alphasep coalescers

Coalescers

www.hatltd.comDS-CD-01 Rev 3

AlphaSEP® DESIGN SHEET

OVERVIEW

There are numerous industrial applications requiring effective physical separation oftwo process liquids. HAT has developed a number of AlphaSEP™ Coalescers tohandle a wide range of duties from severe fouling or viscous service through to finepolishing of clean, light liquids.

Standard Types: FP Flat Plate Coalescers50 – 150 m2/m3 Interface Area

MP Matrix Pack Coalescers150 – 350 m2/m3 Interface Area

High Performance Types: LP Pack Coalescers433 m2/m3 Interface Area

DM Dual Media MeshCoalescers750 m2/m3 Interface Area

CC Cartridge Coalescers>1000 m2/m3 Interface Area

Plate Coalescers



Mixtures of immiscible liquids can generally be separated by a process of settling asa result of the density difference between the two phases. However gravitationalsettling becomes increasingly difficult as the droplet size of the dispersed phasedecreases. The settling process can be enhanced considerably by passing thedispersion through a suitable coalescer pack.

HAT’s AlphaSEP™ FP Flat Plate Coalescer Packs are specifically designed to beused as effective coalescers in dirty liquid-liquid service where a level of phaseseparation is required that cannot be obtained in an empty, gravity separator.Coalescer style, face velocity and configuration will depend on the specificapplication.

TYPICAL ARRANGEMENT OF SEPARATOR VESSEL

Liquid-liquid separator vessels are usually arranged horizontally as shown above.The coalescer pack is used to enhance the separation of liquid dispersions andconsists of angled, flat metal plates with a spacing and style to suit serviceconditions. Generally a 45o slope is used, but this can be increased to 60o forparticularly severe fouling service to ensure any solids fall from the plates to avoidplugging.

COALESCERPACK

Dispersion

Heavy Phase Outlet

Light Phase

Plate Coalescers



Plate spacing is typically 15 – 25mm (giving a bulk surface area between 75 and125 m2/m3), standard pack length is 1000mm and the complete pack is assembledusing a modular system from sub-assemblies. These sub-assemblies are designedto pass through vessel manways and be easily bolted together within the vessel.Unlike other manufacturers, HAT does not normally supply loose panel systemsunless specifically requested, due to the added complexity and lower mechanicalintegrity.

Several styles of AlphaSEP FP packs are available as illustrated below.

Type FP-A

This has the simplestconstruction, being blocksmeasuring 300 x 300mmface area stacked in adiamond pattern.However, the exit pathsfor the phases and solidsare longer so this style isgenerally used for clean,coarse separation.

Type FP-B

A more advanced designof pack, again using 300 x300mm modules, butstacked in a squarepattern. This allows eachrow of packs to bereversed giving thecharacteristic ‘fishbone’pattern, which providesdrainage channels for thedifferent phases andsolids.

Type FP-C

Our most sophisticatedpack constructed fromtrapezoidal modules inwhich the plates are alsoprovided with self-cleaninggutters ensuring thatsolids are depositedbehind the pack ratherthan below it as with theother common designs.The mechanical integrity isalso very high.

Dispersions of droplets sized over 1000 microns tend to be very unstable andseparate rapidly under gravity. Dispersions of droplets sized below 10 microns tendto be very stable and do not easily separate. Flat plate coalescers as shown aboveare very effective in coalescing all droplets as small as 100 microns into dropletsgreater than 1000 microns.

Plate Coalescers



Flat Plate Coalescers operate on the basis of Stokes Law, and are sized to ensurelaminar flow between the plates.

v = { g . d2 . (1 – 2) } / 18 μ

Where:

v = droplet terminal velocity, m/sg = acceleration due to gravity, m/s2

d = droplet diameter, m1 = bulk liquid density, kg/m3

2 = droplet fluid density, kg/m3

μ= viscosity of bulk liquid, kg/m.s

Depending on the degree of separation required, this generally means a liquidvelocity between 1.0 - 3.0 m/min is acceptable using standard plate spacings, tocapture and coalesce the target droplet size.

HAT can simulate most process conditions and / or offer advice on customerdesigned installations.

Oil in Water PredictionInlet and Outlet Droplet Distributions

0

0.00002

0.00004

0.00006

0.00008

0.0001

0.00012

0.00014

0 33 67 100 133 167 200 233 267 300 333 367 400

Droplet Size Distribution, Microns

Rel

ativ

eV

olu

me,

m3/

m3

Inlet

Outlet

Fig 1. Typical Performance Prediction Curve

Matrix Coalescers




HAT’s AlphaSEP™ MP Matrix Coalescer Packs are specifically designed to be usedas effective coalescers in light fouling liquid-liquid service where a level of phaseseparation is required that cannot be obtained in an empty, gravity separator.Coalescer style, face velocity and configuration will depend on the specificapplication. The packs can also be used in gas-liquid service for foam breakingapplications.

Liquid-liquid matrix coalescer packs are usually arranged vertically as shown above.The pack consists of corrugated metal plates with a spacing and style to suit serviceconditions.

Pack surface areas are typically 125 and 250 m2/m3, standard pack depth is 600mmand the complete pack is assembled using a modular system from sub-assemblies.These sub-assemblies are designed to pass through vessel manways and be easilystacked together within the vessel.

Most packs are supplied in stainless steel, but they are also available in exoticalloys as well as stable plastics such as PVDF.

Matrix Coalescers



Sizing

Dispersions of droplets sized over 1000 microns tend to be very unstable andseparate rapidly under gravity. Dispersions of droplets sized below 10 microns tendto be very stable and do not easily separate. Matrix coalescers as shown above arevery effective in coalescing all droplets as small as 50 microns into droplets greaterthan 1000 microns.

The matrix pack used for liquid-liquid coalescing is similar to that used for otherapplications such as structured packing in absorber and distillation towers, and tostatic mixing elements. It is the velocity through the pack that is critical indetermining the effectiveness for each application. In liquid-liquid separation forinstance, at low Reynolds numbers the dispersed liquid droplets will, due to thefrequent direction changes and high surface area, bump into each other and themetal surfaces and coalesce into larger drops which easily separate. As the velocityrises however and the flow becomes more turbulent, these larger droplets will betorn apart and any dispersed liquid layer on the metal surface will be dragged from itand also broken up into a dispersion. In effect the pack becomes an effective staticmixer.

Depending on the degree of separation required and the characteristics of thedispersion, the liquid flux rate should typically be kept below 2 m3/m2.minute forsizing these coalescer packs.

Pack Model Description Applications

MP-250-S 250 m2/m3 surface area with45° plate angle

Best performance in clean service

MP-250-H 250 m2/m3 surface area with60° plate angle

As above, will tolerate some lightfouling

MP-125-S 125 m2/m3 surface area with45° plate angle

Lower pressure dop suits clean,viscous liquids or foam breaking

MP-125-H 125 m2/m3 surface area with60° plate angle

As above, with light fouling

Polypropylene Packs




HAT’s AlphaSEP™ LP Polypropylene Coalescer Packs are specifically designed tobe used as effective coalescers in dirty oily water service where a level of phaseseparation is required that cannot be obtained in a gravity or plate separator.Coalescer arrangement, face velocity and configuration will depend on the specificapplication.

TYPICAL ARRANGEMENT OF LP COALESCER

Inlet Zone

SedimentCollector

Inlet Baffles SedimentCollector

Outlet Zone

CoalescerPack

Polypropylene Packs



Selecting the right coalescing media for the duty depends on many factors withinitial consideration given to the droplet size range in the dispersion and the targetseparation performance.

Droplet Diameter Range Media Type Performance> 1000 micron None 80 – 90% Removal

100 – 1000 micron Flat Plate Pack 90-95% Removal50 – 500 micron Matrix Pack > 95% removal20 – 300 micron LP High Surface Pack >99% Removal10 – 100 micron Dual Media Mesh Pack > 99% Removal

5 – 20 micron Cartridge Coalescer > 99.9% Removal< 3 – 5 micron Specialist Filter N/A

Performance indications for ideally designed vessel and system in a single stage

The high surface area media used in HAT’s LP Coalescers easily passes the EPAMethod 413.2 test for removal of oil droplets 20 microns and larger. Testing at theDanish Institute of Technology confirmed that the media beats the efficiencyrequirements of the European Standard CEN EN 858-1 for >99.9% oil removalregardless of droplet dize.

While removing oil efficiently, the LP media also shows superior resistance toplugging by sludge and iron deposits commonly found in oily water. The roundedrod design of the pack allows self cleaning. As deposits form on the polypropylenesurfaces they quickly reach a critical mass that forces them to slough off the slick,vertical rods and fall into the sludge compartment below the media.

The AlphaSEP LP media has a specific surface area of 433 m2/m3. This can becompared with typical flat plate packs at 100 m2/m3 and matrix packs of 250 m2/m3.

Installation Options

For gravity flow systems commonly a rectangular (non-pressurised) separatordesign is used, whereas for pressurised systems a horizontal, cylindrical separatorwould be installed. In both cases the vessel is divided in to several zones:

Inlet Zone

Where the fluid first enters the vessel a section is allowed for fluid calming, solidssettling, and flow distribution to the next zone. Inlet devices would typically includepipe or trough deflectors or cyclones to encourage maximum initial solidsseparation. A system of baffles would then distribute the fluid for the nextseparation zone.

Polypropylene Packs



Separation Zone

This is where the bulk liquids flow through the coalescer pack and the separation isachieved. The primary factor here is to achieve the correct bulk velocity – too highand the residence time will be insufficient for all the droplets to be captured, alsothere could be a danger of turbulent flow through the media which would undo anyseparation achieved. A Reynolds number around 500 achieves maximumperformance, although on some systems it may be higher where the performance isless critical e.g. the discharge is not into public water.

The packs may be placed across the axis of the vessel to achieve axial flow of theliquid through the media or, where a greater area is required, it may be placed alongthe central axis and the liquid sent in a cross flow arrangement.

Axial Flow Cross Flow

A sediment collection system should be placed under the coalescer pack to removethe solids occasionally. For pressurised systems where access to the pack is morecomplex, consideration should be given to a liquid or gas spray/sparge system tooccasionally aid pack cleaning should it be necessary.

Outlet Zone

The outlet zone is a quiescent, settling zone where the 2 phases are physicallyseparated by means of a skimmer device such as a weir or an overflow bucket ortrough. The size and depth of the skimmer depends on the relative quantity of thelight phase liquid.

Polypropylene Packs



Sizing and Performance

The following curves are typical performance predictions for a pressurised oily watertreatment system where the inlet oil droplet distribution is based on smaller particlesthan would be found in a gravity based system.

Where a droplet distribution is available we can calculate more accurateperformance projections.

Residual Oil in Water

0

10

20

30

40

50

60

70

0 5 10 15 20

Velocity, USgpm/ft²

Residual ppmv

0.80 sg Oil

0.85 sg Oil

0.90 sg Oil

Mesh Coalescers



Mixtures of immiscible liquids can generally be separated by a process of settling asa result of the density difference between the two phases. However gravitationalsettling becomes increasingly difficult as the droplet size of the dispersed phasedecreases. The settling process can be enhanced considerably by passing thedispersion through a suitable coalescer pad.

HAT’s AlphaSEP™ DM Knitted Dual Media Mesh Pads are effective coalescers inboth liquid-liquid and vapour-liquid service. Mesh pad style, face velocity andconfiguration will depend on the specific application.

TYPICAL ARRANGEMENT OF SEPARATOR VESSEL

Liquid-liquid separator vessels are usually arranged horizontally as shown above.The coalescer pack is used to enhance the separation of liquid dispersions andconsists of layers of composite materials chosen to suit service conditions.Generally a metallic wire monofilament is co-knitted with a fibre material which hasa surface which is preferentially wetted by the dispersed phase. For hydrocarbon inwater dispersions, a thermoplastic fibre is preferred and for water in hydrocarbondispersion a specially treated glass fibre is used. It is therefore always important toknow which is the dispersed phase in the mixture. Whilst the right choice of fibrematerial ensures maximum collection of the dispersed droplets, the effect of thedifference in surface free energies of the monofilament wire and fibre materials inclose proximity promotes droplet coalescence.

DM COALESCER

Dispersion

Heavy Phase Outlet

Light Phase

Mesh Coalescers



TYPICAL DM 25 50 25 75 25 25 75 25 50 25

COALESCERPACK Spacer Rods

Style "DS" Mesh(Drainage Layers)

“DM” CompositeMesh(Coalescing Layers)

Retainer Grid Support Retainer Grid

Screen

Dispersions of droplets sized over 1000 microns tend to be very unstable andseparate rapidly under gravity. Dispersions of droplets sized below 10 microns tendto be very stable and do not easily separate. DM mesh coalescers as shown aboveare very effective in coalescing all droplets as small as 30 microns into dropletsgreater than 1000 microns. The coalescer velocity will be typically less than 1 m/minand the pad should be sized as follows:-

Minimum Effective Face Area (Af ) = 1.44 * Q * {L /(H -L)}0.5 (m2)

where: Q = Volumetric flowrate (m3/min)L = Light phase density (kg/m3)H = Heavy phase density (kg/m3)

Generally similar principles apply to coalescer pads in vertical liquid-liquid extractorcolumns. A 150mm thick pad of DM composite knitted wire mesh, preferentiallywetted by the dispersed phase, installed above the packed section will coalescedispersed phase droplets hence improving phase separation and reducingentrainment.

For performance predictions please refer to HAT’s engineers.

alphasep coalescers

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