Sour water: where it comes from and how to handle itSourwaterstrippersarecommoningas processingfacilities,sulphurrecoveryunits, wellhead facilities, and refnery applications. Understandingthevariablesallowsengineersto betteroptimisetheinitialdesignandoperation. Thispaperreviewsoptionsforsourwaterstrip-perconfgurationandpresentsamethodto optimisestripperoperationbyfndingthemost effcientoperatingparameters.Optionsinvesti-gatedinclude:singleordoublecolumnfor increasedproductpurity;additionofacidor causticforimprovedperformance;refuxedor non-refuxedcolumnstomitigatewaterinthe overheadgases;condenserorpumparoundand theireffectsonoverheadcomposition;reboiler, directsteaminjection,oracombinationofthese andtheeffecttheyhaveoncorrosionconcerns. Inaddition,optimisationofthesteamrateis investigated.Overallstageeffciencyfortrayed strippers,HETPforpackedstrippersandindi-vidualcomponenteffcienciesarediscussed basedonavailablesourwaterstripperoperating data. Sources of sour waterGas processingWateristhesinglelargestwastestreaminoil andgasproductionworldwide.Wastewater streams come from a variety of sources, the larg-estofwhichisassociatedorproductionwater. Othersourcesofwastewaterincludewaterused duringstartupandindustrialhygiene,purge waterfromaminesweeteningunits(ASU),and washwaterusedinthetailgastreatingsection (TGTU)ofthesulphurrecoveryunit(SRU).Of thesesources,associatedwateristhelargestin totalvolume;however,thelattertwoarethe largest sources of sour water.Wateralwaysexistsinoilandgasreservoirs, Luke Addington, Carl Fitz, Kevin Lunsford, and Lili Lyddon Bryan Research and Engineering, Inc.Dr. Ing. Mariana Siwek Verfahrenstechnik und Automatisierung GmbHoftensittingtowardsthebottomoftheproduc-tionzone.Whileproductionmayberelatively dryatthebeginningofafeldslife,water-to-hy-drocarbonratioswillincreaseoverthelifeofa wellashydrocarbonsaredepletedandwater beginsmigratingupwardstoareasofproduc-tion.TheUnitedStatesaveragesaroundten barrelsofassociatedwaterperbarrelofoil produced1.Thereareavarietyofimpuritiesfoundinthis associatedwater,suchasoilandgrease, suspendedsolids,BTEX/VOCs,aswellas sulphurandammonia.Table1liststheconcen-trationoftypicalcontaminantsinassociated water from sources in the Gulf of Mexico2 and in Pennsylvania3.Noticethatthelargestconcentra-tionofcontaminantsisthesuspendedsolids whilethesmallestistypicallysulphurspecies andammonia,thosecomponentstypically removed in a sour water stripper.As a waste stream, associated water is disposed of in a variety of ways, depending on the produc-tionsitesgeographicallocation,geological concerns, the types of contaminants in the water, andwhetherproductionisonshoreoroffshore. Theoverwhelmingmajorityofassociatedwater isreinjectedintoeithertheproductionreservoir forEnhancedOilRecovery(EOR)orinto www.digitalrening.com/article/1000741 September 20111Typical associated water contaminant concentrationsGulf of MexicoVenango County, (mg/L) 2 Pennsylvania (mg/L)3Oil and Grease26.62.74-78Suspended Solids14120-614BTEX/VOCs201-1,000Sulphur421-584Ammonia12.22.22-17Table 1depletedorunusedundergroundreservoirs.As muchas95%ofonshoreassociatedwateris disposedofinthisway4.Theimplicationisthat althoughassociatedwaterisahugewaste,much ofitisminimallytreatedandreadilydisposedof back into reservoir rock. Theremaininguninjectedassociatedwateris eitherusedbenefciallyordisposedofonthe surfaceinevaporationponds.Benefcialuses includeagriculturalusewhencircumstances allow,suchasUSonshorereservoirsthat producewaterwithalowsaltcontentandlie westofthe98thmeridian5.Somewaterisalso treatedandreusedingasprocessingfacilities6. Evaporationponds,asameansofonshore disposal,arefallingoutoffavourduetothe additionalprocessingneededandenvironmental concernssuchassaltcontaminationofsurface soil and erosion7. Table 2 provides a summary of US onshore associated water disposal practices.Offshorewaterdisposalpracticesforassoci-atedwatervaryfromonshorepractices.Drilling injectionwellsandsettinguptheinfrastructure togettheproducedwaterfromtheplatform 2 September 2011www.digitalrening.com/article/1000741backtotheinjectionsitecanbecostprohibitive, soassociatedwaterisnottypicallyreinjected offshore4.Someproductionwateristreatedand reused;however,themajorityissimplytreated anddischargedintothesea1.Theprimary contaminantsofconcernforthisdischarged wateraresuspendedsolids,oil,andBTEX/VOCs. Removal of these contaminants, by means ofcoalescersordegassingunits,oftenresultsin theby-removalofanysourcomponents.This wastewater,therefore,doesnotneedtobeintro-ducedtoasourwaterstripper.Thenetresultis thattheprimarysourceofsourwaterbeingsent tosourwaterstrippersinupstreamapplications is not comprised of associated water.Inrarecases,aminesweeteningunitsin upstreamapplicationsmaybesourcesofsour water.Inmostcases,thesweetgastemperature ishigherthantheinletgastemperaturedueto absorptionofacidgascomponentsinthe absorber.Theincreaseingastemperature resultsinwateractuallybeingremovedfromthe aminesolution.If,however,thesweetgas temperatureislowerthantheinletgastempera-ture,watermayactuallybuildupintheamine solutionandberemovedfromthesourliquid condensateintheamineregenerator.Thiscould occuriftheinletgascontainslittleacidgasand theleanaminesolutionisatalowertempera-ture than the inlet gas.Quenchsystemsforsulphurrecoveryunittail gasaretheprimarysourceofsourwaterin upstreamapplications.Hydrogenatingtailgas units,suchasShellsSCOTsystem,areoften usedtoimprovetheoverallremovaleffciencyof SRUs.Inthesesystems,anysulphurremaining Method% of Onshore Produced WaterInjected for Enhanced Recovery57Injected for Disposal36Benecial Use4Evaporations2Treat and Discharge1Others