1

Scientific & Technical ReportImprove Hydrocarbon Condensate Dehydration Performance –Diagnostics and SolutionsGas Processors Association (GPA) Europe Spring Conference25-27 May 2011, Copenhagen

Olivier Trifilieff (olivier_trifilieff@europe.pall.com)Thomas H. Wines, Ph.D. (tom_wines@pall.com)Fabrice Daire, Ph.D. (fabrice_daire@europe.pall.com)Pall Corporation

AbstractHydrocarbon condensate separated from naturalgas carries varying concentrations of impuritiesin the form of water, salts and solids. The effectsof these contaminants can be severe and costly to the condensate stabilization plant andthe export pipeline. Problems that have beenencountered include off-spec condensate andfinal products, compromised plant performanceand maintenance issues including corrosion andfouling of equipment by solid deposits.

Improving the condensate dehydration or‘dewatering’ step requires a good understandingof the nature of the contaminants, as well as thefeatures and the limitations of the separationtechnologies that are used to eliminate these contaminants.

Analytical means and field methods are availablein the industry to evaluate contaminants and todiagnose separation problems in the field. Resultsfrom field surveys highlight that water carryoverfrom existing separators can be significant.Condensate dehydration is often made difficultdue to the formation of stable condensate/wateremulsions caused by the presence of surfactants

such as hydrate inhibitors and corrosioninhibitors that lower the interfacial tension.

Various separation technologies are available toeliminate water from unstabilized condensate.The selection of the appropriate technologyshould be evaluated with care to ensure that it is capable of separating potentially stable emulsions. The evaluation should also considerits maintainability, running cost and investmentcost.

The use of high efficiency polymeric cartridgecoalescers is an effective and economical wayto improve the condensate dehydration step dueto their ability to separate difficult emulsions. Thistechnology features several advantages includingno need for chemicals nor utilities to aid theseparation. The implementation of cartridge coalescers involves certain design considerationsrelated to the presence of solid impurities andthe potential of degassing. Commercial experienceillustrates that the use of this advanced coalescertechnology has been proven as an effective solution to optimize low performance condensatedehydration systems.

IntroductionHydrocarbon Condensate produced with naturalgas increases the profitability of gas developmentprojects. The condensate will be used or marketedunder various forms depending on the productionrate, composition, and available downstreammarkets and transportation network. It can beused as a fuel or blended with crude oil to

increase its API density. It can be fractionatedinto various marketable hydrocarbon productssuch as ethane, propane or LPG (LiquefiedPetroleum Gas) and Natural Gasoline (alsoreferred to as C5+, condensate or naphtha).These products are sold as final products or asfeed stocks to the petrochemical or refining

FCGPAEN

2

Impact of Ineffective Condensate Dehydration

industries. Hydrocarbon condensate that do notrequire any specific processing can be directlysent to the export pipeline; this is typically thecase at offshore production platforms. At onshoreproduction facilities condensate is usually treatedby a stabilization process prior to export. Thisoperation aims at reducing the vapour pressureof the condensate (natural gasoline) by eliminatingthe light fractions to make it safe for storage atatmospheric conditions and for transportation 1,2,3.While a stabilization plant usually involves a single tower process, the condensate may alsogo through a more extensive fractionationprocess to split the lightest hydrocarbon constituents into separate final products. Thenumber and type of columns in the fractionationplant is dependent on the downstream marketsrequirements and the feed condensate composition.

The unstabilized condensate separated from thegas at the production separator carries varyingconcentrations of formation water that is alsosometimes called ‘brine’ due to its intrinsic salinity caused by dissolved salts. The condensatetypically has particulate contaminant present aswell. The effects of these contaminants can besevere and costly to the condensate stabilization

plant and the export pipeline. Problems thathave been encountered include off-spec condensate and final products, poor plant reliability, compromised plant performance andmaintenance issues including corrosion and fouling of equipment by solid deposits.

The dehydration or 'dewatering' of the unstabilized condensate is therefore a necessarystep in processing or transporting hydrocarboncondensate to reduce the ingression of water,salts and solids to as low levels as possible.Hence the dehydration step requires a carefulevaluation of the condensate/water separationtechnology. The formation of stable condensate/water emulsions is a very common challenge thatcan make some separation technologies ineffective in eliminating water down to therequested specification. Improving the condensate dehydration step requires a goodunderstanding of the nature of the contaminantsthat are present in the unstabilized condensateand the analytical means to diagnose separationproblems, as well as a good understanding ofthe features and the limitations of the separationtechnologies that are used to eliminate these contaminants.

The presence of salty, acidic water and solid particulate in the unstabilized condensate isknown to cause various problems in the stabilization plant or in the export pipeline. Fieldexperience in various regions of the world hasshown that the separation of the water phasefrom the condensate can be problematic andrequire specialized equipment. Even though thecondensate viscosity is low and the density dif-ference with water is high, other impurities tendto create stable condensate/water emulsions thatare difficult to separate efficiently.

Literature reports little about problems that operators can experience as consequences ofineffective condensate dehydration. However discussions in the field with operators in theMiddle East, North Africa, Australia and NorthAmerica have reported that several of the following consequences may arise due to water

carryover that contains dissolved salts, and/orsolids:

• Plant upsets and reduced stability of the plantoperation

• Quality issues of the final products such asgasoline and LPG and possible need toreprocess

• Excessive corrosion and deposits inside thestabilizer and re-boiler 4, as illustrated in Figures1 and 2 on the next page

• Increased power consumption due to theingression of excessive levels of water and lossof heat transfer caused by contaminantdeposits

• Frequent shutdown of the stabilization trainfor cleaning purposes, causing a drop in pro-duction and hence a loss of revenue if the flowrate can not be compensated by the other sta-bilization trains

3

The presence of water in the stabilized condensatecan also create corrosion products in the exportcondensate storage tank and in the exportpipeline, also referred to as ‘black powder’ particles. Corrosion of the export pipeline may

also represent a major integrity issue that couldlead to premature replacement of some sectionsof the pipeline if left unattended. Finally, off-specification products can cause issues at the enduser's plant, and complaints.

The cost of ineffective condensate dehydrationis highly dependent on the magnitude of theproblems and the size of the stabilization plant,however it is not uncommon that small plantswith a daily production of few thousands barrelsof unstabilized condensate experience severalhundred thousands of US Dollars of annual lossesof revenues, as reported in a case history below.In the condensate export pipeline, impurities willprimarily affect the integrity of the pipeline itselfdue to the corrosion of the inner walls, when thepipeline is not made of lined or cladded steels.

Typical Contaminants in Hydrocarbon Condensate and Diagnostic Methods

Contaminants found in the unstabilized condensateinclude free, emulsified and dissolved water, salts,acidic components, corrosion inhibitors, hydrateinhibitors (Mono Ethylene Glycol (MEG),methanol, and Kinetic Hydrate Inhibitors), andsolid particles (corrosion products, sand) andsolid-like particles (waxes, gels). Water, salts andparticles impact on the stabilizer operation andthe export pipeline by creating the above mentioned issues so eliminating them is of paramount importance to ensure that these assetsare protected efficiently. This section introducessome analytical methods available in the industrythat can be used to diagnose and quantify theseimpurities.

The impurities that mostly affect the water separation are the corrosion inhibitors, MEG ormethanol as they act as surfactants lowering theInterfacial Tension (IFT) and creating stableemulsions that cause water carryover. Results

from field surveys are detailed below and showthat water carryover is a common issue from various types of separators.

Water in condensate downstream of inlet separators is typically present in concentrationsvarying from few hundreds ppmw (parts per million by weight) up to 5%. The salinity of thewater contamination is determined by the formation water and also varies significantly froma few hundred ppm up to few hundred thousands ppm. Quality specifications of thedehydrated condensate prior to the stabilizer orprior to the export pipeline are project dependentand typically show free water concentrationsranging from <10 ppmv (parts per million byvolume) to <100 ppmv. A very efficient condensate dehydration step also has the advantage of maximizing the recovery of MEGfor its subsequent regeneration, when it is present.

Figure 1:Salt deposits in de-ethanizer reboilertop tubesheetbefore (left) andafter (right) cleaning(by courtesy ofCrew Energy Inc.)

Figure 2:Deposits collectedfrom reboiler tubesat Middle East plant

4

Evaluating Water ConcentrationWater as a contaminant in hydrocarbon liquids hasbeen classified into different categories usually asfree, emulsified, dissolved and total water.

• Free Water: water component that is not dissolved. In some cases it is characterized asthe bulk fraction of water that separates outmore easily, however in terms of the analyticalmethods it is not distinguished this way. Sofor the purpose of this paper, the authorsdefine it as both the bulk water fraction andthe emulsified water fraction.

• Emulsified Water: water that is contained insmall drops typically 0.1 micron to 50 micronand usually more difficult to separate.Emulsified water in the condensate will usuallyform a haze that enables a quick visual evaluation of the condensate quality; a ‘clear &bright’ condensate indicates that the emulsifiedwater left is very close to the solubility limit.

• Soluble Water: water that is dissolved at themolecular level in the hydrocarbon phase. Itis not removed by separators or coalescers.The solubility of water in the condensate isdependent on the fluid temperature and thecomposition of the condensate, its aromaticcontent (increasing water solubility) and as aconsequence it can range between 50 and 500 ppm typically.

• Total Water: sum of the dissolved and freewater.

Total Water – Karl Fischer: Dissolved as well asfree water will be measured together. This testtypically requires samples to be collected in the

field and transported to a lab setting for analysis.Any volatile hydrocarbons will be flashed off forsamples collected at atmospheric pressure. Aback calculation is possible to evaluate the actualwater content by calculating the weight of thelightest fraction that has flashed off.

Free Water – Aqua-Glo*: This method is particularlyappropriate to measure the actual performanceof separators since they only eliminate the freewater portion. Furthermore it can be modifiedby using a water displacement technique to keepthe sample disc under system pressure so thatthe volatile fraction of the unstabilized condensateremains in liquid form. The apparatus for thistest is displayed in Figure 3. This method usesa filter disc that is impregnated with a fluoresceindye that reacts with only free water. A knownvolume of the process fluid is passed throughthe test disc and is then placed in the Aqua-Gloapparatus that contains an ultraviolet light sourceand photometric detector. The UV light causesthe sampled disc to fluoresce and the intensityof the light emitted is correlated to the free watercontent.

For both the Karl Fisher and the Aqua-Glo tests,the process stream is sampled for a short period.The use of a pilot liquid / liquid coalescer allowsfor longer duration testing which can be quitevaluable in assessing periodic slugs that otherwise might be missed.

Pilot Liquid / Liquid Coalescer Test: Testing theprocess stream over longer periods of time canbe accomplished by use of this device. The pilottest equipment is connected to the process anda side stream with a flow rate of only a few litersper minute is sampled. This test measures theamount of water present in the hydrocarbon condensate over several days to weeks and alsois a useful way to demonstrate the removal capability of the cartridge coalescer at actualprocess conditions for the water, salts and solidsspecifications. A photograph of a horizontal pilottest rig is given in Figure 4.

A small test coalescer is used along with a testpre-filter to protect the coalescer from pluggingwith solids. The flow first enters the pre-filterand then enters the horizontal coalescer housing.As the fluid passes through the coalescer smalldrops in the emulsion are forced into close contact

Figure 3:Modified Aqua-Glosampling techniqueusing the waterdisplacementmethod

To SystemSample Port

To PurgeLines

MeteringValves

QuickConnect

Three WayBall Valve

Aqua-Glo Disc Holder

BallValve

SampleCylinder

MeteringValve

Sample Bottle(Water Volume)

FlexHoses

* Trade mark of Gammon Technical Products, Inc.

5

across a fiber bed and emerge with drop sizesseveral orders of magnitude larger. The largedrops settle along the length of the coalescerhousing and removed by a sump. The dewateredcondensate exits at the top of the housing.

Different types of coalescer cartridges can beevaluated as well as varying fluxes to assess themost optimum separation conditions accordingto the actual stability of the emulsion.Throughout the test, inlet and outlet condensatesamples are collected to measure the efficiencyof the existing separator by measuring the waterconcentration as per the Karl Fischer or Aqua-Glomethods. Samples of the separated water are alsocollected to measure the salinity. Samples that

are typically collected during tests are shown inFigure 5.

Evaluating Solid ContaminationTotal Suspended Solids (TSS) Content: it canbe measured by the use of an in-line test jig containing solids collection membranes - typicallyrated at 0.45 micron removal. This method offersthe benefit of sampling under process conditionsso that the correct amount of liquids are processedwithout flashing. The solids weight gain is correctedfor the volume of fluid sampled and the resultsreported in milligrams per liter (mg/L). A figureof the solids sampling apparatus is provided inFigure 6 on the next page.

Particle Size Distribution (PSD): a smaller volume of the liquid condensate is passedthrough a 0.45 micron membrane disc to collectsolids for PSD analysis using the same apparatusused for the TSS membrane preparation. Thesample is prepared so that the solids do not concentrate on the membrane and overlap soas to be able to count discrete particles. Oncethe test disc is prepared, an automatic image analyzer using electronic microscope is used toautomatically count the particles which are classified according to their size.

Figure 4:Pilot Liquid / LiquidCoalescer Test Rig

Figure 5:Typical condensatesamples collectedduring field surveys

Inlet

Pre-filter

Coalescer withsight glass

Water sumpwith sight glass

Condensateoutlet line withflowmeter and

flow control valve

Coalescerinlet

Coalesceroutlet

Separatedwater

6

Elemental Analysis:A Scanning Electron Microscope(SEM) coupled with Energy Dispersive X-ray(EDX) analysis can provide valuable informationconcerning the qualitative evaluation of the elemental composition of the solid material thatcan be interpreted to discern the nature of thesolid contaminants usually classified as corrosionproducts (iron, sulfur, oxygen), salt precipitates(calcium and barium sulfates) or sand (silica).

Dissolved SolidsThe dissolved solid components in the aqueousphase are typically characterized as TotalDissolved Solids (TDS) or by specific ions. TDSis determined by measuring the conductivityusing a portable dip type probe and resistivitymeter. Most commonly, chloride ion concentrationis measured by ion chromatography.

Field Test ResultsWater carryover from separators and the subsequent ingression of water, salts and solidsin downstream equipment are quite common.The reasons for carryover are basically due tothe presence of condensate/water emulsions thatexisting separators are unable to remove effectively, either due to intrinsic performancelimitations or sometimes due to plant capacityincrease that has made the existing separatorundersized. The water carryover issue can be easily evaluated through a field survey using theabove described methods. A summary of theresults gathered at four different plants in theMiddle East and North Africa region is providedbelow.

All four plants were facing various productionissues in the stabilizers and entered troubleshooting programs which included surveys for the evaluation of the condensate contamination. More specific production issueswere reported as follows: Plant A experiencedissues with heat exchanger plugging andreduced capacity of stabilizer, as well as corrosionissues in the export tanks and pipeline; Plant Bexperienced too frequent replacements of themolecular sieve driers used for final condensatedehydration, and off specification products causingcorrosion issues in the export line; Plant C hadsevere fouling issues in the stabilizer, whichrequired regular shutdown for water wash every3-4 months; Plant D experienced fouling of thereboiler and deposits on the column’s trays causing distortions.

The condensate was tested downstream of existingseparators which consisted of gravity settlers,knock-out drums with mesh pads and glass fibercartridge coalescer (Table A). Results of tests

Figure 6:Test Apparatus forpreparing TSS andPSD solids evaluation membranes

Sample disc holder

Pressure gauge

Flow meter

Flow control valve

Table A: Contamination Levels in Condensate at Outlet of Existing Separators

Plant Type of Flowrate TSS Nature Free Water* Condensate Chloride Location Separator Am3/h (BPD) (mg/L) of Solids (ppmw) Visual Appearance (mg/L)

Plant A – Gravity 165 6 FeS, 1800-4800 Hazy 240-310Middle East Separator (24900) CaSO4Plant B – Glass Fiber 62 16 FeS 75 Slightly hazy Not measuredMiddle East Coalescer (9360)

Plant C – Knock-Out 70 3 FeS, 400-500 Hazy 5470North Africa Drum with (10570) CaSO4

Mesh Pad SiO2

Plant D – Gravity 25 12 Iron oxides 2000-7000 Hazy 25000-32000North Africa Separator (3770)

* Free water content evaluated from water volume separated by pilot coalescer

7

downstream of the pilot high efficiencyPhaseSep® polymeric coalescer are also reported(Table B).

The free water at the outlet of the pilot scalecoalescers was not measured at Plants C and Ddue to unavailability of the test equipment. Thevisual inspection of the samples, however didindicate clear & bright and this demonstratesgood coalescer performance with free water concentrations expected to be very close to thesolubility limit as obtained at plants A and B.

These field surveys illustrate that water carry-over downstream of separators can be minor(plant B) to very significant (plants A & D). Water

concentrations measured downstream of separators are case dependent and figures shownshould not be considered as typical of these separators. Nevertheless, the relative significanceof the water carryover is typical of the expectedrelative separation performance of these typesof separators in the presence of stable emulsions,that is gravity settlers being more prone to carryover than knock out drums with mesh pads,and then cartridge coalescers. These field surveys also highlight that a very significantimprovement is achievable as regards to possibilities in further separation performance.The troubleshooting programs carried out atthese plants all concluded that carryover of contamination was the primary root cause forthe problems experienced in stabilizers. In facteven concentrations perceived as minor can actually cause significant problems due to thefact that they often represent large quantitieswhen scaled up to the full flow rate of the installation.

The evaluation of water, salt and solid contamination levels is therefore very useful indiagnosing the root causes for poor condensatedehydration and if possible it is a recommendedstep in searching for ways to improve a stabi-lization plant.

Table B: Performance of Pilot ScaleCoalescer

Plant Location *Free Water Condensate(ppmv) Visual Appearance

Plant A – <16 Clear & BrightMiddle East

Plant B – <12 Clear & BrightMiddle East

Plant C – Not measured Clear & BrightNorth Africa

Plant D – Not measured Clear & BrightNorth Africa

* Measured by Aqua-Glo method at outlet of pilot coalescer

Reasons for Ineffective Dehydration: Presence of Stable Emulsions

This section discusses the reasons for water carryover being due to the presence of stablecondensate/water emulsions that many separationtechnologies are not capable of processing.Carryover due to undersized separators afterplant capacity increase is not discussed here.

EmulsionsEmulsions consist of the three components: oil(representing hydrocarbon or organic liquids),water (including any aqueous mixtures) and surfactants. Depending on the ratio of these components, oil-in-water emulsions or water-in-oil emulsions can exist. The structure of theemulsions is well defined with spherical dropletsof the dispersed phase surrounded by a bulkcontinuous phase and surfactant surrounding thedroplets at the interface. Surfactants contain bothhydrophilic (water loving) and hydrophobic(water fearing) portions in the same molecule.This unique structure allows them to associate

at water-oil interfaces and helps them to stabilize the droplet shape. In order to make anemulsion the system must be subjected to shearor mixing to allow the three components to re-distribute into many small droplet structures.Depending on the stability of the emulsion, theseparation can occur naturally in a matter of seconds or months.

SurfactantsSurfactants can be broadly classified into threegroups: cationic, anionic and nonionic. All surfactants consist of polar or hydrophilic groupsjoined to non polar or hydrophobic hydrocarbonchains. Cationic surfactants contain polar headgroups that have a positive charge while anionicsurfactants have polar groups that have negativecharges. Nonionic surfactants have polar groupsthat are neutral and are typically made up ofethylene oxide groups, but glycols and alcoholsalso can fit this category.

8

The sources of surfactants found in industrialprocesses include: intentional additives, surfactantsfound in nature, and surfactants created inadvertently through reaction processes. Someexamples of surfactants classified this way aregiven below

• Additives: corrosion inhibitors, de-emulsifiers,scale inhibitors, flocculants, Hydrate inhibitorssuch as Mono Ethylene Glycol (MEG) or methanol.

• Natural: petroleum naphtha sulfonates, naphthenic acids and mercaptides in crudeoil5.

Interfacial Tension (IFT)IFT is created at the interface between twoimmiscible liquids. It is the amount of workrequired to create additional surface area. Themeasurement of IFT is based on the differencebetween the surface energies of the liquids. Theunits of IFT are dyne/cm (force per distance)or erg/cm2 (energy per area). The IFT measuresthe stability of an emulsion. The lower the IFT,the more stable the emulsion, and the smallerthe droplets.

The IFT can be measured in the laboratory fromactual condensate and water samples collectedin the field by a number of methods includingthe Du Nouy ring pull method or the drop volume method. Currently these measurementsare restricted to atmospheric pressure and as aresult unstabilized condensate cannot be evaluated accurately and instead only the non-volatile fraction that remains after the lighterends flash can be estimated by these methods.

The drop volume method has the potential tobe adapted to higher pressures and research iscurrently underway to this end.

Effect of Surfactants on IFTIFT between hydrocarbon products and water,such as in a refinery, can be as high as >40 dyne/cm at operating conditions. In the condensate dehydration application accordingto experience IFTs would however typicallyrange between as low as <2 dyne/cm up to 20 dyne/cm at operating conditions. This is alsowell illustrated in the case histories below.

As mentioned above IFT between unstabilizedcondensate and water cannot be measured accurately. To simulate the effect of surfactantson IFT in the laboratory, synthetic mixtures canalso be used. To simulate hydrocarbon condensate, pentane is often chosen as a similarsolvent. For the purpose of this paper solutionswere made up of different concentrations of MEGand water containing 1000 ppm of sodium chloride. The aqueous mixtures were tested forIFT with pentane. IFT tests that were performedpreviously with mixtures of methanol (MeOH)in water and pentane are also presented6. Theresults confirm that these additives have a stronginfluence in significantly lowering the IFT. It isexpected that this decrease in IFT would be evenmore significant in the presence of surfactantssuch as corrosion inhibitors that are routinelyused by industry.

Disarming‘Disarming’ is specific to cartridge coalescerswhose coalescer medium is made of glass fiber.When surfactants concentrate on the coalescerfibers, they are shielded from the passing aqueous droplets resulting in poor separationefficiency. Generally, the disarming phenomenondoes not occur unless the IFT is less than 20dyne/cm. When specially formulated polymericcoalescer medium is used instead of glass fiber,disarming was not observed7. The coalescing performance of a polymeric medium can begreatly enhanced by modification of surfaceproperties which cannot be accomplished withglass fiber medium.

60

50

40

30

20

10

0

Inte

rfac

ial T

ensi

on (d

yne/

cm)

0 10 40 7060503020 80Concentration in Water (%)

MEGMeOH

Figure 7:Effect of MEG andMeOH on Pentane /Water IFT

9

Various sorts of separation technologies are available in the industry to eliminate salty waterfrom unstabilized condensate. They typically consistof gravity settlers, knock-out vessels with meshpads, electrostatic desalters and cartridge coalescers.All technologies have specific features whichmake them suitable for a given set of operatingconditions. For instance not all technologies arecapable of separating stable emulsions with lowIFTs. Hence with the objective of improving thecondensate dehydration step, the selection of theappropriate technology or combination of technologies requires a good understanding oftheir advantages and limitations.

The separation mechanisms involved are gravitydecantation, and coalescence. As a consequenceonly the free and emulsified water is separated;the dissolved fraction remains in the condensate.

CoalescenceCoalescence consists in the enlargement of finelydispersed droplets of the 'dispersed' phase (waterin the case of condensate dehydration) into largerdrops that are eventually able to separate fromthe bulk 'continuous' phase (condensate).

Coalescence can be made through a media thatusually consists of fibers which are made of metalsuch as in demister pads, or made of glass fiberor polymer as in cartridge coalescers.Coalescence can also be made under the influence of an electric field as in electrostaticdesalters.

Gravity Settlers- Separation principle: gravity settlers rely onthe Stokes law and on the residence time givento the water droplets to decant.

- Separation performance: although capable toaccommodate large and fluctuating concentrations of water in the inlet stream,gravity settlers are not capable of separatingvery fine droplets. The sizing of this type ofseparator is precisely not always straightforwardas it requires that the size of the inlet waterdroplets is assumed or measured. Gravity settlersshould be considered for bulk pre-treatment andwill not be effective for stable emulsions.Gravity settlers can often be subject to

significant water carryover in the case thatassumptions made for the inlet droplet size areincorrect or in the case of a decrease in theIFT due to the presence of additional surfaceactive chemicals. Separation of the particulatecontamination is of limited efficiency.

- Maintainability: this separator is easy to maintain due to no specific internals beingpresent.

- Running cost: this separator does not requireany replacement parts nor utilities, thus runningcosts are usually low. In the case a ‘rag layer’forms and thickens over time and affects thecondensate/water interface detection, demulsifying chemicals may be added.

- Investment cost: as a consequence of long residence times to allow for the separation offine droplets, gravity settlers consist of verylarge pressure vessels which can represent significant investment costs when special construction materials and high design pressures are required.

Knock-out vessels with mesh padsThis type of separator has the same features andlimitations as gravity settlers, but it incorporatesinternals in the form of a mesh pad on theentrance of the separator to coalesce the waterand help decantation. Although the installationof the mesh pad does not add a significant investment cost, it can require some cleaningoperations due to the possible plugging of themesh pad due to particulate contamination.While an improvement over decanting, the meshpad is typically very coarse in pore size and willnot be able to separate stable emulsions.

Electrostatic Desalters- Separation principle: electrostatic desalters relyon the polarity of water molecules to coalesceunder a high voltage electric field. The electric field is provided by electrode grids positioned inside the vessel, between whichthe condensate/water emulsion is distributedthrough the inlet header and where coalescencetakes place. The enlarged water droplets settleby gravity to the bottom of the desalter.

Overview of Available Separation Technologies for Condensate Dehydration

Figure 8:Overview of typicalcartridge coalescerlayout in a horizontalconfiguration

10

- Separation performance: thanks to the electricfield that creates almost virtually instantaneouscoalescence, electrostatic desalters are capableof separating relatively stable emulsions containing fine water droplets. Desalters arecapable of processing bulk concentrations ofwater in the inlet stream. The separation canbe affected by sticky deposits that adhere tothe electrodes, as well as the formation of anemulsion or rag layer at the condensate/waterinterface4. Separation of the particulate contamination is of limited efficiency.

- Maintainability: easy to maintain due to no specific internals that are prone to fouling. Thecleaning of the electrodes is sometimesrequired in the presence of heavy hydrocarbonsthat mix with the corrosion particles and adhereto the electrodes. Slugs of water can sometimescause the electrodes to short out requiringreplacement.

- Running cost: a local power supply is requiredto create the electric field. Desalters oftenrequire the injection of wash water (typicallyaround 5%) to get a sufficient population ofwater droplets to coalesce and to extract solublesalts down to the requested specification. Theneed for wash water adds on running costs tosupply a fresh low-salinity water source, as wellas on power consumption costs due to theneed for extra injection pumps. Desalters alsosometimes use demulsifying chemicals to avoidthe build-up of an interface emulsion layer andto enhance the separation.

- Investment cost: desalters usually consist ofvery large pressure vessels with one or moretransformers to generate the electrical field,hence they are relatively expensive equipmentwhose cost is significantly dependent of theconstruction materials and the design pressure.The possible requirement for dilution water alsoimpacts on the investment cost due to the needfor a water source, pump and supply piping.

Cartridge Coalescers- Separation principle: cartridge coalescers usethe ability of the fine fibrous medium to coalesce the finely dispersed droplets. Cartridgecoalescers do not require the use of chemicalsnor electricity to achieve the separation. Theseparation is only based on the ability of themedium to capture the droplet to the fiberthrough adsorption, coalesce two droplets toform a larger one at fiber intersections, andrelease of the droplet from fiber intersectionsdue to increased drag caused by the bulk flow.

Cartridge coalescers can either be vertically or horizontally configured. The horizontal configuration is the most common one. Figure 8below depicts a typical view of horizontal coalescer.

In this configuration the coalescer consists of ahorizontal coalescer cartridge stage followed by asettling zone that relies on the density differencebetween the water and the condensate to separate the coalesced droplets. The coalescercartridges are mounted on a tubesheet (filter plate) and supported by tie-rods. The

11

condensate/water mixture flows from the insideof the coalescer cartridges radially outward causing the enlargement or coalescing of the finewater droplets. The coalesced droplets then flowaxially in the horizontal direction through thesettling zone downward by gravity and are collected in a sump located at the bottom of thehousing at the end of the settling zone oppositeto the condensate outlet nozzle. The level of thecondensate/water interface is monitored in thesump by level control which automatically controls the opening of the drain valve.

Coalescers can also be vertically configured. Thisconfiguration involves the same coalescer stage,while the separation stage is achieved by anothertype of cartridge with hydrophobic barrier capabilities to allow the condensate stream gothrough while retaining the coalesced waterdroplets. A vertical configuration is not suitablefor very low IFT (<3 dyne/cm) due to the inherentfragile nature of the coalesced droplets that makethe separator cartridge become ineffective.

- Separation performance: cartridge coalescershave varying performances according to thetype of coalescer cartridge that is used. Dueto disarming of glass fiber made coalescers inthe presence of surfactants, ‘conventional’ cartridge coalescers are usually restricted toemulsions featuring IFTs of not less than 20dyne/cm typically. Given the features of thecondensate/water emulsion in the condensatedehydration application, ‘high efficiency’ cartridgecoalescers are therefore more appropriate. Highefficiency coalescers are particularly suited tohandle emulsions featuring low IFTs (<15dyne/cm) to very low IFTs (<5 dyne/cm) Highefficiency coalescers are constructed with specially formulated polymer medium withenhanced surface properties that can influencethe adsorption of droplets and the ultimaterelease of the coalesced droplets. Cartridge coalescers can accommodate relatively high (upto 5% typically) and fluctuating inlet water concentrations.

- Maintainability: coalescer cartridges can plugover time due to the presence of particulatecontamination and need to be replaced aftera certain period of time, typically of few monthsto a couple of years. Cartridge coalescers areeasy to maintain, as they only require the

replacement of the used cartridges by newones. The criterion for change-out is the differential pressure across the coalescer, whichwill steadily increase over time while the coalescer is fouled by particulate contamination.Typically recommended change-out for differential pressures is in the range 0.5-1 bar(7 -15 psid). The installation of a particulatepre-filter upstream of the coalescer greatlyextends the service life of the coalescer, beyondone or two years as it is seen in practice. Theparticulate pre-filter is also required to meetsolids contamination specifications.

- Running cost: the separation is achieved without any chemicals or electricity whichenable low running costs. However coalescerand pre-filter cartridges are consumables,whose replacement is dependent on the solidsconcentration, and represent most of the running cost.

- Investment cost: cartridge coalescers are compact technologies that enable smaller pressure vessels. Besides no ancillary equipmentis required since their operation does notrequire specific utilities or chemicals injection.As compared to other conventional technologies,overall investment cost is typically lower.

As described above all technologies have varyingseparation capabilities for stable emulsions. Highefficiency cartridge coalescers certainly representthe most reliable solution for the low IFT featuring condensate dehydration applicationwhen stringent quality specifications are necessary for the water, salts, solids or MEG levels in the dewatered condensate.

Cartridge coalescers require cartridges to bereplaced and this is often perceived as a drawback due to the additional maintenance anddisposal costs it creates. However the selectionof properly designed filters and coalescers canexhibit long service lives and the capital investment for cartridge coalescers can be muchlower than other options due to their smallerfootprint. Cartridge coalescers also do not requirethe use of chemicals nor utilities whose costsshould be taken into account when comparingdifferent separation solutions in terms of operating and capital expenditures.

Considerations for the Sizing and the Design of Cartridge Coalescers

The use of high efficiency polymeric cartridgecoalescers offers an improved means for the elimination of the salty water from the unstabilizedcondensate. The implementation of cartridge coalescers requires however a careful evaluationof the sizing criteria, and it involves certain designconsiderations that are related to the presenceof solid impurities and the vapor pressure of thefluid.

SizingThe sizing of a cartridge coalescer is basicallybased on the condensate flow rate, the physicalproperties of the condensate and the water (density and viscosity) at operating pressure and temperature, as well as based on the IFT betweenthe water and the condensate and the inlet watercontent.

The IFT impacts on the flux per cartridge andhence on the quantity of elements that are necessary to handle a given flow rate thus onthe diameter of the coalescer vessel. Emulsionsfeaturing low IFTs are stable which means thatthe water droplets are very fine in size; thisrequires that low fluxes are considered to ensurethat the droplets are efficiently captured and coalesced within the coalescer medium, andreleased from the coalescer cartridge without anyrisk of shearing and breaking back into finerdroplets. Besides, the IFT impacts on the sizeof the coalesced droplets and hence on thelength of the settling zone located downstreamof the cartridge bundle where the separationtakes place. Therefore the sizing of the coalesceris dependent on the IFT. If possible at existingfields, the IFT should be estimated from actualwater and condensate (non-volatile fraction) samples, so that the influence of all surfactantspresent is taken into account. The IFT can typically range between as low as <2 dyne/cmup to 20 dyne/cm at operating conditions. Inthe case the IFT cannot be measured, as it is thecase in ‘greenfield’ projects, it is recommendedthat an IFT of <10 dyne/cm is considered.

The inlet water content does not impact on theflux per cartridge as cartridge coalescers usuallyhave the ability to handle relatively large amountsof water, typically up to 3 to 5% in volume. Inthe case of higher inlet water concentrations, thecoalescer may have to be oversized by adding

more coalescer cartridges in order to providemore coalescing surface, or a coarse pre-separation device located upstream of the cartridge bundle within the coalescer vesselshould be considered.

Particulate Pre-FilterThe unstabilized condensate contains varyingconcentrations of solid and solid-like particles.Although the solids content is usually in the ppmrange, it may represent a solids loading of several kilograms per day when scaled up to thefull flow rate of the installation, hence the importance of eliminating this solid contamination before entering the stabilizer.Besides, particle contamination tends to increasethe stability of the liquid/liquid emulsion.Cartridge coalescers, although only designed forthe separation of two liquid phases, have to someextent the ability to act as particle filters due tothe fine pore structure of the coalescer mediumand would plug over time. A frequent replacementof the coalescer cartridges is not cost-effectiveover time due to change-out, maintenance andused cartridge disposal costs. So it is usually recommended that a separate pre-filter isinstalled upstream of the coalescer to removeparticulate matter. The installation of a pre-filterextends the service life of the coalescer significantly and reduces particulate concentrationto meet solids specifications. The removal ratingof the pre-filter should be selected according tothe pore size structure of the coalescer medium,as well as according to the size distribution ofthe solid contaminants. The particulate pre-filterincreases the investment cost of the cartridge coalescer solution, but overall reduces the running costs of the coalescer assembly.

DegassingDehydrating unstabilized condensate requires acareful evaluation of the risk of flash off due todrops in operating pressure. The presence of gasinside a coalescer should be avoided at all timebecause gas bubbles may disrupt the coalescingmechanism inside the coalescer medium, henceadversely affect the coalescer performance.Degassing is dependent on the condensate’scomposition and operating pressure and temperature. Degassing is not an issue when thecondensate is processed at a pressure much higherthan the vapor pressure, so that the fluid is kept

12

13

as a liquid state. At the phase equilibrium anypressure drop flashes off the lightest componentshence creating varying volumes of gas. Such conditions are met when operating a coalescerassembly comprising of a pre-filter and a coalescer. The increasing pressure drop acrossthe pre-filter, due to its progressive fouling overtime, may create increasingly large volumes ofgas that can flow to the downstream coalescer.

Particulate pre-filters typically generate less than0.1 bar clean differential pressure (DP), but theycan be typically operated up to 2 bar DP beforechange-out, where corresponding gas volumescould be significant. Figure 9 illustrates gas volumes generated as a function of DP, basedon a Middle East case. Calculations are basedon Peng-Robinson’s equation.

Figure 9:Simulated gas volumes generatedat various DP acrosspre-filter and streamcomposition

Figure 10:Possible arrange-ments to avoid gasfrom entering thecoalescer

Degassing should be avoided, or flash gas shouldbe removed from the condensate before enter-ing the coalescer. Different arrangements can be

considered to avoid gas from entering the coa-lescer, as illustrated in Figure 10.

Calculated �ash gas �ow rate assuming pre-�lter DP with condensate atequilibrium conditions @ 29.5 bar, 49˚C, �ow rate 66000 kg/h (96.6Am3/h)

Flas

h ga

s �o

wnr

ate

(Am

3/h)

Differential pressure across pre-�lter (bar)

6

5

4

3

2

1

00.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

H20 19.93078Nitrogen 3.4435CO2 549.1073H2S 783.3088Methane 989.0007Ethane 292.0128Propane 683.0027i-Butane 460.8483n-Butane 1107.4650i-Pentane 1019.9597n-Pentane 1769.4083n-Hexane 2987.3618n-Heptane 8228.2724n-Octane 8607.7781n-Nonane 7662.4372n-Decane 7468.4384M-Mercaptan 11.8271n-C11 5774.0745n-C12 4083.1141n-C15 13499.2086

Mass Flow (kg/h)

Surge Drum Pre-Filter Coalescer

Condensate to FeedHeater & Stabilizer

Water Water

Water Water Water

Booster Pump

Surge Drum Pre-FilterDegassingDrum Coalescer

Gas

Option 1: Use of a Booster Pump Upstream of Pre-Filter

Option 2: Use of a Degassing Drum after Pre-Filter

Condensate to FeedHeater & Stabilizer

Commercial Case Histories

Crew Energy Inc., Septimus Gas Plant,CanadaThis plant is located in British Columbia and wasbuilt in 2009. It was designed for a gas flow rateof 50 MMSCFD and currently produces andprocesses approximately 38 MMSCFD of gas and100 m3/day (630 BPD) of condensate. The LPGand condensate are recovered through a conventional refrigeration process (complete witha de-ethanizer). The LPG and condensate aresplit in the de-butanizer and both products aresent to onsite storage for future sale. After theInlet Separator, the condensate flows to the condensate pumps then onto the surge vesselprior to entering the de-ethanizer. The de-ethanizerreceives raw condensate from the inlet separatoras well as hydrocarbon liquids from the low temperature separator in the refrigeration skid.

Quickly after start-up the plant encountered acontinuous carryover of water that caused saltdeposits inside the de-ethanizer column and thereboiler, resulting in excessive plant upsets andloss of product quality due to the reduced heattransfer from the de-ethanizer re-boiler. The planthad to go for a monthly-based maintenance program to clean the internals of the de-ethanizerand the re-boiler of the salt deposits and restore

the heat transfer. This maintenance operation wasforcing the plant to shutdown the liquid processing facilities for 12 hours, causing a netloss of production of 50 m3 (315 BBL). The plantevaluated that the combined loss of productionand the maintenance costs for cleaning the re-boiler represented an overall annual cost ofup to 725,000 USD.

Pall Corporation was consulted to perform on-site pilot trials to quantify the water levels in thecondensate and to demonstrate the effectivenessof the coalescer technology in eliminating thatwater down to a specification of 15 ppmv orbelow. Field trials showed a great variability inthe inlet free water contents, ranging from 28ppmv to 1190 ppmv over the test period, withan average free water content of 127 ppmv. Thecoalescer produced a 'clear & bright' lookingcondensate with free water contents rangingbetween 2-9 ppmv, while the separated brinehad a hazy yellowish appearance. The IFT measured between the non-volatile fraction of thedehydrated condensate and the brine collected from the coalescer outlets exhibited a lowvalue of 9.5 dyne/cm at the operating temperature.

Based on the successful results and field datacollected from trials, Pall supplied a coalescersystem comprised of duty-standby 8˝ diameterhorizontally-configured 20 micron absoluterated prefilter vessels, followed by a single 12˝diameter horizontally-configured coalescer vesselequipped with two 40˝ long PhaseSep® coalescercartridges. An overview of the coalescer systemis shown in Figure 11.

The coalescer system was put online in

December 2010. After four months of operation

of the coalescer system the plant did not report

any salt carry-over issue.

14

One possible arrangement considers a boosterpump that is installed downstream of the SurgeDrum and upstream of the pre-filter to overcomethe pressure drop generated by the increasinglyfouled pre-filter. Ideally the pump should delivera discharge pressure that is 3 bar higher.Elevation between the pump and the SurgeDrum should be evaluated with care so that theNet Pressure Suction Head (NPSH) is highenough. Another possible arrangement consists

of incorporating a degassing vessel between thepre-filter and the coalescer, so that gas generatedacross the pre-filter is separated before the condensate enters the coalescer. The sizing ofthe degassing drum is dependent on the residence time that is necessary to eliminate thegas. A possible alternative to this arrangementis to have the pre-filter located upstream of theSurge Drum, so that savings are made on theadditional degassing drum.

Figure 11:Overview of the Pallcoalescer assemblywith coalescer (forefront) and duty-standbypre-filters (background)

15

Offshore gas production platform, AustraliaThis platform has a production capacity of 1815MMSCFD. After the Production Separator, thecondensate flows to Condensate Coolers, onto thePrimary Condensate/water Separator, then ontoCondensate Filters and Condensate Coalescers fordehydration, prior to the export line where thecondensate is exported with the dehydrated gas.

Originally Condensate Coalescers were equippedwith conventional coalescer cartridges. TheCondensate Coalescer is horizontally configured.The plant reported that coalescers were notmeeting the required water content specification,in fact around 1000 ppm water were remainingdownstream of the coalescers. The reasons forthe very low performance of the coalescers wereexpected to be on the one hand, a very stablecondensate/water emulsion, characterised by alow IFT of 13 dyne/cm simulated from actualproduced water samples with pentane becauseof the presence of corrosion inhibitor added atthe wellheads, on the other hand the coalescerswere subject to disarming in the presence of thecorrosion inhibitor that was causing the coalescerperformance to drop over time and required thecoalescer cartridges to be replaced on a monthlybasis.

In 1999 as part of a debottleneck project the plantdecided to upgrade the Condensate Coalescerson one train. Pall's PhaseSep® coalescers wereselected and custom-made bolt-in moduleinternals were designed and manufactured to fitthe cartridges inside the existing coalescer vessel without any modification on that vessel.The retrofit module internals are shown onFigure 12. Each retrofit module holds 31 off 20˝long coalescer cartridges, to handle a total flowrate of 4134 m3/day (26,000 BPD) at 113 bar.

The Condensate Filters were upgraded as wellwith 10 micron absolute rated Pall CorelessProfile® filter technology, in order to protect thecoalescer against solid particles. Upgraded filtersand coalescers were sized to handle inlet freewater contents of 1000 ppmv and 2000 ppmv aspeak conditions, and to produce condensate witha free water content specification of <100 ppmv.

The upgraded Condensate Coalescer has beenperforming according to the plant's expectationssince 2001. Pre-filter cartridges are currentlyreplaced each three months on average. In 2005all remaining trains were upgraded using thesame Pall PhaseSep coalescer technology.

Figure 12:Retrofit module internals to fit insideexisting cartridgecoalescer

Conclusions

Condensate dehydration is often made difficultdue to the presence of stable emulsions thatcause conventional condensate/water separationtechnologies to be ineffective in meeting qualityspecifications.

Improving the performance of the condensatedehydration step requires a good understanding

of the contaminants present. Analytical as wellas field methods are available in the industry fordiagnosing contaminant issues. The stability ofthe emulsion should also be assessed with careduring the selection of the separation technology,to ensure that the technology is capable of separating potentially stable emulsions. To thisend, the presence of corrosion inhibitors and

References

Pall Fuels and Chemicals

25 Harbor Park DrivePort Washington, NY 11050 +1 516 484 3600 telephone+1 888 873 7255 toll free US

Portsmouth - UK+44 (0)23 9230 2357 telephone+44 (0)23 9230 2509 faxprocessuk@pall.com

Visit us on the Web at www.pall.com

Pall Corporation has offices and plants throughout the world. For Pall representativesin your area, please go to www.pall.com/contact.

Because of technological developments related to the products, systems, and/orservices described herein, the data and procedures are subject to changewithout notice. Please consult your Pall representative or visit www.pall.com toverify that this information remains valid.

© Copyright 2011, Pall Corporation. Pall and are trademarks of Pall Corporation. ® Indicates a trademark registered in the USA. is a servicemark of Pall Corporation.

FCGPAEN Printed in USA November 2011

hydrate inhibitors should be well characterizedsince they are the main contributors to the emulsion stability.

Hydrocarbon condensate separated from naturalgas carries varying concentrations of impuritiesin the form of water, salts and solids. The effectsof these contaminants can be severe and costlyto the condensate stabilization plant and theexport pipeline. Problems that have beenencountered include off-spec condensate andfinal products, compromised plant performanceand maintenance issues including corrosion andfouling of equipment by solid deposits.

Improving the condensate dehydration or‘dewatering’ step also requires a good understanding of the features and the limitations of the separation technologies that areused to eliminate contaminants. The selectionof the appropriate technology should be evaluated with care to ensure that it is capableof separating potentially stable emulsions.

Evaluation should consider its maintainability,running cost and investment cost.

Results from field surveys highlight that watercarryover from existing separators (gravity separators, mesh pads and glass cartridge coalescers) can be significant. The use of highefficiency polymeric cartridge coalescers, however, was found to be an effective and economical way to improve the condensatedehydration step due to their ability to separatedifficult emulsions. This technology features several advantages including that no chemicalsor utilities are needed to aid the separation. Theimplementation of cartridge coalescers involvescertain design considerations relating to the presence of solid impurities and the potentialfor degassing. Commercial experience at condensate plants in Canada and Australia showthat the use of this advanced coalescer cartridgetechnology has been proven as an effective andeconomical way to optimize hydrocarbon condensate stabilization plants.

1. Mokhatib, S., Poe, W. and Speight, J., Handbookof Natural Gas Transmission and Processing,Chapter 6, Condensate Stabilization, 1st edition,pp.247-260, September 2006

2. Campbell, J.M., Gas Conditioning and Processing,vol.1, 8th edition, Chapter 2, pp.26-33, February 2004

3. Campbell, J.M., Gas Conditioning and Processing,vol.2, 8th edition, Chapter 17, pp.273-280, February 2004

4. Karimkhani, B. and Khorrami, Z., “Evaluating Effectof Different Operational Parameters in IncreasingPerformance of Condensate Stabilizing Process inGas Plants (Case Study)”, Society of PetroleumEngineers, presented at the 2009 KuwaitInternational Petroleum Conference and Exhibition,December 2009

5. Hughes, V.B., “Aviation Fuel Handling: NewMechanism Insight Into the Effect of Surfactants onWater Coalescer Performance,” Second InternationalFiltration Conference, San Antonio, April 1997

6. Hampton, P., Darde, T., James, R., Wines, T.H.,“Liquid-Liquid Separation Technologies improvesIFPEXOL Process Economics”, Oil & Gas Journal,Vol. 99, No. 16, April 16, 2001

7. Wines, T.H. and Brown, R.L. Jr., “Minimizing LiquidContaminants in Natural Gas Liquids”, presented atthe Gas Processors Association 75th annual meeting,March 1996

AcknowledgmentsThe authors are grateful to Crew Energy Inc. andDave Mills for accepting being used as a casehistory.