Purolite_IonExchangeDesignCalculation

8/13/2019 Purolite_IonExchangeDesignCalculation

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lite Ion Exchange Design Calculation.Help

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urolite Ion Exchange Design Calculation ProgramContents of help:

0 Water Treatment

1 Softening

2 Dealkalisation

3 Demineralisation

4 Working Mixed Beds

5 Polishing Mixed Beds

6 Nitrate Removal

9 Program Difficulty

1 Influent Water Data

5 Design Calculation

6 IX Process Options

7 Treated Water Specifications

8 Neutralisation of regenerants

9 Dealkalisation Options

1 Mixed Bed Options

2 Nitrate Removal

63 Design Calculation - Mixed Beds

64 Mixed Beds

65 Water Analysis

66 Extra Analytical Data

67 RAW WATER origin and pretreatment

68 Cycle Time and Flow Rate

69 Choice of Resin

70 Regeneration

71 Plant Design

72 Treated Water Quality

73 Pressure Drop Calculation

74 Operating Conditions - Working Mixed Beds

75 Operating Conditions - Polishing

76 Design Objectives

77 Overrun

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0 Water Treatment

Select the type of process to be carried out in your plant.

SOFTENING: Exchange of hardness ions for sodium ions.

DEALKALISATION: Removal of hardness associated with bicarbonates (alkalinity) using a weak acid resin. Therogram also includes permanent hardness removal by use of a strong acid cation resin, in the softening mode whicometimes used in breweries.

DEMINERALISATION: Water can be demineralised by means of cation and anion resins in separate vessels.Weakly functional resins can achieve partial demineralisation with economical use of regenerants. More completeemineralisation requires the use of strongly functional resins and higher regeneration levels.

MIXED BEDS: Water can be purified to higher standards using a Working Mixed Bed or further purified aftertandard demineralisation using Polishing Mixed Bed to remove any leakage remaining. Where the inlet load isegligible, this process is termed "polishing". If the ion exchange load is high enough to utilise a substantial proporf the available operating capacity, such as water treatment directly after demineralisation, this is termed a working

mixed bed.

NITRATE REMOVAL: There is a recommended limit for nitrate in potable water published by the World HealthOrganisation. Consequently many countries have placed their own limits to cover the quality of the potable watervailable. Nitrate is removed by strong base anion resins. Where the water to be treated contains sulphate, this isemoved preferentially, and nitrate capacity is reduced because the resin is loaded with sulphate. Purolite 520E is


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elective for nitrate over sulphate and all other common anions, thus all the capacity is available for nitrate removal

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21 Softening

) The standard choice is 1 - Purolite C-100 or C-100E. Only a change to very special conditions, (high osmotichock, very high TDS, presence of oxidising agents etc.) would create a need to select another resin. The Purofinerade offers advantages of a smaller plant and use of less regenerants.

2) Select one of the options shown in scroll box. Option 1 (Co-flow), used by default, is simpler to construct andperate. However salt utilisation and hardness leakage are both high. Option 2 (Counter-flow) offers the lowesteakage.

3) Input the Regeneration level grams per litre of resin:

Co-flow (Option 1): 90-300 g/l

Counter-flow: 40-150 g/l

4) Standard concentration is 10% . Other concentrations will reduce operating capacity especially for Co-flow

peration.

5) Bed depth is important for counter-flow operation. Deeper beds above 0.7 m give higher capacity and lowereakage.

6) The design program calculates capacity and leakage. If results are unsatisfactory, changes in regenerant dosage,mode, and flow rate can offer improvements.

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22 Dealkalisation

Purolite weak acid cation resins are capable of removing cations associated with bicarbonate anions (orarbonates/hydroxides) to reduce total solids, and especially temporary hardness. Its main advantage is thategeneration can be achieved with practically a stoichiometric quantity of regenerant.

The capacity for temporary hardness ions is particularly high, especially at low flow rates. (Removal of temporaryardness can reduce precipitates and scale which normally occur on the boiling of water.) Where bicarbonates aressociated with sodium rather than hardness ions the operating capacity is significantly reduced. It should also be nhat lower feed water temperatures reduce operating capacity significantly. Also low regeneration temperatures incrhe risk of calcium sulphate precipitation. Flow rates should be maintained to ensure regenerant is removed from thesin before precipitation commences.

Dealkalisation can also form part of a demineralisation process, the salts of mineral acids are treated on the strong aation filter which follows the weak acid cation filter. Depending on the proportional load on each filter it can alsodvantageous to allow some or all of the sodium alkalinity to over-run to the strong acid filter. The redistribution ooad can produce a better balance in the size of filters and can have the added advantage that the operating capacityhe weakly functional resin improves if the hardness to alkalinity ratio being treated approaches 1.

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3 Demineralisation

Demineralisation works by exchanging all cations of salts present in the water to be treated to hydrogen, thusonverting the salts to acids. Passing the water through a following strong base resin in the hydroxide form willxchange the anions for hydroxide by acid neutralisation to produce demineralised water of reasonably good qualityo obtain purer water a polishing stage should be added. This will form part of a separate design program.

Unfortunately it is quite difficult to regenerate resins with strongly functional active groups, especially strong basenion resins which have high selectivity for the mineral anions, sulphate, nitrate, and chloride. A large excess ofodium hydroxide is therefore necessary to achieve a good regeneration. The Type-I strong base anion resins Puroli

A-400, A-600, A-500, A-505, are more thermally stable than Type-II resins, Purolite A-200, A-300, A-510 and thre also more selective for weak acids. However they are the most difficult to regenerate. Acrylic Type-I resin Puro

A-850 can offer good silica removal and reasonable regenerability, however this type is also less thermally stable.ype-II resins are also easily regenerated, but silica leakage is often significantly higher.

Of the resins mentioned, Purolite A-500, A-505, and A-510 are macroporous. This more open structure also offersignificant improvement in terms of resistance to organic fouling compared with the gel counterparts. However thecrylic resins Purolite A-850 and A-870 offer an even more effective solution to this particular problem. These reslso have superior resistance to osmotic shock compared to gel- type polystyrenic resins. Substantial savings can be

made to regeneration costs by introduction of resins with weak functionality before their strong resin counterparts.Weak base resins are frequently used in front of strong base resins. These effectively remove mineral acids which c

e regenerated with alkali using only an excess of 20% over theory in many cases. On the other hand strong baseesins often require over 50% stoichiometric excess alkali for effective regeneration. The strong base resins may thee used to remove the weak acids such as silica and carbon dioxide.

Hence there are a large number of process options to choose from. Purolite technical sales staff are knowledgeablemaking the required choices. Purofine variations of these resins may be chosen. They may be used at higher flow rn shallower beds, at lower levels of regeneration, offering considerable savings in running costs and producing betreated water quality. These differences necessitate different operating conditions from those used for standard resino default values for standard resins are not appropriate. If the Purofine option is chosen at the Design Option stageorrect default values may be applied making for a more rapid solution. Of course only Purofine Grades may be usere.

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24 Working Mixed Beds

For operation, please obtain the separate disc from Purolite. Working mixed beds are used to directly ionise a feedwater, typically with low total dissolved solids. They may also be considered when the residual leakage afteronventional 2-4 stage [demineralisation] processes is high. The section on Water Treatmentexplains their use in metail. Influent Water Datadescribes the water to be treated and explains the impact of the water analysis on therocess. Ionic loads are lower than those treated by demineralisation, so specific flow rates and linear velocities mae higher than those used for demineralisation.

Beds should be sized to optimise flow rates. However constraints to meet ionic loads and resin operating capacity pply.

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5 Polishing Mixed Beds

or operation, please obtain the separate disc from Purolite. Polishing is the term applied to the removal of the lastraces of ionic impurities in treated water. For further information see Influent Water Data.Efficient polishing is


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ormally achieved using highly regenerated mixed beds of strong acid cation resins and strong base anion resins.ecause the ionic loads are very low, the flow rates used are usually much higher than those used for demineralisathe bed size is designed to optimise flow rate. The choice of IX process optionsenables selection of three polishingystems, preferred resin ratio, internal or external regeneration, use of Trilite, and, if chosen the volume of inert resequired. The Design Calculationenables sizes of the anion and cation resin components to be calculated.

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6 Nitrate Removal

Nitrate removal works similarly to water softening. The resin is used in the chloride form, and the nitrate ion isxchanged for chloride. The regeneration is made with sodium chloride (usually at a concentration of 10%).

Counterflow regeneration is generally recommended. This gives a lower nitrate leakage. If a higher leakage iscceptable it is generally more economic to blend back raw water than to use Co-flow regeneration. If co-flowegeneration has to be used for any reason, it is often advisable to give the resin a mix after the regeneration rinse.

will disperse the bank of nitrate form resin left at the bottom of the bed and produce a lower nitrate leakage initiallnd a more consistent leakage through the run. In order to further improve the quality of the treated water up to 25%he sodium chloride, may be replaced with a sodium carbonate wash at a concentration of 5-10%. For each reductif 10g/L of sodium chloride a replacement with at least 20 g/L of the sodium carbonate is needed. In any caseignificant losses in performance can often be expected if the sodium chloride level falls below 90g of NaCl/Litre oesin.

he choice of resin will depend upon the feed water. In particular the ratio of nitrate/nitrate + sulphate will determihe choice of a conventional resin or a nitrate selective resin, Purolite A520E. If in doubt, the latter is recommendeny case Purolite A520E is recommended when the above ratio is less than 0.6. In fact advantages in operatingapacity are not usually noticed unless the ratio is less than 0.5, however there are other advantages obtained fromsing Purolite A520E. Firstly, if there are sulphates in the water, over-run of the cycle, can produce water which isigher in nitrate than the original feed solution. This is because the sulphate displaces and concentrates the nitrate ihe ion exchange resin. When the Purolite A520E is used the worst scenario is that the water remains as if there weo nitrate removal treatment. Thus when using a standard resin more careful and expensive monitoring is

ecommended. Secondly the nitrate selective resin does not, on average, substantially remove the sulphate from theeed water by exchange of this ion for chloride. Hence there is less risk to exceed the limits of chloride in potable

water. (WHO limit is 450 mg/L).

he problem of exceeding the WHO limits on chloride and sulphate (250 mg/L) can be lessened by the use of aicarbonate wash after the regeneration. This means that during a portion of the run, chloride is exchanged foricarbonate, while sulphate is also retained in the resin. Thus the average leakage of the anions of mineral acids iseduced.

Where the waters to be treated are high in hardness ions there is a possibility of precipitation of these ions in the rehe use of a small softener to treat the water used to dilute the sodium chloride regenerant and for the water used f

he displacement rinse is required to avoid this problem. The Puredesign softening program can be used if necessars also possible to combine nitrate removal and softening. The SAC and SBA resins may be combined as layers in essel with the SAC resin as the lower layer.

he Puredesign programs for nitrate removal and softening are used to find the solution for each layer in the vesselWhen working out the vessel geometry enough room should be left to accommodate the partner resin. Theecommended aspect ratio (height/diameter) for each layer should be less than 1 and the bed depth of each layerreater than 750 mm.

When conventional resins are chosen, the choice will depend on a number of factors. Type I resin will in generalmaintain a slightly higher capacity than the Type II resin, and give a slightly lower leakage in counter-flow operati

his is so small, it is not shown in the program. If there is any risk of high pH in any part of the cycle, Type-II resi


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re preferred. When operating at higher flow rates, or in vessels of higher aspect ratios (near or above 2) macroporesins are preferred.

he nitrate removal process is rarely if ever affected by organic fouling. The need for quite high levels of sodiumhloride for regeneration to displace the nitrate avoids this problem. Like all resins, high levels of iron in the feed

water should be avoided, see the warning on water analysis. When ion exchange resins are used for potablepplications, the control of bacteria is of great importance. This is particularly true of nitrate removal. Nitrate is autrient, and if allowed to remain on exhausted resin is can support the rapid growth of bacteria throughout the ionxchange plant. Once this happens, it can be difficult to remove. For more information on resin storage and

isinfection, please refer to the Purolite bulletins "The storage and transportation of ion exchange resins" and "Theouling of ion exchange resins and methods of cleaning". Briefly if the plant has to be shut down, the resin should ackwashed, treated preferably with alkaline brine or regenerated, and stored in salt solution.

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9 Program Difficulty

Was the complete water analysis entered? If not, please obtain more data. Otherwise please contact your local saleffice with details of resin type in operation at the time of warning.

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1 Influent Water Data

or further information select one of the options below.

RAW WATER origin and pretreatment

WATER ANALYSIS

XTRA ANALYTICAL DATA

MIXED BEDS

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5 Design Calculation

his help screen covers several applications, so do not be surprised to find comments not specifically relevant to anarticular treatment.

irst screen has been provided for the last filter in the process option design. Each screen provides the full design dor one resin filter. Screens sequenced from the last filter to the first.

t may be useful to choose the resin you require at the outset, if you are familiar with your final requirements.Otherwise a choice can be made to enter any two from cycle time, flow rate, and net run. When these are added thehird value and full design data will be calculated for a set of default values. Any parameters highlighted with a yeletter can be altered to provide the required design conditions. When all values are acceptable "CTRL+ENTER" wirovide the next screen so that details of this filter can be entered and adjusted. In many cases there will be annteraction between the filters. Hence you will be returned to the first screen displayed, so that further changes can

made as necessary. You are invited to proceed through the design until design data for the process is complete. TheHome key provides return to the first screen (SBA or WBA) if further changes are required. At this stage there is a


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ption to neutralise regenerants.


CYCLE TIME AND FLOW RATE

CHOICE OF RESIN

REGENERATION

LANT DESIGN

REATED WATER QUALITY

RESSURE DROP CALCULATION

OVERRUN

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6 IX Process Options

The choice of process options will depend on several factors. The following comments are offered for guidance.Where the plant is small (less than 1-1.5 m3 of resin per filter) a primary objective is to minimise capital cost, byeduction in the number of units and by not using a degassing tower. Degassing towers are optional in all processayouts.

on Exchange Process Option 1: SAC-WBA

This option is not frequently used, particularly on a large industrial scale. Regeneration is very efficient, but water

roduced is of a comparatively high conductivity, and pH can be less than 7 but variable for a major part of thereatment cycle. Silica and carbon dioxide are not removed.

on Exchange Process Option 2: SAC-SBA

Advantages: Reasonable quality treated water used in any design where savings of regenerants are of lessermportance. CF (Co-flow) exhaustion/regeneration can be used where a conductivity of < 20 microsiemens is requi

CTF (Counter-flow) - where < 4 S is required.

on exchange Process Option 3: SAC-WBA-SBA

This is recommended where EMA/Total Anions is substantial. Advantages: Where a degasser is not justified (low

lkalinity in the feed water). Ideal choice where regenerant savings are important. Counter-flow operation is usedwhere low leakage of ions is required and where use of regenerates is minimised. The user should remember to choorrect bead size grades as applicable.

on exchange Process Option 4: WAC-SAC-WBA

This is rarely used. It would only be chosen to treat a water high in bicarbonates where treated water quality is notritical, and regenerant savings are of first priority.

on exchange Process Option 5: WAC-SAC-SBA


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For treating waters high in bicarbonates, a degasser is useful for larger plants. The user should remember to chooseorrect bead size grades as applicable.

on exchange Process Option 6: WAC-SAC-WBA-SBA

This is the most complicated option and the one in which the design program can save the operator the most time.s used to treat waters with substantial concentrations of bicarbonates, and equivalent mineral acidity. Large plants

would be operated with a degasser. The higher capital cost offers compensation in low running costs, low effluentelease, and ease of neutralisation. Layered beds in the same vessels can reduce capital costs. If there are no separat

ompartments in the vessels, the user must remember to choose correct bead size grades as applicable.

on exchange Process Option 7: SAC-SAC-WBA.

This is rarely used as it produces water of low overall quality, with good removal of cations. It is however used wiAC->SBA to follow as a polisher. This can produce a quality almost as good as counter-flow quality, when used

he co-flow mode. The design program can be used for the full design by operating in two separate stages. The treauality from Option 7 is used as influent for Option 2.

on Exchange Process Option 8: SAC-SAC-SBA

This is a useful option when co-flow is chosen, offering some of the advantages of counter-flow operation, both in

erms of regenerant utilisation and in terms of ion leakage in comparison to a single co-flow system.

on Exchange Option 9: SAC-SAC-WBA-SBA

This is used in place of Option 8 where there is substantial equivalent mineral acidity and offers savings in regenerosts. Where bicarbonates are significant and plant is large, use of a degasser is recommended. The user shouldemember to choose correct bead size grades as applicable.

Having chosen the required process option, the degasser option if selected offers a choice of positions. This is onlymportant where a WBA resin has been selected. The presence of CO2 improves the performance of polystyrenicesins, A100, A105, A103 and A106, hence the degasser should be placed in position 2. Acrylic resins on the otherand can give problems if loaded with CO2 so unless it is certain that performance requirements will be met, for Aosition 1 is recommended.

Options for regeneration offer Co-flow and Co-flow Purofine as separate options. It is preferable to choose Purofit this stage if this option is preferred. PUROFINE RESINS can offer a wide range of advantages depending on theonditions of operation. In softening it can offer higher capacity with consequently smaller vessels, it can also offeretter regeneration efficiency and reduced running costs. Also, if required, superior kinetics offer the option to workigher flow rates and smaller bed depths, offering greater flexibility of design. These changes can be achieved with

minimal increase in pressure drop in carefully engineered systems. Early choice of PUROFINE will set default valuo that the program will run more smoothly to the required design. Five counter-flow options are included. PB denacked bed systems with down-flow service, regeneration up-flow, FB denotes up-flow service with regenerationown-flow. Std. covers the more traditional air, water, or resin hold down systems and split-flow regeneration. The

erformance of any individual engineering design is as much a function of the detailed and sophisticated engineerins it is of the resin per se. It therefore makes it very difficult to distinguish performance differences which are causrom regeneration mode rather than from particular engineering virtues. Thus a standard set of performance data haeen chosen for all three main types of counter-flow regeneration mode. Of course choice of the recommended partize ranges can offer differences in pressure loss, and this data is included. The choice of LB denotes the use of aayered bed of resins with weak functionality as an upper layer and strongly functional resin below. Such systems aperated with upflow counter-flow regeneration, and can offer both savings in the number of vessels and economicegeneration. Counterflow Purofine is also a choice. This may offer a useful combination of high quality of treated

water together with minimum rinse volumes and some small gain in operating capacity and /or regenerant savings. may also be possible to achieve mixed bed quality by specific counter-flow design using Purofine grades.


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7 Treated Water Specifications

The program provides the option to work to specifications for both conductivity and silica levels. In any ion excharocess, the ion leakage may be relatively high after regeneration, depending upon the level of regeneration, but wiapidly fall to a base permanent leakage. This value will be maintained during most of the run, hence in general theverage leakage will be close to the permanent leakage. At the end of the cycle, the conductivity will rise, as will thilica concentration, as the resin becomes exhausted. Hence it is necessary to set acceptable end point limits for bot

onductivity and silica concentration, as requested. Accordingly it is important that the end point levels are sufficieigher than the average levels specified, in order that the end point can be clearly identified by the measuringquipment. This is done automatically when average levels are entered. However options are available to set end-oints closer to or further from average levels. The default levels chosen are typical ones usable in a general case.hey are chosen to allow for a general ease of running of the program across the range of designs. Conversely it is

he intention to suggest that any particular design option should be ideal to treat the default water analysis providedddition leakage and end-point default values are given a wider default spread than that which can be achieved inpecific operation. Hence the user should not be surprised if, when a higher average leakage value is entered, a lownd point than the default is suggested.

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8 Neutralisation of regenerants

Regeneration neutralisation is often an essential requirement. To achieve this it is necessary to increase the regenern either the cation system or the anion system. Generally the minimum regenerant levels have been set to achievepecification of the treated water quality as economically as possible. It follows therefore that the regeneration level

with the higher excess cannot be reduced. Usually this is the value which should be fixed.

n some cases the discrepancy is so wide that the computer cannot achieve neutralisation. Unless a change of procption can be made, the only alternative is to neutralise externally.

t can pay dividends to look carefully at changes to leakage levels as a result of the neutralisation exercise. It is

ossible that resin interaction has brought water quality well within specification and both regenerants can now beeduced without loss in performance. Also changes in overrun from weak to strong resins may offer advantages at tigher regeneration level. Moving through the screens several times before finally optimising the neutralisation may

worthwhile. If it is necessary to reduce regenerants after neutralisation has been invoked, it is recommended to storhe file, recover and modify the input data. In some cases reinspection using "Home" will provide a lower regeneratevel to work with. If there is a substantial load of bicarbonate on the resin, the regeneration will produce saltsncluding sodium carbonate. These salts will give a pH over 8, even though the excess hydroxide has been correctleutralised. It is therefore necessary to increase the acid needed to neutralise these salts. In such cases the excess ofcid can appear to be too high to match the anion excess, even when the regenerant mixture is correctly neutralised

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9 Dealkalisation Options

The dealkalisation option contains the choices of direct dealkalisation which uses solely a weak base resin. This opffers removal but allows the permanent hardness to remain in the treated water. A simple softening treatment toollow the dealkalisation affords the possibility of removing all the hardness whilst at the same time giving removalDS associated with the temporary hardness. Where possible it is recommended to place a degasser or some means

educe the carbon dioxide generated. Where the CO2 is still present it is recommended to use a design factor of 0.7or the softener.

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1 Mixed Bed Options

The option to choose working or polishing mixed beds is made at the outset (water treatment options). This providuitable set of default values in the analysis table. Please refer to Influent Water Data. The Flow Rate in m3/h isequired. Working mixed beds usually follow two stage demineralisation. For working mixed beds proceed to resinatio options. If condensate polishing was chosen, further options apply. Make-up can be used to further purify trea

water from a counter-flow plant or a working mixed bed. The Make-up Polishing operates in the same way as themixed bed condensate polishing. The operator is required to choose the correct option according to his needs and

esign accordingly. The option using a separate cation filter may be chosen where the cation load is especially high

or instance where a high capacity for ammonia, amines, or iron is needed. The print-out naturally records that makp or condensate polishing has been chosen. Options of resin ratio are chosen by the operator, having used therogram to determine the volumes of each component required for the chemical treatment. In some cases the volumf one of the components may be lower than the minimum requirement to achieve suitable contact between resin aolution. 40% cation generally offers a slight excess of cation capacity, for most waters. However, condensate, forxample dosed with ammonia may have an excess of cations requiring treatment, because the ammonia is not fullyonised. Likewise iron may be present as soluble oxides, and only the cation component is needed for their remova

Conversely waters high in silica may need an excess of anion resin to achieve the correct component balance. Whereating condensate contains, an excess of cation resin can be preferable, One of the main objectives is to protect thondensate from contamination with sea water which arises from condenser leakage. If chlorides are not containedhe anion resin, this has the advantage of a more sensitive end-point when hydrogen chlorides are eluted, which giv

higher conductivity per ppm of chloride leakage. Higher ratios of cation/anion are designed to deal with metalydroxides arising from corrosion, or for ammonia removal. If low silica leakage is the main priority, stoichiometriatios should be chosen. Internal regeneration is of course simpler and more economic. However, it can give rise toegenerant hide-out in any joints or vessel irregularities, so reducing treated water purity. Also the risk of regeneranassing directly to the treated water distribution is eliminated. In general, better resin separation can be made in anxternal regeneration backwash vessel, than can be made in situ. For condensate polishing at the highest flow ratesxternal regeneration is essential. The regeneration distribution and collection system inside the polisher can increahe pressure-loss prohibitively. The Trilite Option should be chosen where an inert spacer is required. Care must beaken when making this choice. The presence of oil and grease can make the system unworkable by contamination he inert phase. In such cases, it is often recommended to save the interface after backwashing, and reintroduce at thext backwash. This can be done using the two-phase conventional mixed bed design option, or by adding a notionnert to Trilite (say 1mm bed depth). If this option is used the inert data must be deleted from the print-out. For therilite option it is essential to select TL grade resins in order that the inert resin is properly positioned. Other grade

may be selected for comparative purposes on pressure loss etc. For the two phase option, MB and PL grades areecommended for working mixed beds, MB, TL, PL or Purofine grades are recommended for polishing mixed bedsrades should not be used without consulting Purolite. Purofine grades are recommended for the production of Ultrure Water.

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2 Nitrate Removal

Nitrate removal works similarly to water softening. The resin is used in the chloride form, and the nitrate ion isxchanged for chloride. The regeneration is made with sodium chloride (usually at a concentration of 10%).Counterflow regeneration is generally recommended. This gives a lower nitrate leakage. If a higher leakage iscceptable it is generally more economic to blend back raw water than to use Co-flow regeneration. If co-flowegeneration has to be used for any reason, it is often advisable to give the resin a mix after the regeneration rinse.his will disperse the bank of nitrate form resin left at the bottom of the bed and produce a lower nitrate leakage

nitially and a more consistent leakage through the run. In order to further improve the quality of the treated wateo 25% of the sodium chloride, may be replaced with a sodium carbonate wash at a concentration of 5-10%. For eduction of 10g/L of sodium chloride a replacement with at least 20 g/L of the sodium carbonate is needed. In anase significant losses in performance can often be expected if the sodium chloride level falls below 90g of

NaCl/Litre of resin.


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The choice of resin will depend upon the feed water. In particular the ratio of nitrate/nitrate + sulphate will determhe choice of a conventional resin or a nitrate selective resin, Purolite A520E. If in doubt, the latter is recommendeny case Purolite A520E is recommended when the above ratio is less than 0.6. In fact advantages in operatingapacity are not usually noticed unless the ratio is less than 0.5, however there are other advantages obtained fromsing Purolite A520E. Firstly, if there are sulphates in the water, overrun of the cycle, can produce water which isigher in nitrate than the original feed solution. This is because the sulphate displaces and concentrates the nitrate ihe ion exchange resin. When the Purolite A520E is used the worst scenario is that the water remains as if there weo nitrate removal treatment. Thus when using a standard resin more careful and expensive monitoring isecommended. Secondly the nitrate selective resin does not, on average, substantially remove the sulphate from theeed water by exchange of this ion for chloride. Hence there is less risk to exceed the limits of chloride in potable

water. (WHO limit is 450 mg/L).

The problem of exceeding the WHO limits on chloride and sulphate (250 mg/L) can be lessened by the use of aicarbonate wash after the regeneration. This means that during a portion of the run, chloride is exchanged foricarbonate, while sulphate is also retained in the resin. Thus the average leakage of the anions of mineral acids iseduced.

Where the waters to be treated are high in hardness ions there is a possibility of precipitation of these ions in the rehe use of a small softener to treat the water used to dilute the sodium chloride regenerant and for the water used f

he displacement rinse is required to avoid this problem. The Puredesign softening program can be used if necessar

s also possible to combine nitrate removal and softening. The SAC and SBA resins may be combined as layers in essel with the SAC resin as the lower layer.

The Puredesign programs for nitrate removal and softening are used to find the solution for each layer in the vesseWhen working out the vessel geometry enough room should be left to accommodate the partner resin. Theecommended aspect ratio (height/diameter) for each layer should be less than 1 and the bed depth of each layerreater than 750 mm.

When conventional resins are chosen, the choice will depend on a number of factors. Type I resin will in generalmaintain a slightly higher capacity than the Type II resin, and give a slightly lower leakage in counter-flow operati

his is so small, it is not shown in the program. If there is any risk of high pH in any part of the cycle, Type-II resire preferred. When operating at higher flow rates, or in vessels of higher aspect ratios (near or above 2) macroporesins are preferred.

The nitrate removal process is rarely if ever affected by organic fouling. The need for quite high levels of sodiumhloride for regeneration to displace the nitrate avoids this problem. Like all resins, high levels of iron in the feed

water should be avoided, see the warning on water analysis. When ion exchange resins are used for potablepplications, the control of bacteria is of great importance. This is particularly true of nitrate removal. Nitrate is autrient, and if allowed to remain on exhausted resin is can support the rapid growth of bacteria throughout the ionxchange plant. Once this happens, it can be difficult to remove. For more information on resin storage andisinfection, please refer to the Purolite bulletins "The storage and transportation of ion exchange resins" and "Theouling of ion exchange resins and methods of cleaning". Briefly if the plant has to be shut down, the resin should ackwashed, treated preferably with alkaline brine or regenerated, and stored in salt solution.

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3 Design Calculation - Mixed Beds

DESIGN PRINCIPLES:

n principle the design calculation operates in an identical fashion. However in most cases the objectives are quiteifferent. Optimising capacity and ion exchange load are generally less important than optimising linear flow rate apecific flow rate.


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OPERATING CONDITIONS - WORKING MIXED BEDS

OPERATING CONDITIONS - POLISHING

DESIGN OBJECTIVES

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4 Mixed Beds

wo water treatment options are available. Working Mixed Beds should be chosen where the mixed bed is requiredurify a raw water or from a two stage deionisation, or indeed any water where the concentration of total cations onions is roughly in the range of 5-30 ppm CaCO3 or 0.1-0.6 meq/l. For higher concentrations basic demineralisatiollowed by working or make-up polishing mixed bed should be considered. For lower concentrations or where waonditioning, for example with ammonia, is being used, the polishing program is more suitable. Default values withppropriate ionic concentrations are available for all mixed bed applications. For condensate polishing the concept efault values is different. The default value given represents only a kind of average over a period when for exampmall leak has remained undetected. More usually it is preferable to enter data for the pure condensate and if necesshe analysis of a simulated leak to investigate what happens to the performance. Care should be taken to avoid defaalues used for demineralisation by choosing "New Project" from the File options. There is a facility to add ammonr amines to both mixed bed options. These will be included in the load. To estimate the capacity if operation past mmonia break is intended, the ammonia/amine should be omitted.

RON LOADING

The behaviour of iron can be complex. In particular for condensate polishing it is usual that a high proportion of thotal iron is insoluble or particulate. For this reason the entered value is divided by five to calculate the soluble port

which is treated as ionic load. If it is known that the soluble load is higher, that soluble value should be increased b

actor of five to determine the correct ionic load from iron. This applies to all polishing programs, including make-Condensate can be passed through the make-up plant in certain situations, and in is convenient to treat all polishinghe same way. The objective of any design should be to prevent any build-up of iron on the resin. It presence can aesin kinetics of both anion and cation resins. It can cause fouling which eventually becomes irreversible. It acts as atalyst for the oxidation of the resin structure. This in turn can increase the concentration of organic leachables inthe condensate as well as causing slow degradation of the resin. Special care should be taken to avoid iron loadingesin together with residual oxygen when operating with oxygen rich condensate.

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5 Water Analysis

Concentrations may be entered either in meq/l or in ppm of calcium carbonate. Where ionic concentrations are verow, for example, when entering condensate data, more accuracy is obtained by operating in ppm rather than meq/Lhe choice is made at the centre of the water analysis screen. Meq/l may be converted to ppm of calcium carbonat

multiplying by 50. Ions in ppm, "as is" should be converted to ppm of calcium carbonate by dividing the value by tquivalent weight of the ion, and multiplying by 50 (one can use calculator by pressing F8 button). French degreese converted to ppm of calcium carbonate by multiplying by 10. German degrees can be converted by multiplying 7.85 (1 degree DH = 10 mg CaO per litre). If your water contains hydroxides there is a risk of precipitation withinesin phase. Hence the program should not be used before contacting your local sales office. Even quite lowoncentrations of iron can affect operating performance.


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n the case of water softening concentrations above 0.5 ppm in the inlet feed can build up in the resin. This iron isifficult to regenerate and can gradually lead to resin fouling. Regular cleaning with hydrochloric acid, either in sit

materials of construction of the softener permit, or if not, after resin transfer is recommended. This is best done befsubstantial quantity of the iron has the possibility to become permanently fixed to the resin. Hence whenever levef over 200 mg/l become fixed to the resin immediate resin cleaning is recommended. This could occur in 2-3 mon

with an inlet concentration of 0.5 ppm. Where long cycles are used and substantial quantities of iron can be loadedefore regeneration even 0.2 ppm can slowly give rise to fouling. Where it is not possible to use HCl for cleaning,roprietary cleaning agents which may contain citric acid or other suitable complexing agents are recommended. Inertain parts of the world softener size is increased to allow for higher feed water iron concentrations. There appear

e no consistent guidelines to calculate this increase. It must be assumed that this calculation depends on the chemif the iron, the cleaning treatments recommended, the softener design and the operating conditions chosen. Clearly acility is available to adjust the water analysis to produce a correction to the plant load by increasing either theardness or the iron content to achieve the objectives of the operator. Both the hardness and the iron are calculated oad stoichiometrically at the maximum valency. (Hardness as divalent and iron as trivalent). Care should be taken

when cations classified as others are included. If ions should be included in the softening load these should be addeo the iron or the hardness values. Thus transitional metals and other alkaline earth metals should be added in this whe rule is that others will be treated in the same way as sodium, potassium or ammonia. This principle also applieealkalisation and demineralisation.

Likewise there is a similar problem when completing the analysis of anions in water. Because the selectivity of ani

an vary widely, it is even more important to make a correct classification. Anions classified as strong are those whehave as mineral acids, for example phosphate or bromide. The acids of these anions would be taken up by a weakase resin, or selectively held on the strong base resin, if there is no weak base in the line. Those classified as weakor example boric acid are not held so strongly on weak base resins and hence are easily displaced to the strong basesins. Such anions are treated similarly to the bicarbonate ion.

Returning to iron behaviour, in the case of demineralisation, higher concentrations of iron can be safely treated.However sulphuric acid does not remove iron as efficiently as hydrochloric acid. Here feed water iron levels abovepm can give problems, and occasional regeneration with hydrochloric acid is recommended. Where iron is presentolloidal form, or where it is present together with organic matter, it can pass directly through the cation filter, and

may be taken up on the following anion resin. In such cases it is beneficial to carefully consider which anion resinshoose, and again to put in place regular cleaning treatments with alkaline brine, together with less frequent treatme

with hydrochloric acid. As mentioned above iron is often present in colloidal or insoluble form. This is particularlymportant in the case of condensate polishing. It is assumed in any given analysis that 80% is insoluble, and isemoved by filtration rather than by ion exchange. Thus it is known that all iron is soluble, the value entered shouldve times higher. It should also be pointed out that a typical condensate analysis is a rarity. The polishing process islace particularly to deal with excursions from the typical. The program is designed to help in the prediction oferformance longer term, when such excursions occur. However it is not designed to predict kinetic performance inhort term.

There always remains the possibility that some colloids and or complexes can pass directly through the ion exchanlters. If such situations occur, special resins and processes may be introduced to eliminate these problems. Therogram will warn you if different aspects of the analytical data are inconsistent or insufficient. In particular, if the

nalysis is not balanced. You are permitted to proceed if you wish. In some cases, particularly after reverse osmosiwater may be slightly unbalanced.

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6 Extra Analytical Data

The data entered at the top of the screen contains values for data which is extra to specific data for the individual ioncentrations. In particular Total Hardness may be provided instead of calcium plus magnesium values. If both arerovided the calcium and magnesium values will be used. You will be alerted if the data is inconsistent. If only


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ardness is given, this will be treated as calcium to give safest design option (because calcium requires more resin, igher regeneration levels for its removal). Likewise alkalinity will replace bicarbonates, and equivalent mineral aciEMA) will replace chlorides. If chlorides plus sulphates and nitrates do not match EMA, a warning will be displayf only a conductivity value is given a rough softening plant will be calculated by using a factor of 0.65 to obtain aDS level in ppm of calcium carbonate. It is assumed that this is hardness giving a conservative plant.

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7 RAW WATER origin and pretreatment

The origin and pretreatment can be useful for recommending a particular process or cleaning treatment. They are nsed for the design calculation itself. The level of organics after such pretreatment is important. The level of organihould be entered as Kubel 10 min boil either as KMnO4 or O2. Currently this is the most frequently used methodhough the test protocol varies slightly from country to country, it is sufficiently accurate for its purpose. Levelsbtained by other techniques should be converted using the following factors:

Method Concentration

T.O.C. 1 ppm

KMnO4 - 10 min boilKubel) 3 ppm as O2

12 ppm as KMnO4

KMnO4 - 30 min at00C

2-2.5 ppm as O2

8-10 ppm as KMnO4

KMnO4 - 4 hr at 27C 1 ppm as O24 ppm as KMnO4

Ultra Violet 3 ppm

Results using permanganate can also be expressed as O2. To convert from "as KMnO4" to "as O2" divide the resul. It is expected that TOC will become the norm within the next few years. Hence it is necessary to review this

ituation regularly.

The temperature of raw water can be important in demineralisation processes. Temperatures above 35C can precluhe use of Type-II and acrylic strong base resins, and even acrylic weak base resins where a short rinse is essentialproduction of water at less than 50 micro siemens). It will also affect the capacity of weak base resins and the presrop of resins generally. Temperatures above 60C are not generally recommended for strong base anion resins whigh conversion to the hydroxide form of any part of the bed is anticipated. However temperatures up to 70C or ev0C can sometimes be used successfully, provided some loss of resin lifetime is accepted.

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8 Cycle Time and Flow Rate

The program calculates automatically the gross throughput which includes the extra water needed to operate theegeneration and rinses. The net throughput is the water supply required to be produced by the design. This calculats made from the flow rate requirement input in cubic metres per hour together with the required length of cycle.

Alternatively if the total net throughput is known the flow rate will be calculated. In fact any two pieces will be useomplete the hydraulic design. If there is an existing plant the resin volume may be fixed and the other parametersltered to obtain the best option.

CYCLE LENGTH:


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ONIC LOAD

The quantity of resin required is calculated from this value and the gross ionic load. The resin volume may be rouno the nearest unit package volume as required. Of course the application of a design factor reduces the operatingapacity. The design screen shows the theoretical capacity without the design factor in operation. The printout showoth the theoretical capacity and actual operating capacity calculated by applying the design factor.

REGENERANTS

The regeneration conditions are an important part of the design. Sodium chloride is generally chosen for wateroftening but potassium chloride can sometimes be preferred. If this choice is required the program should be opera

with sodium chloride and the stoichiometric equivalent of potassium chloride used. The concentration of sodiumhloride of 10% gives optimum performance. Concentrations of less than 5% are wasteful in water usage and fullotential capacity will not be obtained. For higher concentrations the operator should satisfy himself that the volumegenerant is at least equal to one bed volume, otherwise distribution of regenerant can be inefficient. Concentrationbove 20% can be wasteful for this reason, and are not generally recommended. Although saturated brine has beensed in certain designs, this is very wasteful and there is a risk of poor hydraulics and osmotic shock as the resinwells during rinse. Turning to demineralisation: For cation resins there is a useful choice in regenerants. Hydrochlcid is the preferred regenerant when considering the maintenance of consistent resin performance with limited riskron fouling is reduced, there is less risk of precipitation, and regeneration is generally more efficient so keeping theesin bed cleaner. On the other hand it is more corrosive, fumes can be hazardous, and it can be more expensive.ulphuric acid therefore has its place. Nitric acid is a strong oxidising agent which can de-crosslink resin (increasin

he moisture retention) and can lead to explosive conditions when used incorrectly; hence it is only to be recommenfter consultation with Purolite. Nevertheless hydrochloric acid is an efficient regenerant and the hydrochloric acidata can be used for the plant design. Sulphuric acid should be used at recommended concentrations according to throportion of calcium to total cations. Where the ratio is high, calcium sulphate precipitation can occur within the red. This can be avoided by operating at higher flow rates, so that waste regenerant leaves the bed before it has timrecipitate (operating in this way can cause a risk if the regeneration is interrupted) and by adjusting the acidoncentration to give the best compromise. Please note an average value given in the design screen. The printout gietails for the two stages of the stepwise regeneration, on which this design program is based. If a single stageegeneration is to be used, then the first concentration should be chosen and the design factor of 0.85 should replache standard one of 0.9. It is important that the flow rates are chosen according to the operator's recommendations,

hould always give a resin contact time of greater than 20 minutes (preferably greater than 30 minutes, but not longhan 45 min). Shorter contact times reduce efficiency of regeneration, while longer results in precipitation. The flowate should be carefully chosen, usually 8-15 BV/hr to achieve these objectives.

RINSE VOLUMES

Rinse volumes are chosen according to the resin and design. If the water is heavy in iron or organics a longer rinsolume or rinse recycle should be used.

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1 Plant Design

Vessel design options are controlled by recommendations within the program. Warnings are offered when theonditions are not generally suitable. The design engineers recommendations should be adhered to. It is important tse a bed depth in line with plant diameter to give a suitable aspect (height/diam) of 1-2 in most cases. Tall narrowessels can result in premature resin breakdown. Very shallow beds can give poor ion exchange. A high linear velond deep bed can result in high pressure drop across the bed, high pumping costs, and possible resin breakage. Aesign rating of 0.9 ensures against shortfall in throughput as a result of changes in feed water quality, resineterioration, and some plant design inefficiency. Where the plant is small and designed to a low budget, it may beseful to increase the safety by reduction of this number to 0.8 or less. In some instances, the plant may be flow rat


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ycle time limited and a low design factor may be essential. In such cases there is no need for an extra reduction.

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2 Treated Water Quality

Treated Water quality data is given for the plant as the design proceeds. This cannot be truly assessed until all vessave been evaluated. It should be emphasised that typical values for leakage are generally significantly lower than

hose quoted, for several reasons. The design safety factor ensures that there is excess resin and regenerant. If this isot fully needed because of good engineering design, a lower leakage will result. Plants are also often run to a consafe throughput, effectively increasing the true regeneration level with the same effect. Any reduction in water deman result in better performance of the flow rate sensitive weakly functional resins which results in a higher capacithis in turn can reduce load on the strong resins ultimately improving performance which also can reflect in lower

eakages. For these reasons typically obtained field data cannot be directly compared with design data. Normally threated water quality will deteriorate towards the end of the run. The run will be continued until the water quality ionger acceptable, or it is considered that further loading could prejudice the efficiency of the subsequent regenerathis is particularly important when considering the loading and reversible removal of organics. Leakage end-pointsually significantly higher than the average. This enables detection. The program only considers one parameter onne as an end-point of the cycle, except for mixed beds which are designed separately. The end-point may be hard

eakage for softening alkalinity or hardness for dealkalisation, sodium for cation limited plants, which is linked toonductivity after the anion bed, and usually silica for anion limited plants. Historically, cation limited plants haveeen preferred because increase in conductivity arising from increase of sodium as the cation exhausts, is easy andheap to measure, and the result is instantaneous. On the other hand anion limited plants, required to produce highuality water, will leak silica at exhaustion. This is expensive to monitor, and the analysis result may be so slow thilica has passed to the treated water supply, putting equipment at risk. This is less important when there is a mixeded downstream, but the mixed bed may become prematurely exhausted. one way to avoid the silica release is to buhe silica probe in the anion bed. Alternatively the actual cycle time can be reduced to about 2/3 of the design.

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3 Pressure Drop Calculation

For Water Treatment, the viscosity, based on temperature, will be calculated. For other solutions it will be necessaro provide the viscosity of the solution (sugar syrups, organic solvents etc.) in cps units. Flow rate: to convert fromolume flow rate (m3/h/m3 of resin, BV's/h) to linear flow rate, (m/h), multiply by the bed depth in metres. Pressur

Drop is proportional to bed depth. Resin Grades Specific Process Systems often require specific resin particle sizerades. The codes are as follows:

GradeCode

Detail Mm

T Standard grade 0.3-1.2

MB Mixed BedC or A 0.42-1.2, 0.3-1.2

C High Flow 0.42-1.2

DLLayered bed(WAC,WBA)

0.3-0.63

DLLayered bed(SAC,SBA)

0.63-1.2

L Polishing 0.42-1.0

TL Trilite C or A 0.71-1.2, 0.42-0.85

CL Continuous 0.42-0.85

L Fluidised bed 0.5-1.0


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Special clean 0.42-1.2

O Other customer spec

FC,FA Purofine 0.42-0.71

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4 Operating Conditions - Working Mixed Beds

For working mixed beds (all mixed beds on separate disc), the vessel diameter should be adjusted to give a linearelocity close to 40-60 m/h. For certain waters it may be necessary to operate more slowly. When using the prograesign any type of mixed bed, changing the cycle time, is a very important consideration to achieve the requiredbjectives. This will change the resin volumes of the components and this helps to size the bed correctly. One of th

main problems is that only a small volume of one of the resins is needed. This poses problems in vessel sizing. Bynsuring that enough of each component is available for the computer to overcome the hydraulic constraints for eaomponent allows for initial bed sizing. The desired resin ratio is then calculated manually, and if necessary the beown-sized to meet the optimised requirement. It should be emphasised that a longer cycle time than the one desireot a bad thing, provided the it achieves the objective of optimised bed sizing. The capacity of the resin bed can beffected considerably by the initial water analysis and the treated water quality requirements. Relatively small chann the acceptable quality can make large differences in the optimum resin ratio, which should be recommended, an

ow to measure the end-point. It the bed is cation limited, an increase in sodium as the cation exhausts can cause alow or a rapid increase in conductivity, depending on the flow rate of operation. If the average conductivity is quitow, say less than 1 microsiemens per cm. then the end-point may be 10 times or more higher, say 1-2 micro sieme

However if silica and carbon dioxide do not need to be removed the choice of a mixed bed with a high cation ratiomay allow acceptable water of a higher conductivity, such as 5-20 micro siemens to be produced more economicaln the other hand if low silica leakage is required, a silica meter is the safest way to ensure best water quality isroduced. The analytical response to silica can be slow, so it can be advantageous to bury the silica probe a smallistance up the bed to ensure there is some protection against silica passing to the treated water supply. Alternativelhe cycle time can be shortened to say, 2/3 of the design to prevent silica leakage.

5 Operating Conditions - Polishing

For Make-up polishing, flow rate limitations are even more important than they are for working mixed beds. Optimnear velocity should be set at 40-60m/h, and 30-40 BV/h. There should be less cause to operate more slowly becaf water analysis constraints. It longer cycle times are preferred, this could result in flow rates lower than the optim

As a general rule, both for make-up and condensate polishing, higher flow rates afford better filtration, especially folishing condensate, where removal of suspended solids is an important consideration. The principles of cycle endoint and its measurement also apply to make polishers as well as for Working Mixed Beds.

Optimum linear velocity for condensate polishing can vary between 60-120 m/h depending on the system and thereferred cycle time. In general, because mixed beds designed on flow rate can be calculated quickly by hand, the

dvantages of the program are less apparent. However it is much easier to quantify all details of actual performancewith no extra effort. It is expected that comparison of actual mixed bed performance with design data will allow forncreased sophistication from feed back of practical data from the field.

Currently predictions on quality are quite general, and can be related more to the effect of condenser leakage than teady conditions of operation. The program objectives can be two fold. Firstly to size the plant according to flow-rnd possibly ammonia or amine load. Secondly to simulate the effects of a condenser leak. The design program cansed for both objectives. In the case of the plant design, a typical condensate analysis is required. When a significaondenser leak has occurred, the resin performance can be simulated by entering the condensate leak analysis. Haviured the leak, it is recommended to double regenerate the resin bed using at least 120g/L HCL, and 160g/L H2SOppropriate, and 100g/L of NaOH per regeneration. It may be appropriate and convenient to employ the resin on re


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echnique between regenerations. Also it is useful to have a spare resin charge available to maintain continuousondenser treatment, (where this is necessary). When making a design it is important that sufficient time is allowedhe resin transfer and full separation and regeneration. In the absence of condenser leaks the limiting factor for cyclength is the pressure loss. This allows the possibility for the resin to be as fully regenerated as possible thus increahe purity of the condensate and the kinetics of ion exchange. The specified performance is generally regarded asufficient for most requirements. A number of subtle variations in the engineering and various trace impurities in th

water analysis can have significant effects on kinetics. In general water quality will be superior to the predictedpecification. Problems in solving the polishing designs can occur where the cycle time is very short and at least onf the design factors is low. The principles of the design factor operation applies here as it does for Working Mixed

eds. It is even more important here to recommend that, where necessary, an attempt is made to solve for a longerycle time, or to alter the operating conditions to increase basic driving design factors. It is possible that resin volumre so small that bed depth, pressure loss and flow rate parameters cannot be solved for the cycle time required.

There is no problem in operating a mixed bed for a shorter cycle than the prescribed design. For mixed beds, thehoice of the correct resin grades may be critical according to the design. Quite often the cycle time for condensateolishing is limited by pressure loss rather than by ionic load. Macroporous and supergel resins should be taken offne when the pressure loss exceeds 2 bar/m, and gel types at 1.5 bar/m. This has the advantage of ensuring an evenigher regeneration level than the design, further improving water quality in subsequent cycles, because of higheronversion to hydrogen and hydroxide forms respectively.

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6 Design Objectives

The objectives to be achieved are to minimise pressure drop at optimum flow-rate, while at the same time componradings must be chosen to achieve good resin separation for the regeneration process. For general mixed beds (usiomponents) MB grades are recommended, unless specially good water quality is required. This can require perfectn separation. Trilite grades with an inert spacer to prevent cross contamination of regenerants, or to provide superioeparation on resin transfer is an excellent option in many cases. However, if there is any risk of contamination withr grease, an inert layer is not recommended. The interface may be diverted to a separate catch pot and reintroduceefore the next backwash separation.

Even if resin separation is near perfect after backwash, the use of in-situ regeneration can still allow for contact ofomponent resins with the wrong regenerant at the centre collector. Attempts to place the collector at the interface cail if, for whatever reason, any changes in cation volume take place. Even if the collector is perfectly placed, the

wrong regenerant can diffuse past the collector. From experience, it has been found that it is preferable for the catioesin to be converted to the sodium form, than for the anion resin to be converted to the acid form. The presence organic matter and weakly basic groups can extend anion rinse times significantly. The recommended approach is tury the collector in the cation resin, and to regenerate the anion first. This will convert the cation resin at the colleo the sodium form. However the following cation regeneration will remove most of it, if not all.

For ultra-pure water treatment, excellent separation is achieved with Purofine Resins, and their superior regenerabind kinetics ensures up to 30% longer cycles of the highest purity water. Where high flow rate is a priority, PL grare a useful alternative option, giving low pressure loss, and good cation kinetics.

Typically most types of mixed bed will give a leakage of 0.1 micro siemens or below, in other words a resistivity ver 10 meg-ohm. The capacity will be dependent on the leakage at the cycle end-point, as the leakage often risesradually. The capacity in the program is based on an end-point approximately ten times the average or permanenteakage, around 1-2 micro-siemens depending upon the application. Where the water requirement is intermittent, it ecommended to fit a recycle loop for water recirculation. This can save water on start-up and avoid the inconsistenuality which occurs on start-up after a shutdown.

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7 Overrun

The objective of the overrun is to allow ionic load to pass from the weakly functional resin to the following strongunctional one, in order to minimise total resin volumes in each unit. It should be pointed out that other concepts ofptimisation are possible. Some examples are: Optimisation of use of regenerant quantity, of resin inventory cost,peed of regeneration, rinse minimisation, running costs, and so on. The program allows the user to choose the overe feels is appropriate and to view the effects, and so move to the desired objective. The use of overrun has thedvantage that it can more effectively load the weakly functional resins which also gives more time for loading the

inetically slower weakly functional resin. Also by allowing less selective ions to be displaced to the stronglyunctional resin the capacity of the weakly functional resin can be maximised while still allowing effectiveegeneration of the strongly functional resin. The procedures for overrun may take time. Care should be taken whenperating in high overrun of weak base anion beds where influent water is high in organic load/Total Anions. Therganic load can be displaced to the strong base resin with consequent risk of increased fouling. This is especiallymportant in co-flow operation. If it is required to ensure that there is zero risk of this situation, a safety factornegative over-run) can be applied to the weak base resin design.

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Purolite_IonExchangeDesignCalculation