System and method for drying gas

Description

2 Thedryingagentordesiccantarrangedinavesselofthe dryercantakeonvariousformssuchasforinstancea granularformoranotherextrudedform.Itisalsoknownto provideadryingblockinthevessel.Knowndryingblocks maybeformedbyanopensupportingstructurewhichisat5 leastpartiallycoatedwithadryingagent. Inuseduringdryingthedryingagentpresentinthevessel ofthedryerextractsmoisturefromthegastobedried, thisdryingagentwillbecomeincreasinglysaturatedwith10 adsorbedmoistureandwillintimenolongerbeeffective unlessreplacedorotherwiserejuvenated.Therefore, typically,thedryingagentconcernedisgenerallyrealised intheformofaregenerabledryingagent,orinother wordsadryingagentthatcanberegeneratedafterreaching15 acertaindegreeofsaturation. Whenmakinguseofaregenerabledryingagentitisknown tousedryersbeingprovidedwithtwoormorevesselsof regenerabledryingagent.Thevesselsofsuchdryerscanbe20 operatedinadryingorinaregeneratingmodus.Incaseavesselisbeingoperatedinthedryingmodus,the gastobedriedissuppliedviatheinlettothevesseland driedgasexitingthevesselisdischargedviatheoutlet. Hencethevesselisactingasadryingvessel.Incasea25 vesselisbeingoperatedintheregeneratingmodus,the (saturated)dryingagentisexposedtoaregenerationgas flowthatextractsthemoisturefromthedryingagent. Hencethevesselisactingasaregeneratingvessel.Such aregenerationgasflowcanconsistofafractionofthe30 driedgasand / orhotgasforexamplewhoserelative BE2024 / 5907 3 humidityissufficientlylowtobeabletorealisethe regenerationofthedryingagent.Adryerwithtwovessels maybeconfiguredsuchthatonevesselisactingasa dryingvesselwhileatthesametimetheothervesselis actingasaregeneratingvessel.Oncethedryingagentof5 thedryingvesselreachesacertaindegreeofsaturation theflowofthetobedriedgasandtheregenerationgas canberedirectedsuchthattheformerdryingvesselis actingnowasaregeneratingvesselandtheformer regeneratingvesselisactingknowasadryingvessel.In10 otherwordsthevesselsofthedryerareusedcyclically fordryingandregeneratingasaftereachcycletheroleof avesselisswitchedfromdryingvesseltoregeneration vesselorviceversa. 15 Althoughknowndryersdefinitelyhavetheirmeritsthey consumealotofenergy.Hence,thereisacontinuous interestinfindingsolutionsforreducingtheamountof energyneededtodrythegastothedesiredlevel.Aknown waytodeterminewhetherthegastobedischargedatthe20 outletissufficientlydryisbymeasuringthepressuredew pointofthedriedgas.Thepressuredewpoint(PDP) indicatesthetemperatureatwhichthewatervapourbegins tocondenseoutofthecompressedairintoaliquidform. Inotherwords,thepressuredewpointisusedto25 accuratelydescribethewatercontentinthecompressed air.Alowpressuredewpointindicatesalowwatercontent ofthecompressedair.Theachievablepressuredewpoint variesbetweendryersandistypicallyoneofthecriteria toselectadryertoensurethedriedairmeetsthe30 consumerorapplicationrequirements.ThetargetPDPhas BE2024 / 5907 4 typicallyavalueintherangefrom-70°Cuptoand including5°C. SUMMARYOFTHEINVENTION 5 Itisanobjectiveofthepresentinventiontoprovidean alternativesolutionfordryinggaswhichiseffectiveand moreefficientinthatlessenergyisrequiredfordryinga sameloadofgas. 10 TheinventorhasmonitoredthePDPofthegastobe dischargedattheoutletofthedryerduringoperationof thedryer.Hehasobservedthatduringacycleofthedryer thePDPofthedriedgasisnotstableandonlyapproaches thetargetPDPneartheendofthecycleandthatduring15 theremainderofthecyclethePDPofthedriedgasis significantlylowerthanthetargetPDP.Thusduringa substantialpartofthecyclethePDPofthedriedgasis significantlylowerthanrequiredforthetarget application.20 Onemoreobjectiveofthepresentinventionistoprovidea solutionfordryinggaswhichbringsthepressuredewpoint ofthegasclosertothetargetpressuredewpointforthe applicationduringthewholecycle.25 Toatleastpartiallyaddressoneormoreofthementioned orotherchallengesand / ortoatleastpartiallymeetone ormoreofthementionedorotherobjectives,thepresent inventionconcernsasystemfordryinggas.30 Thesystemcomprisesaninletforthesupplyofgastobe BE2024 / 5907 5 dried,anoutletfordischargingdriedgas,andadryer operativelyconnectedtotheinletandtheoutletallowing thegastoflowfromtheinletthroughthedryertothe outlet. 5 Preferablythedryerisprovidedwithpluralvesselseach enclosingaregenerabledesiccant,eachvesselcomprising anentryandanexit,whereinthedryerisconfiguredsuch thatatleastoneofthevesselsisoperatedinadrying modewhileatleastoneotherofthevesselsisoperatedin10 aregeneratingmodusforregeneratingthedesiccant enclosedintheatleastoneotherofthevessels,and whereintheatleastonevesseloperatedindryingmodeis fluidlyconnectedwithitsentrytotheinletandwithits exittotheoutletwhiledryinggaspassingfromtheentry15 totheexit.Thesystemaccordingtotheinventioncomprisesavariable bypassconduitconfiguredforsplittingoffaportionof thegastobedriedsuppliedattheinletandformixing20 thesplitoffportionwiththedriedgasexitingthedryer upstreamtheoutlet,theby-passconduitbeingprovided withacontrollableadjustablevalveforadjustingthe portionofthetobedriedgassplitoffinthevariable bypassconduitbyadjustingthecontrollableadjustable25 valve;and acontroller,connectedtothecontrollableadjustable valve,configuredtoregulatetheportionofthegastobe driedsplitoffinthevariablebypassconduitbyadjusting thecontrollableadjustablevalvesuchthatapredetermined30 valueofapressuredewpointofthegastobedischarged BE2024 / 5907 6 isobtained.Thispredeterminedvalueistypicallychosen slightly,forexampleafewdegreesC,oruptotendegrees C,belowthetargetpressuredewpointoftheapplication envisaged. 5 Thebypassconduitistypicallyapipeorhoseextending betweentheinletandtheoutletwhilebypassingthedryer. Thehoseorpipecanbemadeofmetalorplastic.The controllableadjustablevalveistypicallyconfiguredsuch thatbyadjustingthevalveacross-sectionalareaof10 conduitislocallychangedhenceaffectingtheflowrateof thegasthroughtheconduit.Thevalvecanbeadjustedsuch thattheflowofgasthroughthebypassconduitis completelycut-off. 15 Thisconfigurationallowstocontrolthesystemsuchthat thegastobedischargedhasavalueofthepressuredew pointclosetothepredeterminedvalueofthepressuredew pointbycontrollingtheportionofthetobedriedgas whichissplitoffandbypassesthedryer.Thebypass20 portionlowerstheloadoftobedriedgastothedryer withoutaffectingtheamountofgasdischargedfromthe systemresultinginsignificantlylowerenergyconsumption. Theamountofenergysavingdependsonthesizeofthe bypassportionwhichdependsamongothersonthetarget25 pressuredewpointoftheapplication.Forinstance,fora targetpressuredewpointof-40°C,thebypassportionis typicallyafewpercentofthegastobedriedsupplied, whileforatargetpressuredewpointof5°C,thebypass portiontypicallyhasavalueintherangefrom20%to25%30 ofthegastobedriedsupplied. BE2024 / 5907 7 Inanembodimentoftheinventionthesystemcomprisesa pressuredewpointsensor,connectedtothecontroller,for determiningavalueofthepressuredewpointofthegasto bedischargedattheoutlet.Thecontrollermaybe5 configuredtoiterativelyadjustthecontrollable adjustablevalvetoasetvalueandtodeterminethevalue ofthepressuredewpointofthegastobedischargedusing thepressuredewpointsensor,whereinforeachiteration thesetvalueisadjustedinordertoreducethedifference10 betweenthedeterminedandpredeterminedvalueofthe pressuredewpoint.Thisiterationiscontinuedtillthe differencebetweenthedeterminedandpredeterminedvalue ofthepressuredewpointreachesastableminimum.Preferablythisiterationisperformedinasmoothway,for15 examplebychangingthesetvalueinanincrementalway whereineachincrementischosendependentontheobserved differencebetweenthedeterminedandpredeterminedvalue ofthepressuredewpointand / orontherateofchangeof thattemperaturedifference.20 Tofacilitatestabilizationofthepressuredewpointof thegastobedischargedonemayopttoprovidethesystem withafixedbypassconduitconfiguredforsplittingoffa fixedportionofthegastobedriedsuppliedattheinlet25 andformixingitwiththedriedgasexitingthedryer upstreamtheoutlet,thefixedbypassconduitbeing providedwithacontrollablevalveforopeningorcutting offthefixedbypassconduit.Thisfixedbypassconduitis arrangedparalleltothevariablebypassconduit.Usingan30 additionalfixedbypassisparticularlyadvantageouswhen BE2024 / 5907 8 thebypassportionexceedsacertainthresholdvalue.Inafurtherembodimentoftheinventionthesystem comprisesafilterpositionedupstreamtheoutletfor filteringthemixtureofdriedgasexitingthedryerand5 thetobedriedgasbypassingthedryerpriorto discharging.Preferablythepressuredewpointsensoris positioneddownstreamthefilterwhichpositivelyimpacts theaccuracyofthepressuredewpointdetermination. 10 Inonemoreembodimentoftheinventionthecontrolleris configuredtocyclicallyswitchthevesselsofthedryer operatedinthedryingmodetotheregenerationmodeand viceversa,andwhereinduringeachswitchthecontroller15 isconfiguredtoadjustthecontrollableadjustablevalve toastatewhereinflowofthegasthroughthevariable bypassconduitisblocked.Althoughtheswitchingisalmost instantaneouslybydoingsothedischargeofgaswitha pressuredewpointexceedingthetargetpressuredewpoint20 ispreventedand / orthestabilizationofthepressuredew pointofthegastobedischargedinthenextcycleis facilitated.Theinventionalsoconcernsamethodfordryinggas25 comprisingthestepsof: -splittingthetobedriedgasinaportiontobedried andabypassportion; -dryingtheportionofthegastobedriedusinga dryer;preferablythedryerisprovidedwithplural30 vesselseachenclosingaregenerabledesiccant, BE2024 / 5907 9 whereinthedryerisconfiguredsuchthatatleastone ofthevesselsisoperatedinadryingmodefordrying thegassuppliedwhileatleastoneotherofthe vesselsisoperatedinaregeneratingmodusfor regeneratingthedesiccantenclosedintheatleast5 oneotherofthevessels; -mixingthedriedgasexcitingthedryerwiththe bypassportionofthetobedriedgasbypassingthe dryer; -regulatingaratioofthesplittingofthegasbetween10 theportiontobedriedandthebypassportionsuch thatapredeterminedvalueofapressuredewpointof thegasmixtureisobtained. Themethodaccordingtotheinventionmaybeexecutedusing15 asystemasdescribedinoneormoreoftheprevioussystem embodimentsorinacombinationoftheseembodiments.Inanembodimentaccordingtotheinvention,themethod comprisesthestepsofmeasuringthepressuredewpointof20 thegasmixtureanddeterminingadifferencebetweenthe measuredandthepredeterminedpressuredewpoint,and wherein,duringtheregulatingstep,theratioofthe splittingofthegasbetweentheportiontobedriedand thebypassportionisregulatedsuchthatthedifference25 betweenthemeasuredandthepredeterminedpressuredew pointisreduced. Inonemoreembodimentaccordingtotheinvention,thestep ofdryingtheportionofthegastobedriedcomprisesthe30 sub-stepsofcyclicallyswitchingthevesselsofthedryer BE2024 / 5907 10 operatedinthedryingmodetotheregenerationmodeand viceversa,andinterrupting,duringswitching,splitting offthebypassportionofthetobedriedgas.5 BRIEFDESCRIPTIONOFTHEDRAWINGS Withtheintentionofbettershowingthecharacteristicsof theinvention,hereafter,asanexamplewithoutany limitativecharacter,apreferredembodimentisdescribed10 ofasystemfordryinggas,withreferencetothe accompanyingdrawings,wherein: figure1schematicallydepictsasystemfordryinggas accordingtoanembodimentoftheinvention;15 figure2showsagraphofacomparativemeasurementof thepressuredewpointofgastobedischargedwith andwithoutusingthesystemaccordingtothe inventionasdepictedinfig.1. 20 DETAILEDDESCRIPTIONOFAPREFERREDEMBODIMENT Figure1depictsanexampleofasystemfordryinggas accordingtotheinvention.Thesystemhasaninlet1to25 whichgas,inthisexamplecompressedair,tobedriedis supplied,andanoutlet2fordischarginggas. Thesystemcomprisesadryerwithtwovessels4A,4B whereinadesiccant5A,Bisenclosed.Thedesiccantinthis30 exampleisadryingblock.Thevessels4A,4Bhavea BE2024 / 5907 11 generalcylindricalshapeandareshowninanupright orientation,althoughtheinventionisclearlynotlimited theretobutapplicablealsotoothershapesand orientationsofthevessels. 5 Thevessels4A,B,whicharegenerallymadefrommetal,are providedattheirbottomwithanentry6A,B.Theentriesof thevesselsareconnectedinparalleltotheinlet1 throughinletpipes7A,B.Eachoftheinletpipes7A,Bis providedwithacontrollableinletvalve8A,Bwhichwhen10 enabledshutoffthecorrespondinginletpipesuchthatno gascanflowfromtheinlet1tothevessel4A,Bconcerned. Whenthecontrollableinletvalve8A,Bisdisabledgasto bedriedcanfreelyflowfromtheinlet1totheentry6A,B ofthevessel4A,Bconcerned.15 Thevessels4A,B,areprovidedattheirtopwithanexit 9A,B.Theexitsofthevesselsareconnectedinparallelto theoutlet2throughoutletpipes10A,B.Eachoftheoutlet pipes10A,Bisprovidedwithacontrollableoutletvalve20 11A,Bwhichwhenenabledshutsoffthecorrespondingoutlet pipesuchthatnogascanflowfromtheexit9A,Bofthe vessel4A,Bconcernedtotheoutlet2.Theentry6A,Band theexit9A,Bofeachvessel4A,Barefluidlyconnected allowingthegastoflowinageneralverticalflow25 directionfromthebottomentrytothetopexit. Thedryer3comprisesaregenerationinput12throughwhich aregenerationgascanbesupplied,forexamplebyblowing inheatedambientair.Theinventionisnotlimitedto30 regenerationgassuppliedbyblowinginheatedambientair, BE2024 / 5907 12 butregenerationgasmaybesuppliedinanyalternative mannerorbyanyalternativemeans,suchasforinstanceby splittingofpartofthedriedgasforuseasregeneration gas.Theexits10A,Bofthevessels4A,Bareconnectedin paralleltotheregenerationinput12throughinputpipes5 13A,B.Eachoftheinputpipes13A,Bisprovidedwitha controllableinputvalve14A,Bwhichwhenenabledshutoff thecorrespondinginputpipesuchthatnoregenerationgas canflowfromtheregenerationinput12totheexit9A,Bof thevessel4A,Bconcerned.Whenthecontrollableinput10 valve14A,Bisdisabledregenerationgascanflowfromthe input12totheexit9A,Bofthevessel4A,Bconcernedand subsequentlythroughthevesselwhiletakingupmoisture fromthedesiccant5A,Benclosedtothecorrespondinginput 6A.Theentries6A,Bofthevesselsareconnectedin15 paralleltoablow-offoutput15throughoutputpipes 16A,B.Eachoftheoutputpipes16A,Bisprovidedwitha controllableoutputvalve17A,Bwhichwhenenabledshutoff thecorrespondingoutputpipesuchthatnogascanflow fromtheentry6A,Bofthevessel4A,Bconcernedtothe20 blow-offoutput15. Thesystemcomprisesavariablebypasspipe18connecting theinlet1totheoutlet2whilebypassingthedryer.This allowstosplitoffaportionofthegastobedriedatthe25 inlet1andtomixthisportionwiththedriedgas,exiting thedryer3throughtheexitpipes10A,B,inthedischarge pipe24upstreamoftheoutlet2.Thevariablebypasspipe 18isprovidedwithacontrollableadjustablevalve19for adjustingtheportionofthetobedriedgassplitoffin30 thevariablebypassconduit.Whenadjustingthevalve19a BE2024 / 5907 13 cross-sectionalareaofthevariablebypasspipe18is locallychangedhenceaffectingtheflowrateofthegas throughthispipe.Thevalvecanbeadjustedsuchthatthe flowofgasthroughthevariablebypasspipe19is completelycut-off.5 Optionallyafixedbypasspipe20maybeprovidedparallel tothevariablebypasspipe18,thefixedbypasspipebeing providedwithacontrollablevalve28foropeningor cuttingoffthefixedbypasspipe.Thiscontrollablevalve10 28allowstocutofthefixedbypasspipewhennobypassis neededordesired. Thesystemcomprisesafilter21positionedinthe dischargepipe24upstreamtheoutlet2forfilteringthe15 gastobedischarged.Betweenthefilter21andtheoutlet 2apressuredewpointsensorisprovidedfordetermining thepressuredewpointofthegastobedischarged. Alternatively,whennofilterisprovided,amixingvessel canbeused.20 Acontroller23isprovidedwhichisoperativelyconnected tothepressuredewpointsensor22,thecontrollable adjustablevalve19,thecontrollableinletvalves8A,B, thecontrollableoutletvalves11A,B,thecontrollable25 inputvalves14A,B,andthecontrollableoutputvalves 17A,Beitherviacontrolcablesorwirelessly(notshownin figure1). Thecontroller23isconfiguredtoregulatetheportionof30 thegastobedriedsplitoffinthevariablebypass BE2024 / 5907 14 conduit18byadjustingthecontrollableadjustablevalve dependingonthevalueofthepressuredewpointofgasto bedischargeddeterminedwiththepressuredewpointsensor 22.Thecontroller23isconfiguredtoswitchthe controllableinletvalves8A,B,thecontrollableoutlet5 valves11A,B,thecontrollableinputvalves14A,B,andthe controllableoutputvalvestoswitchfromanenabledstate toadisabledstateandviceversadependingonthe operationofthedryer3. 10 Theoperationoftheexamplesystemfordryinggas accordingtotheinventionasdepictedinfig.1is explainedasfollows.Thesysteminthisexampleisoperatedcyclicallysuchthat15 duringeachcycleoneofthevessels4A,Bofthedryer3is operatedinthedryingmodeandishenceactingasadrying vesselwhiletheothervessel4A,Bisoperatedasa regeneratingvessel. 20 Atthestartofafirstdryingcyclethedryingvesselis vessel4A,hencethecontroller23hasdisabledinletvalve 8A,andoutletvalve11A,andenabledinputvalve14Aand outputvalve17A.Theregeneratingvesselisvessel4B, hencethecontroller23hasdisabledinputvalve13Band25 outputvalve17B,andenabledinletvalve8B,andoutlet valve11B.Asaconsequenceaportionofthetobedried gassuppliedattheinlet1flowsthroughpipe7A, entersthedryingvessel4Athroughentry6A,andisguided totheexit9Athroughthedesiccant5A.Thedesiccant30 extractsmoisturefromthegasduringtheflowofthegas BE2024 / 5907 15 throughthevessel4A.Thegasthatleavesthevessel4A throughexit9Awillhencebedrierthanthegasthat enteredthevessel4Aviatheentry6A.Thedriedgasthen flowsfromtheexit9Athroughtheexitpipe10Atothe dischargepipe24.5 Thecontrollableadjustablevalve19isadjustedbythe controller23toasetvaluesuchthatasmallportionof thegastobedriedflowsfromtheinletthroughthebypass pipe18tothedischargepipe24whilebypassingthedryer10 3.Atthedischargepipethisbypassportionofthegasis mixedwiththedriedgasexitingthedryer3viaexitpipe 10A.Theresultinggasmixtureisguidedthroughafilter 21totheoutlet2,whichcanbeconnectedtoaconsumer networkand / orapplicationofdriedgas.Attheoutlet2,15 asshowninfig.2,thepressuredewpointofthegas mixtureisdeterminedbymeansofapressuredewpoint sensor22.Inthisexample,thetargetpressuredewpoint fortheapplication25is-40°C.Thecontroller23compares thedeterminedvalueofthepressuredewpointwitha20 predeterminedvalueofthepressuredewpoint.Inthis examplethispredeterminedvalueis-45°C.Basedonthe differencedeterminedthroughthiscomparisonanewset valueforthecontrollableadjustablevalve19is determinedandthecontrollableadjustablevalve19is25 adjustedinordertoreducesaiddifference.Thisisdone iteratively.Asaresultbyvaryingthebypassportionof thegastobedriedastablepressuredewpointisobtained asshowninthecurve26offig.2.Forcomparison,alsothe PDPcurve27withoutanybypassgasisshown,showingan30 unstablePDPcurvewithanaveragePDPvaluesignificantly BE2024 / 5907 16 belowthetargetPDP25. Atthestartofafirstdryingcycletheregenerating vesselisvessel4Bandthecontroller23hasdisabled (opened)inputvalve14Bandoutputvalve17B.Asa5 consequenceincasesaturateddesiccant5Aispresentin vessel4Bthegenerationgasissuppliedtothe regenerationinput12andguidedthroughinputpipe13B. Theregenerationgasenterstheregeneratingvessel4B throughexit9B,andisguidedtotheentry6Bthroughthe10 desiccant5A.Theregenerationgashasasufficientlylow relativehumiditytoextractmoisturefromthedesiccant5B presentintheregeneratingvessel4B.Inotherwordsthe desiccantisdriedintheregeneratingvessel4B.Thehot moistgasthatleavesthevessel4Bthroughentry6Bflows15 fromtheentry6Bthroughtheoutputpipe16Btotheblow- offoutput15whereitisblown-off.Whenduringthedryingcyclethedesiccant5Bis sufficientlyregenerated(dried),theregeneratingvessel 4Bgoesintostandbyandtheflowofregenerationgas20 throughthevessel4Bisinterrupted. Oncethedesiccant5Aofthedryingvessel4Areachesa certaindegreeofsaturation,forinstancewhenthe pressuredewpointdeterminedofthegasmixtureexceeds25 thepredeterminedvalueof-45°C,theflowofthetobe driedgasandtheregenerationgascanberedirectedby switchingthecorrespondingvalvessuchthattheformer dryingvesselisactingnowasaregeneratingvessel4Aand theformerregeneratingvesselisactingnowasadrying30 vessel4B.Inotherwordsthevessels4A,4Bofthedryer3 BE2024 / 5907 17 areusedcyclicallyfordryingandregeneratingasafter eachcycletheroleofavesselisswitchedfromdrying vesseltoregenerationvesselorviceversa. Thepresentinventionisinnowaylimitedtotheformof5 embodimentdescribedbywayofanexampleandrepresented inth.