What is a FLEXIFIBER®

Mist Eliminator?A FLEXIFIBER® mist eliminator is a fiber bed into which mistladen gases enter, and out of which emerges a clean gas streamand a separated liquid stream. Fiber packing in the bed is engi-neered to provide extremely high separation efficiencies. Figure1 shows schematically a FLEXIFIBER mist eliminator. As indi-cated, the bed consists of special fibers, which are denselypacked between two screens. Mist-laden gases enter from theside of the bed and pass in a horizontal direction through thebed. Clean gases emerge from the bed and rise to exit from themist eliminator. Separated liquids are directed downwards andtowards the outer screen, and ultimately drain down the outeredge of the bed.

Typical FLEXIFIBER®

Mist Eliminator InstallationsFigures 3. and 4. show typical FLEXIFIBER mist eliminatorinstallations. Basic components of this system are the FLEXI-FIBER element and the vessel. The element consists of two con-centrically oriented cylindrical screens containing packed fibersin the annular area. The screens are connected to a flange at thetop of the element, and the flange in turn is bolted to the tanktube sheet. Mist-laden gases commonly enter the tank at the baseand pass through the bed towards the element core. Separatedliquids drain downwards through the bed, through the drain leg,and are collected at the base of the tank. Clean gases exit at thetop of the vessel.

CLEANGAS TO

VENT

SEPARATEDMIST TO

COLLECTION

MIST LADENGAS

SPECIALFIBER

SCREENS

Figure 1. Single stage vertical FLEXIFIBER® mist eliminator

FLEXIFIBER® mist eliminator type BD with stainless steel cage

FLEXIFIBER® mist eliminator type BD with FRP cage

1

FIBER

FIBER

FIBER

InertialImpaction

BrownianDiffusion

DirectInterception

Figure 2. Mechanisms for mist collection on fibers

2

VAPOR OUT

SUMP FILL

CONSTANT OVERFLOW

CLEANOUT DRAIN

SUMPSKIRT

BASE RING

TUBE SHEET W/DRAIN PIPE

∆P

∆P

VAPOR IN

Figure 4. FLEXIFIBER® mist eliminator for lube oil tank vents on gas orsteam turbines.

PDI

PDI

Clean Gas Out

Mist LadenGas In

Overflow

Tube Sheet

FLEXIFIBER® mist eliminator Type BD - SFF

Drain Leg With CollectedLiquid

Figure 3. Typical FLEXIFIBER® mist eliminator assembly (forward flow installation).

Basic Mechanism of Mist Separation

The three basic mechanisms for mist separation can best bedescribed by considering the following. A gas stream containingmist particles moves towards a fiber which is perpendicular to thedirection of flow. As depicted in figure 2, the gas streamlinesaround the fiber. The momentum of larger particles, greater thanabout 1 micron, makes them deviate from the gas streamline andhead for the fiber. The larger particles are thus separated throughthe principle of inertial impaction.

Smaller particles, generally smaller than one micron in diameter,tend to follow the gas streamline around obstacles. However, asshown in figure 2, they show considerable Brownian movementand thus diffuse from the gas to the surface of the fiber. A particlehaving a 0.1 micron diameter will have approximately five timesthe Brownian displacement of a 1.0 micron particle and about 15times the Brownian displacement of a 5.0 micron particle.Through proper fiber bed design, submicron particles can thus beeffectively collected. With Brownian diffusion, the collection effi-ciency increases as the particle size decreases because theBrownian displacement actually increases with smaller particlesize.

Particles may also be collected by direct interception. The parti-cle may follow a gas streamline and be collected without inertialimpaction or Brownian diffusion if the streamline is relativelyclose to the fiber. Consider a particle with a diameter of 1 micron.If it follows a gas streamline which passes within 0.5 microns ofthe fiber, the particle will touch the fiber and be collected.

The three mechanisms previously discussed make FLEXIFIBERmist eliminators highly efficient mechanical type liquid entrain-ment separators. While their primary purpose is to remove lowmicron and submicron liquid particles, they will also handle largeparticles at higher efficiencies. They can also handle either largequantities of soluble solids or small quantities of insoluble solidsproviding the particles are very small and there is sufficient liquidin the gas stream to flush the solids through the fiber beds. Smallquantities of very large particles can be handled by collection onthe surface of the bed.

3

FLEXIFIBER® Mist Eliminatortype BD (Brownian Diffusion)

Utilizing the Brownian Diffusion mechanism, Type BD is ableto achieve collection efficiencies of up to 99.95% on all sub-micron liquid or soluble solid particles. Type BD elements arenormally cylindrical in shape, and are available in a wide varietyof materials and sizes. Operating pressure drops are normallydesigned in the range of 50 to 500 mm (2-20 inch) W.G. An interesting feature of the Flexifiber bed system is that, withsubmicron particles, the collection efficiencies are actuallyincreased slightly as the gas flow rate through the bed is reduced.This occurs because at reduced flow rates there is a greater expo-sure time to the fibers. Probability of contact of the particles withthe individual fibers through Brownian Movement is thusincreased.

The type BD fiber beds are also constructed using carbon fibersfor applications that involve fluoride concentrations, high pHservice (typically greater than 9-10 depending on temperature),and for some applications that involve the hydroxyl group. Carbonfibers resist corrosion for these applications that typically attackglass fibers. Many times one will see this type of situation in metallurgical acid plants, spent acid plants, ammonia scrubbingapplications, and the digesting of wood pulp.

FLEXIFIBER® Mist Eliminatortype IC (Impaction Cylinder)Utilizing primarily the impaction mechanism, Type IC fiber bedsare designed to capture and collect particles in the 1 to 3 micronrange economically. Collection efficiencies on 1 micron particleswill vary from 90% on liquid mists with a specific gravity of 1.0to 97% on liquid mists with a specific gravity of 1.8. Operatingpressure drops are in the range of 100 to 220 mm (4-9 inch) W.G. Elements are normally cylindrical in shape and available ina variety of materials and sizes.

The type IC-K fiber beds are constructed with a co-knit wiremesh interior consisting of alloy 20 and fiberglass. The type IC-Mfiber beds are constructed with a glass fiber interior. The exteriorof both elements are wrapped with additional alloy mesh to control liquid reintrainment and promote drainage. Using this type of construction allows maximum operating time betweenwashing of sulfates in sulfuric acid drying towers or absorptiontowers which are its primary applications.

TypeIC

Type IC-K

Essentially 100Up to 99.95+

Essentially 100

95 - 99+

85 - 97

50 - 85

50 - 500(2-20)

100 - 250(4 - 10)

125 - 180(5 - 7)

>3<3

>3

1 - 3

1 - 3

0.5 - 1

BrownianDiffusion

ImpactionCylinder

ImpactionPanel

BD

IC

IP

Type

PrimaryCollection

Mechanism

ElementPressure

Dropmm W.G.

(inches W.G.)Efficiency*

(%)Particle Size

(Microns)

CollectionEfficiency

0.03 - 0.2(5 - 40)

1.3 - 1.8(250 - 350)

2.03 - 2.54(400 - 500)

BedVelocitym/sec

(ft./min.)

Table 1. Comparison of FLEXIFIBER® Element Types.

* In H2SO4 Service

Type BD with Carbon Fibers

Type BD with Glass Fibers

4

FLEXIFIBER® Mist Eliminatortype IP (Impaction Panel)

Type IP fiber beds are most commonly used in sulfuric acidplants. Utilizing primarily the impaction mechanism, collec-tionefficiencies on 98% sulfuric acid mist are essentially 100% on allparticles greater than 3 microns, 85 to 99% on all particles 1 to 3microns, and 55 to 85% on all particles 0.5 to 1.0 microns.Operating pressure drops are normally 50 to 170 mm (2-7 inch)W.G. Elements are normally rectangular in shape and are availablein various metals.

The FLEXIFIBER mist eliminator elements cages are available inthe following materials:

• Carbon steel• Stainless steel• Special alloy steel• FRP• Polypropylene• PVDF• PTFE

We use a large variety of special fibers to suit the chemistry ofvarious chemical processes. The pH of collected liquid and itschemical aggressiveness are parameters taken into considerationto determine the proper fiber to be used in FLEXIFIBER misteliminator elements.

100

95

90

85

80

75

70

650

1

45

6

23

0.5 1.0 1.5

MicronsTYPE BD

MicronsTYPE IC

2.0 2.5 0 0.5 1.0 1.5 2.0 2.5

100

95

90

85

80

75

70

65

% Design Flow

Frac

tiona

l Eff

icie

ncy

(%)

% Design Flow

25%

100%

110%

75%

100%

110%

1

2

3

4

5

6

Typical performance curves for FLEXIFIBER® mist eliminators

TypeBD-FRF MK II

TypeIC-SRF

Type IP

TypeBD-SRF MK I

TypeBD-FRF MK I

TYPICAL FLEXIFIBER® APPLICATIONS

SBURNERBOILER

FLEXIFIBER

CONVERTER

FLEXIFIBER

DRYINGTOWER

FLEXIFIBER

STACK

SO2

SO2

H2ONH3

AIR

BLOWER

sulfuric acid

LOCATION PROBLEM FLEXIFIBER®

Drying tower Acid mists foul catalyst and type IC-K orcorrode downstream DEMISTER®

equipment

Interpass Acid mists corrode expensive type BDAbsorption Tower downstream equipment

LOCATION PROBLEM FLEXIFIBER®

Final Acid mists cause air pollution type BDAbsorption Tower or IC-M

Oleum storage SO3 from vents mixes with and loading area moisture to form acid creating type BD

safety in air and corrosionproblems.

LOCATION PROBLEM FLEXIFIBER®

SO 2 Absorber Ammonium sulfite particles type BDare exhausted causing plume and pollution

ammonia scrubber

STACK

HEATEXCHANGER

FLEXIFIBER

DRYINGTOWER

FLEXIFIBER

SBURNER

FLEXIFIBERCONVERTER

OLEUMTOWER

CONVERTERABSORPTIONTOWER FINAL

TOWER8-11% e SO2

TYPICALLY 10%

AIR

BLOWER

5

6

chlorine plant

LOCATION PROBLEM FLEXIFIBER®

Wet end Brine mists foul drying tower type BD and increase sulfuric acidconsumption in drying gas

Wet end H2 gas carries caustic type BD

LOCATION PROBLEM FLEXIFIBER®

Dry End Acid mists corrode type BDcompressor and reduce product quality

LOCATION PROBLEM FLEXIFIBER®

Neutralizer AN is carried out by type BDexhausting gas causing product loss and pollution

Prill tower Visible plume caused by ANsalts in exhaust gas type BD

LOCATION PROBLEM FLEXIFIBER®

Evaporator Product loss and pollution type BD or IC

H20 VAPOR & SALT

ANODE (+)

BRINE

DRYINGTOWERS

CATHODE (-)

Na OHCONVERSIONTO CAUSTIC

H2 H2 TOABSORTION

CI2

CENTRIFUGALRECIPROCATING

COMPRESSOR

LIQUIDSEAL

COMPRESSOR

TOSTORAGE

TOSTORAGE

CELLCOOLERS

WETCI2

DRYCI2

FLEXIFIBERFLEXIFIBER

H2FILTER

DRYCI2

FLEXIFIBER

FLEXIFIBER

LIQUEFACTION

LIQUEFACTION

(Na CI & H20)

ALT.2

ALT.1

STACK STACK STACK

FAN

VENTVENT

NITRICACIDHN03

NEUTRALIZER EVAPORATORCONCENTRATOR

AIR

AMMONIANITRATE

STORAGE

AMMONIANH3

PRILLTOWER

FLEXIFIBERFLEXIFIBERFLEXIFIBER

ammonium nitrate

7

SO3SOURCE

FLEXIFIBER FLEXIFIBER

REACTOR

STACK

ORGANICS

plastic manufacturing

compressed gas

LOCATION PROBLEM FLEXIFIBER®

Curing Ovens Plasticizer vapors condense in type BD and IPExtruders air causing visible plume andInjection Molding product lossCalendering

LOCATION PROBLEM FLEXIFIBER®

Compressor Oil from the lubricating type BD reservoir creates pollutionproblem & decreases lifeof dryers

LOCATION PROBLEM FLEXIFIBER®

Oleum or SO3 SO3 mixes with moisture in air type BDstorage and forming acid creating safety unloading areas and corrosion problems

Before Reactor Sulfuric acid mist in SO3 gas type BDcauses hazy appearance in final product

After Reactor Sulfuric acid mist causes type BDpollution

sulfonation plant

EXTRUDERCOOLINGCHAMBER

COOLING

FAN

STACK

STACK

PLASTICIZERRECOVERY

STORAGE

FAN

CURING OVENPLASTISOLCOATINGAPPLIED

FLEXIFIBER

FLEXIFIBERFLEXIFIBER

FLEXIFIBER

TO COMPRESSORLUBRICATION OIL

RESERVOIR

VENT

AIR

RECOVERED OIL

8

pulp and paper ammonia based sulfite recovery

LOCATION PROBLEM FLEXIFIBER®

After SO2 Cooler Particulate carry-over type BD resulting in severe opacity

LOCATION PROBLEM FLEXIFIBER®

Ammonia Iron catalyst and oil particles type BDFeed Line cause decomposition of the

ammonia andcontamination of the platinum gauze

Air Feed Line Iron catalyst and oil particles cause decomposition of the type BDammonia and contamination of the platinum gauze

LOCATION PROBLEM FLEXIFIBER®

After Waste Loss of platinum burned off type pt filterHeat Boiler the gauze during normal

operation

Tail Gas Nitric acid mist that is carried over from the absorption type IC tower or formed by reaction or BDof NO2 nd H2O corrodes downstream equipment

FLEXIFIBER

NITRIC ACIDPRODUCTS

ABSORPTIONTOWER

LIQUIDSEPARATOR

HEATEXCHANGERCONVERTER

HEATRECOVERY

TRAINSTATICMIXER

VAPORIZER

WATER

LIQUID AMMONIA

G A S E O U S

A M M O N I A

NO2ABATEMENT

DEVICE

AIRFILTER

TURBINE COMPRESSOR

STEAM AIR

FLEXIFIBER

AMMONIAFILTER

FLEXIFIBER

TAIL GASFILTER

FLEXIFIBER

PT.FILTER

SULFURBURNER

DIGESTER

FORTIFICATIONTOWER WOOD CHIPS

FIBER TO PAPERMAKING PROCESS

EVAPORATOR

BLOWTANK

SO2COOLER

SULFURAIR

STACKGAS

COOLER

MULTICLONES

EXHAUSTGAS

RECOVERYBOILER

(NH4)2 SO3 SOLUTIONS

NH4 HSO3SULFONATION

FLEXIFIBER

nitric acid

asphaltLOCATION PROBLEM FLEXIFIBER®

Asphalt Storage Vapors condense in air type BDand loading area causing plume and pollution

LOCATION PROBLEM FLEXIFIBER®

Saturating Vapors and oil mist cause type BDand coating plume and pollution

LOCATION PROBLEM FLEXIFIBER®

Absorption Tower Acid mists cause air pollution type BD or ICproblem

STACK

FLEXIFIBER

FLEXIFIBER

H2FILTER

FLEXIFIBER

H2FILTER

VACUUM BREAKERTANK VENT

STORAGE TANKFROM OTHER

STORAGETANKS

FAN

STORAGE TANK

STACK

FAN

STACK

FAN

HEADERTO OTHERLOADINGNOZZLES

ASPHALT SYSTEMS

PREFILTERASPHALT LOADING RACK

LOADING NOZZLE

ANNULARHOOD

AROUNDNOZZLE

TRUCK

ASPHALT SATURATING AND COATING

ROLL WINDER

ASPHALTSATURATOR

PHOSPHORUS

FLEXIFIBER

STORAGE

BURNER

STACK

HYDRATOR

PHOSPHORICACID PUMP

phosphoric acid

9

10

COMPRESSOR

ABSORBERS

UREASOLUTION

CONCENTRATOR

DECOMPOSERS

STEAM

STORAGE

STACK

FAN

REACTORPRILL

TOWER

AMMONIA NH3

CO2

CARBON DIOXIDE

FLEXIFIBER

FLEXIFIBER

LOCATION PROBLEM FLEXIFIBER®

Carbon dioxide Oil or water carryover type BDCompressor contaminates reaction and

corrodes equipment

Prill tower Visible plume and pollution type BD

LOCATION PROBLEM FLEXIFIBER®

Evaporator Product loss and pollution type BD

urea

OILRESERVOIR

FLEXIFIBER

RECOVEREDOIL

STACK

TURBINE

FLEXIFIBER

RECOVEREDOIL

STACK

Crankcase ventor Exhaust

Recip, or centrifugalcompressor, vacuum pump

LOCATION PROBLEM FLEXIFIBER®

Turbine oil reservoir vent line Visible emission plume type BDcompressor crankcase vent line along with loss of lube oilgearbox vent line resulting in oil coating vacuum pump exhaust equipment, roofs, and creating

safety hazards

power generation

KOCH-OTTO YORK®

Design & Service Leader in Separations Technology.

©2002 KOCH-OTTO YORK®, A Koch-Glitsch Business GroupDEMISTER®, FLEXICHEVRON® and FLEXIFIBER® are registered trademarks. COALEX™ , YORKMESH™, YORK-AXIFLOW™, SPIRAFLOW™ and DEMISTER-PLUS™ are trademarks for our mist eliminators.

All data in this brochure are for general information only and are based ontests carried out under conditions which may or may not apply to yourrequirements. No warranties or guarantees are expressed or implied. Noinformation contained in this brochure constitutes an invitation to infringe anypatent, whether now issued or issued hereafter. All descriptions and specifications are subject to change without notice.

Printed in the USA.Bulletin FF5603-2 5M0502B Printed in U.S.A.

©Copyright 2002 Koch-Otto York

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