Issues

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34a_m13_r0 13-1

Contents

13.1 Introduction ..................................................................................................................... 2

13.2 Issues to be Addressed for a New Project .................................................................. 313.2.1 Water Source .............................................................................................................. 313.2.2 Water Analysis and Variation ................................................................................. 313.2.3 Effluent Quality and Quantity (Boiler Makeup)................................................ 613.2.4 Environmental Considerations (or Waste Discharge) ....................................... 613.2.5 Financial Perspective ............................................................................................... 7

13.3 Pretreatment ..................................................................................................................... 713.3.1 Raw Surface Water ................................................................................................... 813.3.2 Well Water .................................................................................................................. 813.3.3 Sea Water .................................................................................................................... 913.3.4 City Water ................................................................................................................... 9

13.4 Demineralization (Ion Exchange/Reverse Osmosis) .............................................. 1013.4.1 Low Pressure Boilers and Light Industrial Applications, e.g., Laundries .. 1013.4.2 Medium Pressure Boilers and General Industrial Applications .................. 1113.4.3 High Pressure Boilers and Steam Turbines ....................................................... 1213.4.4 Condensate Polishers ............................................................................................. 1313.4.5 Examples ................................................................................................................... 14

SYSTEM INTEGRATION

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34a_m13_r0table of contents

13.1 Introduction

During the development of any new water treatment project, many equipment issueshave to be addressed. These issues include the capacity, performance, environmentalcompliance, capital cost, operating cost, waste volume, and footprint of the watertreatment equipment. In addition to the “hard” equipment issues, “soft” issues suchas customer preferences must also be addressed.

For new water treatment projects, several process areas must be considered,including pretreatment, demineralization, and condensate polishing (if applicable),as well as any ancillary components necessary to form a complete system. Thepurpose of systems integration is to select the best unit operations that address theissues identified in the first paragraph and assemble them into a functioning system.

This module provides a brief overview of the most significant factors affecting thedesign of a complete water purification system. It is not intended to provide adefinitive discussion of the topic but rather to serve as a starting point for thosewithout systems integration experience. Any system design should be checked by anexperienced process engineer to ensure that no subtle design issues are overlooked.

Module 13SYSTEM INTEGRATION

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13.2 Issues to be Addressed for a New Project

13.2.1 Water Source

The first step in designing a water treatment system is to identify the source of thewater to be treated. This information has a direct bearing on the amount ofpretreatment required and also influences the selection of equipment.

The following list identifies the common sources of feedwater for water treatmentprojects:

• Surface water, i.e., rivers, lakes, and reservoirs• Well water• Municipal water from well or surface source• Sea water• Process fluids such as brine• Condensate• Blended feed: This is a combination of several streams e.g., surface water and

condensate or well water and municipal water.

It is also important to determine if there is any existing pretreatment of the rawwater, e.g., municipal clarification and/or filtration.

13.2.2 Water Analysis and Variation

Once the source of the feedwater has been identified, a complete analysis of thewater must be obtained. To properly analyze the feedwater, samples should becollected over a period of time, preferably several years. A single sampling is noteffective, as it does not provide the necessary information regarding seasonalvariations in water quality. This information is required so that any variations in theconcentrations of individual ions (or other dissolved or suspended material) can beaccommodated in the system design. A design feedwater analysis is prepared thatpresents the water composition that is used to select and size the treatmentequipment.

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The design feedwater analysis should not consist of all of the maximum values ofeach individual ion that have been recorded over time. A water supply would neverhave all ions at the maximum observed values at the same time. Using maximumvalues could result in overly large equipment. It is more appropriate to use theaverage value of each individual ion as the design basis or even two-thirds of themaximum value of each individual ion. The total exchangeable cations and totalanions, expressed as ppm CaCO3, excluding silica and carbon dioxide, are balancedby adding sodium or chloride ions as needed.

The composition of well waters is typically more stable than the composition ofsurface waters. Well waters generally do not vary significantly over time.

The design feedwater analysis should include the following information as aminimum:

• Total dissolved solids (TDS)• Total suspended solids (TSS)• Total organic carbon (TOC)• Iron and manganese• Hardness and alkalinity (these may be calculated from other ions)• Barium and strontium• All major cations and anions• Silica, reactive and total• Carbon dioxide (this can be calculated from pH and alkalinity)• Conductivity• pH• Turbidity• SDI (Silt Density Index)• Free chlorine• Minimum and maximum temperatures

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Table 13.2-1 below is an example of a typical water analysis reporting form on whichan operator records the amount of these substances present in each sample takenfrom the feedwater source. From this data, the design feedwater analysis can bedetermined as previously explained. The various columns can be used to definesamples taken at different times or from different sources. They can also be used toindicate the manner in which the water is changed as it passes through differenttreatment processes.

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tropeRsisylanAretaW

tneutitsnoC nisisylanAsampp A B C D

aC(muiclaC +2 ) OCaC 3 34 0 0 0

gM(muisengaM +2 ) OCaC 3 21 0 0 0

aN(ecnalabotmuidoS +2 ) OCaC 3 82 2.0 2.0 2.0

H(AMF=negordyH +) OCaC 3 8.65 8.65

K(muissatoP +) OCaC 3

SNOITACLATOT OCaC 3 38 75 75 2.0

OCH(etanobraciB 3-) OCaC 3 62 0 0 0

OC(etanobraC 3-2 ) OCaC 3

HO(edixordyH -- ) OCaC 3 2.0

OS(etafluS 4-2 ) OCaC 3 14 14 14 0

lC(edirolhC -) OCaC 3 51 51 51 0

ON(etartiN 3-2 ) OCaC 3 1 1 1 0

4OP(etahpsohP -2 ) OCaC 3

SNOINALATOT OCaC 3 38 75 75 2.0

OC(eerF,edixoiDnobraC 2) OCaC 3 3 92 5 0

OiS(aciliS 2) OCaC 3 7 7 7 2.0

SNOINAELBAGNAHCXE OCaC 3 39 39 96 4.0

Table 13.2-1: Water Analysis Report

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13.2.3 Effluent Quality and Quantity (Boiler Makeup)

The effluent quality required from the treatment system is determined by theintended use of the treated water. For example, boilers that operate at higherpressures require purer feedwater than those operating at lower pressures. Boilermanufacturers have water purity specifications that may include conductivity,sodium, silica, dissolved oxygen, pH, etc.

The flow rate of feedwater required by an application, such as the boiler mentionedabove, depends on the system’s average consumption of water, the peakconsumption rate, the length of the peak, and the amount of storage available. Forexample, a boiler requiring a 200-gpm average flow on a continuous basis wouldhave a different water treatment system than a boiler requiring a 200-gpm averageflow but with 2000-gpm peak consumption rates.

In most applications, the client determines and specifies both the quantity and thefinal quality of water required.

13.2.4 Environmental Considerations (or Waste Discharge)

The generation and discharge of waste materials are also important considerationswhen designing a water treatment system. Various options can be exploreddepending on the client’s needs and requirements, for example:

• The use of process equipment that generates less waste such as reverse osmosis,packed bed ion exchangers, or electrodeionization (EDI) technology

• The application of a rinse recycle step to reduce the waste volume• The application of combinations of weak and strong ion exchange resins to

reduce chemical usage• The use of non-regenerable ion exchangers or exchangers that are regenerated

off-site• The reuse of waste generated by the water treatment system for other in-plant

purposes such as dust suppression or in the scrubber or cooling tower

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Different geographic regions have varying regulations and restrictions on the levelsof pollutants that can be discharged into waterways. These regulations place limitson the composition of the waste streams that can be discharged. Some of the itemsthat are regulated are listed below as examples; however, the prevailing localregulations must be checked to ensure full compliance with the law.

• Total Suspended Solids (TSS)• Total Dissolved Solids (TDS)• pH• Sulphate ion• Chloride ion• Sodium ion• Mass of dissolved solids (mass based discharge)

In some jurisdictions, no net addition of any pollutant is permitted while in others,no liquid discharge is permitted from the facility at all. This latter requirement iscommonly referred to as a Zero Discharge Plant.

13.2.5 Financial Perspective

To select the proper treatment process for any given system, the client’s financialperspective must also be considered. Some of the non-process factors that influenceequipment selection are:

• Capital cost versus operating cost• Anticipated life of the plant• Cost of money (outright purchase versus lease)

13.3 Pretreatment

The pretreatment process involves all equipment upstream of the demineralizingequipment. The purpose of pretreatment is to condition the water by removingcontaminants and constituents that may foul or plug downstream equipment.

Some examples of impurities that are removed in the pretreatment section of a watersystem are TSS, turbidity, color, organics (TOC), iron, and chlorine.

The raw water source heavily influences the choice of pretreatment equipment. Thefollowing sections provide an overview of the variations in equipment design thatmay be necessary for four common water supplies: raw surface water, well water, seawater, and city water.

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13.3.1 Raw Surface Water

With the exception of waste water reclamation projects, raw surface water isgenerally the poorest quality of water that has to be treated; therefore, it requires thegreatest quantity of pretreatment equipment to make it suitable for treatment by oneof the demineralizing processes.

The potential pretreatment processes that may be employed to treat this type of rawwater are listed below:

• Chlorination to control bacteria is almost always a mandatory requirement• Clarification (alum) and filtration (gravity filters) to reduce the TSS and Turbidity• Lime softening if water has high hardness levels• Organic scavenger if the level of total organic carbon (TOC) is high• Activated carbon filtration or a sodium bisulfite feeder to remove free chlorine

The need for an organic scavenger is determined by the type of equipment used inthe downstream demineralization system. If the demineralizing plant includes areverse osmosis (RO) unit, the TOC limit would be approximately 3 ppm; however, ifion exchange is used, the TOC can be no more than 1 ppm. Higher levels of TOCcause fouling of the downstream equipment and require time consuming cleaningprocedures.

If the downstream equipment is reverse osmosis, activated carbon filters are notrecommended as they can be a source of bacteria and can also pass carbon dust ontothe membranes. Chlorine removal by injection of sodium bisulfite is fast and lesscostly than carbon filtration.

13.3.2 Well Water

Well water normally requires less pretreatment than surface water and also has lessvariation in its constituents; therefore, the level of pretreatment required is minimal.

The following list indicates pretreatment processes that can be used for well water:

• Multi-media filtration for TSS reduction• An ion exchange softener upstream of reverse osmosis for hardness reduction

and to decrease the reverse osmosis cleaning frequency• Greensand filters for iron and manganese removal. The limit for these

contaminants is 0.3 ppm (total) if the water is to be processed by ion exchange,and 0.05 ppm (iron) if RO is used. The limit for RO is greatly influenced by thepH and by the amount of oxygen in the water.

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13.3.3 Sea Water

Sea water is extremely high in dissolved solids (i.e., 30,000 to 40,000 ppm)depending on the region of the world. It also contains suspended solids, which canincrease dramatically during storms, and, on occasion, oil if the intake is near ashipping lane.

In the water treatment industry, reverse osmosis with sea water membranesdesalinates the water prior to further purification with brackish water reverseosmosis membranes. The equipment used to pretreat the sea water upstream of theRO is listed below:

• Chlorination to control bacteriological growth is a mandatory requirement• Ultrafiltration can be used as an alternative to media filtration to reduce TSS.

Ultrafiltration is normally higher in capital cost but lower in operating cost thanmedia filtration

• Multi-media filtration to reduce TSS. Normally, two levels of filtration arerequired especially if an open sea intake is used, i.e., roughing filters andpolishing filters. Polymer is fed upstream of both sets of media filters to enhancetheir performances

• Cartridge filtration to protect the RO membranes• Dechlorination using sodium bisulfite

13.3.4 City Water

City water, or municipal water, is potable and is generally of reasonable quality.However, it is normally chlorinated and may contain suspended solids, turbidity,organics, and iron and manganese, all of which must be removed or reduced toacceptable levels prior to the demineralization equipment.

Possible treatment processes are listed below. All of these must be evaluated basedon the quality and constituents of the city water.

• Multi-media filtration to reduce TSS• Dechlorination using either activated carbon filtration or sodium bisulfite feed• Greensand filtration for iron and manganese removal• Sodium cycle softening to reduce hardness and decrease the frequency of RO

cleanings

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13.4 Demineralization (Ion Exchange/Reverse Osmosis)

The demineralization section of the water treatment system is where the ioniccontent, or total dissolved solids (TDS), of the water is reduced to the levels requiredby the user.

Demineralization can be performed by ion exchange (IX), reverse osmosis (RO) orelectrodeionization (EDI) equipment. Some combination of these basic processes isoften used to obtain the optimum treatment process to meet the client’sperformance, financial, and environmental needs.

The TDS of the raw water and the quality of treated water required influence theprocess equipment selection. Some examples of equipment selections are listedbelow to show the complexities that can be encountered.

13.4.1 Low Pressure Boilers and Light Industrial Applications, e.g., Laundries

Simple softening can produce water for this service. The residual hardness level willdetermine the type of softener that should be used. The options are as follows:

• Sodium cycle softener, co-current regenerated, produces less than 1 ppmhardness

• Sodium cycle softener, counter current regenerated, produces less than 0.5 ppmhardness

• Packed bed sodium cycle softener, counter current regenerated, produces lessthan 0.5 ppm hardness with less than half of the waste generated by a co-currentregenerated system or a conventional counter current system

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13.4.2 Medium Pressure Boilers and General Industrial Applications, e.g.,Automotive

Water used in this application normally requires some degree of demineralization toreduce the dissolved solids to acceptable levels. The quality of treated water requireddetermines the treatment processes. Examples of equipment that may be used totreat the water for this application are given below:

• Two-bed demineralizer (cation/anion co-current regenerated) produces treatedwater with an average of 5 to 10 micro-Siemens per centimeter (µS/cm)conductivity and 50 ppb silica. A forced draft decarbonator may be incorporatedbetween the cation and anion exchangers to remove carbon dioxide from thedecationized water and thereby reduce the ionic load on the anion exchanger.

• Two-bed demineralizer (cation/anion counter current regenerated): Thisproduces treated water with an average of 1 to 3 (µS/cm) conductivity and 10 to20 parts per billion (ppb) of silica. A forced draft decarbonator may beincorporated between the cation and anion exchangers to remove carbon dioxidefrom the decationized water and thereby reduce the ionic load on the anionexchanger.

• Reverse osmosis followed by a decarbonator and mixed bed ion exchange: Thisproduces treated water with an average of 1 µS/cm conductivity and 10 to 20 ppbsilica.

• Two-bed packed bed demineralizer (cation/anion counter current regenerated):Produces treated water with an average of less than 1 µS/cm conductivity and 10to 20 ppb silica and with less waste than the other systems; however, the inletturbidity must be less than 1 NTU. This system can be used with or without adecarbonator.

• Two-bed sandwich packed bed demineralizer (cation/anion counter currentregenerated): These units have both weak and strong cation and anion resins toprovide optimum chemical efficiency and reduce operating costs. They producetreated water with an average of less than 1 µS/cm conductivity and 10 to 20 ppbsilica and with less waste than the other systems; however, the inlet turbiditymust be less than 1 NTU. This system can be used with or without adecarbonator.

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13.4.3 High Pressure Boilers and Steam Turbines

For this application, the highest water quality is required to prevent scaling of theboiler tubes and turbine blades. To achieve higher quality, a polishing demineralizeris added to the process equipment arrangement. The polishing demineralizer can bea mixed bed, a polishing cation exchanger, or an electrodeionization unit. Thefollowing equipment examples indicate the range of systems that can be provided toproduce high quality demineralized water.

• Conventional two-bed co-current cation/anion exchangers followed by mixedbed ion exchange. This produces treated water with an average of 1 µS/cmconductivity and 10 to 20 ppb silica.

• Reverse osmosis followed by decarbonation and mixed bed ion exchange. Thisproduces treated water with an average of 1 µS/cm conductivity and 10 to 20 ppbsilica. The RO is normally a single pass design; however, a double pass ROsystem could be used to increase the run length of the mixed bed.

• Reverse osmosis followed by decarbonation and EDI. This produces treatedwater with an average of less than 0.1 µS/cm conductivity and less than 10 ppbsilica. The RO system can be either a single or double pass system depending onthe raw water TDS. In some cases a non-regenerable mixed bed is positionedafter the EDI unit for added insurance.

• Two-bed packed bed demineralizer (cation/anion, counter current regenerated)followed by a cation polisher. This produces treated water with an average of lessthan 0.5 µS/cm conductivity and 10 to 20 ppb silica and with less waste than theother systems; however, the inlet turbidity must be less than 1 NTU. This systemcan be used with or without a decarbonator.

• Two-bed packed bed demineralizer (cation/anion counter current regenerated)followed by a mixed bed exchanger. This produces treated water with an averageof less than 0.1 µS/cm conductivity and less than 10 ppb silica. A decarbonatormay be used between the cation and the anion units to reduce the operatingcosts and in some cases also reduce the capital cost of the system.

Any of the above systems that use two-bed demineralizers could be changed to four-bed systems with weak and strong resins in the cation and anion exchangers if thecomposition of the raw water is suitable.

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13.4.4 Condensate Polishers

Condensate, which is steam that has condensed back to water after giving up itsheat, can be reused in a boiler. Condensate picks up ionic contaminants fromcooling water in-leakage and condenser leakage, along with corrosion products suchas iron and copper oxides.

In some applications, the condensate is returned from a steam host that uses thesteam in the manufacturing process. In such cases, the condensate may containother contaminants picked up from the product (e.g., pulp fiber from a paper mill).These contaminants must also be removed before the condensate can be reused.

There are several different types of condensate polishers. A brief summary of theavailable types is given below (Module 10 has complete details).

• Sodium cycle polisher: This is a cation only polisher that is used to polishcondensate at temperatures up to 275o F in applications for which silica reductionis not a concern. This type of polisher removes trace hardness ions in exchangefor sodium ions and also filters out particulate matter.

• Amine cycle polisher: This is also a cation only polisher that is used to polishcondensate at temperatures up to 275o F in applications where silica reduction isnot a concern but where the addition of sodium is not acceptable. This type ofpolisher removes trace hardness ions in exchange for amine ions and also filtersout particulate matter.

• In-situ regenerated deep bed polisher: This is a mixed bed polisher used in-line(full flow polisher) or side-stream (partial flow polisher), at temperatures up to120oF but preferably not higher than 100oF (to control silica leakage). This type ofpolisher has a potential for leakage of regenerant into the process stream. It alsohas a higher degree of cross-contamination and therefore produces lower qualitytreated condensate than that produced by externally regenerated polishers.

• Externally regenerated deep bed polisher: This is also a mixed bed polisher usedin-line or side-stream, at temperatures up to 120oF but preferably not higher than100oF (to control silica leakage). These units are normally found in centralutilities such as nuclear power plants for which the highest quality is required,particularly for supercritical boilers.

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13.4.5 Examples

The following examples are intended to represent the types of systems used inmodern water treatment systems. They show typical processes, based on the type ofraw water source, the water analysis, and the required performance guarantee. Itmust be stressed that each new system must be selected or designed based on theprevailing water analysis and the “hard” and “soft” parameters dictated by theprospective client. There may be more than one “right” answer to a design problem,and there may be subtle conditions that shift the preference from one design toanother.

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Example 1 Source: Well Water

Water Analysis

Cations ppm as CaCO3 Anions ppm as CaCO3Calcium 583 Bicarbonate 115Magnesium 161 Sulfate 656Sodium 48 Chloride 21Total Cations 792 Total Anions 792

Carbon Dioxide 10Silica 20TEA 822

Other ContaminantspH 10.4TSS 50 ppmTemperature 104oF

Performance (Product Quality) GuaranteeConductivity 20 mmho/cmSodium 2 ppm as NaSilica 0.5 ppm as SiO2

Recommended EquipmentMulti-media filterCo-current strong acid cation exchangerCo-current strong base anion exchanger

Selection Factors1. The high level of TSS in the raw water requires the use of filtration. Since iron and

chlorine are not present, multi-media filtration is selected.2. The required effluent quality is not particularly stringent and can be achieved using a

basic two-bed demineralizer, which is simple to operate and maintain and which is alsolow in capital cost.

3. The client has prior experience with similar equipment.

Comments• At first glance, the TDS in the raw water would suggest the use of RO instead of ion

exchange; however, the reported water temperature is already at the maximum operat-ing temperature for RO membranes. Therefore, ion exchange is selected.

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Example 2 Source: City Water

Water Analysis

Cations ppm as CaCO3 Anions ppm as CaCO3Calcium 15 Bicarbonate 18Magnesium 6 Sulfate 5Sodium 16 Chloride 14Total Cations 37 Total Anions 37

Carbon Dioxide 11.4Silica 10TEA 58.4

Other ContaminantspH 6.5Free Chlorine 1.0 ppmTemperature 50 to 70oF

Performance (Water Quality) GuaranteeConductivity 0.5 mmho/cmSodium 0.1 ppm as CaCO3Silica 0.01 ppm as SiO2

Recommended Equipment SelectionSodium bisulfite feeder10 micron nominal cartridge filtrationCo-current strong acid cation exchangerCo-current strong base anion exchangerMixed Bed Exchanger

Selection Factors1. The very low level of TDS in the feedwater makes this water ideal for treatment by ion

exchange.2. The required treated water quality indicates a need for final polishing using a mixed bed.3. The client requires filtration before the ion exchange beds.4. The free chlorine level is greater than 0.2 ppm and must be reduced. A bisulfite feeder

is selected as the most cost-effective method.

Comments• As an alternative to the sodium bisulfite feeder and cartridge filtration, activated carbon

filtration could be used; however, this would increase the capital cost and require morefloor space.

• The cartridge filter is not indicated by the feedwater data (since particulate matter can bebackwashed out of a co-current ion exchange unit), but the client is concerned aboutparticulate loading.

• Other forms of ion exchange could be used, such as a packed two-bed system (cationand anion exchangers) with a high flow cation polisher. This choice would simplify theoperation and possibly reduce the capital cost of the plant; however, the client prefersthe more traditional approach of using a mixed bed demineralizer.

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Example 3 Source: Surface Water (River)

Water Analysis (Clarifier Outlet)

Cations ppm as CaCO3 Anions ppm as CaCO3Calcium 111 Bicarbonate 110Magnesium 56 Sulfate 100Sodium 63 Chloride 15Potassium 5 Nitrate 10Total Cations 235 Phosphate 1

Total Anions 236


Other ContaminantspH 7.0Organics 10 ppm TOCTurbidity 7 NTUTemperature 35 to 85oF

Performance GuaranteeConductivity 1 mmho/cmSodium 0.03 ppm as CaCO3Silica 0.1 ppm as CaCO3

Equipment SelectionMulti-media filterSandwich packed bed weak/strong acid cation exchangerForced draft decarbonatorSandwich packed bed weak/strong base anion exchanger

Selection Factors1. Because the feedwater turbidity is greater than 1 NTU, filtration is required. No iron or

chlorine is present, so multi-media filtration is selected as the least costly alternative.2. The analysis favors the use of weak cation resin since there is a substantial quantity of

hardness in the water and a reasonable ratio of hardness to alkalinity. The weak resin isvery chemically efficient and greatly reduces the ionic load that the strong resin mustsubsequently remove.

3. A forced draft decarbonator is required since more than 50% of the feed to the anionexchanger is carbon dioxide. By removing this carbon dioxide, the decarbonatorreduces the volume of strong base resin needed in the anion exchanger and alsoreduces the use of caustic.

4. The load on the anion resin is 89% mineral acids and only 11% weak acids. This stronglysuggests the use of weak base anion resin to improve chemical efficiency.

5. An additional factor in selecting weak base anion resin is the presence of up to 10 ppmof TOC. This high concentration would quickly foul any strong base resin and is alsomuch higher than any weak resin can handle on a consistent basis. Adjusting the perfor-mance of the clarifier should control this high level of TOC.

6. Counter current regeneration of the strong ion exchange beds is required to achieve therequired quality of treated water.

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Comments• If clarifier performance cannot be improved such that the TOC is greatly reduced, then

consideration should be given to the addition of an organic scavenger upstream of thecation unit. This would change the analysis of the water being fed into the cationexchanger, especially during the early portion of the service run, when the scavenger isexchanging sulfate and bicarbonate ions for chloride ions. This may alter the ratio ofweak and strong cation resins or may eliminate the weak resin altogether, since the weakresin only removes the hardness associated with alkalinity.

• Because counter current technology is required to meet the required quality, packedbeds are used to reduce the waste volume. If waste is not an issue, other forms ofcounter current ion exchange could be used; however, the packed bed approach isprobably the least costly and most elegant approach.

• Depending on the system and its size, a forced draft decarbonator could be added. Thisaddition reduces operating costs, although it may increases the capital cost of thesystem.

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Example 4 Source: Well Water

Water Analysis

Cations ppm as CaCO3 Anions ppm as CaCO3Calcium 152.8 Bicarbonate 460Magnesium 114.4 Carbonate 20Sodium 448.2 Chloride 238.7Potassium 32.1 Nitrate 1.8Total Cations 747.5 Sulfate 14.6

Hydroxide 2Fluoride 0.4Total Anions 737.5

Carbon Dioxide 22.6Silica 65.1TEA 825.2

Other ContaminantspH 7.75 Barium 0.05 mg/lOrganics 7.2 ppm TOC Iron 0.15 mg/lTurbidity 1.5 NTU Manganese 0.20 mg/lTemperature 60 to 80oF Copper 0.01 mg/lColor 5 APHA TSS 15 mg/lH2S < 0.1 mg/l

Performance GuaranteeConductivity 0.25 mmho/cmSodium 0.02 ppm as NaSilica 0.01 ppm as CaCO3TDS 0.04 mg/l as CaCO3Iron 0.01 mg/l as FeCopper 0.01 mg/l as Cu

Equipment SelectionManganese greensand filtration with potassium permanganate (KmnO4) feedOrganic scavengerAcid feed systemAntiscalant feed systemRO prefilter – 5 micron nominalSingle pass ROForced draft decarbonatorMixed bed exchanger

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Selection Factors1. The feedwater turbidity is greater than 1 NTU, there is 15 ppm of TSS and 0.35 mg/l of

Fe + Mn, making filtration mandatory. Manganese greensand filters are selected toremove the Fe and Mn. When the TSS is substantial, a layer of anthracite is placed ontop of the greensand to increase the run time and prevent plugging.

2. Reverse osmosis is selected as the roughing demineralizer technology due to the veryhigh level of TDS.

3. A forced draft decarbonator is required to remove the carbon dioxide generated by theaddition of acid upstream of the RO.

4. A mixed bed ion exchanger is required to achieve the required treated water quality.

Comments• Particular attention must be paid to the pretreatment upstream of the reverse osmosis

unit due to the presence of iron, barium, H2S and substantial amounts of TOC. Thegreensand filters remove iron, manganese, TSS and possibly some of the color (TOC).

• The analysis reports less than 0.1 mg/l of H2S in the feed. This probably means that theconcentration of H2S is below the detection limit of the laboratory performing theanalysis. If H2S is present, it would preclude the use of any oxidizing agents, since theywould convert the H2S into elemental sulphur that plugs up filters and RO membranes.

• To reduce the scaling potential of the feedwater, acid is fed upstream of the RO to lowerthe LSI to a negative value. The acid injection, in turn, converts some of the bicarbonateions to carbon dioxide, which is not removed by the RO. This carbon dioxide would veryquickly exhaust the mixed bed were it not for the decarbonator that reduces the CO2 tobetween 5 and 10 ppm at the mixed bed inlet.

• The very high level of reactive silica in the feedwater requires the addition of anantiscalant specifically designed to prevent silica scaling (e.g., ARGO SI300).

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Example 5 Source: Municipal Supply

Water Analysis

Cations ppm as CaCO3 Anions ppm as CaCO3Calcium 318 Bicarbonate 200Magnesium 51 Sulfate 151Sodium 198 Chloride 197Potassium 12 Nitrate 29Total Cations 579 Phosphate 1

Fluoride 1Total Anions 579

Carbon Dioxide 2Silica 10.5TEA 591.5

Other ContaminantspH 7.5 to 8.3 Barium 0.08 mg/lOrganics 1 ppm TOC Iron 0.13 mg/lTurbidity 1 NTU Manganese 0.01 mg/lTemperature 36 to 77oF Aluminum 0.3 mg/lFree Chlorine 0.12 mg/l SDI 5

Performance GuaranteeConductivity 0.1 mmho/cmSodium 0.01 ppm as NaSilica 0.02 ppm as SiO2TDS 0.2 mg/l

Equipment SelectionAcid feed systemAntiscalant feed systemSodium bisulfite feed systemRO prefilter – 5 micron nominalSingle pass reverse osmosisForced draft decarbonatorE-CellTM electrodeionization unit

Selection Factors1. The level of suspended solids (indicated by turbidity) in the feedwater does not justify

the addition of media filtration; therefore, only conventional cartridge filtration is pro-vided upstream of the RO.

2. RO is selected as the roughing demineralizer due to the moderately high TDS of thefeedwater.

3. A forced draft decarbonator is required to remove the carbon dioxide generated by theaddition of acid upstream of the RO.

4. To achieve the required treated water quality, a mixed bed ion exchanger or EDI unit isrequired. EDI is selected to reduce the onsite storage and handling of chemicals.

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Comments• The raw water analysis indicates a silt density index (SDI) of 5 in the feedwater. This is

the maximum value for RO feed, so the value should be rechecked and confirmed.Higher values require the addition of media filtration to protect the RO and the cartridgefilters.

• Since an RO is being used, sodium bisulfite is the preferred method of chlorine removal.The membranes have a chlorine tolerance of 1000 ppm-hours.

• To reduce the scaling potential of the feedwater, acid is fed upstream of the RO to lowerthe LSI to a negative value. This, in turn, converts some of the bicarbonate ions tocarbon dioxide, which is not removed by the RO. The carbon dioxide would quicklyexhaust the final ion exchanger were it not for the decarbonator, which reduces the levelof carbon dioxide in the water to 5 ppm.

• An antiscalant is fed upstream of the RO as additional protection against scaling.

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SystemIntegration


Example 6 Source: Sea Water(Open Sea Intake)

Water Analysis

Cations ppm as CaCO3 Anions ppm as CaCO3

Calcium 1032 Bicarbonate 694Magnesium 5318 Sulfate 7389Sodium 28527 Chloride 27288Potassium 495 Nitrate 5Ammonia 4 Total Anions 35376Total Cations 35376


Other ContaminantspH 8.1 to 8.3Temperature 78 to 91oF

Performance GuaranteeConductivity 0.25 mmho/cmSodium 0.05 ppm as CaCO3Silica 0.02 ppm as SiO2

Equipment SelectionCoagulant feederCoagulant aid feederPrimary multi-media filtrationPolishing multi-media filtrationAcid feederAntiscalant feederSodium bisulfite feederRO prefilter – 5 micron nominalSingle pass sea water reverse osmosisForced draft decarbonatorBrackish water reverse osmosisMixed bed demineralizer

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SystemIntegration


Selection Factors1. Since the feed is an open sea intake, two levels of media filtration are required.2. Coagulant or polymer is fed before each filtration stage.3. The seawater RO is provided with an energy recovery turbine to reduce power costs.4. A forced draft decarbonator is required to remove the carbon dioxide generated by the

addition of acid upstream of the RO.5. To further reduce the ionic load prior to the final demineralization step, a brackish-water

RO is needed after the seawater RO, due to the extremely high level of TDS that seawater contains.

6. A mixed bed demineralizer is used to achieve the final water quality.

Comments• Ultrafiltration could have been used instead of media filtration for the pretreatment of

the seawater. This would have resulted in lower operating costs but higher capital costs.• Thermal evaporation could have been used in place of the seawater RO, but in this case

thermal evaporation has higher capital and operating costs.• Since an RO is being used, sodium bisulfite is the preferred method of chlorine removal.

The membranes have a chlorine tolerance of 1000 ppm hours.• To reduce the scaling potential of the feedwater, acid is fed upstream of the RO to lower

the LSI to a negative value. This, in turn, converts some of the bicarbonate ions tocarbon dioxide, which is not removed by the RO. The carbon dioxide would very quicklyexhaust the final ion exchanger were it not for the decarbonator that reduces the level ofcarbon dioxide in the feed to 5 ppm.

• An antiscalant is fed upstream of the RO as additional protection against scaling.• The permeate from the sea water RO is still high in TDS, (approximately 500 ppm);

therefore, a second RO pass is required prior to final demineralization.• The final water quality can be met using either conventional mixed bed ion exchange or

EDI technology. Since chemicals are already being used for other parts of the plant(e.g., condensate polishing), the conventional approach is desirable.

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SystemIntegration


Example 7 Source: Condensate

Water Analysis

Conductivity 10 to 15 mmho/cmHardness 5 to 7.5 ppm as CaCO3Iron 0.1 to 0.2 mg/l as FeCopper 0.02 to 0.1 mg/l as CupH 8.0 to 8.5Temperature 180 to 210oF

Performance GuaranteeHardness 0.1 ppm as CaCO3Iron 0.02 ppm as Fe

Equipment SelectionSodium cycle condensate polishers

Selection Factors1. Since the operating temperature is very high and no silica reduction is required, a simple

sodium cycle cation polisher is the process of choice.

Comments• An amine cycle polisher could also be used for this application; however, the client has

no concerns about the sodium content of the treated condensate.

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SystemIntegration


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Example 8 Source: Condensate

Water Analysis

Total non-volatile dissolved solids 50 ppbSuspended Solids 20 ppbAmmonia 800 to 1200 ppb as CaCO3Iron 10 ppb as FeCopper 5 ppb as CuSilica 20 ppb as SiO2Sodium 5 ppb as CaCO3Chloride 5 ppb as CaCO3Temperature 90 to 120oF

Performance GuaranteeTDS 25 ppbTSS 10 ppbCation Conductivity 0.1 mS/cmTotal Iron 5 ppb as FeTotal Copper 2 ppb as CuSilica 5 ppb as SiO2Sodium 1 ppb as NaChloride 2 ppb as Cl

Equipment SelectionExternally regenerated mixed bed condensate polishers

Selection Factors1. The required performance guarantee requires the use of a mixed bed condensate

polisher.

Comments• To maintain the low levels of cross-contamination required by this process, external

regeneration of the mixed bed condensate polisher is used.

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