Ion Exchange Process Design

© j Woolley 2012 Ion Exchange Design Process Watercare Ltd International Joe Woolley © j Woolley 2012 Aim ofionexchangeprocess To reduce Dissolved theTotal Solids (TDS) ofthewaterthat specified to for subsequent use. © j Woolley 2012 ae opsto TDS - Composition Water Organics (humates, fulvates etc) are generally attracted to anion etc) fulvatesare generallyattracted resin (humates, Organics Hardness Temporary Hardness Permanent Cations Mg Na Ca K Anions HCO SiO NO SO CO Cl 4 2 3 2 3 HCO CO EMA Alkalinity 3 2 HCO CO 2 3 © j Woolley 2012 • • Resins) functional Process (Strongly Demineralisation The IonExchange • Strong base anionresins (SBA)exchange OH (OH portion and areregenerated of TDS by dilutesodiumhydroxide portion and areregenerated of TDSby diluteacidsolution(H Strong acid cationresins (SAC) exchange H Feed Water Feed Water – Anion exchange better from acid solutions acid from better Anionexchange – hydroxides cation insoluble of Preventsprecipitation – – Water becomes decationised resulting in a solution of weak and strong strong and weak of a solution in resulting decationised becomes Water – – Weak and strong acids removed acids strong and Weak – acids - ) Æ Cation (H + form) Æ Anion (OH + - ions with cation - form) ions with anion Æ Demin Water + ) © j Woolley 2012 • • • • • Cycle Exchange Operating Ion The Demineralisation regeneration (Co-flow regeneration) follows:operating cycleisas demineralisation plant with downflowservice and downflow The Ion exchangebatch process process isa Resin rinsing Resin regeneration Resin bedbackwashing Demineralisation service flow/resin exhaustion Regeneration cycle © j Woolley 2012 SiO Ca, Mg,Na, K Process is SAC Demineralisation Simplest The Water Raw 2 , HCO Na leakage Water.Decationised 3, Cl, NO 3 , SO 4, Æ H Strong Cation SBA + SAC Acid Form HCl, HNO from HCO SiO 2 , CO OH Strong Anion Base SBA - 2 3, 3, Form ( carbonic acid mainly acid mainly ( carbonic ) H 2 SO Demineralised Water Demineralised 4, Na &SiO 2 leakage Service Flow © j Woolley 2012 SAC +SBA SAC RESIN Mg Na Ca K HCO SiO NO SO CO Cl 4 2 3 2 3 SBA RESIN Service Flow © j Woolley 2012 • Cation ResinExhaustion Cation exchange where – (R (M • (R • •( - H + R ) +(M - + - H M A + - + ) is the regenerated cation exchange resin ) exchange cation is theregenerated ) is the dissolved salt in salt in the rawwater ) isthedissolved ) cation resin is theexhausted + A - ) ÅÆ (R - M + ) + (H ) + A - ) Service Flow © j Woolley 2012 • Anion ResinExhaustion Anion exchange where – (R (R • (H • •( + OH produced in the cationexchangeprocess above R + + - + ) +(H A A OH - - ) anion resin is theexhausted ) is the acid produced from the anions in therawwaterand theH ) from theanions is theacidproduced - ) is the regenerated anion exchange resin ) anion exchange is theregenerated + A - ) ÅÆ (R + A - ) + (H + OH - ) + ions Service Flow © j Woolley 2012 • • SAC&SBA – Resin Selectivity Strong base anion(SBA) exchanger Strong acid cation(SAC) exchanger SiO – SiO – SiO – bed resin the tobreakthrough Nafirst – resin weaklyheld bycation Namost – a SAC/SBA plant exhausts plant a SAC/SBA through the resin bed resin through the 2 2 2 / HCO / HCO / HCO 3 3 3 breakthrough often occurs when occurs often breakthrough therefore the first tobreak first the therefore most anion resin weaklyheld by most ain nosAffinity Anions Cations Mg Ca Na H K - + + 2+ 2+ + HSiO HCO SO NO OH Cl 4 - 3 2- - 3 - 3 - - Service Flow Higher Lower © j Woolley 2012 The Chromatography Effect The Chromatography ƒ Raw water Raw Partly usedcation resin SO Ca 2+ 4 2- , Mg , Cl - , NO 2+ , Na 3 - , HCO + 3 - , SiO Ca Mg Na H + 2+ 2+ + 2 • SO H + , (Equilibriumleakage Na ABSORPTION OF IONS CHROMATOGRAPHIC 4 2- – – , NO Decationised water reproducible reliable and extremely efficient, adsorption process is remain at topofbed adsorbed first and more attractive get ions 3 - , Cl - , CO Service Flow 2 , SiO 2 + ) © j Woolley 2012 The Chromatography Effect The Chromatography ƒ Raw water Raw Partly usedcation resin SO Ca 2+ 4 2- , Mg , NO 2+ 3 - , Cl , Na - , HCO + 3 - , SiO Ca Mg Na H + 2+ 2+ + 2 • SO H + , (Equilibriumleakage Na 4 ABSORPTION OF IONS CHROMATOGRAPHIC 2- – – , NO Decationised water flow distribution of water depends on good shape "front"of through the bed gradually movedown displaced and attractive are ions through thebed, less as more ionspass 3 - , Cl - , CO Service Flow 2 , SiO 2 + ) © j Woolley 2012 The Chromatography Effect The Chromatography contaminant ions contaminant alwayscontain some and will regenerated cannot befully resins and SBA SAC ƒ Raw water Raw Exhausted cationresin SO Ca 2+ 4 2- , Mg , NO 2+ 3 - , Cl , Na - , HCO + Ca Mg Na H 3 - + 2+ , SiO 2+ + 2 SO H + , (Equilibrium leakage Na 4 2- , NO • 3 - ABSORPTION OF IONS CHROMATOGRAPHIC , Cl Decationised water – – – - , CO minimal calcium breakthrough is over-run, therisk of unless is the unitgrossly is sodium through break to ion first reaches the distributor occurs when first front breakthrough of ions 2 , SiO 2 Service Flow + plus Na + slip) ) © j Woolley 2012 Selectivity Profiles Selectivity and SBA SAC Summary Service Flow © j Woolley 2012 • • • • Resin Capacity Operating capacity issubstantially lowerthan Totalcapacity Many useunitsofgramsCaCO Operating capacity Total capacity: – Quoted in equivalents/litre of resin and equivalents/kg ofresin resin andequivalents/kg of Quotedinequivalents/litre – process ion exchange usedinthe capacity total ofthe Proportion – ofresin resin andequivalents/kg of Quotedinequivalents/litre – the resin on sites ionexchange total Represents the – 3 ir frsn–g ofresin– / litre CaCO 3 /l Resin Service Flow © j Woolley 2012 • Operating Capacity Operating design featureanddependson: capacity isa – Economic constraints of the design the of constraints Economic – Contact time – level regeneration Chemical – Regeneranttypeandconcentration – point) (end specification water Product – “health” resin and capacity Resintotal – Service flow time – Feed flowrate water – water raw of TDSandcomposition – Service Flow © j Woolley 2012 • • Conditions Operating Service Flow Typical Operated to predetermined Operated breakthrough to point lwae 40BV/h Flowrate: 8 - – Anion breakthrough based on silica – variable feed water variablefeed – silica Anionbreakthroughbasedon – conductivity basedon Cationbreakthrough – (common) set-point Batch – – For a given flowrate, lower dP and higher capacity can be achieved with canbeachieved capacity lower dPandhigher Foragivenflowrate, – Early breakthrough zone. leadtoadeeperreaction Higherflowratecan – serviceflow) % full (<20 flow distribution givepoor Verylowflowratecan – narrow bead size distribution and smaller beads. and smaller narrow beadsizedistribution (>60 m/h) bedcapacity and lower resin • Special distribution system distribution Special • Service Flow © j Woolley 2012 • • • • Co-Flow Exchange Process– Ion The Demineralisation Resin rinsing Resin regeneration Resin bedbackwashing Demineralisation service flow/resin exhaustion © j Woolley 2012 • • • • Resin bedbackwashing Assists: Prevents: Required to: 60% Flow to expandresin bedtypically 40- – Efficiency of demineralisation & regeneration process regeneration & demineralisation of Efficiency – drop Highbedpressure – bed resin the Reclassify – fines andresin suspendedsolids Remove – bed resin De-compact – Reducedserviceflow • beadbreakage Resin • Bed Backwashing © j Woolley 2012 specific resin typesspecific resin for conditions Technical operating supplier’s forprecise Data Sheet Note: Consultresin • • • • Conditions Typical Operating Backwash flowrate dependson: 2 to4BVbackwash volume Use de-cationised water(co-flow anion) Use raw water (coflow cation) – Resinbeadsizedistribution – size bead Resinmean – – can depend on feed water solids content and can be extended as andcanbeextended solids content candependonfeedwater – Water temperature Water necessary Bed Backwashing © j Woolley 2012 Backwash on Temperature Effect of At equilibrium Bed Backwashing © j Woolley 2012 • • • • Exchange Cycle Ion The Demineralisation Resin rinsing Resin regeneration Resin bedbackwashing Demineralisation service flow/resin exhaustion © j Woolley 2012 Which Cation Regenerant? Cation Which • • H C Hydrochloric Acid HCl – CheaperOPEXand CAPEX – Lower efficiency – concentration high bulk withdilution Heatof – TC ratio high TH/ with regeneration Difficult – – More expensive OPEX Moreexpensive OPEX andCAPEX – required volume Greaterstorage – control Needsfume – iron removal Goodfor – – Offers higher resin capacity for given regen level (g given regenlevel for capacity higherresin Offers – during regeneration w/v) (e.g. 5% concentration Canbeusedathigh – 2 SO even onhardwater 4 Sulphuric Acid – acid /l Resin ) © j Woolley 2012 • Regimes Regeneration used to achievean economic working capacity inbothSACand SBA resins. Note: requirement is alwaysA stoichiometric large excessofregenerantover Co-flow regeneration Process is: – Leadsto: – heldion strongest the displace required to ofregenerant Largerquantity – flow the service directionas same inthe Regenerantflow – on the longest path to the bed exit the path to on thelongest • Used when treated water spec isnotstringent Usedwhenwater treated • More forgivingofpoorfeed water quality • equipment Lowercost / simplest • verylowTDSwater toachieve Higherregenerantuse/cost • flow of service on resumption Higherleakage • Resin regeneration © j Woolley 2012 Co-Flow Regeneration High regenerantusage Mechanically simple Mechanically Spent regeneranttodrain * Lower capital cost capital * Lower Lower Lower water quality FEATURES: Feed water Treated water Resin regeneration Regenerant © j Woolley 2012 in leakage resin bedresults regenerated of Traceat bottom cations Profile Regeneration SAC Co-flow Resin regeneration © j Woolley 2012 • Counter-Flow Regeneration Counter-Flow used to achievean economic working capacity inbothSACand SBA resins. Note: requirement is alwaysA stoichiometric large excessofregenerantover Counter-flow regeneration Process is: – leads to: regeneration to co-flow Compared – – Highest quality regen chemical on least exhausted resin means higher means resin exhausted onleast chemical Highestqualityregen – flow service tothe direction intheopposite Regenerantflow – quality inservice • Used when treated water with a higher specification is required with ahigher specification Usedwhenwater treated • than regeneration equipment co-flow complex higher cost/more Historically • use or Lower higher capacity regenerant • of flow service Lowerleakageonresumption • resin at outlet service regenerated Highest • Resin regeneration © j Woolley 2012 Counter-Flow Regeneration Counter-Flow Mechanically complex Mechanically Uses lessregenerant Higher quality water Higher capital cost Higher capital FEATURES: Feed water Regenerant NOTE: Counter-flow regeneration may be difficult when bedifficult regeneration may NOTE: Counter-flow water has elevated suspended solids suspended has elevated water Spent regenerant todrain • Treated water Different designs: Resin regeneration • • • • Packed bed Packed Split flow down Water hold holddown, Air © j Woolley 2012 polishing zone polishing creating highly regenerated, is very Resin atserviceoutlet Regeneration Profile Regeneration SAC Counter-flow Resin regeneration © j Woolley 2012 • • • Plants Regeneration Counter-flow Bedsin Compact Maintaining The answerto holdthebedinplace is by: Upflow of regenerants wouldtend tofluidise and mixthe bed disturbed during regeneration. Effective counterflow regeneration requires thattheresinbedisnot – – – – Packed Bed regeneration) flow(Co-Counter Split down Water hold Airhold down Resin regeneration © j Woolley 2012 quality dependent onfeed outlet qualityis Co -flowregenplant Resin RegeneratedSAC Counterflow and Co-flow from Leakage Resin regeneration © j Woolley 2012 • Obtained Quality Treated Water A SBA SAC – – Counter-flow Regeneration (25 Counter-flow Regeneration – Co-flowRegeneration(25 – Sodium • Silica • Conductivity • Silica • Conductivity • Tp 1) (Type 0.05 - 0.2 mg/l as Na 0.2mg/l 0.05 - asSiO 0.05mg/l 0.002 - . 2 0.5 - asSiO 0.5mg/l 0.1 - 30 5 - o C) P P S/cm S/cm o C) 2 2 Resin regeneration © j Woolley 2012 specific resin typesspecific resin for conditions Technical operating supplier’s forprecise Data Sheet Note: Consultresin • • Operating Conditions Operating Typical ResinRegeneration SBA resin SAC resin – Dosage 60 to 160g NaOH/litre ofresin NaOH/litre Dosage60to160g – NaOH 3to6% – 2 to 4 BV/h – resin of 160gacid/litre Dosage60to – – 3 to 6% HCl or 0.7 to 3% H 0.7 to 3to6%HClor – – 2 to 8 BV/h dilute acid flow acid dilute BV/h 2to8 – • (often to suit neutral effluent) (oftento suit neutral • •H 2 SO 4 tends to use highrate tends touse 2 SO 4 (g CaCO (g Capacity Resin 3 /l) Regenerant Usage Resin regeneration anion resin cation resin (g/l) © j Woolley 2012 • • • • Exchange Cycle Ion The Demineralisation Resin rinsing Resin regeneration Resin bedbackwashing Demineralisation service flow/resin exhaustion © j Woolley 2012 specific resin typesspecific resin for conditions Technical operating supplier’s forprecise Data Sheet Note: Consultresin • • • Resin Rinsing Fast Rinse Slow/Displacement rinse resin beds. Required to removeregenerant&eluted contaminants from the – Flowrate as feed water flowrate until treated water quality achieved waterquality treated flowrate until Flowrateasfeed water – save water to resins andanion round cation water Recirculation of – 1-2BV) Ideallyrinsetodrain(min – regeneration chemical the of Continuation – flow. water ordilution (typical) 5BV/h Downflow waterat of3BV – • Co flow plant will recycle to below achievable outlet quality to Co below achievable flow plantwillrecycle • Resin rinsing © j Woolley 2012 Alternatives toSAC Alternatives • • Examples are: economics of treating range offeedwatercompositions. a Alternative plant layoutsalternative and resins forimproved – Use Weak Base Anion (WBA) resin before SBA resin SBA before resin (WBA) Anion Base UseWeak – resin beforeSAC (WAC) resin Cation Acid UseWeak – SBA unit the before AddaDegasser – Æ SBA © j Woolley 2012 Role of the Degasser Role ofthe exchanger Cation Degasser exchanger Anion Degasser © j Woolley 2012 *After SACResin Degassing (Mg) (Na) (Ca) (K) H H (HCO SiO NO CO SO CO Cl 2 4 2 3 2 3 ) Can be degassed * Can bedegassed Can bedegassed Residual CO 2 ” 5mg/l Degasser © j Woolley 2012 The Degasser • • • • From cation exchanger From cation Does little workthe raw water if alkalinity is low Takes loadoffAnion column. Loweroperating cost dioxide usingair Used toreduce alkalinity in Relies on equilibriumbetween CO Packed column Packed Reservoir decationised ~~~~~~ ~~~~~~ ~~~~~ @ @ @ @ @ @ @ @ @ @ @ @ 2, @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ HCO @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ 3, water bystripping carbon and pH Air Fan Toexchanger anion Degasser © j Woolley 2012 • Summary A G–SBA DG– SAC - rae ae ult sSC-SBA - asSAC quality Treatedwater – sump degasser from Requiresre-pumping – requirement reducedNaOHregenerant dueto savings Operating cost – plants larger savingson Capitalcosts – is resin less therefore reduced, SBA unit the anion loadon Bicarbonate – CO reducesthe Degasser – – Degasser considered when alkalinity is >1 meq/l (>50 g CaCO (>50g >1 meq/l alkalinity Degasserconsidered is when – for SBA resin. SBA for required. 2 to <5mg/l 3 ) Degasser © j Woolley 2012 • • • • • Resin (WAC) Cation Acid of Weak Role Can be used in SAC vessel as layered bed or separate WAC Can beusedinSACvesselas layeredbedorseparateWAC vessel excessacid required of to regenerate the SACresin Regenerated SAC (“thoroughfare”)in serieswith utilises the large Regenerated quantities with low of acid Higher capacity than SACeq/l total resins(4 capacity) bicarbonate Used for cationremoval (usually associated Ca andMg) with Feedwater – Acid – theory 105%of – hardness” “temporary – Æ SAC Æ Æ WAC WAC Æ SAC Weak Acid Cation Weak Acid © j Woolley 2012 • Resin (WBA) Base Anion Weak Role of Weak resin base anion Weak – Can be regenerated in series with SBA resin using the excess alkali using theexcessalkali SBA resin series with Canberegenerated in – theory) (130%of alkali of low quantities Regeneratedwith – theSBA protect (helps high organicload with onwater Canbeeffective – off theload resin,taking SAC after (FMA) acids strong Usedtoremove – CO Doesnotremove – polyacrylic Polystyrenic or – from SBA (“thoroughfare”) SBA from regenerated easily andis resin) resin the SBA • Alkali Alkali • Æ SBA Æ WBA 2 or SiO 2 Weak Base Anion Base Weak © j Woolley 2012 • • • • • • Layered Bed Option • Can be difficult to operate. to Can bedifficult resins functionality and strong weak between difference volume is alarge there whenNot alwayssuitable cost savings incapital is in Main advantage Resin bed separation (stratified bed) maintained on resin backwash by: onresinbackwash bed)maintained (stratified Resin bedseparation beds. individual resin by stillbemet must criteria Resin beddesignandoperating compartments separate in below strong cango Weak resin compartment same in resin abovestrong located can be bed resin Weak functionality – Minimum bead size overlap or very narrow bead size distribution of the two resins distribution bead orverynarrowbeadsize Minimum size overlap – of Density the resins difference – downflow regen upflowservice– Schwebebett– – taiidbd–dwfo evc upflowregen – service downflow bed Stratified – – (special gradesrequired) (special © j Woolley 2012 • Choice ofResinandProcess Choice dependenton: – Environmental Obligations or constraints or Environmental Obligations – Economic constraints (CAPEX OPEX)& – design mechanical Plant – be treated to Flowrateofwater – specification Treatedwater – Raw water composition – Temperature • content Silica • chemicals Resin degradation • Resinfoulants • ofTDS composition Chemical • © j Woolley 2012 • • • • • Water High Organics Organic minimised design fouling canbe by good Alternatively, useacrylic SBA often help. can aSBA (styrenic oracrylic)before A WBA Organics foul anionresins,particularly SBAstyrenic gels feature A highlevelorganics of may beaseasonal feature or apermanent Regularresinmaintenance – watertemperature above feed Raiseregentemperature – time contact LongCaustic – Demin Process Options Process Demin © j Woolley 2012 When Higher WaterQualityRequired Treated © j Woolley 2012 • • • Water Higher Quality Producing Install polishing system.a Options are: reduced When higher treated waterquality isrequiredthis leakage must be the equilibrium leakage fromtheSACandSBAresins Residual conductivity, sodium andsilicaintreated, due to water is – SAC Polishing bed (Catpol, Hipol) SACPolishingbed(Catpol, – bed Polishing mixed – – Counterflow regen system offers better quality than co flow regen thancoflow quality better offers regensystem Counterflow – system Polishing © j Woolley 2012 • Mixed BedIonExchanger Reduces residual ions leaked from cation and anion resins andanion cation from Reduces residualionsleaked Demineralised Water Demineralised Mixed SAC Mixed and Type1 Exchange Resin SBA SBA H OH + , (Na - , (SiO + ) 2 ) OH H + - regenerant inlet orexitregenerant inlet / distributor, Central collector Deionised Water Deionised Polishing © j Woolley 2012 • • Polishing Mixed BedIonExchange Operating sequence Design ServiceFlow – – SAC resin volume selected to be just above central collector, orbeds collector, central above be just to selected volume SAC resin – used resins 1 SBA Type SAC and – separated by inert layer which surrounds the central collector central the layer whichsurrounds separated by inert • High regeneration levels Highregeneration • used Higherchemical concentrations • of500mm resin depth minimum requires Eachcomponent • m/h) Runsathigh linearrate(45-65 • exhaustion. neverrunto Resins • resin. bed SBA of SAC and Type1through themixed Feed in down-flow • Polishing © j Woolley 2012 Treated Water Obtained Quality Water Treated quality treated water is tobe quality treatedwater achieved. to ifthedesign bestrictlyadhered must Note: specifications and operating All thedesign – Co-flow or Counter-flow regeneration (25 regeneration Co-floworCounter-flow – – Treated water quality from quality Treatedwater – SAC – resin beds – no quality advantage noquality beds– resin Sodium • Silica • Conductivity • Æ SBA Æ Polishing MB Polishing 0.01 - 0.1 mg/l as Na 0.1mg/l 0.01 - SiO <0.02 mg/las <0.1 P polishing S/cm mixed beds: mixed 2 Û C) of the main SACandSBA the main C) of Polishing © j Woolley 2012 • • • • • Cation Polisher • • • Can normally achieve0.01 ppmNa <0.1µS/cm &< oslc eoa notasrobustmixedbed No silica removal – Small resinvolume, highlyregenerated, high BV/H regenerant) Na isdominantcontaminant at SBAoutlet(mainlyfrom caustic Used to removeNaOH leakagefromSBA bed Usually used withcounterflow regenerated SAC andSBA No additional No regeneration cost Very costeffective – Can be used as a silica inferential endpoint device (HCO inferentialendpoint silica a Canbeusedas – or150m/h 500BV/H typically Operateat – – Acid thoroughfared with SAC unit. SAC with Acid thoroughfared – on anion) 3 breakthrough breakthrough © j Woolley 2012 SiO Ca, Mg,Na, K Process is SAC Water Raw 2 , HCO Na leakage Water.Decationised 3, Cl, NO 3 , SO 4, Æ H Strong Cation SBA + SAC Acid Form Æ SAC SiO HCl, HNO 2 , CO OH Strong Anion Base SBA 2, - 3, Na &SiO Form H 2 SO 4, 2 leakage SiO Form SAC 2 H leakage + Service Flow © j Woolley 2012