- shallow pond


Decanter: a continuous settling centrifugeDewatering on the conical extension: Sludges and pasty productsDewatering on the conical extension: Sludges and pasty products

Product:C - pasty products - high filtration resistance

Conveyor flight

Dewatering:- by sediment compression - liquid flows to cake surfaceand (if possible) meanders

Decanter bowl:- deep pond

back ito pond.


Decanter: a continuous settling centrifugeInfluences on the separation: Machine based parameter

Bowl diameter:

Influences on the separation: Machine based parameter

pond volume / residence time, max. speed / G-force

Slenderness ration (l/d): ( )length of clarification zone (cyl. Length) /residence time

Geometry of conical extension: yslippage force, torque-level, dewatering-kinetics

Conveyor geometry: y g ypitch, flight-angle, number of flights

Material and surface quality of the bowl and the conveyor flights:q y y gfriction forces / slipping


Decanter: a continuous settling centrifugeInfluences on the solids transport and dewatering: Number of flights

The geometry, e.g. the number of flights is important with respect to the solids conveying Especially for crystalline products the dewatering will be influenced by the

Influences on the solids transport and dewatering: Number of flights

conveying. Especially for crystalline products, the dewatering will be influenced by the cake formation/ geometry in front of the flight.

Rule of thumb: a double flight conveyor decreases the “cake height” by half.

Double flightSingle flight


Decanter: a continuous settling centrifugeInfluences on the separation: Hydraulic lift disc

Discharging pasty products like cell-biomass or sludges often requires a „helping hand“ by employing hydraulic pressure

Influences on the separation: Hydraulic-lift-disc

by employing hydraulic pressure.

This led to the development of the so-called „hydraulic-lift-disc“ (orig. baffle-disc).

The result of using a baffle-disc is both better sludge conveying and higher dry-solids via a press-dewatering.

Radius < neutral

Neutral line

Compressing gap

19

Co p ess g gap


Decanter: a continuous settling centrifugeConveyor design: Baffle Disc and flightsConveyor design: Baffle Disc and flights


Decanter: a continuous settling centrifugeInfluences on the separation: Effluent discharge; 2 and 3 phase

The discharge of effluent via paring device enables for foam-free and gas-free discharge d d f i dj t t f th d d t ll

Influences on the separation: Effluent discharge; 2 and 3-phase

under pressure and for an in-process adjustment of the pond-dept as well.

Heavy phase

Light phase

2-phase, 3-phase, 3-phase,

Light phase

p ,paring disc

p ,conventional

p ,paring device


Decanter: a continuous settling centrifugeInfluences on the separation: Hard surfacingTo comply with the abrasion properties of many solids, a special surface protection is needed.

Influences on the separation: Hard surfacing

Below, the maximum surface protection is shown: Tungsten Carbide Tiles.


Decanter: a continuous settling centrifugeProcess demands: Sealing systems

To comply with the process demands regarding containment, e.g. ATEX regulation, different sealing systems are on the market

Process demands: Sealing systems

g y

Lip-seal

Espey-Seal:

23

Multi-chamber seal


Decanter: a continuous settling centrifugeInfluences on the separation: Operational parameter

Throughput:

Influences on the separation: Operational parameter

g pResidence time of liquid- and solid-phase in the centrifugal field, i.e. the clarification zone and the dewatering zone.

Bowl speed:pG-force, shear-force, vortices

Differential speed (Δn):Solids capacity / residence time, dry-solids, dewatering p y , y , g

Weir or paring-device setting: Pond dept, dry beach,


Decanter: a continuous settling centrifugeInfluences on the separation: Differential speed Δn

Differential speed

I i th diff ti l d lt i

Influences on the separation: Differential speed Δn

Increasing the differential speed results in:

Decreasing of solids residence time in the dewatering zone, increasing of solids capacity (if possible in terms of dewatering kinetics).

Increasing of residual moisture

Increased turbulence in the clarification section, possibly resulting in decreased separation efficiency subsequently demanding a reduced capacity.p y q y g p y

GetriebeGear-boxGetriebe

Planetary gear-box

Gear-box

Differential speed control

Planetary gear-box, 2- or 3-stage

25

1. and 2. Stage


Decanter: a continuous settling centrifugeInfluences on the separation: Differential speed ΔnInfluences on the separation: Differential speed Δn

Gear Box

Getriebe

Pinion

Differential speed Δn: n – nBowl Conveyorinnn PinionBowl −

=Δ


Decanter: a continuous settling centrifugeInfluences on the separation: Differential speed ΔnHow to set differential speed:

Influences on the separation: Differential speed Δn

Variable Δn via a special d i h

Variable Δn via a hydraulic drive (Rotodiff) setting the pinionsecondary motor setting the

pinion speed.(Rotodiff) setting the pinion speed.


Decanter: a continuous settling centrifugeInfluences on the separation: Product based parameter

Density difference of the phases to be separated

Influences on the separation: Product based parameter

y p pSettling velocity, capacity

Particle- or / and droplet-size and shape; PSD,Settling velocity, sediment compressibility, cut-sizeg y, p y,

Physical-chemical properties of the phases involvedMaterials to be used, product sensitivities

Flow behavior and viscosity of the carrying fluidFlow-behavior and viscosity of the carrying fluid

Solids concentration in feedConveyor geometry, capacity

Sediment behaviorflow-behavior, filtering-resistance, torque requirement


Decanter: a continuous settling centrifuge

…need a break…


PIERALISI Decanter Technology1

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